Project Electronics For Everyone AUDIO LEVEL METER PROJECT ...

AN ARGUS SPECIALIST PUBLICATION

OCTOBER 1983

Project Electronics For Everyone

AUDIO LEVEL METERPROJECT TO BUILD

ULTRASONKINTRUDERALARM3ensitive Dopplershift designdetects movement

IGH VOLTAGE METER PROJECTmeasures up to 10,000 volts

SPECIALEIGHT PAGE

CIRCUITSUPPLEMENT

-OVER 20CIRCUITS

New cats for old !SEND US THE COVER FROM ANOTHER COMPONENT SUPPLIERS CURRENTCATALOGUE, PLUS A 40p STAMP, AND WE'LL SEND YOU A FREE COPY OF THELATEST (SUMMER) AMBIT CONCISE COMPONENT CATALOGUE. ALTERNATIVELYYOU CAN SIMPLY BUY A COPY FROM YOUR NEWSAGENT - OR SEND 80p TO

THE ADDRESS BELOW

ambitINTERNATIONAL

* MANY PRICE REDUCTIONS: PRICE ON THE PAGE

,14

'Telephone:P277l 230909

'Telex:9951 94 Ambit G

200, North service Road, Brentwood,Essex CMI4 4SG

* AVAILABLE AT NEWSAGENTS, OR DIRECT FROM ......

ambit INTERNATIONAL200 North Service RoadBrentwoodEssexCM14 4SG

Telephone 0277-230909Telex 995194 AMBIT G

Data 0277-232628 REVVTEL))300 BAUD DUPLEX

2_

OCTOBER 1983VOL 5 No 10

1ROJ"CTS*AUDIO LEVEL METER 11An accurate, 10 -LED bargraph level meter.HI -VOLTAGE METER 28Protect your equipment, protect yourself.*TRUMP CARD 58Connects the Jupiter ACE to ZX add-ons.*ULTRASONIC INTRUDER ALARM 63Don't make a move . . .

URESTHE FX-COMPUTER 16HE reviews a teach -yourself electronics kit.CAREERS IN ELECTRONICS PART 6 20Customer Service engineering in computers.ALL ABOUT ELECTRONICS PART 4 48Starting on semiconductors.*MODEL RAIL COMPETITION 54Design a computer -controlled railway layout.

'ECIAL*GIANT CIRCUIT SUPPLEMENT 34Eight pages of all-purpose circuits.

icGULARSMonitor 6What's On Next 18Breadboard 24Forward Bias 26Buylines 32HE Bookshelf 43Points Of View 44PCB Service 69PCB Printout 70Classified Advertisments 73

Editor: Ron KeeleyAssistant Editor: Helen Armstrong BATechnical Illustrator: Jerry FowlerAdvertisement Manager: David KitchenerAssistant Advertisement Manager: Joanne JamesManaging Editor: Ron Harris BScChief Executive: T. J. Connell

Audio Level Meter - page 11

Ultrasonic Intruder Alarm page 63

FX-Computer Review page 16

Hobby Electronics is normally published on the second Friday of the month prior to the cover date.Hobby Electronics, 145 Charing Cross Road, London WC2H OEE, 01-437 1002. Telex No 8811896. Published by Argus Specialist Publications Ltd.

Origination by Ebony Typesetting, Trion House, 13 Dean Street, Liskeard, Cornwall PL14 4AB..Distributed by S. M. Distribution Ltd, 16/18 Trinity Gardens, London SW9 BDX.

Printed by QB Ltd, Colchester. Covers printed by Alabaster Passmore.Notice: The contents of this publication including all articles, designs, plans, drawings and programs and all copyright and other intellectual property rights therein

belong to Argus Specialist Publications Limited. All rights conferred by the Law of Copyright and other intellectual property rights and by virtue of internationalcopyright conventions are specifically reserved to Argus Specialist Publications Limited and any reproduction requires the prior written consent of the Company. All

reasonable care is taken in the preparation of the magazine to ensure accuracy, but Argus Specialist Pulications Ltd cannot be held responsible legally. ©Copyright1983 Argus Specialist Publications Ltd, Member of Audit Bureau of Circulation.

Hobby Electronics, October 19833

Ilk .q.Step-by-step

fully

illustratedassembly

and Otting instructions

are includedtogether

With circuit descriptions.Highest

qualityortents

arecodeushroughout.

%I....1.1t aim v-.

ft

AT -80

BRANDLEADING ELECTRONICS

NOW AVAILABLE IN KIT FORM

Electronic Car Security System Arms doors, boot, bonnet and has security loop to protect

fog/spot lamps, radio/tape. CB equipment Programmable personal code entry system Armed and disarmed from outside vehicle using a special

magnetic key fob against a windscreen sensor pad adhered tothe inside of the screen Fits all 12V neg earth vehicles

Over 250 components to assemble

SX1000Electronic Ignition

Inductive Discharge Extended coil energy

storage circuit Contact breaker driven Three position changeover switch Over 65 components to assemble Patented clip -to -coil fitting Fits all 12v neg. earth vehicles

SX2000Electronic Ignition

The brandleading systemon the market today

Unique Reactive Discharge Combined Inductive and

Capacitive Discharge Contact breaker driven Three position changeover switch Over 130 components to assemble Patented clip -to -coil fitting Fits all 12v neg. earth vehicles

SPECIAL OFFER"FREE" MAGIDICE KIT WITHALL ORDERS OVER £45.00

IM NM A fr'

VOYAGER Car Drive Computer A most sophisticated accessory Utilises a single chip maskprogrammed microprocessor incorporating a unique programmedesigned by EDA Sparkrite Ltd Affords 12 functions centredon Fuel, Speed. Distance and Time Visual and Audible alarmswarning of Excess Speed. Frost/Ice, Lights -left -on Facility tooperate LOG and TRIP functions independently or synchronously Large 10mm high 400ft-L fluorescent display with autointensity Unique speed and fuel transducers giving aprogrammed accuracy of + or -1% Large LOG & TRIPmemories 2,000 miles 180 gallons 100 hours Full Imperialand Metric calibrations Over 300 components to assembleA real challenge for the electronics enthusiast,

TX1002Electronic Ignition Contactless or contact triggered Extended coil energy storage circuit Inductive Discharge Three positionchangeover switch Distributortriggerhead adaptors included Die castweatherproof case Clip -to -coil or remotemounting facil ity Fits majority of 48.6 cyl.12V neg. earth vehicles Over 145components to assemble.

TX2002Electronic Ignition

The ultimate system Switchablecontactless Three position switch with

Auxiliary back-up inductive circuit Reactive Discharge Combined capacitive

and inductive 0 Extended coil energy storagecircuit Magnetic contactless distributor trigger.head Distributor triggerhead adaptors included

Can also be triggered by existing contact breakers Die cast waterproof case with clip -to -coil fitting Fits

majority of 4 and 6 cylinder 12v neg earth vehicles Over 150 components to assemble

All SPARKRITE products and designs are Cully covered by one or more World Pal, a

SPARKRITE 82 Bath Street. Walsall West Midlands WS 1 30E England

SELFASSEMBLY KIT

SX 1000 £12.95SX 2000 £19.95TX 1002 £22.95TX 2002AT 80VOYAGERMAGIDICE

£32.95£32.95£64.95£9.95

PRICES INC VAT POSTAGE & PACKING

111111=1 IMO ME MI

NAMEADDRESS

MAGIDICEElectronic Dice

Not an auto item but great funfor the family

Total random selection Triggered by waving of hand

over dice Bleeps and flashes during a 4 second

tumble sequence Throw displayed for 10 seconds Auto display of last throw 1 second in 5 Muting and Off switch on base Hours of continuous use from PPS battery Over 100 components to assemble

All IMTel 109221 614791 Allow 28 days for delivery

I ENCLOSE CHEQUEISI/POSTAL ORDERS FOR

KIT REF

CHEQUE NO

HE 10

CUT OUT THE COUPON NOW!

4 Hobby Electronics, October 1983

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LOW PROFILESOCKETS BY TI

° 999

14 9pin 10p16 pin 11p18 pin 16p20 pin 18022 pin 22p24 pin 24p28 pin 26p40 pin 30p

TRANSISTORS MPSA70 50pAD161 /2 40pBC107 14pBC109C 14pBC117 20pBC169C 109BC172 12pBC177 /8 17p130179 18pBC182 /3 10pBC184 10p13CI87 30p

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PCBMOUNTING

RELAYS6 or 12V DCCoil SPDT 2424DC 160p6 or 12VDCCoil OPOT 5ADT

DC240V AC 200p

DCCoilv SPOT 10A

DCAC 225p

WIRE WRAPSOCKETS BY TI

8pin 25p14 pin 36p16 pin 40018 pin

5PP20 pin 60p22 pin 65p24 pin 70p28 pin 90p

pin 100p

VERO BOARD

OPTO

ELECTRONICS

25577 40pOC P71 180p0E1512 120pOR 960 1209

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ISOLATORS, ,

30p1a!r1.124 Inn

MCS2400 1900MOC3020 150pI LQ74 240pTILI 1 70p

12 70TIT..P

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SWITCHESTOGGLE SWITCHES

Subrn n atureSPST felp, SPDT 660ppm 70pRotary SwitchesIP120w, 2P6w, 3P4w,4P3w 55pDIGITASTSWITCHES MPPush to make

18,0,61150Push to break 181ackIlOpSlide Switch DPQ7 10pSquare PCB Swam 6$p

LEDs

0125"TIL32 55pTIL209 Red 911

TIL211 12pTIL212 Ye 14p111_216 Red 18001'TIL2 00 Red 10PTI L222 Gr 12pTIL228 Ye 14p

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DIODESBY127 12p81/X36300 2139

0A47 tip0490/91 9p04950A200

LINEAR ICs

AD7581 1150p

RUGBY ATOMIC CLOCKThis Z80 micro controlled clock/calenderreceives coded time data from NPL Rugby. Theclock never needs to be reset. The facilitiesinclude 8 independent alarms and for eachalarm there is a choice of melody or alternativelythese can be used for electrical switching. Aseparate timer allows recording of up to 240 laptimes without interrupting the count. Expansionfacilities provided.

Ready BuiltTI articles atUnit11.00....... 1145 15.00 carr.

Reprint of +

BBC FLOPPY DISC DRIVES

Dual drive 51/4" 800K £699 + £8 carr.B B C Single drive 51/4" 100K £230 + £6 carr.

BBC COMPATIBLE DRIVESThese drives are supplied in BBC matching

colour cases.

M I C R 0 COMPUTER SINGLE 100K £150 200K £215'400K £265

OFFICIAL DEALER SINGLE WITH PSU 100K £185 200K £260'Please phone for availability 400K £330

DUAL WITH PSU 200K £355 400K £475'800K £595

* These drives are supplied with a switchBBC Model B £399 between 40 and 80 tracks.

Drive Cables: Single £8 Dual £12AS DESCRIBED IN

JUNE/J ULY/ AUGUST

(Ind VAT) Carr £8/unitModel A to Model B Disc Manual & Formatting

Diskette £17.50kit £50ISSUE

NIICROTRAINERComplete Kit £64.00 + 11.00 p&p8V 1.8A PSU £7.00 + 70p p&p1802 Ref. 17.00IDEAL for HOBBYISTS -- learn andexplore the workings of microprocessorsand unravel the mystical field of computers.INVALUABLE for training centres, schoolsand industries - gives effective insight intomicros to engineers, electricians etc notdirectly involved in the computer field.INEXPENSIVE - a truly low cost teachingaid - in fact a short step towardsdeveloping new ideas and systems.

upgradeFitting charge £15

Individual upgrades also availableWORD PROCESSOR 'VIEW'

16k ROM £52TELETEXT ADAPTOR £195WORLDWISE 8K ROM £39

TORCH Z80 DISC PACK £780Business, Education and Fun

Software in stockFLOPPY DISC INTERFACE

INC. 1.2.0.5. £95 and £20 installation

MICRO TIMERThe programmable clock/ timer is a 6502 baseddedicated micro computer with memory and 4 digit7 segment displays to form an extremely versatiletiming device with following features: 24 hour 7 day timer 4 completely independent switch outputs 6 digit 7 segment display output to indicate

real time turn-off times and reset times Individual outputs to day of week, switch and

status LEDss

entry through a simple matrix pad

Further details on request0 f 1Complete Kit 156.0.

+7.00 p

& pPSU 1700

r

0p p Er pConstruction details supplied

TFA ;I 1 N( )N I .VI' IC i I'1);PLEASE ADD 40p p&p & 15°70 VAT

(Export: no VAT, p&p at Cost)

MAIL ORDERS TO: 17 BURNLEY ROAD, LONDON NW10 1ED Orders from Government Depts. & Colleges etc. welcome.SHOPS AT: 17 BURNLEY ROAD, LONDON NW10 Detailed Price List on request.ll

(Tel: 01-452 1500, 01-450 6597. Telex: 922800) hock items are normally by return of post.

.....,

alik

Hobby Electronics, October 1983 5

MONITORFlying SignalsHawk Electronic Test Equipment ofMaidstone have announced threepieces of equipment of interest,primarily, to small industrial users.

For the Apple micro, comes a 32channel input/output card allowingexternal control and data feedback, withfour 8 bit bi-directional I/O ports, four16 bit interval timers, two serial toparallel, parallel to serial registers andhandshake capability. The card costs£49.50 all-inclusive and comes withdocumentation and a sample program.

Anther card allows the Apple tofunction as an IEEE 4888 Controller fortests, measurements and control. Thiscard can run up to fourteen separatecontrollable devices, with atransmission path of up to 20m. The on-board software interfaces directly withBasic and Applesoft strings. The GPIBInterface Card costs £189.00 inc. VATand p&p.

Hawk have utilised advances inanalogue to digitial flash converters todevise their Tele-Scope 200S digitalscope, which uses an ordinary domesticTV set as a screen, via the UHF aerialinput.

The Tele-Scope can digitise signals atthe rate of one per 100ns and displaythem indefinitely, allowing fortransient, single -shot capture up to250kHz.

The Tele-Scope costs £89.00 for thekit, or £109.00 for a built and testedunit, with special parts availableindividually as necessary. The manualincludes circuits and layouts, and is alsoavailable separately. Prices areexclusive of VAT and p&p.

Further information from HawkElectronic Test Equipment, ParkwoodIndustrial Estate, Bircholt Road,Maidstone, Kent ME15 9XT Tel:(0622) 686811.

Electrician -Free PlugAt last, the perfect present for theelectronics wizard who has everything.Particularly the boffins who raise theirheads from their algebra only to bestymied by the necessity of putting anelectric plug on their Fully RotatingModel Creation Of The Universe: the(almost) tool -free plug.

The TL-Handyplug, "A revolution in

plug design", to quote its makers,actually does only require one smallscrewdriver (or screwdriver substitute)to wire it up to a standard appliancecable, although a bit more wiretrimming would be needed for a cablewith a flat -cut end. The side of the plug(which looks, otherwise, no differentfrom an ordinary plug) incorporates asmall blade in a channel, which can beused to strip the inner cores of the flex,automatically to the required length.

The base of the plug releases byoperating one screw through 90degrees, and the bare ends of the wiresare secured by locking clips. All verysimple, and reported by our technicaldepartment to work very well.

Its other accomplishments areclaimed to be speed of wiring, childprooffeatures, impact resistance, flameresistance, and the availability of anaccessory to help disabled people use it.The Handyplug is available fromretailers at around £1 .25, but for furtherinformation you can contact Toby LecMarketing Ltd., Park Bridge Mill, ParkRoad, Blackburn, Lance. Tel: (0254)679911.

Heath KitsThe Heath Co. in the USA hasappointed independent distributors inEurope for its well known Heathkits. Theformer Heath Electronics has changedits name to Zenith Data Systems Ltd.,and will in future be concentrating on itsown microcomputers and HeathAssembled Robots. In the UK, thedistributors for Heathkits will be our oldfriends Maplin Electronics.

The old showroom in TottenhamCourt Rd., London has been closeddown. Any technical or other enquiriesabout kits obtained either fromTottenham Court Rd. or from theirGloucester address should beaddressed to: Zenith Data SystemsLtd., Heathkit Division, 11B BristolRoad, Gloucester GL2 6EE, in writingonly; any kits needing servicing shouldbe sent to that address.

Kits obtained through Maplin, on theother hand, will be dealt with by Maplinthemselves, at Maplin ElectronicSupplies Ltd., P 0 Box 3, Rayleigh,Essex SS6 8LR. Tel: (0702) 554155.A free Heathkit catalogue is availablenow from Maplin.

New Hobby ShopTwyford Electronics has been set upwith the aim of supplying componentsand accessories to hobbyists atcompetitive prices -this is what we liketo hear. They are situated about 100yards from Twyford Station, about sixmiles out of Reading in Berkshire, andbelieve they are the only componentssuppliers for a considerable distance.They will be doing mail order as well asover the counter sales. We don't have aprice list or catalogue for them as yet but

doubtless by the time you read thissomething will be available.

Phone, call or sent SAE to TwyfordElectronic Ltd., 22 Station Road,Twyford, near Reading, Berks. Tel:(0734) 340333.

Exploring JupiterJupiter Cantab have announced a 16KRAM pack and a 48K RAM pack, pricedat £34.95 and £79.95 respectively, forthe Jupiter ACE micro. As well as these,nine games tapes are now available, viz:Gobbledegook, Zombies and Potholes,and Othello for 19K memory; GreedyGobbler, Blow Up The World, MissileMan, Spacefighter Pilot, Overtaker,Brands Hatch, Moo (I), Hangman, Fish("swimming upstream to eat thefloating detritus ...") and Flutterer. Theninth tape is a Monitor tape (no relation)which enables the user to explore theinner workings of the computer and testprograms.

Jupiter also have a new address,which is Jupiter Cantab Ltd., CheshuntBuilding, Bateman Street, CambridgeCB2 1LZ. Tel: (0233) 313479. Aglossy leaflet describing the ACE is alsoavailable.

Jupiterlog RANI

Here Comes The CavalryYou have obtained all the errata, testedall the components, checked all the dryjoints, reversed all the electrolytics andchanged the fuse. It still doesn't work.Do you despair? Do you give upelectronics and take up flowerarranging? No indeed! You contact WEBLogic Systems Ltd., who will build, testand/or repair any unstarted or partiallyand completed projects (I quote).

Logic Systems quoted around £10-£20 as an average cost for the completeassembly of most projects, and expectnormally to turn a project around withinfive days of receipt.

Anyone interested, contact WEBLogic Systems Ltd., at GainsboroughHouse, 15 High Street, Harpenden,Herts. AL5 2RT. Tel: (05827) 62119.


MONITOROrgan KitsAs more people turn to home musicmaking as a hobby, and the interest inhome computers and electronicscontinues to grow, home -buildelectronic organs can give you twohobbies in one - the enjoyment ofputting together your own instrumentfrom a set of easy -to -assemble kits, andplaying your completed organafterwards. As an added bonus, you alsosave money when comparing the cost ofkits against that of a comparablecommercial instrument.

The kits in question are produced inGermany by the Dr. Bahn company; theywere the originators of the electronicorgan kit over thirty years ago, and therange is now available in this countryfrom Swankit Instruments.

The latest computer techniques areemployed in the design of these organs,not only to make the building easy, butto give the best tones and effects. Therange begins with a small singlekeyboard portable organ, as a starterproject. Even people with no experienceof electronics at all can get involved. Theinstructions are designed to be easy tofollow, with clear diagrams. If youshould have any problems, expertadvice is just a telephone call away. Atthe other end of the range there areseveral large three keyboard machines,with enough features to keep theexperienced amateur or professionalplayer happy for years. The proprietor ofSwankit Instruments is GrahamWatkins, who is himself a keen amateurorganist.

For information contact SwankitInstruments, Chantry Park, Henfield,W. Sussex BN5 9JE. Tel: (0273)494238.

ShortsHouse of Instruments have announcedthe first group in a brand new range ofoscilloscopes from Trio. CS -1010, CS -1012, CS -1020 and CS -1022 are10MHz single and dual trace and20MHz single and dual tracerespectively. All the new range havelarge six inch rectangular CRTs withilluminated inner -face graticule andhigh accelerator potential. All haveextremely high input sensitivity of1 mV/cm which is continuously variableto 5V/cm. 1 mV/cm is particularlyvaluable in conjunction with the 20nsec/cm to 0.5 sec/cm sweep speed for

These full feature oscilloscopesmeasure a neat and compact 260(W) x160(H) x 400(D) mm and weigh from 8.1kg. They have all the performance andreliability you could expect from a highquality, professional oscilloscope.Thehy are fully guaranteed for 00 yearsincluding free pick up, repair and return.Models with a tilt stand/carryinghandle will be available. Please ask forfree data sheets, prices or furtherinformation from House OfInstruments, Clifton Chambers, 62

High Street, Saffron Walden, EssexCB10 1EE. Tel: (0799) 24922.

The Electronic Organ ConstructorsSociety is just that. They apparentlyhave branch meetings in various partsof the country and publish a smallmagazine (A5, well printed, colouredcard cover. The April issue has 4Opp andI would guess it is published twice yearly).The emphasis in this issue is ontraditional, theatre -style organs and noton rock music and synthesisers, just toput it in context, but the emphasis isgenuinely on electronics nonetheless,with technical articles on a simple andadvanced level, as well as area meetingreports and members' advertisements.

Contact the Membership Secretary,Mr. W. Lewis, 8 St. John's Wood Rd.,London NW8 8RE.

Micro Peripherals have introducedthe Juki 6100, a low cost 18CPSdaisywheel printer designed for wordprocessing use with personaland small business micros. The Juki6100 is a full featured daisywheelemulating Diablo 630 protocol, fullycompatible for use with Wordstar.Features include 18CPS bi-directionallogic seeking; subscripts andsuperscripts; bold and shadow printing;character pitches 10, 12, 15 andproportional; graphics mode; 1/120 inmin character spacing; 1/48 in linespacing; 2K buffer memory; 100character Triumph Adler compatible'drop in' daisywheel; 13 in platen with11 in print line; linear motor for accuratepositioning and low noise; IBM 82compatible single/multistroke ribbons.

A centronics compatible interface isprovided as standard with an RS232serial and current loop interface as anoption, and papers handling is either byfriction feed or optional tractor feed. Theprice is £399.00 ex. VAT. Further detailsfrom: Micro Peripherals Ltd., 69 TheStreet, Basing, Basingstoke, Hants.Tel: (0256) 3232.

Elkan Electronics have just launcheda new idea for Dragon 32 users (notforgetting Tandy TRS-80 ColorComputer users). This is the "DragonSupermarket". There's now no need tosearch through endless magazines orcontact numerous different suppliers -the "Dragon Supermarket" is a phonecall or a FREEPOST (no stamp required)away.

In addition, the "Dragon Super-market" is distributed free everymonth with "Rainbow" and "ColorComputer News", two magazines fromthe USA which are devoted entirely toDragon 32 and Tandy color computers.Enquiries to Elkan Electronics, 11 BuryNew Rd., Prestwich, ManchesterM25 8JZ. Tel: 061 798 7613.

Ancom Ltd. write to say that theyhave just issued a four -page leafletspecifying their wide range oftemperature and humidity measure-ment instrumentation. The rangesinclude digital thermometers,temperature indicators, controllers,annunciators, semi -intelligent devicesand monitoring instruments, plus a

psychrometer and a hydrometer.Ancom also do custom panels for non-standard requirements.

The leaflet we have at Hobby doesn'tinclude prices, so specify, when writing,if you want a price list. Contact AncomLtd., Devonshire St., CheltenhamGL50 3LT. Tel: (0242) 513861.

Stotron's new main product cataloguehas more than 160 pages and includesgreatly enlarged ranges of Alarms,Connectors, Displays, LED Lamps,Mains Filters, Indicators, Switches,Relays, and many more products. A fewof the suppliers that feature heavily areArcolectric, Aries, Bulgin, C & K,Fabrilec, Hirose, ITW-Licon, Liton,National, Rafi, Roxburgh, Sifam, Starand Teka.

All product lines are held in stocksometimes more extensively than thesuppliers! Prices are aimed generally atthe one-off and small quantity ordermarket and there is no minimum ordercharge. For your copy of the cataloguecontact Stotron Ltd., 72 BlackheathRd., Greenwich, London SE10 8DATel: 01 691 2031.

The first batch of ORIC's speciallycommissioned software is nowavailable from dealers. The five titles inthe series are: Oric Multigames (f 7.95),a set of five family games comprisingBandit, Projectiles, Colour Match, Questand Reversi; Oric Flight (f 7.95),simulation of aircraft landing; Zodiac(f7.95), a sophisticated role playingadventure game; Oric Chess (f9.99),five levels of difficulty with superbgraphics; Oric Base (f9.99 to includemanual), a data management programwhich incorporates an easy to learnQuery language. All cassettes are forthe 48K model.

The Forth tape is also expected to beavailable very shortly and will cost£17.95, which includes the price ofthe manual.


MONITOROric PrinterOric Products' first peripheral for theOric I - the specially designed four-colour plain paper printer - is nowavailable from retail outlets, priced£169.95. The printer, which featuresthe Alps mechanism and an internalpower supply, comes complete with aconnecting lead, no other accessoriesare required. The Oric Colour Printer(MCP40) is plugged directly into the Oricexpansion port and can be used withboth 48K and 16K models.

Four colours - black, blue, red andgreen - are provided by rolling ballpoint pen dispensers. The printerfeatures full alphanumeric capabilityand graphics specification, and sampleprograms are included in thecomprehensive manual.

The Oric Colour Printer measures10.75x6.37x2.50in high (lowering to1.25in at the front) and is identical incolour to the micro - grey with bluestripes. The printer runs on 220/240volts and, with a minor adjustment, canbe used in the USA on 110 volts. Sparepens and paper rolls will be availablethrough retailers.

The Oric MCP40 has a standardcentronic interface and can be usedwith any microcomputer having a

centronics interface.Oric Products will be mounting a

summer promotion until mid -September, offering a start-up pack ofsoftware valued at £40 with every 48Kmachine sold. The software packagewill contain four tapes - HomeFinance, Teach Yourself BASIC, OricFlight and Multi Games. Although thetitles are subject to change theproportions of one home business, oneeducational and two gamesprograms will remain unchanged.Oric I 48K retails for £169.95.

The 16K Oric I - due in retail outletsfrom early July onwards - will also besold with a software pack 'alued at£30) containing adaptations of theprograms produced for the 48K. Onceagain there will be one home businessprogram, one educational one and twogames tapes. The 16K plus softwarepackage will retail at £129.95.

Digital DMMKeithley Instruments' Model 128 handheld DMM claimsto be one of the lowestpriced digital 'beeper' DMMs around. Itoffers 0.5% accuracy, 31/2 digitresolution (1mV, OR1), 10A capability,resistance to 20MR and five functions.

The beeper indicates levels above thethreshold when set to volts or amps, andbelow the threshold for ohms. Thethreshold is adjustable so that it can beset to the most useful point, from 10 to300 digit, for the given situation. Highimput impedance (10MR) when thebeeper is activated makes the 128useful for sensing CMOS and other

logic levels. The beeper can bedeactivated by a slider switch. The 128has full overload protection, rotaryswitches and a colour coded faceplate.Battery life is 350 hours with alkalinebatteries, and the price is £119 plus VATand P&P.

Keithley have also recentlyintroduced a range of four industrialstandard digital thermometers, twomodels (865 for fahrenheit and 166 forcentigrade) being therm istorthermometer and two, (the 868 and869) with platinum resistancetemperature detector sensors. Theselatter are the only four wire RTD hand-held thermometers on the market atpresent.

Futher information from KeithleyInstruments Ltd., 1 Bolton Rd.,Reading, Berks RG2 ONL. Tel: (0734)861287.

Control ModulesFor MicrosCentec Electronic Systems aredesigners and suppliers of hardwareand software primarily for educationand industry. One of their specialities isa range of control modules with BASICor machine code, with which your microcan be programmed to switch lights,measure voltages, control motors etc.Centec have actually worked ondevising hardware for a SchoolsCouncil "Microelectronics In Control"course which is now taught in many

schools, often as part of GCE '0'level courses.

Their range includes a universalbuffer module, A to D and D to Aconverters, DC motor and current buffermodule, and a considerable list of otherunits both available now and underdevelopment. Compatible microsinclude the ZX81, Spectrum, Menta,380Z, 480Z at present and others,including the BBC, to come.

Centec's 8 -bit analogue to digitalconverter is designed to convert yourcomputer system into an automatic dataacquisition and analysis system,enabling you to automate the collectionof any type of data for which the righttransducer or sensor is available. It canmonitor up to sixteen analoguechannels and can be used by almost allBASIC and assembly languageprograms. The price is £42.95 one-off.

A range of mains switching unitswith one channel, two channels or fourchannels, features 5A per output socket(1 OA available optionally), LED monitorson socket outputs, 4mm sockets forconnection to a computer, separatepower supply and isolation fromcomputer voltages. Units are priced£91.95, £29.95 and £49.95respectively.

A separate power unit for the ZX81features regulated DC output voltage,external voltage adjustments, shortcircuit protection, style to blend with theZX81, among others. It is designed topower external hardware withoutoverloading the micro, uses the micro'spower supply and plugs straight in. Thefixed 5 or 12V models are £6.95 eachand the variable 5 to 12V model is£7.75. P&p is 45p per order.

Orders and enquiries to CentecElectronic Systems, 47 Spur Rd.,Orpington, Kent BR6 OQR. Tel:Orpington 35353. HE


II

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TheProt° oardNow circuit designing is aseasy as pushing a leadinto a hole ...No solderingNo de -solderingNo heat -spoiltcomponentsNo manual labourNo wasted time

For quick signal tracingand circuit modificationFor quick circuit analysis anddiagrammingWith or without built-in regulated power suppliesUse with virtually all parts - mostplug in directly, in seconds.Ideal for design, prototype and hobby

NOMODELNO

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UNITPRICE

PRICEINC P&P15% VAT

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10 PB203AK 2250 24 85 00 100 05 5V: 15V8. Kit

Tomorrow's tools for today's problemsGLOBAL SPECIALTIES CORPORATION rc.s.c

G.S.C. (UK) Limited, Dept. 14UUnit 1, Shire Hill Industrial Estate,Saffron Walden, Essex. CB11 3AQ.Telephone: Saffron Walden 10799) 21682Telex: 817477

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FOR IMMEDIATE ACTION - The G.S.C.24 hour 5 day a week service For FREETelephone (0799) 21682 and give us your Barclaycard, Access, catalogue II

I American Express number and your order will be in the post immediately tick boxBIM MIN 11110

(UK) Limited, Dept.l4UUnit 1, Shire Hill Industrial Estate, Saffron Walden, Essex CB11 3AQ.

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Audio Level Meter

R. A. Penfold

The golden secret of first-class soundreproduction is a reliable set of levelmeters. Our versatile log -driven peak -reading audio level meter can be builteither with a 10 -LED bargraph display, orten separate LEDs, and cased either as partof another piece of equipment orseparately, alone or as a pair . . . whateveryou want.

ALTHOUGH not so long ago ordinarymoving -coil meters were almostinvariably used for audio levelindication (the exceptions being the socalled "magic eye" indicators), thesedays LED or liquid crystal displaysseem to have largely taken over inthis area. Superficially these look verysimilar to the old "magic eye" typeindicators, but they are not just anexpensive alternative to a high qualitymeter movement, and most typesactually offer a higher level ofperformance than simple analogue VUmeters. The latter are averagereading, apart from some of thosefitted to expensive items of equipmentsuch as professional mixers. Thedrawback of the simple type is thatmany instruments, such as pianos,have a high peak -to -average signallevel, so that the meter tends tounder -read and severe distortion canresult.

LED and liquid crystal levelindicators are normally designed to bepeak reading so that accurate andmeaningful results are obtainedregardless of the input waveform.Some give the option of average -reading so that someone who isfamiliar with the vagueness of thistype of meter and prefers to use it cando so.

This audio level indicator isrelatively simple and inexpensive, butnevertheless has a high level ofperformance. It uses a ten LEDbargraph display, and the LEDthreshold levels are spaced at 3dBintervals. If, for example, the circuit isset up so that the highest LEDswitches on at +6dB, this would giveLED threshold levels of -21, -18,-15,-12, -9,-6,-3, 0, +3, and+6dB. However, the unit can be set upto have any threshold levels withinreason, but the spacing between thethresholds will always be 3dB and itis not adjustable. The circuit has theprofessional standard attack anddecay times of 2.5ms and 1srespectively, and it gives very accurateand reliable results. The unit will fitinto most situations without difficultyas it has a full drive sensitivity whichis adjustable from about 20 to 900millivolts RMS.

System OperationThere are few stages in this unit, ascan be seen from the block diagram ofFigure 1.

The amplifier at the input is merelyused to boost the gain of the circuit ifnecessary. Its voltage gain isadjustable from about 50 times tounity, and this gives the unit itsadjustable sensitivity.

Two precision rectifiers are fed withthe output of the amplifier, and theiroutputs are mixed together. The tworectifier stages are not the same, andthe important difference is that onedoes not invert the input signalwhereas the other does. They bothprovide a positive output signal. Ineffect, one rectifier provides an outputwhile the input signal is positive andthe other provides an output while it


Audio Level Meter

THE VU METER, now somewhatlong in the tooth, was developedto fulfill the need for a device toindicate the relative volume levelsof programme material - speechand music - so that overloadingof circuits could be avoided. Beingcalibrated somewhat arbitrarily,its background and use can besomewhat mysterious. Here, then,the mystery is explained.

The history of the developmentof the VU meter - more properlycalled a Standard VolumeIndicator - can be traced back to1921 when American engineersset out to broadcast the ceremonyof the burial of The UnknownSoldier by means of telephonelines and public addressamplifiers. In order to minimizedistortion, the level at whichoverloading of the various lineamplifiers occurred wasdetermined by experiment, andthis level was taken to be thereference level. A "volumeindicator" was then developedconsisting simply of a 2dB stepattenuator, calibrated in decibelswith respect to the reference level;a triode valve detector and amilliammeter. The method usedwas to adjust the attenuator sothat the signal peaks reached themid -scale point of the meter oncein ten seconds, on average. Thevolume level was then readdirectly from the attenuator scale.This instrument provided anindication of the volume levelsbut exerted no control over theselevels.

The next stage of advancementcame in 1942, when it hadbecome apparent that the largenumber of similar instruments bythen existing was causing

The VU meterconfusion. The AmericanStandards Association publishedthe results of a collaborationbetween engineers of theColumbia Broadcasting System,Bell Telephone Laboratories andthe National BroadcastingCompany, and in adopting therecommendations as a Standard,introduced the now universallyaccepted Standard VolumeIndicator.

In the course of the workleading up to this Standard theeffectiveness of both RMS andpeak -reading meters wasestablished as being virtuallyequal for systems extending overshort distances. Group -delayeffects (the term applied to thedelay of different frequencies bydiffering amounts, which can bequite appreciable in long -haullinks) however causeddiscrepancies in the peak -levelmeter readings, and therefore theRMS meter, happily of simplerdesign, was chosen for furtherdevelopment.

The final design consists of anRMS reading voltmeter, slightlyunderdampened to promote easierreading at peak level,calibrated in both VolumeUnits (hence the term VU) and inpercentage of maximumpermissable level. The scale has abuff -coloured background - saidto reduce eye fatigue. Ininstruments designed for usewith different systems, anattenuator is normally provided tosuit the meter to the job in hand.More usually, the meter ispermanently installed in onepiece of equipment, and the OVUpoint will have been set at thelevel where overloading is just

beginning to occur.Its most important

characteristic is that if offersfreedom from cumbersome andunnecessary absolute RMSvoltage measurements. Anoperator, faced with a number ofmeters, treats each in an identicalfashion, rather than having toknow how the appropriate voltagelevels at each measurement pick -off point.

Most people will meet the VUindicator while adjusting taperecording levels. In this case, theindicator should be treatedaccording to the type ofprogramme material. The meterdeflection should be observed forabout one minute for music, andfor five to ten seconds for speech.Opinions are divided, at thisjuncture, whether to accept theoccasional deflection of unusualamplitude as being the peakreading or not. The highestpossible recording level isdesirable to maintain a goodsignal-to-noise ratio and widedynamic range, but the danger ofoverload distortion is alwayspresent. With today's noise -reduction systems andcompanders, S/N ratio is not theproblem it was, and so it isprobably better to operate at alower level. On the other hand,most equipment manufacturerswill be erring on the side ofcaution in their calibrations, andabsolute maximum peak levels of+1 or +2VU will, in all probability,do no harm. In the end, individualequipment characteristics andpersonal preferences will dictatethe exact method of use.

Steve Roberts


Audio Level Meter

PR1470k

C1220n

R110k

R3100k

6

IC1 R4

4 741C 100k

R2100k

2

6

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101

IC2aTL072 y D2

TILCST732 V D3

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R5100k

R6100k R7

220R

18 17 16 15

LED1-10BARGRAPH

DISPLAY

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IC3LM3915N

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Figure 2. The circuit. Ten LEDs can be used instead of the bargraph unit.

is negative. This gives fullwaverectification so that the circuitresponds to both negative and positiveinput half cycles, and this is animportant feature since many signalsencountered in practice, such as voicesignals, are far from symmetrical.Halfwave rectification could result inover or under reading by 6dB or more!

The output of the rectifiers issmoothed by the next stage, and it ishere that the required attack anddecay time constants are set. The fastattack enables the circuit to respondproperly to transients, and the slowdecay time merely preventscontinuous and very rapid changes inthe display, which would make itpractically unreadable.

The final stages are the bargraphdriver and the bargraph itself. Anormal (linear) drive is not ideal forthis application as it would not quitecover a wide enough dynamic range,and in terms of dBs to LED thresholdswould not be at convenient figures.The use of a logarithmic bargraphdriver which is specifically intendedfor this sort of application solves boththese problems.

The CircuitFigure 2 shows the full circuitdiagram of the Audio Level Meter. Theinput amplifier is based on ICI, andthis employed in the standardoperational amplifier non -invertingmode. PR1 provides an adjustableamount of negative feedback over ICIand enables its voltage gain to bevaried over the limits specified earlier.

The two rectifiers each use onesection of IC2. IC2a is used in thenon -inverting circuit while IC2b isutilised in the inverting rectifier. Eachrectifier is effectively an operationalamplifier working in the appropriateamplifying mode and followed by adiode (D1 or D4) which provides therectification. The diodes introducesevere non -linearity since they require

4

a forward voltage of about OV6before they begin to conduct readily;extra diodes are therefore used in thefeedback path of each amplifier tointroduce a non -linearity whichcounteracts the distortion in therectifying diodes and gives overallgood linearity. For this system tooperate properly the output potentialof each amplifier must be changedvery rapidly, and it is essential to usea device that has a suitably highslew -rate. ICs such as the TL082,LF353, and CA3240E are all suitablealternatives to the TL072, but aslower type such as the LM1458 isnot suited for this application.

C2 smooths the rectified signal, andthe value of C2 together with the lowoutput impedance of the rectifiercircuit and the low value of R7 givesthe circuit this required fast attacktime. The decay time is largelydetermined by the value of C2 inconjunction with some of the resistorsin the rectifier circuit, and due to thehigh value of the latter the circuitachieves a long decay time.

An LM3915 bargraph driver (IC3) isused; this device is probably not aswell known as the popular LM3914device. However, these two ICs aresimilar, and the LM3915 is merely thelogarithmic version of the (linear)LM3914. IC3 is used in the bargraphmode as this gives the clearest display

5 61 71 8

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for this type of application, but thisdoes give a fairly high maximumcurrent consumption of about 75 to80 milliamps from the positive supplyrail. A much lower maximum currentdrain can be obtained, if preferred, bydisconnecting pin 9 from the positivesupply rail so that IC3 operates in thedot mode. Incidentally, the negativesupply current is virtually constant atabout 5 milliamps.

ConstructionAll the components including thedisplay are mounted on the printedcircuit board, as shown in thecomponent layout diagram of Figure3. Construction of the board is verystraight forward, and none of the ICsare MOS types requiring any specialhandling precautions, but make surethat the diodes are fitted the right wayround and the single link wire is notoverlooked.

It is advisable to fit the display in a20 -pin DIL IC socket. This helps toraise the device above the othercomponents so that the board can bemounted vertically behind the frontpanel of the case with the displaybehind a cutout. Of course, ifpreferred the display can be mountedoff -board, and individual LEDs can beused instead of a proper bargraph

INPUT 0 AMPLIFIER

PRECISION1k WAVE

RECTIFIER

PRECISION1k WAVE

RECTIFIER

SMOOTHING

10 LEDBARGRAPH

DISPLAY

Figure 1. A block diagram of the Audio Level Meter.

LOGBARGRAPH

DRIVER


Audio Level Meter

INPUT

DISPLAYLED1-10

LINK

C3

I

Figure 3. The components, with one wire link.

Parts ListRESISTORS(All 1/4W 5% carbon)R1 10kR2, 3, 4, 5, 6 100kR7 220RR8 1k5R9 to R18 1k

POTENTIOMETERSPR1 470k 0.1W

horizontal preset

CAPACITORSC1 220n

polycarbonateC2 10u 16V

tantalum beadC3 100u 16V

axial electroC4 10u 25V

radial electro

SEMICONDUCTORSIC1 741C

op -ampIC2 TL072CP

dial BIFET op -ampIC3 LM3915N

bargraph driverD1, 2, 3, 4 1N4148

signal diodeD5 to 14: 10 LED bargraph display

any colour

MISCELLANEOUSPrinted circuit board; 20 pin DILholder for bargraph display;Veropins; screened cable, wire,solder, etc.

BUYLINES page 32

display. An advantage of usingindividual LEDs is that LEDs ofdifferent colours can be used, and thiscan give a clearer and more attractivedisplay, but it can be difficult toproduce a really neat display. If you douse a proper bargraph display, makesure that it is connected the right wayround. The normal method of.identifying the polarity seems to be byhaving the device identification andother markings on the side of thedevice which has the anode pins. Ifthe board is mounted horizontally (asshown in Figure 3) the display willread from left to right, like aconventional meter. Of course, itcould be mounted vertically if it is feltthat this would give a more easilyinterpreted display.

Mechanically construction must bevaried to suit the way in which theunit will be used. It can beconstructed as a self-contained unitpowered from a couple of 9 voltbatteries and housed in its own case,and a two pole on/off switch wouldthen have to be included in the unit.Alternatively a mains power supplyunit could be used as the powersource. In some cases it might bepossible to add the unit to an existingpiece of equipment, or to build it intoa piece of audio gear you areconstructing.

If it is built as a separate unit thelead which connects it to the mainitem of equipment will have to be ascreened type with the outer braidingconnecting to the earths of the twopieces of equipment. This is not just amatter of preventing stray pick-up ofhum and other noise from givingmisleading readings from the unit,because without the use of ascreened cable it is quite possible thatnoise could be fed into the main pieceof equipment. It might also benecessary to use a screened lead if

V+(9 -12V)

V- OV

V-(9 -12V)

the unit is housed in the main item ofequipment.

Of course, the signal take -off pointwill depend on what type ofequipment the meter is used with. Itcould, for instance be used to monitorthe output of a preamplifier or mixer,but it is obviously not possible here togive detailed instructions on how theunit can be connected to numerousitems of audio gear. This issomething that the constructor mustdetermine for his or her self, but inmost cases the correct method ofconnection will probably be fairlyobvious.

AdjustmentThe finished unit only requires oneadjustment, and this is to set PR1 forthe correct sensitivity. In order to dothis the main piece of equipment isfed with an audio signal thatrepresents a level of OdB (withcontrols on the main equipment beingadjusted for the correct signal level aswell, if necessary). PR1 is thenadjusted just far enough in aclockwise direction to give a readingof OdB from the display.

It is unlikely that the meter willprove to be over -sensitive even whenset at minimum sensitivity, but ifnecessary a resistor of about 470k invalue can be connected in series withthe input to reduce the sensitivity to asatisfactory level.

If an average reading circuit isrequired it is merely necessary toraise the value of R7 to about 10k sothat the attack time of the unit islengthened and it responds lessreadily to transients. In the interest ofobtaining an easily -read display it isadvisable to retain the long decaytime of the circuit. H E


ELECTRONICS

MULTIPURPOSE STORAGE BINSSet of 10 high quality storage bins which can be wall mounted orstacked in almost any configuration.Each bin measures approx. 109mm wide x 53mm high x 100mmdeep and is of high impact co -polymer plastic construction. Suppliedwith 2 wall mounting bars. Ideal for storing components of hardwarein workships, garage, home etc.

EXCELLENT VALUE at only £4.95 per set (p&p £1.50)

SPECIAL OFFER - RECHARGEABLE BATTERIESManufactured by Saft or Gould - Limited stocks available.*1-1P7 (AA) pencells 0.5Ahr £0.85p ea.*HP7 (AA) pencells 0.5Ahr tagged £0.90p ea.*HP7 (AA) pencells 0.5Ahr vented, quick charge 1 50mA

3-5hrs £1.00 ea.*HP11 ('C' size) 1.2Ahr £1.90 ea.*HP11 ('C' size) 2.OAhr £2.25 ea.*HP11 ('C' size) 2.0Ahr tagged £2.30 ea.*HP2 ('D' size) 1.2Ahr £2.00 ea.*HP2 ('D' size) 4.OAhr £3.25 ea.*HP2 ('D' size) 4.0Ahr tagged £3.30 ea.*SUB 'C' 1.2Ahr £1.45 ea.Please add 10% for post and packing.

All goods fully guaranteed. Despatch by return of post.Prices apply U.K. only. Trade enquiries welcome.

All orders to:MEON ELECTRONICS

P.O. Box 34, Luton, Beds LU1 1 LSTel: Luton 28606

LB ELECTRONICSFRUSTRATED EXPORT ORDER BRAND NEW& BOXED. EPSOM FX80 PRINTERS E350.00+ VAT (carriage£12 tnt)

SPECIAL OFFERS (while stocks last)Mullard .2" Red L.E.D.'s 0.06p, 7805 38p, 7805KC 5 Volt 1.5A 75p,78H05 5V 3 AMP £3.50p, 5K 3/." multiturn trim pots 14 for£2.50p

DISC DRIVE BONANZAPERTEC FD650 DSDD £199 + VATTEAC FD -55F 1/2 Height DSD 80 track/

40 track selectable at our new low price £199 + VATPAPST 3" Box Fan 220 volts 50hz require

luf capacitor £7.95 p/p £1.00As above but 12" 22mhz band width £88.70 + VATASCII coded qwerty Keyboard ,manufactured by Alphanumeric(Woking UK). Model 60K brand new plus data £19.95p p&p£1.5025 WAY 'D' Types, plugs £1.85, sockets £1.85 (solder tail) p&p30p. Telephone for bulk prices.8" Drive Cabinets complete with power supply (LINEAR) to taketwo 8" Drives, Brand New £99.95p + VAT (carriage cost)Twin 5" Cabinets with power supply £30.00 + VAT (providing adisc drive is purchased from us, if drives purchased elsewhere£40.00 + VAT)9" Green Phosphor Monitors Brand New and Cased CompositeVideo Input 1 8mhz band width £80 + VAT each (carriage cost)Textool 24 dil Zif Skt (used) £3.95p p&p 30pBrand New 13" Colour monitor fully cased. Full warranty 540 x236 pixel. RGB TTL Input plus apple Input £220 + VAT(carriage at cost).BNC Lead Bonanza coax lead with BNC plug at one end, 2 metresplus £1.00 p&p 30p and 10 metres plus £2.50 p&p 75pr! LB ELECTRONICS3/4,,,, 11 HERCIES ROAD, HILLINGDON,

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American]Express

ELECTFT1111111FX-COMPUTER

Teach -Yourself Computer and ElectronicsConstruction Kit

A complete introduction to the "How, Why andWhat" of Computers and Electronics in the most

practical way ever devisedTHE KIT IS BATTERY -OPERATED ANDCOMPLETELY SELF-CONTAINED. NO

TELEVISION OR OTHER EQUIPMENT ISREQUIRED. VERY EXTENSIVE MANUALS ARE

INCLUDEDMinistry of Science and Technology, Japan -

Prize Winning ProductThe FX-COMPUTER is the ideal introduction to thestudy and understanding of computers and electronics.The kit offers remarkable versatility because the com-ponents are interchangeable and circuits are con-structed by simply plugging specified components intothe board provided in accordance with the instructionmanuals. You quickly understand the principles involv-ed and new circuits can be easily devised, built anddismantled. No soldering or wiring is involved, no toolsare required; the components themselves complete thecircuits.No previous knowledge is required - very extensiveeducational manuals have been provided by English ex-perts in computers and electronics. Working throughthe manuals you will soon be able to write programmesand "run" them and understand how computers work.The following are just a few of the programmes in theComputer Manual (there are too many to list here) andalso a few of the projects in the Electronics Manual:Flow to instruct the Computer and Store Information into Memories. Use of dif-ferent Instructions and Programming Techniques. Adding, subtracting, multiplying,dividing, averaging, counting up, counting down, etc. etc. - in Decimal and Hex-adecimal. Converting Hexadecimal to Decimal, storing Random Numbers. Games:Tennis, Catch -the -Rat, Gun Fight, Slot Machine, etc. Using the Computer as aMusical Organ, storing and playing -back tunes, etc. OVER 100 PROGRAMMESSHOWN IN THE COMPUTER MANUAL PLUS EXPLANATIONS ANDDEMONSTRATIONS OF ALL TECHNICAL TERMINOLOGY.Electronic Components and How they Work batteries, conductors, resistors,capacitors, diodes, transistors, lamps, photo -electric devices (CdS cell is included inthe kit), oscillators, burglar alarms, control systems, organ, lie detector, etc., etc.OVER 65 PRACTICAL WORKING PROJECTS SHOWN IN THE ELEC-TRONICS MANUAL.

All this is in ONE kit, costingabout the same as the cheapest

"Basic" ordinary ComputerThe price is only £69.95 plus £3.00 P&P

(overseas rates quoted on request)TRADE ft EDUCATIONALENQUIRIES WELCOMED

Send cheque/PO/Access/Barclaycard toDEPT. HEFX. Electroni-Kit Ltd

It's not JUST a corn uteriELECTRONI-KIT LTD.

388 ST. JOHN STREETLONDON, EC1V 4NN (01-278 0109)


FX-Computer

A Hobby Electronics hardware review

The FX-COMPUTERThe arrival of theCommon, orGarden,microcomputer hasmade teach -

yourself -computingone of the world'smost popularpastimes. Now,using the sameapproach, we haveteach -yourself-

electronics - is itan advance?Read on . . .

Terry WestwoodThe Japanese are said to valueeducational achievement more thanany other nation, so it's hardlysurprising when they come up with aself -training kit, for youngsters, in thatapparently most essential of modernattainments, Knowing What To Do WithA Microcomputer. The FX Computer isdescribed as "A complete introductionto the How, Why and What ofComputers and Electronics in the mostpractical way ever devised". It'scertainly an attractive idea. The'computer' is completely self-contained,not needing (and indeed prohibiting) anymains connection, while the actualcomponents for experimentation areindividually built in to plug-in plasticmodules - an idea also used inindustrial training kits, which removesthe need for soldering and (more to thepoint) extensive desoldering, whenexperimenting with circuits.

The FX-Computer itself owes more inappearance to one of those fancy radiosets, covered in knobs, dials,loudspeakers and switches, than to amicrocomputer. The casing is made of areasonably tough plastic, but some ofthe joints give the impression of beingrather flimsy. The 'peg -board' where themodules are plugged in to make up thecircuit is so arranged that the modulesplug in and stay put reasonably reliably- a matter of some importance, as theunit is designed to be used upright. The

young (or not -so -young) experienced inthe use of Lego bricks will not besatisfied if the modules start droppingout onto the tabletop! But so far thisdoes not seem to be a problem; how themodules stand up to extensive wear andtear remains to be seen. For storage, thearea containing the modules is coveredby a clear plastic lid which hinges intoplace.

Pure And SimpleThe power for all the circuits is takenfrom six HP7-type batteries. This canprove expensive to run. It's a distinctadvantage, though, for young children,to have something which has noconnection to the mains. Circuits arebuilt up, simply by pugging thecomponent modules into the 'peg-board' in the right configuration.The modules are made of transparent,green -tinted plastic, with a componentsymbol etched in white on the top, so it'seasy to see what components are beingused. The actual component is alsoeasily visible through the plastic.Connection is made via flexible metalstrips on the sides of the modules, likeordinary battery -holder contacts.

The peg -board matrix providesthe power connections, and alsoconnects to other 'modules' within theoverall unit, for instance an amplifierwith a volume control and

loudspeaker, and a CdS cell which actsas a light -sensor for some of theexperiments. Extra space is provided forfuture expansions such as a meter (andthe FX's makers provide a number of kitswhich can be used to extend the FX'scapabilities).

Two manuals are provided: one giving65 electronics experiments, and theother with 100 computer programs. I

can't recommend the manuals toohighly. It's well known that a picture isworth a thousand words; this dependson the picture of course, but in this casethe pictures are not only clear andillustrative, but pictures and text leadnaturally on from one point to thenext, making the whole thing supremelyeasy to follow, and I wish that a fewother writers of self -instruction bookswould take a tip or two . . . For eachproject, the electronics manual givesclear instructions, circuit diagrams,outline identification and layoutdiagrams, with a simple and directapproach and with many ideas to aid thereader. This makes it much easier forthe reader to associate these differentaspects of project work. Being laid outstep-by-step fashion, it will take acomplete novice up to the point wherehe or she can build a series of simplecircuits and understand basicelectronics. Also provided are a pair ofsmall cables for connection to externalmodules, provided with the kit.


FX-Computer CAPACITOR

Symbol Diagram

SMALL LARGE

Shape

Ceramiccapacitor

ElectrolyticCapacitor

A capacitor stores direct current (charges up) by way of two metalplates positioned face-to-face.

The amount of electricity stored (the electrostatic capacity) dependsupon the size of the metal plates. Larger plates - more capacity (F).

1 F = 1,000,000µFt µF= 1,000,000 pF

When a capacitor is fully charged the current stops flowing. Alternatingcurrents however (e.g. voice signals, dial tones) continue to flow. Alter-nating current changes its flow direction and a capacitor repeats chargingand discharging.

A simple description of capacitors andcapacitance.

Dubious ConnectionsDespite the obvious merits of thesystem so far I have some complaints.The first and most annoying,considering that the FX-Computer is nota cheap bit of equipment, isthat some ofthe modules did not have accurately -machined connectors, resulting inirritating open -circuits. Not a lot of usewhen you are trying to learn aboutelectronics without learning to solder!Also, some of the circuit symbols on themodules could be confusing to a novice.For instance, some components can beused simply as links, but this is not verywell indicated. Maybe the use of analternative colour for those moduleswould help? The explanations of thecircuits, so far as they go, are fine, butthey do not go into enough detail to buildup the kind of understanding whichcould lead to building more complexcircuits - for this reason, theelectronics is kept at a very basic levelindeed. Also, there are simply notenough components. For instance,there is only one transistor - so youcannot even build a bistable. And youcan't bias that transistor accurately, asthere are not enough resistors andcapacitors (although there is a goodselection) to produce a full E20 standardset.

Taking that complaint to its 'logical'conclusion (!) is my most seriousgrumble: that is there is no logic or ICtutoring whatever, a factor whichseriously undermines the FX-Computer's claim to be a completeintroduction to computers andelectronics. The most essential link isomitted altogether! With the greatincrease in the use of digital as opposedto analogue electronics, this kind ofthing is to be regarded as basic, not an'extra'.

So let's look at the actual computermodule. This plugs in in exactly thesame way as the components, but is agreat deal larger. Using the sameconnections, it provides the facility to

learn about interface circuitry. The inputis a hex key pad, which is also used asthe tonic sol-fa for music programs. Theoutputs come in the form of a seven -LED strip, as single -figure sevensegment display, and a loudspeaker, sothat no television or monitor screen isneeded.

The computing manual, as with theelectronics manual, contains manygood descriptions and clear diagrams.The flow charts describing the setexercises are easy to follow, and themanual takes you through an organizedlearning path, building up knowledgeand confidence as you progress. Onceagain, we have a good idea, butwith some serious drawbacks. Thecomputer is designed to do teachingdemonstrations, and that is all it can do.It can't be interfaced to any equipmentnot specifically designed to go with theFX-Computer system. The languageused is a very low-level machine -codetype, which does not bear a great deal ofresemblance to the high-levellanguages normally used bymicrocomputer owners. And themanual, again, is excellent as far as itgoes, but does not give enough detailfor the bright enthusiast to progressfurther.

An Odd CoupleThere is a case of trying to put a quartinto a pint pot here: the FX does not haveenough memory to provide a high-levellanguage, yet tutition in a machine codegives the absolute novice no realintroduction to practical computerprogramming, while those who areinterested in code programming willfind that the FX's level of electronics islaughable; even were each section ofthe FX's teaching scheme moreextensive and ambitious, they wouldstill be mismatched. I felt that there was

TESTING FX-MELODY AND CLOCK(where fitted)

11 Insert the tanneries ano press the Stop switch of the

clock to test the clock unit.21 Turn on the main switch to light the pilot isms. A tune

will play eutornatiully; control the volume by turningVolume swith.

31 Press the key ...di to light the Urn,0) If the above operations cen be peNolmad correctly the

kit ie functioning properly.

IF, AFTER THOROUGHLY CHECKING, THE KITDOES NOT FUNCTION CORRECTLY, CONTACTYOUR DEALER OR DISTRIBUTOR.

' .-.1 IIII 18:88 1 WI000

/

' ^""1, - ' -.):" Z T ' ' 1 s' - . 1

- Tio T T T I II lae.-r, ..._431',----v-7-7-,7-707G7G7G

-,6B,1-.11111(11--14,, 1

0

1 1 1 1..1-. 0 . 0 .. 0 0 . . .IIIIIIi

-,..,.

.---c-

_ _0_0_0 _e leiTdoe- -

Each project is accompanied by anassembly diagram showing thecomponent modules.

a big jump in understanding betweenthe electronics projects and thecomputing projects, and that thedesigners could have improved whatlinking there is between these twosections.

I feel that the FX-Computer is a goodstart in electronics for children

No.22 Use of TIY,AIY and AMto store date in memory

PROGRAMaadrass I command

FLOWCHART

C START00 T Y '10

01 1(0) 0 I Point to address 50.

02 KA03 JUMP' F Ar

04 <0> 0 'bKeyKey "P';e:w'rde'ad -golt'; next

05 key clown? MP.

0607

AC,

KA1

0Display character on hexLED.

_LVES

; Ar-0809

:JUMP<0>

F

0OA <E>

Key 0,11 ores.,

OB00

'JUMP<0>

F

0

er

-reYES

NO

No - go to next step.

OD (7> 7

OE AM 4 Move contents of Ar to est-OF AIY B i dress pointed to by Yr,

10 <1> 1ryr. ,t wyr Add 1 to Yr.

11 JUMP, F12 <1) 1

cern,13 <1) 1

Check for car,NO

14 JUMP F No - go to 02.

,'0> 06 <2> 2

This program is another example of two KA commands beingused in different ways. At the first KA, the program waits ifa key has not been pressed; at the second it waits if a key hasnot been released.Program ends when data has been stored at all 16 addresses50-5F,

Part of a programing instruction,showing a listing and flow diagram.

beginning at about 10 to 14 (or adultswith no previous experience), but I

would not want to pay the price (f 69.95)for the system as it stands for my son ordaughter. What with low-cost microsavailable, and an increasing variety ofself -teaching booklets, not to mentioncomputers in school, there are too manygood alternatives for anyone withdetermination. Perhaps I feel a con-fidence that parents not acquainted withcomputers would not feel, but as for thechildren - they have plenty ofconfidence, and will probably meet withplenty of opportunities to learnsomething about computers!

Electronics is another matter - andit's worth noting that the samecompanies (just for the record, theDenshi Block Mfg. Co. Ltd., and theGakken Co. Ltd.) and their UKdistributor, Electroni-Kit Ltd., also dealin a whole range of electronics self -teaching modules, in the same style asthe FX system, but without theprogramming part. These are known asEX (sic) kits, and come in a variety ofprices and sizes, and Electroni-Kit do abrochure describing the contents.Electroni-Kit, of course, do their ownrange of small self -teaching kits as well.You can write to them at Electroni-KitLtd., 388 St. John Street, LondonEC1V 4NN.

Mind you, the FX-Computer has beenawarded a design prize by the JapaneseMinistry and Science and Technology,so somebody obviously thinks it's goingto work. I continue to feel that it's a verygood idea which just isn't capable ofgiving full value within its adoptedformat. But, who knows - it may startsome interesting trends. H


COMING SOON TO . .

NgL 0

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EQUALIZERThe professional solution to many problems in audio equalisation!

Parametric equalisers are flexible and precise. They can be used in place of graphicequalisation systems in many situations, and for many other jobs where a graphic would

not be equal to the task.The HE Para -Q is a stereo parametric equaliser designed to semi-professional standards but

that can be built at an amateur's price.Up to 20dB of boost or cut is available at any centre frequency from 50Hz to 1 1 kHz and the'Q', which sets the bandwidth around the centre frequency, is variable up to a maximum of

25, allowing either a very narrow or a wide band of frequencies to be operated on.It can be used for equalisation or hifi systems, home recording studios, for music synthesis

or any other musical signal conditioning application.

PERSONAL CASSETTE BATTERY SAVFRA "home base" power supply unit to save your batteries when you're listening to your

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charge at home while you're on your skates in the great outdoors!

MORE FOR THE MOTORISTTwo easy -to -build car accessory projects, to give your motor that extra touch of class.

IN CAR ENTERTAINMENT OFFERA very special offer will be available to readers of Hobby Electronics, only, in our November

issue.If you've ever fancied a top class in -car stereo system but have always backed off at the

price, you must see next month's issue for this sensational offer!

!Please reserve me

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Atthough these articles are being prepared for the next issue, circumstances may alter the final content.


1

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YOUR CAREER ..YOUR FUTURE . YOUR OWN BUSINESS . YOUR HOBBY

THIS IS THE AGE-OF ELECTRONICS !the worldt fastest goNth industry...

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We have had over 40 years of experience in training men and women successfu ly in this subject.

Our new style course will enableanyone to have a real understandingof electronics by a modern, practicaland visual method. No previousknowledge is required, no maths, andan absolute minumum of theory.

You learn by the practical way ineasy steps, mastering all the essentialsof your hobby or to start, or further, acareer in electronics or as a self-employed servicing engineer.

All the training can be carried out inthe comfort of your own home and atyour own pace. A tutor is available towhom you can write personally at anytime, for advice or help during yourwork. A Certificate is given at the endof every course.

You will do the following: Build a modern oscilloscope Recognise and handle current electronic

components Read, draw and understand circuit diagrams Carry out 40 experiments on basic

electronic circuits used in modernequipment using the oscilloscope

Build and use digital electronic circuitsand current solid state 'chips'

Learn how to test and service every typeof electronic device used in industry andcommerce today. Servicing of radio, T.V.,Hi-Fi, VCR and microprocessor/computerequipment.

British NationalRadio8cElectrtmics School Reading,Berks.RG1 1BR

COLOUR BROCHURE

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Careers In Electronics

CAREERS IN 902ELECTRONICS uka

Expertise in computer electronics does not only lead to thelab. It can lead to a career as a Customer Engineer, andfurther. This month we look at a special training course,

and some other career routes in digital hardware

A Customer Service Engineer in anybusiness needs a combination oftechnical and management skills whichputs him not so much with a foot in eachcamp, as with both feet in both camps-unlikely as this may sound. This isdoubly true of customer engineers incompanies dealing in computer sys-tems, where very expensive andspecialised equipment is being sold,often in quantity, to non -specialistcustomers, many of whom (at thepresent) are dabbling in computersystems for the first time.

Customer Service Engineers areresponsible for installing computersystems on the customer's site, and alsomaintaining equipment and solving anyproblems which arise, also on site. Thiscalls for a fairly high level of technicalskill, coupled with the ability to handle apossibly irate or anxious customer tact-fully and maintain his confidence inengineer, company and system!

The Customer Engineer is very muchhis company's direct ambassador. (Thevast majority of computer engineers arestill men. This is due to lack of womenapplicants - as one college departmentsaid when asked why they had onlytaken in one woman engineer in a year:"We accepted all the applicant we had".)

He may also have the role of sales-man for his company to estJblishedcustomers, consulting them on theirfuture needs and advising them whichequipment to install. Taking into accountthe competition from ever -hungryrivals, this can be a very responsible jobindeed.

All -Rounders NekdedIt's not surprising that computersystems companies have had somedifficulty getting enough engineers ofthe calibre they want, even from amongcollege leavers (or school leavers) withthe right technical background. This isthe reason why five major computersystems companies have bandedtogether with a technical college of goodrepute, the Polytechnic of CentralLondon (PCL) to devise a full-time, two-year course in computer technologywhich not only leads to a TEC (TechnicalEducation Council) Higher Diploma, butis tailored specifically to the needs of thekind of company involved, and is more

Helen Armstrong

INTERPERSONAL SKILLS

DIGITAL SYSTEMS

COMPUTER PERIPHERALS &DATA TRANSMISSION

OPERATING SYSTEMS &COMPUTER APPLICATIONS

THEORY & PRACTICE OFCOMPUTER MAINTENANCE

CUSTOMER RELATIONS

DIGITAL ELECTRONICS& TECHNIQUES

ENGINEERING FUNDAMENTALS

COMPUTER ARCHITECTURE &ASSEMBLER

MATHEMATICS & HIGHLEVEL PROGRAMMING

7'Polytechnic

ofCentral London

10--

8-cc

2-of

broadly-based than most technicalcourses.

The five companies involved are DataGeneral, who specialise in broad, com-patible product lines from micro-processors to multi -processor systems,plus peripherals; Data Logic, who dealin hardware, consultancy and customerservice; the Digital Equipment Corpor-ation, who invented the minicomputer,Harris Communication and InformationProcessing, who produce advancedequipment for information technology,and Hewlett Packard, a major computerand instrumentation manufacturer.

Hewlett Packard is one of the world'sbiggest electronics companies, andtheir Computer Systems side, whichthey developed comparatively recently,is their fastest -growing and principal

market area now, with 56% computerproducts.

World sales in 1982 well exceededfour billion dollars, (£169 millionpounds in the UK) and there are 1300Sales and Service employees in the UK,out of more than 67,000 employeesworldwide. They are well known in theirfields for measuring instruments, andmedical electronics, but their computerproducts belong in the mainframe andminicomputer class, with desktop andrealtime technical computers, businesscomputers, and factory automationsystems, word processing and apersonal computer aimed at business-men. Their pride and joy.is the desktop -sized HP9000, which has the capacity ofa 32 bit mainframe and is based on theircustom NMOS In microprocessor.

Difficult ChoiceWhile we're on the subject of careersin electronics, Hewlett Packard wasformed in California in 1939 by BillHewlett and Dave Packard - in PackardSr.'s garage - with a new form of audiooscillator designed by the partners.Great oaks from little acorns - butthat's another story.

Mike Faithful!, an electronics en-gineer of long experience both outsideand inside Hewlett Packard, spoke toHobby Electronics both about the PCLcourse, and generally about entry intothe many fields of electronics embracedby a large engineering concern.

As well as being an electronics man,Mike is also responsible for inter-viewing candidates for the PCL courseon behalf of Hewlett Packard - one of apanel of assessors representing the fivecompanies involved.

"The main problem in selectingpeople has been the combination ofskills needed. Even the initial screeningcan be tricky, because PCL are used toselecting people by their academicachievements. That, and the fact thatmost applicants are very young. Young-sters change a lot in two years. You haveto be able to spot a Customer Engineerin his unfledged state!"

There are, of course, minimumacademic qualifications required.Candidates should have obtained (orexpect to obtain) four GCE passes,including one at A level, in a mathe-matical or physical science subject, and



an 0 level in English. Equivalentqualifications from TEC, CGLI, OND orONC are also considered. Once the ap-plications have been screened,applicants are interviewed by the selec-tion panel. Each successful applicantwill be sponsored specifically by one ofthe sponsoring companies.

Students on the course, as well astheir local authority grant, get a bursaryof over £600 from their sponsor, as wellas employment by the sponsoring firmduring the long vacation at around f350a month (which is tax free for anyonewith normal student status, giving areal taste of practical working experi-ence. It's also an opportunity for thetrainee to work in different departmentsof the sponsoring company and see howthe whole show runs.

Success RateEmployment is not actually guaran-teed at the end of the course, but Mikemade it sound as if the traineeshave to try quite hard in order to fail."We have a better than 90% successrate" he says. "I'm astounded, whenyou look at the difficulty in selecting rawrecruits." Nor do the sponsors have acast of thousands to choose from:although they advertise in the press andapproach local careers offices, they onlyjust made their quota of students thisyear. This is less because the studentsthey are looking for are rare creatures(although they are) than because con-ventional academic selection is gearedmore to qualifications and less to theright mix of technical aptitude andpersonality.

However, where a likely applicantdoesn't have the required qualifi-cations, Hewlett Packard is sometimesprepared to offer in-house training fortwo years, along with day release to takea TEC course, before the trainee goesout into the field. This is not common-place in computer engineering,although it's not uncommon in otherfields of electronics. As Mike explained,"Computers are just too big." Othertypes of equipment can be brought backand serviced in the companyworkshops, allowing an even workflowand time enough to allow day release.Computers need to be serviced on site- and immediately, or sooner - so thatthe service force needs to be constantlyon call.

But Hewlett Packard's swift expan-sion on the computer side has led themto regard good customer engineers asan investment. Before the PCL coursewas devised, there was no standardtraining for customer engineers, andcompanies relied on attracting experi-enced engineers from their rivals - orpoaching, as it is known in the trade! Butthis 'free exchange of talent' can nolonger keep up with demand.

Casting an eye down the course'ssubject list is instructive: Mathematicsand High Level Programming, ComputerArchitecture and Assembler, Engineer-ing Fundamentals and Digital Elec-tronics and Techniques are followed byCustomer Relations; Theory andPractice of Computer Maintenance,

Students at the Polytechnic of Central London: computer engineering callsfor the ability to unravel the mysteries of the computer both through its ownlanguage and through the hardware itself.

Operating Systems and ComputerApplications, Computer Peripherals andData Transmission, and Digital Systemsare followed by Interpersonal Skills.Definitely, the candidates' ability, orpotential ability, to present themselvespositively, and communicate well is animportant factor in selection. MikeFaithfull adds that interpersonal skillsare highly rated by computer companies,but, in his opinion, not highly ratedenough: he would place their import-ance at 30% to 70% with engineeringskills.

TeamworkBecause the role of the customerengineer involves not only being able toinstall, maintain, repair, extend andtrouble shoot computer systems, butalso being able to do so under the noseof the customer, the course emphasisesteamwork and the combination ofindividual and collective efforts from thestart.

"There is not the emphasis on in-dividual marks that you expect on anormal academic course" Mikeexplains. "Obviously individual study isessential, but within the college thework is structured as it would be in abusiness context. There is both grouppressure, and group help. Everyone ison first name terms and has to worktogether on projects and presen-tations."

The sponsoring companies don't

remain aloof from the process; seniorstaff from the Managing Director down-wards hold lectures and seminars fortheir students and pass on the benefit oftheir first-hand experience in thebusiness - a style of motivatingmanagement commonplace in the USAand still uncommon in the UK. HewlettPackard have found that, given thechance to contribute ideas, use theirinitiative and take responsibility,employees are more involved in theirwork, and happier (not to say more pro-ductive) for it.

Says Mike "We're looking for leadersrather than followers" - but he has norigid way of defining the right applicant.Attention to detail - a businesslikestyle of dress, the ability to pay attentionto and show an interest in the panel'squestions, and express himself well inreturn, being firm without beingaggressive and polite without beingtimid - are some of the bald charactertraits which a successful candidatemight show, but Mike admits that it is'gut reaction' which decides the finalchoice. This is the more important assuccessful students could well graduatefrom customer engineering to manage-ment or more specialised engineering,and the selection panel has thisprospect in mind.

So much for the 'personality' aspectsof customer engineering; what aboutthe engineering? The academic qualifi-cations are fairly basic, less than wouldbe needed for, say, a university course


Careers In Electronicsin engineering, and a comprehensiveeducation in computer engineering isgiven at the Polytechnic. So whatdivides one candidate from another atselection stage? "They need a feel forpractical things" says Mike. "We'relooking for people who have a strongamateur interest in practical things:electronics, car mechanics, housewiring, amateur radio, - people whocan make things work. Some peoplethink we must be looking for people whohave ZX81 s and know a bit of BASIC -but this has very little relevance tohardware."

Mike has reason to appreciatepractical ability with electronics.Starting from a hobby interest in elec-tronics, Mike took the decision to workat something he enjoyed, and workedhis way up from mechanical assembly("I knew how to solder") via prototypewiring and R&D at British Aerospace (heworked on Concorde and is proud of thefact that his 'bits' are still part of thedesign) to Hewlett Packard while stillunder thirty. He reckons that five years'practical experience in industry - forthe person who is attentive and watchesout for opportunity - is as effective asfive years' study but "The piece of paperis always worth having if possible."

No Time Like The PresentMike believes that the present is avery good time for anyone wishing towork in computer engineering to getinto the Customer Engineer side. Theindustry is expanding very fast, and agood supply of skilled people is neededto get the machinery up and running. Ina few years, with servicing techniquesmore automated and standardised, thedemand for skilled troubleshooters willhave shrunk considerably, and the fieldwill be carved up among technicians outon the road servicing and replacingmodules, and a smaller backup force ofhighly skilled customer engineers forthe real problems. Today's customerengineers are looking forward to a

future where their versatility will opendoors into management, Research andDevelopment and higher -levelcomputer engineering.

Hewlett Packard also take in graduatesfrom the 'Milk Round', their represen-tatives visiting nineteen universities in1982 and, again, look for personal aswell as academic qualifications. Onceaccepted, the graduate will be bothsponsored out on training courses -IEE classes, for instance - and is en-couraged to extend his or her ownknowledge and put ideas forward intheir field. There are also apprentice-ships on the bench electronics side.They seek for, and take in, people fromall kinds of sources - local advertising,YTS schemes, Job Centres, schools andcolleges, and also employ a fair numberof sandwich course students who arenot destined for future employmentwith the company.

One important tribute to theirmotivational style of management isthat engineers who have completed thetraining course successfully nearlyalways accept employment with the

company, although not compelled to doso, where some big corporations findthemselves losing their trainees afterthe minimum time contracted, as theygo in search of greener pastures or amore congenial atmosphere. Andbefore we leave Hewlett Packard to lookat a couple of other companies whoemploy Customer Engineers, someadvice from Mike Faithfull for anyonewho has ever applied for a course or apost - or several - and has beenunlucky. "Keep trying" he says. "Don'ttake disappointment personally. If youkeep applying, you will find the rightplace eventually. A lot of failures aresimply bad luck; but it does pay to checkthat your approach has been right."

Other CompaniesAnother large company whichsponsors students in a course which isspecifically linked to industry needs isFerranti Computer Systems. The coursewhich they sponsor at the UniversityCollege of South Wales at Bangor, alongwith GEC Marconi Electronics, aims tocombine undergraduate study withindustrial experience in an integratedfour-year course, with a full ten weeksof industrial training during the longvacation - a rather different deal fromdoing a general arts or science degree!

Sponsored students receive a bursarywhile on the course, and a salary whileworking in industry. The course isdivided into Engineering Science,Mathematics and Physics forEngineers, and Support Technology?thelatter including Production, Commerceand Industry, Quality and Reliability andthe appropriately -named 'HumanComponent' course! The wholetraining, while very comprehensive, isfar more specifically aimed at practicalrequirements than the purely academic,theoretical education offered by normaluniversity courses. Application to thisand similar courses is through UCCA inthe usual way for a University.

Basic entry requirements for thecourse are A levels (Grade C or above) inMaths and Physics, plus 0 levels inEnglish Language and two othersubjects, or an ONC, OND, or TECequivalent.

Ferranti also operate a GraduateTraining Scheme of between one andtwo years for graduate engineers andprogrammers at their technical trainingcentre in Bracknell - fields fall roughlyinto Engineering, Programming andTechnical Documentation. Training is acombination of on-the-job, andcoursework at the centre.

Computer giants IBM recruit bothexperienced Customer Engineers -often ex -BBC or British Telecom - anduntrained applicants with A levels inMaths and Physics or equivalent qualifi-cations. Training takes at least fouryears, and is a combination of on-the-job and classes; again, as the CustomerEngineer is effectively a representativefor the company, emphasis is placed ona businesslike approach and ability tocommunicate, as well as technical skills.

Apart from Customer Engineering,IBM have an intake of Higher TECstudents for jobs in product testing, testengineering and quality control; muchof IBM's equipment is designed by themin-house, including microprocessors, sothere are computer -related jobs in

Above: the memory board from the HP9000 desktop computer, compared insize to an ordinary fountain pen. Below: Generating graphics on the HP9000itself.



production engineering and productionmanagement as well. Graduates arerecruited on the 'Milk Round' for designand R&D careers, and at the other end ofthe scale there are jobs in testing andassembly on the manufacturing side -all under the umbrella of one largecompany.

Allied Business Systems have alsoswitched from recruiting, primarily,experienced customer engineers withGCE or OND/HNC qualifications, totaking on trained but inexperiencedengineers, often from TOPS courses.These trainees are given a ten weekinitial training course in the company'sproducts, and another four weeks later.In other fields - R&D, workshop andproduction engineering, ABS recruitmostly experienced engineers, throughelectronics employment agencies. Suchagencies are also a source of experi-enced customer engineers - goodcustomer engineers are still sufficientlyscarce for a company like ABS to feelthat it is not worth their whileadvertising through the press; agencyrecruitment, while it is expensive, canget the right people for the job, quickly.And as always at the business end ofindustry, people are in demand whohave specific skills and, even moreimportant, the know-how in using theirskills to get results.

The message is, that if you want towork with computer hardware, it pays toconsider training with a specific bias in

One of Hewlett Packard's several R&D

that direction. This can mean seekingeither a sponsored course, or a traineeposition in a computer systemscompany. Sources of information arethe usual ones: schools and localauthority careers offices, advertising inlocal, national and specialist press,TOPS for older students, andspeculative applications to firms in thefield. Discerning use of directories andthe periodicals rack in your nearestcentral library is called for. Training for a

and manufacturing sites.

specific career is hard work and calls fordedication, but the rewards can be con-siderably more discernable than thosebeyond a purely academic university orpolytechnic course.

Many thanks to Mike Faith full andHewlett Packard for talking to us aboutthe Polytechnic of Central London'sComputer Technology course; thanksalso to ABS, Ferranti and IBM forsupplying further information. HE

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THE PREMIER SHOW FOR THEELECTRONICS ENTHUSIAST!

Cunard International Exhibition Centre, Cunard Hotel,Hammersmith, London W6

Improved VenueWe have transferred BREADBOARD to the Cunard Hotel, offering improved facilities to thevisitor, including car parking and ease of access by rail, tube and car, all in a modern attractivesetting. See below for our arranged reduced hotel/rail fare package to attract enthusiasts fromall parts of the country.

Planned Features include Lectures: covering aspects of electronics and

computing. Electronics/Computing Advice Centre. Demonstrations: electronic

organs/synthesisers. Holography presentation. Practical demonstration: 'How to produce

printed circuit boards. Computer Corner -`Try before you buy'.

FRIDAY November 25th10am - 6pmSATURDAY November 26th10am - 6pmSUNDAY November 27th10am - 4pm

Amateur Radio Action Centre. Computer controlled model railway

competition. Pick of the projects - Demonstration of the

best from ELECTRONICS TODAYINTERNATIONAL, HOBBY ELECTRONICSand ELECTRONICS DIGEST.

Giant TV screen video games. Robotic display.

Why not make your visit to Breadboard '83 themost enjoyable yet. At these *prices, why notbring a partner, do your Christmas shopping,have an evening on the town, see the lights,and have a weekend in London!

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HOLIDAY WEEKEND PACKAGE* Accommodation in a first class hotel with private bath, direct dial telephone, radio and

colour television.* Return 2nd class rail travel from local British Rail station to London.* Ticket to Breadboard '83.* Breakfast at the hotel.* Prices quoted are inclusive of service and VAT.

Please note this offer closes on 1st November 1983.

REGION SINGLE

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1 Night 2 NightsBeds, Berks, Bucks, Essex, Herts,Kent, Surrey and Gtr London

£29.25 £54.25 £47.75 £84.75

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£32.50 £57.50 £57.25 £94.25

Avon, Derbyshire, Dorset, Glos,Gwent, Herefordshire & Worcs,I.O.W., Leics, Lincs, Norfolk,Notts, Somerset, Staffs,Warwickshire, West Midlands

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Cheshire, Devon, Glams, Humber,Lancs, Gtr Manchester,Merseyside, Powys, Shropshire,West & South Yorks

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Cornwall, Cumbria, Dyfed, Glwyd,Gwynedd, North Yorks

£44.25 £69.25 £75.00 £112.00

Borders, Cleveland, Durham,Dumfries & GallowayNorthumberland, Tyne & Wear

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Central, Lothian, Strathclyde £51.75 £76.75 £89.50 £126.50Fife, Tayside £55.00 £80.00 £95.00 £132.00Grampian, Highland £58.25 £83.25 £101.50 £138.50

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Date of arrival: 25th Nov E 26th Nov ENumber of nights: 1 night E 2 nights ElRoom(s) required: single E twin E

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I 17-1

2.S

Forward Bias

Questions, answers and errata from readers and writers.

The Bat Light(HE June '83)There were three errors in the BatLight diagrams: R12 was omitted fromthe Component Overlay although itwas quite clear in the photograph of theassembled Bat Light board; inFigure 1, R10 etc. should be connecteddirect to V+ and not via C2 and ZD2;in Figure 2, R1 etc. should be connec-ted direct to V+, not via C2 and ZD2,while the positive rail should go to theop -amps.

However, if the project is construc-ted according to Figure 3, with R12added as shown here, the projectshould work with no problems.

The diagrams show the correctdetails from Figure 1 (above) andFigure 2 (below left), and the wholeof Figure 3, the component overlay,with R12 added.

0 V

v+ o-tWis-

Ova

R10100R rAr ZD2

alik 15VC2100n

11 ICILM324

Did You Notice Our SneakPreview?

The sharp-eyed among you will havenoticed that the Sound PressureLevel Meter, as featured on page17 of the September issue, had two

probes which were not described inthe project.

Were they for inserting into thelistener's ears? Or for investigatingthe sub-plughole noise generated bydraining bathwater? No. In fact, theybelong to the Hi -Voltage Meter, asfeatured on page 28 of this issue. Youweren't going mad. We were.

COLLECTED BOOBS

TremolekoSwitch Two (SW2) wasinadvertently omitted from the PCBoverlay drawing of this project. Itshould connect between the twospare pads (because we left theswitch out!) situated between R2 andPR1.

Continuing excerpts from the Hobby Electronics Errata Box.

Tantrum Amplifier(HE October '79)Figure 1: SW2 is incorrectly drawn; thecorrection is shown here. The PCB iscorrect.Parts List: The push button switchesare obtainable from RS Components (viayour local components stockist). Youneed four 2 -pole changeover switches,four buttons, and a four-way mountingbracket C2, 102 can be PCB mountingelectrolytic tapes.

The text running from p.11 over top14 has been scrambled - however, itis all there and the meaning will be clearto anyone reading it through.

Balance Control: Disconnect theends from C13 and C113 and take themto the sliders of RV3a and RV3brespectively.

LEFT TAPE 0/P

I -SVV1a -0-

I 1

F -TO SW2b I

SVV2a

TO RIGHT AMP

Multi Option Siren(HE October '79)Circuit Diagram: Many people havewondered what happened to RV4. Lookcarefully at the photograph, and you'llsee that lack of space meant that it hadto go on the back of the box.

Figure 3: The wire coming from thejunction of R12, R3 should be markedSK1 not SW1.

HEBOT I(HE November '79)The original HEBOT is now totallyextinct, as the chassis and motor are nolonger available.

Digi-Die (HE January '80)Figure 5: The labels IC2 and IC3 on theOverlay should be swapped over. Thelink from IC2 pin 16 and IC3 pin 14 to thepositive supply has gone missing -justwire in a link from these pins to the padthat goes to the battery positive(junction of R1 and R2).

Short Circuits: Noise Gate(HE January '80)Circuit Diagram: Q1 is a P -channel FETas shown, and not N -channel as stated H Ein the text.


ADDITIONS TO OUR LISTRADIO MOBILE CAR RADIO SPEAKERS9" x 4" 4 ohm 5 watt - £1.70. 6" x 4W' 3 ohm 4 watt - E1.35;6" x 4" 4 ohm 4 watt - £1.15. 6" x 4" 16 ohm 5 watt - £1.15;5" round 8 ohm 10 watt -- £2.30. 6W' round extra thin for dooror back shelf. In fact these are only 11/2" thick 16 ohm 5 watt -£1.75; 5" round 16 ohm 5 watt chassis size 51/2" square (approx).- £1.15; 5" round 4 ohm 5 watt chassis size 51/2" square (approx).- £1.15; 5" round 4 ohm 6 watt with built in tweeter - £1.15.9" x 3" 8 ohm £1.15.IMPORTANT NOTE: The speaker prices above do not includepostage but 10 or more speakers are post free otherwise addE1.50 per order.

STABILISED POWER SUPPLY (Mains Input)By LAMDA (USA) - Ideal for computer add-ons, d.c. output.Regulated for line volts and load current. Voltage regulation .1%with input variations up to 20% - load regulation 1% from noload to full load - or full load to no load. Complete in heavy dutycase - Models available: 5v - 6A E17.25. 5v - 9A E23. 12v - 1.5A£13.25. 15v - 1.2A £13.25. 24v - 2A E23.

PREPARED APPLIANCE LEADSBuy these, they will save you time and money. Prices are for smallquantities but if you are buying E100 lots or more - halve theprices. Twin circular, white .5mm length 54" - 23p; 3 corecircular, white 99" - 1.25mm - 57p; Twin circular black 77",.5mm - 23p; 3 core circular, black 88" .5mm - 35p; 84" .5mm46p; Twin circular black 114" 1.25mm - 69p. Twin circular white200" .75 fitted 2 pin continental plug one end - 57p; 3 corecircular white 54" .75mm core sizes fitted continental two Pinand earth plug one end and new type 3 flat pin appliance connectorat other end - 75p.

MINIATURE TOGGLE SWITCHES As used on Tvcameras and other lightweight equipment. American made by theArrow Company.Arrow ref. TCH3E Single pole changeover, centre off - 46p.Arrow ref. TSH3PCL Single pole changeover PCB mounting - 46p.Arrow ref. TC6M Double pole changeover, centre off - 69p.

REED RELAY KIT High inductance coil, moulded to take4 reeds, operated by three volts DC or 12 ma. Could be used toclose 4 circuits, or with the external magnets supplied, you couldhave two normally open, i.e. two changeovers. An exceptionalbargain at 99p for the coil -4 reeds and 2 magnets.

ROCKER SWITCHES Standard size fit 11.5 x 28mm cutout. Single pole on/off - 23p; Single pole changeover 28p; Singlepole changeover with centre off - 30p; Single pole on/off withneon - 46p, for double width cut out DpSt 36p, DpDT 46p.

NICAD BATTERY CHARGERS This, although intendedto charge button cells, bring leads from the contacts and then it willsuit almost any Nicad battery, charge rate approximately 15mAbut easy to vary.

MIXER MOTOR If this had a case around it, it would be acomplete mixer as it has a speed control switch giving threechanges of main speed and it also has a gear box with two socketsfor paddles. Three lower speeds are available from these sockets.E3.45 - post 60p.

LOW VOLTAGE SWITCH Approx 11/2" diameter, thecover unscrews to enable the switch to be fixed and to keep thecontacts covered, contacts look capable of up to 10 amps. 23p.

PILOT BULBS Standard round 11mm 6.5v .3a by Philips.Box of 10 price 50p.

12 volt MOTOR BY SMITHSMade for use in cars, etc. these are serieswound and they become morepowerful as load increases. Size31/2" long by 3" dia. They havea good length of Y." spindle -Price £3.45.Ditto, but double ended £4.25.Ditto, but permanent magnet £3.75.

EXTRA POWERFUL 12v MOTORMade to work battery lawnmower, this probably develops up to1/2 h.p., so it could be used to power a go-kart or to drive acompressor, etc. etc. £7.95 + E1.50 post.(This is easily reversible with our reversing switch - Price £1.151.

MAINS MOTORSWe have very large stocks of motors from 2 watts to '4 hp. Most ata price well below cost, let us know your requirements. Some newones just arrived.67 R.P.M. Motor: 1/10 hp. reversible mains operated split phasemotor with gear box - shaft fitted with chain sprocket £11.50 plus£2 post.100 R.P.M. Motor. 1,5 hp. Mains driven reversible motor withgear box, 1/2" shaft from gear box -- Very powerful £1650 plus £3post.BALANCED MOTOR: Disc or tape drive motor 150Orpm reversible- mains operated. 3" dia 2%" long with good length 3/8" spindleE4.60 plus 80p post.

CROSSOVER NETWORKS2 -way: 4 or 8 ohm impedance - power input up to 25W, crossoverfrequency 2kHz with wiring dig. 87p each.3 -way: 4 or 8 ohm - power input up to 60W, crossovers at 700kHzand 3500kHz with wiring diagram. £1.15.

- BARGAIN OF THE YEAR -The AMSTRAD Stereo Tuner.This ready assembled unit is the ideal tuner for a musiccentre or an amplifier, it can also be quickly made into apersonal stereo radio - easy to carry about and which willgive you superb reception.

Other uses are as a "get you to sleep radio", you could eventake it with you to use in the lounge when the rest of thefamily want to view programmes in which you are notinterested. You can listen to some music instead.

Some of the features are: long wave band 115 - 270 KHz,medium wave band 525 - 1650KHz, FM band 87 -108MHz, mono, stereo & AFC switchable, tuning meterto give you spot on stereo tuning, optional LED wave bandindicator, fully assembled and fully aligned. Full wiringup data showing you how to connect to amplifier or head-phones and details of suitable FM aerial (note ferrite rodaerial is included for medium and long wave bands. Allmade up on very compact board.

Offered at a fraction of its cost: only £6.00+ £1.50 post + insurance.

THIS MONTH'S SNIPA PRESTEL UNIT, completeexcept for 6 plug-in IC's- so far as we knowthe unit wouldwork once themissing IC'sare fitted.Price: E19.75+ £2.00 Post.Contains all theitems listed below.

VIEWDATA EQUIPMENTORACLE VB 100 PCB This is the heart of many viewdatasystems, including the Prestel Unit which we are currently selling .This board uses 25 I.C.'s, 5 transistors, 2 crystals and very manyother components. It has a TV aerial input and a TV UHF modifier(AZTEC UM 1233). We offer this board, new, unused and completeexcept for 6 of the 25 I.C.'s at £5.75. The plug in holders for themissing I.C.'s are on the board wired ready to receive them.MINIKEY SERIES KL This is an American made membranekeyboard withsilver contacts as used on Prestel to dial into theBritish Telecom phone system. It is really miniature, only 60mm x65mm x 5mm thick. It has 16 press buttons, giving standard 0-9numbers and ABCD facilities. There are two other buttonsengraved asterisks. This is an extremely well made board. £4.60.

TELEPHONE LINE TERMINATION UNIT As usedwith Prestel but undoubtedly suitable for other applications. Impor-tant components are phone line isolation transformer and 3 ClareReed Relays. All mounted on a pcb with I.C. and other componentsP.C.B. size approximately 7" x 1%" - £3.45.VOLTAGE STABILISED POWER SUPPLY As usedwith Prestel this has a mains input transformer with a 13v - 0 - 13v20 watt mains transformer. Rectifiers and semiconductors allmounted on P.C.B. size approximately 435" x 2". The stabilised DCoutput from this is -27v - 12v -0 +0 +12v +27v. Price £4.60.INSTRUMENT CASE As used with the Prestel unit thiscomprises an all chassis and a moulded tront plastic cover securedto the chassis by self -tapping screws. Overall size approx 12"x 10"x 2%" deep. On the front is fitted the minikeyboard as describedabove and although originally intended for Prestel, this case shouldhave other uses including telephone answering machine, etc.Price E5.75 £1.50 post.

X-RAY EQUIPMENTBeautifully made by the American GEC Company. We have a wholerange of spares, all unused. X-RAY TROLLEY - This could bemotorised, mains or battery driveb with self retractable flex lead,so it could be used for carrying other mains operated equipmentwhich need to be rnanouvered easily in a relatively confined space.Switching and breaking is done from the handle and there is ampleroom and capacity for heavy transformers and smaller equipment.The overall size of this trolley is approx. 3' x 2' x 3'6" Price £69.X-RAY HEAD This comprises the x-ray tube in a radiation proofhousing with plug in lead connectors. The tube enclosed in thehousing is a hospital size tube and unused and new. Price E69.EHT TRANSFORMER & RECTIFIER UNIT We estimate that theoutput voltage of this is probably 30 or 40 KV. Completely enclos-ed in an oil filled container, size 13" x 14" x 15". There are fourrectifier sections, each using 20 EHT rectifiers connected in seriesthese plug in for ease of replacement. The unit is powered by a600 cycle supply. Price £69. 600 CYCLE SUPPLY UNIT Mainsoperated through a step down transformer, this contains all theelectronic components to operate the equipment. Price £57.50.

MINI MONO AMP on p.c.b., size 4"x 2" (app.)Fitted volume control and a hole for a tone con-trol should you require it. The amplifierhas three transistors and we estim-ate the output to be 3W rms.More technical data will be includ-ed with the amp. Brand new,perfect condition, offered at the verylow price of £1.15 each, or 10 far £10.00

[Things you can make include Multi range meter, Lowohms tester, A.C. amps meter, Alarm clock, Solderingiron minder, Two way telephone, Memory logger, Liveline tester, Continuity checker, etc. etc., and you will stillhave hundreds of parts for future projects. Our 10Kgparcel contains not less than 1,000 items - panel meters,timers, thermal trips, relays, switches, motors, drills, taps,and dies, tools, thermostats, coils, condensers, resistors,neons, earphone/microphones, nicad charger, power unit,multi -turn pots and notes on the 50 projects.

YOURS FOR ONLY £11.50 plus £3.00 post.

50 THINGS YOU CAN MAKE

MINI -MULTI TESTER Deluxe pocket size precision mov-ing coil instrument, Jewelled bearings - 2000 o.p.v. mirrored scale.11 instant range measures: DC volts 10, 50, 250, 1000.

AC volts 10, 50, 250, 1000.DC amps 0 - 100 mA.

'ysie...y.a..-, ...' , ..".-.. Continuity and resistance 0 - 1 meg ohms'. ' . : in two ranges. Complete with test prods

' ilk7;1% - , ,and instruction book showing how tomeasure capacity and inductance as w:11.Unbelievable value at only £6.75 + 60p

...t post and insurance.

1

FREE Amps range kit to enableyou to read DC current from 0 -10 amps, directly on the 0 - 10scale. It's free if you purchasequickly, but if you already own aMini -Tester and would like one,send £2.50.

J. BULL (Electrical) Ltd.(Dept. HEI, 34 36 AMERICA LANE,

HAYWARDS HEATH, SUSSEX RH16 3QU.Established30 YEARS

MAIL ORDER TERMS: Cash, P.O. or cheque with order. Orders under£12 add 60p service charge. Monthly account orders accepted fromschools and public companies. Access & B/card orders accepted day ornight. Heywards Heath (0444) 454563. Bulk orders: write for quote.Shop open 9.00 - 5.30, mon to Fri, not Saturday.

EXTRACTOR FANSMains operated - ex -computer.Woods extractor

5" - £5.75, Post £1.256" - £6.95, Post £1.25

5" Plannair extractor£6.50. Post E1.25.

4"x4" Muffin 115v.£4.50. Post 75p.

4"04" Muffin 230v.£5.75. Post 75p.

9" American made£11.50, post £2.00.

12 volt 61/2" extractor£6.90, post £1.50.

AUTO & ISOLATION TRANSFORMERS2 KW ISOLATION TRANSFORMER 230v in 230v out withtapped primary and secondary, facilities any voltage changes thatmight be needed. This is a very heavy transformer, American madebut not encased. The terminals are along the top on insulationboard panels. Both primary and secondary are split so this souldalso be used as a 2KW isolation step down transformer. £57.50.Carriage at cost depending upon the distance. This is approx halfthe regular price.2 KW AUTO TRANSFORMER Similar type of transformer to meabove but has only the one winding. £28.50 + carriage £3.1 KW ISOLATED AUTO TRANSFORMER It is not generallyrealised that many of the American made tools intended for 115v,if used on building sites and similar damp conditions must beisolated from the mains for safety reasons, as in many cases theinsulation of this equipment is not good enough for 230v. Wehave American made isolated auto transformers, completelyenclosed in sheet metal case with carrying handle with 230v leadand 110v American type plug. Price £46.00 + £4.50 post.300 WATT AUTO TRANSFORMER completely encased, lead forthe 230v input, American type plug for the 115v output £6.90+ E1.50 post.100 WATT AUTO TRANSFORMER not enclosed terminals, outputprimary with tappings for voltage adjustments. Made to rigidspecification for the GPO £4.60 + £1 post.AMERICAN 2 PIN FLAT SOCKETS for use with these auto trans-formers - E2.30 each.

3M FACSIMILE EQUIPMENT - send or receive adocument in 4 minutes. This equipment is used for sending lettersand almost any data through the telephone system - "Mail byPhone". The machines we have are the 3M 600BB with autofeedcomplete with ansafonettes and connector box. We have threesets of the equipment, it is not old, in fact it was used only forabout a year 11980-811, believed t6 be in good order and certainlyin a very good condition - cost new over £10,000. We will accept£500 the lot - buyer to examine and take away on an "as seen"basis.

VENNER TIME SWITCHMains operated with 20 amp switch, oneon and one off per 24 hrs. repeats dailyautomatically correcting for the lengthen-ing or shortening day. An expensive timeswitch but you can have it for only £2.95.These are without case but we can supplya plastic case - £1.75.Also available is adaptor kit to convertthis into a normal 24 hr. time switchbut with the added advantage of up to12

ideal controller for the immersion heater.Price of adaptor kit is £2.30.

IONISER KITRefresh your home, office, shop, work room, etc. with anegative ION generator. Makes you feel better and workharder - a complete mains operated kit, case included.

£11.95 plus £2.00 post.

OTHER POPULAR PROJECTSR C Bridge Kit £9 953 Channel Sound to Light - with fully prepared metal case. £14.95Ditto - made up £25 00Big Ear, listen through walls £9 50Robot controller - receiver/transmitter £9 50Ignition kit - helps ,carting, saves petrol, improvesperformance . . . ......... E13.95Silent sentinel Ultra Sonic Transmitter and receiver . . £9.50Car Light 'left on' alarmSecret switch - fools friends and enemies alike . .

3 - 30v Variable Power Supply2 Short & Medium wave Crystal Radio .

3v to 16v Mains Power Supply Kit .

Light Chaser . . - three modes .

Mullard Unilex HiFi stereo amplifier with speakersRadio stethoscope - fault finding aidMug stop - emits piercing squarkMorse Trainer - complete with keyDrill control kitDrill control kit - made upInterrupted beam kitTransmitter surveillance kitRadio MikeFM receiver kit - for surveillance or normal FMSeat Belt reminderCar Starter Charger KitSoil heater for plants and seedsInsulation Tester - electronic meagerBattery shaver or fluorescent from 12v . .

Matchbox Radio - receives Medium WaveMixer Pre -amp - disco special with caseAerial Rotator - mains operatedAerial direction indicator40 watt amp - hifi 20hz - 20kHzMicrovolt multiplier - measure very low currents withordinary multitesterPure Sine Wave GeneratorLinear Power output meter115 Watt Amplifier 5Hz 25kHzPower supply for one or two 115 watt ampsStereo Bass Booster, most items

£350£1.95

£13 80E3.99E1.95

£17.50E16.75

£4 80£2 50E2 99£3 95£6 95£2 50£230£6 90£3.50E3 00

£14 00£16 50£795£6.90£2 95

E16 00£29 50

E5 50E9 50

£395£5 75

Ell 50£1350E17.50

£8 95


III Hi -Voltage Meter

Hi -Voltage MeterLightning from a clear sky? Check it out

with the HE Hi -Volt Meter.James E. AmanDANGER 10,000 VOLTS!! But nowthis meter tames the kilovolts and bringshigh voltage measurement easily intothe range of the experimenter'spocketbook. If you've been left"holding the probe", and gettingnowhere because of the 1 kV limit onyour ordinary voltmeter, then this is thelogical expansion to your complimentof bench test gear. And at aroundf 15, one really can't afford not tobuild this project, if only to "save thebacon" of your digitally delicatedevices.

High Voltage CircuitThe meter uses (now) readily availableultra -high value thick film resistors tomake up the bulk of a resistor chainforming voltage divider. Themeasuring device is a MOSFET inputop -amp which sports the facility ofbeing able to sense voltages belowthe negative supply rail, making dualsupplies unnecessary. Thus with theextremely high input resistance of1000MR coupled to the FET op -ampwe realize a circuit capable ofmonitoring up to 10 kilovolts withoutsignificantly affecting the circuit undertest. When metering 10kV, an inputimpedance of 500 megohms draws20uA which suggests that a resistorof a quarter watt is a bit "near theknuckle". Increasing the inputimpedance to 1000 meg ohms andusing 0.4 watt resistors was moreacceptable. Resistors 1-10 reduce thevoltage across R11 to a manageablelevel, which is then sensed by IC1,and produced at its output to drive thecurrent meter. IC1 is connected as avoltage follower, which presents thesame voltage at the output as it seesacross R11 (its input). It therefore isacting as an impedance transformerand supplies current to the 100uA

Parts ListRESISTORS PR2 5k horiz(All 1/4 watt 5% unless noted) presetR1-10R11R12R13

100M 0.4W100k 1%

4k72k2

CAPACITORSC1

C2

100ndisc ceramic

1000u 16Vradial electro

POTENTIOMETERS SEMICONDUCTORSRV1 10k bin IC1 CA3140PR1 10k horiz MOSFET op -amp

preset ZD1, 2 BCY88C3V3

MISCELLANEOUSM1 panel meter

100uASW1 2 -pole 6 -way

rotaryPCB; case (see Buylines); HV probeand leads (see text); PP3 battery andclip; knob, wire, nuts and bolts etc.

BUYLINES page 32


Hi -Voltage Meter

H.V.PROBE

OVPROBE

R1 R2 R3100M 100M 100M

R4 R5100M 100M

R6 R7 R8100M 100M 100M 100M

R9 R10100M

R11100k

ZD13V3

ZD23V3

+9V

CA 3140

RV110k

PR25k

PR110k

METERZERO

R132k2

R124k7 2

SW1

M1100uA

FSD

NOTES:IC1 = CA3140R1-10 = 100M 0.4WZD1,2 = 3V3 ZENERSM1 = 100uA METER FSD

Figure 1. The circuit, in two parts.

meter. This is connected with a seriesresistor (adjustable for calibration)making it into a voltage meter,reading in kilovolts.

CalibrationThe calibration procedure is sweetand simple. First zero the meter onthe 5kV range, with the probesshorted together, via R16 on the front

Figure 2. The simple component layout.

H.V. PROBE

+9V

OFF' 7

ON '8 SW1

C10.1uDISC

OV 4

+ C21000u16V

B17 PP3

-I- 9V

/7777

panel. On the 10kV range simplyconnect 1V DC across R11 (negativeto earth) and adjust PR1 to a full scalereading of 10kV. Then, on the 5kVrange connect OV5 DC across R11and adjust PR2 for a full scale readingof 5kV. The meter face should bescaled 0-10kV in 1 kV steps across thetop of the meter and 0-5kV in 1kVsteps across the bottom of these samegradations.

5kV

3

A

ConstructionConstruction of this project shouldpose no real problems. The highimpedance resistor chain should besoldered and trimmed, leaving nosharp points on the leads. The meter -zero pot should be mounted on thefront panel and the meter should bewired between the wiper (pin A) ofSW1 and earth, as shown in thecircuit diagram. Care should be usedwhen installing IC1 , as it is staticsensitive.

Probe connections can be madethrough the case either by means of4mm banana plugs and sockets or by(in the interest of safety) feeding theprobe wires directly through matchingholes in the case. In the latter casethe leads should be knotted on theinside of the case, as a strain relief,and held in place with Superglue.

A HV probe with a rubber -bootedcrocodile clip may be used instead.The experimenter may prefer to testthe HV source by first clipping themeter to the points under test andthen switching on, but make surepower is off before approachinghigh voltage points! This method,used with sensible caution, can proveto be a safer and a less nerve rackingprocedure, since the probe isn't athand during "power on" testing.

HEHobby Electronics, October 1983 29

AMPLIFIERS

r BIPOLAR MODULES

LE"Over the last few years we have received feedback viathe general public and industry that our products arefrom Taiwan, Singapore, Japan, etc... I LP are one ofthe few 'All British' electronics Companies manufacturingtheir own products in the United Kingdom. We have provedthat we can compete in the world market during the past12 years and currently export in excess of 60% of ourproduction to over twenty different countries - includingUSA, Australia and Hong Kong. At the same time we areable to invest in research and development for the future,assuring security for the personnel, directly andindirectly, employed within the UK. We feel very proudof all this and hope you can reap some of our success.

I. L.Potts - Chairman

WE'RE INSTRUMENTALIN MAKING A LOT

OF POWER

In keeping with I LP's tradition of entirely self-contained modulesfeaturing, integral heatsinks, no external components and only 5connections required, the range has been optimized for efficiency,flexibility, reliability, easy usage, outstanding performance, valuefor money.With over 10 years experience in audio amplifier technology ILPare recognised as world leaders.

ModuleNumber

OutputPowerWattsMIS

LoadImpedance

n_

DISTORTIONT.H.D. I.M.D.Typ at 60Hz/1KHz 7KHz 4:1

SupplyVoltage

Typ

Sizenun

WTgms

Priceinc.

VAT

HY30 15 4-8 0.015% <0.006% ± 18 76 x 68 x 40 240 £8.40HY60 30 4-8 0.015% <0.006% ± 25 76 x 68 x 40 240 £9.55HY6060 30 + 30 4.8 0.015% <0.006% ± 25 120 x 78 x 40 420 E18.69HY124 60 4 0.01% <0.006% ± 26 120 x 78 x 40 410 E20.75HY128 60 8 0.01% <0.006% ± 35 120x 78x 40 410 £20.75HY244 120 4 0.01% <0.006% ± 35 120 x 78 x 50 520 £25.47HY248 120 8 0.01% <0.006% ± 50 120 x 78 x 50 520 £25.47HY364 180 4 0.01% <0.006% ± 45 120 x 78 x 100 1030 £38.41H0368 180 8 0.01% <0.006% ± 60 120 x 78 x.100 1030 £38.41

Protection: Full load line. Slew Rate: 15v/ps.Risetime: 5ps. S/N ratio: 100db.Frequency response -3d13) 15Hz - 50KHz. Input sensitivity: 500mV rms.Input Impedance. 100K n. Damping factor, 100Hz >400.

PRE -AMP SYSTEMS

ModuleNumber

Module Functions CurrentRequired

Price inc.VAT

0±6 Mono pre amp Mic/Mag. Cartridge/Tuner/Tape/ 10mA £7.60Aux . Vol/Bass/Treble

HY66 Stereo pre amp Mic/Mag. Cartridge/Tuner/Tape/ 20mA £14.32Aux + Vol/Bass/Treble/Balance

FO'73 Guitar pre amp Two Guitar (Bass Leadl and Mic +separate Volume Bass Treble + Mix

20mA E15.36

13±78 Stereo pre amp As H Y66 less tone controls 20mA £14.20

Most pre -amp modules can be driven by the PSU driving the main power amp.A separate PSU 30 is available purely for pm amp modules if required for£5.47 (inc. VAT). Pre -amp and mixing modules in 18 different variations.Please send for details.Mounting BoardsFor ease of construction we recommend the B6 for modules HY6-HY13 E1.05(inc. VAT) and the B66 for modules HY66-H078 £1.29 (inc. VAT).

POWER SUPPLY UNITS (Incorporating our own toroidal transformers)

ModelNumber

For Use With Price inc.VAT

PSU 21X 1 or 2 HY30 £11.93PSU 41X 1 or 2 HY60, 1 x HY6060, 1 u HY124 £13.83PSU 42X 1 x HY128 £15.90PSU 43X 1 x MOS128 £16.70PSU 51X 2 x HY128, 1 x 180244 £17.07

MOSFET MODULES

ModuleNumber

OutputPowerWatts

rms

LoadImpedance

_0_

DISTORTIONT.H.D. I.M.D.Typ at 60Hz/1KHz 7KHz 4:1

SupplyVoltage

Typ

Sizemm

WTgms

Pricemc.

VAT

MOS 128MOS 248MOS 364

60120180

4-84-84

<0.005% <0.006%<0.005% <0.006%<0.005% <0.006%

t 45t 55± 55

120 x 78 x 40120 x 78 x 80120 x 78 x 10(l

420850

1025

130 /I1139.85145.10

Protection Able to cope with complex loads without he need for very specialprotection circuitry (fuses will suffice).

Slew rate: 20v/ps. Rise time: 3ps. S/N ratio: 100dbFrequency response i-3dB): 15Hz - 100K Hz. Input sensitivity 500mV rmsInput impedance: 100K .n_ Damping factor: 100Hz >400.

'NEW to ILP' In Car Entertainments

C15Mono Power Booster Amplifier to increase the output of your existing car radioor cassette player to a nominal 15 watts rms.

Very easy to use.

Robust construction. £9.14 (inc. VAT)Mounts anywhere in car.

Automatic switch on.

Output power maximum 22w peak into 411Frequency response I-30131 15Hz to 30KHz, T.H.D. 0.1% at lOw 1KHzS/N ratio (DIN AUDIO) 80dB, Load Impedance 331Input Sensitivity and impedance (selectable) 700mV rms into151(.0. 3V rms into 811Size 95 x 48 x 50mm. Weight 256 gms,

C1515Stereo version of C15.

Size 95 x 40 x 80. Weight 410 gms.

£17.19 (inc. VAT)

ModelNumber


PSU 52X 2 x HY 124 £17.07PSU 53X 2 x MOS128 E17.86PSU 54X 1 x HY248 £17.86PSU 55X 1 x MOS248 E19.52PSU 71X 2x HY244 £21.75

Please note X in part no. indicates primary voltage Please insert "0- in place ofX for 110V, "1" in place of X for 220V, and "2- in place of X for 240V.

ModelNumber


PSU 72X 2 x /40248 122.!54PSU 73X 1 x rlY364 122154PSU 74% 1 0 HY368 124.21PSU 75X 2 x MOS248, ' x MU' -.3G8 124.21'

-4


TOROIDALSThe toroidal transformer is now accepted as the standard inindustry, overtaking the obsolete laminated type. Industry hasbeen quick to recognise the advantages toroidals offer in size,weight, lower radiated field and, thanks to I.L.P., PRICE.Our large standard range is complemented by our SPECIALDESIGN section which can offer a prototype service within 7 DAYStogether with a short lead time on quantity orders which can beprogrammed to your requirements with no price penalty.

*Gold service available.21 days manufacture for urgentdeliveries.

*Orders despatchedwithin 7 days ofreceipt for single orsmall quantity orders.

*5 year no quibbleguarantee.

TYPE SERIES SECONDARY RMSNo Volts Current PRICE TYPE SERIES SECONDARY RMS

No Volts CurrentPRICE TYPE

SERIES SECONDARY RMS PRICENo Volts Current

15 VA 00010 6+6 1.25 120 VA 40010 6+6 10.00 300 VA 70013 15+15 10 00

62 x 34mm 00011 9+9 0.83 90 x 4Ornm 4011 9+9 6.66 110 x 50mm 70014 18+18 8 33

0.35KgRegulation

19%

0x0120x0130x014

12+1215+1518+18

0.630.500.42

£.5.12+ p 8 p 00.78

1.2KgRegulation

11%

4001240013401144

12+1215+1518+18

5.004.003.33 £7.42

2.6Kg 7015 22+22 6.82Regulation 70016 25+25 6 00 £10.88

6./0 70017 30+30 5 00

00015 22+22 0.34 + VATE0.89 40015 22+22 2.72 + p & p £1.72 7018 35+35 4.28 + p & p C2 05

00016 25+25 0.30 TOTAL £6.79 40016 25+25 2.40 + VAT £1.37 70026 40+40 3.75 + VAT C194

0x017 30+30 0.25 4001740018

30+3035+35

2.001.71

TOTAL £10.51 7x025 45+45 3.33 TOTAL 014.8770033 50+50 3.00

(encased in ABS plastic) 400284x029

110220

1.090.54

70028 110 2.7270029 220 1 36

40030 240 0.50 70030 240 1 25

30 VA 10010 6+6 2.5070 x 30mm 10011 9+9

11..2"5

55:001121 86.6696 500 VA 80016 25+25 10.00

0.45Kg 1x012 12+12 £5.49 11016x040VmA

192+,912140 x 60mm 80017 30+30 8.33

Regulation18%

1001310014

15+1518+18

1.000.83

+p&p£1.10+ VATC0.99

1.8KgRegulation

541350014

15+1518+18

5.334.44

4Kg 80018 35+35 7.14 £1438Regulation 80026 40+40 6.2510015 22+22 0.68 TOTAL £7.58 8% 50015 22+22 3.63 E8A3 4% 8025 45+45 5.55 + p 8 p C2 40

10016 25+25 0.60 50016 25+25 3.20 + p & p 01.72 8033 50+50 5.00 + VAT C252

10017 30+30 0.50 50017 30+30 2.66 + VATC1.52 80042 55+55 4.54 TOTAL C19 30

50018 35+35 2.28 TOTAL £11.67 80028 110 4.54

50 VA 20010 6+6 4.16 50026 40+40 2.00 8029 220 2 27

80 x 35mm 2411 9+9 2.77 50028 110 1.45 80030 240 2.08

0.9Kg 20012 12+12 2.08 50029 220 0.72Regula13%0tion0

2201301415+1518+18 611:6386£.13 50030 240 0.66

2015 22+22 1.13 + p 8 p £1.35 625 VA 90017 30+30 10.41

2x016 25+25 1.00 + VAT £1.12 140 x 75mm 90018 35+35 8.922x0172x028

30+30110

0.830.45

TOTAL £8.60 225 VA110 0 45mm

6001260013

12+1215+15

9.387.50

5Kg 90026 40+40 7.81 £17.12Regulation 9025 45+45 6.942029 220 0.22 2.2Kg 60014 18+18 6.25 4% 90033 50+50 6.25 + p 8 p C2 55

20030 240 0.20 Regulation 6415 22+22 5.11 90042 55+55 5.68 + VAT C2 95

7% 60016 25+25 4.50 E9.81 90028 110 5.68 TOTAL C22 62

80 VA 30010 6+6 6.64 60017 30+30 3.75 + p 8 p £2.05 90029 220 2.8490 x 30mm 30011 9+9 4.44 60018 35+35 3.21 + VAT £1.78 90030 240 2.60

1Kg 3x012 12+123,33

6x026 40+40 2.81 TOTAL 013.64Regulation 3x013 15+15 2.66 £6.66 60025 45+45 2.50

12% 3x014 18+18 2.22 + p & p £1.72 6x033 50+50 2.2530015 22+22 1.81 + VAT £1.26 6x028 110 2.043x016 25+25 1.60 TOTAL £9.64 60029 220 1.02 ALSO AVAILABLE3x017 30+30 1.33 60030 240 0.93 Sizes up to and including 5KVA are3x028 110 0.72 manufactured to order.3x029 220 0.3630030 240 0.33

The benefits of ILP toroidal transformersILP toroidal transformers are only half the weight and height of their laminated

equivalents. and are available with 110V. 220V or 240V primaries coded as follows: '

IMPORTANT: Regulation - All voltages quoted are FULL LOAD. Please add regulation figure to secondaryge to obtain offload voltage.

NEW PRODUCTSHYBRID REGULATOR MODULESThe HR314 and HR614 regulated power supplies providea constant 13.8 volt d.c. output at up to 3 Amp or 6 Amprespectively. The modules are encapsulated to an integralheatsink and are fully short circuit protected making themsuitable for home or bench running of CB, car stereos orany 12 volt d.c. equipment required for many hobby orprofessional applications.

HR314 £10.23 inc. VATHR614 £18.51 inc. VAT

For mail order please make your crossed cheques or postalorders payable to I LP Electronics Ltd. Barclaycard/Accesswelcome. Trade orders standard terms.

For 110V primary insert '0' in place of X in type number

For 220V primary (Europe) insert "1- in place of "X in type number

For 240V primary (UK) insert '2.. in place of "X in type number

Also available at Electrovalue,Mapl in

TECHNICAL SPECIFICATIONS

MODULE HR314 HR614

Output Voltage +13.8v ± 5% I 13.8v 15%

Output Current Up to 3A Up to 6ACurrent limit (nominal) 3.5A approx 7A approxMaximum Input Voltage .30v .30vMinimum Input Voltage +16v .16vMaximum Input Voltage for nominal

output current+20v .20v

Maximum output current at 30v input 1.8A approx 3.5A approx

Output ripple (100Hz) - See Note 1 <10mV rms <10mV rms

Size in mm. 76 x 68 x 40 high 120 x 78 x 40 high

POWER SUPPLY UNITS: comprising toroidal transformerplus 90 x 50 x 55 mm high printed circuit board containingsmoothing and rectification

PSU31X Suitable for running one HR314 at full rated current.PSU56X Suitable for running one HR614 at full rated current.

£13.17 inc. VAT£19.13 inc. VAT

For 110v operation insert 0 in place of X - brown primary leads.220v (Europe) operation insert 1 in place of X - pink primary leads.240v (UK) operation insert 2 in place of X - orange primary leads.

Post 10 ILP Electronics 110 Graham Bell House RollerCanterbury C T2 7EP Kent EnglandTelephone 102771 54778 Telex 9(t5780

p.i divisu)n ul

ELECTRONICS LTD.Hobby Electronics, October 1983 31

Buylines

Audio Level MeterAn all-purpose audio level meter thatwill find a home in many hifi systemsand in semi-professional recordingstudios, where constant attention tothe recording level is always required!

Most of the components are readilyavailable, with only the TL072 and the10 -segment LED array likely to provedifficult. The TL072 is stocked byRapid Electronics, for instance, aswell as several other suppliers, butthe LED array may have to be ordered- quote the Radio Spares partnumber 586-706 (for a red display) or588-033 (if you'd prefer green), andyour favourite supplier should be ableto get it for you. Alternatively suitabletypes (again in red or green) arestocked by Technomatic.

Polycarbonate capacitors can besomewhat hard to come by, and are alittle expensive for the averagehobbyist: polyester types are anadequate substitute, and although thePCB is laid out for an axial capacitor,a C280 or equivalent polyester can be'made to fit'.

Because of the many differentpotential applications of the Audio

Level Meter, a case has not beenspedified. However the cost, excludingcase and PCB, should be in the regionof £6.50.

Ultrasonic AlarmThe first thing to note is that a case orother enclosure has not beenspecified for this project. Although theauthor suggests standard metal orplastic boxes, a favourite trick is todisguise an alarm system such as thisas an otherwise ordinary piece ofhousehold equipment - a bookshelfloudspeaker unit, for example. So, allthings considered, we decided toleave the final choice to theindividual.

The dimensions of the project caneasily be judged from the PCB foilpattern reproduced on page 72,allowing virtually any shape ofenclosure to be designed around it.

The components are almost allstandard and can be obtained fromone of the larger mail ordercompanies, such as MaplinElectronics. Several of the transistorsspecified may not be available, butsubstitutes such as the BC184 or

BC209 for the BC239; or BC182,BC237 for the BC171, are quiteacceptable. Similarly 1/3 watt resistors,which may be supplied in someinstances, can be used instead of thespecified 1/4 watt types.

The estimated cost of the UltrasonicAlarm, excluding PCB and case, isaround £10.00.

Hi -Volt MeterAstute readers may have noticed the"special preview" of this project onpage 17 of the last issue. Yes, that'sright - we made a mix of the pix.However as you'll see by comparingthe pictures in the September issuethe two projects use virtually identicalmeters and are housed in a box thatlooks ... well, they're very similararen't they?

That being so, we again called uponGreenweld Electronics, who oncemore came to the rescue with an offerto supply all the components for just£21.95, including case, meter andhigh voltage probes. This price, asusual, excludes the cost of the PCBfrom our very own PCB service.

Trump CardThe Trump Card PCBs and 23 -way -Ace edge connector are beingsupplied by Innovonics, 147 UplandRoad, East Dulwich, London SE22 for£5.95 including VAT, p&p.

Us LIVES AGAIN,1From the past it came, growing daily, striking terror into the hearts of lesser publications, and spreading its influence acrossthe country in its quest to infiltrate every town, every home, every mind.Not a horror story, but a success story. And if electronics theory strikes terror into you, then you neea the help of Elec-tronics - It's Easy. Originally a long -running series in Electronics Today International, Electronics - It's Easy was printedas a set of three books. They sold out. It was reprinted as a single volume. It sold out. Now this phenomenally successfulpublication is available again, in its third reprint. Electronics - It's Easy is a comprehensive and simply -written guide whichexplains the theory land the practice) of electronics step by step. Every aspect of the subject is covered, starting with thebasic principles and working through to the how and why of today's technology.You can'obtain your copy of Electronics - It's Easy by mail order using the coupon below. Make cheques or postal orderspayable to ASP Ltd, alternatively you may pay by Access or Barc:aycard.

r -Send to: Sales Office (Specials),513 London Road, Thornton HeathSurrey CR4 6AR

Please send me copies of ElectronicsIt's Easy. I have enclosed £ (£4.95 eachincluding p&p).

1

NAME

ADDRESS

Please debit my accountMy Access/ Barclaycard No isSignature

L


CircuitSupplement

The HE Basic Circuit Selectionis a collection of everyday -

useful circuits that form manyof the most used elements of

circuit design.

This selection is presented bycourtesy of Bernard Babani

(publishing) Ltd, and shows afew of the many circuit designs

available.

Although constructional detailsare not given, practical

instructions for assemblingmany of these circuits are

contained in the relevent book.


Circuit Supplement

555 OscillatorsThe 555 timer integrated circuit has been featured in a great many projects forthe electronics constructor, and this is not surprising when one considers thelow cost and versatility of this device. It is well worthwhile being familiar withthe capabilities of this device, and it will be considered in some detail in thissection.

The standard 555 astableconfiguration shown will probably befamiliar to most readers. It is really aform of relaxation oscillator with C2 firstcharging to two thirds of the supplyvoltage though R1 and R2, and thendischarging through R2 to one third ofthe supply voltage. The operatingfrequency is therefore set by the valuesgiven to R1, R2 and C3, and is given bythe formula:

Frequency = 1.44/(R1 + 2R2) C2 Hz

The reason for adding the value of R1to double the value of R2 (rather thansimply adding the two values together)is that R2 is both the charge anddischarge paths of C2 and therefore hasdouble the effect of R1. Rather thancalculating the operating frequencywith the resistance in ohms and thetiming capacitance in farads it is betterto use Megohms and microfarads. Thisavoids having very low figures for thecapacitance and very large figures forthe resistance.

Typical values for the timingcomponents would be 4k7 for R1 and R2plus 100nF for C2 giving an operatingfrequency of just over 1 kHz.

There are, of course, certainlimitations on the circuit values, and it isadvisable to keep the combinedresistance of R1 and R2 to no more thanabout 10MR. A resistance substantiallyhigher than this could gi e ratherunpredictable results or might result inthe circuit failing to oscillate at all. Thisis due to the very low currents thatwould be present in the timing circuit,and consequent effects tiny inputcurrents drawn by the 555 or leakagethrough C2 might have.

There is also a limit on the minimumvalue R1 should have, and this can becalculated by dividing the supply voltageby 0.2. This would, for example, give afigure of 45R with a 9V supply. Inpractice it is often necessary to use avalue very much higher than thisabsolute minimum figure, and onereason for this is simply to keep thedissipation in the 555 down to areasonable level. It should also beremembered that an internal transistorof the device places a virtual shortcircuit from pin 7 of the 555 to thenegative supply rail during thedischarge period of C2, and apart fromany effects on the 555 itself, a low valuecomponent in the R1 position will give a

C1

100pF

R1

+ve

R2

7

6

12

555

2

Figure 1. The trusty 555 geared up as an

high dissipation in this resistor and avery high current consumption duringthe discharge period. A minimumresistance of about one kilohm istherefore more realistic.

Pin 3 is the output of the 555, and thisterminal goes high while C2 is chargingand low when it is discharging. Thisgives a rectangular waveform at theoutput of the device, but it is not asquarewave having a one -to -one -mark -space ratio. This is simply because C2charges through both R1 and R2, but itdischarges thorugh R2 alone (plus theinsignificant impedance of thedischarge transistor within the 555).

The output of the 555 gives a peak topeak voltage almost equal to the supplyvoltage used, and it is at a lowimpedance. The device has a form ofclass B output stage, and it can sourceor sink up to 200mA. However, withhigh output currents the output is pulledwell away from its normal (no load)level, and a combination of large outputvoltage and high current cannot besupplied directly by the device.

An output signal can be taken fromacross C2, but this is only permissible ifa very low output current is taken sinceany loading here obviously has an effecton the charging and discharging of C2.The higher the values of R1 and R2, theless cutput current that is available. Thewaveform across C2 is roughlytriangular, but C2 charges anddischarges exponentially and so this is

T1C003 nF

astable oscillator.

0Out

-ye

0

obviously not a linear triangularwaveform. Also, like the output at pin 3,the mark -space ratio of the signal is notone-to-one.

A slight shortcoming of the 555 is thatonce per output cycle the supply is"crowbarred" and a negative voltagespike is introduced onto the supplylines. C1 is included to decouple thisnoise.

C3 is also a decoupling capacitor, andthis removes any stray pick-up at pin 5of the 555.

Any electronic circuit will onlyoperate between certain supply voltagelimits, and this is something which mustalways be borne in mind. For the 555device the minimum and maximumsupply potentials are 5V and 15V. The555 actually has a maximumpermissible supply voltage of 16V, butwith any figure of this type it is advisableto leave a small safety margin and 15Vis therefore the maximum nominalsupply voltage. The maximum operatingfrequency of the device is at least500kHz, and there is no properly definedlower limit to the operating frequency.The lower limit is determined by thequality of the timing capacitor C2 whichfor very low frequencies must be apolarised type such as a tantalum orelectrolytic type. Although in theory it isperfectly alright to use a capacitor of(say) 100uF with a total timingresistance of several megohms, inpractice this is unlikely to work. The


Circuit Supplement II

C11001.IF

R1

555R2

1

00nF

0+ve

0Gatesignal

0Out

-ye0

Figure 2. The gated astable can be used for producing tone -bursts or a gatedclock signal.

T2

C1100pF

R1

R2 D21N4148

D11N4148

OT2

555

0+ve

5

TC11nF

0Out

-ye

Figure 3. The mark -space ration can be varied continuously if R1, R2 arereplaced by variable resistors.

leakage resistance of the capacitor maywell be only a few hundred kilohms, andthis would limit the charge voltage to alevel which would not permit correctoperation of the circuit. Tantalum typesare generally much better in this respectthan electrolytic capacitors, and such acombination of timing componentvalues might work well using a

tantalum capacitor.A point that is sometimes of

importance, especially when the 555 isused in very low frequency applications,is that the first half of the initial cycle islonger than that obtained onsubsequent cycles. This is simply due toC2 starting with zero charge on the firstcycle, whereas it starts with a chargeequal to one third of the supply voltageon subsequent cycles. This is not uniqueto the 555 by any means: in fact mostsimple C -R oscillators produce a longerinitial cycle.

Gated OscillatorThe 555 can be used as a gatedoscillator, as shown. This circuit isbasically the same as the one shown

above but instead of pin 4 of the 555being taken to the positive supply rail itis fed with the gating signal. Pin 4 mustbe taken below about OV5 in order toswitch off the oscillator, and the outputgoes to the low state when the circuit isgated off. The input current to pin 4 isonly about 100uA. If pin 4 is left floatingit is normal for the oscillator to operate,incidentally.

The current consumption of the 555varies from about 3mA with a 5V supplyto about 10mA with a 15V supply (it isabout 7 to 8mA with a 9V supply).

Adjustable Duty CycleAs mentioned earlier, it is possible toproduce a 555 astable circuit that cangive any desired mark -space ratio, and acircuit of this type is shown. This hassteering diodes D1 and D2 which directthe charge current through R1 and thedischarge current through R2. Thus a 1 :

1 mark space ratio can be obtained bysimply making R1 and R2 the samevalue. If R1 is made larger in value thanR2 the charge (high) time is madeproportionately longer than the discharge

(low) time. Similarly, making R2 higherin value than R1 makes the discharge(low) time proportionately longer thanthe charge (high) time.

The formulas for calculating theoperating frequency and high outputtime are slightly different since R2 is notin circuit while C2 is charging. Thus inthe frequency calculation the timingresistance is simply R1 plus R2 ratherthan R1 plus double R2. Similarly, thetiming resistance when calculating thehigh output time is simply R2 and not R1plus R2. The two diodes have a marginaleffect on the frequency, charge, anddischarge times, but this will notnormally be large enough to be ofsignificance.

Frequency ModulationAs mentioned earlier, the operatingfrequency of a 555 astable can bemodulated by a control voltage. Thisdiffers from the normal 555 astableconfiguration in that the decouplingcapacitor at pin 5 of the device has to beremoved and the control voltage isapplied to this pin instead.

Pin 5 of the device connects to theinternal potential divider circuit whichsets the two thirds of the supply voltagethreshold level at which the 555triggers from the charge mode to thedischarge one. By taking pin 5 abovetwo thirds of the supply voltage theoperating frequency is decreased sinceC2 has to charge to and discharge froma greater potential, and therefore takeslonger to do so. Taking pin 5 below twothirds of the supply voltage reduces thevoltage to which C2 has to charge anddischarge so that both processes takeless time and the operating frequency isincreased. The output waveform at pin 3remains unchanged, but there is a slightchange in the waveshape and theamplitude of the signal across C2.

Pin 5 of the 555 does not connectdirectly to the internal potential dividerof the device, and the threshold voltageat which the device triggers from thecharge state to the discharge one is notequal to the voltage fed to pin 5. Thislimits the degree of control that can beobtained using a control voltage fed topin 5, and the frequency is reduced by alittle more than 50% if the control input istaken to the positive supply voltage. Theoutput frequency is slightly more thandoubled if the control terminal is takento one third of the supply voltage, and itcan be boosted a little further if it istaken slightly lower in voltage.However, if it is taken too low in voltagea malfunction occurs and the outputfrequency reduces considerably. It istherefore advisable to keep the controlvoltage between one third of the supplyvoltage and the full supply potential.

The control range is not very great butit is useful for applications such asmodulated tone generators.

This circuit and description are takenfrom "Practical Electronic BuildingBlocks, Book 1", BP1 17, by R. A.Pen fold, published by Bernard Babani(publishing) Ltd.


Circuit Supplement

Basic 555 MonostableThe 555 timer IC can be used as a monostable multivibrator, and is oftenthe most cost effective choice when a circuit of this type is required.

The basic 555 monostableconfiguration is shown in Figure 1.

Normally the input of the circuit isheld at more than one third of the supplyvoltage, and under stand-by conditionsthe internal discharge transistor of the555 hold C1 in uncharged state and theoutput at pin 3 is low. If the trigger inputis taken below about one third of thesupply potential the circuit is triggered,pin 3 of the 555 goes high, and theintenal discharge transistor switchesoff so that C1 can charge by way of R1.This continues until the chargepotential on C1 reaches two thirds of thesupply voltage, and the circuit thenreverts to its original state. At least, itreturns to its original state provided thetrigger input has been taken back aboveone third of the supply voltage.

The output pulse has a duration of1.1CR seconds, and the minimum pulselength is about one microsecond, andthe maximum pulse duration is limitedonly by the maximum practical timingcapacitance (as for the astablemode).

Manual TriggeringAn improved method of manualtriggering is shown. Here R3 normallyholds the trigger input at virtually thefull positive supply voltage, but a briefnegative pulse will be produced at theinput when BP1 is operated due to C2charging via R3. This gives the brieftrigger pulse, and no matter how longPB1 is depressed, it is the time constantof R3 and C2 that sets the length of thetrigger pulse. R2 rapidly discharges C2when PB1 is released so that thecircuit is almost instantly ready foranother operation of PB1.

The trigger pulse applied to IC1 is onlya few microseconds in duration, and thecircuit will obviously work properly withoutput pulse lengths of around 10us ormore. For shorter pulse lengths of onlyabout 1 us or so it would be necessary todecrease C2 in value, although trigger-ing might become unreliable if thiscomponent is made much lower invalue.

Reset FacilityIn the monostable mode pin 4 of the 555device is the reset terminal, and thisshould normally be in the high state.Taking this pin low during the outputpulse can cause the pulse to beimmediately brought to an end. Thecircuit shows how to add both manualand electronic reset facilities to a 555monostable.

This circuit and description are takenfrom "Practical Electronic BuildingBlocks Book 1", BP1 17 by R. A. Penfold,published by Bernard Babani(publishing) Ltd.

R1

IC1555

InC1

3 Out

0+5 to 15V

=3

100iF

-ye0

Figure 4. Basic 555 monostable. It is triggered by briefly taking pin 2 below 'AV+.

R310k

C2I nF

R21M

PB1Start

Al

IC1555

0+5 to 15V

111=33

Out

100pF

Figure 5. The length of the trigger pulse can be controlledaround the trigger switch.

Resetin

-ye0

by an RC network

RI

TRIVN1OKM

O

P81Reset

In

R210k

ICI555

TCI

0Out

0+5 to 15V

cz100pF

Figure 6. The monostable can be reset by taking pin 4 low, either manuallywith a switch or by taking the gate of TR1 a few volts positive.

-ye0


Circuit Supplement I

Emitter Followertosses due to loading can be substantially reduced using a buffer amplifier.Loading of one stage on another, orloading of a circuit of some kind on atransducer such as a microphone, canproduce a large reduction in signal level.

An emitter follower has 100%negative feedback and therefore onlyunity voltage gain, but the full currentgain of the transistor is realised so thatonly a small input current is needed togive a comparatively large outputcurrent, and the required high to lowimpedance conversion is thus obtained.It should perhaps be pointed out that anemitter follower stage does not actuallygive unity voltage gain, but in actual factgives marginally less than unity gain(about 0.96 being the typical voltagegain obtained). This very small drop insignal level is not usually of anypractical significance though.

The input impedance of the circuit isequal to the parallel impedances of R1,R2 and the input impedance of Tr1.These give an input impedance ofroughly 100k using the specified values.The output impedance of the circuit is2k2, but this does not take into accountthe effect of the source impedance ofthe input signal. This lowers the outputimpedance of the circuit to a figurewhich can be calculated by dividing thesource impedance by the current gain ofTr1 (which is about 520 at the collectorcurrent used here). In fact the basic 2k2

output impedance of the amplifier is inparallel with the impedance obtainedfrom the calculation detailed above, butin practice the output impedance of thecircuit will normally be so low that this2k2 is of no consequence.

Although the output impedance of thecircuit is likely to be only about 100R orless in a practical situation, and normalloading of the output will notsignificantly reduce the output signallevel of the unit, it is important to bear inmind that the maximum output currentof the circuit is equal to the emittercurrent of Tr1, or about 2mA using thevalues specified. In other words, tryingto provide an output signal of a few voltspeak into a load impedance of only abouta hundred ohms will not givesatisfactory results since the outputcurrent capability of the circuit will beinadequate on signal peaks, andclipping will occur. The purpose of acircuit of this type is to match a sourceimpedance of (say) about 10 or 20k to acomparatively low input impedance of(say) about 1 or 2k without producingthe massive loss of signal level thatwould occur using direct connection ofthe two pieces of equipment.

The circuit is not intended to bea powerful amplifier and will not workas one.

The circuit will work reasonably well

9

C1220n F

In

TR1BC109C

C2 out41,7

R32k2

Figure 7. A simple emitter followercircuit is often used to reduce loadingeffects.on any supply potential of between 3Vand 18V. The current consumption froma 9V supply is about 2mA, and thischanges roughly in proportion toalterations in the supply voltage.

Due to the large amount of negativefeedback employed in the circuit thenoise and distortion levels are bothextremely low.

This circuit and description are takenfrom "Practical Electronic BuildingBlocks, Book 2", BP118, by R. A.Pen fold, published by Bernard Babani(Publishing) Ldtd

General Purpose AmplifierThis unit can feed any speaker having an impedance of 8 ohms or more and willproduce a maximum output of about 1 watt into an 8 ohm load when used witha fresh battery

This simple design is intended forgeneral purpose use, and it is an ex-tremely useful piece of equipment to havearound. It is surprising the number ofoccasions on which an amplifier of thistype can be put to good use. The circuitdiagram of the unit is shown.

The circuit is based on the popularLM380N IC which has the advantageover most other ICs of requiring very fewdiscrete components to complete apractical amplifier. A practical amplifiercan be constructed using this IC and justthree discrete components. These arean output DC blocking capacitor (C5)an input DC blocking capacitor (C4), anda supply decoupling capacitor (C1).

There are two drawbacks to using justa basic circuit of this type in the presentapplication, and these are theinadequate voltage gain and inputimpedance of the circuit. The LM380Nhas typical input impedance and voltagegain figures of 150k and 50respectively. Ideally for this applicationthese should be about ten times higherin each case, so that the amplifier couldoperate from high impedance low levelloads, such as a crystal microphone.

Therefore, in order to boost the input

i=:=1C1"1°610011F

SK1r-d_Ain

C247nF

R122K

VR1--_4_R2

2M 4.7Klog.-

C4100nF

TR1BF244B

I

J. C3

T10µF

14I.C.1LM380N

cr0-- +9VS1

On/off

C5470p.F

L.S.

8-25J

veFigure 8. The LM380N has built-in thermal and short circuit protection, makiniFiTthe ideal device for test and breadboard situations.

impedance and voltage gain of the basiccircuit a FET common sourcepreamplifier stage has been added. Thisutilizes Tr1. VR1 is the volume control,and this doubles as the gate biasresistor for Tr1. C2 provides DC blockingat the input. S1 is the on/off switch,and this can be ganged with VR1 if

desired. C1 is the only suppdecoupling capacitor that is required fthe entire amplifier circuit.

lyOr

This circuit and description are takenfrom "Popular Electronic Projects",BP49 by R. A. Penfold, published byBernard Babani (publishing) Ltd.


Circuit Supplement

FiltersFilters are required in many applications, and are often implemented by passivecapacitor and inductive networks. Inductors are, however, bulky, expensiveand somewhat difficult to obtain. The use of operational amplifiers withfrequency selective feedback allows filters to be designed using only resistorsand capacitors.

Low Pass FiltersSimple Low Pass FilterThe simplest possible low pass filter isshown. The capacitor C has infiniteimpedance at DC, and the low frequencygain is determined by R1 and R2 asdescribed below. As the frequency risesthe impedance of C decreases causingthe gain to fall.

The roll off frequency is given by:

f= 1

2nCR2

Classical Low Pass FilterThe classical operational amplifier lowpass filter is shown. This has unity gainat low frequencies. To simplifycalculations, R1 and R2 should beequal, and C1 should be twice the valueof C2.

The cut off frequency is then given by:

f- 4 n RC

If R1 = R2 = R, C2 = C and C1 =2C.With the relationships above the filter

is said to be critically damped and thecut off is far sharper than the simplefilter. If C1 is not twice C2 the cutofffrequency is given by:

1f2 n R

if R1 = R2 = R.

Dependent on C1 and C2 the responsecan be made gentle or peaky as shown.

Similar low pass filters are the basisof audio scratch filters.

High Pass FiltersSimple High Pass FiltersThe simplest high pass filter is shown.At high frequencies the gain will bedetermined by R1 and R2 (and theamplifier itself). At low frequencies Cwill have significant impedancereducing the gain. The cutoff frequencyis given by:

1

f2 n CR1

Note that the high frequency gain will bereduced by the limited bandwidth of theamplifier itself.

Classical High Pass FilterThe circuit is identical to the low pass

vinRI

R3

ovFigure 9. Simple op -amp low passfilter.

vou,

Figure 10. The classical filter gives asharper cutoff.

Gain Cl > 2C2

Critical dampingCl = 2C2

Freq.

Figure 11. Response curves of theclassical filter circuit.

Figure 12. The classical high passfilter.filter with the capacitors and resistorsinterchanged. Ideally the componentsshould be chosen such that C1 and C2are equal and R2 is twice the value ofRl. The cutoff frequency is then givenby:

/--2

4 n RC

where Cl = C2 = C, R1 = R and R2 = 2R.The general equation with C1 =C2 = C

is:

f- 1

2nCOR1 R2)

Gain

R2 > 2R1

At high frequenciesCritical CiOrnpong °rVhflergam will foilR2 = 2R1

Frequency

Figure 13. High pass filter responsecurves.

v,

Figure 14. The simplest high passfilter circuit.

R3

R1 C1

C2 R2

V 0

55

ovFigure 15. A single -amplifier bandpass filter.

opt

Figure 16. An alternative band passcircuit.

with the ratio of R1 to R2 determiningthe response at cutoff.

The high pass filter is widely used as arumble filter in audio circuits.

Bandpass FilterIntroductionA bandpass filter will, as its nameimplies, pass a specific band offrequencies and reject frequencieshigher or lower than the specified band.A bandpass filter is specified simply bytwo parameters; the centre frequencyand the ratio of the centre frequency tothe -3dB bandwidth (denoted by 0). Thehigher the value of Q, the sharper theshape of the curve shown.


Circuit Supplement

Vin

Figure 17. A two stage bandpass filter.

3 dB

3 dB bandwidth Frequency

Centrefrequency

Figure 18. The response obtained bya bandpass filter.

v,n out

Figure 19. A turnable notch filter.

Single Amplifier Bandpass FilterThe circuit is widely used as a bandpassfilter. To simplify calculation R1, R2, R3should be equal (denoted by R) and C1and C2 should be equal (denoted by C).The centre frequency, fo, is then givenby:

fo -2 rr RC

N7 -2 -

The Q of the circuit is determined by R4and R5 with:

R5N/ 2Q = 4R5 - R4

An alternative single amplifier circuit isshown. The components should bechosen such that R1 and R2 should beequal (denoted by Ft) and R3 should bechosen to be 2R. Cl and C2 should bemade equal (denoted by C). Theequations are somewhat simpler, with:

1

fo -2 n RC

and Q = R52R5 R4

out

Figure 20. This notch filter hasadjustable Q.

v,,

vo,

Cl C2

Figure 21. The high Q notch filter.

Two Stage Bandpass FilterThe circuit is easier to comprehend thanthose of the previous section, althoughit uses two amplifiers. IC1 is a low passfilter, and IC2 a high pass filter. Thecentre frequency is determined by:

1

fo -2 n RC

if R1 = R2 =R3 = R4= R and Cl = C2 =C3 =C4 = C.

The bandwidth is determined by thecutoff frequencies. If the aboveequalities do not hold, the upper andlower frequency cutoff can bedetermined separately.

Notch FiltersIntroductionA notch filter is the opposite of a

bandpass filter in that it rejects a band offrequencies. Commonly the notch filteris used to reject 50Hz mains hum (60Hzoutside Great Britain) in sensitive audiocircuits and measuring instruments.The centre frequency and Q of a notchfilter are defined in a similar manner tothose of a bandpass filter.Single Amplifier Notch FilterThe circuit gives a notch filter of veryhigh Q. To simplify the design, thevalues should be chosen such that:

R1 = R2 = RR3 = R/2C1 = C2 = CC3 = 2C

If the above conditions are met, thecentre frequency is given by:

1fo =

2nRC

Two Amplifier Tunable Notch FilterThe circuit can be tuned by a singlevariable capacitor, C1. Normally C1 willbe a few hundred picafarads and the C2several microfarads. As usual, thedesign is simplified by the resistorequalities below:

R R2 = R3 = RR4 = R5 = R/2

The centre frequency is then given by:

for = 1

n R \/C1C2

Adjustable Q Notch FilterThe circuit allows the Q of a notch filterto be varied by a single potentiometerwithout varying the centre frequency.The potentiometer can be anyreasonable value, the Q of the circuitbeing determined by the ratio Ra/Rb. Asusual, some equalities must beobserved:

R1 = R2 = RR3 = R/2Cl = C2 = CC3 = 2C

The centre frequency is given by:

1

fo- 2nRC

The adjustable Q notch filter is veryuseful in low level measuringinstruments.

Practical ObservationsThe obvious is sometimes overlooked,but it should be noted that in all theabove equations resistors must be in

' OHM and capacitors in FARADS givingresults in Hz (cycles per second forolder readers!)

Where equalities are given, precisionresistors (at worst 1% tolerance) shouldbe used and close tolerance capacitors.Multiples and division by two is oftenneeded in the equations, and this is bestachieved by one value of resistor andcapacitor throughout, and using parallelor series combinations to produce themultiples required.

It will often be found that none of thepreferred value resistors or capacitorsgive the required frequency. Seriescombinations of resistors should beused in preference to variable resistors.This is inelegant, but one of the sad factsof life in filter design. Alternativelyprecision wire wound or thin filmresistors can be ordered to specificvalues. Although prohibitivelyexpensive for home "one -offs" thisapproach is economically viable forproduction runs. The inherentinductance of wire wound resistorslimits their use to low frequencycircuits.This circuit and description are takenfrom "How To Use Op -Amps", BP88, byE. A. Parr, published by Bernard Babani(publishing) Ltd


Circuit Supplement

Audio Operational AmplifiersSome operational amplifiers are primarily designed for use in audio frequencyamplifiers despite the fact that these devices were originally designed for useas DC amplifiers.

Operational amplifiers can be used intwo basic modes of amplification; theinverting mode and the non -invertingone. This circuit is for an invertingamplifier (we will consider a non -inverting amplifier shortly).

R3 and R4 are used to bias the non -inverting input (and also the output) toapproximately half the supply voltage.C2 filters out any hum or other noisewhich might otherwise be coupled tothe non -inverting input of IC1 from thesupply lines via the bias circuit. This alsoremoves any stray feedback from theoutput of the amplifier to the non -inverting input and thus reduces therisk of instability.

R1 and R2 are a negative feedbackcircuit which determine the inputimpedance and voltage gain of thecircuit. By giving these two componentsthe appropriate values it is possible toset both these parameters with a highdegree of accuracy, and this makesoperational amplifier based circuits (ordiscrete circuits using similartechniques) ideal for use where it isessential to be able to set the gain andinput impedance reliably andconsistently.

The input impedance is equal to thevalue given to R1, and the voltage gain isequal to R2 divided by R1, or ten timesusing the specified values for thesecomponents. C1 and C3 are merelyDC blocking capacitors.

Obviously R1 and R2 can be givenvalues to set almost any desired inputimpedance and voltage gain. However,there are definite limitations on thevoltage gain that can be obtained, and toa lesser extent on the input impedancethan can be achieved in practice.

If we take the voltage gain first, itmust be borne in mind that the gain -bandwidth product of the LF351 deviceis 4MHz. In other words, the maximumfrequency the amplifier must handlemultiplied by the voltage gain of theamplifier must be no more than 4MHz.For an amplifier that must cover the fullaudio band (which extends from about20Hz to 20kHz) the maximum voltagegain that can be used is clearly 200times (20kHz multiplied by 200 equals4MHz). In most cases the LF351 will beable to provide sufficient voltage gainusing a single stage of amplification, buttwo stages connected in series can beused where additional voltage gain isneeded.

In theory there is no limit on the inputimpedance that can be achieved using acircuit of this type, but in practice thereis the problem of obtaining resistors of

C12p2

In

R347k

3

R110k

C2 R4

1pF 47k

0 0 -ye

7

IC1LF351

C3

+4p7

R2100k

Out

0+9 to 30V

Figure 22. The circuit for an inverting amplifier using the LF351 op -amp, biasedfrom a single supply rail.

sufficiently high value, especially ina combination of high

voltage gain and high input impedanceof 10 Megohms and a voltage gain of100 times would require R1 to have avalue of 10M, and R2 to have a value of1000M. This is clearly not a practicalproposition, and in cases of this type it isbetter to use a low gain buffer stage togive the high input impedance, and aseparate high gain stage to step-up thevoltage gain to the desired figure.

Problems can arise with this type ofdue to the input capacitance of theoperational amplifier effectively makingthe negative feedback, to a degree,frequency selective, so that unwantedpeaks or dips in the frequency responseare produced. This is only really likely tobe a problem in circuits that are used toprovide low voltage gain and a highinput impedance, and the result isnormally a roughly doubling in gain at afrequency of few tens of kilohertz withthe response falling away atfrequencies above the peak. Where lowgain and high input and impedance areneeded it is better to use a non -inverting amplifier since a lowimpedance feedback network can thenbe used, and the input capacitance ofthe operational amplifier becomesinsignificant.

Bearing in mind the limitationsmentioned above, the appropriatevalues for R1 and R2 are easilycalculated. R1 is simply given thenearest preferred value to the therequired input impedance, and then thisfigure is multiplied by the requiredvoltage gain to give the value of R2 (and

again the nearest preferred value mustbe chosen).

Non -Inverting AmplifierThe circuit of an operational amplifierused in the non -inverting mode isshown. R3 and R4 bias the non -inverting input to IC1 to about half thesupply voltage with R5 being used tocouple this bias voltage to IC1. C2decodes any hum or other electricalnoise on the supply lines so that it is notfed to the input of the amplifier. Thevalue of R5 is equal to the required inputimpedance of the amplifier, and C2provides DC blocking at the input (andshould have its value chosen to suit theinput impedance of the circuit).

R1 and R2 are the negative feedbacknetwork, and the voltage gain of thecircuit can be calculated by first addingthe values of R1 and R2, and thendividing this figure by the value of R1.The specified values given to R1 and R2can be any two that have the correctratio to give the desired voltage gain, butin practice it is not a good idea to havelow values that will heavily load theoutput of the operational amplifier, or tohave high values that would result in afar from flat frequency response due tothe input capacitance of IC1. In practiceit is therefore advisable to have the totalvalue through R1 and R2 at somethingin the region of 25 to 100k.

In order to choose suitable values forR1 and R2 first decide on a value for R2,and any value of a few tens of kilohmsshould do. Then divide this by one lessthan the required voltage gain to findthe correct value for R1. The nearest


Circuit Supplement

2p2

R322k

C2 R42.i2 22k

R5

In

Figure 23. The LF351 in non -inverting

preferred value to the calculated figureis the used. C1 is a DC blockingcapacitor which gives the circuit 100%negative feedback and unity voltagegain at DC so that the circuit is biasedproperly. At audio frequencies it mustnot add significantly to the impedanceprovided by R1, and the correct value iscalculated in the same way as the valueof the input and output couplingcapacitor values are obtained.

The distortion performance of theLF351 is extremely good with thedistortion level being only about 0.02%provided the output is not heavily

mode.

R291k

0C44p7

Out

0+9 to 30V

0 -ye

loaded, the circuit is not driven intoclipping and the amplifier is not used atvery high gain levels. If used at fairlyhigh voltage gains the distortionperformance does reduce at high audiofrequencies, although the distortionlevel is still likely to be less than 0.1%.

The noise performance of the LF351 isalso extremely good with an outputnoise level of only about 500uV even ifthe amplifier is used at a high voltagegain of one hundred times.

One point that must be emphasized isthat although in theory it is perfectlysatisfactorily to have a non -inverting

amplifier with an impedance of(say)5Mand a voltage gain of one or two hundredtimes, and the LF351 is quite capable ofachieving these performance figures, ina practical situation it is highly unlikelythat such a circuit could be made tooperate satisfactorily. The problem issimply that there would inevitably be acertain amount of stray feedbackfrom the output of the amplifier to theinput, and as these two points are in -phase it is almost certain that instabilitywould occur with the circuit breakinginto oscillation. It is therefore better touse two stages of amplification with thefirst giving the high input impedanceand the second providing the voltagegain.

This enables better separation to beobtained between the input and theoutput so that stray feedback can bereduced to an insignificant level. It isalso a good idea to have the secondstage of amplification of the invertingtype so that the input and output of theamplifier as a whole are then out -of -phase, and any stray feedback willtherefore be of the negative variety. Thiswill not cause instability, but will simplyresult in a small reduction in the highfrequency gain of the amplifier.

This circuit and description are takenfrom "Practical Electronic BuildingBlocks, Book 2", BP1 18 by R. A.Penfold,published by Bernard Babani(publishing) Ltd.

Supply SplitterMany op -amp circuits require dual balanced power supplies of up to 12 voltseach and, while a special power supply circuit can be built, a simple supplysplitter is more convenient if a single -cell supply is already available.

A method of obtaining dual balancedsupplies is to use a supply splitter thatgives a low impedance centre -tap on asingle supply, rather than generatingtwo equal supplies and connectingthem in series. A supply splitter such asthe one shown in the circuit diagram isintended for use with an existing benchpower supply, and is not an independentunit. This particular circuit will workwell with supply voltages of between15V and 30V, and each of the outputrails has a potential equal to half theinput voltage (thus 30V is needed atthe input to give dual 15V outputs forexample). The unit will readily handlecurrents of up to 100mA, and it shouldnot be necessary to fit Tr3 and Tr4 withheatsinks.

The circuit is really just an unity gainamplifier having a high imputimpedance and a low output impedanceclass B output stage. A class B outputstage is used as this gives the unit a lowquiescent current consumption (onlyabout 2mA). Trl and Tr3 are commonemitter amplifiers, but as there is 100%negative feedback from Tr3's collectorto Tr1's emitter these give only unitgain. Tr2 and Tr4 form a complementary

+SK1 CD

R110k

INPUT

Cl10pFit

-SK2Figure 24. This supply splitter will prove its usefulness to

7

IC1741C

4

TR1dC107

TR3TIP42A

C2100pF

n R2U 10k

TR2BC177

TR4'-TIP41A

output pair for Tr1 and Tr3. There is100% negative feedback from theoutput of the unit (Tr3 - Tr4 collectors)to the inverting input of IC1, and thisgives unit voltage gain from the non -inverting input of IC1 to the output. R1and R2 bias the non -inverting input ofIC1 to half the supply potential, givingthe same voltage at the output, but at

+SK3

OUTPUT

(3 SK4OV

+ C3100pF

ED -SK5

the experimenter.

a very low impedance. The threecapacitors are needed to maintainstability.

This circuit and description are takenfrom, "Popular Electronic Circuits Book2", B98, by R. A. Penfold, published by

H EBernard Babani (publishing) Ltd.


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This new development in Soldering Irons combineslight weight (80g.) with unique one -handed operation.Solder is housed in the transparent handle andapplied directly to the joint by turning the serratedwheel (located in the handle) with the index finger,allowing a clean, bright joint to be made every time.To renew the solder, the spring clip at the end ofthe handle is released, the cap is removed and a refillis inserted.

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Points Of View

Feel like sounding off?Then write to the Editor stating your Point of View!

Facing The InterfaceI write to you in desperation. I havebeen an interested and happy readerof your brilliant mag since it first hitthe newsagents' shelves - an'Everyday Electronics' convert / be!

Since then I've built many projects,short circuits, etc. which have alwayseventually worked. Recently Ipurchased a ZX Spectrum, havingread your "Spotlight on theSpectrum". I soon started on the I/Ointerface board (HE September '82).This time I cannot seem to get it towork! Hours have been spent withcircuit diagram, manual andmultimeter, but no result!

I beg of you - understanding thatyour are busy people - please take alook at the notes I have enclosedtabulating my results and incomparison with what you know to behappening inside the chips try tosuggest reasons for my dilemma.Testing Results:Construction believed to be of goodstandard. Using PCB. Connection toSpectrum using ribbon cable ratherthan "piggy back" method. Using a 23x23 way connector. Polarising keyposition 3.1) Components all correctly fitted inaccordance with mag article, all solderjoints sound. PCB tracks appear OK.2) Computer functions correctly innormal mode.3) Everything appears OK - thingsdon't get warm!4) The first PRINT IN 65503 givescorrect 255, thereafter all inputcommands give result 56.5) Outputs don't seem to change atall. Usually at OV4 (using 20kR/Vmeter).6) Ribbon cable connections all seemOK and correct.7) QUERY: the fact that pin 11B onthe connector is not A 15 on Spectrumbut 1013QGE - is this supposed to beso?Thank you most sincerely,A.D. Fraser,Gosport,Hants.

It's difficult for us to tell, at the wrongend of a letter, whether the problemwith a non -working project is becausethere is a fault in the design/printedcircuit or whether there is aconstructional error.

Some project errors do becomeapparent very quickly, while othersturn up only after numerous queriesfrom readers.

In the case of the relatively 'old'project such as this one, when noerrors or mistakes have already been

brought to light, the most likely causeis a construction error.

In this case a clue is given by yourquery in para 7 of the testing results:pin 11B on the connector is notSpectrum address bit Al 5 - nor is itsupposed to be the Spectrum 1 ORQEline. It is, in fact, the ZX81's Al 5 line!

When using the I/O board witha Spectrum, this connection is non-operational since, as specified withNotes to the Circuit, the output ofIC3c is NOT linked to IC3d.

It appears that you are confusingthe alternative link -wires intended toadapt the boards for use EITHER witha Spectrum OR with a ZX81.

If you make sure that the links arewired in as per note "For 10 MappedVersion (For Use With TheSpectrum)", you should find that theproject performs exactly as required.

Thank you by the way for anexemplary enquiry. If all ourdistressed enquirers made it quite soplain exactly what they had done withwhich project, we would have a muchbetter chance of sorting theirproblems out for them. Also, goingthrough your test procedures point bypoint often reveals oversights whichhelp to sort out a problem straightaway.

Note: you are nearly always closerthan you think. Mr. Frazer hadproduced nine -tenths of his ownsolution and would only have neededa small flash of extra information toproduce what we now hope is a finalanswer.

Personal ProjectDear Sir,I'm a regular reader of your magazine,ever since I picked up your November'82 issue at the local newsagent. Yourmagazine is very interesting,especially your page.

I haven't built any of your projectsso far because I haven't found anythat suit my requirements. I'mparticularly interested in the personalstereo cassette recorder and I'mlooking forward to building one. I hopemy idea will be considered. It will bedifferent to play a machine you made byyourself.Yours sincerely,Wing Lee.

Certainly no shortage of ambitionhere! What can I say to thisdetermined gent, who not only readshis Hobby even when he isn't buildinga project, but plans to build his ownpersonal stereo? I positively quail toadmit that we are not very likely to do

a personal stereo project, because thecommercial companies have got itdown to such a fine art that nomagazine could possibly compete withthem-not a hope! By the time all theparts which are too complicated tomake at home have been provided(including the case) there would belittle left to do but the assembly, andit would still be more expensive andless reliable than the ones you canbuy in the shops. So it's not feasibleas a magazine project. Sorry!

. . . And You Thought YouHad Power Supply ProblemsDear Sirs,Thank you for your January article.Suppled by overhead 220/380V linesin a rural area, power failures arecommonplace here during frequentsummer evening electrical storms.The failures last for plus/minushours, but up to nine hours. Cookingis by gas stove from a cylinder. Therefrigerator can cope. Dinner can beby candle light but it would bepleasant to have the use of thegramophone or TV for an hour or so.Using a clamp meter, the hifiaverages less than the load of a100W bulb, but can peak for briefintervals up to TV levels or highermomentarily in extreme cases. TheTV has a high load switch on.

I use a car battery as a burglaralarm, fed by an SCR controlledvariable charger. The battery is astandby for a vehicle, and is my basicpower supply for electronics. It iscoming to the end of its life after fouryears.

It seems that a 300W DC/ACinverter as suggested by you is theanswer. However I am not sure if asine wave is necessary. Fuses shouldnot blow at peaks or switch on. Sucha project would be welcome.

On a related subject, so manycircuits for AM radio, but what abouta pure FM circuit from 12VDC supply,concentrating on purest sound withmaximum simplicity, merely tuningand volume, assuming correct tone inthe first place?Yours faithfully,E. Strang,Krugersdorp,South Africa.

Fascinating to see how the other halfof the world manages! Your projectsuggestions have been noted withthanks. On a general note, don'tforget that if any reader hasdeveloped a circuit or is inspired to doso by someone else's suggestion, we


Points Of View are always happy to have a look atthem (the circuits, not the readers .. .)

with possible publication in mind.Think of the glory! (It'll keep yourmind off the money.)

Howling ErrorDear Sir,Mr. Biggins' history brought back somany happy memories that it mayseem a bit churlish to point out amistake (The Electronic Revolution, HE'83):

The accumulator was used for thefilament (cathode) not the anode (or"plate") which required a 100 -volt drybattery the size of a brick.

The instability causing "howling"was due to feedback from the anodeto the aerial circuit giving "reaction",and was a characteristic of the"superregenerative circuit", not thesuperheterodyne which came later.

Amateur radio construction beforethe war received its greatest setbackwhen the highly efficient superheterodyne came into being in theearly 30s, as they needed professionalassistance to tune or "trim" theintermediate frequency transformer.

My first licence was a "provisional"dated October 1923.Yours faithfully,A.H. Jenkins,Dringhouses,York.

Thanks for these additions andcorrections to "The Birth of Broad-casting" (HE February '83). Yes, thearrival of equipment with "non-user-servicable parts" does tend todiscourage enthusiasts accustomed tobeing able to do everythingthemselves. But time usually brings anew crop of enthusiasts with somedifferent approaches, or new ways ofusing the old ones, as we're seeingwith amateur radio. We're told thatgeneral electronics is taking aknocking from home computing just atthe moment, but I'd like to think thatthe new generation of computerwizards won't be content to sail oninto the twenty-first century entirelyignorant of what goes on inside themicro, far from it. They'll probably allbe reading "Hobby Chip ManufactureToday" or some such rag!

Recharging NiCadsDear Sir,I am interested in a NiCad chargerworking off my car battery.

The NiCad is seven amp hours'capacity, 12V nominal - so chargingcould be constant current 0A2 to 0A5at 15V5.

What is the simple way of doingthis? / did read in Power SupplyProjects (see HE Bookshelf) about theDC step-up, ie IC1, TDA2030. Thisone is however OA 1 to 9V. The carbattery is, say, 14 to 11v.

Your advice will be greatlyappreciated.R. W. Kakebeeke,Johannesburg,South Africa.

Charging NiCad batteries from a carbattery requires special circuitry -but don't worry. We're working on itfor HE in the future.

Transmitter NeededDear Sir,I have for some time now beenreading your articles in HobbyElectronics. I am a student readingVocational Education which includesElectronics. I read and carry out somesimple projects.Your article that really spurred me towrite to you is that in HE October '82,'Radio Rules'. Transmitters were themain theme. I was so excited and Ithought by the time I am through, mydream of making my own transmitterwould have materialised. But alas thewhole text was just theories. I feltreally disappointed I must say.

Please can you give me atransmitter circuit because I have notbeen able to lay hands on any. (Imean a functional circuit, a circuitwith the component values inserted). /can make do with a low -poweredtransistor circuit or one using valvesor both. Maximum power should bekept within the amateur range of150W, because I hold an amateurlicence.

Thank you.Fleming Udofiah,Abak,Nigeria.

If you're going to build your own radiogear, you should look at a fewpossibilities. We and our radio -orientated relations here do not havea design which would obviously fulfilyour needs without involving you in alot of trouble and expense as well,and also we're not entirely clear whatyou are looking for - do you need areceiver as well, for instance, or doyou already have one?

I suggest you contact the RadioSociety of Great Britain, if there areno similar societies which can helpyou out in Nigeria, and tell them whatyou want. The will probably be able toadvise you. The RSGB are now atAlma House, Cranbourne Rd.,Potters Bar, Herts EN6 3JW.

The Tesla ControversyDear Sir,I have just read your January issue(sea mail takes time to reach us here)and found the "Wireless Goes ToWar" article most interesting.However, surely there should bemention of Nikola Tesla, whotransmitted signals by wireless beforeMarconi, and whose patents wereupheld against Marconi?

On page 56 the caption to the lowerright photograph says that thepurpose of the "fan" is not known.I'm sure that the Science Museummust know that the "fan" is a wind

driven generator, used to power thewireless equipment. Battery powersupplies with engine drivengenerators were not in use in 1914-1918!Yours truly,Martin Berner 9Y4TAM,Trinidad,The West Indies.

Tesla, it seems, was a genius whomthe highest pinnacles of fame weredoomed to elude. Consulting HEDecember '78 for its article "TheTesla Controversy", we find that Teslaseems to have discovered the LightSword, for which credit subsequentlywent to Obi -wan Kenobi, and alsoinvented the Tesla coil which, addsthe article, is known as the Ruhmkorffcoil.

More seriously, Tesla was the kindof genius whose greatest ideas wereso far ahead of his time that theynever achieved much in the way ofcommercial exploitation. This, ofcourse, makes them difficult to fitneatly into any brief history of moderntechnology. But who knows where histheories will appear again in thefuture?

As for the now -famous fan, whenyou receive your March HobbyElectronics in May (by which time weshall be preparing the issue forAugust) you will find some pertinentcomments from our resident balls offuzz, and your mind will be at rest bythe time you receive your October issuejust in time for Christmas.

Don't Switch The SwitchDear Sir,I intend building the Touch Switch (HEOctober '81) and would like to installit in my car, running off 12 volts.

I would be very grateful if you couldadvise me of any modificationsnecessary and suggest a suitablerelay to operate accessories such asfog lights, etc.Yours faithfully,G. Chamberlain,Ebbw Vale,Gwent.

There shouldn't be any problems witha 12V supply - just connect theswitch directly. Check the currentdrawn by the lights you intend to useand make sure you have the rightcontacts. We're not auto -electricexperts here, but suggest that around10A would be suitable. The relaymust be a 12V one, of course. HE


Multicore makes soldeThe Five Core AdvantageOnly Multicore wire solders have a 5 -core, or 4 -coreflux construction. The 5 -cores identify noncorrosive fluxes; the 4 -core, water solublefluxes.If you were to slice through a section ofMulticore cored solder you would seeseparate round cores of flux symmetricallyarranged around its perimeter. Only athin wall of solder separates the fluxcores from the surface.What are the advantages of theMulticore construction?1. Because the flux is peripherally

arranged it will react and flowfaster.

2. Flux voids are eliminatedwith Multicore. That's whyyou can depend on con-tinuity of the flux stream forcomplete wetting . . . everytime.

3. Because wetting is faster, complete and uniform,you use less solder and transmit less heat to thejoint area. With Multicore Solders, you get thehighest purity metals, vigorous fluxing action anda wire solder that meets all applicable Internationalstandards.

Ersin MulticoreContains 5 cores of non-corrosive flux.Uses: For all electrical joints.Handy Pack: Size 19A 60/40tin/lead 1.22mm dia£1.50 RRPTool Box Reel: Size 3 60/40tin/lead 1.6mm dia£4.37

Multicore SavbitIncreases the life of yoursoldering bit by 10 times.Uses: For all electrical work.Reduces copper errosion.Handy Pack: Size 5 1.2mmdia £1.38 RRP.Tool Box Reel: Size 121.2mm dia £4.37

Ersin MulticoreContains 5 cores of non-corrosive flux.Uses: Small transistors,components and fine wire.Handy Pack: Size PC11560/40 tin/lead 0.7mm dia£1.61 RRPTool Box Reel: Size 10 60/40tin/lead 0.7mm dia £4.37

Digitise at up to 10 MHz. Store, then display on a UHFTELEVISION. Single shot Capture up to 250 KHz. StorageFacility for less than £100.The Tele-Scope is a new concept in data capture utilisingthe latest Digitising techniques. The Tele-Scape acts -controls - displays much like a conventional scope butdoes much much more.A kit version is available for £89 and a Built unit for £109. Amanual is included and specialist parts are availableseparately.Prices exclude V.A.T. at 15% with postage and packing at£2.95 inc. The manual is available separately for £1.50 inc.which is refundable on subsequent purchase of a unit.

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XK113 MW RADIO KITBased on ZN414 IC, kit includes PCB, wounderial and crystal earpiece and all componentso make a sensitive miniature radio. Size: 5.5 x

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HOME LIGHTING KITSThese kits contain all necessaiy components and tullinstructions & are designed to replace s standard wallswitch and control up to 3000 of lighting.TDR300K Remote Control £14.30

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All About Electronics

ALL. ABOUTNICS

Our new Beginner's Series tells you all you'd like to knowabout electronics. From start to finish. All about

components and circuits, all the theory you need to getstarted in the world of electronics.

TECHNICALLY SPEAKING, a semi-conductor is an element which belongsto a particular group within the PeriodicTable! Those readers who have studiedPhysics or Chemistry to any depth willknow that the Periodic Table is simply amethod of collating all known elementsin tabular form. Figure 1 shows thePeriodic Table and the elements in theshaded box: C (carbon); Si (silicon) andGe (germanium) form the group weknow as semiconductors. Althoughofficially, carbon is a semiconductor, itis not used in the manufacture ofelectronic semiconductor componentsfor technical reasons. All semiconduc-tors are made with germanium, andparticularly silicon.

Electronically speaking, the termsemiconductor has been applied to themany electronic components which areconstructed with the use ofsemiconductor materials. Electroniccomponents belonging to the semi-conductor family include: transistors,integrated circuits (ICs), diodes,thyristors, and triacs.

So that we can understand theoperation of these semiconductorcomponents, we must first look at thematerials which are used in theirconstruction - the eleme"nts ofsemiconductor materials themselves.Figure 2 represents a minute section ofsuch an element - so minute that eachcircle in the figure is an atom of theelement. Each atom is linked (bonded)toan adjacent atom by a covalent bond. Asemiconductor atom has four electronsin its outside 'orbit' of electrons -and acovalent bond consists of one electronfrom one atom and one electron fromthe adjacent atom. So, a covalent bondis literally a shared pair of electrons.

Breaking The BondsAn individual covalent bond is not astrong one and it is quite simple to

Keith Brindley

1

H

TRANSITION ELEMENTS

2

He

3Li

4

Be

5

B

itC,

7

N

8

09

F

10Ne

11

Na12CMg

13AI

4 A. -,14SiItZ

15P

16S

17CI

18Ar

le,

19K

20Ca

21

Sc

22Ti

23V

24Cr

25Mn

26Fe

27Co

28Ni

29Cu

30Zn

31

Ga.. 3

,

.=lial l

33

As

34Se

35Br

36Kr

37Rb

38Sr

39Y

40

Zr41

Nb42

Mo43Tc

44Ru

45Rh

46Pd

47Ag

48Cd

49In

50Sn

51

Sb52Te

53I

54Xe

55Cs

56Ba

57.La

72Hf

73Ta

74W

75Re

76Os

77Ir

78Pt

79Au

80Hg

81

TI82Pb

83Bi

84Po

85At

86Rn

87Fr

88Ra

891Ac

'LANTHANONS58Ce

59Pr

60Nd

61

Pm62Sm

63Eu

64Gd

65Tb

66Dy

67Ho

68

Er

69Tm

70Yb

71

Lu

TACTINONS90Th

91

Pa

92U

93Np

94Pu

95Am

96

Cm

97Bk

98Cf

99Ea

100Fm

101Md

102No

103Lr

Figure 1. The Periodic Table of Elements. Those three elements 'n the shadedarea, C (carbon), Si (silicon), Ge (germanium) form the group known assemiconductors.

remove an electron and use the electronas a charge carrier through the material,in the same way that electrons carrycharge through any other conductor.The force required to break the bond andremove the electron is greater than theforce needed with a good conductor say,copper, and so the semiconductordisplays a certain amount. f resistanceto current flow. As we saw last month,of course, carbon (semiconductor) isactually used to make certain types ofresistors.

But resistors are purely passivedevices: if we apply a voltage across aresistor, a current will flow through itaccording to Ohm's Law and to theformula:

Remember?

VR

It doesn't matter which way round theresistor or voltage is in the circuit, theeffect will be the same. A resistor ispassive and is acted upon by appliedvoltages and currents - the effect isdependent only on the size of thevoltages and currents. The actualelectronic components which havebeen given the name semiconductors(and remember this doesn't includecarbon resistors!) are very muchcleverer and more useful than this.Such semiconductor component areactive: they can be used to act upon andcontrol the applied voltages andcurrents.

We form these active components bycombining slightly different types ofsemiconductor elements. Thesedifferent semiconductor types are madeby adding small quantities of impuritiesto change their electrical character-istics. Adding impurities to asemiconductor to change its electrical



N N

=0=0=II II II

SEMICONDUCTORATOM

0=00- SHARED ELECTRON

=N0=H0=0=N N N

PAIR(COVALENT BOARD)

Figure 2. A minute section ofsemiconductor material showingatoms and covalent bonds.

characteristics is known as doping.Doping is done in two ways to make twoseparate types of semiconductormaterial:

N -type - formed by adding atoms ofelements with five electrons in theiroutside 'orbit'. Four of the electronsform covalent bonds with electronsfrom adjacent semiconductor atoms,leaving one electron unattached.These free electrons are used ascharge carriers (Figure 3).

P -type - formed by doping thesemiconductor with atoms ofelements with only three outerelectrons as in Figure 4. These threeelectrons form covalent bonds withthree adjacent atoms but whatshould be the fourth covalent bondhas a missing electron - we call it ahole. Doped semiconductor holescan be thought of as charge carriersin exactly the same way thatelectrons can be thought of as chargecarriers in type semiconductormaterials. The holes are, of course,positively charged though (themissing negatively charged electroncreates a positively charged hole, getit?).

The first active semiconductor devicewe shall look at is a diode. Diodes arethe simplest of semiconductor devices:we call them two -terminal devices andthey are formed by combining one layereach of n -type and p -type semiconduc-tor as shown in Figure 5. At the junctionbetween the two layers is a regionknown as the depletion region. Thedepletion region is an area where nocharge carriers (either electrons orholes) exist because they are repelled byelectrostatic charges.

Stop The CurrentWhen a positive voltage is applied to thep -type layer (as in Figure 6) the effect ofthe electrostatic charges are lessenedand the depletion region is narroweduntil finally at a certain voltage (aboutOV2 for germanium diodes, OV7 forsilicon diodes) it disappears and chargecarriers can cross the junction andcurrent flows. With a voltage applied the

=0=0=0=HNHA N

=N0=0=0=II II II

=0=0=0=II II

FREEELECTRONS

Figure 3. N -type semiconductor. Puresemiconductor material is doped withatoms which have five electrons inouter orbit. Four electrons pair withelectrons of adjacent atoms leavingone free electron.

DEPLETION LAYERWHERE NO CHARGE

ELECTRONS CARRIERS EXIST

N -TYPE

LEAD

HOLES

=0=0=0=NNNN H N=0 00

=0=0 0=N N

MISSINGELECTRONS("HOLES')

Figure 4. P -type semiconductorformed by doping pure semiconductormaterial with atoms having only threeelectrons in outer orbit. This leaves ahole for a missing electron.

NARROWDEPLETION LAYER

+ + +

+ + +

+

+

+

+

+

+

+ + +

+ + +

+ + + + + + + + +

+ + + + + 4- + + +

P -TYPE N -TYPE P.TYPE

NEGATIVE POSITIVELEAD - LEAD LEAD

Figure 5. A diode, formed by acombination of P -type and N -typesemiconductor material. No voltage isyet applied across the diode.

VOLTAGE

INPUTMy AC

SINEWAVE)

TIME

VOLTAGE

1__I 1__I

TIME

OUTPUT

Figure 7. Application of an AC voltageto a diode gives a halfwave rectifiedoutput.

Figure 6. A diode with a positivepotential applied to the P -typesemiconductor layer. Above OV7 (for asilicon diode) current flows.

VOLTAGE

TIME

Figure 8. Output voltage of a cell is avery smooth DC.

other way round ie, negative to the p -type layer, holes are attracted towardsthe negative lead. A sort of electronic'vacuum' is formed at the junction, thedepletion region widens and no chargecarriers cross the junction ie, no currentcan flow.

We have made a device which willallow current to flow in one direction butnot in the other.

Now, how can we use such a device?A quick look at the circuit in Figure 7shows one way. The AC input(alternating between positive andnegative) after being applied to thediode has all of its negative half cyclesremoved. Incidentally, you should beable to see how the circuit symbol of a

diode in Figure 7 displays quitegraphically how current passes in thedirection of the arrow head but whenvoltage is reversed current cannot flowagainst the bar.

The output voltage of the circuit inFigure 7 is not AC because there are nonegative cycles so it must be DC.Because only half a cycle of the totalinput waveform appears at the outputwe say the output is half -wave rectifiedDC. Admittedly its not a very smooth DCvoltage. The voltage from a DC cell forexample is perfectly smooth (Figure 8).But don't worry we'll see how we canimprove the smoothness of the rectifiedDC waveform later.By combining four diodes (Figure 9)


All About Electronicswe form what is known as a bridgerectifier. This gives a full -wave rectifiedDC voltage output from an AC voltageinput. Operation of the bridge rectifiercan be explained with reference toFigure 10a and b.

Diodes In PairsFigure 10a shows how the circuit workswhen the AC voltage input is in apositive half cycle - point A is positivewith respect to point B. Diodes D1 andD3 both conduct but diodes D2 and D4do not. So current passes through diodeD1 through the load resistor R1, andfinally through diode D3. During thenegative half cycle (Figure 10b) diodesD2 and D4 conduct, but diodes D1 andD3 do not. Now current passes through(from terminal B this time) diode D2,through the load resistor (in the samedirection as in the positive half cycle)and finally through diode D4.

Any type of diode has a set ofparameters (or limits) which definewhat the diode can be used for. Forexample, an application in which diodesare often used occurs in a meter whenwe wish to measure AC voltages andcurrent. If you remember from theAugust issue of HE, the metersdiscussed were only used to measureDC voltages and currents. They simplywould not work for AC! A meter can beused however, to measure AC voltagesand currents if the AC voltage or currentis rectified first (Figure 11). Now, theparameters of the diodes used in thebridge rectifier of Figure 11 must begreat enough to ensure that any voltageor current measured will not damagethe diodes. Say, for example thatcurrents up to 1A and voltages up to1000V ratings must be used. Otherapplications might call for higherratings.

It's time now to consider how toimprove the rectified DC voltages whichdiode rectifiers give and make them assmooth as possible. We do it with theaddition of a single electroniccomponent - and we have met thecomponent already: the capacitor.Figure 12 shows a capacitor used tosmooth the rectified DC output of abridge rectifier. Use is made of thecharge -holding capability of thecapacitor to maintain the voltage at thepeak of the full -wave rectified waveformduring the trough till the next peak.When a capacitor is used in such a wayit is called a smoothing (or morecorrectly speaking, a reservoir)capacitor, for obvious reasons.

Of course, simple addition of acapacitor to a rectifier circuit cannotcompletely remove all the peaks andtroughs which occur, but they can bereduced to acceptable limits. There willalways be, for example, a smallvariation in voltage - which is knownas ripple - but as long as this is heldwithin, say ±100mV, of the desired DCvoltage then it is acceptable for mostpurposes. If we need a more accurateDC voltage then there are othercomponent and complex circuits whichcan reduce ripple even further but we

VOLTAGE VOLTAGE

INPUT(10V AC

SINEWAVE)

TIME

OUTPUTTIME

Figure 9. A bridge rectifier, consistingof four diodes, giving a full -waverectified DC output from an ACsinewave input.

INPUT

a)

( b )

D1

LOADRESISTOR

Figure 10: a) what occurs during thepositive half cycle of input sinewave b)what occurs during the negative halfcycle.

ACVOLTAGE

TO BEMEASURED

Figure 11. Measuring an AC voltagewith a DC meter.

AC INPUT

VOLTAGEAT OUTPUT

RIPPLE

I It II

VOLTAGE IFCAPACITOR

NOT PRESENT

OUTPUT

Figure 12. A reservoir capacitor usedto smooth the full -wave rectified DCoutput of the bridge rectifier to anacceptable ripple.

N

P v/COLLECTOR (C) P

BASE (B)

EMITTER (E) P

NPN TRANSISTORSTRUCTURE

ACOLLECTOR (C)

BASE (B)

EMITTER (E)

PNP TRANSISTORSTRUCTURE

Figure 13. NPN and PNP transistorconstructions.

don't need to know about such methodsyet. More about those another month.

Introducing TransistorsThe diode is the simplest of activesemiconductor devices - as we havealready seen, it is a two -terminal device.The next type of semiconductor is athree -terminal one and its commonname is a transistor. Within the familyof transistors there are a number ofdifferent types. This month we shall lookonly at the variety known as bipolartransistors. In later months we shalllook at other varieties such as fieldeffect transistors (FETs) and alsoconsider four -terminal semiconductors.

Bipolar transistors are made bycombining three layers of dopedsemiconductor material so that two PNjunctions (ie, combinations of p -typeand n -type semiconductor) are veryclose together. There are two differentways this can be done of course:

with the central layer ofsemiconductor being p -type and the

outside layers n -type (forming whatwe know as an NPN transistor)

with the central layer n -type and theoutside p -type (forming a PNPtransistor).

The central layer is always called thebase and the outside layers are theemitter and the collector. Figure 13shows both the NPN and PNP transistorconstructions. Although the emitter andcollector are made of the same type ofmaterial, there are ususallyconstructional differences within thetransistor which mean that their-1-01es ina circuit cannot be reversed.

Circuit symbols for NPN and PNPtransistors are shown in Figure 14. Thearrowhead on the emitter of both typesshows the general direction of currentthrough the transistor when theemitter -base junction is forward biased(ie, the base is more positive than theemitter in an NPN transistor or theemitter is more positive than the base ina PNP transistor).

In the following discussion abouttransistor operation I am going todescribe only the NPN transistor, butPNP operation is similar - only the



Figure 14. Circuit symbols for NPNand PNP transistors.

ELECTRON FLOW

N TYPE P -TYPE N -TYPE

ELECTRONFLOW

EMITTER (OV) BASE (+V) COLLECTOR (+V)

Figure 15. Basic format and appliedpotentials to an NPN transistor.

SMALL BASE B

CURRENT (1b)

LARGECOLLECTORCURRENT (Id)

Figure 16. Summarised action of anNPN transistor.

Figure 20. Studying currents within atransistor circuit.

10V DC

0

'BASE CURRENT

BULB

'TRANSISTOR'

Figure 17. Likening the action of atransistor to that of a mechancialpush-button switch.

RESISTOR10V DC

BULB

C

TRANSISTOR

Figure 18. The circuit of Figure 17 -using a transistor.

10V DC

BULB

COLLECTOR

CCURRENT (Id

TRANSISTOR

Figure 19. Automatically switching atransistor using a thermostat.

10V DC

R11k

VINR2

BASECURRENT I lb)

COLLECTORCURRENT (Id)

01

polarities of all applied voltages andcurrents should be reversed. I shall alsoassume use of silicon transistors, so abase -emitter voltage of OV7 is used inall calculations. Figure 15 shows thebasic format of an NPN transistor. Thecollector of the transistor is held at apositive potential to the emitter. The PNjunction between base and emitter actsas a diode. So with no voltage applied tothe base no current flows from base toemitter. However, if a positive voltage(greater than 07V) is applied to the base,the diode is forward biased andelectrons flow from emitter to base (ie,current flows from base to emitter).

If the base is made thin, some of theelectrons moving from emitter to basewill carry on and move into the collector(because they are attracted to thepositive potential of the collector). If thebase is thin enough and the transistorconstruction is good a high percentageof the electrons entering the emitter(say 95%) will pass to the collector. Thusa larger current will flow from collectorto emitter than that from base toemitter.

If we remove the positive voltagefrom the base the collector -to -emittercurrent (known as the collector current,Ic) stops. What we have made is asimple machine - in which a smallcurrent (created by the application of a

potential difference to the base) causesa large output current. This issummarised in Figure 16.

The ratio of the collector current, Ic, tothe current from base to emitter (thebase current, Ib) is:

Iclb

= 13 (the Greek letter, beta)

and depends primarily on the type oftransmitter used. For example a

common transistor, the BC109, has a 13of about 200, ie for a base current ofOmA1 a collector current of about 20mAwill occur.

Application of base current (Ib)effectively switches the transistor frombeing an insulator to a conductor. Whenthe transistor has no voltage connectedto its base the collector to emitterresistance is very high (about 20M). Wesay the transistor is 'off'. When avoltage is applied to the transistor basethe resistance from collector to emitteris low (about 10R) and we say thetransistor is on.

In a nutshell, that's all the transistor- any transistor - is really: a device,the resistance of which can be variedelectronically (by the voltage to its base):a transferrable resistor - TRANSISTOR- get it?

Switching CircuitsWhen the resistance of a transistor isvaried from high to low by theapplication of a voltage to its base, thetransistor is acting as an electronicswitch, and another way of looking atthe operation of a transistor is shown inFigure 17. The 'transistor' is showngraphically as a push-button switch,and the 'base current' is shown as afinger about to operate the switch. Asthe finger (base current) operates theswitch (transistor) the resistance of theswitch goes from high (when it is open -circuit) to low (when it is closed-circuit)and the current passes through thebulb, lighting it.

Figure 18 shows the same circuit butreplaces the switch and the finger witha transistor. Circuit operation, however,is identical: apply a base current and thebulb lights. The base current can, in fact,be supplied from the positive voltagesupply to the bulb as in Figure 18. Notethe resistor in series with the base, tolimit the base current to a maximumlevel - too large base currents willcause high power dissipation which willirreparably damage the transistor.

Base current could be provided by say,a thermostat (which is simply atemperature controlled switch) as inFigure 19, so that when temperaturefalls below a certain minimum, thethermostat closes providing basecurrent and automatically turning onthe bulb. Of course, it might not be abulb: it could be a heating pump, or aboiler etc.

It really doesn't matter what providesthe base current to the transistor - itcould be temperature (as in thethermostat example above), amagnetically operated reed -switch,another transistor, a computer, orwhatever -the fact is that in this type ofcircuit the transistor is operating as anautomatic electronic switch with onlytwo states: on and off. When basecurrent flows, the transistor is on; whenno base current flows, the transistor ison; when no base current flows, thetransistor is off.

Let's look further into this transistorswitch circuit. Figure 20 shows atransistor with a 1k collector resistance,(ie, the resistor between the transistorcollector and the positive supply rail,R1). This could be a bulb as in Figure 18,or a relay which will turn almostanything on and off! Resistor R2 is thetransistor base resistor.

Calculating The CurrentFirst we will consider the collectorcurrent. I said earlier on that thecollector current, Ic, was a function of 13and the base current, Ib:

lc = 13 X lb

Well, Ic is also a function of the collectorresistor, R1. Take for example the casewhen the transistor is on; its resistanceis low (about 1 OR) and can be neglectedcompared with R1 (1k). So the collectorcurrent is defined primarily by the'collector resistor and the power supply


All About Electronicsvoltage by the formula (which, ofcourse, we all know!):

+10V

lc= V +5V

OV OV

10 = 10mA1000

Now we can calculate the required basecurrent to turn on the collector current- we know that the transistor 3 = 100so for a collector current of 10mA, thebase current needs to be:

R

101 00

x 10-3lb 100uA

3

(Not a lot!) The base resistor, R2 cannow be calculated as being:

VR2R2 - lb

where VR2 is the voltage across R2.This voltage depends on two things; thevoltage at the base, and the voltage atthe input V,r,. The voltage at the base iseasily worked out because it is thevoltage at the emitter (OV) plus thebase -emitter voltage OV7 - the base -emitter junction is a diode -remember?. Let's say the voltage Vn isto be 5V, then the voltage across R2:

VR2 = 5 - OV7 = 4V3

Therefore

R2 100x310-6 = 43000R = 39k (NPV)=

So, with a base current of 100uA, 10mAof a collector current flows and, with nobase current, no collector current flows.This is exactly what we wanted from ourtransistor switch.

In an electronic switch mode,transistors are either fully on (known assaturation) or fully off. But whathappens in between these two limits?Let's look at the circuit of Figure 20again but apply an input voltage of Vm ofsay 2V65. This sounds inconvenient butwhen we calculate the voltage acrossthe base resistor, R2:

2V65 - OV7 = 1V95

and calculate the base current:

lb - VR2_ 39 x

1-9510 50uA!R2

then we see that the collector current:

lc =13 x lb = 5mA

ie, half the collector current of theprevious calculation. In other words thetransistor is half on. This illustratesanother type of transistor operation -linear mode operation.

A transistor operating in its linearrange can be likened to a control valve ina water system. If no base current flowsthe 'control valve' is closed and nocollector current flows. But when the

101/ DC

VOLTAGE

+5V

0V

-5V

BIASCURRENT

R239k

TIME

10V DC

+5V

OV

-5V

INPUTWAVEFORM

Figure 21. Attempting to use the circuit of Figure 20 to amplify a AC sinewave.

Figure 22. Turning the transistor half on, by applying a fixed bias current to thebase, allows the transistor to be used with AC input.

'control valve' is half open, or a quarteropen, or an eighth open; half the fullcollector current, a quarter, or an eighththe full collector current flows. We thushave linear mode transistor operation,the most important point of which is thatthe large collector current is controlledby a small base current. We havedeveloped a very simple currentamplifier generating a large currentfrom a small current the gain of which isthe transistor's 3 over the linear range,ie:

amplifier gain = 3 =-lclb

The amplifier circuit of Figure 20 iseffectively a DC circuit only - it will notoperate with AC voltages and currentsFigure 21 shows why not. The input topoint A, ie, the input voltage, Val to thetransistor is a sinewave, varying from+5V to OV to -5V. During the positivehalf cycles the transistor is operationalin its linear range and its resistancevaries from maximum (about 20M) tominimum (about 10R) as the sinewavevaries. The lower the resistance of thetransistor, the lower the voltage point 3because the effective resistance of thetransistor in series with the collectorresistance R1 forms a voltage divider.So the output voltage (over the positivehalf cycle of the input sinewave) is theinverse of the input voltage!

I Say, AC, I See!But what happens as the input voltagevaries over the negative half cycle?Well, the transistor is off (and can't goany more off) so the output voltage staysat maximum. Thus the output voltagewaveform is an inverse half -waverectified version of the input voltagewaveform. An AC current cannottherefore be amplified by this simplecircuit. So, do we amplify an AC current?

If a fixed direct current (which

permanently turns the transistor halfon) is applied to the base, at the sametime as the sinewave output is appliedthen the collector current will vary upand down with the base current and allparts of the AC input waveform will beamplified. Figure 22 shows one way ofsupplying this fixed DC input. Becausethe collector resistor, R1, and thepower supply voltage (10V) are thesame as in Figure 20 we know that acollector current of 5mA means thetransistor is half on. And with a 13 of 100we know that the required current is50mA to turn the transistor half on.Thus the voltage across the resistor, R3is:

10 - OV7 = 9V3

So the required resistor value:

VR3 = 9V3R3 - = 186000lb 50 x 10-6

= 180K (NPV)

The current to turn the transistor half onis known as the bias current, resistor R3is the bias resistor, and the standingcollector current is known as quiescentcurrent.

We have now designed a very simpleAC current amplifier from a transistor,with a gain 13, which is also a voltageinvertor.

That's about all for this month -we've covered a lot of ground and learntsome new ideas about electronicsemiconductor components. In the nextfew months you'll see othersemiconductor circuits and othersemiconductor components, particu-larly those in the large family ofintegrated circuits (ICs), but the basis ofsemiconductors (ie, this month's topic)is applicable to them all.

HE52 Hobby Electronics, October 1983

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I

Light Soldering Developments Limited, 97-99 Gloucester Road, lam mum ,,pm. mem mom.oCroydon, Surrey CR0 2DN. Tel: 01-689 0574.

um 10,HE/10/83 401/\it


Competition

This is the Great

0

Computer -Controlled Model RailwayCOMPETITION

Sponsored by Oric Products International Ltd., Beatties ofLondon Limited and ASP Software (a division of

Argus Specialist Publications Ltd.).

WHEN it was proposed that thereshould be a Grand Computer ControlledModel Railway Competition for the1983 Breadboard exhibition, we rapidlybecame bogged down with seeminglyendless complications. We spent mostof the time during discussions simplyexplaining jargon: what, to a computerhardware man, is a "dead frog"?Something unpleasant by the roadside,was the popular answer! On the otherhand our modelling consultant wassomewhat bemused by the manyacronyms that punctuate conversationsbetween computer buffs: who, or whatis a PIA? Bits of what? What is a multi-plexer, and so on, and on, and on . !

In the end we were all quitebewildered - but this confusionultimately gave us the clue to ourComputer Controlled Model RailCompetition: no one, it seems, trulyknows how best to marry a computer toa complex model rail layout or what itshould do and, particularly, how itshould be done.

We decided, finally, that the simplestand best approach would be to throwthe thing wide open, with only a fewessential restrictions. The only rule ofthe competition, then, is that thewinning entry will be that whichdemonstrates the most ingenuity,

usefulness and practicality in adapting amodern home computer to control amodel railway layout - the what, howand why we quite happily leave to ourreaders!

The essential limitation we feltobliged to impose is that the layoutshould measure no more than 6ft by 2ft- in other words, something that can betransported to the Breadboardexhibition in Hammersmith in lateNovember this year.

We anticipate that most of the entrieswill be from constructors who have anexisting computer interfaced layout, butthe competition is open to all comers soanyone who wants to "have a go" willbe welcome in the lists. For the benefitof those who fancy their chances at theGrand Prize, here are a few ideas thatresulted from the meeting of the mindsin Hobby's editorial offices (we won'tmention the ideas that evolved later,down at the Royal George!).

A fairly simple software applicationwould be to write a program for storingand modifying timetables and operatingschedules; an extension of this ideawould be an interface to positionsensing circuits so that an operator

would know not only when the nexttrain was due to leave, but also when itwas safe to start down the track.

One of the most obvious ideasproposed was to program a mimic boardwhich could show not only the tracklayout but the condition of signal lightsand with 'train in section' indication:colour would be necessary for user -friendliness!

Ways to adapt microprocessortechnology to model train control: oneoption that might be easily constructedwould be to computer -control sectionsof track rather than individual trains.However completely automatic runningis not the goal of most railwaymodellers, so any system should allowlots of room for the operator to controlthe layout himself.

And that is about the limit of the ideaswe came up with before brain fog set in.We'll leave it to the inventiveness andcompetitive spirit of our readers to stunthe judges with brilliant projects weshould have thought of . . . but didn't!


Competition

FIRST SECOND THIRDPRIZE PRIZE PRIZE

Hot off the production line, anOric 48K colour computer,donated by Oric Products

International Ltd.

Gift vouchers to the value off50, redeemable on model

rail products at any Beatties ofLondon shop.

f25 worth of games and utilityprogram tapes from ASP

Software.

Entry forms, together with an entrance fee of f1.00 (cheque or money orders only, please) should be sent to:The Exhibition Manager, BB83, ASP Exhibitions, 145 Charing Cross Road, London WC2H OEE.

Closing date is 31st October 1983. Judging will take place at Breadboard '83, Cunard Hotel, Hammersmith, LondonW6, on either Wednesday 23rd or Thursday 24th November 1983. Entrants will be informed of the day on which theywill be required to present their layouts at the exhibition. Finalists will be asked to demonstrate their layouts at some

time(s) during the open days of Breadboard '83 (25, 26, 27th November) and layouts will be available for collectionbetween 1600 and 1800 hours on Sunday 27th November. The judges decision will be final and no correspondence

will be entered into.

Entry Form

PLEASE USE BLOCK CAPS

NAME:

ADDRESS:

TEL NO: AGE ON 30TH NOV. 1983

BRIEF DESCRIPTION OF LAYOUT AND FUNCTIONS:

SCALE: SIZE OF LAYOUT: (MAX 6FT X 2FT)

COMPUTER USED

COMMERCIAL PERIPHERALS USED


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* 10 SECOND ENTRY DELAY allows owner to dis-arm thesystem, by inserting the key plug into a dashboard mountedsocket, before the alarm sounds. (No holes in externalbodywork, fiddly code systems or hidden switches). Re -closing the door will not cancel the alarm, before or after itsounds, the key plug must be used.

INSTANT ALARM OPERATION triggered by accessories orbonnet/ boot opening.

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1 Assembled ready to fitD.I.Y. parts kit

TWIN OUTPUT for cars and motor cycles with dual ignition

[1Twin, Assembled ready to fitTwin, D.I.Y. parts kit

INDUCTIVE DISCHARGE 112 volt only)

I 1

£2.8/0 £19.95£1,540 £14.95

£3 c45 £29.95f24,5.5 £22.95

Assembled ready to fit £15.15 £12.75

LPrices Include VAT. P+P f1-00 (UM E

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Assembled ready to fitD.I.Y. parts kit

37 95f2495

I enclose cheque/postal order OR debit my Access/Visa card

VISA I 11 II I!Name

Address

Code


EUROPA ELECTRONICSMail Order to 160 High Road. Willesden, London NW10 2PB

TEL: 01-907 1659

SEND FOR A FREE LIST OF OUR LARGE RANGE OF ITEMSALL DEVICES ARE NEW, FULL SPEC AND GUARANTEED

Post & Packing: Add 30p to all orders under £5.VAT: All UK orders add 15% to total cost including p&p.

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Retail Shop: North Parade Electronics. Mollison Way.Edgware, Middlesex.

Build and test yourown circuit with the NewVerobloc Kit c4jw

OFF w`

Try the new prototyping method of building andtesting circuits with the British -made Verobloc kit.It consists of:

1. Verobloc. 2. A pad of design sheets for planningthe circuits. 3. A component mounting panel for thelarger components, i.e. switches, etc.

You can expand the circuit area by simplyinterlocking two or more Veroblocs and, of course,with normal usage, they can be used time and timeagain without damaging contacts or component leads.The glass nylon material is virtually unbreakable andable to withstand temperatures from -60°C to +120°C.

So take advantage of our special price of £5 per kit(including VAT) by completing the coupon below, ortelephone (04215) 62829 (24 hours). This offer closesDecember 31st, 1983.

We are exhibiting at the following exhibitions, so whynot come along and see the products for yourself.

Personal Computer World, The Barbican,September 28 -October 2. Stand No. 159.

Electronics Hobby Fair, Alexandra Pavilion,October 27-30. Stand Nos. 625 and 725.

Our new catalogue containing over 150 new products isavailable from mid -October.

BICC Vero Electronics Limited,Retail Dept., Industrial Estate,Chandlers Ford, Hampshire,S05 3ZR.

BICC vero

rwish to purchase Verobloc kit/sat £5 per kit inclusive of VAT for a total of £

I I enclose my cheque/postal order or Debit myAccess/Barclaycard No. (Delete where appropriate)

IName:Address:

Postcode

VISA


Trump Card

11- RU IPCA RD

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00 0 444 584. 4gt**744.0 40 404. 40 :10:44t40 G.

Colin FreestoneTRUMPCARD is a simple but veryeffective project for owners of theever more popular Jupiter Acecomputer. At present the Ace, evenwith the recent release of 16K and48K RAM packs, still does not yetenjoy large scale hardware support,such as that available for the ZX81 orSinclair Spectrum, that would allowthe Ace user to extend the range ofhis computer activities.

The Ace, a versatile and usefulcomputer, is becoming particularlypopular for control applications. Intime, a wide range of hardwareaccessories will no doubt becomeavailable for it (such as the RAM I/Oboard and the Joystick Controller inlast month's issue of HobbyElectronics!) but in the short term,users who might like to experimentwith speech synthesizers and similiardevices are bound to be somewhatfrustrated.

The solution, though, is quite simple.The Ace and the ZX81 are very similarin may ways, and so it has provedsimple enough to design an interfaceboard that will allow most ZX81 add-ons to be used with the Ace.

Trumpcard is simply a small dual -sided PCB edge connector that can bewired to re-route the ZX81 signallines to correspond with thecorresponding Ace signals. The onlylimitation is since the Ace does notproduce the control signals ROMCSand RAMCS (ROM and RAM ChipSelect), Trumpcard cannot beguaranteed to operate reliably with anZX add-on that makes use of thesesignals.

The connections between the two setsof edge connectors are made withshort lengths of coloured wire -single stranded 'bell wire' is best.Coloured wire makes it easier to keeptrack of the links as they are madeand also to fault -find, if this is laternecessary. The colour scheme isoptional, but that outlined in Table 1is logical and consistent.

The first step in assembling theTrlimpcard is to modify the edgeconnector socket so that it can bewired onto the PCB. The socket is a

23+23 way (double sided) type withthe keyway at one end and must havewire -wrap length pins.

Take a pair of long -nosed pliers andinsert one jaw between the rows ofpins; grasp one row firmly betweenthe jaws and bend the pins outwardby about 30° (you may need two bitesat this, carrying out the operationfrom either end if the jaws are notlong enough). Then bend theopposite row outwards by the sameamount.

When this has been done, the nextstep is to bend the pins back inwards,but this time from the base so thatthe ends of all the pins all lie paralleland just far enough apart for the PCBto slip between the rows.

With the Trump Card,hardware designed forthe Sinclair Spectrum orZX81 can be used withthe Jupiter ACE (withvery few exceptions).Simple to make, it willadd enormously to theACE's versatility as acontroller.

To achieve uniform bending in thesecond operation, hold the body of theconnector against the edge of a tablewith the bottom row lying flat on thetable surface; then push down, gentlybut firmly, bending the pins inward.Repeat for the other row and continueto bend both rows until the PCB justfits between the rows.

Now with the polarising key on theright and the ZX key -slot at your topleft, align the socket with the Aceedge connectors on the PCB, makingsure that they all line up accurately.Push the pins onto the tracks, butleave about 5mm of free copper forsoldering on the link wires. If the pinshave been bent correctly, they will alllie neatly against the copper pads,


Trump Card

TABLE 1AACE PIN TRUMPCARD SIGNAL 2K PIN TRUMPCARD COLOUR LENGTH ROUTE

NUMBER NUMBER NUMBER (INCHES)(ACE EDGE) (ZX EDGE)

1A 23A OV 4B 20B WHITE 21/4 EDGE2A 22A OV 5B 19B WHITE 21/4 EDGE3A 21A +9V 2B 22B GREY 21/4 EDGE4A 20A +5V 1B 23B GREY 21/4 EDGE5A 19A CLK 6B 18B PINK 21/4 EDGE6A 18A Al 1 15B 9B ORANGE 21/4 EDGE7A 17A Al 2 14B 10B YELLOW 21/4 EDGE8A 16A A13 13B 11B YELLOW 21/4 EDGE9A 15A A14 12B 12B YELLOW 21/4 EDGE

10A 14A Al 5 11B 13B YELLOW 21/4 EDGE11A 13A D4 10A 10A YELLOW 11/4 DIRECT12A 12A D3 9A 9A ORANGE 11/2 DIRECT13A 11A D5 8A 8A GREEN 11/2 DIRECT14A 10A A2 9B 15B BROWN 2 HOLE 215A 9A Al 0 16B 8B ORANGE 21/4 EDGE16A 8A A9 17B 7B ORANGE 21/4 EDGE17A 7A A8 18B 6B ORANGE 21/4 EDGE18A 6A A7 19B 5A RED 21/4 EDGE19A 5A AO 7B 17B BROWN 21/4 EDGE20A 4A D1 5A 5A BROWN 21/4 DIRECT21A 3A D6 7A 7A BLUE 21/4 DIRECT22A 2A WE NC NC23A 1A (SLOT)

TABLE 1BACE PIN TRUMPCARD ZX PIN TRUMPCARD COLOUR LENGTH ROUTE

NUMBER SIGNAL NUMBER NUMBER (INCHES)(ACE EDGE) (ZX EDGEI

18 1B NL2B 2B INT 11A 11A PINK 2 HOLE 13B 3B NMI 12A 12A PINK 2 HOLE 14B 4B H LT 13A 13A PINK 2 HOLE 15B 5B MREQ 14A 14A PINK 2 HOLE 16B 6B IORQ 15A 15A PINK 2 HOLE 17B 7B RD 16A 16A PINK 2 HOLE 18B 8B WR 17A 17A PINK 2 HOLE 19B 9B BUSAK 18A 18A PINK 2 HOLE 2

10B 10B WAIT 19A 19A PINK 2 HOLE 211B 11B BUSRQ 20A 20A PINK 2 HOLE 212B 12B RESET 21A 21A PINK 2 HOLE 313B 13B M1 22A 22A PINK 2 HOLE 314B 14B RFSH 23A 23A PINK 2 HOLE 315B 15B A6 20B 4B RED 13/4 DIRECT16B 16B A5 21B 3B RED 13/4 DIRECT17B 17B A4 10B 2B RED 13/4 DIRECT18B 18B A3 10B 14B BROWN 2 DIRECT19B 19B Al 8B 16B BROWN 2 DIRECT20B 20B DO 4A 4A BLACK 23/4 HOLE 321B 21B D2 6A 6A RED 23/4 HOLE 322B 22B D7 1A 1A PURPLE 23/4 HOLE 323B 23B (SLOT)

Table 1. Wiring chart for the Trumpcard. Each TRUMPCARD NUMBER connects to the opposite EDGE via a length ofcoloured wire. The non-standard Trumpcard numbering is related to the conventional ACE and ZX81 numbering system,and the middle column shows the signal on each pin.

Figure 1. How to bend the pins on the edge -connector socket for soldering to

ready for soldering.Make sure the socket is running

parallel with the edge of the PCB andquickly solder the outside pins to holdit in place. Then you can proceed tosolder the remaining pins; for best

results use a good hot iron and touchthe tip to both the pin and the track.Don't use too much solder, to avoidbridges between track pins, and don'toverheat, as this can result in a dryjoint.

the PCB.

At this stage the link wiresshould be prepared to the lengthsrecommended in Table 1. Pare offabout 3mm insulation from each endand when all have been trimmed, thewiring can commence.


Trump Card

ZX-EDGE

TRUMPCARDNUMBERS

TRUMPCARDNUMBERS'

ACEKEYWAY

ACE -EDGE

BOTTOM SIDE('B' CONNECTIONS)

ZX-EDGE

ACE -EDGE

TOP SIDE('A' CONNECTIONS)

ACEKEYWAY

Figure 2. Wires are routed either via the HOLES in the PCB, DIRECT from edge toedge, or between the pins of the EDGE connector as seen in the photograph.

Start with the underside, at the Aceedge, and work from pin 2B across tothe other end. The wires go by threedifferent routes; either directly fromedge to edge, via one of the threeholes or, when you come to the otherside, between the pins of the Aceedge connector ('Edge' route in Table1). When attaching the wires to theZX-edge be sure to leave at least4mm of track free to accept the ZXadd-on socket!

When the underside is complete,turn the PCB over and wire up the topside; this time most of the links go viathe 'Edge' route, with a few directconnections and one link via Hole 2.

TestingWhen the wiring is complete, test allthe connections thoroughly, then plugonto the Ace and attach the ZX add-on of your choice (the RAM pack isbest for testing purposes).

Power up, and you should get anormal screen; a white -out or loss ofsynchronisation (rolling screen) meansthat something is wrong, somewhere.

Assuming that all is well and that aRAM pack is attached, type

15384 @.

This is the Ace's RAM TOP systemvariable, and with 16K RAM attached

ACE EXPANSION

col

PORT ZX81 EXPANSION PORT

+5VI

07NC Dv

INT OV +9V RAMCS

NMI w ca +9V T.23KEYWAY,2+

HIT K c. +5V OV K DO

MREO CLK OV cn DI

.IORQ Alt CLK D2

Al2RD AO D6

Al3WR Al co co 135

BUSAK . A14 A2 . ,o D3

WAIT 8 Al5 A3 8 8 D4

BUSRO D4 A15 INT

RESET W.; D3

7...1 D5

Al4 NMI

w

A2

Al3 r, HLT

RFSH 7: Al2 MAID

W31-10A6 <7.1.CA A10 All CA

A5 En 8i A9 A10 8; 5 RD

A4 A8 A9 .7.; WR

A3 CO' A7 AD EO Co. BUSAK

AO WAITAl CA i8 A7 41 ZA

Do 8 8 Dl A6 do No BUSRO

RESETD2 D6 A5 ti

WED7 A4 2 N M1

- I - ROMCS 5 RFSH

BOTTOM TOP PCB SIDE(BOTTOM)

COMPONENT SIDE(TOP)

Figure 3. The ACE pins have been re-numbered according to the con-vention used for the 2X81.

it should return 32768. If the valuereturned is 16384 then the pack isnot connecting properly and theseating of the pins should be checked.

If you do not have a RAM packavailable, test the TRUMPCARD withsome other add-on with which youare completely familiar, to assureyourself that it is working properly.Then, when you have successfullycompleted the project, you have addeda formidable acce,,sory to your Acecomputer.

In the absence of any fixedconvention for numbering the Acepins in chart form, we have taken theliberty of re -arranging the author'ssystem, for the sake of consistency,to conform with the well establishedstandard for the SinclairZX81 /Spectrum computers. Thusthe 'Ace pin number' in Table 1, followsour convention (see also Figure 3),while the 'Trumpcard Number' isthat etched onto the Trumpcard PCB(see Figure 2). Later issues of thePCB will follow the new numberingsystem. H E

Parts ListTrumpcard PCB; 23+23 -way edgeconnector socket, keyway atposition 23; 46 lengths colouredwire (see text), solder etc.

BUYLINES page 32


H.E. PROJECT KITSI.C.s TOOLSTRANSISTORS RESISTORSCAPACITORS HARDWARE

Make us your No. 1 SUPPLIER OF KITS and COMPONENTS for E.E. Projects. We supply care-fully selected sets of parts to enable you to construct E.E. projects. Kits include ALL THE ELEC-TRONICS AND HARDWARE NEEDED. Printed circuit boards (fully etched, drilled and rollertinned) or Veroboard are, of course, included as specified in the original article, we even includenuts, screws and I.C. sockets. PRICES INCLUDE CASES unless otherwise stated. BATTERIESARE NOT INCLUDED. COMPONENT SHEET INCLUDED. If you do not have the issue of E.E.which includes the project - you will need to order the instruction reprint at an extra 50p.each. Reprints available separately 50p each + p. & p. 50p.

WHISTLE SWITCH Aug 83 less micSTEREO SPREADER Jly 83SOFT FUZZ July 83SINCLAIR SOUND BOARD Jun 83 less caseTRAFFIC LIGHT TOY June 83 less standBAT LIGHTicarbettery indroalorlJune831esscaseTTL LOGIC PROSE June 83AUTO TESTER May 83STALL THIEF May 83 (Inc relay)STEREO VOICE OVER UNIT Apnl 83OPTIONAL MIC PRE AMP April 83 (no case)AUTO POWER DOWN April 83 no caseLINEAR OHMETER Mar 83LOW RANGE OHMETER Mar 83PHASE FOUR Dec 82STEREO NOISE GATE Dec 82TAPE/SLIDE SYNCHRONIZER Dec 82SIG EAR Dec 82MICROAMMETER ADAPTOR Dec 82ODOMETER Nov 82DIANA V.C.O. NorCB SQUELCH UNIT Oct 82'JUNIOR' SLOTCARCONTROLLERSept82 e5.130(leescaselZX INTERFACE BOARD Sept 82 Inc edge con £11.33T.V.I. FILTER July 82 £5.33AUTO WAH June 82 £18.98 Inc case or E12.28 less caseAUTO GREENHOUSE SPRINKLER June 82 £14.38

less pump and power SupplyTELEPHONE TIMER June 82 £33.42 lass power SupplyPOWER SUPPLY DESIGN12V 500MA June 82 1E948ECHO REVERS UNIT May 82 Le. case £33.98

Economy case W83 £3.76 extraDIGITAL THERMOMETER May 82 excluding case

bezelAUDIO SIGNAL GENERATOR May 82CABLE TRACKER May 82DIGITAL CAPACITANCE METER Apr 82SIGNAL TRACER Apr 82BIKE ALARM Apr 82DIGITAL DICE Mar 82BICYCLE SIREN Mar 82NOISELESS FUZZBOX Feb 82MASTHEAD AMPLIFIER Feb 82DRUM SYNTHESIZER Dec 81 Full kitGUITAR HEADPHONE AMPLIFIER Dec 81

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IN CAR CASSEIIE POWER SUPPLY Dec 81 £4.77SCRATCH FILTER Nov 81 Mono £5.82 Stereo CB..LED VU METER Nov 81 less caseSIMPLE STYLUS ORGAN Nov 81 less caseMETRONOME Nov 81TELEPHONE BELL REPEATER Oct 81

Med linking wire extraCOMBINATION LOCK Oct 81 less solenoidBABY ALARM Ocl 82 E8.70 Fig 8 linking wire'DIANA' METAL LOCATOR Sept 612REACTION TESTER GAME Sept 81VARIABLE BENCH POWER SUPPLY Aug 81ULTRASOUND BURGLAR ALARM July 81ELECTRONIC DOOR BUZZER July 81ELECTRONIC METRONOME July 81CONTINUITY CHECKER June 81ENVELOPE GENERATOR June 81AUDIO MIXER June 81PUBLIC ADDRESS AMPLIFIER March 81 £19.46

Extras - horn speakers £6.83 each PA MIS £4.40FUZZBOX March 81 £10.96WINDSCREEN WIPER CONTROLLER March 81 £8.20

£1 2.96£3.50

£24.96£5.80 less case

£8.20£10.80£8.20£7.53

STEAM LOCO WHISTLE March 81PHOTOGRAPHIC TIMER March 81HEATBEAT MONITOR Feb81TWO-TONE TRAIN HORN Feb81MEDIUM WAVE RADIO Feb 81BENCH AMPJan 91NICAD CHARGER Jan 81CHUFFER Jan 81, lase caseBATTERY CHARGE MONITOR Dec 82 £5.77MEMORY BANK -MINI SYNTHESISER Noylt Dec80 £28.96TRANSISTOR TESTER Nov 81 06.54 inc test leadsGUITAR PRE -AMP Sou 80 £6.85 case extra £2.29INTRUDER ALARM Oct 80 E20.96TOUCH SWITCH Sept 80 £2.75 less case & contactsGUITAR PHASER Sept 80 £16.28SOUND OPERATED FLASH TRIGGER July 80 no ski £5.33FOG HORN June 80 £6.64SPEED CONTROLLER FOR R/C April 80 C1 7.55 (Poss..)DIGITAL FREQUENCY METER April 80 C39.96GUITAR TUNER Nov 79 E12.82CAR ALARM Feb 79 £12.91

£4.57E4.96

£12.71£1 3.67

14p metreE18.65

7p metre£34.50ft 2.81E26.981719.98

£5.96C4.99E5.71

£17.96£5.33

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SOLDERINGITOOLSANTEX X5 SOLDERING IRON 25W £5.48SOLDERING IRON STAND £1 .98SPARE BITS Small standard, large, 85p each

For 55 + X25SOLDER. Handy sizeSOLDER CARTONDESOLDER BRAIDHEAT SINK TWEEZERSDESOLDER PUMPHOW TO SOLDER LEAFLETLOW COST CUTTERSLOW COST LONG NOSE PLIERSWIRE STRIPPERS 8 CUTTERSPRICISION PETITE12V P.C.B. DRILLDRILL STANDGRINDING STONEGRINDING WHEELSAW BLADEBRASS WIRE BRUSHBURRVERO SPOT FACE CUTTERpin insertionVEROPINS (pk of 100) 0.1" 52pMULTIMETER TYPE 1 (ID £5.48O opv)CROCODILE CLIP TEST LEAD SET.

10 leads with 20 clips 99pRESISTOR COLOUR CODE CALCULATOR 21pCONNECTING WIRE PACK TYPE ED.

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BOOKS: ELECTRONICS & COMPUTING205 First BookotHi-FieLoudsepeaker Enclosures £0.95 Semiconductor Data Book Newnes £8.95221 28 Tested Transistor Projects £1.25 Basic Electronics Theory and Practice £7.98223 50 Projects Using IC CA31 39 £1.25 Microprocessor for Hobbyist £4.75225 A Practical Introduction to Digital IC's £1.25 Burglar Alarm Systems E5.55226 Howto Build AdvancedShortWave Receivers £1.95 Electronics. Build and Learn E3.90228 EssentialTheoryfortheElectronic Hobbyist E1.95 Electronic Projects in Music £3.90BP39 50 IFET) Field Effect Transistor Projects E1.75 Electronic Projects in Photography £3.90BP40 Digital IC Equivalents and Pin Connections E3.50 Electronic Projects in Home Security £3.90BP41 Linear IC Equivalents and Pin Connections £3.50 Questions and Answers Electronics £2.70BP42 50 Simple L.E.D. Circuits £1 .50 Electronic Projects in the Car £3.90BP43 How to Make Walkie-Talkies £1.95 20 Solid State Projects Car and Garage £4.80BP45 Projects in Opto-Electronics El 95 110 Electronic Alarm Projects £5.98BP47 Mobile Discotheque Handbook £1.35 Computing is Easy £4.25BP48 Electronic Projects for Beginners £1.95 ZX81 Users Handbook £5.75BP49 Popular Electronics Projects £1.95 ZX81 Basic Book £5.75BP56 Electronic Security Devices £1.95 Fun with Electronics £1.25BP58 50 Circuits Using 7400 series IC's £1.75 24 50 CMOS J.C. Projects £1.35BP59 Second Book of CMOS IC Projects £1.50 BP24 52 Projects Using IC 741 £1.25BP61 Beginners Guide To Digital Techniques £0.95 BP44 IC555 Projects E1.95BP70 Transistor Radio Fault -Finding Chad £0.50 BP50 IC LM3900 Projects £1.35BP71 Electronic Household Projects £1.75 BP65 Single IC Projects C1.50BP75 Electronic Test Equipment Construction £1.75 BP69 Electronic Games El .758P78 Practical Computer Experiments £1.75 BP72 A Microprocessor Primer E1 75BP79 Radio Control for Beginners £1.75 BP73 Remote Control Projects £1.95BP80 Popular Electronic Circuits - Book 1 £1.95 BP74 Electronic Music Projects £1.75BP81 Electronic Synthesiser Projects £1.75 BP76 Power Supply Projects £1.758P82 Electronic Projects Using Solar Cells £1.95 BP83 VMOS Projects £1 95BP85 International Transistor Equivalents Guide £2.95 BP84 Digital IC Projects £1 95BP87 Simple L.E.D. Circuits - Book 2 E1.35 BP88 How to Use OP -Amps £2.25BP92 Easy Electronics -Crystal SetConstruction E1.75 BP90 Audio Projects £1.95BP94 Electronic Projects for Cars and Boats £1.95 SPOT Electronic Timer Projects £1.95BP98 Popular Electronic Circuits - Book 2 £2.25 BP95 Model Railway Projects Cl .95BPI 01 How to Identify Unmarked IC's £0.85 BP97 IC Projects for Beginners £1.95BP103 Multi -Circuit Board Projects £1.95 BP99 Mini Matrix Board Projects £1.95P108 International Diode Equivalents Guide £2.25 BP105 Aerial Projects £1.95BP109 The Ad of Programming the 1K ZX81 £1.95 8P106 Modem OP -Amp Projects £1.95BPI 14 The An of Programming the 18K ZX81 £2.50 BPI 15 The Pre Computer Book £1.95BP119 TheArt of Programming theZX Spectrum £2.50

How to make and Design your own PCBs £1.95292 Handbook of Integrated Circutis ous) Equiv.& Substitutes £1.95222 Solid State Short Wave Receivers for Beginners £1.25227 Beginners Guide to Building Electronics Projects £1.95BPI First Book of Transistor Equivalents and Substitutes E1.50BP14 Second Book of Transistor Equivalents and Substitutes £1.75BP27 Chad of Radio. Electronic, Semi -conductor and Logic Symbols £0.50BP32 How to Build Your own Metal and Treasure Locations E1.958P36 50 Circuits Using Germanium, Silicon and Zener Diodes E1.50BP37 50 Projects Using Relays SCR's and TRIACS £1.95BP51 Electronic Music and Creative Tape Recordings f1.95BP53 Practical Electronics Calculations and Formulae £2.95BP57 How to Build Your Own Solid State Oscilloscope E1.95BP60 PracticalConstruction of Pre -amps. ToneControls, Filters &AIM E1.45BP66 Beginners Guide to Microprocessors and Computing £1.75BP67 Counter Drive and Nueral Display Projects £1 .75BP86 An Introduction to BASIC Programming Techniques Et .95BP107 30 Solderless breadboard Projects - Book 1 £2.25BP110 How to Get Your Electronic Projects Working El .95BP117 Practical Electronic Building Blocks- Book 1 £2.25Elementary Electronics. Sladdin. Excellent theory and 35 constructional

projects. Uses &Dec. First steps to CSE level £3.95Interfacing to microprocessors and microcomputers £5.75

Speakers min Bohm 87p; 64 ohm 89p; Brimboard breadboard £8.9880 ohm 98p Verobloc breadboard £4.20

Crystal earpiece 85p PCB etching kit £4.98Magnetic ea i rpiece 15p ZX81 edge connector £2.25Stethoscope attachment 89p Ferrite rod 5 inch 59pMono headphones £2.98 PP3 clips 10pStereo headphones £4.35 PP9 clips 11pTelephone pick up coil 72D 2 station intercom £6.75Min buzzer 6V 50p; 1 2V 85p IC sockets 8 pin 16p; 14 pin 17pEuro breadboard £8.40 16 pin 18pS Dec breadboard £8.98

ADVENTURES WITHMICROELECTRONICS

ADVENTURES WITHDIGITAL ELECTRONICS

Similar to 'Electronics' below. UsesI.C.s. Includes dice, electronic organ,doorbell, reaction timer, radio etc.Based on Bimboard 1 bread board.Adventures with Microelectronics£2.98Component pack £29.64 lessbattery.

Entertaining and instructive. Includesdetails of some digital ICs and 8 pro-jects: shooting gallery, 2 way trafficlights, electronic adder, computerspace invaders game etc. No solder-ing.Adventures with Digital Electronicsbook £3.25Component pack including bread-boards £42.50 less batteries.

ADVENTURES WITH ELECTRONICS D7=:,

An easy tofollow booksuitable f or all ages. Ideal for beginners. No soldering,uses an S -Dec breadboard. Gives clear instructions with lots of pictures. 16projects -including three radios, siren, metronome, organ, intercom, timer,etc. Helps you learn about electronic components and how circuits work.Component pack includes an S -Dec breadboard and all the components forthe projects.Adventures with Electronics £2.85. Component pack £18.98 lessbattery.

FUN WITTELECTRAICerEnjoyable introduction to elec-tronics. Full of very clear full colour,Iictures and easy to follow text.'deal for all beginners - children

end adults. Only basic tools needed.64 full colour pages cover all as -Ipacts - soldering - fault finding -components (identification and howthey work).Also full details of how to build 6 pro-jects - burglar alarm, radio. games,etc. Requires soldering - 4 pages(Clearly show you how.COMPONENTS SUPPLIEDALLOW ALL PROJECTS TO BEBUILT AND KEPT.Supplied less batteries & cases.FUN WITH ELECTRONICSCOMPONENT PACK £15.78BOOK EXTRA £1.25Book available separately.

30 SOLDERLESS BREADBOARD PROJECTSBook 1 by R. A Pent old

Clearverobloc layouts and circuit diag rams. Includesf uzz box, radio, metronomes,timers, transistor checker, switches etc.Introduction gives basic information on components including resistors,capacita-tors, I.C.s, transistors, photocells etc. Ideal for beginners as well as those withsome experience.Complete kit Including verobloc, book and components (less batteries)£24.75Less book £22.50, less verobloc £20.25. Book only £2.25.

ZX SPECTRUM AMPLIFIER250mW output. Volume control. Internalspeaker. Very simply connected using load/save lead. Puts real power even into thesimplest "Beep" commands. Adds a real"zing" to musical programs and games.Requires PP3 battery - not supplied. Verylow current drain. Supplied ready builtcomplete with demo software and instruc-tions.

ORDER AS: ZX SPECTRUMAMPLIFIER (SAHE) £6.98

ZX SPECTRUM SUPER AMPLIFIER250mW output. Now add synthesizer qualityto those "Beep" comands. Super circuit withadjustable ATTACK, SUSTAIN and DECAYenvelope controls. Plus variable ECHO.Generates a wide range of special effects.Five graduated controls. Internal speaker.Very smart case. Requires batteries - notsupplied. Very low current drain. Ready builtcomplete with demo software and instruc-tions.ORDER AS: ZX SPECTRUM SUPER

AMPLIFIER (SSAHE) £17.98

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GSCSUPERKIT

.1"1211141°_;

Sel-lastruetiosIOW Ektrosic Wit

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. Udall. to, kg men

GSCSUPERKIT

£19.90

Learn the wonders ofdigital electronics!

This practical kit forbeginners comes completewith an instructionmanual, components, and

EXP300 breadboard to teach you all the basics ofdigital electronics. The course needs no solderingiron; the only extra you need to buy is a 40battery.Using the same board you can construct literallymillions of different circuits.The course teaches boolean logic, gating, R -S andJ -K flipflops, shift registers, ripple counters, andhalf -adders.It is supported by our theory courses

DIGITAL COMPUTER LOGIC£7.00

which covers: basic computer logic; logical circuitelements; the design of circuits to carry outlogical functions; flipflops and registers; andDIGITAL COMPUTERDESIGN £9.50Our latest, most up-to-date course on the design ofdigital computers, both from their individual logicelements and from integrated circuits. You arefirst shown the way in which simple logic circuitsoperate and then, through a series of exercises,arrive at a design for a working machine.Other courses available include:MICROPROCESSORS & MICROELECTRONICS @ £6.50COMPUTER PROGRAMMING IN BASIC @ £11.50GUARANTEE No risk to you. If you are not completelysatisfied, your money will be refunded upon return ofthe item in good condition within' 28 days of receipt.CAMBRIDGE LEARNING LIMITED, UNIT 91 RIVERMILL SITE,FREEPOST, ST IVES, CAMBS, PE17 4BR , ENGLAND.TELEPHONE: ST IVES (0480) 67446. VAT No 313026022

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TYPE 161B

DUAL POWER SUPPLY KITINCORPORATES A POSITIVE & A NEGATIVE REGULATED SUPPLY

BOTH ARE ISOLATED it ADJUSTABLE 1.3V TO 16V D.C.Interconnect to give 2.6V to 32V or- 1.3V/0/ + 1.3V to -16V/0/ + 16V

Output current 1A at 16V to 0.35A at 1.3VRipple is less than 1 mV

£25.99inc. P Et P and VAT

Built Et Tested£37.95 inc. P&P and VAT

Comprehensive designdetails with calculationsare included so that the kit is an excercise in power supply design. Thekit, which uses quality components, is complete with instructions. Casepunched and stove enamelled in attractive blue and grey with a printedfront panel to give a professional finish.Excellent for the beginner, the experienced amateur and as a tutorial forschools and colleges.

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My all-inclusive prices quoted in the Catalogue arethe lowest. All below normal trade price - some at

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Ultrasonic Intruder Alarm

UltrasonicIntruder Alarm

In the darkness, something stirred . . . the nightwas pierced by an unearthly wail. The HE

Ultrasonic Intruder Alarm had done its workagain.

R. A. PenfoldIDEALLY, every property would beprotected by a comprehensive burglaralarm system but the cost, plus thedifficulty of installation, makes it animpractical proposition in many cases.However, a fairly simple and self-contained system can be built at lowcost, installed with minimal difficulty,and offer a worthwhile improvementin security. It is a unit of this type thatis described in this article.

The system is of the ultrasonicDoppler -Shift type and when used, ineven quite a large room, it will detectmovement virtually anywhere in theroom and sound the alarm. The alarmgenerated is a frequency modulatedtone of quite high pitch and fairly highvolume, which should alert theoccupants of the building and(hopefully) scare away the intruder -who is unlikely to wait around to seeif anyone responds to the alarm!

The circuit includes a switch -ondelay which enables the user toactivate the alarm and move awaywithout triggering it. A delay toprevent the alarm from soundinguntil a few seconds after it has beentriggered could also be included, sothat the user has an opportunity toswitch off the unit before the alarmsounds. However with this particulartype of alarm, such a delay couldmake the unit less effective and morevulnerable, and with a small alarm forinternal use having the alarmgenerator operate briefly each time itis switched off is not a majordrawback. A switch -off delay has,therefore, been omitted from the unit.

System OperationFigure 1 shows the various stages ofthe unit in block diagram form; thereare two separate sections - thetransmitter and the receiver.

The transmitter is by far thesimpler; this is just an oscillatoroperating at a nominal frequency of40kHz and feeding into a specialtransducer. A frequency of 40kHz isused because this is where the

AMP

RECEIVINGTRANSDUCER

TRANSMITT NGTRANSDUCER

40k1-1.OSCILLATOR

A.M.DETECTOR AMP

TIMER L.F. OSC

Figure 1. The block diagram, showing the transmitting and receiving stages.

transducer is most efficient and it isan ultrasonic frequency so that thesound waves produced by thetransducer are too high in pitch to beheard by human ears. An intrudercould not be alerted to the presenceof the alarm by hearing the output ofthe transmitter.

A second ultrasonic transducer isused at the input of the receiver; thispicks up sound waves from thetransmitting transducer and convertsthem to small electrical signals. The

two transducers are mounted side -by -side and some of the pick-up is duesimply to sound waves which traveldirect from one transducer to theother. This accounts for only part of 'the received signal though, and alarge part of it is received indirectlydue to reflections from the walls,furnishings, or any other objects inthe room (including people).

Signals received via the stationaryobjects will be at the transmittedfrequency but, due to the well known



- 100uR3 R44k7 2k2

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100n

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R8 C4k7

C7470p

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*AA/V.R7

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Doppler Shift effect, sounds receivedby way of any object which ismoving towards the transducers willbe raised in frequency, while anypicked up via an object that is movingaway from the transducers will bereduced in frequency. The frequencyshift depends on the speed at whichthe object moves, but for someonewalking around a room, it would be alow audio frequency of between a fewtens of Hertz and a few hundredHertz.

The frequency shifted signals mixwith the non -shifted ones, butbecause of the varying phase of thetwo signals they first add together togive a strong signal and then tend tohave a cancelling effect on eachother, so that a much weaker signal isproduced. Thus the strength of thereceived signal varies at the shiftfrequency, and an output at this

03

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R110k 5

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R9470k

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frequency can be obtained using anordinary AM demodulator (ie, arectifier and smoothing circuit). Ofcourse, with no Doppler Shift there isno audio output from the detector,since the received signal will be ofconstant strength. The output fromthe receiving transducer is unlikely tobe very large, and would typically bewell under one millivolt RMS. A highgain amplifier must therefore be usedahead of the detector to give ausable signal level.

Further amplifiction is needed inorder to bring the output of thedetector to a sufficient strength todrive the next circuit, which is a latch(bistable) circuit. This permanentlyswitches on an audio oscillator whenan input signal, no matter how brief isreceived. This is an essential feature,as the alarm would otherwise onlysound while someone was actually

RESISTORS(All 0.25W 5% carbon)R1, 6, 10, 13 10kR2 33kR3, 6 4k7R4, 5 2k2R7 330kR9 470kR11 47kR12 15kR14 100kR15 22kR16 1MR17 8k2

POTENTIOMETERRV1 22k

0.1W hor preset

CAPACITORSC1 100u 10V

radial electroC2 100p

ceramic plate

Parts List

11 9

R1310k

R1522k

R12 R14 C915k 100k 10u

R161M

12 810

IC1d

13 9

C10 100n

NOTES:IC1 = 4001IC2 = 4046BEIC3 = 4047BE01,2,3 = BC239Q4 = BC171D1,2,3 = 1N4148RX,TX = ULTRASONICTRANSDUCERS

moving around the room. A timercircuit disables the latch for a fewseconds after switch -on so that theswitch -on delay is produced. A lowfrequency oscillator is used tofrequency -modulate the audiooscillator so that a more effective andpenetrating alarm is produced.

The CircuitThe full circuit diagram of theUltrasonic Intruder Alarm is shown inFigure 2; the transmitter is builtaround 1C3. This is a CMOS 4047BEdevice which can be used in a varietyof monostable and astable modes butin this circuit is employed as astraight -forward free running astable.RV1 is adjusted for the outputfrequency that give optimumefficiency from the circuit. The4047BE has anti -phase outputs atpins 10 and 11, and by connecting the

C3 I u 50Vradial electro

C4, 5, 10, 12 100npolyester

C6 4u7 50Vradial electro

C7 470pceramic plate

C8 6u8tantalum

C9 10u 25Vaxial electro

C11 330pceramic plate

C13 10npolyester

SEMICONDUCTORS01, 2, 3 BC239

high gain NPNQ4 BC171

NPNICI 4001 BE or 4001 UBE

quad 2 -input NOR

IC2 4046BEphase locked loop

IC3 4047BEastable/monostable

DI, 2, 3 1N4148signal diodes

MISCELLANEOUSSW1 SPDT

min. toggle or keyswitchRX Ultrasonic transducer

type R40-16AWD Ceramic resonator

type PB2720TX Ultrasonic transducer

type T40-16B1 9 Volt battery

preferably NiCadBattery connector; printed circuitboard; IC sockets; wire etc.

BUYLINES page 32



RV122k

R178k2

2

14

C11330p

1C340478E

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10

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ON

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transmitting transducer across these(rather than from one output to earth)the voltage fed to the transducer isvirtually doubled. This gives a usefulboost to the performance of theequipment. The output impedance ofthe 4047BE is not very low, but thetransducers are piezo types with animpedance of a few hundred ohms,typically, so a low drive impedance isnot essential.

A two -stage, direct -coupledcommon emitter amplifier is used atthe imput of the receiver section. Thisis probably the most cost effectiveway of obtaining the required highgain at the signal frequency of 40kHz.As the receiving transducer is also apiezo type it can be direct coupled tothe input of the amplifier. C2 rolls -offthe response of the amplifier at radiofrequencies which help to avoidproblems with breakthrough of radiosignals, as well as reducing the risk ofinstability.

The AM demodulator is a standardconfiguration, with D1 and D2providing the rectification while R6and C5 smooth the rectified signal.The audio ouput from the demodulatoris coupled by C6 to the input of asingle stage, high gain, commonemitter amplifier based on Q.

R10, R11, and two CMOS NORgates (connected here as inverters)form a simple latch circuit, and thishas in input fed from the output ofQ3 via D3. Under stand-by conditionsR7 biases Q3 so that it has a lowcollector voltage, arid the input ofthe latch is not taken high. However,if there is a suitable output from thedetector, the collector of Q3 willswing positive and negative of itsquiescent level, and on the firstpositive half cycle the latch will betriggered to the high state. D3ensures that the latch cannot betaken back to the low state onnegatative excursions of Q3'scollector.

At switch -on C8 will charge throughR9 and the base -emitter junction of

Q4. This switches on Q4 whichconsequently holds the input ofthe latch in the low state. Thisprovides the switch -on delay and alsoensures the latch is initially set to thecorrect state. After about 15 secondsthe charge current for C8 becomestoo low to hold Q4 in the on state,and the circuit is then able to functionnormally. SW1 is the on/off switch,also used to discharge C8 when theunit is switched off so that a freshswitch -on delay is produced when it isturned on again.

The audio oscillator uses a 4046BECMOS phase locked loop, but it isprimarily the voltage controlledoscillator (VCO) section that is usedhere. One of the phase comparators isused as an inverter which gives anti -phase outputs to drive theloudspeaker, the latter being aceramic resonator which is wellmatched to the high drive voltage andlow current available from IC2.

IC2 is frequency -modulated by alow frequency oscillator formed usingthe remaining two gates of IC1. Thisprovides a roughly squarewaveoutput, but filtering by R15 and C9converts this to an almost triangularwaveform which sweeps the VCOsmoothly up and down in frequency ata rate of a few Hertz. The VCOoperates at frequencies of around 2 to4kHz where the AWD (AudibleWarning Device) has optimumefficiency and despite the low powerat which it operates, provides a highvolume.

A mains power supply unit capableof giving a well smoothed 9Voutput could be used to power theunit, but NiCad batteries represent agood alternative; six AA cells in aplastic battery holder are suitable. Theunit could be powered from ordinary(non -rechargeable) batteries, but with

a quiescent current consumption ofabout 10 milliamps and the unit likelyto be used for prolonged periods thiswould probably be an uneconomicway of doing things!

ConstructionDetails of the printed circuit board areshown in Figure 3. All threeintegrated circuits are CMOS typesand the appropriate handlingprecuations should therefore be taken.It is advisable to fit IC2 and IC3 in DILIC sockets, but as IC1 is a veryinexpensive type it could reasonablybe deemed not worthwhile to use asocket for this device.

The ultrasonic transducers can bemounted direct on the board, eithervertically or horizontally if they aresoldered onto pins. They have verynarrow separation, and it might bepossible to obtain improvedperformance by mounting them off -board and using greater separation.However, the prototype gives excellentresults with the tranducers mountedon -board, and it is probably notworthwhile experimenting withgreater separation. The circuit shouldwork properly using any normal 40kHzultrasonic transducers and it is notessential to use the specified types(but obviously alternatives might givereduced performance).

C8 must have a low leakage levelor the switch -on delay could begreatly extended, possibly not endingat all! A tantalum bead component istherefore preferable to an electrolytictype.

Mechanical construction of the unitmust be varied to suit your particularrequirements. Alarms of this generaltype are often disguised as someordinary household object such as abook or a small bookshelf

In the prototype, the transducers are mounted directly on the board.



[11

41-b4 0

<1°144 o

cla tC3

0 E 0

Figure 3. The components.

loudspeaker. However, the unit isalmost certain to be triggered beforeany intruder realises what it is andcan simply be built as a normalproject fitted to a standard plastic ormetal box. It should not be possiblefor an intruder to easily switch off theunit, so SW1 should be concealed insome way. The AWD is mounted onthe exterior of the case, and the twoultrasonic transducers are fittedbehind cutouts which enable the

PIEZO BUZZER

sound waves to flow freely to andfrom the transducers.

AdjustmentThere is only one adjustment to makebefore the unit is ready for use, andthis is to set RV1 for optimum results.This can be done simply by trial anderror, but there is a much quicker wayif a multimeter is available. Themultimeter is used to monitor the

voltage across C5, and RV1 isadjusted for the highest obtainablevoltage reading. The two ultrasonictransducers should be aimed into areasonably empty space while thisadjustment is'made. There may betwo peaks at slightly different settingsof RV1 and in this case the morepronounced of the two settings shouldbe used.

If the switch -delay is considered tobe too short it can be extendedsomewhat by increasing R9 to about 1megohm, or using a higher valuecomponent for C8.

To a certain extent the performanceof the unit will depend on where inthe room it is located and where it isaimed. With a little experimentation asuitable position for the unit shouldsoon be found. With this type ofdetector there are normally a few"dead" spots in the room where theunit is insensitive, but it should bepossible to obtain good sensivity overthe majority of even quite largerooms. Remember that the unitresponds to movement, not just to thepresence of an object. Also bear inmind that false alarms can beproduced by such things as curtainsblowing in the wind, pets movingwithin the protected area and eventurbulence in the air caused by aheater. Obviously the unit should bepositioned where false alarms of thistype are not likely to occur. HE

NEW- K2585Codelock

(844.02 + VAT)

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Velleman electronic kits can be purchased directlyfrom us at the address below and are also availablefrom the following stockists:Enquiries from Retail Shops always welcome.Free illustrated catalogue and price list available onrequest.

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K2588 -Sound to light

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Annley Electro, Bedminster Down, BristolBaxol Tele Exports, Post Rathdrum, Co. Wicklow.Bradley -Marshall Ltd., 325 Edgware Road, LondonS& R Brewster Ltd., 86-88 Union Street, PlymouthCamlab Electronics, 27 Faringdon Road, Swindon, Wilts.Gaines Electronic Components, 3 West Street, Fareham, Hants.L.R. Hanney, 77 Lower Bristol Road, Bath, Avon.Hemmings Electronics, 15 Brand Street, Hitchin, Herts.R. Jones Electronics, 267 Rectory Road, Grays, Essex,Lovering Bros., 76 King's Road, Reading, Berks.Marshall Electronics, 86 West Regent Street, GlasgowTwyford Electronics, 22 Station Road, Twyford, Berks.


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THERRY'ADD-ON KEYPADA compact 16 button keypadsuitable for use with cherrykeyboard to extend its functions.Supplied brand new with dataA 4 x 4 non -encoded singlemode keyboard.05 linc. V.A.T1

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RECHARGEABLE BATTERIESAA or HP7 size batteries 4 for £3.00'UK C/P 30p1Charger takes up to 4 any size1'-V rechargeables also. I x PP3 size E6.95'UK C/P 650

DIGITAL MULTIMETERSo w ilh case IrotarH swilchesl+Side button - case £2.951025C 813 range 6.2A DC2 meg ohm £23.50KD305111 16 range 100 OC2 meg ohm £26.95K 030C 26 range IAAC/DC 20 meq ohm £29.50

1(055C II 28 range 10A AC/OC 20 meg ohm £32.50Melon 3000 30 range 10A AC/DC20 meg ohm £33.246010 28 range 10A AC/OC 20 meg ohm £34.4070304 AS6010 high acc 0.1'e basic E41.30K0615 16 range 10A DC 2 meg plusHfe tester £39.95SIFAM 22008 21 range 2A AC/DC 20 meg £39.95Bench ModelsTM355 29 range LEO IDA AC/DC 20 megThandar £86.25TM356 26 range LCD 10A AC/DC 20 megThandar £97.75TM351 29 range LCO 10A AC/DC 20 megThandar £120.75SIFAM 250024 rangeLCD 2A AC/DC 20 meq £99.95ALSO IN STOCK Thurlby. Metric and Beckman.Professional series incl. True Rms. etc.

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Pair £3.50

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Pair £3.50

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Pair £3.00

MULTIMETERS IUK C/P 65p1HM102132 20K/V 10A OC 20range & cool buzzer £13.50ETC5000 21 ranges. 50k/ V.Range doubler 10A OC E18.95TMK500 23 ranges 30k/V.12A DC plus cont buzzer £23.95NN56R 20K/V. 22 range pocketETU102 16 range 21( /V pocket830A 26 range 30k/V. 10A AC/DC overloadprotection. etc360TR 23 range 100K/V. Large scale 10AAC/DC plus HleAT2100 31 range 100K/11 deluxe 120AC/DCAT1020 18 range 20k/V Deluxe plus HfetesterYN360TR 19 range 20k/V plus Hfe tester

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IN STOCKLarge range of semi -conductors, tools. components.accessories. cordless and electronic telephones.

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LAG27 10 Hz to 1 MHz £90.85AG202A 20 Hz to 200 kHz 'List £94.501 £83.50RF

S6402 100 KHz to 30 MHz (list £79 501 £69.50LSG1 7 100 KHz to 150 MHz E79.35

LOGIC PROBESLP10 10 MHZ £28.50OLP50 50 MHZ with carry case andaccessories £52.33

HIGH VOLTAGE METERDirect reading 0'40 KVlok/voii £23.00 (UK C716711161111111/

DIGITAL CAPACITANCEMETER0.1 gl to 2000 mId LCD 8 ranges0M601 3 £52.75

TRANSISTOR TESTERDirect reading PNP NPN etc.ICI £21.95!UK C/P 65p1

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. SAE by post

!tilt% 'NM' Series NAME& SC'

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°/SINGLE TRACE UK C/P £3 003030 15 MHZ 5mV 95mm tube plus componenttester CP £300 £177.10SC1 10A Miniature 10 MHZ battery portablePost free £171.00

HMI03 15 MHZ 2mV 6 x 7 display Piuscomponent tester C P £300 E181.70 Optional carry rase £6 84 AC adaptor C6 69Nicads El 2 50 DUAL TRACE (UK C/P £4.001D T 520 Oval 20 MHZ £241.50HM203/ 4 Dual 20 MHZ plus componenttester E303.60CS1562A Dual 10 MHz 'List £321.001 £269.503131 Dual 15 MHZ component tester £27610CS1566A Dual 20 MHZ All facilities KM £401 151

HM204 Dual 20 MHZ plus component tester £349.50sweep delay £419.75OPTIONAL PROBE KITSAl £7.95 01 X10 £10.50 010 E9.45

VARIABLE POWER SUPPLIES[UK C/P fl 001PP24I 0/12/24V. 0/ IA £35.00PP243 3 amp version £59.95PS1307S 8/ I5V7 amp twin meter E24.95

HENRY'S

FREQUENCY COUNTERSPFM200A 200 MHZ hand held pocket8 digit LEO £77.60MET10013 (WILED bench? ranges 100 MHZ E102.35MET6008 digit LED bench 3 ranges 600 MHZ £132.25METI000 8 digit 1E0 3 ranges I GHZ £182.85TF040 8 digit LCD 40 MHZ. Thandar £126.50TF2003 digit LCO 200 MHZ. Thandar £166.75

Cubegate Limited

404-406 Edgware Road. London. W2 lEDComputer 01 402 6822. Components 01-723 1008Test Equipment & Communications: 01 724 0323

AUDIO ELECTROrlICS301 Edg ware Road. London. W2 1BN01-7243564 (All mail to this address(

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CHORUS UNIT: A solo voice of instrument sounds like moreCOMPRESSOR: Limits & levels maximum signal strenghtECHO UNIT: With double trackingFREQUENCY DOUBLER: Raises guitar frequency by 1 octaveFREQUENCYCHANGER&WAVEFORM MODIFIER -Tunable unitFLANGER: Fascinating effects plus phasingFUZZ: Smooth distortion whilst keeping natural attack & decayGUITAR EFFECTS: Multiplevariation of level &f ilter modulationGUITAR OVERDRIVE: Fuzz plus variable filter qualityGUITAR SUSTAIN: Extends effective note durationJABBERVOX: Voice disguiser with reverb & tremoloMAD-ROJ: Variable sirens, incl police, galaxy, machine gunsMETRONOME: With audible & visual beat & down -beat markingMICROPHONE PRE -AMP: with bass & treble switchingNOISE LIMITER: reduces tape & system hissPHASER: with automatic & manual depth & rate controlsREVERB: with variable delay & depth controlsRYTHMN GENERATOR: 15 switchable rhythmsRING MODULATOR: with integral oscillator controlROBOVOX: versatile robot type voice modifierROGER 2 -GONG 2 gongs sounded at end of transmissionSCRAMBLER:Codes& decodes t ran sm issions a uthorised chansSPEECH PROCESSOR: for clearer transmissionSTORM EFFECTS: Automatic & manual, wind, rain, surfTREMOLO: deep temolo with depth & rate controlVOCODAVOX: modular vocodaVODALEK: Robot type voice modulatorVOICE -OP -SWITCH: with variable sensitivity & delayWAH-WAH: with auto -trigger, manual & oscillator control

KIT1 62 £26.60KIT133 £12.38KIT1 68 £38.10KIT98 £9.34KIT1 72 £29.66KIT153 £18.73KIT91 £9.28KIT42 £13.54KIT56 £17.53KIT75 £9.36

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MANY OTHER GREAT KITS IN CATALOGUE such as Autowah, bass boost, call sing,comparator, frequency generator, Funkywobulo!, harmonofa, hum -cut, mixers,sequencers, synthesiser interface, treble boost, tone control, vibrato, voice filter, voiceoperated fader, Wheeby-jeeby!, wobblewah. Plus digital synthesiser, junior syn-thesiser, envelope shapes, D -A converter, multiwaveform VCO, Keyboards, contacts,etc. Send SAE. for comprehensive catalogue (overseas send C1).

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EVERYONE KNOWSthat TOOLMAIL offer the largest range of D.I.Y. toolsavailable by post and that their 128 page colourcatalogue contains over 2,000 quality tools.But did YOU know that the range includes almosteverything required by the Electronics Hobbyist: -Soldering Irons, Desolder Tools, Miniature Tools,PCB Holders, Drills, Pliers, Cutters, Tweezers, ICExtractors, Screwdrivers, Craft Knives, Hole Punches,Test Meters, Needle Files, Glue Guns, Nut Drivers,Wire Strippers, Component Formers, IC Inserters,De -solder Braid, and complete Electronics ToolKits.The catalogue normallycost £1 but is available FREEto Hobby Electronics readers. Send 50p postage foryour personal copy.

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PARNDON ELECTRONICS LTD.Dept. 22, 44 Paddock Mead, Harlow, Essex. CM18 7RR. Tel: 0279 32700

RESISTORS: Vu Watt Carbon Film E24 range ± 5% toleranceBandoliered and colour coded. Full Range 1R0 -10M.

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RECTIFIERS1 Amp 3 Amp

50V 3p 14p100y 4p 14p200V 5p 14p400V 6p 19p600V 8p 20p

1000V 9p 25p

31/2 Digit LCD Display: 1 colon, 3 decimal pointsplus/minus sign and lo bat indicator.

Complete with low power 7106 A/D converter display driver.Driver set £8.95

Display £3.50 Driver £6.50

DIODES: IN4148 £1.60 per hundred

DIL 8 pin -lop. 14 pin - 11p. 16p pin - 12p. 18p pin - 19p. 20p pin -21pSOCKETS 22 pin - 23p. 24 pin - 25p. 28 pin - 27p 40 pin - 42p.

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DIODESIn4148 2p each or 61.50/100'n4031/40132/4003 3p eachZener Diodes 400mW (13ZY88C)4p each or £3 per 100

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18 12p 42p20' 14p -

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15 deg c/w 24p eachTo 5 push on 913 each46 x 46mm Finger type drilled To3 7 deg

22 16p - 10 per value .. 95p c/w 28p each24 15p 53P 1000 Assorted values 55 x 55mm Finger typed drilled To328 19p - 50 value... E8 4.5 deg c/w 31p each40 ' 26p 92p

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CAMTEC CIRCUITS AND SYSTEMS LIMITED5 York Road, Bognor Regis, West Sussex P02 1CIW

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11%

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Mail order onlyWe are the specialist of electronic kits and rack mounting cabinets. A catalogue withcomplete range of products including pre -amp modules, power amp modules, pre andpower amplifier modules, complete kits of amplifiers, equalizers, reverberationamplifiers (with cases), alarm clocks, appliance timers, CB amplifiers, test equipment,control modules, music generator, battery flourescent light and high quality rackmounting cabinets etc. with illustrative pictures now available at the cost of 35p +25p p&p.Professional rack mounting cabinet Panel Size Rear Box Price

W H (inch) W H D19 x 5 17 x4.5 x 1019 x 4 17 x3.5 x 1019 x 3.5 17 x3 x 1019 x 3 17 x 2.5 x 1019x2.5 17 x 2 x 1019 x 6 17 x 5.5 x1219 5 17 4.5

AL STEEL27.54 23.5425.24 21.2424.09 20.0924.09 -22.94 18.9428.69 24.6927.54 23.54x

19 x 4x x12

17 x 3.5 x12 25.24 21.2419 x 3.5 17 x3 x12 24.09 20.0917 x 3.5 15.5 x 3 x9 21.79 17.7917 x 2.5 15.5 x 2 x 9 20.64 16.6417 x 4 15.5x 3.5x 1225.24 21.2417 x 3 15.5 x 2.5 x 12 24.09 20.09Please add £2.50 p/p per item

* Wholly made of black anodised aluminium sheets * Suitable for high qualityamplifers and many other purposes * Top, side and rear cover removable for access* Separate front mounting plate * Heavy gauge front panel is of brushed aluminiumfinish enhanced with two professional handles * With ventilation slits and plasticfeet.The low cost steel version is also available. The size and features as well as the frontpanel is the same as the aluminium cabinets except the rear box is manufactured fromsteel painted in black.

CONTROL MODULES

1116-17ga

TY-7 Electronic touch switch£2.90 Kit £4.50 Ass.

TY-11 Light activated switch£2.20 Kit £3.50 Ass.

TY-18 Sound activated switch(Clap switch) £4.50 Kit £5.95 Ass.TY-38 Sound activated switch(voice -switch) £5.50 Kit £7.50 Ass.TY-41 Infra -red remote control(Receiver and transmitter)

£17.20 Kit £21.95 Ass.

HI -Fl AMPLIFIER MODULES

TA -323A 30W + 30W stereo amplifier£18.95 Kit £23.95 Ass.

TA -820 60W + 60W stero amplifier£27.50 Kit £33.50 Ass.

TA -920 70W +70W stereo amplifier£35.50 Kit £42.50 Ass.

7

12monthguarantee

'1=

From your Local Dealer or Direct from Manufacturers

LIM TED

- NM ST. PLYMOUTH PLI 3HG

RECHARGEABLE

BUMPPRIVATE OR TRADE ENQUIRIES WELCOME

FULL RANGE AVAILABLESEND SAE FOR LISTS

£1.45 for booklet "Nickel Cadmium Power" TRADE PRICES FOR SCHOOLS & COLLEGES

SANDWELL PLANT LTD656 Chester Road, Erdington,

Birmingham 021-373 9487After Hours: Lichfield 57977Now open Saturday mornings

p-BECOME ARADIO AMATEURTrain now for the Radio Amateur Licenceexamination. No previous knowledgeneeded, only a few hours per week of homestudy for 3 to 6 months. Post coupon nowfor details or tel. 0734 51515 (24 hr service)

British National Radio & Electronics School Reading, Berks. RG1 1BR1FREE brochure without obligation from:

British National Radio &Electronics School IREADING, BERKS. RG1 1BRCA -at"

Name

Address

68

0752-665011 TRADE ENQUIRIES WELCOME L HE/10/846 BLOCK CAPS PLEASE j


e#*--'

HE PC B S E RV I C E Ready

pde

eade,PRINTED CIRCUIT BOARDS (PCBs) for HE projects have often represented an \ Siobstacle for our readers. Some of you, no doubt, make your ownbut our PCB Service saves you the trouble.NOW you can buy your PCBs direct from HE. All (non -copyright) PCBs will be availableautomatically from the HE PCB Service. Each board is produced from the same master asthat used for the published design and so each will be a true copy, finished to a high stan-dard.Apart from the PCBs for this month's projects, we are making available some of thepopular designs from earlier issues. See below for details. Please note that only boards forprojects listed below are available: if it isn't listed we can't supply it.August 81 June 82 January 83HE/8108/1HE/8108/2

RPM MeterThermometer

£1 77£1.67

HE/8206/1

HE/8206/2

Power SupplyDesign £2.48

Auto-Wah £3.08

HE/8301/1HE/8301/2

Chip ProbeSwitched Mode

Regulator

£1 82

£1 96September 81HE/8109/1HE/8109/2

Power PackReaction Tester

Game

£1.69

£1.71

HE/8206/3

HE/8206/4&5

Auto GreenhouseSprinkler £3.45

Telephone Timer(Set of Two) £6 50

February 83HE/8302/1HE/8302/2

Incremental TimerDigiTester PSU

£7.13£6.70

HE/8109/3 'Diana' Metal March 83Detector £3.31 July 82 HE/8303/1 Loudspeaker

HE/8207/1 Tanover £2.13 Protector £2.51

October 81 HE/8207/2 TVI Filter £1 78 HE/8303/2 Overvolt Cutout £2.25HE/8110/1 Combination Lock £2.65 HE/8207/3 Computer PSU £7 68

HE/8207/4 Solar Radio 1 98 April 83November 81 HE/8304/1 6502 EPROMMER £7.18HE/8111 /1 &2 Sound Torch August 82 HE/8304/2&3 Ducker

(Set of Two) £5.31 HE/8208/1&2 Digital Millivoltmeter Main Board £3.56(Set of Twol £4.34 Preamp Board £2.31

December 81 HE/8208/3&4 Audio Analyser HE/8304/4 Power Down £2.10HE/8112/1 Pedalboard Organ £5.64 (Set of Two) £11.55

May 83

January 82HE/8201/1 Intelligent NiCad

Charger £2.83

September 82HE/8209/1&2 Signal lights

Main Module £1.96

HE/8203/1HE/8305/3HE/8305/4

BBC InterfaceStall ThiefAuto -Test

£4.82£2.50£2.50

Junction Module £1.70 June 83February 82 HE/8209/3 ZX Interface £3.34 HE/8306/1 Sinclair SoundHE/8202/1 Relay Driver £2.07 HE/8209/4 Slot Car Controller £1.98 Board £2.80HE/8202/2 Mast -Head Amp £1.08 HE/8306/2 CB Rap Latch £1.65

October 82 HE/8306/3 Bat Light £2.25March 82 (Car battery monitor)HE/8203/1 Digital Dice £1.40 HE/8210/2 Negative Voltage HE/8306/4 Traffic Light Toy £2.56

Generator £1 49 July 83April 82 HE/8210/3 Squelch Unit £2.52 HE/8307,'1 Soft Fuzz £2.77HE/8204/1 Digital Capacitance

HE/8204/2HE/8204/3

MeterDual Engine DriverBike Alarm

£4.02£3.27£2.45

November 82HE/8211/1 Pedometer/

Odometer £2.13

August 83HE/8308/1HE/8308/2HE/8308/3

Whistle SwitchAce InterfaceEnlarger Timer

£4.40£352£292

May 82 December 82 HE8308/4 Auto -Winder £298HE/8205/1&2

HE/8205/3HE/8205/4

Digital Thermometer(Set of Two)

Echo-ReverbCable Tracker

£4.62£5.63£1 85

HE/8212/1HE/8212/2HE/8212/3&4

Phase Four £2.83M icrolog £3.98Tape/Slide

(Set of Two) £5.26

September 83HE 8309 1HE 8309 2

TremolekoSPL Meter

£3 14£4.22

HE/8212/5 TV Amp £5.70 October 83HE/8212/6 Lofty £2.61 HE 8310/1 Ultrasonic Alarm £3.19HE/8212/7 Noise Gate £3.60 HE 8310/2 Audio Level Meter £3.09HE/8212/8 Low Cost Alarm £2.30 HE 8310/3 High Voltage Meter £3.47

PLACE an order for your PCBs using the form below (or a piece of plain paper if you prefer not tocut the magazine), then simply wait for your PCBs to drop through your letterbox, protected bya Jiffy bag.

HE PCB Service, Argus Specialist Publications Ltd, 145 Charing Cross Road, London WC2H OEEI enclose a cheque/Postal Order made payable to ASP Ltd,for the amount shown below Price.ORI wish to pay by Barclaycard. Please charge my account number

VISAOR

I wish to pay by Access. Please charge to my account number

SIGNATURE

NAME(BLOCK CAPITALS)

ADDRESS(BLOCK CAPITALS)

Please allow 21 days for delivery

Boards Required Price

Add 45ppErp 0.45

Total Enclosed £


PCB FOILPATTERNS

ThoULTRASONIC ALARM

HE 8310 3HIGH VOLTAGE METER

4). o-

HE 8310 1

O

1

II311151171191111111311151117111912111213

o

IIIIIIIIIIIIIIIIII I)

Above. The PC.R foil pattern for theTrump Card is copyright by INNO-VONICS, but is made available forhome constructors by permission.

Left: The Ultrasonic IntruderAlarm PCB layout.

Below Left: The Hi -Volt Meter PCBlayout.

Below: The Audio Level Meter PCB islaid out for a 10 -LED module, but tenseparate LEDs can be used instead.

cornr:T :11

.128 \°°°

00 c=111.11)47D O 00D O 0000 00D O 00 1300C100 00DO 00DO 00D O 00

AUDIOLEVEL METFR

70Hobby Electronics, October 1983

DOUGLAS ELECTRONIC COMPONENTS90 Wellington Street, Stockport, Cheshire. SKI 3A0

164 BOOKS - CROSSOVERS - CABLE -COMPONENTS - CONNECTORS - DECKS FUSES

- HEADPHONES - LEADS MICROPHONES -MULTIMETERS - PROJECT BOXES -

SOLDERING IRONS SPEAKERS - STYLI &CARTRIDGES TOOLS - VEROBOARD ETC.

Tel:061-480 8911

ri SAVE £££'s ON HOME HEATING BILLSUNIQUE DIGITAL THERMOSTAT

POSSIBLE FUELSAVINGS OFUP TO 25%

Normally manufactured exclusively for the trade. Features: Continuous readout of ambient temp via 3 digit 7 segment display LED indicates when pump is in operation 0.2°C Hysterises 240v 3A control contacts 0 Switched set temperature

High specification - Simple to calibrate -Connect in place of existing thermostat -Requires 240v 2VA supply - Kit includes allnecessary components, Enclosure, diagramsand instructions.

Kit price only £29.95. Assembled Price £45.00plus £1 p&p (prices Include VAT)

Send cheque or PO to: DICON ELECTRONICS LIMITEDBond Street, Bury, Lancs BL9 7DU Tel 061-797 5666

PERMACON

Proved over many years in commercialuse, now available to the hobbyist at

competitive prices.STANDARD CONNECTORSTWO PITCHES .1 AND .15FOUR CONTACT STYLES

Further details from:

COLN BROOKELECTRONICS LTD

Crabbs Abbey, StowbridgeKings Lynn, West Norfolk

PE34 3PE

POSITRON ICSTWO PROFESSIONAL POWER SUPPLY UNITS NOW IN

If you are looking for the basic tool of electronics then thesefeatures should impress:1. 0-30 VOLT OUTPUT2. 0-3 AMP OUTPUT3030-1.5 AMP OUTPUT

301.53. INTEGRAL MULTIMETER GIVING FULLY SIX RANGES4. HIGHLY STABLE IN VOLTAGE AND CURRENT MODS5. PRICE, YOU WON'T FIND SIMILAR PERFORMANCE

FOR TWICE THE PRICE6. IN KIT, STEP BY STEP INSTRUCTIONFrom kit or built and tested you will have a highly controlablepower source of exacting design, engineering and quality.

UNIT 301.5

Kit £45(Built & Tested) £60

303£55£70

P&P £2.50. VAT not inc. Please allow 21 days delivery

POSITRONICSUnit 4, New Enterprise III, Montgomery Street

Sparkbrook, Birmingham B11 1DSTel: 021-350 2267

FREE BOOKLETon

BURGLAR ALARMSwith

LOWEST U.K. DIY PUBLISHED PRICESPHONE OR WRITE FOR YOUR COPY

051-523 8440AD ELECTRONICS

217 WARBRECK MOOR1 AINTREE, LIVERPOOL L9 OHU

MICRO -MIKE®The Most Useful InspectionTool You'll Ever Own . . .

. And One Of TheLeast Expensive

The Powerful Pocket Microscope that'sperfect for close inspection and measure-ment in all scientific work.Professional quality optics. Available in 10x to50x magnifications. Scale reading 0.001 inch or0.1mm. No moving parts. Easy to use. Alwaysin focus. Rugged aluminium and glass construction. Virtually indestructible. Guaranteedfor a lifetime of service.

Optional Micro-Lite attachment nowavailable for full illumination in

hard -to -see areas10x, 20x, 40x, 50x Models £10.35Measuring models with 0.1mm Scale E12.65Micro-Lite Clip on accessory light E8.60

Hirsh Jacobson Merchandising Co. Ltd.91 Maryfabona High St., London W1M 3DE

Tel. 01-935 4709Prices include postage and VAT

State magnification required


I am enclosing my Cheque/Postal Order/ International moneyOrder for (delete as necessary) £ (Made payable to A.S.P. Ltd)

OR Debit my Access/Barclaycard

VISA (Delete as necessary)

amm*

All classified advertisements must be paid for in advance.

HOBBY ELECTRONICSCLASSIFIED ADVERTISEMENT - ORDER FORM

If you have something to sell now's your chance! Don't turn the page - turn to us!Rates of charge: 30p per word per issue (minimum of 15 words).and post to HOBBY ELECTRONICS, CLASSIFIED DEPT., 145 CHARING CROSS ROAD, LONDON WC2

Please place my advert in HOBBY ELECTRONICS for issues commencing as soon as possible.Please use BLOCK CAPITALS and include post codes.ClassificationName (Mr/Mrs/Miss/Ms)

(delete accoraingiy)Address

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HORIZON(mEol;EndCs)TRON ICS

..... :.-- Dept. H/H Charlotte St. Rugby Tel: 78138illiliPrime quality. TERRIFIC PRICES. Mail order only

REGULATORS151 00nok ore 060

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ABOVE Just a few exmples Send S.A.E /ListADD. 65p p8p to all orders under 05.00VAT: add 15% VAT to total order value

FREE CAREER BOOKLET

PROBLEMS WITHTHAT PROJECT?

We will -* BUILD* TEST* REPAIR

All your Electronics Kits and projects.Prices from only £5.00

* Call us now for a quote. *

WEB Logic Systems Ltd15 High Street, Harpenden, Herts.

05827-62119

72

Train for success, for a better job, better pay

Enjoy all the advantages of an ICS DiplomaCourse, training you ready for a new, higherpaid, more exciting career.

Learn in your own home, in your own time, atyour own pace, Through ICS home study, usedby over 8 million already! Look at the widerange of opportunities awaiting you. Whateveryour interest or skill, there's an ICS DiplomaCourse there for you to use.

Send for your FREE CAREER BOOKLET today-no cost or obligation at all.

min NMI WM NMC G BASIC riELECTRONICS

NC FtGRADIO (--1'AMATEUR'S Exam I I

RADIO Er AUDIOI ENGINEERING

RUNNING YOUR'OWN BUSINESS

AUTOMECHANICS

ELECTRONICENGINEERING E,COMPUTER f-liiPROGRAMMING L___IiTV Er AUDIO iElSERVICING 1ELECTRICAL INSTALL- F-1ATIONS/CONTRACTING L___I

C Er G BASIC MECHANT7ICAL ENGINEERING

I

Name

IAddress

P Code

icsDept M 261

Dlvolon of 'l LondonEducation Corporation SW8 4UJ (311a122hou99rs1/'

160 StewarIS Road

EM 111.111 .110 .= MIN MN =IIHobby Electronics, October 1983

HOBBY ELECTRONICS CLASSIFIEDLineage:30p per word (minimum 15 words),semi -display £7.50 per single column centimetreRing for information on series bookings/discounts

All advertisements in this section must be prepaid.Advertisements are accepted subject to the terms andconditions printed on the advertisement rate card (available on request)

01-437 1002EXT 282

Send your requirements to:Julie Bates,ASP Ltd.,145 Charing Cross Road,London WC2H OEF

BOOKS & PUBLICATIONS

PARAPHYSICS JOURNAL(Russian translations). Psy-chotronics, Kirlianography,heliphonic music telekinetics.Computer software. SAE 4 x9":- Paralab, Downton Wilts.

SERVICES

JOHNSON INTRODUCES THE NEW

ele-RecorderAutomatically record everytelephone call

BoBont compactunobtrusive

Superb 2 wayspeech quality British Telecomapproved

Records op to8 hours on a standardC120 tapeJohnson Electronics (Works), Star Warahoosa,

Camden Goods Dapot, Cheat Form Road,London NW1 01.286 6119

C95 I + C2 p&p)

PLANS 'N DESIGN

AMAZING electronic plans,lasers, gas, ruby, light shows,high voltage teslas, van degraph, surveillance devices,ultrasonics, pyrotechnics, newsolar generator, 150 more pro-jects, catalogue S.A.E., Plan -centre, Bromyard Road Indus-trial Estate, Led bury HR8

FOR SALE

POWERAMPLIFIERS 200Watt £11.95! Case and con-trols. Volume balance andsockets. 4 x MJ3001 outputs100 + 100 Watts!! (R.R.P. +data = £38.40). Kia, 8 CuliffeRoad, Ilkley.

NEW "Maplin VIC20 TalkbackKit" LKOOA. Built and rested.£33. A. Harvey, S8 St. MichaelsGrove, Fareham, Hants.

COMPONENTS

BUMPER BOX OF BITSWOW!! We've got so many components

stock. we can t possibly list them all!!-So buy a box, in it you'll find resistors.capacitors, displays. switches, panelsand transistors, diodes, IC's, etc.. coils.pots . .. and so on. All modern parts -guaranteed at least 1000 items. Mini-mum weight 10Ibs. ONLY £8.50 inc. 48page catalogue 50p.

ELECTRONICS WORLDIF Dews Road. Salisbury

Wilts SP2 7SN

ALARMS

BURLAR ALARM EQUIP-MENT. Please visit our 2,000sq. ft. showrooms or write orphone for your free catalogue.C.W.A.S. LTd. 100 RooleyAvenue. Bradford BD6 1 DB.Telephone 0274-308920.

ULTRASONIC ALARMSELF-CONTAINED

LOUDSPEAKER DESIGN* Easy installation* Adjustable sensitivity control* Automatic reset after time out* Motion Detection using

"Doppler Effect"* Delay time features for exit and

re-entry to premises* External speaker or siren can be

connected to the phono jack forremote monitoring

* Normally open relay contacts forauto switching of external devicesduring alarm mode

* Applicable for home security systems:Screw terminals available for theconnection of normally closed (NC)type magnetic or trap switches

* AC/DC operation (requires mainsadaptor)

Fabulous value RRP £39.99.Our Price £19.99 + E2.50 p.p.8. insurance(Note: we have a few units returnedunder guarantee which are uncheckedand sold without guarantee @ £12.00+ pp.Send cheque, postal order or phone withcredit card detailsAccess - Barclaycard - Diners

as ST WOO6-10 Market Road,London N7 9PP.Telephone: 01-609 4526

COMPONENTS

"V I% IfAuto Electronics,

103 Coventry Street,Kidderminster

Tel: (0562) 2179Brand new components byreturn post or ring withAccess/Barclaycard numberfor same day despatch.

All manufacturers guaran-teed new stock. All at mostcompetitive prices. Cata-logue available only 50p. Allprices inclusive of VAT.

N STOCK New telephoneplugs and sockets also ZX81plugs and spectrum plugs andwide range of burglar alarmequipment and all accessoriesfor same plus large range ofcomponents. Shudehill SupplyCo. Ltd., 53 Shudehill, Man-chester 4. 061-834 1449.

HOBBY SHOP

DAVENTRY

HIGH MARCHEMOS DAVENTRY N N11 4H0

Tel: (03272) 5523* Open Mon -Sat 9am-4pm* Both retailers and wholesalers* Vast stocks of components* Large 'walk -round' electronics

supermarket

IRELAND

IRELANDCall A & A ELECTRONICS

for wide range of kits17 Cuala Road

BrayCo. Wicklow

Tel. 01-862422

LANCASHIRE

ETESON ELECTRONICSEDE 15B Lower Green,

Pouton-le-Fylde,Blackpool

Tel: (0253) 885107

Open 9:30am-12.30, 1.30-5.30.Closed Wed & Sun

Electronic Component Specialists

EQUIPMENT

AERIAL AMPLIFIERS Im-prove weak television re-ception. Price £6.70. S.A.E. forleaflets. Electronic Mailorder,Ramsbottom, Lancashire BLO9AG H.

JOIN OUR FREE mailing listfor bargain electronics offers.Write to: Van Gelder Ltd, P.O.Box 10, Southend-on-Sea,Essex SS2 6QG or phone(0702) 548681.

KITS

FREE SOLDERING IRON STANDWith every soldering iron purchased, kitcomes complete with quality British 17watt iron, spring stand, inbuilt sponge,solder and instructions. Ideal for PCBwork. Only £7.99 + 75p P&P. R.A.J.,63 Penn Road. Datchett, Berks SL3 9HT.

TODMORDEN

PROFESSIONAL OR HOBBYIST?

Come and have a look at the EMPORIUMBargains galore - catalogue available

Electronic, Electrical and Mechanical Nuts& Bolts, Resistors, Capacitators, Meters,Semiconductors and much more.

A. C. TOWNLEY LTDHarehlll MIII

HarehIll St (off Burnley Rd), TodmordenOpen 8.30-5.30 Sets till 1pm

(lunch 1-2pm)

TYNE & WEAR

NOW OPEN IN NEWCASTLEFOR THE BEST IN ELECTRONIC

TEST EQUIPMENT ANDACCESSORIES

Marlborough Electronic Components15 Waterloo Street,

Newcastle NE1 4DE1Tel: 818377

Open 9am-6pm Mon -Sat Easy ParkingStockists of: Transistors. Resistors,

Capacitors, I.C. Diodes, Electronic BooksEtc. Repairs undertaken

W YORKSHIRE

ACE MAILTRONIX LIMITED3A Commercial StreetBatley, West YorkshireTel. 0924 441129Open: 9-5.30pm Weekdays

9.30-1 pm SaturdaysRetailers and wholesalers

KITS

PRINTED CIRCUITS. Makeyour own simply, cheaply andquickly! Golden Fotolac light-sensitive lacquer - nowgreatly improved and verymuch faster. Aerosol cans withfull instructions, £2.25. De-veloper 35p. Ferric chloride55p. Clear acetate sheet formaster 14p. Copper -clad fib-reglass board, approx. 1mmthick £1.75 sq. ft. Post/packing75p. White House Electronics,Castle Drive, Praa Sands, Pen-zance, Cornwall.

DIGITAL WATCH replace-ment parts, batteries, displays,backlights, etc. Also reportspublications charts. S.A.E. forfull list: Profords Copners Drive,Holmer Green, Bucks HP156SG E.


r 46I

HOBBY ELECTRONICSCLASSIFIED ADVERTISEMENT - ORDER FORM

If you have something to sell now's your chance! Don't turn the page - turn to us!Rates of charge: 30p per word per issue (minimum of 15 words).and post to HOBBY ELECTRONICS, CLASSIFIED DEPT., 145 CHARING CROSS ROAD, LONDON WC2

Please place my advert in HOBBY ELECTRONICS for issues commencing as soon as possible.I am enclosing my Cheque/Postal Order/ International money Please use BLOCK CAPITALS and include post codes.Order for (delete as necessary) £ (Made payable to A.S.P. Ltd) Classification

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H.E. ADVERTISERS INDEX OCTOBER 1983A.D. ElectronicsAmbit InternationalAudio ElectronicsBib AudioBicc VeroB K Electronics

71IFC67

46, 4757

IBC

House of InstrumentsICSILPKelan EngineeringLB ElectronicsLitesold

3372

30, 31531553

B.N.R.S. 19, 68 Magenta Electroncis 61Branime Marketing 62 Marlborough Electronics 33J. Bull 27 Meon Electronics 15Cambridge Learning 62 Parnden Electronics 68Camtec Circuits & Systems Ltd 68 Phonosonics 67Colnbrook Electronicds Ltd 71 Positronics 71Dataplus Developments 46 Rapid Electronics 10Dicom Electronics 71 Brian J. Reed 62Douglas Electronic Components 71 Sandwell Plant 68Electroni-Kit 15 Silica Shop OBCElectronize Design 56 Sparkrite 4Europa Electronics 57 S&R Brewster 68Gardner Precision Engineering 33 Technomatic 5G.S.C. 9 T K Electronics 47Hawk Electronics 46 Tomorrows World 23Hirsh Jacobson 71 Velleman (UK) Ltd 66Hodder & Stoughton 53 W.E.B. Logic Systems Ltd 72Horizon Electronics 72


TYPE'A'

TYPE 'C'

TYPE 'E'

MULLARD SPEAKER KITSPurposefully designed 40 watt R.M.S. and 30watt R.M.S. 8 ohm speaker systems recentlydeveloped by MULLARD'S specisliet teem inBelgium. Kits comprise Mallard woofer 18' or5'1 with foam surround and aluminium voice coil.Mullard 3' high power domed tweeter. 13.K.E.built and tested crossover based on Mullardcircuit, combining low loss components: glassfibre board and recessed loudspeaker terminals.SUPERB SOUNDS AT LOW COST. Kits suppliedin polystyrene packs complete with instructions.8' 40W system - recommended cabinet size 240x 216 x 445mmPrice 814.90 each + 82.00 P ft P.5' 30W system - recommended cabinet size160 x 175 x 295mmPrice 813.90 each + 8110 P 8 P.

Designer approved flat pack cabinet kits,including grill fabric. Can be finished with iron onveneer or self adhesive vinyl etc.8' system cabinet kit 88.00 each + 82.50 P e P.5" system cabinet kit E7.00 each £2.00 P Et P.

di) 80 LOUDSPEAKERThe very best in quality

and value.Ported tuned cabinet in hard-wearing black vynide with protec-tive corners and carry handle. Builtand tested, employing 10in Britishdriver and Piezo tweeter. Spec: 80watts RMS; 8 ohms; 45Hz-20KHz;Size: 20in x 15in x 12in; Weight:30 pounds.

Price: £49.00 each£90 per pair

Carriage: £5 each £7 per pair

STEREO CASSETTE TAPEDECK MODULEComprising of a top panel and tape mechanism coupled toa record/play back printed board assembly. Supplied asone complete unit for horizontal installation into cabinet orconsole of own choice. These units are brand new, readybuilt and tested.Features: Three digit tape counter. Autostop. Six pianotype keys, record, rewind, fast forward, play, stop andeject. Automatic record level control. Main inputs plussecondary inputs for stereo microphones. InputSensitivity: 100mV to 2V. Input Impedance 68K.Output level: 400mV to both left and right handchannels. Output Impedance 10K. Signal to noiseratio: 4540. Wow end flutter: 0.1%. Power Supplyrequirements: 18V DC at 300mA. Contractions: Theleft and right hand stereo inputs and outputs are viaindividual screened leads, all terminated with phono plugs1phono sockets provided). Dimensions: Top panel 5Iin

11Iin. Clearance required under top panel 2Iin.Supplied complete with circuit diagram and connectingdiagram. Attractive black and sliver finish,Price 1:28.70 + 12.50 postage and packing.Supplementary parts for 18V D.C. power supplyI transformer, bridge rectifier and smoothing capacitor)

LOUDSPEAKERS POWER RANGETHREE (DUALITY POWER LOUDSPEAKERS (15", 12'! and 8" See 'Photo).Ideal for both Hi-Fi and Disco applica-tions. All units have attractive cast alu-minium (ground finish) fixing escutcheons.Specification and Prices.15" 100 watt R.M.S. Impedance B ohms.50 oz. magnet. 2" aluminium voice coil. Res.Freq. 20 Hz. Freq. Reap. to 2.5KHz. Sens.97dB. Price: E34.00 each + £3.00 P&P12" 100 watt R.M.S. Impedance 8 ohms.50 oz. magnet. 2" alum in ium voice coil. Res.Freq. 25Hz. Freq Resp. to 4 KHz. Sens.95dB. Price: £24.50 each + £3.00 PEP8" 50 watt R.M.S. Impedance 8 ohms. 20oz. magnet. 11/2" aluminium voice coil. Res.Freq. 40Hz. Freq. Rasp to 6 KHz. Sens.92dB. Black Cone. Price: £9.50 each. Alsoavailable with black protective grille Price:9.99 each. P&P E1.50.

12" 85 watt R.M.S. McKENZIE C1285GP (LEAD GUITAR, KEYBOARD, DISCO) Z'aluminium voice coil, aluminium centre dome, 8 ohm imp., Res. Freq. 45Hz., Freq.Resp. to 6.5KHz., Sens, 98dB. Price: £23.00 + £3 carriage.12" 85 watt R.M.S. McKENZIE C1286TC (PA., DISC012" aluminium voice coil. Twincone. 8 ohm. imp., Res. Freq. 45HZ., Freq. Resp. to 14KHz. Price £23 + £3 carriage.15" 150 watt R.M.S. McKENZIE C15 (BASS GUITAR, PA.) 3" aluminium voice coil.Die cast chassis. 8 ohm imp., Res. Freq. 40Hz., Freq. Resp. to 4KHz. Price: £47 + £4

,,carriage. A

PIEZO ELECTRIC TWEETERS - MOTOROLAJoin the Piezo revolution. The low dynamic mass Ino voice coil) of aPiezo tweeter produces an improved transient response with a lowerdistortion level than ordinary dynamic tweeters. As a crossover is notrequired these units can be added to existing speaker systems of upto 100 watts (more if 2 put in series). FREE EXPLANATORY LEAFLETSSUPPLIED WITH EACH TWEETER.

TYPE 'A' IKSN2036A)3" round with protectivewire mesh, ideal for bookshelf and mediumsized Hi-fi speakers. Price £4.29 each.TYPE 'B' IKSN1005AI 3'0," super horn. Forgeneral purpose speakers, disco and P.A.systems etc. Price £4.99 each.TYPE 'C' (KSN6016Al2- 5" wide dispersionhorn. For quality Hi-fi systems and qualitydiscos etc. PrIce £5.99 each.TYPE 'D' IKSN1025Al2" 0 6" wide dispersionhorn. Upper frequency response retainedextending down to mid range I2KH z I. Suitablefor high quality Hi'fi systems and qualitydiscos. Price £7.99 each.

TYPE 'E' IKSN1038A13%" horn tweeter withattractive silver finish trim. Suitable for Hi-fimonitor systems etc. Price £4.99 each.TYPE 'F' IKSN1057A) Cased version of type'E'. Free standing satellite tweeter. Perfectadd on tweeter for conventional loudspeakersystems. Price £10.75 eachP&P 20p ea. (or SAE for Piezo leaflets).

TYPE 'D"

TYPE 'F"

PA011711C

BK ELECTRONICSPrompt Deliveries

VAT inclusive

prices

Audio Equipment

Test Equipment

by

Thandar

and

Leader

HOBBY KITS. Proven designs including glassfibre printed circuit board and high qualitycomponents complete with instructions.

FM MICROTRANSMITTER (BUG) 90/1 05MHz with very sensi-tive microphone. Range 100/300 metres. 57 x 46 x 14mm (9 volt)Price: £7.99pDIGITAL THERMOMETER -9.9°C to +99.9°C. LED display. Com-plete with sensor. 70 x 70 mm 19 volt) Price: £27.60p3 WATT FM TRANSMITTER 3 WATT 85/115MHz varicap con-trolled. professional performance. Range up to 3 miles 35 x 84 x 12mm (12 volt) Price: £12.49pSINGLE CHANNEL RADIO CONTROLLED TRANSMITTER/RECEIVER 27MHZ Range up to 500 metres. Double coded mod-ulation. Receiver output operates relay with tamp/240 voltcontacts. Ideal for many applications. Receiver 90 x 70 x 22 mm 9/12 volt) Price: £16.49 Transmitter 80 x 50 x 15 mm (9/12 volt)Price £10.29 P&P All Kits +50p. S.A.E. for complete list.

BSR P256 TURNTABLEP256 turntable chassis S shaped tone arm Belt driven Aluminium platter Precision calibrated counter balance Anti -skate (bias device) Damped cueing lever 240 volt AC operation (Hz) Cut-outtemplate supplied Completely manual arm.This deck has a completely manual arm and isdesigned primarily for disco and studio usewhere all the advantages of a manual arm are

required.Price £31.35 each. E2 50 P&P

POWER AMPLIFIERMODULE

New model.Improved specification

0.E M.'s

NEW OMP100 Mk.II POWER AMPLIFIERMODULE Power Amplifier Module completewith integral heat sink. toroidal transformerpower supply and glass fibre p.c.b. assembly.Incorporates drive circuit to power a compatibleLED Vu meter. New Improved specificationmakes this amplifier ideal for P.A., Instrumentaland Hi-Fi applications.SPECIFICATIONOutput Power:- 110 watts R.M.S.Loads:- Open and short circuit proof 4/16

. ohms.Frequency Response:- 15Hz - 30KHz -3dB.T.H.D.:- 0.01%.S.N.R. (Unweighted):- -118dB *3.5dB,Sensitivity for Max Output:- 500mV @ 10K.Size:- 360 x 115 x 72 mm Price:- £31.99 +£2.00 R2.1. Vu Meter Price:- £7.00 + 50p P&P.

CONTACT BARRY PEARNE Tel. 0702 52752

HOME PROTECTION SYSTEMBetter to be 'Alarmed' then terrified.Thandar's famous Winder' Burglar Alarm System.Superior microwave principle. Supplied as three units.complete with interconnection cable. FULLYGUARANTEED.Control Unit - Houses microwave radar unit, rangeup to 15 metres adjustable by sensitivity control. IThree position, key operated facia switch - off - test- armed. 30 second exit and entry delay.Indoor alarm - Electronic swept freq. siren.104dB output.Outdoor Alarm - Electronic swept freq. siren. 98dBoutput. Housed in a tamper -proof heavy duty metalcase.Both the control unit and outdoor alarm contain re-chargeable batteries which provide full protectionduring mains failure. Power requirement 200/260 VoltAC 50/60Hz. Expandable with door sensors, panicbuttons etc. Complete with instructionsSAVE £128 Usual price C228 85BKE's PRICE E99.pap£4

SAE olour brochure

B.K. ELECTRONICS

M IX ERSI3iscoOMP PRO MIX MONO

OMP PROMIX MONO DISCO MIXER(As illustrated).4 Inputss-2 hag.

I Aux. plus Mic.with override.Active bass and treble tone coot's.Individual level controls plusmaster volume. Monitor output(head-phone) for all inputs.Output.775mV 240Vac"1.ze:19" x 51" xPrice .C49.99 + £2.00 P&P®STEREO DISCO MIXER with

7 band graphic. Vu display. Allfacilities. £99.99 + £2.00PbP

UNIT 5, COMET WAY, SOUTHEND-ON-SEA, ESSEX, SS2 6TR* SAE for current lists. * Official orders welcome. * All prices include VAT. * Sales Counter. *

* All items packed where applicable in special energy absorbing PU foam. * Please phone 0702 527572 *

VISA

75

100 FREE PROGRAMSFROM SILICA SHOP WITH EVERY PURCHASE OF AN

ATARI `12$8rATARI PRICES REDUCED!

We at Silica Shop are pleased to announce somefantastic reductions in the prices of the Atari 400/800personal computers. We believe that the Atari at its,new price will become the U.K.'s most popular per-sonal computer and have therefore set up the SilicaAtari Users Club. This club already has a library ofover 500 programs and with your purchase of a 400or 800 computer we will give you the first 100 free ofcharge. There are also over 350 professionally writ-.ten games and utility programs, some are listedbelow. Complete the reply coupon and we'll sendyou full details. Alternatively give us a ring on 01-3011111 or 01-309 1111.

wATARI 400 £129

wARk3R2 IK 400 £178

ATARI 800£279Lwith 16K

400/800 SOFTWARE & PERIPHERALSDon't buy a T.V. game! Buy an Atari 400 personal computer and a game cartridge and that's all you'll need. Later on you can buy the BasicProgramming cartridge (E351 and try your hand at programming using the easy to learn BASIC language. Or if you are interested in businessapplications, you can buy the Atari 800 + Disk Drive + Printer together with a selection of business packages.Silica Shop have put together a full catalogue and price list giving details of all the peripherals as well as the extensive range of software that is nowavailable for the Atari 400/800. The Atari is now one of the best supported personal computers. Send NOW for Silica Shop's catalogue and price listas well as details on our users club.THE FOLLOWING IS JUST A SMALL SELECTION FROM THE RANGE OF ITEMS AVAILABLE:ACCESSORIESCablesCassettesDiskettesJoysticksLe Stick JoystickMisc SuppliesPaddles

ADVENTURE INTScott Adams AdsNo 1 AdventureIndNo 2 Pirate AdvNo 3 Mission ImpNo 4 Voodoo CastNo 5 The CountNo 6 Strange OdY)No 7 Mystery FunNo 8 Pyramid of DNo 9 Ghost TownNo 10 Sac Island 1No 11 Sav Island 2No 12 Golden VoyAngle WormsDeflectionsGalactic EmpireGalactic Trader

L Lunar Lander

Mountain ShootRearguardStar F I iteSunday Golf

AUTOMATEDSIMULATIONSCrush Crumble CrnpDatestones of RynDragons EyeInvasion OrionRescue at RigelRicochetStar WarriorTemple of ApshaiUpper Reaches Aps

BOOKSBasic Ref ManualCompute Atari DOSCompute Bk AtariCompute MagazineDe Re AtariDOS Utilities ListDOS2 ManualMisc Atari BooksOp System ListingWiley Manual

BUSINESSCalculatorDatabase ManagemtDecision MakerGraph -ItInvoicingLibrarianMort & Loan AnalNominal LedgerPayrollPersonal Finl MgmtPurchase LedgerSales LedgerStatistics 1Stock ControlTelelink 1VisicalcWeekly PlannerWord Processor

CRYSTALWAREBeneath The PyramFantasyland 2041Galactic QuestHouse Of UsherSands Of MarsWaterlooWorld War III

DYNACCIMPAlpha FighterChompeloCrystalsForest FireIntruder AlertMonarchMoo np robeMoving MazeNominoes JigsawRings of The EmpSpace TiltSpace TrapStud PokerTriple Blockade

EDUCATIONfrom APRAlgicalcAtlas of CanadaCubbyholesElementary BiologyFrogmasterHickory DickoryInst Comptg GermLemonadeLettermanMapware

Maths -Tao -Toe ScramMetric & Prob Solvg States & CapitalsMugyeump Touch TypingMusic TermsiNotatnMusical Computer EMI SOFTWAREMy First Alphabet British HeritageNumber Blast Cribbage/DominoesPolycalc DartsPresidents Of U.S. European Scene JigQuiz Master .Hickory DickoryStarware Humpty DumptyStereo 3D Graphics Jumbo Jet LanderThree R Math Sys Snooker & BilliardsVideo Math Flash Submarine CornmdrWordmaker Super Cubes & Tilt

Tournament PoolEDUCATIONfrom ATARIConv FrenchConiaGermanCr.. 1Italian

nv SpanishLnergy CzarEuropean C & CapsHangmanInuit To Prog 1/2/3KingdomMusic Composer

ENTERTAINMENTfron)(Alien EggAnthillAttankAvalancheBabelBlackjack CasinoBlock BusterBlock 'ErnBumper Pool

CastleCenturionChecker KingChinese PuzzleCod.rackerComedy DisketteDice Poker .

Dog DazeDominationDownhillEastern FrontGalahad & Holy GrlGraphics/SoundJan -OJukeboxLookaheadMemory MatchMidas TouchMinotaurOutlaw/HowitzerPreschool GamesPro BowlingPushoverRabbotzReversi IISalmon Run747 Landing SimulSeven Card Stud

Sleazy AdventureSolitaireSpace ChaseSpace TrekSultans PalaceTact TrekTerryWizards GoldWizards Revenge

ENTERTAINMENTfrom ATARIAsteroidsBasketballBlackjackCentipedeChessEntertainment KitMissile CommandPan ManSpace InvadersStar RaidersSuper BreakoutVideo Easel

JawbreakerMission AsteroidMouskattackThresholdUlysses/Golden FlWizard & Princess

PERIPHERALSCentronics Printers.Disk DriveEpsom PrintersProgram RecorderRS232 InterfaceThermal Printer16K Memory RAM32K Memory RAM

PERSONAL INTfrom APEAdv Music SystemBanner GeneratorBlackjack TutorGoing To The DogsKeyboard OrganMorse Code Tutor

ON LINE SYSTEMS Personal Fitness PrgCrossfire Player PianoFrogger Sketchpad

PROGRAMMINQAIDS from AtariAssembler EditorDsembler (APX)Microsoft BasicPascal IAPXIPilot (Consumer)Pilot (Educator/Programming Kit

SANTA CRUZBasics of Animation

'Bobs BusinessDisplay ListsGraphics MachineKids 1 & 2Horizootal Scrolling

Memory MapMini Word ProcessorPage FlippingPlayer Missile GrPlayer PianoSoundsVertical Scrolling

SILICA CLUBOear 500 programswrite for details A

FOR FREE BROCHURES -TEL: 01-301 1111ror tree brochure and rewews on aw range of °Moron. products please telephone 01.301 I 1 -'911

To order by telephone lost quote your name address [read card number and order requirementsand leave the rest to us Post end packing is FREE OF CHARGE in the UK Express 24 noundeliver, available at an additional charge SHOP DEMONSTRANON FACILITIES - we Mode fug facibbes at Our shoe m Sidcup Mendel,.

Saturday gam . 5 30pm ,crams Thuryclay Ion Friday atairilMAIL ORDER -we are a specialist mad order company and are able to supply goods direct to your

doer MONEY BACK UNDERTAKING - il you are totally unwire,. m. your purchase you may return' to

us n 15 days. On receipt of the goods m salistactory condition we will give you e lull refund PART EXCHANGE SECOND HAND MACHINES -we offer a pert exchange scheme to trade m many

Makes ot T V games Tor personal computers COMPETITIVE PRICES -our prices aliens end service are very competitive We ere never knowingly

undersold and will normally match any tow. Prier quoted bli Or COrnOWdere HELPFUL ADINCE - arra.. on Me solar:Wily of venous computers AFTER SALES SERVICE - evadable on dir computers our of guarantee

VAT - all prces goofed above include VAT at 15kk CREDIT FACILITIES - we offer credo over T2 24 v to norms please ask Ter awes,

SILICA SHOP LIMITEDDept, HE 1083 1-4 The Mews, Hatherley Road, Sidcup,Kent DA14 4DX Telephone 01-301 1111 or 01-309 1111

'1111 fill 'III

11111'1111111

111" III

'4111111111 .111111 .111

III

r FREE LITERATUREI am interested in purchasing an Atari 400/800 computer and wouldlike to receive copies of your brochure and test reports as well asyour price list covering all of the available Hardware and Software

Nome

Address

Postcode

Hobby Electronics HE1

Project Electronics For Everyone AUDIO LEVEL METER PROJECT ...

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