April 1987

UK £1.30IR £1.89

(incl. VAT)

11 11 1451005

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April 1987

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MAIL ORDERS TO: 17 BURNLEY ROAD, LONDON NW10 lEDSHOPS AT: 17 BURNLEY ROAD, LONDON NW10

(Tel: 01 208 1177, Telex 922800)305 EDGWARE ROAD, LONDON W2, Tel: 01 723 0233

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PLEASE ADD 50p p&p & 15% VAT(Export: no vnT, p&p at Cost)

Orders from Government Depts. & Collegesetc. welcome.

Detailed Price List on request.Stock items are normally by return of post.

please mention ELEKTOR ELECTRONICS when contacting advertisers

13 Editorial14 News

ELECTRONICSTECHNOLOGY23 Electronic potentiometers.31 Secondary breakdown in power tran-

sistors.36 Linkwitz filters.44 Where electronic messages have the

edge.

48 RIMS: counting atoms.56 Local area networking.57 Schools equipment for tomorrow's

tists

Valve preamplifierp. 26

Facsimile interfaceP. 39

Where electronic messages have thescien- edge

p. 45

PROJECTS20 Feedback in loudspeakers: acoustic feed-

back is rarely used, but R Conell suggestssome ways of experimenting with it in a low -frequency loudspeaker.

26 Valve preamplifier -2: part 2 completes thisinteresting design with a multi -voltage supplyand a relay control board.

34 Preset extension a simple -to -build 10 -fre-quency preset unit for the Elektor ElectronicsFunction Generator as designed by MKistinger.

39 Facsimile interface: a multi -standard fac-simile converter that can be used with anygood -quality short-wave receiver, a BBC orC64 computer, and an Epson compatibleprinter.

52 MSX extensions -5: this second part of theEPROM programmer looks at the way it iscontrolled from the MSX computer anddetails the supporting software.

INFORMATION46 New literature; 58 New Products;68 Readers' Services; 70 Terms of business;77-78 lnfocards.

GUIDE LINES71 Switchboard; 74 Buyers guide; 76 Classified ads;76 Index of advertisers.

April 1987Volume 13Number 144

In next month'sissue:

Spot sine wavegeneratorHow does thehuman computerwork?Decoding satelliteTV signalsBursting thebubble mythMIDI signal redis-tribution

This month's frontcover shows a laserbeing used in in-dustrial processingof heavy sheetmetal. A laser(acronym of lightamplification bysimulated emissionof radiation) is asource of intensemonochromaticcoherent radiationin the visible,ultraviolet, andinfra -red regions ofthe spectrum. Amore detailed lookat lasers will bepublished in a forth-coming issue.

EE

April 19874

Moroi:It LT DUNBEATABLEPRICES ON

PROCESSORS2,93CP",: 1820ZaO DART 1).90Ze13 DMA £5.50250 PIO £2.257.83 510/1 11.90230A CPU 12.70ZSCA DART r2302.50A CTC 15.00162A DMA 020ZIOA PIO 12.60ni3A £6.001.608 CPU SLSO2.68 CTC f4-902503 DART 17.90zaca PIO £4.902605 3bO)0 £5.50&OM _ f4.25376513.008154 17.908212 £2.20V.-55 12.59

SAVE "E"sDATA SHEETS ONLY £1 EACHUNREPEATABLE TTL PRICES TTL 74LSCOMPLETE RANGE STOCKEDFROM 00 - 65 ONLYFROM 67 155 ONLYFROM 157 - 175 ONLYFROM 176 - 195 ONLY

PRICES SMASHEDON OUR MEMORIES

DRAM Iv NMOS 150-.S4164 64E x 1. 10.9341255 256K x I f2.394416 16K x 1 £20041464 64K x 1 £5.90SRAM 51i NMOS 150952114121E x 4 0.502126.12 18 , fi £2.50SRAM 5. CMOS 1500561I618 2K P. 8 £1.306Z34LP elt ... a 12.406225812 mit . 8 125.00EPROM 5. LIMOS 250952716 28 x 8 __ £2.952132 46 x 8 £2.652764 1.9927128 16%SKxx 58 1

f2.45

27255 P -IC x 8 13.7527512 512K x 8 £9.90EPROM 5. cmos 250n527064OM27C256 32K x 8 00.0027C512 5I2K x 8 £14.80LEPROM 2509S2815A 28 x 6 £13.50264A 8K x 6 145.00

10.20 ea£0.60 ea10.65 en£0.75 ea

7411C HIGH SPEED PHONE FOR STANDARDCMOS LOGIC CMOS AND LINEAR PRICES

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ULTRA HIFI CLASS APOWER AMPLIFIERS

The worlds most advanced active Class A MOSFET power amplifier, designed forlistening to, whilst engineered to break all performance limits.

* * * 50-150W 01? 4-16ohms, one unique module * * *THE 'SUPERMOS' There's no other amplifier module that can offer ANY

of these advanced features:

Integral heatsink_ noexternal componentsSimply mounts onto a flatpanel, no awkward shapedhoksis to cut.PSU requirements :30 - .145V DC. full details with each amplifier.Bad the ultimate in class A sound quality at a fraction of the cost of buil units. SUPERMOSmodules E59.95 each total inc. SAE for deta2s.Coming soon, a true HiFt hybrid 24pin class A op -amp is the Superpre-amp

* Active class A MOSFET OtP (cool runningl* Distortion typically 0.0002% (2ppm)* Slew rate greater than 250V/1s* High current capability of SOamps p -p* Very low feedback for superb sound quality* Unique gain stage for exceptional power supply

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. RACK STYLE CABINET* Suitable for instrume7ts. r arr; 2,-3 ,"3r,. omer purposes 3rTop. side aridrear covers removable for access * Black anocisect alumn.urri front panel * Separate frontmounting plate * Heavy gauge front panel is of brushed aluminium fmish enhanced with twoprofessional handles * With ventilation slits arid plastic feet * Rear box manufactured from steelpainted in black. Rack mounting or free standing. Comes in quick assembly flat package

Order Code Panel SizeW H Imchl

Rear BoxWHO Price

NME19102 19 , 2.5 17. 2.0 10 22.50NME19103 19 3.5 17 3.0 10 24.50NME19105 19 525 17 5.0 10 25.50

NME19123 19. 3.5 17 . 3.0 12 25.5014ME19125 19,525 17.5.0 12 27.50NIVE19127 19, 7.0 17 . 6.5 . 12 29.95

Please add £3.170 P&P for the fast item and £1.50 for ea= = : : !!,2171. To order send chequepostal order please allow up to 7 ders despatch fc. c!earanx_ Quantity discounta.-ailable. Customers who require high, :nformar,;7 riaEe SAE Mal Order only.

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CIDE-E=FROM JAYTEE

THE SPECIAL DISTRIBUTOR FOR SPECIAL AMPLIFIERSILP have long been recognised as manufacturers of top qualityamplifiers.

All ILP products are built to extremely high specification for theultimate in hi-fi performance. They're unique in being completelyencapsulated with integral heatsinks, and can bolt straight onto thechassis. They're also extremely robust, ensuring high levels of reliabilityas well as performance.

ILP Amplifiers are now available through Jaytee. The UK Distributorwith the availability and service to match the quality of the amplifiers.POWER BOOSTER AMPLIFIERSThe C15 and C1515 are power booster amplifiers designed to increasethe output of your existing car radio or cassette player to 15 watt rms.C15 15 watts £10.65C1515 15 15 watts £19.78ILP LOUDSPEAKER £78.61power - 350 watt rmssize 12 inchesimpedance 8 ohmsrange . 20 Hz to 5 KHz

FOR FREE DATA PACK PLEASE tiWRITE TO OUR SALES DEPT. Ili

PREAMPLIFIER MODULESAll modules are supplied with in line connectors but require potentiometers.switches. etc. If used with our power amps they are powered from theappropriate Power Supply.Type Application Functions PriceHY6 Mono PreAmp Full Hi Fi facilities £ 8.95HY66 ... _Stereo Pre -Amp Full Hi A facilities E14.55HY73 ....Guitar Pre -Amp Two Guitars plus MicrophoneHY78 ....Stereo Pre -Amp As HY66 less tone controls £14.25NEW! HY83 Guitar and Special Effects Pre -Amp as HY 73 Plus Overdrive andReverb E18.95MOUNTING BOARDS: For ease of construction we recommend the B6 forHY6 E0.95 666 for HY66-83 0.45.

IMOSFET MODULES Type

Ideal for Disco's. public address andapplications with complex loads Hine fv10S128transformers etc.). Integral Heatsink slew MOS248rate 20v/us distortion less than 0.01% M05364

BIPOLAR MODULESIdeal for Hi Fi. Full load protectionintegral Heatsink, slew rate 15111,sType Output Load Im- Price

Power pedenceWatts Inns)

HY30. 15 4-8... £10.95HY60 30 4-8... E10.95HY6060.. 30 -i- 30 4-8... £22.95HY124... 60 4 . £17.95HY128 60 8 _ E17.95HY244... 120 4 . £23.45HY248... 120 8 £23.45HY364 180 4 . . £34.95HY368 180 £36.45Distortion less than 0.01%

Output Load PricePower lmpedenceWatts irms) 060 4 8 £35.95120 4 8 £42.25180 4 £67.45

POWER SUPPLY UNITType For Use With PricePS1130 PRE AMP £9.45PSU212 1 or 2 HY30 .. . . (17.20PSU412 1 or 2 HY60. 1 HY6069.

1HY124 £19.25P5U422 1 NY128 .. .. f:21.35P511432 1 M05128 E22.35PSU512 2 HY128. 1HY244 _ ._ £23.70PSU522 2 HY124 023.70P511532 2 8105128 024.65PSU542 1 HY248 .. 124.65P511552 1 MOS248 £26.126PSU712 2 HY244 £28.35P51.1722 2 HY248 E29.30PSU732 1 HY364 129.30PSU742 1 HY368 £31.25PSu7S2 2 MOS248. MOS364 £31.25All the above are for 240v operation

Jaytee Electronic Services, 143 Reculver Road, Bettinge,Herne Bay, Kent CT6 6PL Telephone: (0227) 375254All Prices include VAT. Post & Packing

please mention ELEKTOR ELECTRONICS when contacting advertisers

EE

April 1987

Managing Editor: Len SeymourTechnical Editor: J BuitingAdvertisement manager: S Brooks

Editorial offices:Standfast HouseBath PlaceHigh Street, BarnetHerts ENS 5XETelephone:Editorial (UK): 01-441 6098

(Europe): +31 4402 89444Advertising: (0227) 66106

Telex: 22828 (elektr glA Khmer Group CompanyOverseas editions:Publitron Publicacoes Tecnicas LtdaAv 1piranga 1100. 90 andarCEP 01040 Sao Paulo - BrazilEditor: Juliano BarsaliElektor sariRoute Nationale; Le Seau; B.P. 5359270 Bailleul - FranceEditors: D R S Meyer;G C P Raedersdorf

Elektor Verlag GmbHSiisterfeld-Stralle 25100 Aachen - West GermanyEditor: E J A KrempelsauerElektor EPEKaraiskaki 1416673 Voula - Athens - GreeceEditor: E XanthoulisElektor Electronics PVT Ltd.Chhotani Building52 C, Proctor Road. Grant Road (E)Bombay 400 007 - IndiaEditor: Surendra lyerElektuurPeter Treckpoelstraat 2-46191 VK Beek - the NetherlandsEditor: P E L KersemakersFerreira Er Bento Lda.R.D. Estefania, 32-1°1000 Lisboa - PortugalEditor: Jorge GoncalvesIngelek S.A.Plaza RepUblice Ecuador2-28016 Madrid - SpainEditor: A M FerrerIn part:Kedhorn Holdings PTY LtdCnr Fox Valley Road ErKiogle StreetWahroonga NSW 2076 - AustraliaEditor: Roger HarrisonElectronic Press ABBox 63182 11 Danderyd - SwedenEditor: Bill CedrumInternational co-ordinatingEr technical manager:K S WairavenInternational editorial secretariat:G W P v Linden; M Pardo

Distribution:Seymour Press Ltd., 334 BrixtonRoad, London SW9 7AG.Typeset Et composed in theNetherlands by GBS, Beek (L).Printed in the Netherlands by NDELZoeterwoude.Copyright = 1987 Elektuur BM_

ABC

Quo vadis, transputer?

Inmos's IMS T414 transputer has brought nearer the dream of a computernot bigger than a suitcase, yet powerful enough to model a nuclear ex-plosion, or to plot a space vehicle's path to distant planets.

Where even powerful present-day computers may take hours to processcertain graphic images, the transputer can produce highly complexgraphics as quickly as the operator can think. When used in supercom-puters, the transputer allows the simulation of experiments hitherto poss-ible only in laboratories. This of course makes these processes cheaperthan the real thing.

The key to the transputer is parallel processing. Conventional computersprocess data serially-one task at a time. The transputer processes sev-eral different parts of an operation simultaneously, often millions at atime, by linking a number of processing elements together. This speedsup the process, but creates complex design and programming difficult-ies. To simplify the programming of parallel processors, a new program-ming language, Occam, was developed in 1983.

So far, so good. A story of yet another great British invention. Why, then, ismost of British industry so slow in accepting the transputer which couldbecome the world's standard chip for supercomputers?

It can not be because the transputer is not what Inmos has claimed it tobe. A small number of British companies, such as Floating Point Systems,Meiko Ltd, and Smith Associates, among others, have designed hardwareand software based on the transputer, the performance of which com-pletely confirms Inmos's claims.

There is, of course, the problem of software compatibility, but this is oftenexaggerated, and is also likely to arise when performance improvementsin conventional systems are required. A number of computing expertsquestioned on this score felt that much existing software can be con-verted to Occam.

Nor can it be claimed that either the transputer or Occam is difficult touse: according to transputer expert and co-author of The Inmos Saga,Mick Lean, the essence of both is their simplicity.

The worrying aspect about British industry's apathy is that the world atlarge is not going to be so backward. The transputer is such an import-ant step forward in computer technology that if it is not exploited to thefull in Britain some foreign competitors will grasp the chance offeredthem on a plate with both hands-and we will have failed to reap thebenefits of yet another great British invention.

AL,Nt&AUL 64 P20.4 ATCets

EE

April 198714

NEWS NEWS NEWS NEWS NEWWorld semicon-ductor marketin 1986A report by Dataquest. acompany of The Dun & Brad-street Corporation, and a worldleader in industrial and hightechnology market analysis,says that the three top chip sup-pliers, measured in US dollars,are Japanese companies.NEC retained its number oneposition, but Hitachi andToshiba replaced Motorola andTexas Instruments in 2nd and3rd place respectively. The top10 suppliers, with revenuesgiven in millions of dollars, areshown in the table.Exchange rate fluctuations hada significant impact on thislisting. Expressed in US dollars,the world semiconductormarket grew by 26.1% in 1986compared with 1985. By thismeasure, Japanese producerschalked up a growth in world-wide factory shipments ofalmost 40%. European pro-ducers had the next best rec-ord. with a 15% increase infactory shipments, and theNorth American region faredworst with only a 6.4% growth.A different situation emergeswhen factory shipments fromthe three regions are expressedin local currencies. Then, theNorth American region stillshows a 6.4% growth, of course.but Japan reaches only aslight increase of 0.2%, whileEuropean producers have amarket decline of 7%.Cochrane CommunicationsLtdCCL House59 Fleet StreetLondon EC4Y 1JU

RANK1986 1985

COMPANY REVENUES1985 1986

cga CHANGE

1 1 NEC 1984 2638 332 4 Hitachi 1671 2305 37.93 5 Toshiba 1468 2261 54.04 2 Motorola 1830 2025 10.75 3 Texas Instruments 1742 1820 4.56 6 Philips-Signetics 1068 1356 27.07 7 Fujitsu 1020' 1310 28.48 10 Masushita 906 1233 36.19 11 Mitsubishi 642 1177 83.310 8 Intel 1020' 991 -2.8

All revenues roundedSource: Dataquest

Scope probefrom LefaxThe Lefax SCOPE -PROBE has beendeveloped to meet the need foran integrated oscilloscope andlogic probe. The instrument hasthe obvious advantage that theoperator has the display alwaysin his line of vision.The instrument is powered froman internal alkaline batterywhich has an average life ofabout 12 hours in continuoususe.The probe tip can be detachedif required, so that the instru-ment can be used hand-held oras a bench unit: it can acceptstandard oscilloscope leads ifneeded.The SCOPE -PROBE has a fre-quency coverage of 10 Hz to20 kHz in five ranges; mostwaveforms can be displayedover the entire range. It also in-cludes a direct -reading d.c.voltmeter with 0-10 V and 0-20 Vscales.The price of the instrument is£89.95 excl. VAT and p&p.The instrument should be of in-terest to repair and main-tenance engineers; laboratorystaff; schools and technical col-leges; and government retrain-ing centres.Lefax LimitedUnit 6Genesis Business CentreRedkiln WayHorsham RH13 3QHTelephone: (0403) 54135

Communi-cationengineeringbackup fromDACCOMFounded on the conviction thatengineering quality is more im-portant than corporate strategy,Fleet -based DACCOM can pro-vide a wide range of services tothe communications industry athome and abroad. Services of-fered include consultancy; pro-ject management; feasibilitystudies; radio surveys; training;design; and fact file. Moreover,the company has availablequalified, experienced person-nel on an as -required basis toenable producers to smooth outany peaks in activity.DACCOM122 Tavistock RoadFleet GU13 8EETelephone: (0252) 623315

New functiongenerator fromITT

The new Type GX239 FunctionGenerator from ITT Instrumentsis a universal instrument pro-viding a choice of sine wave,square wave, and triangularwave signals, in addition to DCand pulse outputs.The generator has an outputfrequency range of 0.2 Hz to2 MHz, selectable over sevendecadic increments by frontpanel push -buttons. As a result,it is equally applicable to low -frequency and high -frequencyuse, and typical applicationsare likely to be found in vi-bration testing, general audiocircuit testing, AM radiotesting, ultra-sonics, and servo -systems tests.ITT Instruments346 Edinburgh AvenueSlough SL1 4TU

a EE

April 1937

NEWS NEWS NEWS NEWS NEWAdvanceduniversaldigital filterA real-time universal digitalfilter. developed by Fern Devel-opments for use in speech pro-cessing. anthology, psycho -acoustics, electrophysiology,and geophysics, offers linearfiltering capabilities which aresaid to be superior to those thatcan be achieved with conven-tional analogue techniques.The benchtop Era, based on adesign conceived by theMedical Research Council, is a512 -coefficient finite -impulse -response, non -recursive filterthat offers an unlimited numberof totally different filtering ac-tions. the anti -alias (pre-pro-cess) and post -process sectionsuse high -precision programm-able low-pass filters.The filter unit has an operatingbandwidth of 0.30 kHz. attenu-ation rates of typically 4000 dBper octave. and up to 512

weighting coefficients for sym-metrical responses.Fern Developments Ltd7 Springburn PlaceCollege Milton NorthGlasgow G74 5NU

Surface MountDevices marketto treble by1991According to Surface -mountedDevices in Europe, a 231 -pagereport just published by Frost &Sullivan. the European demandfor SMDs will treble to almostS2 billion by 1991.Surface -mount technology-SMT-was pioneered in Japanfor cameras, calculators, andother consumer electronics.The current Japanese marketfor SMDs is some six times thesize of Europe's.At present, SMDs account forless than a tenth of all electroniccomponent sales, but will climbto nearly a fifth by 1991. Pen-etration will be highest then incapacitors (well over a quarter

of all capacitors will be SMDs),integrated circuits (more

:::an a fifth of all ICs will beSMDs).The report deals with tencategories of SMDs, thoughthese are broken down intotheir constituent product types.Estimated market shares of sup-pliers show AVX Corporationto lead Philips in capacitors;Corning and Philips head upthe field in resistors; and TexasInstruments is well in front inmemories and other ICs.

SURFACE MOUNTCOMPONENTS MARKET

-- 45

-35 $

3.0

20

1.5

1.0

0.5

0.0

85 86 87 88 89 90

Year

B

0n

gi Passive Components

Active Components

Total

ircR t,.s. .

r -r.

Frost & Sullivan LtdSullivan House4 Grosvenor GardensLondon SW1W ODHor106 Fulton StreetNew YorkNY 10038

Grundig do itwith robotsHelping Grundig on the road tosuccess is a new robotic VCRproduction line which, thecompany says, is in advance ofany other in the world today.Making VS400 machines, whichwill retail in the UK at aroundthe £400 mark. the productionline cost over £5 million to in-stall. It was designed and builtentirely by Grundig engineers

and took a mere nine months tocomplete from putting pen topaper in the drawing office tothe first complete machinecorning off the 130 -metre longproduction line.When on full production, theautomated plant is expected toproduce at least one millionVCRs per year each one takingjust 35 minutes to make plusanother two hours in soaktesting. Each machine goesthrough 87 work stations andthrough automatic quality testson its way to completion.The new VCR line is just thefirst of a planned series ofdevelopments which will con-tinue to radically changeGrundig's approach to videoproduction.Grundig International Ltd42 Newlands ParkLondon SE26 5NQ

SMA assemblyof PCBsThe WS1500 combination work-station from Surface MountedProduction Systems Ltd is in-tended for the surface -mountedassembly (SMA) of printed -circuit boards (PCBs). It incor-porates a precision dispenser,vacuum pick-up, infra -redsoldering unit, and a solderingiron. PCBs up to 7 x 4 inches canbe accommodated.The VV5I500 enables prototypedesign and development,single or small batch pro-duction and repair work onsurface -mounted circuit to becarried out at one workstation.It is priced at less than £2000.

Surface Mounted ProductionSystems LtdUnit 5Sandbank Industrial EstateDunoon PA23 8PB

More powerfrom VidorbatteriesIncreases of up to 20% in the ca-pacity of lithium thionyl chlor-ide-TCL-batteries size TO4/5(1/2AA) and size T06/5 (AA),now rated at 0.85 Ah and 2.0 Ahrespectively, have been an-nounced by Crompton Vidor, aHawker Siddeley company. Themaximum current drain figuresof these batteries have alsobeen improved.With a capacity loss of only 2%per year for the first 10 years'shelf life, Vidor TCL batteriesare recommended for use inlong-term, low -current appli-cations in electronic equip-ment. These include CMOSmemory back-up in civil andmilitary telecommunicationsequipment. data processingsystems, industrial process con-trol. And a variety of electro-mediCal and laboratory equip-ment.All batteries in the rangeare recognized under Under-writers Laboratories-UL-com-ponent programme.Crompton Parkinson LtdWoodlands HouseThe AvenueNorthampton NN1 5BS

Ultra -low -profilemodem trans-formerElectronic Techniques havedeveloped an ultra -low -profileline -matching transformer foruse in moderns. Measuring only15 x 20 x 11 mm, the PI165 offershigh standards of match, iso-lation, frequency response,balance and distortion. It is saidto satisfy the stringent isolationand safety requirements ofBritain's telecommunicationsauthorities.Electronic Techniques(Anglia) LtdViking WorksKirtonIpswich IPIO ONX

EpiE

r, 1937

NEWS NEWS NEWS NEWS NEIN1

Cirkit in SaudiArabiaCirkit electronic constructionkits are used extensively byhundreds of students at theDharhan Technical Training In-stitute as part of their 2 -yearpractical training programme.Cirkit, a specialist distributor ofelectronic components kits,and modules to industry andthe hobbyist, established anEducational Division last year toservice the growing techno-logical needs of schools, col-leges. and universities.With vested interests in thefuture of the British electronicsindustry, Cirkit places a strongemphasis on supporting practi-cal education as pan of its cor-porate policy. This led to thecompany's origination of theYoung Electronics DesignerAwards Scheme-YEDA.Seen in the left-hand photo-graph is student Imad IbraheemAl -Mohammed demonstratinghis project, a Cirkit tracer robot,to some high ranking officials.In the top right-hand photo-graph Saleh Hashbool Al-Ghamdi is seen receiving hisCirkit certificate from SheikhNasser Asser, President of CivilAviation. Pictured at the left is

Saleem S Al-Quarni, Director ofthe Institute. In the lower right-hand picture: Prince Turky BinAbdul-Aziz, Colonel Com-mander of the King Abdul-AzizAir Base in Dharhan, SheikhNasser Assar, President of CivilAviation, and Saeed Al-FarhanAI-Ghamcii, Director -General ofAirways Facilities during a re-cent graduation ceremony ofTDDI.

Cirkit Holdings PLCPark LaneBroxbourne EN10 7NQ

Triple SDIsuccess forEASAMSEASAMS, the GEC systemshouse, has started the year witha run of successes with threeSDI-Strategic Defence Initiat-ive-contracts in one week twofrom the MoD and the thirdfrom Hughes Aircraft Corpor-ation.In the UK, EASAMS will lead anindustrial consortium of severalBritish companies in the largestSDI study let to date through theMoD. The work is for the BattleManagement and Command,

Control and Communications(BM/C3) in the EuropeanTheatre of Defence. In addition,as pan of a second successfulbid by the same consortiumwith Ferranti as prime contrac-tor, EASAMS will receive ashare of a study for an AlliedTest Bed.The export order from the USAis particularly interesting.Hughes were in competitionwith twelve major internationalconsortia. The Hughes team,consisting of EASAMS, Matra(France), Selenia Spazio (Italy),and Krupp -Atlas (FederalGermany) have won phase 1 of a£6 million contract from the USArmy Strategic Defence Com-mand to study Theatre DefenceArchitectures.EASAMS LimitedLyon WayFrimley RoadCamberley GU16 5EX

New kits foraudiophilesAUDIOKITS are introducingnew high -quality audio ampli-fier kits, new high-grade audiocomponents, and better sup-port services for hi-fi en-

thusiasts who enjoy building ormodifying equipment for bettersound quality.AUDIOKITS is the first supplierto introduce bulk foil resistorsto audio constructors. Thesecomponents are manufacturedto the highest standards of ac-curacy with low internal capaci-tance and inductance, as well asa very low temperature coef-ficient (better than 4 ppm/°Cover the temperature range0.60 °C).Foil polystyrene capacitors, in-tended for exacting telecom-munications filter circuits, arenow available in values up to250 nF.Specially manufactured low -

noise versions of all trans-formers used in their kitscan also be supplied by thecompany.AUDIOKITS PrecisionComponents6 Mill CloseBorrowash DE7 3GUTelephone: (0332) 674929

Following a recent agreement,Hawke Systems now distrib-utes VME bus products ofElectronic Modular Systems.Seen in the photograph arefrom left to right: LindsayHughes, Product MarketingSupport, Hawke Systems;Russell Ward, ManagingDirector, EMS; Hazel Scott,VME Business Manager,Hawke; and Graham Fage,Sales Manager, EMS. Furtherinformation from EMS BrayHouse Martin Road Cordwallis Industrial Estate Maidenhead SL6 7DE or HawkeSystems Amotex House 45 Hanworth Road Sunbury -on -Thames.

!FEEApril 1937

NEWS NEWS NEWS NEWS NEWi

New VortexFlowmeterKent Industrial Measurements'new Vortex Flowmeter GLS isthe result of years of researchand development by thecompany to produce a flow -meter offering low cost yet highaccuracy and long-term re-peatability.

The principle of the device isstraightfoward: a bluff body atthe sensor upstream end shedsvortices onto a cylindricaldownstream bluff body, whichvibrates at the vortex sheddingfrequency. A piezo-electrictransducer outside the pipelinesection, but connected direct tothe bluff body, detects this fre-quency and the transmitter con-verts it to either a frequency oran analogue 4-20 mA currentoutput.

Kent Industrial MeasurementLtdOldends LaneStonehouse GL10 3TA

World's fastestcomputer forcivilian marketThe world's fastest real-timecomputer, designed for usewith military over -the -horizonradars*, will be available onthe civilian market from Micro-system Services Ltd (MSS)

under an agreement signedwith Marconi Radar SystemsLtd. Both MSS and MarconiRadar feel that the ultra -fastXN-10 digital signal processingunit has applications in suchfields as speech and image pro-cessing, seismic research,sonar, automatic testing, tele-communications. and others.In its basic form, XN-10 iscapable of carrying out 10

million decimal calculationsper second. When a number ofthese units are connectedtogether, thousands of millionsof calculations per second canbe achieved.* See Elektor Electronics,September 1986, p.20

Marconi Radar Systems LtdWrittle Road WorksChelmsford CM1 3BN

Strong hybridcircuits marketin EuropeAccording to The Hybrid Cir-cuits Market in Europe (E905)a new report from Frost &Sullivan, the hybrid circuitsmarket in Europe will growat an average annual rate of27.8%, from $1 billion in 1985 to$4.4 billion in 1991 (in constantdollars, 1986 exchange rates).Europe's space industry, whichreceived a boost after theAmerican shuttle disaster, is anideal application field forhybrid circuits because of theneed for high complexity elec-

tronics in very small quantities.At the same time, the increasinguse of microprocesors in dom-estic appliances opens the wayfor more use of hybrid circuits.The automotive field looks es-pecially favourable.Because hybrid circuits are in-volved with so many differentuses of electronics, this276 -page report is really asurvey of electronic appli-cations in general.Frost & Sullivan LtdSullivan House4 Grosvenor GardensLondon SW1W ODHOr

106 Fulton StreetNew York NY 10038

New divisionalstructure atDowtyThe Dowty Group has formedtwo new electronics divisionsto create five group divisionswith a turnover of over £527million. The two new divisions,Electronic Systems and Infor-mation Technology, have a jointturnover of £161 million basedon 1985/86 figures. The objectof the changes is to provide amore clearly focused, market -oriented base from which theGroup can further penetratemaritime, defence, and infor-mation technology markets.Dowty GroupArle CourtCheltenham GLS1 OTP

HYBRID CIRCUITS IN EUROPE1986

Thick Film Circuits $944.7M

Thin Film Circuits SE15.9M

SMT S200.1M

W -V -Er S.M..,

Avel-Lindbergfor fire fightingservicesVarious fire brigade head-quarters have recently beenequiped with tactical com-puters which. when a 999 call isreceived, are fed with the lo-cation of the fire. The computerthen gives the best route to thefire, displays the nearesthydrant to the fire, selects themost suitable appliance and thenames of the crew, and in-dicates where the applianceshould be parked in the mostadvantageous position in re-lation to the fire and the hydrant.It also displays any potential firehazards in the area and showswhich appliances should bemoved to provide cover forthose attending the fire.The power supply for thesesystems is obviously very im-portant, and to ensure conti-nuity Avel-Lindberg have sup-plied uninterruptable powersupplies at each location. In ad-dition, the company also sup-plies Home Office approvedconverters that enable radio-telephones and other elec-tronic equipment fitted to fireappliances to be powered fromthe appliance's batteries.Avel-Lindberg LtdSouth OckendonEssex RM15 STD

EE

April 1987

NEWS NEWS NEWS NEWS NEWI

AQAP-1approval forfrequency con-trol productsA range of cold -weld crystals,crystal filters, and crystaloscillators with NATO AQAP-1approval, manufactured by theC R Snelgrove division of LeighInstruments, are now availablein the UK from Piezo Products.Quartz crystals are available forthe frequency range 14 MHz to200 MHz.

Piezo Products LtdMillstream Trading EstateChristchurch RoadRingwood BH24 3SD

PeopleDr Marc Faktor. who spentmore than two decades re-searching the optical and elec-trical properties of materials,and in doing so helped to putBritain in the world forefront ofoptoelectronic technology, waslast January awarded BritishTelecom's Martlesham Medalfor outstanding contributions toscience and technology.

The council of the Institution ofElectrical Engineers has an-nounced the following elec-tions to Honorary Fellowship ofthe IEEE.Professor W E J Farvis CBEBSc(Eng) FRSE for his outstand-ing contribution to the pro-fession, particularly through hisactivities in the field of elec-trical engineering education.

Sir Robert Telford CBE DL MAFEng for his outstanding con-tribution to the development ofthe UK Defence Electronics In-dustry, particularly in connec-tion with his service as Man-aging Director and latterlyLife President of the MarconiCompany.

The Council has also an-nounced that the 65th award ofthe Faraday Medal has beenmade toProfessor D E N Davies CBE

DSc FEng FRS for his outstand-ing contributions to the devel-opment of radar systems, no-table to techniques of elec-tronic scanning and to novelradar arrays. and also for hispioneering researches on op-tical fibres sensors and the useof optical fibres for signal pro-cessing.

Mr Andrew Glasgow OBE hasbeen appointed ManagingDirector of Marconi Communi-cation Systems Limited atChelmsford. He was formerlyManaging Director of MarconiSpace Systems at Portsmouth.

Mr John Powell has been ap-pointed Financial Director ofMarconi Communication Sys-tems Ltd of Chelmsford. He waspreviously Financial Director ofMarconi Space Systems Ltd atPortsmouth (see photograph).

Mr Angus Cairns has been ap-pointed Managing Director ofEASAMS, a GEC company,which was probably the first UKSystem and Software Company.The company was formed in1962 and operates in both thedefence and the civil sector.

Mr Kevin Thomas has been ap-pointed UK Sales Manager ofAdvance Bryans InstrumentsLtd. the Mitcham -based manu-facturer of digital plotters andrecording systems.

Mr Tom Smith has retired fromhis position as Divisional Direc-tor of Design after a careerspanning 46 years with A FBulgin & Co PLC. He will, how-ever. continue his associationwith the company as a con-sultant.

Avel-Lindberg_on the QE2

An 8 kVA uninterruptablepower supply-UPS-from Avel-Lindberg will play a vital role inmaintaining power to the GECGEM -80 micro -based Uni-Con-trol monitoring unit. which willalert QE2 maintenance staff tothe performance of the ninediesel engines, the associatedgenerators, the two largestelectrical propulsion motorsever manufactured, and theship's existing equipment, in-cluding pumps. water systems,and so on.The UPS system will ensurecontinuity of electrical power tothe monitoring unit and willautomatically take energy fromthe battery if the supply fromone of the ship's alternators isinterrupted for any reason.The Avel KD system is based ona ferro-resonant technology,which has been proven in ser-vice tohas a mean-time-between-fail-ures-MTBF-of over 50.000hours, and has a low compo-nent count.Avel have also provided twoother important power supplysystems which provide powerto the engine control andmanagement equipment on aline of four and a line of fivediesel/alternators.The photograph shows acouple of uninterruptablepower supplies being tested.Avel-Lindberg LimitedSouth OckendonEssex RM15 STD

For DDD ask BAL

BAL Components have been ap-pointed UK distributors for thecomplete range of products ofData Delay Devices Inc of Clif-ton, New Jersey. Included in therange is a vast selection ofdelay lines, pass -band filters, at-tenuators, and frequency con-verters.

BAL Components LtdBermuda RoadNuneaton CVIO TQF

ElectronicwheelchaircontrollerBase Ten Systems has won acontract worth E400.000 for thesupply of microprocessor -based controllers for electri-cally powered wheelchairs.The contract, placed by theDisablement Services Branch ofthe DHSS. involves the develop-ment of equipment to meet therequirements laid down by theDHSS and to manufacture thecontrollers and associatedjoystick mechanisms at BaseTen's plant at Farnborough.The system has undergone ex-tensive testing by Salford Uni-versity's independent testservice in addition to failure -mode analysis to ensure that it isfail-safe in operation.Base Ten Systems Ltd12 Eelmoor RoadFarnborough GU14 TQN

19 EE

NEWS NEWS NEWS NEWS NEWHarrier GR5 ATEcontract forFactronFactron Schlumberger hasbeen awarded the prime con-tract for provision of avionicthird -line testing for the RoyalAir Force fleet of Harrier GR5s.The GR5 is the UK version ofthe McDonnell -Douglas HarrierAV88, which is fitted with a mixof US and UK avionics.This multi -million pound con-

, tract, won under the MoD'scompetitive tendering prin-ciples against competition fromeight other consortia fromaround the world, is expectedto extend over a two-yearperiod. It is for the supply of atotal test solution for over 150modules and PCBs, which willbe achieved by enhanced ver-sions of Factron's commercialgeneral-purpose automatic testequipment-ATE-plus associ-ated applications software, fix-turing. and support facilities.Factron SchlumbergerFerndown Industrial EstateWimborne BH21 TPP

Silicon chipplant for AntrimAntrim is the site chosen forNorthern Ireland's first siliconchip factory. The developmentis part of a £4 million expansionplan by Lucas Stability Elec-tronics, a local concern. Theplant will employ 200 people.The expansion will allow Stab-ility to introduce a new range ofsilicon -chip -based componentsfor use in the protection of sen-sitive electronic systems fromlightning, nuclear radiation,and static electricity. The mainmarkets for the new productswill be Federal Germany, Italy,and the USA.Lucas Industries PLCBrueton HouseNew Road'Solihull B91 3TX

EventsINSPEX-Measurement andInspection Technology Exhi-bitionon 30 March - 2 April at theNational Exhibition Centre,Birmingham.

Command, control, communi-cations, and management in-formation systemsSecond international con-ference, organized by the Insti-tution of Electrical Engineers,to be held at the BournemouthInternational ConferenceCentre on 1-3 April. Furtherdetails from the IEE SavoyPlace London WC2R OBL telephone 01-240 1871

Fibre optics in communi-cationsNational lecture under theauspices of the IEE and IEREto be held at the EngineeringLaboratories. University ofCambridge, TrumpingtonStreet, Cambridge, on 2 April at7.00 p.m.

Technician engineers: theireducation, training, and role inother countries. How do wecompare?Discussion meeting chaired bySir Monty Finniston FRS at theRoyal Society of Arts, JohnAdam Street, London WC2 on7 April at 2.30 p.m.

Frequency control and syn-thesisThis conference, organized bythe Institution of Electronic andRadio Engineers, will be held atthe University of Surrey on 8-10April.

Physics education and the'new technology'The 1987 Annual Conference ofthe Education Group of The In-stitute of Physics will be held atBrighton Polytechnic on 10-12April. Further information fromThe Meetings Officer The In-stitute of Physics 47 BelGraveSquare London SW1X 8QX

Application of multivariablesystem techniquesThird international symposiumin Plymouth on 13-15 April.Further details from the Insti-

tute of Measurement and Con-trol 87 Gower StreetLondon WCIE 6AA tele-phone 01-387 4949.

Sonar transducers-past, pres-ent, and futureConference at the University ofBirmingham on 14-15 April.Further details from Dr B VSmith Department of Elec-trical and Electronic Engineer-ing University of Birmingham P 0 Box 363 BirminghamBI5 211'

The British Electronics Weekincorporating the All-Elec-tronics/ECIF Show. ElectronicProduct Design. Fibre OpticsConference. Circuit Tech-nology, and Power Sources andSupplies, will be held on 28-30April at Olympia. London

The benchtop FLEXICURE ultra-violet source, developed byMacam Photometrics for thefast curing of UV adhesives, isclaimed to be unique in thatthe radiation can be directedprecisely to where it isrequired by flexible lightguides. Available with one,two, or three flexible outputs,in a variety of sizes andconfigurations, the unit isadaptable for remote -controland automatic operation, andcan be made to specialrequirements. MacamPhotometrics Ltd 10 KelvinSquare Livingston EH545DG.

Inmostransputer fromRapid SiliconRapid Silicon is handling salesof Inmos's Type IMS T800transputer, which is capable ofsustaining over 2.25 millionfloating-point operations persecond.

The IMS T800 possesses all thecapabilities of, and is pin -compatible with. the estab-lished IMS T4I4. In addition, ithas an on -chip floating-pointunit, instructions -to -supportgraphics. 4 Kbyte of zero -wait -state RAM, and a maximum datatransfer rate of 50 Mbyte/s-twice that of the INS T414.For further information, phone(0494) 26271, or write to

Rapid SiliconRapid HouseDenmark StreetHigh Wycombe HP11 2ER

Belgian AirForce order forHawkerSiddeleyThe Belgian Air Force hasplaced an order worth nearly£400,000 with Hawker SiddeleyDynamics Engineering forequipment to update its exist-ing fleet of Sea King helicoptersto the latest standard of MKIAfuel control systems for theRolls Royce Gnome gas turbine.Belgium has now joined the ma-jority of Gnome operators, in-cluding the RAF, Royal Navy.Royal Norwegian Air Force,Swedisch Air Force and Navy.German Navy, and AustralianNavy in taking advantage of theincreased in-service reliabilityprovided by the MK1A controlsystem.Used in combination with thelatest first -line field test set, theMKIA controls enable the oper-ation of the engine's fuel systemto be checked at levels notpossible previously. This in -situdiagnosis provides greater air-craft availability and a conse-quential reduction in operatingCosts.

Hawker Siddeley DynamicsEngineering LtdBridge Road EastWelwyn Garden City ALT 1LR

EE

April 198720

FEEDBACK IN LOUDSPEAKERSby R Corlett

Electrical feedback is the backbone of many an electroniccircuit. Acoustic feedback is not nearly so common, but

R ConeIl suggests some ways of experimenting with it in alow -frequency loudspeaker.

Ever since Thiele and Smallpublished their works on loud-speaker theory. it has beenpossible to calculate fairly ac-curately what the ideal enclos-ure is for a certain type ofloudspeaker, or converselyhow a loudspeaker will behavein a certain enclosure. Accord-ing to Small, a closed box willbehave as a second -order high-pass filter, while Thiele showsthat bass reflex and trans-mission line boxes act as fourth -or sixth -order filters. From this itis clear that a closed box willgive better bass reproductionthan an open system.The performance of a filter isdetermined by its quality factorQ and its resonance frequency11 This is also true of a completeloudspeaker system, includingthe enclosure, when the total Q

is designated Q:' and the res-onant frequency fc. In an idealbass system, these quantitiesshould have values as follows:

Q:c= 0.5 to 0.7. and

fc<30 Hz.

Moreover, the volume of theenclosure should preferablynot exceed 100 litres; thefrequency range should begreater than 300 Hz; and the dis-

Fig. 1. Block schematic of proposed set-up with modified drive unit.

tortion should not exceed 1%.It is virtually impossible to meetthese requirements with apassive speaker system. par-ticularly as regards Q:c and fc.In an active system, it is fareasier to approach the ideal.Frequency response equaliz-ation is one way to tackle theproblem. Basically, it is better,however, to make use of a con-trolled system. Unfortunately,such a system is prone tospurious oscillations, whichcan, however, be obviated bynegative feedback.

Basic controlledsystemControl is possible by convert -

2

I I

L TL071

136096-2

z

Fig. 2. Circuit diagram of the impedance converter. The pin -outof the TL071 is shown in Fig. 3.

ing some of the acoustic outputof the loudspeaker into an elec-trical signal and returning thisto the input of the power ampli-fier. To this end, a low -mass ac-celeration pick-up has to befitted to the cone of the driveunit.The block schematic of a poss-ible arrangement is shown inFig. 1. The left-hand box con-tains the control electronics. fol-lowed by the power amplifier,which has a gain of about 30 dB,and the loudspeaker system.The control electronics consistof an adder that combines theleft- and right-hand signals, alow-pass filter with a cut-off fre-quency of 100 Hz, and a differ-ence amplifier where the fil-tered input signal is reduced bythe correction signal from thefeedback loop.The power amplifier can be ofany type. but its gain shouldpreferably be about 30 dB. Asmaller gain would requiresome adjustment of the controlloop, while a higher gain in-creases the tendency to oscil-lations in the loudspeaker sys-tem.The loudspeaker system con-tains the drive unit, fitted withthe acceleration pick-up, M,and an impedance converter,IC,.

Impedance converterThe impedance converter-seeFig. 2-consists of a Type TL071operational amplifier. Its pin -

out is shown in Fig. 3. This stageshould be fitted as close aspossible to the accelerationpick-up. preferable direct ontothe chassis of the drive unit asshown in Fig. 7.

Control circuitsAdder IC2 in Fig. 3 combinesthe two stereo signals into amonaural signal. PotentiometerPI sets the input level for low-pass filter IC3-IC.e. This Besselfilter has a cut-off frequency of100 Hz and a roll -off of 24 dB/oc-tave. A similar filter was de-scribed in the December 1985issue of Elektor Electronics.The control amplifier proper isformed by IC9: the values of R9,

and C9 determine the tran-sient response of the overallsystem. These values will bereverted to under Setting up.The control signal is deductedfrom the filtered audio signal insubtractor IC6. The output ofthis stage is fed to buffer IC7 via.two low-pass sections. R16 -C,and RIT-C12. These sectionsfurther suppress any tendencyto oscillation and are absolutelynecessary.

Fig. 3. Circuit diagram of the control electronics.

It is possible to omit impedanceconverter ICI and buffer IC7,but the values of the low-passsections between IC6 and IC7should then be recalculatedwith due account of the inputimpedance of the power ampli-fier.

Modifying the driveunitThe acceleration pick-up ismade from a piezo tweeter fromwhich the chassis has been re-moved as shown in Fig. 4. Theconnexion wires have been cut

at the terminals, not at thecrystal end. The remainingcone is then cut to the same sizeas the piezo disc.The resulting acceleration pick-up may be fitted over or underthe dust cap of the woofer. Thelatter method is preferable, butonly possible if the dust cap hasbeen fastened with a ther-moplastic glue. The cap maythen be removed quite easilywith a heated knife as shown inFig. 5. The removal of the capshould, of course, be carriedout with the greatest care toavoid damage to the cone of the

drive unit or its speech coil.Once the dust cap has been re-moved, it should be stiffenedwith a thin layer of epoxy resinand a piece of glass fibre clothat its inside-see Fig. 6. Theepoxy resin may be used at thesame time to fix the pick-up inplace. In the mean time, thewoofer should be kept upsidedown to prevent dust enteringthe air gap.After the epoxy resin hashardened, a thin flexible wireshould be soldered to each ofthe two short connexions of thepick-up. These wires should

EE

April 1987

also be glued to the dust cap toprevent them vibrating inunison with the cone later.Next, the dust cap can befastened onto the cone again,preferably with thermoplasticglue to enable removal at a laterstage if necessary. Before glu-ing it in place, however, piercea small hole in the cone throughwhich the flexible wires arefed. These wires should beglued to the cone in the sameway as those to the speech coil.Finally, they should be connec-ted to the impedance converterboard as shown in Fig. 2 and

Fig. 4. Piezo tweeter after its chassis has been removed.

Fig. 5. Removing the dust cap from the cone of the bass drive

unit.

EE

April 1987

Fig. 6. the dustcap should be stiffened on its inside with a thinlayer of epoxy reson, which can be used at the same time to fixthe acceleration pick-up.

Table 1

Harmonic distortion at 96 dB at 1 m distance

Frequency (Hz) 30 40 70 100

Without feedback 4.5% 1.7% 0.65% 0.85%With feedback 1.5% 0.6% 0.5% 0.65%

Maximum sound pressure at 40 Hz withdifferent enclosure volumes

Volume (litre) 50 70 100

Without feedbackWith feedback

98 dB101 dB

100 dB103 dB

102 dB105 dB

System parameters measured in a70 I enclosure

Ow fc f3 dB

Without feedback 1.9 48 Hz 29 HzWith feedback 0.6 17 Hz 20 Hz

Fig. 7. The modified bass drive unit: note how the impedancechanger is fixed to its chassis.

Fig. 7. They should preferablybe of about the same length asthose to the speech coil.The drive unit is then ready foroperational use-see Fig. 7.

Setting upAll the constituent parts of thesystem should now be intercon-nected as shown in Fig. 1. Shortout RI, and C9 with the aidof a switch to disable the con-trol circuit. When the switchis opened momentarily, one ofthree things will happen: the loudspeaker remains

quiet; the system oscillates at a low

frequency (<100 Hz); the system oscillates at a high

frequency (>1 kHz).In the first case, everything is inorder and the system can be

8Aims -ding Obis= 32.11/4c0

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taken into use.In the second case, the con-nexions from the pick-up to theimpedance converter boardmust be reversed.In the third case, the oscil-lations must be damped bychanging the values of a fewcomponents. First, increase C12to 1n8 and, if this does not help,Cli to 11.4F. If that still does notcure the problem, reduce thevalue of RI, and increase that ofCS. Resistor Ru affects thelower cross -over frequency,while Cs alters the Otc of thesystem. The author has builtseveral of these systems andlation problems. Do not forgetto remove the switch fromacross 121, and Rs.

FinallyThe frequency characteristicsin Fig. 8 show the results of themodification: it is quite evidentthat the lump between 30 and100 Hz in the response of thesystem disappears when thefeedback is introduced. Theresponse between 20 and 30 Hzis also much improved.A number of pertinentmeasurements are tabulated inTable 1.The system with feedback wasalso compared with a numberof top quality loudspeakersystems: in all cases, it per-formed equally well over thebass range, in spite of its costbeing only a fraction of that ofthe competition.

Fig. 8. The frequency response curves of the system with and without feedback.

EE

April 1987

ELECTRONICPOTENTIOMETERS

by T Scherer

An exploratory look at all -electronic replacements forpotentiometers in high quality AF applications.

Potentiometers are, arguably,not the best way of controllingthe volume and tone settings inan AF amplifier. We all knowthat they can cause scratchingnoises when operated, collectdust, and sometimes developcontact problems aiving rise totroublesome discontinuities inthe operative range. High qual-ity potentiometers for AF appli-cations are not only difficult toobtain, but also notoriously ex-pensive. In the following sec-tions we will briefly examine a

number of low-cost alternativesto potentiometers used invarious circuit sections of AFequipment.

The carbon trackpotentiometerThis most commonly usedvoltage divider is generallycomposed of a carbon filmdeposit on a ceramic base ar-ranged in a three-quarter cir-cular form (2700). The poorcontact definition of the wiper

on this thin carbon film readilygives rise to scratching noisesmade audible in the loud-speakers. Furthermore, dustand foreign particles can easilyenter the potentiometer enclos-ure, and block certain sectionsof the carbon track, so that theamplifier falls still at particularvolume settings, making the ad-justment very difficult.Stereo potentiometers of thecarbon film type are a furthersource of trouble. With most in-expensive types, the tolerance

on synchronicity of the set re-sistance is often no less than20%, even with linear law types.The voltages at the wipers of alogarithmic stereo poten-tiometer can also differ by some20%, causing a volume differ-ence between the channels of amaximum of 2 dB, which maybe noticeable in listening.Potentiometers are generallymounted on equipment frontpanels. and are connected tothe electronic circuit with theaid of shielded wires that often

la Opto-couplers

LT 10

100n

10

LT 10...10 000

R/K0

1000 I I

ii0/41-.......",t2t EU Nit=

in 5i -1-1-1 -14100v.\ 11 III

M...A4=1C1=11074

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10 000

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1000

100

10

0.1

001

20...

LT 20

a--Inlik I I I I I

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H I l

LT 200

Y.

®j 1LT200f1LT 201

l l I Il 1

_1.i !PI III El 5

0,1 1 10 100 1000ID (mit)

15V

Fig. 1. Experimental stereo volume control circuit based on the use of a LED-LDR optocoupler.

EE

April 1987

carry very low signal level atrelatively high impedance. Thismakes the amplifier suscep-tible to noise, hum and strongRF fields, which can still bepicked up by the carbon trackin the potentiometer (plastic en-closures!), and even in thecable shield.In conclusion, it is reasonableto say that the standard carbontrack potentiometer is un-suitable for a great many criticalapplications.

24

Stepping switchesRotary (wafer) switches withfixed resistors at the contactsare, in principle, a good way toeffect volume and tone settingin an amplifier. The tracking isadequate, and scratchingnoises due to spindle move-ment are effectively ruled out.However many rotary switchesof suspect quality do developcontact problems after pro-loged use. A major difficulty inthe designing with steppingswitches is the finding of typeshaving the number of positionsrequired to ensure a sufficientlysmooth adjustment range.

Wire -woundpotentiometersLong ago in the history of elec-tronics, all potentiometers andresistors were made from resist-ance wire. For a number ofspecific applications, the wire -wound potentiometer is still inuse. Ganged types with motordrive units can be found insome of the most expensivetypes of amplifier. This appli-cation. however, requires soph-isticated mechanical engineer-ing on the one hand, and a fairlycomplex electronic control cir-cuit on the other, making thewhole set-up rather cumber-some and expensive at thesame time.

An LDR-basedpotentiometerThe first attempts at making afully electronic potentiometerwere carried out with combi-nations of LDRs (light depen-dent resistor) and a small bulb.Although the results were quitesatisfactory for AF equipmenton the market in the early 1960s,we would nowadays reject theLDR-and-bulb control for incor-poration in Hi-Fi equipment inview of the noise production,

Fig. 2. OTAs in use as a Hi-Fi stereo volume control.

rumble sensitivity, and poortracking characteristic of thestereo versions.We all know that each andevery electronic component re-mains subject to continuous en-hancement by the joint force ofmanufacturers and their re-search laboratories. TheGerman firm Heimann, for in-stance, took up the long forgot-ten LDR for further research,and used two of these devicestogether with a LED to make anoptocoupler that has adequatefeatures for Hi-Fi applications.The LDRs in their Types LT10xxand LT20xx optocouplers areof excellent quality, and es-pecially the LT20xx shoulddo very well as a stereo po-tentiometer with adequateTacking properties-see Fig. lafor the pinning and R -Id curves,and Fig. lb for a suggested ap-plication circuit.

An OTA-basedpotentiometerA fairly simple potentiometerreplacement can be realizedwith the aid of an OTA (oper-ational transconductance ampli-fier), which is essentially anamplifier with current -con-trolled gain. The gain range ofabout 80 dB, the extensiveusable frequency range andlinearity of the current -gain cor-relation, make an OTA such asthe Type LM13600 eminentlysuitable for the applications weare zoncerned with here.Those who want to experimentwith these devices will find thesuggested circuit in Fig. 2 ofuse for further expenments.The only drawback associatedwith OTAs is their limiteddynamic range, which results ina maximum attainable signal-to-noise ratio of about 80 dB.

Analogue multiplexersThe circuit shown in Fig. 3 is ahigh -quality, all -electronicvolume control featuring 16 dBand 2 dB steps as controlledfrom a 6 -bit digital input. TheICs in this circuit are the well-known Type 4051 eight -channel.analogue multiplexer/demulti-plexer, which is in essence anelectronic version of an 8 -way,single pole rotary switch. Thecontacts are inputs 0-7, the poleis output Z, and the switch pos-ition is set with the 3 bits at theA -B -C inputs. Example: apply-ing binary code 010 to the A -B -Cinputs of the left-hand multi-plexer connects input 2 (pin 15)to output Z. The input signal forDpamp A? is therefore takenfrom the -32 dB contact on theresistor ladder. The resistors atthe inputs of the second multi-plexer driving A5 are dimen-

EE

April 1987

3

00 -Al

Volume control

t3

8V 8V

(7i) IS

045

-3248

-48 dB

U-6448

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coda

,ves vo-3

3

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C 21

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07 16

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A1._0.3= 3/4 T1_074All resistors 1%

OdB

-2413

-448

-648

-11413

H

H

a

a

3

a-1048

-12dB

-144B

U

CD4051

V

a

9 10 11

Digital catrc1

A

67:311

z

0 BV

BV

Fig. 3. A 6 -bit high quality volume control circuit that uses CMOS analogue multiplexers.

4 Tore control

By®

le1506

0

0

von

3 VSS

0

CD4051

4 Z

A

C

Ala

ClBV

A4= 1/4 T1.074

CV

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A

44Bass Treble 1 03

160,

Digital control

20L

CD4051

VIES

2

H

0

0

0

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8V

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17C31a

Table 1

INPUT STATES "ON"

1 INHIBIT CI

B I A CHANNELISI-

I CD4051B

0 0 1 0 0 0

0 0 1 0 1 1

1

0 0 1 1 0 2i

0 0 1 1 1 3

I 0 1 iI

0 0 4

0 1 1 0 1 5

1

0 1 1 1 0 61

0 1 j 1 1 7

1 X i X X NONE

sioned to give 2 dB attenuationsteps, so that the overall rangeof this electronic potentiometeris from 0 to -96 dB as set with6 bits. A balance control can bemade with two of these circuits,operated on the basis of soft-ware.The tone control section shownin Fig. 4 uses the same prin-ciple as the above volume ad-justment. The resistors as part

Iof the R -C filters in the feed-back loop of A. are selectedwith 3 -bit codes for bass andtreble.Use high -stability resistors andcapacitors when constructingthese circuits, and provideample decoupling of thesupply lines. The opampsshould be low -noise types suchas the TL074 indicated in thecircuit diagram. The digital ad-justment of the volume and tonecontrol circuits is a matterwe leave in your hands. Youmay want to use an up/downcounter, a microprocessor port,or a special switch to arrangefor the correct bit combinationsat the multiplexer control inputs(consult Table 1).

D

Fig. 4. Using electronic switches instead of a potentiometer in a tone control circuit.

EE

April 1987

VALVE PREAMPLIFIER 2

The main task of the boards de-scribed in this final instalmentof the article is to enable thepreamplifier to operate at thetop of its potential. To ac-complish this, one board holdsa relatively extensive powersupply, the other a combinationof logic circuits for driving thevarious relays in the preampli-fier.

The power supplyThe present design is no ex-ception to the rule that high -quality AF circuits, whetherpreamplifiers or power ampli-fiers, invariably call for the useof no -compromise supplies thatare based on the use of con-servatively rated components ofthe best quality available.The proposed supply is,therefore, a relatively complexcircuit, set up to deliver threevoltages to the preamplifierboard, and two to the relay con-trol circuitry. The high -voltage(1W) rails for the preamplifierare stabilized with a seriesregulator to ensure optimumoperation of the cascadedtriodes, and also to effectivelykeep low -frequency noise outof these highly sensitive sec-tions.Not all components in thepower supply are accommo-dated on a printed circuitboard. With reference to thewiring diagram shown inFig. 10. a varistor (SIOV S10K250) is fitted across the mainslines to suppress noise andvoltage peaks. The contacts ofthe double -pole mains switchhave shunt capacitors whichafford protection against induc-tive transients being superim-posed onto the mains when theamplifier is switched off. With-out these high -voltage capaci-tors, the loudspeakers in theaudio system would be in realdanger of being damaged bypowerful clicks-or worse.bangs-originating from thepreamplifier. The mains trans-former, Tr. supplies four

by J P Guts

The design is completed with a multi -voltagesupply and a relay control board.

voltages from its five secondarywindings. Where a transformeras shown is difficult to obtain ormake, two or more may be usedto provide for the various alter-nating voltages.The circuit diagram of the valvesupply appears in Fig.6. The6.3 V secondary of Tr onlypowers the filament of the HTrectifier valve, Vloi, a Type EZ80or EX81 used in a full -wave rec-tifier circuit fed from the centre -tapped 360 V windings on Tr.When REG is activated, thecathode voltage of Viol issmoothed with the aid of R127and C129. Series regulator IC illis a special high -voltage type,protected against excessivedissipation and reverse voltagewith zenerdiodes D119-D1z1 andshunt D122. The HV rails for theLINE and MD preamplifiers areadequately decoupled with theaid of R -C filters R125 -C130 andR129 -C13,, respectively. Seriesresistor 1112.5 also serves to pro-

tect IC111 from being damagedby a short-circuit on the +350 Vrail.As an alternative to the regu-lator circuit. power resistor R128can be fitted to drop the cath-ode voltage of Viol to +350 V.Since it derates the regulationof the supply. this solutionshould not be adopted, how-ever, if the amplifier is to workoptimally. Moreover, the outputfilter capacitors could then beblown out owing to overvoltageif the valves were removed fromtheir sockets, or if the preampli-fier board was not, or not yet.connected to the supply. TheTL783 is not very expensive andeffectively prevents all thismisery from happening.The filament supply (+UO is ar-ranged to "float" at about +90 Vwith respect to ground with theaid of voltage divider R130 -R131 -C132. This ensures that thecathode -to -filament voltage ofthe upper triodes in the pre -

Fig. 6. Circuit diagram of the HV and filament z.upply.

amplifier stages does not ex-ceed the safe limit. The filamentsupply based around the TypeLM317 regulator is adjustablewith Ploi and features a "soft -start" facility (realized withR134-C134-T1o1) to enable thevalves to heat up gradually atpower -on, thus extending theuseful life of the emissiveelements.The +12 V & +13 V supply forthe relay control circuitry isshown in the lower left-handcorner of Fig. 7. Note that therectifier diodes have shuntcapacitors to suppress noise,and that D113 raises the commonconnection of IC109 to about I Vwith respect to ground in orderto obtain a sufficiently highrelay coil voltage from the 7812regulator.

Relay controlThe relays on the source selec-tor board are controlled by thelogic circuit shown in Fig. 7.When the power is firstswitched on, the LINE OUTrelay (REF) is energized after aslight delay, but it is de-activated immediately when thepreamplifier is switched off. Toensure noise -free switching op-eration of the preamplifier, theLINE OUT relay is briefly de-activated if either the TAPE -MONITOR or the SOURCESELECT switch is operated.With reference to Fig. 7, thelogic configuration at the con-tacts of S2 is inverted by gatesNios-Ni05 and applied to 4 -bitcomparator IC1c6. The A=B out-put of this chip is high when-ever the two nibbles at theAe-A3 and Be -B3 inputs areequal. Delay networks R117-

R118-C11t, R,19-C11E andRia-C iT cause the B nibble todiffer very briefly from the Aone when S2 is turned to selectanother source input for thepreamplifier. The negativepulse at the A=B output of IC,ostriggers monostable multivi-brators MMVioi and MMV102.which are configured to pro-

vide a delay of 0.5 and 1 sec-ond, respectively. MonostableIvIMViin disables the selectedrelay via the relevant NOR gateN.02 -N104, while MMV.02disables the LINE OUTPUTrelay via N123-N220-Nlis. Whenthe delay caused by UMW),has lapsed, the newly selectedinput signal is connected to thepreamplifier input via the rel-evant relay contact. Similarly,the line output connection is re-stored when the delay causedby MMV202 has lapsed.When TAPE/MONITOR switchSi is closed, a positive pulse isgenerated with the aid of N109,delay network R121 -C115, andNAND gates Nna-N222. Thispulse triggers MMV.G2 so thatthe LINE OUT relay REF is de-activated. After a delay causedby 11224-C222, TAPE/MONITORrelay REE is energized. The lineoutput relay is re -energizedafter the delay caused byMMV202 has lapsed. During theabove operation, the sourceselection and TAPE OUT con-nections are not broken.

The LINE OUT relay can not beactivated before N123 is enabledwith the aid of the Q signal fromFF.01, which forms part of thepower -on delay and failuredetection circuit.Binary counter IC112 controlstwo timing sequences. After adelay of about half a minute.output Quo switches on the highvoltage with the aid of relay G.After another 30 seconds, out-put Q of FF.o. enables N123 toactivate the LINE OUT relay.The binary counter is clockedby its internal oscillator, whosefrequency is determined withR101 -C220.

Schmitt -trigger gate N125 pro-vides a power -up delay for therelay control circuitry, in orderto ensure the correct initiallogic states of IC11z, Fflo, andFF102. Gate N124 makes it poss-ible to control the LINE OUTrelay by an optional failuredetection circuit, which shouldprovide a logic low level at theERR input in response to adirect voltage component orexcessive noise at the (pre) -

amplifier output. There are twoways of restoring the LINE OUTconnection to the power ampli-fier: either RSTA is made logichigh by, for instance, pressing apush button connected to thisinput, or RSTB is similarly madelogic low. The latter operationcauses the previously detailedpower -up cycle for the highvoltage to be restarted, beforeREF- is re -energized.

ConstructionBefore commencing the fittingof parts onto the supply andrelay control board, this mayhave to be cut to suit a par-ticular arrangement in the pre-amplifier enclosure. The tracklayout and component mount-ing plan for each section of theboard are shown in Fig. 8(power supply) and Fig. 9 (relaycontrol circuitry).

The high voltage supplyTo allow for adequate heat dis-sipation. all power resistors on

M EE

April 1987

the supply board must be fittedslightly off the circuit board.Filament voltage regulator IC110is fitted onto two heatsinksclamped back to back. Thehigh voltage regulator, IC112,

needs only one heatsink, whichmust none the less be ad-equately sized.Should electrolytic capacitorC129 prove hard to obtain in thestated voltage rating, it is poss-ible to replace it with two seriesconnected 10011F; 250 V types,each fitted with a 470K; 1 W

shunt resistor for equal voltagedistribution. The circuit boardshould allow plenty of space toaccommodate these additionalparts.The use of the stabilization cir-cuit with IC11,3 requires thevoltage across C129 to be nomore than 450 V, and no lessthan 400 V. Series resistor R127may have to be adapted to staywithin these limits. If it is di-mensioned for an output in theregion of 400 to 420 V, itbecomes possible to use a450 V rated capacitor in the C129

7

Re A: Ttr-etRe 5: CD.RE C Fe4n.Re 0,1a. E Tape KmRe F:Liae 001Re 6: tfrs Vonace

12V

13V

H101_14104 =1C101 = CD 4001N105-14110 =IC101. C04154/4111_Nt17 = 1C103 = ULM 2631H119_24121 =10101 = CD 4093104Y101-M11V102 = IC105 = CD 4093H122-14125 =10107 = CD 4093FF101}7102 =10105 = CD 4013

0103C.143acx : C4.

CSJ4 I 172, 0INV

O 409-01427.47 4444004Tjf 1

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Fig. 7. Circuit diagram of the relay control circuitry.

EE

April 1987 28

Fig. 8. The printed circuit board for the power supply.

Fig. 9. The printed circuit board for the relay controller.

lei EP

Ar.,r1 1937

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47n

2 5 01AC

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11

rsre- AWN,rn 20001

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11,11.010

Fig. 11. Suggested front panel layout.

Parts list

Power supply board

Resistors: (+5%)

R127 = 1K0; 5 W '

flin=3k3; 5 W 'RI2i=4K7; 1 WRile= 180XR131 = 62K

R132 =220R

R133 = 1K8

R114= 100K

11,35;1313s=47K; 1 WR137:=33OR

8113=470R; I WNei =25OR preset

Capacitors:

Cia=4711; 500 V axial Cite =220p; 385 V can -type radialCu, =47p; 350 V axialCin= 100p; 100 V axialC113=22000; 25 V radialC137 = 2211; 16 axial

C135 = 100p; 16 V axial

Semiconductors:

Mrs = 1N4001

incl.= 1N540113113:Di3c--:D321= zenerdiode 39 V;0.4 W

Diu= 1N4004BC55713

ICI le = LM317

ICiss =TL783 or 783

Valve:

E280 or EZ81 with 9 -pin socket forPCB mounting

Miscellaneous:

Heat -sinks for (see

component overlay).ReG = PCB -mount relay; singlecontact. e.g. SiemensV23127 -E0002 -A101 (12 V).*

PCB Type 87006-2 lout asrequired).

Supply parts not on this board:

2 capacitors, 47n; 250 Vsm.s.

resistor 2M2: 1 W.varistor Type Sl0K250

(Siemens).'Mains transformer: 2 ,c360 V;50 mA, 6.3 V; 1 A, 13 V: 1.5 A,14 V; 1 A.The transformer may be made byMajestic Transformer CompanyLtd

180 Windham RoadBournemouth BH1 4QYTelephone: 102021 34676

Or

Avel-Lindberg LimitedSouth OckendonEssex RM15 5TD

Telephone: (0708> 853444

Mains entrance socket with built-in fuseholder.

Double -pole illuminated mainsswitch.

Parts list

Relay Control board

Resistors: 1=5%)

Rio, =220KR1or;Rsie:1112, RI24 incl. =Fito3;RIv:Rict;R:12. - Wu;

incl. =10KR154 = 1K0

R,xt= 68Klilts= 150KRios =100K11111 =1008

Ain =22R

Capacitors:

C101 ... C114 incl.=n; 100 VC1G5 = 1000p; 25 V axial

C'oe:C10,;Cyrz...Cils Incl. =100nCies =22p; 16 V axialCit-§ =470p; 16 V axialCile= 150nCIII:Cul=22011Cfl2=InC113 = hi; 16 V axial electrolyticCals. ..Cq incl. = 470p ceramic -Cile=470nC121 = ly; polyester/polycarbonate/MKT

Semiconductors:

Dlot 1N4148C11°3...D1iz incl. =1N4001IC1°1=4001

IC102 =4069

IC103 = ULN2004

ICIes:ICio,=4093ICIes =4098

!Cies= 4063ICies=4013ICI:n=7812ICII:=4060

Miscellaneous:

Heat -sink for ICIe%.

Push -to -make switch for RSTA EtRSTB (option).

Si = miniature SPST.Sr =4 -way rotary switch; single

pole.

Note: ready-made foil Type86111-F can be used for theinput selector board at the rearof the enclosure. It is regrettedthat the front panel foil is notavailable ready made.

s These Siemens parts areavailable from ElectroValue Telephone (0784) 33603 (Eghambranch). or 061-432 4945(Manchester branch).

position. Whatever type of ca-pacitor is used, however, itshould be safely rated abovethe maximum expectable volt-age, including the effects of in-creased ripple and mains fluc-tuations.If a valve -less power supply isrequired, the EZ80 or EZ81(Vvii) may be replaced by twosilicon diodes Type 1N4007.whose cathodes are joined andconnected to socket pin 3,

while the anode of one diodegoes to pin 1. the other to pin 7.Note that R127 may have to be in-creased to compensate for theensuing lower voltage dropacross the rectifier.When the power supply boardis completed, it can be testedby applying the relevant alter-nating voltages from the trans-former. The high voltage relayREG can be energized with theaid of an external 13 V supplysome 30 seconds after applyingpower to the mains transformer.As various parts in the powersupply are at a dangerouslyhigh potential, it is stronglyrecommended to keep onehand in your pocket whilemeasuring any voltage in the

circuit. Never touch any com-ponent while the power ison, and make sure the HVsmoothing capacitors are com-pletely discharged beforeworking on the board.Use a well -insulated 10R; 5 Wresistor to discharge the highvoltage capacitors before com-mencing work on the supplyboard.

The filament supplyThe filament supply voltage forthe valves on the preamplifierboard must not exceed 12.6 V. Itmay be a good idea to set Pio,for a supply output voltage of12.0 V to extend the useful lifeof the filaments. Remember thatthe +th and -11 rails are atabout +90 V with respect toground, and, therefore, poss-ibly dangerous to touch.

The relay control circuitryThe circuit board for the relaycontrol section is shown inFig. 9. With the parts list andcomponent overlay to hand, itscompletion is straightforward.Fit regulator IC103 with a fairlylarge heatsink to handle the dis-sipation. Do not forget any of

The completed supply and relay control boards.Continued on p. 51

SECONDARY BREAKDOWN INPOWER TRANSISTORS

by Sue Cain 8- Ray Ashmore

This article examines the different types of secondary breakdownthat occur in power transistors, and investigates the phenomenathat cause them. It concludes that secondary breakdown is a

function of transistor technology, and cannot always beimproved without some trade-off in other parameters.

One of the basic failuremechanisms in power tran-sistors is second breakdown.This term includes variousphysical phenomena which arecompletely different. They de-pend on the different use oftransistors in the circuits andhave in common the electricaland thermal instability inherentin transistors themselves.The conduction behaviour of anemitter base junction and thecurrent gain of a transistor de-pend significantly on the tem-perature and increase as afunction of the temperature.Electrical and thermal in-stabilities may act simul-taneously within the device,thereby giving rise to destruc-tive second breakdown mech-anism.An understanding of this mech-anism is of areal importance fora safer optimum application of apower transistor.A distinction should be madebetween direct second break-down (Is; b) which is dis-tinguished by a normaldirection of base current /s(entering into an NPN transistor)and inverse second breakdown(Estb), when Is is in the op-posite direction (extracted froman NPN transistor). The limits towhich a transistor may be usedwithout entering into Es, b aredefined by the reverse bias safeoperating area (RBSOA).

Direct secondbreakdownIt is important for the power cir-cuit designer to know the locusof the /c-VCE points definingthe boundary between stableand unstable operation of for-ward biased transistors. Thislocus defines the SOA safeoperating area, that is. the area

of the logic-logVcE planewhich may be used without anyrisk in DC current conditions orwith different width pulses at aknown temperature. A typicalSOA is shown in Fig. I. Thelimits of this area are as follows:1) The A -B section represents

the upper limit of the collec-tor current that may normally beused, generally limited by wirebonds. Operation at higher cur-rents may cause damage to thewires of their bonding.2) The B -C section is the -I

slope curve section (i.e. thesection with constant dissi-pation) defined by:

VcEIc=Pmax-=(Timax-T0)/R6 [1]

This section therefore indicatesthe maximum dissipable powerof the device. Tr x is the maxi-mum temperature which thecollector -base junction mayreach, over which the devicereliability may be compro-

mised. In power Transistors,Tfir.x varies between 125 and200 degrees Celsius and gener-ally depends on the metallurgyand the type of package. Ro isthe thermal resistance betweenthe collector -base junction andthe case, including all the sili-con and package system. Theincrease in the maximumdissipable power when thepulse width decreases (Fig. 1)corresponds to the decrease ofZe with respect to Re.3) Section C -D corresponds to

the second breakdownphenomenon (or L b) and limitsthe maximum power that thetransistor can dissipate. Thismay occur even at relatively lowVCE voltages.4) Section D -F is the limit due to

the transistor's BVcEo.Second breakdown is aener-ated by the electrical and ther-mal instability of the transistor.The main causes of this insta-bility are:

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10 MS

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I II! 1 I

i Iii i

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NI 1

BUV48/BUX48 --I-10.BUV48A/BUX48A-'1P1II I 1 i i 1 1111 1 1

68 2 4 6 8 2 4 6 8 2 4 6 81 10 102 103 VCE (V)

Figurerisk inknown temperature.

1. Safe operating areas which may be used without anyDC current conditions or with different width pulses at a

1) The VBE of a directly biasedbase -emitter junction, at con-

stant current, decreases lin-early with temperature, with a=2 to 2.5 mV/°C slope. The

base current of the transistormay therefore be expressed by:

le=.1e[exp(eVBE- 'Taal [2]

and, when VBE is kept constant,it increases with temperature.2) The her at the relevant

voltage values increases as afunction of temperature accord-ing to the law:

hFr=hfsb exp(LEg/k7)1 [3]

Where' L.E'gr is an activationenergy which is a feature of thetransistor.3) The thermal conductivity of

silicon decreases when tem-perature rises, causing aworsening of the thermal resist-ance of the transistor.When these three phenomenaare taken into consideration, itmay be observed that a pulse ofpower P= VCEI generates:a) an increase of the junction

temperature. giving rise to anincrease of Is and h/i, andtherefore to an increase of Icwith a following increase of Pand, therefore. a further tem-perature increase.b)a dissipation to the exter-

nal environment, controlledby the thermal resistanceRo = drldP which tends tostabilize the device.The situation evolves towardsstability when:

L/c2 alc= VIERLk: a T

is smaller than I, or instability if>1.In this way. a stability factor, S.may be defined that will be afunction of VCE and Ic:

aks=RevcE-T [4]

EE

April 1987

When S>1, so called "thermalrunaway" occurs and the junc-tion temperature increaseswithout any limit, thereby de-grading and possibly damagingthe transistor. The failure gener-ally occurs when the surfacetemperature becomes greaterthan the eutectic temperaturebetween silicon and the contactmetal (front aluminium) with aconsequent melting of the alloy.A localized temperature in-crease may also damage thecrystal, or the inner tempera-ture of the device may reachvalues high enough to melt thesilicon.To understand Is/b phenomenawhich give rise to a reduction ofthe maximum power that thetransistor can dissipate as VCEincreases (zone D -E), it isnecessary to take into accountthat device operation is nothomogeneous on all the dicearea. There are disuniformitiesin the emitter base current den-sity that may be due to junctiondisuniformities, crystal defectsand, most of all, to the emitteredge concentration phenom-enon.The voltage drop due to thebase current flowing throughthe cross resistance rbb' givesrise to a disuniformity of Vat atthe junction, and therefore tothe disuniformity of the currentdensity Jr (see Fig. 2).A side drop of 26 mV reducesthe injected emitter current bya factor lie, where e is the baseof the natural system of logar-ithms (= 2.71828...).A concentration of the currentat the emitter periphery istherefore generated, so the ac-tive silicon area is reduced andhot spots occur, leading to aneffective increase of the ther-mal resistance. As a result, themaximum dissipable power isdecreased.When VCE is increased, the ef-fect of the base -collector elec-tric field is to increase the basecurrent concentration.Different techniques may beadopted to limit the is hphenomenon. Fundamentally,these consist of minimizing themechanisms that trigger elec-trical and thermal instabilities inthe transistor. The basic tech-niques are:1) minimization of crystal dam-

ages, metal impurities, anddoping disuniformities;2) optimization of package and

die attach techniques tominimize the thermal resistance

on which the stability factor Sdepends. Disuniformities of sili-con die bondings to the casemay give rise to adverse vari-ations of Rg as a macroscopicparameter for the dice as awhole, but also to significantvariations between differentpoints, giving rise to prematuresecond breakdown;3) increase of the base thick-

ness to reduce the high cur-rent densities (due to emittercrowding) flowing through thecollector base junction (wherethe electric field is localized),so that the density of the dissi-pated power is decreased.High base thicknesses, how-ever, will result in lower cut offfrequencies and slowerswitching times;4) optimization of the horizontal

geometry;5) introduction of distributed

ballast resistances connec-ted in series with the base, theemitter or both, which tend togive a negative feedback tothermal runaway, thereforestabilizing the device.The introduction of a ballast re-sistance in series with the baseof the emitter may reduce fromJ3 to J2 the current density in thehot spot. The emitter ballast re-

sistance is generally obtainedby opening emitter contactsthinner than the emitter strip. Inthis way it is possible to limit thecurrent density at the bound-aries of the emitter. Theseresistances show the drawbackof increasing the saturation.voltage of the transistor by theamount Vcasao = RE/asaii.On the other hand, the baseballast resistance is obtainedthrough a "N+ pocket" (in thecase of NPN), around the emit-ter area. This N+ diffusion, be-ing unbiased, cannot be tra-versed by the base current, sothis is forced to flow below theN+ through a small sectionand, in the case of a diffusedbase, encounters a higher re-sistance on the way to the edgeof the emitter. In this way it ispossible to improve /stb signifi-cantly.It should be noted that the SOAlimits are temperature depen-dent and suitable derating mustbe applied.

Reverse secondbreakdownThe reverse breakdownphenomenon (Es/b) is also dueto thermal and electrical in -

Figure 2. The voltage drop resulting from the base currentflowing through the cross resistance rbb" gives rise to adisuniformity of Vet at the junction, and so to the disuniformityof the current density JE.

Figure 3. The common emitter characteristic curves for atransistor.

stability of the transistor. Asalready mentioned, it is dis-tinguished from /sib by thepresence of a reverse /B (i.e.with a direction opposite to thenormal direction of a transistoroperating in the active zone)and by high VCE values of thetransistor. The device may be inthese working conditions dur-ing turn-off with an inductiveload.In Figure 3 the common emittercharacteristic curves for a tran-sistor are shown.It is easy to understand thebehaviour of these curves whenthe common emitter gain ex-pression is considered:

hFr = Ar1(1-11F) [5]

for high VCE values. AF is re-placed by MAF.For low Vice values, M is an in-significant factor, being veryclose to 1: it increases whenVCE is increased according tothe following expression:

M = 1/[1-Vcr/BVcsor] [6]

From expressions (5) and (6) it isclear that h -r depends on VCE,becoming infinite whenMAr=IIBVcEo.The negative slope section,which is a feature of the curveswith Is<O, is due to the fact thatA decreases at low values of theemitter current.During turn-off with an induc-tive load, the transistor has tooperate with negative base cur-rent and a high value of Ic. Itoften has to reach a workingarea above VCEO. remainingthere all the time required forthe inductance to be dis-charged. Fig. 4 shows the be-haviour of Ic, VCE, la and thepower dissipated by the transis-tor during turn-off.The area of the dissipatedpower corresponds to theenergy stored by the induct-ance. 1/21,12. which is dis-charged into the transistor andthis is called secondbreakdown energy (Es (b).Like 1_ b, the voltage drop dueto the reverse la flowingthrough the side resistance rbb'makes the centre of the emitterstrip more biased than itsperiphery. In this way, a currentconcentration occurs at theemitter centre.Let us analyse the case of anNPN transistor with diffusedbase and epitaxial collector, i.e.with constant concentration NDof donors doping particles.Poisson's equation is:

EE

April 1987

Figure 4. The behaviour of /c. VCE, /8 and the power dissipatedby the transistor during turn-off.

5 critical field

E

base collector N- N +substrate

87061-5

Figure 5. Typical electric field behaviour when the collectorcurrent is limited to low values.

6 EN N+

critical field

J" CR

J"2

base collector substrate

87061-6

Figure 6. The condition created by the intermediate layer insertedbetween the collector and the substrate in order to obtain highEs b values.

dE/dX=dVIdX=p(x)/i [71

The X axis is normal to the sili-con dice surface, (x) is thecharge per unit volume, E is thedielectric constant of silicon.When the collector current islimited to low values, expres-sion [7] becomes (q being theelectron charge):

dEldX=q1k/i [8]

and the electric field behaviouris similar to that shown in fig-ure 5 for Jc = JO,.The voltage Vcs (= Vcr) isgiven by the area of the EXgraph and is smaller thanprimary breakdown voltagedue to the reaching of criticalfield E. In the presence ofsignificant values of currentdensity Jc, the expression [8] ismodified due to the n concen-tration of electrons flowing atthe speed V through the deple-tion layer.

dEldX=[q(IVD-n)]le 191

where n=Jc/qVAt constant Vcs, the arealimited by E has to remain con-stant. When Jc increases, theEX slope varies (r2) until itssign is changed (0) and E1-1 isreached (re:). At this point ava-lanche local multiplication ofelectrons occurs with an uncon-trolled current increase-andso a strip is formed with a veryhigh temperature that gives riseto either crystal damage or sili-con melting. Possible crystaldefects, metal ions, and junc-tion disuniformities further ex-aggerate this phenomenon. Theavalanche multiplication is veryfast and very localized so thedevice remains externally cold.The Es'b behaviour is not in-fluenced by the die bondingquality. High Es/b values can beobtained with a proper geo-metric design to limit the cur-rent crowding and, most of all,by inserting a second epitaxiallayer N of intermediate dopingbetween the collector and thesubstrate.The intermediate layer createsthe condition shown in Fig. 6.When the current density in-creases (f2) the electric field atthe interface N -/N is increased.Before the critical field Ec, isreached at the interface, thecontribution of layer Nbecomes significant in sustain-ing the voltage. A further den-sity increase (J'3) reduces theelectric field at the interface

N -/N and the breakdown is nottriggered until the critical fieldis reached at interface NIN±.For a good power transistorwith Vcrotsus)=450V, the cur-rent density Jrc, correspondingto EC; is of the order of20A/mm2, i.e., greater by a fac-tor 10 when compared to theaverage current density givenby the ratio between maximumsaturation current and emitterarea.The Es i) behaviour is also in-fluenced by the conditions out-side the transistor, Res, VEE, L.The base conditions are es-pecially important, as theyregulate the crowding phenom-enon.The system most commonlyused by power designers to re-duce the EsIla effect during turnoff with inductive load is aclamping or 'snubber' circuit,that limits the voltage peak be-tween collector and emitter.The presence of the clampingcircuit allows only a minimalamount of the energy stored inthe inductance to be absorbedby the transistor, and Esibbecomes independent of thevalue of L and practical RBSOAlimits may be defined.The presence of high VCE andnegative base current, Is, maygive rise at high current to thepreviously described Es,b

phenomenon, even in thepresence of the clamping cir-cuit. The multi-epitaxial tran-sistors show a better behavioureven in the presence of aclamp.The reverse bias safe operatingarea establishes the maximumswitchable current with induc-tive load versus clampingvoltage in very harsh base con-ditions that simulate the realbase driving conditions in thecircuits.The temperature is not a majorfactor in the Es,b and so theRBSOA rating can be con-sidered to be independent oftemperature.

ConclusionSecond breakdown perform-ance is a function of transistortechnology and cannot alwaysbe improved without sometrade-off in other parameters.The application conditionshave a considerable effect onboth Is/b and Esib capability.

* Sue Cain is with BA Electronicsand Ray Ashmore is with SOS.

EE

April 198734

PRESET EXTENSION FORFUNCTION GENERATOR

by M Kistinger

A simple to build, ten -frequency preset unit for the ElektorFunction Generator that features an adjustable sweep function, a

LED indication, and much more at a very small outlay.

The AF Function Generator de-scribed in Elektor Electronics,December 1984, has generateda lot of interest, which is mainlydue to the instrument beingversatile, relatively simple toconstruct, and sufficiently ac-curate for a great many appli-cations. The preset extensionproposed here is a separatelyhoused, 10 -way programmableancillary intended to drive thegenerator's VCO input. Fre-quencies that are often used fortest and measurement pur-poses can be called up at theflick of a switch. and there isalso a facility to successivelyselect all ten of them at variablespeed, providing a 10 -fre-

quency sweep function. Fur-thermore, the extension pro-vides an output signal to triggeran oscilloscope with any one ofthe ten available frequencies.Ease of control is the key wordin this design. Once you haveset the ten generator outputfrequencies with the aid ofmultiturn presets, you can sel-ect manual operation on the ex-tension and press the SINGLESTEP key until the relevant fre-quency is enabled, as indicatedby the associated LED. If theMAN/AUTO switch is in the AUTOposition, the VCO voltages aresuccessively output at a ratedefined with the SPEED poten-tiometer and the FAST,SLOW

push-button selector. A BCD(thumbwheel) switch is used toselect the period of one of the10 available VCO voltages fortriggering an oscilloscope.Standard components are usedthroughout this extension,which will quickly prove an in-dispensable add-on unit thatcan save you quite some time insetting the generator's outputfrequency.

Circuit descriptionThe circuit diagram of the pro-posed extension is shown inFig. I. At the lower left is thepower supply, which delivers+5 V for the logic circuits, and+10 V for the sweep oscillator,IC; and the VCO outputdrivers, TI -TB-, . The lattervoltage is provided by a pre-cision regulator Type LM317(IC12) to ensure the stability ofthe ten VCO drive levels. The+5 V supply is conventionallybased on a Type 7805 regulatorwhich can easily handle the150 mA current demand of the(Lsyrn circuits.With S3 set to MAN., depressionof SINGLE Sr 1.r push-button S2causes Ni and delay networkRI c -C, to provide a trigger pulseto the B input of monostablemultivibrator ICz whose outputperiod is defined with R12 -C2.As Ss is open. the pulse at out-put Q of IC2 is passed throughgates N15 and N17 and fed to theclock input of counter IC3.If Ss is in the AUTO position, Nisblocks the SINGLE site pulsesfrom ICz, and IC3 is arranged tobe clocked from oscillator IC,via level translator T12. Poten-tiometer PI and FASTiSLOW push-button St allow precise settingof the VCO sweep speed. Notethat S3 is actually part of theSPEED potentiometer, so thatturning this fully counter -clock-wise automatically enablesmanual selection of the directvoltage level from the preset ex-tension, and hence of the func-tion generator's output fre-quency.Counter IC3 is advanced bypulses from N17, and the BCDcode at its QA-QD outputs is ap-plied to the XOR gates in IC4, aswell as to BCD -to -decimal de-coder ICs. The Type 74LS90

counter is set up to count from 0to 9, and is reset to state 0 atpower -on with the aid of Cs -RicThe trigger signal for the os-cilloscope is obtained fromN1 N,: and Nis -Nis, whichfunction as a 4 -bit comparator inconjunction with IC: and a BCDswitch for selection of the rel-evant trigger pulse. The outputof N15 goes high if the logicstate of outputs QA-QD on IC3matches that of the A -D lines onthe BCD switch.Any one of the 10 outputs ofdecoder ICs can enable an as-sociated driver stage, whosedirect output voltage is defined

with a multiturn preset. If, for in-stance, output 9 of ICs goes low,the output of open -collector in-verter N12 goes high. TransistorTto is turned on, LED D20 lights,and a portion of the emittervoltage is fed to the VCO inputof the function generator, viathe wiper of P12 and summingdiode Dio. The circuit aroundTii serves to raise the groundpotential of the extension so asto increase the active range ofthe presets in the analogue out-put stages. It should be notedthat this arrangement makes itimpossible to feed the presetextension from the generator's

Parts list

Resistors ( +5%):

RI;R3=4K22: 1%Rz =1COK

1:14:13.1s=5K6

RER12:1323...Rzo incl. =10K

= 1K5

137;R3D.... R19 incl.:1142 =1KO

REF19:R11;1313= 1K2

Riii:RIA=22OR..Ria incl. =270R

RA,=1GOR

PI =500K linear potentiometerwith SPST switch (Si)

P2=5K0 presetP3... P12 incl. =4K7 multitumpreset

Capacitors::

CI:Cs= 100nCz =42; 25 VC3 = 10y; 10VC3;C:= 1p; 35 VCs =4;17; 63 VCs =1000;,; 40 VCs= 47u: 63 VClo=100: 35 VCis =202: 25 Vde.coupling capacitors (100n) as

required

Semiconductors:

131=1380C1500

incl.:Dzz=1N4148Dit...02, incl.= LED023= 1N4007IC, =741IC2=74121

IC3= 74LS90

(Cr =74LS%ICs=74LS42

=7406

ICs =74LS02ICs;ICts = 74LSOO

IC11=7805 plus heat -sink

IC12= LM317T

T. .Tio inc1.=BC549B= BC2378

Tiz=BCY59

Miscellaneous:

Ft =100 mA; delayed action.Fuseholder for Ft.Tr, =15 V; 200 mA.SI;Sz= push -to -make button.SI= part of Pr.Si = SPST mains switch.Suggested enclosure: Verobox

Type 75-3007C (180 120

40 mm).

Prototyping board (Veroboatd) asrequired.

BCD Thumbwheel switch

EE

April 1987

1

Cal

tap

Fast

PortaS4

10V

R

5V

0

C2

7TS20la 30 11 101

0 Ai ruc C

5 a 1C2

74121

B =TsI B80C1500

LtO 17T

712

5V

1114007

ICS IC3 ICSO

C51

:177 5OA

121A 13

1C3 Oe11

74LS90 cc 9C 13

9-0551 552...531 552

10 61.71

N20...t423 = IC4 = 741585

12

2

DD

5123

511_116 = ICS = 7405127_1 12 .IC7 = 7405t113,t114 = Ir3 ICS = 74LS02ti15-1117 =3/4 tC9 = 74LS001118,1119 =1,21C10 = 741-500

71_710 = 10x BC549B711 = BC2378T12 = 8CY5901_010= 1514148

5V

5V

0

BCDthumbwheel

switch

Trigs,

A

R14 RTR

1C41 741586

5V

161

Sync. Out

520

513

10V

0

8output &hints

544_1411T2_79

R21_R2SR31_1138P4_Pl 1D2-09

012_019

R39

020

RIO

D21

D22

1114149

64107-1

10y

supply. Also, observe that thepulse level at the SYNC our ter-minal is 5 Vpp with respect tothe extension ground potential,not that of the function gener-ator. LED D21 serves the doublepurpose of raising the basepotential of T17 and functioningas the on/off indicator of thepreset extension.

Construction andsetting upThe proposed extension circuitis readily built on a piece of

Veroboard and housed in anABS enclosure that can beplaced on top of the functiongenerator or the associatedsweep generator.Although not shown in the cir-cuit diagram, the supply lines tothe logic circuits should bedecoupled with 100n capaci-tors. Keep the wires to theswitches and the oFvn poten-tiometer as short as possible.The frequency indication LEDscan be fitted in a neat row onthe front panel. complete withnumbers 1-10 for easy refer-ence.

After building the circuit, it issuggested to adjust the outputvoltage of IC12. Use a DMM andset P2 for a reading of 10.00 V.Turn Pi to MAN and checkwhether operation of St causesthe LEDs to light in succession.Turn Pt to AUTO and checkwhether the sweep speed canbe adjusted with PI and S. Ifnecessary, adapt or C: todefine the sweep speed. TurnPt back to MAN and use a DC -coupled oscilloscope to seewhether the VCO voltages areall stable and free from digitalnoise and ripple.

Finally, connect the extensionto the VCO input on the func-tion generator, and adjust the 10presets for the test frequenciesyou require.

Function generator. ElektorElectronics, December 1984.Sweep generator: ElektorElectronics, November 1985.

Th

EE

April 1987 36

LINKWITZ FILTERSA brief look at the theory and practice of passive and

active Linkwitz cross -over networks.

An analysis by SiegfriedLinkwitz in the January 1976

issue of the Journal of the AudioEngineering Society shows thatconventional cross -over filtershave a negative effect on theradiation pattern of a multi -wayloudspeaker system as regardsboth directivity and amplitude.On the basis of his research,Linkwitz proposed a new typeof network that gives a uniformradiation pattern and constantamplitude. This filter, which isessentially a Butterworth -de-rived type, was first describedby Riley and is, therefore, some-times referred to as a Linkwitz-Riley network.For simplicity's sake, the follow-ing discussion is based on atwo-way loudspeaker system.For optimum results, Linkwitzsuggested that the filter mustmeet three requirements: there must be no phase shift

between the outputs of theloudspeakers at the relevantcross -over frequency to pre-vent an upward or downwarddisplacement of the radi-ation pattern;

the signal attenuation at eachfilter output must be 6 dB in-stead of the usual 3 dB to pre-vent peaks in the sums of thesignals;

the phase shift between theoutput signals must be con-stant at all frequencies to re-tain the symmetry of theradiation pattern above andbelow the cross -over fre-quency: this condition isconveniently met by the useof symmetrical filters in boththe low-pass and the high-pass sections.

Linkwitz found that these re-quirements can be met by cas-cading two identical second -order Butterworth filters.Higher -order types may, ofcourse, be used, but in practi-cal applications these are lessinteresting. It should be notedthat in any case the filter mustbe an even -order type, sinceeach order causes a phase shiftof 45° at the cross -over fre-quency.

Fig. 1 shows the amplitude andphase shift behaviour of a But-terworth filter, and Fig. 2 thoseof a Linkwitz-Riley network.Note the 3 dB peak of the But-terworth filter. This can not beobviated by increasing theseparation of the cross -over fre-

quencies of the low- and high-pass sections, because thiswould violate the first require-ment of zero phase shift be-tween the outputs. For clarity'ssake, the two characteristics arecombined in Fig. 3 to highlightthe difference between them.

1

ALM)

-3-3

-27

-Is-11

-21

-742114 1111 Mr

"11.114120./ an

- In30

-120

--tn

87049-1

Fig. 1. Butterworth network: amplitude and phase characteristicsover the audio frequency range. The fat line represents the sumof the outputs of the filters.

VSU - 110

90

- ..e... . II

-..-ve

Fig. 2. Linkwitz network: amplitude and phase characteristicsover the audio frequency range. The fat line represents the sumof the outputs of the filter sections.

3

-17

-It

-71

- ButterworthUnkwitz

IliIr

Item :113, an

87048-3

11

Fig. 3. Butterworth and Linkvvitz characteristics combined tohighlight their differences. The networks used had a slope of24 dB per octave.

The Linkwitz curve is rathermore rounded in the vicinity ofthe cross -over frequency, andstarts falling off somewhatearlier. The slightly differentphase shift of the two filtersshould also be noted.The foregoing discussion istrue only if the signals aresinusoidal. The pulse (or step)response of the Linkwitz filtercauses the same problems asthat of a Butterworth filter,assuming that both filters haveseparate low- and high-passsections. Even a Linkwitz filteris therefore not perfect.

A practical filterA Linkwitz filter may be de-signed as a passive or as an ac-tive type. The circuit diagram ofan active design is shown inFig. 4: this may be constructedon the printed -circuit boardshown in Fig. 5. Note that thisboard is identical to that usedfor the electronic cross -overnetwork published in theSeptember 1984 issue of ElektorElectronics.The circuit of Fig. 4 is for athree-way loudspeaker system.The network has cross -over fre-quencies of 500 Hz and 5,000 Hzand roll -offs of 24 dB per octave.Stage AI serves as a buffer forthe input signal before this issplit three-way. The low-passsection is formed by A5 and AG;the middle -frequency sectionby A7 and At (high) and Al andAlt (low); and the high-pass sec-tion by Ali and Al2. Each sec-tion is provided with a poten-tiometer for setting the level ofthe output signal (Ps, P2, and P3respectively), and a stage tobuffer the output (A2, A3, and A4respectively). The powersupply lines are stabilized byvoltage regulators IC7 and ICt.The cross -over frequencies maybe altered with the aid ofTable 1 (any frequency) orTable 2 (the 17 most likely fre-quencies). The values inTable 2 have deliberately notbeen rounded off to the nearest

EE

April 1987

4

4.1N4C01

15V

15 V

Al A2 . ICI = NE55321(A3 ,A4 = IC2 = NE5532NA5 , A.5 1C3 = NE5532T4Al ,A8 ICANE5532NAS AID - ICS = NE5532N

Al2 IC6 = ressnrii

15V

15V

.. C13.= I=

878484

Fig. 4. Circuit diagram of an active Linkwitz filter.

5

II

04

tD

013 .LeveN. C12 .L

H Fo -6 0 C 6 0-11-0 0 0

I -2"

-6- 0114 1:r6 0-11-0 -6-,

cc U D

Cs

Cls-jit-° C11-° I N.3 C 2f3---430

6-II:Pc 20 0-1 P:, cis T E ..,,.

07 C25 011 Nib.

0-11-0 0-1 /-0 001R220 1=112143 CHR11 JO

C36°1 I-° 342)-1-LR23 HD Cr-I FO

C24°11110

' C31 C23CHio1(9).,. I C 6

orlons I C4

fionei 1 tnetritl i1

(D°-,,0

iciou01 it:7,0001,61000u0-1 R21 FO Fo 5 1.0

04R240 p 17F° .2.04 flic2 ac'-I

FO0-V1141-0

C30C34

B±_oClEt 017 C33C>i10 0.tR16 }CI^ C14°1 F°

Fig. 5. The printed -circuit board for constructing the Linkwitz filter of Fig. 4.

standard E12 or E24 value.The sections may also be givena slope of 12 dB per octave byusing As, As, A10, and Al2 asbuffers. Resistors Rio, 1111, Ria,and R19, as well as capacitorsC2; C28, C35, and Cie, are thenreplaced by wire links, whileRid, R15, R22, R23, C23, C2/, C3i,and C32 are omitted.The circuit may be adapted foruse with a two-way system bythe omission of the entiremiddle -frequency section, ex-cept for A3 which is housed inthe same package as A.t.If the slope is changed to I2dBper octave, the connexions toone of the loudspeakers mustbe reversed, because the phaseshift at the cross -over frequencyis 180° here. In a three-waysystem, this should be done atthe middle -frequency speaker:in a two-way system at thetweeter.A passive filter may be con-structed as shown in Fig. 6. Thevalues of the actual compo-nents used should be as closeas possible to the calculatedones. otherwise the filter willbecome a cross between aLinkwitz and a Butterworth

Fig. 6. Passive Linkwitz sections (a) with a 12 dB per octaveslope, and (b) with a 24 dB per oktave slope.

type. If the filters are given a12 dB per octave slope. the con-nexions to the middle -fre-quency loudspeaker (in a three-way system) or those to thetweeter (in a two-way system)should be reversed.The loudspeaker impedancemust be corrected in a mannerthat ensures that it is constantand ohmic at the cross -over fre-quency. The corrected im-pedance of the loudspeaker, Rin Fig. 6a and 6b, should be

ascertained as detailed in Loud-speaker Impedance Correction(EE, May 1986),

Table 1 low-pass section 12 dB, octave low-pass section 24 db/octave

IICA CA CC A1O

I=Cg

I C4 = Ca 1 12frfRwhere R=4.7-10 kQ

CeCo

IC4i = Cc= i 2121rfRCs= Co = 1 /212,rfR

where R=4.7-10 kQ

high-pass section 12 dB, octave high-pass section 24 dB/octave

R I 11111RA I

111141RC

c

Ic RI

C CC C

R B IRA = Re=1/2afCwhere C=4.7-10 nF

ReI"

R4 = Rc=1121217fCRe= RD --= 1 2/2r7fCwhere C = 4.7- 10 nF

Table 2

Low-pass 12 dB/oktave Low-pass 24 dB/ oktave High-pass 12 dB -octave High-pass 24 dB -octave

C=4n7C=4n7R= 5k6 R = 5k6

f (Hz) RA = Re !kg) f (Hz) RA= Rc(10) Re= RD 11(Q)I (Hz) CA= CH Inn 1 (Hz) C4 =Cc (nFl Ce= Co (nF)

100

200

300

400

500

600

700

800

1,000

1,500

2,0002,500

3,000

3,500

4,000

5,000

10,603

239

120

79.8

59.9

47.9

39.9

34/29.9

23.9

16

12

9.587.98

6.84

5.99

4.79

2.39

478

240

159.6

119.8

95.8

79.868459.8

47.8

32

24

19.16

15.96

13.68

11.98

9.58

4.78

100

200

300

400

500

600

700

800

1,000

1,500

2,000

2,500

3,000

3,500

4,000

5,000

10,000

284

142

94.7

71.1

56.8

47.4

40.635.5

28.4

18.9

14.2

11.4

9.47

8.12

7.11

5.68

2.84

100

200

300

400

500

600

700

800

1,000

1,500

2.000

2,500

3,000

3,500

4,000

5,000

10.000

402

200

134

100.4

80.4

6757.4

50.2

40.226.8

20

16.1

13.4

11.5

10.04

8.04

4.02

201

100

67

93.2

40/33.528.7

25.1

20.1

13.4

10

8.04

6.7

5.74

5.024.02

2.01

100

200

300

400

500

600

700

800

1,000

1,500

2,000

2,500

3,000

3,500

4,000

5,000

10,000

339

169

113

84.7

67.7

56.4

48.4

42.333.9

22.6

16.9

13.5

11.3

9.688.47

6.77

3.39

39 EE

April 1987

FACSIMILE INTERFACEby W A L Passchier

A multi -standard fax converter that is easy to build and set up,for reliable use in conjunction with any good quality SW receiver,

a BBC or 064 computer, and an Epson compatible printer.

Facsimile-or fax for short-is acommunication techniquewhereby graphic information isconverted into electrical signalsfor transmission to a receiverwhich, ideally, reproduces ahard copy printout of theoriginal. Facsimile stations canbe received on the short-wavebands, and are intended pri-marily for the transmission ofweather charts (meteorologicalservices), press photographs,and handwritten messages.A facsimile receiver is tradition-ally a rather complex electro-mechanical apparatus whichdoes not lend itself to DIY con-struction. Numerous radio ama-teurs, however, are the proudowners of Creed, Muirhead, orSiemens facsimile chassis ob-tained from surplus outlets at afraction of the original price.These machines are not gener-ally difficult to modify foramateur use, but remain fairlycumbersome to handle deviceswhen compared with the morerecently introduced computer -based versions.The electromechanical fac-simile receiver is generallybased on the recording of thereceived image either on elec-trolytic or on photosensitivepaper, secured on the outersurface of a revolving drum.When electrolytic paper isused, intensity -modulated cur-rent is fed to a metal styluswhich transfers the image ontothe paper. The photosensitivemethod is essentially identical,but uses a combination of alamp, an aperture, and a lens toilluminate the spots that makeup the received picture. Theintensity of the light beam, orthe current fed to the stylus,determines the density of theindividual pixels, giving thenecessary picture definition.Facsimile signals are mostlytransmitted as a frequency shiftkeying signal (FSK; denotationF4), similar to cassette -baseddata storage and retrievalavailable on many home com-

Facsimile interfaceFeatures: Crystal controlled sync circuit for reception of 1, 2 and 4 Hz

services. Immediate hard copy production on a graphics compatible printer. Fast software for BBC and C64 computers. Simple interfacing to userport (BBC) or expansion port IC64). Sensitive input (250 mVpp min. Cassette recorder interface for separate recording of SYNC pulses

and composite facsimile. Auto -sync and picture adjustment controls enable reception from

any fax track onwards.

puters. The centre frequency isusually 1900 Hz, and white andblack correspond to a fre-quency shift of +400 Hz and-400 Hz. respectively. At thereceiver side, a sheet of paperis secured onto a drum with astandard diameter of 152 mmand a minimum length of550 mm. A worm drive and

clutch assembly are used inconjunction with a precisionelectric motor to make thedrum revolve at 120 revolutionsper minute. Prior to the recep-tion of a new picture, the systemis synchronized with the aid of anumber of black lines with aninitial white period. as will beseen below.

After every complete revolutionof the drum, this is arranged tomove laterally for the recordingof the next vertical track. Apartfrom 120 rev/min stations. thereare also services that operate atother multiples of 60, e.g.,60 rev/min and 240 rev/min. Byconvention, a fax station is,therefore, often referred to as a1, 2. or 4 Hz service.The size of the picture elementsrecorded on paper is usually ofthe order of 0.1 to 0.2 mm,whence the use of precision -made mechanical parts in faxmachines.The facsimile picture shown inFig. 1 is purposely printed as itwould have been positioned onthe scanning drum of a conven-tional, electromechanical faxmachine. The writing of theweather chart proper com-mences on completion of anumber of drum revolutionsduring which the black lineswith initial white portions arewritten-see the black bar withthe white block in the top left-hand corner of the picture. Thecorrect horizontal aspect of thepicture as it is written onto thepaper is ensured only when thetransmitter and the receiveroperate at the same, or verynearly the same, clock fre-quency. If the receiver clockoperates at a fixed offset withrespect to that used in thetransmitter, vertical lines willappear to slant, causing the pic-ture to become confused anddistorted.The interface proposed in thisarticle is based on the use of acomputer and a graphics -com-patible printer to produce fac-simile pictures. Pixel data isread and loaded into a RAMbuffer on reception of a "drumadvance" pulse (or rather linefeed in the electronic version),which is derived from the inter-face clock. Eight fax lines areloaded to form a string of datathat can be printed horizontallyby a printer set to operate in thedot imacm mode.

EE

April 198740

as

Fig. 1. Example of a weather chart taken from the drum of a facsimile receiver.

The circuit is versatile-it canhandle signals from 1, 2 and4 Hz stations-as well as simpleto construct from commonlyavailable parts.

Circuit descriptionFigure 2 shows the circuitdiagram of the interface, whichtranslates the fax signal from an -SSB receiver into pulses thatcan be processed in a com-puter system.

Timebase.The central clock signal is ob-tained with crystal -controlledoscillator/divider ICI and themodulo -I0 dividers in IC2.Switch section Sia selects thesignal from IC, output Qs

(102,400 Hz), Qs (204,800 Hz), or01 (409,600 Hz) for propersynchronization with 1 Hz, 2 Hz,or 4 Hz stations, respectively.The signal at the pole is dividedby 100 in IC2, and made suitablefor recording as a sync track ona tape or cassette recorder with

2SS Ste, f-31 3.0TSA AUTO SYNC

PA CIATPAST

Si ti -41.1 S611)1 M}-lYt KC P.A.,'

-11--

gr it. 7-CS

731111S 4±14±-F.

SV

.1120

A

IA

A2

ur

SDI

V

O

013

noBCS17

.1.

PTEL FAX

IC2= 4535N1JN=K3= 033:1I044 1. 14HYZ =1CS = 4535At_ 1C7 = nemNS -H7 = ICS =1:25F11.112 =1C11-= 353

Fig. 2. Cifcuit diagram of the facsimile interface.

Parts list

Resistors I +5%):

RI= 100RR2 = 1K0

133:134;RI, =18K

115:F12:Rio =27K

Re;Ris =47K

R3:R22:Rts;Rzi;R22;R32= 10K

RcRzs;Rz4:R22=1M0

11,1 =2K2

R13 = 10M

R14 = 56K

Rio =12K1317:R27 =3K9

RI3=470RRao = 100K

Rzs =6K8

Rzs =220K

Rzs = 180K

Rao =33K

P,; P2 =100K presetPz= 470K presetPa =10K presetPs = 10K linear potentiometer

Capacitors:

Cl:CEC1D:C17:C25 =10n

C2 =68nC3;Cs;CECII:CIECtEC22:C25-,C27;

Czn = 100n

C4;Cli 10y: 16 V

CEC: =22n

Ci2=47nCt4:C23;C24= 100p ceramic

C15=65p trimmerCla =3n3

Cio =470nC2; =150n

Inductor:

LI= SM10-683 146151 68 mHvariable inductor

Semiconductors:

DI;D4D3=1N4148ICI =4030

1C2 = 4518

IC3;1Cs=4040

IC4 =4030

ICs=4538(Cs = TBA120S

IC r TL084

ICs =4025

IC,0=4047ICI, =4013TI:T2;T3=BC547

Miscellaneous:

Si = 2 -pole 3 -way rotary switch.Si = miniature DPDT switch.S3;54;55= push -to -make button.Xi = 6.5535 MHz quartz crystal. PC board Type 87038 (see Readers

Services).

C64 interface as per Fig. 3 (ifrequired).

K, = 6.3 mm socket for jack plug.K2 = 5 -way DIN socket.K3= 7- or 9 -way DIN socket.(Note: the stated sockets are

suggested types).Suitable metal enclosure.

' Available fromCirkit PLC;telephone (0992)

444111

the aid of networkWhether the system syncpulses originate from the inter-nal clock. or from the cassetteREPLAY interface set up aroundT2, they can be "speeded up"or "slowed down- by pressingS3 or respectively. When S3 isclosed, N3 receives an ad-ditional clock signal from theoscillator based around NI -N2.As N3 is an XOR gate, its outputfrequency is then higher thanthat of the system clock, andhence IC3 is clocked at a higher

rate, causing the LINE SYNCpulse to come sooner than nor-mal. Therefore. the pressing ofS3 forces the picture to shift tothe left; this is useful whentuning in to a picture whosesync bar has already beentransmitted. The amount of cor-rection can be set withWhen Sz is closed. T3 tem-porarily connects the inputs ofXOR gate lir., so that clockpulses from N3 can not advancecounter IC3. Hence theLINE SYNC pulse from MMV:

is delayed, causing the pictureto shift to the right. Preset P2controls the amount of right-ward correction.Depending on the position ofS2a. either the sync pulses fromthe REPLAY interface, or thosefrom the internal clock section,trigger monostable multivi-brator MMVi. which outputs thePIXEL SYNC pulses that have aperiod determined with R31 -C24 . The PIXEL SYNC signal isused to flag the presence ofvalid pixel data for the com-

3

U-r

FAXO

inFA X0-1F0

0 C 1°g X1

Ll

0 003.1F.0 C10

00- R10

f/7-19- \R B

R23R26

-0

-0-6-0-0

P BO S50 0-1P11 -0 *

00

U (5 +-ay

0'44EO 030-1R 27 FOP2 54

0

ofir.0 )99940,4C15

wc- Ct0ft)

CU Na a a a a 70-70 IF -AD 66666 db(L)

0.c180-1R19 rQC D

C 0

CC Di0 00 0000

F E Gi 1-0 0 0,,OI J 63

# 5 V0 A

D¢ r,0 C./

DD

IP.,

0-11-0 FOC13 C22

0P

0 4-

C82

Fig. 3. Track layout and component mounting plan for the FAX interface.

puter to read from the PBO line.This ensures the correct com-pilation of pixel data for theprinting of one 8 -bit wide lineon the printer.

Automatic synchronizationcircuit.The RESET input of counter IC3is driven with a signal obtainedfrom an automatic sync gener-ator composed of IC10, N5, FF1 &

FF2 , IC3, and N6 -N7. Depressionof SO forces resetting of IC3 togenerate a LINE SYNC pulsewhen the transmission of thepicture commences; after somepractising, you will be able tohear when this happens bycarefully listening to the re-ceiver's AF signal. When SO isopen, the circuit detects theprolonged absence of pixeldata during the writing of theblack vertical lines to the left ofevery picture. The white inter-ruption at the beginning ofevery black track, however, isrecognized as the absence ofpixel data during 32 clockpulses. For the_auto-sync circuitto produce a LF pulse, it mustdetect 32 successive whitepixels. i.e., noise and spuriouspulses can not cause erroneoussynchronization.

Tone decoder.The fax signal from the SSB(single side band) receiver, orthe cassette recorder, is ap-plied to quadrature FM de-modulator IC6, the well-knownType 113A120S. This demodu-lator is tuned to a centre fre-quency of 1900 Hz with Cs andvariable inductor L. The rawfax signal from the demodulatoris cleaned and shaped with theaid of a 47 n capacitor, C12, andactive low-pass filter At. set upas a second -order Butterworthsection. Besides faithfullyremoving noise and spurioussignals from the facsimile infor-mation, the active filter has anadditional advantage in that itproduces a certain amount ofovershoot that is useful for rais-ing the contrast level of theneedle -shaped pulses. OpampA2 is a simple amplifier withpresettable gain, and A3 is thepulse shaper that decides be-tween the black and whitesignal levels. The pixelfax datafor the computer port line isoutput by level translator T1.A power supply is not includedin this design, but we are confi-

4C64

Expansion port

+5V+5V

DOTCLK

02

RES

Ric/

DO

1:11

D2

0304

05

D6

D7

AO

AlA2

A3

101102

DUD

0110

00

5V

0

5 3

4

0

cur a

FF1

13--_

ty

0

0

5

Al

20

22

21 33

00

20 329 31

0 18 30

0000

0

17 296 2

5 214 25

38

00

37w 36

0 V

00

00

7

00

0

CAIC'ClA2

VIAR55 6522Rw

PAO

D

DO

PA1

02 PA2D3

PA4P

05 PAS

PAS

D7 PA7

RSO

RSIRS2s

C

C81

C82

P80

40

74L574

ICentronics

39

2 2

3

4 4

-O0

00

5 5

67

a 8

9

19

FF1 = 1/21C2= 74L574

20

24

25

26

29

30

21

22

23

2728

00000

0

0

0

00

00

0

0

0

ACKN

STROBE

DO

DI

02

0304

D5

D6

07

DATAPARALLELOUT

PIXEL SYNC

UNE SYNC

PIXEL FAX

GND

CND

Fig. 4. Construct this interface circuit if you have a Commodore C64 computer.

dent that the omission will notpresent insurmountable prob-lems. A suitable supply can bea very conventional circuit setup to deliver 12 V and 5 V atoutput currents of the order ofseveral tens of milli -amperes; aType 7812 and 7805 voltageregulator fed from a commonmains transformer will do ad-equately in this case, while youmay also consider taking the+ 5 V and +12 V from the com-puter's built-in supply, assuggested in the circuit dia-gram.

Construction andsetting upThe use of ready-made circuitboard Type 87038 makes theconstruction of this fax interfacelargely a matter of routine;simply fit all the parts as shownin Fig. 3. There are no specialprecautions for the completionof the interface board, as thisholds standard componentsonly. However do not forget toinstall all eight wire links on theboard. as these are easily

overlooked due to the whiteoverlay lines that indicate theposition. Fit the interface boardin a metal enclosure and usewhatever sockets and matingplugs you think suitable for theconnections to the receiver andthe computer.For the setting up of the inter-face you need a good qualitySSB receiver tuned to a strongfacsimile station. Alternatively,you may find the use of re-corded data available fromcassette more convenient; drivethe interface from the cassetterecorder's external loud-speaker or earphone outlet byconnecting this to RI. Later on,you will be able to use IC2 for re-cording and playing back of thedata and sync, recorded separ-ately on the left and right trackof the tape.Set P3 and Ps to the centre oftheir travel, and PI for minimumamplification (wiper turnedfully towards R6). Presets PI andP2 are adjusted to personalpreference, and can be set tomid -travel initially.Trimmer capacitor CIO is ad-justed until the vertical lines on

the hard copy page run straight;a slanting line indicates that theclock frequency needs furtheradjustment. For a precise set-ting of the demodulator centrefrequency. apply a 1600 Hzsinewave to the interface, andmeasure the direct voltage atthe output of A2. Turn the corein Li to find the adjustments thatgive a maximum and a mini-mum value on the voltmeter,then carefully turn the coreback to obtain a reading thatlies exactly in between thepreviously noted extremes.Now adjust P3 and PI to set theextremes to 4 and 8 V, and redothe adjustment of LI.

At the computer sideMachine language routineshave been developed to enablethe use of the fax interface witheither a BBC or C64 computer.The programs essentially ac-cumulate data in a buffer andredirect this to the printer.The connection to the BBCcomputer is extremely straight-forward by making use of thebuilt-in user port. The Com-

43 EE

April 1987

LIST18.17Eren.71.0:MSUICK25.Xtr&-..471.1:1910.Mal2e.rly5e7_:m250.918F1TFOUl70THENCOT0104301'01022,2,PRINTTA812.51CHRS129-f8-CNI11135,3178I01-- start program In normal lade -TA1112.71EHR1124-11 -C11118.13S,3279INT-- start program in inverse node -TAB12.133,3308I07- halt program with .BAIAX. -TAB125.2111 -.RETURN. --,34REPEATC.CETAIRTILC.13,71,71.0-130201003548 (Cl Euxion 30 June 196545Se connect pixelsync to COI52 ...erect linosyoc to C8253 connect pirelfax to PEW6070 FACAIAlle docOdIRA routine for I 4 2 Hs stations

90100000A 17E631100098 = AF11621211PA . 41E6113102 = 47188140ACR . 12768150PC9 = 4Ft6C1641011 = 17E6017e1t9 = 17167ISIMLITE = 1FF*01902001.101147,81NE1.17e00205S111 OF 14007 32069EN Of NODE 7 HINES c 17100210018 NC% 600228709 05.0 TO 2 STEP2380S.14cs248(2C5OPT OR250 BEGIN 5E1260 LDA VIM STA ley \ clear printerbagers270 LOA !tee STA 187260 TAT29e LDX 8478Me AA STA 16871.9310 1NT32e EKE AA318 INC 11734e CPX &BF360 ENE AA374 STA P3I8T1.1 \ initialisation

380 STA POINT2.1331 LDA 8174 STA 472 6 default

382 LOA 8170 STA £74

384 LDA 1174 STA /75

386 LDA 8424 STA 476390\4e0 LDA /lee . STA 0098.le LOA 9117 . STA DORA120 LDA 9188 STA 7CR430

LOA 0403 STA ACR45e LOA SIVF STA IfF.6e LDA fAiS /SR PRINT.70 LOA 0105 /SR PRINT.8e LOA $108 JSR PRINT \ Linefeed 8/72 inch495 LDA /400 STA 472446%5110 LOA Isle51e LDA 5040628 LOA 905,0536 LOA 110]

640 ma.a. ASL to560 BCC RESTB555 SNP ERR560 RESTS SEC570 SON 172569\64e LDA 173

610 SIX 124620\630 LOA /75110 STA 175668\6606re688690645144\

LOX 8140LOT 1/1.3CLOA flOD111* 8108LDA flee

\ P8 all input\ PA all Owtlwt . Print\ C82 10.1. indagoodent . CS1 IN L\ CA2 OUT handshake CA2 10 L\ PS latch en. PA latch en.\ BIT 7 set with IM

Status printer. tat 7 set as tansy

STA 17035 STA 117430STA 17030 STA 17430STA 17037 . STA /7437STA A7037 . STA 47837

\ double density\ 128 dots/In. For 960 byres

ready for printing

. TAX : LOA 174STA P0INT1.2STX POIN12.2 \ -rapped begin buffers

TAX LEN /lbSTX 176

STA PASTA £70STA 1NFR

...Fred eta buf ferr.

\ rotate ASS.X\ print ASS.T\ force CO to set CAt\ ready for 8 tines\ clear CO2 . liresync

710.WAITW- LDA (018220 APO $1461720 BED WAITNS

\ mask CS2 . liseernt

760 LDA 847D STA TIFFS \ clear flogs except CAI/50\760 -FAST LDA INFR STA 180 SOL A770 BCC FAST780 LDA LDS791 AND $0.18 \ sash CBI pixel clock800 BRE PIXEL810 LDA 480 , AND 5102 \ reek printer ready820 5I1 POSTE83e 3SP FAST15.0\

850.PIXIL LOA P8 , ECe 171 lay/Tans byte

864 LSS A871300I51I ROL EUFV.X880 Dec494 EKE FASTBee910sze9309.0960450478%968.195TTE ASL A72BO* BCC FASTeft. 006 47781O 00I512 LDA SUFF.Teta STA PA Print tote934 IMe48 BKE FAST*58 INC POINT2.2060 LOA 00I0T2.2078 CRP 176 \ end of buffer?080 Ira FAST090 ASL 172Ube JWP FAST190%204.79INT STA PA210 READ LOA SATS AND $182 \ mask CAI , Printer eeeer220 Ste READ230 ITS240\250.ERN CLI260 SRI270 EOL93 4FF error maser280 SOUS -Prin.,r orcrrun error -284 EOUD 1104304eA07207 IOUS -Please pros ,FRFAx.-288 (MUD [80010...0A289 EOUS -Program290 EOUB 480 close error ...Ins

300\364 Erb CLI RTS40014111TIECT424fRINT-Facsiiilly denuder for i 2 H. ntAtio.SA3ACALL BEGIN

INC 00I511.2LOA POIN11.2 CRP 176 \ end of buffer?IKE FASTDEC ATV , 8E0 SWAP \ if 8 lines readLOA /73 - STA POI511.2 \ else point to begin ofLDY sue \ and restore X to 168ATP WAITNS

iarefe01 high byte pointer

\ not if status.0\ t-Clote status

buffer

Finished Printing I:offer, RteTwx.e

LIST 735.99e735 UZI THIS SOUTINE ION 4 11= STATIONS736748 RESIT LDA 917D751\7641 FAST LOA WS771 Sin FAST858 PIXEL LDA FS068 LSV A070-701512 POL NUFf.Xnia INS890 BSI FAST

410 LDA 70I011.2 Cie 175926 BWE FAST931 DEC 470440 LOA 473954 LOX elAit960AWITTE LOA INFR965 BrE BESET970 LOA SAO : AND 1402975 BED PETRI908 ASS 8.72990 BCC WAITNL

STA DOR

: AND $1.10

EOR 671

clear flaws except CAI

5 mask CS& pivot clock

\ lov/ninv byte

\ hith byte Painterand oiAtuffer?

. EEO SWAP N. if 8 line. read

.STA 70101I.2 \ else point to begin of buffer

\ and restor X to ENSTA 480 - AND 0408 mask NI.

salt printer ready

\ not if mlAtuAm0

Table 1. Facsimile decoding program for the BBC computer.

Table 2

1 If peekr4440951=7716+6then4010 for 1016384 to 1667320 readarpokei.a30 ne5,140 t:_. -.c chrS(147);- fax -decoder elektor 564'-50 rr,,,60 r::,, rrmgra= can not be interrupted with-;70 r:.:- ._1 of the c54 keyboard.80 pr -In._90 print -however swItchins the printer to °Mince%100 prInt"will halt the progran after some tine. -110 print"and return control to basic. -120 print125 print130 print -select between printing nodes:" print140 print" normal lel-150 print" inverse4I/-:print160 print -enter your choice.please-170 getaS:if and aS<>n- thenl7O180 if aS.-1" then poke57161.8.255190 if aS=-n- then pcke5716.8.0200 sys41409632000 data120.169.112.133.143.169.0.133.142.168.162.120.145.142.200.208.251.23032001 data143.228.143.208.245.141.215.64.141.251.64.169.112.133.90.169,116.13332002 dana91.169.116.133.92.169.120.123.93.169.0.141.8.222.169.255.141.3.22232003 data169.8.141.12.222.169.3.141.11.222.169.255.141.14.222.169.27.32.18.6532004 data169.65.32.18.65.169.6.32.18.65.169.0.133.189.169.27.141.60.112.141.6032005 data116.169.78.141.61.112.141.61.116.169.192.141.62.112.141.62.116.16932006 data3.141.62.112.141.63.116.6.89.144.3.76.29.65.56.102.89.165.90.170 . 16532007 data91.133.90.141.216.64.134.91.142.252.64.165.92.170.165.93.132.:,432008 data93.162.64.160.60.169.13.141.1.223.169.6.133.67.169.6.141.13.2i:.32009 data13.222.41.5.240.249.169.12.:4: L:'.277.173.13.222.133.94.42.144.24i.32010 data165.94.41.16.203.9.165.94.4' -6.185.64.173.0.222.69.88.7432011 data62.0.120.232.205.221.236.2:,.; ,:--..7,0.197.92.208.211.198.87.240

32012 data143.165.9r.:1' 7:-.144.193.102.89.185.0.112

32013 data141.1.222.Z...=1:.:,2.238.2I.,32014 data185.64.141.I.28.1..173.13.222.240.249.86.88.108.2.160.25.65.17332015 data25.65.205.118.0.208.182.14.::4.0.76.205.64.141.1.222.173.13.222.4132016 data2.240.249.96.88.0.88.96.76.:1-64.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0ready.

87038-72

Table 2. Facsimile decoding program for the C64 computer (not suitable for 4 Hz stations).

modore C64. however, requiresan extension port interface asshown in Fig. 4. This circuit isso simple that it is readily con-structed on a piece of proto-typing board, connected to thecomputer by a short length offlat ribbon cable terminatedwith an expansion port con-nector.The software for the BBC microis an assembler -in -BASICprogram listed in Table I, whilethat for the C64 appears inTable 2. and makes use ofmachine language POKEd intothe memory and called up witha SYS command. Both programscan only be halted with ageneral system reset; on theBBC the program is automati-cally restarted with an OLDcommand, on the C64 it iserased from the memory, andmust be reloaded from tape ordisk. Reception of 4 Hz stationsis not possible when the C64computer is used.

EE

April 198744

1 Table 3

Facsimile stations

Frequency Callsign Operating(kHz) hours (GMT)

Mode Note(s)

Bracknell, England (2 Hz)2618.5 GFE 25 21.00-3289.5 GFA 21 00.00-24_004610.0 GFA 22 18.00-4782.0 GFE 21 00.00-24.00

WXWXWXWX

APT 09.00-12.00GFA 21 slaveAPT 09.00-12.00

Mainflingen, Federal Germany (2 Hz 8- 4 Hz)117.4 DCF 37 00.00-24.00 WX134.2 DCF 54 00.00-24.00 WX/MET

Paris. France (2 Hz)8185.0 FZE 82 00.00-24.004047.5 FTE 4 20.00-

12305.0 FTM 30

WXWXWX

special formatFZE 82 slave

Moskow, USSR (1 Hz)5355.0 RND 77 18.00-7750.0 RAW 78 16.00-23.00

15950.0 RBI 77 10.00-21.00

WXWXWX

Frankfurt, Federal Germany (2 Hz)139.0 DCF 39 10.00-22.00 PIX

WX = weather chart transmissionsMET = METEOSAT occlusion charts

APT = automatic picture transmission1 Hz = 60 rev./min. 2 Hz = 120 rev. /min 4 Hz = 240 rev.!min

Table 3. These are only a few of the dozens of FAX stationsoperating in the European part of Region 1.

Getting started withfaxWhen you have completed theinterface, aligned it, and havekeyed in the software, it is timeto see what the while set-up iscapable of doing. As alreadystated, you need a SSB receiverto pick up the signals fromamateur and professional faxstations. This receiver shouldhave a reliable BFO (beat fre-quency oscillator) to enableprecise tuning to the oftenweak signals. After a while, youwill be able to unhesitatinglyselect the typical buzzsaw-likefax signals from the loud hub-bub that generally exists on theovercrowded short-wave bands.Table 3 lists a number of fac-simile services that can be re-ceived throughout Europe.There are many more stations inoperation, but these are gener-ally run at relatively low outputpower and intended for veryspecific use only.The use of the BFO in conjunc-tion with the proposed inter-face requires some practisingto develop a feeling for ob-

taining the best definition of thereceived pictures, and this alsogoes for the operating of cor-rection controls S3 and S4. Thebest way to gain experience infax reception is to make record-ings of both weak and cleartransmissions, and play theseback into the interface, so that asignal is constantly availablewithout the need to re -tune thereceiver if a service signs offjust when you intend to makethe final adjustment... St

CORRECTIONSDual variable supplyApril 1986, p. 32 ffTo prevent exceeding Vgsirnao of powerMOSFET Ti when the supply is set tothe maximum output voltage, it is

suggested to fit an 18 V; 400 mW zener-diode across the A -K connections ofThi.

High power AFamplifierMay 1986. p. 65.The suggested heat -sink should be theFischer Type SK93, not the SK39 asstated in the parts list.

True-RMS meterDecember 1986, p. 45The correct signal assignment for thecontacts on S6C iS: Sec contact a =Op 2; Sec contact b = Dp 1; Sec con-tact c = Dp 3.

COMPUTERSCOPE-2(October 1986)Hard copy of the screen image may bemade in one of 3 ways:1. Write the screen contents into a disk

and print it later2. Use a printer with an RS232 interface_

3. Use the Electron interface on the BBCto free the printer port.

Figure 10 of the article is wrong in several

areas and should be replaced by newFig. 10 shovm here.

PRINTER

PA 0

PA

PA 2

PA3

PA 4

PA 5

PA6

PA7

READY

P87

P8663

PBS

P84

P8 3

PB2

Pa 1

P80

DRIVE -UNIT

USERINPUT/OUTPUT

86100-10

45 EE

April 1987

WHERE ELECTRONICMESSAGES HAVE THE EDGE

by Barry Fox

The new age of infor-mation technology isfounded on one simpletruth. It is quicker, easier,and cheaper to sendpulses of electricity downa telephone wire or over asatellite link than it is totransport people or pack-ages by road, sea or air.The telex service has untilnow been the standardmeans of sending text.Telex is a reliable warhorse but has its ownsnags. The equipmentis bulky and expensive,trained operators areneeded to send mess-ages, and the servicerelies on dedicated lines- that is to say specialcircuits designed to carrytelex pulses rather thanspeech.It is still not widelyrecognized that almostevery personal computer,either desk top or port-able, can be used forelectronic mail throughone of the available ser-vices. It is the modernalternative to sending cor-respondence by telex. Textis sent from one computerto another along a con-ventional telephone linevia a central message -handling computer.Already script writers,translators, bankers,journalists, and lawyersare using electronic mailto send text from home tooffice. Sales teams use itto keep in touch with theirheadquarters while mov-ing round the country. Mu-sicians use it while on tour.Electronic mail terminalscan work equally wellfrom an office desk or ahotel room far away.

Digital pulsesIn its simplest form, ahome computer sendsmessages either to thescreen or to a printer. If it

is programmed with ad-ditional communicationssoftware, it can sendsimilar messages from itsoutput - usually an RS -232- socket. This output is inthe form of a stream ofdigital pulses, similar totelex, but much faster.They can be sent down ashort wire cable to amatching computer sys-tem. This is how severalcomputers are networkedin an office. The pulses willnot travel reliably down aconventional telephoneline so they must first beconverted into audibletones which the telephonenetwork handles likespeech.A special device called amodem - short for modu-latorldemodulator - isneeded to convert thecomputer pulses intosound tones. It is connec-ted between the computeroutput and the telephoneline socket, while a corn-

puter at the other end ofthe telephone line has amatching modem.This converts incomingtones back into digitalpulses which are thendisplayed on the com-puter screen or printed onto paper.

Four servicesElectronic mail providesa mail -box system intowhich messages can bedropped by one user tobe picked up later byanother. A host computerhandles the messageswith a system of passwordsto ensure that messagescan only be picked up bythe people to whom theyare addressed.In Britain there are fourelectronic mail services.The most successful so faris Telecom Gold which isrun by British Telecom andhas around 30 000 sub-scribers. Rival services are

Alan Freeman, Britain's western region sales manager atTelecom Gold, uses his electronic mail -box to communi-cate with customers and colleagues.

offered by Easylink-a sub-sidiary of Cable andWireless; Comet fromlstel-a subsidiary of BritishLeyland; and One-to-One-a private companynow owned by UnitedStates Telecom's companyTelesis. Each of these ser-vices offers a messagedrop facility.When someone workingfrom home or a hotelroom wants to contact anoffice, he or she calls therelevant electronic mailtelephone number andsends a message which isheld in a message ser-vices computer. Later, theperson at the office callsthe same electronic mailnumber and reads themessage off the computer.The text can be viewed onscreen, stored on mag-netic disk for subsequentword processing, orprinted direct on to paperlike a telex.Any office wanting to useelectronic mail should firstfind out what services areon offer. The Telecom Goldservice in Britain is derivedfrom the ITT Dialcom sys-tem developed in theUnited States of America. Itis now used in over adozen countries aroundthe world, and is provingincreasingly popular.

How to buyMost businesses thatdecide to install an elec-tronic mail system will findit cheaper in the long runto buy the hardware andsoftware through a dealerwhose purchase price in-cludes the cost of instal-ling the equipment, get-ting it up and running,and teaching the staffhow to use it. Once asystem has been installed,staff may very soon won-der how they ever livedwithout it.

9S7

FF46

NEW LITERATURE NEW LITERATURE

Radio WavePropagation(HF bands)by F C Judd G2BCXISBN 0-434-90926-2Soft cover146 pages - 215 x137 mmPrice: £8.95This new book will be appreci-ated by short wave listeners andradio amateurs for its detaileddiscussion of the numerousaspects of an ever fascinatingsubject, radio wave propa-gation.The author, F C Judd, is wellknown among the radio ama-teur fraternity for his publi-cations covering the design andconstruction of aerials.The book starts with an historicaccount of the discoveriesmade in the field of experimen-tal propagation research, withspecial attention to the work ofE V Appleton. Then follows a

of thephysical aspects of ionisation,refraction, the conditions of theweather and the ionosphere,diffraction, and echo times. Onthis is based the definition ofthe various layers that are nowknown to constitute the iono-sphere, each with its particularbehaviour for radiowaves. Thissection of the book, like theones to follow, is copiously il-lustrated with graphs, charts,and oscillograms to aid in mak-ing the discussed subject aslucid as possible.The chapters on the eleven -yearsolar cycle and ionosphericanomalies present a well-founded argument in favour ofthe need for observation andsubsequent interpretation ofthe effects these phenomenahave on world-wide radio con-tacts.In the chapter on ionosphericradar systems the author tacklesas subject that is still full ofmystery to many. There aregood introductions into theworkings of OTHR (over thehorizon radar), both asemployed by the American andRussian military authorities. Es-pecially the section on thenotorious Woodpecker, thepowerful. Ukraine -based wide -

band radar, unravels some ofthe system's technical proper-ties by means of a close analysisof the pulse structure.The chapter on the function ofthe transmitting aerial providessound advice for radio ama-teurs on how to dimension aparticular aerial system for opti-mum directivity, which, in thecontext of short-wave propa-gation, is quite different fromthe methods that apply to VHFand UHF aerial design. With theaid of a number of well -detailedgraphs, the author showsbeyond doubt that the aerialradiation pattern can betailored to obtain an illumi-nation area in a specificionospheric layer, with an aimto use this for its propagationcharacteristics.All the theory presented in thebook is put to use in the lastchapter on F -region propa-gation data. There are tables,graphs, and questions andanswers to demonstrate howradio amateurs can utilize thisionospheric region for best DKIn conclusion, the book is an in-dispensable aid in understand-ing the mechanisms of radiowave propagation, and de-serves a place on any radioamateur's bookshelf.William Heinemann Limited10 Upper Grosvenor StreetLondon W1X 9PA

The Slow ScanCompanionby C G Dixon G8CGK, J WoodG3YQC and M WoodingG6IQM.100 pagesPrice £3.50 (Soft cover)Slow scan television (SSTV) isessentially a method to transmitpictures at a bandwidth that isgreatly reduced with respect tothe normal television broadcastservice. Throughout the years,radio amateurs have worked onimproving a technique thatwould enable them to send andreceive pictures world-wide,i.e., farther than would be poss-ible when working with wide -band television on 70 centi-

metres and up. There are nownumerous radio amateurs allover the world who delight inreceiving and transmittingSSTV images, and this newbook will be hailed by them asa comprehensive study ofgeneral aspects as well as up todate practical designs of SSTVequipment.The writers have included asection on commercially avail-able SSTV equipment, andSSTV based on the use ofvarious types of home com-puter, but have not forgottenthose many enthusiasts whowould like to build their ownSSTV transmit and receive con-verters. These converters arestate -of -the -an designs whoseoperation is set out in clearlywritten circuit descriptions, fol-lowed by constructional detailsand a suggested calibrationprocedure.It is fair to say that the bookcovers all aspects of construct-ing SSTV equipment, from thecomplexity of the digitalmemory to the straightforwarduse of, say, an EHT powersupply. Therefore, readers ofany level of proficiency inbuilding electronic circuits willhave no difficulty in findingsuitable designs for the variousbuilding blocks that make upan SSTV receiver or a transmit-ter.

BATC Publications14 Lilac AvenueLeicester LE5 1FN

ComputerEngineer'sPocket Bookby Michael TooleyISBN 0 434 91967 5Price: £8.95 (hard cover)203 pages - 196 x 95 mmThis third in the series of re-cently published Newnespocket books is a most wel-come reference compendiumof facts, figures, circuits, anddata for designers, students,service engineers, and all those

interested in computer andmicroprocessor systems.To be able fully to exploit thepotential of microprocessorsand microcomputers, it is be-coming increasingly necessaryto abandon the old, and some-what rigid, boundaries be-tween hardware and software.Within industry, there is alreadya growing demand for softwareengineers. These crusaders ofthe information technologymovement are not primarilyprogrammers, nor are they ex-clusively electronic engineers.Their talents lie with the inte-gration of software and hard-ware into functional and op-timized systems.The skills required of these in-dividuals are difficult to define,but they centre on an aware-ness of, and familiarity with,electronic and microelectroniccircuitry, coupled with a de-tailed knowledge of pro-gramming in either assemblylanguage, or an appropriatehigh-level language. In ad-dition, some knowledge ofcomputer interfacing and com-munications is highly desirable.Newnes Computer Engineer'sPocket Book aims to provide thesort of information such in-dividuals require daily, but it isalso of value to software andhardware specialists.A pocket compendium cannever replace standard worksor detailed specifications, butthe present book covers a vastrange of subjects at a practicallevel with some explanatorytext in appropriate places.Once purchased, it will, nodoubt, soon become as much apan of the student's or practis-ing engineer's toolkit as hispocket calculator.William Heinemann Ltd10 Upper Grosvenor StreetLondon W1X 9PA

47 EE

April 1987

NEW LITERATURE NEW LITERATURE

NewcataloguesCatalogues listed here maynot be free of charge,although many of them are.Furthermore, some busi-nesses whose catalogue isincluded may deal withtrade or professionalcustomers only; where thisis known, it will be indi-cated by "TRADE ONLY".

Electrovalue catalogueWith more pages (sixty), more -items. more illustrations. Elec-trovalue's latest catalogue istheir best yet. This catalogue(Spring issue) with its attractivegreen and black cover is noweven easier to refer to. particu-larly when it comes to findingthe transistors you want out ofthe hundreds listed. The sameis true of the seemingly endlessnumbers of other items soughtby anyone interested in elec-tronics today.Items range from spacers tocomputers, software, and opto-electronics; many are bySiemens whose componentsare world renowned for theirquality and variety.Consistent with Electrovaluepolicy, this latest catalogue isfree to whosoever would like tohave one. Prices are quotedthroughout and remain constantat least to publication of thenext issue in about four months.You do not even need to stampyour envelope when writing fora free copy of this latestcatalogue. Simply address yourrequest to Electrovalue Ltd.,FREEPOST, 28 St. Judes Road,Englefield Green, Egham, Sur-rey, TW20 8BR or phone Egham(0784) 33603 and it is sent you byreturn.

Greenweld catalogueThe 1987 Greenweld catalogueis a single source for an exten-sive range of electronic kitscatering for all abilities: fromthe novice to the professional.It contains amplifiers; transmit-ters; receivers; power supplies;

panel meters; timers; doorbells; running lights; sound -to -light units; dimmers; and manymore, together with an exten-sive range of computer inter-faces that enable most popularcomputers to be linked with theoutside world.

Greenweld ElectronicComponents443 Millbrook RoadSouthampton SO1 OHXTelephone: (0703)772501/783740

Stetomike headsetsA new full -colour informationpack on the British ApprovalsBoard for Telecommunicationsapproved Stetomike telephoneheadsets is available free on re-quest fromGN Danavox (Gt Britain) Ltd1 Cheyune WalkNorthampton NN1 5PTTelephone: (0604) 36351

A 28 -page booklet detailing theprocedures a user needs CO

follow to use a BBC microcom-puter via the GPIB interface soas to communicate with, andcontrol, Solomon's 1250 Fre-quency Response Analyser,FRA, is available fromSolartron InstrumentsVictoria RoadFarnborough GU14 7PWTelephone: (0252) 544433

Imhof has just published a fullcolour catalogue covering itslatest major product introduc-tion. the Image case range.The Image case range consistsof two product types, 19" Casesand Cased Cardframes, whichhave been designed to beaesthetically pleasing, versatileand functional.The 8 -page catalogue gives fulldetails of sizes and depthsavailable. panel options. ac-

cessories, with complete tech-nical specifications for theentire range, and is organisedto make choice and ordering aseasy as possible.Imhof-BedcoAshley WorksAshley RoadUxbridge UB8 2SQTelephone: (0895) 37123

Verospeed's comprehensivenew product catalogue hasbeen expanded with over 800additions to the existing 13,000lines covering all product areasfrom electronics and com-puters to tools, cables and pro-duction equipment. Copies ofthe catalogue can be obtainedfree of charge fromVerospeedStansted RoadBoyat Wood Industrial EstateEastleigh SO5 4ZYTelephone: (0703) 641111

National Semiconductor's lineof surface mounting ICs is de-tailed in the 34 -page brochureSurface Mount ProductAvailability Guide, which liststhe most important data on eachproduct. It includes analogueICs, gate arrays, interface cir-cuits, logic components, mem-ory chips, microprocessors,and discrete transistors inSOT -23 and SO -8 packages.

National Semiconductor(UK) Ltd301 Harpur CentreHome LaneBedford MK40 1TRTelephone: (0234) 47147

EE

April 198748

RIMS: COUNTING ATOMSby Dr Kenneth W. D. Ledingham, Department

of Physics and Astronomy, University of Glasgow

Resonant Ionisation Mass Spectroscopy (RIMS) is a unique,ultra -sensitive analytic technique which can detect down to the

level of a few atoms. It is applicable to any sample, whethersolid, liquid or gas and can be used to assay every element inthe periodic table apart from helium and neon, as well as any

stable or radioactive isotope. It is likely to find importantapplications in fundamental and applied physics, and to

become a valuable tool in the semiconductor industry andin diagnostic medicine.

The need to develop newanalytic ways to measure ultra -trace quantities of elements invarious substances is becomingurgent in many branches ofscience. engineering andmedicine. There are alreadymany sensitive analytic tech-niques, including neutron orphoton activation analysis, in-ductively coupled plasmaspectroscopy. atomic absorp-tion and various kinds of massspectroscopy, particularlysecondary -ion mass spec-troscopy (SIMS). The sensitivityof these techniques for traceanalysis is usually limited to theorder of parts in 107 or 10B.In the last few years problemshave arisen that require ultra -trace analysis at the previouslyunheard-of sensitivities of partsin 109 to 1052 or even further.Already three areas which re-quire such analysis have beenidentified and as techniquesare developed many more ap-plications are likely to becomeapparent.Firstly, it is essential to reducethe minimum detection limit ofimpurities in silicon if improve-ment. especially in miniaturis-ation, of the semiconductormanufacturing process is to bemaintained. Secondly, Pro-fessor M. Baxter of the ScottishUniversities Research andReactor Centre, near Glasgow,has speculated whether there isa health risk from the presenceof very low -activity p emitters inthe environment. They are verydifficult to monitor becausethey are likely to be below thesensitivity range of conven-tional nuclear counter tech-niques.Finally, the presence of trace

amounts of certain elements inhuman body fluids and tissuesis considered to be essential tohealth. This is a poorly under-stood branch of biochemistryand widely divergent figuresfor trace metal concentrationsin apparently healthy peoplehave been published. But thereis growing evidence that manyof the studies are flawed bygross analytic inaccuracies andthat new, reliable techniquesare necessary at sensitivitylevels of parts in 109.During the middle and late1970s the possibility of applyinglaser techniques of single -atomdetection to ultra -trace analysisattracted interest. The tech-nology had been pioneeredlargely by Professor V. S.

Letokhov of the Academy ofSciences in Moscow and Pro-fessor G. S. Hurst of Oak RidgeNational Laboratory, USA. Res-onant Ionisation Spectroscopy,RIS as it has come to be known,can detect one atom of aspecific type in a backgroundof 1016 others in gaseous phase.The implications of this degreeof sensitivity for many disparatefields of research are likely tobe enormous.

Resonant IonisationSpectroscopyWith the development of in-tense, tuneable, pulsed lasersthe simultaneous absorption ofseveral photons by a singleatom or molecule to produce afree electron and a positive ionbecame experimentally feas-ible.In the simplest RIS process. apulsed laser is tuned preciselyto the wavelength required to

excite the atom or moleculefrom its ground state of energyto an excited state that is uniqueto the element under study. Asecond photon. of the samewavelength and from the samelaser pulse, interacts with theatom in its excited state andcauses an electron to be re-leased from it, thereby creatinga positive ion. This process canbe made more selective by ad-ding further resonant steps inthe excitation process. using asecond laser tuned to anotherfrequency. Five different laserschemes, represented in thefirst illustration. can ionise allthe elements in the periodictable, except helium and neon.From left to right in the diagramthey are:(a) A((zi,w "-

This reaction means that twophotons of the same wave-length (that is, with angularvelocity cr1) create the ionpair.

(b) A(2 w

The laser wavelength is fre-quency doubled into theultra -violet and then mixedwith the fundamental tocreate the ion pair.

(c) A(colcor.wi or core -)AIn this process threephotons are absorbed withtwo colours being involved,indicated by co and 4.2.

(d) A(20.),, w1w2e-)A-One colour is frequencydoubled (2w1) and anotherphoton of a second colour isabsorbed as well as one ofthe original photons.

(e) 0.1 te-)A -

In this case usually threephotonsof the same colourare absorbed to create theion pair.

The second diagram is theperiodic table of elements withone of the five schemes beingascribed to each. after Pro-fessor Hurst. In the early days ofthe technology, the electronscreated in the resonance pro-cess were detected by ionis-ation or proportional counters.Soon, however, it became ob-vious the ultra -trace isotopicselectivity was needed, too. somass spectrometers were in-troduced to detect the positiveions. Although both magneticsector and quadrupole massspectrometers have been usedby different research groups.the arrangement preferred nowincludes a time -of -flight massspectrometer.

Resonant IonisationMass SpectroscopyWhen laser techniques areused to detect ultra -traceamounts of elements or iso-topes in a substance or matrix.three separate steps are in-volved. A typical laser time -of -flight mass spectrometer isshown in the third illustration,indicating the steps. Firstly. apulsed, charged, argon beamor a neutral argon beam, ablatesor creates neutral atoms fromthe surface of the solid sampleto be assayed. Ideally, the atomscreated should be accuratelyrepresentative of the solidunder analysis and to dateargon ablation has been shownto be largely matrix -free. Thistechnique is now considered tobe superior to the laser ablationtechnique, which is a high -temperature method known tocause matrix problems be-cause it favours the easily

49 EEApril 1987

vapourisable materials.SIMS, already mentioned, alsouses an ion beam to ablate thesurface of the sample butanalyses only the charged ions,which are created in numberssome two or three orders ofmagnitude fewer than theneutrals. Because they arecharged. these ions are emittedat a rate that is a function of thechemical composition of thesurface. RIMS and SIMS aremade quantitative by makingcomparisons with well charac-terised standard samples, so ifthere are any matrix problems,any quantitative analysis islikely to be inaccurate.Having created a cloud ofvapour above the target, RISlasers then selectively ioniseatoms of the chosen element inthe vapour cloud, which aresubsequently accelerated intothe time -of -flight mass spec-trometer. Secondary ionscreated by the ablation processcan be rejected by electrostaticfields or by varying the time be-tween the ion -beam pulse andthe RIS laser pulse. The normallaser arrangement to achievetotal elemental coverage is anNd:YAG laser powering two dyelasers, one of which has fre-quency doubling facilities.Typical lasers of this kindoperate with pulse lengths ofseveral nanoseconds at rep-etition rates of some tens persecond. The transverse spatialdimensions of the beam aretypically a few millimetres. Oneof the strengths of RIS is that thephoto -ionisation process can bemade almost 100 per cent ef-ficient, that is, it reaches satur-ation. By saturation of the RISprocess, we mean that everyatom of a quantum selectedspecies which was in its groundstate before being subjected tothe photon field of a pulsedlaser is converted to a positiveion and a free electron duringthe short duration of the laserpulse. Because saturation oc-curs when laser fluences, bywhich we mean energy perunit area. are typically about100 mJ cm -2, conventional com-mercial lasers require modestfocusing of a 3 -mm beam. It ishoped that RIMS will become aroutine ultra -trace analytic tech-nique. so a short analysis time isdesirable, of the order ofminutes. For this purpose thelow repetition rate of Nd:YAGlasers (30 sec ') is a limitation.Two of the severe limitations of

rt-r+++++++++

a, a A. AL.

A(cu, ,cue -)A+

These five different schemes, using a pulsed laser or lasers to excite an atom or a molecule fromits ground state of energy, can ionise all the elements in the periodic table except helium and neon.

1 II Ill iv V VI VII VIII 0

1H

s 3Li : 46e ::::::,T

58::::+r

++66- +

-'-

0:47- r 71

4- +A + -I,

-rr -, 1-

+ 404-4-

\ 11 Na*2711-11.1-1.:-

:T2 -114g:

//V13 Al

-'.- -e-ei-i-4'11-÷÷1--e1+415 P +1_.16S+4417÷++++++++++++++A

d 1 _÷-1

19K

(7//20 Ca 21 Sc 22 Ti

XX23 V 24 Cr\\ 's 25 Mn \,\26 Fe

\NNN\s

27 Co....\

NN\NNiL+28 Ni \,

::29 Cu::

.

: :30 Zn: 31 Ga///

. 4.-++.-----,:32 Ge:..*,++++++++++++++++

33 As + 34 Se ++35 Bri-- ----36 Kr-+++++

. . . . ,'2?37 Rb//// /1\

NS '38 Sr\N

--.7.-,--'3,3u i -T.:-=-Z-1"-=-17:.7_.:

--------,\_,-±-L_-±,\iNN\.\\N\\IfrH..,,41 Nb,\

:\N\N\\\\N\:-r.42 Mo,14-31c -72\

_71:711 It-44 Ru \,,

\NiiN 45 Rh \\N\.N :

46 Pd

",--i- r r Ir -. - -" . - r4-54 Xe ++++++

i :47 A g i i 48 Cd////N\i\-49In/N50// Sn \::51

\'-.-Sbii i:52Te :;4- 4531+4+++++

. I . 1

t 55 Cs 56 Ba =72 Hi -7Y- 73Ta=-: -74W_-\ 75 Re -::.-76 Os ---_77 Ir-_-: 78 Pt::

79 Aui i i 80 Hgi 81 -11-i]

./ / 7/,:82 PIDli i 83 Bii i 84 Po. i

'7??..v87 Fr,//7"'88 Ra\\N\

67 /'/La

W j59/60/jCe/Pr N

61

Pmo

i'SmEu\Gd

6, 3.

' 6.:

47\\

6 5

TbDy/yHo/Er//6 6X61 / 6 8 69 /Tmilb\LUX

7 ,' 15'

\92 195,\\AmN 99\'

\Es\

Periodic table of elements, with one of the five schemes of the first diagram ascribed to each.(After Professor Hurst.)

conventional mass spec-troscopy can be eliminatedwhen tuned lasers are used toproduce the ions for massanalysis. In a conventional massspectrometer the ions to beanalysed are normally electron -

beam induced, so molecular in-terferences and isobaric effectscannot be avoided. A massspectrometer cannot easilydistinguish between CO andN2, for example. This is aphenomenon known as mol-

ecular interference. Nor can itdistinguish between 4°Ca. 40Kand 40Ar because they areisobaric; that is, they have simi-lar masses. These ambiguitiesare avoided when RIMS is used.The final step of the RIMS tech-

EE

April 198750

pique is to count and measurethe mass of the laser -inducedions, using a time -of -flight (TOF)mass spectrometer. A TOF in-strument is a non-magneticsystem in which the ions firstaccelerate through a series ofclosely spaced electrodes andthen pass through a field -freeregion (D) of considerable di-mensions, of the order of onemetre, to be detected by an iondetector such as a chan-neletron. In its simplest formthe transit time (t) of the ion inthe field -free region is pro-portional to the length of thefield -free region and to thesquare root of the ion mass (m).For an accelerating voltage of1000 V, with D equal to 1 m, t isabout 20 }AS for a singly ionisedmass of 100 atomic mass units.There are several advantages tobe gained by using a TOF massspectrometer firstly, entiremass spectra can be accumu-lated in a very short time and anentire spectrum can be re-corded for each laser pulse;secondly, TOF systemsmeasure isotopic ratios very ac-curately, because they measurethem under identical con-ditions; finally, the accuracy of aTOF spectrometer depends onelectronic circuitry instead ofextremely accurate mechanicalalignment, so it is simpler tomake. The time-honoured dis-advantage of TOF instruments islow resolution due to the poorlydefined spatial and temporalcharacter of conventional ionformation. But that scarcely ap-plies when the ions are formedby lasers, because the laserspot has a tight focus and thelaser pulse is so short, between5 and 10 ns.In the last year a number ofgroups in the USA, the SovietUnion and Europe have beenset up to exploit the sensitivityof RIMS. Already it is claimedthat the technique is capable ofdetecting impurities at the levelof 1 part in 1010 in a routineanalysis time of 5 minutes.

Future DevelopmentThe design of the RIMS instru-ment so far described is by nomeans optimised. A number ofpromising lines of researchhave yet to be investigatedwhich may lead to better sensi-tivity. Each of the three steps inthe RIMS process will be con-sidered. to see whether im-provements are possible.

Mirrors

Sample

Yd:YAG pump laser

Mirrors

Dye laser 1

Dye laser 2

Argonablation beam

Acceleratingelectrodes

R.I.S. laser beam

Field free regionPositive

Pump

ion detector

Block diagram of a TOF resonant ionisation mass spectrometer, outlining the three separate stepsin its principle of operation.

During the past few years, agreat deal of attention has beenpaid to photon. electron and ionablation of solids. At present,argon ablation of the sample isthe most popular technique,though recent developments inmetal -ion beams such as thoseof gallium and caesium mightincrease the ion -sputtered yieldper unit incident current. Whatis not in question is that thesemetal -ion beams can be fo-cused to far smaller spots thanan argon beam, down to submi-cron focal dimensions, so theyare likely to be of great import-ance in future for precisionscanning of sample surfaces.Over the next few years. it is im-provement of the RIS step that islikely to contribute most togreater sensitivity. While anNd:YAG pumped dye lasersystem has a repetition rate of30 pulses s-', copper vapourlasers have recently beendeveloped. in particular byOxford Lasers (UK) which havea repetition rate of 6500 pulsess-1, capable of pumping dyelasers to provide saturation in-tensities. This is likely to in-crease the efficiency of RIMSconsiderably, especially in

detecting minute quantities ofthe actinides. recently demon-strated by Professor Kluge andProfessor Trautmann of the Uni-versity of Mainz. At present.however, there are electronicdifficulties in handling data atsuch a large rate. The problemsarise from not having enoughstorage capacity and from thetransfer rates of available high-speed transient recorders.One possible improvement insensitivity may be understoodby considering the steppedphoto -ionisation process in thefinal diagram. In (a) an electronin its ground state absorbs aphoton and is promoted to anexcited state with a cross-sec-tion that is typically about 10-"to 10-12 cm'. Another photon isabsorbed and the excited atomis ionised. The photo -ionisationstep is characterised by a smallcross-section 0:011 of 10-17 to10-'3 cm2 and therefore by alarge laser fluence beingneeded to achieve saturation.The fluence is achieved byfocusing. so that the volume ofinteraction with the ablationcloud is small. If, however, pro-cedures (b) and (c) are adoptedthe probability of ionisation is

greater by two or three ordersof magnitude. In process (b) theatom is excited to close to thecontinuum (a Rydberg state)and then finally ionised withhigh efficiency using a pulsedelectric field.Another possibility of improve-ment is shown in (c) where thefinal ionisation step is to a so-called auto -ionisation state,above the ionisation level buthaving a large cross-section.Considerable research isnecessary to identify the auto -ionisation states in a number ofelements before this powerfulprocedure can be adopted. Ifprocesses (b) and (c) can beused then the saturationfluences of the laser are greatlyreduced. so that the beam neednot be focused. The volume ofinteraction is then bigger.

Future ApplicationsOne exciting aspect of thistechnology is that there arelikely to be important appli-cations in both fundamental andapplied physics. In connectionwith fundamental physics, ap-plications of RIMS to solarneutrino experiments. double

EE

April 1987

(a) (b) (c)Autoionisation stateA - _e -

Ionisation to continuum Ionisation by electric fieldfrom a Rydberg state

Rydberg state

Ionisation via anautoionisation state

Stepped photoionisation process. (a) An electron in its ground state absorbs a photon and is raised to an excited state. (b) The atomis excited to a Rydberg state and finally ionised by a pulsed electric field. (c) The final step is to an auto -ionisation state, to give alarge cross-section.

beta decay, baryon conser-vation and magnetic monopolesearches as well as detection ofquark atoms and superheavyatoms are being actively pur-sued. In particular, a detectorbased on the 61Br (v, e) "Kr tomeasure the 'Be neutrinosource in the Sun has beenshown to be feasible becausethe long-lived (2 x 105 year) "Kr

can now be counted with RIMS.In applied and commercialscience, the applications ofRIMS are likely to be very farreaching. In the semiconductorand electronic industries RIMScan identify impurities thatrestrict performance of high-speed, high -density integratedcircuits. The technique can ex-tend downwards the present

minimum detection limits forcontaminants by perhaps threeorders of magnitude or greater.In the medical field, early diag-nosis of certain diseases byusing trace -element concen-trations in body tissues andfluids is a very attractive possi-bility but must be carried out ina non-invasive way by using assmall quantities of material as

possible. Finally, RIMS canassist in selecting sites for stor-ing hazardous nuclear wastesby using ground -water datingtechniques as well as allayingpublic concern by ensuringthat environmental monitoringbe made as sensitive as poss-ible.

0314/6

Continued from p. 30

VALVE PREAMPLIFIER 2the 16 wire links on the board.and use 10 soldering pins forthe connection to the inputbusboard. A 10 -way PCB -mountplug and mating socket is ofcourse the best solution, butthese components are probablyhard to obtain, as they aremainly used in industrial appli-cations.

Wiring the preamplifierAll the usual rules apply to thewiring of this preamplifier;make the mains and supplyconnections in relatively strongwire. and protect the ends withinsulating sleeving to ensureoptimum safety. The signal con-nections can be made in nor-mal screened wire. or, if this is

preferred, in RG58 coax. If theboards and external compo-nents are interconnected asshown in Fig. 10, there is littlechance of earth loops arising.Note that there are only twoconnections to the preampli-fier's enclosure.Inputs ERR. RSTA and RSTB arenot connected. As to the mains

section, the noise suppressioncapacitors, as well as the 2M2resistor and the varistor, are fit-ted direct onto the contacts ofthe double -pole mains switch.As shown in the wiring dia-gram, the lamp inside the mainsswitch is powered by the fila-ment supply: this is so arrangedto provide a visual indication ofthe power -up delay. The mainssocket at the rear of the pre-amplifier enclosure is pref-erably a type with a built-infuseholder.The amplifier is housed in astandard 19 inch enclosure witha height of 3 units (133 mm). Asuitable type is the NME19105from T J A Developments Dept. ER 53 Hartington Road Lonon Eli 8AS. Finally, asuggested front panel layout isshown in Fig. 11. while the Type86111-F foil can be used for thebusboard fitted into a rec-tangular clearance in the rearpanel of the enclosure.

Sv

A look inside a prototype of the valve preamplifier.

Aprd 19E8

MSX EXTENSIONS 5:EPROM PROGRAMMER (2)

The supporting software for the programmer is an EPROM -residentblock of Z80 machine code that provides a deluxe menu, help

pages, a built-in test routine, and, of course, EPROM statusinformation plus error reports.

After last month's discussion ofthe programmer hardware, wewill now study the way it is actu-ally controlled from the MSXcomputer. To begin with, how-ever, we will briefly detail theworkings of intelligent pro-gramming. already hinted atlast month.

The intelligent pro-gramming algorithmAs the holding capacity of theirEPROMs increases, it is logicalfor manufacturers to devise pro-gramming methods that enableloading these devices within anacceptable time. Should the"old" 50 ms per address pro-gramming method apply to, say,a Type 27256 EPROM (32 K x 8),roughly half an hour would beneeded for the device to becompletely loaded. Intel, Fujit-su, National Semiconductor,and other leading EPROMmanufacturers have, therefore,come up with various versionsof an intelligent programmingalgorithm to speed up theloading process. As its nameimplies, this method relies onthe use of a microprocessor.ruling out the possibility to usetimers with a fixed outputperiod for the generation of theprogramming pulses. The flow-chart shown in Table 4 showsthat the essence of the in-telligent algorithm lies in theraising of Vcc from +5 V to+6 V, and the variable length ofthe programming cycle. Theprogram -and -verify loop canonly be left with the byte eithercorrectly programmed, or stillincorrect after a 25 -pulse cycle.Therefore. with relatively fewprogramming pulses requiredfor a byte to verify correctly, the

Hr

S T*01..5Ppr,

1 $.(11L, -

;NFLMARY(DI"' AL

value of variable x is relativelylow, and less time is needed forthe address to be loaded. Fol-lowing the variable number ofprogramming pulses, an ad-ditional pulse of 3x ms ensuresthat programmed databytes areabsolutely stable in theEPROM. At this stage, anexample might help to illustratehow the algorithm works:A specific byte requires 9

pulses for it to be stored cor-rectly in the EPROM. The pro-gramming cycle thus takes(9 x1)±(3 x 9)=36 ms.Figure 8 illustrates that a pro-gramming cycle can be quitelong. In fact, intelligent pro-gramming is not necessarilyfaster than normal (50 ms),fast -I (20 ms), or fast -2 (10 ms)timing arrangements, since theworst case cycle duration is25 + (3 x 25)=100 ms. In practice,however, you will soon find thatnewly purchased, intelligentlyprogrammable EPROMs gener-ally require only the minimumpulse time of 4 ms per addressfor reliable loading. Returningto the previously mentioned

Type 27256, 3 minutes or sothen suffice to completely loadthis device.The intelligent programmingmethods adopted and rec-ommended by Intel Unfelt -gentprogramming, and Fujitsu(Quick Proml) differ onlymarginally as regards the dur-ation of the programming pulse,the number of iterations beforethe EPROM is rejected as faulty,and the pulse multiplicationfactor. National Semiconduc-tor's algorithm, however, isbased on the use of 0.5 mspulses, a maximum iteration of20, no multiplier, and a Vpplevel of 13 V instead of the moreusual 12.5 V. This MSX EPROMprogrammer does not supportNational's algorithm, but none-theless gives good results withtheir chips.As could be expected, thetiming of the programmingcycles is interrupt -based andjointly controlled by the CPU inthe computer and the CTC inthe I/O & Timer cartridge. Thecontrol program arranges fortimer Ti in the CTC to provide

the number of programmingpulses required to successfullyload a byte into an EPROM ad-dress. Iteration and pulsemultiplication are effected inaccordance with the flowchartshown in Table 4. Extensivetests have shown that theadopted algorithm gives satis-factory results with the vast ma-jority of intelligently program-mable EPROMs.Although not expressly indi-cated in the flowchart, the con-trol program and the CTCensure that EPROM data andaddress lines are stable beforeany write action can take place.For this purpose, timer To in theCTC provides 4µs long delaysas detailed in last month's instal-ment of this article.

Program descriptionAn MSX compatible micro canhave up to 4 primary slots.numbered a 1, 2, 3, each with amemory capacity of 64 Kbytesand subdivided in 4 pages of 16Kbytes. It is also possible for aslot to be expanded. whichmeans that it comprises foursub -slots X-0. X-1, X-2 and X-3. Intheory, therefore, there can be amaximum of 16 slots identifiedas 0-0 up to and including 3-3.Since the Type Z80(A) CPU isan 8 -bit microprocessor, itsaddressable memory area is64 Kbytes, that is, four pages,but these can be part of any (ex-panded) slot. It is, for instance,possible for the system tooperate with page 0 from slotpage 1 from slot 2, and pages 2and 3 from slot 3-2. The absoluteaddress ranges are thus: page 0= 0000 -3FFF; page 1 =4000-7FFF; page 2 = 8000-BFFF;page 3 = C000-FFFF.Pages can be swapped and

Interactive EPROM programming

( START

11.

ADDRESS = G

Vcc = 6 VVpp = 12.5 V

X-4-0

APPLY 1 PROG. PULSE m3)

ERR

No

VERIFYONE BYTE

OK

YES

ERR

FAIL

OK

APPLY ADDITIONAL PROGRAMMINGPULSE (3X ms)

ADDRESS + 10

YES

Vcc = 5.0 VVpp = 5.0 V

OK

( PASS )FAIL

5700244

Table 4. Intelligent programming of EPROMs essentially entails applying no more pulses than strictlynecessary for correct loading.

Fig. 8. This oscillogram shows that addresses may differ inrespect of the number of programming pulses required forloading a byte. Upper channel: address line AD; lower channel:(8x11-1-24 ms for the first byte, (1}_1)=3 for the second and third.

EE

April 1987

switched on and off by meansof particular system commands,which will not be gone into inthis article. Page 0 is usuallyreserved for the MSX BIOS(Basic Input/Output system),and page 3 for the system stackand scratch blocks, variables,the keyboard buffer, etc. Atpower -on, an MSX computer in-variably examines pages 1 and2 in all slots for the presence of(E)PROM-resident programs,which are immediately startedif a particular identificationcode is found in the first 16 ad-dress locations. If such an iden-tifier is not found, the BASICROM on page 1 is enabled, andthe machine boots up accord-ingly.The control program for theEPROM programmer comes inthe form of a ready -pro-grammed EPROM Type 27128(16 Kbytes), available throughour Readers' Services undernumber 552. This EPROM is in-serted in the socket on the car-tridge board for MSX com-puters, described in ElektorElectronics, February 1986. Inthe following section we will setout how to connect all add-onunits to make a functional set-up.

The programmer software im-mediately runs from page 1 atpower -on. After completing thenecessary initialization rou-tines, the program finds outwhich slot has RAM in pages 1and 2 for use as the EPROMdata area (32 Kbyte maximumsize. 4.000-B1-1-12). it copies partof itself into the highest poss-ible RAM area on page 3, that is,

ELEKTOR MSX EPROMMER

EPROM TYPE:

PROGRAMMING VOLTAGE:

EPROM BEGIN:EPROM END:

MEMORY BEGIN:MEMORY END:

BLANK CHECK:PROGRAM:VERIFY:READ AND RUN CHECK SUM:DISPLAY MEMORY:

PROGRAM MODE:

CHECK SUM:ADDRESS COUNTER

RESULT: PROGRAMMED

27128

12.5V

8H0888 :

&H3FFF

8H4888 :

8H7FFF

YESYESYESNONO

I NTELL

8/488808H3FFF

Fig. 9. Screendump of the command input screen (settings areexamples).

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April 1987

it inserts itself between thestack and string & scratchblocks. After all this has beendone, control is returned to thecomputer's normal start-up pro-cedure, which means in mostcases that BASIC will be started.The EPROM software can nowbe run by typing CALLEPROMx, where x is the car-tridge address area, 0, 1, 2, or 3.The program, when called,automatically selects the appro-priate slot(s) for the RAM buffer,and then switches back towhere it came from with theaid of routines on page 3. Allswitching between RAM andEPROM resident subroutinesin the programmer is invisibleto the user, and makes it poss-ible for the proposed soft-ware to run on any MSX com-puter equipped with at least64 Kbytes of RAM. Extensiveuse is made of vector -addressing, and all keyboardand screen input/output isrouted via the BIOS on page aTo make sure that data for orfrom the EPROM is not over-writing the system stack, orpossibly the RAM -resident por-tion of the control programitself, it is a good idea to checkwhether there is enough roomfor your data by typingPRINT HEXS(FRE(0)+ &H8000).The address returned shouldbe higher than the top locationyou need, observing that part ofthe available memory is usedfor the string and stack blocks.which extend downwards.Those MSX users in possessionof a computer with a disc drivemay have to limit the DISK -BASIC workspace somewhat byholding down the CONTROL -key during power -up as ameans of telling the sys-tem there is but one virtualdisc drive available. Simi-larly, holding down the SHIFTkey disables the disc unitaltogether.

Command summaryAlthough the proposedprogram is extremely simple touse, it is none the less rec-ommended to study this briefsummary of the available func-tions. commands and options.After typing CALL EPROMx.you should see the welcomescreen. Pass on to the helppages with EPROM data andprogram information by press-ing any key. You can leafthrough the help pages by

pressing the appropriate cursormovement keys. The commandinput screen can be called up atany time by pressing the spacebar.The following keys are usedduring the command inputmode:Cursor ' and . select the itemyou wish to work on.Key H returns you to the helppages.Key P causes the screen con-tents to be dumped to a printer(make sure this is properly con-nected. else you will get a NOPRINTER error).Key T runs a test program thatcauses all functions on the pro-grammer to be successivelyenabled with aid of CTC inter-rupts. indicated by the flashingPGM LED. Make sure thatjumper Ji is not installed, andnever run the test with anEPROM inserted in the ZIFsocket.The space bar selects thevarious options for the com-mand items (toggle function).Key S causes the program tostart executing your set of com-mands. Always make sure thatthe command screen showswhat you want before pressingS.

Key I enables the storing ofBASIC programs in EPROM.The software automaticallyarranaes for the correct in-italisation of the memory begin& end. and EPROM begin &end addresses. Link addressesare automatically adapted toenable the BASIC program tobe run from EPROM.With reference to Fig. 9, theseare the various parameters youneed to define before the pro-

grammer does what you want itto do:EPROM TYPE and PRO-GRAMMING VOLTAGE: con-sult Table 1 or the relevant helppage and use the space bar toselect the appropriate EPROMtype; notice that EPROM BE-GIN & END change in accord-ance with the holding capacityof the relevant EPROM type. It ispossible to program part of anEPROM by keying in the rel-evant hexadecimal addressrange. The program accepts en-tries in hexadecimal only, andproduces an error message ifyou try to define an impossibleaddress range, or if the EPROMBEGIN & END entry is not inaccordance with the MEMORYBEGIN & END entry. Example:you want to program the firsthalf of a Type 2764 (8 Kbyte):EPROM BEGIN = 0000;EPROM END = OFFF; MEM-ORY BEGIN = 4000-, MEMORYEND = 4FFF.BLANK CHECK should be afairly well-known facility; it

checks, with the aid of EPROMBEGIN & END, whether thespecified address range con-tains only bytes FF, indicatingthat data can be loaded there.PROGRAM speaks for itself.This function uses bothEPROM BEGIN & END andMEMORY BEGIN & END.VERIFY checks whether theEPROM contents and the RAMbuffer contents are the same.and evidently uses EPROM BE-GIN & END and MEMORY BE-GIN & END to determine whataddress ranges are to be com-pared.READ AND RUN CHECKSUMloads the data from the EPROM

Table 5 Port C command data

: EPROM READ VERIFY WRITE

!2716 OB 08÷Vpp 28+Vpp12732 OF 0C+ Vop 68 4- Vpp

2764 OB 08+ Vpp 28 4 Vac27128 OB 08 4- Vao 28 i Vpp

1 27256 08 418+Vp.p 68±Wp27512 OF OC + Vop 68 ÷ Vpp

i 2516 OB OB 68+ Vpp2532 OB OB 68÷Vpp

L2564 OB 08 48+ Vpp

All entries in hexadecimal.Vpp =5 V : 3. Vpv= 12.5 : 2. Vpp =21 V : 1_ Vp!, -25 V : O.MS bit on port C is programmed as input.,

Table 5. Command bit configuration at the Port C input.

into the buffer and adds thevalues of all bytes to produce a16 -bit checksum.DISPLAY MEMORY offers theuser the possibility to load theEPROM contents into the com-puter for examination on thescreen (hexadecimal and ASCIIformat, 8 bytes per line,preceding address). You cannot alter the displayed bytes.PROGRAM MODE simplyselects normal, fast -1, fast -2, orintelligent programming as ap-propriate for the specific typeof EPROM. Consult Table 1 orthe relevant help page.ADDRESS COUNTER at thelower end of the screen is aI6 -bit counter that keeps trackof the EPROM location cur-rently read from or written to.

The RESULT line at the bottomof the screen can be used todisplay the following messages(H returns to the help pages):ADDRESS ERROR is a generalmessage to tell you to re -do theEPROM BEGIN & END and/orthe MEMORY BEGIN & ENDentry before pressing S again.BLANK reports that the statedaddress area contains onlybytes reading FE The EPROMarea is not copied into RAM.NOT BLANK reports that one ormore bytes in the specifiedEPROM area do not read FEThe address counter displaysthe first address encountered.and the program is halted.READING COMPLETEDspeaks for itself. The contents ofthe EPROM are available forexamination with DISPLAYMEMORY. For modification,you will probably want to resortto BASIC or a suitable utilitypackage.VERIFIED reports that theverification routine has com-pleted without finding errors.VERIFY ERROR indicates thatone or more differences existbetween the contents of theEPROM and that of the RAM.The address counter displaysthe first incorrect address en-countered, and the program ishalted.REPROGRAMMABLE indicatesthat a verify error was found,but the relevant byte isreprogrammable, i.e.. any of itsbits reads logic 1 when itshould be logic a Logic lowlevels in EPROMs can only bechanged into logic high by ex-posing the chip to a dosage ofultra -violet light.NOT PROGRAMMABLE re-

ports that the address indicatedby the address counter cannot be loaded correctly, evenafter applying 25 programmingpulses (see Table 4, intelligentprgramming only).EXECUTION STOPPED isdisplayed in response to thepressing of the RESET switchon the EPROM programmer.DEVICE I/O ERROR indicatesthat the computer is not receiv-ing interrupts from the car-tridge, which is possibly set tothe wrong I/O address.NO PRINTER is a message thatspeaks for itself.ILLEGAL COMMAND ORDERinforms you to re -do the YES/NO setting of one or more com-mands. Note that it is allowed tochose YES for BLANK CHECK,PROGRAM and VERIFY; theprogram performs these stepsin the correct order, without theneed for intermediate com-mand starting with S.

As already noted, it is advisableto think well before pressingthe S key and so start theprogram. If you get an errorreport, do not get into a panic,but study the command screento trace the fault and under-stand its nature. Once you have

worked with this EPROM pro-grammer for some time, youwill notice that it is highly user-friendly and easy to get goingwith the aid of the help pages,which are instantly available atthe pressing of key H.If you do not know how toprogram an EPROM which isnot included in Table 1, simplybegin with the lowest program-ming voltage, 12.5 V, to see ifanything happens to the con-tents of the device: you can notdamage it in this way, providedyou do not select intelligentprogramming, as this causesthe Vic line to be raised to 6 Vduring the programming cycle.In conclusion of this section, afew more tips. When anEPROM is stated to be pro-grammable in the normal(50 ms) mode. it is worth whileto try out the effect of selectingfast -1 or fast -2 programming tosave time. If you want to docu-ment the program settings for aspecific EPROM. it is a goodidea to use the screendump op-tion for the recording of thechecksum and other relevantdata. Remember that a Type27512 (64 Kbyte) EPROM mustbe programmed in two 32 Kbytepasses. Press CONTROL

Fig. 10. One slot can hold both the EPROM and the I/O cartridge.

to return to MSX BASIC, andtype CALL EPROM): to run theprogrammer again. Use anassembler or a machinelanguage utility package towrite bytes into the RAM bufferfor loading into an EPROM, butmake sure that data is not over-written by stack or buffer usageof any program you run in com-bination with the EPROM pro-grammer software.Keep in mind that runningBASIC programs that use PLAYcommands require the com-puter to be reset and hence theEPROM programmer softwareto be re -initialized. This isbecause the proposed programlocates its jump table and vari-able map in the voice queuearea. In more general terms, donot use the EPROM program-mer software before you aresure that there are no other pro-grams, or remnants thereof, stillaround somewhere in the com-puter's memory. The best wayto avoid trouble is to reset themachine with the EPROM car-tridge inserted.Finally, Table 5 shows the con-trol words for the variousEPROM types. These 7 -bitswords are specific to the

type to be dealt with,and can be used by anyonecontemplating the writing of hisown version of the control soft-ware.

Getting startedCommence with fitting jumpersB, D, E and I on the EPROM car-tridge board, then mountEPROM ESS 552 in the 28 -waysocket. Plug this cartridge intoa slot of the MSX computer. andplug the I/O & timer cartridgeeither in a remaining slot, or inthe one provided on theEPROM cartridge board_ Con-nect the EPROM programmerto the I/O & timer cartridge viathe 50 -way flat ribbon cable.and you have the system readyfor use-see Fig. 10. Please notethat it is not possible to use theadd-on busboard for MSX com-puters. in conjunction with thetimer & I/O cartridge. Do notyet fit an EPROM in the ZIFsocket, switch on the power.and call the program on com-pletion of its initialisation. Afterviewing the welcome andcopyright screen, go to thecommand screen and run thebuilt-in test routine prior toworking on any EPROMs. If allLEDs on the programmer's front

!EEApril 1987

panel can be seen to go on andoff at regular intervals, thereis good reason to assume thatthe hardware and softwarefunctions satisfactorily, and it ishigh time to set the system towork on any EPROM that youmay have available.

AR

We regret that we can not pro-vide information on the use ofthis EPROM programmer withcomputers other than those inthe MSX series.

Previous articles on MSX exten-sions have appeared in the fol-lowing issues of ElektorElectronics:January 1986 (I/O bus. digitizer,I/O port);February car-tridge board);March 1986 (add-on bus board);January 1987 (I/0 and timer car-tridge).

EE

April 1987 56

Local Area NetworkingThe proliferation of personalcomputers (PCs) as a businesstool has driven the need for adistributed processing environ-ment where many microcom-puters can share expensiveperipheral devices, such asprinters and hard disk drives.The capability to networkequipment also enables usersto share files and programs andto centralize backup facilitiesand procedures.Local Area Networking has twomain requirements. It must beimplemented in VLSI, to sim-plify design and lower theoverall "per node" cost of con-nection to a network. Second,the LAN must also run standar-dized software and conform toan industry standard, so thatend users can interconnectequipment from different ven-dors without worrying aboutprotocols.The IEEE 802.3 standard(EthernetTm) has gained wideacceptance by both large andsmall companies as a -high-speed (10 megabit/second)LAN. However, because of itscable requirements, it can berelatively expensive to imple-ment. In response to thisdrawback, Thin Ethernet, alsoknown as CheapernetTm - wasdeveloped. Thin Ethernet usesless expensive coaxial cableand features a "node -inte-grated" transceiver. ThinEthernet maintains full compati-bility with Ethernet's 10 mega-bit/second data rate.Another network sponsored bythe IEEE 802.3 committee isStarLAN' 't, a I megabits -per -second implementation thatfeatures a "star" configuration.Each node is connected toanother central hub in point-to-point fashion.

Continuing development ofLAN interface chips has driventhe LAN connection cost pernode down to new levels, mak-ing networks affordable at allbusiness levels. Because of itscost-effectiveness, the personalcomputer connection segmentof the LAN marketplace isforecast to grow faster than anyother segment. According toDataquest, revenues in 1990 willtop US$ 528 million. Revenuesin 1985 totalled US$ 181.7

million. The installed base ofnetworked PCs will be 3.7million in 1990, up from 438,000in 1985.

Current StatusThe decision by 3Com andNovell to port their LANoperating stems to NationalSemiconductor's DP3890 Net-work Interface Controllermarks the first time a semicon-ductor supplier has taken an ac-tive role in making networksoftware standard with theirchips. This makes it easier fordesigners to use the chips in anetwork, rather than having towrite software themselves. Fororiginal equipment manufac-turers (OEMs), DP8390 compati-bility with 3Com's 3+ networksoftware and Novell's AdvancedNetWare means an easy path toLAN design for IBM-compatiblePCs. OEMs can use NationalSemiconductor's tool kit con-taining DP839EB LAN evalu-ation boards and 3Com 3+network software to developnetworking and workgroupcomputing products. Or theycan use Novell's developmentkit and the DP839ER or theDP8390 LAN chip set, to designlocal area networks.3Com and Novell are respon-sible for setting "de facto- stan-

APEX Microtechnology's latestpower operational amplifier.the Type PA73M. offers oper-ation up to 30 V: outputs ofup to 5 A: a high -efficiencyclass C output stage: and MILSTD -883C screening. Furtherdetails from APEX's UK rep-resentatives: Pascall Elec-tronics Ltd Saxon House Downside Sunbury -on -Thames TW16 6RY.

dards in the PC LAN industry.3Com is the leading vendor of

.LAN add-on boards for PCs.with a 19 percent share of themarket, according to Dataquest.Novell's NetWare, with 60.000installations, is the most widelyused PC LAN operating system.It supports 35 local area net-work systems, including3Com's Etherlink and EtherlinkPlus. AT&T's StarLAN and IBM'sPC Cluster and Token -RingNetwork.Support from two predominantLAN suppliers reflects theemergence of the DP8390 asthe standard LAN chip set ofchoice among system design-ers.

National's Local AreaNetwork Chip SetFocusing specifically on theIEEE 802.3 local area networkstandard encompassing Ether-net, Thin -Ethernet (Cheaper -net), and StarLAN compatiblenetworks. National designersdeveloped three integrated cir-cuits: an Advanced Network In-terface Controller (DP8390NIC), a Serial Network Interface(DP8391 SNI) and a CoaxialTransceiver Interface (DP8392CTI). The chip set was the firstcomplete VLSI implementationto meet the entire IEEE 802.3standard. Its availability makesNational Semiconductor wellpositioned to provide the rap-idly expanding PC LAN marketwith its cost-effective chip set.In particular. the DP8392 wasthe first monolithic chip im-plementation of a cabletransceiver. The high level of in-tegration saves users a signifi-cant amount of board space. Infact. the network chip set is theonly one that fits on a short -slotPC card.

A new MSDOS emulator forArcom's 80188 processorboards provides a low-cost PC -based development path. Thepackage, called APPCOM. issupplied in an EPROM byArcom Control Systems Ltd Unit 8 Clifton Road Cambridge CB1 4WH.

The DP8390 NIC features two16 -bit DMA channels thatdeliver all the data -link layerfunctions required for datapacket transmission and recep-tion. The DP8391 features apatented digital phase lockloop for most reliable datareception. The DP8392 CTI im-plements all driver. receiver,jabber and collision -detectingfunctions required by the IEEE802.3 cable transceiver. In ad-dition, the DP8392 exceeds theone million hour MTBF re-quired in the 802.3 specificationfor transceivers.Illustrating National Semicon-ductor's technological breadth,three distinct process techno-logies were used in fabricatingthe chips: microCMOS for theDP8390, a high-speed oxideisolated bipolar process for theDP8391 and a junction -isolatedbipolar process for the DP8392.The DP839EB evaluation board,containing the chip set, plugsinto any IBM PC -compatiblecomputer and incorporates allof the components required toprovide a LAN interface toEthernet or Thin Ethernetnetworks.The entire LAN chip set andevaluation board are all cur-rently in production.

Ethernet is a trademark ofXerox Corporation.Cheapernet is a trademark ofNational Semiconductor Cor-poration.StarLAN is a trademark of AT&TBell Laboratories.

(Source: National Semicon-ductor)

EE

April 1987

SCHOOLS EQUIPMENT FORTOMORROW'S SCIENTISTS

by David Tawney, MA FlnstP*

From magnifying glassesto microscopes, callipersto computer interfaces.pipettes to pH meters: therange of equipment in thecatalogues of educationallaboratory suppliers is vastand continually changingin response to technologi-cal and educational de-velopments.

The introduction of micro-computers such as theBBC B and the RM 380Z toschools in the UnitedKingdom has been rapidlyfollowed by the develop-ment of computer inter-faces whose purpose iseither to enable data fromschool laboratory ex-periments to be captured,processed and displayed,or to control simple de-vices.Similarly, the rapid adop-tion by industry of biotech-nological techniques hasled Britain's major sup-pliers to sell kits by whichthese techniques can besimulated in schools. How-ever, not all new equip-ment is stimulated byrecent technological inno-vations: an educationalconcern to introducescience and technologyto pupils aged five to 11has led to much recent in-terest in construction kits.There are several reasonswhy the range of edu-cational laboratory equip-ment is so wide. First,science is taught in Britishschools over the agerange of five to 18. Sec-ondly. as the emphasis ison giving pupils hands-onexperience, suppliers havelearned how to provideequipment that schoolscan afford in quantitiessufficient for classroomwork. Some of it is, ofcourse, for demonstrationby teachers but much ismeant to be used bypupils working in groups

Using Griffin & George programmable scientific instruments.

of two and three. Pupilpractical work is a cor-nerstone of education andso equipment must bestrong and relatively inex-pensive.

HighereducationequivalentThe high degree ofspecialization by Britishpupils who stay on after16. in many cases to pre-

pore for a course at a uni-versity or polytechnic, issometimes criticized but ithas advantages. The levelreached by these pupils istypical of first or evensecond year universitystudents in some countriesand so equipment that isuseful for higher edu-cation is produced in thequantities that schoolsneed and at prices theycan afford.Britain does not have acentralized educationalsystem and schoo:s aregiven extensive choices in

the courses they providefor their pupils. There areeight area boards offeringexaminations for the moreacademic pupils, andwhile procedures ensurecomparability betweenthese examinations,syllabuses do vary whichincreases the range ofequipment needed.In the 1960s and 1970s,there was considerablein British schools, muchsupported by money fromthe Nuffield Foundation orfrom the government -funded Schools Council.

EE

ADO 1987 58

This stimulated corre-sponding innovationsin equipment, anotherreason why the range is sowide.In the late 1970s and early1980s, most of the newcourses were revised andthese revisions, togetherwith restrictions on moneyfor education caused byfalling school rolls and theworldwide slump, haveeliminated from the sup-pliers catalogues any-thing that has provedunpopular. Much of whatis left - still very extensive- has been refined overat least a decade.British schools tend to buytheir laboratory equip-ment from three maingeneral suppliers: Griffin &George (GG), Philip Harris(PH) and Irwin-Desman (ID).However, a number ofspecialist firms are alsoused. For example, inter-faces for coupling equip-ment with microcomputersto capture data or dem-onstrate control are of-fered by all three of themajor suppliers as well asthe specialists.

Many functionsAn example is themeasurement module sup-plied by Educational Elec-tronics (EE) which enablesdata from the outputs of arange of instruments -Hall probe for measuringmagnetic fields, pH meterand so on - to be re-corded and strikinglydisplayed in several formson a television monitor. Arange of sensors is beingdeveloped to go with thisand other computer inter-faces. One of the mostinteresting recent devel-opments using micro-electronics is the GiPSI(Griffin ProgrammableScientific Instrument).There is concern thatmuch of the more sophisti-cated equipment used ineducation spends muchof its time on the shelf andis used only when its turncomes round in the sylla-bus so this instrument hasmany functions and willmeasure current, voltage,resistance, magnetic field,

pH, light levels, and so on.The function wanted isselected by connecting amodule containing an ap-propriately programmedread only memory (ROM)and fitting overlays overthe control panel makes iteasy to use.Another current growtharea is electronics teach-ing kits. There have formany years been smallcomponents of electronicsin some school physicscourses but such physicsteaching has recentlybeen modernized andseparate school elec-tronics courses developed.The emphasis has shiftedfrom simple introductionsto semiconductor diodesand triodes to a systemsapproach to digital elec-tronics and to operationalamplifiers.There are currently manyapproaches to teachingelectronics embodied inkits. The equipment forone very popular course,"Micro -electronics for All' ,

intended for 11 to 13 yearolds but in fact used forolder pupils as well, isavailable from Unilab (U).Ideas underlying micro-electronics - or infor-mation technology as it issometimes called - arelearned through solvingsimple control problems.Other kits drawing interestare the IndependentSchools Micro -electronicsCentre (ISMEC) kits avail-able from Griffin & George,Philip Harris, and Unilab.Unilab specializes in elec-trical and electronicequipment for educationat competitive prices suchas power supplies, meters,radiation counters, signalgenerators, and so on, allitems that can, of course,be obtained from thegeneral suppliers.

Move toplasticsIt is easy to look just at re-cent major developmentsand forget that the bulk ofpurchases made by edu-cational establishmentsare for consumables,notably glassware andchemicals, both supplied

by Griffin & George andPhilip Harris. Anothercompany that specializesis BDH Chemicals. A devel-opment over the last fewyears has been the slowacceptance by schools ofplasticsware in place ofglassware. Early examplesof plasticsware stained tooreadily but recent prod-ucts are more satisfactoryand stand up to pupil usemuch longer than glass.Many of the top pan bal-ances bought during theboom in science edu-cation in the 1960s and1970s are now wearing outand schools are replacingthem, as funds permit, withelectronic balances withdigital displays. These arevery quick to use so thatfewer are required for aclass. Griffin & George,Philip Harris, and Irwin-Desman all supply bal-ances but there are alsoseveral specialist suppliers,notably Oertling.There are several ranges ofmicroscope and specialistfirms such as Prior havesuitable instruments for theeducational market. Re-cently, biologists haveshown interest in kits forenvironmental studiescontaining meters thatmeasure pH, conductivity,temperature, light level,and so on. An example isan enzyme kit which pro-vides insight into the in-dustrial use of biotech-nology.A recent growth point hasbeen equipment for pri-mary school science. Theeducational emphasis ison using what can befound in the home andthe classroom with theminimum use of specialequipment but some isneeded, such as simplekitchen -type scales,magnifiers, thermometers,construction kits, and soon. Specialist primaryschool companies such asE.J. Arnold and Osmiroidhave equipment suitablefor primary science edu-cation.

Checking forsafety.The School Science Ser-

vice provides informationand consultancy onschool science equipmentand safety for the majorityof British schools. Its taskis to examine and testequipment and makerecommendations toteachers. Copies of itsreports can be obtainedoverseas through theBritish Council or throughsubscribing to the serviceas an overseas associate.Frequently the service isobliged to be critical ofcertain products but sup-pliers usually make modi-fications in the light ofcriticisms.

E.J. Arnold Lid, LockwoodDistribution Centre,Parkside Lang Leeds,West Yorkshire, England,L511 STD.

BDH Chemicals Ltd, BroomRoad, Parkslone, Poole,Dorset England, BH12 4NN.

Educational Electronics,28 Lake Street, LeightonBuzzard, Bedfordshire,England, LU7 8RZ

Griffin & George Lid,Bishops Meadow Road,Loughborough, Leicester-shire, England. LEH ORG.

Philip Harris Ltd, Lynn Lane,Shenston, Staffordshire,England, WS14 OEE.

Irwin-Desman Ltd,294 Purley Way, Croydon,Surrey, England, CR9 4QL.

Oertling, W & T. Avery Ltd,Smethwick, WatleyWest Mid/and England,866 2LP

Osmiroid, E.J. Perry Ltd,Gosport Hampshire,England, P013 OAL.

Prior Scientific InstrumentsLtd, London Road, BishopsStortford, Hertfordshire,England, CM23 5ND

Unilab Ltd, ClarendonRoad, Blackburn, Lan-cashire, England, 881 9TA.

David Tawney is director of theBrunel University -based SchoolScience Service of Britain'sConsortium of Local Authoritiesfor the Provision of ScienceEquipment (CLEAPSE).

59 EE

April 1987

OW PRODUCTS o NEW PRODUCTS NEIA1

NewshockproofmultimeterNew from ITT Instruments is theMX112, art analogue multimeterfitted with a rubber stock -absorbing surround whichmakes it ideally suited to field -service use in the electrical andautomotive industries.The MX112 is designed for easeof use, with only two inputsockets provided for all func-tions and ranges and full pro-tection on all ranges includingthe 10 A current range.In addition to the rubber shockabsorber, the MX112 incor-porates a shockproof move-ment. The panoramic dial isbacked by a parallax correctionmirror, and a colour -codedrange indicator is used with apatented slide switch to pro-vide easy, unambiguous read-ings of functions and rangescales.The instrument offers eightmultimeter functions on 42

ranges, plus capacitance anddecibel measurements anda dwellmeter function forcarrying out measurements oncar engines.AC and DC voltages of up to1600 V can be measured, whilethe current facility providesmeasurements from 50 µA to10 A. Resistance ranges go upto 2 megohms.The instrument's sensitivity is20,000 ohms per volt on ACranges. DC accuracy is ±2% of

full-scale deflection, the corre-sponding figure for AC being+3%.All ranges are protected up to220 V, and the instrument isdesigned to meet the IEC414safety standard.ITT Instruments346 Edinburgh AvenueSloughBerkshire SL1 4TU.Telephone: (0753) 824131Telex: 849808 ITTCOM GTelefax: (0753) 824160.

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Versatile I/OSystem forIBM -PCs®

Users of IBM -PCs and otherpopular RS232 -interfaced com-puters can now utilise a ver-satile and very economicallypriced expansion system to col-lect and generate digital andanalogue inputs and outputs.The system, available fromElectronics and ComputerWorkshop Ltd. (ECW), is basedon a series of multi -slot mother-boards that accept standard I/Ofunction cards. An intelligentRS232 -interfaced version, theK2612, compatible with IBM -PCs, has been added to therange, allowing many moreusers to interface theirmachines to the outside world.The system is a fully expan-dable method of connecting a

wide range of analogue anddigital signals to a computer fordata acquisition and control ofmany types of electrical circuit.The plug-in series now in-cludes an eight -channel ana-logue input multiplexer, A/Dand D/A conversion, Centronicsprinter port, eight -channellogic input, real-time clock anda general-purpose output cardwith a choice of relay and triacoutputs.For the more adventurous, a'breadboard' plug-in allowsusers to develop their own I/Oprojects.

IBM and IBM PC are registeredtrademarks of InternationalBusiness Machines, Inc.Electronic & ComputerWorkshop Limited117 Broomfield RoadChelmsfordEssex CM1 1RY.Telephone: (0235) 262149

(3582:8)

New PacketRadio TNCMany amateurs do not realisehow easy it is to get on the airwith packet radio. All you needis a computer with an RS -232 in-terface (available on most homecomputers). a "Terminal NodeController" (TNC) and a trans-ceiver (or receiver for SWL 's).Most activity is on 2 metresalthough HF activity is increas-ing rapidly. Frequencies tolisten on are 144.675 (data call-ing), 144.650 (packet repeaters)and 14.103 (main HF operation).Only a simple communicationsprogram is required for yourcomputer, the TNC with its Z-80processor handles the difficultbits! The majority of commer-cially available communicationssoftware will work without anyproblem, but there are somespecially written programsavailable (which give splitscreen operation and otheruseful features) for the morepopular machines. Some ofthese are available at a nominalcharge or even free!

The TNC-220 is a newly de-

signed successor to theTNC-200 and other TNC-2"clones", giving more featuresat lower cost. It uses a single -chip modem that is softwareswitchable between two radioports, conveniently supportingboth VHF and HF packet oper-ation. Each of the TNC-220radio ports may be configuredwith jumpers for 300 or1200 bauds. Switching betweenports is entirely done in soft-ware and no cable changing,no switch setting and no retun-ing is required! Both ports haveprovision for an active band-pass filter to optimize HF oper-ation, one filter is standard. Anoptional tuning indicator willmount inside the cabinet. Astandard modem disconnectheader is provided to allow theuse of accessory highspeed orsatellite modems.An assembled TNC-220 in-cludes radio and power con-nectors, complete operator'smanual and command refer-ence card. The kit also containsa detailed, step-by-step as-sembly manual.The TNC-220 has the familiarTAPR command set and AX.25Level 2 Version 2 protocol run-ning on a Z-80 processor with32 K bytes of EPROM and 16 Kbytes of batterybacked RAM. AZilog 8530 Serial Communi-cations Controller performs allpacket HDLC in hardware. TheRS -232 port includes a jumperto select TTL interfacing to yourVIC-20, C-64/128 or other TTLcomputer. Five large. color -

coded LED's clearly indicatethe TNC-220 status at a glance.The power switch is located onthe front panel. TNC-220 isenclosed in a rugged extrudedaluminium cabinet. The attract-ive Pac-Comm two-tone bluefront panel has large, clearlabels on all indicators andcontrols.The TNC 220 comes in kit formor ready assembled: prices are£149.95 and £169.95. respect-ively, inclusive of VAT and P&P.

Andrews Computer ServicesLimited6 Ash Hill CloseBushey HeathHerts WD2 1BW.Telephone: 01 950 9381. (3582:3)

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April 1987 60

OAT PRODUCTS o NEW PRODUCTS NEVNew self-containeddigital trainerThe FLT -102 Digital TrainingLaboratory from Flight Elec-tronics provides a comprehen-sive workstation for thoseinvolved in advanced digitalelectronics courses.

Self -containment is the essenceof the unit which provides totalindependence to users. Built-infeatures include a multi -railvariable DC supply, Four -rangedigital voltmeter, function gen-erator. seven segment displays,logic switches, functionswitches, pulse switches, andlogic indicators. Time -effectiveand tidy circuit work soonreplaces the unreliable 'birds -nest'. Components with 0.3 to0.8 mm leads can be pluggedinto the large 1680 tie -pointbreadboard which accepts allDIPs.Having all support equipmentso close to hand makes the unitideal for all applications requir-ing an independent digitalworkstation. The range of in-puts, displays and options en-sures that a comprehensivecoverage of digital circuitry canbe achieved. The unit offers athoughtfully built and reliablebase, for all training establish-ment and individual require-ments.The built-in regulated DCsupply is fully short-circuit pro-tected. Ranges are +5 V/1 A,±5 V/0.5 A, and 0 to ±15 V/0.3 A. The function generatorprovides 1 Hz to 100 kHz con-tinuously, variable over fivedecade ranges. Wave outputs

peak -to -peak are sine 0 to +5 V.triangle 0 to ±3 V, and square 0to ±5 V. DVM provides fourranges from 199.99 mV to199.99 V FSD. Pulse buttongenerates 10 ps pulse. A 30 -dayevaluation period can be ar-ranged. The FLT -102 costs £250.Flight Electronics has recentlylaunched its fifth annual cata-logue, containing a comprehen-sive range of training systemsand associated equipment. It isavailable free of charge fromthe address below.Flight Electronics Limited,Ascupart Street,Southampton SOl 1LU.Telephone: (0703) 227721Telex: 477389 FLIGHT GFax: (0703) 330039 (3582:17:F)

New miniaturequartz crystalA miniature ceramic packaged8-20 MHz AT -cut quartz crystal,the ETA CX-AT, is announcedby Stanler Components Ltd. forboth surface mounting andthrough -the -board applications.The CX-AT is designed for usein simple Pierce oscillators andis manufactured with a photo-lithographic process usingstate -of -the -an equipment andMicroCrystals' know-how ac-quired in producing millions ofcrystals for ETA's famous watchmovements.The rugged miniature ceramicpackage is one quarter the sizeof an eightpin mini -DIP.These crystals have low aging,

high stability and low powerconsumption and can be sup-plied with standard frequencytolerances down to +/-50 ppmwith tighter tolerances availableon request. They can also be re-leased to full military specifica-tions.

Stanler Components Limited21 Benfield wayLakes RoadBraintreeEssex CMT 6YS.Telephone: (0376) 40902Telex: 987911 STANCO G

(3582:15:F)

Coupler/Splittersfor Fibre -opticLANsEdward Fletcher & Partners,who recently announced arange of terminated fibre -opticdata link cables starting at alength of 100 mm, now say thatthey have the facilities to makelow -loss fibre -optic coupler/splitters (biconical tapercouplers). In optical sensing,and local area networks (LANs),their main use is to tap datafrom a computer or other nodeinto a ring network linking of-fices together, or to take dataout of the ring. The use of fibreoptics in the LAN provideshigh -security interference -freecommunication for high-speeddata exchange between com-puters and other digital devicesin the network.

Coupler/splitters can be sup-plied in either of two grades ofplastic -coated silica fibre(p.c.s.): 50/125 or 85/125 grade.Standard types have four 200micron fibre tails. These acceptlight down any of the four tails,splitting it equally into the twoopposite tails. Very little light istransmitted through the fourthtail, providing a 50:50 or 3 dBsplitter. Other splitting ratioscan be supplied to order. in-cluding ins. couplers withmore than four tails.With cleaved fibre ends, and in-put to one port only, the inser-tion loss (excess loss) is typi-cally 1 dB, with a maximum of2 dB. The output/input signalratio is -0,6 dB, and directivity(backscatter into the adjacentinput port) typically 40 dB, witha minimum figure of 16 dB.

Couplers can be spliced into asystem or can be terminatedwith specified connectors. Dif-ferent diameters of coupler areavailable, and electrically non-conducting materials can besupplied if required.As well as computer appli-cations. coupler/splitters canbe used for the effective inter-communication or networkingof word processors, facsimilemachi- -s, telex terminals, elec-tronic mailbox devices, printersand much more, permittingmaximum use of available com-puter power and bulk memoryresources.Edward Fletcher & PartnersLimited25 West Park RoadKewSurrey TW9 4DB.Telephone: 01-876 2204Telex: WTC. LDN 884671 (EFP)

(3582:4:F)

Of PRODUCTS NEW PRODUCTS NE\ilProgrammableVHFmillivoitmeterThe 3440A is a reliable and cost-effective programmable RFmillivoltmeter with advancedcircuitry. Manufactured byBallantine. and available fromUK distributors PPM, the instru-ment provides superior per-formance. speed and con-venience in a meter that is

unrivalled in its class.Advanced circuitry and stabilitymake the flexible unit wellsuited to system measurement.field. and laboratory use. Theeasy to operate true RMS instru-ment features high resistance tohostile RF environment. shock.and vibration. Reliability isfurther enhanced using a solidstate monolithic chopper stab-ilised amplifier, audible noise isreduced to zero. Inside theprobe a self-regulating heaterkeeps the detector diodes at a

constant temperature elimin-ating calibration errors causedby temperature variation.Signals over the frequencyrange 10 kHz to 1.2 GHz aremeasured in eight ranges from1 mV to 3 V (FSD). Up to 30 mVresponse is true RMS permit-ting highly accurate non -sinus-oidal waveform calibration.From 30 mV to 3 V responsechanges from true RMS to peak -to -peak linear. An analog 'curvematching' circuit computes thechanging characteristic andcorrects it providing a high -linearity meter response overthe higher ranges. Ranges areprogrammable with TTL logicor optional IEEE488 buscoupler.

Probe design is enhanced util-ising a spring tip, a 50 ohm ter-minated adaptor mates withBNC or N -type connectors. Alsoavailable are a 50 ohm teeadap-tor, an unterminated (BNC/N)adaptor, and a 100:1 capacitivedivider.Traceable true RMS from 100 NVto 30 mV. 10 kHz to 1.2 GHz.Volts and dB level operation is100 pV to 300 V and -60 dB to+60 dB, 10 kHz to 1.2 GHz.Simplified relative gain/lossmeasurements - zero dB refer-ence continuously adjustableover 3 dB range.PPM Instrumentation LimitedHermitage RoadSt. JohnsWokingSurrey GU21 1TZ.Telephone: (04867) 80111

(3582:10:F)

Dual powersupply unit hastrue parallelmodeThe PL230 Quad -Mode Dualfrom Thurlby Electronics is adual 30 V, 2 A laboratory benchpower supply whose outputscan be automatically con-figured into any of four modesincluding true parallel.The four modes are selected bya bank of push-button switches.In isolated mode. the two PSUsoperate entirely independentlyof each other. In series mode.the two outputs can be set in-dependently but are internallylinked, whilst in series -trackingmode the master voltage con-trol sets up equal voltages onboth supplies. In parallel mode,the master unit is converted intoa true 30 V, 4 A PSU with thecurrent being measured on onemeter and no discontinuity oc-curring at any point.In independent mode, eachPSU has an output range of0-31 V and 0-2.2 A. Both line andload regulation are better than0.01% and ripple and noise arebelow 1 mV. Operation can beconstant voltage or constantcurrent with automatic cross-

over and indication. Remotesense terminals are provided tomaintain regulation at high cur-rents.Voltage and current levels aresimultaneously monitored tohigh resolution (10 mV and1 mA) using twin digit (3999count) meters per output. Adamping switch is incorporatedon the current meter to enablerapidly fluctuating currents tobe averaged out. A DC outputswitch enables each output tobe set precisely in terms of bothvoltage and current levelsbefore connection to the load.The PL320 Quad -Mode Dualmeasures 10 x 6.9 x 13.6 in.(255 x 175 x 345 mm) andweighs 191/2 lbs (9 kg). It costs£339. A dual 30 V-1 A version isalso available costing £269.Thurlby Electronics LimitedNew RoadSt. IvesHuntingdonCarobs EE17 4BG.Telephone: (0480) 63570

(3582:23)

Power line filtersprotectsensitivecircuitryA 3 -pole wide -bandwidthpower line filter from Rendar isdesigned for protection of sen-sitive circuitry against supply -borne interference.Featuring very high insertionloss, and offering a range ofcurrent ratings, the filter issuitable for many applicationsincluding protection of logiccircuitry and radio interferencesuppression of appliances.This high -quality product ismade by Feller of Switzerlandand is approved to UL. VDE andSEV specifications. A very highdegree of protection against in-terference coupling is providedby the rustprotected metalenclosure. The compact unit,with climatic classification toDIN 40040:HPF, is portable orrack -mountable, and offers theoption of universal tab or solderconnection.

Voltage rating is 250 VAC, cur-rent rating 1. 3. 6 or 10 A.Rendar LimitedDurban RoadSouth BerstedBognor RegisWest Sussex P022 9RL.Telephone: Bognor Regis(0243) 825811Telex: 86120 (3582:24:F)

1/2 Watt powersupply on achipNew from broadline distributorVerospeed is an AC to DCpower converter IC which onlyrequires a single filter capacitorto make a complete 5 Volt;100 mA power supply. Ideal forapplications where size, weight,component count and low costare all important. the MAX610IC can function directly from a110 V or 240 V AC mains supplywith the addition of a currentlimiting resistor and capacitorto provide up to 1/2 Watt ofregulated power.Packaged in an 8 pin plasticDIP, the device can dissipate750 mW (at 25°C) and can ac-cept various repetitive or non -repetitive AC inputs. Operatingtemperature range is 0 to 70°Cand maximum output current is150 mA.The MAX6I0 is a power supplyIC and as such must be en-closed to avoid any shock haz-ard.VerospeedStansted RoadBoyatt Wood Industrial EstateEastleighHants SOS 4ZY.Telephone: 0703 641111 (3582:21)

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April 1987

PRODUCTS NEW PRODUCTS NEViiNew battery-

operated,portableoscilloscopeElectronic Brokers has in-troduced the Thandar SCI10Abattery -operated, portable os-cilloscope which has a band-width of DC to 10 MHz and asensitivity of 10 mV/div to50 V/div in 12 ranges.Ease of use and batterypowering enable this instru-ment to be effectively em-ployed in service applicationswhere conventional mainspowered instruments cannot beused.The SC1IOA can be mains- orbattery -operated and has atypical power consumption of350 mW, with bright line autoand economy triggering modesfor ease of use and battery con-servation.The instrument has a 32 mm x26 mm screen with a blue -whitephosphor display and fivehorizontal and four verticalgraticule divisions. External ad-justments include intensity,focus, and trace rotate.Timebase sweep times are0.1 us/div to 0.5 s/div in 21

ranges and the calibration ac-curacy is ±3% for 0.2 ps/div to0.5 s/div ranges with ± 10% for0.1 ps/div.Coupling is switchable d.c., a.c.,TV frame or TV line. The inputimpedance is 1 Mir in parallelwith 47 pF, with maximum inputbeing 350 V DC and peak ACprovided the DC componentdoes not exceed 250 V.A range of optional accessories

are available including ACadaptor, carrying case,rechargeable battery units, pro-bes and bench instrumentracks.

Electronic Broker Limited140-146 Camden StreetLondon NW1 9PB.Telephone: 01-267 7070Telex: 298694Fax: 01-267 7363 (3582:11:F)

New cableidentificationsystemA low cost approach to cableidentification has been taken byTMK Instruments with theirbrand new TEM 6000 TracelTCable Identifier. Designed andmanufactured in the UK the in-strument could not be easier touse with just the ON/OFFswitch, operating instructionsand battery low indication onthe TEM 6000 which acts as thesignal transmitter for the sys-tem.Costs are reduced and flexi-bility increased by using a stan-dard Digital Multimeter as thereceiver to identify up to 10

lines of any length and size.with the DMM being availableand probably necessary forother tests. Ideal for all cabletracing applications thislightweight handheld or "hangon" device saves time andhence money in sorting outthree phase installation and linecommunication wiring.TracelT is powered by a single

9 volt battery, is housed in ahigh impact resistant ABS casemeasuring only 102 x 61 x26 mm and weighs a mere170 gms. This latest instrumentfrom TMK comes ready for usewith: eleven numbered testleads 155 mm long fitted withcroc-clips. battery, operating in-structions and a carrying case.The TEM 6000 costs ex-clusive of VAT.

Harris Electronics (London)138 Grays Inn RoadLondon WC1X 8AX.Telephone: 01 837 7937

(3582:12:F)

Low noiseSATCOMamplifiersFerranti is now offering un-cooled Ku -Band low noiseamplifiers with a maximumnoise temperature of 150 Kelvinand a typical performance of135 Kelvin.The new amplifiers cover the10.95 GHz to 12.75 GHz (Ku) fre-quency bands and are suitablefor use in any Ku band earthterminal.The amplifiers are manufac-tured to the highest quality stan-dards in a facility which isapproved to DEF STAN 05-21,and feature state-of-the-art tech-nology in both devices and cir-cuits to achieve the ultra lownoise temperature.Amplifiers can be supplied to

standard specifications, orcustomised to meet individualcustomer requirements byusing alternative amplificationstages from an extensive libraryof modular designs.In addition to the basic ampli-fier both redundant and non -redundant amplifier sub-systems are available togetherwith local or remote monitor/control systems.Ferranti Electronics LimitedMicrowave DivisionFirst AvenuePoynton Industrial EstateStockport SK12 1NE.Telephone: (0625) 871611Telex: 666786 (3582:1)

New high-speed RAMRapid Silicon have added thenew IMS 1630 high-perform-ance, 8 K x 8 static RAM to theirrange of INMOS memory de-vices.The IMS 1630 is a very highspeed CMOS device that com-plies with 1.6 micron designrules. It requires no externalclocks or timing strobes,features equal address accessand cycle times and is fully TTLcompatible.A Chip Enable function is pro-vided and can be used to placethe device in a low -powerstandby mode, thereby reduc-ing power to 25 mA ('ra levels).By using CMOS levels, standbypower can be decreased evenfurther to only 14 mA.The IMS 1630 is available inthree versions with address ac-cess/cycle times of 45. 55 or70 nsec. Device characteristicsinclude common data inputsand outputs. single +5 V ±10%operation, and a fast write cyclewhen outputs are disabled.All versions of the device aresupplied in a JEDEC standard28 -pin 600 -mil ceramic DIP.

Rapid SiliconRapid HouseDenmark StreetHigh WycombeBucks HPU 2ERTelephone: (0494) 26271

(3582:22)

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April 1987

0/ PRODUCTS NEW PRODUCTS NE14,New high-performancecomputer partsNow available from Bedford -based RR Electronics is theSiemens SAB80286 high-per-formance microprocessor, withup to six times the performanceof the SAB8086.Designed for multi-user andmulti -tasking systems. theSAB80286 has built-in memoryprotection which supportsoperating system and task iso-lation as well as program anddata privacy within tasks. It

is upward -compatible withSAB8086 /8088 software.The SAB80286 also supports vir-tual memory systems by pro-viding a segment -not -presentexception and restartable in-structions. Also new in the RRrange of microprocessor partsis the SAB82258 advanced DMAcontroller for 16 -bit microcom-puter systems. It is designed es-pecially for the 16 -bit micro-processors SAB80286 andSAB8086/88/186/188. Operationwith other processors is sup-ported by a remote mode.The controller has four in-dependent DMA channelswhich can transfer data at up to8 Mbytes/sec at 8 MHz clockfrequency in a SAB80286 systemor up to 4 Mbytes/sec at 8 MHzin a 8086/186 system.This wide bandwidth enablesfast data transfer or the use ofmultiple peripherals at thesame time. The device isfabricated in advanced +5 V N -channel Siemens MYMOS tech-nology, housed in a 68 -pin

CLCC package.The controller works with allfive Siemens 16 -bit processorswithout extra support and inter-face logic because it has anadaptive bus interface tohandle the different signals.functions and timings.Because of this. bus compati-bility with identical timingis attained with processorsSAB80286/80186/8086. Compati-bility with the 8 -bit bus versionof processors SAB8088 and80188 is also guaranteed bydefining the physical bus widthof SAB82258 as 8 bits. by meansof software.RR Electronics LimitedSt. Martins WayCambridge RoadBedford MK42 OLF.Telephone: (0234) 47211

(3582:18:F)

16 -channelADC card forIBM PC,Model PC26 from AmpliconLiveLine Limited is a low cost,16 -channel, 12 -bit ADC card forthe IBM PC' or equivalentcomputer.Supplied complete with sam-pling software and user manual,the analogue inputs may besampled at up to 200 times persecond using Basic. 2,000 persecond using Turbo Pascal orfrom one per hour to 30,000 persecond using an additional soft-ware package PC28A.Input voltages may be uni-polar

or bi-polar, the conversion tech-nique is successive approxima-tion with 35 micro secondsconversion time.The PC26 is suitable for usewith any compatible colourgraphics card enabling data tobe easily displayed and assimi-lated.Economically priced at £193,

the PC26 occupies one slotin the computer and is de-spatched the same day fororders received up to 5pm.

IBM and IBM PC are registeredtrademarks of InternationalBusiness Machines, Inc.Amplicon Liveline LimitedCentenary Industrial estateBrightonEast Sussex BN2 4AW.Telephone: 0800 525 335(freephone)(0273) 570220Fax: (0273) 570215Telex: 87563. (3582:6r)

IntegratedprogrammabletemperaturesensorI.D.E., a division of BeamlistLimited. announce the in-troductionof an integrated pro-granunable temperature sensorcircuit.The TEMPO1 is a low operating

voltage (down to 1.2 V) mono-lithic temperature sensor thatcan be externally set to anydesired set point (0°C to+85°C). At the preset level thedevice will give a frequencyoutput (which is also program-mable) that will directly drivemost typesducers.To operate the device, all that isrequired are 4 resistors 2 lowvalue capacitors and a trans-ducer (output). The device itselfneeds to be in contact or closeproximity to the surface to bemonitored.In addition the product has amonostable action which "selfchecks" the operation by out-puting a different frequencyduring the positive temperaturegradient.The part is designed with lowvoltage and low current con-sumption in mind and is idealfor battery-powered appli-cations. The TEMPO1 is avail-able in both 8 -pin DIP and 8 -pinsmall outline package.Further information is availablefrom:

Beamlist LimitedUnit 2The HollowayBath RoadLittlewick GreenBerkshire SL6 3QT.Telephone: 062 882 2529Telex: 849910Fax: 07357 5257 (3582:14)

Of PRODUCTS NEW PRODUCTS NE1AReal-timegraphicspackageThere are currently manyGraphics Packages availablethat attempt to exploit the BBCMicro's graphics facilities, manyof which can produce im-pressive pictures. This is fine ifyou are content with the `pic-ture' being the final productwith no further real applicationof your efforts.The REALTIME GRAPHICSSYSTEM, however, promisesmuch more. This uniquepackage allows you to createany 3D wireframe object andthen to use the resulting 3D ob-jects with the REALTIMEGRAPHICS language ROM inyour Basic or Assembler to pro-duce some stunning animatedsequences.The system is supplied on a32 K Graphics Rom and fivediscs with a 115 page Manualwhich features an integrated setof design and applicationsfacilities. These consist of themain 3D Design System Disc,Multi -plotter Driver Disc. Appli-cations Disc, Database LibraryDisc, a Realtime DemonstrationDisc and the REALTIMEGRAPHICS language ROM. Onbootup the main Design Systemdisplays a main menu whichleads the user through a hier-archy of well designed & in-teractive sub -menus.Although the Design systemworks perfectly well with singledisc drive setups, a 'Configura-tion option allows the user totake advantage of dual drives sothat a larger database library ofmodels can always be on-lineduring a design process. The'System Editor' is the heart ofthe Design system and providessome sophisticated facilities tocreate complex structures witha minimum of data entry.These include an interactive`Editor for creating & editingmodels using a simple 3D Move& Draw vector format with each3D line having its individualcolour and linetype (solid ordotted) specified for multi-coloured objects.The most powerful feature ofthe Design system is undoubt-

edly the 3D 'Macro' facilitywhich allows any objectcreated by the 'Editor or 'Pro-file' to be used as a macro, i.e. abuilding block, which can begenerally modified in differentways by stretching, rotaring &positioning it to form part of amore complex object. Thecomplete object can then in -turn be used as a macro to formpart of an even more complexobject. This is another particu-larly powerful recursive feature.In this way complex objects canbe built up with the minimum ofdata entry.Hence a designer can easilycreate a huge database libraryof models, assuming an unlimi-ted supply of discs, to providea varied selection with whichto make the design processeasier. A `Filer' option providesfacilities to maintain theselibraries.The complexity of your designsis only limited by your imagina-tion and the Beeb's memory.The 6502 Second Processor isfully supported so even morecomplex objects can becreated. Hardcopy facilities arealso provided for Epson com-patible printers while agraphics to disc dump allowsuse of other printer drivers andfurther image processing byscreen -image oriented softwaresuch as 'AMX ART'. Incidentallythe system's menus are con-trolled entirely by cursor keyshence it is also 'AMX MOUSE'compatible.A Data Convertor is also pro-vided to allow the REALTIMEGRAPHICS SYSTEM to be inter-faced to other CAD Systems orapplications. Hence design orscientific data from othersystems can be read into theRealtime Graphics System for3D Manipulation. Data from thissystem can just as easily be out-put to a textfile for processingby other applications.The Realtime Graphics System/Language package costs£79.95, inclusive of VAT, and isavailable from

Silicon Vision Limited47 Dadley GardensHarrowMiddlesex HA2 ODQ.Telephone: 01 442 2274 (3582:5)

Miniatureprinter forportableinstrumentationIdeal for use in portable instru-ment applications, a miniaturedesk -top printer unit from Elec-tronic and Computer WorkshopLtd. (ECW), provides 40 charac-ters/line text and high resol-ution graphics output for alltypes of portable instrumen-tation.The printer, the MP -234-40, iscontained in an attractive blackmoulded case and contains theprinter mechanism with theplain -paper roll. Room is pro-vided for a controller board,such as the MP -181 parallel in-terfaced board, while the frontpanel can include a calculator -style keypad and display, if re-quired.The MP -234-40 utilises a high re-liability plain -paper printingmechanism which uses 58 mmwide plain paper rolls andgives 240 graphic dots per line,with a dot spacing of 0.2 mm.The mechanism gives a qualityprint appearance of use in port-able equipment, instrumentfront panels and other dataprinting applications.ECW offers the MP -234-40

printer at a mail-order price of£74.63, including post/packag-ing and VAT.

Electronic and ComputerWorkshop Limited171 Broomfield RoadChelmsfordEssex CM1 1RY.Telephone: (0245) 262149

(3582:16)

New softwarefor electronicdesignSchema, a new low-costschematic capture program, of-fers a complete solution to elec-tronic circuit design fromconcept to printed circuitboard. Easy -to -use, Schemaenables even first time users to

draw schematics quickly andefficiently and create designdocumentation automatically.The package is supplied byEngineering Solutions Limited,which specialises in a range oflow cost hardware and softwaretools for professional engin-eers.The Schema package forms ahighly -integrated engineeringtool. consisting of a DrawingEditor, Object Database andPost Processors.The powerful Drawing Editor,accessed through a mouse -driven interface, features real-time interaction, three zoomlevels for optimum viewing,regional editing and commandrepetitionThe Object Database contains alibrary of the most popularanalog, discrete, CMOS, micro-processor and memory de-vices, as well as many generalpurpose objects whith simplifythe creation of schematics andflow charts. Schema's post -processors can generate hard -copies of the drawings, bills ofmaterials, wire and net lists anddesign rule check and usagereports.The package runs on IBMPC/XT/AT' computers andcompatibles and supports mostpopular graphics cards,printers, plotters and mousedevices. Schema operates effi-ciently from either dual floppydisk or hard disk -basedsystems, and is also designedfor large local area networkconfigurations.An interactive evaluation diskand instructions are available atnominal cost from Engineering'Solutions.

IBM and IBM PC XT/AT areregistered trademarks of Inter-national Business Machines,Inc.

Engineering Solutions LimitedKing's House18 King StreetMaidenheadBerkshire SL6 1EF.Telephone: (0628) 36052Telex: 849462 TELFAC GFax: 0628 74928 (3582:9)

79 EE

April 1987

£1 BAKERS DOZEN PARCELSFr -a per parcel is 11.00. but if you order 12you get one extra free.All the parcels laded below are brand new componentsUnless /narked sit.

1 - 5 13 amp ring main jur,-tion bores2 - 5 13 amp ring main spur bores

-3 flush eamuical snitches7 - 4 in flex line snitches with neon8 -2 89 watt brass cased elements9 - 2 mains transformers with er la sezonclaries

10 - 2 masts transformers with 12w Ea sermridarith11 - 1 extension speaker cabinet for 61.3- awake -12 - 5 octal bases for relays or saves13 - 12 glass r:1 switches14 - 4 OCP 70 photo transistors15 - 25 assorted germanium thavaraors 0C45 etc16 - 4 tape heath. 2 record 2 erase17 - 2 utha song Penal -Ours and 2 etto recenws18 - 2 15000 ofd computer grade elmtralcs19 -2 light dependent reastors20 -5 afferent nacro owtchth21 - 2 meats mterterence suasessorsZ2 - 225 watt crossover units23 - 1 40 wart 3 way crossover wit28 - 1 6 digit counter meats solace29 - 1 BOAC in Right stereo unit (second hand)33 - 2 Woad battery chargers31 - 1 key snitch with key32 - 2 hininary snitches33 - 2 aerosol cans of ICI Dry Lubricant34 - 96 v. 1 metre lengths cams -coded connecting33 - 2 ale spaced 2 gang tuning condensors37 - 2 solid rawl.rruic 2 gang tuning condensor538 - 10 compression trimmers39 - Long and Medium wave tuner Laso 4 . 465 KC IF transformers41 -6 Rocker Switches TO amp Mains SPST43 - 5 Racier Switches 10 amp SPOT Centre Off44 - 4 Rocker Switches 10 amp DPDT45 - i 24 hour time switch maw* operated fs.h.I46 - 1 6 how dock aneswitch48 -2 fir operated reed switch reisys49 - 10 neon valves - make good raght Lights50 -2 12 tIC or 24V AC 4C0 relays51 - 1 i- 12 y 2C 0 vay sensitive relay52 - 1 I2v SC relay53 - 2 mars operated relays 3 8 amp changeovers54 - 10 rani of 32 gold paled IC sockets Itotal 320

sockets)55 - Hocking mechansm with 2 keys56 - Meaature Uniselector with circuit for electric ligsanv57 - 5 0035' House switches59 - 2 fat maenads - ideal to metre current transfamerCO - 5 ferrite rods 4" 5 '16" diameter awiaM61 - 4 ferrite Sob aerials with LEM wave cols62 -4 203 nun earpieces63 - 1 Mulard Tboistor !avow rood:3a64 - 10 assorted knobs la spindle -s

- 5 afferent thermostats. rids bi-frietal66 - Meoratg brake - stops rotation instentry67 - Low pressure 3 boat snitch

- 225 wed pOn. 8 ohm70 - 2 25 watt pots 1000 ohm71 - 4 were word pots - 18. 33. 50 and 103 ohm73 - 4 3 wart wire wound pots 50 ohm74 - 50 "3 watt carbon rAm resstors food spread 10 valv.-75 - 20 2 watt carbon resistors 10 values76 -3) 1 watt carbon resistors 15 df values77 - 1 time urn -rider ado -table 1-e) rents78 - 5.5 amp stud rectifiers 407i81 - 2 3)a panel mountirg slicTiok fuses82 - 4 porcelain fuse holders and fuses84 - 10,1 sit mains voltage suppressor coal -macesBS - I mails shaded pis motor fs" suck 11 shaftB6 -2 5" eh fan Wades fit 1i" shaft87 - 2 3" plastic fan bad. fa 1." shahEH - Miura motor suitable for above Lead-.89 - 1 mains -motor with gear but 1 rev per 24 hours91 - 2 mains motor with gear bat 16 rpm93 - 4 11 per moulded bases for relays94 -5 FOG rare bases95 - 4 skirted BSA rate bases96 - 1 thermostat for fridge98 - 1 rnatonsecl Stud Sr/Ch Is h

101 - 1 212 boos delay snitch103 - 1 .5. - or. war supply unit104 - 1 .1- - - . Supt14 urn

- 1 E :. -g and panel socket1E6 . 2 1.7. t._-; read bleepers107 5 __ - zr redo cabinet with hawseICS - 13 . _ -Ye ripe volume controls110 - 10 Ssier rice volume comas112 - 1 ratting Cad 170 watts114 - 1

115 - . - . 24y117 - 4 be .t at- "...nate clips118 - Teak effect eaters:.- ....raker cabinet120 - P.C.b. with 2 anus -.a and 17 other recs.122 - 19 moo - . ' white p.v.c. thaw124 - TO asserted s r= -3. :132 -2 pang boxes zraws. ideal for interrupted

be3 _witch etc_155 - 3 - .azi push button tuners with knobs16/3 - 1 ==- 7 boa. sloping metal front, sizeI6 95mm,

a. r-- depth 45rran241 - 1 :.= speaker (wary flail 6 St 15 ohm made for

Pat _

243 - 2 sin vs 6- x 4- 15 ohm 5 wan made for Ratio

2£6 - 2 riser* tram -formers SV i,A secondary spa primaryso OK also for 115V

267 - 1 mains transformer 15V IA secondary PCB mounting318 - 1 Metal box with par in id. am 6" Iona 3E" wide

2- deep326 - 1 4 an clock work terse switch323 - 1 clock ctispay 13mm figures LCD330 -2 in -0-6v mains trareOnner 3A p.c b. mg -amino350 - 40 double pole leaf switches351 - 2 1 watt record payer amps335 - 1 Tuf 6133y 5241z metal cased condenser

EHT CAPACITORS - new dab -are of 121v ceramics 'fag!. 2.for El. ref 130439, Sky cwarnms 220pf, 4 for El. ref 80440swamies 15014. 5 for El. ref 80441.

MOW . 11W TRANSFORMER to isolate sou or yours frommar* to earth shock dangers. We are able to offer these trarformers at less then the price of a normal auto transformer.price for the 500w rafts to 115.- isolation transformer is CIOca us E5 post, ref 10P6THIS MONTH'S SNIP er Me car starter charger 1987 modelFr, mrse offered in its spec" designed metal case Wish ma, ,= compact and efficient unit. Compateh. palt =

..-esent for the motorist_ Special snip' price of 05.51 :stage.

VENNER TIME SWITCHMains operated with 20 amp snitch, cron and one off per 24 hrs repeats dailyautomatize:), correcting for thelengthening a the shorten no day. AnexPensive time switch but you can haved for coly 12-95 without case, metal case- 82.95, adaptor let to convert [Iles intoa normal 241v. titer switch but with theadded advantage of up to 12 on:offs per24hrs Thus makes an ideal condoler for

EnEteetneity Board. the immerion heater. Price of adaptorGuaranteed 12 months- kit in 12-31:112 volt MOTORS BY SMITHSMade for use trl cars. etc these arewry powerful and easy, rowsige Si

long by 3-69. They have agood Josiah of la" spindle110 no E3.451 Bhp 15.75 1 6 hp f7.50

th.1-0 1.,11i11

C of pans for a date charnel sound to tight unitcontrol:rig over 2003 watts of fighting Use this at home if youwish bit a * plenty rugged enough for cEsCO work_ the unit tohoused O an attractive two tone metal case and has contras foreach olivine', and a master on -off The auto input arid outputare by '4". sockets- and three panel mountang fuse holders plan.de thyristor protection. A four pet plug and socket teak-tete easeof connecting lamps. Special price is £14.95 n kit form.TELEPHONE BITS SOCKETS ETC toe 87 phonth.Master socket (hat surge arrestor - ringing tuudynea. act andtakes 13,7 plug £356Extension socket 12.95Dual adaptors 12 from one socket) 13.95Cord terminating with B.F. plug 3 metres . 12.95Kat for corrceeting odd entry terminal bor to new d T Mailersocket. complete with 4 core cable. cable atm and 2 BTegension sockets L11.50EXTENSION TELEPHONE CABLE 4 core. standard cams coda100 metre reel. 19-59 or 20 metres. 12. tot 2P9625A ELECTRICAL PROGRAMMERLeant in your 5seep. Hare radio playing andkettle tong as you wale - switch On Lights toward off saruders - have a warm ho -use to co-me home to. You can do a: these and more. Bya famous maker with 25 amp on off snitch.Independent 60 Minute rniernOrY taggelA beautrfail unit at 1250400W MAINS TO 220V ISOLATION TRANSFORMER Toroidalwound so very compact Has a separate 10V winding Much canbe added or subtracted to the other winding to case -fine voltagecontrol. Nonierle £40. our prCe LIO plus E2 post. ref 1099.50V 2A FULLY SHROUDED MAINS TRANSFORMER Uprightrrountog with Sr.1 winding for plot fights, etc. Elea:3Maymade transformer. Price 13. ref. 3P10.6 RPM 50W MAINS DRIVEN MOTOR AND GEARBOX. Thishas 3 sq rrouniing plates and is appro.. 4" deep- ltd ashaded pate motor but has a de.-c.e tined an the 5,1 of theshaft to make it stop the moment the current is switched offBr and ea -n, price M. ref 5P74TANGENTIAL BLOWER HEATERS We roe have re.onatgestacks of these, in fact it anything we Isere a mare vaned VC,.than 13S1 veal. We can sutras-1.21CW - quite catotelv the smalest wing -amid blase healer wehave on had. meas..- approx. 6 6 4. This could betotter the tlEng for a = bedroom or to fit uncles desk or table is

in ad -1,,, to normal heating tuna.-. rot into a s- , s could be a pipe unfreeew- -- thfre than a c - even a pant stripper.

- - t-.er or hard E f1 post, ref 5P23.2.5KW - width appro. _e motor/ eiemthas made up of-3.n 1 2kw sections_ so is ..stch suppled you can have 2kw.

odd blow. Over tee: out el ninateS fee risk ShOuld- a or ae Rove be 'ingested Fan dada are metal Price £5

- : 50 post. ref 59623KW - width allOnai. 13- plus motor, element made up of lkwand bre section. suppled with 4 section rocks swatch. easo.reng3kw, 25w Ilsw and cold blow Pure £6.95 of., E2-0) PastSTEPPER MOTOR by Amanda- - Step arga7 5._ Cal resistance 27 of fr - . _ - 14. Sire ap-prox. 21k- Ma by Irv" deep on 3 :5,1-a,: plate_ PM isin fact me bi auctorial motors with P. _ rotors. App41110 pulsecauses a 75. step angle of spindle_ Number of steps dram,.which a rotates and a slated at winch it rotates is determined bythe bagged impulses. Property used this providft an cleat me -hod of speed and position control_ Brand new and areeeed.

Prge £5, ref SPILL

IONISER KIT Refresh your home. &foe, shop, workroom. etc_ with a negative 10P1 genvalot Palates you feelbetter and wan harder - a corrave mains operated kit. caseinchMed.E11.95 plus C200 post

BIG GLASS FIBRE SHEETS. Vortf.taty unlareek.Mle, size 4'alsIxot Flat. aPlarat. 1/16- third- Ideal for elastronic kvamls.also roof repay- Car ports, greenhouses, etc. E2 each_ Minimumwarmly we cart despatch is 10, Carnage cost £650 per 10,£8.50 for 15HOLROY0 GEARBOX. This has a ratio of 30 I. It 6 51.s"high. 4"s" wide. 4" dick. Int-et Output shaft is a".11 looks a very capable um: hand a few horomov.eNov and unused. price EIO - E2. ref 16P11

J & N BULL ELECTRICALDEPT. EL. 250 PORTLAND ROAD

HOVE, BRIGHTON.SUSSEX BN3 5QT

MAIL ORDER TERMS CASH. P 0 -- pos.. Orawslsr azd ..17 sot-. a3 . = - Orfkr-4 aCCEVIECI

and A. s .ccciedPita, Boanton i0273, 34643

TWO POUNDERSFc.,ase-g ci we BAKERS Donn ftPARCELS. we are now earotheing some BAKERSDOZEN C2 PARCELS. We tad ti -at yam wit ag---re that most are obeytinsel bargares bat you can sal get a IM ewe as won de C1 percer,yeti bay 12 you get another free`

292 - Wat inC.1121g trarmaar, 1.511 crecs.xl 113411 rreroxysnitch and thermostat

1.4 -24 wets psi yeah sesame dannets fa saw as for WIlard U111LEX Amplifeth

296 - ILG watt mans re 115 was astatraerdamer nett steta2_EaaPTS.

278 - Mere manor with gear bar as vacate steel meteorSales word so sit.kia fa further speed control

299 - Torso and wt switch Bored, Iths fronted and with SnobsCantras up to 15 ants. Ideal to proawn Wears hee_.-a-s.binary chargers etc

2910- 12 vat 5 err* mans trangcemer- Power ard. mods* Mand Unee, EP3070 inote sacs t,_

amp mot. r '_'-.sex 9701 in 60216)2912-- Usk t-asisim motor - Eafarced rota am

. Cie,-:-.ed 153) rprn2P14 -b; 7 - ern: swank2915- -'r - ra atams. cants* etc.2P17- 7 1' mace with gear boe., deg tp

2918- Ler5d'gas teat oti va'se mars solenoid spectra21.19- Disco snitch motor dives 6 a more 10 arc chase over tee

ac sw¢sles roppEed reedy for mans ace -Mon2P20- 20 metres extensian lead. 2 cat - deal rnthu Bock as

Decker garden tools2921- io wan &I -Wes. Mora C matte to coon 11732722- Motor Ofht. switch 20 secs on a off after path2P24- Cfooknak operated 12 hoe snitch 15A rtiOV21.25- WOO watt &w hat mans rrANO, driasZE26- CConler rthetteba mars operated 3 digt2927- G.,06,:,*Knoler 6 inch foxed Barn 12 wan2928- Ora Pump - Sways useful couciles to amii cal2931- 4 metres 98 way intwoomeong nire wry to grip to use de

coca separately2912- Hot Wye asp mans - 4 rood %PUCE 17...tInrAg - ,

WI working and deregere a bit ol history2934- Sohamd Si- Verve roans emanated2933- 270 B P.M. Geared Mains Man 1" sect gale ponewt.

large vougli to dent a rasing avid a a tattierfa east -mg stones etc.

2P43- Blown a ermicta fan. motor inset so very corgenttossed_

2P45- Os taro.* drD cCntrOl Est comathe and wilt c-aseTelephow ringing sew reckon mans to 50 with and chan-ges flecewcy from 50 Hz MB Hato give eight frgeg tow

2949- Fre tilt -nom, break glens EVOIth n rani can cow21.51- readoteme annifer. with peamp and narrai

2993- V- - extra panerful nth 11," sea and gaol lengthc' e both erth

2961- 1 - - n oval kit for Unto.2962- 1 ;.- C-oodimass 15zeim mamas for antis.276.1-- 1 f, e Oz-ded fan 6 enth maim maze21'67- I 12r 0-12y 2 amp math ow -earner2Pe- 1 15.-0-12Y 2 orate mains tranearnn2P69- t 2J1.,42Eoc 60 rnA Er 6.3 V 54 mans2700- 1 EM 1 time motor two speed and *manta2772- 1 115v liksfrn fen I- . 4- epic,2P75- 1 2 hour tsar, plugs into 13A socket2E12- Sc 09v 2 amp maks trasforwZ1134- Malan board nets pew kos2PE5 - 253r0-29. !-rA Mans qa.--)trner21.29- 113 tears tams swath2993- 33 mart tone switch :,ease 5,73.51 con:role,2P%- 134 maw on sztn C1. _ very schoh,x +.1 EC2797- mars Oanskerret 24. chi rrounteg2P98- 21)rn 4 care zek.uhceu e outer2P39- 500 rued pat tyre= se es fie sk.An cane

29161 - nano transformer 1St 4A sorsa racurarg291178- tor Virg IlOrcm2P119- 5" wide 0.36 Acfresi,e. ons tape 33m, add El post 31 rot t.

bang

OVER 400 GIFTSYOU CAN CHOOSE FROMrea. Sitte :titre -4)3,7.M.- :in irt,j d:Zr

iietX ad to.: :were sated q a Mromen mob II. bad 7 rempata

aufel -x S rdoe "fee e Lacer. te ercced: =ram* main or totter* art

f5 POUNDERS*sPi 12 volt pump ecrrorete voth a tap svincti592 Swea, " -. ,r complete suitable fa op to Mina=SFS 75. - = transformer to mirth stur senate borsch

- _ no £3 postage d sou can't crAect as this is 3

596 1.E. _ _ ' 6- gong. se-loa fa oralca dpro - area rental Er GPO but garvanteed

5918 rma".co arise water Dung as fined to many washi-o rtuthree

5r6 2 Let. rrmator sue, sun alana trammanw and FM reeerier

5923 mat urgent -di blow heats. 13n5P24 '.hp motor. or caTharta. Mr. nuns opera -ton 1453an

Mt theact add £3 post575 spe.1 effeCiS dghtng switch. Up to 6 clareins of tar. Fm

can he on a off fa varying one periods5927 ca fridge ale. 12Y ha. h.Th stereo am:Min5832 1:4cie mans coerated p_ahor pu'l eatenoct so E.,

El 51573 nothun toad from telephone auto dater. ;Seta was

'wised as as ICs5P37 24 5.0diSCh, 2 C. -Oni and cdOciaesk resent. Er

1.4Erig Lo 534 Ada 11 postToP41 5 , tan poet wee' sin, enter 12 mats_51.45 _ 7: svotches5918 tea_ ova-, . n Wei ca -n-. et -GPO5P51 207., t -3:a :". ... My to 115. to idsSP52 mans = :1.1' . ICA uptight trounh-o. add f2 pos-5951 mins , frsi Speed Ercen5953 Amstrad saw. Fl.t and Lad and 5.4M5962 rffkiv targentia 'eater. add f1.53 post if not to:eating

LIGHT CHASER KIT Mato, ci6,-er, switch bars,with casnectrori Magrarn. used in connection With 4 setsof X -as fights makes a nay eye catching display forhome. shop or dem. only £5 ref 51156.

MINI MONO AMP on p c..b size 4 7' app IFated volume control and a hole for a tone con -trot should you rewire it The arglifierras three trans:mots and we than.ate the output to be 3W rmsMore teChnnel data yeff be includedwith the amp. Brand new.perfect concEtiOn, Offered at the verylaw price of 11.15 each, or 10 for nom

olease mention ELEKTOR ELECTRONICS when contacting advertisers

IN METERS ..WE'RE MILES A

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Multimet eers fromour /arge range

A. Pocket Digital MultimeterA calculator size autoranging DMM whichreads lmV-400V DC, 1mV-400V AC, 0.111-2M.O. and has a continuity buzzer.Overall size only 120 x 75 x 15mm.Order Code YN78K

Hobb'' 7)igital MultimeterAvery high quality multimeter at a very lowprice! 14 selectable ranges covering AC andDC volts, DC current and resistance. Also has adiode junction test range.Order Code YM63T Price £28.95

Auto Ranging Digital Multimeterwith Transistor TesterA 6 position rotary switch selects off, volts,ohms/continuity, 20M.0., 200mA/hF:-. or 1 OA.Features include display hold, NPN and PNPtransistor tester, autorange override and lowbattery indication.Order Code YM64U Price £45.95All prices include VAT. Please add 50p towards postage.Prices firm until 9th May 1987. Subject to availability.

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ELECTRONIC SUPPLIES LTD.Mail Order: P.O. Box 3. Rayleigh, Essex SS6 8LR. Tel: Southend (0702) Sales: 554161,Enquiries: 552911: Trade sales: 554171. Trade enquiries: 552961.

ShopsBirmingham: Lynton Square, Perry Barr. Teleptone: 021 356 7292.London: 159-161 King Street. Hammersmith W6. Telephone: 01 748 0926.Manchester: 8 Oxford Road. Telephone: 061 236 0281.Southampton: 46-48 Bevois Valley Road. Telephone:0703 225831.Southend-on-Sea: 282-284 London Road, Westcliff-on-Sea, Essex. Tel: 0702 554000.All shops except Manchester closed all day Monday.

Pick up a copy of our 1987catalogue from any branch ofW.H. Smith for just £1.50.Or to receive your copy bypost just send £1.50 - 40pp & p to Mail Order address.If you live outside theU.K. please send £2.50 or 11International Reply Coupons.