RESULTS OF OUR SUMMER COMPETITION · Isolation amplifier Inter -IC communications Make our ()1st]...

THE INTERNATIONAL MAGAZINE FOR ELECTRONICS ENTHUSIASTSSeptember 1990 UK £1.70

S-VIIS RGB converter

I Iigh-current U1. tester

LF-I-IF test prohe

Isolation amplifier

Inter -IC communications

Make our ()1st] PCBs

RESULTS OF OUR SUMMER COMPETITION

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CONTENTSSeptember 1990Volume 16Number 181

In our next issue:Guitar tunerChopper opampsNegative resistanceMeasurement techniquesSingle'double symmetri-cal power supplyuP controlled telephoneexchangeMedium power audioamplifierDubbing mixerSelective preamplifier

Front coverElectronic and electrical engi-neering involves people andis for people - it covers awide spectrum of activitiesfrom the construction of thesmallest piece of electronicequipment. hardly visible tothe naked eye. to work onhuge power stations generat-ing electricity for a wholecommunity.Electricity and its associatedtechnology is so much a partof our day-to-day life that weoften take it for granted. Itcontributes to the manufac-ture of almost all productsfrom paper to food. from oilcans to oil rigs. from pushchairs to space vehicles. Ithelps to make our daily lifemore comfortable by runninghousehold appliances: itenables us to communicate.whether to our friends at theother side of town or to busi-ness colleagues on the otherside of the world: it con-tributes to our health in thecontrol and operation of hos-pital equipment.There are career prospectsfor many able men andwomen in electronic andelectrical engineering - seeCareers in Electronics onpage 60.

Copyright = 1990 Elektuur BV

ABC

62 WINNERS OF OUR SUMMER COMPETITION60 CAREERS IN ELECTRONICS22 & 64 PROFILES of Cricklewood Electronics.

Lord Transformers and Brian Price Bohm Organ Studios

LEADER11 Father of the microchip: a tribute to Robert Novice

AUDIO & HI-FI

37 PROJECT: Stereo playback amplifierby T. Giffard

COMPONENTS

15 Inter -IC communicationsH. Stenhouse

49 Isolating amplifiers

COMPUTERS & MICROPROCESSORS

28 PROJECT: ROM copy for 8052 -BASIC computerby E. Vermeulen

GENERAL INTEREST

14 PROJECT: Digital car engine lock with alarmb Nlithesh

18 PROJECT: Sound generatoran ELF' design

23 PROJECT: Infra -red remote controlby Giffard

30 Make your own PCBsby J. Buiting - Technical Editor

32 PROJECT: Automatic headlights switchby J. Ruffell

54 In quest of a pangram - Part 2by Lee C.F. Sallows

INTERMEDIATE PROJECT

34 Three in a rowby T. Giffard

RADIO & TELEVISION

46 PROJECT: S-VHS/CVBS-to-RGB converter - Part 1

by II. Reelsen

TEST & MEASUREMENT

20 PROJECT: LF/HF test probeby J. Bareford

26 PROJECT: 1.5 GHz prescalerby R. BOnsch

40 PROJECT: High -current hfe testerfrom an idea by C. Sanjay

MISCELLANEOUS INFORMATION

Electronics scene 12: New books 58: Events 59: Readers'Forum: Letters 62: Switchboard 63: Readers services 65:Terms of Business 66: Buyers guide 74: Index of advertisers 74.

We regret the omission duringprinting of the following warn-ing at the end of "Mini FMTransmitter" published in theJuly/August 1990 issue (3rd col-umn, page 35).

WARNING

Readers are advised that, al-though the use of the Mini FMTransmitter presents no prob-lem in many countries, its usein the United Kingdom is notallowed. It may also not be insome other countries and ad-vice should therefore besought from the relevantauthorities before constructionis begun.Anyone using the equipmentin the United Kingdom facespossible prosecution under therelevant section of the Wire-less Telegraphy Act.As a consequence, printed -cir-cuit board 896118 will beavailable only outside the UK.

Infra -red remote control - p. 23

S -VHS CVBS PAL -to -ROB converter

p. 46

ELEKTOR ELECTRONICS SEPT EMBER 1990

Please mention ELEKTOR ELECTRONICS when contacting advertisersATN-FILMNET DECODERELEKTOR MARCH 1989

Anyone in Western Europe in possession of a privatereception system for TV satellites must, at some time,have noticed that some channels can not be watch-ed unless an appropriate decoder is bought orrented. Hence, working on descrambter circuits is apopular and highly interesting pastime withtechnically inclined owners of satellite TV receivingequipment.This ATN-Filmnet decoder is remarkable for its re-liability, selectivity, automatic switch -over capabilityand low cost. Thanks to its versatile design. thedecoder is suitable for use with many commerciallyavailable indoor units.

Ordering andpaymentII Transfer total value of order to

GIRO account no. 4354087 (In-ternational Postal Order)

Eurocheque (do not forget tosign and fill in holder'sguarantee card number).

MI Bonk droft on N.M.B. Lindenloan Rijswijk Netherlands. Bank accountnumber 669561398.

All payments must be accom-panied by full name and ad-dress of customer.Postage and packing: £ 7,50 onall orders.EXPORT: divide total value oforder by 1.185.Meek -it ElektronikaMail Order ServicePaviljoensgracht 35A2512 BL DEN HAAGThe NetherlandsTelephone: (+31) 70 609554during normal business hours).

Astec modulatorUM1286 100.107 £ 4,90

MITSUMI TUNERUHF+ VHF 100.108 £ 7.50

VIDEO + AUDIO I.F. 100.116Amplifier module £ 11.40

SPECIAL PARTS SERVICEWe are the no 1 suppliers of hard -to -findcomponents for Elektor Electronics project&Always contact us first it you see art unfamiliar component. Items includeanalogue & digital ICs (NCI. SMD). precisionresistors (1%. 0,1%), capacitors (MKTstyroIlex). inductors (Neosid. Take), transducers,enclosures (Telef. OKW) and quartz crystals

ATN-FIlmnetdecoder

Kit like elektor.£ 59.00100.109

PLL-based synchronization regenerator Automatic encoded non -encoded switch -over Digital timing used throughout design Video processor is transparent to other satellite TV

channels Decoder retains multi -language Teletext Service Three buffered video outputs: VCR; monitor;

remodulator Separate FM synchronization receiver module for

fitting in indoor unit Simple -to -connect to most types of indoor unit, in-

cluding Elektor Electronics IOU Few alignment points No expensive components CMOS design ensures low current consumption

FOR THE SAT -TV -FANSInductor set for Filmnet-decoder:7AIS + 3893A + 586HM 100.110 £ 9.90

PLOTTER MARK-IIcompletely reworked version: see ElektorElectronics March 1990. Max. width 50 cm. All mechanical parts supplied ready -

drilled, filed and tapped, so get going atonce.

All guides made from stainless steel. Stableand attractive, they make the Elektor Elec-tronics plotter a fully-fledged product

Complete kit, including 2 stepper motors, 3pen lift solenoids, HPGL software on disk(IBM), stepper motor control board

100.100 £ 169.00

Separate parts also available: Mechanical parts set, incl. 3 pen lift

COLOUR TEST PATTERN GENERATORA PAL -compatible colour video source thatsupplies a number of test patterns for aligning television sets.A test pattern generator is virtually indispens-able for troubleshooting in television setsbecause it supplies a video signal that is

known to be stable, and thus easily displayedand synchronized on an oscilloscope.

Ina case and front! £ 99,-100.111

MICROPROCESSOR -CONTROLLEDFREQUENCY METERA professional grade multi -purpose frequencymeter, designed by Elektor Electronics, that can bebuilt by many at otfordable cost. Described inElektor Electronics December 1984, January &February 1985. 11665B -based prescaler.

Frequency meter:0.01 Hz to 1.2 GHz.

Pulse duration meter:0.1 s to 100 s.

Pulse counter:0 to 10° pulses

Period meter:10 ns to 100 ns

Sensitivity:input A: 10 mV,_; (Z, = 2 Mg);Input B: TTL or CMOS compatible (Z = 25 kg);input C: prescaler input: 10 my,-; (Z = 50 0).

II Auto -ranging and completely menu -driven.III 6 or 7 digit accuracy.

Kit includes power supply,prescaler and enclosure 100.112£ 169.00

BASIC COMPUTERwith Intel 8052AH-BASIC

£ 89.00100.117

solenoids, 2 stepper motors and HPGL soft-ware on disk (IBM) 100.102 £ 145,00 Analoge moduleStepper motor control board eps 880162 100.113 £ 30.00

100.103 £ 45.00 Digitale module' Main transformer prim -110.220 Volt

100.104Pen lift soldenoid (each) 100.105

£ 14.00£ 9.00

eps 880163Adres dekoder

100.114 £ 17.00

Stepper motor (200 steps) 100.106 £ 23.00 eps 880159 100.115 £ 11,00

FIEF:TOR ELECTRONICS SEPTEMBER 19911

FATHER OF THE MICROCHIPRobert Noyce who, together with Jack Kirby, was theco -inventor of the integrated circuit, died on 3 June.just after our previous edition had gone to press.

Noyce was born in Iowa on 12 December 1927. theson of a Congregational minister. He was an outstand-ing student at High School, showing particularpromise in mathematics and science subjects. He readphysics and mathematics at Grinnell College in hishometown and gained his bachelor's degree in the yearthat William Shockley invented the junction transistor(the point -contact transistor had been invented a yearearlier by John Bardeen, Walter Brattain and WilliamShockley).

While still an undergraduate, Noyce became inter-ested in solid-state physics, then taught at Grinnell byGrant Gale. His particular interest lay with the transis-tor, a device that would be part of his life for 42 years.After eraduatine at Grinnell, he went to the Mas-sachusetts Institute of Technology where he took hisdoctorate in physical electronics in 1953.

Noyce began his working life as a research engineerat the Philco Corporation in Philadelphia. which had justset up a new centre for research into semiconductors.

In 1956, Shockley set up his Semiconductor Labo-ratory in Mountain View. California, where Noyce anda number of other noted physicists joined him almostfrom the start. However, Shockley, unlike many of hiscontemporaries did not combine his scientific bril-liance with entrepreneurship and he was, moreover, adifficult man to get on with. Consequently. Noyce anda group of colleagues left Shockley to found a semi-conductor division at the Fairchild Camera and Instru-ments Corporation. ( Another illustrious figure atFairchild, working under Noyce, was Charlie Sporck,now president of National Semiconductor).

At that time, the circuit design requirements, partic-ularly in computers, of thousands of connections be-tween transistors and other components were gettingthe better of electronics engineers. While at Fairchild,

Produced and published by ELEKTORELECTRONICS (Publishing)

Ecfitorpublisher: Len SeymourTechnical Editor: J. ButtingEditorial Offices:Down HouseBroomhill RoadLONDON SW18 4J0EnglandTelephone: 081.877 1688 (National )or +44 81877 1688 (International)Telex: 917003 (LPC G)Fax: C81-874 9153 (National)or -44 81874 9153 (international)Advertising: PRB Limited3 Wolseley TerraceCHELTENHAM GL50 1THTelephone: (0242) 510760Fax: (0242) 226626Subscriptions:World Wide Subscription Service Ltd.Unit 4, Gibbs Reed FarmPashley RoadT10EHURST TN5 7HETelephone: (0580) 200657 (National )or +44 580 200 657 (International)

European Offices:Postbus 756190 AB BEEKThe NetherlandsTelephone: +31 4490 89444Telex: 56617 (elekt nI)Fax: +31 4490 70161Managing Director: M.M.J. Landman

Overseas editions:FRANCEElektor sariLes Trois TilleuisB.P. 59; 59850 NIEPPEEditors: D.R.S. MeyerG.C.P. RaedersdorfGERMANYElektor Verlag GmbHSfisterfeld Straffe 255100 AACHENEditor: E.J.A. KrempelsauerGREECEElektor EPEKanskaki 1416673 Voula - ATHENAEditor: E. Xanthoulis

Noyce conceived a way of eliminating the cumber-some wiring by etching the transistors and other com-ponents on to a single slice of silicon and connectingthem by metallic lines.

While Noyce was developing his version of the in-tegrated circuit, Jack Kirby, a staff scientist at TexasInstruments, came, completely independently, to thesame development. Consequently, both men are recog-nized by the US Patent Office as inventors of the mi-crochip. It is now history that their invention revolu-tionized electronics, made possible comprehensive in-creases in computer power, and gave the world manynew products, from pocket calculators through mi-crowave ovens to computerized flight plans for civiland military aircraft.

Despite his success at Fairchild, Noyce felt that healso had a contribution to make to the commercialworld and in 1968 he and a colleague, Gordon Moore,left Fairchild to form the Intel Corporation in Califor-nia's Silicon Valley. Under his leadership, Intel devel-oped and marketed the first central processing unit(cpu), or microprocessor. which is used, for example,as part of an automatic control system or as the mainelement of a microcomputer.

Unlike Shockley. Noyce proved himself to be an en-trepreneur par excellence as well as a brilliant scien-tist, and he soon became a distinctive fieure in thethrusting world of computers and allied equipment.

He played a prominent part in the commercialworld of electronics and became a spokesman and lob-byist for the US semiconductor industry. At the timeof his death he was president and chief executive ofSematech Inc. a research consortium set up to try andcatch up with Japanese developments in the semicon-ductor manufacturing industry. He was honoured bythe US Government on a number of occasions: in 1980he received the National Medal of Science from Presi-dent Carter and in 1987 the National Medal of Tech-nology from President Reagan.

INDIAElektor Electronics PVT LtdChhotani Building52C. Proctor Road. Grant Road (E)BOMBAY 400 007Editor: Surendra lyerISRAELElektorcalP 0 Box 41096TEL AVIV 61410Pubffsher: M. AvrahamNETHERLANDSElektuur BVPeter Trecicpoelstraat 2-46191 VK BEEKEditor: P.E.L. KersemakersPAKISTANElectra -shop35 Naseem PlazaLasbella ChawkKARACHI 5Editor: Zain AhmedPORTUGALFerreira & Bento Lda.R.D. Estefani, 32-1'1000 LISBOAEditor: Jeremias Sequeira

SPAINResistor Electronica AplicadaCalle Maudes 15 Entlo C.28003 MADRIDEditor: Agustin Gonzales BueltaSWEDENElectronic Press ABBox 550514105 HUDDINGEEditor: Bill CedrumUSA & CANADAElektor Electronics USAPO Box 876PETERBOROUGH NH 03458-0876Publisher: Edward T. Dell

Distribution:SEYMOUR1270 London RoadLONDON SW16 4DH

Printed in the Netherlands by NOB.Zoeterwoude

ELEKTOR ELECTRONICS SEPTEMBER 1990

£4 MILLION TO HELPDEAF PEOPLE USE THE PHONE

British Telecom is to provide £4 million ina major initiative to help deaf people makebetter use of the telephone.

A national relay service for the deaf andhard -of -hearing. developed and run by theRoyal National Institute for the Deaf withsupport from British Telecom. will replacethe current Telephone Exchange for theDeaf (TED). It allows deaf people to makeand receive telephone calls in text format ona computer screen.

NEW CRICKLEWOOD CATALOGUECricklewood Electronics has recently pub-lished its new 160 -page catalogue with over2400 new items. New ranges include hobbykits, microphones. speakers, headphones.video heads and aerials.

The catalogue, the company's fifteenthannual, is Cricklewood's 'shop window' forwhat the company describes as one of thelargest ranges of electronic components inthe UK.

More information on this catalogue maybe found on the inside back cover of thisisse.

INTELLIGENT DATABRIDGE FORTELETEXT TRANSMISSIONS

MRG Systems have developed an intelli-gent databridge. Type CT300. that enablesa national television station to transmit localteletext information from its central trans-mitter.

The CT300 not only reads incoming tele-text, buffers it. and retransmits it. but canalso decode and modify incoming packetsbefore transmission. Up to 200 pages of in-coming text can be replaced by locally gen-erated pages. Pages and control informationcan be derived from a personal computer viaa modem and the equipment's serial -lineinput.

The databridge can be controlled via aserial line or from its own 32 -character LCDand keypad.

Details from MRG Systems Ltd, WillowHouse, Slad Road, STROUD GL5 1QG.

d,4-dr) `I I 1.71 ci CI: 'I G4LI,E (;:) nr.J1JCi-D

CIRKIT CENTRALIZESDISTRIBUTION OPERATIONS

An improved and more efficient customerservice will be the result of a move to intro-duce centralized stocking arrangements byCirckit Distribution from the first of thismonth.

From that date. with the full aereementof its major electronic components andequipment suppliers. the company will sup-ply theirextensi e catalogue direct from onecentral warehouse at their Broxboume head-quarters.

The regional office at Portsmouth will beable to display instantly all product linestock information on screen via the com-puter link with Broxboume.

See Cirkies advertisement on page 9 formore information on its products.

A .F. POWER AMPLIFIERS FORPUBLIC ADDRESS AND CINEMAS

A ranee of small -size high -power four -channel al. amplifiers, the Quatro Series.intended primarily for public-address sys-tems. but also suitable for cinema sound sys-tems. is available from Monitech.

The units in the new series have a newlydesigned layout that makes them more com-pact than similar amplifiers with the samepower output. All amplifiers. 250 W. 500 \Vor 750 W per channel. fit into standard elec-tronics racks.

Nionitech. P 0 Box 313. CAMBRIDGECB4 4\1 N.

LUROPE'S FIRST FOUR -MEGABITCOMPUTER CHIPS

The Japanese semiconductor giant NEC haschosen its Scottish plant to produce ad-vanced four -megabit microchips for the firsttime outside Japan.

The company has announced a £30 mil-lion investment in the factory in Livingston,which will enable it to manufacture a neweeneration of silicon wafers capable of pro-ducing four million functions on a chip thesize of NEC's existing one -megabit wafer.

In what will be Scotland's first major in-ward investment from Korea. Amkor/Anam, the world's largest semiconductor as-sembler, is to buy the ITEQ Europe Com-pany in Irvine. The Korean company plansa f20 million expansion in the Irvine plant.

More information from the Scottish In-formation Office. GLASGOW.

NEW LONDON VENUE A SUCCESSFOR COMPUTER GRAPHICS

SHOWSLondon's Alexandra Palace will again be thevenue for the (tenth) Computer Graphicsand Desktop CAD events on 6-8 November.organized by Blenheim Online.

Research carried out by Blenheim On-line confirms that visitors were delightedwith last year's move to the Palace. first ope-nend in 1873 and recently restored to itsoriginal Victorian splendour while incorpo-rating the latest technology and expertise ap-propriate to a modern exhibition centre.

Computer Graphics is a broad -basedshow covering supercomputing and visual-ization. industrial design. broadcast and an-imation. business and presentation graphicsand graphic design.

Desktop CAD. its sister show. is specifi-cally aimed at desktop solutions for archi-tects. eneineers and technical designers.

Blenheim Online Ltd. Blenheim House.Ash Hill Drive. PINNER HA5 2AE.

NEW SUPERCOMPUTER FROM ICLThe world's most powerful computer. code-

named ESSEX. which was launched recentlyby ICL. is said to be able to support tens ofthousands of terminals anywhere in theworld. Substantial orders for it have alreadybeen received from France and the UK.

Key to the power of ESSEX is a new high-performance processor that is 254. morepowerful than any other single processorcurrently available.

More information from InternationalComputers Ltd. 1CL House, LONDONSW15 1S\\

WIDENING THE APPEAL OFVIDEOCONFERENCING

A new electronic system from GEC -Plessey.System 261. which cuts the cost of video-conferencing appreciably, has recently beenused for the first time in a transatlantic link-up between Intelmart, the world's leadingteleconferencing exhibition and conferencein \Vashington and a videoconferencing stu-dio near London.

Videoconferencine is the fast-growingtechnique of holding face-to-face businessmeetings by sending pictures. voice and dataover a digital telephone link. However. toensure a high -quality picture. a transmissionhas until now needed the equivalent of up to32 lines for just one conference. By contrast.System 261 can operate over just one line.

GEC Plessey Telecommunications. P 0Box 53, COVENTRY CV3 I HJ.

ELEKTOR ELECTRONICSSEPTEMBER 1990

AMPLIFIERS WITH 40 DBREVERSE ISOLATION

THROUGH 1 GHZAvantek has introduced two new thin-filmhybrid amplifiers. Type uTo/p-c-573 anduTo/uTc-1076. That provide guaranteed re-verse isolation of 42 dB over 10-500 MHzand 40 dB over 10-1000 MHz respectively.

For the -573 units, gain is 12.5 dB. noisefigure 4.5 dB. power output +10.0 dBm andinput and power vswR of 1.7:1. For -1076units the figures are: 11.0 dB gain. 6.0 dBNF, +9 dBm power output and vswR of 1.8:1input and 2.0:1 output.

Avantek Inc., 481 Cottonwood Drive.MILPITAS. CA 95035-7492. USA. or. inUK: Wave Devices. Laser House, 132-140Goswell Road. LONDON EC I V 7LE.

WORLD FIRST FORBRITISH TELECOM

Britain is the first major country in the worldwith a long distance telecommunicationsnetwork that is entirely digital.

The closure of the last old-style electro-mechanical exchange at Thurso in Scotlandand the transfer of its customers' phone linesto a new digital system makes British Tele-com's long distance network the most ad-vanced in the world.

BT's trunk modernization programmewas based originally on 53 System X trunkexchanges supplied by GEC -PlesseyTelecommunication-OPT. It began early in1985 with exchanges in Birmingham.Coventry. Leeds and the City of London.

The initial phase was completed inNovember 1988 when the 53rd exchangewas cut -over, in Norwich. This was accom-panied by a system enhancement that in-creased exchange power and call -handlingcapacity. Currently, each System X trunk ex-change can handle up to 1.5 million call at-tempts every hour.

The digital trunk network has been intro-duced as an overlay to the existing analoguetrun k network that went back to the start ofSTD in 1957. Since 1988. BT has acceleratedphasing out the analogue trunk exchangesand transferring the calls they handle to thedigital network.

To cater for growth in calls over its net-work. BT has ordered 16 extra trunk ex-changes. Four have already been brought into operation this year-all in central Lon-don-and three more will come into servicebefore the end of the year. The remainderare due to come into sen ice during the nextfour years.

All digital trunk exchanges are con-nected with each other and with the threedigital international exchanges that handlecalls to and from other countries.

The digital trunk transmission networkthat links the exchanges increasingly usesoptical fibre. Since 1983. all new cabletransmission systems ordered from industry,for the trunk network have optical fibre. Inconsequence. optical fibre makes up aboutthree-quarters of the trunk transmission net-work-amounting to more than 400 000 kmof fibre-the remainder being dividedroughly equally between coaxial cable andmicrowave radio.

The combination of digital switching andtransmission and the high proportion of fibregives very high quality levels. Currently.more than 99 per cent of calls over the net-work are handled on first attempt withoutproblems caused by equipment faults orcongestion.

The trunk network is paralleled by datahighways interconnecting all the trunk ex-change processors. These highways providea common channel for all the informationabout calls carried on the network itself. Callrouteing information. which sets up the end -to -end connection. uses the internationallyagreed cctrr No. 7 signalling system to givecall set-up times of less than a second. BT'sC7 network is the world's largest of its kind.

EASY -PC SPEEDS THE WORLD'SPRINTED CIRCUIT BOARDS

Number One Systems. developers ofBritain's most popular PCB design program.have just released the latest. fastest -ever re-vision of EASY -PC. Although this award -winning program has long been famous forits high re -draw speed. a complete re -ap-praisal of the screen drawing algorithms hasmade drawing complex layouts even faster(up to ten times).

DESIGNAWARD

Furthermore. the keyboard handler hasbeen re -written to accept a wide range of in-ternational keyboards. including the widelyused French. German. Italian. Spanish andUS/UK English versions. .A direct charactercode input option ensures that the entire al-

phanumeric PC character set can be includedin layouts and schematics-. regardless of thenational keyboard in use.

The new EASY -PC has the kind of speci-fication needed to succeed in the wordwidemarket. It can be used in the design of boardsup to 430 mm square. with up to eight copperlayers and two silkscreen layers per board.A 1500 tc-equivalent capacity and surfacemount capability ensure that the most com-plex layouts can be accommodated.

PCB designers struggling with other. lessfriendly PCB design programs can also takeadvantage of the new EASY -PC, importingtheir old designs through EASY -LINK. Thisprogram translates Gerber photoplot formatfiles from any package into the EASY -PC fileformat.

Further information from Number OneSystems. Harding Way. Somersham Road,St Ives. HUNTINGDON PE17 4WR.

NEW SATELLITE SYSTEM?Inmarsat and Motorola Inc. will study thefeasibility of a low -orbiting satellite systemthat could support pocket mobile telephoneservices worldwide.

The Iridium Satellite CommunicationsSystem. proposed by Motorola. could revo-lutionize mobile communications world-wide with its constellation of 77 small low -orbit satellites. Customers will be able tocommunicate globally by small pocket tele-phones. Calls could be interconnected di-rectly to anywhere in the world by on -boardsatellite switching and inter -satellite links.

Inmarsat. 40 Melton Street. LONDONNW I 2EQ.

LOW COST TRANSIENT STATUSTRIGGERING

The NanoTECH TRIGGER fulfils an impor-tant need in the daily activities of design, de-velopment and service engineers v. orkingon digital circuits. especially those that aremicroprocessor -based. It is suitable for usewith most 74 -series logic families, and 5-Vpowered 4000 -series CMOS.

When a set of user -specified conditionsis met. the TRIGGER provides a TTL active -low trigger pulse at its output. This pulsemay be used to initiate data acquisition byan oscilloscope. bus or logic analyser. or totrigger a breakpoint or interrupt circuitry inthe system under test, or any in -circuit em-ulator or other equipment attached to it.

Inexpensive (1:79.95 plus VAT) and easyto use, the TRIGGER is designed to monitorchips in DIL packages on 0.3 inch spacing.

Further details from NanoSecond Tech-nology, Ltd. 344-346 High Street. Cotten -ham. CAMBRIDGE CB4 4TX.


14

DIGITAL CAR r,\ ONE LOCK WAJ

The circuit described here is a car theft deterrent that locks thestarting motor until a pre-programmed code is recognized.

The code fed into the memory of the carengine lock is retained in a memory untilit is intentionally cleared by the rightfulowner of the car.

The operation of the circuit is relativelysimple. Bistable 'CIA -ICI° forms a de -bounce circuit for the clock pulses gener-ated by Si while the code is keyed in. Thepreset code is latched in memory IC2 andthe code entered is decoded by 1C3. If thepreset code matches the code entered, andthe ignition key is switched on, thyristorThi is provided with gate current, andfires so that the starting motor is powered.When no code or a wrong code is keyed inwith the ignition switch on, Th2 fires andactuates the horn.

The operation of the circuit may beillustrated by assuming that code 0101(example) is to be entered. The sequencein which the switches are pressed is asfollows:

P.U. Mahesh

(Si) -> (Si) (S2, Si) -) (Si) (S4 , igni-tion)--+ start

Here, (S2, Si) means that S2 is pressed, Siis pressed, Si is released, and S2 is releasedin that order. Note that pull-up resistor R3ensures that a '1' is loaded when only Siis actuated. The least -significant bit (LSB),which is keyed in first, is not used in IC4,so that the data is actually 010. Assumingthat dataline D4 of IC3 is logic high be-cause the associated switch in Ss is closed,the preset code matches the code entered.When the START switch, S4, is pressedwhile output QD of IC2 is high, multi-plexer 1C3 is enabled via its G input by alow level supplied by NAND gate ICIc.Since the code is right, the output (pin 5)goes high, and the W output goes low. Agreen LED, D3, lights to indicate that thecorrect code has been entered. TransistorTi conducts and keeps the gate of Th2 low.

At the same time, the low level at W of themultiplexer turns off TI so that Thi is firedvia Rto.

When the wrong code is keyed in, out-puts W and Y of the multiplexer are highand low respectively. Upon turning theignition key, Th2 is fired, and the hornsounds to alert passers-by and the ownerof the car that someone is attempting tosteal the vehicle.

Upon leaving the car, the owner mustactuate the lock and the alarm by pressingS3. A standard 5 V regulator is incorpor-ated into the circuit. LED Ds lights whenthe associated fuse, Ft, blows as a result ofa short circuit.

The complete circuit is easily built on apiece of veroboard. It is recommended tocheck the operation of the digital circuitybefore connecting the transistors and thethyristors.

RI

CLOCK

R2

INPUT52

44-

ID -SV

RESET!,;

19mem

START!

O

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Ca

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C2 ji:27.. Cs

2::117. 1,0


m

INTER -IC COMMUNICATIONS:THE I2C BUS

Reduction of the number of interconnections on a printed -circuitboard results in lower production costs and increased reliability.

Well aware of this fact, manufacturers of consumer electronics havesought ways to make inter -IC communications less complex.Philips Components have found a solution in the form of their

patented I2C bus, the main features of which are described in thisarticle.

An increasing number of complex inte-grated circuits, ranging from real-timeclocks to frequency synthesizers, is pro-vided with an interface. Not surpris-ingly, the bus is found in a widevariety of electronic equipment, includingtelephones, car radios, television sets andvideo recorders.

The aim of this article is to provide anintroduction into the main features andcommunication protocols of the net-work. The acronym I2C stands for Inter -ICCommunication, and the network was de-veloped by Philips to reduce the numberof connections between integrated cir-cuits. This proved feasible in practicemainly because many ICs have a largenumber of pins that carry information thatis not time -critical and, therefore, suitablefor conveying via a relatively slow serialbus with fewer connections than would berequired for a high-speed parallel inter-face. The implementation of the l'C bus ona real-time clock chip, for instance, mayreduce the number of pins from 40 to asfew as 8. This results in a much simplerPCB design with all the benefits of lowerproduction cost and smaller risks of faultsdeveloping in equipment. However, anumber of connections, including thosefor the supply voltage, for clock signals,etc., can not be replaced by a serial com-munication protocol. It will be clear thatthese connections remain necessary as be-fore.

All ICs that use the 12C bus are in prin-ciple connected to two lines as shown inthe example application in Fig. 1. A cen-tral bus interconnects two microcontrol-lers, a memory, a gate array and an LCDdriver.

In spite of their wide diversity as re-gards function and application, all I2C-compatible integrated circuits have onecommon feature: all control commandsand data are conveyed via a serial bus,according to a predefined communicationprotocol. The serial bus takes the form ofthree lines: ground, clock (SCL) and data(SDA).

H. Stenhouse

GATEARRAY

MICROCOMPUTERA

ADC

12c

BUS

SDA

SCL

MICROCOMPUTERB

LCDDRIVER

STATIC RAMOR EEPROM

Fig. 1. Typical 12Cbus configuration.

pull. upresis ors

SDA (Serial Data Line)

R

11 'VDU

SCL (Serial Clock Line)

SCLK SCLK

.SCLKN 2 DATAN21DATANliSCLKN1_1OUT OUT I OUT OUT

SCLK DATA I SCLK DATA I

' IN IN INL_ _ L _ . _ . _DEVICE 1 DEVICE 2

Fig. 2. Connection of I2C interfaces to the I2C bus.


16CON1PONENTS

Ar3

:late 41.4

9C0074 - 13

Fig. 3. Timing of bit transfer on the 12Cbus.

Normally, any I2C configuration has atleast one master (an IC capable of initiat-ing the data exchange processes andgenerating a master clock signal) and oneor more slaves (ICs that do the actualwork). A master may be a microprocessorsuch as an 8048, an 8051 or a 68000, whichare all available in special versions with abuilt-in I2C interface. Two I/O port linesof the microprocessor are used as SDAand SCL lines. Together with the groundline, this implements an l'C bus whichallows serial communication between'bused' devices at a data rate of up to100 kbit per second.

Control programs for theIC busThe two communication lines, SD.A andSCL, are connected to open -drain or open -collector outputs, and have one, common,pull-up resistor. This arrangement iscalled a wired -AND structure. Adding orremoving one or more components onthe bus therefore does not affect the oper-ation of already connected ICs, nor does itaffect the software that runs on the sys-tem. In fact, the software is capable ofautomatic detection of the hardware con-figuration. This allows programs to bewritten for complex systems that do notprovide certain features unless the rele-vant chips are connected to the bus. Theabsence of these chips is automatically de-tected by the master controller which in-terrogates certain addresses.

Existing software may be extended

-1

_ I wiikf.

s s

Fig. 5. Development kit for I2C applications.

with subroutines written for add-on ICswithout affecting the operation of the ICsalready installed. This allows existingcontrol programs to be used for a longtime without the need of a completely newversion every time the hardware is modi-fied. This high level of compatibility isachieved by virtue of the fixed addressesof the ICs on the l'C bus.

Two linesBoth SDA and SCL are bidirectional lines,connected to a positive supply voltage viaa pull-up resistor (see Fig. 2). When alloutput transistors of connected devicesare off, the bus is free, and both lines arehigh. When an IC is ready to transmit adata block, it pulls SDA low to mark astart condition. From that moment, allother ICs 'know' that the bus is in use.Arbitration procedures come into effectshould two or more ICs claim access to thebus simultaneously. When the start condi-tion is recognized, the SDA line is avail-able for carrying databits. The clock line,SCL, determines the validity of the datalevels on the SDA line as shown in Fig. 3.

The start of any data exchange via thebus is marked by SDA going low while

vr.v fra- roveesv ItAg",-

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or I., reA.1 41.6 '=1-ety-,2 art sv-a ced

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Fig. 4. Timing of data transfer on the I2C bus.

SCL is high, i.e., by a start condition (seeFig_ 4). The level on the SDA line is readby all ICs on the bus during the positivepart of the clock pulse. However, only the[C selected by the transmitted addresscode responds to the information by ac-tually loading the data and returning anacknowledge pulse. This pulse is gener-ated by the addressed slave device pullingthe data line low for one clock period,after the eight clock periods reserved forthe databits (see Fig. 4).

When none of the ICs in the systemresponds to the transmitted data, the mas-ter does not receive an acknowledgepulse. This means that either the ad-dressed slave is busy performing somereal-time function, the address is wrong,or there is no device that responds at theparticular address. The bus is free againafter the transmission of the last data bit.Both SCL and SDA revert to high, and thebus may be used to convey the next datablock.

The function of the SCL line is to gener-ate one clock pulse for every transmitteddatabit. Each master must generate itsown SCL signal. Although the frequencyof this signal is not fixed, certain mini-mum timing specifications must be ob-served. In practice, the I -C bus allows amaximum data speed of about 100 kl3it/s.

AddressingEach IC on the I C bus has its own, unique,7 -bit address, which is determined by themanufacturer and burned into the chip.The Type PCF8583 real-time clock chip,for example, is selected by sending thebinary code 101000x. The last bit is notpreset (x is 0 or 1) to allow two identicalICs to be used in parallel by tying their AOinputs to ground or to the positive supplyto set the address to 1010000 or 1010001respectively. Similarly, certain ADCs, I/Ochips and memories mar be hard -wired tomap them at one of up to eight addressesin a cluster.

The data blocks conveyed via the 12C


1NTER-IC COMMUNICATIONS: THE 12C BUS

THE RANGE OF I2C-BUS COMPATIBLE ICs

General-purpose ICs

LCD driversPCF8566

PC F8576

PCF8577(A)

PCF8578 79

96 -segment LCD driver:1:1 - 1:4 MUX160 -segment LCD driver:1:1 - 1:4 MUX64 -segment LCD driver:1:1 - 1:2 MUXRow. column LCD dot-matrix driver:1:8 - 1:32 MUX

I/O expandersPCF8574 8 -bit remote 1 0 port

(I2C-bus to parallelconverter

PCF8584 8 -bit parallel to I2C-busconverter

SAA1064 4 -digit LED driverSAA1300 5 -bit high -current driver

Data convertersPCF8591 4 -channel. 8 -bit MUX

ADC & one DACTDA8442 quad 6 -bit DACTDA8444 octal 6 -bit DAC

MemoryPCA8582B

PCF8570PCF8570C

PCF8571PCF8582A

256 -byte EEPROM(automotive temperaturerange & error correction)256 -byte static RAMas PCF8570 with alter-native slave address128 -byte static RAM256 -byte EEPROM

Clocks/calendarsPCF8573 clock calendarPCF8583 256 -byte RAM clock

calendar

Application -oriented ICs

Video/radio/audioPCF8200 voice synthesizer

(male female speech)SAA1136 PCM-audio Ident word

Interface (IDI) for com-pact disc

SAA1300 tuner switching unitSAA3028 transcoder (RC -5) for

IR remote controlSAA4700 data line processor for

VPSSAA5243` enhanced computer -

controlled teletext (ECCT)processor

SAA9050'51 digital PAL NTSC colourdecoder

SAA9055 digital SECAM decoderSAA906263.64digital deflection controllerSAA9068 picture -in -picture (PIP)

controllerSAB3035 '36 37digital tuning circuits for

computer -controlled TVSAF1135 dataline-16 decoder for

VCRTDA8405 15 stereo`dual sound

processorTDA8421 audio processor with a

loudspeaker channeland a headphonechannel

TDA8425 audio processor with aloudspeaker channelonly

TDA8433 deflection processorand sync controller

TDA8440 video audio switchTDA8461 PAL NTSC colour

decoder and RGBprocessor

TEA6100

TEA6300

TEA6310T

TSA5510

TSA6057

TelecommsPCD3311 12

PCD3341

PCD3343

PCD3346

PCD3348

UMA1000T

UMA1010T

UMA1012T

FM IF and digital tuningIC for computer -con-trolled radiosound fader control andpreamplifier sourceselector for car radiosound fader control withtone and volume controlfor car radioPLL frequency synthe-sizer for TV and VCRPLL frequency synthe-sizer for radio

tone generator (DTMFmodem music)advanced 10'110 -numberrepertory pulse,DTMFdialler with LCD controlmicrocontroller with224 -byte RAM 3K ROMmicrocontroller with128 -byte RAM 4K ROM/256 -byte EEPROMmicrocontroller with256 -byte RAM'8K ROMdata processor (DPROC)for mobile telephonesfrequency synthesizer(0.45 - 1.1 GHz) formobile telephonesfrequency synthesizer(50 - 600 MHz) formobile telephones

Table 1. Overview of I2C-compatible integrated circuits manufactured by Philips Components. Not shown here is a wide range ofmicrocontrollers and memories.

bus invariably consist of 8 bits. The hit thatfollows the address indicates the start of aread or a write operation with the selectedIC. Bit 8 is low for a write operation, andhigh for a read operation.

ApplicationsThere is much more to the concept of theI -C bus than can be described in this ar-ticle. The full specification of the systemmay be found in Ref. 1.

The I -C bus is relatively simple to im-plement on almost any microcomputersystem that has at least one user port. Ifnecessary, external buffers may have to beadded to make such a port bidirectional.Interestingly, Philips Components recent-ly introduced a special chip for this pur-pose: the PCF8584. Somemicrocomputers, including the AcornArchimedes, even have an I -C interface as

a standard feature. Developers of smallstand-alone microprocessor systems may

Fig. 6. Databooks on I2C devices, publish-ed by Philips Components.

find the 1:C; version of the 8048, thePCF84COOT, a good starting point for thedesign of a dedicated control system.

Finally, an interesting example of theuse of a 8051 microcontroller in combina-tion with the SAA5243 I -C -bus Teletextdecoder may he found in Ref. 2.

Reference:1. The PC -bus Specification. Philips Compo-nents publication.2. Computer -controlled teletext decoder.Elektor Electronics October 1989


SOUNDGENERATORThe sound generatordescribed here, designedand marketed as a kit byELV, is capable ofproducing up 256 differentsiren -like sounds, including the popular Kojak-, FBI-, and Hawaii -Five -0 types. Compact,easy -to -build and suitable for use in conjunction with alarm systems in and on premisesas well as on vehicles, the unit is complete with an on -board 20 -watt amplifier.

The type of sound is selected with fourslide switches on the front panel of thesound generator. Since each slide switchhas four positions, a total number of 256(4x4x4x4) different sounds are available.An output stage is included in the circuitto provide a solid 20 watts of audio powerat a supply voltage of 12 V to 15 V. Theslide switch at the extreme left on the frontpanel functions as a three -level volumecontrol and as an on/off control.

Circuit descriptionCircuit 10, a Type \E556, contains twomultivibrators. One of these, ICib, gener-ates the basic siren sound. Switch S4allows four different basic sounds to begenerated by selecting one of four timingcapacitors C7-C1o. The output of 101+,pin 9, drives the power output transistor,T1, direct via resistor R14. Depending onthe position of volume switch S5, the loud-

speaker is either disconnected ('off'), con-nected direct to the collector of Ti (volumelevel 3), or connected via series resistorsRes or R16 (volume levels 2 and 1).

Evidently, a single oscillator does notmake a siren, let alone one capable of pro-ducing up to 256 different sounds. CircuitICib, is, therefore, frequency -modulatedby applying a signal to its control voltageinput, pin 11. This modulation signal issupplied by a second oscillator, formed bythe parts to the left in the circuit diagram.

The second multivibrator in the circuit,ICIa, operates at a much lower frequency.than 1013. The oscillation frequency isdetermined by one of four capacitors C1-C4 connected to ICia via the 'frequency'switch, Si. The other frequency -determin-ing parts are RI and R2, which set thecharge and discharge periods respective-ly.

When S2 is set to the position shown inthe circuit diagram, R3 is connected in

parallel with R2, so that the input of bufferopamp IC2 receives a sawtooth signal. Inthe other extreme position, i.e., when 52 isset to the top position, R3 is not connectedso that a triangular waveform is pro-duced. The two centre positions of theswitch produce a rectangular waveformand a combined rectangular/logarithmicwaveform (as shown inset in Fig. 1). Thelatter is obtained with the aid of compo-nents C6, R7 and R3.

Opamp IC2 forms a buffer between themodulation waveform generator, ICia,and the tone generator, ICib. The level ofthe modulation signal fed to ICib is deter-mined by the position of switch S3, whichconnects one of four series resistors Rs-Ri1 between the output of IC2a and pin 11of ICib. Switch S3 thus determines themodulation intensity.

Summarizing the above, the functionsof the slide switches in the circuit are asfollows (front panel marks in brackets):

tJ

14

55E

"3it 1

s A4foil

2 7

0 Siren typeO -

as0-0-g

-1-c6-01 O

0-0

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Ir-1-61bade sound s

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S14

5S

s.43 5T2C.)10

909510 -11

Fig. 1. Circuit diagram of the sound generator.

ELEKTOR ELECTRONICS SEPT EMBER 1990

19SOUND GENERATOR

r ;laaae811.2000 00 000 oo

cn

O 00 001

C7 if. CB C9

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Fig. 2. Track lay -out and component mounting plan of the PCB for the sound generator.

Si (frequency): modulation frequencyS2 (siren type): modulation waveformS3 (modulation): modulation intensity54 (basic sound): fundamental siren fre-quencyS5 (volume): sound level and on /off con-trol

The four switches St -St allow 44=256 dif-ferent sounds to be generated at three vol-ume levels.

For the highest possible sound level(particularly in alarm systems), it is rec-ommended to use a pressure -chambertype loudspeaker with a sufficiently highpower rating (?.20 W). For other applica-tions, standard loudspeakers may be usedwith good results. The minimum loud-speaker impedance is 4 0.

ConstructionThe sound generator is a relatively simplecircuit which should not present difficul-ties in assembling. Moreover, the unit issupplied in kit form, which obviates prob-lems with obtaining certain components.

Start the construction by fitting andsoldering the low -profile parts, followedby the higher parts, on the single -sidedprinted circuit board shown in Fig. 2. Theoverlay printed on the component side of

the board indicates the position of theparts mentioned in the parts list.

To assist in their cooling, the 5-Wpower resistors are mounted at a smalldistance above the printed -circuit board.

The use of a relatively flat enclosuremakes it necessary to bend the powertransistor, Ti, towards the PCB surface asshown in the photograph of the com-pleted board. By virtue of its low internalresistance, and the fact that it is driven ata fairly high level, Ti dissipates relativelylittle heat, even at full output power. Con-sequently, the transistor does not requirea heat -sink.

After a careful visual check of the com-pleted board, this may be fitted into theenclosure supplied with the kit. Connectthe supply voltage to PCB terminals STl(-12 V to +15 V) and ST2 (ground). Con-nect the loudspeaker to terminals ST3 and5T4. Drill holes in the enclosure to pass thesupply wires and the loudspeaker wires.Make knots in the wires at the inside of theenclosure to provide strain reliefs. Finally,fit the top half of the enclosure and secureit with the screws supplied.

Practical useWhen a 4-0 loudspeaker is used, the unitdraws a peak current of up to 4 A. When

COMPONENTS LIST

content of kit supplied by ELV France

Resistors:1 6.80 5W1 1001

1

2

2

1

1

32

1

1

221"/ 5W

loon 5W1k2k26k89k1

10k100k330k680k

Capacitors:1 1nF1 1n51 2522 4n71 22nF

1pF 16V2112 16V

4p7 16V10pF 16V22pF 16V

Semiconductors:1 NE5561 TLC2711 BD250C1 1N40012 1N4148

R15R8

R16

R14

R3;119

R7;RioRilR4

R4;R5:R5Ri ;R2R13

R12

coC10

Ca

Ca;C7

C.=

C3

C2

CICa

IC1

IC2

-17

D3

Dt:D2

Miscellaneous:5 2 -pole 4 -way slide switch4 solder pin1 printed -circuit board1 enclosure

used in a switched circuit, e.g., as a horn,the sound generator may be powered viaa push-button or a relay with a suitablecontact current rating. Use as a horn ispossible because the siren starts to soundthe moment is it powered. It should benoted, however, that in many countriesthe use of a siren as a sound actuator de-vice in or on vehicles, and in some casesin or on premises as well, is restricted toemergency services. The use of a siren ingeneral may also be subject to speciallicenses, rules or regulations as regardson -time, sound type and sound level.

A complete kit of parts for the soundgenerator is available from the de-signers' exclusive worldwide distribu-tors:

UV FranceB.P. 40F-57480 Sierck-les-BainsFRANCETelephone: ,-33 82837213Fax: +33 82838180


20

JVHE TEST PROBE

For most electronic test and measurement applications, a moderndigital multimeter represents excellent value for money. However, inspite of the high input resistance, the accuracy of a DMM degrades

rapidly when the frequency of the measured voltage rises above400 Hz or so. This article describes the basics of designing apassive test probe to overcome this limitation and extend the

usable frequency range of a DMM to about 100 MHz.

The accuracy of digital multimeters is, ingeneral, sufficient for all practical pur-poses. Although there are low-pricedmodels that give usable results above themaximum input frequency of 400 Hz(stated by the manufacturer), DMMs witha guaranteed frequency range of 20 kHz,50 kHz or even 100 kHz are rare and quiteexpensive.

An ideal passive signal rectifier flipseach negative half -cycle of a sinusoidalvoltage in between two positive half -cycles. The result is a direct voltage ofwhich the peak value is roughly equal tothat of the alternating voltage-irrespec-tive of its frequency.

The inertia of a moving -coil meter in ananalogue voltmeter provides an certaindegree of integration of the measured al-ternating voltage. The result is a built-inaveraging function that smooths theripple on the direct voltage supplied bythe rectifier. Since a DVM is an all -elec-tronic instrument, a capacitor is requiredat the output of the rectifier to provide therequired smoothing and ensure correctmeasurement results.

All diodes have a certain thresholdvoltage below which they do not conduct.For the application we arc dealing withhere, the threshold voltage and thereverse leakage current must be as smallas possible. Small -signal germaniumdiodes of the point -contact type have thelowest threshold voltage, followed bySchottky diodes, normal germaniumdiodes and silicon diodes, in that order.The forward voltage drop is not a staticcharacteristic but depends to some extenton the current passed by the diode, or, inother words, the load resistance at the out-put of the rectifier. Obviously, the highinput resistance of the DMM (typ. 10 Milor more) is advantageous here, since apartfrom presenting a small load to the recti-fier diode it also allows a small capacitorto be used for the previously mentionedaveraging function. As a consequence, thesmoothing capacitor may be a high-gradetype, e.g., a polystyrene capacitor, avoid-ing large leakage currents typically intro-duced by, for instance, electrolyticcapacitors.

J. Bareford

Simple: the single-phaserectifier

A rectifier circuit in its simplest form isshown in Fig. 1. It consists of a diode, D, abuffer capacitor, C, and a resistor, R. The

Fig. 1. The single-phase rectifiermeasures the peak value of the alternatingvoltage

input resistance, R of the measuring in-strument exists in parallel with R. WhenR is omitted, R, alone determines the timeconstant of the R -C network. Since thediode passes the positive half cycles only,the capacitor is charged to the peak valueof the alternating input voltage minus theforward drop across the diode. The R -Ctime constant determines the lower fre-quency limit and must, therefore, be largerelative to the period of the input signalwith the lowest expected input frequency.The time constant must, however, not bemade too large to avoid an excessivelyslow meter response. The capacitor valuesshown in Figs. 2, 3 and 4 may be used foreasy reference and as starting points foryour experiments.

Provided a suitable diode is used, thesingle-phase rectifier will give good re-sults. The use of a point -contact germa-nium diode results in a virtually linearfrequency response up to about 10 MHz.Above this frequency, the response de-grades slowly to about -3 dB at 100 MHz.The output voltage is 100 mV to 200 mVsmaller than the peak value of themeasured alternating voltage (the peakvalue equals 1.414 times the effective orroot -mean -square value).

Fig. 2. The Villard circuit is a voltagedoubler. i.e.. it measures the peak -to -peakvalue of the alternating voltage. The circuitshown here is dimensioned for a frequencyrange of 10 kHz to about 1 MHz.

Fig. 3. RF version of Villard rectifier withpoint -contact germanium diodes.

C1 02

Fig. 4. Villard circuit with Schottky diodesfor optimum linearity.

In the small -signal range, Schottkydiodes such as the Type BATS5 are betterthan germanium types because they havea smaller reverse leakage current thanpoint -contact germanium types. The one


LFIFIF TEST PROBE

disadvantage of a Schottky diode, namelyits slightly higher forward voltage drop(150 mV typ.), is made good by the betterdefined conduction voltage (the V -I curveshows a sharper rise than a germaniumdiode). In practice, the DVM reading forsignals smaller than 1 Vrms is always alittle lower than the actual effective value.

The Villard rectifierThe circuits in Figs. 2, 3 and 4 all containtwo capacitors and two diodes. Theseparts provide voltage doubling. If idealdiodes were used (i.e., diodes with a thre-shold voltage of nought) the voltageacross the output capacitor would beexactly two times that across R in Fig. 1.This voltage represents the peak -to -peakvalue of the input voltage, or

Upp = x 2 x 1.4141

The operation of the Villard rectifier isbest explained by assuming a point intime where a negative half cycle of theinput voltage arrives at the input of thecircuit in Fig. 4. Diode Di conducts, andcapacitor Ci is charged to the peak valueof the half cycle. When the positive cyclestarts, the voltage at Ci is added to thepeak value of it. This is because diode Diblocks, but D2 conducts, so that C2 ischarged to the peak value plus the voltageacross C. Thus, the voltage across C2 rep-resents virtually the peak -to -peak value ofthe input voltage:

Lk: = ( Up + UC I ) = Up p

Capacitor C2 and the resistance Ri of theDM\l form the previously mentionedtime constant.

The Villard/Delon rectifier not onlysupplies a higher output voltage than asingle-phase rectifier, it is also more sen-sitive. Furthermore, its input resistance isroughly equal to that of the DMM at theoutput. Initially, the measured voltage is

only briefly loaded as the capacitors arecharged_ After a few cycles of the inputsignal, the charge current virtually disap-pears, and the input signal is loaded onlyby Ri and the reverse leakage currents ofthe diodes.

Basically, the circuits in Figs. 2, 3 and 4differ only in regard of the time constant,and, therefore, the frequency range. Thecircuits in Figs. 2 and 3 contain a seriesresistor at the output to protect the diodesagainst output short-circuits. In view ofthe high value of R1 (>1 Mi) these resis-tors do not significantly affect the timeconstant.

The circuit in Fig. 2 is dimensioned foraudio signal measurements and providesa linear peak -to -peak voltage reading forsignals between 20 Hz and about 1 MHz,provided the DMM input resistance is notsmaller than 10 MS2. When a DMM withR1 = 1 MO is used, the capacitor valuesmust be increased to 820 nF. The curvesshown in Fig. 5 were recorded with a1 DMM and 100 nF capacitors.

The circuit in Fig. 3 is basically thesame but adapted to give a frequencyrange of 300 kHz to about 300 MHz, de-pending on the type of diode used. The7 pF capacitor at the input allows the rec-tifier to be coupled lightly to the circuitunder test, avoiding excessive loading oftuned circuits while these are adjusted.

Finally, the circuit in Fig. 4 is set up fora frequency range extending from audioto about 1 MHz. Its remarkably straightresponse curve is shown in Fig. 6. The sen-sitivity is also remarkable: the rectifier'starts' at signal levels as low as 33 mVrmsor about 100 mVpp, while at higher inputlevels (up to 2.5 Vpp) the direct outputvoltage is equal to the peak -to -peak valueof the input voltage minus a constant dif-ference of 0.1 V.

Practical notesThe combination of a DMM and a passiveLF/FIF probe may in many cases replace

7 E

:Hi! rielaa

a much more expensive high-gradeLF/HF millivoltmeter, and in additionprove useful for audio purposes, includ-ing filter adjustments, frequency responserecordings and frequency response cor-rections (tape recorder calibration, adjust-ments on equalizers, etc.). The passiveprobe also allows loudspeaker enthusi-asts to record, with the aid of a simplesignal generator, the frequency responseand steepness of cross -over filters. Pro-vided a linear microphone is available(e.g., an electret reference microphone), itis possible to perform frequency responsetests on loudspeakers.

In the RF range, a probe of the typedescribed here enables small signals to betraced and measured. Critical adjust-ments on filters and oscillators no longerpresent problems caused by overloadingand detuning effects.The germanium diodes used in the cir-cuits in Figs. 2 and 3 are obsolete typeswhich may, however, be around some-where in your junk -box. Recuperating anold TV set may also provide you withtwenty -odd OA -type diodes of differentpower ratings. Use the ones that are physi-cally the smallest since these, in general,have the lowest stray capacitance (a recti-fier diode from somewhere around theTV's power supply is obviously not worthtrying in a probe).

Alternative types with the prefix AAare still current components and may beused instead of the 0A174. Arranged inorder of decreasing sensitivity, these in-clude: AA113, AA112, AA119, AA118,.AA138 and AA137.

For AF applications, the difficult -to -obtain germanium diodes may be re-placed by germanium transistors with an'AC' prefix (AC151, AC152 and similartypes). Simply cut off the emitter terminal.The collector becomes the anode, and thebase the cathode, of your (admittedly rela-tively large) germanium diode.

Fig. 5. Frequency response of the circuit in Fig. 2 at two typical AF voltage Fig. 6. Correlation between input voltage and outputlevels and a terminating resistance of 1 MO. The roll -off frequency will be a factor voltage for the circuit in Fig. 4. Excellent linearity isof 10 lower when a 10 -MO DMM is used. achieved by the use of a Schottky diode.


PROFILES:by Bernard Hubbard

CRICKLEWOOD ELECTRONICSAfter their management buy-out, Syd Wedeles and his part-ner Clem Clemente increased the turnover of CricklewoodElectronics by some 80 per cent.

Says Syd Wedeles. now a director of the company: Wesimply concentrated on stocking the items that our cus-tomers wanted. That was the secret".

That was in 1981 and since then the former jazz drum-mer and his fellow director have successully increased theturnover of the London -based electronic components com-pany year after year. during a decade when a large numberof their rivals have gone out of business.

"At one time. there were about fifty electronics retailersbetween here and Paddington: nov. there are only a fewleft," says Syd.

Syd and Clem have achieved their success by a policy ofstocking the possibly widest range of components in theUK within their 1000 square feet of retail premises on theBroadway. Cricklewood. NW London.

"Our range is unrivalled." says Syd. "we have over fivemillion components in stock at any one time and if anyonecontacts us and asks for new components, we endeavour tostock them".

All Cricklewood products are branded components andtheir prices are pitched at a highly competitive level.

Said Syd: "We offer a same -day dispatch service onmost in -stock items-and that's the majority".

The range includes capacitors. connectors. resistors,semi -conductors. switches. relays, transducers. loudspeak-ers. tools, kits and test equipment.

Cricklewood Electronics publishes, at regular intervals,a catalogue -160 pages this year: its largest todate-which is mailed to thousands of customers. "These

LORD TRANSFORMERS

Difficulties in obtaining supplies of toroidal transformersresulted in Richard Lord launching another business. Al-ready head of Lyon Force, an electronic component manu-facturer of Rochford. Essex, Richard was busy hunting forsuch transformers and was experiencing such problems thathe decided he ought to start manufacturing them for him-self.

Richard told Elektor Electronics recently: "We were ex-periencing not only difficulties in the supply. but also anextremely bad attitude from existing suppliers: so much sothat I decided there must be an opening in this market forus".

That was four years ago and since then Lord Transform-ers has grown to such an extent that it rivals the existingbusinesses in turnover.

Says Richard: "We supply standard laminated transform -

A Cricklewood staff member with a bunch of newly arrived mail orders.

we have built up over the past nine years".The majority of orders come over the phone, but on Sat-

urdays there's normally a crush of customers in the shop.Between five and ten per cent of the orders come fromoverseas-particularly Yugoslavia. Nigeria and the MiddleEast. Staffed by a team of six, the business is always eagerto give advice to customers, many of whom are companiesrather than individual enthusiasts. The company is knownfor its generous discounts on volume sales.

Having steadily built up the business for the past fifteenyears. Cricklewood Electronics is poised to enter a new era:it is looking at properties in other parts of the country in abid to establish a chain of Cricklewood Electronics retailoutlets.

For further infOrmation on Cricklewood Electronics. seethe inside back cover of this issue.

ers and specialized ferrite and air core types for switch -mode power supplies and Psws and RF applications".

"We offer customers a fast turn -around of high -qualitytransformers at highly competitive prices".

Most of the materials used in the company's manufactureare purchased in the L.K.

The majority of orders come from within the UK, but 35per cent come from overseas, particularly France. Germanyand Australia. "We manufacture certain sizes for stock. butthe majority of our sales are made to order".

Richard maintains: "There has been a significant up-surge in the use of toroidal transformers in recent years.particularly of the flat pancake type".

In the future, Lord Transformers plans to specialize inthe larger sizes of transformers, that is, the sizes most peo-ple have difficulty in obtaining.

For products and prices contact Lord Transformers. 3Featherby Way, Purdeys Industrial Estate, ROCHFORDSS4 1LD, Telephone (0702) 5-14549, Fax (0702) 541075.

ELEKTOR ELECTRONICS SEPTEN1BER 1990

INRA-QECONUO

EMOTE

Two recently introduced integrated circuitsfrom Plessey, the Types MV500encoder/transmitter and the MV601receiver/decoder, allow a versatile16- or 10 -channel infra -red remotecontrol system to be built from aminimum number of components.

T. Giffard

As an example of its application, the infra-red (IR) system described here is used inconjunction with the recently publishedCMOS preamplifier (Ref. I ). The transmit-ter and the receiver are described separ-ately below.

Infra -red transmitterThe circuit diagram in Fig. 1 shows thatthe Type MV500 integrated circuit fromPlessey Semiconductors requires only ahandful of additional parts to make aninfra -red transmitter for remote controlapplications.

The MV500 contains an 8x4 -linedecoder for up to 32 keys, and a transmit-ter section based on PPM (pulse -positionmodulation). The on -chip oscillator worksreadily with an inexpensive 455 -kHz ce-ramic resonator. The actual clock fre-quency is uncritical and may lie between400 kHz and 1 MHz.

The IvIV500 operates from supply volt-ages between 3 V and 9 V. Since ABS en-

closures with a compartment for a 9-V(PP3-size) battery are readily available,the circuit was designed to operate from a9 V supply.

Three IREDs (infra -red emittingdiodes) Type LD271 are connected inseries and fitted with reflectors to ensurethe highest possible infra -red efficiencygiven that the circuit is powered from 9 V.The current through the IREDs is pulsedby Ti under the control of the output sig-nal supplied by the MV500. The IRED cur-rent is limited by a 10-52 resistor, R2. Sincethe peak IRED current is about 400 mA, abuffer is required in the form of capacitorC2. Note, however, that the low duty fac-tor of the IRED current pulses results in an

average batters' load of 1.4 mA to 1.8 mAonly.

When no key is pressed, the MV500switches itself to a 'sleep' state in whichits current consumption is negligible. Thechip is active only when a key is pressed,to which it responds by transmitting theassociated code. The RATE inputs (pins 14and 15) allow three different data trans-mission speeds to be programmed asshown in Table 1. The desired speed is setwith the aid of wire links A, B, C and D Aand C for 1, B and D for 0).

The keyboard has several options. Theprinted -circuit board of the transmitter(see Fig. 3) accommodates ten push -but-tons, but the relevant section may also becut off and a separate 16 -key membrane-type keyboard connected via Ki. The con-nections are made in accordance with thematrix configuration in a Molex key-board. For other keyboard makes, the wir-ing may have to be changed. The ten -keyversion of the transmitter was developedspecifically for the CMOS preamplifier.

Infra -red receiverThe infra -red receiver circuit (Fig. 2) con-sists of three parts:

an input stage comprising IR sensor Dtand preamplifier ICia remote control receiver/decoder TypeNIV601a level conversion circuit for the outputsignals

Fig. 1. Circuit diagram of the infra -red remote control transmitter based on Plessey'sNIV500. The shaded keys are not required in all cases. The IR signals received by Di are fed to a


24GENERAL INTEREST

RATE INPUTS RATE VALUE(CLOCK CYCLES)

B I A

0

0

0 output inhibited

2048

1024

1 512

Table 1. Setting the transmission speedwith the aid of wire jumpers.

Type SL486 high -gain amplifier which hasan on -chip AGC (automatic gain control)circuit. The output signal supplied by ICIis fed direct to the input of the MV601. TheMV601 subsequently converts the PPMsignal into a 5 -bit dataword, accompaniedby a 'data ready' and an 'output enable'signal. These signals, in combination withthe momentary or latched modes of theMV601 (selected with wire link C) enablea simple link to be made to a micro-processor circuit.

The clock oscillator in the MV601 mustoperate at the same frequency as the trans-mitter with a maximum deviation of .4`;-;7.Resistor R2 prevents the on -chip oscillatoroperating at harmonic frequencies pro-duced by some types of ceramic resonator.The RATE inputs of the MV601 must havethe same logic configuration as those ofthe transmitter chip. A high level (logic 1)is established simply by leaving the rele-vant input open (jumpers A and B for data

rate A and data rate B respectively).The remarkably high noise immunity

of the IR remote control system is ensuredby the fact that the MV601 does not supplyan output word until two identical PPMcodes have been decoded. Reception of adata is signalled by LED D2.

Since most microprocessor interfacecircuits work with signal levels of 5 V, alevel converter is provided on the receiverboard. This function is assumed by twoanalogue multiplexers Type CD4051. TheVEE (substrate) terminals of these ICs maybe connected to a negative supply voltage.

IVire links E and F enable the outputsof IC3 and IC4 to supply either active -lowor active -high signals. The 16 output linesof the two ICs correspond to the maxi-mum number of keys in a (membrane)keyboard used at the transmitter side.Jumper D must be fitted when the levelconverters are used.

Voltage regulator ICs in the powersupply is required when the supply volt-age is 6 V or higher; the maximum inputvoltage is 15 V.

The outputs of the level convertermay be connected to the CMOS preampli-fier, or to control inputs of equipmentwith a similar electronic control system.

Remember that output XO of multi-plexer IC3 (pin 13) is actuated when nosignal is received. Hence, switch Si is notused at the transmitter side.

The dimensions of the printed -circuitboard for the receiver have been kept as

Ca

C3

-061.4 Or

01-°--' 51

tiffBP 104

71

EMI

acb Dec (_;)6Ynit C3

ICI01-Z. 2 CO7

SUBSxi ccTt

Po'

CA- g REG PC

1C21

22aISV

1

13

ts

VA

56

Ctl

ITO

OSC et

5V VEE

C19

a

11

C

93 9

/2 270

0It,100--4

7

510

1C-3

L C 77

D515 it

:!!!' 4051

;"

PS

01 213 '4 IS tE

4)BC5476a cr a

1 2 3 6 7 6

02

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BC557B

16

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2

71

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9_0

6

osc 5. E t

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WW1 2tt

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A 5 C

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OC14 0A51-737-4

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7"-° are-.WEE

ICE

tt4051

43 AA IS el a a

0 a ri43 11 12 53 44 15 16

13

1,4

O CE

-51565 .1

Fig. 2. Circuit diagram of the infra -red receiver. Two CMOS analogue multiplexers Type4051 provide ready interfacing with a microprocesor system.

00000000

0

A

0- 0

-00O.,:

0

0

0

0

00

-0 O."-- -0

0-00

Fig. 3. Single -sided printed -circuit boardfor the IR transmitter.

COMPONENTS LIST

INFRA -RED TRANSMITTER

Resistors:2 1051 RI;R21 10k R3

Capacitors:2 1001IF 10 V2 100pF

Semiconductors:3 LD2711 BC6391 MV500

C1;C2C3;C4

Di;D2;D3

ICI

Miscellaneous:3 reflector for LD2711 ceramic resonator 455 kHz Xt1 flatcable connector Molex Kt

7583-0816 keyswitch, e.g., Monacor/ S1-S16

Monarch MS-660/SW ormembrane keyboard (4x4matrix Molex kV)

1 9-V PP3 battery with clip Bti1 ABS enclosure with battery

compartment, size approx.100x60x25 mm

2 3 -way pin header2 jumper


i \FR \-n D REMOTE CONTROL

i

Fol OIR 5 10

0-01 [0 0 C>114"C12O 1

20000000141000000013

U

Cl

C16 E IVA 7-'1131

7 2 1 8 4 6COO 0 0 0 0 0

5121f.+:1Drx altsa I;

,.....;\____,_lo026 0,6-761 ":: 0-7.431

g7:41.00 0

o_oci4 1/4-0,"

( OHO 2 2,.0t!gisl al, 0 0

g73.110 %dj.` riE;t2.. crr ,W

.i.T 0.0 00 0 0 C17

)0 0123 )0C100 r. 13 11 ° 16 14 00 U 00000000

15 10 9 12999

IC5

A K.1 \\N

Fig. 4. Single -sided printed -circuit board for the IR receiver.

small as possible to enable ready installa-tion into existing equipment. The quies-cent current drawn by the receiver isabout 16 mA.

Video Mixer - Part 3March 1990, p. 23-29In the circuit diagram, Fig. 12, the com-mon junctions of pull-up resistor net-works 8161 and R162 should be shown -asconnected to ground, not to the positivesupply voltage. The relevant printed -cir-cuit board, 87304-3, is all right.

Simple AC millivoitmeterJanuary 1990, p. 22-25At relatively high frequencies, a part ofthe input signal may bypass the attenua-tor, causing erroneous meter indications.This may be prevented by fitting physi-cally small capacitors in positions CI andC13, and fitting a metal, grounded, screenbetween them.

RF inductance meterOctober 1989, p. 16-20On the component overlay (Fig. 2 andready-made PCB), the resistor marked`R12' below rotary switch Si should bemarked 'R2'.

Reference:1. All -solid state preamplifier. Elektor Elec-tronic; December 1989, January 1990.

CORRECTIONS

Mini EPROM viewerJune 1990, p. 44-47In the circuit diagram, Fig. 2, the transis-tors in positions Ti -T4 should be TypesBC337, not BC547B.

Electronic loadJune 1990, p. 16-19In the circuit diagram, Fig. 1, the transis-tors in positions Ti -T2 should be TypesBD239C, not BC239C.Please add to the parts list:

,T2 = BD239CR24-R33 = 0033, 5W

Slave mains on -off controlJuly/August 1990, Supplement circuitno. 044

Relay Ret should be a 24-V type, not a

COMPONENTS LIST

INFRA -RED RECEIVER

Resistors:4702200.150k56012

47k100k10k

Capacitors:1 22uF 16V tantalum1 10uF 16V tantalum1 6}18 10V radial1 681.IF 10 V radial1 22nF1 4n71 150nF1 15nF6 100nF1 270pF1 100pF

1 470nF

Semiconductors:1 BP1041 LED1 BC55761 BC54713

1 SL4861 MV6012 40511 7905

Ri

R2

R3

R4

R5

R6

R7

CiC2C3C4

C5

CsC7C8C9;C13-C17C10CiiC12

Di

D2

T1

T2

ICi

IC2

IC3:IC4IC5

Miscellaneous:1 ceramic resonator 455 kHz Xi1 14 -way PCB -mount header Kt1 printed -circuit board 90408514086

12-V type as shown in the circuit diagram.

Mini -drill controlJuly August 1989, Supplement p. 39Resistor R9 determines the start value ofthe output voltage, i.e., the speed of themotor when it is not loaded. The value ofR' may be calculated from

RT. ( R_ P7V

Dark -room clockFebruary 1990, p. 62-66In the circuit diagram, Fig. 2, the marks'A' and 13' next to juniper JP2 should betransposed.Set to position B, this juniper switches onthe decimal point when the circuit is usedas a minute counter.The decimal point is switched off whenthe jumper is set to position A (secondscounter).


26

1.5-GHz PRESCALER FORFREQUENCY METERS

Most simple and inexpensive frequency meters have a maximuminput frequency of 10 MHz or 100 MHz. Decimal prescalers thatenable frequencies in the gigahertz ranges to be measured are

expensive and usually require a special type of RF preamplifier. Notso with the SDA4212 from Siemens, which offers new ways ofbuilding a compact, low-cost 1.5-GHz divide -by -100 prescaler.

The SDA4212 features a high input sensi-tivity and excellent large -signal beha-viour. Unlike many other prescalers, theSDA4212 does not require its input signalto be kept within certain limits for correctoperation of the internal divider. Over thefrequency range of 70 MHz to 1200 MHz,the SDA4212 accepts input signal levelsbetween 5 mV and 400 mV (typicalvalues). The prototype circuit constructedon the printed -circuit board shown herehas a frequency range of 20 MHz to1,600 MHz.

The internal structure of the SDA4212is shown in Fig. 1. The input circuit isformed by a difference amplifier. Next, ahigh-speed divider divides the signaleither by 64 (pin 5 'high') or 256 (pin 5low'). The ECL-level output signal(1 Vpp) is supplied at pin 6 or 7 by a sym-metrical driver stage.

Circuit descriptionThe circuit diagram of the prescaler isgiven in Fig_ 2. The two Schottky diodes atthe input protect the SDA4212 against ex -

R. Bonsch

cessive input voltages. The M (mode)input of the chip is tied to the positivesupply line to achieve division by 64. TheECL-to-TTL level converter at the outputof the SDA4212 is formed by LS-TTL gatesNi, N: and N3. The first gate, NI, is anAC -coupled linear amplifier. Its gain is setto about 10 times with the aid of feedbackresistors RI and R2. Gate N2 provides fur -

Fig. 1. Block diagram of the SDA4212 from Siemens.

ther amplification and a well-defined TTLsignal. The ECL-to-TTL level convertorused here is easily reproduced, requiresno adjustment and is hardly affected bychanges in the ambient temperature.

The 74LS390 that follows the SDA4212contains two divide -by -5 counters. Thefirst Qo output (pin 9) goes high on thefifth input pulse. At the same time, theinput signal of the 74LS390 appears in-verted at the output of N5. This means thatgate N6 is blocked for one -fifth of the timeand allows the signal to pass for four -fifths of the time. In other words: four ofevery five input pulses arrive at the inputof the second divide -by -5 counter.

The above divide operation is dupli-cated in the second counter. Gates N5 andN- are required to compensate signal de-lays in the dividers and to ensure that the74LS390 can reach its maximum input fre-quency.

The output of the prescaler supplies aTTL signal whose frequency is

1/64 x4/5 x 4/5 = 16/1600 = 1/100

times the frequency of the input signal. Itshould be noted that a dual -rate countersuch as the one applied here supplies anoutput signal whose mark -space ratio isirregular. Fortunately, this is not a prob-lem for most frequency meters. The out-


1.5-GHz PRESCALER FOR FREQUENCY METERS

8...20V

*see textN1-N4 =1C3 = 74LS00115-118 =1C4 = 74L502

Fig. 2. Circuit diagram of the 1.5-GHz prescaler. Note the absence of an RF preamplifier ahead of the divider chip. IC2,

COMPONENTS LIST

Resistors:1 2200

1 2k21 4k7

1 10k

Capacitors:3 10nF SMA1 47nF SMA2 47nF ceramic1 10pF 25V radial1 1pF 16V radial

Semiconductors:1 1N4001

1 1N41482 HP28001 78L051 SDA42121 74LS001 74LS021 74LS390

RiR2

R3

R4

Ci;C2;C3C4

C5;C6C7

Ca

DiD2

D3:D4IC1

IC2

IC3

IC4

IC5

put signal may not be suitable for PLL -based circuits, however.

The prescaler is powered by a 5-1.regulator Type 78L05 (ICI). Diode D2 atthe common terminal raises the outputvoltage to about 5.7 V to push the highestinput frequency of the SDA4212 to themaximum specification. Diode Di pro-tects the circuit against reverse supplyvoltages. The relatively low consumptionof 30 to 50 mA enables the prescaler to bepowered by a battery.

ConstructionA number of surface -mount assembly(SMA) parts are accommodated on theprinted -circuit board (Fig. 3) to ensure theshortest possible connection between theinput of the circuit and the SDA4212. The


Fig. 3. Track layout and component overlay of the PCB for the prescaler.

1A parts are fitted at the track side of theboard.

The board is single -sided with a rela-tively large unetched copper area aroundthe SDA4212 to ensure adequate screen-ing and decoupling of the high -frequencyinput signals. The SDA4212 must be sol-dered directly on to the PCB.

Fit the completed circuit board in asmall metal enclosure. The prescaler maybe coupled to the circuit under test either

capacitively by means of a short wire, orinductively (at a low impedance) bymeans of a wire loop. Both methods re-quire the prescaler to be located fairlynear the circuit under test, but avoid therisk of signal attenuation by the capacit-ance of long (coaxial) test cables.

28

ROM -COPY FOR 8052 -BAS

In an earlier article onour popular 8052 -BASICcomputer we showed away to replace the8052AH-BASICmicrocontroller with themuch cheaper 8032 or80C32 and an externalEPROM. This month wetake a second look atunloading the BASICinterpreter from the8052AH-BASIC andtransferring it to anEPROM. We also availourselves of theopportunity to get togrips with serialcommunicationprotocols for the BASICcomputer.

E. Vermeulen

Although many of our regular readerswill be familiar with the BASIC computerpublished in Ref. 2, it does no harm toinform others that this computer is amongthe most popular construction projects ofthe past few years. The BASIC computeris an extremely versatile single -boardmicrocontroller system based on Intel's8052AH-BASIC processor. This chip fromthe MCS52 family of 8 -bit processors fea-tures an on -board BASIC interpreterwhich can be accessed via a 3 -wire seriallink to an external RS232 -compatible ter-minal. In addition to an on -board EPROMprogrammer, the system puts a number ofeasily controlled user ports and timers atthe programmer's disposal, and is markedby versatility and simple construction. Ifyou are not convinced of this, we suggestyou look at the way the BASIC computeris used in the telephone exchange to bepublished in a forthcoming issue.

The current consumption of the BASICcomputer may be reduced considerablyby replacing the 8052AH-BASIC proces-sor by the 80C32. Add an external EPROMthat contains the machine code for theBASIC interpreter and you have a low -power BASIC computer suitable for bat-tery operation.

MPUTER1000 REM1010 REM *2 8052 - AH BASIC V 1.1 (INTEL)1020 REM **

1030 REM. ** ROHCOPY1040 REM ** by E Vermeulen **1050 REM ** **1060 REM ** THIS PROGRAM TRANSFERS THE BASIC **1070 REM ** INTERPRETER IN THE ROM BURNED IN THE **1080 REM ** 8052AH-BASIC PROCESSOR TO A 2764 EPROM **1090 REM ** BY USING THE ON -BOARD EPROH PROGRAMMER. **1100 REM ** INTERPRETER 8052 IC: 0000H-1FFFH **1110 REM ** RAM ADDRESS (IC5) ON CARD: 2000H-3FFFH **1120 REM ** EPROM ADDRESS ON CARD (2764): 8000H-9FFFH **1130 REM ** **1140 REM ** 8052 -AN BASIC Copyright by INTEL **1150 REM ** For futher information refer to Intel's **1160 REM ik. HCS BASIC - 52 User's Manual **1170 REM ** Order Nunber : 270010-003 **1180 REM ** Intel Corporation (UK) Ltd. **1190 REM ** Pipers Way, Siiindon SN3 1RJ **1200 REM ** phone (0793) 696000 **1210 REM ** * *

1220 RE)! ******** ****************************** ************1230 REM1240 PRINT"** PART 1: HOVE INTERPRETER TO RAM AT 2000H-3FFFH"1250 PRINT:PRINT1260 ETOP=1FFFH: REM : RESERVE RAH FROM 2000H1270 DIM A(15): REM : DIMENSION ARRAY 1x161280 FOR X=0000H TO 1FFFH STEP 16: REM : SET ROM ADDRESSING1290 FOR Y=0 TO 15: REM. : IN BLOCKS OF 16 BYTES1300 A(Y)=CBY(X+Y): REM : READ 1 BYTE ROM, PLACE IN ARRAY1310 Z=X+Y+2000H: REM : COMPUTE CORRESPONDING RAM ADDRESS1320 XBY(Z)=A(Y): REM : WRITE BYTE IN RAH1330 B=XBY(Z): REM : READ IT BACK FROM. RAM1240 REM : AND COMPARE WITH BYTE IN ROM1250 REM : ERROR? => REPORT AND STOP1360 IF A(Y)<>B THEN ?"PROGRAM ERROR ,ROM= ",A,.RAH=.,B:END1370 NEXT Y: REM : 16 -BYTE LOOP13801390 PHI. X," ",:PHO. A(0)1400 PHO. A(8),A(9),A(10),A(111410 NEXT X:1430 PRINT"** PART2: SET INTERNAL14501460147014501490 DBY(18H)=OFFH:1500 DBY(19H)=00H:1510 DBY(1AH)=7FH:1520 DBY(1BH)=20H:1530 DBY(IEH)=00H:1540 DBY(1FH)=20H:1550 W=0.05:1560 R=65536-W*XTAL/12:1570 DBY(40H)=R/256:1580 DBY(4IH)=R .AND. OFFH:1590160016101620163016401650166016701680169017001710172017301740175017601770 PGH :REM ** PROGRAMMING INSTRUCTION **1780 PRINT1790 PRINT:PRINT"** PART 4: CHECKING INTERNAL POINTERS FOR ERRORS"1800 PRINT1810 H=DBY(IAH):L=DBY(18H):HL=H*256+L1820 IF (DBY(30).0R.DBY(31))<>0 THIN 1830 ELSE 18401830 PRINT"INCORRECT PROGRAMMING OF EPROM AT ADDRESS",:PHI.HL:END1840 PRINT"PROGRAMMING FINISHED ** NO ERRORS **.:PRINT1850 PRINT1860 PRINT.** PART 5: DIRECT COMPARISON BETWEEN RON AND EPROM":PRINT1870 PRINT1880 FOR X=0000H TO 1FFFH :REM ** ADDRESS IN ROM1890 Y=X+8000H :REM ** ADDRESS IN EPROM1900 A=CBY(X):B=XBY(Y) :REM ** READ OUT RAM AND EPROM1910 PRINT.ROM",:PH1.X,:PRINT. =>.,:PHO.A,. =",1920 PHO.B,:PRINT" <=.,:PH1.Y,:PRINT" EPROM",CR,1930 IF A<>B THEN PRINT"EPROM ERROR":END1940 NEXT X:PRINT:PRINT1950 PRINT"EPROM CORRECTLY PROGRARMED":PRINT:PRINT1960 PRINT"PROGRAN FINISHED, BYE !!!"1970 END

REM : SHOW 16 -BYTE LINE ON TERMINAL,A(1),A(2),A(3),A(4),A(5),A(6),A(7),),A(12),A(13),A(14),A(15)

REM : LOOP FOR ENTIRE ROM (0000H-1FFFH)MEMORY FOR PROGRAMMING PROCEDURE"

REM : INTERPRETER (size = 8 Kbyte)REM. : NOW IN RAM FROM 2000H TOT 3FFFHREM : THE EPROM (also 8 Kbytes)REM : OCCUPIES 8000H TO 9FFFHREM : TARGET ADDRESS LOW BYTE -1REM SOURCE ADDRESS LOW BYTEREM : TARGET ADDRESS HIGH BYTEREM : SOURCE ADDRESS HIGH BYTEREM : NUMBER OF BYTES LOW ADDRESSREM. : NUMBER OF BYTES HIGH ADDRESSREM : W=WIDTH OF PROGRAMMING PULSE IN SECREM : R=RELOAD VALUEREM : SET VALUE OF R (LOW BYTE)REM : SET VALUE OF R (HIGH BYTE)

DBY(38)=DBY(38) .AND. OF7H: REM : RESET BIT 38.3 FOR 50nSEC PULSESPRINT:PRINT:PRINT SPC(25),.** SETTINGS OKAY **":PRINT:PRINT

PRINT"** PART 3: PROGRAMMING THE EPROM"

FOR R=1 TO 5:PRINT:NEXT RPRINT"** SWITCH ON THE PROGRAMMING VOLTAGE":PRINTPRINT.** BE SURE TO APPLY THE CORRECT VOLTAGE (12.5V OR 21 VOLT!":PRINTFOR R=1 TO 3:PRINT:NEXT RPRINT"PRESS ENTER TO START PROGRAMMING"PRINT"OR PRESS ESCAPE TO STOP":PRINT:PRINTPRINT"PLEASE TYPE <ENTER> OF <ESC>",K=GET:IF K=0 THEN 1710IF K=1BH THEN PRINT:END: REM ** 1BH is ASCII -code for EscIF R<>0DH THEN 1710: REM ** ODH is ASCII -code for EnterPRINT: PRINT: PRINT"BUSY PROGRAMING EPROM"PRINT:PRINT"THIS WILL TAKE ABOUT 7 HINUTES":PRINT

This program is available on di(5'4 -inch 360K IBM format)order number 1441 (see thReaders Services page).

k

e

Fig. 1. Type this listing of RONICOPY.BAS into your favourite word processor.


29ROM -COPY FOR 8052 -BASIC COMPUTER

Do you copy?All that is needed to transfer the BASICinterpreter from the 8052AH-BASIC to a27C64 EPROM is the program listed inFig. 1. Simply get your original BASICcomputer on line, and type in the listingon your terminal or PC. Check what youhave on your screen against the printedlisting. If this is all right, save the pro-gram. Plug an empty 27C64 EPROM in theZIF socket on the BASIC computer board,apply the correct programming voltage,and RUN the program. The 8052AH-BASIC does the rest, i.e., it transfers itsown BASIC interpreter to the EPROM.Some seven minutes later, the EPROM isready for use in a 80C32 -based version ofthe BASIC computer.

Procomm and the BASICcomputerSome problems may crop up when theBASIC computer is connected to an 113MPC or compatible running a communica-tion program like Procomm_ These prob-lems arise mainly from the absence of anyform of hardware handshaking on part ofthe BASIC computer. Also, while down-loading a listing generated on the PC, theBASIC computer needs time to convert theASCII data into token codes. This oper-ation, carried out by the BASIC interpreterin the 8052AH-BASIC, starts after recep-tion of a carriage return (CR) characterfrom the terminal. During the token con-version, the 8052AH-BASIC does notmonitor the serial port. The result is thatcharacters may be lost in the downloadingprocess when the terminal does not waitfor the BASIC computer to complete itstoken conversion operation after everycomplete line of BASIC instructions. Oneway of solving the handshaking problemsis to reduce the bit rate on the serial linkto a value where the time needed for thetoken conversion is simply not noticed.

Waiting for 62A fairly reliable method of ensuring soft-ware handshaking is to have the PC waitfor the prompt (>) transmitted by theBASIC computer. This can be achieved byprogramming ASCII value 62 for the pacecharacter in Procomm's ASCII transfersetup menu. First, however, go to the linesettings menu (ALT -S) and select option12 to set the serial data speed and formatto 19,200 bits/s, no parity, 8 databits and1 stopbit. If necessary change the settingas required for the COM port you intendto use. Save the settings.

Next, call up the setup screen by typingALT -S. Select item 2, the terminal setup.The parameters necessary for the BASICcomputer are shown in the screendump inFig. 2. Return to the setup screen, and se-lect item 6, the ASCII transfer configura-tion. The settings used by the author areshown in Fig. 3_ The pace character (op-tion 3) is set to 62 to force the PC to wait

TERMINAL SETUP

1) Terminal emulation VT -52 10) Break Length (ms) 350

2) Duplex FULL 11) Enquiry (CTRL -E) OFF

3) Flow control NONE

4) CR translation (in) CR

5) CR translation (out) . CR

6) BS translation DEST

7) BS key definition BS

8) Line wrap OFF

9) Scroll ON

OPTION ==,. ESC. Exit

Fig. 2. Screendump of Procomm's terminal setup menu with parameters set for the BASICcomputer.

ASCII TRANSFER SETUP

ASCII UPLOAD

1) Echo locally NO2) Expand blank lines NO

3) Pace character 62 (ASCII)4) Character pacing 0 (1/1000 sec)5) Line pacing 5 (1/10 sec)

6) CR translation NONE7) LF translation NONE

ASCII DOWNLOAD

8) CR translation NONE9) LF translation NONE

OPTION ==. ESC. Exit

Fig. 3. Screendump of Procomrn's ASCII transfer setup menu. Pace character 62 forcesthe PC to wait for the prompt transmitted by the BASIC computer.

for the BASIC computer after sending aline of BASIC. The character pacing maybe left at 0 in most cases. The line pacingis best set to 5 as shown, although this isnot critical.

When the pace character is set to 0,Procomm ignores any character returnedby the BASIC computer. This setting isstill useful, however, when the softwarehandshaking is not used, and the seriallink runs at a relatively low baud rate.When software handshaking is not used,some experimenting with the characterpacing and line pacing parameters may berequired for best results. A lot depends onthe length of the cable between the PC andthe BASIC computer, and also whether ornot this cable is screened. Fortunately, thewait times that may be programmed inProcomn-i will allow vou to find a com-promise between fast data transfer and asfew as possible errors.

Uploading the ROMcopyprogramAssuming that you have typed the listingin Fig. 1 into vour favourite word proces-

sor (set to ASCII output), the procedure tosend the program to the BASIC computeris as follows. First, save the file as ROM-COPY.BAS on floppy disk or hard disk.Next, run Procomm, and get the BASICcomputer on line by pressing the spacebar. Type PgUp to.enter the upload menu.Select option 7, ASCII PROTOCOL. Typethe filename (if necessary, preceded by thedrive station and/or the path, e.g.A: \ ROMCOPY.BAS) followed by a re-turn. The upload process can be followedon the screen. On completion, type LIST tocheck the loaded file against the listing.RUN the program and you have yourBASIC interpreter available in EPROMafter about seven minutes.

References:1. CMOS replacement for 8052AH-BASIC.Elektor Electronics January 19902. BASIC computer. Elektor Electronic:: No-vember 1987.

Procomm is a registered trademark of Da-tastorm Technologies, Inc.


MA YOk OW\Experimenting with electronics is great fun and many of you will have no

objection to a drawer full of projects that never made it beyond the stripboardstage. However, once a circuit is known to function reliably, the last step is

inevitably to put it on a printed -circuit board. In this magazine we monthly offerthe PCB artwork for numerous projects, so all the designing and checking has

been done for you. The next logical step is to make a flying start with theproject by buying one of our ready-made PCBs produced to professional

standards. However, in case a PCB is not available ready-made, there is noother way than to produce it yourself.

This article discusses the basic steps in-volved in making one's own PCB fromavailable artwork, i.e., the design (draw-ing) and design checking stages are notcovered. It is assumed that artwork of thetype normally published in this magazineis used to produce a printed -circuit board.

The first thing to note is that the track-layouts are printed as a reverse (mirrorimage) of the original, i.e., as if they wereviewed from the component side. The rea-son for doing this will be reverted below.Second, the lay -out is always at full-size,i.e., at 100%. Third, every track lay -out hasan associated component mounting plan(or overlay), which shows the positions ofthe components at the component side ofthe board. The values of the componentsand the type indications are in accordancewith the parts list printed next to, orbelow, the track lay -out and the overlay.Unfortunately, you can not produce yourown component overlay unless you havefairly sophisticated photographic equip -

Fig. 1. Home-made UV exposure unit suit-able for use with a vacuum pump for opti-mum contact between the photosentivelayer on the board and the emulsion on thefilm.

ment. The overlays shown in the articlesare used for printing on the PCBs suppliedready-made through the Readers Ser-vices.

The artworkThe term artwork for a PCB commonlyrefers to the drawings that 1) show thepattern of the copper tracks at the trackside of the board and 2) show the positionsof the components at the component sideof the board.

Several things must be kept in mindbefore deciding to make one's own PCBfor a particular project. First, the tracklay -out must be relatively simple. We donot recommend making PCBs with a hightrack density, as in that case the artworkis usually produced on a computer. Tokeep the board as small as possible, thetracks are then relatively thin and difficultto reproduce reliably with simple equip-ment. This means that a PCB with manyICs, or a double -sided PCB, is better pur-chased ready-made than made at homewith all the risks of almost invisible trackinterruptions and short-circuits in be-tween IC pins which can take hours totrace. The results in not a few cases aredisappointment, burnt dinners and anugly PCB with lots of wires running at thetrack side. Also bear in mind that a ready-made PCB has a component overlaywhich consists of the component symbolsand reference numbers printed in white,and the track lay -out printed in black. Thelatter makes it easy to follow the trackpattern while viewing the componentside. Most artwork shown in the maga-zine is produced to certain conventionsyou have come to recognize and appreci-ate over the years.

The materialsThe minimum bill of materials for makinga printed -circuit board from a lay -out inthe magazine looks like this:

transparent (mylar) filma piece of (positive) photo -resist copperdad board (single- or double -sided)

an UV (ultra -violet) light exposure unita quantity of sodium hydroxide (causticsoda) pellets (developer)a quantity of ferric chloride pellets (et -chant)two polystyrene or glass trays as used inphotographic darkroomsa small heating platea thermometerrubber gloveslots of clean waterplastic flasks or other containers for thedeveloper and the etchanta pair of polystyrene tongsa saw or another suitable cutting devicea high-speed drill on a standa can of solder spraytin-plating materials (optional)

All of the above tools and the chemicalsare available in various sizes and quan-tities from electronic mail order firms. Inmany cases, complete PCB productionkits are offered, although a drill on a standis not usually included.

Exposing and developingAlthough some of you appear to get awaysuccessfully with photocopies on paper, itwill be necessary in most cases to transferthe lay -out found in the magazine to atransparent film. If you do not have thenecessary dark -room equipment to dothis, your local photographer or printermay be able to help you. The film usedshould not be too thick. Interestingly,some photocopying machines are capableof copying on to film transparencies orpeel -off film material such as Frisket.Whether or not this method of producinga film from a lay -out printed in the maga-zine is usable depends largely on thethickness of the film and the quality of thetoner. Do not be surprised if the machine'gobbles up' your film and keeps it hiddensomewhere inside until a well -trained ser-vice technician arrives! Normal transpar-ent foil must never be fed into aphotocopying machine because the heatapplied to burn the toner into the materialwill cause it to melt and remain stuck onthe drum.


MAKE YOUR OWN PCBs

Fig. 2. Look at the letters and numbers to see the difference between the mirror image oa PCB track lay -out (left) and the 'real' track lay -out (same PCB shown to the right). Thelay -outs in this magazine are usually printed as reverse images to prevent parallax effectsduring the exposure period.

The rear side of the film is secured onthe glass plate of the UV exposure unit,i.e., the emulsion side of the film is indirect contact with the copper side of thecircuit board placed on top. The track -layouts found in the magazine are printedas mirror images to enable this direct con-tact so as to prevent parallax effects (smallimage -shifting) with relatively thick filmsor paper. Before putting the PCB on top ofthe film, peel off the light -resistant plasticcover. It is very important for the board tobe pressed as firmly as possible on to thefilm, particularly if the board is fairlylarge.

UV exposure units may be purchasedready-made, usually complete with twoor four UV tubes. The photograph in Fig. Ishows a home-made type with four LTVtubes, a built-in mechanical timer and aconnection for a vacuum pump (notshown). The pump is capable of creatinga fairly strong vacuum, ensuring a highand equally distributed contact pressurebetween the photosensitive layer on theboard and the emulsion side of the film.The UV unit shown has been used success-fully many times for the production ofrelatively large circuit boards. Rememberthat ultra -violet light is harmful to theeyes, so make sure that the UV unit can beclosed properly.

In general, the exposure time is fairlyuncritical_ As a rule of thumb, a unit withfour 20 -watt tubes and the film at a dis-tance of about 5 cm will be on for about5 minutes. The optimum exposure timedepends on the type of film and thephotosensitive board, and will have to befound empirically.

The developer may be made during theexposure time. Depending on the size ofthe board, a quantity of sodium hydroxidecrystals is dissolved in water in accord-ance with the instructions on the package.Use water of about 25'C and stir the solu-tion to make sure all crystals are dis-

solved. After exposure, the board is im-mersed in the developer, and the tray isgently agitated. After one to two minutes,the track pattern should become visible asthe solution turns light blue or purple.Clean the board with plenty of runningwater. Although the developer is reu-sable, it is best disposed of after about tentimes' use.

Etching and drillingThe etchant, a ferric chloride (FeCI3) solu-tion, is prepared at the concentration andtemperature recommended by the manu-facturer. Always wear rubber gloveswhile working with the etchant: althoughmost of you will be aware of it, it is anaggressive, highly corrosive and toxic sol-ution. Never use metal trays, spoons,tongs or flasks in combination with theetchant.

Depending on the temperature, theconcentration of the etchant, and theamount of copper to be etched away, theetching process will take between 10 and20 minutes. The glass or polystyrene traymust be agitated gently during the entireetching process, while the temperaturemust be kept between 40EC and 50°C.Higher temperatures do not make theetching process any faster. If necessaryadd a little water to compensate the lossdue to evaporation. A small aquariumpump that feeds bubbles into the etchantis a good alternative to haying to agitatethe etching tray. Likewise, a glass, immer-sion -type heating element as used inaquariums may be used to ensure theright etching temperature. As you can see,it is worthwhile to visit your local petshop!

When the board is ready, use a pair ofpolystyrene tongs to remove it from thetray. Clean the board thoroughly underrunning water to remove all etchant. Theetchant solution is reusable and may be

WARNING

During the production of printed -cir-cuit boards chemicals are used whichare possibly aggressive and corro-sive. Strictly follow the manufacturers'or suppliers' instructions for handlingand storage of these chemicals. Weargoggles and protective gloves, andensure that the space you are workingin is amply ventilated. Contact yourlocal council on environmentallysafe ways to dispose of used de-veloper, etchant, empty cans, andother packaging materials.

poured back in its container. Althoughferric chloride etchant is known to beusable even when it is thick with dis-solved copper, its concentration may bekept at a usable level by adding a littlehydrochloric acid from time to time.

Allow plenty of time for the PCB to drybefore spraying the track side with solderlacquer.

Even a perfectly produced board maybe spoilt when it is not drilled properly. Inmost cases, you will find that a high-speeddrill on a stand is a must after all the effortyou have put into making the PCB, Theoptimum drill speed depends on the drilldiameter and the board material. Ingeneral, it is best to purchase a set of spe-cial high-speed PCB drills with diametersbetween 0.7 mm and 1.5 mm. Normalhigh-speed steel (HSS) drills may be usedfor the larger holes (e.g., the ones in thecorners of the PCB). As you will soon dis-cover, drilling a PCB is a fairly boring andtime-consuming job. Brush off the dustfrom time to time and check for burrs atthe component side.

The PCB is now ready for assembly.Use the component overlay found in themagazine as an orientation aid to fit theparts at their respective positions.

SUPPLIERS

A wide range of materials, tools andequipment for making printed -circuitboards is available from UK -basedelectronics mail-order companies in-cluding

Maplin Electronics PLC, (0702)554155

ElectroMail, (0536) 204555

Cirkit Distribution Ltd., (0992)444111

VeroSpeed, (0800) 272555

ElectroValue Ltd., (0784) 33603 or(061 432) 4945

Cricklewood Electronics Ltd., (081452) 0161


L. _1

AUir A C HEAD SW

This circuit automatically switches on the headlights of a car after the engine isstarted. In countries like Sweden and Canada, car drivers must have their

day -running lights on, even in broad daylight. Accordingly, cars manufacturedor imported into these countries often have an automatic lights -on controlwhich, although it can not be disabled, leaves the normal light switch in

function. A similar circuit with automatic switch -on, switch -off and reduced lightintensity is described here.

J. Ruffell

Although a motorcyclist driving with hisheadlight on is a familiar sight even inbroad daylight, many of you will find itstrange at first to see car lights duringdaylight hours. In Sweden, however, it isnot allowed to drive a car or any othermotor vehicle without switching theheadlights on. This traffic rule is imposedfor reasons of safety, and has promptedcar manufacturers exporting to Sweden todevise circuits that switch the lights onand off at the same time as the engine.Similar regulations for the use of car lightsare currently proposed by other countrieslike Holland.

Evidently, the switching on action ofan automatic lights controller servessafety, and the switching off action pre-vents the annoyance of a flat battery after,say, a few hours of shopping with the carleft on a misty parking lot.

To extend the life of the bulbs, the auto-matic light switch reduces the operatingvoltage to about 805 of the battery volt-age. Tests have shown that the reductionin light intensity is not noticed under day-light conditions. The circuit allows thedriver to switch on the headlights whenhe thinks this is necessary. When the 'nor-mal' light switch takes over, the lamps arepowered with the full battery voltage.

Circuit descriptionFigure 1 shows the circuit diagram of theheadlight switch. The number of parts hasbeen kept to a minimum to enable thecircuit to be fitted in a compact, alumi-nium, enclosure, for which there shouldbe room in almost any car. The circuit isconnected to the car's electrical systemwithout the need to break or modify exist-ing connections.

When the engine is started, the car'sheadlights and rear lights are switched onautomatically. Pulse -width modulation isused to power the lamps at about 80% oftheir nominal working voltage, which isautomatically restored to 100% when thedriver switches on the lights.

The heart of the circuit is formed byopamp ICI, a CMOS type TLC271. Theoscillator it forms part of supplies a 50 Hz

signal of which the duty factor can be setto a value of between 0.7 and 0.9 with theaid of preset PI. For other ratios, resistorsRRa and R7 have to be given differentvalues. The output signal of the opampcontrols output transistor Ti via a buffer.The output transistor is a power MOSFETType BUZ11 capable of switching loads ofseveral tens of amperes (30 A nominally).

_ r

When the FET conducts, the 'on' resist-ance of the drain -source junction is as lowas 0.04 Q, so that the dissipation remainsbelow 2 IV even in worst -case conditions.The MOSFET is protected against voltagesurges by a VDR (voltage -dependent re-sistor), R14.

Transistor T2 switches the opamp-based oscillator on and off. When the en -

1M4001Pi Al

BC55712

7,1ST

2,1

1N4145

a.

130

1C1

TLC271

AS

Ts,

HEN

2.1 1N/14Sor es

ti12V

0

T .1=1At)

25Tmin

PT

MEI

I At,ISE isp

80547

1.)

143

BC5471=i

T

TT)

(raI

- ita

S

(URI

Fig. 1. Circuit diagram of the day -running lights controller.

AL TOM.ATIC HEADLIGHT SWITCH

Fig. 2. Printed -circuit board for the lights controller.

SI = Ugbt switch52 = dip beam switch53= Igaltioa switch

Iballet,/ :

12V :

Fig. 3. Connection diagram. The terminal numbers follow the Bosch convention.

gine does not run, the alternator does notrun either, so that terminal D+ is at a lowpotential. Consequently, T2 conducts, CIis kept fully charged, and the oscillator isdisabled. When the alternator voltage ispresent at terminal D+, T2 will block aftera few seconds, enabling the oscillator tostart working.

The rectangular oscillator signal is buf-fered and inverted by T3, which, together

Boschcode

Function

15 battery voltage (switched)

30 battery voltage (unswitched)

31 chassis

56b dimlights

58L parking light and lefttail light

58R parking light and righttail light

Dr alternator voltage

with T4, C2, Cs, Dt, and D7, forms a voltagedoubler to ensure that the MOSFET isdriven with a sufficiently high gate volt-.age. Here, this voltage is about 21 V, or6 V higher than the voltage across thelamps when the engine runs_

Diodes D. and DQ serve to keep theparking lights (if available on the car) infunction_ The battery voltage is filteredand limited to 15 V by components R II -Csand Ds respectively. The circuit is con-nected to the electrical system of the carvia terminals 58L and 58R.

ConstructionThe circuit is best constructed on a printedcircuit board of which the artwork isshown in Fig. 2. The only parts not accom-modated on the board are the N.10SFET,Ti, and the associated VDR, RI4. Both aremounted on one side of the metal enclo-sure. For optimum suppression of voltagesurges, the VDR must be fitted as close aspossible to the transistor. The photographshows the prototype fitted in a Hammondenclosure, for which there should be

COMPONENTS LIST

Resistors:6 10k.O.

2 4710:2

1 4k71 100kce

1 3301 470.0

1 1M11

1 SIOV-S07K201 25k.0 preset H

Capacitors:1 330n1 22uF 35V1 1000liF 25V1 2201F 25V1 47uF 25V

Semiconductors:1 TLC2711 BUZ11

1 BC5572 BC5475 1N41481 1N4001

1 15V 0.4W zener2 1N5408

RI - R5:Ri0R6;R3

R7

R9

RI 1

Ri 2

R13

R14

Pt

CiC2C3

C4

C5

ICIT1

T2

T31-4Di ;03:D4;113:D7D2

D5

D8;D9

Miscellaneous:2 3 -way PCB terminal block Ki:K31 2 -way PCB terminal block K2

1 15A (slow) fuse with cable holder1 enclosure Hammond 1590B1 insulation set for Ti

ample space either in the engine compart-ment or below the dashboard.

Spade receptacles and short, heavy-duty wires are used to connect the unit tothe appropriate points in the car's electri-cal system. In most cars, an extra connec-tion to any of these points can be madewithout problems by fitting two-wayspade terminals.

The completed unit is fitted at a suit-able location behind or underneath thedashboard. As already noted, the connec-tion to the car's electrical system is in par-allel, i.e., you need not cut any of theexisting wiring.

The codes with the terminals indicatedin the circuit diagram follow the Boschconvention which is used in many cars.Table 1 lists the functions of the relevantterminals to assist owners of cars in whichthe Bosch code is not used.

The electrical connection of the auto-matic headlight switch is illustrated inFig. 3. The unit is powered when the igni-tion switch is closed. Upon detection of asufficiently high alternator voltage at ter-minal D+, the unit powers the headlightswith a pulse -width modulated voltage.When the dipped lights are switched onby the driver, terminal 56b carries the bat-tery voltage. Consequently, transistor Tiis short-circuited so that the headlightswitch has no effect on the lamps, whichthen light at their full intensity.

ELEKTOR ELECTRuNICS SEPTEMBER 1990

34

INTERMEDIATE PROJECT

A series of projects for the not -so -experienced constructor. Although each articlewill describe in detail the operation, use, construction and, where relevant, the

underlying theory of the project, constructors will, none the less, require anelementary knowledge of electronic engineering. Each project in the series will be

based on inexpensive and commonly available parts.

This month's project is anall -electronic version of thewell-known one-armedbandit found in amusementarcades. Apart from the funin building and using thisportable mind -teaser, youhave your free introductioninto pseudo -random numbergeneration.

T. Giffard

A one-armed bandit is a gambling ma-chine that is played by inserting a coin,pulling a heavy lever (or pressing a but-ton) and waiting anxiously for three ident-ical fruit symbols to appear behind theglass cover as the rolling drums come to astandstill. Unfortunately, this rarely hap-pens, and the owner of the machine hasthe financial advantage. However, mostof us will admit that it is great fun to playa few games, if only for the thrill of it, thenoise of the lever, the clicking sounds asthe wheels stop, and, of course, the chanceof winning.

In terms of electronics, not much isneeded to build a circuit that does basi-cally the same as the one-armed bandit,with the exception, of course, of insistingon your money! The fruit symbols are sim-ply replaced by LEDs ( light -emittingdiodes), and the drums on which they re-volve are replaced by counter circuits. Os-cillators form the electronic equivalent ofa mechanical assembly that powers thewheels.

The result of these 'transformations' isa circuit in which three counters, uponbeing triggered, start to operate. Eachcounter has a number of associated LEDsat its outputs that indicate the counterstates. These LEDs are arranged verti-cally, so that one horizontal row consistsof three LEDs, each of which belongs with

THREE IN A ROW

C

R1

9V

0

0

no -

CI

MOM130-

700

0tc2 Q1 0 60

4017 02D3

430 02

CL_ 0409

055 0501

08

07 6 DA

069 - DI

1115 ..._C2MON EIi A 05 RS

T2 13

13

12 NO11.14

'53Imam

103,

CLX

CO

1C3

4017 0203

ERA

0505

07

05

09

3 Ot6

017

7 Du II1"+

I 018

so!:

6 013

13

R6

101 = 4093

C

1130n

IC 1c

C4min720n

,4

09

1C401

4017 0203

LK 04

05

JrsrE to

13

0,5

07

05

9

3

2 026

02561-4.

7 D21 rl10

D27

02C1b.r5

6 D22

2310,1

9 t9

Ti

e9V

(1) C7 V Cs CS1C3 MI=

MINMINN

100M 0 100,1

'Clto

0C9

1013

i6v

0

9all6._9V.

905822X -11

Fig. Circuit diagram of the electronic game.


THREE ININ A ROW

a different counter. The upshot is that wehave three independently operating run-ning lights, of which the indicators, in thiscase LEDs, start to flash when a button ispressed. When the button is released, eachof the three running lights will stop at aparticular LED. Statistically, one in 81runs will result in three LEDs in a rowremaining on when the 'play' button isreleased.

The LEDs may be provided with labelsor fruit symbols similar to those used in areal one-armed bandit. Alternatively,numbers may used, and the rules of thegame modified accordingly, for instance,a jackpot may be won when three ninesappear.

Circuit descriptionThe circuit diagram of the 'three -in -a row'game is given in Fig. 1. The indicators areformed by LEDs D1-D27 which are ar-ranged in three vertical rows of nine LEDseach. The counters are formed by threeintegrated circuits Type 4017 (1C2, IC3 andIC4). Three of the four NAND Schmitt trig-ger gates contained in the Type 4093 pack-age are set up as oscillators. Theremaining gate, ICib, functions as aninput buffer for the touch -sensitive

'play/stop' button.When contact S is not touched, the in-

puts of IC Ib are held at a high potential byresistor R1. Since the gate is an inverter, itsupplies a low output level which keepsthe rest of the circuit disabled.

When contact S is touched, the skinresistance of the finger takes the two in-puts of IC lb low. This happens because theskin resistance, although it can takevalues from a few kilo -ohms to a few hun-dred kilo -ohms depending on factors suchas the degree of moisture, is much lowerthan 10 Mil, being the value of RI.

The result of touching contact S is ahigh level at the output (pin 4) of IC16.Consequently, the oscillators built aroundgates ICia, Ietb and ICic start to operate.Their output signals have a frequency ofabout 10 Hz and are fed to the clock inputs(CLK, pin 14)) of the respective counters.

The counters are divide -by -ten (de-cade) types of which the operation is illus-trated by Fig. 2. As shown by the insettiming diagram, outputs Q0-Q9 go highone after another on arrival of the clockpulses. The desired 'running light' effectis therefore simple to create by connectingLEDs to the Q outputs of the counter.

Resistors R5, Rn and R7 limit the LEDcurrents to a safe value. Note that only one

CLOCK

4017

L E.41 lam°. ° s

ITITE17113-01171I 4

RESIT

aLOCK Isgs4L1

fl

r-71

.r7.KsWtr 01711

Temni a agram lc, 4017

906022X .12

Fig. 2. Pinning. internal structure and tim-ing diagram of the 4017 decade counter.

LED in a group lights at a time, and thatthe 4017s supply virtually the battery volt-age when an output goes high. Since a redLED drops about 1.6 V when it is on, eachseries resistor will have to be dimensionedfor a drop of 7.4 V (assuming that the bat-tery voltage is 9 V). The values shown inthe circuit diagram result in a LED currentof 7.4 V/1.5 kS/ a- 5 mA. This is, in general,ample current to make a red LED lightvisibly. In case you want to increase thebrightness, use somewhat lower valuesfor resistors Rs, R6 and R7. Bear in mind,however, that you can not go much higherthan 5 mA because this is about the maxi-mum current that can be supplied by theoutputs of the 4017.

COMPONENTS LIST

Resistors:1 10MS-2

3 1Mt1

3 1k5

Capacitors:6 100nF1 82nF1 120nF1 101iF 16V

Semiconductors:27 red LED1 40933 4017

RtR2;R3;R4R5:R6:R7

CI;C3:C5-C8C2

C4

Co

Di-D27IC'IC2;1C3;1C4

Miscellaneous:1 6V or 9V battery Bt1

1 ABS enclosure with battery compartment.Approx. size: 86x140x32 mm, e.g. Pactec.

Fig. 3. PCB track layout (mirror image) and component mounting plan.


36INTERMEDIATE PROJECT

Fig. 4. Completed circuit board before it is fitted into the enclosure.

The Q9 output of each counter is con-nected to the reset (RST) input, so that thecounting process continues as long as con-tact S is touched.

The frequency -determining capacitorsin the oscillators have different values so

that the LEDs in the associated group (col-umn of nine each) do not 'run' at the samespeed. This is done to prevent playerswith extremely fast finger movementsfrom winning the game over and overagain.

THREE IN A ROW.cp

0 0 00 0 00 0 00 0 00 0 0

0 0 00 0 00 0 0

i

906022-F

Fig. 6. Suggested front -panel design.

Fig. 5. Parts needed to make the touchsensitive play stop control.

Finally, the value of capacitor CI issuch that the LEDs will keep flashingabout one second after releasing thetouch -sensitive contact. This is done tomake the game more realistic.

ConstructionThe printed -circuit board for this projectis etched and drilled with the aid of themirror -image of the track layout shown inFig. 3. Fitting the components on theboard as per the overlay (also shown inFig. 3) and the parts list is fairly straight-forward. Make sure the ICs are fitted theright way around, and also observe thepolarity of the LEDs-in most cases, theshort terminal is the cathode.

A game like 'three in a row' will not bea success unless the electronics are housedin an attractive enclosure. Make a copy ofthe component overlay (Fig. 3) and use itas a template for drilling the holes for the2 LEDs in the top half of the enclosure.

The touch -sensitive switch to start andstop the game is made from a phonosocket and an M3 bolt as shown in Fig. 5.A section of the threaded part of the boltis covered with thin insulating tape tomake it fit tightly inside the phono socket.

Finally, the game may be poweredeither by a pack of four 1.5 V batteries ora single 9 V PP3 battery. The average cur-rent consumption is about 15 mA, so thata 9 V battery will last for about 15 hours.

0

0

S

S

S

0

S

S

S

ELF.KTOR ELECTRONICS SEPTEMBER 1990

k)

0 P,AYBACK PREAThe TDA1522 from PhilipsComponents is apreamplifier chip for tapeand cassette recorders.The circuit presented hereis remarkable for its lownoise level, built-inclick -free mute circuit anddirect -coupled inputs forthe playback heads.

T. Giffard

The TDA1522 is a good starting point fora playback amplifier irrespective ofwhether this is installed on a 'bare' chassis(reels, motor, drive, etc.), or fitted as anupgrade in an existing recorder. As re-gards component count and complexity ofthe circuit, the TDA1522 compares fa-vourably with many opamp-based alter-natives.

The TDA1522 contains two high -gain,low -noise amplifiers and an internal mutecircuit that allows totally click -free con-trol. The chip does not require bias settingnetworks, provided its internal regulatorreceives a supply voltage of 73 V orgreater. There are no special requirementsas regards supply voltage filtering, sincethe suppression of 100 Hz hum (from abridge rectifier) is about 95 dB.

The playback heads are connected di-rect to the inputs of the TDA1522, i.e.,without the usual coupling capacitors.The advantage of this direct connection isthe absence of clicks and other noises onthe tape. Such clicks are usually caused bya coupling capacitor, whose charging cur-rent flows through the head.

High amplificationFigure 1 shows the circuit diagram of theplayback amplifier. The two playbackheads (left and right channel) are con-nected direct to the respective inputs,pins 4 and 6, of the TDA1522. Playbackheads typically have a resistance of 300 Qand an inductance of 80 mH. Since theinput resistance of the amplifiers in theTDA1522 is about 200 kf2, the signal in-duced in the heads is hardly loaded.

Since the heads supply a very smallsignal, the amplifiers must produce littlenoise themselves, and in addition providea high amplification factor. The noise levelof the TDA1522 is specified at 5 nV/X1-1z(at RG = 0 0), while the amplification isdetermined by a feedback network. Sincethe amplifiers in the TDA1522 are non -in -

S1

R2

R3

MAIN FEATURES

Supply voltage 7.5 V - 23 V(8.5 V typ.)

Current consumption: 5 mA (typ.)

open -loop gain: 90 dB

Output voltage: 1.5 Vrms (typ.)720 mVrms

(at 0.3 mV inand 315 Hz)

Distortion:(720 mVrms, 1 kHz,

RL = 4k7)

Input resistance: > 200 tal

Output resistance: < 1 1(0

Us

R81N4148

R6SBB

140k

vt

D1

Cl

C7

220p

10p

supply

TDA1522

R4

Fig. 1. Circuit diagram of the low -noise stereo preamplifier for tape heads.


38AUDIO AND HI -1:1

V315 H:

111111111101111,HZ.

12

Fig. 2. Frequency response of the preamplifier (120 ..s de -emphasis).

2C.

40

60

3 6 ti2,5'Vs

OCC:E2-1.3

Fig. 3. Attenuation as a function of the mute voltage applied to pin 2 of the TDA1522.

verting types, the amplification of each ofthese is defined by an internal 140 kS2 re-sistor and an external resistor (R7 and RN).For AC signals, the external resistors (onefor each channel) are taken to ground byelectrolytic capacitors. With resistori-alues of 8.2 a the theoretical gain is84.6 dB, disregarding the effect of the de -emphasis networks Rs -C4 and R6 -Cs.

Frequency responseA network consisting of a 5.6 kS2 resistor(Rs; R6) and a 22 nF capacitor is connectedin parallel with the 140 k1.1 resistor in theTDA1522. This network makes the gain ofthe preamplifier frequency -dependent(about 68 dB at 315 Hz)- Since the reac-tance, Xc, of the capacitor drops as thefrequency rises, the degree of feedbackrises so that the amplification drops. Fig-ure 3 shows the frequency response for apre -emphasis of 120 us, the standardvalue for tape type 1 ('ferro' or iron -oxide). The 0 dB Level is defined at a fre-quency of 325 Hz. Other tape typesrequire a corresponding change in thetime constant as advised by the manufac-turer. The circuit is simple to modify: for

70 us tapes, for instance, change Rs and R6to 3k3. Similarly, for 90 us tapes (chro-mium -dioxide Cr0,), the theoretical valueof these resistors is 4k1 (the nearest valuein the E96 series is 4k12; otherwise, use aseries network of a 3k9 and a 220 cl resis-tor).

When the feedback networks R5 -C4and 126-05 are omitted, the frequency re-sponse becomes linear and the amplifica-tion, a, depends on one resistor only:

a =1 + 140k /R7

where R7 is substituted by Rs for the am-plification in the other channel.

Without the feedback parts, the circuitmay be used as a low -noise stereo pream-plifier with high -impedance inputs andlow -impedance outputs. One possible ap-plication is, therefore, with dynamicmicrophones.

Mute circuit-I he click -free mute circuit in the TDA1522may be used together with, for instance, amute switch, a VOX (voice -operated con-trol) or a squelch circuit. The mute func-

Fig. 4. Track layout and componentmounting plan of the PCB for the preampli-fier.

COMPONENTS LIST

Resistors:2 4k72 68k2 5k62 802

Capacitors:2 10uF 10V radial1 2u2 25V radial2 22nF2 220pF 10V radial

Semiconductors:2 1N41481 TDA1522

Miscellaneous:1 on off switch

R ;R4R2;1=13

R5:R6

R7:R6

C1 :C2

C3

C4;C5C6;C7

D1:D2ICI

Si

ELENTOR ELECTRONICS SEPTEMBER 1990

STEREO PLAYBACK PREAMPLIFIER

tion is controlled with a direct voltageapplied to pin 2 of the TDA1522. The rela-tion between the control voltage and thesignal attenuation is shown in Fig. 3. TheIC operates at full amplification whenpin 2 is not connected, or held at a voltagegreater than 6 V. Below this level, the out-put signal is lightly attenuated at first.Below 2 V, however, the attenuation in-creases rapidly as shown by the curve.The output signal is virtually blockedwhen pin 2 is connected to ground ormade low by a digital control signal. Themost important characteristic of the mutecircuit, however, is that it operates in aclick -free manner. In the application cir-cuit (Fig. 1), pin 2 is connected to an elec-trolytic capacitor, C3, and to the positivesupply line via R2 and R3. This networkforms a power -on delay that preventsswitch -on noises, including those pro-duced by circuits ahead of the preampli-fier. The mute function is controlled by anexternal single -pole on/off switch or apush-button connected to junction R2 -R3.

Printed -circuit boardThe circuit shown in Fig. l is built on theprinted -circuit board shown in Fig. 4. Theexternal connections are simple-seeFig. 5. Note that the two centre terminals

stop here:Authorizer offers uniquesystem protectionComputer criminals no face a new. formi-dable. opponent: the Authorizer. developedby DSS innovative electronics. The Auth-orizer Access Control Device (ACD) is apiece of hardware of the size of a match -box.To access a protected (host) computer. theuser connects the Authorizer between theserial port of his computer and the modem.When the host system is called. it automat-ically requests a unique code stored in theAuthorizer. The connection is broken whenthe code is either not sent or not valid. Theidentification request and the subsequentcode check performed by the host are so fastas go by unnoticed by the calling user. whodoes not even have to enter a password.

Basically. the ACD is a number manipu-lation device. There is no relation betweenreceived numbers and processed numbers.while the total number of combinations is astaggering 16 million. On receipt of a callfrom a user with an ACD. the host returns arandom number. The ACD responds with anumber that is the result of an operation onthe received number and a unique base num-ber stored in the ACD. The code received bythe host is checked with the aid of a MasterAuthorizer, which serves to identify the cal-ler using the unique base number.

The complex security routine in the ACDitself is also protected. After programmingan ACD, it is impossible to ever read itscontent. DSS does not record the ACDs' basenumbers and so can not produce a copy of a

iZ si 17,2.Z,..0 .-.-r- -

r ° °is ap - -mg vS-? G-1

2,90.0.8 S li Op3 o a e ---to

4.0( .

4 1,-44V 0 .2.

. *0

+211it

asst4

9...20V® S1

9 f 0 mute..

Fig. 5. Wiring digram showing how to connect the preamplifier board in an existing taperecorder. Screened cables must be used at the input to prevent noise and hum.

at the input side of the circuit board (nearR7 and Rs) must be connected to ground(0 V of the power supply), since these ter-minals form the ground path of pin 5 ofthe TDA1522.

The connections between the headsand the PCB must be kept as short aspossible and made in single screenedcable. Also make sure that the heads areconnected in phase.

NEW PRODUCTS

particular ACD. unless the client providesthe relevant base number. In theory. the cod-ing system used allows 100 billion uniqueACDs to be produced.

DSS also supply the master authorizerprogram and the controller unit to be in-stalled at the host computer. The use of aseparate control unit instead of a an im-plementation in the host obviates the needfor system -specific software and hardware.and also prevents the s) stem operator gain-ing access to the security information.

For further information on the ACD. con-tactDSS innovative electronics b.v. Accus-traat 25 3903 LX Veenendaal HOL-LAND. Telephone: +31 8385 41301 Fax:+31 8385 26751

Although the wiring at the low -imped-ance output of the preamplifier is lesscritical, it is recommended to use screenedcable for relatively long connections.

Test voltages in the circuit are the sup-ply voltage at pin 8 of the TDA1522, andthe voltage between pin 1 and pin 9,which should be about 3.7 V when thechip is functioning.

Turn your scopespectrum analyserRF spectrum anal,ers are the kind of choiceinstrument that most electronics engineersand technicians mould love to have. Onlytrouble is. conventional instruments costthousands of pounds. Laplace InstrumentsLtd however break this price harrier withtheir Spectrum Probe which effectively con-verts an conventional oscilloscope into aI-100 MHz spectrum analyser. The unitcosts £2-19. complete.I.aplace Instruments Ltd. Musters House Bexton Road Knutsford WA16 OBU.Telephone: 10565) 50268. Fax: 10565153519.

49

HIGH -CURRENT hL.

STER

A conventional current gain tester is too unreliable for measuringand comparing the d.c. gain of power transistors because it fails toset the collector current at a value that reflects the actual working

conditions in, say, the output stage of an audio power amplifier. Thetester described here measures the large -signal gain, hFE, of n -p -nas well as p -n -p transistors at a collector current of up to 10 A, yet

does not require a bulky power supply.

Complementary power transistors withmatching d.c. gain characteristics areoften used in power amplifiers to preventproblems with thermal drift, unbalancedoperation and, worst of all, unacceptabledistortion. Similarly, in series -regulatedpower supplies, it is often required thattwo or more parallel -connected powertransistors have virtually the same gain toensure equal current distribution.

Selecting power transistors withmatching gains from a batch is definitelyworthwhile for the above applications.Two problems may arise, however. First,the conditions under which the powertransistors are to operate differ consider-ably from those presented by a conven-tional hie tester. The tester typicallymeasures the small -signal gain of the tran-sistor at a collector current not higher than100 mA or so, while in 'real life' the powertransistor may carry up to 100 times morecurrent, causing its junction temperatureto rise and the d.c. gain to change. Thismakes low -signal hie testing of little usefor power transistors.

The second difficulty follows from thefirst: assuming there is a need to test athigh collector currents (several amperes),the cost and size of a suitable power sup-ply and a heat -sink for the transistorunder test may be prohibitive factors.Also, an ammeter to read the collectorcurrent during the test may not be avail-able.

Principle of operationThe present circuit overcomes the aboveproblems in an elegant way by pulsing thecollector current at a duty factor of about0.01. This enables the circuit to bepowered by a supply of modest currentrating-say, 1 A or so. An impractical col-lector current meter is also avoided byreversing the principle of current gainmeasurement: set a certain collector cur-rent and measure the (much smaller) basecurrent that produces it (see the inset col-umn on the design background). Thismeasurement is performed during the'on' time of the collector current, and thevalues obtained are processed by a

from an idea by C. Sanjay

sample -and -hold circuit whose timing iscontrolled by the same generator that sup-plies the pulses to the transistor undertest.

Basic test circuitThe basic test circuit for n -p -n transistorsis shown in Fig. 1. Pulses with a duty fac-tor of about Vico cause Ti, T4, Ts and theTUT (transistor under test) to conduct forabout 13 ms and block for about 150 ms.Because of the presence of a 3.9-V zener

diode, Dz, transistor T4 limits the voltageacross the collector resistor, IL:, of the TUTto about 3.3 V. If the voltage rises abovethis level, T5 is blocked and consequentlythe TUT also. The maximum voltageallowed across IL thus establishes a con-stant collector current, at which the basecurrent may be measured to obtain the hFEvalue.

Capacitor Cp between the base and thecollector of T4 prevents oscillation in thecurrent source by allowing some time forT5 to start conducting. The disadvantage

HIGH -CURRENT hit: TESTER

Fig. 1. Basic circuit of the current -gain tester configured for n -p -n transistors. The transistor under test is allowed to draw a relatively high current with a small duty factor frombuffer capacitor Cp via collector resistor Rc. A sample -and -hold measurement circuit derivesthe current gain parameter, hFE, from the level of the pulsed base voltage. The test circuitis in principle the same for p -n -p transistors.

of this form of compensation is that Cp isbriefly connected to a higher voltagewhen 14 switches off. However, transis-tors T2 and T3 prevent current surgesthrough T5 and the TUT by pulling thebase of T3 to ground in between pulses.

The (high) current that flows throughthe TUT during the 1.5 -ms long 'on' timeis supplied by a reservoir capacitor, Ch.

For p -n -p transistors, the basic test cir-cuit is duplicated with complementarytransistor types. The same zener diode Dzand the same power resistor Rc are used,however, to enable comparative gain teststo be carried out on pairs of complemen-tary TUTs.

A sample -and -hold circuit measuresthe voltage drop across the base resistor,Rb, of the TUT. This measurement is per-formed under the control of the generatorpulses. The output voltage produced bythe sample -and -hold circuit is fed to amoving -coil meter, M, provided with a1 -to -infinite scale. The indicated value ismultiplied by two factors, the collectorcurrent multiplier and the sensitivity, toarrive at the hFE value.

Circuit descriptionFigure 2 shows the circuit diagram of thehri- tester for n -p -n and p -n -p power tran-sistors. The pulse generator is formed byopamp ICia, which is wired as an astablemultivibrator. Two series -connectedLEDs, D3 and D4, supply the 3.9-V refer-ence voltage for the current source. Thered LED, D3, drops about 1.8 V, and thegreen LED, D4, about 2.1 V.

The base current drive circuits consistof TI -T5 for n -p -n TUTs, and Ti-T6-Tio forp -n -p TUTs. Depending on the range se-lected, the base of the TUT develops avoltage across one of the six resistors con-nected to the contacts of switch S. Duringthe 1.5 -ms long measurement period, elec-tronic switches IC3c and IC3d are closed,while 1C33 and IC3b are open. This resultsin the voltage developed across the baseresistor being stored in capacitor C3. Theelectronic switches change state duringthe 'off' period of the generator outputsignal, so that the measured voltage existswith reference to ground and can be fed tothe meter driver, opamp IC1B. CapacitorC-1 smooths the output voltage supplied

DESIGN BACKGROUND

U,

+Up

Fa.,171.11

The static forward current transferratio. hFE, of a bipolar transistor ina common -emitter circuit is definedas the ratio of d.c. output current tothe d.c. input current, or

hFE=lb

provided that keo, the collector cur-rent with the base open -circuited, ismuch smaller than I.

In the test circuit,

3.3VRc

Substituting:

band /b=UR

nb

I x RbhFE=-,

uRb

The values of Rc result in k valuesof 1 A. 2 A. 3 A, 4 A. 6 A and 10 A.

Examples:1. When k = 1 A: Rb = 10 Q andUR° = 2.5 V (full-scale deflection):

1

2.5x

10= 4tiFE-

2. When k = 1 A: = 24.9 Q andURp = 2.5 V (full-scale deflection):

hFE=1 x22.54.9-

10

3. When k = 3 A; /30 = 249 n andURO = 1.75 V:

hFE=3 x 249

- 4271.75

Note:The d.c. gain parameter, hFE. mustnot be confused with the common -emitter small -signal short-circuit for-ward current transfer ratio, hi..which is defined in terms of a.c. as

Sicsile= alb

with the output short-circuited to a.c.


42TF's I N1LASI. RENIENT

10V

5.1f

18 16

17

10V

81

C91-.1

20 10 000116 V

19 21

S49

IC1 = TLC272

IC3 = 4066

R3

IC1a

R4

IMmi C1 2x10 On

R26

18'

P1

10k

M1

1C0 JA

1N4148

IC1b

R7

C4

3x BC5578

TIP 125

R13

BC547B

TIP120

3x BC547B

C3i=1221

T IC3b

IC3c

4

15V

54b

S4a.

829

3°r8 2

lk

7

S4c

9

S1

CC 0

0

TA'

C6 C5t31 IC1 r.13 IC3101 100n25V

819

816

R17

R16

R14

R25

E

2W

0 / 0 12

4d

R24 R23 R22 R21 R20

c c

900078 13

101/

Fig. 2. Circuit diagram of the hFE tester. The contacts of push-button S4 serve to configure the circuit for use with n -p -n and p -n -ptransistors.

ELEKTOR ELECTRONICS SEPTEMBER 199U

HIGH -CURRENT lit ..TESTER

by the sample -and -hold circuit.Preset Pi at the output of 1C1B serves to

set full-scale deflection on the moving -coilmeter when the base resistor drops 2.5 V.Note that the meter deflection is inverselyrelated to the liFE value, creating the needfor a meter scale from infinite (no deflec-tion) to I (full deflection), similar to thatused on an analogue ohm -meter.

The collector currents for the six avail-able ranges are determined by power re-sistors connected to the contacts of switchS2. The circuit is switched from n -p -n test-ing to p -n -p testing by eight toggle con-tacts on switch S4.

The power supply of the has tester isconventional and based on a three -termi-nal 10-V regulator Type 7810 (IC2). Theunregulated input voltage to the circuitshould be between 15 V and 20 V.

ConstructionStart the construction by fitting the sixbase resistors (V( types from the E96series) on the 'sensitivity' switch, S3. Eachof the resistors is soldered between itsterminal on the switch and a commonjunction. Resistor R23 goes to the switchterminal marked '1', R24 to switch termi-nal '2' and so on. Next, connect approxi-mately 10 -cm long light -duty wires to thepole and the resistor junction.

The collector current switch, 52, alsohas the associated resistors, in this caseRi-1-R19, fitted direct at its terminals. Re-sistor R19 is connected between switch ter-minals 'I' and '2', resistor RIS betweenswitch terminals '2' and '3', and so on. Thepole of the switch and the last resistor, R14.are connected to the circuit board by two5 -cm long insulated wires. The respective

PCB terminals are marked 'A' and 'D'.Fit the ten wire links on the printed -cir-

cuit board as indicated by the componentoverlay (see Fig. 4). Next, fit all parts onthe board as indicated by the parts list andthe component overlay.

LED D4 is not fitted on the board, but

COMPONENTS LIST

Resistors:1 608 5W2 39 k_0.

1 27ki..2

5 10k02 1 MS2

2 47003 18k01 0033 3W1 0022 2W2 0027 1 W1 OL-156 1W

1 1i151 1k01%1 249.0 1%1 1000 1%1 2409 1%

1 100 1%1 2i491%2 1k01 10k0 preset H

Capacitors:2 100nF3 3nF31 220nF1 27nF1 10uF 25V radial1 100uF 25V radial1 10.0001.IF 16V radial

Semiconductors:2 1N41481 green LED (3 mm)1 high -efficiency

red LED (3 mm)4 BC54784 BC557B1 TIP1201 TIP1251 TLC2721 78101 4066

RiR2:R4

R3

R5;R7:R9;R12;R27R6;1:130

Re:Rit1110;1113;R26

R14

R15

R16:R17R18

F119

R20

R21

R22

R23

R24

R25

R28;R29Pi

CI:CSC2:C8C3

C4

C6

C7

C9

D1;D2

D3

D4

Ti:T2:T3;T9T4:T6;T7:T8T5

T10

IC1

IC2

IC3

Miscellaneous:1 push-button with 1 make Si

contact2 1 -pole 6 -way rotary switch S2;S31 locking changeover switch S4

Schadow type F-8U.,EE.Accessory parts: indicatorbutton FA200, upper and lowercap halt M14, spring washer,plastic nut and front panel cap(parts set type ZFA)

1 100-µA moving -coil meter Mt

typee.g.mMonacorp-2 (Monarch)

1 printed -circuit board1 front -panel foil1 enclosure Telet LC850

900078900078-F

Fig. 3. Track lay -out (mirror image) and component mounting plan.

ELEA:TOR ELECTRONICS SEPTEMBER 1990

44TEST AND NIEASCRENIENT

connected to it via 10 -cm long wires. TheLED is an used on the front panel as a 'test'indicator that flashes when the associatedbutton is pressed.

The vertically mounted power transis-tors, Ts and Tin, and the voltage regulator,IC2, do not require heat -sinks. Use IC soc-kets for the TLC272 and the 4066. Thecompleted printed -circuit board and thewired range switches are shown in Fig. 5.All wires are soldered direct to theboard-solder terminals must not beused.

TestingIt is recommended to test the completedboard before fitting it into an enclosure.Connect the moving -coil meter, the threeswitches and the power supply (15-20 VDC) to the board.

Temporarily disconnect R30 from pin 1of IC3, and connect it to the junction of avoltage divider that supplies 2.5 V a1-ki2 resistor and a 50052 preset connectedbetween the +10-V line and ground).Switch on and check the output voltage ofthe potential divider. Adjust the presetuntil +2.5 V is produced. Next, adjust Pifor full-scale meter deflection. Remove thepotential divider.

Connect an oscilloscope and check thepresence of a 10-Vpp rectangular signal atpin 13 (negative -going) and pin 12 (posi-tive -going) of IC3. Because of the smallduty factor of the signal, it may be necess-ary to switch the input of the scope toDC -coupled.

Connect a test transistor to the circuit.Check that the two LEDs drop 3.9 V or avoltage within 10% of that value. If they

Fig. 4. Completed PCB ready for fitting into the enclosure.

do not, use other LEDs (e.g., a high -effi-ciency type for the red one).

Finally, connect R311 to pin 1 of 1C3again.

AssemblyThe instrument is relatively simple tobuild in an aluminium enclosure TypeLC850 from Telet. A ready-made frontpanel (Fig. 7) finished in light and dark

blue is available to give the tester an at-tractive appearance, in line with previousinstruments in this series.

First, remove the existing scale fromyour moving -coil meter and replace itwith the scale cut out from the front panelfoil. Carefully re -assemble the meter andconnect short wires to it.

Next, cut and drill the metal frontpanel of the LC850 case, using the drillingtemplate supplied with the front panel foil

2N3055

E

CIFLARGEI

,L4

SASE -101.11,-AE

i 1 : i 1

CD -11C10. CAMP, 110,-1

TA

"FE c=IMIM1111111 =InNM=

///=_.11111 maim a.--.BaVia. 41;1.-11111EIRSIM1111111111M111111 I 11111111=111000111M

COVLION EvITTER

111111111111111111111111111

niaiassisinmwasosau Imov 3

COLLEC OE CuPRE IT lc At

4 TIP 31 NPNTIP 32 PNP

IFLAINGEI

3 33

TOP VIEW -9

-.eE. .C°

5Ic.3

mi.ECTcw- 7 - - , =

waLTATL (., : -,

CASE ,,,afkin.PT..

I;

i

1 1

so 1 ;..GO Il'40

1 \o_1

11 I s

C -01=CUM. 111111MT 11,1

900078-14

Fig. 5. For your reference: hFE curves of three well-known power transistors (courtesy Harris Semiconductor, formerly RCA).


HIGH -CURRENT hry. TESTER45

to mark the holes.Before applying the self-adhesive foil

to the metal front panel, make sure alldrilled holes have the right diameter. Thisis easily checked by temporarily fittingthe front panel controls, the two LEDs (the'power' indicator and the 'test' indicator),the three wander sockets and the meter.

The pnp/npn switch, 54, secures thePCB to the front panel. Determine how farthe PCB can he moved towards the frontpanel without the rear side of the metertouching any component on the board.Check that you can secure the switch tothe front panel with the aid of the lockingnut at the inside and the threaded cap atthe outside. Mark the final position of theboard on the bottom plate and drill thefour holes for the M3 screws in the cor-ners. Use short PCB spacers or a couple ofnuts and washers to fit the board at thecorrect height above the bottom plate.

Next, remove all parts from the frontpanel, and carefully apply the self-ad-hesive foil. The two 3 -mm LEDs are gluedin position at the rear side of the panel.They do not protrude from the front panelfoil.

Fit the range switches (complete withthe resistors soldered at the terminals),the wander sockets, the 'test' push-button,the on/off switch and the meter on thefront panel. Cut the spindles of the rangeswitches to the required length, and fit thecollet knobs. The second pointer on thecollector current switch, a small solidtriangle, is applied as a rub -off symbol onthe collet.

Secure the PCB on the bottom plate ofthe enclosure. Next, fit the front panelwith all parts on it. Secure it to the casewith the four self -tapping screws sup-plied. Finally, tighten the threaded cap ofthe npn/ pnp switch.

The remainder of the wiring work isstraightforward. The 'power' indicator, a3 -mm LED, and the associated on/offswitch are connected to a DC adaptersocket on the rear panel of the enclosure.A 1 -kit series resistor is used for the LED.

1ff ire

Fig. 5. A look inside the completed prototype. Note that the resistors are soldered directto the terminals of the rotary switches.

The input voltage connections are made inlight -duty red and black wires.

Practical useA iev.- points must he made as is theuse of the hFE tester. First, alwa v, makesure the n-p-n/p-n-p switch is in the rightposition. You may destroy a transistor ifyou do not stick to this rule. Second, makesure you get the emitter, base and collec-tor terminals right. Third, always start thetest in the lowest collector current range,1 A, and the lowest sensitivity, lx. In-crease the sensitivity until a usable meterindication is produced. The hFE value iscalculated from

meter value x L multiplier x sensitivity

Familiarize yourself with the operation of

the instrument by measuring the currentgain of a few power transistors from yourjunkbox. The curves in Fig. 6 show therelation between the collector current andthe current gain of the well-known2N3055 and the complementary pairTIP31/TIP32. Bear in mind the maximumcollector current of the transistor undertest-a medium -power transistor such asthe BD139, fin- instance, will almost cer-tainly be destroyed when the tester is setto the 10 A range.

Having built the instrument you are ina position to select matching pairs of com-plementary power transistors for yournext power supply or AF amplifier. Be-cause of the low duty factor of the collec-tor current passed through the transistorunder test, it is not normally required tofit this on a heat -sink, not even while test-ing in the 10 A range.

0

ED

Fig. 7. This front panel foil (shown here at 66''= of true size) is available ready-made to give your current gain tester a professionalappearance. The meter scale is cut out from the foil and applied to the moving -coil meter.

ELEKTOR ELECTRONIC'S SEPTEMBER I9 9n

S-VHS/CVIS-110-2 5.)D.) OWLE2

PART 1: INTRODUCTION

Although the technical advantages of the Super -VHS video systemare well proven, many owners of an S -VHS video recorder balk at

the expense of a compatible monitor or TV set with separateluminance and chrominance inputs. This article describes an

obvious missing link in the apparently ever -incompatible field ofvideo equipment connections. An advanced circuit is discussed

that converts S -VHS or CVBS (composite) video signals into RGBcomponents. The upshot is that you can use your existing monitorwith an RGB input (i.e., with a SCART or Euro-AV connection) tobenefit from the improved picture resolution offered by an S -VHS

video recorder. This month we discuss the basics of the videostandards involved.

The compatibility issue has played a sig-nificant role in the development of boththe NTSC and the PAL TV transmissionsystems. In both cases, there were twoconflicting aspects: on the one hand, exist-ing monochrome TV sets were not to beaffected by colour transmissions; on theother hand, existing bandwidths of about5 MHz for the luminance (brightness) sig-nal were to be maintained.

The compatibility requirement auto-matically dictates that the black -and -white information (luminance or 'Y'signal) must also be conveyed in colourtransmissions. The Y signal forms the sumof all basic colours, red (R), green (G) andblue (B), but only as far as their relativebrightness is concerned. From perceptionexperiments, the brightness appears todetermine the overall sharpness of the pic-ture. Hence, the luminance band widthmust be as large as possible (up to 5 N1Hz)for monochrome as well as colour TV sets.However, this raises the problem of whereto put the colour information.

Colour components andtransmissionAny colour can be reproduced on a pic-ture tube by actuating in the correct pro-portion the basic colours it is composed of.The final colour is obtained by controllingthe intensity at which the RGB pixels atthe inside of the picture tube light up. Tothe human eye, the three individual basiccolours in a pixel group appear as one,composite, colour or hue at a particularsaturation.

The need to convey R, G and B, is,therefore, obvious. Since the sum of the

H. Reelsen

equivalent luminance values of all three isalready contained in the Y signal, onlytwo further signals, R -Y and B -Y, aregenerated by means of a differential oper-ation with the Y signal. R -Y and B -Y aretherefore referred to as the colour dif-ference signals. Before these signals aretransmitted, they are given relativebrightness factors. The resulting chromin-ance signals may be written as

U = 0A9(B-Y)V = 0.88(R -Y)

and the luminance, Y, as

Y = 0.3R 0.59G 0.11B

The RGB intensity information requiredto control the respective electron guns inthe picture tube is obtained from the R -Y,B -Y and Y information with the aid of anaddition operation in a matrix circuit.

A problem that remains to be solved ishow to include the colour difference sig-nal in the bandwidth already occupied bythe Y signal, without causing interferenceon monochrome TV sets, or reducing thepicture sharpness on colour sets. At thispoint, design engineers are in a position toprofit from a characteristic of human eye,namely its reduced ability to resolve col-our contours as compared to brightnessvalues. This means that the colour infor-


S-VHS/CVBS-To-RGB CONVERTER47

Y = luminance = 0.3R + 0.59G + 0.118U = 0.49(B-Y)V = 0.88(R-Y)U + V = chrominanceThe amplitude of a subcarrier fc. is modulated with U and V:

sin 2/act modulated with U U sin 2:70and

cos 2afct modulated with V -, V cos 27:fctThe complete PAL signal, X,

X = Y + U sin 2ect ± V cos 2afct

Uu Co

t

Fig. 1. Signal waveforms resulting from quadrature modulation of the colour difference signals Uu = 0.49( B-Y) and U. = 0.88(R-Y). Drawinga' shows the quadrature-modulated signal U. while b and c show the modulation signals Uu and U.:. which for clarity's sake are formedby a sinusoidal waveform and a rectangular waveform respectively. Drawings 'd and 'e illustrate how these signals are modulated on tothe 90 -degrees shifted carriers. The waveform shown in drawing 'a' is the result of adding

mation may be transmitted at a relativelylow bandwidth without significantly de-grading the overall sharpness of the pic-ture. In the PAL system, the colour (orchrominance) bandwidth is about 1 MHz.

The colour difference signals are read-ily embedded in the frequency spectrumof the Y signal by making use of the factthat the spectral lines of the Y signal occurat even multiples of the line frequency(15,625 Hz). Also, the amplitude of thesespectral lines decreases with frequency.

The colour difference signals modulatea subcarrier of which the frequency, fc, isan odd multiple of the line frequencydivided by four, plus the picture refreshfrequency (see Ref. 1):

f, =1135 x (15,625/4) 25 (Hz)

This causes the spectral lines of the colourdifference signal to be slotted in betweenthose of the Y signal. The colour subcar-rier frequency is set at 4.43361875 MHz,and the colour difference signals arequadrature-amplitude modulated(QAM). The B-Y and R-Y componentsmodulate the amplitude of the colour sub -carriers of 0 degrees and 90 degrees re-spectively (see Figs. Id and le). Thecarrier itself is suppressed, so that it hasan amplitude of nought in the absence ofa colour difference signal. This is done tokeep the picture free from interferencecaused by the otherwise continuouslypresent subcarrier.

In order to eliminate the risk of phase

shifts in the transmission path, the phaseof the R-Y component is inverted everyother picture line. Details of this operationpeculiar to the PAL system may be foundin Refs. 2 and 3.

The use of amplitude modulation withsuppressed carrier requires a phase- andfrequency -synchronized subcarrier at thereceiver side. In a TV set, the modulatedR-Y and B-Y components are recoveredfrom the chrominance subcarrier with theaid of a 4.433 -MHz quartz crystal oscilla-tor whose phase and frequency are cor-rected every 64 ps by a 2 -us long burstsignal slotted into the rear porch in theblanking period at the end of every pic-ture. The burst consists of 8 to 11 cycles ofthe colour subcarrier frequency and fol-lows the line sync pulse as shown in Fig. 2.A phase comparator is used to keep thecrystal oscillator synchronized to the re-ceived burst, which also contains the PALswitch signal for the line -by-line R-Yphase reversal. This arrangement ensuresthat the R-Y signal in the receiver is in-verted in synchronism with that at thetransmitter side to ensure that the de-modulation operation can work correctly.

In practice, the 'packaging' of the lumin-ance and the chrominance informationinto a single CVBS (chrominance-video-blanking-synchronisation) signal is notwithout problems_ Since the colour sub -carrier falls in the spectrum of the lumin-

ance signal, it causes a finely patternedtype of interference known as moire. Lu-minance circuits in all modern TV sets aretherefore fitted with a 'colour trap', whichis a relatively simple filter that removesmost of the moire effects with the excep-tion of those occurring at areas with sharpcolour transitions. Here, large phasejumps give rise to subcarrier sidebandsthat fall outside the stop band of the 4.43 -MHz colour trap_ Unfortunately, Y signalsin this stop band are also suppressed,which results in reduced picture resolu-tion because some of the high -frequencycomponents disappear. Incidentally, mostmonochrome sets also contain a colourtrap to eliminate moire.

The (possible) interference betweenchrominance and luminance also worksthe other way around: since the lumin-

ClankingIe.e130;i

while163;i

syzehtcrisation pulseEurSt

pi.:tur ;horizontaltte.kir.g

52 sec

Fig. 2. Structure and timing of a compo-site video signal (PAL standard).


48RADIO AND TELEVISION

ance band includes the frequency rangefor the colour subcarrier, high -frequencyY signals can cause interference in the fre-quency range around 4.43 MHz. The re-sult is a quasi -random type of patterningand colouring in and around picture areasof fine detail. Notorious examples of thishappening can be seen virtually everyevening in jackets, shirts or ties of peopleon television.

Standard VHS videorecordersSome 15 years ago, during the develop-ment of the VHS video system, a lumin-ance bandwidth of 3 MHz was deemedsatisfactory for VCRs considering thetechnical limitations imposed by thedrum head speed and the tape consump-tion. In the original VHS system, the col-our subcarrier is mixed down to 627 kHzto keep it well way from the lower end ofthe spectrum of the Y information, whichis recorded as a frequency -modulated(FM) signal (see Fig. 3)

The FM recording improves the signal-to-noise ratio of the Y signal and makes itlargely independent of amplitude vari-ations of the tape signal. The frequencysweep ranges from 3.8 MHz to 4.8 MHz.

Returning to the colour information,this is recorded as an analogue signal in'helical scan' mode (Ref. 3). The different

allow ready separationof the two signals. However, the band-width of the colour information is inevit-ably reduced to about 500 kHz. The resultis noticed as 'smeared' colour transitions,to which the reduced (3 -MHz) luminancebandwidth adds an impression that thepicture is blurred.

These imperfections of the originalVHS system were soon recognized byVCR manufacturers. Their answer, theHQ video recorder, was based on smallimprovements to the recording methodand a better edge definition of the Y sig-nal. The resultant picture quality im-provement was marginal and not really astep forward. It was, however, the bestthat could be achieved given the need forcontinued compatibility. Clearly, real im-provements to the picture quality offeredby VCRs could be achieved only by chang-ing some of the standards.

The Super -VHS systemThe bandwidth of the recorded video sig-nal was increased significantly (at theexisting relative speed of 4.85 m/s be-tween the tape and the head) by virtue oftwo technological developments. First,new metallurgic techniques allowed thesize of the air gap of the video head to bereduced. Second, tapes with a very highmagnetic particle density became avail-able.

To maintain compatibility with olderVHS recorders, the S -VHS SVtitenii is basedon the same method of colour recording(see Fig. 3). However, the frequency

Chrominanceband

627kHzLuminance band

0 1 2 3

AChrominance

band627kHz

38

1MHz

4 J 6 7 MHz48

Luminance band 1.ElIHz

1 2 3 4 5

5MHz400 lines

654

7 MHz

Fig. 3. Typical standard -VHS and S -VHS spectra. In both cases. the quadrature-modulatedcolour signal is recorded with the aid of a carrier which is mixed down to 627 kHz. while theluminance signal (Y) is recorded in FM. S -VHS recorders use a luminance carrier frequencyof 5.4 MHz and a frequency sweep of 1.6 MHz. This offers a bandwidth of 5 MHz for the Ysignal. as opposed to about 3 MHz for the standard -VHS video recorder.

sweep of the Y signal is shifted up to aband from 5.4 MHz to 7.0 MHz to give amuch higher noise margin. At the sametime, the frequency of the FM subcarrierallows the luminance signal to be re-corded at its full bandwidth of about5 MHz.

In most standard VHS video recorders,the chrominance and luminance signalsare processed separately until they arecombined to give a CVBS signal with allthe previously mentioned risks of runninginto trouble with interference.

By contrast, the S -VHS system is basedon separate chrominance and luminancesignals right up to the two associated out-puts on the VCR. Evidently, this separ-ation is not perfect when, for instance, aTV programme is recorded, since then thechrominance and luminance componentsmust be extracted from the composite sig-nal before they can be recorded, playedback and fed separately to a monitor. Theprocess of extracting the components haspitfalls as described before. Not so, how-ever, with video sources that do supplythe components separately. Examples in-clude S -VHS cameras, some prerecordedS -VHS video tapes and MAC decoders.

Connection problemsSo far, so good. A look at the rear panel ofthe TV set, however, reveals that there isat best a SCART connector, which doesnot allow luminance and chrominancesignals to be taken in separately. The TVset is, therefore, not S -VHS compatible.This unfortunate discovery forces ownersof S -VHS recorders to connect the monitorand the recorder via a CVBS link, forgoing

most of the advantages of better picturereproduction offered by the new videosystem.

Considering the cost of an S -VHS com-patible monitor, the only way to benefitfrom the separate chrominance and lu-minance signals supplied by S -VHS re-corders and other video sources is toconvert these to RGB signals that can heapplied to the existing monitor or TV setvia its SCART input. Neat month's secondinstalment of this article discusses a cir-cuit to accomplish this. In addition, thecircuit provides a colour transition im-provement (CTI) function, and is capableof converting CVBS to RGB.

From composite to RGBAlthough most standard video recordershave a SCART socket, this rarely suppliesRGB signals. Likewise, most set -top TVtuners and indoor units for satellite T\'reception supply a CVBS (compositevideo) signal only. A problem arises whenthis equipment is to he connected to ahigh -resolution colour monitor with anal-ogue RGB inputs, or a TV set with aSCART (Ettro-AV) input. In both cases,the converter to be described next monthcan link this equipment and ensure opti-mum picture quality.

References:1. Chrominance-locked clock generator.Elektor Electronics July/August 1988.2. Video line selector. Elektor ElectronicsApril 1990.3. Video Handbook (second edition). by R.van Wezel. Published by Heineman New-nes, ISBN 0 434 92189 0.


ISOLATING AMPLIFIERUntil recently, isolating amplifiers were generally accessible to professional

engineers only. These integrated circuits, widely used in laboratory andindustrial measuring instruments, were simply too expensive for amateurs.

Now, Burr Brown have available a series of isolating devices that,without any relaxation of specification, are available

at prices that are affordable for most.

An isolating amplifier. as its name sug-gests, is a circuit between whose input andoutput no electrical connection exists (atleast in theory). Normally, such a deviceconsists of an input amplifier, a modulator.an isolating barrier. and a demodulatorwith a voltage follower at the output. Thesignal paths in the input and output sec-tions are electrically fully isolated fromeach other. An important feature of an iso-lating amplifier is that it has a completelyfloating input. which helps eliminate cum-bersome connections to source ground.

Fundamentals

The block diagram of a typical isolatingamplifier is shown in Fig. 2. The inputsection may take one of many forms. froma complete instrumentation amplifier withprogrammable gain to a simple impedanceconverter that uses only one input pin.

The signal at the output of the inputsection is superimposed on to an HF carrierto enable it being transferred across the in-ductive or capacitive isolating barrier.

Fig. 1. Capacitive isolating barrier.

There are isolating amplifiers with anoptical barrier. These devices do not needa modulator or (external) low-pass filtersfor reducing the modulation residue at theoutput.

Of the three types of isolating barrieralready mentioned, inductive, capacitiveand optical, the inductive one is the oldestand most widely used. Although it has notthe bandwidth of the less expensive opti-cal type, it has some important advan-

1:1:: a yen high isolating voltage (up tokV l and great accuracy (see later).The barrier of a typical capacitive type

is shown in Fig. 1. The two spirals in thecentre form the I pF coupling capacitorstow hich the modulated signal is appliedin push-pull. Since the capacitors and thetwo signals are of equal value. the resul-tant sum signal is zero. This is vital as oth-erwise energy might he transferred fromthe input to the output, which would mani-fest itself as interference. This techniqueaffords good bandwidth without detrimentto the precision of operation or the maxi-mum isolating voltage.

Theory of operation

The descrirlion that follows is based onBurr -Brow n's Type ISO 122P isolatingamplifier. This device uses an input andan output section that are galvanically iso-lated by matched 1 pF isolating capacitorsbuilt into the plastic package. The input isduty -factor modulated and transmitteddigitally across the barrier.

Von

andinput

ground

VisoIMRR

isolationcapacitance

and resistance

isolationbarrier 7

MEEou putground

900048-18

Fig. 2. Block diagram of a typical isolating amplifier. Fig. 3. The isolating voltage exists between the two earths.

50COMPONENTS

The output section receives the modu-lated signal. converts it back to an ana-logue voltage and removes the ripple com-ponent inherent in the demodulated signal.

The input and output sections are lasertrimmed for accurate circuit matching.after which they are mounted at oppositeends of the package with the isolating ca-pacitors mounted between the sections.

Modulator. The input amplifier. Al inFig. 4. integrates the difference betweenthe input current (Vin/200 ki2) and aswitched -±100 uA current source. Thiscurrent source is implemented by aswitchable 200 µA source and a fixedWO µA current sink.

To understand the basic operation ofthe modulator, assume that Vi = 0.0 V.The integrator will ramp in one directionuntil the comparator threshold is ex-ceeded. The comparator and sense ampli-fier will force the current source to sv. itch:the resultant signal is a triangular Y. a e -form with a 50% duty factor. The internaloscillator forces the current source toswitch at a frequency of 500 kHz. If Vinchanges. the duty factor of the integratorwill change to keep the average d.c. valueat the output of Al near zero volts.

Demodulator. The sense amplifierdrives a switched current source into inte-grator A2. The output stage balances theduty -factor modulated current against thefeedback current through the 200 ki2 feed-back resistor. resulting in an average valueat the V, pin equal to Vi. The sampleand hold amplifiers in the output feedbackloop serve to remove undesired ripplevoltages inherent in the demodulation pro-cess.

Signal and power connections. Eachpower supply pin should be bypassed with1 tiF tantalum capacitors located as closeto the amplifier as possible. Thefrequency of the modulator/de-modulator is set at 500 kHz by aninternal oscillator. Therefore. if itis desired to minimize anyfeedthroueh noise (beat frequen-cies) from a d.c./d.c. converter.use a pie filter on the supplies asshown in Fig. 5.

Parameters

Although it is as easy to work withmost isolating amplifiers as it iswith opamps, there are a few pa-rameters that need closer examina-tion or that do not exist in opamps.Typical voltages in isolating am-plifiers are shown in Fig. 3.

Vsigis. as in opamps. the differ -

C 3G

Pr..firQV

0Ci

0ICCIA

-115QPF210.11

1

C--4; 7 .,

0 8 0.v., Grd -v 0 0

-V= Gr.12

900018. 12

Fig. 4. Block diagram of the ISO 122P.

ential input voltage: its level is -±10-15 V.Vcm is the common -mode voltage.

that is, the voltage between the signal in-puts and the input earth. The maximumlevel at either input pin. with respect toearth, should not be higher than Vcm-inpractice about ±10 V. If levels higher thanthat are needed, there can be no earth atthe input. only at the output. It may also beimpossible to use an earth. In that case,Viso becomes the reference.

Viso is the maximum isolating voltagebetween the reference earths of the inputand output signal. Its level may be severalkilovolts.

CMRR. the common -mode rejectionratio. shoe, the change in output voltagewith respect to output earth for simultane-ous changes in input voltages referred tothe input earth, that is. Vcm.

INIRR. the isolation -mode rejectionratio. is AViso/AVam.

The foregoing parameters can now be

Fig. 5. Decoupling for linear and switch -mode power supplies.

used to express the amplication function:

V,=a(Vsi,±Voi/CMRR±Viso/IMRR)

where a is the amplification factor.Another important parameter is the ac-

curacy. which takes acoount of tempera-ture stability, long-term stability, amplifi-cation error and non -linearity, which arewell known from opamps. Peculiar to iso-lating amplifiers is the leakage current.which expressc the input error current asa function of the isolating voltage and fre-quency. In data sheets these are normallygiven as 240 V and 60 Hz respectively:the leakage current is expressed in µA.

NVARNING. In medicine, isolatingamplifiers are used primarily for groundloop elimination. Readers are warned notto use isolating amplifiers (for instance.for mains isolation) in equipment that is infrequent contact with their bodies.

Basic circuits

Isolating amplifiers. like all cir-cuits that combine digital and ana-logue techniques. are particularlysensitive to external interference.Reference has already been madeto the need of decoupling capaci-tors at the power supply pins.

Since the ISO 122P superim-poses the signal on to a 500 kHzcarrier. the transfer function forsignals at frequencies up to 25 kHzmay be considered linear. Athigher frequencies. the output con-tains more residual modulation asmay be seen from Fig. 6. A sinu-soidal input at a level of 10 V anda frequency, f. of 2 kHz results inan undistorted output signal. The

ISOLATING .AMPLIFIERS

SINE RESPONSE- 2444

500

Tm-03 I

STEP RESPONSE

-13

-70

1000 0

SINE RESPONSErt - 20012)

SO

Ter* (p.$)

STEP RESPONSE

700

900048 16

Fig. 6. The higher the input voltage, the greater the modulation residue and distortion.

Fig. 7. Active low-pass filter for the suppressionof modulation residue.

same is true for a rectangular sienal eventhough the leading edge rising to +10 V isseen as a small overshoot.

When the frequency is increased by afactor of 10. the modulation residue on thewaveforms is clearly visible. Furthermore.the edges of the rectangular sienal havebecome less steep and the input rise timehas increased appreciably.

Most of the modulation residue may beremoved with the aid of an active low-passfilter of the first or second order as shownin Fig. 7. The cut-off frequency of that fil-

0

E -10

-20

-30

-40

SIGNAL RESPONSE TOINPUTS GREATER THAN 250kHZ

0

V. /V0 100kHz

500kHz 1F, Hz

Input Frequency

FreqOut 250

200

150

100

50

1.5MHz

900048 - 20

ter is 100 kHz, when R1=R2=13 kf2: R3==385 C1=100 pF: C2=4700 pF. Formost applications, this is a good compro-mise between effective bandwidth andmodulation suppression.

Error sources

Normally. the maximum signal frequencyof a scanning circuit should be limited tohalf the scanning rate-at least, accordingto the relevant Nvquist or Shannon theo-rems. However. here there is a little lee-way: up to 50 kHz. the specified band-width. the output signal is identical to theinput signal as far as frequency and levelare concerned. Over the range 50-250 kHzthe amplification factor drops from I to

0.063 but there is no discernible increasein distortion.

At even higher frequencies. the isolat-ine amplifier produces a relatively smallnoise sienal at a frequency below 250 kHzin addition to the normal output signal.This behaviour may he explained with theaid of Fig. 8. The composition of thewhole output signal may be considered insteps for which on the one hand the fre-quency behaviour and on the other the am-plitude must be taken into account.

The triangular characteristics show therelation between input frequency and theinterference frequency at the output(straight y-axis). When the input fre-quency lies between 250 kHz and500 kHz. the interference frequency drops,rises again when the input frequency in-creases to 750 kHz. drops until the firstharmonic (1 MHz) is reached. then risesagain, and so on.

The amplification factor may also beevaluated from Fig. 8, and it is seen thatat frequencies above that of the carrier. it

CC

z

160

140

120

100

80

60

40

1

IMRR vs FREQUENCY

10 100 1k 10k

Frequency (Hz)

100k 1M

900048-19

Fig. 8. For input signals above 250 kHz. operation of the isolating amplifier Fig. 9. To work with high isolating frequencies, the circuit must be de -is no longer linear. signed for smaller maximum isolating peak voltages.

COMPONENTS

has a pronounced irregular behaviour. Forexample, a 10 -volt. 800 kHz input signalresults in an attenuated (-30 dB) 800 kHzoutput signal (this may be read from theampliciation characteristic and the left-hand y-axis). At the same time. a 200 kHzinterference signal is produced ( whichmay he read from the triangular character-istic and the right-hand y-axis). At the200 kHz point on the x-axis it will be seenthat the interference signal is attenuated bya further 10 dB. Expressed in figures. thismeans that the output consists of a800 kHz signal at a level of 316 mV andone of 200 kHz at a level of 100 mV If theinterfering signal is eliminated with theaid of a filter, the isolating amplifier canwork with signal frequencies that arehigher than the carrier frequency.

The same applies to the isolating volt-age. to which the Nyquist theorem is, ofcourse. equally applicable. To eliminate aninterfering signal caused by the isolatingvoltage from the output. the ININIR as afunction of frequency should be added toFig. 8. For example. when fis0=1000 Vat 800 kHz. the IN1NIR= -62 dB as may beseen from Fig. 9. Part of the output signal.viz. 794 mV at 800 kHz. was already seento he an interfering signal. From Fig. 8 itis seen that the output additionallytains a 200 kHz sienal at a level 30 dBbelow that of the first interfering signal.that is. 92 dB below 1000 V or 25 mV.

In this connection. Figures 10 and 11should also be taken into account. Themaximum permissible isolating voltagedecreases with rising frequency. Further-more. when Viso rises and the rise timeexceeds 1000 V/tis, the triggering of thesense amplifier may go awry with the re-sult that the condition of energy -less sig-nal transfer is no longer met. and a corn -

SPECIFICATIONSAt T.. 25'C and V.1 . V.2 ±15V unless otherwise noted.

PARAMETER CONDMONS MIN TYP MAX UNITS

ISOLATIONVoltage Rated Continuous AC 60Hz 1500 VAC100% Test 1 1s, 5pc PD 2400 VACIsolation Mode Rejection 140 dBBarrier Impedance 10- II 2 a II pFLeakage Current at 60Hz V . 240rms42 V 0.18 0.5 gArrns

GAIN V. . 310VNominal Gain 1 VN

Gan Error 1.05 1.30 %FSRGain vs Temperature 310 pprne.cNonlinearity 1.008 1.015 %FSR

INPUT OFFSET VOLTAGEInitial Offset ±5 350 mV

vs Temperature ±200 jilit*Cvs Supply 12 mVN

Noise 4 µVP. HZ

INPUTVoltage Range ±10 VResistance 200 kA

OUTPUTVoltage Range ±10 ±12 VCurrent Drive 35 115 mACapacitive Load Drive 1000 pFRipple Voltage2, 10 mVp-p

FREQUENCY RESPONSESmall Signal Bandwidth 50 kHzSlew Rate 1.5 V/p.sSettling Time Va. 310V

0.1% 50 Ps0.01% 150 Fs

Overload Recover Time 150 Ps

POWER SUPPLIESRated Voltage 15 VVoltage Range 14.5 318 VQuiescent Current: V., 3.4.5 36.5 mA

V. 34.5 36.5 mA

TEMPERATURE RANGESpecificaton 0 70 `COperating -25 85 `CStorage -25 85 `CB,, 100 °CilN

NOTES: (1) Tested at 1.4 X rated, fail on 5pC partial discharge leakage current on live successive pulses. (2) Ripple frequencys al carrier frequency (500kHz).

Table 1. Technical specification for the ISO 122P at TA = 25 -C; Vst = Vs2 =a715 V and RL = 2 kO.

2.1k

1k

100

0

ISOLATION VOLTAGEvs FREQUENCY

1111 Illlllll[lllllllllMINE Max DC Rating IiiMINIMMIE111.1111 IIII.111111.1111111.111111

1111111111111111111311111111111111111

IMO Degraded VIII111111111111111 1MM11uI1111011 Performance

111111111111111111111111111.III

Typical 111111111111=11111EL1111 11111Mi 11

111111011111111111Performance 11111.1111.1.1111EIN 111E1111

100 1k 10k 100k 1M

Frequency (Hz)900048 - 14

OM 100M

loomA

1mA

10pA

-J1µA

0.1µA

ISOLATION LEAKAGE CURRENTvs FREQUENCY

SERENENE111111111111 /AIRnimmutimmon111111111111mmisimanmar.movau

liENR;21111emminsiummteutt

.........11111111111VIMM"All MIMI Mill MENI111111--a:mm.1=z=

111111111111111111/411E11 240Vrms

1111.1111P4IPAII11111.1111.11111111111111111111

10 100 1k 10k

Frequency (Hz)900048-15

100k 1M

Fig. 10. Isolating voltages at high frequencies cause degrading of the out- Fig. 11. At high frequency isolating voltages there is no longer en energy -

put signal. free transfer across the barrier.

ISOLATION AMPLIFIERS 1Dl Load

150122P

15

150122P+V

15

16

0.3µF

0.3µF

4

PWS740-33

PWS740-2

3 2 1

eyry6 5 4

To PWS740-1

7

16

10

0

0.30F

0.3µF

1 4

PWS740-3

3 6

PWS740-2

2

MIS6 5 k

2k0 10kil

0.01µFT

0.1µF

XY10

X

MPY100

Y

To PWS740-1

(V2)

V2(RD, + Rm)

(VI)

VL=1/3(110, +110,)

900048

RD2

Fig. 12. Typical application of an isolation amplifier: a measuring instrument with current. voltage and power indication.

mon mode current flows across the barrier.It should be noted that supply voltagesbelow ±15 V reduce the maximum per-missible slew rate by about half.

A typical application: apower measuring instrumentFinally. as an example of what kinds ofapplication may be satisfied with a typicalisolating amplifier such as the ISO 122P(although other types may also be used, ofcourse). we have chosen a power measur-ing instrument, whose circuit is shown inFig. 12. The instrument can indicate theload current. the source voltage and the re-sulting power dissipated in the load.

One of the isolating amplifiers is usedto evaluate the source voltage with the aidof potential divider RDI-RD,. and theother to measure the load current with theaid of current sensor R,. Both amplifiersare connected in an identical manner.

The input earth that serves as the refer-ence for the input potential at pin 15 is notgrounded. Only the output sections are re-

ferred to ground potential.The Type PWS740-1. PWS740-2 and

PWS740-3 devices are Distributed Multi-channel Isolated DC -to -DC Convertersfrom Burr -Brown. These converters areable to produce up to eight ±7-20 V sup-ply voltages, which are galvanically iso-lated from one another. from a single 7-20V direct voltage. Currents of up to 60 mAmay be drawn from each of the resultingsupplies.

Although this is not a cheap way ofproducing power supplies. it guaranteesthat no interference will be transferredfrom the mains to the isolating amplifiers.

The NIPYI00 is a four -quadrant multi-plier -divider that, apart from multiplica-tion, performs analogue square -root anddivision without the bother of external am-plifiers or potentiometers. Here it is usedto compute the power. P =t1 / 10.

Since the multiplier always divides by10. the output of the voltage -indicatingamplifier may be used directly as the mul-tiplicand. whereas that of the current-indi-eating amplifier must first be amplified by

10 before it can be so used..The Type OPA602 high-speed preci-

sion operational amplifier. also from Burr -

Brown, is used as an active low-pass filterand impedance converter. Other types ofhigh-speed precision operational amplifiermay. of course, also be used.

Further information on all devices dis-cussed in this article may be obtained from

Burr -Brown WorliN ide HeadquartersP 0 Box 11400TUCSON. AZ 87734USATelephone (602) 746 1111Fax (602) 889 1510Or

Burr -Brown International Ltd1 Millfield HouseWoodshots MeadowWATFORD WD1 8YXEnglandTelephone (0923) 33837Fax (0923) 33979.

N QUEST OF A PANGRAM PART 2

Combinatorial explosion

At long last the program was finished andstarted. Roughly a million combinations hadalready been tested during the developmentperiod. The trouble with previous versionshad been their hopelessly' slow speed. Eventhe latest program could only test somethinglike ten new combinations per second. Thiswas still sluggish, but bearing in mind thehefty letter crunching involved (16x16 ad-ditions in calculating the SUMPROFILE alone,for ekample). I thought it probably couldn'tbe greatly improved upon. Vaguely I won-dered how lone it would take before a solu-tion popped up. Being a greedy consumer ofvaluable processor -time, the program ran atnights as a low -priority 'batch job' on theComputing Centre's vox 11/780 machine.Every morning I would hasten to call tip thejob file. running my eye swiftly down thescreen in search of 'EUREKA% which wouldprecede a printed record of the magic com-bination of number -words. As day suc-ceeded day without result. the question ofhow long it would be before all possibilitieshad been exhausted gradually assumed im-portance. It was a matter I had never givenany serious attention. 107 cases had alreadybeen examined. Let's see, how many wouldthere be altogether ...?

The calculation is an absurdly simple oneand even now I blush to recall first seeingwhat the result implied. Programmatically,the ten totals in each of the sixteen rangesare cycled exactly like the 0-9 digits on therotating number disks of the familiar tape -counter or odometer. Advancing this soft-ware counter a single step results in the nextcombination of totals being clicked into po-sition. ready for the pangram test. The all -zero state will correspond to the first or low-est set of number -words: the bottom row ofscale numbers in Fig. 2. Just as the mechan-ical counter begins at 0 and steps in turnthrough every number (that is. every possi-ble digit sequence) up to the highest. so theprogram runs through all possible combina-tions up to that coinciding with the top rowin Fig. 2. In effect, we are systematically ex-amining every single histogram that can beplotted. About halfway through the process,the example shown for the near -solution to-tals will come up for testing. How many suchgraphs can be drawn in Fig. 2? The answeris clearly the same as that number displayedon our sixteen -digit odometer after stepping

by Lee C.F. Sallows

through all possible positions: a string ofsixteen 9s (plus one for the zero position) =1016. Is there a golden vein running throughthe ten -deep strata? A milk \ nipple crown-ing the Gaussian breast? At a speed of tencombinations per second, to find out is goingto take 1016/10 seconds. A pocket calculatorsoon converts this to more intelligible units.

In searching for anautogram, my computerprogram could only test

something like ten new com-binations per second. How

long would it bebefore all possibilities were

exhausted?

There seemed to be something wrong withthe one I was using. Every time I worked itout, the answer was ridiculous: 31.7 millionyears!

I was so unprepared for the blow con-tained in this revelation that initially I couldhardly take it in. The whole object of turningto a computer in the first place had been tocanvass huge numbers of combinations fast.Now that the truth had dawned. I began curs-ing my naivety in ever embarking on such afool's errand. True, I was an electronics en-gineer. not a professional programmer.However. the more I contemplated the kindsof speed at which a realistic program wouldhave to run, the more preposterous the wholecomputer venture appeared. Conceivably, asomewhat faster program could be written.But even checking at a rate of one millioncombinations per second, it would take threehundred and seventeen years to run throughthe ten -deep range of possibilities!

Yet. thoughts of millions of combina-tions per second put me in mind of niega-ken:. And megahertz brought my thoughtsback to Electronics. This in turn promptedan idea. a fanciful notion. for the first fewdays no more than an idle phrase repeatedin the head. a good title perhaps for a sci-ence -fiction story: The Pangram Machine.

Initially. I didn't take the thought seri-ously. I was disconsolate after the embar-rassing failure of the computer project. and

the absurd expression 'pangram machine'mocked hollowly at the back of conscious-ness. Yet suddenly the vague intuition beganto crystallize: in a flash I saw how a centralprocess in the program could be simulatedelectronically. Taking this mechanism as astarting point. I tried translating other as-pects of the algorithm into hardware. Itworked: it was easy. A few hours later. I wasamazed and thrilled to find the broad out-lines of an actual design already clear in mymind.

The Phoenix now emerging from theashes of the Pangram Quest soared serenelyto the sky. smoothly circled. swiftlyswooped. and soon bore me off, a helplessprisoner in its relentless talons. For the nextthree months I would be pouring all my en-ergy into the development and constructionof a high-speed electronic Pangram Ma-chine.

The Pangram Machine

How seriously should a word puzzle betaken? Though only the size of a smallishsuitcase, the apparatus to emerge from threemonths' intense activity packed more thantwo thousand components on to thirteen spe-cially designed printed -circuit cards. Morethan a hundred of these were integrated cir-cuits, each containing on the average some-thing like fifty transistors. Foresight of thiscomplexity might have dissuaded me fromstarting. In the event, the completed ma-chine turned out to involve a good deal moreelectronics than originally planned.

At the heart of the device is the electronicequivalent of a continuously -stepped six-teen -digit odometer: a clock -driven cascadeof sixteen Johnson counters: see Fig. 3 forall that follows. The clock is a simple 1 MHzsquare -wave generator producing a contin-uous train of 106 pulses every second. Asmentioned above. however. even checkingat this rate. ten -deep ranges would take 317years to explore. A reduction was thereforedemanded, the choice of new range -lengthbeing determined primarily by the availabil-ity of standard 8 -output devices. Eachcounter is thus a circuit with eight outputsthat become actuated consecutively by suc-cessive pulses presented to its single input.Before the clock is started, a RESET buttonon the control panel (see photograph in PartI on page 57) enables all counters to be ini-tialized or 'zeroed', meaning that all '0' out-

IN QUEST OF A PANGRANI

Y counter

5 417 16 15 14 13

Unused

15 -voltsupply

F

H

0

Initial4, text\constants

2 1 0

,1544 .3

2z.

F counter

9 8 7 6 5 417 16 5 4 3 2 1

Unused

y channel

49 1,48 ky 48 t5

0

4

/

E counter

32 313029 282726 25

OResetcounters

f channel

7 6 5 4 3 2

32 31\30T 8313127

.1

2 R2 3

1 0

ClockStop

26125

'17 7z/Claimed number

2

41

T

U

R I1

YesEbaiancel--0- Zero?

True number

YesbalaFncel--0- Zero?

Ybalance

Yes

--I--YesZero?- -

Allyes?

Fig. 3. The design of the Pangram Machine.

puts are made active. As the clock ticks. theactuated output of the first counter in thechain changes from '0" to I to 2'. etc.. sothat after seven clock pulses output '7' willbe actuated. whereupon the next pulse reac-tuates '0' and the process begins anew.

Coupling between counters is like be-tween odometer disks in that. after complet-ing one cycle. it is arranged fora single pulseto be sent to the input of the follow inscounter in the cascade. Eight cycles of thefirst are thus needed to step the secondcounter through one. In this way. every newclock pulse results in actuating a uniquecombination of sixteen output lines. After816 pulses. all combinations w ill have beenrun through and. unless halted. the entireprocess will begin again.

Even so. calculation shows that runningtime must still he measured in rears unlesssome further limitations are introduced. Infact. the cycle -length of counters is individ-

ually presettable. With a preset cycle -lengthof 5. for instance. a counter's '0' line be-comes re -actuated on the sixth input pulse.while outputs '5'. '6' and "7' remain Un-used. In this vay. the range -length for dif-ferent letters is individually adjustable, anda shorter total running time can be achieved(at the price of narrower ranges). Figure 3shows that the v -counter's cycle -length hasbeen reduced to 3. for example. Later weshall turn our attention to the actual set ofranges used.

Now. just as in the computer program.the object of actuating different combina-tions of output lines is to call up sets of PRO-FILES whose corresponding elements will beadded together so as to form a SLMPROFILE(as discussed above: I leave the initial textconstants temporarily out of account ). Elec-tronically. the instantiation and addition ofPROFILES may he achieved by the use of dig-ital or analogue techniques. The former is

far preferable. but costly. The analogue tech-nique is less predictable in performance but.in this case at least. made attractive b itsrelative simplicity. Here. as elsew here. fi-nancial limitations meant that design was in-fluenced by what the junk -box had to offer.In the end. I was forced to use an analogueapproach but. since other parts of the cir-cuitry are digital ( the counters. forexample ).the overall design is really a hybrid.

Accordingl. the PROFILES 'called up' byactuated counter outputs take the form of re-sistor fan -outs feeding specific patterns orprofiles of discrete current levels into six-teen common lines representing the Si M -PROFILE. E% counter output is associatedwith a predetermined number -word (shownin counter -boxes). An actuated output is onetransistor connected to a 15 -volt supply andthus able to deliver current: non -actuatedoutputs are simply left unconnected (theseare so-called open -collector outputs 1. The

56GENERAL INTEREST

PROFILE of each number -word is imple-mented as a set of resistors connecting thecounter output to appropriate SUMPROFILElines. These are the horizontal lines E. F. ...

...Y shown in the diagram. (Sixteen 0.5 S2 re-sistors, not shown but electrically important.connect each of these to ground or 0 V).

Current drawn from actuated outputsthus divides into a number of resistor -ad-justed streams and is distributed over the E.F. Y lines of the SUNIPROFILE so as to rep-resent the contribution of each PROFILE -number. PROFILE summing is therebyachieved almost without doing anything: thecurrent produced in each SUNIPROFILE line(and hence the voltage across its 0.5 SI re-sistor) is simply the aggregate of the subcur-rents injected into it via the resistors in thepresently actuated set of PROFILES.

The number and value of the resistorsused in each case depend entirely on the PRO-FILE being simulated. Choosing an arbitraryunit of current to represent one letter. doublethis value will stand for two. and so on. Infact, with the exception of seventeen whichalone contains four e's. values in thePROFILES are always 0. 1. 2 or 3. Since 0 isindicated by no current = no connection. allPROFILES (excepting that for seventeen) canbe implemented by resistor sets built upfrom just three discrete values of resistance:x a x/2 S2. and.v/3 SI. yielding current levelsof 1.2. and 3 units. respectively. (In reality.x= 3920 O. a high value relative to the 0.5resistor over which the sum voltage falls:this is important for achieving summing lin-earity). A concrete example is shown for they -counter's three and four. The small diag-onal zigzags are the resistors. The numbersprinted alongside represent not their resis-tance but the number of current units(15 V/3920 S1= 3.82 mA I they pass into thesum PROFILE line: three = 2 e's. 1 h, 1 r.1four = 1 f. 1 o. 1 r. 1 ti.

So far. so good: the current entering each+ input of the boxes marked BALANCE is ameasure of the number of e's, f s. etc. actu-ally occurring in the present set of sixteenactuated number -words: every microseconda new set is switched in . But the SUMPROFILEis incomplete without the initial text con-stants-themselves comprising no morethan a special PROFILE and thus representableas a set of fixed -bias currents. Hence. a fur-ther array of sixteen resistors is connectedpermanently from the 15 V supply to eachSUN1PROFILE (see Fig. 3).

Now, in the program SUNIPROFILE. totals(representing true letter frequencies) arecompared with the labels of the PROFILES (thenumbers corresponding to the number -words) to check for pangramhood. Theselabel -numbers are simulated by an extra re-sistor -determined current derived from each

counter output ( top row of resistors). E -labelcurrents are fed to the - input of the E BAL-ANCE box. and so on. Comparison of SUM -PROFILE and label currents takes place in theBALANCE boxes: each box is a differentialamplifier whose output voltage is a fixedmultiple (the amplification factor) of the dif-ference between its two input currents (orvoltages. depending on how you look at it 1.In this way. SUNIPROFILE and label -numbersare weighed against each other in the BAL-ANCE: only if they are equal will the outputvoltage be zero. or close to zero, volts. Ofcourse, all sixteen pairs are weighed simul-taneously.

The rest ought to be obvious. The "Zero?'boxes are window detectors: circuits sig-nalling a logic 1 ('yes') if their input voltagelies within a predetermined voltage range or'window'. The window in this case is a nar-row one (±50 mV i centred on 0 V. All win-dow -detector outputs go to a sixteen -inputAND gate. If sixteen zeros turn up together.the AND gate v. ill fire. thereby stopping theclock. freezing the counters, and turning on

an inessential but comforting EL REKA! lampmounted on the control panel. The magic setof number -words sought will now be repre-sented by the frozen combination of actu-ated outputs. In order to signal which theseare, counter positions are indicated (in bi-nary code) in the form of sixteen groups ofthree LEDS visibile through a red perspexfront panel. When a table is used to translateLED patterns into number -words. it will re-main only to double-check the result byhand and, if it is correct. ring for the cham-pagne.

Though all very well on paper, in realitythe analogue techniques used in the machineare messy. Circuit capacitance and amplifiersettling times set a practical limit to thespeed of operation. When the clock ticksand switches in a new set of PROFILES. elec-tronic havoc breaks loose as overshoots. os-cillations. glitches, and gremlins conspire todrive window -detectors into palsied indeci-sion. After a while. electrons begin to sim-mer down and circuits settle into a newsteady state. For this reason, rather than

Ranges of Number -Words

NEAR -SOLUTION

LETTER TOTALRANGE

RANGE LENGTHINITIAL

CONSTANT

E 27 25-32 8 7

F 6 4-9 6 2

G 3 2-7 6 2

H 5 3-8 6 2

11 8-14 7 4

L 2 1-4 4 1

N 20 17-23 7 10

0 14 12-17 6 11

R 6 3-8 6 2

S 28 24-30 7 21

T 21 18-24 7 7

U 3 1-6 6 1

V 6 3-8 6 2

10 7-13 7 5

4 1-6 6 1

Y 5 3-5 3 1

Fig. 4. Ranges of values of number -words as actually built into the Pangram Machine.

-I-IN QUEST OF A PANGRAM

going straight to the STOP input of the clockas shown in Fig. 3. the AND gate output isactually sampled some 900 nanosecondsafter clock pulse onset-that is, at the lastmoment of the clock cycle. only 100 ns be-fore the next pulse arriv es. This idea, amongothers. was due to Willie van Schaijk. with-out whose friendly and expert assistance themachine might never have left the ground.Using the (rn..) technology at my disposal.a clock frequency of I N1Hz was the highestI was able to achieve in these circumstances.Given more funds, it would probably not bedifficult to improve on this by a factor of 10.Digital techniques bring their own prob-lems: I am not convinced that a worthwhilegain in speed could be won for the large in-vestment needed.

Although all 16 counters have eight out-puts each. it is impossible to exploit theseunrestrictedly, since to examine all possiblecombinations at a clock rate of 1 MHz wouldstill take 816/106 seconds = 8.9 years. Rangelengths were therefore tailored to each letterso as to retain a reasonable chance of findingthe pangram while bringing the running timedown to about one month. Flexibility wasmaintained by providing printed -circuitcards with easily altered solder links allow-ing preadjustment of each counter's cyclelength. Selection of the ranges to be usedwas a ticklish business. involving carefulanalysis of letter frequencies in number-words. Those finally settled upon may beseen in Fig. 4 (numbers under RANGE standfor number -words).

Notice that e. having a high frequencyand being therefore less predictable thanother letters, receives the maximum rangelength of 8. On the other hand. v. occurringexactly once in every number -word fromtwenty upwards but in no others, can appearonly 3. 4. or 5 times in the pangram giventhe ranges for e. n, s. and r. This is hardly atrivial insight: were v's range length in-creased to 4. ten days would be added to therunning time. As it is. to run through thecombinations generated by the ranges inFig. 4 will take [8x6x6x6x7x4x7x6x6x7xx7 x6x6x7x6x3]/106 seconds = 31.36 days.Anything longer would have been unen-durable.

In the program. the PROFILE for one con-tained -1 in the s -position to cancel whatwould otherwise be an s too many in the ini-tial s -constant. However. minus values arenot resistor -representable in the machine.As may be seen in Fig. 4. there are only threeletters (1. a. x) in whose ranges one occurs.To deal with these cases, after reducing theinitial s -constant by 3, an s is added to thePROFILES of number -words higher than towin their ranges. The range for /thus becomes:one. two + s, three + s. Par + s: in other

words. number -words above one bring theirplural s with them. There is no reason thatthis couldn't be done for every number -wordin every range (with corresponding reduc-tion in the s -constant ). but it would mean alot of extra resistors.

Failure

After twelve weeks' concentrated effort. themachine drew near to completion. As a prO-totype, it had posed a host of technical prob-lems to be faced and overcome. First. therehad been a pilot phase to investigate the fea-sibility of an analogue implementation.

After twelve weeks'concentrated effort, the

world's first pangram ma-chine drew near to comple-

tion, and was ready fortesting

How fast could the critical summing andbalance circuitry perform? Despite normalpessimistic expectations, small-scale trialsyielded promising results. The only way todiscover whether the full-scale versionwould function satisfactorily would be tobuild it. At length the longprogram of desi gnand construction culminated on the day themachine stood ready for a crucial test: wouldit successfully identify and halt at a magiccombination?

To find out. I introduced deliberatechanges in the resistor -represented initialtext constants: by feeding the machine withfalse data about letter frequencies in the in-troductory text. I could trick it into haltingat a prearranged pseudo -magic combina-tion. Subtracting o and adding an i and ashould cause it to stop at that combinationof real totals represented in the previouslydiscussed hand -produced solution:'twenty-one'. the true number of is. then replacing'twenty-nine'. Using the 'manual clock' and'select counter' controls to preadvance thefive highest or 'most significant' countersin the odometer chain (u, v. w, x. y) to theirappropriate totals (3. 6. 10. 4. 5). it M. ouldtake only a few minutes for the faster -Q. -

cline counters to reach the remaining num-bers in the magic combination. Starting theclock. I watched anxiously as the changingpattern of binary-coded LED displays re-ported the steady increment of counter po-sitions.

Suddenly and soundlessly the counters

locked. the EUREKA! lamp came on. and thecorrelation monitor confirmed 16 hits in arow. This was it: the machine had passed theacid test. With the correct text constantsloaded and a few other loose ends tied up.one week later all was ready for the launch-ing of this singular rocket on its 32 -day voy-age into the unexplored regions of logolog-ical space.

Lift-off came almost eight months afterthe publication of Rudy Kousbroek's auda-cious challenge. Cees Wegman. a spiritualgodfather to the project who had watchedsympathetically through the long months asI gracelessly declined from suave insou-ciance to crazed intensity. came along to per-form the deed of honour. A bottle of winewas broached. and three of us sat withglasses raised as he ceremoniously clickedthe starting switch to RUN (it was a fittingtableau for some quixotic latter-day Ve-lasquez. I couldn't help musing).

The ensuing period found me hoveringnervously over the machine. Among otherthing.. there was the nagging worry of ma-chine reliability: what guarantee was thereof faultless operation over so long a period?The answer. of course. was none. All I coulddo was maintain sporadic surveillance withan oscilloscope, and halt the machine atthree-day intervals to perform checks withthe pseudo -magic combination. After awhile the suspense became nerve-racking.Mornings were worst. On waking, the firstthought in consciousness would be has ithalted? It took nerves of iron to go patientlythrough the morning's ablutions beforetensely descending to the living room wherethe machine was installed on my desk.Opening the door with great deliberation. Iwould quickly go in and transfix the ma-chine with a questioning gaze. And therewould be the flickering LEDS as the countersslowly switched their way through the2.71x1012 combinations. One million asecond for 31.366 days. It was a torturingexperience. The novelty of watching the ma-chine soon wore off and the edge of expec-tation blunted. but a single second's dis-tracted attention was accompanied by thethought that another million chances had al-ready elapsed. so perhaps Now??? ... and myglance would be wrenched back to the twin-kling array of lights. After months of fren-zied activity in building the machine, thisperiod of enfored waiting was a cruel con-trast of frustrated inertia and protracted dis-appointment.

But it was highly conducive to thinkingup means for shortening that time. Beforelong. I saw that by halting the machine atkey points in its travel and limiting the cycle-

length of certain counters through calcu-lated intervals. redundant checks on pre-

58

DESIGN AND TECHNOLOGYOF INTEGRATED CIRCUITSby Donard de CoganISBN 0 471 92237 4230 pagesPrice £14.95 (soft cover)Design and Technology of integrated Cir-cuits is part of the Wiley EEE textbook se-ries in Electronic and Electrical Engineer-ing. which has been developed to fulfil therequirements for course texts arising in uni-versities and polytechnics. The series isaimed at undergraduate level.

The first chapter gives a brief historicalreview of components. materials and tech-nologies that should help to provide a per-spective for the remainder of the book. Thesecond chapter provides a minimalist ap-proach to solid-state devices, treating theminitially as black boxes with specific prop-erties. This is, of course. modified in laterchapters when reference is made to optimiz-ing component design for use in particularmicroelectronic applications.

It is assumed that the reader has a reason-ably- good knowledge of physics. A knowl-edge of chemistry is an advantage but not ab-solutely essential as most of the required ma-terial is provided as 'asides' in the text.

There are bibliographies at the end ofseveral chapters that are intended as guide-lines for further reading. There are alsomany worked examples and most chapterscontain a range of tutorial exercises.John Wiley & Sons LtdBaffins LaneCHICHESTER P019 IUD

POWER ELECTRONICS HAA'DBOOKBy F.F. MazdaISBN 0 408 03004 6417 pagesPrice £60.00 (hardcover)Although thirty years have elapsed since theinvention of the thyristor. power electronicsis still regarded as a relatively young tech-nology. Nevertheless, in those few years ithas brought about a tremendous improve -

In quest of a Pangram

dictably invalid blocks of combinationscould be obviated. Temporarily truncatingthe 1 -counter's range to exclude eighteenand nineteen, for instance, meant that allvalues oft contained ay so that v could occuronly four or five times. Testing cases forwhich y= three could thus be skipped duringsuch a phase. Using dodges of this kind, Iwas able to slice nearly ten days off the orie-

NEW BOOKS

ment in the power -handling capabilities andswitching speeds of power semiconductors.During the same period. advances in micro-processors and microcomputers have had agreat impact on the control strategy forpower electronics.

In a single volume Mr Mazda has col-lected a vast amount of material relating topower components. circuit design and ap-plications. The material is provided in athoroughly practical form with theoreticalinformation presented as formulas. whosederivation is not given. Books where suchderivations may be found are given in a bib-liography.

The book is divided into three parts. Thefirst deals with power semiconductor de-vices. thermal design. EMC and power semi-conductor protection. The second coversstatic switches, AC line control. direct AC fre-quency converters. forced commutationtechniques. DC -to -DC converters and DC linkfrequency converters. The third describessome of the applications of power semicon-ductor circuits: power supplies, electricalmachine control, heating and lighting, andelectromechanical applications.

A very useful book for practising powerelectronics engineers and students of thesubject.Butterworth Scientific LtdVestbury House, Bury StreetGUILDFORD GU2 5BH

SEQUENCESEdited by Renato M. CapocelliISBN 3 540 97186 6549 pages - 56 iollustrationsPrice £35.00 (hardcover)This volume contains all the papers pre-sented at the 1988 Advanced InternationalWorkshop on Sequences: Combinatorics.Compression and Transmission, which

inally estimated running time.Meanwhile, the grains of sand-and of

hope-were running out inexorably. Daysucceeded day and week succeeded weekwith no sign of an EUREKA! Twenty-twodays after launching. the machine hadchecked out every (undisqualified) combi-nation of number -words within its capacitywithout finding the magic pangram. Sinceoscilloscope monitoring and a subsequenttest with the modified initial text constants

brought together for a week computer sci-entists, leading mathematicians and expertsin various allied fields.

The work provides an up-to-date viewof the status of a number of relevant topicsin theoretical computer science and sug-gests directions for future research. It con-stitutes a valuable working tool for mathe-maticians. computer scientists, researchersand graduate students interested in combi-natorics. combinatorial algorithms, cryp-tography. information compression andtransmission, and mathematical applica-tions in engineering fields.Springer-Verlag London Ltd8 Alexandra RoadLONDON SWI9 7JZ

CABLE TELEVISIONTECHNOLOGY AND OPERATIONSby Eugene R. BartlettISBN 0 07 003957 7425 pages - illustratedPrice £39.50 (hardcover)Even though cable TV systems represent amulti -million pound market, it is surprisingto note that relatively few technicians haveat least a basic knowledge of their designand operation. Although the book is aimedprimarily at entry-level cable TV techni-cians. it should also prove useful as a refer-ence work for those already familiar withthe subject. This is mainly by virtue of theemphasis on elementary background andthe abundance of reference material.

The book covers everything to do withcable TV systems. from the power supplyto the cable termination at the subscriber'sabode. planning. installation and testing.Chapter 3 is of particular interest because itprovides an excellent introduction to trans-mission line technology. covering signal re-flections. cable losses. the choice of coaxcable. line amplification and minimum sig-nal levels specified by various FCC regula-tions. Chapter 6 discusses test and measure-ment procedures for cable TV systems, pro-viding a detailed description of the function

showed the machine to be functioning prop-erly. I was not in any serious doubt aboutthis negative result.

The crushing truth was that there neverhad been a needle in the haystack: the Questfor the Pangram had failed.

The third part of this article, reproducedby kind permission of Springer-Verlag,Heidelberg and New York, will appear inthe October issue of Elektor Electronics.

of video insertion test (VIT) lines. as wellas instructive notes on how to carry outsuch tests and interpret the results.

Although the subtitle of the book indi-cates that HDTV systems are discussed, rel-atively little information is provided onthis subject, probably because the fivestandards (for different technical areas)agreed by the CCIR during the 17th PlenaryAssembly last May were not know at thetime the book was written. However, thedepth of information given in the bookprovides a solid basis for the practical im-plementation of HDTV signals on futurecable TV systems.

Cable Television Technology and Op-erations is a useful. if not essential. desk -and -field reference work for all cable TVtechnical staff: system engineers and de-signers. operators. installers and man-agers.

McGraw-Hill Book Company (UK) LtdShoppenhangers RoadMAIDENHEAD SL6 2QL

WORLD SATELLITE TV ANDSCRAMBLING METHODSby Frank Baylin, Richard Maddox andJohn McCormacISBN 0 917893 11 5

IEE MEETINGS2-7 Sept - Knowledge -based systems

for process control*.2-7 Sept - Switching and signalling in

telecommunication networks*.2-7 Sept - Measurement technology

(DC to VHF)*.3-7 Sept - Optical fibre communica-

tions*.9-14 Sept - Electronic product testing

and testability*.10-13 Sept - Solid-state device research.11-12 Sept - Digital signal processing

for radar and sonar applications.11-12 Sept - Mechatronics-designing

intelligent machines.17-21 Sept - Train control systems*.17-20 Sept - Applied optics and opto-

electronics.21-25 Sept -International Broadcasting

Convention.* Vacation school.Information on these events may be ob-tained from the IEE. Savoy Place. LON-

NEW BOOKS

342 pages - illustratedPrice £27.00 (UK); £29.00 (Rest of Eu-rope); £33.00 (outside Europe)World Satellite, Tv and Scrambling Meth-ods is a 'must' for anyone. professionaland amateur alike. interested in the tech-nology of satellite television and scram-bling systems. The authors have exploredall components of home satellite systemsfrom the point of view of a technicianwho must understand their design. opera-tion and repair. It complements the re-cently released 3rd edition of Ku -bandSatellite TV - Theory. Installation andRepair and the popular The Home Said-lite TV Installation and TroubleshootingManual also published by Baylin Publica-tions. Circuit and block diagrams of mostcomponents are presented and clearly ex-plained throughout the book.

Nearly one third of the book is devotedto a detailed study of broadcast formats.including NTSC. PAL. SECANI and MAC, digi-tal techniques. as well as basic scramblingand encryption methods. This material is abackdrop to a discussion of all American

DON WC2R OBL, Phone 081 240 1871.

The British Amateur Radio TeledataGroup's Annual Rally will be held atSurrey Hall. Sandown Park race courseon Sunday. 16 September from 10.30 to17.00. Details from Mr Peter Nicol, Tele-phone 021 453 2676.

MIDT_LiMjTR,',3

The North Trafford College is again of-fering a Radio Amateurs' Course start-ing this month. Theory on Mondayevening. or Wednesday morning: Morsecode on Tuesday evening or Wednesdayafternoon: Amateur television on Wednes-day mornine: Advanced morse code onMonday evening. Enrolment dates are 5-7September. Details from Mr J.T. Beau-mont. course tutor. at theNorth Trafford College.Talbot Road, Stretford.MANCHESTER M32 OXH:

and European current satellite TV tech-nologies. including the VideoCipherll.RITC. IRDETO. Oak Orion. Filmnet. SkyChannel. EuroCypher. H -MAC. D2 -MAC,VideoCrypt and Teleclub Payview III sys-tems.

The preceding information is a preludeto the chapters on troubleshooting and set-ting up a test bench. Thoughout the text.the expert guidance on testing. servicingand tuning is complemented by over 200photos, diagrams. tables and wiringschematics.Baylin Publications24 River GardensPurley, READING RG8 8BX

DIGITAL TELEVISIONEdited by C.P. SandbankISBN 0 471 92360 5Price £75.00 (hardcover)This large work on the new televisiontechnology, edited by the BBC's DeputyDirector of Engineering. was publishedrecently and will be reviewed in the Octo-ber issue of Elektor Electronics. The bookis available fromJohn Wiley & Sons LtdBaffins LaneCHICHESTER IUD

Telephone 061 872 3731

An RAE course will he held on Wednes-day evenings from 19.30 to 21.30. com-mencing 19 September, at the PoverestSchool. Poverest Road, ORPINGTON.Details from the course tutor. Mr A.E.Betts. at the Bromley Adult EducationCentre, Aylesbury Road, BROMLEYBR2 OQR. Telephone (0689) 31123.

The Meld Adult Education Centre, nearCrawley. West Sussex. is offering a coursefor the RAE examination starting inSeptember. Details of times and costs maybe obtained from the college (ask forMarie Rice) on (0293) 26467.

Frost & Sullivan are holding a number ofseminars this month on InformationTechnology. Data Communications. Mi-crowave Radio Systems and PacketSwitching. Details from Frost & Sulli-van, Sullivan House. 4 Grosvenor Gar-dens, LONDON SWIM ODH, Tele-phone 071 730 3438.

60

CAREERS IN ELECTRONICSAlthough the recent Quarterly Surrey ofEmployment Prospects showed a declinein job prospects in the electronics industryduring the first half of this year. there is nodoubt that career prospects for electronicengineers and technicians in the long termare excellent. What's more. these pros-pects are there for both men and women:slowly but surely the number of womenworking in electronics and computer engi-neering is growing.

The new professional Institution for In-corporated Engineers and EngineeringTechnicians in Electronic and ElectricalEngineering-IEEIE-has published a ca-reers brochure aimed at attracting moreyoung people into the profession. particu-larly at Incorporated Engineer and Engi-neering Technician levels. The brochure,containing comprehensive information onthe profession. also defines the qualifica-tions required for membership of an enei-neering institution such as the IEEIE.

The electronics and electrical industrymay be divided into five groups:

Energy and Power.Transport:Contracting & Building Services;Electronics. Communications andInformation Engineering:Measurement, Control andAutomation.

The incorporated engineer(I Eng)

Incorporated Engineer (Electronics andElectrical) is a title awarded by the IEEIE.Those holding the title are practical engi-neers. playing a most vital role in industry.They often can -y managerial responsibilityas leaders of teams or they may occupypositions involving individual responsibil-ity for large amounts of complex equip-ment. Incorporated Engineers maintainand manage existing technology at peakefficiency.

The academic qualification for Incor-porated Engineers (Electronics and Elec-trical) is a Higher National Diploma orCertificate awarded by the Business &Technician Education Council-BTEC-in England. Wales and Northern Irelandor the Scottish Vocational EducationCouncil-SCOTVEC-in Scotland. Withthe rapid advance of technology. BTechdegree courses are being developed for In-corporated Engineers.

The Engineering Technician(EngTech)

Engineering Technicians apply proventechniques and procedures to the solutionof practical problems and carry a measureof technical responsibility, often under theguidance of engineers or scientists. Theyrequire personal abilities enabling them towork effectively as members of an enei--neering team.

Engineering Technicians are normallyrequired to possess a National Certificateawarded by the Business & TechnicianEducation Council-BTEC-or the Scot-tish Vocational Education Council-SCOTVEC.

More information on the EngTech andlEne qualifications may be obtained fromthe IEEIE. which accredits courses, but fordetails of specific courses you should con-tact y our local polytechnic or college. Ad-dress enquiries toCareers OfficerIEEIE

HouseSavoy Hill.LONDON WC2R OBSTelephone 071 836 3357

The Chartered Engineer(C.Eng)Chartered Electrical Engineer is a titleawarded by the Institution of ElectricalEngineers-IEE. Those holding the titleare primarily concerned with the progressof technology through innovation, creativ-ity and change. the development and useof new technologies. the promotion of ad--vanced design and production methodsand the pioneering of new engineering ser-vices and management techniques.

Chartered Electrical Engineers are nor-mally required to have obtained a BEngdegree accredited by the IEE.

Further information may be obtainedfrom theIEE Schools Liaison Service.Michael Faraday House.Six Hills Way.Stevenage SG1 2AY.

Details of courses of stud% are a% ail -able from universities. polytechnics andcertain colleges.

Women in Electronics

The Belling Charitable Trust has given fi-

nancial support to the IEEIE to enable theup -dating and re -printing of a bookletaimed at encouraging more young womento choose en gineering as a career.

The new publication. entitled Tales of12 Women - who are glad they chose En-gineerins,,, is produced in association withthe CHMT-Caroline Haslet' MemorialTrust-and contains information on win-ners and finalists of the prestigious YoungWoman Engineer of the Year Award (seebelow ). Tales of 12 {linnet' is freely avail-able to schools and colleges in an aim tomotivate more female students to pursue arewarding and exciting career as an Incor-porated Engineer.

With more young women forgingahead in the engineering industry. it is ex-pected that the standard of competitorswill be exceptionally high for this year'scoveted Young Woman Engineer of theYear award.

Nominations, from suitably qualifiedyoung women under the age of thirty. forthe 1990 award should be submitted by

1990.Having successfully completed the

necessary technical education and training.all entrants will be required to prove them-selves capable of holding a responsibleposition at Incorporated Engineer level.

The aim of the award, sponsoredjointly by the IEEIE and the CHN1T, is tohighlight the exciting career prospectsavailable for women in electronic andelectrical engineering.

Winners of the award in previous yearshave been chosen from the whole spec-trum of electronic and electrical engineer-ing-telecommunications. electricity sup-ply. electrical consumer goods, electricalcontracting. defence, instrumentation.food processing and aerospace. It is hopedthat their example will motivate and en-courage more girls to embark upon profes-sional careers leading to Incorporated En-gineer status.

In addition to gaining prestige associ-ated with the award. the 1990 YoungWoman Engineer of the Year will receivea silver rose bowl and a prize of 000. Themost promising younger entrant will re-ceive the CHMT's Mary' George MemorialPrize of f 100.

Copies of the award nomination formand brochure are available fromThe Secretary,IEEIE,Savoy Hill House,

CAREERS IN ELECTRONICS

Savoy Hill,LONDON WC2R OBS,Telephone 071 836 3357.

The Caroline HaslettMemorial Trust

The Caroline Hasten Memorial Trust is acharitable body whose aims are to providescholarships and other educational oppor-tunities for women who are already pursu-ing careers in the electrical industry or inother fields requiring qualifications in sci-ence. mathematics. engineering, homeeconomics and allied subjects.

The original trust was established in1945 to commemorate the 21st birthday ofthe Electrical Association for Women ofwhich Caroline Haslett was the first direc-tor. Its aim then was to provide scholar-ships and travelling exhibitions fordemonstrators and housecraft advisers inthe electrical industry.

After Dame Caroline Haslett's death in1957. the Trust was reconstituted as amemorial to her and the scope of its workwas extended to encourage more womento train as engineers, scientists and mathe-maticians.

Believing as it does that the country isnot making sufficient use of its womanpower. the Trust takes particular note ofwhere there is a recognized shortage oftrained people in order to see how farwomen can help to fill the gap. Today theTrust helps women who w ish to train tobecome engineers at any level, providingscholarships for support during undergrad-uate training or whilst at technical college.

IMP Europe:at the leading edge inmicrochip technology

IMP Europe has built up an enviable repu-tation for designing. manufacturing andmarketing MOS Custom and Semi -customintegrated circuits at the leading edge oftoday's technology. The company is grow-ing faster than ever, with record bookingsgenerating real career prospects. We offera unique work environment that combinessubstantial international support with afriendly team atmosphere. For ambitiousindividuals the pace of our success repre-sents the opportunity to develop theirskills and take a genuine share in our fu-ture.

Our growing customer base covers thewhole of Europe, and we can offer theright individuals the opportunity to work

directly with customers in designing someof the most challenging ASICS in the indus-try. If you think you could meet the chal-lenges we have to offer, particularly in ourDesign and Layout Departments, wewould like to discuss our current vacan-cies with you.

IMP Europe is the leader in the designand manufacture of mixed analogue anddigital ASICS. one of the fastest -growingproduct segments for the semiconductorindustry. The company has successfullyused its proprietary cell -based designmethods and cstos process techniques tosupply alue-added mixed analogue/digi-tal and complex digital chips to customers.primarily in the telecommunications. com-puter. consumer appliance and militarymarkets.

Contact:Rachel Dainton.Personnel Manager,IMP Europe Ltd,Windmill Hill,Whitehill Way,SWINDON SN5 9YZ, England.Telephone (0793) 875327;Fax (0793) 875328.

Opportunities with AdvancedPower Supplies Limited

.Advance Power Supplies Limited was ac-quired by Farnell Electronics PLC in 1988and now forms part of the Farnell Elec-tronics Manufacturing Group. Based inBishops Stortford, it employs almost 400people and focuses its efforts on standard

and custom designs of switch -mode powersupply units. In-house capability includesmetalworking and finishing. printed -cir-cuit board manufacture. full design. pro-duction. windings and testing facilities.

The company is able to offer an excel-lent four-year training scheme for techni-cians. the first year of which is spent at alocal Industrial Training Centre. at the

same time enrolling for day release at alocal Technical College to pursue furtherqualifications.

Once the first year has been completed.trainees will return to the Company andwill begin to spend between 6 and 12weeks in every internal department.Throughout this process, trainees will con-tinue to attend college on a day releasebasis.

At the end of the four years. traineeswill have gained tremendous experienceand knowledge both from the internal andthe external training. allowing them to em -hark upon a career in the Company.

The Company is committed to a con-tinuing training and development pro-gramme and will sponsor employees at alllevels to take further education to allowthem to prosper within the organization.

For further information contact:Frances A. Barrett,Personnel Manager,Advance Power Supplies Limited,Raynham Road,Bishops Storiford, Herts, CM23 5PEEngland,Telephone (0279) 655155,Fax (0279) 655322.

Macro: if it came to thecrunch, could you build aradio or television receiver?

If the answer to the above question is yes.we would like to talk to you.

Macro is a highly technical companywhich recognizes that dedication. exper-tise and enthusiasm can be more importantthan a piece of paper from a university.

We specialize in the distribution of. anddesign -in support for, all manners of semi-conductor.

Our growing customer base in radio,audio and TV needs high calibre technicaladvice and guidance at all stages in the de-sign process.

If this sort of work would interest you.call Adrian Lenard. Karen McGahey orGill Waters on (0628) 604383 to discussthese posts further.Macro Marketing Ltd.Burnham Lane,SLOUGH SL1 6LN, England.

SUVVIER -1996 COMPET IONCongratulations to Mr. C. Izzard fromSheffield. who has won the Satellite TVReceiving System.

The winners of the year's free sub-scription to Elektor Electronics are:

N1. Bird - Chessington. Surrey.Mr. L. A. Cruz - Santa Cruz de Tenerife.\1r. R. Guttmann - Maylands. Australia.Mr. N. Lathia - Luton. Beds.Mr. D. \lcBright - Paignton. Devon.Mr. A. N IcGuire - Airdrie. Strathcl de.Mr. A. \likkonen - Horsens. Denmark.Mr. C.W. Murray - Aldershot. Hams.

LETTERS

Letters of a general nature, or expressingan opinion. or concerning a matter ofcommon interest in the field of electronics(in its widest sense'. should be addressedto The Editor at our London offices Theirpublication in Elehtor Electronics is at thediscretion of the Editor.

THE 8031/8731 MICROCONTROLLERDear Sir-I'm writing to you to point outan error in the above article which appearsin your July/August 1990 issue on pages36-37. The author has made a fundamen-tal mistake in paragraph 2. where he says:"The memory may be doubled to 128 K ifthe Harvard architecture is used. A Har-vard architecture is defined as a separatedata and program memory."

A Harvard architecture is not simplyhaving separate data and program memo-ries but, more importantly. separate ad-dress/data buses for data and programmemories. The use of separate buses al-lows simultaneous instruction. fetch anddata access and hence ereater processorthroughput-see diagram below.

E,T.r. .4

CINTOKIL

ALU

cormRZLIJNIT

DATA119.t:Re

IZTAUCT0,5

Harvard processor architecture.

O

0

Mr. L.G. Randall - LondonMr. A. Soares - Cartaxo. Portugal.

Our thanks and commiserations to allthe other competitors.

The correct answers to the six ques-tions on p. 39 of our June issue are:

I. William Bradford SHOCKLEY in1948 (not John BARDEEN or WalterHouser BRATTA I N: they and Shockley in1947 invented the point -contact transistorfor which the three shared the Nobel Prize

re LA I)

The 8051 microcontroller family. onthe other hand. has a single set ofaddress/data buses shared between pro-gram and data. In other words, there is nodifference in architecture between teh8051 and any other commonly used mi-crocontrollers. In fact. none of the 8051family manufacturers claim to have usedHarvard architecture in the microcon-troller.

This is a classical example of someonemisusing a jargon word without fully un-derstanding.

One more small mistake. the 8031 isthe Rom -less version of the 8051, whilethe 8751 is the EPROM version: there is no8731 as stated in the title.

I hope you can clarify these mistakes to!.'our readers.S.C. Lu, LondOn.

The author replies: "Mr Lu is absolutelyright in his comments: sorry for the mis-takes and any inconvenience these mayhare caused". (Ed]

MAC DECODINGDear Sir-In addition to the articles youhave already published on MAC decodingin the past. would it be possible for you toconsider some more satellite projects. suchas the following three.1. an RGB-PAL adaptor to interface the(MAC) decoder into a domestic TV or toloop back composite video through the re-ceiver (most Tv receivers in Britain haveno SCART or even RGB input. only an IFinput).2. An add-on unit for vcRs using the new

HE WI{ -\\\ NERS

for Physics in 1956). The name transistor.by the way. is a contraction of transfer ofcurrent across a resistor.

2. NOT gate or inverter.

3. The siemens (S).

4. Super regenerative.

5. FORmula TRANslation.

6. Music Instrument Digital Interface.

As-rEc A-r233xx-3 tuner/demodulator (asatellite receiver could be buillt for under£50 using the the vcR's modulator cir-cuitry).3. A video bandwidth reducer to improvethe contrast on weaker satellite transpon-ders like we and RAI at 13 E.4. A SECAM(L)-PAL transcoder circuit.

Furthermore. in the article "Experi-mental me reception" (Elehtor Electronics

LNB used was theUniden UST 980 dual -band. This LNB couldbe used with any Marconi -based receiverif a separate polarizer pulser were used.because the voltage outputs are 12 V and18 V (for horizontal and vertical polarityrespectively). Therefore. if the LNB werecoupled. say. to an Amstrad receiver.pressing the polarity button would triggerthe arts band. thus increasing the capabil-ity of an inexpensive receiver. Couple it tothe long-awaited NI.NC decoder and a serialrotator and much more fun could be had.Bill Jarvis. Merseyside.

Thanks for your enthusiastic Olen whichhas been copied to the designers of the,w.4c decoder. I understand that theRGB-PAL decoder and a composite Videooutput will be included in any case: ap-parently they are already in the final de-sign stages.

Thanks for the suggestions as regardsthe use of the Uniden LAB-these certainlylook very interesting for many readers.

1E4

SWITCHBOARD

Switchboard allows all PRIVATE READERS of

Elektor Electronics one FREE advertisement of'

up to 108 characters, including spaces. comma,.

numerals, etc. per month.Write the advertisement, which must rely:

to electronics, in the coupon on this page: itMUST INCLUDE a private telephone number orname and address: post office boxes are notacceptable.

Elektor Electronics 4Publishinv can notaccept responsibility for any correspondence ortransaction as a result of a free advertisement orof any inaccuracy in the text of such anadvertisement.

Advertisements will be placed in the order inwhich they are received.

Elektor Electronics IPublishing.right to refuse advertisements without givingreasons or without returning them.

FOR SALE. New 3 -phase tester (ESTmeter) - only £5. I am also interested inpenfriendship on electronic and digitaltechnologies.Amir Sadeq Hashemy, 32 Sepid Lane,Khayam Street, Tabriz 51736, Iran.

FOR SALE. Top Two Tx 15 Watt withmodulator. Data available from RSGB -£200. Make fortune - send SAE.GM3VOX; Telephone 03552 65212.

WANTED. User instructions and servicemanual for Commodore 8296 or photo-copies.Phone Mr Davies on (0928) 25788.

SWAP OFFERED. My Fender Show-man Amplifier with new valves for yourdual -beam 15 MHz oscilloscope or better.Niall McGrath, 68 Atherfold Road, LON-DON SW9 9LW, Phone 071 274 4984.

WANTED. Dragon 32 or 64 disk drive.Also required with interface.Phone A.J. Smith on 061 370 3280.

PENFRIENDS. Looking forward tohearing from penfriends whose interestslie in electronics and spectrum 128/48programming.Nasser Ghadiri, 44 Ark Street, AB 250Avenue, 81647 Isfahan, Iran.

FOR SALE. 16 char. 5x7 LCD plus 14 -key keyboard. Full GCT diagram. £15each.P. O'Reilly, 37 Laleham Ct, ChobhamRoad, WOKING GU21 4AX.

WANTED. Power triode Type 8005,USA manufacture. Good price paid.Phone Mr Reynolds on (0438) 355325.

EXCHANGE. Transistors 2i.: TypeCFY17. 2. 2 r CFY18-20, 4,MGF 1502, 6xNERF 966 for a small tape recorder.K. Kraus, Ejpovice 96, 337 01 Rokycany,Czechoslovakia.

FOR SALE. 100 new assorted resistors£1.00. Buy £5.00 worth and receive someother components free.R. Hynard, 71 Tothale Turn, Netherley,LIVERPOOL L27 4Y0.

FOR SALE. Elektor Electronics digitalcapacitance meter - £28. Practical Wire-less 4 -digit frequency counter. 10 Hz -200 MHz - £30.Phone R. Hearn on (0502) 566026.

WANTED. Manual for Philips TV re-ceiver Type 14GR1221.A. Chanturiya, 9 Russell Chambers,Bury Place, LONDON WC 1A 2JS.

WANTED. Radio and television servic-ing books covering the years 1950-1964.Phone Terry on (0702) 231950

FOR SALE. Hi -power Coutant switch -mode power supplies: 2-7 V. 20 A: 35 V,4 A; 24 V. 4 A; 12 V, 4 A; 12 V, 1 A; 5 V,1 A. Cased, very good condition. £35 plus£3 p&p.P. Underhill, 34 Mayfield Road.WORCESTER WR3 8NT.

PCBs - low cost and fast supply. Only28 pence sq/cm. All done on high -qualityfibre -glass from your, our or EL\' filmsor photocopy.Lazar Trajkovic,Jnkovac. 34313NATALLNCLYugoslavia

Send this coupon to: Elektor Electronics(Publishin2). Down House. BroomhillRoad. 1_0 \ DON SW18 -LJQ.

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hens and E.-ddress MUST Coe rsyea r.ste

WANTED. IC Type 'MA 2521.Phone L. Tye on (0372) 56507.FOR SALE. Elektor Electronics 3,15-16, 18-28, 32-69, 73, 78-80; total 51issues. £25 plus postage.Phone Alan Olrog on 081 5-16 4311.

FOR SALE. Thermionic valves. trans-formers and Band 2 VHF FM1SignalStrength Meter.Phone Peter Rogers on (0525) 376310.

FOR SALE. 8088 -based boards and XTturbo controller for multi -screen graph-ics display.Phone Norman Campbell on 067 182 523for information.

64Please mention ELEKTOR ELECTRONICS ::'hen contacting advertisers

BRIAN PRICE BOHM ORGAN STUD OS

Thirty years ago. Dr Bohm started as the first one in Europe tooffer complete DIY organ kits. The idea was received enthusiasti-cally by many. Not just because they could build their own organ.but also because it soon became clear that the musical possibili-ties and the sound quality of the Bohm designs were second tonone. This is still so today.

Over the past thirty years, tens of thousands of music lovershave spread the name Bohm all over the world through personalrecommendation. Year after year. the Bohm development teamhas improved the DIY system. always using technical innovationsand facilitating the building of organs from kits.

To Bohm. innovation is of prime importance. In their laborato-ries and in co-operation with artists, new ideas, new concepts,new modules and nev. instruments are created continuously. Li-censes have been granted. and are still being granted. all over theworld: from the one -finger automatic accompaniment BOHNtxr.which you will find in most electronic organs. to the PN1 technol-ogy of the N1CSICA DIGITAL range for renowned orphan manufac-turers.

Building yourself even the largest Bohm instrument is not theprivilege of technicians and electronics experts: anybody not hav-ing two left hands can build himself with Bohm. Moreover. build-ing yourself with Bohm is very instructive. All over the world.many thousands of people have experienced the introduction tomodern electronics in this practical way.

Bohm is represented in many countries all over the world.Their importer in the United Kingdom is Brian Price Bohm

NEXT MONTHIN ELEKTOR ELECTRONICS

Guitar tuner

Chopper opamps

Negative resistance

Measurement techniques

Single double symmetrical power supply

uP controlled telephone exchange

Medium power AF amplifier

Dubbing mixer

Selective preamplifier

Make sure of your copy by filling in this coupon andhanding it to your Newsagent.

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(your newsagent)Please reserve for me copies ofElektor Electronics at £1.75 eachName -

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Organ Studios. They can supply all Bohm organ kits. MIDI equip-ment and many other items that will appeal to all electronic musicenthusiasts.

One such item is the Keyboard Scanner for Touch SensitiveKeyboards Type E510. which has been included in several arti-cles published in Elektor Electronics over the past few years.

The E510 scans up to 128 keys (>10 octaves) with a change-over contact. Eve* time a key is pressed or released, the velocityis calculated by measuring the time. At the same time. everypressing and releasing is tested for validity. The key has only tobe recognized if it goes from BE to BS or vice versa. This ensuresthat contact bouncing does not lead to misinterpretation.

The time measurement is effected by a seven -bit reversecounting counter. To prevent underflow. the counter is disabled assoon as it reaches the value 1.

An internal FIFO register allows fully polyphonic playing. thatis. several keys may be pressed simultaneously.

The serial output transmits as a serial signal according to NIIDIspecification: key on; key off; key number: key channel, and ve-locity. If the channel number input is left open or is logic 0. thedata is transmitted on mu channel I: if the input is logic I. datais transmitted on MIDI channel 2.

For further information on a wide range of electronic musicequipment. contact Brian Price Bilihm Organ Studios at 66Ashchurch Drive, Wollaton, NOTTINGHAM NG8 2RA, Tele-phone & Fax: 10602) 284766.

IT PAYS TO SUBSCRIBE TOELEKTOR ELECTRONICS

If you take out an annual subscription to ElektorElectronics, you not only save money compared with buy-ing the magazine from your local nev.sagents. but you ha,the convenience of having it delivered to your home and thepeace of mind that you will not miss any issue. The totalcover price for the 11 issues appearing in 1991 will amountto £21.65 in the United Kingdom: more overseas, becauseimporters and their retailers have to add their (perfectlylegitimate) expenses. The (post paid!) subscription rates for1991 are:United Kingdom £20.50Outside Europe - surface mail £25.50AIRMAIL:

Europe & Eire £26.50Middle East & North Africa £31.00South East Asia. Central & southern Africa.Central & South America. USA & Canada E35.5nAustralia. New Zealand. Far East andPacific regions 13N.OUThe differences in these prices are caused merely by thepostage: the basic subscription price is well over 2(.i belowthe cover price and is the same all over the world.Write now for your subscription to:Elektor Electronics World Wide Subscription ServiceLtd Unit 4 Gibbs Reed Farm TICEHURST EastSussex TN5 7HE England Phone 10580) 200657.

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"THE BEST DEALS sirOF THE DECADE -7;-471 Cloico

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IN ELECTRONICS IN .....

CRICKLEWOODELECTRONICSNEW 90'SFIRST EDITIONCATALOGUE

Cricklewood Electronics newcatalogue of the decade offersa host of new features & theusual Cricklewood benefits,including: One of the largest ranges of

components in the UK Fast and Efficient same day

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Quantity discounts available Discount vouchers includedF1 No minimum orderSe

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T, Cricklewood Electronics Ltd, 40 Cricklewood Broadway, London, NW2 3ETTel: 081-450 0995/452 0161 Fax: 081-208 1441 Telex: 914977

Contents Include: -

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Cricklewood Electronics1990 Component Catalogue

Please send copies of the 1990 CricklewoodElectronics Catalogue at £1.50 to:NameAddress

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I.EKTOR ELECTRONICS SEPTEMBER 1990

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