the magazine for the radio & electronics experimentalist june 1990 … · 2018-10-03 · (43...

THE MAGAZINE FOR THE RADIO & ELECTRONICS EXPERIMENTALISTJune 1990 £1.70

mit 71gie roriivw

Elect

r

Remotelycontrolled stroboscopePLL sine wave generator

MIDI master keyboardFAX interface for PCsMini EPROM viewerCRO calibrator

WIN A SATELLITE TVRECEIVING SYSTEM!

by taking part in our exciting Summer Competitionon page 39 of this issue.

For fast delivery telephoneyour order on 01-205 9558using VISA,Access Card

=1. MkOrders welcome fromgovernment depts &educational establishments

TECHNOMATICTechno House 468 Church Lane, London NW9 8UF.

Tel: 01-205 9558 Fax: 01-205 0190

All prices ex VAT.Prices are subject tochange without notice.Please add carriage(a) £8.00 (Courier)(b) £3.50(c) £2.00(d) £1.50

rchimedes COMPUTERS

A3000 (no monitor)A3000 (for TV use)A3000 Acorn ColourA410/1 (no monitor)A410/1 Acorn ColourA410/1 Taxan 770-Acorn 420/1 systems420/1 (no monitor)420/1 Acorn Colour

Acorn 440/1 systems440/1 Acorn Colour440/1 Taxan 770-

Techno 410 1 systemsupgraded to 420 1 spec.

Acorn Colour system £1559Taxan 770- system £1799

Carriage £8/computer £12/system

£649£698£829

£1199£1340£1559

£1699£1888

£25792809

TECHNO 410/40 UPGRADESA410/1 upgraded to 4 MB RAlv1 and 40 MBHard Drive complete with Mouse Mat. 1

box of 3.5" discs, printer lead and FirstWord Plus Release 2.

Our 40 MB Hard Drive is a high spec. AutoPark.25ms. quality drive with a reliable Toshibamechanism.

techno 410/40 with Acorn Colour Monitor£1699

techno 410/40 with Taxan 770- £1899Finance available on charaeabla basJs.

What we offer in addition to efficientsales service and professional backup!We not only offer professional advice when you are purchasing your systembut we will also provide friendly assistance afterwards. All our products carrya 12 month full warranty for parts and labour.

SPECIAL FINANCIAL DEALComputers alone or complete systems can bepurchased at NO EXTRA CHARGE over 9months. The deposit will be payable with theorder followed by 9 monthly payments. Pleasephone or write for full details and a personalquotation. Subject to status_ we should be ableto despatch your order within 7 days of receivingyour order.

TECHNO 410/1 SPECIAL

Offer extended due to popular demand.Archimedes 410 1 upgraded to full440 1 specification with 4 MB RAM

and 50 MB Hard Disc (Acorn)plus

Taxan 770- Multisync Monitorand including

a packet of discs. a printer leadand a mouse mat.

for only £1999 carr £12an chargeable bas,s

1090 VOUCHER ON CASH &CREDIT CARD SALES

Cash and credit card purchasers of Archimedescomputers and complete systems will receive avoucher to the value of 10% of the purchaseprice. Vouchers will be valid for 90 days from thedate of issue. Vouchers are not available orTechno bundled packaceS

GENIUS DIGITISING TABLETThe latest model of the Genius GT1212A PC tablet adapted for use with Archimedescomputers offers a resolution of 1000 lines/in over a 12" x 12" working area and connectsthrough the serial port of the computer.

The Tablet is operated by moving a four button puck controller over the special surfaceand a two button stylus with switched tip is also available.The software to drive the tablet is supplied as a module to operate within the RISC OSdesktop environment. Once loaded, several commands are available to control the tablet:

turn the tablet on or offselect relative or absolute coordinates etc.change puck movement sensitivity

Three of the puck buttons act as standard mouse buttons and the fourth allows specialoperations such as changing the size of the tablet work area.The tablet can virtually take over all the functions of a mouse making the use of graphicspackages much simpler. The puck has a set of cross -wires which allow simple andaccurate transfer of technical drawings. The optional stylus will make tracings, linedrawings etc much easier and more accurate.

The standard Archimedes mouse or a Tracker Ball can be left connected and can evenbe used as alternatives for some operations.

The package includes the tablet. puck. software and mains power supply.

GT1212A Tablet C259(a)Optional Stylus £35(d)

TECHNO DTP PACKAGE

Archimedes 410 1 ColourSystem upgraded to

full 420 1spec with 2 Mb RAM and

20 Mb Hard discfeaturing our technoSCAN

package and either

Acorn DTP PackageFirst Word Plus Rel 2.

Logistix

or

Impression and Pipedream 3and a free mouse mat

for only £1777 carr £12Finance available on chargeable basis.

Special Educational Subsidy onthe Techno DTP package.

R140 UNIX SYSTEMLimited Period Offer

R140 Base Systemwith

Taxan 770-- and PC Emulatoror

Viking IIplus

Ethernet Card andAdministrators Guide

for only

£3000and it also includes on -site

maintenance contract.

F-This advernsernent can orni shoe. an examplethe range of products stocked by Technomatic. SDsand for our latest BBC catalogue providingdetailed information and prices on BBC Compute:Systems. Peripherals. Software and Books.

NAME

ADDRESS

Post Cede

Return to Technomatic Ltd. Techno Hous.:468 Church Lane. London NW9 8UF EE

TEL! 01 205 9558

(43

CONTENTSJune 1990Volume 16Number 179

In next month's issue:36 -PAGE SUPPLEMENT OF

CONSTRUCTION PROJECTS

Square -wave generatorCar -theft deterrent

INMARSAT'S Standard C

Sound demodulator forSAT TV receiversBattery testerSCART-plug FM mini sender

Versatile NiCd batterychargerTft-level 100 MHz crystaloscillator

Front coverComputers that recognize

sounds are faced with enormous

problems, including the fact that

there are a very large number of

different words in a lang

and so much variation in the way

they are spoken.

This puts huge demands on

computers that are required to

interpret quickly the information

fed in by the electronic 'ear'. A

British system. known as Arma-

da. is one of the first large

vocabulary speech recognition

systems to be based on an array

of transputers, each capable of

handling 10 million instructions a

second. As it works in real time.

it can process continuous

speech.

Seen in the photograph. a

scientist at the Royal Signals

and Radar Research Establish-

ment illustrates the science

behind the Armada system,

which uses a technique known

as hidden Markov modelling.

Broadly, the system recog-

nizes words by using statistical

models of their constituent

sound. Unlike other systems. it is

said to be able to recognize

words that do not ()cc.:

training data. needs

training when new spear are

introduced and can easily be

reconfigured for new applica-

tions.

Speech Research Unit, Royal

Signals & Radar Establishment.

St Andrews Road, Malvern

WR14 3PS. Fax (0684) 894540.

39 WIN A SATELLITE TV RECEIVING SYSTEM!

LEADER11 Optical fibre telecommunications link remote areas

COMPONENTS34 Electronic fuses

A Bourns Electronics product60 ACL: Advanced CMOS Logic

by F.P. Zantis

COMPUTERS & MICROPROCESSORS

14 PROJECT: Facsimile interface for IBM PCs andcompatibles

\I. Brochand. F6BFX. and G. Warin. F6DCK36 PROJECT: Automatic power -down for PCs

by J. Ruffell44 PROJECT: Mini EPROM viewer

by J. Ruffell

ELECTROPHONICS24 PROJECT: MIDI master keyboard - Part 1

by D. Doepfer

GENERAL INTEREST211 PROJECT: Remotely controlled stroboscope

an EL\' design40 PROJECT: Rear window wiper coupler

by G. KleinePROJECT: Four -sensor sunshine recorderby J. Ruffell

62_ PROJECT: R -2R resistance network in SNITby H. Bierv.ith

53

INTERMEDIATE PROJECT41 Power zener diode

by K. Walters

RADIO & TELEVISION511 Aztex 24 cm FN1 ATV transmitter and 24 cm GaA

FET preamplifierA review by Mike blooding. G6IQM

SCIENCE & TECHNOLOGY56 'Intelligent' road systems

by Prof. Peter Hills. University of Newcastle -on -Tyne

TEST & MEASUREMENT

16 PROJECT: Electronic loadby G. Boddington

30 PROJECT: PLL sine wave generatorby J. Bareford

4S PROJECT: CRO calibratorby D. McBright

MISCELLANEOUS INFORMATION

Electronics scene 12: Events 63: New books 63:Letters 64: Switchboard 64: Reader, services 65: Terms 66:Bu)ers guide 74: Index of advertisers 74

Profile of Wilmslow Audiop. 59

Facsimile interface for IBM PCsand compatibles. p. 14

MIDI master keyboard. p. 24

tr,

Mini EPROM viewer. p. 44

ELEKToR ELECTRONICS JUNE 1990

Please mention ELEKTOR ELECTRONICS when contacting advertisers

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IMPORTANT NOTICE: PLease note that from 6 May 1990 our Telephone and Fax code will change from 01 to 081

\IIEWCONI ELECTRONICS PLEASE ADD 70p P & P and then 155, VAT.OFFICAL ORDERS from Govt. & Educational Estaofisnments are accepted.

77 LTPERTON ROAD WEST OVERSEAS Greets. postage AIR SURFACE charged at cost. VAT notPLAISTO\V. LONDON E13 9LT applicable for EXPORT orders. Stock items by return of post.

PLEASE PHONE WRITE FOR ITEMS NOT LISTED N.B. Prces subject to chance without notice & stook av&ability

ELEKTOR ELECTRONICS JUNE 1990

%11

Produced and published by ELEKTORELECTRONICS (Publishing)

Editoripublisher: Len SeymourTechnical Editor: J. BestingEditorial Offices:Down HouseBroornhill RoadLONDON SW18 4JOEnglandTelephone: 081-877 1688 (National)or +44 81877 1688 (International)Telex: 917003 (LPC G)Fax: 081-874 9153 (National)or +44 81874 9153 (International)Advertising: PRB Limited3 Wolseley TerraceCHELTENHAM GL50 111-ITelephone: (0242) 510760Fax: (0242) 226626European Offices:Postbus 756190 AB BEEKThe NetherlandsTelephone: +31 4490 89444Telex: 56617 (etekt nI)Fax: +31 4490 70161Managing Director: M.M.J. Landman

Overseas editions:FEDERAL GERMANYElektor Veriag GmbHSusterfeid Stralle 255100 AachenEditor: E.J.A. KrempelsauerFRANCEElektor sariRoute Nationale: Le SeauB.P. 53; 59270 BailleulEditors: D.R.S. MeyerG.C.P. RaedersdorfGREECEElektor EPEKariskaki 1416673 Voula - AthenaEditor: E. XanthoulisINDIAElektor Electronics PVT LtcChhotani Building52C, Proctor Road. Grant Raab iE)Bombay 400 007Editor: Surendra lyerNETHERLANDSElektuur BVPeter Treckpoetstraat 2-46191 VK BeekEditor: P.E.L KersemakersPAKISTANElectro-shop35 Naseem PlazaLasbella ChawkKarachi 5Editor: Zain AhmedPORTUGALFerreira & Bento Lda_R.D. Estefani, 32-1'1000 LisboaEditor: Jeremias SequeiraSWEDENElectronic Press ABBox 550514105 HuddingeEditor: Bill Cednim

Distribution:SEYMOUR1270 London RoadLONDON SW16 4DH

Printed in the Netherlands by NDB.Zoeterwoude

Copyright & 1990 Elektuur BV

ABC

OPTICAL FIBRE TELECOMMUNICATIONS

LINK REMOTE AREAS

Outer areas of the United Kingdom inNorthern Ireland and Scotland are poised tobecome hubs of world business, thanks to atelecommunications revolution.

The Northern Ireland development sternsfrom a £100 million boost to its economyfrom a joint initiative between its Depart-ment of Economic Development. BritishTelecom and the European Commission.

Central to the plan is the award of 0.25million from the European Regional Devel-opment Fund as part of the European Com-munity's programme of Special Telecommu-nications Action for Re-gional Development(STAR).

British Telecom waschosen to implementSTAR. which the com-pany is integrating intoa broader programmeworth about £100 mil-lion over the next threeyears. The Northern Ire-land award will help todevelop a full opticalfibre telecommunica-tions network withinthe province, linkingwith the rest of theUnited Kingdom and offering et,,t!ss todatabases in continental Europe.

The total investment package will giveNorthern Ireland a world-beating telecom-munications infrastructure, creating oppor-tunities for high growth computing -basedindustries. and offering the business com-munity a vital technological and marketing.edge for the unified European Market after1992.

The technology will make it possible forbusinesses to operate from almost any-where. From 1992. this should shift North-ern Ireland into a strategic position for com-munications between Europe and America.

Northern Ireland. the only UK region in-cluded in the STAR programme, already hada head start with a highly developed BritishTelecom network. As a result, the STAR in-vestment there will now be used to bring infurther advances some five years ahead ofschedule. The infrastructure will be phasedin over the next two years.

Decentralized departments. Large or-ganizations are capitalizing on the technol-ogy that makes remote working possible,particularly for back office type jobs whereit is easy to monitor output.

British Telecom has demonstrated how

far the idea is possible by transferring its di-rectory assisted service to locations out ofLondon. many of them in the north of Eng-land. The company now handles NorthernIreland directory services from London-derry, and uses Portadown to deal withmany of London 's directory enquiries.

In the north of Scotland. an ambitious£16 million communications project in-volves a partnership between British Tele-com and the Highlands and Islands Devel-opment Board.

The Highlands and Islands Initiative will

Part of the new telephone directory enquiry service for London is located in Portadown.

put remote rural areason an equal footing withthe major cities of Eu-rope by providing tech-nology five years aheadof rural European rivals.The backbone of thescheme will be a fullydigital network that cantransmit and processeven kind of communi-cation at high speed.This will put businessesin peripheral areas suchas Lerwick. Wick andUllapool on an equalfooting with firms in the

large cities.The network is being enhanced by the

support of a newly formed British Telecomcompany. Net v. ork Services Agency Ltd(NSA). which will run a host computer forlocal businesses to develop and make use ofvalue-added and data services.

The revolution in the modem office hashappened as telecommunications respondsto the needs of business for fast, accuratetransmission of voice and data.

The catalyst has been the link -up of com-puting and telecommunications technology.For the past few years, British Telecom hasbeen setting up a fully integrated single dig-ital network (ism) to combine all the quali-ties needed to handle telephone data andother services.

This single public switched network willenable users to send data, text. facsimile.graphics and other features as easily asspeech.

An international service introduced in1989 links British Telecom's ISDN with simi-lar networks being introduced in the UnitedStates and Japan.

Establishing, an integrated digital net-work that offers 1sDN-based services is onlythe first step in a trend that will continue


LEADER

into the 2Ist century. It will lead to amerging of communication, computing.control, information and entertainmentServices.

Video conferencing. The inflexiblenature of the old analogue system madeit increasingly unsuitable for the newer,more specialized communicationsneeds. British Telecom responded bycreating a variety of specialist. cus-tomized networks and services. mostlybased on digital technology.

MegaStream and KiloStream providehigh -capacity digital private circuits,while VideoStream provides a nationaland international private video-confer-encing service. SatStream provideshigh-speed private links based on the ix-TELSAT and EUTELSAT ssstems, satellitelinks owned by partnerships betweencountries.

On a broader scale, high-speed datacommunications can be provided overpublic networks. The public data net -

SOLDERING WITHOUT CFCsA new soldering process. resulting from ajoint project between the British OxygenCompany 1130C1 and the Multicore Solders

ronmentally harmful CPC (cholorofluorocar-bon) solvents in the assembly of surfacemount printed circuit boards.

The process uses a controlled reactive at-mosphere to decompose into gases the or-ganic binder of a specially formulated soldercream. As it leaves behind only solder and aclean circuit board, there are no residues toremoved, which is normally done with sol-vents containing CFCs.

The soldering process may be carried outwith standard equipment used in printed cir-cuit board manufacture. including a conven-tional screen printer and a component pick-

and -place machine, along with a convey-orized oven designed for use with a com-bustible atmosphere, such as has been usedfor many y ears in the hybrid electronic cir-cuit industry.

Details from Multicore Solders Ltd.Kelsey House. Wood Lane End. HEMELHEMPSTEAD HP2 4RQ. Fax (0442) 69554.

NEWSCASTER IN YOUR POCKETThe world's first 'pocket new sflash service'has been launched by the BBC and MercuryPaging. It allows users of a new radio pagerinstantly to receive BBC teletext news -flashes on the unit's display screen anywherein the UK.

Via Merucry's Messenger One paging

work is to data what the telephone is tovoice. It provides a reliable and securedata transmission service nationwide.and it is the largest fully managed datanetwork in the United Kingdom. Theservice is linked internationally to morethan 120 network in over 80 countries.

Fibre optic technology-pioneered inEurope by British Telecom since1966-represents the future for high -

quality, high-speed communications.These hair -thin fibres of purest glass cantransmit huge quantities of informationon laser light pulses at phenomenalspeeds.

This is ideal for delivering vastamounts of uncorrupted computer data.high -definition television, and two-wayvideo. It also makes possible develop-ments such as home shopping or re-motely fed computer applications.

As technology evolves, costs willcome down. For example, the STAR part-nership in Northern Ireland should lead

g_L c_34111 =

Via'1-4 e v-1:P7)Si I .1

Enthusiasts hunting for bargains at the recentlyheld All Formats Computer Fair. Another ofthese fairs will be held on 9-10 June.Details from Bruce Everiss. Corner Cottage,Southam Street. KINETON CV35 OLN. Telephone(0926) 640137.

service. subscribers can be sent messages inthe normal way. and in addition can obtainautomatically updated news items coveringworld events. The average number of news -

flashes on BBC's Ceefax teletext service is12 a day. covering national and internationalnews.

The service will operate 365 days a year.with the BBC taking full news gathering andeditorial responsibility.

Although believed to be the smallest andlightest message pager in the world -itweighs a mere 113 g. including an AA typebattery said to last for up to three months innormal use - Messenger One can accept and

to significant reductions in the cost ofnew non -voice services. Special digitalequipment at 44 points across theprovince will allow advanced communi-cations from an ordinary telephone line.Specially switched transmissions downsimple telephone lines from computer tocomputer were previously availableonly to large businesses able to afforddedicated private circuits.

The extension of advanced data facil-ities into remote areas of Northern Ire-land will mean that electronic mail.Prestel and many computing processeswill be just as accessible in small townsas in Belfast.

The conversion from analogue todigital is the key that will unlock the fullpotential of teleworking. The public net-work will become a huge computer towhich everyone will have access.whether from office or home.

hold up to 16 alphanumeric messages to-talling nearly 2000 characters of text or data.This is typically the equivalent of 300words.

Woodlands. 80 \Vood Lane. LONDON W12OTT. telephone 081 743 5588.

PROTECTION AGAINST STATICELECTRICITY

A range of products to protect sensitive elec-tronics components against damage by elec-trostatic discharge is available from VitecComposite Systems. The products protectcomponents during manufacture. test, repair.transportation and storage.

For the service engineer there is aportable 'Safe Handling Area' consisting ofa mat packaged in a wallet. The mat is madefrom conductive scrim coated on both sideswith a dissipative material. One-piece con-struction ensures continuity over the wholesurface. It is provided with two pockets thatcan hold circuit boards. The mat may becomplemented by wrist straps and earthingcords and may be printed with the servicingcompany's names or symbols.

Vitec Composite Systems. Soudan St..Middleton. MANCHESTER M24 2DB.F.A.X 061 655 3361.

NEW INSTITUTION IS 25 YEARS OLDFollowing the amalgamation of the Institu-tion of Electrical and Electronics Incorpo-rated Engineers and the Society of Electron-

ELEKTOR ELECTRONICSJUNE 1990

ics and Radio Technicians, the new Institu-tion of Electronics and Electrical Incorpo-rated Engineers was launched in April. Thenew institution has 25 years experience sinceboth the forming bodies were founded in1965. The combined resources are to be usedas a springboard for the new institution.which is based at Savoy Hill House. London.

The new institution has over 27.000members. It will he by far the largest non -chartered engineering institution and thefourth biggest of the fifty or so nominatedbodies of the Engineering Council - bothchartered and non -chartered.

Speaking at the launch. the IEEIE's newpresident. major -general G.N1. Hutchinsonhighlighted three topics on which the institu-tion is placing particular emphasis during itsfirst year: the institution's links with indus-try: its work on continuing professional de-velopment: and the role of the IEEIE in theEuropean Community.

IEEIE. Savoy Hill House. Savoy Hill.LONDON WC2R OBS. Telephone 081 8363357.

FASTER PUBLIC DATACOMMUNICATIONS - BY RADIO

The world's first public data communicationsnetwork using radio links has recently begunoperating commercially in the UK.

Based on packet radio switching, it al-lows much faster access to computer sys-tems than dial -up modems. Typically, a retailpoint -of -sale credit card check or electronicfunds transfer can be made in seven secondscompared with existing telephone -basedmethods taking 30-40 seconds or evenlonger if the called number is engaged.

Dedicated to transferring data rather thanvoice communications, the Paknet high-speed radio -based network is owned equallyby Racal Telecom and Mercury Communica-tions. With advanced error detection and cor-rection techniques, it provides a standard ofaccuracy normally expected from expensiveleased telephone lines, at much lower cost.

At present the network covers the GreaterLondon area, but Paknet plans to have 100base stations in service by next March, cov-ering areas in which about half the popula-tion of Britain is located.

Paknet Ltd, Coombe House, CoombeSquare, THATCHAM RG13 4FJ, Fax (0635)72340.

IDENTIKIT FOR CARSThe concept of using a computer to build upphotofit pictures of wanted criminals hasnow been developed to identify vehiclesused in criminal activities such as abduction,robbery or hit-and-run traffic accidents.

I C1110111 (i

Known as Motorfit, the system has beenproduced by a member of the Dorset policeforce. It evolved as a result of incidents dealtwith by sergeant Simon Grantham whofound that there was a lack of support equip-ment to help witnesses in vehicle identifica-tion. His research that led to Motorfit wasfunded by the Home Office under a schemeaimed at helping police forces to researchand develop projects of benefit to the police.Sgt. Gramtham was helped by SouthamptonUniversity, several software companies andthe Dorset police's organization and plan-ning department.

The result is a system that is similar inconcept to the well -established photofit sys-tem, but instead of building up an image of aface, it helps to identify the make and modelof a car seen by a witness. A series of ques-tions are put to a witness and from the an-swers information is fed into a computer thatanalyses all the details and presents a fullcolour picture of the vehicle concerned on avisual display unit linked to it.

Sgt. Simon Grantham, Dorset PoliceHeadquarters, Winfrith, DORCHESTERDT2 8DZ.

NEW MARITIME DISTRESS SYSTEMG 0 -AHE AD

A new global maritime distress system de-veloped by the International Maritime Orga-nization in London has been given the go-ahead and will be introduced between 1992and 1993.

The new system, described as one of thebiggest advances in maritime communica-tions since the beginnings of radio, willmake use of satellite communications andother new technologies and will result in thegradual phasing out of radio telegraphy,which has formed the basis of the maritimedistress system since the early days of thiscentury.

The Global Maritime Distress and SafetySystem, or GN1DSS as it will be known, is de-signed to overcome the shortcomings of thepresent system, which is a combination ofradio telephony and morse with a required

range of only 150 nautical miles. Currently,reception can be affected by bad propagationconditions and other factors, and ships stillvanish without trace because a distress mes-sage is not sent in time or not received.

Before the end of this century, it will becompulsory for all ships to carry equipmentthat will not vary according to the size of theship, as now, but according to the area inwhich it operates. GMDSS will divide theearth into four areas: Area 1 is within therange of VHF coastal radio; Area 2 is withinthe range of coastal MF radio; Area 3 iswithin the range of INMARSAT satellites thatcover the whole globe except for small areasof navigable water in polar regions; andArea 4 covers the remaining sea areas.

Equipment that will be required byGMDSS includes satellite communicationsthat will automatically send a distress mes-sage giving the ship's name and position atthe touch of a special button, digital selec-tive calling (Dsc), NAVTEX, radar transpon-ders and satellite emergency position -indi-cating radio beacons (Emus).

International Maritime Organization, 4Albert Embankment, LONDON SE1 7SR.

AGREEMENT ON HDTVHigh -definition television-nurv-expertsrepresenting 16 countries from Europe, theAmericas and Asia Pacific meeting underthe auspices of the CCIR (International RadioConsultative Committee) in Atlanta lastMarch have agreed on additional parametersfor the development of HDTV standards.

There have been important developmentsin HDTV around the world in the past fewmonths and the CCM is building on these de-velopment with the view of establishing rec-ommendations for standards that meet therequirements of a broad range of broadcast-ing and non -broadcasting applications.

During the meeting in Atlanta, in an ef-fort to achieve a global consensus on a fullset of parameters for a single world-wideHDTV studio standard, new approaches weredeveloped that will enhance the prospectsfor complete harmonization of HDTV.

Significant work remains in the defini-tion of a reference system and interfaces, aswell as application -specific standards forrecording, transmission and emission. Stud-ies are required in the areas of opto-elec-tronic conversion, improvements in colourrendition beyond those achieved with the in-terim primaries, and in the use of linear andquasi -linear derivations of luminance andcolour difference signals.

More details from the Press Office, Pub-lic Relations Division, International Tele-communication Union, Place des Nations,CH -1211 GENEVA 20.

ELEKTOR EI.E(7TRONICS JUNE 1990

PACS VPCs A

\nigFACID COWPA L

FO2!ISLES

M. Brochand F6BFX and G. Warin F6DCK

The authors, two dyed-in-the-wool radio amateurs, describe howthe facsimile decoder we published early last year for Atari and

Archimedes micros can be adapted to run on EGA -based IBM PCsand compatibles. In addition, they present the required software,PCFAXPC, which, as an extra feature, supports fax transmission!

HardwareThe decoder described in Ref. 1 requires afew minor modifications to enable it towork with an IBM PC. Fortunately, mostmodern PCs accept TTL levels at their RS-232 port, so that the connection between itand the fax decoder need not be morecomplex than when an Archimedes orAtari computer is used. Apart from itssimplicity, the advantage of the RS -232link is that it ensures the correct pulsetiming, irrespective of the clock speed ofthe PC. In fact, the sampling frequency ofthe fax board (determined by a quartzcrystal plus associated 4060 divider) is indirect relation to the bit rate set on theRS -232 port.

To ensure perfect synchronization, thefax board also provides the central clockin the transmit mode. This clock,2.4576 MHz, allows a bit rate of 19,200 persecond on the RS -232 port. Other quartzcrystals may be used (e.g., 4.9252 MHz),provided that the clock at the input of the

=4 in -rive A iS EEZ.:14A1

EYE

4040, pin 10, is 19,200 Hz to give a samp-ling rate of 19,200/12=1,600 per second.Hence, the 2 -lines -per -second fax stand-ard would require an image resolution of800 pixels per line. Since the EGA cardoffers only 640 lines, 160 are simply ig-nored.

When the 2.4576 MHz crystal is re-tained, connect the 4060 to the 4040 viapin 6 instead of pin 14. This modificationis not required when the 2.4576 MHz crys-tal is replaced by a 4.9252 MHz type.

The authors found that the centralVCO frequency of the decoder must not beset too high to keep it within the pass -band of communications receivers. Tocentre the pass band at 1800 Hz, changethe following component values:R2=100k, C2=22 nF and C4=10nF. Alsochange I'4 to 4k7, and R14 to 470 ft

It is worth while to change P4 to apotentiometer fitted on the front panel ofthe decoder to enable the adjustment to bechanged in accordance with the standardof the received signal.

!E:a

. ET;ffa.

,2,c

E.7 5:11p:E,6

efrO

1- /- I I 1 I 1.4.4.11.1 I I -1.-rtaiLLIPiiiI I I 1~1. I I

i. I r I I.. 1 I-1,0I I. t Girl

The Type NE367 synchronization de-tectors are no longer used and may beomitted, along with their associatedpassive parts R7--Rit, C7-04, Di and D2,P2 and 1'3. The 4011 (ICs) must remain onthe board, however, since gates N2 and N3remain necessary.

Using the decoder modified as de-scribed above, the authors have achievedexcellent reception results with variousfacsimile stations, including meteorologi-cal and press photo services. In all cases,the LED -based read-out (described as anoption in Ref. 1) proved an invaluabletuning aid.

The PC connectionReceive modeOnly two wires are required:

around of the decoder is connected topin 7 (GND) of the 25 -way D -connectorat the PC end (or pin 1 of the AT -style9 -pin version);the signal output of the decoder (pin 10of the 7-1150) is connected to pin 3 (RxD;received data) of the 25 -way D -connec-tor at the PC end (or pin 2 of the AT -style9 -pin version).

When a 25 -way D -connector is used, con-nect pin 4 (RTS) to pin 5 (CTS), and pin 8(DCD) to pin 20 (DTR) to make it perma-nently high. The connections for the 25 -way as well as the 9 -way D -connector areshown in Fig. 1.

The program defaults to the use of serialport CONI1:. To run the program withCOM2:, actuate either NUM LOCK orCAPS LOCK and exit the welcome screenby pressing the '2' key. The PC may run at4.77 MHz or S MHz.

Transmit modeIn this mode, the datawords supplied tothe computer at a rate of 1600 per secondare ignored and serve to generate hard-ware interrupts. Each of these is acknow-ledged by the CPU sending out atone-via the PCs internal loudspeaker-whose frequency corresponds to therelative intensity of the currently ad-

ELEKIOR ELECTRONICS JUNE 199U

FACSIMILE INTERFACE FOR IBM PCs AND COMPATIBLES 1

Fig. 1. Connections between the faxdecoder and the RS -232 input on the PC.

dressed pixel on the screen. The necessaryconnection between the PC and the micro-phone input of the transceiver or trans-mitter is shown in Fig. 2. Do not omit the100-nF capacitor since one terminal of theloudspeaker in the PC is usually at +5 V.Obviously, the transmit mode works onlywith the decoder board switched on.

Fax transmission is simple: load a pic-ture from disk and press the (for 'trans-mit') key. The image is sent following atone that allows the receiving station toget synchronized.

Control softwareThe control program, FAX EGA22, writtenin Turbo Pascal 4, handles the receive aswell as the transmit mode with the aid ofPC hardware interrupt OCR.

The receive mode brings you picturestransmitted by radio amateurs, VLFutility stations, and meteorology servicesincluding low -orbit satellites. The .DOCfile provides all the necessary backgroundinformation on the program (produceyour own copy of the manual by sendingthe file to your printer).

The software is contained on two dis-kettes. Disk ESS119-1 contains:

the control program, FAXEGA22.EXEa video driver, EGAVGA.BGItwo example picture files.

Disk ESS119-2 contains three furtherexample image files of 112 Kbytes each.

The PCFAXPC program can be used onany IBM PC or compatible fitted with acolour or monochrome EGA card. Con-trary to what might be assumed, themonochrome mode is likely to give the

Fig. 2. Fax transmit connection.

Screen photograph of a weather chart received with the fax decoder.

best results since it provides up to 14 le-vels of grey. In the EGA colour mode, upto 11 shades are available of a single col-our. Owners of a VGA -based computermust use a utility program (supplied withyour computer or with the VGA card) toswitch to EGA emulation.

Controls summaryThe help menu is accessible via the ESCkey. Press it again to return to the pro-gram. The functions of the keys used tocontrol the program are as follows:

F1 to Flo allow the grey levels or the col-our shades to be changed within a certainrange. Use F5 for monochrome operation.

DEL clears the screen without changingthe cursor position.

HOME clears the screen and moves thecursor to the top line without changing itshorizontal position

PgUp moves the cursor to the first linewithout changing its horizontal positionand without clearing the screen.

moves the cursor about 10 mm to theleft (use this function to centre the imageduring the run-in and sync periods).

-, moves the cursor about 10 mm to theright (use this function to centre the imageduring the run-in and sync periods).

CTRL +- moves the cursor about 1 mm tothe left.

CTRL moves the cursor about 1 mm tothe right.

M writes the current image to disk. Afterpressing NI the screen is cleared and youare prompted to enter the file name. Thefile is saved and the image appears again.

W retrieves an image file from disk. Afterpressing W you are prompted to enter thename of the requested file. Reception isblocked once the image appears on thescreen. Press Q to receive a new image.

1, 2, 3 display, 2, 4 or 6 fax lines respec-tively on one picture line.

END exits PCFAXPCQ blocks reception and allows an image tobe frozen without disconnecting the inter-face.

S resumes reception after Q or W.

P writes lines from the right to the left (forpress photo stations).

C writes lines from the left to the right (formeterological stations).

I creates a horizontally mirrored image.Useful as a correction to swap the P and Qmodes once the image is on the screen.

T switches to transmit mode.

D go to DOS without leaving the program.

Example image files andPC Paintbrush

The program comes with a number ofexample files that contain press photo-graphs and weather charts. These filesallow the quality of the images to begauged before commencing the construc-tion of the interface. To load one of theseexample images, leave the welcome menuby pressing any key except ESC. Next,press W and enter the name of the re-quested file.

Note that the file load and displayoperations take a while, so do not pressany keys in the mean time.

The transmit routine of the PCFAXPC pro-gram accepts image files made with thewell-known drawing program PC Paint -Brush and the associated image captureutility, Frieze. These powerful programsallow you to design your own images orcapture existing graphics images.

Reference:I. Facsimile interface for Atari ST (andArchimedes). Elektor Electronics January1989.

FLEKTOR ELECTRONICS .JUNE 1990

10

!PCTRONIC WADG. Boddington

For testing power supplies and transformers, an appropriate,preferably adjustable, load is indispensable. Often, a number ofinterlinked high -wattage resistors are used for this purpose, but

that is not alway satisfactory. feasible or safe. The electronic loaddescribed here is a much more flexible and suitable solution.

The load is based on a number of powertransistors. The output current, which isthe sum of the collector currents of thesetransistors, is converted into heat that islost by convection and radiation through asuitable heat sink.

The base current of the transistors is ar-ranged at a value that results in the re-quired level of emitter -collector current.Since the base -emitter voltage that deter-mines the base current of a transistorvaries with temperature (=-. 2-8 mVPC), anopamp is used to iron out any consequentvariations of the base current.

The end result is an adjustable loadwith a 'resistance' value ranging from al-most zero to infinity and a thermal ratingthat depends solely on the power transis-tors and the manner in which these arecooled.

The load may operate in either the con-stant -current mode or the constant -resis-tance mode. In the first, the current re-mains constant irrespective of the appliedvoltage, while in the second it is directlyproportional to the applied voltage.

A waveform generator (triangular, si-nusoidal and rectangular) enables the 're-sistance' to be modulated.

Circuit descriptionEach of the power transistors, Ts -T12, inFig. 1 can draw a collector current of up to2 A with an appropriate heat sink. Resis-tors R24 -R33 provide a measure of currentfeedback, which ensures equalization ofthe currents drawn by the individualpower transistors.

Resistance simulationEach group of power transistors, T3 -T7

and Ts-Ti2 respectively, is driven by onehalf of dual opamp IC2 via a driver transis-tor, Ti and T2 respectively. The driver isnecessary since the opamp can not providethe required current by itself. Note that thetwo groups are connected in parallel, since

Dissipation: 300 \V (up to 1 kW withforced cooling)

Adjustable from 0.25 S2 to 00Voltage range 4-60 VMaximum current 20 AOperating modes: constant current

and constant resistanceInternal or external modulationInternal waveform generator

(triangular, sinusoidal orrectangular)

"U" and "T" are strapped togetherplained later.

The inverting input of the opamps isconnected to the emitter resistor of the firstpower transistor in each group. The non -inverting inputs are connected in paralleland linked to the pole of switch Sib. Thispole receives one of four different controlsignals via the switch contacts.

When St is in position 1 (7), terminal"P" carries part of the voltage, as set by P2 -R9, that exists between terminal "L.:" andearth. The opamp tries to reduce the po-tential difference between its inputs to vir-tually zero. It will therefore increase thebase currents of the power transistors, andthus the load current, until the voltagedrop across R24 (RN) and the input voltageset by P2 are equal. When the input voltagerises, the potential at the non -inverting in-puts, and thus the load current, increases.This means that the circuit behaves as a re-sistance, the value of which may be setwith the aid of P2.

as ex -

Modulation and constant currentOpamps 10,3 and ICib form a simple

function generator that produces rectangu-lar waveforms when St is in position 2 (8)and triangular waveformslvhen the switchis in position 3 (9). The frequency is ad-justable over the range 5-50 Hz by P3.

The signal from the generator is ampli-fied in ICid and fed, via SIB and "P", to the

non -inverting inputs of control amplifierIC2 where it serves as reference voltage.Since this potential is no longer dependenton the input voltage to the load, an in-crease in the input level no longer leads toa higher load current. In fact, if the signal,whether triangular or rectangular, is usedas the control signal, the circuit functionsas a modulated constant -current source.

The load current is modulated in thesame way as the control signal. The gain ofICid, which determines the depth of mod-ulation, is set by P1.

Potentiometer P4 enables an offset to beadded to the control sign al. This offsetmakes it possible to shift the modulationlevel with respect to zero. In other words,Pi sets the level by which the currentvaries, while P4 determines between whichvalues modulation is effected, for instance,between 2.5 A and 3.0 A. This assumes, ofcourse, that the unit or device under testcan provide currents at those levels.

External modulationOpamp ICic serves as an inverting, unity -gain amplifier. Its output signal is availableat contact 4 of Si. It may be fed with an ex-ternal modulating signal via Kt. The inputmust be between 0 V and +10 V. The con-trol characteristic may be set between3 AN and 1.5 A /V for each power transis-tor. If, for example, the voltage at Ktchanges by 100 mV, the output currentvaries by 3 A with Pi set to maximum andby 1.5 A with P1 set to minimum.

Constant -current operationWith Kt connected to ground, it is possible,with the aid of P4, to arrange a constantcurrent to flow through the power transis-tors.

Lower loadsIt is not necessary to use all ten powertransistors: the circuit operates perfectlywell with just one, but the permissible loadis then, of course, reduced to 1/10. If the


ELECTRONIC LOAD

POSITIONS OF SWITCH S1

1 (7) Resistance, adjustable with P2.

2 (8) Internally -modulated constant -

current source (triangular).

3 (9) Internally modulated constant -

current source (rectangular).

4 (10) Constant -current source,

adjustable with Pi; may be

externally modulated via

POTENTIOMETER FUNCTIONS

Pi Sets depth of modulation.

P2 Sets value of resistance.

P3 Sets modulating frequency.

P4 Sets constant -current mode or

modulation level.

group Ts - T12 is omitted, T2, C4, R29-R.13and R19-R23 may also he omitted. Themaximum load current is then 10 A.

Construction and alignmentThe load is best built on the PCB shown inFig. 2. This figure does not show the partof the board for power transistors Ts-T12and associated components since this isidentical to that for T3-T7. Before any startcan be made with populating, the boardmust be cut into four with a fine hacksaw.

Screw each of the two long parts to a5 mm thick aluminium bracket. Since thecollectors of the power transistors will beat the same potential, there is no need forinsulating washers, provided that the heatsinks and aluminium brackets are isolatedfrom the enclosure.

Do not fit the emitter resistors too closeto the board, because even in normal oper-ation these get fairly hot. The same appliesto R22 and R23.

The choice of enclosure depends in thefirst instance on the heat sinks used. Therequirements of these are fairly stringentbecause they have to dissipate some300 W. The dissipation may be increased to1 kW if forced cooling is used.

The only calibration is in the provisionof a scale for P2. For that purpose, a labora-tory -type power supply with variable Out-put and capable of providing an outputcurrent of at least a few amperes is re-quired. Measure the voltage and currentfor a number of positions of P2 and calcu-late the corresponding resistance. The re-sulting scale is linear for input voltagesgreater than about 4 V.

Ri

K1

0R7

R2

10

RS

IC1 = LM324

5IC1b

R3

EMI

P3 b IWO OM100k

R4

R5 IC1a

CIDI

6

Ca

e 10k

bra R12

P4

RIO

100k12

ELMICId

13

R13

4

II R14P1

100k

0

R15

a 012V

709

1820

ID

R9

C2

713n 1kb

P2

ENO

R22...R33 = 51.173...T12 = 2N3055

95-242 - 11

a

0

O

Fig. 1. Circuit diagram of the electronic load.


1151-TEST MEASUREMENT

PARTS LIST

Resistors:RI .R2.R5,R7,R8,R14,R15 = 10 kR3,RIO-R13 = 100 kR4 = 47 kR6= 1k5R9 = 6k8R16,R18.R19.R21 = I kR17,R20 = 100 S2R22.R23 = 22 0, 5 WPI .P3 = 100 k. linear potentiometerP2 = I k. linear potentiometerP4 = 10 k, linear potentiometer

Capacitors:Cl = 1µ5C2 = 470 nC3,C4 = 390 pC5.C6 = 100 nC7 = 10 µF. 16V

Semiconductors:D1 = 3V3, 400 mWT3-T12 = 2N3055ICI = LM324IC2 = LM358

Miscellaneous:K1 = PCB mounting socketS1 = 2 -pole, 6 -position rotary switch2 off aluminium angle bracket, 5 mm

thick2 off heat sink, SK42, 75 mm, 1.5 KAV(Dau UK Ltd - 0243 553031)

+("/" 0 n 0 s R20 0 o 6 .. .1'44

(-1-1 ®IIS R81----;0 0\... -/ R21

ID 3 R2 P30 K1 R7 in R10 0- 823 C4 E a

"fcli-

0 C D r, 1R11 R3T2

(.3C2 0 a,u02. 0 3 D .0 810 R4

Ti C U-

D I 812 RS_ 0 b0

0 0- 822 ko;-7c a

1 TONr c -a -blc R13 RB

0I R17 T bo o o p4 R14 9 Di

: + 0 1

0 0 0 P18 0 S 0 815g 1 Lli.. 0 10 0 010-11-0000tvl L K y©0 ./. P1Lb- a -c-i Cl Si

L U K 824 825 0- -0 0] 827 [0 0-1 828

1.4)

odr)

CS) (IN)T3 T4 T5 T5 T7

829 93D 831 1--0 0-1 832 0- 833 I.°.1-0

ell

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I

)\

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I0II T© T9 T10 T11 T12

Fig. 2. Printed -circuit board for the electronic load. Note that the part for the second group of power transistors is not shown.


Fit the potiometers and switch onthe front panel of the enclosure to-gether with two heavy-duty, spring -loaded, insulated terminals. Con-nect points "U" and "T" to the posi-tive terminals, and the earth pointsto the negative terminal.

To ensure that sufficient currentflows through the power transistors,the load needs its own 12 V powersupply, for which a simple unit witha 500 mA transformer and a Type7812 voltage regulator will do fine.

Limiting valuesThe maximum values the powertransistors can tolerate are not thosefound in their data sheet, that is, 60V, 15 A, 115 W. Instead, the maxi-mum dissipation is determinedfrom the safe operating area (SOA)shown in Fig. 3. This shows that themaximum collector current de -

100

I

V

sa.LIa0Izo'

'.1....1

O

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'

15

TEMPERATuR E (Tc I 25. C(CURVES MUST OE DERATED

UNEARLY WITH INCREASE Li --._._,_.IN TEMPERATURE( -'== ilWNW, 3.11tE-11111 -

:CONTI NU US=........, PULSED _ = --.=-

__ ii=NtliMiii_ra_..,

_____ _____ _ __" -'' _-i

- r62%',....=-- 250 µ>t

--,.. -,,,.., 1.1ii.

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----- C, -smna-

-:-t4 ,.....

-Li&- FOR SINGLE =ril MOHR EPETITIVE ... = _ - ..PULSE . = ..

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r =....

I 3 .1911191 :== --. ..... . . I -

= . -- --- V,..,01/12.21 EC V (24.1:555 :7 . . -- -1 i ,===-.1-

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COLLEC TOR- TO-EadiT TER vOLTAGE(VcEl- V 32C5..23.00.52

900042-12

creases with a rising collector -emitter volt-age. Conversely, when a current of 15 Aflows through the transistor, its collector -emitter voltage should not exceed 8 V. It isimperative that at no time the C -E voltageexceed the limit for a given current andvice versa. But that is not all. The SOAcharacteristic in Fig. 3 refers to a maxi-mum dissipation of 115 W at a case tern -

Fig. 3. Safe operating area of Type 2N3055 transistor.

perature of 25:C. With rising temperature,the dissipation is degraded at a rate of 0.65IV/°C. This means that at a case tempera-ture of 80 'C the maximum dissipation isonly 80 W and at 140 it is only 40 W.

The design of the load allows for eachpower transistor to tolerate a current of upto 2 A, so that the input voltage can go upto close to 60 V. If that is not sufficient, the

ELECTRONIC LOAD kg'D

2N3055 transistors should be re-placed by types with a higher rating.

FinallyThe load is intended for use with di -red currents, but alternating currentsmay be used by inserting a bridgerectifier between the current sourceand the load. The rectifier must, ofcourse, be rated at the maximum cur-rent through the load.

The internal resistance, Ri, of astabilized voltage source is calcu-lated from:

Ri= AUnz/

where AL/m and Alm are the changesin modulating voltage and currentrespectively. In the "controlled con-stant -current" mode, the current isset with Pt and P4, while the changein voltage at the output terminals ofthe load may be measured with an

oscilloscope.The internal generator is also useful for

determining whether the internal resis-tance depends on frequency.

In the "preset constant -current" mode,it is possible, for instance, to discharge abattery at a preset current. Measuring theexact capacity of the battery at a number ofdischarge currents is then a simple matter.

SATELLITE COMMUNICATIONS ON THE ROAD

The car glides silently through the sim-mering desert air, heat waves -and sand ris-ing in its wake. A few miles behind thecar follows an unmarked blue truck.

In the back seat of the car. a manreaches for the telephone at his side. Hespeaks a couple of words into the mouth-piece. and within a few seconds he is talk-ing to a banker in London. The connexionis crystal clear.

It sounds easy, but behind this simpletelephone call from the LISA to London is

a complex array of telecommunicationstechnology. The call is relayed from thecar via a mobile radio link to the nearbytruck. where it is patched into a satellitecommunications terminal. The call isbeamed up to a satellite orbiting highabove the earth's equator. then down to anearth station in Great Britain. where it isin turn connected into the British publictelephone network.

All this is made possible by a newtechnology pioneered by the US electron-

. I

ics manufacturer \ iagnavox. The truck isactually a complete mobile communica-tions centre built by Magnavox to providehigh -quality communications on a world-wide scale. The stem is especially use-ful for remote locations not covered bycellular networks or other mobile tele-phone services.

Further information on this systemfrom Magnavox. 9 Brandywine Drive,Deer Park, NEV YORK 11729. phone1516) 667-7710, fax 15161667-2235.

-e 1.ta.;-.2..aA crererca, M, LS69ce s711


g.=.1. 14 T -e ete,a 3 a =Ate/T" --s zir:*ac.f 3 Vey, .--ts rl,riC

msceze re-,:;?. V..e.14-:

The Ce.".Z"7-:-= rr ;c.:_7-.. :L: . La'5

F))L

TOY ONBOSC0

_J

This mains -powered stroboscope, designed by ELV, offers a widerange of settings as well as an external trigger feature so that it can

be used as a slave flash unit.

A stroboscope is an instrument that pro-duces light flashes with an intensity fargreater than may be obtained with com-mon light bulbs. The flash is a brilliantburst of light produced as a result of firinga gas (usually xenon) in a glass envelope,by means of a high -voltage pulse. Sincethe rate of the light flashes can be control-led accurately, moving objects illumi-nated by the stroboscope appear to standstill. This effect is obtained when the flashrate of the stroboscope corresponds to theperiod of the movement of the illuminatedobject. Useful applications of a strobos-cope include the visual examination of ro-tating or relatively fast moving objects orparts such as flywheels and camshafts.Among the less useful, but certainly inter-esting, applications are lighting effects ontheatre stages, on dancefloors, in disco-theques and window sills.

The stroboscope presented here hastwo basic modes of operation:

as a continuously operating stand-alonelight effects unit with an adjustable flashrate of 0.5 to 5 flashes per second (= 30 to300 per minute);as a slave flash unit with an adjustabletrigger delay of up to one second. In thismode, the stroboscope is triggered by alight flash from another unit. After theset delay, the slave stroboscope producesits own flash. Exciting lighting effectsmay be obtained by using a single(mother-) stroboscope and an array ofslave units, each with its own triggerdelay.

Operation and controlsThe stroboscope is simple to use since thecomplete circuit is contained in a singleABS enclosure that can be pluggedstraight into a mains outlet.

Operating the TRIGGER push-button inthe lower right-hand corner of the frontpanel switches the unit from stand-alone(continuous) operation to slave operation,or vice versa (toggle function). A greenand a red LED indicate the respectivemodes of operation.

The functions of the FLASH RATE andDEL11 controls are self-evident: both arebased on potentiometers and thereforeoffer a continuously variable setting. Thelight sensor located in the lower left-handcorner of the front panel has a lens to boost

ELV Mains Stroboscope

its sensitivity. This sensitivity, and that ofthe associated circuitry, is such that evenrelatively weak flashes, or flashes from adistance of 10 m or more, are reliably de-tected to enable the stroboscope to be trig-gered. Although the unit is largelyinsensitive to light from normal bulbs orsound -to -light units, two points should benoted in relation to the external triggeringmode:

the sensor must not be illuminated directby a constant light source;flickering luminescent tubes may causeerroneous triggering owing to the lightpulses they emit.

The shape of the reflector behind thexenon tube ensures a light distributionthat is particularly suitable for effects ap-plications. Since a straight xenon tube isused, the reflector is L-shaped rather thanspherical as in, for instance, a torch.

Circuit descriptionPower supply and flash tube circuitThe power supply of the circuit consists ofmains transformer Tri, diodes DI -D6 and

capacitors 0-C3. Note that although amains transformer is used, the circuit isnot isolated from the mains: a path existsvia RI, R2, DI, D2 and C2. This means thatthe circuit must never be used when it isnot enclosed in the ABS case suppliedwith the kit. After removing the strobos-cope from the mains outlet, always wait atleast 30 s before opening the enclosure soas to allow the flash capacitors to get ridof their lethal high voltage.

Diodes D3 -Do and capacitor C3 pro-vide voltage regulator ICI with its directinput voltage. The output voltage of I0 is15 V.

The mains voltage is applied to a two-phase voltage doubler, D1 -0 -D2 -C2, viapower series resistors RI and R2. The flashvoltage of about 600 V exists between the+terminal of CI and the -terminal of C2.The xenon tube, Hi, is fired by a high -fre-quency, high -voltage burst at its triggerelectrode. This burst is provided by thedischarging of C4 across the primarywinding of the firing transformer, Tr2.Voltages in excess of 10,000 V occur at thispoint.

The firing capacitor, C4, is charged viaR3a, Rah and the primary winding of Tr2.When thvristor Thy] is fired via R4, it con-ducts and enables C4 to be discharged viathe primary winding of Tr2. The voltageinduced in the secondary winding firesthe xenon tube. Since the xenon gas in thetube conducts during the flash, 0 and C2are rapidly discharged. The energy storedin these capacitors is thus converted tolight_ When the high voltage has fallen toabout 100 V, the xenon tube turns into ahigh impedance again, so that the buffercapacitors can be charged again via RI andR2. The firing capacitor, C4, is alsocharged again via R3a and R31-.. The valuesof the components used in the firing andsupply circuit around the xenon tube aresuch that up to five flashes per second canbe produced_

Continuous operation and mode selec-tionWhen the stroboscope is used in the stand-alone mode (continuous operation), thefiring pulse for thvristor Thyi is providedby an oscillator formed by IC3c-IC3d. Thisis a fairly conventional two -gate stablemultivibra tor with potentiometer Rio ac-ting as an output frequency control. Resis-tor R17 may have to be adapted to ensure


111REMOTELY CONTROLLED STROBOSCOPE

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Fig. 1. Circuit diagram of the stroboscope. Note that there is no electrical insulation between the circuit and the mains.

the highest flash rate of 5 per second withR19 turned fully counter -clockwise. Whenthis highest flash rate is exceeded, in-crease R17 to 120 ka When it is too low,change R17 to 82 kcl. When R19 is turnedfully clockwise, the flash rate should be0.5 per second, i.e., one flash is producedevery two seconds.

The oscillator output signal is appliedto input pin 5 of NAND gate IC4d. An-other NAND gate, IC4a, is provided withexternal trigger pulses. The bistable com-posed of ICSc-IC4c and push-button Tatdetermines whether the oscillator outputsignal or the external trigger output volt-age is passed to IC4d. Each time the push-button is pressed, the selection changesbetween IC4b (continuous trigger) andIC4,3 (external trigger).

A differentiating network, C14 -R25,changes each level transition at the outputof IC -id into a positive -going needle pulse,

which is fed to inverter IC5d. The two par-allel -connected inverters that follow IC5d,IC5c and IC5i, make this pulse positiveagain for firing Thyt via R4.

External triggerWhen photodiode Di detects externallygenerated light flashes, amplifier IC -2.csupplies a positive output pulse, which isconverted into a negative -going rectangu-lar signal by comparator IC2b. This signalsets bistable 1C3a-IC3h via pin 1. The out-put, pin 4, changes from high to low sothat buffer pair IC5a-IC5b supplies a posi-tive pulse. This results in Cu beingcharged via potentiometer Rh. When thedelay has lapsed, comparator togglesand provides IC-ta with a negative pulse.Provided the stroboscope is in the con-tinuous trigger mode (selected by Tat),the pulse obtained from the external trig-aer circuit causes the xenon tube to fire as

described above. It also causes the rapiddischarge of Cto via RI5 so that bistableIC3a-IC3b is reset via its second input,pin 6. The result is that 01 is rapidly dis-charged via IC5a-IC5b and D7 to preparethis circuit for a new trigger pulse. Theshort delay introduced by Ris-Cio is re-quired to prevent the stroboscope beingtriggered by its own light flash.

The flash sensor circuit around photo -diode Du has an automatic sensitivitycontrol function to cope with changingambient light conditions. Transistor Tiprovides Dit with a current that causesthe diode to drop about half the supplyvoltage. This voltage is fed to IC2a via R12for comparison with a reference level ap-plied to pin 2 of the opamp. When theambient light intensity increases, the volt-age across Dtt drops. The current source,T1, and the opamp, IC2a form a controlloop that ensures a point of optimum se -1


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COMPONENTS LIST

contents of kit supplied by ELV France

Resistors:1 100L2

5 1k0R6

R4:R7;f111;R23;R24

2 2k7 5W R1:R23 10k RB;R10;R131 12k R181 47k R154 100k R9;F112;R17:R212 270k R3a;R3b4 1M.O. R14;R20;R22;R252 100k potentiometer Ri6:R19

Capacitors:1 120pF1 1 nF

2 lOnF1 15nF 400V1 47nF1 luF 16V4 1011F 16V

2 100F 350V1 1001.1F 25V

Semiconductors:1 78151 LM3241 CD40111 CD40491 CD40932 BC5481 BC5581 TIC1062 1N40076 1N4148

1 LED 3mm red1 LED 3mm green1 BPW34 with lens

C9C8

C13;C14C4

C6

Ci0C5;e7;Ct1;C12C1:C2C3

1C1

1C2

1C4

1051C3

T2;T3T1

ThyiDi ;D2

D3;D4;05;015:

0809011

Miscellaneous:1 mains transformer: Tri

sec. 15V/100mA1 tube firing transformer Tr21 fuse 100mA slow Sit1 xenon flash tube Hi1 push-button switch Tai2 PCB -mount fuse holder1 reflector12 solder pin4 PCB spacer 30 mm1 M3x15 mm screw2 M3:420 mm screw4 M3:55 mm screw11 M3 nut2 solder eye 3.2 mm30 cm 0.22 mm2 flexible wire10 cm 0.75 mm2 flexible wire15 cm silvered wire2 printed -circuit board1 ABS enclosure with moulded mains plug

:c 2. Track lay -outs and component overlays of the two printed -circuit boards.


REMOTELY CONTROLLED STROBOSCOPE

Fig. 3. Construction of the reflector,which is secured to the PCB with the aid ofthree M3 screws. These also serve to carrythe xenon tube voltage.

sitivity of the photodiode in relation to theambient light intensity.

ConstructionThe circuit is constructed on two printed -circuit boards -see Fig. 2. Construction ismostly straightforward on the electronicside; the following descriptions thereforedetail mainly certain points in the mech-anical work.

Start the population of the flash tubeboard with the nine wire links. Fit the twopotentiometers at the track side of theboard, and secure them with the nuts pro-vided. Push-button Tat is mounted on twosolder pins to enable it to protrude fromthe from panel. The reflector is fitted withthe aid of three screws as shown in Fig. 3.The cathode (marked by a black ring) andthe anode of the flash tube are connectedto solder eves fitted on M3 screws. Nutsare used to provide the correct mountingheight of the reflector.

The high -voltage transformer, Tr2, ismounted on to the board as indicated bythe component overlay. The firing voltageis carried by the flexible, insulated wire atthe top of the transformer. Carefullyremove the insulation material over a dis-tance of about 12 mm at the end of thiswire. Wind this wire end around thexenon tube, roughly at the position indi-cated in Fig. 3, and join the turns of thewinding by soldering rapidly and care -

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Fig. 4. Bend one pin of the high -voltagepulse transformer and solder it as shown.

Fig. 5. Completed flash tube board (left) and transformer board (right).

fully. This completes the construction ofthe flash tube board.

It should be noted that ELV may sup-ply a high -voltage transformer whoseconnections are different from the type forwhich the PCB was originally designed.Fortunately, the replacement transformeris readily fitted -see Fig. 4. Solder a shortflexible wire to the high -voltage outputterminal which is at the top of the trans-former after this has been fitted on thePCB. The other end of this wire is securedto the flash tube as described earlier.

The construction of the transformerboard is straightforward and requires nodescription other than that power resis-tors RI and R2 are mounted at a height ofabout 10 mm above the transformerboard.

The two boards are connected with 6flexible wires between the correspondingpoints 'a' to 'f'. Connect the photodiode tothe circuit with two short lengths of wire-the electrical orientation is marked onthe component overlay (look at the line inthe box printed on the PCB: it marks theanode of the BPW34, which is also visibleas a kind of line in the photodiode).

Next, fit the completed boards into theenclosure. Use two short lengths (approx.50 mm) of insulated 0.75 mm- wire to con-nect input terminals ST1 and ST2 to themoulded mains voltage (live and neutral)pins in the enclosure. The two boards arestacked and secured to the bottom half ofthe enclosure with the aid of fourM3x35 mm screws and associated 30 -mmlong spacers. Each of the four screws isinserted into a corner hole of the flash tubeboard. Next, fit the spacer, and insert thescrew into the corner hole in the transfor-mer board. Place this 'sandwich' into theenclosure and secure the screws in themoulded threadings.

To prevent the reflector or other partsof the circuit being touched while the stro-

boscope is operating, the rectangularclearance for the xenon tube is covered bya 2 -mm thick perspex plate, which is se-cured to the inside of the enclosure with alittle glue. Also with safety in mind, makesure that the LEDs and the mode controlpush button, Tat, are mounted at a heightthat enables them to protrude I to 2 mmfrom the front panel; they must fully oc-cupy the relevant holes so as to preventany likelihood of the circuit beingtouched.

The spindles of the two potentiometersare cut to a length of about 10 mm abovethe front panel. Finally, screw the top partof the enclosure to the bottom plate, fit thecollet knobs on the potentiometer spind-les, and fit the coloured caps.

A complete kit of parts for the strobos-cope is available from the designers'exclusive worldwide distributors (re-grettably not in the USA and Canada):

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


NM MASTER KEYBOARD

PART 1: CIRCUIT DESCRIPTION AND CONSTRUCTION

D. Doepfer

The multi -purpose MIDI controller described here is based on amicrocontroller and a special MIDI keyboard processor. the E510.

The circuit is ideal for upgrading many types of existing keyboard,synthesizer, or even grand piano with a MIDI interface.

The microprocessor section in the blockdiagram, Fig. 1, is based on an 8031 fromIntel. This 8 -bit processor provides an ex-tensive instruction set, powerful I/O ca-pabilities, an internal 1024 -bit RAM andan 8 -bit arithmetic logic unit (ALU). For-tunately. the 8031 is inexpensive andwidely available. Its main characteristicsare:

four bidirectional 8 -bit ports, PO -P3, twoof which remain available when PO andP2 are used for the data and address busrespectively.a serial full -duplex I/O channel withprogrammable bit rate and data formattwo 16 -bit timerstwo external interrupt inputsfive interrupt sources (two external;three internal)two interrupt levelsa 128 -byte internal RAMup to 64 KByte program memory (withexternal EPROM)up to 64 KByte scratch/data memorY(with external RAM)

In the present application, port PO and bitsP2.0 -P2.4 of port P2 are used to interfaceto the program memory, an EPROM (seeFig. 2). Port P1 and bits P3.4 -P3.7 of portP3 form a kind of data and address bus forvarious functions on the controls board.The other four bits of port P3 are used forspecial applications:

P3.0: serial input for MIDI data fromE310P3.1: MIDI outputP3.2: VCO interrupt for modulationwheelP3.3: input for pedal status

Terminal P3.0 (serial input = RxD) of the8031 is connected to the serial (MIDI) out-put of the E510 (ICs). The MIDI outputsignal provided by the microcontroller istaken from port line P3.1 and fed to two5 -way DIN output sockets, K2 and K3, viabuffers ICI la, ICI lb and ICI lc.

Terminal P3.2 (INTO) is connected tothe output of VCO (voltage controlled os-cillator) IC4b. The VCO control voltage at

input pin FC2 is provided by the WHEELpotentiometer connected to ST3. The VCOfrequency is determined by the controlvoltage and the value of C4. The 8031measures the relative position of thewheel by counting the bit rate of the signalreceived at P3.2. The wheel is assigned aMIDI function, e.g., pitch -bend, modula-tion or volume, with the aid of software_

Terminal P3.3 (MTh reads the posi-tion of the break -type switch in the SUS-

TAIN pedal connected to K4.

The program memory formed by EPROMIC3 is addressed by the processor viadata /address demultiplexer IC2 and portlines P2.0 -P2.4. The address latch enable(ALE) signal of the 8031 allows port PO to

processor

MIDI OUTTxD

RxD

DATADATA

ADDR

E510

EPROM ADDR

workpedal wheel contact

rail

restDisplay LEDs contact

rail

keys

0

KEYBOARD

900039 1

Fig. 1. Block diagram of the miDi master keyboard.

ELEKTOR ELECTRONICS .11.:NE 19911

MIDI MASTER KEYBOARD PART I

supply the least -significant address byte(A0 -A7) and to act as an 8 -bit wide data -bus (D0 -D7). The double function isachieved by time -multiplexing: the LS ad-dress byte is latched when ALE is actu-ated.

Once the LS address byte is latched inIC2, port PO functions as a databus thatallows the processor to fetch instructionsfrom the EPROM. A read operation onpart of the 8031 is marked by PSEN goinglow, which actuates the EPROM via its OE(output enable) terminal. The EPROMthat contains the control program may bea 27128 (16 KByte) or a 2764 (8 KByte).

Quartz crystal Qt and the associatedcapacitors, 0 and C2, sets the processorclock frequency at 12 MHz. The standardMIDI bit rate of 31,250 per second isderived from this clock by means of soft-ware.

The CPU is reset at power -on by a briefpulse supplied by network R1 -C3.

Keyboard interfaceThe keyboard scanning circuit is based ona dedicated MIDI controller, the E510(Ref. 1, 2). This chip has been developedfor scanning keyboards capable of sup-plying velocity information. The output ofthe E510 supplies serial MIDI data withNOTE ON/NOTE OFF and velocity informa-tion. It does not, however, supply addi-tional control data such as PROGRAMNUMBER, PITCH BEND or MODULATION. TheE510 transmits data on CHANNEL 1 only.Auxiliary functions such as redirection toother channels, transposition and split -as-signment are carried out by the 8031.

The E510 has seven address outputs(AO -A6) which select one of 128 keys.When a key is pressed, an internal contactspring is pressed against a gold- or silver-plated contact rail. This establishes a con-nection between the contact rail and thekey contact. Since it has a rest contact anda work contact -which are closed whenthe key is not pressed or pressed respec-tively - any one addressed key can as-sume three states:

it is not pressed: the rest contact is closed,and the work contact is open;it is being pressed: both the rest and thework contact are open;it is fully pressed: the rest contact is open,and the work contact is closed.

The time that lapses between the openingof the rest contact and the closing of thework contact is measured by the E510 andprovided as the VELOCITY parameter.When the rest contact is opened, an inter-nal counter counts down from 127 and isstopped when the work contact is closed.The counter value thus represents thespeed at which the key was pressed.

The key scanning and addressing oper-ations performed by the E510 are fairlyunusual since the keyboard is taken up inan 8x8, 8x9; 8x10 or 8x1 I matrix, depend-ing on the number of keys. The three least -significant bits, AO -A2, are connected to

address multiplexer ICs. When ad-dressed, one of the eight outputs of thisdevice provides a high level on the associ-ated rest contact rail, Gl-G8, in the key-board matrix. The four MS address bits.A3 -A6, are applied to demultiplexers IC-,and IC10. Outputs Y0 -Y7 of these devicesare connected to the associated work con-tact rail (Al -All) and the rest contact rail(R1 -R11) via pull-up resistors Rs -R29.

All 11 rest contact rails and 11 workcontact rails are connected to the inputs ofNAND gates IC6 and IC7 respectively. Theoutputs of these gates are connected to thetwo rail inputs, BS (work contact rail) andBE (rest contact rail), of the E510.

The E510 requires only an external 4 -MHz quartz crystal and two small capaci-tors to obtain a clock from the internaloscillator. Resistor R2 is required to termi-nate the open -collector MIDI output of thecontroller. The MIDI data produced by theE510 is fed direct to port line P3.0 of the8031.

The circuit is powered by an externalmains adapter capable of supplying 7 to12 V at about 300 mA. The on -board 5-Vregulator based on a 7805 is conventional.A number of ceramic and tantalum capa-citors are fitted at various points on thesupply lines to ensure a well-decoupledsupply voltage.

Controls boardThe circuit diagram of the control/indica-tor circuit is shown in Fig. 3. The controlof this circuit is assumed by the 8 -bit da-tabus formed by CPU port I'l and the 4 -bitaddress bus formed by P3.4 -P3.7. The da-tabus is connected to all datalines of I/Odrivers ICI -ICs. Of these, IC2-1C5 arewrite -only registers, and ICI a read-onlyregister. Address lines P3.4 -P3.7 are con-nected to demultiplexer 106, which arran-ges the register selection. The selection isaccomplished with the aid of the Y0 -Y4outputs, which are connected to the OE(output enable) inputs of the read-onlyregister, and the CLK (clock) inputs of thewrite -only registers. This creates the fol-lowing functions of the demultiplexeroutputs:

address Y IC Function Register

0 YO 1C1 8 keys read1 Yl 1C2 8 LEDs write2 Y2 IC3 1st display write3 Y3 IC4 2nd display write4 Y4 ICS 3rd diSplay write

The status of the eight keys is requestedvia a non -inverting three -state driverType 74HC541, whose inputs Al -A8 arefitted with pull-up resistors so that an ac-tuated key produces a logic 0. 1Vhen thedriver is selected via its OE input, thedataword at inputs Al -A8 is transferredto databus P1 from which it can be read bythe processor via port 1. When the driveris not selected, its outputs YI-Y8 areswitched to high impedance.

Thus, to be able to read the status of the

Many parts for this project, includingthe programmed EPROM (IC3), theE510 MIDI controller (IC5). the swit-ches, the printed -circuit boards and61-, 76- and 88 -key keyboards areavailable from

Doepfer MusikelektronikLochamerstrasse 63D-8032 GrafelfinoWest -GermanyTelephone: +49 89 855578Facsimile: +49 89 8541698

The E510 MIDI controller is also avail-able from C -I Electronics, P.O. Box22089, 6360 AB Nuth, Holland.

eight control key the processor must firstselect the '8 keys register by placing theappropriate address nibble on P3_4 -P3.7.The data on the i'l bus is latched into thewrite -only registers (IC2-IC5) at the lead-ing edge of the relevant clock signal (Y1 -Y4 of IC6).

The registers that drive the eight LEDsand the 7 -segment LED displays via cur-rent -limiting resistors are octal D-bi-stables Type 74HC574. The displayactuation logic is reversed: writing a 0turns on a LED or display segment.

Construction of the boardsThe two circuits discussed are accommo-dated on two double -sided, through -plated printed -circuit boards (see Figs. 4and 5).

All ICs with the exception of the74LS629 are CMOS types which should behandled with the usual care to preventdamage from static electricity. Since tan-talum capacitors are particularly prone todeveloping internal short-circuits, eachdevice must be checked with anohmmeter before it is fitted. Note theorientation of the polarized components,which include the ICs, diodes, electrolyticcapacitors, the single resistor array, theLEDs and the switches. All capacitorsmarked G on the boards are fitted to af-ford adequate decoupling of the supplyvoltage. Each pair of capacitors consists ofa 100-nF ceramic type and a 10-4tF tanta-lum type in parallel. The voltage regulator(102) is bolted direct to the board,together with its heat -sink.

The controls board has components atboth sides. First; fit the capacitors, IC soc-kets, resistors, the resistor array and pinheaders at the side of the printed overlay.Note that the resistor array, RAI, is a po-larized part: its common terminal ismarked by a dot which is also found backon the component overlay. Next, fit thekeys, the displays and the LEDs at thereverse side of the board. These parts areshown in dashed outlines.

The fitting of the switches requires spe-cial attention. First, solder one of the fourterminals, and check whether the switchrests flat on the PCB surface. If necessary


26 ELECTROPHONICS

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ELENTOR ELECTRONICS .1UNE 1990

IIMIDI MASTER KEYBOARD PART 1

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Fig. 3. Circuit diagram of the controls display board. The connection to the main board is made via pin header ST2.

align the position before soldering theother pins. This simple procedure pre-vents irregular key positions which spoilsthe look of the keyboard and causes diffi-culty with the clearances in the frontpanel.

Since the faces of the LED displaysmust be roughly level with the key bases,they are fitted at a certain height above theboard surface. The best height is thatwhich results in the faces of the displaysbeing about 1 mm below the top side ofthe key bases (i.e., not the kevtops!).

The rectangular LEDs may be solderedto the board after provisionally fitting thecontrols panel. This is done to ensure thattheir height and position align readilywith the clearances in the front panel(Fig. 6).

Cables and connectionsThe main board is connected to the con-trols board via a 16 -way flatcable, and tothe 88 -key keyboard via a 40 -way flat-cable. The ends of the two cables are fitted

with IDC sockets (note the position ofpin 1 of the IDC socket with respect to thecable and pin 1 of the header on theboard).

The author can supply an adapterboard with mounting instructions to en-able the main board to be connected tokeyboards with 76, 61 or 49 keys. Thisadapter is plugged on to Sit and providesthe relevant connections to the keyboardfrom there.

Modulation wheelThe potentiometer that forms the modula-tion wheel is connected to header ST3 onthe main board. The wheel may be a typewhich re -adjusts itself by means of aspring (mainly for a pitch -bend function),or one with normal action (for all othercontrol functions, including modulation,volume, panorama and portamento).

Since the full 270= range of the poten-tiometer will not be covered when themodulation wheel is operated, the re-quired compensation is provided by the

control software. The range of the WOcontrol voltage is defined by preset Pt,and the actual value within that range bythe modulation wheel.

The wheel potentiometer must not besecured until the complete circuit hasbeen checked for correct operation. In-itially, set the associated preset, Pt, tominimum resistance.

When a re -adjusting wheel is used(pitch -bend function; this is automaticallyselected at power -on), the preset is ad-justed until the circuit sends a MIDI par-ameter value of 401-i (64o) (do not operatethe wheel). When a MIDI monitor withparameter selection and a data read-out isnot available for this alignment, connect aMIDI receiver (e.g., an expander), and ad-just the preset until there is no tone shiftwith the wheel at its rest position. Thesoftware provides a self-adjusting func-tion for the parameter range around 4011,to afford a kind of compensation for mech-anical tolerance on the rest position of thepotentiometer.

In case a normal (non -re -adjusting)


28 ELECTROPHONICS

wheel is used is used, the VCO preset isadjusted until the modulation poten-tiometer covers a range of about 00H to7FH. Small deviations from these valuesshould not cause problems and may betolerated. Repeat the adjustment with aslightly different value for Pi in caseeither the lowest (00f I) or the highest (7FH)value is sent long before the end stop ofthe potentiometer is reached. When thepreviously mentioned MIDI monitor isnot available for checking the relevantdata, the modulation wheel is best as-signed the function of volume control.This allows you to check whether the vol-ume can he reduced to nought at the corre-sponding wheel position.

AssemblyThe completed and tested controls boardis secured to the front panel (Fig. 6) withthree M3x15 mm or M3x.20 mm screwsand plastic PCB spacers. The distance be-tween the panel and the board should be13 mm. This is achieved by fixing each ofthe three \13 screws to the front panelwith the aid of a 10 -mm long spacer andan M3 nut. Next, mount the controls board

COMPONENTS LIST

MAIN BOARD (E510.8031)

Resistors:3 10k R ;R3;R3023 1k0 R2:138 -R29

4 220. R4 -R71 10k preset V P1

Capacitors:4 22p C1:C2:C5;C82 101.1.F 10V tantalum C3;Cio1 1p0 10V tantalum C42 100pF 10V tantalum C7:C86 100n ceramic C9;C18-C247 2p2 10V tantalum C11 -C17

Semiconductors:1 1N4001 Di1 8031 or 8051 ICI1 74HC573 1C2

1 2764 or 27128 1C3

1 74LS629 1C4

1 E510 IC52 74HC133 lCa;1C72 74HC138 IC8:1C9

1 74HC237 ICI°1 74HC04 1C1

1 7805 IC12

Miscellaneous:1 2.20 -way pin header ST1

1 2 -4 -way pin header ST21 DC supply socket for

PCB mounting2 5 -way DIN socket for BU2;BU3

PCB mounting1 stereo 6.3 -mm jack BU4

socket for PCB mountingIC sockets

1 Heat -sink for 1C12

000000000

O 0 0 00O 0 0 00O 0 0 00

O 0 0.0 00001 0 0 0O 0 o e.

00O 0 0, 0O 0 0-0 0O 0 0 0-0 0O 0 0 0-00 O 6 6-0 000 p 0 6-0 00 Z0 0 0-000 0 0 0-0O 0 6 0-060 0. 0 0O 0 0 0 0 00 0 0 0 0 0O 0 0 0 l 00 0 0 D 00 0' 0 0 00 0 0 0 0

O 1 0 0 0

1.1 00 0 0

0 0/

0 0 0

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0

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Fig. 5. Track layouts and component mounting plan of main controller board.

EI_EKTOR ELECTRONics .1u NE 1990

AUDI MASTER KEYBOARD PART I 29

Fig. 5. Track layouts and component mounting plan of the controls indicator board.

COMPONENTS LIST

CONTROLSDISPLANOINDICATOR BOARD

Resistors:8 3900 R-i-Re24 lkO R9 -R321 SIL 8..10k RA1

Capacitors:1 100n ceramic1 2112 10V

CiC2

Semiconductors:8 LED red rectangular D1-D83 LTS546AP La1:LD2;LD31 74HC541 IC1

4 74HC574 1C2-1051 74HC138 IC6

Miscellaneous:1 2x8 -way pin header ST28 locking SPST push-button Ti-T8

and secure it with the remaining N13 nuts_Cover the displays with a bezel glued tothe front panel.

The mounting bracket for the modula-tion wheel is fitted from below to the frontpanel with the aid of 5 -mm long PCB spa-cers. The completed and wired front panelis secured to the left side panel of the flightcase.

Next timeThe concluding part of this article willdeal with the function test and trouble-shooting procedures. In addition, someattention will be given to the menus of-fered by the keyboard, as well as to thevelocity curves and the default presets. Zi

IC 51741+:57',

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i

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1 f

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rii.ED ;3,LED :5 __:!,:.c

r73,kii...38.4 i-,,a71 1.-.5.' , e..,-

D2!LED C.!i_rED

IR./39erg.9

Ck/ LED DV LED

1.

86-866.2

118-5

65.062.35

24 35

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Fig. 6. Cutting and drilling details of the front panel.

ELEKTOR ELECTRONICS .1LNE 19911

30

PLL INE WAVE GENERATORJ. Bareford

Precise frequencies that can be set very accurately are much more eas-ily generated with the aid of digital technology than with

analogue techniques. A snag with digital signals is, however, that theirshape is rectangular rather than sinusoidal as required for many tests

and measurements. The generator described in thisarticle uses digital techniques, yet provides true sinusoidal signals

It is fairly simple to generate frequencieswith the aid of, for example, an MS-DOScomputer working with GW-BASIC. With-out spending any extra money, every PCowner thus has a variable tone generatoravailable. Unfortunately, the signal is rect-angular and, therefore, not suitable for anumber of tests and measurements.

If the generator is to be used without acomputer system, another source of digi-tal reference signal is required. For a num-ber of applications, a simple variablesquare -wave generator will be perfectlyacceptable. Where greater accuracy is re-quired, a stable crystal oscillator with pre-set scaler must be used.

Control of the VCO

The generator is based on a combinationof a phase -locked loop (PLL), here a Type4046, and an integrated function genera-tor, Type XR2206.

The principle of a PLL is shown inFig. 1 The two most important parts of aI'LL are a phase (410) comparator and avoltage -controlled oscillator (VCO).

The VCO will oscillate when a signalat a given frequency is fed to it. This fre-quency is determined by an external RCnetwork. The output of the VCO (2) is fedto one of the inputs of the phase compara-tor; the other input of this stage is pro-vided with the reference frequency (11.

The output of the phase comparator(3) is the difference between the two inputsignals. It is invariably a rectangular sig-nal of which the mark -space ratio de-pends on the phase difference betweenthe two input signals.

A low-pass filter at the output of thecomparator integrates the pulses, whichresults in a signal whose absolute level isdirectly proportional to the phase differ-ence of the input signals. The output be-comes constant at the instant the loop islocked; this normally occurs at a phasedifference of 90

Technical specificationInput impedance

Sensitivity

Frequency range

Output impedance

Harmonic distortion

Si open

>10 MCi

1-12 VP-13

500 Hz - 100 kHz -

10 Hz -1 kHz**

600 Ci

0.5% (typical)

closed

Fig. 1. Block diagram of a phase -locked loop (PLL).

As shown in Fig. 2, the 4046 used inthe generator contains two different phasecomparators. The first one of these is asingle XOR gate, whose output is 1 if thelevels of the two input signals are notequal. This comparator is not suitable forthe present circuit because it requiressymmetrical input signals and it will lock

harmonics of the input signals. Signalsassociated with this comparator areshown in Figure 3.

The second comparator is rather morecomplex and perfectly suitable for thepresent purposes. It is not sensitive toasymmetry of the input signals, since itoperates on the edges of these signals.Moreover, it does not lock to harmonics ofthe input signals. This means that the si-nusoidal signal is of exactly the same fre-quency as the reference signal. Associatedsignals are shown in Fig. 4.

An additional advantage of this stage isthat it allows connexion to an LED thatlights when the loop is locked to indicatethat the output signal is as stable as thereference signal.

The output of the second comparatorhas not two but three states, dependingon the input signals: 0, 1 or high imped-ance. The dependence of the output signalon the input signal is clear from Fig. 4.When the output of the comparator ishigh impedance it has no effect on the cir-cuit following the comparator; it is, as itwere, not present.

The period of time that the output is 1or 0 depends directly on the phase differ-ence between the input signal and the ref-erence signal. If the input signal is first tohave a leading edge, that is, is in advanceof the VCO signal, the output becomes 1.If the VCO signal is first, the output be-comes 0.

The low-pass filter following the com-parator converts the output pulses into adirect voltage. This voltage increaseswhen the comparator output goes high; itremains constant when the comparator


FLU SINE WAVE GENERATOR

ILOY, PASS FILTER OUTFUT1

output is high impedance; and it decreaseswhen the comparator output goes low. Thismeans that the direct voltage is directly pro-portional to the phase difference between theinput signal and the VCO signal.

Since the direct voltage is used to controlthe VCO, the circuit stabilizes at a given set ofconditions. In the present comparator that

happens when the phase difference betweenthe input signal and the VCO signal is Or andnot 90' as is usual in PLLs. Because of this, theVCO frequency is exactly the same, and asstable, as the input signal.

:CLI,AAATCF-

r1.

Ls_

SI 1111AL

14

2 Frii.!E [CIO I Qui

hi&SE [CIO I! OUT

P1.4A-IEPSES

DEIJOOLLATOROUT

Vis

LOR?AZFILTER

890097-12

Fig. 2. Block diagram of the Type 4046 phase -locked loop (PLL).

SIGNAL IN

COYPARATOR lh

PHASE COY? I OUT

VDD

VSS

VOH

VOL

VOH -VOL

PHASE COMPARATOR I

1_ 1

890097 - 13

Fig. 3. Signals associated with phase comparator I.

SIGNAL IN x'00Vss

COMPARATOR INVOH

PHASE COMP II OUT

VOL

PHASE COMPARATOR II

vot,

VCOIN VOH

VOL -

890097-14

Fig. 4. Signals associated with phase comparator II.

From rectangular tosinusoidal waveform

Even a Cursory glance at the circuit diagramin Fig. 8 shows that instead of the VCO in the4046 a separate VCO, formed by 1Cs, is used.This circuit, strictly speaking a function gener-ator, has the important advantage that it pro -

Fig. 5. Phase comparator II in the 4046 and the VCO in the XR2206 form agood -quality PLL.

- rn*

pILeT

and

SGT

Co

Fig. 6. Circuit diagram of the XR2206.

Fig. 7. The VCO input of the XR2206 is. strictly, a current -controlled outputacross which a fixed potential of 3 V exists. Applying a counter potential

Uf via resistance R1 sets the input current.


TEST & MEASUREMENT

Fig. 8 Circuit diagram of the sine wave generator.

0 0

0-0-o

0*13 1-0ea1R 2 1-0

0I1=2"1 1-0 0-01120 0--01-0 Cs0-*/-01=13ciiRis 140 (}1RB 2,,o-1-4-0 4

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aps

1.0

70 a) 0

0.11=14 1-0 DD

i° G-Ic'1714° °A114?1 20-0c 0-1,4-0 0-11=2 1-0.07_40

CHRIS 1-43 C10

nru

0

0-i 0-0 C3

0-1-2 i-0

D

t -

to

0000-I FOC9

07-0 c e

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cqR151-00 ri Cti R 14 143

In

00

PARTS LIST

Resistors:R1 = 220 kR2 = 10 MR3, R8. R17 = 1 kR4 = 10 kR5, R13 = 12 kR6, R7, R16 = 100 kR9, R10 = 4k7R11=22 kR12 = 1k5R14 = 560 RR15 = 1 M

Capacitors:Cl = 10 nC2 = 470 u, 16 VC3. C5 = 1 u. 16 VC4 = 10011, 16 VC6. C7 = 100 pC8, C14 = 47 p, 16 VC9 = 680 nC10 = 8n2C11 = 10 (1. 16 VC12 = 200 u. 16 VC13= 1 n

Semiconductors:IC1 = 4046IC2 - IC4 = CA3130IC5 = XR2206IC6 = LF356IC7 = 78L05Dl. D3. D4 = 1N4148D2 = LED (green)

Miscellaneous:Si = SPST switchPCB 890097-1

Fig. 9. Printed circuit board for the sine wave generator.

ELEKTOR ELECTRONIC. S JUNE 1990

vides both a rectangular and a sinusoidal sig-nal, since it has a sine wave converter onboard. Moreover, the IC remains perfectly reli-able at low frequencies, so that it is truly lin-ear over a wide range of frequencies.

The XR2206 is used in exactly the sameway as that in the 4046 would have been. Itsinternal circuit is shown in Fig. 6.

Reverting to Fig. 8, opamp IC3 betweenthe phase comparator and the VCO performsthree distinct functions. In the first place, it in-verts the control voltage for the VCO, becausea decreasing voltage at pin 7 of IC would re-sult in an increase in the output frequency.Secondly, its output signal has been arrangedto allow it driving the VCO over its full range.Finally, the input of the VCO is controlled bya current rather than by a voltage. In otherwords, the control input of the VCO is in real-ity an output across which a fixed potential(110) exists and from which a current flows.The output voltage of IC3 determines the po-tential difference across R$ and thus the valueof the current that will flow. The frequency, f,is determined from:

f = (U,, - / (3xCxRs) [Hz]

in which U = 3 V; /if = the output voltage ofIC3; C = Cie or, if Si is closed, C9+Cio.

It may be calculated that, depending onthe position of switch Si. a frequency range of6 Hz to 125 kHz is available.

The remainder of the circuit is virtually

nothing but the connexions between the vari-ous components.

The output of the phase comparator isconnected to the VCO via low-pass filter RI -R2 -R3 -C4 and buffer IC2 in a manner that pre -dudes any feedback to the comparator.

Diodes D3 and D4 shorten the time re-quired by the circuit to lock by enabling thequicker charging and discharging of IC4. Thisis possible because at higher voltage levels Riis connected in parallel with T2. This causesthe impedance to decrease from 10 MO forsmall signals (PLL locked) to about 220 IQ forlarge signals (PLL not vet locked).

Since the PLL may be used over a fairlywide frequency range, the low-pass sectionhas a fairly large time constant to ensure goodstability. Because of this, the PLL takes a rela-tively long time to lock. The 'acceleration' pro-vided by the diodes is therefore welcome.

Diode D2, which is controlled by opampIC3, lights to indicate that the PLL is locked.The opamp is connected to pin 1 of the PLL,which is specially provided for this purpose.A constant high level exists at this pin as longas the PLL is locked. As soon as the PLL tendsto drift, small pulses appear at this pin andthese are used by diode Di to arrange for thefast discharge of C13. The voltage across C13then drops to a level that causes the output ofICs to become low. This in turn results in D3being extinguished to indicate that the fre-quency is not stable.

Finally, a number of components are nec-

0Fig. 10. Photograph of the completed printedcircuit board.

PLL- SINE -WAVE GENERATOR

AMPLITUDE LOCKED

500Hz -100kHz

10Hz 1kHz

RANGE OUTPUT

890097 - 16

Fig. 11. Suggested front panel layout.


PLL SINE WAVE GENERATOR

essary for the proper functioning of ICs:resistor R and capacitors C9 and Cto de-termine the frequency range; Si makes itpossible to choose between the tworanges;

resistors R9 and Rio set the d.c. operatinglevel at the output (pin 2);preset P3 determines the amplitude of theoutput signal;preset Pi serves to shape the output wave-form;resistor R13 is the collector resistor for theopen -collector output of the VCO;

circuit IC" forms the output stage proper.

Construction and alignment

The circuit is intended to be built on the PCboard shown in Fig. 9 and Fig. 10.

A number of soldering pins must be fittedon the board to facilitate connexions to otherequipment.

The ICs may be soldered direct to theboard.

With careful work, and particular attentionto the polarity of the diodes and electrolyticcapacitors, nothing should go amiss in popu-lating the board

Commence the alignment by setting allpotentiometers to the centre of their travel.

Connect the output of the generator to anoscilloscope.

Apply a rectangular signal of I kHz, at alevel of 5 V, to the input of the generator. Asstated at the beginning of this article, this sig-nal may emanate from a computer, simplesquare -wave generator or crystal oscillator.

Open Si and connect an external ±12 Vsupply to the supply lines of the circuit.

If all is well, the oscilloscope should nowshow a reasonably well -shaped sine wave. Ifnecess-ary, adjust Pi to make the signal as trulysinusoidal as can be judged. Once that isdone, adjust P2 to make the signal look evenbetter. Since the two potentiometers affect oneanother, the alignment must be carried out afew times. After correct alignment, the har-monic distortion is not greater than 0.5%.

The optimum position of P3 depends onthe desired output level: be careful not to pro-duce distortion of the output through over-driving.

If you prefer a continuously variable out-put level, that can be provided by a smallmodification. This consists of replacing R14 bytwo soldering pins. Connect a 1 IS/ poten-tiometer between the pin that is connected tothe output of IC0 and earth. Connect thewiper of the potentiometer to the other pin. Acontinuously variable output signal is thenprovided via Ca

The suggested front panel shown in Fig. 11should he given a calibrated scale to give a(relative) indication of the output signal.

34

ELECTRONIC' FUSES

Bourns Electronics has for some time marketed a series of circuit break-ers that, in a number of applications, form good alternatives to the usual

glass fuses. Known as MultiFuse, the devices aresimilar in their basic characteristics to positive temperature

coefficient (PTC) resistors made from doped barium titanateceramics, but are of a totally different construction based on

conductive polymer composite materials. An important advantage of theMultiFuse is that after it has been tripped by an overload it needs only a

short period after the overload has been removed to regain its normaloperational characteristics.

Automatic circuit breakers are, of course.not new. Many electric coffee -makers anddeep fryers have a thermal trip device thatswitches off the mains when the appliancegets too hot. After the heating element hashad time to cool off. the trip element re-turns to its original position and the appli-ance operates normally again.

The MultiFuse has a similar function.As soon as the current through it exceeds acertain value, its resistance increases sig-nificantly. This reduces the current to asafe value so that the load does not getdamaged.

However, in contrast to the usual elec-tro-mechanical circuit breaker, the Multi -Fuse is an electronic component that hasno moving (mechanical) parts. The advan-tages of this are clear: a mechanical circuitbreaker is sensitive to vibrations. producessparks when it is operated. and. after atime. presents an increasing resistanceowing to corrosion of the contacts.

Ceramic positive temperature coeffi-cient (PTC) resistors that occasionally arcused in protection circuits operate in amanner similar to that of the MultiFuse.They have the serious drawback, however.of a much longer switching time. Anothersnag is that their resistance may decreasesignificantly. even to the point of a shortcircuit, when the voltage across them istoo high.

Principle of operationAlthough the basic characteristics of theMultiFuse are similar to those of a PTC.the construction of the two devices is quitedifferent. Whereas a PTC is made fromdoped barium titanate ceramics, the Multi -

Fuse is made from conductive polymer. Inthe past two decades substantial progresshas been made in research on conductivepolymer materials. In these materials, con-

ductive particles-carbon black in the caseof MultiFuse-are dispersed in a poly-meric matrix of a suitable plastic material.

The properties of the conductive poly-mer composites used in MultiFuse lead toimprovements in device characteristicsthat are not obtainable with conventionalPTC resistor technologies. In the low re-sistance state, resistances as low as a fewmilliohms can be obtained. The PTC ef-fect. which is the basis of the current -lim-iting function, can increase resistance bytypically 5-7 decades. This PTC charac-teristic is maintained over and beyond theoperating range of MultiFuse. CeramicPTC resistors on the other hand can ex-hibit a negative temperature characteristicunder overvoltage when their temperaturerises beyond the anomaly temperature.

Properties of conductivepolymers

To better understand some of the charac-teristics of MultiFuse devices, it is neces-sary to look at the underlying properties ofconductive polymers.

The conductive poymer materials usedto produce MultiFuse devices are tilledwith carbon black. The carbon black parti-cles form themselves into chains insteadof randomly dispersed particles. The re-sulting electrical conductivity of the poly-mer composition is of the order of 0.01 S(=1 Q.-1 cm -I).

The type of carbon black and the vol-ume ratio of carbon black to polymer de-termine the value of electrical resistivity.Changes in the volume ratio will causechanges in resistivity. A lower ratio of car-bon black to polymer means a decreasednumber of conductive chains and thereforean increase in resistivity.

For MultiFuse devices a crystallinepolymer is used. The crystalline structure

of this material disappears in the region of125 °C. The resulting increase in polymervolume reduces the ratio of carbon blackto polymer and a very large resistance in-crease results within a very narrow tem-perature band. This anomalous positivetemperature coefficient of resistance ex-plains the "switching" characteristic ofMultiFuse devices.

Figure I shows the link between vol-ume and resistance. An increase in resis-tance of six orders of magnitude over afew tenths of a degree Celsius is typical.The figure also shows that the PTC char-acteristic is persistent far beyond theanomaly temperature.

With cooling of the device below theanomaly temperature the polymer starts torecrystallize and more and more of theopened carbon black chains are re-estab-lished. Although most of the carbon blackchains are closed again after minutes. thefurther crystallization process takes time.This fact leads to the slight increase in re-sistance after trip: after a cooling period of1 hour. the value of the resistance is stillup to 20 higher than original. However.the resistance value will return within 24hours to within the tolerances specified bythe makers.

MultiFuse devices are manufactured toyield a basic resistance close to its mini-mum specified value. When they are de-livered. they have never been tripped andtheir volumetric ratio of carbon black topolymer is at a maximum.

Designing in a MultiFuse

The questions you need to answer whendesigning with MultiFuse- devices include:1. What is the maximum normal currentthat can pass throught the circuit at themaximum ambient temperature withouttripping the device?

ELEKTOR ELECTRONICS UNE 1991)

ELECTRONIC FUSES

6

5

4

3

2

1

0

-1

Resistance /Volume./ I

I

20°C 130'C

Temperature890180 - 11

3

2

1

Fig. 1. Resistance and volume as a function of temperature.

Co

0)

(,)U)0)cr

Initial basic resistance

1stTrip

Typical after -trip basic resistance

II

II

II

II

II

I

94h 24h2ndTrip

Time

890180 12

Fig. 2. Recovery of basic resistance after trip.

PartNumber

V maxV rms

I ,,DA rms

R m nOhms

R nomOhms

R maxOhms

i:,-:7.Arms

P 0W

ImaxArms

1.1F -R020 0.20 1.83 2.67 4.50 0.30 0.40

1.1F -R025 0.25 1.25 1.83 3.10 0.38 0.45

MF-R030 0-30 0.87 1.27 2.20 0.45 0.50

1.1F -F1040 50 0.40 0.55 0.81 1.33 0.60 0.55 4:.

?.1F -R050 0.50 0.49 0.75 1.20 0.75 0.75

MF-R065 0.65 0.30 0.46 0.75 0.98 0.90

MF-R075 0.75 0.25 0.39 0.52 1.13 0.90

MF-R090 0.90 0.19 0.34 0.48 1.35 1.00

1.4F -R110 1.10 0.08 0.13 0.23 1.87 1.00

%1F11135 1_35 0.06 0.10 0.17 2.30 1.10

MF-R160 1.60 0.05 0.08 0.14 2.72 1.20

MF-R185 1.85 0.04 0.06 0.11 3.15 1.30

MF-P.230 30 2.30 0.03 0.05 0.09 3.91 1.40 4C:

MF-R250 2.50 0,02 0.04 0.08 4.25 1.50

MF-R300 3.00 0.02 0.03 0.06 5,10 200MF-R400 4.00 0.01 0.02 0.04 6.80 2.50MF-R600 6.00 0.005 0.01 0.03 10 2 3.50

MF-R800 8.00 0.005 0.01 0.02 13.6 4.00

MF-S200 15 200 0.03 0.04 0.08 3.00 100

MF-S350 3.50 0.02 0.03 0.04 5.25

MF-T110 250 0.11 13 17 25.0 0.17 1.00

1.1F -T145 0.145 7 8.5 13 0 0.22 1.00

Electrical specifications of a number of types of MultiFuse at an ambient temperature of 20 C.

What is the maximum current that canpass through the circuit at the minimumambient temperature without causing dam-age to circuit components?3. What is the maximum fault current andvoltage to which the device will be ex-posed?

A practical example

Suppose that a resistive load of 33 S2.for instance, a motor, transformer or heat-ing element, is to be protected aeainst

overcurrent with the aid of a MultiFuse.In normal circumstances, the highest

current is 150 mA. the highest ambienttemperature is 70 =C and the maximumvoltage is 30 V.

On the basis of these data. the mostsuitable type of Multi Fuse is chosen fromthe table: in this case. the MF-R030. Thishas a hold current of 160 mA at a tempera-ture of 70 'C and will. therefore. not tripin normal circumstances. Also. it canstand a voltage of 60 V. which is morethan adequate for the requirement. At

room temperature. the MF-R030 has aminimum resistance of 0.87 Q. so that if ashort-circuit occurs, the maximum currentthrough the device is 34.8 A. This is lowerthan the maximum allowable current of40 A. This example makes it clear that thedevice will not trip spontaneously andwill survive the short circuit condition inthis application.

Then there is the question whether thedevice will trip fast enough to protect theload. The relevant datasheet of the makersgives a typical response time at a specifiedcurrent value at 20 °C: 0.4 s at a current of2 A. that is an 12t of 1.6. Therefore, energyequivalent to 52.8 joules ((121 x RL) maybe deposited into the load before the Mul-tiFuse trips. If data on the load indicatesthat the load can withstand more energythan that amount before it fails. this partic-ular MultiFuse device may be the rightone for the application.

To confirm your choice. measure the/2t failure curve for RL and compare itwith the J2 trip curve for the MultiFusedevice. If the curve for the MultiFuse de-vice is below that for the load, the loadwill be protected.

Further information and datasheets from:Bourns Electronics Ltd90 Park StreetCamberleySurrey GL -15 3N1Telephone (0276) 69 23 92Telefax (0276) 69 10 37


36

AUTOMATIC POWER -DOWN FORPCs

There are many programsthat take of lot of precious

time, even on relativelyfast PC -AT computers.

Examples includeelectronic circuit

simulators, sorting routines,disk compression

programs, and PCBauto -routers. Eventually,the enjoyment of the PC

user sitting back andsipping coffee or tea as

the machine crunches itsway through masses of

data turns intoimpatience. After a fewsuch sessions, you have

seen it all happening, andtime-consuming programs

are usually banned tonight-time hours.

Unfortunately, this meansthat the computer remainson long after finishing the

relevant program. Thecircuit presented heredoes away with this

disadvantage of off-peak,unmanned computing byenabling the computer to

shut itself down.

Although the circuit is designed specifi-cally for IBM PCs and compatibles, it maybe used with other types of computer aswell, provided the user is sufficiently artfait with the hardware. In principle, theexternal part of the automatic power-down circuit could be located in the com-puter. Apart from the difficulties that maybe expected from working on the powersupply of the PC, this option is likely toinfringe on electrical safety requirements.With that in mind, a separate enclosurethat contains a mains -rated relay, a con-trol circuit and a low -voltage power sup-ply will be preferred in many cases.

J. Ruffell

Fig. 1. Block diagram of the power -down controller.

Block diagramThe block diagram of the circuit is shownin Fig. I. The keyboard is connected to thePC via the auto power -down unit to en-able it to function as an on -control. In theexternal switching box, the keyboardclock signal is 'tapped' and fed to the con-trol circuit fitted in the computer. Thisarrangement enables the control circuit toswitch the computer on when a key ispressed.

The control circuit switches the com-puter on, and off again when required. Ashort delay is provided to prevent thecomputer being switched off by a 'hang-ing' program. The switch -off procedurestarts with a small program making da-tabit D1 of the address at which the con-trol board resides logic high. After awhile, this address is read back. If the 1 isstill there, the relay is de -energized after adelay of about 10 s (useful for parking thehard disk).

Bit DO at the control board addressdetermines whether or not the keyboardis to remain on when the computer isswitched off. The 'keyboard active' option

allows the computer to be switched on byany key action. The other option, 'key-board disabled' is useful for applicationswhere the computer will remain off for arelatively long period, or where the risk ofaccidental key actions (cleaners in youroffice...) must be eliminated. The key-board remains enabled %Olen bit DO ishigh during the write operation that startsthe switch -off sequence. A low at DOcauses the keyboard to be switched offwith the computer (note that the keyboardis powered separately by the auto power-down unit).

Circuit descriptionFigure 2 shows the circuit diagram of theauto power -down control. Only a few ofthe signals on the PC extension bus con-nector are used. The 10 -bit I/O addressbus, AO-A9, is connected to an addressdecoder formed by comparator ICi andOR gate IC2c. The I/O address occupiedby the circuit can be set between 300H and31FH with the aid of DIP switch Si. Theoutput signal of the address decoder atpin 10 of IC2c is split into I/O read and


AUTOMATIC POWER -DOWN FOR PCs

11

0

B29

828

B27

826

B25

924

323

B22

921

920

B19

18

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9

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313

912

311

910

B9

38

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95

95

94

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92

31

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A31 AO

A30 AlA29 A2

A28 A3

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A26 A5

A25 A6

A24 A7

A23

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5V 12V

12V

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12V

Fig. 2. Circuit diagram of the auto power -down controller. The parts in the shaded block are fitted external to the computer.


38COMPUTERS AND MICROPROCESSORS

Signal Pin designation Signalname

trackside

GND

namecompo-nentside

801 I A01I/0

CHCK

RESET 802 A02 D7

+5V B03

IRO2 B04

-5V B05

DREQ2 606

A03 D6

A04

A05

D5

D4

A06 D3

+12VI B07 A07 D2

reserved BOB'A08 Di

+12V I B09

GND B10

MEMW

A09

A10

DO

II0CHRDY

611 All AEN

MEMR B12 Al2 A19

lOWC B13 A13 A18

IORC I B14 A14 A17

DACK3 B15 A15 A16

DREQ3 816 A16 A15

DACK1 B17 A17 A14

DREQ1 B18 A18 A13

DACKO B19 A19 Al2CLK B20 A20 AllIRQ7 B21 A21 Al 0

IRQ6 B22 A22 A9

IR05 B23 A23 A8

1604 B24 A24 A7

IRQ3 B25 A25 A6

DACK2 B26 A26 A5

TC B27 A27 A6

ALE B28 A28 A3

+5V B29 A29 A2

OSC B30 A30 Al

GND 631 A31 AO

For easy reference: signal assignment onthe PC expansion slot connector. Note that'track side' and 'component side' refer toinsertion cards.

write signals by lC and IC3a respective-ly. When the CPU writes to the addressoccupied by the circuit, the logic levels ondatalines DO and Dl are latched into bi-stables IC4a and IC4b respectively. The da-tabit in 1C4a indicates whether or not thekeyboard must remain on, while that inIC4b indicates that the switch -off sequencehas been started. Bistable lett, is wired asa monostable multivibrator, which can betriggered only when Dl is high. Thisforms the first security measure againstaccidental switching off. The secondmeasure is that the auto -power down ad-dress must be read within the monotimeof IC4b. Only when this is achieved is themonostable formed by ICsb started_ Noth-ing happens in the circuit during the delay

of about 10 s introduced by ICsb. How-ever, the delay allows the system shut-down (or hard disk parking) program tobe loaded and run from a batch file. Afterthe 10-s delay, ICsb resets bistable IC:sa vianetwork R13 -C11. As a result, the relay isde -energized via Ti so that the computeris switched off.

The computer may be switched on inthree ways. All three have in common thatIC5a is set so that the relay is energized.

The first way is by means of the RESETswitch, S2. This is the RESET key fitted onmost PCs. When S2 is pressed, the clockinput of ICsa is made high via OR gate IC2a(the data input of IC5a is permanentlyhigh). To retain the original function ofthe RESET key, it is connected to the com-puter via T4. This allows it to be used asbefore when the computer is on.

The second way to turn on the com-puter is by means of a pulse -applied to theExT input (pin 8 of connector Kt). Theleading edge of the pulse clocks IC5a andswitches the computer on. The pulse maybe supplied by external equipment or acomputer peripheral that requires a rela-tively long period of computer activity. Itshould not be used for short intervalssince frequent switching on and off mayreduce the lifetime of the computer_

The third way to switch the computeron is via the keyboard. As already dis-cussed, this works only if databit DO ishigh when the CPU writes to the I/O ad-dress occupied by the circuit. Since it ispowered by the auto power -off circuit, thekeyboard is on irrespective of whether thecomputer is on or off. In virtually all cases,a key code is sent when any key is pressed.The accompanying clock signal is fed toOR gate 1C2b. This gate passes the clockpulses only when the keyboard is actuallyon (this is done to prevent interferencefrom a disabled keyboard), and when atleast a second has lapsed since the com-puter was switched off. The delay is pro-vided by R11 and Cat which maintain abrief high level after the switching off.

The keyboard interface brings us to apart of the circuit that is fitted into anexternal enclosure instead of into the com-puter. In the circuit diagram, this sectionis shown with a shaded background. Thekeyboard connection consists of two DINsockets to establish the connection to thecomputer. All terminals of K4 and Ks areinterconnected with the exception of thekeyboard supply pin 5 (remember that thekeyboard is powered by the auto power-down supply). The keyboard clock signalis 'tapped' at K4.

The power supply is conventional withtwo LEDs, Di and D2, to indicate thepresence of mains voltage and the state ofthe relay respectively. The unregulatedvoltage of about 12 V across C13 is broughtdown to 3 V by IC6 on the control boardin the computer_

Programming and adjustingThe programs that start the power -downsequence can be as simple as shown

below. The examples are written in TurboPascal. First, a routine to switch off thecomputer only:

VAR DUMMY: BYTE;

BEGINPORTIS3001:= 3;DUNIMY := PORT[S3001END.

This works provided the auto power -down circuit is assigned 1/0 address 300Hby appropriate setting of the DIP swit-ches. The second example switches thecomputer off but leaves the keyboard en-abled:

VAR DUMMY: BYTE;

BEGINPORT( S3001 := 2;DUNIMY := PORTE5300iEND.

The executable programs made in thisway may be included in a batch file, justbefore the park (or shutdown) routine forthe hard disk.

Preset P1 is relatively simple to adjust.Use the program that leaves the keyboardenabled. The computer is not switched onvia the relay (it is in normal use). initially,set Pt to minimum resistance, then run theauto power -down program. If necessaryadjust Pt until LED D2 goes out; this indi-cates that the circuit works. Press any key;the computer must be switched on again.Try a few settings of Pi until the circuitresponds reliably to the software. In casethe relay is de -energized with Pt set tominimum resistance, or when nothinghappens with Pt set to maximum resist-ance, the value of C9 may have to be re-duced or increased respectively.


39

WIN A SATELLITE TV RECEIVING SYSTEMAnswer the following six questions and then say in not more than twelve words why you

read Elektor Electronics. Write the answers and the phrase on the coupon below and send it

to the address shown, where it should reach not later than Friday, 22 June 1990.

The first correct answer taken from the post -bag will win a magnificent satellite TV

receiving system that will connect to any existing television receiver. The next 10 correct

answers will win a year's free subscription to Elektor Electronics. The winners will be

announced in the September 1990 issue of Elektor Electronics (on sale 16 August 1990).

1. By whom and when was the junction transistor invented?2. In electronics, what is a negator?3. What has replaced the mho?4. What is the name of the method of reception of UHF radio signals in which the

detector is a squegging oscillator?5. What is FORTRAN an acronym of?6. What, in electronic music or electrophonics, is MIDI?

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EI.EKTOR ELECTRONICS JUNE 19911

40

REAR WINDOW WIPER COUPLER

From any point of view; it is convenient tocouple the rear window wiper on our carsto the windscreen wiper. Since the rearwindow of a moving car does not getnearly as wet as the windscreen, it sufficesif the rear wiper operates only once forevery 8, 16 or 32 wipes of the windscreen.

At terminal 53e (green/black wire) onmost cars, which is the return of the wind-screen wiper motor, the clock signal forthat motor is present. This signal, which isa square wave, is applied to the clock inputof counter 10 via R2-R3. The Q3 output ofthe counter goes high every eighth clockpulse, and the Q4 output once every six-teenth clock pulse. The output pulse is ap-plied to monostable 1C2 via switch Si. Themonostable may be a Type 4528 (as drawn)or a Type 4548. At each trailing edge at pin5, the monostable output (pin 6) goes highat a frequency of 1.5-16 Hz. When thathappens, T3 is switched on, the relay is en-ergized and the rear wiper operates.

The supply for the circuit is taken fromterminal 53e also: during the intervals be -

G. Kleine

tween the dock pulses, this terminal is at apotential of 12 V. In that state, Ti isswitched on and Ci charges. When theclock signal is present at the terminal, Ti isoff so that 0 cannot discharge. Diode Di

limits the supply to 5 VNetwork Itt-Its-Cs-T2-D2 ensures a reg-

ular reset of the circuit during the wind-screen wiper interval.

BC5478

DI flC=I

5V6MINN

!eV

C2'

A.166

0

T202

516BC 5476 C3 11617.10

toy L -j...,

16V

0mi.

0ai Re'

1N4001T Ez111,2:-(),

Ca

2 ,-,BC165

34:02 - O

NEXT MONTHIN ELEKTOR ELECTRONICS

36 -PAGE SUPPLEMENT OF CONSTRUCTION PROJECTS

Simple square -wave generator

Car theft deterrent

INMARSAT's standard C

Sound demodulator for SAT TV receivers

Battery tester

SCART-plug FM mini sender

Simple. versatile NiCd battery charger

TTL-level 100 MHz crystal oscillator

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EE

INTERMEDIATE PROJECTA series of projects for the not -so -experienced constructor. Although each article

will describe in detail the operation, use, construction and, where relevant, theunderlying theory of the project, constructors will, none the less, require an

elementary knowledge of electronic engineering. Each project in the series will bebased on inexpensive and commonly available parts.

POWER ZENER DIODE

K. Walters

Power zener diodes are rare, hard -to -obtain and quite expensiveelectronic devices. The circuit described here is based on a handfulof common discrete parts that simulate a high -power zener diode.

Apart from the saving in cost, the discrete equivalent has anadditional advantage in that it can be set up to meet a wide range of

output voltage and power requirements without the need ofchanging components.

Many voltages, whether direct or alternat-ing, are far from constant. Examples offluctuating alternating voltages includethose supplied by the mains and manytypes of generator. In the case of directvoltages, sources like car batteries, inex-pensive DC adapters and solar cells come

to mind. Fortunately, most electronicequipment can cope reasonably well withtoo low a supply voltage, which is notusually worth worrying about because itis unlikely to cause damage. Overvoltage,however, often has disastrous effects evenwhen the nominal supply voltage is ex-

ceeded by as little as 15%. Examples ofeasily damaged components include cer-tain types of battery and chips from thenow obsolete 7-I-TTL series.

In many cases, such damage may beprevented by inserting a regulator be-tween the voltage supply and the equip-ment or circuit to be powered. Two typesof regulator are available for this purposeas discussed later.

Although they may consume powerfrom an alternating voltage source, mostelectronic circuits work from direct volt-ages, that are usually regulated (alternat-ing voltages are fairly difficult to regulatewith simple means).

Most of you will be familiar with the7Sxx and 79xx series of three -pin fixedvoltage regulators (Fig. 1). These devicesare widely used in many circuits becausethey are both inexpensive and simple touse: all they require is an input and anoutput decoupling capacitor, a small heat -sink and, importantly, an input voltage

Fig. 1. Circuit symbol of three pin fixedvoltage regulator.


42 INTERMEDIATE PROJECT

internalresistance

voltageSOUrCe

series regulator

1 cutputtrisect voltage,

,..:3e.13

Fig. 2. Principle of series regulation.

internalresistance

wattageSVaCt

Untegu.

ed*eltage

output(fixed voltage)

Fig. 3. Principle of shunt regulation.

that is at least 3 V higher than the outputvoltage, but not so high as to exceed themaximum specification (which is usuallybetween 30 V and 40 V). These regulatorsare available in a wide range of outputvoltages (both negative and positive) andoutput currents (100 mA to 2.5 A).

Series or parallel?The basic circuit shown in Fig. 1 is a seriesregulator. The regulating device is essen-tially an adjustable resistor connected be-tween the voltage source (input) and theload (output) -see Fig. 2. In practice, theseries resistor nearly always takes theform of a power transistor. The circuitcompares the voltage across the load witha reference level. The difference betweenthese voltages is used to provide the seriestransistor with a proportional base volt-age. When the output voltage drops, thedifference voltage rises so that the series

transistor is driven harder. This, in turn,causes a lower series resistance so that thecircuit counteracts the load variation bykeeping its output voltage constant.

A series regulator based on an 78xx or79xx integrated circuit typically has a rela-tively wide input voltage range with theminimum level defined as 3 V above theoutput level, and the maximum leveldefined by the permissible dissipation,which is the product of the voltage acrossthe regulator and the output current. Un-fortunately, the minimum voltage droprequirement may be a problem in a num-ber of applications. For these, a differenttype of regulator is required.

Parallel regulationIn a parallel (or shunt-) regulator (Fig. 3),the regulating element prevents the volt-age across the load exceeding a certainvalue. The zener diode is the simplestshunt regulator, although transistor arealso commonly used for this purpose.

The operation of the shunt regulator isbased on the internal resistance, Ri, of thevoltage source. Assuming that the voltagerises above the level established by theregulator, Ri drops the resultant voltagedifference. In more practical terms, theshunt lowers its resistance so that the volt-age source sees a heavier load. The result-ing current increase thus counteracts thevoltage rise.

The shunt regulator is relatively ineffi-cient since it passes more current as thevoltage rises above the maximum level. Itsadvantage, however, lies in the absence ofa voltage drop between the voltage sourceand the load.

Returning for a moment to the pre-viously mentioned example of the solarcells, it will be evident that series regula-tion is of little use in that application: themaximum output voltage of the cell willseldom be high enough to cater for the 3-Vdrop caused by a series regulator used tocharge a battery. The reasons for applyinga shunt regulator are fairly obvious here.

Fig. 4. Typical silicon diode U -I charac- Fig. 5. Typical zener diode U -I characteristic. teristic.

Fig. 6. Power zener diode equivalent withstepped zener voltage adjustment.

Zener diodeThe voltage/current characteristic of anormal diode and that of a zener diode areshown in Figs. 4 and 5 respectively. In thecase of the normal diode, the current in-creases sharply when the forward voltagerises above 0.6 V. The diode blocks whenthe voltage is reversed (negative), result-ing in a small leakage current.

The curve in Fig. 6 shows that the for-ward voltage characteristic of a zenerdiode is almost the same as that of a nor-mal diode. When the voltage is reversed,the current remains small initially, butthen rises suddenly at a particular value.At this value, the zener voltage, the deviceprevents the reverse voltage increasing bypassing more current. The effect is, ofcourse, bound by practical limits: thezener diode must be capable of handlingthe current that flows when the voltagerises.

1Vhen applied to our example of thesolar cells, a zener diode would affordsufficient protection against overvoltageon the batteries when there is intense sun-shine. Unfortunately, it is not that simplein practice.

Power zener diodeIt may %Yell happen that the zener diodecan not handle the current supplied by thesolar cells because its maximum dissipa-tion is exceeded. Most zener diodes havea maximum dissipation of 400 mW or1.3 W, while 5-W types are also found oc-casionally. Zener diodes with a higherpower rating are expensive and hard tofind, whence the idea to make one fromdiscrete components. This has a furtheradvantage in that it allows the zener volt-age to be made adjustable.

Figure 6 shows the principle. The baseof a medium -power transistor is con-nected to the junctions of a series ofdiodes. Since a normal (silicon) diodestarts to conduct at a forward voltage ofabout 0.6 V, the rotary switch allows thecollector -emitter voltage at which thetransistor starts to conduct to be set insteps of 0.6 V. When the switch is set toposition 1, the circuit simulates a 0.6-Vzener diode, or 3.6 \' when the switch is


POWER ZENER DIODE

Fig. 7. Power zener diode equivalent withcontinuously adjustable zener voltage.

set to position 6. The maximum current isabout 1 A in both cases.

Figure 7 shows an alternative circuitwhich provides a continuously adjustablezener voltage. The base -emitter voltage oftransistor Ti rises with the voltage acrossthe circuit. When this voltage reaches thelevel at which Ti starts to conduct, Tr con-ducts also since its base is made negativewith respect to its emitter. Hence, T2 isdriven harder as the base voltage of Tirises so that any increase in the voltageacross the circuit is counteracted by alarger load current.

Since the base of Tt is connected to apotential divider, 121-(R2-1-130, the point atwhich the base voltage of 0.6 V is reachedis determined by the input voltage leveland the setting of Pl. This creates a zener

Ultra -fast co -processorsbreak price barriers

IIT Inc. can now supply the 2C87. a high-performance numerics co -processor that isplug and object -code compatible with80287. The IIT 2C87 is a low -power CMOSdevice capable of operating at clock rates upto 20 MHz. Its low current demand makes itideally suited for lap -top computer im-plementation.

The 2C87 is less expensive than a 80287-16. yet performs most of its functions in farfewer clock cycles. When combined with thefaster clock frequency (the 2C87 can operateon the same clock as the 80286). the floatingpoint processor achieves performance at

A least two times faster than the 80287. Whenused with an 80286 processor the computingsystem fully conforms to the IEEE FloatingPoint Standard. The new co -processor in-cludes a built-in instruction to calculate a4x4 matrix transformation. This results inthe capability to perform matrix transforma-tions 6 to 8 times faster than the 80287. Inaddition. the 2C87 provides extra functionswhich are not available on the 80287. Thebenchmark test and the table compare theperformance of the 2C87 with the 80287.The IIT 2C87 is housed in a 40 -pin ceramicpackage.

Fig. 8. Suggested construction of thepower zener circuits (Figs. 6 and 7) onuniversal prototyping board size -1 (UPBS-1)Do not forget to fit the power transistors withheat -sinks.

NEW PRODUCTS

Also new from HT is thclaimed to operate up to 50'; later than80387 in the same application.

Integrated Information Technology Inc.(IIT) 2540 Mission College Blvd. SantaClara. Califirnia 95054 C.S.A. Tele-phone: (408) 727-1885. Fax: (408) 980-0432.

LK representative:DMST Ltd. Mead House PinknessDrive Maidenhead Berkshire SL6 6QD.Telephone: 10628) 777700. Fax: (0628)27237.

diode with an adjustable zener voltagebetween 2 V and 12 V. Provided T2 isfitted with a reasonably sized heat -sink,the circuit is capable of passing up to 1 A.The shunt current may be increased to 8 Aby replacing the BD139 in Fig. 6 with adarlington transistor Type TIP130 (notethat this results in a zener voltage whichis 0.6 V higher than that of the BD139-based circuit). The same current boostmay be achieved in the circuit of Fig. 7 byreplacing the BD140 by a TIP135.

7-2C87

:45.:E 2:33

18:11813

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INSTRUCTIO!:

C.:1V1 :73iCLES REQUIRED

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MINI EPROM VJ. Ruffell

'WU

This circuit complements the mini EPROM programmer featured afew months ago (Ref. 1). The simple -to -build unit allows data loadedinto most of the currently used types of EPROM to be examined in a

straightforward manner.

It may be argued that a full-blownEPROM programmer with PC control is,in many cases, superfluous luxury whenonly a small part of the contents of anEPROM is to be examined. The EPROMviewer discussed here allows this to bedone rapidly and in a simple manner withthe aid of three keys for address selectionand EPROM type, and, of course, a cleardisplay to indicate the relevant data.

Simplified circuit diagramIntegrated circuit ICs is a suitable startingpoint for the description of the operation

TYPE

551151

254

512

SET

EPROM VIEWER

UP DOWN

1111

of the circuit shown in Fig. 1. For the sakeof clarity, this diagram is a simplified ver-sion of the full circuit diagram, which isdiscussed later.

When the circuit is switched on, IC5, adecade counter, and dividers ICI-IC3, arereset by an R -C network. The reset condi-tion is indicated by all LEDs (Db, D7 andDs) and all decimal points in the displaysLDt-LD4 remaining off. Circuit IC5 con-trols all functions of the EPROM viewer.By pressing the SET key, it is provided witha single clock pulse, so that counter IC4 isenabled via an electronic switch. Theother counters, ICI, IC: and IC3, remain

disabled. Thus. , Illy IC4 is set by actuatingthe CP and tx)v.- \: keys. By pressing the SETkey, 1C3 is actuated. The next key actionsactuate IC:, and, lastly, IC). This selectionallows the four nibbles that forms theEPROM address to be set (one nibble =four bits = one hexadecimal number). Thedecimal points on the 7 -segment LED dis-plays indicate the current nibble selection.

The next three states of IC5 determinethe EPROM type selection. The types aredivided into three groups: xx512, x x256 orxxl 28, and xx64. When ICs reaches one ofthe last three states, 10-IC4 are trans-formed from four discrete 4 -bit countersinto a single I6 -bit synchronous counter.At the same time, the. display is switchedfrom an address read-out to a combineddata /address read-out: the data byte inthe EPROM is shown on the two least -sig-nificant displays, and the least -significantEPROM address byte on the two most -sig-nificant displays. This combined displaymode is indicated by the decimal pointson the 'data' displays, LID] and LD:.

The EPROM address may be set bypressing the LT or DOWN key. It is possibleto cross page boundaries (one page = 256addresses). This is achieved with the aidof the cARR). output of IC:, which enablesIC3 and in addition causes 106 to switchvia a monostable, so that the full addressis briefly displayed again. After the monotime has lapsed, the display reverts to thecombined LSB-address/databyte indica-tion mode with the two actuated decimalpoints. The next action on the SET keyCauses ICs to reset itself, allowing a newfunction to be set.

MAIN SPECIFICATIONS

Reads 8-KByte. 16-KByte. 32-KByteand 64-KByte EPROMs.

Full address entry or one -addressup down mode.

Combined address data read-outmode.

Multiplexed 7 -segment LED display.

Three -button control.

Optional computer interface.

Ideal for small-scale EPROM appli-cations.

ELEKTOR ELECTRONICS .It NE i9911

MINI EPROM VIEWER 45

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0!C2

0

set scooter 4set cocottesset e.,antes 2

A-3

cony

cleatop IC2down

EN

set scooter 164112a

255

41.

A1S

0

carry

clewan ICI

,..s /21015 OA1/4\

AO

EN

A14

06

07

EPROMTYPEselec-

tion

Da

Al

EPROM

07 HD0

1/2IC14 0

0

-0°0-

1/2 lc 14 0A

OD

01.

c 3.

IC17

hex todecimaldecoder

49 dp

02 0

clock

IC7

00GI

02;s

034o o 05-0607 -

LDS LD3

CI

02.

04 05

LD2

Cp

I-0

900290./1

Fig. 1. Simplified circuit diagram of the EPROM viewer.

The 4 -digit LED display is multiplexedunder the control of counter IC7. The dis-plays are rapidly actuated and turned offagain by the respective outputs of IC7. Thedata associated with a particular addressis simultaneously fed to the 7 -segmentdecoder, 1C17, via data switches IC13, ICI4and IC15. Since the outputs of IC7 are al-ternately connected and not connected, ashort delay is introduced during whichthe data switches are allowed to changestate. The delay effectively prevents'ghosting' of the display owing to the set-tling time of the switches and the displaydriver transistors, Tt-T4.

Circuit IC16 distributes the multiplexsignals in two ways across the switches.The distribution shown in the circuit diag-ram enables the combined 'LSB-ad-dress/data' read-out, the otherdistribution the 'full address' read-out.

The real thingThe full circuit diagram, shown in Fig. 2,

differs from the previously discussed sim-plified version in a number of ways. Thisis mostly due to practical realizations oftarget functions set out in Fig. 1. Take, forinstance, the OR gate for the reset functionof ICs in Fig. 1: in the actual circuit, thistakes the form of a diode -resistor combi-nation, DI -R5. Similarly, counters ICI -1C4are not actually reset but preset with value0000, which has the same effect. Thesimple up/down control suggested byFig. I is actually realized by a clock pulsegenerator, NAND gate 1043, a delay, Re -Cs, a re-triggerable monostable, IC6a, andIC9c. The latter controls the level of theUP/DOWN inputs of the counters. Theclock pulses for the counters are providedby IC6a, whose monotime is set to about2 ms to cope with fast actions on the keys.The 2 -ms delay must be taken into accountif the circuit is controlled by a computervia terminals A, 13 and C.

The EPRONI type selection circuit mustensure the correct signals at pins 1, 26 and27 of the EPROM used. Pin 26 is either not

connected (xx64 types) or forms the A 1 3input (all other types). This allows A13 tobe connected to EPROM pin 26 with im-punity. The situation is a little more com-plex in the case of pin 1. Fortunately, asingle three -input OR gate, IC -12b, does itall. If an xx512 is selected, this gate passesaddress signal A15. In all other cases, itholds pin ] logic high. Pin 27 is controlledin a similar manner: with xx64 and xx128types, it is logic high, while with xx256and xx512 types signal A14 is applied viaICI -2.c. The valid address ranges for thefour EPROM types that may be used areas follows:

EPROM size address range

xx64 8 KByte 0000 - 1FFFxx128 16 KByte 0000 - 3FFFxx256 32 KByte 0000 - 7FFFxx512 64 KByte 0000 - FFFF

The circuit is powered by a single 5 V rail.The power supply used must be capable

ELEKTOR ELECTRONICS JUNE 199n

46 CON1PUTERS AND MICROPROCESSORS

imm

1M4144

C

6

466

IC7

TNCI T1St

.11/11,14 1:: I

6

a z21-Z

-41

11-

W 6A= :urAo Gal F6

...; 472 .'t 442 no

rW44e ty,74 !_ ...L., 47 e:

MGT 4 .a ...1, ,.., PICT111 a 7 AS 1 .t_V ;n141

..,..., 4 la . 4.: vi

MI6

El

Cat

- 1=1.1:;

MEM

cra. CI

.1. tray

EPROM 4.x.241

O7 0.30.

71..!? -1 a a =,.,ta a

sy 9U.C.01

oaMI6

C

doz

M.

Kt tats

T32"1CZ K7

®

tr .::C

9 T-

6M1

ICE 7414CT 113LS =74/4C114KZ 7414= 02K13= 74.4014CU= 714141.075

1-r.F11G1 IC 1 107

-'- .2.I

-4-14. 1) -

g

ra416

C17CCula

3C

F

W ED

tI

Y4.4.

1. a

N EM

01,

.-^II II4a'II 4 6.! 13-

. -2 a111

Ls ICS4711 mn

(1,c -C7 c- sea cao Cu2 £13 IC14gal CO Cif C17

01.3- ° T 9 9 T -T T

Fig. 2. Complete circuit diagram of the EPROM viewer. The EPROM to be examined is plugged into the zero -insertion force (ZIF) socketmarked IC18.

VPP 1 CA

Al2 2A7 31

A6 41A5 5(-A4 61

A3 71

A2

Al 9

AO 10rDO IIDI 121(D2 131

141

2764 27128

728 VCC327 PGM

326 NC A7 31

125 A8 A6 41

24 A9 AS 51

123 A71 A4 61

)22 OE A3 7(321 A10 A2 8[320 CE Al 9

119 D7 AO 101

Vpp IL,Al2 21

.318 06 DO 111.

P17 05 131 12 Li

016 DS D2 131

03 141

8K x8

728 vcc2 27 PGM

'326 A13'725 A8324 A9

323 Ail)22 OE321 A10)20 CE119 D7

NJ 18 06

)17 05316 04715 D3

16K x 8

27256 27512

Vpp 1 Co

Al2 24A7 3

A6 4CA5 sC

A4 6(;A3 71A2 81,Al 9

AO 1014'

DO 11(DI 1202 131

141

728 VCC A15 10,727 A14 Al2 2(,P26 A13 A7 31'

-::P25 A8 A6 4f324 A9 A5 5C-1 23 All A4 61

322 OE A3 71

321 A10 A2 8(320 CE Al 91

/119 D7 AO 101

18 D6 DO 116

017 05 01 125016 04 D2 131.

315 03 141

32K x 8

328 VCC

) 27 Al41326 A13125 A8324 A9323 All722 OE Npp321 A10

720 CE

/119 07118 D6

117 05316 D4)15 D3

64K x 86901E6.14

Fig. 3. Pin -outs of the EPROMs that can be handled by the viewer.


\ II \I [PROM VIEWER

COMPONENTS LIST

U Cie

c11 001 1-0r o a

oe

C122.

Cl

T4 T3 T2 T14-04,1 4-0-41C7 0-e 0 0 0 0 Cl

0 0 0 0 00110J J CI

Q a a15

0(915 lo 01915 )) 0(9170(914 )000:119 {0

42.D7

0(913 0 '

0 1rU

S3

_/

03 DB

4!

()-1 OfR 2010Ci9

C 7 OGI [00 CO112 10

Cis 0-011-0

0000 000000 0000

a

00000000000000

Si

2.

O 0C1 1itCB

C13

92

\/ N

Fig. 4. Component mounting plan of the double -sided. through -plated circuit board.

of providing a regulated 5 V at up to 0.5 Ato cater for the relatively high current con-sumption of the LED displays.

ConstructionThe printed -circuit board for the project,shown in Fig. 3, is double -sided andthrough -plated. Construction is mostlystraightforward soldering work with ref-erence to the parts list and the componentmarks printed on the board. Position ICisrepresents a 28 -way zero -insertion force(ZIF) socket to ensure that the EPROM tobe examined can be fitted and removedfrom the viewer without its pins beingdeformed. Depending on the height of theenclosure used, it may be necessary tomount the LEDs, the displays, the ZIFsocket and the switches at a certain heightabove the board. The displays are con-

veniently given the appropriate height bystacking a few IC sockets. A bezel may beused to improve the readability of the dis-plays.

The circuit has only one adjustment:Pi. The preset defines the time duringwhich the full address is shown when themost -significant address byte changes.This time may he set to a value between0.3 s and about 5 s.

Finally, always switch off the circuitbefore inserting or removing an EPROM.

Reference:1. Mini EPROM programmer. Elcktor Elec-tronics January 1990.

Resistors:4 1k29 100k

1 10k

2 220k3 270f22 2201.2

2 47k1 3k91 2M5 preset H

Capacitors:1 220nF4 100nF9 22nF1 10p1 1 it0 10 V radial1 lOn1 10uF 10 V radial1 470uF 16 V axial

Semiconductors:9 1N41483 LED red 3mm2 1N40014 HD11070 (common

cathode)4 BC3374 74HCT1912 74HCT40171 74HCT1231 74HCT141 74HCT1321 74HCT141 74HCT1571 74HCT40754 74HCT2411 NE589N (Signetics)

R1 -R4

R5-RB;Rit;R21 -R24

R9

R10;R12

111.3:R14;Rt5

1316:1:117

R18;R20

R19P1

CiC2;C3;Ci8:C19C4;C9-C16C5C6C7CB

C17

D1 -05:D9 -D12136:07;D8

013:D14LD1-LD4

Ti -T4ICI-ICAIC5:1C7

IC6ICe

IC9IC10

IC12

IC13-1C16IC17

Miscellaneous:1 28 -way ZIF-socket ICi8

(e.g. Textool)3 push-button ITN type St ;S2;S3

61-102040001 enclosure (200,:110x30 mai)

e.g.. Boole type EG20301 printed -circuit board 900030


48

CRO CALIBRATORD. McBright

A true -square -wave signal is useful for measuring the performance ofthe Y -amplifier of an oscilloscope. In particular, it enables three parame-

ters to be checked: gain, amount of tilt produced by theamplifier and the frequency response. The calibrator described here pro-

vides such a signal.

The calibrator delivers a true -square -wavesignal to facilitate (see Fig. 1):

(a) measurement of the gain of the Y -amplifier by displaying a signal whosepeak -to -peak level has been set accurately;

(b) measurement of the amount of 'tilt'produced by capacitive coupling circuitsalong the flat top, at a frequency of about50 Hz;

(c) checking the frequency response ofthe Y -amplifier (but not its rise time) set bythe frequency correcting trimmers in thecoarse gain switch and in the probe at afrequency of 500-1500 Hz.

The calibrator is also useful when theoscilloscope is used in the 'variable gain'mode to measure accurately the level of adisplayed signal (especially if the scope ishome -built!).

The principleThe principle used in the calibrator is a

simple but effective one for which only ahandful of components are needed to pro-duce a good square wave.

First, the level of a direct voltage is setwith the aid of a DC voltmeter. The voltageis then 'chopped' to produce a squarewave of known amplitude, and this is usedas an AC signal to calibrate the oscillo-scope.

Since the calibrator is connected di-rectly across the output terminals, the ac-curacy of the system is determined chieflyby the accuracy of the voltmeter used. Forlevel measurements, the voltmeter remainsconnected all the time, but is only readwhen the calibrator is switched to SET UP,since the square wave in the cm_ positionproduces a reading of approximately halfthe peak -to -peak value. However, whenthe calibrator is used for checking the fre-quency response, the voltmeter should bedisconnected to reduce any shunt capacitythat might degrade the signal.

Level measurements may be made intwo ways:

first, the DC level is set with the aid of a

voltmeter, after which the oscilloscopeis adjusted to the resultant squarewave;the square wave, as viewed on the os-cilloscope, is adjusted to the requiredlevel, after which the calibrator isswitched to SET UP and the voltmeterread to give the peak -to -peak level.The output impedance, with terminat-

ing switch 54 open, is of the order of 600 SI,

but this will be modified by the resistanceof the connected voltmeter. With 54 open,the output voltage range extends fromover 4 V to less than mV when both

P -Pthe coarse (52) and fine (P2) are set cor-rectly. When 5.1 is closed, R21 is connectedin parallel with the output, which causesthe voltage range to be halved: this makessetting up easier at some levels.

Since the meter terminals are wired in

m1111.

a) Height(Ideal shape)

TPk - PkHeight

I6) Tilt c) Overshoot or undershoot

900071 - 11

Fig. 1. The calibrator enables three parameters to be checked.

C2

BC2378 ICI =1 IC2 =I0 22µ

168

=RN6 8 n

CBE

SETERE: ,t,/RI

Pi

5

EMI

ICI b

ifFts

TRIG'

H

CAL

SST UP

C3

M1.40931C2 =40669

2n2

13

12

1C2e

55

2

Ork4.F802378

Rif

1C2a

RIP

EMISE7LEY0.

flR16

12

H

fl

RA

3

U

1C2d

n

56

RIP

R22

H

CS

2214 '177PIBA 16A

IC2b

524

0-

Ra RE: R121 Rta

*R17 PR RII

U

PETER

H54

TERM

Ft5= 15:11= 1E50 ,11.5RA = 161355 = 150T/ 111k5R7.63313 . 167E152RA .ATECI = EA30 //152RIO = tit = 97//10

S2: a = 1Ce$V = tORaY

2.3V

C/E, OCT

53

01 0r- - - -1

CA -

OR21

8

SEC -221 t2

Fig. 2. Circuit diagram of the CR0 calibrator.

ELF.KTOR ELECTRONICS JUNE 1990

CR() CALIBRATOR

parallel with the coaxial outlet, the con-nexion to the scope may be taken from ei-ther. However, since the output imped-ance is relatively high, connexions madein screened cable should be kept as shortas possible.

A separate output of about 1 Vpp isprovided for use as a triggering signal.The calibrating square wave is delayedsome 20 us relative to this output.

The frequency range is of the order of30 Hz to 3 kHz.

The circuitThe variable oscillator is based on SchmidtNAND gate ICia: oscillations result fromthe 'toggle' action of the gate on networkRI -P1-0. The output signal of the oscilla-tor is divided between 1Cib and ICic.

Circuit ICib provides an output ofabout 1 V across 60011 for triggering pur-poses.

After a delay of some 20 us providedby network R4 -C3, circuits TO( and ICidproduce a square wave and an invertedsquare wave respectively. These signalsare used to drive the control circuits of the

A SPEAKER FOR ALL SEASONSFieldtech has introduced a range ofweather-proof drive units. The cones aremade from transparent polyester filmmaterial and are thus unaffected bywater and less prone to tearing anddegradation than conventional cones.

The units are particularly suited to en-vironments where water or excess hu-midity may be encountered. Their robustconstruction means that they are rela-tively unaffected by rough handling,while dirty/dusty surroundings will notsignificantly affect their operation. Theyare ideal for use as sounders and alarmswhere multiple tones are required, par-ticularly in portable or exterior mountedequipment.

The units are available in 10 sizes,ranging from 1 in. (23 mm) to 4 in.

analogue switches.One input of ICic is connected to the

mother contact of CAL/SET UP switch Si.This switch, when in position SET UP (CND),keeps the analogue switches connected tothe emitter of Ti; in position CAL (÷9 V), itallows control of 1C1c and ICid by thesquare wave.

Circuit IC2 is connected as a change-over switch with its mother (common)contact, connected to coarse level controlS2a, switching between the reference volt-age at the emitter of Ti and GND. Theswitches in 1C2 are connected as paralleledpairs in series with small isolating resis-tors: Rs, R6, Ris and Rib. The base voltageof Ti is set by 'fine level' control P2. Thepotential across P2 -R19 is stabilized byzener diode Di.

The choice of output impedance waslimited by the series resistance of the ana-logue switches and their inability to han-dle high currents. Ideally, 75 SI or 50 il.would have been preferred, but since thiswas not possible without greatly reducingthe maximum output voltage, 600 LI waschosen.

The square -wave output of the calibra-

(100 mm). Maximum power input rangesfrom 0.1 W to 12 W Nominal impedanceis 8 Q.

Fieldtech Heathrow Ltd, HuntaviaHouse, 420 Bath Road, Lomgford, WESTDRAYTON U B7 (XL.

NEW MOSPOWER TRANSISTORSFROM SILICONIX

Siliconix has introduced eight new N10-

SPOWER transistors in the TO -257 pack-age-the smallest isolated hermeticpower MOSFET package currently avail-able. This compact new package allowsdesigners to pack higher power densitiesinto a given space and results in lowerdrain -to -ground capacitance, which re-duces EM! currents.

Siliconix Ltd, Weir House, OverbridgeSquare, Hambridge Lane, NEWBURYRG14 5UX, Telephone (0633) 30905_

LONG-TERM PROTECTION OFELECTRONIC CIRCUITS

APL, a new acrylic lacquer from Electrol-ube, provides long-term protection ofPCBs, enclosures, containers and boxesagainst wear, humidity and handling.

The flexible, transparent coating is es-pecially useful on instruction/informa-

tor has a rise time of about 0.08 Lis and, atsome levels, small overshoots at the samespeed. These are, however, fast enough tobe ignored in any measurements for whichthe calibrator is designed.

The current drawn from the 9 V batten,lies between 5 mA and 11 mA.

Construction

All components, except the potentiome-ters, switches and terminals which shouldbe fitted to the front panel, may bemounted conveniently on a piece of ver-oboard of about 75x75 mm.

Stand-off pins should be used for con-necting the wiring to the various controlsand the batten,. The board, together withthe battery, is fitted in a 150x100x60 mmenclosure.

Only two precautions are necessary:decoupling capacitors C2 and C4 should bemounted as close as possible to the rele-vant ICs, and, because of the presence of'fast edges', connexions to coarse levelswitch S2, the output terminals, and fre-quency control Pi must be kept as short aspossible.

tion panels where decals, logos, letteringand numbering must be protected yet re-main clearly visibile. With an operatingtemperature range of -55 'C to +125 "C,

the product provides excellent adhesionand resistance to mould growth, anddries to touch within 20 minutes of appli-cation (optimum properties are achievedin 24 hours). Because it contains no phe-nols, it is non -corrosive to cadmium andzinc plate, while the absence of iso-cvanates ensures it can also be solderedthrough without producing toxic gases_An additional safety feature is that thecured product is self -extinguishing.

Electrolube Ltd, Blakes Road, WAR -GRAVE RG10 8A1. 1r, Telephone (073 522)4031.


50

ZTEX 24 CM FM ATV PANSMITTER ND24 CM GaAs FET PRE MPLIFIU

Ever since it was first exhibited at last year'sLeicester Show. the Aztex 24 cm FM ATVtransmitter has created a lot of interest and Ihave often been asked for details of this unit.These requests prompted me to do a detailedreview to satisfy the many enquirers.

Before commencing the review. I hadsome correspondence with designer KenStevens. G4BVK, from which I quote: "Inthe design of a transmitter. the need of a sta-ble output is one of the governing factorsand in the 24 cm model the Type SP5060phase -locked loop was specified. The use ofsurface -mounted components was anotherway of maintaining stability."

"The video pre -emphasis network, whilstbased on the standard CCIR circuit was de-signed to gi\ e an HF lift in addition to thatgiven by a standard CCIR network. This over-comes the HF losses in the modulator in addi-tion to providing the normal in, lift. Intro-ducing some kind of DC restoration on thesignal was also deemed necessary before itwas injected into the modulator. and thecuit adopted to achieve this is very effectivein stopping the video content from alteringthe black -level position."

"The two sound inputs are mixed activelywith the aid of a Type TL072 opamp beforethey are fed to the modulator. There is a sep-arate PCB -mounted preset for adjusting theline input only: the front panel sound controladjusts the composite level of both inputs. Asub -carrier injection level preset is also pro-vided on the PCB."

Description

The unit comes fully assembled in a die-castbox measuring 188x120x57 mm and has aremovable lid secured by six cross -headscrews. The professionally, produced frontpanel contains the mains on -off switch:channel selector: two potentiometers-onefor the sound and the other for the video de-viation: and four LEDs:one indicating theconnection of the DC supply. one indicatingtransmit. and two indicating which channelis selected.

The rear panel contains an N -type socketfor connecting the aerial: a BNC socket forthe video input; two sockets far the audio in-puts; a phono socket for the line input and a114 inch socket for the microphone. The DCinput is via a 3 -pin plug: a lead with a

A review by Mike Wooding, G6IQM

TECHNICAL SPECIFICATION

Frequency - channel 1channel 2

RF power outputHarmonicsModulation systemAudio sub -carrier

Video input

Audio inputs

Power consumption

1249 MHz

1255 MHz

2.5 W (typical)

<50 dBcFM with built-in emphasis

Preset to 6 MHz: 17 dBbelow carrier (variablewith deviation setting)1 V p -p into 75 Ll

Dynamic microphoneAdjustable line input

(VCR. etc.)

1.6 A at 13.8 V

matching line socket is provided.My only criticism of the outward appear-

ance of the unit as supplied was the lack ofidentification of the connection points at therear of the unit. Whilst no one is likely toconfuse the aerial socket or the power plugwith any other, confusion could arise be-tween the two audio inputs and. perhaps, thevideo input. I understand. how ever, thatthese deficiencies are attended to in produc-tion models (the review model was only thefourth or fifth made).

Internally, the transmitter is laid outneatly, with the mother board housing theaudio amplifier, modulator and sub -carriergenerator circuits. and the video circuits.The bOard is held in place with four nuts.bolts and spacers. so that removal for anyservicing will be an easy matter.

All the RF circuits are contained in asmall die-cast box, occupying about onethird of the main case at the right-hand side.This has the advantage of providing a furtherlevel of screening between the baseband andRF sections of the transmitter. The N -type RFoutput socket is mounted through the casedirectly into the inner box and is soldered di-rect to the PCB. so that no RF cables flowaround inside. Interconnections between theRF box and the mother board is effected byseveral feed -through terminals carrying thebaseband signal. power supply and fre-quency switching control signals.

The RF assembly is bolted to the maincase with the same bolts securing the inter-nal PCB via spacers. The N -type aerial socketis bolted to the RF box and a clearance hasbeen drilled through the main case. Thus. al-though a little intricate, removal of the RF as-

sembly and circuit board for servicing can beeffected fairly easily. although some care isrequired. The circuitry is designed in state-of-the-art surface mount technology Orr).

Three user adjustment points are pro-vided inside the transmitter: a preset pot -meter for audio sub -carrier injection level: atrimmer capacitor for setting the audio sub -carrier frequency: and a preset potmeter forthe line audio level. The supply is protectedby a miniature wire -ended fuse soldered be-tween two posts on the mother board.

Bench tests

The test equipment used to carry out the lab-oratory tests is listed below. I would like tothank Roland Hall. GOGSA, for his assis-tance with the analyser tests and plots.

Marconi 2383 Spectrum Analyser &Tracking Generator.Racal Dana 9087 Siimal Generator.Philips PN15646 Television Patternerator.Hewlett Packard 435A Power Meter.Hewlett Packard 8481A Power Sensor.Racal Dana 1998 Frequency Counter.Philips PNI3226 Oscilloscope.Fluke 8050A Digital Multimeter.Racal Dana 9232 Bench Power Supply.

Frequency stability.Because of the crystal -controlled PLL ex-citer, the frequency stability is good asshown in Table 1. It is seen that the total

TIME FREQUENCY

switch on 1249.02623 MHz10 sec 1249.02611 MHz20 sec 1249.02581 N11-17.

30 sec 1249.02569 MHz411 see 1249.02559 MHz.r.;) I sec 1249.02558 MHz6(I sec 1249.02549 MHz70 Sec 1249.025.4 MHz80 sec 1249.025-H MHz90 sec 1249.(12: \IHz

100 sec 1249.112_':-- N1Hz

110 sec 1249.12555 \tHz120 sec 124011'-',:. N1Hz

3 min 12_-)12:'16 MHz10 min 1249.(12.:113 MHz

15 min 1240.1 L-11 MHz20 min 124',.( C.401 MHz30 Min 1249.02389 MHz


AZTEX 24 CM FM ATV TRANSMITTER -A REVIEW

TINIE POWER

-,,,,, itch on 2.72 NV5 min 2.54 W

10 min 2.46W15 min 2.37 W20 min 2.35W25 min 2.34 W30 min 2.34 W

Table 2.

Fig. 1. Spectrum obtained using a plain red pat-tern.

Fig. 2. Spectrum obtained using 1007, saturatedcolour bars.

Fig. 3. Spectrum obtained with a Philips Pt,15534

test card.

drift of the review unit amounted to only2200 Hz over a 30 -minute period fromswitch -on.

Power output and harmonics.The RF power output was monitored over a30 -minute period at 1249 MHz: the resultsare shown in Table 2. After the initial 20 -minute period during which the powerdropped by 0.37 W (0.65 dB). the output. toall intents and purposes, remained constantat 2.3 W. A similar check was carried out at1255 MHz: here the initial power output wasslightly higher at 2.84 W. with the final out-put settling at 2.54 W.

The harmonic content of the unmodu-toted output was very low. indeed, probablythanks to the out -of -band rejection character-istic of the SCI043 PA output device. Thesecond harmonic was measured at slightlyless than 50 dB down on the carrier. Thirdand subsequent harmonics were not de-tectable above the -75 dB noise floor of theanalyser.

Video and audio characteristics.A modulation index of 0.5 v. as ascertainedby applying a 5 MHz sine v. aye to the videoinput and, viewing the output on a spectrumanaly ser. adjusting the video amplitude (de-viation front the signal generator so that thesidebands coincided with the recommendedmodulation index of 0.5. The output fromthe signal eenerator was then measured andthis level used as the reference .output levelfrom the Philips TV pattern generator for theplots shown in Figures 1.2 and 3.

The audio sub -carrier generator is nor-mally set for UK use at 5.9996 MHz. but canbe easily reset to the 5.5 MHz Europeanstandard with the sub -carrier oscillator trim-mer. which is accessible when the top coveris removed from the transmitter.

At maximum video deviation, the sub -carrier level was measured at 17 dB belowcarrier. but this relative difference becomesereater as the video deviation is reducedwith the VIDEO control on the front panel. Atminimum deviation. the sub -carrier wasmeasured at 32 dB below carrier. With astandard video input level of 1 Vp.p, it wasnecessary to set the VIDEO control at approxi-mately, 50G to achieve a normally deviatedpicture, and at this setting. the audio sub -car-rier was measured at about 24 dBc. whichproved to be quite sufficient for good audiowith P5 contacts. Nevertheless. I did adjustthe sub -carrier injection control on the mainPCB and brought the relative level back to17 dBc at this VIDEO control setting. Thisprovided very good audio fidelity commen-surate with picture reception.

In all fairness. I should point out that ifthe input video level to the transmitter is ad-

justed so that the VIDEO control on the trans-mitter is set towards fully clockwise in oper-ation. the audio sub -carrier level is satisfac-tory without internal adjustment.

On -air tests and conclusions

Overall. I was very impressed with theworkmanship and presentation of the trans-mitter. Upon receipt, it was simply a matterof connecting 13.8 V. plugging in the cam-era and microphone. connecting the aerial.switching on. and adjusting the audio andvideo controls. This is ideal for those of uswho are not of the home-brewine fraternity.In my opinion. this is currently the only unitavailable that satisfies this need.

Furthermore. the very useful output levelOf around 2.5 \V is enough to drive a 2C39Avalve linear to quite a useful output tin mycase to about 60 W). The colour handlingcharacteristics of the unit eave excellent re-sults. as did the audio response. when testedover a P5 path.

Apart from the criticism mentioned ear-lier on. 1 do not like the use of a soldered -infuse. Although to some of us obtaining andchanging this should failure occur would notbe much of a problem. at some stations itcould be a daunting task.

The Aztex ULNA 23-24 GaAsFET preamplifier

MANUFACTURERS SPECIFICATION

Typical gain 17 dB

Noise figure 1 dB

Bandwidth 1250-1350 MHz -±1 dB

Rejection 8 dB at 700 MHzDC supply 7-18 V

The ultra -low -noise preamplifier comes in ablue hammer -finished die-cast case measur-ing 110x60x30 mm with N -type input andoutput sockets provided at the sides. The topcover of the case is secured by four cross-head screws. NOTE: this enclosure is notwater -proof, as stated by the manufacturers,and therefore needs to be mounted inside an-other weather -sealed enclosure for exter-nal/mast mounting.

The printed -circuit board is secured bytwo of the N -type socket's fixing bolts oneach side. The DC supply is fed into the boxby two insulated solder terminals and is pro-vided with a reverse polarity protectiondiode.

The GaAs FET is a Type ATF10135. oneof the latest Avantek products. It is mountedon a vertical pat screen soldered to the maincircuit board. A brass horizontal top screenis soldered to the vertical PCB screen and is


RADIO & TELEVISION

also clamped to the side of the box undertwo of the retaining screws of the N -type out-put socket.

Input and output tuning trimmer capaci-tors are mounted at each socket and a biaspreset potmeter is located on the main PCB.

Bench tests

The test equipment used to carry out the lab-oratory tests consisted of:

Marconi 2383 Spectrum .Analyser andTracking Generator.Fluke 8050 Digital Multimeter.Racal Dana 9232 Bench Power Supply.

Air tests and conclusions

The flat, even response of the preamp overthe entire 23-24 cm band meant that I wasable to tune to signals at the RMT2 repeaterinput and output frequencies (1249 MHz and1318.5 MHz respectively) without any lossof preamplitication. This was a new experi-ence for me as my own homebrew GaAsFET preamp is a half -band unit, which re-quires adjusting when tuning from one endof the band to the other.

Also, the very low noise figure of thepreamp means that the 15.5 dB or so of gainappears to be a great deal more when com-pared with results obtained from otherpreamps with perhaps higher gain figures(not the least my own unit! i. Noi:e figures

LOW-COST INTRODUCTION TOSURFACE -MOUNTED ASSEMBLY

Surface -mounted components are muchsmaller than conventional ones and can.therefore, be used closer together. leading tosmaller circuit boards with the same functionor the addition of further functions to aboard of the same size. This allows equip-ment to be updated or improved withoutchanging its outer appearance.

The disadvantage of such a system is thatit normally requires automatic machinery toposition the components on the board. The'Microline' range from Flint Distribution of-fers an entry system to take an introductorystep into this technology without undue ex-pense. It includes an infra -red reflow oven.vacuum pick-up pen. rotary component tray.screen/stencil printer and static -safe wristrest. The low cost of the system allows pro-duction to be started with minimal outlay:the system may be expanded at a later stageif required.

The retlow oven. designed to take sur-face -mount boards up to 100x160 mm, mea-sures only 260x290x160 mm (WxDxH). Ituses infra -red panel emitters similar to those

Fig. 4. Gain vs frequency characteristic over theband 249-2240 1,1Hz. The reference input levelwas -20 dB and the centre frequency of thecharacteristic is 1249 MHz. It can be seen thatthe 0 dB gain points are at about 600 MHz and1700 MHz (frequencies above 2200 MHz are ig-nored). The -3 dB band extends roughly from1318 MHz to 1500 MHz.

are complex and I do not intend to go intothese, but I can say that this unit with itsnoise figure of around 1 dB will take a lot ofbeating.

My overall impression of the preamp isof a sound. well -made unit that providesvery good performance. I wholeheartedlyrecommend anyone requiring a preamp forthe 23-24 cm band (which, to my mind. justabout includes everyone working 24 cm FM

in larger ovens together with a sensitive pro-portional temperature controller and timeralarm. Double -sided assembly is possible byusing standard solder cream for the first sideand repeating the operation with low -tem-perature solder for the second side.

The 'kilter' is a rotary tray holding 30 re-movable lidded containers for components:it -is covered by a Perspex lid with accessholes.

The vacuum pick-up pen allows the easy

Fig. 5. Gain vs frequency characteristic over theband 1250-1350 MHz with the centre frequencyat 1300 MHz. It is seen that the response in the23-24 cm band is very flat with a positive gainslope. The reference input level was -20 dB andthe gain at 1300 1.1Hz was measured as 16.1 dB.The gain at 1249 MHz was measured as 15.5 dB.while at 1318 MHz it was 16,4 dB.

ATV) should serious!\ consider this unit.

The Aztex TVTX 24 cm FM ATV transmit-ter is priced at £220 plus £2.50 p&p. and theAztex ULNA 23-24 GaAs FET preamp retailsat £52 plus £1.50 p&p.

Both units are available only from theSevernside Television Group. 15 WitneyClose. Safford. BRISTOL BSI8 3DX. Tele-phone (0255) 873098.

picking and positioning of components onthe board.

The static -safe wrist rest supports the op-erator's wrist, allowing precise movementclose to the board. thereby improving place-ment speed and accuracy.

The screen/stencil printer takes screenprinting frames or a holder for stencils ofconnector patterns to be etched or drilled.

Flint Distribution Ltd. Enterprise House,Ashby Road, COALVILLE LE6 2LA, Faxt0530) 510275.

RECEIVER AND TRANSMITTERBOARDS FOR LOW -POWER SECURITYLow-cost receiver and transmitter hoards forlow -power security applications are avail-able from Quantelec. They use surfaceacoustic wave frequency sources operatingat 418 MHz. are approved to NWT 1340. andoffer an easily applied solution to RF controlproblems.

Further details from Quantelec Sales Ltd.110 Corn Street, WITNEY OX8 7BL.

ELEKTOR ELECTRONIC JUNE 1990

FOUR -SENSOR SUNSHIRECORDER

J. Ruffell

Although it is almost impossible to imagine present-daymeteorology without electronic equipment, sunshine is still widely

measured with the aid of the classic, all -mechanical,Campbell -Stokes recorder. The electronic instrument described in

this article offers far better accuracy than the Campbell -Stokesmeter. It measures the total time during which sunshine is detected,

and records this information with the aid of a computer.

The recording of the duration of sunshinetime over a certain period is among thedaily routines of meteorologists. Themeasurement is usually carried out withthe aid of the Campbell -Stokes recorder, adrawing of which is shown in Fig. 1. Therecorder consist of a sphere arranged tofocus the sun's image on to a bent strip ofcard on which the hours are marked.When the sun shines with sufficient in-tensity, the sphere focuses the light on thepaper, which is burned at that spot. At theend of the day, the length of the burnttrack on the paper enables the sunshineduration to be calculated. Interruptions inthe track indicate passing clouds. Al-though the inaccuracy of the Campbell -Stokes recorder is fairly high at 10 to 20 .

the instrument is still widely used for lackof an better alternative.

Like the original Campbell -Stokes re-corder, the all -electronic version dis-cussed here has no moving parts. Itsmeasuring principle does, however, re-quire a computer for data recording pur-poses. In principle, any computer may be

used for this application, provided theright interface and control program areavailable_ In this article we will assumethat a 8052 -BASIC computer board is used(see Refs_ 1 and 2).

Four sensors: a newprincipleThe electronic sunshine recorder is basedon four photodiodes Type BPW2 1 whichmeasure the ambient light intensity. Sincemeteorologists hold that there is sunshineif there is a shadow, the position of eachof the four sensors enables it to measure adifferent light intensity when the sunshines. When the illumination is homo-geneous, as is the case with an overcastsky, all sensors measure the same lightintensity. When the sun shines, the sensorthat is best aimed at the sun receives thehighest light intensity. The computer con-nected to the sensor assembly runs a con-tinuous calculation on the position of thesun, while accounting for the geographi-

Fig. 1. Artists impression of a Campbell -Stokes sunshine recorder.

cal coordinates, the season and the localtime. In this manner, the system alwaysknows which sensor faces the sun andthus receives more light than the others.Next, the average light intensity on allfour sensors is measured_ The system de-tects sunshine when the sensor aimed atthe sun measures a substantially higherlight intensity than the sensor with theweakest illumination. This approachmakes the accuracy with which the num-ber of sunshine hours is recorded depend-ent on the measurement frequency only.While an accuracy of about 30 minutes perday is quite good for a Campbell -Stokesrecorder, the present circuit is capable ofresolving seconds of sunshine -quite animprovement!

Sun position calculationsThe fact that the movements M the planetsin the solar system are regular makes itfairly easy to provide reasonably accuratepredictions for the position of the moon,the sun and planets in relation to theearth. This means that the sunrise andsunset times on earth may be calculated.In his article "Calculating the position ofthe sun" (Ref. 3), R. Walraven proposed a


54 GENERAL INTEREST

Fig. 2. Prototype sensor assembly en-closed in a glass vessel. The photodiodesare mounted on small pieces of stripboard.

Fortran computer program for calculatingthe position of the sun in the sky aboveany location on earth, with an accuracy of0.01'. This program has been used as thebasis for developing a BASIC version thatworks in conjunction with the real-timeclock function available in most PCs.

The program has been adapted furtherfor use on the single -board BASIC com-puter. Since this has a real-time clock, thesystem may be used as a stand-alone ap-plication that works around the clock forsunshine recording. In this set-up, the PCmay collect measured data when requiredby connecting it to the BASIC computervia its RS -232 interface. The program that

runs on the BASIC computer is availableas a ready -programmed EPROM.

Sensor assemblyThe photograph in Fig. 2 shows that thefour photodiodes are fitted together toform a in a transparent sensor. Eachphotodiode faces one of the compass di-rections, north, west, south and east. Sincethey are enclosed in a perspex, plastic orglass cover, they may be used for manyyears without the need of being serviced.

The control program that runs on theBASIC computer performs light intensitymeasurements at regular intervals. Thedata so obtained is collected and pro-cessed statistically by the PC at a latertime. The sun position calculations enablethe computer to know which photodiode(measurement sensor) is expected tomeasure the highest light intensity. Thephotodiode that measures the lowest lightintensity forms the reference. The systemdecides that there is sunshine if the lightintensity on the measurement sensor isfour times greater than that on the refer-ence sensor.

The sensitivity of the photodiode usedin the sensor assembly is highest for lightincident at right angles to the face of thediode. The altitude, a, of the sun variesbetween 0' and 90' in the tropics, but thisreduces the further north or south one isfrom that region; in the UK (and most ofnorth and central Europe, the southernparts of Canada and the northern states ofthe USA) it varies from 0' to 65'. In thisarticle that value is used, and the sensorassembly is therefore constructed in amanner that ensures that the maximum

Fig. 3. Determining the optimum sensorposition with respect to the earth surface.

deflection of the direction of the light withrespect to the normal, It (the line perpen-dicular to the plane of the photodiode), is32.5'. In other regions of the earth thatangle needs to be adapted as appropriate.The maximum deflection of 323' causes asensitivity reduction of 75c7, , which is stillacceptable in this application.

The computer calculates the sensitivityas a function of the position of the sun andthat of the sensor. This is done to make themeasurement independent of the positionof the sensor relative to the sun, so that theangle at which lights falls upon the sen-sors (angle of incidence) has virtually noeffect on the collected data. The drawingin Fig. 3 shows that each photodiode ismounted on a post or plate that is at anangle, 13, of 375` (90'-32.5') with respectto the earth surface (this angle needs to beadapted in other regions). The assemblymust be mounted such that photodiode I)faces north, Di west, 02 south and D3 east.

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Fig. 4. Circuit diagram of the sensor amplifiers and the VCO that enables the measured values to be recorded by the BASIC computer.

E 1.1-.KTOR ELECTRONICS .I I NE 19911

FOUR -SENSOR SUNSHINE RECORDER

81,82=3 x1N4C431

0

4:4,:47 I

Fig. 5. Suggested power supply.

Electronics!The circuit diagram of the sunshine re-corder is shown in Fig. 4_ The whole cir-cuit is in fact a peripheral device whoseoutput data is applied to the BASIC com-puter.

The currents supplied by photodiodesD2-D5 are first converted to voltages byICia, ICib, ICI, and IC2b. Next, the voltagesare applied to analogue multiplexer IC3,of which the channel selection inputs, Aand B, are controlled by the computer. Acommunication protocol is required to en-sure correct data transfer between the sen-sor and the BASIC computer, which maybe separated by several meters. Voltage -to -frequency tv-f) conversion is used forthis purpose: the sensor assembly sup-plies a signal whose frequency is deter-mined by the light intensity on theselected photodiode. Opamp IC4 buffersthe multiplexer output voltage and con-trols the VCO (voltage -controlled oscilla-tor) built around IC,. The VCO is arelatively complex circuit to ensure therequired accuracy.

The VCO output signal is sent to theBASIC computer via output connector K2.The advantage of v -f conversion is that theBASIC computer can accept the measuredsignal direct without the need of addi-tional hardware.

A simple time -base circuit (Fig. 6) pro-vides 250 -ms long enable pulses to thetimer on board the 8052AH-BASIC pro-cessor. The number of pulses read fromthe count register indicates the frequencyof the measurement signal and thus theintensity of the light that falls upon theselected sensor.

The EPROM -resident control programalternately selects the measuring sensorand the reference sensor by addressingthe analogue multiplexer, ICI, via controllines A and B. Immediately after each se-lection, the frequency of the signal on theoutput line, F, is measured. Next, the pro-gram corrects the sensitivity of the sensorsand converts the measured frequency intoa corresponding illumination intensity.The result of this process forms the basisof the sunshine/no sunshine decision.

Fig. 6. Timebase for use with the BASIC computer.

Construction and testBoth the interface circuit and the time -base circuit are so small that they are eas-ily constructed on veroboard orprototyping board. Wiring is not criticalsince only low frequencies are involved.Care should be taken, however, to fit allthe decoupling capacitors indicated in thecircuit diagram as close as possible to therelevant ICs.

The interface has four adjustments, thetime -base circuit only one_ If a frequencymeter is available, adjust the preset on thetime -base board until 32.768 kHz ismeasured. If you do not have access to afrequency meter, set the preset to thecentre of its travel.

Initially, presets P2, P3 and PA on theinterface board are also set to the centre oftheir travel. Turn Pi to maximum resist-ance and install jumper Ji to connect thenon -inverting input of IC4 to ground. Ad-just P2 until the output of IC4 is at 0 V_

Preset Pi determines the sensitivity ofthe VCO. This sensitivity, in turn, deter-mines the full-scale measurement value,which may lie between 500 pi A and100011A for each sensor. The prototypewas set for 700 LtA, which corresponds toan illumination of about 100 lux. Thisvalue is achieved by setting the amplifica-tion of IC4 to 14'7 times (= variable 'Au' inthe control program).

The adjustment is fairly simple: apply1 V to the input of the (Tamp and adjustPi until the output voltage is 1.429 V.

Next, adjust the VCO. Remove jumper12 and apply -10 V from an external sup-ply to the VCO input resistor, Rin. AdjustP3 and P4 until an output frequency of100 kHz is obtained at terminal F on con-nector 1(.2. In some cases, this requires a10-k1 resistor to be fitted between thepositive supply line and the collector ofTi. This adjustment results in a VCO sen-sitivity of 10 kHz/V and completes thesetting -up procedure.

The control programInsert the EPROM (order number 5921)with the control program into the relevant

socket on the BASIC computer board, andconnect the interface to the BASIC com-puter as shown in Fig. 4. Apply power,and point D. to the north. Press the spacebar on the external terminal hooked up tothe serial port of the computer. Wait forthe 'ready' message and type RUN. Thecontrol program prompts you to enter thetime zone with respect to GreenwichMean Time (GMT), the latitude and longi-tude of your location (consult an atlas!)and, finally, the height above or below sealevel. After accepting the geographicaldata, the program asks you whether or notsummer/winter (daylight savings) time isused. The last prompts are the local timeand the date.

The calculations and other programoperations that follow the data entryphase take a minute or two_ On their com-pletion, the system is ready to start theactual measurements. Since it makes nosense to measure at night, the recordingperiod covers the time between30 minutes before sunrise and 30 minutesafter sunset. Nighttime readings are sim-ply not processed. The instructions on theterminal tell you how to retrievemeasured data.

As already stated, the terminal may bereplaced by a PC running a communica-tions program. A log and a file store func-tion are valuable in that case. Oneprogram that was found well suited to theapplication is Procomm. Alternatives to afull-blown PC include the hand-heldPsion Organiser shown in the introduc-tory photograph.

References:1. BASIC computer. Elektor Electronics No-vember 1987.2. Peripheral modules for BASIC com-puter. Elektor Electronics October 1988.3. Calculating the position of the sun. SolarEnergy Vol. 20; p. 393-197. By R. Wal-raven, Dept. of Land, Air and Water Re-sources, University of California, Davis,CA 95616, U.S.A.


56

OENCE EC[ N.0 OGY`INTELLIGENT' ROAD SYSTEMS

by Professor Peter Hills, Director of the Transport Operations Research Group,University of Newcastle upon Tyne

In spite of periodic oil 'crises' and fitfulbouts of environmental concern, in almostevery country the dominance of road vehi-cles over other forms of transport cannotbe denied. Traffic congestion in Europe isset to go on rising well into the next cen-tury. In the UK. latest revisions to officialforecasts by the Department of Transport.published early in 1989. acknowledge thatthe persistent upward trend of car owner-ship could double the amount of road traf-fic within 20 years.

Building roads can not of itself preventthe spread of congestion: indeed, it is ar-gued that building more roads in citiesmay often make matters worse. Even if theobvious response to rising demand forroad space were to be increased supply. itcould not be provided fast enough to catchup with the predicted growth of traffic.Moreover, vehicle users have a poor per-ception of the actual costs that their use ofthe congested road system is causing toothers while significant components ofthese costs. notably pollution and acci-dents. are borne by the community atlarge. This inefficiency of pricing is com-pounded by the inefficiency of routeingbecause, at the outset of many journeys,drivers have only a hazy idea of what traf-fic levels they are likely to meet. A sur-prisingly high proportion of them do notkn ow the shortest route to their destina-tion. let alone the quickest: most decisionsabout journeys are based on a mixture ofhunch and hearsay. To add to all this. find-ing somewhere to park at the destinationwill get progressively harder as congestiongrows.

In spite of this gloomy prediction. oneway forward lies in the harnessing of in-formation by making the road system morethan just the infrastructure for vehicles toreach their destinations. Making it also areliable source of up-to-date informationabout the service it can provide. given thattraffic conditions are changing all the time.requires that each driver should be able tocommunicate with the road system in an'intelligent' two-way conversation. Thatwould improve efficiency through betterdecisions about journeys, better trafficcontrol, fewer accidents and less pollution.

I shall go on to describe work on a techno-logical means of attaining this two-waycommunication between moving vehiclesand the roadside.

The DRIVE programmeLaunched in January 1989. the EuropeanCommission's DRIVE programme is one ofimaginative and wide-ranging research,costing some £40 million over three years.It brings together. in 73 different consortia,multidisciplinary groups from universities.government agencies. industry and poten-tial users to explore ways of applying in-formation technology to the problems ofroad traffic. A further programme. DRIVEII. to run from 1992 to 1997. is being

planned to develop the ideas and applythem in practice. It is called AdvancedRoad Transport Telematics and will com-pete for funds with other research pro-grammes in the EC.

One of the consortia in the present pro-gramme is co-ordinated from Newcastle. Itcomprises the Unix ersit\. jointly with thePolytechnic. three separate Philips compa-nies (in the UK. Sweden and Federal Ger-many) and two potential users, namelyCompagnie de Signaux et Equipe-mentsElectroniques (csEE) in France and Em-presa de Investigacao e Desenvolvimentode Electronica (EID) in Portugal. The con-sortium is working on an automatic two-way communications system for traffic

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Fig. 1. Growth of car ownership in various countries between 1950 and 1985. (Source: InternationalRoad Federation Statistics).

UFA:TOR ELECTRONICS JUNE 1990

INTELLIGENT' ROAD SYSTEMS

Microwave oscillator

Horn antenna

Roadside transmitter

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Detector

Signalprocessing

Microprocessor

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Vehicle -mounted receiver

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veloped under the European opic.E programme.

1 2 mm

18.7 mm

Fig. 3. Rectangular microstrip antenna with stubmatched feeder.

monitoring and pricing, with the aid of mi-crowave technology. The intention is toapply the system to the automation of mo-torway tolls in France and to a parking in-formation and management scheme in Lis-bon. The following is a description of thework.

Microwave systemThe aims of the research work at Newcas-tle have been to investigate the feasibilityof using a low -energy microwave link fortwo-way data communications between ashort -ranee transmitting beacon at theroadside and moving vehicles. and to de-velop and test the equipment necessary forthe system.

The transponder unit for the vehiclewas developed in microstrip circuit tech-nology to make all the microwave -fre-quency components needed. Microstriptechnology is highly suited to traffic appli-cations because the circuits have a lowprofile, are small and may be madecheaply. The associated logic and auxiliarycircuits for the vehicle unit will be madecompatible in size and profile with thetransponder microstrip circuitry by the useof custom-built very large scale integrated(VLSI) circuitss. This has not yet beendone, so the signal processing and logiccircuits described are built from discretecomponents.

The roadside transmitting unit has been

built from off -the -shelf components. It isbattery powered, small enough to beportable and it can be set up at the road-side on. say. a lamp -post or gantry.

Field trials to find out how thetransponder performs when mounted in avehicle have been very encouraeine. Sub-stantial amounts of error -free data havebeen received by the device when mountedeither on the windscreen or on the sidewindow of a vehicle moving at up to 40km/h. More field trials are planned for thisyear at vehicle speeds up to 120 km/h.

Background to developmentWork began at the University and thePolytechnic in September 1985. with twosurveys of the literature to investigate (a)what sy stems were already available fortraffic monitoring and control applications,and (b) the various types of microstrip an-tenna that might be used and the methodsof analysis used to predict their perfor-mance.

Existing systems use a variety of tech-niques to communicate with vehicles, in-cluding inductive loops in the road surfaceand local radio broadcast systems. Mostare restricted to a low data transfer rate ofa few hundred bytes per second. This indi-cated the need of a system with a high datarate. At the proposed 2.45 GHz operatingfrequency of the system under develop-ment, it is expected that the microwavecommunications link can transfer severalthousand bytes of data from the roadsideto a passing vehicle.

Figure 2 shows a block diagram of thecomponent parts of the roadside unit andthe transponder. The vehicle -mountedtransponder under development comprisesfour distinct components: an antenna: a de-tector with associated circuits: a signalprocessing unit; and a microprocessor anddisplay unit. The prototype roadside unitwas built from off -the -shelf components

xx x x Experimental Theory

0 degrees

E -PLANE POLAR PATTERN

0 degrees

H -PLANE POLAR PATTERN

Fig. 4. Radiation polar patterns of a 2.45 GHz rectangular antenna.


58 SCIENCE & TECHNOLOGY

and comprised a BBC microcomputer togenerate the data to be transmitted over themicrowave link, a microwave oscillatorand modulator, and a pyramidal horn an-tenna.

Prior to transmission over the link, thedigital data stream generated by the road-side microprocessor has to modulate themicrowave -frequency carrier generated bythe roadside unit. Several techniques ofdigital modulation were considered. in-cluding frequency shift keying (FsK).phase shift keying (PsK) and amplitudeshift keying (ASK). Although FSK and PSKhave bet -ter performances in terms of biterror -rate, ASK was chosen for the proto-type system because it simplified the de-sign of the transponder demodulator.

Vehicle transponderMicrostrip circuit technology has beenused for all the microwave -frequencycomponents of the vehicle transponder cir-cuit. Microstrip circuits are made by aphoto -etching process. similar to that usedin the manufacture of printed -circuitboards. A conducting pattern is etched onthe upper surface of an insulating sub-strate. about 1-2 mm thick. with a metalliceround-plane on its lower surface. The mi-crostrip structure may be made cheaply:because of the low profile and small sizeof the circuits it is very attractive for vehi-cle -mounted applications where low costand small size are at a premium. It is ex-pected that the final version of the vehicleunit will use a single custom-built VLSI cir-cuit to perform all the signal processingand logic functions, thereby maintainingthe low profile of the transponder. Theprototype, however, used discrete compo-nents for these circuits.

Several eeometric shapes were consid-ered for the microstrip antenna. includingcircular ring, annular ring and rectaneular.Theoretical and experimental studyshowed that their performance characteris-tics were similar. We selected a rectaneularshaped antenna because it could be fedfrom a microstrip feeder line, thereby re-taining the low profile of the circuit. Toensure maximum energy transfer to orfrom an antenna via its feeder is is neces-sary to match the characteristic impedanceof the feeder to the impedance of the an-tenna itself. This was done in two ways:the first by a quarter -wave matching trans-former, and the other by stub matching. Inthis, a short length. or stub. of feeder is at-tached to the feeder itself and is short-cir-cuited at its far end. By adjusting the pointof attachment of the stub to the feeder andthe length of the stub itself. it is possible tocancel out any effects of a mismatch and

thus effectively match the feeder to the an-tenna. Both methods of matching may beemployed in practice with the use of mi-crostrip lines, and it was found that anyloss throueh mismatch was kept to not lessthan 25 dB below the sienal level. Figure 3shows the arraneement of using a stub on a

Band-pessfilter

Input

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Fig. 5. Vehicleborne diode detector circuit withfilters.

50 S2 microstrip feeder. The dimensionsrelate to an antenna operating at 2.54 GHz.

A detector circuit is necessary to re-cover the digital data signal from the ASKmodulated microwave sienal received bythe antenna. The circuit is shown in Fig. 5.where a Schottky barrier diode and filternetwork based on microstrip were em-ployed. A band-pass filter was used at theinput and a low-pass filter at the output toremove residual carrier and unwantedproducts eenerated by the diode in the de-modulation process. The radio -frequencypower from the receiving antenna mayvary over the range 0.1 ttW to 10 ttW, de-pending on the distance from the transmit-ter. while the demodulated digital wave-form output from the detector has a peakvalue of between 2 mV and 250 mV.

Processing and logicIn the final design. the signal processingand logic circuits will be put together incustom-built VLSI circuits. For testing theprototype. discrete components were used.Signal processing is needed to increase thevoltage amplitude of the digital pulsesfrom the detector and to reshape them tocompensate for any distortion to the sienalthat may have taken place during transmis-sion and demodulation. To do this, a di-rect -current stabilized amplifier and a leveldetection circuit were used.

To perform the logic functions on boardthe receiver. a microprocessor was used. AType 6502 was chosen because of its com-patibility with existing 'smart card' tech-nology. The microprocessor may be astand-alone item and perform all the pro-cessing needed at the receiver or, for moreadvanced applications, it could be inter-faced with a more powerfUl microproces-sor and display unit fitted in the vehicle.

Roadside beaconAs shown in Fig. 2. the roadside unit con-sists of a 6502 microprocessor, a mi-crowave oscillator, a modulator and a hornantenna. The antenna has its radiation pat-tern shaped to cover transmission to eithera single lane or a multi -lane road. Thetransmitter should be designed to feed sev-eral antennas to cover different approachesto a road junction, thereby reducing thecost of a large number of units. The micro-processor may work as an autonomousunit or be coupled to a central controlcomputer governing all the beacons in acertain area. The prototype unit is fullyportable, battery powered and measures200x300x400 mm.

System performanceField trials were carried out to test the per-formance of the transponder in a movingvehicle, mounted either in the side windowor on the windscreen to find out the bestplace to tit it. Results showed that. whilethe vehicle is in range of the roadside bea-con, substantial amounts of error -free datacan be received. No interference was ob-served either from sources in the vehicle.such as the engine. or externally fromother vehicles or objects blocking or re-flecting the microwave transmissions.

At a speed of 19.2 kilobytes per sec-ond, over 1000 bytes of data were trans-ferred to the vehicle. This amount isenough to send a small digitized map orreal-time information relating to prevailingtraffic and road conditions.

So far. the serial ports of the roadsideand vehicle microprocessors have beenused as the data input and output ports.This has restricted the data rate to 19.2kilobits/second. However, if the proces-sors' parallel ports were used to generatethe data, much higher rates would be avail-able to test the prototype system. though aparallel -to -series data conversion would beneeded prior to the transmission or recep-tion by the microprocessors. Preliminarytests have shown that error -free data canbe received successfully at rates of up to200 kilobits/second.

To improve the flexibility of the sys-tem. the present stage of developmentunder the DRIVE Programme is to make thes stem into a full two-way data communi-cations link that would enable a vehicletransponder to 'talk back' interactively tothe roadside beacon. That would greatlyenhance the system capability, especiallyin the fields of vehicle fleet control. auto-matic toll collection and route euidance.This in turn would herald the beginningsof an 'intelligent' road system capable Ofreducing congestion substantially.


at

PRO

MS

PLE:

..OW AUDIO

by Bernard Hubbard

Wilmslow Audio of Knutsford in Cheshire offers one of thewidest ranges of loudspeaker kits and drive units in theUnited Kingdom. Founded some thirty years ago. the com-pany recently moved into new. 10.000 sq.ft. premises atWellington Close. Parkgate Estate. Knutsford.

In the new showroom, Mike Aldington. one of the direc-tors, told Elektor Electronics: -We offer very competitiveprices and nowhere else are you likely to find the interest.the product knowledge and the sound advice that is basedon so many years in this specialist market".

"ln addition to loudspeaker kits and drive units, we offera wide choice of hi-fi products and public-address equip-ment: all models selectedfor sound design and relia-bility and in keeping withthe Wilmslow Audio philos-ophy of value for money".

Mike stresses: "Our or-ders come from all over theworld. We have orders fromJapan. France. Germany andthe United States. to namebut a few".

Drive units range in pricefrom £4.95 to £350.

Most of the kits are cre-ated from boueht-in compo-nents. but the company doesmanufacture cross -over net-works.

The company dispatches the majority of orders on thesame day of receipt of instructions, depending on the avail-ability of the equipment. of course.

Mike continued: "DIY loudspeakers can be as good asready-made units with considerable savings. We offer themost popular models in three forms".

"The BASIC kit. which includes all drive units and cross-over filters (although the filters are sometimes in easilyassembled kit form). The BASIC kit usually provides allthat is necessary if you're upgrading a pair of speakercabinets"."The PLUS kit, which includes all the items in the BASICkit, as well as wadding, terminals. T nuts and bolts, re-flex tubes ( where applicable). etc. This is the kit to buyif you're building the cabinets from your own materials"."The TOTAL kit. which includes all items in the PLUS kit,with the addition of cabinets in flat -pack form. These areaccurately machined from smooth MDF board and arevery easy to assemble. Baffle apertures. etc.. are cut andrebated where applicable and it is a simple job to con-struct a pair of loudspeakers to a professional standard".

"Using the Wilsmlow Audio iron -on veneer." he says. "it ispossible, with a little care and attention to detail. to achievea finish that is at least the equal of commercially produced

r:

*re'

cabinets. Only the very best of ready-made loudspeakerscome close to the solid construction achieved with theWilmslow Audio TOTAL kit. Power handling of a loud-speaker is difficult to quantify and often misunderstood.While there is an obvious limit to the power handling of aparticular design, do not worry too much about using anamplifier that has a nominal output that is greater than thequoted power handling of your speakers. In domestic use,you are more likely to damage the speaker with too smallan amplifier than with one that appears to have too great anoutput-.

"A high level of efficiency and sensitivity is not a measureof quality-it means thatyou get a lot of sound perwatt of power, but thathas no significance inas-far as the quality of thesound is concerned, al-though a low poweredamplifier will more easilybe driven into clippingwhen used with speakersof low efficiency. In gen-eral. the larger the cabi-net. the more extendedthe bass response what-ever cabinet design is em-ployed. However. thisdoes not mean that allspeakers of the same size

\vill have a similar bass extension as this results from sev-eral aspects of the individual speaker design. Do not con-fuse good bass response with extended bass response. Ex-tended but 'boomy. ill -controlled bass is by no means aspleasant to listen to as a tightly controlled but less extendedbass response. Room dimensions inhibit perceived bass re-sponse. A small, relatively insensitive speaker. such as ourmicro monitor design, will provide all the sound quality.volume and bass response that you could desire in a smallroom and yet would be quite incapable of providing thebass response. power handling and volume that you mightrequire for a noisy party in a large room".

The company is looking forward to 1992, because itknows that the prices for such kits are high in continentalEurope and once various restrictions have been removedand the barriers are down, Wilmslow Audio believe thatthey are in for an even rosier business than they are cur-rently enjoying. Whatever. the company and its team of sixpeople are very much in sound heart.

11Thnslow Audio's advertisement appears on page 9 of thisissue.


ACL: ADVANCED CMOS LOGICF.P. Zantis

Almost ten years ago, the CMOS logic technology took a giant stepforward with the introduction of the HC and HCT series.

However, in the intervening years, it has become clear that eventhese fast logic devices can not replace all types of bipolar (TTL)

circuit. The introduction of the fourth CMOS generation. AdvancedCMOS Logic or ACL, means that now even the fastest TTL logic

circuits. ALS, may be replaced by CMOS devices.

For the efficient operation of fast bus andtransfer systems, it is essential that shorttransit times are combined with a largefan -out. This was not possible with CMOSlogic until the arrival of the ACL series.This new CMOS technology also takes us astep further on the way to removing thedisparity between high switching speedsand low power dissipation. Another draw-back of itchic-r circuits is their sensitivityto electrostatic charges: ACL devices haveall but lost this sensitivity.

The essential characteristicsOf ACL, TTL, HC/HCT. ECL, and121 logic circuits are comparedin Table 1.

ACL technology

ACL devices are manufacturedin time -proven cmos technol-ogy. The thickness of a singlewafer has been reduced to1 pm. however. A number ofproduction improvementsmake it possible for certainproperties of the circuits to beoptimized. For instance, thetransfer resistance of not onlythe output terminals, but alsoof the internal junctions, hasbeen reduced sienificantly.Moreover. the relatively largeparasitic capacitances found initc/ttc-r devices are virtuallyabsent from ACL circuits. Allthese improvements make itpossible for ACL circuits to beused in applications that untilnow were the preserve of Titlogic.

Characteristic dataThe transit delay in ACL chipsis about 3 ns per gate, so that.in theory at least, operating fre-

quencies of up to 160 MHz are possible.The maximum permissible output currentis 24 mA per gate. It is of no relevancewhether the eate functions as a source oras a sink. This level of current is highenough to enable direct driving of high -gain transistors. such as darlingtons.

Low power dissipation is of ereat im-portance in many circuits, because it al-lows greater packing density. extends theduty cycle in battery operation, and in-creases the reliability of the system be-

cause of the lower temperature.Thanks to CMOS technology, the power

dissipation in ACL circuits is very low: inquiescent operation, it is only a few nWper gate. which rises to 1-2 mW duringoperation at I MHz. As an example. Fig. 1shows the relation between dissipationand operating frequency for an ACL11008and a similar TTL circuit (four AND gates).

The signal-to-noise ratio is also verygood. The output varies from 0.1 V (lowlevel) to Ub -0.1 V (high level) at a load

current of 50 i.tA (equivalent to50 CMOS inputs). At the fullload current of 24 mA. the lowlevel is 0.5 V and the highlevel. Ut, - 0.8 V.

The change -over thresholdsat the inputs are type -depen-dent. In CMOS compatible de-vices, they lie between 30' and70q of the supply voltage. Inrn. compatible circuits, theyare 0.8 V (low level) and 2 V(high level).

The operating temperature ofstandard ACL versions extendsfrom -40 CC to +55 °C: typeswith an extended range of-55 °C to +125 °C are alsoavailable.

Power dissipation Transit time SignatInoise Int

at f = 1 MHz ratio (Ub = 5 V) de

egration

nsity

TTL

HC HCT

ECL

IZL

ACL

medium

small

high

very small

small

short

long

very short

medium

very short

small

large

very small

medium

very high

small

very high

ve7y high

Table 1. A comparison of the most important families of logic circuits.

Fig. 1. Power dissipation in an ACL 11008 (4 AND gates) and a 74LS08. Alloutputs switched simultaneously. Ambient temperature = 25 =C. Supply volt-age = 5 V. Output load = 50 pF.

Circuit design

Very fast logic devices switchwith very steep edges and thiscreates a few difficulties. Forinstance, parasitic reactancesand line reflections in the cir-cuit may cause functional inter-ference. To obviate such diffi-culties with ACL chips, no at-tempt was made to achieve pincompatibility with ttchicr orTTL devices. Instead, ACL cir-cuits are designed in flow -through architecture. which


ACL: ADVANCED CBIOS LOGIC

G4D -

CND , .3Y

Fig. 2. Comparison of the pin -outs of an ACL cir-cuit and a similar TTL chip.

means that the internal structure. as wellas the pin -out, is as much as feasible inline with the signal flow. This results in anumber of supply connections being paral-leled. inputs and outputs of gates beingwell isolated. and the less frequently usedcontrol connections being grouped at theupper or lower part of the package. Thesemeasures result in an average reduction ofthe inductive layer in and around the chipby a factor of 3.8 in standard OIL packagedcircuits and higher in other housings.

When ACL devices are used in bus-ori-tented systems, notable simplications arepossible in the wiring of the printed -circuitboard. However. the great advantages ofthe unorthodox pin -out become really con-spicuous when ACI circuits are used in

conjunction with multi -layer PCBS.

Figure 2 gives a com-parision between the pin -outs of a Type ACT 11000ACL circuit and a Tfl. chipType 7400. Note that theACL device needs twomore pins.

The pin -outs of a num-ber of important ACL cir-cuits in a standard DILpackage are shown inFig. 3.

AC11000 .ACT11000QUADRUPLE 2-TIPUT

POSITIVE -NAND GATES(TOP VIEW)

_ 18

1 2A

28Vcc

VCC

3A

k 384A

AC11014 ,ACT11014HEX IHVERTERS

(TOP VI.E1..*.

1Y

2Y

3Y

CND

GNU

GND

GND

4Y

5Y

6Y

IA

2A

3ANCVcc

VetNC

AC11002 , ACT 11002QUADRUPLE 2 -INPUTPOSITIVE -NOR GATES

(TOP VIEW)

IA.-1?2Y 2I

CND

CND

.3?

4Y

4B

18IC

VccYee3A

IC 38

ACI1004 . ACT11004HEX INVERTERS

1Y

2Y

3Y

CND

GND

CND

CND

4Y

SY

6Y

(TOP VIEW)

AC11074 .ACT11074DUAL D.TYPEPOSMVE-EDGE ACI1135 , AC T11133

TRIGGERED FLIP-FLOPS 3- USE TO B -USEram CLEAR AND PRESET DECODERSiDEMULTIPLEXERS

(TOP VIEW) (TOP VIEW)

-1PRE - 1CLK

10- V ID10

CND - et-V

2171 C-2 LR7.20 20a-2PCE 2CLX,

AC11133 .ACT11139 AC11157. ACT11157QUAL 24..BIE TO 4-UNE CUADRUPLE 1 OF 2 DATA

DECODERS TEMULTIPLEXERS SELECTORS/MULTIPLEXERStTOP VIEW) (TOP YEW(

1Y1

1Y2

1Y3

CND 2Y002Y1,2Y2

2Y3

1YO

YO -; IAct: 18Eid

Vcc

2d2A

la 28

AC11161,ACT11161SYNCHRONOUS OBITDECADE COUNTERS

(TOP VIEW)

RCO

OAOB

CND

CND

CND

CND

OCQa

ram

CLR

CLX

A

aVcc

VccC

D

ENP

ENT

A/B1Y

2Y

CND

CND

GND

GND

3Y

4?G

IA

182A

28VccVcc3A

384A

1B

AC11162 .ACT11162SYNCHRONOUS 4 -BITBINARY COUNTERS

(TOP WEle()

RCO

OAQa

GND

GND

CND

GND

OCOD

LOAD

Y I - YO

Y2-. VI -L A

Y3- .i,BmtGUO -

-e C=4Y4 .= .: VccicY5nt lc. GIY6 '-, .,,G2AY7 Iiii_.G.2)3

AC11160 ,ACT11160SYNCHRONOUS 4 -BITBINARY COUNTERS

(TOP YEW)

RCO

OAOa

CND

GND

CND

CND

OaOD

LOAD

CLR

A

aVccVcc

SU

C

ENT

AC11174 ,ACT11174HEX 0 -TYPE

FUP-FLOPS WITH CLEAR(TOP YEW)

IQ

2030

ONO

CND

CND

CND

40SO

60

ID

2D

3D

VccVcc405D

ED

CLX

r.cc73 -13

Type coding

ACL circuits are availablein two different versions:1. The 74AC series withcmos compatible hieh/lowthresholds (U, = Ub / 2)for operation from supply

voltages of 2-5.5 V.2. The 74ACT series with TTL compatiblehigh/low thresholds (U, = 1.5 V) for oper-ation from 4.5-5.5 V.

The type coding consists of six eroups.the meaning of each of which is shown inTable 2. Note that group 5 defines thelogic function in the same way as for rn_and HC/HCT circuits. Also. group 4 is al-ways 11. indicating that the supply con-nections are located at the centre of thehousing (and thus there is no pin compati-bility with HC/I [CT or TTL devices).

Protection against electro-static chargesAll switching inputs and outputs are pro-tected against static charges. This holdsgood for potentials of whatever polarity atlevels up to 2 kV. The protection circuits.consisting of two diodes connected asshown in Fig. 5. are equivalent to a 100 pFcapacitor being earthed via a 1.5 1:12 resis-tor across the input or output. Proper oper-ation of the protection circuit may there-fore be verified by the circuit shown inFie. 4.

The difficulty with efficient protectionis that the protection elements, integratedon the chip, can, owing to their small size.cope only with relatively low levels of en-ergy. In ACL circuits, taking the valuesstated earlier on, protection is guaranteedup to an energy. E. of

E = CU2I2 =10-10 x 4 x 10612 = 0., m.1

The diodes in the protection circuitshave a forward foliage of about 0.9 V anda reverse (zener) voltage of around 17 V.

Group 1- blank = standard versionSNJ = meets MIL STD 883

JANB = meets MIL STD 38510

GROUP 2- 74 = temperature range of -40 =C to +85 2C

54 = temperature range of -552C to -125 = C

Group 3 - AC = CMOS compatible thresholds

ACT = TTL compatible thresholds

Group 4- 11 = supply connection in centre

Group 5- conventional functional type coding. e.c

000 = quadruple NAND gate074 = dual D -type bistable

Group 6 -N = plastic DIL caseNT = plastic slim -line DIL caseJ = ceramic DIL caseJT = ceramic slim -line DIL case

D = plastic miniature case

Fig. 3. Pin -outs of a number of important ACL devices.

ELEKTOR ELECTRONICS J L N E 19911

Table. 2. ACL circuits are type -coded by these six groups.

62 COMPONENTS

Summary

The ACI. series gives the designer the op-portunity of putting to use all the advan-tages of CMOs technology. such as highsignal-to-noise ratio and small power dis-sipation. at fairly high operating frequen-cies.

The pin -out is unorthodox and notcompatible with either TrL or HC/HCT cir-cuits. It is, however, of paramount impor-tance in realizing the excellent propertiesof the ACL devices.

ACL circuits may replace TrL as well asHC/HCf chips. and are already widely usedin new designs. There is no doubt that ACLtechnology will become the new standardfor integrated digital circuits.

Fig. 4. Test circuit to verify the proper operationof the protection circuits in an ACL device.

0

terminal

r

inputsise toi

-==

to chip

0

Fig. 5. The protection diodes in an ACL circuitare connected as shown here.

R -2R RESISTANCE NETWORK IN SMT

The sit R -2R network intended for use in,say, a digital -to -analogue converter, is con-structed in surface -mount technology (sm-r).It is inexpensive, precise, space -saving andallows unusual values to be obtained. It isdescribed here in a digital -to -analogueconverter that uses a CMOs latch Type 4042.

The latch and the associated R -2R net-work are connected in the feedback loop ofan LF356. The network uses 100 kSI resis-tors (the 2R resistors are made up of twoseries -connected 100 Id) resistors).

H. Bierwith

The output voltage of the converter iscalculated from:

= - P )16R(2-103 -2-10 ;-.- 2- 2 1+ 2-300)

The Qs in the formula have a value of 0 or1, depending on the state of the latch out-put. The factor (R1-1-Pi)/6R is the amplifi-cation, A, which may be set between 0.4and 2.0 by Pi.

The supply voltage for the latch, whichis also the reference voltage for the net-

work, LI may be be-tween 5 V and 15 V:the logic levels atlatch inputs Do-D3and at CLK must be inaccord with that volt-age. The reference

SIL

2

O IEM

10 11

00 01 02 03

IC14042

at

0E214

P2

LF356

IC2

5V

0

CO Dl D2 D

0 003 DI 02 03

voltage must be decoupled direct at theinput of the tc.

The circuit is calibrated by making theinputs of the latch 0 and adjusting P2 foran output of 0 V from the opamp. Then,load the data inputs with Fhe, and adjustP1 to obtain maximum output voltage.

If a larger number of bits is to be pro-cessed, two or more PCBs may be con-nected back-to-back.

Moreover, the PCB may be used withother components, such as diodes, capaci-tors, combinations of resistors and diodesor simple potential dividers for measuringinstruments.

The current drawn from the LI, supplyis 75 !Lk; that from the 5 V supply is about7.5 mA


63

DIGITAL SATELLITECOMMUNICATIONSby Dr. 'Fri T. HaISBN 0 672 22547 6574 pages - 245x160 mmPrice £43.00 (hardcover)Digital Satellite Communications, aimedat practising engineers and advanced stu-dents in satellite systems, communica-tions and related areas, is, perhaps, cur-rently the professional reference book onthe subject.

Although Dr Ha says that the book ad-dresses fundamental principles of satellitecommunications in which the mathematicshave been kept to a minimum, I found it afairly complete treatment of the subjectand the mathematics not too difficult.

The book starts with very useful lists ofacronyms (many of which can not easilybe found elsewhere) and symbols used.

The geometry of artificial satellites inspace is covered in great detail with plentyof clear drawings and mathematical treat-ment.

In spite of the word 'digital' in the title,and most systems are, of course, digital,analogue systems are also covered in de-tail. Examples are used throughout thebook, while each chapter closes with anumber of problems (for which no an-swers are provided). Appendices are notgiven at the end of the book, but rather atthe end of the relevant chapter - unortho-

IEE MEETINGS5-7 June- Advanced infra -red detectors

and syqems.27-29 June - Expert planning systems.

Readers are also advised that each yearthe IEE organizes a range of conferences.vacation schools, technical seminars andworkshops on subjects within the fields ofelectrical, electronic and control eneineer-ing. and computing.

Information on these. and many other.events may be obtained from the IEE,Savoy Place, LONDON WC2R OBL.Telephone 01-240 1871.

The PC User Show and the EuropeanUNIX User Show will take place simulta-neously on 19-21 June at the OlympiaHall. London. Information on these showsmay be obtained from ENIAP Interna-tional Exhibitions, 12 Bedford Row,LONDON WC1R 4DU. Telephone 081404 4844.

1 / r r \ I( e.'11

r' J

dox but useful.Apart from the geometry of satellites,

the book covers earth stations, satellitelinks, frequency division multiple access,time division multiple access, speech in-terpolation, satellite packet communica-tions, digital modulation, carrier and sym-bol timing synchronization and satellitespread spectrum communications.

I have no doubt that Digital SatelliteCommunications will become, and remain,a cherished reference book of many forquite some time to come.McGraw-Hill Publishing CompanyShoppenhangers RoadMAIDENHEAD SL6 2QL

BATTERY REFERENCE BOOKby T.R. CromptonISBN 0 408 00790 7734 pages - 250x190 mmPrice £120.00 (hardcover)Not so long ago, most people thought of abattery as of a car battery or a torch bat-tery. Nowadays, there exists a wide varietyof batteries, primary and secondary, rang-ing from minute button cells to large in-stallations weighing several hundred tons.Indeed, there is such an assortment of bat-

./

The tenth Networks exhibition and con-ference. organized by Blenheim Online,will take place on 19-21 June at the Na-tional Exhibition Centre, Birmingham. Anumber of other events are also oreani-zaed by Blenheim. among them: The Eu-ropean Satellite Broadcasting confer-ence at the QEII Centre. London. on 5-6June: the High Tech Buildings confer-ence at the Tara Hotel. London. on 6-8June. the Software Tools exhibition andconference at the Wembley ExhibitionCentre. London. on 12-14 June: The In-ternational Mobile Communications ex-hibition and conference at the QEII Cen-tre. London. on 12-14 June: and theImage Processing conference at the QEIICentre. London. on 7-8 June. Detailsfrom Blenheim Online. BlenheimHouse, Ash Hill Drive, PINNER HA52AE, Telephone 081 868 4466.

teries that it is doubtful whether anyoneknows their details without referring toone or more reference books. But, untilBattery Reference Book became available,what reference book(s)? I and many of mycolleagues had nothing to refer to but themanufacturers' data sheets.

Mr Crompton, formerly research man-ager at Oldhams Batteries, has now givenus in one volume a guide through the sub-ject in a logical sequence. The work cov-ers electrochemical theory as it applies tobatteries; battery selection; theory, design,electrical and performance characteristics;applications of various types of battery;and theory and practice of battery charg-ing. It includes information from batterymanufacturers about the performancecharacteristics they supply. A number ofappendices cover suppliers of primary andsecondary batteries; battery standards; bat-tery journals; and trade organizations andconferences. Finally, there is a useful glos-sary, bibliography and very detailed index.

Battery Reference Book should prove agodsend for designers of all types of bat-tery -operated equipment, battery manufac-turers, and electrical and electronic engi-neers and technicians who use batteries intheir work. It should also prove useful toresearch organizations.Butterworth Scientific LtdWestbury House, Bury StreetGUILDFORD GU2 5BH.

An INFRA -RED Technology and Appli-cations exhibition and conference will beheld at the Wembley Exhibition Centre.London, on 26-28 June. Details from theorganizers. Evan Steadman Group, TheHub, Emson Close, SAFFRON WAL-DEN CB10 1HL.

The International TelecommunicationUnion has issued a Call for Papers forpresentation to the Technical Symposiumat TELECOM 91. which will be held inGeneva on 10-15 October 1991. Papersmust be based on original research, devel-opments and approaches carried out dur-ing the period between TELECOM 87 andTELECOM 91. They should concernthemselves with the technical aspects oftelecommunications. technologies, net-works and services. Abstracts of proposedpaper. on no more than one A4 page,should be submitted before 15 October1990 to The Forum 91 Secretariat. ITU.Place des Nations. CH -1211. CiFNEVA 20


64

J-.112:ADE:TE1IJj\jj

LETTERS

Letters of a general nature. or ex-pressing an opinion, or concerning amatter of common interest in thefield of electronics (in its widestsense). should be addressed to TheEditor at our London offices. Theirpublication in Elektor Electronics isat the discretion of the Editor.

HORN LOUDSPEAKERDear Sir-In the excellent article on the"Horn Loudspeaker" (May 1990). you donot mention from whom the McFarlow driveunits are available in the UK. Where can Iget them from?K. Stevens, Winchester.

Sorry for the oversight abOut which we havehad a number of letters and telephone callsfrom other readers. The suppliers are:Bochako, 46 London Road, Kingston-upon-Thames KT? OQF. Telephone 081 541 4433.Fax 081 547 1096.

[Ed]

ORDER FULFILMENTDear Sir-I am very unhappy about yourhandling of readers' orders. Twice in the pastyear I have had to wait almost eight weeksbefore I received the PCBs I ordered. Com-pared with the speed with which some ofyour advertisers turn around orders yours issnail's pace. Can't something he done aboutthat. as I'm sure I'm not.the only sufferer.What makes matters worse is that in spite ofthe delays you cashed my cheque immedi-ately on one occasion and credited my creditaccount on the other long before I receivedthe goods. I feel that that is an unfair (evenillegal?) practiceP. Fairelough. Edinburgh

We try to adhere to the undertaking given inour Terms of Business that "Although everyeffort will he made to dispatch your orderivithin 2-3 weeks from receipt of your in-structions. we can not guarantee this timescale for all orders." Note that we say 'dis-patch', not 'deliver', as we can not be re-sponsible for the postal services in readers'area or country. All goods are now sent byRecorded Delivery'.

all customers' orders are handled by ourcentral computer processing and stores de -lament in the Netherlands: to avoid delay.iev are transmitted there daily by fax from

a -3 over the world. Note that NO STOCKS

are held at our London offices.At the time of transmission. my office

manager in London knows whether an itemis available or not. If not. the customer isadvised immediately. Unfortunately. whatcan not he known at that time is that, sinceorders are handled in strict chronologicalorder. it may happen that stocks of a partic-ular item have run out by the time certainorders for that item are being processed.This sometimes causes a delay of 2-3 weeks(here we are in the hands of our suppliers).hut normally much less. There is. therefore.usually no time to advise customers whomay lire in the UK. but equally well in NewZealand or Bra=il. of the delay.

Some 50 orders are packed together andsent as one consignment from Holland toLondon. Ihtfortunately. sometimes. but notoften. the consignment is delayed by customs

at Dover. Harwich or London.As you can see. it would be very difficult

to organke having customers' chequescashed. or credit card accounts credited.only. say. 4-5 days before goods are sent tothem from our London office_ Furthermore.hear in mind that we. in common with allmail order firms. do not dispatch any ordersuntil we hare received payment (that is. cus-tomers' cheques are cashed or credit cardaccount is debited) since that is our onlywar of avoiding bad and irrecoverabledebts. [Ed]

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FOR SALE. Model 10C calculator Hewlett Packard

with peripheral control and more. Hewlett Packard

9863A Tape Reader. £50 o.n.o. Phone (0734)

589544.

FOR SALE. Dumb terminals (2), computer chips.

EPROMs. etc. very cheap. Phone

3rC

Send this coupon to: Elektor Electronics'Publishing). Down House. BroomhillRoad, LONDON SW18 4JQ.

Block capitals please - one character to each be


Na7e a -z a:: ___ !.!,E-,7 ze g:..en here


160 PAGES OF"THE BEST DEALSOF THE DECADE"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

personal service Very competitive prices; .\

Quantity discounts available- Discount vouchers included No minimum orderFill in the coupon and post it with your Cheque.PO etc for £1.50 to receive your 1990 Crick-lewood Electronics Catalogue and voucherswhich you can use against your next pur-chase.

Contents Include: -Aerials & Aerial AmplifiersBatteries etcBooksBoxes & CasesCable & Wire CapacitorsConnectorsCrystals & InductorsFuses

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DECot--

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NO

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-

HardwareHeat EvacuationKitsOpto ElectronicsPanel ComponentsPrinted Circuit PracticeResistors

SemiconductorsSound & VisionSwitches & RelaysTest EquipmentTools & BenchwareTransformersValves

- Cricklewood Electronics1990 Component Catalogue

Please send copies of the 1990 CricklewoodElectronics Catalogue at £1.50 to:NameAddress

Remittance enclosedJ

Cricklewood Electronics Ltd, 40 Cricklewood Broadway, London, NW2 3ETTel: 081-450 0995/452 0161 Fax: 081-208 1441 Telex: 914977


rifrk"1 yotii-4 p&p-4 tieWe believe ours do!!!Precision laboratory oscilloscopes. Triple -trace 20MHz 3 channels -3 trace. XY mode allows Lissajous patternsto be produced and phase shift measured. 150mm rectangular CRT has internal graticule to eliminate parallaxerror. 2Ons div sweep rate makes fast signals observable. Stable triggering of both channels even withdifferent frequencies is easy to achieve and a TV sync separator allows measurement of videosignals.Algebraic operation allows the sum or difference of channel 1 and 2 to be displayed. 50mV div output from CH1 available to drive external instrument e.g. frequency counter. Also available. 40MHz triple trace oscilloscope.Similar to the model described above but with 12kV tube that is super bright even at the highest requencies.This instrument also has a delayed sweep time base to provide magnified waveforms andemirate time interval measurements.

TOA40 (20MHz Triple Scope) £349.95TOB40 (40MHz Triple Scope) £549.95

TEST EQUIPMENT -Choose from the extensive range featured in our new 580 pageElectronics Catalogue. Available in all our shops or from IVIISNIITH for £2.25 or £2.75Cy mail. No carriage charge if ordering Catalogue only.

CREDIT CARD HOTLINE0702 LSitt 1 opPHONE BEFORE 5PM FOR SAME DAY DESPATCH

ILA- '

)11,.0,1444 tj- 4:4411* t

a ;

111 20MHz

ff.,_6 111h, ELECTRONICSP.O. BOX 3, RAYLEIGH, ESSEX. SS6 8LR.

All items subiect to availability, all items will be en e i our shops inBirmingham. Bristol. Leeds. Hammersmith. Edgware. Manchester. Nottingham,Newcastle-upon-Tyne. Reading. Southampton and Southend-on-Sea.Add Carriage 75p. ALL PRICES INCLUDE VAT.

the magazine for the radio & electronics experimentalist june 1990 … · 2018-10-03 · (43...

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