=~ THE ELECTRONICS MAGAZINE Meee ees ty bd COU (OUe OL alse March 1990 770268. 451012 | 3 15) <3 Coit) Sinewave inverter Rrra) ted Pee Come Tc ae) oad omy Be omen aCe) for LCD moduleson CONTENTS March 1990 Volume 16 Number 176 In the April issue Video ine selector Geter Automatic main switch S232 spitter Bridge rectifiers revsted Code locking circuit Line aligation tester The multi MAC chip concept + The digital madel train — final part + Video mixer ~ final part + Intermediate project: test tox Front cover Molecular electronics will be as itlerento today’s elec- tronics 2s semiconductors are tom the valve technology of 40 years ago. This the belief of scientists who are ‘now working on $20 milion programme in Britain, backed by the Department of Trade and Industry's Link Pro gramme of collaborative research between rivers tis and industry One familiar example of molecular electronios in use today isthe liquid crystal ds- pay seen in watches and cal ‘ulators-and even head-up ‘ispays fr pilots-that respond vigorously to elec cal orheat signals. Here, sciemtsts at Imperial College, London, are working m2 pojctto build new types of molecular’ switches for use in waveguides. Inthe field of conventional eectron- ics, electrons flow through wires and devices lke simple transistor switches. Inthe optical equivalent, ont rave els down planar optical ‘waveguides through tmolecu- lar switches. These switches ‘can be made by coating lass substrates wih a spe- Gal polymer. nthe picture it is being studied with a new technique known as time resolved evanescent wave- induced fuotescence spec: troscopy. Geen — | ean Soe Compression techriquesrevoltonze video PROJECT: Replacement for TCA280A 60 Temperature compensation for LCD moxiles by M. Clarkson “COMPUTERS & MICROPROCESSORS PROJECT: Plotter Mark II with a contibution by B. Lewetz 0 Low-cost V/I display module by Molid Abdul Sumi __ ELECTROPHONICS aS ae $8 PROJECT: BBD sound effects unit by T. Giffard "GENERAL INTEREST 4 41 PROJECT: Power line monitor by J. Ruffell| 44 PROJECT: Surge suppressor by J. Ruffell 52 PROJECT: The digital model train - Part 12 by T. Wigmore __ INFERMEDIATE PROJECT 14 Part 9: 1C monitor by J. Ruffell RADIO & TELEVISION 19 PROJECT: VFO stabilizer by J. Bareford 20 PROJECT: Interval control for camcorders by Ph, Bosma 23 PROJECT: Video mixer—Part 3 by A. Rigby 37 Experimental BSB reception by RG. Krijasman, J.C. Stekelenburg & J. Buiting 47 PROJECT: Aucio/video modulator an BLY design ‘SCIENCE & TECHNOLOGY 50 RAD: keynote of club life at Harwell by H. Cole, senior scientist at Harwell Laboratory ‘TEST & MEASUREMENT 36 al trigger for oscilloscopes G1 PROJECT: Square-wave generator by M. Clarkson ‘MISCELLANEOUS INFORMATION Electronics scene 12 &13; Events 18; Corrections 43; Letters 58; Switchboard 59; Readers services 63; Terms 64; Buyers guide 74; Classified ads 74; Index of advertisers 74 We regret that owing to legal restrictions we can not pub lish “SAVE decoder — Part 2" as planned. At the same supply and design difficulties, have made it necessary 10) Postpone “Sinewave invért- cr"; no new date can as yet be zziven for its publication Maplin’s new distribution centre p.I8 Power line monitor, p. 41 ELEKTOR ELECTRONICS MARCH 1990Pouce se ptisod by ELEKTOR ELECTRONICS (Publishing) “Tauphone: 018771626 natona) at ran Talon 957008 Fancotert 1S Arona) rd 1874 9183 leaonah Reversing anaging Decor: MA Landman Feber cena o or vl Gm Stet Sane 25 S100 actor Eaton £0 Krerpstouse France Inge SA Republi Eevecor 2aeoieNocta ‘SWEDEN. Eleorc Frees AB Box S505 ‘at0s Huctinge Ealor Bil Coarum Distbatin: ‘SEYMOUR 270 London Road Tonbon ste 40H Piniod inthe Nethotands by NOB, Zosterwouse Conjret ©1980 Enewe BV : ABC ELBKTOR ELE FRO [CS MARCH 1990 COMPRESSION TECHNIQUES REVOLUTIONIZE VIDEO SURVEILLANCE Modem technology has a habit of producing the necessary equipment to meet the challenge of the new requirement. In this case. the primary challenge is the closer integration of the member countries ofthe European Community now less than two years ahead ‘The technology is that of the state-of-the-art. videoconferencing, designed to make the closer integration a reality for many officials end busi- nessmen, A front runner in the development of such equipment is GEC Plessey Telecommunica- tions (GPT): GPT Video System products are al: ready in use in organizations and major compa nies in Europe and other pacts of the world The Buropean market inte eration of 1992 may be said to have been anticipated because two videoconfereneing studios employing GPT Video Sys- tems codecs and studio eguip- ment were set up in the Euro pean Parliament in Luxem- bourg and the Commission's Berlaymont Building in Brus- sels in 1985. The continuing development of video com- pression techniques for this purpose has meant that many other applications in video surveillance can now benefit from the improved transmission eff ciency provided by these systems and the conse- «quent reduction in system costs, Efficient data transmission is conditioned by the amount of information that can be trans- ferred from source to recipient over a link in & siven period without undue analogue network ing that incurs various delays during the trans- missions in the modems used. Secondly, the transmission of high resolution monochrome or colour video signals over long distances is highly dependent on the bandwidth avilable and the degree to which the video signal ean be mul tiplexed with othe signals that use the Tink Itis importa, therefore, tha the multplex- ing efficieney can be optimized within the con straints of preserving integrity. The employment of statistical multiplexors, as opposed 10 time di- vision multiplexors, enables bandwidth uiliza tion requirements by channels to be reduced as compression techniques lessen the sumber of data characters tobe transmitted. Data compression methods. The final economy in achieving efficiency is thus 10 employ video compression to achieve & high compression ratio. This involves processing the source signal so that the information in it is reduced to a form for which the time taken to transmit is minimal, yet the form is such that the signal can be reconstituted completely to its original format atthe receiving end. There are ‘many techniques that can be employed in obtain ing data compression by encoding the signal be- Video conferencing studios are ‘springing up all over the world fore transmission and decoding it on receipt. Examples of these include simplistic methods such as null suppression, which scans a data siream for repeated blanks or nulls and replaces them by indicators. Bit mapping is used where there is a high proportion of specific types. of character such as numerics and the map indi cates the presence or absence of characters. Diatomic coding enables one cheraeter to represent a pair providing a compression ratio of 2:1, while an extension of this, patern substitu- tion, allows a special character code to be subst tuted for a predefined character pattern, Forms ‘mode operation, used when data from one CRT is to be transmitted to another, considers some information Fixed, such as a printed format, or variable, such as the data to be inserted. ‘There are various other tech niques of increasing complex- ity for stripping out redundant information and reducing what remains by skilful coding ‘These have improved over the last few years, as have the akin ‘methods of security coding. In consequence, state-of-the art encoders and decoders (codecs) necessary for modern transmission networks have achieved considerable sophistication, Such is the ingenu- ity of GPT's new range of codecs, the GVS10 se~ ries, that, employed in a closed circuit television (CCTV) network, a remarkably high compres- sion ratio can be achieved, resulting in an im= Provement in the efficiency of a CCTV analogue system by a factor of up 0 150, Flexible codee system. ‘The GVS10 offers considerable flexibility to the user and can be configured to take account of pplication changes and enhancement ofthe sys- tem employed. Basically, the picture image de- rived from the analogue output ofthe video cam- lta is compressed and digitally coded by the en- coder and then transmitted in real-time to the de~ coder, which converts it back to an analogue pic- ture, displayed on a control room monitor. In this process, the intial signal is memorized by the encoder so that it becomes necessary t0 transmit only changes in the picture information to the encoder ‘The value of this feature can be illustrated readily. In a surveillance role for crowd monitor- ing, where the picture is changing constantly, high transmission speeds and bit transfer rates are necessary, However, for the remote surveil- lance of premises the incidence of intruder de- tection is hopefully rare and the picture is static for long periods. Consequently, a low bit-rate signal is permissible and signals from a number of cameras can be multiplexed together, provid- lerable saving in-network costTransmissions can be made at data rates of 2.048 Mbit/s down to 56 kbit/s and a number of encoders can be con- nected 10 a single decoder. This enables a polling network to be set up with a single control position in a central spot to moni- tor 4 number of remote locations. Bach encoder can be configured to provide a Uunique identity as part of its transmission, ‘0 that the decoder can ascertain which lo- cation is being monitored, In the event of connexion to an unad- dressed decoder, or the loss of video input, or a transmission fault, the decoder ‘video output is blanked automatically. The GVS series has facilities for local and re- ‘mote diagnostics via a display on the front panel. The equipment operation is fail- safe, EYES DOWN FOR ELECTRONIC LIARDICE The centuries-old five-diee game called Liardice, which is based on poker and has millions of followers around the world, has gone electronic. Electronic Liardice is tiny instrument scarcely larger than a credit card that al- Iows the game to be played in places where its traditional wooden or plastic dice would take up too much space or be liable to get lost. ‘The new version is an interesting ex- ample of the latest gate-array-chip tech- nology that allows chips for specialized applications to be custom-built by overlay- ing the required interconnexions on a col- lection of elements on a standard chip. It generates random numbers for the dice from reading the internal clock at the in- stant the “roll” button is pressed. ‘Campus Martius Sales Ltd, Timothy's Bridge House, Timothy's Bridge Road, STRATFORD. UPON-AVON CV37 9RN, England, The new N-channel dua-gate MES-FET Type CF379 from the Siemens spectrum of GaAs transis: ‘ors in sulace mounting packages is particularly sulable for input stages in mobile telephones or satelite reveivers, Even al 1.75 GHz it exhiots @ gain of 17 oB with a maximum noise figure of 1.8 B (Photograph courtesy of Siemens) ‘Speeding up decisions. International videoconferencing is beeom= ing well established. For example, the law firm of Bebner & Company, which spe- cializes in Roman law used in continental Europe, is planning to provide 40 infor- mal videoconferencing units in Britain Where businessmen can consult experts in legal, financial, banking and marketing alters at videoconferencing centres in other European countries. December 1988 saw the opening of Cable & Wireless’ videoconferencing link between Hong Kong and Singapore. Other recent orders for GPT video codecs origi- nate from Italy for Marconi Italia, Japan for KDD, and Finland for Finnish PTT, company Nese, electronics manufacturers [Nokia and shipbuilder Warsi, ELECTRONICS SCENE! FREE BOOKLET EXPLAINS NOISE The eradication or avoidance of excessive noise in workplaces has become of Paramount importance to companies throughout Europe because of the new ations that came into effect last Jan- uuary. This has created a huge market for sound monitoring equipment, but many businesses affected by the new regulations still have not the skills or equipment to as- sess noise levels, et alone find solutions. A simple guide to noise measurement is available from Lucas CEL Instruments, ‘one of Europe's leading manufacturers of sound monitoring equipment The 24-page booklet covers, among ‘others: physical properties of sounds the decibel and A-weighting scale: the hearing process and hearing problems; oveupa- tional deafness; and noise induced stress. Another video link using GPT video- ‘equipment will connect the Royal Bank of ‘Scotland with its Spanish associate Banco Santander. Many international companies have installed or are installing their own internal networks to speed the decision- ‘making process. In this context the secu- rity aspect is well covered by crypto en- coders and decoders associated with the GVS10 system, ‘The fact that compression makes the management of a series of locations spaced over a long distance far more cost- effective has not escaped the attention of such organizations as British Rail, which is installing GVS10 codecs within @ net- work monitoring its unmanned level crossings. . Free copies of the booklet are available ‘from Lucas CEL Instroments 35-37 Bury Mead Road, HITCHIN SGS ART, Phone (0462) 422411 DEVICE WILL PREVENT TRAINS. PASSING RED SIGNALS British Rail has started work on a new safety system that will prevent trains passing red signals. The first pilot scheme is expected to be ready for test commis- sioning later this year. BR has been planning what it describes, as an Automatic Train Protection (ATP) device since 1988 and has recently asked 12 firms to bid for the job of producing the first of two pilot systems. UK rail experts say the latest advances in technology have opened the door to an ATP system that will work successfully on the BR network, which includes some of the busiest lines in Europe, Such a system will work by interacting between the signals, the tracks and the trains, feeding information to a receiving device on the train. An on-board computer will check the information received against the train's performance characteris tics and adjust the speed ofthe train if nec essary. In this way, the ATP will control a train's speed if the driver does not do so, in ‘onder that it can always brake in time for a red signal and keep within speed limits ‘The first pilot scheme is expected to be installed towards the end of this year on lines between London and Aylesbury and Banbury. These lines are currently being re-signallled and will soon have brand new trains. A second pilot scheme will follow on the main line from London to Bristol. Both systems will be evaluated to estab- lish how a BR network-wide protection system can best be provided. BLEKTOR ELECTRONICS MARCH 1990‘A new electronics centre set up by Ford of Britain is claimed to house the most mod- etn test equipment in Europe for automo- tive electronic system, including. the world’s most advanced spark plug lnbora- tory and what is thought to be the largest anechoic chamber for research into car audio systems, The £10 million complex forms part of the company's research and development centre at Dunton, It will be the headquar- ters of its European electronics operations and the focus of electronic systems re search and development for Ford vehicles ‘made throughout Europe. The centre is working closely with British broadcasting organizations andl the European Broadcasting Union in the de- velopment of radio data systems (RDS) that avoid the need to retune manually t0 the strongest signal in different areas, and allows drivers to be given traffic informa. tion automatically. CCaracalis anew secure, requency hopping tactical radio for police and pararlitary forcas developed by Racal Taetcom. It provides upto 2820 channels in tho range 90-97.975 MHz, The set can be pro ‘grammed to operate in ether simplex or two-te- ‘quency simplex (halt-dupex} modes. Controls have boon kopt toa minimum for ease of operation and user convenience. The volume control has a squelch overide poston which, when sect. ind cates the radio's selcal address. Should the radio develop a faut ths postion wil alow a fat cade to be shawn in aden tothe address. REAL-TIME COMPRESSION ON INTEL'S VIDEO TECHNOLOGY Intel Corporation's Princeton Operation hhas recently announced a video compres ELEKTOR ELECTRONICS MARCH 1990 sion breakthrough for DVI™ Technology, iving multimedia application software developers and personal computer users the ability to compress video footage in real time, at 30 frames per second (fps), on 4 personal computer. The ability to com- press motion video in real time, a symmet rical process, and to play it back immedi ately at full speed and on the full sereen of ‘ computer, is now possible through the DVI software advance known as RTV (for real time video), version 15. Bridging the gap betwoen thebestof Bruel & Kjae/'s sound lovel metors and the company’s top-ot the: ‘ange laboratory real‘ime signal analysers the new ‘Type 2143 Realtime Frequency Analyser usted hore. it provides analysis down to 1/24 octave, in teal time, in th fed, Large intornal memory plus disk storage alow for storage of set-ps and reer- ence data for field use, The 2148 weighs lass than 10g and its battery eis nt less than four hous COMPUTER GUIDES EMERGENCY ‘SERVICES An advanced computer system designed by Marconi Command and Control Sys- tems helps fire brigades, civil defence au- thorities and other emergency services to effectively manage action and resources. MACE (Mobilization and Command Equipment) interfaces with normal radio ‘communications systems, the public tele- phone network, or any other communica- tions network. In addition to continuously updating the current holdings and status of ‘equipment at every station in the opera- tional area, the system also holds specialist databases, such as information on haz~ ardous chemicals and explosives. It can also provide pre-determined response lev- els for every building or type of incident, further aiding resource management. SHOOTING STARS FOR ‘TRINITY HOUSE Sending messages by shooting stars and navigational buoys powered by wind and sea are among new marine aids currently being evaluated by Britain's Corporation of Trinity House (TH), one of the world’s ‘oldest maritime organizations Much has changed since King Henry VIII empowered Trinity House to erect beacons to safeguard English ships and their sailors. Communication techniques have become increasingly sophisticated and the role of Trinity House reflects this. Of the 85 lighthouses it now operates in England, Wales, and the Channel Islands, (Scotland has its own maritime organiza- tion), 60 have been automated and the re- mainder will all be unmanned by the end of the century. In the past year the last of the corporation's 13 light vessels switched 10 total automation, while of its 400 buoys ‘many are solar powered today. One technique currently undergoing a ‘two-year trial is the exploitation of shoot- ing stars, or meteor-burst communication. From the manned Rona Lighthouse, 56 km north of Scotland, Trinity House is bounc- ing digitized data to monitor and pro- ‘gramme unmanned lighthouses, light ships and buoys. Computer equipment monitors shoot- {ng stars and uses their trails to transmit information during the split second they flash through the sky. The relatively low cost and long range of meteor burst sys- toms offer great advantages over conven- tional forms of radio and satellite commu nication. Meteor bursts—vast numbers of mete- ors streak through the earth's atmosphere every day—leave a white hot tail when they hurtle towards the planet at speeds of up to 72 kin/s. The cosmic projectiles are vaporized by the friction caused by their contact with the air, and the air torn apart by their entry into the atmosphere forms a short-lived tral of ions. ‘The technique has already been used to gain knowledge of weather conditions and breakage in Alaskan pipelines. Now from Flight Electonics is the FLT-82 training system. Based onthe industry standard 8020;8050 seras of microcontoles, the FLT-22s designed to teach stedens a wide vay of ndustial control ap- plications. The system comes with everything you need fo get started, including power supply and cable to connect the system toa terminal or a PC running terminal emulation sotware. Detals from Flight Electronics, Ascupart House, SOUTHAMP. TON SO1 LU, Telophone (0703) 227721. mtINTERMEDIATE PROJECT series of projects for the not-so-experienced constructor. Although each article will describe in detail the operation, use, construction and, where relevant, the underlying theory of the project, constructors will, none the less, require an _ | __ elementary knowledge of electronic engineering. Each project in the serles will be based on inexpensive and commonly available parts. 9. IC MONITOR J. Ruffell Digital probes come in many shapes and versions. All of these, however, suffer from a single disadvantage: they can monitor the logic level at only one IC pin at a time. To overcome this limitation, we propose a 16-way IC monitor with a probe that can be clipped on to virtually any commonly used logic dual tegrated circuit with up to 16 pins. Ideal for getting to grips with digital circuits, this IC monitor gives an instant indication of all input and output levels simultaneously. Interestingly, it automatically finds the power pins of the IC under test and works with most TTL and CMOS circuits. The circuit of the IC monitor (Fig. 1) con- sists of 16 identical smaller circuits powered by one supply. The operation of the input circuits will be described with reference to the top one, which consists of Di-Dit-Ris-Ne-Re-Dis ‘The IC monitor is powered by the cir- ‘cuit under test via the two supply pins of the IC it is connected to. This means that the power supply of the circuit under test ‘must be capable of supplying an addi~ tional current of up to 504)’ mA to power the IC monitor. Make sure this is the case before connecting the monitor! ‘You are probably aware that pin 14 of d-way DIL logic ICs is usually the posi- tive supply terminal, and pin 7 the ground terminal. For 16-way ICs, the re- spective pins are usually 16 and 8. Unfor- tunately, there are also many ICs which deviate from this rule of thumb —their power connections are at pins other than Vor 16, and 7 oF 8, The IC monitor, how. ever, finds the power pins automatic How? Let's examine the input cir Tittle closer. If-a valid logic level is measured at ppin 2 of connector Ki, it will be either a 1 ‘or a0. Whichever, the absolute voltage is invariably a little lower (for a 1) than the positive supply vollage, or a litle higher (for a 0) than 0 V. This is because the ‘swing of logic IC outputs is nearly always smaller than their supply voltage owing to the forward drop across the output transistor(s). Invariably, only two of the diodes Dir-Des will therefore conductand pass the supply current because they are the ones connected to the highest poten tial —the supply voltage. (On the above assumption that pin 2 of Ki carries a logic level and not the positive or negative supply voltage, diodes Dis and Dir block, but the monitor circuit is powered by two other diodes. The logic level is applied to the input of inverter Ne via series resistor Ris. Depending on the measured logic level, the inverter sup- plies either a low output Jevel (input = high), ora high output level (input = low), Hence, the LED at its output, Dis, lights only if the measured level is high (1). TTL and CMOS ‘There are a large number of significant differences between ICs from the TTL BLEKTOR ELECTRONICS MARCH 1990(transistor-transistor logic) and the CMOS (complementary metal-oxide silicon) fam- ily. The most important difference is the supply voltage range of about 4.5-5.25 V for TTL circuits against about 3-18 V for most CMOS ICs (note: there are many ex- ceptions to this rule). Since the IC monitor is to be suitable for use with TTL as well as CMOS ICs, it ‘would appear logical to use CMOS inver- tors from the well-known CD4000 series, since these have the larger supply voltage range. Unfortunately, the outputs of these ICs can not sink enough current to drivea LED direct. The alternative, 16 discrote current amplifiers, must be rejected be- cause it would require a quite complex circuit, There is, however, an IC family capable of working at relatively low sup- ply voltages and sinking the current re- quired to light a LED: the 74HC series, ‘The one disadvantage of the 74HC series, the maximum supply voltage of about 6 V, is fairly simple to overcome by using a series regulator which limits the supply voltage taken from the circuit under test to a value which is safe for the inverters in the IC monitor. This regulator is a discrete circuit, Rsi-Dav-T2, Before its limiting action starts, the output voltage Of the series regulator follows the input voltage quite accurately, which is an im- portant requirement for 5-V digital sys- tems. Circuit T-Ree-Dee forms a voltage source which limits the LED current(s) to an acceptable level at relatively high sup- ply voltages. Let's assume that the circuit under test works at a supply voltage of 12 V, and that the voltages across Dir and Dis are about 2 V. Without Ti, the series resistor for the LED would have to drop about 10 V. Similarly, for a system opera- fing at 5 V, the drop would work out at about 3 V, which evidently requires an- ‘other resistor value. The solution to this problem has been found in the use of a series resistance, Ti, whose value in- ‘creases automatically with the supply voltage. Since Ts limits the LED voltage to about 2 V, a single resistor value (22 Q) may be used for the full range of the sup- ply voltage. Open input? In general, inputs of CMOS ICs must never be left open. You may have found out already from experiments that an open (ton-connected) CMOS input causes the IC to heat up and destroy itself rapid- ly. The actual_destruction is. normally caused by excessive current drawn by the output stages. Obviously, this effect must be avoided at al thmes and calls for on additional function ofthe IC monitor: de- tection of open CMOS inputs, The circuit to do s0 18 an oscillator, NisNieRinPr-C. When. switched on with Si, it supplies alternating tow and high Tevels to the inverter ates via 22MA resistors. When the osellaor is ‘switched off, these resistors ensure well efined Tow Tevels atthe inverter inputs ELEKTOR ELECTRONICS MARCH 1990 Ie Montror Fig. 1. that do not receive a logic signal from the Circuit under test. The high resistor value of 2.2 MQ ensures at the same time that measured signals do not see an additional load, so that the inverters can follow the high and low levels reliably, Finally, note the type of diode in posi tions Di~Das: the 1N4151 is used rather than the perhaps more familiar INS148 because ofits lower forward voltage drop, which is essential for correct operation of the circuit, Construction Since the circuit is quite complex by the standards used in this series of articles, it is best to build the IC monitor on the printed-circuit board shown in Fig. 2. This board is available ready-made through the Readers Services. For those with ac- cess to a photographic dark-room and the Circuit diagram of the 16-input IC monitor for TTL and CMOS digital circuits, necessary etching and drilling equipment, the mirror image of the track side of the circuit board is shown to enable a trans- parent film to be made from a photocopy. Since the pad density is fairly high in places, the PCB must be soldered with great care and precision. Work accurately and use a low-power iron and little solder to prevent short-circuits between adjacent tracks and pads. Start the population with the wire links. Next, fit the passive parts (capaci tors, resistors, IC sockets, the preset and the pin header). Lastly, mount the transis- tors and the diodes (but not the LEDs) taking good care to maintain the correct orientation. The power transistor, Ts, is fitted with ‘a small U-shaped heat-sink (TO-220 style) to assist in its cooling. The heat-sink is bolted on to the board together with the transistor. An insulating washer isnot re-ATE PROJECT PPPPPPP PPP eee 0 bw bet 2 bs) om is 0 bw Fig. 3. quired. Be sure to leave the terminals of the BD175 long enough so that they can be bent at right angles for inserting into the PCB holes without touching the heat-sink Next, mount each LED such that the lower side of its plastic body is about level with the top of the heat-sink. Do not fit the completed PCB into the enclosure as yet. Initial test Use a pair of light-duty flexible test leads with small crocodile clips to connect a DC power supply of 5-18 V to any two pins of connector Ki. Set Pi to the centre of its travel. Set switch S; to position B inverter inputs logic low). If the circuit works 50 far, the LED associated with the pin con- nected to the positive supply voltage will light. Set $1 to position A (oscillator on) and check that 14 LEDs flash, Adjust for the required flash rate. Next, systemati- cally connect the positive and negative “Track lay-out (reflocted) and component mounting plan of the printed: Ria Rey Ras Res Rer ax oy Ras ss Rar Poe, RevReaius Aurea = 2M2 ‘n= 22001 W si = 6000 i= (MO preset H Capscitors: Crs 191225 Cen 110 (CeiC4C5= 100 C= 4708 ‘Semiconductors: Di-Dis = LED} red; Sim da, | Dir-Dia=1NA151 Si ee icult board for the I tester. COMPONENTS LIST Dea = 2V7; 400 mW zener dodo ‘Dat = 6V8: 400 mW zener diode 1Cr1OzI0a = 744014 Ts BDI75 Ta= 8039? Miscellaneous: Si = miniature toggle switch = sway angled pin header for POB ‘mounting. Ke 16.way IDC socket Ko 16-way IC test chp (2.9. ElecroMa ‘stock number 428-027), ‘O-220 v1 10-126 style heatsink Approx. 50 om 16-way flatcable. PCB Type 896140 (ope Readers Services age) TOR ELECTRONICS MARCH 19904 1 1 i 1 Hl i 1 1 1 i { 1 t i ' | { i 1 i ' i 1 i 1 1 1 1 1 i { i 1 i ' i i t Le i Fig. 3. Test clip wiring and connections. Fig. 4. The test cable is made from an IDC, a length of fatcable and a 1é-way IC test clip. supply wires to all other inputs to verify the operation of the associated diodes (eg.-pair Dir-Dis for Ki pin 2) Case and test cable The completed, tested and adjusted printed-circuit board is fitted ina suitably sized ABS enclosure, for which a sug- gested front-panel lay-out is. given in Fig. 5 (ready-made front panel adhesives are not available). Cut a rectangular slot in one of the short sides of the enclosure to enable an IDC (insulation displacement connector) to be connected to Ki ‘The construction of the 16-way flat- cable between the IC monitor and the test clip is Ilustrated in Fig. 4. Contrary to what many electronics retailers and con- nector manufacturers would have you be-' lieve, an IDC is faiely simple to fit on to a flatcable of almost any width, without the use of special (very expensive) tools. Cut the cable as straight as you can using a large pair of scissors, Insert it be- tween the socket (or header) and the asso- ciated cap, taking care to align the individual wires in the cable with the V- shaped clamps which are to receive them, Note the position of pin 1 on the connec- tor, which is usually marked, Make sure this pin is at the side ofthe single coloured wire in the flatcable. Most IDCs have a U-shaped cap with snap-in fittings on the side guides, which readily lock with the main connector. Carefully place the cap on the socket, pressing it down with equal force at both extremes to prevent one guide locking, be- fore itis due. Use hand force to clamp the flateable between the socket andl the cap. Check whether the flatcable and the socket are at right angles. Next, use a BLEKTOR ELECTRONICS MARCH 1990 small plece of wood and a light hammer, or a carefully operated vise, to press the cap further on to the socket until the parts click together. Apply a little more force to ensure a good connection. Some IDCs have an additional cap that functions as a strain relief. Fold the flatcable back and fit this second cap. Connect the pins of the 16-way IC test clip to the corresponding wires at the ‘other side of the flatcable. Be sure to eon rect the flateable wires to the same pin numbers as Ki (Ki pin 1 goes to test clip pin 1, etc.) Finally, use an ohmmeter or a continuity tester to check whether all con: nections arein accordance with the circuit diagram, Practical use No doubt you will soon find the IC moni- tor an indispensable and easy-to-use test instrument for a wide variety of digital circuits. Open inputs are traced rapidly by switching 5: to the oscillator position. Any fone LED which starts to flash in addition to already flashing ones indicates an open input (remember that slowly changing logic levels applied to the IC may cause LEDs to flash if the oscillator is switched off with S:). Ifthe frequency of measured logic level exceeds about 25 Hz, the rele- vant LED no longer flashes, but appears to lightat reduced intensity. Finally, make a habit of switching off the circuit under test before placing the clip on an IC. a a Gmonitor & Fig. 5. Suggested front-panel lay-outMAPLIN OPENS NEW £2 MILLION DISTRIBUTION CENTRE ‘As par of its planned expansion campaign and still remain able to honour its pledge to eus- tomers for a same-day mail-out service, Maplin Electronics PLC has recently opened 3 new £2 million distribution centre at Womb ‘well, Barnsley. Local MP Terry Patchett unveiled a com- ‘memoratve plague in the presence of a gather- ing of directors, staff. local suppliers and members of the local and trade press. For directors Roger and Sandra Allen, and Doug Simmons, it was a milestone on the road to further success for a business that began as a part-time venture in the back bedroom of a house in Essex in 1972. Roger Allen, the managing director, told Elekwor Electronics: “We began by making up kits, but we had such difficulty in securing ‘components that we decided to go into the business of supplying electronic components”. ‘With its dedication to its customers, the Maplin business has grown to such an extent that itis currently handling over 13,000 orders ‘a week with an average order value of £18.00 Hence the need for this purpose-built distibu- tion contre, ‘The new 95,000 sq.ft. centre, whieh stands ‘on a five-acre site, has been created to ensure that orders are dealt with on a same-day dis patch basis. The centre is avast Aladdin's cave Cf electronic tems, from the smallest compo- nent to complete electronic equipment. Tacoming mail orders are dealt with atthe head office in Hadleigh, Essex, and these, as well as telephone orders, are processed with the aid of comprehensive computer programs written entirely within the company. Dispateh dials are sent immediately in data form over private circuits tothe new distribution centre SES IEE MEETINGS ‘5-8 Mar — Digital communications 8.9 Mar— Safety related contro systems, 18-23 Mar — Digital signal processing devices and apy 19-22 Mar —UK IT. 30 Mar — Network technology. Information on these, and many other, events ‘may be obiained from the IEE, Savoy Place, LONDON WC2R OBL, Telephone 01-24- 1871, ‘The SI Semiconductor International and INTERNEPCON will take place concur- rently from 20 to 22 Mareh at the National Exhibition Centre, Birmingham, Details from the organizers Reed Exhibition Companies Ltd, Oriel House, 26, The Quadrant, RICHMOND TW9 IDL, Telephone 01- 948 9900. where they are printed and prepared for dis- patch to the customer — all in one day! Details of aver 300,000 customers who have bought from Maplin aver the past three years are held on a computer data-base and these customers are mailed twice a year with information of new items, Tn the October mail-shol, customers are en couraged to purchase the annual catalogue Which has complete information on the total range of 7,000 stock lines. The eatalogue may be bought by mail-order or from any branch of WH Smith, who account for the distribution ‘of about 130.000 out ofthe 200,000 catalogues sold, Eighty per cent of Maptin’s tumover comes Irom private individuals who are purchasing for their hobby. Maplin publisies a bi-monthly magazine that gives technical information and constructional details of a number of projects ‘The company now has 11 retail shops in major towns and cities, including London, Bristol, Manchester, Birmingham, Leeds, Not OSyenTs A fiveday course on direct broadeastsatel- lite television is being organized jointly by ERA Technology and Professor B.G. Evans ofthe University of Surey. It wil take place from 26 to 30 March at the University in Guildford and is intended to provide dete sates with a sound technical background in satellite TV and supporting technologies, as well asthe commercial insight o take fll ad- vantage of current nd developing business opportunities. Deals from ERA Technology Ltd, Cleev Road, LEATHERHEAD KT22 7SA, Telephone (0372) 374151. ‘The Financial Times eighth conference on Television and Satellite Broadcasting, ‘which will be held in London on 28 February and 1 March, coincides with a crucial turing tingham, Southampton, Westcliffe, Neweastle and Reading. From the customer records buill up on the ‘computer, Maplin has been able to identify 19 ‘more areas in the country where Maplin shops could be sited and it s planned to have total ‘f 30 shops operational by the end of 1993. AA very small proportion ofthe ready-made ‘modules that ae Yor sale are manufactured by Maplin using out-workers, bur the vast major- ity ofthe product cange comes from manufac turers in the UK and abroad, Because of the very wide range of stock lines, the company buys from numerous sup- pliers, most of whom are in the UK (some 500) but some (about 25) inthe Far Eas ‘The main Maplin computer, based at Hadleigh, is equipped to process 90 orders si- ‘multaneously: it has 675 Mbytes of on-line disk storage. This is used for order processing, supplies to the shops, stock control and pu- chasing. A smaller, 32-line, computer serves the distribution process at Wombwell. Stock crders from the shops are received in data form via the telephone and a complete Elec- tronic Point of Sale system is being designed. ‘All the Maplin computer software has been converted to run under the operating system rnamed ric and this, apart from being an ideal system for commercial use, also has the advaa- tage of allowing a range of hardware being used without the necessity of alterations tothe software, Apart from expansion in the UK, Maplin intend to penetrate more deeply into continen- tal European countries and so be able to sell direct to greater numbers of individual cus- tomers there by early 1992, . point for the media industries, both in the UK and in the rest of Europe. One year into the irect-toshome satellite evolution in Europe, top speakers will be examining the implica~ tions of Britain’ legislative moves towards eregulating broadeasting and the creation of new channels, the scheduled launch of British Satellite Broadcasting and the impact of a second Astra satellite, Details from Financial ‘Times Conference Organization, 126 Jermyn Street, LONDON SWIY 4UJ, ‘Telephone 01-925 2323, ‘The Digital Cordless Communications con- ference, to be held at the Meridian Hotel, London on 12 March, and the Open Systems & Interoperability conference to be held at the QEM Centre, Westminster, London from 26 to 29 March, are organized by Blenheim Online Ltd, Blenheim House, Ash Hill Drive, PINNER HAS 2AE, Telephone 01- 868 4466. . ELEKTOR FLECTRONICS MARCH 1990VFO STABILIZER ‘The stabilizer presented here enables the precise tuning of HF oscillators for up to 100 MHz if these havea frequency control input. That input is normally used for va- rying the capacitance of a varactor. ‘The signal at the input of the circuit is amplified by a fast operational amplifier, IC). The output of this opamp isa rectan- gular signal that is applied to the D (data) input of bistable FF), The clock input of the bistable is provided by generator ICs The two outputs of the bistable are the product of the clock and the input signal ‘The frequency of this composite signal lies between 0 Hz and half the clock fre quency. To ensure the best possible con- trol characteristic, the output signal of the bistable is compared with a reference sig- nal that hasa frequency one quarter of the clock. To that end, a second bistable, FF2, is connected as.a binary scale; its input is provided with a signal whose frequency is half that of the clock applied to FF. ‘The differentiating network at the out put of FF uses only the negative pulses of the output signal, whereas that al the out- put of FF: uses only the positive pulses. All these pulses are combined in an inte- grator, resulting in a stable control volt- age. Since both the Q and the Q output are used, the ripple is halved. If the frequency of the input signal is not stable, the amplitude of the integrated signal varies. The variations are used to conteol the oscillator in a manner where the deviations are negated The clock is constructed around a ‘CD4060 and an inexpensive wateh crystal ‘The crystal may, of course, be replaced by yaya ’ 2 oe 2 a different type, as long as this has the required stability, The clock frequency, and thus the re- quired grid, is set with the aid of jump leads. The frequency on row B must al- ways be half that on row A. ‘The construction and alignment should not present any undue problems if the circuit is built on the PCB shown below. The oscillator is sot to exactly its centre frequency by Cs: this can be veri fied at test point TP, which carries the buffered clock frequency. ‘The circuit is powered by a 12-V sup. ply that is brought down to 5 V and siabi- lized by regulator ICs. Indicator Ds remains out as long as Jong as the oscillator frequency is stable. If the frequency drifts, the IED lights, its colour and intensity indicate in what di rection drift occurs and how serious the drifts. The integrating action may be disabled by Si, which allows the cireuit to settle down more rapidly than with it on, i COMPONENTS LIST u BeRH BID wasesaay pacitors: 22 ceramic 4ur 18 1000 coramic 10nF coramic 47OpF polystyrene ‘60pF vimmer ‘ope apr spOMeT 47uF 18V $000 MKT SRW soos ee ang Semiconductors: 1Net48 bicolour LED A733 TAFT4 or 74374 0° 748874. Ie cpdoso Lean ‘crystal 32.768 kre FLEKTOR ELECTRONICS MARCH 1990INTERVAL CONTROL FOR CAMCORDERS Philip Bosma Prices of camcorders have shown a welcome reduction over the last year or so, and an increasing number of enthusiasts are using these successors to the 8-mm and 16-mm film camera. The circuit described here is an accessory that allows recordings to made of events that take a relatively long time. The opening of a flower, for instance, can be filmed at regular intervals and then played back in a few ‘The recording principle of the camcorder is basically the same as that of a film camera: a Series of individual pictures is captured and subsequently played back to reproduce the original visual impress: ions. The camera of a camcorder has a range of shutter speeds, in economy mod- els ranging from ¥%0 to Yinop and in the more luxury models from lo to Yoon Short shutter times allow the user to make recordings of relatively fast events as they occur in, for instance, sports. By contrast, long shutter times are required to ensure sufficient intensity of incident light on the recording element, which is usually a CCD (charge-coupled device), As in film cameras, these shutter speed are not suit- able for slow-motion filming, which there- fore requires a different approach ‘The usual method is to make short rec- ordings at regular, adjustable, intervals, When these recordings are played back at the normal speed, the relatively slow event is reproduced at a much faster rate. In this manner, a slow event with gradual change that takes, for instance, an hour, may be shown in a few minutes or even a few seconds. ‘The circuit described here is switched on automatically during a predefined period of time. After each recording peri- od, the camcorder is switched back to the stand-by state, the length of which is also defined by the user. The circuit effectively disables the interval switch (or pause switch) in the camcorder. This switch is usually of lite use and offers a fairly crude control Practical use ofthe control is simple: fit the camera on a tripod or mount it on a table, aim and focus it on the flower, and switch on the interval control. After half an hour, or an hour, or even longer, de- pending on the flower, a perfect recording hhas been made of the flower opening, The circuit The circuit diagram shown in Fig. 1 could hardly be simpier. Note that only one IC is used, and that about half the circuit serves no other purpose than the contral seconds. Fig. 1. Circuit diagram of “with adjustable on and ot time: ‘of an indicator LED. The result is a small Gircuit board fer which a compact enclo- sure should be easy to find. A single 9-V PP3-size battery is used to power the in- terval switch, Since the circuit consumes little power, the battery should offer suf interval control, which is basicall ‘an astable multivibrator ficient capacity for extended periods of ‘operation. ‘The interval control is basically an as- table multivibrator with adjustable fre- quency and duty ratio. Resistors Ri, Re and Ri determine the voltage at the non- ELEKTOR ELECTRONICS MARCH 1990inverting input of opamp Ai. Because of foedback resistor Rs, the voltage at the non-inverting opamp input is either Vi or 34 of the supply voltage, depending on the ‘output voltage of the opamp. The hys teresis so created in the switching beha- viour of the opamp causes it to function as a kind of Schmitt-trigger. The R-C combi on between the inverting input and the output of the opamp extends this func- tion to that of a multivibrator. ‘The opamp output is high ifthe voltage across C1 is lower than 0.25UIs. The time needed to charge C: from the low trigger threshold, 0.25Uh, to the high trigger thre- shold, 0.75Ub, is determined by preset P2 and potentiometer Ps. The total resistance set with Ps and Ps is in direct proportion to the time the opamp output remains high. When the voltage across Ci exceeds the high threshold level, the opamp out- put goes low. As a result, C) discharges until’ the lower trigger threshold is reached. Diodes D1 and Dzallow different Limes to be set for the charging and dis- charging of Ci, Transistor Te conducts as long as the ‘opamp output is high. In this condition, the remote control inputs of the cam: corder are connected via MOSFET T so that the recording function is switched on. ‘This lasts until Ci has discharged to the lower threshold level, when the opamp toggles and T2 is switched off. ‘The component values in the muti brator allow maximum recording-on and recording-off times of about 400 s to be sel. A minimum setting is provided by preset P: to ensure that the camcorder has suificient time to produce a synchronized picture. This minimum recording interval Is called the backspace time and is speci- fied in the user manual with most cam- corders. If the backspace time is not known, its fairly simple to establish from a few experiments. ‘The second part of the circuit is the recording-on indicator set up around ‘opamp A2. Thisis configured asanastable multivibrator of which the duty factor and, output frequency are fixed. Itis started the moment At supplies a high level. Diode Ds causes the on-time of As to be much shorter than the off-time so that LED Ds flashes. This is done to reduce the average current consumption of the circuit to about 3 mA whilst ensuring a clear indi- cation that a recording is being made. Building the control Figure 2 shows the component mounting plan and the mirror image ofthe track side ‘of the small PCB, Construction of the cit~ ‘cuit is straightforward. Start by fitting the solder pins, followed by the resistors, presets and capacitors. Next, mount the diodes, the integrated circuit and the tran- sistors, Use little solder and work accur- ately. Potentiometers Prand Pv areeither sol dered direct to the board, or connected to it via short lengths of insulated wire, Finally, fit the circuit into a small ABS ELEKTOR ELECTRONICS MARCH 1990 enclosure with a battery compartment. ‘The timing controls, the on /off switch and the indicator LED should be fitted on the top panel for easy access, ‘The interval control is connected to the camcorder by a short length of 2-wire cable. A 3.5 mm jack plug is used at the side of the interyal control, and a 3- or -pin DIN plug at the side of the cam- corder, . COMPONENTS LIST Resistors: 5 IMO AuiAeRsRaPr 1 4K7 Be 1 860k Ra 1 3M3 Fe 1 4% Fe 1 1500 Roo 2 50k preset H PriPe 2 2MBIin. potentiometer Ps;P Capacitors: 1 220 tev co 1 sno 46v Ge + 1000 3 1 19. t6V Ge ‘Semiconductors: 2 iNatas, DriDeiDa 1 LED ou 1 BCS«7B 1 1 BSI70 t 1 Those Ics Miscellaneous: 13.5 mm jack socket kK 1) miniature SPST swich Si + Poa o000e 9 oso ‘& ‘ela beries @ weve Ol I ] i Fig. 2. Single-sided printed circuit board {or the interval contol. The tima controls, Ps and Ps, may be soldered direct to the board.REPLACEMENT FOR TCA280A The "Computer-contralled slide fader” we published in 1988 (Ref. 1) was based on dimmer chip Type TCA280A. In spite of this device being a Philips Components preferred product at the time, it proved difficult to obtain for many readers. When approached, Philips Components ad- mitted that they had taken the TCA280A ‘out of production without prior warning, and that no pin-compatible replacement ‘was available. It has taken us some time to find a suitable replacement and have found that the Type TCA785 from Siemens isa good, but not pin-compatible, substitute, which also required some redesigning of the ‘original circuit, The result is shown in the circuit diagram, Fig. 1 ‘The VSYNC input is provided with a 50 Hz square wave, which is used inter- nally for mains synchronization. The IC is powered via Rz, D:,Ciand zener diode Ds ‘An internal current source, set by Pi ‘and Rs, causes a linearly rising voltage on Ca, At each zero crossing of the mains voltage, Cs is discharged rapidly, so that the potential across it has a sawtooth ‘waveform. The amplitude depends on the setting of Pr The sawtooth voltage is compared with a control voltage that is applied to pin 11 of ICi via filter Ri-Cs. Ifthe saw- tooth voltage rises above the control volt- age, a pulse is generated at pin 14 or 15, depending on the current half cycle (po: tive or negative) of the mains voltage. The two outputs are connected t0 a triac via diodes Ds-De and resistor Rs, which en- able the triac to be triggered. The instant Cree Ne ue Resistors: Ria2rk Re=ga0a a-ak a= 104 Bot = ak? Fie 1500. Pri 100K preset H Pes 10k near poteatiomster | Copsctors: Gr 70 25 V (ite at ack ie) CaC2= 1000, Gs= 1850p a ‘= TCAT85 (Siemens; ElectroValue Lc.) Miscellaneous: “Si= miniature SPST svrich, "PCB Typo 894076 (sos Roaders Servicas page): : Fig. 1. that the triac begins to conduct is, there- fore, dependent on the control voltage at pin 11, resulting in a voltage-controlled dimmer. The control voltage may be pro- vided by the slide projector or a poten- tometer. In the latter case only, itis also possible to dim 12-V halogen lamps. Zener diode Ds then needs to be replaced by an 8.2 V type, The dimmer is aligned by adjusting Ps in the off condition, when the control volt- age is at a maximum, until the lamp just glows, The slide projector is aligned by setting the relevant potentiometer on the projec: tor PCB to the centre ofits travel, when the lamp(s) should be out ‘When that is done, the lamp(s) should be switched on and off a couple of times Circuit diagram of the TCATOS-based lamp dimmer circu. to make sure that the two potentiometers (Pi and that on the projector board) are adjusted correctly. Since the control characteristic of the TCA7S5 is different from that of the TCA280A, It is not advisable to mix the two devices: When Si in the present dimmer is closed, the projector lamps are off: in other words, for normal operation, Si must remain open and it may, therefore, be omitted in some cases, . Reference: 1. *Computer-controlled slide fader" Elekior Electrowics March 1988 and April 1988, Fig. 2. ‘The printed-circuit board may be used for four lamp dimmer circuits. TORVIDEO MIXER PART 3: KEYBOARD A. Rigby & G. Dam This penultimate instalment discusses the third module in the video mixer: the keyboard with its many switches and controls for picture mixing and special wipe effects. ‘The keyboard circuit forms the user inter- face of the video mixer. The block diagram in Fig. 11 shows the general structure, om mam] Pan om Each of the switches shown ina horizontal =m ene | | eon] | EN row roughly at the centre of the diagram as has its own LED indicator. The switch states are demultiplexed to give two or, in i aur ] ayer | | scr some cases, four independent control sig- nals. The diagram also shows thatthe out- | —— Put signals of switches Se-Siz and Su-Sss aresynchronized to the vSyNc signal. This ae seat | [sean | fate || seen | | oer ‘means that any action on the keyboard + st Lh 5 does not take effect until the VSYNC pulse = = = = = = is generated in the mixer. The ES oe we se oe ES synchronization eliminates unexpected | Ld |L™' J LU} LUE) | Le) switching effects occurring at random in —— stants during the current raster. we—>amen] [acne The lower part of the block diageam wome—2—f irene] | SCY contains an EPROM plus associated logic > Ar control circuits, The loading of state levels = ae Te = supplied by switches $1-St and S52 is re er set Pe] st, synchronized by VS¥Nc to ensure that the on —_—__— elfect associated with a particular switch ae = becomes visible at thestart ofa new raster Pe == ee ee ise only. wt TE =i Aiter buffering, EPROM datalines DO- DS areused direct in the mixer. Datalines mere ta Dé and D7, however, are fist applied toa ee! Lhof-ddecoder to give the required control signals SCI5-SCIB. The combination of oe _| | eee control lines MC1-MC6 and buffered da talines DO-D5 provides a total of 64 differ- tent combinations, or 256 combinations if ore SC15-SC1B are added. Each combination represents a particular picture wipe or mixing effect. Fig. 11. Block diagram of the keyboard unit, BLEKTOR ELECTRONICS MARCH 1990Fig. 12. Circuit diagram of the keyboard module in the video mixer. ELEKTOR ELECTRONICS MARCH 1990VIDEO MIXER PART 3: KEYBOARD 2 Q Q @ Q BLEKTOR ELECTRONICS MARCH 1990Clearly, a total of 256 possible combi nations results in an unwieldy number of effects, Therefore, a selection has been made on the basis of practical use. Ob- ‘oully tis telecon lanabective, nutthe S14: XROO-XKOE 75 75.35 35 35 79.95 75 75 3595 95 35 35 75.75 user of the mixers free to design and store xxio-KF 7719 30 37 37 73097 77 30.7.3 37 20.977 his own set of effects, as discussed later. S16: XNZ0-XK2E 65 05 45 25 25 45 05 &5 6505 45 26 25 45 05 65 Jn the basic version of the mixer, the S175 HKBO-KKOE 67.07 47-27. 27 47.07 67 62.07 47.27. 27.47 07 67 EPROM contains only one of 16 possible banks of picture effects —up to 15 may be added as required. The effects obtained from the above selection are stored in the Si S253 54 Si s2 S354 $152.63 s4 515253 8 S18: XKAD-KREF 6D 0D 4D 20 2 40 0D 6D 6D GD 49 20 20 40 OD 6D 9192 XXSO-AKSF GF GR 2A IF 2F 2K GA SF GF GA 20 2F 2P 2A GA GE first bank of the EPROM, and may be 520: XX60-XX6F 09 €9 29 49 69.29 69.09 09 69 29 49 49 29 69 09 called up by a total of 20 keys. The first S21: XXTORKTE 66 06 46 26 26 46 05 G6 55 06 46 26 26 46 06 66 keyboard area consists of 16 keys, Sie-S:0; while the second area consists oF four 522: XXBO-XXBP 50 40 00 19 10 09 49 So 50.00 40.20 30 40 00 50 keys, Si-Ss. The latter allows the user to select one of four effects offered by one $23: XNOO-XKOF BS BD PS FS FS 50 PS BS BS FOAS FS FS FD BS BS S24: XXRO-XXAP BD 87 87 BO BD 37 77 RD 3D.B7.B7 7D 30.37.77 7D key from the first (20-key) area. you find this difficult to follow, look at the front- 325: XXGO-KKEE 35 35 75 35 35 35 35 75 35 753535 75.35 3535 panel lay-out (Fig. 14) which provides all the necessary information for effective 526: XXCO-KNCF TF OF AP 3 3 4 OF TP 3P OF AF 1 aP ar OF 1 control of the mixer. S27: XKDO-¥XOP OA 62 2E 4A AR 28 GE OA OA GE 2E 4A 4A 28 GEOR As already stated, only a small part of ‘528: KKEO-XXEF GF 6F 2F 2F GF 2F GF 2F GF 6B 2E 2P 2F 26 6E 6P the EPROM capacity is used, which leaves the user plenty of room to store new ef- fects combinations. The possibilities and rules that apply to customizing theeffects Table 1. Content of the EPROM type 2764 in the keyboard cl set are detailed further on in this article, each databyte to earn how to program your own set of pict ‘The banks with custom-designed effects the data in Table 2 (below) for reterence. are accessed with the aid of the block se- 29: KKEO-XKEE OF 6 2B 42 4E 25 6 OF OF GE IF AP AF 2P GF OF ull. Analyze the function of mixing and wipe effects. Use inieiest . = en Tos eae | names Tose | Fenelon Signals SWandavaretaton rom he_| sie ei | Rati, Vaaetors | Kemiom sadn ta cae ear al | trctogstosacmamammarterse | TTT. 1 Eevou tmepucedly wl thee a lg tical as well as the horizontal syne pulses. | g| /2] |_|. als ale 35) 8/3) 8) 2s) al 2) 2] | 2 3| 2 Practical circuit tugn | 2) 2| 2) §| £] 8/9 BER ESE a2 ‘The circuit diagram of the keyboard cir- nibble _ | |} cult is given im Fig. 12. Although a si- [BR oaapw [60/6 Jo] Tbs] b6 aa eae ol alee Sable Greut tif the simplest in she i | — o000 0 x i i x) | Portiations Sts ithese-ice ema oo ea] |< wl |x : | group of four switches of which only one is selected at a time. This selection is ar |9010) 2 | x | |* x x mua wecmenmmaetananoam 105 %3| 9 |x Bla x x me 3 aputOk pate Eachawiteh Regen | associated activity LED which isdrivenby , |°1 90) 4 * it x # | an outputof outer ice Tresswncung foros) 8 | xl | lal x ELL | | signals supplic 12 leave | wetomecer sews MPFR toy io) | |x x x x SwitchesSi~St providethetwoaddress | 91 14) 7 K ta) x x) x| signals AD and Al which seee EPROM. | | resident effects and patterns. Switches |10 00) & ) |* * | Soe ae ately amend Ss fice] 6 ae x a“ ground ortbepecttveeeppiyrel Acuw. [0 " yy tion of one of these switches is recorded 10 19) & | by the bistable tht folows it The be 1011] 8 xf | feo)» | | 5 ‘Coton ane contig a soca 0D ale lel | | types whose output signals are fed direct 1700) © | Ode pis cliedat selene [ive 6 xloof |x «| bbufferiCsi which drives fiveswitch-status |, j| g sl |x | : «| tebe ThetwoKCsinthetapletchand corer [i111] xf lols Liel | Leds ofthe circuit [Ge and [Ca form a priority tncnder for switches Sie-S. If one of the eight encoder inpats is made high, the | x= tunclon selected | ‘output supplies the binary value of the | (4) » uncon slected bu ovetidden | number ofthe relevant input. Iftwo keys fare pressed simultaneously, the highest value is passed to the output. Since two Independent decoders are used, ICs and Table 2. Correlation between EPROM content and picture mixing eects. ELEKTOR ELECTRONICS MARCH 1990514 0000: 76 78 28 95 35 75 95 75 75 35 78 38 95 95 75 75 pet dbeddbgtssggs $1 2 5459 St S254 $2 51 52 5459 51 $294 53 ‘ Wsw= 0 | SW ‘ VSW- 1 ‘ ‘Tobie 3. Sinteen byles ar reserved foreach switch In keyboard area 1. Use the data In Table 2 to establish the associated mixer functions. ICs2 are cascaded via their EI/EO (enable in/out pins. This ensures that ICs is dis- abled if one of the keys S21-So» is pressed, ‘The outputs of the priority encoder are connected to a 4-bit latch, IC, via three OR gates. The fourth data input of the laich is connected to the GS (group select) output of ICe2. Asa result, ICS supplies a bit key identification code. Gates Nes— [Noe suppress key bounce pulses and other interference, The 4-bit key code is fed di- rect to address inputs Ad-A7 of the EPROM. Address inputs A8-Al1 are given their respective levels by DiL switch Block Sw. Address line A12 is grounded, so that only the lower 4 Kbyte of the EPROM is used. The EPROM through the Readers Services, all switches in Siw must be closed. Alternatively, four wire links may be installed, EPROM address line A3 is connected to the VsW signal. Bistable ICs7 ensures that level changes of the VSW signal are synchronized {0 the line-syne signal to prevent video source switching in the cu rent picture line, Address line A2 is switched by the BSW signal, while the levels of AO and Al are determined by switches $1-Ss, The rela- tion between the EPROM address and the effect on the picture is discussed further VIDEO MIXER PART3:KEYBOARD PBJ Construction The last module of the video mixer desk consist of two printed-circuit boards which are available ready-made as one piece through the Readers Services. The PCB is double-sided and through-plated First, use a fig-saw to cut out the part which is to hold the mains transformer and the two PCB terminal blocks. The edges of this part of the board are indi- cated by holes. Mount the transformer and the termi- nal blocks on the supply board and put it aside for fitting into the enclosure later. The hole in the keyboard PCB created by removing the supply board forms a clearance for the slide potentiometers Mount the following parts at the EDS side of the board: IDC cable headers KSW1, KSW2 and KMC, and voltage regu lator ICs, Be sure to observe the opposite orien- tation of SIL resistor arrays Ruse and Ress, Switches Si, Sy and Srv are self-lock- ing types, In some cases, the size of Crz forces this capacitor to be mounted at the EPS side of the board. Since the LEDs are intogral to the swit- ches, these parts are mounted at the same time. To reduce cost, all ICs, except the EPROM, may be mounted without soc- kets. come se ea ry Fig. 13, ELEKTOR ELECTRONICS MARCH 1990 Front-panel lay-out shown at approximately 30% of true size. panel layFig. 14. Component mounting plan for the double-sided, through-plated Keyboard POB, Note that the transformer section le oul out ELEKTOR ELECTRONICS MARCH 1990,Resistors: Rize fhe terAise= 3300 Rise Rise RissAissiAier Riese Fis = 10K Ruse = 100k Rise isn Au isos «2708, Fre sz = 447 (Bway SIL resistor array) ‘Capacitors: (Gize-Crar = 1000 Grze= 10 rat = 3800 Ko Semiconductors: 1GesiGe1 = 409 IGaeiGee = 740200 Ger Gere = 7aHO74 IG = 744CT244 (Ca iCsn 1050 = 4075 COMPONENTS LIST 15 Osa = 744107305 Gas = 2764 (order number 5861; s20 Feaders Services page) Ise « 7abi0175 (esp = 4071 sn iOx2 = 4532 us-butlon uth integrat fed LED (Dataswitch 61-10404010), S:Sos;$27« toggle switch with inioral ree LED (Dataswitch 61-20404010, Sie = 4-way DIP sult block. ‘Tri = mains franstormar 20 Vows VA) Ki:Ke = S-way PCB terminal block VIDEO MIXER PART 3: KEYBOARD KMO1:KSWs = 20-way PCB header. KS = 26-way PCB neador, Gy. 2: 26-way 100 plug Qy.4 Bo-nay IDG socket, Qy. 4: 250m 20-way latcable Qty: 1: 4.6m 20-way lteablo Qiy. 1: 60 em 26-waytlatcable Enclosure’ e.g, ESM EP30,20+ PCE Type 87304-3 (o0e Readers Services abe) Front-pane!toll Type 87904-F (see Readers ‘Services page). * FTW Switches Division of TW Limited » ‘Norway Road = Hisea + PORTSMOUTH P08 SHT. Telephone: (0705) 694971 ESM + 179 Rue de Fawvolloe + 92400 CCourhevole France. Telephone +331 47.6850 96, Telex: 20512, The remainder of the construction is straightforward. Work accurately and use Little Solder to prevent short-circuits. Al ‘ways remember that fault-finding in cir cuit like this can be costly and time-consuming, Custom effects: over to you Table 1 shows the structure of the con- tents of the EPROM Type 2764 for this project. The & databits of the EPROM con- trol a number of functions of the mixing desk, The relations between the bits and the functions are summarized in Table 2 The two least-significant bits, DO and D1, select one of four horizontal effects volt. ages. Similarly, D2 and D3 select one of four vertical effects voltages, Databits D4 and D5 select the source that determines the horizontal reference voltage for the switching of Fst: this source is either the vertical effects voltage or the horizontal wipe potentiometer. Databit D5 controls the inversion of the picture. The two most- significant databits, D7 and D8, select the {input signal source. The table and the bit assignment should enable you to analyse the function of each databyte in the ‘stand ard’ EPROM fairly quickly. ‘The logic levels present at the EPROM address inputs determine which of the da- tabytes is applied to the EPROM da- talines. This address emanates from switches Si-S« and Si1-Sw, and the Hsw and VsW signals. The functions of the en- tries in Tabie 2 are explained below, First, however, assume that the remaining ad~ dress lines are low. The table contains 16 lines, one for each effect switch in area 1. The remaining address locations in the ‘standard: EPROM are empty. Each line invariably contains 16 bytes, each of which can be selected inclividuatly by applying therele- vant address, Table 3 lists the functions of all variables. If, for instance, switches 51 and Sis are pressed (horizontal wipe), the first byte in the EPROM is initially put on the databus. Write down the binary struc- BLEKTOR ELECTRONICS MARCH 1999 ture of the byte. From Table 2, itis ana- lyzed as follows: + Input I/II is used; * the horizonal reference voltage is sup- plied by the potentiometer; + the horizontal effects voltage isa ramp; ‘the vertical effects voltage isa ramp. When Hsi is active —as a result of the horizontal ramp exceeding the reference evel set with the potentiometer —the fifth byte s applied to thedatabus. Again refer: ring to Table 2, input 1/2 is selected. This mode causes a horizontal wipe effect with the position of the picture transition being determined by the slide potentiometer for the horizontal effects, ‘The function of the EPROM-based con: trol words is similar for the vertical effects (assume that Seand $+ are pressed), Desig, ning and storing one's own picture effects is not simple. The tables and analysis of the ‘default’ effects in the EPROM, how: ever, should provide sufficient informa- tion to get you started The Ia instalment of this stile wil appear in ext mantis tse of hktor Ehstroice, Pats t and 2 appeared in the January and February 1989 ise respectively Fig. 15. Example of a picture-mixing ef- fect in four stages.The circuit described here is a mor by Mohd Abdul Sami based solely on information supplied by th practical experience by Elektor Electronics ication to the “Digital V/I Display” published in this magazine some years ago". It can display more than one analogue input (on different read-outs), although it uses only one analogue-to-digital converter. The circuit diagram shows that the multi- plexer, IC4, is clocked by the MSD (most significant digit) output of analogue-to- digital converter (ADC) ICI via switch ICSe. As soon as the MSD output reveals that the relevant input has been converted and channelled to the output, the counter increments and another analogue input is selected by the ADC. The design is such that only one switch and one BCD-to-7. segment decoder (IC2 or IC3) are enabled at any one time, When the counter increments, its out put disables the blanking input of the ap- propriate 7-seement decoder, At the next increment, Q3 resets the counter and the cycle repeats itself. Although it is possible to have three read-outs, the clock of the CA3162 is not really fast enough to ensure correct persis- tence of all three displays, although they remain perfectly readable, Ifa third read-out is used, Q3 of IC4 must be connected to the contral input of an additional switch, Q4 to the blanking input of the decoder, and Q5 to the reset of the counter, The input voltage range is 0-0.999 V. ‘The reference potential of all inputs is the LO input of IC1. . (1 July/August 1987, Supplement, p.5 x MULTIPLEXES DISPLAY. x 23 a8) rca 0481 wacom sv ELEKTOR ELECTRONICS MARCH 1990The circuit described here is a mor by Mohd Abdul Sami based solely on information supplied by th practical experience by Elektor Electronics ication to the “Digital V/I Display” published in this magazine some years ago". It can display more than one analogue input (on different read-outs), although it uses only one analogue-to-digital converter. The circuit diagram shows that the multi- plexer, IC4, is clocked by the MSD (most significant digit) output of analogue-to- digital converter (ADC) ICI via switch ICSe. As soon as the MSD output reveals that the relevant input has been converted and channelled to the output, the counter increments and another analogue input is selected by the ADC. The design is such that only one switch and one BCD-to-7. segment decoder (IC2 or IC3) are enabled at any one time, When the counter increments, its out put disables the blanking input of the ap- propriate 7-seement decoder, At the next increment, Q3 resets the counter and the cycle repeats itself. Although it is possible to have three read-outs, the clock of the CA3162 is not really fast enough to ensure correct persis- tence of all three displays, although they remain perfectly readable, Ifa third read-out is used, Q3 of IC4 must be connected to the contral input of an additional switch, Q4 to the blanking input of the decoder, and Q5 to the reset of the counter, The input voltage range is 0-0.999 V. ‘The reference potential of all inputs is the LO input of IC1. . (1 July/August 1987, Supplement, p.5 x MULTIPLEXES DISPLAY. x 23 a8) rca 0481 wacom sv ELEKTOR ELECTRONICS MARCH 1990PLOTTER MARK-II with a contribution by B. Lewetz The plotter we published roughly two years ago is among our most popular projects thanks to a relatively simple mechanical construction and the availability of an associated stepper motor driver board. Although a number of readers have sent us suggestions for software drivers that would enable the plotter to be used with popular computers, only Mr. Lewetz’ contribution proved to meet the requirements as regards use of the driver on IBM PCs, and (at least partial) compatibility with the industry-standard HPGL plotter command language. Before introducing the software, however, we avail ourselves of the opportunity to propose some improvements to the mechanical design of the plotter. Like its predecessor (Ref. 1), the Mark-ll version of the plotter uses paper mov ment for the Y-direction, and pen mov ment for the X-direction. As such, the operation of the plotter is not unlike that of a matrix printer, The platen which causes the paper movement is operated direct by a stepper motor. The pen car- riage is coupled to another stepper motor via a string. Small solenoids control the pen up/down movement, The simple mechanical construction and the possi- bility of customizing the plotter width in accordance with the maximum required Paper width are important factors. that made us prefer the above arrangement over the more complex X-Y variant, ‘The plotter works in conjunction with ‘control board which translates a bit-pat- tern applied to its input into the corre- sponding control signals for the three solenoids and two stepper motors. The circuit is based on two special stepper motor driver ICs from Motorola which obviate complex bit shift and timing oper- ations for the control of the half-step and ELEKTOR ELECTRONICS MARCH 1990 full-step modes as well as the for- ward/reverse movement of the stepper motors at the required accuracy. The chips, Type MC3479, allow the 8-bit wide Input of the control board to be driven by a Centronics (printer-) port, which is available on almost any IBM PC-XT, AT or compatible. Connection details are given in Fig. 2 ‘The control board used for the new version of the plotter is that discussed in Ref. 1: no changes are required, and the circuit works in conjunction with the soft- ware package described further on. Mechanical work ‘Since the mechanical construction of the plotter is discussed at length in Ref. 1, there is no need to repeat it here. The new working drawings, Figs. 1 and 3, and the associated parts list reflect most of the ‘mechanical changes made to the original design. The most important change is that the Mark-ll version is about 10 em wider, ‘which allows A2 paper to be used side. ways and A3 paper lengthwise. Four paper rollers are used instead of two for improved accuracy of the Y-movement Also, the platen is fitted with a 12 mm diameter bearing at the free side to reduce friction (see Fig. 4: the original had a nylon bushing). Further improvements to the original design have been suggested by numerous readers. The use of a lathe to reduce the diameter of the platen at the locations of the sandpaper grips, for instance, may be gone round by covering the platen in flex- ible conduit. The same is suggested forthe paper rolls. It should be noted, however, that these modifications may result in dif ferent step sizes for the horizontal and vertical movement, which may require software-controlled compensation. Further suggestions as regards im- proving the mechanical stability of the plotter entail the use of 4-mm thick alumi- rium, stainless steel or silver steel. One of our readers in Greece, a lathe operator by profession, has built the plotter from Stainless steel, using sintered metal for theMAIN SPECIFICATIONS Hardwa + beam pte fornaper size upto DINAZ (6945420 mn) * repeatebity:<0.1 mm + Seolouts sitipe constuction + tonto board wth cntronics input Software: + parialy HPGL compatibe 6 commands ‘Suppored) + plot commands sont via Certraics port + compatible wih Elekior Elecironcs plot ter diver Board + sotare spodler “+ configuration te + programmaia plot speed ‘+ muttasking Turbo-© cont! program + aunciary programs for: + keyboard control + plot fle formating = fulthal-step operation bearings, and PTEE (teflon) for the rollers, ‘The use of high-grade metals, however, requires a wide range of tools and other special materials from your local, hard ware shop, and, of course, access to a Tathe. ‘The nylon string fs a crucial part and requires special attention because it must be secured in a manner that eliminates any risk of slipping on the spindle of the X-motor. One string end is secured to the cartiage at the side of the string wheel From there, the string goes to the string wheel where it makes'a left turn towards the X-motor. The carriage is pushed to the extreme left (X-motor side), and the string is wound! on to the motor spindle (part id 10) until one particular point in the string is always in contact with the spindle, This, means that the total length of the wound part ofthe string is equal toor greater than the maximum X-distance that can. be travelled by the carriage. The point in the string is secured at the top of the motor spindle with the aid of an M3 screw Software ‘The software driver developed for the plotter runs on IBM PCs and compatibies. ‘The driver is written in Turbo-C (Borland version), and is capable of reading plot files with a reduced command set to the HPGL, Calcomp or Gould standard. The program converts the data and commands in these files into coordinate numbers in the relevant plot area before it sends, via the Centronics port, the necessary motor and pen control commands to the plotter driver board. Tobe able to generate a usable plot file, the CAD program which is used to make the drawing must have plotter types Fig. 1. General parts identification of the plotter. Fig. ab. Ase Pw-0 we ~ 100 2X=0 | 2y=0 K=0 3-0 MX -= 1700 My = 2000 S04 83-4 G0 PT~55 lant Byes PS-3 Rant x= 100 SY = 100 Parts identification for the cide plates which held the stepper motors, ‘Number of pens Pause at pen change (0/1) ‘Wait time after pen actuation (clock eyeles; 1-255) %ailference between pen t and pen 2 (600-500) ‘Y-diference betwoan pen 1 and pen 2 (-500~500) Xalference botweon pon 2 and pen 3 (-500-500) Y citference between pon 2 and pan 2 (-800-600) Maximum X-coordinate (0-100) Maximum Y-coorcinate (010000) Step duration (clock cycles; 1-285) Parallel port number (1/2) Ful-step mode Systom clock (1-255) Loudspeaker on/off (0/1) Slowtast (011) Plot language (1=Caleomp; 2-Gouid; S=HPGL) raw frame (0/172) Yoseale (1-1000%) Yeseale (1=1000%) Table 1. Parameters in the driver configuration file, wononian ss. ELEKTOR ECTRONICS MARCH 1990HP7220, Calcomp 81 or Gould 6200 in its device driver list. On completion of the rawing, the plot file is not sent direct to the Centronics port, but toa file which is temporarily stored on disk. ‘The plotter driver program, MON- DRIAN-EXE, is called up with the plot file name as an extension, for instance: MONDRIAN NOZZLE.CAL To enable the driver program to find the plot file, it must efther be listed in the same subdirectory, or the PATH configura- tion must be set aecordingly. ‘The program starts witha menu screen which shows the current options and par- ameters. The lower window on the screen shows the plotter commands as they are read and converted ‘The program works on two tasks ina guasi-simultaneous manner: the conver- sion of plot coordinates into step pulses for the motors, and, in the background, the sending of calculated values to the plotter contro! board via the Centronics Interface. A problem may arise from the assignment of processor time to these tasks. Ifthe calculations run too fast, the plotter forms a bottleneck after a relative- ly short time. Conversely, if the calcula- tions run much slower than the actual plotter control, the plotter wastes time ‘wailing for new commands from the com- puter. The time sharing problem is elimi- nated by an auxiliary program, REALTIME COM, which establishes an opti- mum time ratio for the two processes on the basis of the computer type used, plouer Ks Fig. 2 Connections between the PC Cen- tronies port and the input of the plotter driver board. ‘The driver program may be called up ‘with a test switch: MONDRIAN /T to check quickly and without wasting paper whether the drawing fits on the re Quired paper size. If not, the scale factors must be modified accordingly. Parameters and configuration file The plotter driver program is simple to configure for different mechanical con- structions (as already noted, the construc- tor determines his own plotter width). The PLOTTER MARK.tt EB configuration file on the disk, MON DRIAN:Sy', contains the start parameters — an example is shown in Table 1. The file contains ASCII characters only and may be edited witha word processor. Each line starts with a two-letter parameter identi- fication and a default value, which can take up to three digits. As shown in the example, each line is made complete with comment When called up, the contre] program searches for MONDRIAN S¥S and loads the user-defined configuration. If the file can not be found, default values are adopted for the parameters otherwise loaded from MONDRIANSYS. A fair number of configu- ration options is available, from the num ber of pens to the zoom factor and the plot language. The aX parameters (X-Y dif- ference) allow drilling inaccuracies in the ppen holes to be compensated: in this man- nner, the inaccuracy caused by a pen (= colour) change can be kept smaller than O41 mm. Limitations Ie should be noted that version 1.0 of ow ORIANEXE cecognizes only "ax HCL Hewlet-Packare, Graphic Language commands, while the language has mony inate Ie aempegpes ior het cama Gould formats: Only sh commands are supported, Fortunately, many problems | cated. by. this limtkaton nay be | prevented by using the right. plotter ever: Most CAD programs alld the ser to ables 9 pardeuir poter diver Som a mens drng istllton of the SOFTWARE ON DISKETTE The plotter driver program and con- figuration utiities described in this article are available on a 5Yinch 360 KByte MSDOS formatted floppy ‘isk under order number ESS117. Details on cost and ordering are ‘given on the Readers Services page elsewhere in this issue. ELEKTOR ELECTRONICS MARCH 1990,Fig. 8. Dimensions ofall nylon and alumintu ‘stainless steel parts that must be cut, fled, turned and drilled. ELEKTOR ELECTRONICS MARCH 1990{all mensions in mn) 4, side plate; et, aliminiom; 60:70x3 mn, 2. side plat right aluminium; 60708 mm. 3, angled support bracket for X motor shaped aluminium: 20.404 mu; length 60 mm. 4, square connection ber; aluminium 40x40 mm; 808 ma long. '5 ound conection bar, aluminlunstain- less sts! rod; dia. 6 mm; 808 mm ong, 6. round support bar for pon carriage; dimon- sions a5 5. 7, round guide bar for pen cariage: dimen- sions es 5. £8. round bar for pressure rol alumi- runifstailass sto! rod; cia, 8mm: length 501 mm. 2 plain; round aluminum bar; ola. 12 mm; Jength 514 mm 40, shaft aluminium: dia. 12 mm; length 40mm, 11. titlever for pressure ols spindle: U- shaped alumi beam 10x03 mm; fength 48 om, 12, $2011), 18, angled support bracket or sting wheel; MECHANICAL PARTS LIST U-shaped aluminium beam 15x15:2 mm; length 14mm. 44, pen cariage; U-shaped aluminium ‘bearn 25x60: mm; length 60 mm. 16, pen positing plate; aluminium: 8:50:2 mm, 18, cable quide; U-shaped aluminium beam 428 man; fonath 808 rm. Miscellaneous parts: offside bearings; nyion; Skitly 08-6 4 off bushing for platen nylon; Skity 68-4 or 08-6, ot suliabe ball boanng. off washer rings for Yomotor; internal a, 3 mm; thickness 2 en 2off rubber pressute rots (@.9. cable grom: met). ‘4off fing rings for da. 6 mm spindle (e.9, Skify 1141-8). 4 off sirng whee! 3 off avindar head screws Ms. 2otf eyindor head aoraws Méx0 (for xing paitno.9). 4 off cinder head screw M20 with 3 nuts, ‘of MaxS scree with countorcunk head, 4ooff ovinder head soraws MSx40 (fr xing ‘stopper motors) 2 off eylinter head screws MBx50 (for xing parino, 18) 2 off eyindor head screws M10 {for fixing sting). 2 off eyinder head screws M15 (for xing spring brackets). 4 of headless adjuctmont screws NES (lor fiaang part nos. 9 and 10). off bolts M265 (lor fing pen it mage ate) 16 of hexagonal nuts MS. 2 off springs for pressure rols spindle, Sting; wound fishing ina ‘ine grade sandpaper (for securing on lator). Electromechanical parts: 2 olf stepper motors; 200 steps. dual phaso bxpotar, 200 mAphase (6.9, Barger 2 used n isk aves). 3 off pon lit electomagnets: 12 V;€.9. Bin- er Magnete Type 40031-09800. Distbutor of Sty products in the UKs ‘Salter Fasteners » Saler Springs & Press ings Limited « Spring Road « Smethwick» Warley» West Midlands B68 1PF. Tele- ‘hone: (021 853) 2929, Telex: 357877, Fig. 4A ball-bearing may be used where the plate is secured to the side plate, Fig. 5. Detailed construction of @ paper roll. package. Programs like AutoCad and AutoSketch, for instance, use only six plot commands ifa Hewlett Packard plotter is installed: circles and ellipsoids are drawn with the aid of Move and PLOT sequences rather than with the much more powerful ELEKTOR ELECTRONICS MARCH 1990 ARC command. This means that only a subset of basic HPGL commands is used. Since the present driver program, MON- DRiaNExE, is capable of handling the six basic commands, it should be suitable for many CAD packages, provided they can be configured to save plot files with the reduced set of HPGL commands. . itor Plotter Ori | stop at new pens nove pe up hove to pen down rove t ove te wove t ove 1 wie 599/1798X ave & i pea up nue - gress any key Reference: 1. Plotter. Elektor Electronics May 1988 and Jane 1988, vane plot connands cnicom irane size 1700/20 selling clock locks per step pen noverenti00 el p- pause 5 stop ‘Screen dump of the plotter driver program, NONORMNLEKE,DIGITAL TRIGGER FOR OSCILLOSCOPES The circuit described here enables an os- cilloscope to be triggered when a pre- sletermined binary code word is applied to one of the cizcuit’s inputs. Integrated circuits ICi and IC2compare the 16 input levels with the code set by switches Si and S. Ifone ofthe inputs has. a dataword that is equal for not less than 100 ns to that set by Si and S2, pin 19 of IC. goes high. Note that, because of the pull- Up resistors, open inputs are treated as high. ‘When pin 9 of IC1 is high, monostable MMV2is triggered and outputs a negative pulse from its pin 4. The length of this pulse is 0.1-1.5 us, depending on the set- ting of Pi. If during that time the pre- determined trigger value disappears, no triggering takes place. Potentiometer Pi is a logarithmic type to enable very short times to be set accurately. ‘The output pulse from MMV: triggers second monostable, MMV:, whose ‘monotime has boen set to 1 us by Res-C:, Either the positive signal from the Q output or the negative signal from the © output, depending on the setting of Si, may be applied to the oscilloscope. ‘The printed circuit board is relatively small. Most resistors are mounted up- right. [f difficult to obtain locally, the four single-in-line (IL) resistor arrays may each be replaced by eight vertically fitted resistors whose top wires are cut short for connecting to a horizontally running wire to the +5 V line, . A. Rigby af [ss [ole fs Li Troon ae CNTs Resistors: RreRie= 19k Ri7-Fa0 = 100k Retas = 2 Ree 470.0. Pr = 100k ogarthmic potemiometer ‘Capacitors: Gi=i0p. Gen a7p Ga ino Gee 1000 ‘Semiconductors: [C102 74HCTEES iGa=74Hert23 Miscellaneous: ‘S152 G-way DIP switch. So minature SPOT switch, Kr = BNC socket. Qty. 18: miniature tost cp. Enclosure: @.¢., KW A8010 085 PCB 694042 ELBKTOR ELECTRONICS MARCH 1990EXPERIMENTAL BSB RECEPTION R.G. Krijgsman PE1CHY, J.C. Stekelenburg PEIFYZ and J. Buiting PE1CSI Awave of publicity recently swept over the UK announcing the launch of the five-channel BSB TV-satellite. Everybody seems to have an opinion on this event, and pages of comment have been written on it, even in technical magazines, without proof of the availability of receive equipment. The bottlenecks are, as we learn from informed sources, the aerial and the D-MAC set-top decoder. Well, squarial or no squarial, Elektor Electronics is proud to be the first international electronics publication to present pictures of MAC transmissions received from BSB and other DB satellites. Rather than gazing into a crystal ball, we show you a glimpse of a multi-standard MAC decoder for home construction that is currently being designed. At the time of writing (mid-January 1990), the launch of BSB's five high-power TV channels is due this spring. From technical Point of view, BSB offers two novelties: D- MAC and the flat dish or squarial, Other technical aspects such as the use of the DBS Frequency bend (11.7-12.5 GHz), circular polarization and_medium-level transmit powers (approx. 5$ dBW) will certainly be now for many satellite-TV enthusiasts, but are familiar from other broadcast services whieh have been in use for over « year al ready. DFS Kopernikus (23.5° E) has about the same transmit power as BSB, while both TDP-1 and TV-SAT2 use D2-MAC, high transmit powers (61 dBW) and circular po- larization in the DBS band. Keen satelite TV experimenters may also have noted the very strong signals from the two DBS TV transponders on host the Olympus satelite. One channel is currently allocated to RAL Italy, the other to British Telecom. The RAT channel is transmitted in PAL, while British Telecom alternately use PAL and D2-MAC, the latter for parts of the BBC-TV Europe programme. TDF-1, TV-SAT2 and Olympus are positioned at 19° west. BSB is positioned at 31° West, whieh is more favourable for the UK because it allows the satellite's spo beam to cover the target area at roughly equal signal strength, and because the dish elevation is not too lov Strong but ul Whatever the st MAC picture 2 standard PAL monitors and TV seis used by hhundreds of thousands of satellite-TV vie vers in Europe. This is because the MAC standard uses a totally different method of picture and sound transmission, which is Partly digital and time-multiplexed rather than frequency-multiplexed. Although set- top decoders for MAC channels are not yet available, itis surprising to note how many non-technical dish owners are aware of the ‘existence of the MAC system, and even the meaning of the acronym, This awareness must be partly due to 1wo D2-MAC channels telligible dard, C-, D- of D2-MAC, fon the Astra TV satellite: Seansat TV-1000 tnd TV3 (one of which is encrypted at low level) Both TV-SAT2 and TDF-1 are running experimental transmissions. TDF-1 has four transponders which are used for promotional purposes and technical experiments. TV- SAT2, the West-German DB satelite, ear ries four TV channels which run in parallel with DFS Kopernikus and Asira, Remark ably, some of the programme material on TY-SAT2 isin PAL, while the satelite trans mits in D2-MAC. So much for techaieal im provements! ‘The transmissions received from BSB uring its pre-operational use that started in December 1989 are also experimental. Three transponders are already encoded, and one is in‘clear’ D-MAC. As could be expected, the signals are strong and totally noise-free. Experimental equipment The equipment used for making the accom anying colour photographs was assembled Fig. 1. KTOR ELECTRONICS MARCH 1990 {Layout of experimental equipment used for making the colour photographs in his anticiPhotograph 1. BSB still test pleture (0-MAC). Photograph 2. BSB colour-bar test chart (D-MAC}, Photograph 3. ARD-1 Fu-Bk-type test chart (TV-SAT2; D2-MAC). Photograph 4, TDF-1 station identification (02-MAC) LU ek aay Tuesda) alm fe) Aaa Xero om nO CuO) asa 09.30 AROUND OUR SCHOOL pee Eolas 11.30 SOBA prec Ug ias gang DEVELOPMENT AND. PLANNING Se ase cy MATERIAL FROM CAMBRIDGE 14.00 CLOSEDOWN Photograph 5. European info programme (D2-MAC; Olympus). Photograph 6. RAI Fu-Bk-type test chart (PAL; Olympus), ELEKTOR ELECTRONICS MARCH 1990imomomocknoln Sxcolilico Rotetan (iki dis CTT em iam Photograph 7. BSB still test picture (D-MAC). Photograph 8. Nordie-channel identification (ECS4; 02-MMAC) Photograph 10. BSB still test picture (O-MAC), Photograph 9. Outdoor unit set up on a photographer's tripod in the garden. Photograph 11. Video clip in brilliant colours on TDF-1 (D2- mac}. ELERTOR ELECTRONICS MARCH 1990Satellite Position Country EIRP Channels TV standard Programmes’ TVSAT2 19° W West-Germany 61 dBW 4 (Iho) D2-MAc Eins-Plus, SAT, RTL-Plus, SAT-1 BOB} STW United Kingdom 85 4B 5(tho) —O-MAC ‘The Movie Ghannal, The Sports Channel, Galaxy, : ‘Now, The Power Station TOF 19°W France BI dBW 4 (rho) D2-MAG Misceilaneous/ to be assigned ‘Olympus 19° Ukitaly @20BW 3 (hcirhe) O2-MAGIPAL —_RAI.'B.T. World Servioo/BEC TV Europe/Discovery * experimental son/ces. the = Hightshand circular polarization. ihe = let-hand circular polarization. experimentally o testa protorype of a multi- standard MAC decoder which is currenty being developed in the Elekior Electronics fengincering department. A preliminary de- scription of this unit, which we hope to pub- lish later this year, is given further on, ‘The general layout of the equipment is shown in Fig. 1. The outdoor unit used for the experiments consists of a 60-cm off-set dish and a Type ST-080 LNB from Uniden ‘The latter is a fairly unique unit because it can_be switched from CSS-hand (10.95— 11,75 GHz) to DBS-band (11.75-12.5 GHz) reception by means of wo supply levels on the LNB downlead coax cable, The noise figure of this LNB is also remarkable at 1.94B. A linear polarizer could be used with impunity because there is (as yet) no inter- ference trom other satellites a the UK DBS Position of 31° W (for the Euro-DBS posi- tion, 19° W, we use a pieee of teflon in the round feed-horn to turn the linear polarizer with magnetic H/V selection into a circular feed). It must be noted, though, that the use of linear polarizer for circular signals re- sults ina signal degradation of at least 3 dB. The indoor unit is 8 Type CX-8520R from Connexions. The baseband output of this re cciver is modified to provide the large banc width required by the MAC decoder insufficient bandwidth results in high bit error correction rates). Nextin the configuration isa purpose-de- signed de-emphasis/AGC unit which is con. trolled by a digital signal supplied by the MAC decoder. This unit, which exists as an experimental design, isa quite elaborate cit- cuit to meet the EBY specifications in re- spect ofthe de-emphasis for D-MAC as well 8 D2-MAC (these specifications are not the same as those used for PAL}. The AGC fune= tion makes the operation of the de-emphasis section independent of the baseband signal level. This is an important aspect which en sures that many types of indoor unit ean be used with the decoder, What's cooking? The heart of the system is formed by an experimental multi-standard MAC decoder based on the Type DMA2280 chip from ITT (Untermetall). The decoder, of whieh an in: side view is shown in Fig. 2, is controlled over a 4-wire cable by # PC running the CLIMB (Command Language for InterMe- tall Bus) interpreter from Intermetall. This interpreter allows sequences of read/write operations to the nearly 100 registers in the chips on the decoder board to be given a program structure, and werks in eonjunction with a PC insertion card, The PC is, of course, required during the design stages only t0 establish the optimum program flay and register contents, If these parameters are known, almost any’ small microprocessor system can take over this task, running an EPROM-based. program. The’ auihors/de- signers are currently thinking of using a Z80 and some peripheral chips for this applica ‘The MAC decoder supplies RGB signals which are fed direet 10 a high-resolution monitor via its SCART input. Note that the decoder has registers for just about every picture setting, from color saturation and brightness to horizontal syne delay and pic lure positioning. Remarkably, the decoder obviates anything to do with PAL, SECAM. or remodulators because it drives the RGB circuits in the TV direct 10 ensure the best possible picture resolution. The MAC ‘ecoder has an option for automatic 16:9-10 3:4 aspect ratio conversion, which allows future HDTV transmissions to be seen on a standard (3:4) TV set of monitor, Some ex perimental 16:9 transmissions have already been received from TDF-1 Fig. 2. Impressions Talking about picture resolution, he quality ofareal MAC picture (nota PAL programme transmitted in MAC) is impressive even if you are used to day-to-day TV reception at good quality. The colours inthe still pictures and the test charts transmitted by the BSB re, in a word, brilliant, and do not suffer from boundary effects and other colour i regularities. Cross-colour and moiré effects are completely absent, and the pieture resol- ution is suddenly 6.5 MHz as compared to a lousy’ 3.5 MHz that can be resolved by most current PAL TY sets. Transitions be- tween deep red and blue, notorious in the PAL system for their blurred picture areas, are sharp as never before (note the coloured oval in the BSB logo, and R-to-B transition inthe the TDF-1 ident). The sound accompa- ying the MAC programmes is in stereo at CD quality. Each BSB channel may have up to eight of these high-quality sound chan nels . Colour photographs for this article made by Robert Krigsman on 4 January 1990, Inside view of the prototype mull: MAC decoder.POWER LINE MONITOR J. Ruffell Most of us are aware that computers and other digital systems can go haywire just like that. If neither the hardware nor the software can be blamed for the hang-up, spikes on the mains voltage are the most likely cause of the trouble. The power line monitor described here enables you to determine whether or not spikes occur frequently on a particular mains outlet, and whether or not digital equipment needs to be powered via a mains filter to reduce the risk of hang-ups or Sudden transient disturbances of the mains voltage are commonly referred to as surges or spikes. Since their peak valt- age can exceed the normal mains voltage by hundreds of volts, itis not surprising that mains-powered equipment behaves erratically or breaks down altogether. Un- fortunately, the occurrence of spikes is, fairly difficult to record reliably, the rea sons for which are mainly + the occurrence of a spike is difficult to predict; + thevoltagerisehasa very short duration (typ. 10-500 ns), + voltage peaks in excess of 1,000 V are no exception; + the recording instrument must be con- nected to the mains line. Principle of operation ‘The principle behind the power line moni- tor is shown in Fig. 1. Resistor Rs forms a load for the rectified mains voltage. As- suming that the mains frequency is 50 Hz, the frequency of the voltage on Ro 100 Fiz because a full-wave rectifier, D DD, is used. Spikes typically have a much higher frequency and are, therefore, rea detected with the aid of a high-pass filter, Ci-Ri, where R: is the input resis ance of the detector circuit, The 3 dB roll- ‘off frequency of this high-pass is about 16 kHz, while its time-constant, +, equals, Fig. 1. Principle of spike detection. ELEKTOR ELECTRONICS MARCH 1990 total break-downs. RiC1=10 us. The function of Re may be less ‘obvious in this basic circuit. Without it, however, Ci would be charged to the peak value of the mains voltage (approx. 340 V). This would cause the diodes in the bridge rectifier to start conducting again if the mains voltage rises above this peak value. As a resull, a 200-V spike during the mains zero crossing could not be dk tected since it would end up in the brid, rectifier. Rivis, therefore, fitted to ensure that the voltage on Ci follows the rectified voltage accurately. Hence, spikes are not MAIN SPECIFICATIONS tsgger level adjustable in sx steps: 60; 100 ¥; 250 V; 500 V: 1000 V response time: <80 ns potential detector output via opto- Coupler (Uctinani=32 V) bultin mains power supoly visual and audible spike indicationCircuit description Figure 2 shows the circuit diagram of the power line monitor. The mains voltage is, rectified by a bridge circuit composed of four diodes Type IN4007. This diode is used because of its peak reverse voltage specification of 1.500 V. The value of Re is 2 compromise between acceptable dissi pation and sufficient Ioading of Ci. The high-pass filter is formed by Ci and R-Re. The minimum working voltageof Ci must be 630 VDC since the device has on it the rectified voltage of about 340 V. The resis~ tor ladder network, Ri-Rs, has only the spikes across it ‘The ladder network and the associated rotary switch allow spikes at a certain level to be attenuated before they are ap- plied to the trigger input of the detector, Ci, via the pole of Si. A Type 7HHCT221 dual MMV is used because of the foilow- Ing specifications, of which the import ance is undisputed in the application ‘cuit: ‘+ the inputs are protected up to 25 kV typical: + the input capacitance is low at 35 pF typical; + the minimum width ofthe trigger pulse is dns; * the trigger level is accurately defined at 1.3 V, which enables a simple voltage divider to be used, Note, however, that the actual minimum trigger pulse width is determined by the inputattenuator and the stray capacitance ofthe input protection diodes, Ds-Die, and the trigger input of ICis. This R-C combi- nation forms a low-pass filter that causes spikes to be detected only if they are longer than 50 ps. ‘Monostable multivibrator (MMV) ICis is triggered when the attenuated spike voltage exceeds the trigger threshold set with Si. On triggering, outputs Q and Q supply a 20-ms pulse. The pulse at the Q output is fed to IC, which lengthens it 0 about I second. During this time, LED Di: and buzzer Bz1 signal the occurrence of a OPERATION AND CONTROLS Range switch (Si): set to expected ‘s0IK8 level. Spikes exceeding sot loval ate detected and indicated. Test switch (S:): press to test trigger funetion (manual rigger) LED (Ds): ont Indicator LED Dri and buzzer Ba: spike indica- eee E a= og T eek ene ps Fig: & Gul diagram ofthe powerline mono Fig. 9. Printed-circult board overlay and track yu (reflected), ELEKTOR ELECTRONICS MARCH 1990eee ois | RiP = 4KB7 1% Ra 1900 1% a= 7887 1% 5-268 1% Fe= anes 1% r= de 135 Fes 130 1% a= 1004 1 W io» 8200 is» 680K | RigAi =4700 Rina Ak Ree aM Fis 10k Fig 270k ‘Capacitors: Ci tno; 630 Cacscr= 1000 | 3 = 470q: 25 V; raed Ces 1n0 (Co 2u2; 16 Viradial Ge= 100 ‘Semiconductor Bi=De= 1Naoo7 spike. The detection circuit may be tested by pressing Su; this causes ICis to be trig- gered manually. ‘The O output of ICw drives an opto- coupler, ICs, to create a potential-free out- put, ie, an output that is not at mains Potential and, therefore, safe (within limits) for connection to other equipment. Connector Ks may be wired to the input Of, for instance, an event counter to estab- lish the number of spikes that occur dur ing a certain period. The output may also be used to stop a digital clock, or for other time-keeping purposes, to enable the origin of the spike to be traced. Another application is the use of a storage oscillos- cope to determine when and why a par- DC-AC converter July/August 1989, p. 49-51 ‘Only when used in conjunction with the external timebase circuit, the 4047 in the converter supplies an output signal with fa duty factor other than 0.5, This causes the primary transformer winding to become saturated, and the dissipation in the power transistors to rise to uncon- trollable levels. To prevent this happen- ing, fit wire links 2-3 and 4-5 to keep the 4047 operating in the astable mode. Con- nect pin 2 of the timebase circuit (100 Hz signal) to pin 3 of the 4047 via a 10 kO. resistor. Remove Riand Ci from the main converter board. Attention: none of the above changes applies to the free-running version of the power converter. BLEKTOR ELECTRONICS MARCH 1990 Ds = LED 5 mm groan DeiDe‘De.Dio = 1N4t48 Dr =1Nsoot Dit «LED; mm; red Ty-805a78 IG: = 7aner221 (Qe 75.05 163 = GNY2t oriL10 (Siemens; Electro. Value Lis.) ‘Wiscllansous: i= 2poe baa rotary swich or PCB ‘mounting: paste spin Se mintatre pusho-make button Bis BV active buzzer = fuse: 50 ma ow wih POB-mount noe Th #9 V90.35 VAmains transformer Kis 2ay mainerated terminal oc Ke 2ay terminal dock ABS mains spl ase; outside dmon- sons 120:65440 mm PCB Type 900025 (ae Readers Senices page. ticular computer broke down owing to a mains surge. Because ofthe limited drive capacity of the 74HICT221, the LED in the optocoupler is not fed with its maximum current. This smieans that the external collector resistor for the optocoupler must not be smaller than 10 K@2 to ensure that the phototran- sistor is just driven into saturation. Be sure to connect the external collector resistor and the emitter of the optocoupler to the positive supply and ground respec- tively of the recording equipment (whether digital or analogue), never to the +5 V and ground lines of the power line monitor, since these may be at mains potential CORRECTIONS Simple AC millivolt meter January 1990, p. 22-2 In the cireuit diagram, Fig. 1, the voltage shown at the base of To is measured with respect to the positive supply rail Dark-room clock February 1990, p. 62-66 The value of Riv (1 KO) is best increased to 10 kA to prevent Ts overloading the Qi3 ‘output of ICi, which may cause erroneous clocking of IC In Fig. 4, pin 9 of IC1 should also be circled to indicate that a through-contact ‘The +5 V voltage for the power line monitor is provided by a standard power supply based on a mains transformer and a fixed-voltage regulator, [C2. Note that the use of this supply does not mean that the low-voltage part of the circuit is safe to touch. Construction and initial test With safety in mind, It is best to construct the circuit on the printed-circuit board shown in Fig, 3. This board is mounted into a so-called power supply enclosure which is supplied complete with line and neutral pins for plugging into a mains outlet. Capacitor Cs is not shown on the over lay, but may be connected in parallel with Ris at the track side of the board. The rotary switch must bea type witha plastic shaft, and the push-button must be fitted recessed, so that none of its metal parts protrude from the enclosure. Allequipment connected to Kz must be powered from a separate supply, battery or adapter. ‘The operation of the monitor is simple toverify by plugging it intoa mains socket and switching a nearby fluorescent tube ‘on and off a few times. Set to the most sensitive range (30 V), the monitor is near: ly always triggered if the mains outlet is ‘on the same line as, and within 10m from, the tube lighting, The number of ‘hits’ will bbe found to decrease as the sensitivity of the monitor is lowered, and the distance to the tube is increased. . wire must be fitted in the relevant PCB hole, Vocal eliminator July/August 1989, supplement p. 5-6 Pins 5 (input) and pin 6 (input) of ‘opamp A2 must be transposed in the ci cuit diagram, Voice recorder from Texas Instruments June 1989, p. 43-45 ‘The supply voltage pin numbers of ICs, ICs and ICs are given incorrectly in the circuit diagram in Fig 6. Pins 18 of IC2 and IC, and pin 4 of ICs, must be connected to ground, Pins 9 of IC: and ICs, and pin 8 of ICs, must be con- nected 0 #5 V.SURGE SUPPRESSOR J. Ruffell Itis an annoying but generally accepted fact that much mains-operated equipment produces surges and other interference on the mains, But we do not have to put up with clicking noises from AF equipment as the refrigerator switches on, or a computer that stops working when the hts are switched on. All that is needed to Prevent these irritating effects is a good-quality mains filter. Ideally, any mains outlet supplies an al- ternating voltage of a root-mean-square (cms) value and a frequency specified by the national (or local) electricity supplier (Gm the larger part of the UK, these values are 240 Vens ancl 50 Hz. respectively), In practice, however, this is hardly ever so, In not a few cases, the mains voltage is occasionally corrupted by high-frequency signals, data-bursts, brief luctuations, surges and dips. Although mains signalling is a well defined area’, some types of mains inter- com operating at carrier frequencies of 100 kHz and Up are notorious sources of interference. Pulse-like interference often emanates from dimmer circuits, switch- mode power supplies in computers and defective or poorly decoupled household equipment like coffee machines and re- frigerators. In some countries, the electricity sup- pliers themselves use the mains lines to convey control information for nor mal/reduced rate switching of domestic power consumption meters, To avoid problems with any equip- ment powered from the mains, a mains filter as the one described here must work in both directions, which means that both ‘mains-borne interference and interference generated by the equipment must be sup- Pressed. The filter proposed here is suit- R owe! é able for use with 220-240 V mains systems operating at 50 Hz. Design considerations ‘The mains filter is basically a passive low- pass with a roll-off frequency of 50 Hz. Its likeness to a low-pass filter for audio ap- plications. is only superficial however since the high operating voltage and the associated considerations as regards safety govern the use of special compo- nents. In many countries, standards have been set up that define the maximum ca- pacitor values used in the filler, often de pending on whether mains-powered equipment is wall- or floor-mounted, or portable. These capacitor values are a ‘carefully established compromise be- tween acceptable switch-on and switeh- ‘off currents on the one hand, and the risk of electrical shock in the case of defective ‘or improperly connected earthing on the other: Capacitors alone can not secure the re- quired slope steepness of the filter, The attenuation outside the pass-band is im- proved considerably by using one or more chokes. These come in at least three ver- sions. In general, the choke with the hig- hhest inductance is the most effective. However, if reactive loads are powered, the voltage drop across the choke rises with inductance. In practice, this means that the filter has to be geared accurately to the load and the nature of the antici- pated interference. ‘The simplest version is the saturation choke. When the mains is switched on, this type of inductor possesses a high in- ductance, which rapidly becomes smaller as the current causes the ferrite-iron core to become saturated. The interference suppression grade is nearly always speci- fied for symmetrical (balanced) inter- ference, that is, interference that exists between the live (L) and neutral (N} line ‘The multiple-winding current-com. pensated toroid choke is more effective but also more expensive than the satura tion type. Strong capacitive coupling be- tween the circuit and the enclosure causes an asymmetrical current (between L/N and E) to flow into the equipment through the earth wire, and half of it back into the ‘mains through the ive or neutral line, The partial interference current causes the choke, of which the windings are inserted in the phase or neutral line, to be damped so that the magnetic fields generated in the windings cancel one another. The in- ductance of both chokes is small for the load current and therefore introduces a small voltage drop only. The bar-type choke is best used for loads over 100 A that produce mainly symmetrical interference (between live and neutral). In contrast to the saturation choke, the inductance of a bar-type choke remains constant, Practical circuit ‘The circuit diagram of the mains filter is given in Fig. 1. The mains voltage is ap- plied via connector Ki. Components Ci ‘and R2 form a potential divider for the on/off indicator, Ds. Capacitor Ci dis- * Mains signaling inthe UK is subject to the | provisions of British Standard BSGE99, Fur. ‘her information on the subject may be ob | tained trom BIMSA (BEAMA Interactive and | Mains Systems Association), Leicester House, 8 Leicester Strat, LONDON WO2H BN, Telephone: (01-437) 0578. l ELEKTOR ELECTRONICS MARCH 1990(GENERAL INTEREST charges via resistor Ri when the filter is disconnected from the mains. Diode De is connected across D) to keep the reverse voltage across the LED within safe limits. Voltage peaks exceeding 250 V are elimi- nated by varistor VDR) Capacitors C2 and Cs must be clase-X2 types. Similarly, Csand Cs must be class-Y types. These type codes indicate an a.c. working voltage of 250 V and apply to metallized polyester or polypropylene ca- pacitors with good self-healing properties should arcing occur in the dielectric ma- terial. X2-class capacitors may not be used in positions where their failure would ex- pose anybody to electric shock. Conse- quently, these capacitors are connected Detween the live and neutral lines to en- sure that failure can only cause a blown fuse (in the case of a short-circuit) or re: duced filter operation (in the case of an open-circuit). Both effects are annoying, Dut not dangerous. The requirements of the Y-type capaci tors, Ce and Cs, are more stringent (see B.S. 6201, part3,and [EC 161), LikeCzand_ Fig. 1. Cireull dlagram of the surge suppressor. & aS. ‘ ¥| B' © v- 0 le B ~ gs Fig, 2, Track lay-out (mirror image) and component mounting plan of the printed-circult board for the mains filter COMPONENTS LIST “Resistors: Miscellaneous: A 1 ElecvoVakue Limited «28 St Judes Road = R= M0038 W {= choke 2x0 ml Type O62 3 or Englefield Green Egham + Surrey TW20 Fe>3k3.059W ‘24 mH typo RD 82-64 ‘OHB, Telephone: (0784) 39608. Toiox Fu 300k 033 Ft = fuse 2.5 A siow (or RDS2-3) 5A ‘264475, Fax (0784) 95216, Nonhorn YOR’ = Stokaso' _slow (or R062) brent: 680 Bumage Lane « Manchester Kiem Sway POB serow trina lock MiS (NA. Telephone: (061 432) 4048, Capacitors: {pin distance 10 mn). : Gh» 150m; 690 VDC ABS enclosure 11011065 mm. 26.0, RS Comporentsstook no. 115.219, GzGs= 470n; 250 VAG class x2 ? Panet-mount mains socket wthinegra use. _2,g,, AS Components stock no. 114-496. (GaGe= 2n2; 250 VAC clase V3 hk : Pant mount nising receptaci, + Schafinar UK + Headloy Park = Area 10+ ‘Semiconductors: : 8 To sno (rt avaate rou ‘Headley Road East - Woodley READING. ‘DieLeD nnd : the Readers Sarvcas). __ RIGS SW. Telephone: (0794) 697179. “Dea 1NAC07 ELEKTOR ELECTRONICS MARCH 1990Gs, they cause degraded filter operation in the case of open-circuit failure, More im- portanily, however, a short-circuit in either Cs or Cs causes the live (L) or neu- tral (N) line to be connected to the pratec- tive earth line. Hence the following warning: Never use capacitors of a different type oor rating than those indicated. ‘The inductance in the filter is formed by a current-compensated choke. The printed- circuit board allows two different types from Schaffner to be fitted, These types differ in respect of maximum load current and inductance. The 2x10 mE{ inductor Type RD62-3 is rated for up to3 A, and the 2x4: mH Type RD62-6 for up to 6 A. Construction For reasons of safety, the mains filter must not be constructed on any other board than that shown in Fig. 2. Construction is straightforward with the possible excep- lon of Li, of which the mounting depends on the type used. The larger and more expensive 6-A inductor is fitted upside- down on the PCB. The underside af the choke has four colour-marked wires. The two dark-coloured wires are the input connections (at the side of C2 in the circuit diagram). The two light-coloured wires are the output connections (at the side of Digitrap-2 CD filter Sage Audio have recently introduced two types of passive filter that are claimed to eliminate residual quantization noise at the signal outputs of CD players, This noise occurs typically at the sampling fre- {quency (44.1 KFiz) and harmonics thereof. A sample of the Digitrap-2 version was tested in the Elektor Electronics engineer ing department with some interesting re- sults, The filter was inserted between a swept frequency generator and a signal level recorder. The result of the first testis shown in Fig. 1. The response is virtually straight to 10 kHz, but then rises toa peak of about +4 dB at 33 kHz. The claimed attenuation of 30 dB at 44.1 KHz was, however, about correct, The measured re sponse could not be improved by varyin the filter load impedance between 600 £ and 1 MQ, The source impedance, how- ever, appeared to be the cause of the un- wanted peak. When changed from about 10 @ to 470 Q, the response curve became straight within 0.1 dB, the peak at 33 kHz disappeared, and the attenuation at 44.1 KHz was 30 dB as before, Figure 2 shows the results. The phase shift was also measured and found to be quite smooth well up to 20 kHz, In all, the Digitrap-2 is a well-designed and correctly working AF filter when connected to the right source impedance. Next, the Digitrap-2 was subjected toa subjective listening test by connecting it to sin the circuit diagram). The photo- graph in Fig, 3 shows the R1D62-6 on the completed board ‘The smaller 3-A inductor Type RD62-3. fs fitted in the normal manner with the ‘connections inserted direct into the rele vant PCB holes. Do not test the mains filter hefore it is NEW PRODUCTS 4 CD player with 8-times oversampling, ‘The loudspeakers used were electrostatic types for the high and middle ranges. In this high-end equipment configuration, the Digitrap-2 had a small, but definitely noticeable, effect: it made the overall sound a little smoother. Whether or not this is desirable is, obviously, a matter of fitted into the relevant equipment, or —if it is to be used for various appliances— into a separate ABS enclosure without any ‘metal part. The prototype shown in the introductory photograph has a mains socket and a mains plug for panel mount- ing as used on personal computers, i a personal taste, but it also depends on the Quality of the available audio equipment In conclusion, the Digitrap-2 js recom- mended to users of CD players who want toget the most out oftheir high-end auidio equipment configuration. Care should be taken, however, not to connect the filter to a CD player with an output impedance smaller than 200 0. More information on the Digitrap series may be obtained from Sage Audio Electronics * Construction House + BINGLEY BD16 4]H. ELEKTOR ELECTRONICS MARCH 1990Many inexpensive or older TV sets lack a SCART or other composite video input, and can only be connected to a video recorder or other equipment via an RF modulator. The modulator described here —a design by ELV— operates at a UHF TV channel between 30 and 40. Use is made of a single-chip RF modulator that couples low cost to excellent sound and picture quality. ‘TV sets that lack an external video input are still manufactured and sold in large numbers. In many cases, these sets are relatively inexpensive types manufac tured in Far Eastern countries, Unforts- nately, upgrading such a TV set with an external video input is not possible in general because the chassis is at mains potential. Not a few owners of a low-cost ‘TV set are therefore faced with connection, problems if the set is to function as a dis- play for, say, a computer that has a com- posite video output but lacks an RF modulator. The present modulator covers the fre- ‘quency range from 545 MHz to 625 MHz, Which corresponds roughly to UHF TV channels 30 to 40. The circuit consists of two parts: a modulated RF oscillator ina small metal box; @ motherboard on to which the RF oscilla tor, the SCART socket and the supply volt age regulator are fitted. ‘The motherboard and the RF oscillator form 2 compact unit fitted in an ELV Microline enclosure as shown on the above photograph. The modulator is powered by an external mains adapter with an output voltage of 12-15 Vat about 250mA. ‘Since the RF oscillator isa separate mo- ELEKTOR ELECTRONICS MARCH 1990 MAIN SPECIFICATIONS: ‘High outputlovel: approx, 100 mV (G0.dBuv) + Good frequency stabitty + Low spurious radiation ‘+ Aucio-ideo input with SCART socket ‘+ Adjustable sound suboarre requency + Suitable for upgrading existing eau; ‘ment dule in the modulator, it may be used without the motherboard to upgrade existing video equipment with a TV out- put The circuit The circuit diagram of the RF oscillator with modulation input is given in Fig. 1. ‘The heart of the circuit is formed by IC, a Type TDAS660P single-chip multi-stand- ard VHF/UHF audio/video modulator from Siemens, ‘The amplitude of the sound signal ap- plied to pin 6 of the SCART socket, Bun, 1s set with Pi, Note that the SCART socket and the preset are not contained in the RE-tight metal enclosure. The sound sig- nal is capacitively fed to the FM (fre- quency-modulation) sound input of the TDASO6OP via Ci-C-Ro. Components R:- Ce-Ry form a pre-emphasis network. The frequency-modulated sound subcarrier is added to the vision signal by the RF mixer im the TDA5660P. ‘The sound subcarrier frequency (UK: 46.0 MHz) is set by a parallel tuned cir- cuit, Li-Ciu, The vision-to-sound carrier ratio of 12.5 dB is ensured by Ro. Capaci- tor Cx connects the AM (amplitude- modulation) sound input of the ‘TDAS660P to ground for alternating volt- ages. The CVBS (chroma-video-blanking. sync) signal taken from pin 20 of the SCART socket is terminated into Rry and capacitively fed to video input pin 10 of the modulator chip via Cis, A clamping circuit at this input establishes a fixed synchronization level, while an automatic gain control circuit that acts on the peak white values compensates amplitude changes of up to 6 dB. Both the clamping Circuit and the gain control circuit are ine ternal to the TDAS660P, Capacitor Cir fl- ters the current pulses produced by the peak white detector, and its value deter- mines the time constant of the gain con trol. ‘The modulation index of the AM vision signal is set by the potential at pin 12 ofRADIO AND TELEVISION the TDAS660P. If no resistor is connected to this pin, the modulation index is 0.8 (80%) for negative video modulation. Note that pins 12 and 2 (reference voltage) are decoupled to ground to prevent inter~ ference. The symmetrical oscillator on board the TDAS6609 is bonded out to pins 3-7. ‘The external tuned circuit is formed by inductor Ly in combination with capaci- tors Cs and Cio, and variable capacitance diode Di, Capacitors Cs and Csi prevent the direct voltages at pins 3 and 11 being short-circuited via Ls, The oscillator has a separate ground connection bonded out topins. ‘The anode of varicap D) is grounded for direct voltages by Rs. The oscillator frequency is adjusted with the aid of a tuning voltage supplied by preset Rs and applied to Di via Rs. Capacitors Ceand Cis decouple the RF voltage generated by the oscillator. ‘The modulated RF signal (AM vision and FM sound) is taken from the outputs ofthe balanced mixer in the TDAS660P via pins 13 and 15. The output impedance of 300 2 balanced is transiormed down to 75.0 unbalanced by L2, a Guanella trans- former, perhaps better known as a balun. Capacitor Cis, finally, feeds the modu lated UHF signal to the RF output socket vvia terminal ST ‘The modulated RF oscillator is powered by a regulated voltage of 10 V. A 12-V supply may also be used in case the oscillator is incorporated into existing equipment, The output voltage must, however, be regulated, ‘The motherboard has on it the RF oscil- Iator module, the SCART socket, Bus, the sound level control, Ri,and the 10-V regu- lated power supply. The circuit diagram Of the latter unit is shown in Fig. 3. The unregulated voltage applied to socket But may lie between 14 V and 17 V. The cur- rent consumption of the modulator is less than 30 mA, so that a small mains adapter may be used, ‘The power supply itself is a standard design based on a three-pin fixed voltage regulator Type 7810 (IC2). LED Ds fune- tions as an on/off indicator. The mini- mum and maximum voltage that may be applied to Bur is 12,7 V and 25 V respec- tively. Construction The main point to note about the construe- tion of the modulator is that the RF osci Jator must be thoroughly screened to ensure mechanicalas well aselectrical sta- bility and at the same time prevent spuri- fous radiation of the UHE signal. Start the construction by populating the oscillator board: fit and solder the two wire links, the six resistors and the vari- cap. Next, fit the capacitors, making sure that the ceramic types are pushed as far as possible towards the PCB surface. Fit preset Re and inductors Li and L2. Do not fit the balun the wrong way around: the connection that consists of four joined Fig. 1. wires goes to Cis. Finally, fit the TDAS660. Do not use an IC socket Inductor Lsismade by winding 2 turns of silver-plated wire around a 3-mm drill for pencil, Take the inductor from the fo mer and space its turns evenly by about 2mm. Inserts terminals inta the relevant PCB holes and push it as close as possible to the PCB surface. Solder the terminals at the track side, Finally, fit four solder terminals at the track side of the board, and one solder terminal (STs) at the component side. Bend the strip of tin-plate screening supplied with the kit at the indicated places to form a box. Join the ends by soldering. Fit the oscillator board into the box and ensure that the track side is about 3 mm above the lower edge of the tin- plate box. Solder the board to the inside of the box at all four sides. Work quickly to prevent overheating, and use a high: power (50-W) solder iron to ensure a smooth and firm connection. Mount a narrow strip of tin-plate ver: tically between the two rows of IC pins at the track side of the board as shown in the photograph in Fig. 4. Like the box, this strip is soldered over its entire length, Insert the panel-mount TV plug into the side panel hole, and secure it by solde- ring. Usea short length of light-duty wire to connect the centre pin of the plug to terminal STs. Proceed with the population of the motherboard, which contains few parts only. LED Ds is soldered to terminals ST: and ST1z, Four additional solder terminals are fitted to enable the sides of the RF ‘oscillator box to be secured later. Inspect the two boards for short-cir- ‘cuits and bad solder joints, and correct, any errors if necessary. Mount the bottom ‘Circuit diagram of the RF osciliator section based on the TDASSENP, cover on to the oseillatorbox, making sure that it does not touch any of the four solder pins which should be about central in the holes provicled in the cover, Solder the bottom cover to the sicles of the box. Place the oscillator box on the mother board and insert the four terminals into their respective holes. Solder them at the track side of the board. Next, solder the four terminals on the motherboard to the sides of the oscillator box Adjustment ‘The adjustment of the modulator is rela- tively simple and does not require special test equipment. Connect the modulator to the video source, the TV set and the mains adapter Tune the TV toa free channel between 30 and 40. Adjust Rr until the remodulator is tuned to the TV channel. The tuning range of the preset should cover the UHF range between channels 30 and 40. If this is not so, carefully stretch or compress the turns of La until the required range is covered. Next, adjust the sound channel. Turn Fig. 2. lated power ‘Circuit diagram of the 10-V regu- SUPPLY. ELEKTOR ELECTRONICS MARCH 1990the corein Li until the sound on the TV set is clear and undistorted, If the modulator works to your satis faction, mount the top cover on the oscil lator box, and secure it by soldering. Next, place the complete assembly into the ABS Microline enclosure. The printed and pre- drilled front-panel supplied with the kitis fitted last by pressing it firmly from one side so that it clicks into the enclosure, CNT e es Resistors: AN =630, Rie to Aa = 6k | Felice 22 RaRe= 47k r= 50 preset Ar = 10k preset V ‘Capacitors: GCecr Cen 195 “Guts = bp2 CuO10= 608 ie 1009 rn zap Cis 209 Gie= tno C205 10h, CeiCre = 22; craic Cin47n ‘Cris 4700 CI7160) = 1044 18 C= 4704525 V ‘Semiconductors: 1G» TOASEEO? 12= 7810. D1 = 885055 ‘Dz 1Nagot Ba-=LED;3 mm; red Misceltanoous: = tnt, ae balun ‘Bus = SCART socket for PCB mounting. Bue = jack socket for PCB mounting. ‘Sh =fus0; 125 mA. z /. 42 tinplate box (complet). Qy.1: TV.com pl. Qiy.1: PCB-mount use holder. Qy.11: solderpin, 85 mm ght city wie. A complete kit of parts for the audio/video modulator is available from the designers’ exclusive world- ‘wide distributors (regrettably not in the USA and Canada): ELV France BP. 40 : F-57480 Sierck-les Bains FRANC) a Te 1: +33 82837213 Fates ase ‘Also see ELV France's advertisement elsewhere in this issue. ELEKTOR ELECTRONICS MARCH 1990 Below: completed RF oscillator module seen from the PCB track side. Note the screen fitted vertically in between the pin rows of Integrated circuit. This to keep spurious radia- rte 2 minimum. ‘of the completed RF modu- lator assembly. The RF oscillator box is ‘mounted on to the main board. Note that the top cover has been removed for an internal view of the oseilator. AUDIO'VIDEO MODULATOR Above: component mounting plan of the RF oscillator board. Right: component mounting plan of the motherboard.SCIENCE & TECHNOLOGY RESEARCH AND DEVELOPMENT: KEYNOTE OF CLUB LIFE AT HARWELL by H. Cole, CEng, MIERE, Senior scientist at Harwell Laboratory Harwell Laboratory, situated about 50 miles to the west of London, isthe largest United King- dom Atomic Energy Authority (UKAEA) re search establishment. It has an annul tumover in the region of £140 million and employs 4250 people. The laboratory was st up in 1946 to carry out research into all aspects of atomic ‘enetgy and furnish the scientific and technical information needed for Britain to embark on 3 nuclear power programme. The result of this carly work culminated in the commissioning in 1956 of Britain’ frst nuclear power station: a 200 MW plant that is still feeding power into the national grid, Today there are |7 nuclear power stations operating in Britain and one (a pressurized water reactor—pwn) is under construction, To ether, these satisfy about 20% of the country’s ‘electricity demand, Since 1965, the laboratory has undertaken an inereasing amount of work that is uncon= nected with nuclear research and, although there is still « substantial nuclear programme, this now accounts for little more than half of ‘the financial tumover. The non-nuclear work involves Haison with wide sector of industry and commerce and ranges in scope from the neutron radiographic examination of jet engine turbine blades to the ultrasonic inspection of hundreds of miles of rail track and consumer gas distribution pips Fines. Clients range from small private compa- nics t0 giant multinationals; contract values ‘ean be as little as hundreds of pounds or at great as several millions, Cost sharing ‘The ever increasing complexity of present day technologies and the need for innovation and the development of new materials and pro- cesses have demanded facilites that are often beyond the finaneial and material resources of al but very large ereanizations; hence the need for a rescarch establishment like Harwell ‘Clients may visi the laboratory and hire the fa- cilities and scientific back-up for as long as they wish without having to embark upon ex= pensive in-house alternatives. They can also Join one of the many cost-sharing research and ‘development clubs that are operated by the lab oratory. Harwell’ first club, the Heat Transfer and Fluid Flow Service (itFs) was set up in 1968 and is operated jointly with the National Engi- neering Laboratory and, since 1983, with AAtomi Energy of Canada Limited. Other clubs were added during the 1970s but growth in their numbers began in earnest during the 1980s as industry began to emerge from the in ‘emational recession Harwell now operates a total of 30 clubs covering a wide spectrum of industrial technol: ‘ogy and the number is growing by about two every year Club-funded research and development programmes give members the advantage, for ‘relatively modest outlay, of sharing the bene ‘An example of fled high strength marine bolt ‘examined by the Offshore Bolting Materials Club ‘of Harwell Laboratory. fits accruing from a particular project while maintaining confidentiality with rogard to po- tential (aon-elub) competitors. Multinational membership ‘There are essentially two types of Harwell elub activity. The fist is basic research with 10 ob- viously exploitable end product in mind but which may provide valuable background infor: ‘mation for subsequent commercially viable de velopment programmes. Examples of this in- clude materials evaluation programmes for solid-state gas sensors and the development of techniques for studying combustion behaviour in advanced patrol engines The second kind of club activity i the de- velopment of technology to support a compa y's activities on a wider seale than would be tackled in-house. It is this area of work that calls upon the special skills and facilities of Harwell. Examples include the formulation of offshore inspection techniques and associated rumentation, and of an inspection system for composite materials ‘The detailed structure and operation of the various clubs varies considerably to suit their particular activities. Some larger elubs may have nearly 200 members, whereas the smaller, more specialized, ones may have about ten ‘The work undertaken by a club may be con- fined to a particular type of industry, such as offshore inspection, whereas other more broadly based clubs may span a wide range of industries. The Composite Metal Jointing Club, for instance, has a membership draw from the serospace, automobile, adhesive and compos +s manufacturing industries, Clubs with a multinational membership at: tract financial suppor from the European Com ‘munity and cover research and development that is advantageous to member states. Typical of the many internationally funded ones is the Residual Fuel Oils Club, which studies the combustion characteristics of low-quality residual fuel oils. Membership fees generally range from about £5,000 to £15,040 per year but can be much higher. Some club fees are de pendent on company turnover and are gener ally larger for overseas organizations, For small British companies, the fees are usually in the region of £3,000 a year Guided by members Most club projects are of limited duration and are organized into phases, the results from one phase determining the direction and extent of the next. Some clubs, like the Diesel Engine Working Party, have successfully completed their programmes and ceased operation. Oth- ers, such as HTS, have tolling progremimes that fare regularly redirected along lines that reflect ‘he current priorities oftheir members. For many elubs, support funding from the British Government or from the European Community often approximates to that of the ‘member's contribution. For some clubs, how- ever, less government funding may be forth- coming and be limited to a simple membership contribution fee. This applis inthe case ofthe Offshore Inspection Service Club whose only ELEKTOR ELECTRONICS MARCH 1990form of government Funding isa single mem- bership fee. In spite ofthese diferences in funding and composition, one strong common feature among the Harwell clubs i that the work un dertaken i guided by the members and rflets their priorities, providing a firm base for the subsequent transfer ofthe resulting technology. “The Biotechnical Separations (sist) Club provides consultancy, design and reports and Cartes out basic and applied research on all s- pects of downstream processing for the biotechnology industry. Membership is deawn from chemical, pharmaceutical and food pro- cessing companies, and others with specialist medical and biotechnology interests “Another elub, Composite Metal Joining provides design criteria and design tools and data required for load-carrying adhesive joints between polymer-based composites and met- als. The membership includes European auto- motive and component manufactures, aerospace companies and adhesive and compo. nent suppliers. World-wide membership ‘Heat Transfer and Fluid Flow Service (HF13), the oldest Harwell club, has over 185 mem- bers. Collaborators are the National Engineer- ing Laboratory and Atomic Energy of Canada 1t provides computer programs, design reports, literature digests, consultaney and access to a lurge imernational research and development ‘programme on heat transfer and fluid flow. The substantial world-wide membership includes large chemical and petrochemical companies, process plant contractors and small heat ex- changer manufacturers ‘The Fouling Forum has over 200 members and works in collaboration with the National Engineering Laboratory. It provides a forum forthe interchange of ideas and for technology transfer on the subject of fouling of heat ex change services in a wide range of process plant. Membership ofthis low-cost information exchange club includes all wets members and is also open to other subscribers, The Metal Matrix Composites Club is con: cemed with research and development imo the properties of, and processing methds for, alu- ‘minium alloys reinforced with ceramie and other fibres as well as processing routes for specific components. Membership covers sev- cra industries and includes aerospace, automo bile and component manufacturers and materi- als suppliers. Metals and engines ‘The Midas Club provides a service forthe min- erals exploration production and processing in- dustries. I develops new or improved analyti- cal methods for interpreting data from neutron and gamma ray-based interrogation probes as used by the oil, gas, coal and metalliferous minerals industries, The members include ‘major oil companies and their contractors plus 4 number of coal mining companies and their ELEKTOR ELECTRONICS MARCH 1990 RESEARCH & DEVELOPMENT: KEYNOTE OF CLUB LIFE AT HARWELL, a customers, Offshore Inspection Research and Develop ment Service produces new or improved in spection techniques for offshore structures. The ‘current programme includes work on ultrasonic time-of-flight and eddy current inspection ‘methods and a project on the detection of tight cracks, The membership is draven from the ‘major offshore operating and inspection com- pics Offshore Bolting Materials is small club ‘operated in collaboration with Wimpey Labo: ratories, It develops improved bolts and bolting materials for use on offshore structures. Its members come from the major cil companies and safety authorities, ‘The Petrol Engine Working Party applies the Harwell-developed laser-Doppler anemom= etry and CARs (coherent anti-Stokes Raman spectroscopy) techniques and associated inst mentation to studies of air flow and combus- tion within operating internal combustion petrol engines. ts members are drawn from en zine and component manufacturers and a fuel supply company. Fuel efficiency Supported by Britain's Department of Trade and Industry and the European Communit, the Plasma Etching Club undertakes collaborative ‘programmes for devising techniques for the dry processing of very large-scale integrated cir cuitry. The work involves the formulation of silicon-based devices and different aspects of etchant chemistry. The members of this club are suppliers of high-purity chemicals and uses und of specialized processing equipment Positron annihilation is a non-destructive {esting (xbT) technique developed at the Na tional NDT Centre ai Harwell. It relies on the ‘emission of positrons (positively charged elec- tons) from a small radioactive source and the Injection ofthese paticles into the object being examined. The positrons, on entering the ob- ject, are quickly annihilated by the more nu- ‘merous negatively charged electrones and give rise 10 a pair of gamma rays, each of 0.51 MeV kinetic enerey and traveling in opposite direc tions, for each anniilation event. ‘The detection of these gamma rays from ifferent directions can indicate the presence of defects in the object being examined, show the ‘onsct of fatigue in metals and alloys, or enable the moisture content of resin composites 10 be determined, ‘The Positron Annihilation Club investigates the application ofthis novel technique and its members are drawn mostly from the aerospace industry. ‘The Residual Fuel Oils Consortium studies ‘he application of laser-based instruments and associated analytical facilities to the combus- tion characteristics of low-quality residual fueks—such as those used in marine and indus- trial type engines—to see if they can be burned more efficiently. This is an international con soriium involving medium speed diese! engine ‘manufacturers, 8 component manufacturer, an oil company and representatives of the ship- ping industry. Improving batteries Separation Process Service (ss) is a collabora live club operated with the government's War- ren Spring Laboratory of Stevenage. It pro- Vides reports, consultancy and access 10a large research and development programme in tive separation process areas: solids drying: gas cleaning: solidtiquid and liquid-separation: and crystallization. Membership covers a wide spectrum of process plant users, contractors and manufacturers, The Solid State Battery Club carries out e= search into solid-state rechargeable lithium ba {eries with the aim of developing the technol- ‘ogy required for safe, rugged, light-weight ver sions suitable for producis ranging from power tools and portable consumer produets 19 vehic= ular traction. The wide-ranging membership represents battery manufacturers, companies with facilities and expense in the methods likely to be required in battery construction, and potential users of the final product. Eliminating microchip errors A new collaborative research project aimed at improving the quality, reliability and pesfor ‘mance of semivonductor devices the Soft Er rors Club, was launched recently by Harwell’s Micro-electronic Materials Centre. ‘The membership brings together leading United Kingdom semiconductor manufactur cers, users, materials suppliers and scientists with the objective of dramatical reducing the problem known as "soft errors” in micro-clec~ lwonic cixcuits Soft errors, more properly called single event upsets, are caused by alpha particles ‘emitted by naturally occurring radioactive im- purities in the materials used to make inte- grated circuits, The alpha particles cary sufft- ent electrical charge to alter the contents of ‘memory cells, hereby causing computational errors. The more closely packed the memory cell the greater is the risk of single-event up- The research programme will extend the technique developed at Harvell, known as fis sion track autoradiography (F14). This makes use of optical mieroseopy fo count the number of fission tracks that have occurred in a thin polyamide film coating on a semiconductor specimen that has been irradiated by neutrons erived from a nuclear resetor. This technique alone is capable of detecting the presence of ‘uranium impurity atoms at concentrations as Jow as two parts per million. ‘The Sot Errors Club is essentially a two- ‘year programme and has the financial support of the British companies EDL, 1wwOs, Ana- ‘artic and Britain's Department of Trade and Industry. The club remains open to United Kingdom organizations and overseas compa fies that havea signficam manufacturing pres ence in Britain, .THE DIGITAL MODEL TRAIN PART 12 —- ADDRESS DISPLAY by T. Wigmore The address display is a small extension unit that is used in conjunction with the mother board. It indicates to what locomotive address a given controller is set and whether a ‘The address display, which may be fitted to each and every Iocomo- tive controller, improves the ease Cf operation of the system. Its not strictly essential, but will be found very useful with concentrated multi-train operation, If addresses in the locomotive controllers have been set via the S252 interface, that is, not by hardware, it is convenient if the address setting is displayed to in- dicate that it has been set correctly. Furthermore, the address dis- play indicates whether a given lo- comotive controller is active, When a controller is taken out of action or when the control of the relevant locomotive is taken over by the serial interface, the corre- sponding address display is quenched, except in one condition. When the system is in the stop mode and a locomotive address is set via the RS232 interface, the dis play will indicate that address al- ‘though the controller is inactive. Because of this arrangement, addresses may be set in the con- trollers via the RS232 interface and checked while the system is still in the stop mode. When the system is then actuated, the displays of all non-active controllers will go out ‘A controller is not active if: ‘+ Lis not connected to the mother board; + the operating switches arein position “out of action” thigh Impedance at pins 4 and 5 of the DIN connector); ‘+ acontroller with higher priority has been set to the same address; * the locomotive with the rele. vant address is given a control instruction via the RS232 inter face, ‘The last condition noeds ampli- fication. Any control instructions to locomotives via the RS232 inter- face will deactuate the controllers locomotive controller is active. ef. BSSe +11 E Fig.79, The circult of the address display i simplicity itself, that serve the locomotives with the same address. The control of any locomotive that is operated via the 1RS232 interface may be reverted to manual by the locomotive enable command <37>. When this instruc tion is given, the display of the as- sociated controller will light again. Circuit description As is clear from Fig,79, the circuit Of the address display is simplicity itself, because the control is pro- vided by the mother board. The circuit proper consists of two BCD-to-7-segment decoders with integral register and the displays, The decoders are connected to the identically-named locomotive address bus on the mother board via lines LAO-LA7 (LA = locomo- tive address) Line Sn carries the selection sig- nal that becomes active as soon asa given controller is selected. The se- Tection causes a certain locomotive address set by hardware to he read and then to be written into the reg- isters of the BCD-to-7-segrnent de- coders. If there is no controller con- nected, the display is quenched at ‘once by the system writing FFH to it. The display is also quenched if the system signals a controller with higher priority, that is, a higher controller number, which is set to the same address or if the locomo- tive with the associated address is controlled via the serial interface. If no address has been set by hardware, the system verifies whether an address for the relevant controller has been given via the S232 interface. If so, the address that has been converted to BCD format is sent to the display circuit It is for this reason that the buffer for reading the locomotive address {IC) on the mother board) must be a bidirectional type. ELEKTOR ELECTRONICS MARCH 1990THE DI AL MODEL TRAIN - PART 12: ADDRESS DISPLAY = Pop 0, PARTS LIST SO re ee oe EAS e 101, 02.4549 (SA ype} SIE 2 Laser moras SE ars By SIRES Construction as rs || teats ste Se UZ RWS | econ A 9 | MR ed Sa (surface mount assembly) type. In the case of the ICs, there is no choice: they must be SMA types. ‘The boards are not wider than the displays to enable a number of units to be mounted side by side (unless only one locomotive con- troller is used, of course). Furthermore, the most conve. nient type of construction is the sandwich type in which sors are used for makin ‘The printed-circuit board in Fig. 80 allows up to four display units to be constructed. The mother board can handle up to 16 displays, s0 that if the maximum is chosen four PCBs are required. Before the construction proper can be started, the board must be cut (lengthwise) into two identical strips if four adjacent units are wanted or into eight parts if four discrete units are required. The fol- Towing notes apply to the building, of one unit only ‘Some assembly instructions are given in the caption of Fig. 81 + Mount both 7-sogment displays onto the top “water” ‘Fit both right-angle wire links to the non-copper side ofthe lower wafer” ‘Mount decoupling capacitor C, at the copper side of the upper water”, [fan SMD type proves unoblainable, use a small ceramic type and mount this as shown in Fig. Sia. ‘Mount IC, and IC; at the copper side, Pins I-8 are located at the bevelled side of the devices These sides should point to one another, ‘Connect the two wafers together with the aid of the resistors as shown in Fig. 81b, The capper side of each wafer should face downwards, The resistors should bbe of the smallest commercial type to ensure a compact unit “Loop the power lines in between the fwo wafers (top right and un- Fig. 61. Construction of the boards asa sendwich: 81a~ the decoupling capacitor is aid lat on the boerd; —dermeath LD) with the aid of two ‘81b~ through connexions are made with the aid ofthe resistors; 81¢~the power lines arelooped through; short lengths of equipment wire {8d the sandwich is ready for connexion to the mother board. as shown in Fig, BLBKTOR ELECTRONICS MARCH 1990ooaoooo0seaaonooes ‘A~ supply line earth B— current limiting resistors © connexion loc address bus D-SMD-type IC E—dlodes for loc addressing F—mother board G—jumper H-DIL switen Fig. 62 Showing where connexons from the display unit are ‘made on the mather board. Interconnexions Apart from the power lines, there are nine connexions between the address display and the mother board—see Fig. 82. ‘The power lines (0'V and +5 V) may be looped to other display units via lengths of normal equipment wire. Each and every display unit may be used in conjunction with hardware for set ting the locomotive addresses—see also PROTECTED QUAD POWER DRIVERS Providing interface between low-level signal processing circuits and power lands, Sprague's ‘UDN25478 and UDN25I7EB quad. power drivers combine logic gates and high-current bipolar outputs with complete output protec- Each of the four outputs will sink 600 mA in the ON state. The outputs have a minimum breakdown voltage of 0 V and a sustaining voltage of 40 ¥. The inputs are compatible with TTL and 5V CMOS logic systems and include internal pull-down resistors to ensure that the ‘outputs remain OFF when the inputs are open: circuited Overcurrent protection for each channel has beon designed into the devices and is actue ated at about 1.3 A. It protects each output from short circuits with supply voltages up to 25 V. When a maximum driver output eurrent is reached, that output drive is reduced lin- carly, maintaining 2 constant load current. If “locomotive addresses” in Parts 7 and 8, If that is done, itis convenient to remove certain parts to the track side of the mother board. Two possibilities are shown in Fig. 83, In the first (Fig. 83a), the eight diodes are fitted at the track side. The connexions to the cathodes may be used for connect- ing lines LAD-LA? to the display unit. To make the whole easily removable, the dis- play unit may be provided with a “semi IC the over-current or shart-citeult conditions con tinue, each channel hasan independent thermal Jimi circuit that will sense the rise in junction temperature and turn OFF the individual chon- nel that isa faut. Foldback circuitry decreases the output current if excessive voltage is pre- sent across the output and assists in keeping the device within its SOA (safe operating area). Each output also includes diagnostics for Increased device protection. If any output is shorted or opened, the diagnostics can signal the controlling circuitry through a common FAULT pin, ‘The UDN2547B/EB can be used to drive various resistive loads ineluding incandescent lamps (without warming or limiting resistor) With the addition of external output clamp odos, it may be use to drive inductive loads, such as relays, stepping motors, or solenoids, The UDN25178 is a Té-Lead power DIP, while the UDN2547EB is a 28lead power PLCC for surface-mount applications. Both packages are of batwing construction to pro- vide maximum power dissipation over the temperature range of-20°C to+85°C. Fig. 63. Combination ofan address display and hardware for setting locomotive addresses. socket”. The setting of the loc addresses may be effected by fixed wire links or jumpers at the track side of the mother board. ‘The second design (see Fig. 836) uses ‘an &-pole DIL switch at the track side of the mother board for setting the addresses, ‘Bear in mind that if an address is set by hardware, a locomotive controller can no longer be allocated an adilress via the se rial interface. . | HOWTO ORDER TOPLAGE AN ORDER, cbianpie nd debory maton equ tsa feats spt raurrasoschion oanestanesatancs ‘et ori gee sane Seance 22157 ‘Sprague lect UK) Sieatcoreoer ert. Pies, Sms Sarah. Sear Sinn iar Sie ion ELEKTOR ELECTRONICS MARCH 1990BBD SOUND EFFECTS UNIT Phasing, vibrato and reverberation are commonly used sound effects in modern music. The effects unit described here is a high-end piece of audio equipment that will make many musicians and sound engineers sit up. Based on a state-of-the-art bucket-brigade delay (BBD) chip, the unit is capable of many popular sound effects, including ADT, Under normal circumstances, sound travels at a speed of about 340 m per sec- ond. This means that short echoes occur in relatively small rooms already, giving the so-called reverberation effect. Acoustic perception experiments have proved that the human ear is capable of detecting a sound delay as small as 5 ms only (corre- sponding toa distance of about 1.95m). In particular, short reflections with their as- sociated differences in regard of level delay, and spectral composition create an Impression of space with the listener. Most electronic musical instruments are not based on sound created ina reson. ant cavity of any size or shape, and as a result produce a relatively ‘lat’ sound Reverberation may be adcied by electronic means to add warmth to the sound of these instruments. In the present sound effects units, reverberation is achieved with the aid of adjustable degrees of feed chorus, phasing and real-to- bback and attenuation, which results in a remarkably natural effect. Bucket brigade delay ‘The drawing in Fig. 1 shows the basic set up of an analogue delay line based on a bucket brigade memory. The memory is essentially a series of sample-and-hold circuits, each of which consists of elec- tronic switches and capacitors. The anal- ‘gue signals stored in the capacitors are sampled under the control of a central clock signal. At each clock pulse, the sample is shifted one capacitor to the right, hence the name ‘bucket brigade’ (che precursor of today’s fire brigade! Alter 1 clock pulses, the analogue sig. nal is advanced 1 positions in the mem ory. A double clock is used to prevent the contents of two ‘buckets’ affecting each other as a result of the shift operation. 1 ce [ m2 907 D ft \ ppb PLEKTOR ELE TRONICS MARCH 1990 lite reverberation. Hence, clock 1 and clock 2 ate in opposite phase. To ensure acceptable distortion of the input signal as a result of the sampling ‘operations, the clock frequency must be at least two times the highest frequency tobe sampled (Nyquist’s sampling theorem), A low-pass filter at the input of the bucket brigade delay limits the frequency range to a usable value. The output of the BBD chip also has a low-pass filter, in this case to remove the elock signal component Reverberation Reverberation is an acoustic effect which ‘occurs, in principle, in every room of which the walls have sound reflecting properties, The sound reflections are noted by generating a short acoustic sound burst, eg, a hand clap. This sound will reach the ear directly as well as indi- rectly via reflections. The time it takes any reflection to reach the ear is in direct pro- portion to the time taken by the sound to reach the point where itis reflected. The amplitude of the reflection depencis an the length ofthe path and theacoustic proper ties of the reflecting surface, Stone walls, for instance, absorb very little sound, ‘whereas curtains have virlually no reflec- tive properties. In many cases, sound reaches the listener via different paths. The amplitude of the reflections as a func- tion of time is illustrated in Fig. 2 The decay time is the time that lapses before a particular sound is so weak that it is no longer perceived. This parameter depends on the construction of the listen ing room and the materials used. A natu-Bi FLECTROPHONICS ral sounding reverberation effect requires at least 1,000 reflections per second, which, as a further proviso, must reach the listener at a certain irregularity. Reverberation: the electronic way Figure 3a shows the simplest configura- tion of a reverberation unit based on con- trolled feedback. The associated amplitude-vs-time diagram is given in Fig. 3b. To achieve a decay effect, the am- plitude of the reflections is reduced as a function of time with the aid of a voltage attenuator. In practice, the reverberation time, t, is defined as the time required to reduce the sound energy by a factor of 10° (60 dB). In Fig. 3a, this time may be calcu- lated by counting the number of ‘needle pullses’ between the instant the sound is generated and the instant its amplitude is 60 dB smaller. Next, the number of needles is multiplied ‘with the delay Lime, 1, of the reverberation unit, hence, f= 60/a8 ‘here cis the atenuation per passage. A practical example: a reverberation unit has an attenuation of 3 4B and a delay of 80 ms. An attenuation of 60 dB Js, therefore, reached after 20 passages, each of which introduces a ‘delay of 5 ms. The reverberation time, t, is 20:60 ms= 15 Inpractice, reverberation times of the order of one or two seconds pose prob- lems because they requice an extensive Ges long) delay line, Acceptable resulis for’ reverberation times longer than about 0.5 5 are only achievable with digital delay lines. Lower attenvation and a greater number of passes are usually not feasiblein view of the risk of oscillation A second problem arises from the equal distances travelled by the gener- ated reflections. Such a constant patter can only occur ina spherical room, which, in the ease of the above example (0-ms delay time) has a radius of 16.6 m, Evi- dently, such a room is at best rare in the real world An annoying side-effect of equally long t reflections is the creation of a comb-filter response —see Fig, 3c, Ata delay of 20 ms, the distance between two peaks equals 100 Hz. The comb filter effect introduces 2 variation in the attenuation which is simple to calculate if the normal attenua- tion of the circuit is known. From the above example, a normal attenuation of 3 4B means that the signal is attenuated by a factor of 0.7 after a single passage through the reverberation unit. The vari- ation in the attenuation owing to the comb filter effect is (1+0.7)/(1-07), ie, 5.7 times or about 15 dB. Obviously, an am- plitude ripple of 15 dB is not acceptable for hifi stereo applications. Yet, many reverberation units produced in the past 2 A ‘eatin 4, Fig: Ampltde-ime diagram of pulse-shped sound ard The rllectons causal by 3 a no - * b. il- vm fd | Li cy Fig. &._ Simplest configuration ofa delay Vow with feedback (a) and the snvocited tmpiudectme cagram fb, Te itequanoyreepenee el sucha deey un tot un tt ofa comb titer (3¢). 4 — B OHH [> | Fig. 4 Improved reverberation principle based on individually controlled delay lines, ELEKTOR ELECTRONICS MARCH 1990Fig. 5. Basic circuits for phasing (Sa) and vibrato (Sb) used the above principle simply for lack ofa better (electronic) alternative. Multiple reverberation A naturally sounding reverberation effect can only be achieved by using different delays of non-related durations. The block diagram of a reverberation unit based on this principle is shown in Fig. 4. From ‘practical experiments, at least four delays are required for acceptable results. The sound effects unit described here has six different and non-related delays, while the attenuation for each of these is ad- justable to givean optimum room simula- tion, ‘The delays used in the sound effects: unit allow an estimate to be made of the size of the simulated room. A sound delay of 10 ms corresponds toa total path length of 33 m, or a wall distance of 1.65 m. The maximum setting, 100 ms, simulates a wall distance of 165 m. Sound effects ‘The BBD sound effects unit offers a var- lety of sound effects which may be set to individual liking with a large number of controls, As examples, the degree of feed- back for the delayed signals may be ad- justed; the ‘clean’ (input) signal may be mixed with any one delayed signal. Fur. thermore, the unit allows single delay to be used, The ADT-effect (automatic double- tracking) is commonly used in modern music technology to give the sound more substance. Basically, the signal is briefly delayed (t=1-5 ms) and then mixed with the original, [fused ina multiple way, the result is the Chorus-effect. Here, the delay time is not constant but subject to small, irregular changes caused by modu- lation of the clock signal by a pseudo-ran- dom signal generator, for which the sound effects unit has an external input. The chorus-effect may use one or more delay lines in the unit, provided the out- pput signal is not fed back to the input. The delayed signal is, therefore, simply added to the output signal. Vibrato and phasing are based on modulation of the clock signal with a triangular, low-frequency, signal sup- plied’ by, for instance, an LFO (low-fre- quency oscillator). The vibrato-cffect is obtained by using the delayed signal only, while for phasing the modulated as well as the delayed signal are added to the output signal. The different ways of generating these two sound effects are il- lustrated in Figs. 5a and 5b. The sound effects are rather different also. Strong brato brings to the mind a worn tape re- corder or gramophone with speed regulation probloms, while phasing is as- sociated by many with the Flammond-ef- fect based on doppler shift and achieved ‘with the aid of rotating loudspeakers. Phasing uses the previously men- tioned comb-filter response that occurs at short delays (refer back to Fig, 3). The modulation of the clock signal shifts the points of maximum attenuation (poles) of the comb filter (Fig. 6) periodically, and so ‘causes a spatial sound effect, Both vibrato and phasing use delays smaller than 10 ms, which allows ready use of a BBD IC. Fig. 6. ELEKTOR ELECTRONICS MARCH 1990 ‘Typical comb fiter response of @ delay line. The sound effect, BRD SOUND EFFECTS UNIT PART 1 MN3011/MN3101 BBD chip set ‘The Type MN3OI1 from Panasonic (a Mat- sushiia company) contains a 3328-stage bucket brigade delay line in PMOS tech- nology. The pin-out and internal configu- ration diagram in Fig. 7 shows that six taps on the delay are bonded out to pins. ‘The delay times associated with these pins are suitable for reverberation appl tions. The shortest reverberation time is available at pin9, the longest at pin 4. The actual delay times achieved with the IC are determined by the frequency of the ‘lock signals which are applied in oppo- site phase to pins 2 and 10. The maximum and minimum delay times at two clock frequencies, 10 kHz and 100 kHz, are given below: BBD output Delay at —_Delay at (in) fe=t0 kH2 {e110 kHe (ms) (ms) 1) 198 4.98 20) sa ast 3) 50.7 597 46) 86.3 863 (5) 199.5 18.95 644) 186.4 16.64 ‘The operating voltage of the MN3O11 is 15 V typical and 18 V maximum, At a supply voltage of 15 V, the current con- sumption is 8 mA typical. The direct volt- age at the signal input must be adjusted for minimum distortion. Starting from a level of half the supply voltage, potential change of up to 2 V may be necessary. The amplification of the BBD chip is 0 dB typi- cal (unity gain), but may lie within 4 4B of this value. The maximum input level is stated as 1Vime at 2.5% transient harmonic distortion (THD). At the nominal input level of 770 mVeme (I kHz), the THD is 0.4% typical A bandwidth of 10 kHz is achievable at a clock frequency of 40 kHz, From practi- cal measurements on the chip, the noise level is between ~70 and -72 dB ata clock of 40 kHz, The pinning and internal configura- tion of the clock driver chip Type MN3101 are given in Fig, 8. External components are used to determine the clock oscillator frequency, which is divided by two and subsequently shaped to provide the oppo- site-phase clock signals for the MN30L1 ‘The MN3IO1 has an on-board voltage source that supplies about 14/15Vea. This voltage is required for the BBD chip. The current consumption of the MN3i01 3 mA typical at 15 V. a ‘The final part of this article will be published next month:LETTERS Lotters of a general nature, or ex- pressing an opinion, or concerning a matter of common interest in the field of electronics (in its widest sense), should be addressed to The Editor at our London offices. Their publication in Elekior Electronics is atthe discretion of the Editor. PRINTED-CIRCUIT BOARDS In view of the many letters we have had in response to my answer in last month's ‘issue to the leuer of Mr Virgis, we have re- considered our position and have decided (on a solution that we feel will please most, iff not all, of our readers. As so often, the solution is so simple that you feel like say- ing to yourself: “why haven't we thought of that before?” Apparently, what I said about it being impossible to produce a PCB from the lay- out published in the magazine is not en- tirely true. Accordingly, from this month (on, we will publish not only the compo- nent layout, but also the track side, of all printed-circuit boards, whether they are available ready-made or not. However, the track side will be reproduced as a mirror mage: this will enable anyone to make, or have made, artwork from which the board can be produced, Because of this change, artwork for PCBs relating to projects published from the March 1990 issue onwards can no longer be supplied. Artwork for boards pertaining to projects published before this, ‘month will remain available at the terms ‘outlined in our Readers’ Services section. [Editor] EUTELSAT TV CHANNELS. Dear Sir — You mentioned last month (Feb, 1990) that EUTELSAT had switched a number of its services. Can you tell me where I can obtain information on the TV ‘transmissions from EUTELSAT I? A. Pemnfors, Gothenborg, ‘The information is available from the Eu- ropean Telecommunications Sateltite Or- ‘ganization, Tour Maine-Montparnasse, 33 Avenue du Maine, 7575S PARIS CEDEX 15, France. Details of the TV transmis sions from EUTELSAT I, F4 and F5, are ‘showm in the tables below. [Ed] RADIO MAKES A COMEBACK Dear Sir— Asa rider to your excellent ar- ticle “Radio makes a comeback” (January 1990), may T point out that in-car receivers, with RDS are coming down in price. The recently introduced Sharp in-car radio-cas- sette units, model nos RGF 872 EE and RGF 896E, for example, retail at around £249.00 and £299.00 respectively. M. Young (Young Evett & Young Ltd), London. Interesied readers who are unable to ob- {ain brochures on these radios from their local delaer should contact Sharp Elec tronics (UK) LTd, Thorp Road, Newton Heath, MANCHESTER M10 9BE, Tele~ hone 061-205 2333. [ed] UPDATE FOR ATN FILMNET DECODER Dear Sir — We had been wamed by the itor thatthe mode of encryption used on the ATN Filmnet decoder (Etektor Elec- tronics, March 1989) was liable to change. Indeed, the decoder gave an excellent and trouble-free performance until late De- ccember 1989, ‘When my decoder and that ofa friend simultaneously failed to decode properly, it appeared thatthe unit was still reinsert TELEVISION CHANNELS ON EUTELSAT | - F4, FS " Fé (13 degrees East) WV. Bee care: ido adit gg i fas ee ae aw sera EMA ous oot mr. AS 1 4 noo 666 % ora fv 208 le ss x mt ergo Wat Ns a oh ime oe x pee Wash Wout 4H hae 680 x mL Gee ae one WORD GaN kh hae to % PL Som Wost SHAVSON = «§ ks % ml Sorte fmoror§ Hes to > ml Gok Wa uci 1 4 ie 50 % tL powow Ss Wast fer > Y 10666 8 % tom 2B Wot EG é ¥ ‘ton sa % ml Geet iM ner 5 Yo is % PAL See Wat cat ® Y ko $e s ma Gtr et immcwn BY hide sis % mal Ger Wet {0 (he acon uve Chr ch Sed en Hompert en 9 F5 (10 degrees East) =a 7 Weote Aude Bonds va SeaMbIG sae ] i RALINO 1H nO ma a Wot = fH Hee BS FA) iced ua Soc iese Nemo 3 Hw PAL cor West ae $f me PAL Ser = 8 Net | OS i or Sa at Se © Wet coms = Yl), «BNA Semi 5 (et ELEKTOR ELECTRONICS MARCH 1990ing the composite syne pulses correctly into the new signal. The line and frame holds were steady, but the picture con- sisted of positive and reversed images, separated slightly and alternating at a slow rate of flicker that seemed to be at half the normal frame speed, and most irritating to watch. There are two toggle mechanisms in the decoder, and it was obvious that nei- ther could cope with the new mode of slow image reversal. It was a simple pro- ‘cess f0 suppress one or other image by dis- abling a toggle, but the flicker remained. By studying the circuit description (not for the faint-hearted) and experimenting with various time-constants, I was fortunately able to devise a simple by-pass operation that clocked the bistable at the required rate and restored the decoder to its former perfect function. Remarkably, only one re. sistor and one capacitor are needed as shown in the sketch below: 13 poy pint3 cartonste 1c7 | into 90706111 AA switeh was included, in case the pre- vious mode of encryption is resumed in the future. From the PCB layout it ean be seen that IC3 pin 13 is accessible at the third inter-board link pin from the right, and IC7 pin 10 is connected to two legs of 2, so the board need not even be removed. from its box. The leads to the switch need not be sereened. DrM. Ball, Chesham Bois. Thonk you for your interest and helpful suggestion. The author has replied as fol- lows: “I have tested your solution on a working decoder, but found the operation > I Let us now use a quarter of a Type LM339 voltage comparator as a practical ‘example—see Fig. 5. The first thing to note is its open-collector output, which means that a pull-up resistor is required at the output, This resistor must be sufficiently small not to introduce any errors in our caleulations. ‘The Vem of the LM339 is greater than V+ / 2, assuming that V+ =5'V. The bias ‘current is around 0.25 1A, so that the cur- [ Jrou Fig. 5. Square-wave generator based on 1/4 Type L339 voltage comparator rent, jg through R; and Ry may be set to 25 A. We then obtain the folowing, values R= V4 / 2ie= 100K Ry= Ry =100kQ Since the offset of the LM339 is <5 mV, ‘we may take dV = 200 mV. Then, from [9] Ry=12MQa Assuming we want f = 5 kHz and a charging current, / = 25 WA, then, using (we obtain a value for C of 12.5.0, ‘The value of Ry is Ry= Ve / 2k = 50K, When the output of the [M339 is high, the circuit in Fig. 6 may be used to calcu- late the optimum value of the pull-up re- sistor, Rout Fig. 6. Simpified circuit to calculate the voltage op across Roy. If we allow a drop of 200 mV across Rygtv-and taking into account that Ve Ve) / Ry=2 A and i= (+-V)/ Ry=S0nA, ‘we obtain a value for Ryu of Ryyn = 200 mV / (i, +i) = ui PN 200 / 52 = 38 kA. In practice, the value may be reduced to, say, 2.2 kQ and even further for low- impedance loads, but take care as the low uiput voltage of the LM339 may suifer. Fig, 7. Diagram ofthe final circuit ofa kHe square-wave generator. ‘The completed circuit is shown in Fig. 7. The prototype under test yielded a high period of 94 1s and a low period of 96 us. The final frequency was 5263 Hz. It was calculated that the capacitor value should be 12.5 nF to give a frequency of 5208 Hz, Since a 12 nF type was used in the prototype, the actual frequency was rather higher, but well within satisfactory tolerance, Fig 8 Replacing A by aresistor-diode network {as shown enables the mark-to-space ratio of the ‘output to be altered as required. ‘The high and low periods, that is, the mark-to-space ratio of the output voltage, may be varied by replacing R, by two re- sistors and tivo diodes as shown in Fig, 8,1 shall leave the derivation to you. / ELEKTOR ELECTRONICS MARCH 1990