personal FM AIR-MAIL COPY conllenca video graphics This article is a complement to the VDU card published in this issue. It gives the background information on how an image is formed on a TV screen and how a video card, in particular, works. autotest While a multimeter is essential equipment for anybody involved in elec- tronics, it is out of its depth when confronted with a normal car. What is needed in this case is something a bit special, with good voltage, current and resistance ranges and able to measure RPM and dwell angle as well. 64 k on the 16 k Dynamic RAM card Computer users who already have the Elektor 16 k Dynamic RAM card published in April 1982 can now update it by fitting 64 k chips in place of the existing 16 k ICs. high-speed CMOS A new family of logic circuits, high-speed CMOS, is now becoming avail- able in your local electronics shop. This exciting new technology will provide a full range of circuits which are pin-compatible with many LSTTL devices, and have the speed of LSTTL, but the high immunity to input noise and low-power consumption of CMOS. VDU card This card is basically an interface between a computer and a cathode ray tube. It receives a signal from the computer indicating what the com- puter wants to display on the screen and converts it into a video signal. This is fed to the cathode ray tube which then displays the appropriate letters, numbers or graphics symbols. personal FM Not so long ago the 'in' thing in radios was the matchbox-sized radio, or the watch radio, but these left a lot to be desired as regards reception and sound quality. However, it is perfectly feasible to make a good quality FM receiver that is still small enough to be easily carried in a pocket. precision voltage divider Or — 'How to get high-stab resistances without high-stab headaches'! alarm extension I The mains wiring of a house can be used as a medium through which | signals can be transmitted. All that is required is to plug a transmitter | into one socket and a receiver into another socket and if the telephone, for example, rings you can hear it wherever the receiver is plugged in. This month's front cover shows the prototype of our ’Personal FM'. Even though it is true that 'a picture paints a thousand words', the sound quality from such a small radio has to be heard to be believed. Incidentally, the 'head' is not one of our designers. Elektor designers have more inside their heads than this (we hope). Junior Synthesizer 9-56 Music and computers may seem to be poles apart and combining the two is surely better left to those who have the time and resources for this sort of 'playing'. In fact it is not at all difficult to make a computer play music! All you need is a Junior Computer and a loudspeaker. simple MOSFET test 9-58 Before throwing away any expensive MOSFETs which are merely suspect, it is wise to test them. This is easily done with a multimeter and we show you how. technical answers 9-59 Simple phase shifter for bridge circuit missing link 9-59 market 9-60 readership survey — first results! 9-62 printed circuit board layouts 9-63 switchboard 9-68 EPS service 9-80 advertisers index 9-82 9-03 elektor September 1983 advertisement * STILL THE ONLY CATALOGUE FOR THE COMPLETE RANGE OF COMPONENTS. BATTERIES, CRYSTAL FILTERS, RF * FIRST WITH ONLINE COMPUTER SHOPPING \* FIRST FOR INNOVATION WORLD OK RADIO & ELECTRONICS CATALOGUE * FIRST FOR VALUE MOSFET, TOKO COILS, CHOKES, ALPS PLOTTERS, SOLENOID CASSETTE MECHSETC. * FIRST FOR CHOICE * FIRST FOR SERVICE COMPONENTS FOR ELECTRONICS, COMMUNICATIONS & COMPUTING ambit NTERNATIONAL INTERNATIONAL Understandably Britain’s most popular and relied-upon suppliers of SEMI-CONDUCTORS I.C.s COMPONENTS COMPUTING EQUIPMENT TOOLS, BOXES, CONNECTORS and much, much more OUR SUMMER PRICE LIST TELLS ALL S&nri far vruir FREE nnnv hv return The VIA 6522 reveals ite secrefs — ORDER YOUR COPY NOW— GET THE COMPLETE PICTURE advertisement elektor September 1983 The name to remember m electronics. ROA DRUNNER WIRING SYSTEM^ ' I ~ - jff > | Using this low cost, simple \i\ technique, you will speed up J */ your wiring times and produce * a very professional result! I Please take advantage of our special I 1 offers and order now! \ Used extensively in industry this is a truly professional system ideal | 5 for the home engineer. I § EXCLUSIVE OFFERS TO ELEKTOR READERS . £ EUROI NTROK IT ROADRUNNER IRON , £ MNI) ONLY - . ONLY , g ]JnL«f£16-99 -j^.£5'99|° r 20% SAVING! i 20% SAVING! . ^ NORMAL PRICE NORMAL PRICE I Consists: S/Eurocard. w.nng pencU 4 diff Spec -240V 17W H,gh temp ,ron. suitable ! BE in nl W ' re ^ ! bobbins - ,or s°Wenng enamelled wire I O 1 0 glue strips. 30 press strips. 1 00 so Full instructions with kit. These otters are tully Inclusive ot carriage, packing and VAT. Roodrunner Electronic Product/ Ltd. VISA UNIT 3 THE HASLEMERE INDUSTRIAL ESTATE WEYDOWN ROAD, HASLEMERE. SURREY. We welcome orders using England. GU27 i bt. Access & Barclaycard TEL: 0428 53850 Junior- P&perware The floppy disk is probably the most significant mass storage medium for microcomputers. It seems incredible that so much data can be stored on a simple plastic disk at such speed and with such precision. Unfortunately, it is not enough to just connect a floppy disk drive to a microcomputer. Without software the hardware is useless! Where can you get all the necessary source listings, hex -dumps, and EPROM modifications? In the Elektor Junior paperware, of course! Junior paperware 1 contains the modifications of the PM/PME EPROM and the source listings and hex-dump of the software cruncher and puncher; Junior paperware 2 gives the source listing of the bootstrap loader for Ohio Scientific Floppys and the hex-dump of the EPROM. BUY NOW WHILE STOCKS LAST! Elektor Publishers Ltd Canterbury / V1ARCO TRADING. DEPT. KK9 elektor September 1983 advertisement of scientific instruments World leaders in multimete rs Beckman Instruments Ltd, Electronic Components UK Sales and Marketing Organisation Mylen House, 11 Wagon Lane, Sheldon, Birmingham B26 3DU. Tel: 021-742 7921 Teleic336659 . T90 meters at £50.60 1 I want to g o di g ital! Beckman instruments are used worldwide in medicine and science, in industry and environmental technology, where precision and reliability are vital. This same perfection in design and manufacture goes into Beckman digital multimeters, themselves widely used in testing, measurement, research and engineering because of their accuracy and their intelligent features. Now the electronics enthusiast has access to the same standard of reliability in the T90, T100 and Tl 10 models. All models undergo 100% factory testing. Their accuracy is guaranteed to be held over a long period and reliability is outstanding, thanks to fewer components and interconnections. All components are of the highest quality and include a CMOS integrated circuit and gold inlaid switch contacts. The digital display can be read at a glance, and all functions are selected with a single rotary switch, rather than with confusing rows of push buttons. Battery life is exceptional - 200 hours at continuous operation. The T90 gives an accuracy of 0.8% Vac and is remarkable value for money at £43.45 (+VAT). The T100 is a full range function meter with 0.5% accuracy at £49.00 (+VAT), while the T110 offers even greater accuracy of 0.25% plus an t audible continuity indicator at £59.00 (+VAT). •* — pp BECKMAN VISA T100 meters at £57.00 fine. VAT p&p) T110 meters at £68.50 One. VAT p8.pl _ I I enclose a cheque/P.O. payable to: Please send me full data on the Beckman enthusiast's Beckman Instruments Ltd for £ multimeter range. (Tick box if required) Name Address advertisement elektor September 1983 Name Address THE COMPLETE PACKAGE! MICROPROFESSOR PLUSTHE STUDENT WORK BOOK // SSB-MPF Speech l Synthesizer Board A low cost ^ tool for learning , W teaching and prototyping. Micro-professor is a lo w-cost Z80 based micro computer which provides you with an interesting and inexpensive way \ to understand the world of microprocessors. Micro-Professor is a complete hardware and software system and is a superb learning tool for students, hobbyists and microprocessor enthusiasts, as well as an excellent teaching aid for instructors of electrical L engineering and computer science courses. Micro- Professor 9*5 0 (+£4.00 p&p) Now with the Student Work Book available Flight offer you the complete package. An easy to follow manual that will help further your understanding of microprocessors. s,uden, Bo£ £16-00 Synthesizer Board A vocabulary of up to 400 wore based on the TMS 5200 chip. SGB-MPF Sound Generation Board W7 fr Auto rhythm - 6 different rhythms, Sound Synthesizer and Hi-fi speaker. PRT-MPF ! Printer Board Memory dump utility. BASIC program listing. Z80 disassembler. T Please send me Oty 1 Micro-Professor £99.50 1 (+£4.00 p&p) 1 Student Work Book £16.00 ' SGB-MPF board £79.50 EPB-MPF board £99.50 SSB-MPF board £99.50 [ PRT-MPF board £86.25 ' I enclose cheque/ P 0 for £ FLIGHT Electronics Ltd EPB-MPF EPROM Programming Board For all +51/ 1KB / 2 KB / 4 KB EPROMS I Read /Copy /List/Verify Capability. EKR 9 Mail Order only "M Prices include VA T. Please CxJ allow 28 days for delivery. Byphoneorpost FLIGHT ELECTRONICS LTD. Quayside RdSouthampton, Hants S024AD.Telex.477793. Tel.(0703) 34003/ 27721. 9-17 While researching the background for the VDU (Video Display Unit) card published elsewhere in this issue it occurred to us that it might not be a bad idea to look at how all those characters appear on the screen. In other words, how is the image of the characters built up and what does a video card do exactly? That is what we will try to clarify in this article and even if you have no intension of building a VDU card, it is still an interesting subject. how does a video card work? Figure 1 . To build up the image in a normal TV set, interlacing is used. This A video display unit is used to show on a screen all the various letters, numbers and signs that are produced by a computer. But it is more than just some sort of television set! It also includes the necessary electronics to convert the desired characters into video signals so that the monitor can work with them. However we will first look at how a monitor (or a TV set) builds up its image from the video signals it receives. How the image is built up A monitor (as a display screen used with a computer is generally called) is really only a ‘stripped down’ television set. Or if you prefer: a TV set is an expanded version of a monitor! The monitor only contains the display tube and the necessary driver electronics and it is supplied with an actual video signal. The bandwidth of a monitor is much wider than that of an ordinary TV set. Typically a good monitor has a band- width of 20 MHz, while the TV only has 5.5 MHz (this is the limit of the transmitter bandwidth). The reason why such a large bandwidth is necessary is a subject to la 83082-1 b which we will return later. In television the video signal is modulated onto a carrier wave, so that a receiver and decoder section are also needed to regain the pure video signal from the received signal. The principles of how a television builds up an image on its screen have been dealt with in detail before in Elektor (September 1977, p. 9-33) so there is not really any need to go into the nitty-gritty here. However, there is no harm in running through the major points again. An image is built up of 625 lines at a frequency of 25 Hz (25 images per second). This frequency is high enough to prevent the human eye from detecting any annoying flicker. Each image is divided into two parts, each of which consists of 312'/2 lines, called rasters. One raster consists of all the uneven lines, the other has all the even lines. These moving images on the rasters then appear as one static image with no flickering. This tech- nique is known as interlacing and its prin- ciple is shown in figure la. As the diagram shows, one raster begins with a half line and the other raster ends with a half line. By ending with a half line, the raster synchronization pulses come a whole num- ber of times the line period (the time taken to scan one complete line on the screen) after the last line synchronization pulse, whereas otherwise the raster synchronization pulses appear one half of a line period later (see figure 2). That difference of a half line defines at what height the electron beam starts writing the next line after the fly-back. Because a half line period corres- ponds exactly to the height of a half line on the screen the result is that the lines of the two rasters appear precisely between each other. That is the system used in television, but if we have a static image (such as a screen full of numbers) then these two interlaced rasters cause an annoying ‘jumping’ effect and this is something to be avoided in monitors for computer systems! However, there is a trick to prevent this effect from occurring. We have more than enough lines on the screen so we simply use half of the total number of lines and write the same raster on the cathode ray tube 50 times per second. That can quite easily be achieved with ‘software’ by ensuring that the raster synchronization pulses always appear at the same interval after the last line synchron- ization pulse. This is called a non-inter- laced image and is possible with a normal TV set or with a monitor and this is the 9-18 method generally used to produce a flicker- free image (figure lb). For each character a matrix of dots is used, 5 x 7 or 7 x 9 are commonly used. Writing a line of letters or numbers on the screen is achieved as shown in figure 3. One row of dots at a time is written for the whole row of characters. So with a 5 x 7 matrix, 7 image lines are needed to write one row of charac- ters. In figure 3 we show a number of these video signals with the modulation needed to write the word shown. Each pulse after the line synchronization pulse means that the electron beam is then lit on the screen. For clarity the pulses are shaded and the lines drawn close together to show how a charac- ter is put together. As this diagram shows, the word ‘VIDEO’ would appear on the screen. The VDU card does not use a 5 x 7 matrix, but 5 x 8 dots. The advantage of this extra line at the bottom is that we can make the lower case letters more ac- curately. An empty line is drawn between every two lines of characters on the screen so that the characters are separated from each other. Therefore there are actually 9 image lines per line of characters. The VDU card normally puts 24 x 80 characters on the screen, but that is not to say that 216 (= 24 x 9) lines are all that are needed as in that case the first line would be right at the top of the screen. We also need some room at the side of the screen to prevent any of the characters from being lost here. So what we want in fact is a rectangular piece in the centre of the screen where all the characters will appear. Figure 4 shows how this appears on the screen. A total of 297 lines (33 character lines) and 128 characters can be written on the screen. Therefore we use a space of 216 lines of 80 characters in the centre. The small part of the diagram magnified shows how the VDU card builds up an actual character. We then have a 5x8 matrix for the characters, a space of lations we can quickly see what the word is. 9-19 5 video graphics elektor September 1983 card builds up an image because it is not exactly the same as is shown in figure 4a. Figure 4b is somewhat different and shows what space the 80 x 24 characters occupy in the total memory field of the card. The actual written part is at the start, while all the empty space is to the right and to the end. However, we want empty margins all round the edges of the screen and this is achieved by stating in the memory field where the horizontal and vertical synchron- ization pulses should occur. This means in fact that the very bottom part of the address range actually appears at the top of the screen because the monitor starts writing from the top of the screen again after the raster synchronization pulse.The same is true of the margins at the left and right of the screen but in this case they depend on the line synchronization pulse. All the 'digital traffic’ is controlled by the CRTC (Cathode Ray Tube Controller) on the video card. This IC has the following tasks: ■ locating the address of the character which must be written on the screen ■ converting that character into the rele- vant dot matrix. ■ producing the horizontal and vertical synchronization pulses at the right times ■ sending the matrix points of one line to the video input of the monitor. Horizontal and vertical synchronization pulses can also be combined, as in the Elektor VDU card, to form a 'composite video' signal. The controller also has some other func- tions such as choosing the desired point matrix, the number of characters per line and the number of lines per image, the choice of interlaced or non-interlaced image and so on. It also drives the cursor which is visible on the screen and controls the connection for a light pen, which is an ‘option’ on the VDU card. The block diagram of figure 5 shows the main parts of the VDU card. Apart from the multi-function CRTC it also contains a video RAM and a character ROM. The video RAM stores all the characters which must be written on the screen. If 80 x 24 characters must be written on the screen then 1920 (= 80 x 24) memory locations are needed so a 2 K RAM is used. The ROM contains information on the dot build-up of each character, including the graphics symbols. The CRTC controls communi- cation between the video card and the rest of the computer system via the address and data buses (they are actually combined to form the system bus). Data that must appear on the screen is read by the control- ler and then placed in the appropriate memory location in the video RAM. To read out the data in the RAM the CRTC runs through the whole address range of the memory so that the 80 characters of a line are read out one after another. The data now goes to the character ROM and here the dot pattern for these characters is located. Referring back to figure 3 we see that a character is written on eight lines. In the case of the Elektor VDU card each series of 80 characters is read out 8 times, and each time the dot pattern for a single image line is read. All the dots for this line then go to a shift register and they are then output in serial form. When this is combined with the synchronization signal provided by the CRTC the result is a complete video signal. This article was merely intended to be a brief description of the operation of a VDU card and monitor. We have referred in particular to the Elektor VDU card as published in this issue but most other systems operate in much the same Way. However we hope that any questions about this subject have now been cleared up, so now you know what to expect when you build your own! M 9-21 Autotest elektor September 1983 | Our essential friend, the multimeter, is rather out of its depth when confronted with the internal combustion engine. Here a rugged, easy to use, instrument with 'no moving parts' is needed. The Autotest meets these requirements as well as adding a few 'extras' that are seldom found on the average multimeter. A high-current range combined with the ability to read RPM and dwell angles are not only useful but necessary when servicing auto electrics. electronic servicing instrument for cars Of necessity, today’s motorist is extremely economy conscious and is therefore more likely to attempt car repairs that were pre- viously the domain of the ‘expert’. However, this often leads to the need for specialized equipment, even in the ‘electrical’ depart- ment. Of course, our multimeter will take care of this . . . but will it? In practice, the ordinary multimeter is not really at home with the internal combustion engine for a number of reasons. ■ The average multimeter has far too many ranges, not in itself a problem but it can be difficult to operate (especially with greasy hands). ■ The current range of a multimeter in- variably stops at 1 amp. The fact that even a car parking light draws almost 2 amps renders our sophisticated multimeter rather useless as soon as a bonnet is opened. ■ A good usable low-resistance range is not usually a feature of multimeters. The normal, cramped scale leaves a lot to be desired when looking for corroded bulb holders. ■ Robusticity! Or to put it another way, how would your £50 - £100 multimeter Table 1 The Autotest ranges 10 mA 10 mV 100 mV 0.1 Si ion 10 RPM 0.1° fare when propped somewhere under the bonnet while attempting to read the output of a voltage regulator of an engine running at 3000 RPM? ■ ... and while on the subject of RPM . . . but no, your meter can’t read that, can it! How about dwell angles . . . By now it will be apparent that a test meter for use on cars is a rather special beast, so much so, that those used by the ‘experts’ can be very expensive. The Elektor Autotest has been designed to take over the job that our multimeter was never intended to do. As a glance at table 1 will show, it manages this with comparative ease. The ‘robusticity factor’ is also very high due mainly to the use of a printed circuit board and a liquid crystal display. The Autotest ranges Most of the work in the circuit (shown in figure 1 ) is carried out by a 7106, a 3)4 digit A to D converter from Intersil. This IC is capable of directly driving the liquid crystal display and includes its own clock oscillator and internal reference source. The Autotest has been designed to be as simple to use as possible and, for this reason, some terminals have more than one function. In practice, this is an ideal situation. The resistance range When measuring resistance, connect the test leads between the COM and R terminals and switch SI to poation A. A constant current, generated by transistors T4 and T5, is de- rived from the reference voltage which appears between pins 32 and 1 of the 7106 (IC3). The constant current is fed to the R terminal and is passed through the resistance to be measured. The consequent voltage 9-22 drop across the resistor is then measured and 20 A shunt resistor R31. Where do we get the reading will correspond to the value of a 20 A shunt from? the resistor. A shunt resistor which will handle 20 A for The constant -current level can be switched the current range can be an expensive item, to one of two values by S2 to cater for the However, since extreme accuracy is not so two different resistance ranges. With switch important to us in this instance, a suitable S2 in position A the current will be 10 fiA shunt can be manufactured quite easily, (determined by R20 and P4), in position B it Copper wire with a diameter of 1.5 mm has will be 1 mA (R21 and P5). Fuse FI protects a resistance of 1.01 SI per 100 metres. For the circuit against a voltage being inadver- the 0.01 £2 we require for a 20 A current tently applied between the COM and R ter- range, a length of 99 cms will therefore be minals. If this occurs, only the fuse will needed. To ensure complete accuracy a blow and no damage will be caused to any 1.2 m length of wire can be taken and a other components. current of 1 A passed through it. With an accurate voltmeter find the length of wire The voltage range which gives exactly 0.01 volts dropped be- To measure voltage, connect the test leads tween the two meter leads. Allow about between terminals COM and +. The voltage 1 cm more at each end for soldering and reading is derived from the voltage divider then wind the wire into a coil and connect it network consisting of resistors R1 . . . R5 as shown in figure 2. The coil diameter is not (R31 has negligible effect) with switch SI in important provided it is of a suitable size to position B. Again, two ranges are provided, fit into the space allocated to it. The leads 20 V and 200 V, by switch S2. going to the meter circuit must be connected directly to the shunt coil itself (there must Current range be exactly the measured length between the For the current range, connect the leads be- connections to N and M) because otherwise tween terminals COM and 20 A. Only the inaccuracy will result as the contact resis- one 20 A range is provided: this will be suf- tance will also be measured, ficient to cater for virtually all applications This then provides us with a very economical in car electrics. The current reading is 20 A shunt but it is not without a disadvan- derived from the voltage drop across the tage. A current of 20 A across a 0.01 SI Figure 1. The relative for the Autotest is mainly due to the fact that most of the work is carried out by the A/D converter, IC3. 1 ‘resistor’ will produce a power dissipation of the order of about 4 watts. The shunt coil will then be the equivalent of a 4 W electric fire! The temperature rise itself is not so much of a problem if adequate ventilation is provided but, as the shunt warms up, its resistance will increase. This is definitely not a desirable feature, even on a very cold day! Unfortunately, there is no real answer to this problem without the expense that we are trying to avoid. However, if readings are taken as quickly as possible (in about two or three seconds for example), a reasonable accuracy can be expected. Of course, lower current readings will be less affected. It is worth noting that resistance wire could be used in place of copper wire although it is quite expensive and not very freely available. However its temperature coefficient is about fifty times better! The length will of course have to be recalculated. It is not advisable to reduce the length of the shunt coil in an attempt to increase the cur- rent range of the Autotest. The temperature rise will be significantly faster and it will be very difficult to achieve an accurate current reading. RPM measurement The contact breaker points in the ignition system of the car are the source of the signal used for RPM measurements in the Autotest. The circuit is connected to the car as shown in figure 3. The COM lead can of course be connected anywhere on the chassis of the Figure 4 shows the waveform produced by the cb points. When the cb points open, a positive pulse is passed to the input of the Autotest and, via R7 . . . Tl, triggers the monostable multivibrator (IC2). The output of this IC will be a square wave with a constant pulse width of 3.9 ms. The puke frequency will be that of the cb points opening. This waveform is integrated with the result that the charge level on capacitor C4 will be directly proportional to the fre- quency of operation of the cb points, and therefore, the engine speed. The voltage across C4 is read and displayed as RPM. Preset PI is included for calibration purposes and will be discussed later. A distinct advantage of this principle is that the configuration of the engine (4 or 6 cylinder) under test is of little concern. The circuit can cater for all types by selecting the value of R13 and calibrating PI (see ‘Calibration’). Dwell angle measurement At this point, it may be as well to clarify exactly what 'dwell angle' is. It is common knowledge that the firing of the spark plugs in an interned combustion engine is con- trolled by the contact breaker points in the ignition system. For maximum efficiency, it is important not only that the cb points open at the correct instant, but also that they are closed for the correct period of time. This is determined by the cb cam profile and - accurate setting of the cb points! In exact terms, the dwell angle is the angle through which the contact breaker cam rotates while the points are closed. It will be obvious then that the dwell angle will alter if the cb points are either badly set or worn. Thus the dwell range of the Autotest will be able to tell a few tales on the condition of the cb points! The circuit for the dwell range shares the same input terminal (and most of the com- ponents) with the RPM range. However, there k an added problem with the signal waveform from the cb points. In contrast to the RPM range, we need to know when the points close in order to derive the dwell angle. Therefore the cb waveform must be debounced and inverted. After being voltage-limited by R6 and Dl, the cb signal is inverted by gates N1 . . . N3, while for debouncing the circuit for the RPM range k used. The function of the dwell circuit is better explained by the use of the timing waveforms of figure 5. The upper waveform is the signal which can be expected from the cb points, complete with 'ringing'. The second waveform shows that the overshoot has been removed (by Dl, N1 and N2) by the time the signal reaches the output of gate N2. The 7555 monostable (IC2) is triggered on the positive going edge and provides a clean square-wave output with a puke width of 3.9 ms. Thk is then combined with the output of N2 to produce a final, debounced, inverted signal at the output of N3. After integration, the voltage across ca- pacitor C5 will correspond to the dwell angle. Thk is then read by the 7106 and, when calibrated by P2, provides a direct reading of the dwell angle. A voltage level of 50 mV at the wiper of P2 will produce a reading of 50.0 (degrees). The A/D converter and display A few points of note about the 7106 A/D converter. For full-scale indication on the dkplay, an input voltage level of 200 mV Autotest elektor September 1983 Figure 3. The 'circuit diagram' of the primary ignition system consists of the contact breaker points, the coil and a Figure 4. The waveform which can be expected from the contact breaker circuit. Much needs to be done to it before it can be used. Figure 5. The timing waveforms of the dwell will be required between pins 30 and 31 from the 7106. Transistor T6 and gate N4 provide an indication on the display when the supply voltage becomes low enough for the battery to need replacing. As current consumption of the circuit is only of the order of 1.5 ... 2.5 mA, the battery should have a fairly long life. The car battery MUST NOT be used as a power supply for the circuit as this will cause a short to occur between COM and 1. The 71 16 can be used in place of the 7106 as IC3. However, there are minor differences between them. The 71 16 has been provided with a ‘HOLD’ input at pin 1. If this is to be utilised, the wire link on the printed circuit board can be replaced by a switch to enable the display to be ‘frozen’. It must be em- phasised that this only applies to the 7116 since pin 1 on the 7106 is the +Ub supply pin and the wire link must be fitted. A second link is used to adapt the circuit to the 7106 or 7116 depending on which is used. The two FETs, T2 and T3, are used as very- low-leakage diodes and, together with R17 and R18, protect the input against high vol- tage levels which may cause damage to the IC. The position of the decimal point on the liquid crystal display is determined by switches Sic, S2c and gates N5 and N6. Construction of the Autotest Virtually all of the components (excluding the shunt) are mounted on the printed cir- cuit board shown in figure 6: construction therefore should not pose any problems. The liquid crystal display is mounted on the track side of the printed circuit board with pin 1 of the display towards P3. It is strongly advised that open socket strips are used for mounting the display. The internal wiring of the Autotest is illustrated in figure 7. To provide some measure of shielding from possible interference, due to static or the ignition system, the interior of the case (if it is plastic) can be lined with aluminium foil. This must then be connected to point N on the printed circuit board (not to lor 0 V). Take particular care to ensure that the foil 9-25 Autotest Resistors: R1,R14,R15= 1 M 1% R2= 10 k 1% R3,R6,R29 = 100 k R4 - ion R5= 1 k 1% R7- 15k R8 . . . RIO * 10k R11.R12- 100k 1% R13 = 2k2 1% I2k21) R16.R30 = 47 k 1% <47k5) R17,R18= 560k R19 = 22 k 1% (22k1) R20- 120 k 1% (121 k) R21 - 1k2 1% (1k21) R22* 15k 1% R23 = 8k2 1% (8k25) R24 = 220 k R25. . . R28 - 1 M R31 =0.01 n see text PI = 2k5 ten turn preset P2 = 50 k ten turn preset P3 = 1 k ten turn preset P5 = 500 n preset Capacitors: C1.C2.C11 - 10 n C3 = 39 n (MKC) C4 = 22 m/4 V C5 = 220 n C6.C8 = 100 n C7= 100 p C9 = 470n (MKC) CIO = 220 n (MKC) Semiconductors: D1 = 3V3/400 mW D2 . . . D4 ■ 1N4148 T 1 ,T6 » BC 5478 T2.T3 = BF 256A T4.T5 = BC 557B IC1 ■ 4001 B IC2 = 7555 IC3= 7106 (7116) IC4 = 4070 Miscellaneous: FI = 50 mA fuse F2 = 25 A auto fuse LCD = liquid crystal display NDP530- 035A-S-RF-PIC (Norsem Tel: 0734-884588 ) 5006-16 from Boss LTD (Tel. 80638/ 716101) Plastic case: Bimbox 2006-16 does not cause any shorts to the printed cir- cuit board or the internal wiring. If a metal case is used, it should be connected to point N directly. The printed circuit board fits, for instance, in the Bimbox 2006-16 (5006-16 metal) from Boss Industrial Mouldings Ltd. The BOC 450 case from West Hyde can also be used with very minor modifications to two mounting holes of the board. The switches are mounted and secured through the holes provided in the middle of the printed circuit board. Calibration For the initial calibration, switch SI should be placed in position B, S2 in position A, and resistor R1 must be short-circuited with a wire link. Apply a reference dc voltage of 150 mV between + and COM. Preset P3 is then adjusted to give a reading on the dis- play of 150.0. The link across R1 can now be removed and both switches SI and S2 placed in position A. A resistor with a known value (about 10 kS2) is then connected between the COM and R terminals. Preset P4 is adjusted to give a reading that corresponds to the value of the resistor. For example, if the resistor used has a value of 10 k£2, the reading will be 10.00. A similar calibration is carried out with a 100 n. In this case, S2 will be in position B and preset P5 is adjusted to pro- vide a reading of 100.0. The next step involves calibration of the dwell range. With the input terminals of the Autotest open-circuited, and switch SI in position D (the position of S2 is immaterial), 9-26 adjust P2 to display a reading of 90.00. This corresponds to a dwell angle of 90 Finally, for the RPM range, the small auxili- ary calibration circuit of figure 8 will be re- quired. This circuit generates a pulse wave- form with a frequency of 100 Hz, which, for our purposes, corresponds to an engine speed of 3000 RPM for a four cylinder four stroke engine. Connect the generator between the + and COM terminals and adjust PI to give a reading on the display of 3.00 (RPM = reading x 1000). The dwell range can be used for engine speeds up to a maximum of 3000 RPM with the circuit as it is. However, if it is thought necessary to measure the dwell angle at higher engine speeds, this can be accomplished with a minor modification to the circuit. A switch in series with a 100 kJ2 resistor can be connected across the points marked ‘X’ in the circuit diagram (left of R10). In practice, this is not usually necessary since it is adequate for most purposes for dwell measurements to be made at lower engine speeds. Although higher engine speeds will show a defective spring on the contact breaker points, it will be very difficult to reach firm conclusions because the automatic advance/retard mechanism may cause an, apparently, unstable reading. This problem can be aggravated by faults in the valve timing, carburettor or even the closed circuit breathing system if it is fitted. At low speeds, however, experience will soon shown whether the points are correctly set or need adjustment. It must be noted that the dwell angle for a specific engine is determined by 9-27 the manufacturer and can be found in the manual for the vehicle in question. It is not not all engines are 4 cylinder! For other engine configurations a different value for R13 will have to be found. This will not be a problem since a value of Ik5f2 will provide an adjustment range of between 16 mV and 42 mV at the wiper of PI. Calibration for all engine configurations (with the possible exception of 9 cylinder 7 stroke engines) can be carried out using the same calibration test circuit of figure 8. For a 5 cylinder/4 stroke engine, 100 Hz will be equal to 2400 RPM and PI should be adjusted for a reading of 2.40. With a 6 cy Under engine, 100 Hz will correspond to 2000 RPM and a reading of 2.00. The values of lk5£2 for R13 and 1 kfi for PI (an adjustment range of 16 mV to 26 mV) will cater for both these engines. The Autotest can be used on both positive normally possible (or necessary) to 'improve' and negative earth vehicles. However, for it. positive earth, the polarity of the leads will The Autotest is now fully calibrated but, have to be reversed. u It has been more than a year since we published the dynamic RAM card (April 1982, Elektor No. 84), but it is proving to be very popular. Many readers have asked about the possibility of replacing the eight 16 k memory ICs with 64 k chips. Many people suggested how this could be done and all these ideas prompted us to investigate the feasibility. What we came up with is a sort of check list of modifications, which you can tick as you go along. 64 k on the 16 k Dynamic RAM card 64 k on the 16 k Dynamic RAM card elektor September 1983 524 288 bits = (8 x 64 k) - (8 x 16 k) Figure 1 . This is the pin designation for a 4164 dynamic RAM 1C. Com- parison with a 4116 shows that they are pin compa- tible except for pins 1, 8 and 9: an extra address line is added (A7) and the —5 V and +12 V supplies are removed. from an idea by K. D. Lorig We have often thought that we are rather fortunate since electronic components are one of the very few commodities that actually decrease in price. This is currently the situation with the 64 k dynamic RAM ICs, which are also, incidentally, becoming more readily available from a number of different sources. Considering the fact that the majority of 4164s (the first two digits vary from manufacturer to manufacturer) require only a single 5 volt supply, the dynamic RAM card could use 64 k RAMs. Some of the advantages to be gained are, more ‘bits per pound', the connectors on the bus card can still be used (an 8 x 64 k 1 card is enough for all the memory space addressable by an 8 bit microprocessor) and the current consumption will be less. The only drawback is the need for ‘surgery’ to the existing circuitry. Basically, to qua- druple the capacity of the memory card all that is needed is to cut a few tracks and make a few new connections. Deletions Rather than leave anything to chance we have drawn up a list of everything that has to be done, starting with ‘demolition’ and finishing with ‘reconstruction’. All modifications are shown in figures 2 and 3 which are the circuit diagram and printed circuit board layout respectively. ■ Remove IC11 . . . 19 from their sockets. ■ Take out capacitors C3, C12 . . . C15, C19 and C20. ■ Remove the strap parallel to IC9. We mean the first strap to the right, between the IC and the connector. It connects pin 9 of the 4116s to +5 V. ■ Cut the tracks joining: - pin 2 of IC4 (N18) to ground - pin 2 of IC5 (N19) to ground (remember to remake the connection to ground that this breaks) - pin 8 of IC12 . . . 19 to +12 V - pin 1 ofIC12. . . 19 to -5 V - pin 6 of IC7 (N29) to pin 5 of IC2 (N47) - pin 5 of IC2 to pin 10 of IC8 (N31) - pin 2 of IC10 to ground - pin 3 of IC 10 to ground - pin 2 of IC10 to pin 3 of IC10. Check the breaks with a (lack of !) conti- nuity tester. New connections The next stage consists of making connec- tions between 9-29 ■ pin 8 of IC12 ... 19 and pins la/lc of the connector (+5 volt supply) ■ pin 6 of IC7 (N29) and pin 10 of IC8 (N31) ■ pin 8 of IC8 (N31) and pin 5 of IC2 (N47) ■ pin 8 of IC6 and pin 2 of IC5 (N19) ■ pin 4 of IC10 and pin 2 of IC4 (N18) ■ pin 2 of IC 10 and pin 19c of the connec- tor (A14) ■ pin 3 of IC10 and pin 19a of the connec- tor (A15) ■ pin 18 of IC4, pin 18 of 1C5 and pin 9 of IC12 ... 19 (A7) ■ pin 9 and pin 10 of IC7 (V-W) ■ pin 12 and pin 13 of IC7 (X-Y). Except for decoding the desired addresses the output pins of the address decoder IC1 1 leave in two groups, one connected to the V/W input of IC7 and the other to the X/Y input and each is connected to the high logic line via a 470 fi resistor. If it is decoded as indicated in the diagram the card will be addressed between 80000 and 2BFFF with- out interruption. This is the configuration used for the Junior Computer with DOS. Make the connections shown in figure 3 as two lines from ground to pins 4a and 4c of the connector. Additional components When all the modifications mentioned above have been made most of the work is done. All that remains is to substitute a 74LS159 (open collector outputs) for the 74LS154 (IC 11). If it has not already been done Cl can be replaced by an 80 pF variable capaci- tor. This is to enable the timing relationship between the triggering of MMV1 and the start of the refresh pulse to be set to prevent the refresh from occurring too soon. It is a good idea at this stage to run through everything done so far just to check that all is as it should be. Then the last thing to do is to inert all the new memory ICs in their sockets. They are available from a number of different manufacturers, most of whom are Japanese, and have different ‘names’, except that the last two digits are always ‘64’. Some possible examples are F 4164 (Fairchild), MB 8264 (Fujitsu), HM4864 (Hitachi), ITT 4164, MSK4164 (Mitsubishi), MK 4564 (Mostek), NMC4164 (National Semiconduc- tor), UPD 4164 C/D and so on . . . the choice is yours. In the article on the 16 k DRAM card the principle of the refresh was described in detail and a program was given for checking the memory, so as a final check it is worthwhile to run this program to check the 524 288 bits of your ‘new’ card. M new high-speed CMOS logic LSTTL Speed Speed is not magic, but it has its price: fast logic circuits use more current. TTL yyj technology is fast and greedy, CMOS on the other hand is slow and economical. CMOS Current now ' ac * vances ' n CMOS technology are making it possible to combine TTL n i mntinn speed with CMOS economy. A new family of logic circuits, high-speed CMOS, corisu rn pxion combines the speed of LSTTL with the advantages of CMOS and looks set to become the standard and eventually replace both the CMOS and TTL technologies. The present situation Bipolar digital ICs have been around for some fifteen years. This first, and for a long time only, technology for logic elements is still the fastest and, through TTL and ECL, also the most successful. Its big drawback remains the power dissipation. CMOS technology, on the other hand, offers low current consumption, a wide range of supply voltages, and high immunity to input noise. Its drawback is the lack of speed. During the past few years CMOS has become somewhat faster, and TTL, through the LS version, a little less power-greedy. None the less, the two technologies are still separated by a wide gulf. At present, it would appear that CMOS just about offers the best compromise between speed and power dissipation High-speed CMOS combines the speed of LSTTL with the advantages of CMOS. The youngest member of the TTL family, the ALS version, is faster than LS and has only half its current consumption. How CMOS has become faster Standard CMOS and the majority of buffered CMOS-ICs are manufactured by the metal-gate process. Figure 1 shows a 1 2a HE4000B new high-speed CMOS logic elektor September 1983 n-channel p-channel 2b n-channel HC MOS p-channel cross-section of a chip made in this tech- nique: it represents the complementary n-channel and p-channel transistors. The parasitic capacitances between drain, gate, and source are added for clarity. The switching speed of a MOS transistor is determined by the time required for the charging and discharging of the internal parasitic capacitances and the external (load) capacitance. This time is dependent not only on the value of these capacitances but also on the current gain, hf e , of the transistor. A transistor with a higher hf e can deliver more current and charge the capaci- tances faster. A consequence of the metal- gate process is that transistors have relatively large gate regions which overlap to some extent with the drain and source. Small current gain and correspondingly large capacitances are the inevitable result. To increase the switching speed, it is neces- sary to reduce the parasitic capacitance as well as to raise the gain of the transistor. This is achieved in the silicon-gate tech- nology which since the mid ’70s has been used in the production of CMOS-processors, memories, and also the HEF 4000B family of buffered CMOS-ICs. These CMOS elements are about three times as fast as the standard metal-gate 4000 series. Figure 2 shows the structure of an n- and a p-channel transistor on a chip of the HEF4000B family. The gate electrode is no longer of aluminium, but of polycrystal- line silicon embedded in a layer of silicon oxide. Polycrystalline silicon can be etched in thinner layers than metal so that in silicon-gate technology the position of the gate with respect to the drain and source can be established more accurately, resulting in an overlap between them which is smaller than in metal-gate devices. This reduces the parasitic capacitances. Shorter gate length and thinner S1O2 isolating layers under the gate lead to increased current gain. Silicon-gate CMOS originally used gate thicknesses of about 6 /jm which were later reduced to 4 fjm. A further reduction to 3 ixm combined with even more precise positioning and thinner isolating layers produced an improvement in switching speed by a factor 5 and an increase in output current by a factor 10. This completed the technological quest for a new CMOS-logic Figure 2b. HCMOS is also produced by the the transistors. HCMOS therefore provides higher output currents at higher switching speeds. 9-33 new high-speed CMOS logic elektor September 1983 Figure 3. Gate-propagation delay as an indication of switching speed. The graphs show that HCMOS is not only much faster than metal-gate and silicon-gate CMOS, but also has a slight edge over LSTTL. 3 4 - - 6 V and the 74 HCT series for operation from 5 V ± 10% and TTL input levels. Otherwise the two series are identical. The abbreviation HC comes from High-speed CMOS; the additional T in the HCT series stems from TTL compatibility. This com- patibility is an attractive feature of the HC family: as far as the user is concerned, an IC in the 74HCT series is now nothing more than a 74-LS IC with much smaller power consumption. Dreams do come true some- times! Both the HC and HCT versions are fully buffered and have symmetrical outputs (that is, same value current at HIGH and LOW logic levels). Furthermore, of the 120-odd types contained so far in the HC family, several are available as unbuffered inverters and these are suffixed HCU (the ‘U’ stemming from Unbuffered). These types are intended for constructing RC or crystal oscillators, variable-threshold trigger circuits, and other circuits operating in a linear mode. Although the 74-HC family is intended to offer an equivalent for every IC in the 74-LS series, it also makes available some popular ICs from the 4000 series. These are mainly circuits for which there are no equivalents in the TTL series. Thus, for instance, that popular counter and oscillator Type 4060 is available as 74HC4060 or 74HCT4060 in the high-speed CMOS series. Clock- frequency is 40 ... 60 Hz (with load capaci- tance of 15 pF) depending on the manufac- Figure 4. In contrast to LSTTL. HCMOS switches an output current of 4 m A in both logic states. i 3 family which, as regards speed and output current, is equivalent to the LSTTL series. The 74 HC and 74 HCT series The relation between the new high-speed CMOS and the 4000 CMOS family refers only to the positive characteristics of the latter: low power dissipation, high immunity to input noise and a wide range of operating temperatures. Externally, however, the high-speed CMOS resembles the TTL series: pinning, logic functions and type numbering are the same as for TTL. This fortunate decision by the high-speed CMOS manufacturers can only be greeted with relief as it precludes the introduction of a second standard for the 4000 series CMOS. Equally sensible is the decision to make the high-speed CMOS available in two versions: the 74 HC series for operation from 2 . . Speed and output current (fan-out) The real advances compared with previous CMOS logic lie in the improvement of speed and fan-out which in high-speed CMOS are comparable to those in TTL. Figure 3 shows graphs of the typical gate-propagation delay vs load capacitance for metal-gate CMOS, silicon-gate buffered CMOS, LSTTL and high-speed CMOS. It is clear that HCMOS is only slightly faster than LSTTL, but its smaller increase in gate-propagation delay at higher load capacitances makes for a larger increase in output current. Typical gate propagation delays in a HCMOS gate are 8 ns at 10 pF, 10 ns at 50 pF, and 11.5 ns at 100 pF load capacitance. It is also interesting to compare other logic versions of the TTL family, particularly the new 'advanced' ALS series which is two to three times faster than LSTTL. Table 1 gives a comparison of a number of typical circuits in the 74 series. The buffered versions of the HCMOS family alle have identical output stages. These are, as in CMOS, symmetrical and deliver a current of about 4 mA at both HIGH and LOW. The bus driver outputs can even supply 6 mA in both directions. Figure 4 gives a comparison between the output- current levels of HCMOS and LSTTL. At LOW level output there is no difference between the output currents: both types provide 4 mA at 0.4 V. When the output is logic 1 and the supply voltage is 5 V, a HCMOS circuit delivers 4 mA at an output voltage of not less than 4.2 V while the LSTTL version provides only 0.4 mA at 9-34 not less than 2.7 V. A standard HCMOS output can, therefore, like that of an LSTTL circuit, be connected to up to 10 LSTTL inputs. The fan-out with bus driver output is 15 LSTTL loads. In the case of HCMOS loads, the input currents (typically 1 n A) have practically no effect, so that the fan-out is limited only by the input capacitance (typically 5 pF) and not by the drive power. One output can be connected to up to 20 HCMOS inputs without any noticeable deterioration. If speed and signal-to-noise are not important, it is possible to connect up to 4000 inputs to one output. Only then, at least in theory, is an output current of 4 mA reached. Current consumption, increase at higher switching frequencies Lower current consumption not only reduces operating costs, but because of the reduction in heat, it also improves reliability. The quiescent current of HCMOS is, like that of CMOS, negligibly small as, in contrast to TTL, the leakage current is of the order of only a few pA. During switching, however, internal and external capacitances have to be charged which means an increase in current. The higher the switching fre- quency, the higher the current consumption. In that respect, there is no difference between HCMOS and CMOS, but HCMOS circuits can switch much faster and therefore have a correspondingly higher power dissi- pation. The quiescent current in TTL circuits is already so high that additional current consumption becomes only notice- able at very high switching frequencies. Figure 5 shows this basic difference between HCMOS and LSTTL. If only one circuit is considered, as in the figure, the power dissipation of HCMOS and LSTTL reaches the same value at an operating frequency of only a few MHz. A practical system, however, consists of a much greater number of ICs which in turn contain several el- ements such as gates, flip-flops, and the like. LSTTL circuits use the same current what- ever their operation; in HCMOS only those elements which actually switch consume power. For instance, in a counter with 10 flip-flops using LSTTL circuits, all flip- flops dissipate the same power, but if HCMOS circuits were used, each flip-flop would consume only half of what the preceding one does. This fact tips the balance firmly in favour of HCMOS, as is shown in figure 6. In a standard micro- computer system with a 2 MHz or 4 MHz CPU, HCMOS circuits would use only a fraction of the power LSTTL devices do. Even in a system with a 10 MHz micro- processor, the power dissipation in HCMOS circuits would be only about one eighth of that if LSTTL devices were used. Supply voltage, input level, and signal-to-noise ratio The supply voltage for the HC and HCU versions of the HCMOS family can vary between 2 ... 6 V. The extension of the lower voltage limit to 2 V is particularly interesting in view of future generations of microprocessors and memories which new high-speed CMOS logic will require a supply voltage of less than elektor September 1983 5 V. Non-stabilized power supplies and batteries can be used without any problems, while one lithium cell or two nicad cells can serve as emergency supply. The switching levels in HCMOS lie further apart than in LSTTL as can be seen clearly from figure 7. That means on the one hand a higher immunity to noise, but on the other that the inputs of HCMOS devices cannot be connected to the outputs of TTL circuits if the supply voltage is 5 V. ICs in the HC version can, however, be 5 9-35 8 Figure 8. The permitted supply voltage variation of i 10 per cent in the 74HCT (TTL-compatible) series is twice that of the LSTTL. The 74 HC series can operate from supply voltages down to 2 V. Figure 9. This shows the real improvement in input protection against HCMOS as compared with CMOS. 1 i i combined with LSTTL types if the supply voltage is 3 V. None the less, HCT types are TTL compatible if the supply voltage is 5 V. Input levels and immunity to noise are similar to LSTTL. In contrast to the 74 LS version, the 74 HCT tolerates a supply voltage variation of ± 10 per cent (see figure 8). Compared with the already hard-wearing CMOS circuits of the 4000 family, the inputs of the HCMOS inputs are even better protected against electrostatic dis- charges. The input protection circuit shown in figure 9 contains a poly-silicon resistor which limits the current through the pro- tection diode and also reduces the speed with which the current rises. The diodes themselves are also more robust than those used in CMOS ICs. Manufacturers HCMOS are produced by a whole series of manufacturers and, for this article, data and other information of the following were used: Philips/Valvo, RCA, National Semiconductor, Motorola, and Fairchild. The ICs produced by these manufacturers in the 74 HC, 74 HCT, and 74HCU series are identical in all important parameters. Agreement exists between National Semi- conductor and Motorola on the one hand and Philips/Valvo and RCA on the other as to common development of HCMOS and exchange of masks. Small differences do exist in the stated values of propagation delay and maximum clock frequency. Whereas there is conformity as to gate- propagation delays with typical values of 8 to 9 ns at 15 pF loads, flip-flops and counters produced by RCA and Philips are slightly faster than those of the other manufacturers. For instance, the maximum clock frequency of the 74HC74 is typically 60 Hz (RCA) or 40 Hz (National Semi- conductor) at 15 pF load. Guaranteed minimum values could not be compared owing to lack of relevant information. Table 2 shows small differences in the type coding: each manufacturer has his own prefix. More important differences exist in the packaging: only Philips/Valvo and RCA have so far planned to manufacture their Table 1 new high-speed CMOS logic elektor September 1983 Table 2. Type-coding of HCMOS Manufacturer HCMOS HCTMOS HCUMOS General PhilipsA/alvo RCA Fairchild 74HC04 PCF 74HC04 CD 74HC04 74HC04 74 HCT04 PCF 74HCT04 CD 74HCT04 74 HCU04 PCF 74HCU04 CD 74HCU04 Semiconductor MM 74HC04 MM 74HCT04 MC74HC04 MC 74HCT04 MM 74HCU04 MC 74HCU04 * not yet available Note: the table shows the HCMOS types corresponding to types 7404 (TTL) and 74 LS04 (LSTTL) TTL Transistor-Transistor Logic circuits with operating frequencies up to 35 MHz and input current levels of around 1 .6 mA STTL high-speed version of TTL which is about three entire HC programme in LSTTL compatible package. All other manufacturers are re- stricting the production of LSTTL compat- ible devices to a small number of types, mostly buffers, decoders, and similar 'computer-related' ICs. Application HCMOS devices are not cheap: their prices are noticeably higher than those of LSTTL circuits. This new technology seems, there- fore, in the first instance to be of interest only where CMOS is too slow and the power consumption of LSTTL is too high. As soon as prices become more attractive, however, it is probable that particularly the HCT series will replace LSTTL, while the HC series is likely to invade the domain of the 4000 CMOS family. As far as practical application is concerned, ICs of the HCT series can be used alongside LSTTL types in a circuit as required. In an existing circuit, HCT-MOS-ICs can replace LSTTL-ICs without further ado. In principle, it is possible to convert a TTL or LSTTL printed circuit board to HCMOS, but it is then necessary to change all TTL or LSTTL devices by HCMOS ones: they cannot be mixed. If in doubt, use the following rule: provided the supply voltage is suitable, a HCMOS-IC can drive a TTL-IC, but it is not possible for a TTL-IC to drive a HCMOS- IC. Another point to watch when converting circuits is that unused MOS-inputs (and those of HC/HCT/HCU-MOS) must be connected without fail to either the + supply line or earth. An unused TTL-input may be left open-circuited: remember that such an input is logic 1 ! Finally, it should be noted that some manu- facturers have given different names to the new technology. Fairchild, for example, call it FACT: Fairchild Advanced CMOS Tech- nology. RCA use the name QMOS. This does not, however, alter the fact that all use the type-coding as indicated in this article. What of the future? At least fifty different HCMOS-ICs are now available in standard production form and it seems likely that this number will have doubled by the end of the year. A number of these new devices have already found their way into the catalogues of several electronic component suppliers. Future issues of this magazine will no doubt contain circuits with HCMOS. Already we have spotted interesting circuits like a single-chip telephone modem in the HC data book of one manufacturer. Sounds promising, times as fast but has double the power requirement; it can attain frequencies up to 1 00 MHz LSTTL TTL circuits in which Schottky transistors and diodes are used in a con- figuration to give a compromise between pation. Operating and power dissipation is about 2 mW as compared to the standard 10 mW ALSTTL Advanced version of LSTTL which is slightly faster and has only about Emitter-Coupled Logic where high speeds are MOS Metal Oxide Semi- n-channel or p-channel CMOS Complementary MOS logic which employs n-channel and p-channel transistors 9-37 video for computers in conjunction with H. Vermeulen In Elektor we like to keep up to date, and we feel that the time has come for a new video card. The VDU card described here is not simply a modern receiver for the old and still popular Elekterminal, rather it is a new design intended to use all the possibilities of a modern computer. It can display 24 lines of 80 characters on the screen, graphics are available, and there are several other possibilities. Numerous Junior Computer users have long been waiting to be able to equip their computer system with its own video card. However, this card is intended not only for the Junior but also for other processors, such as the 6800 family and the Z80. The accompanying article in this issue ‘Video graphics’ describes the principles of a VDU card and is good background material for anybody who is not totally familiar with the subject, so, rather than duplicate any of that here, we will simply describe the circuit for the VDU card. At the same time, we must explain what the further possibilities of this card are and this is where we will VDU card . . . and terminal? Here we will consider the VDU card a: independent unit. In this form it can l connected directly to the expansion bus of the Junior Computer. The only extra com- ponent needed is a 2716 EPROM with a VDU output program in place of the printer monitor program. Figure 1 shows the main components which make up the VDU. First is the actual VDU card, with the Cathode Ray Tube Controller (6845), a 2K video RAM (6116), and the character generator the block diagram is shown in the descriptive article. The charac- ter generator consists of a 2732 EPROM in which all the ASCII and graphics symbols are stored in the appropriate dot-matrix layout (incidentally, graphics are possible by means of ‘poke’ commands, but we will return to that later). The card can be con- nected via a 75 SI video output to a monitor. A connection for a light pen is also included on the card but no software for this purpose has been given in this basic version. It will be a simple matter to incorporate this at a later date. The diagram also shows the 2716 which contains the video routines for the Junior. The standard format on the screen is 24 lines of 80 characters and because of the band- width required, a proper monitor or a TV set with a video input (not the normal aerial input) is needed. The card also has an interface to adapt the VDU board for a Z80 processor. Similarly, other 6502 computers can be connected to it, as can the 6800 family. Because complete address decoding is possible on the card it can be adapted to practically every modern computer with one of the processors men- tioned; AIM 65, SYM, VIC 20, VIC 64 and so on. One thing to remember is that the VDU card uses the Elektor bus and if it is to be used with other systems, the user will have to work out the connections and video routines himself. The composite video signal produced by the VDU card can be fed into any monitor. Both the synchronization pulses and the contrast can be adjusted. The whole image can also be inverted to provide black characters on a light background. The cursor can be made to flash or light continuously. The VDU card can be used with the oscillator containing Cl, C2 and LI, or these components can be replaced by a 15 MHz crystal, as shown dotted in the circuit diagram. If this is done the image on the screen will be rock steady. The card is slightly unusual in that all the timing on the card works with synchronously clocked TTL switching. The advantage of this is that no timing faults can occur, even with this high frequency. As you can see there are already quite a few Figure 1. Thii is a sketch of the VDU card.'*" 1 9-39 940 3 VDUca elektor ! possibilities with the VDU card but there are even more to come. As a follow up to this VDU card we will shortly publish a CPU card especially developed to complement it. These two cards will together form the basis of a universal terminal with RS 232 interface and VT 52 protocol, so that it can be con- nected to virtually any computer. Figure 2 shows the main parts of this system and of course this terminal can be connected to any computer which has an RS 232 interface. The CPU card contains a 6502 micropro- cessor, 2 VIAs (Versatile Interface Adapter), an ACIA (Asynchronous Communications Interface Adapter) an EPROM and a RAM. Thanks to a set of through connections on the board the transfer format, speed, num- ber of start and stop bits and the type and number of control bits can be adapted to whatever computer is connected to the terminal. Similarly there is a choice of eight different screen-image formats. All that is needed to make up a complete terminal is a VDU card, a CPU card, a monitor and a keyboard. The terminal could, for example, communicate over the tele- phone lines via a modem, with a computer in some other part of the globe, but because of its VT 52 protocol it could also be con- nected directly to a 16 bit computer. A connection for a printer is, of course, provided. It is also possible to use the CPU card and VDU card together as the basis for a complete computer system, as figure 3 shows. This example is connected to a 16 bitter but, in principle, that could be any type of computer. The terminal software is located in a 2716 EPROM on the CPU card which can have a maximum of 8 K of random access memory and 16 K of read only memory. Clearly there are already quite a few possi- bilities for this two-card combination and certainly there are more than we have men- tioned. However we will leave it at that until the article on the CPU card. The VDU card in a nutshell Figure 4 shows the circuit diagram for the VDU card. At the left is the system bus and here we see that address lines AO . . . A 10 are connected to the B inputs of the 2 into 1 multiplexers, IC12 . . . IC14. Also address lines A3 . . . A15 are inverted by N1 . . . N13. Complete address decoding is thus possible because the addresses are available either normally at points A3 . . . A15 or inverted at points A3 . . . Al5. Address decoding for the video RAM is carried out via N37, and for the CRTC via N38. The numbers beside these two gates refer to those used with the Junior Computer. In this case the video RAM is in the range D000 . . . D7FF and the CRTC is between D800 and D80F. When N37 gives a chip-select signal the video RAM (IC15) is addressed from the system bus by the microprocessor. By this the address inputs of the 6116 are connected to the address bus of the system via the A inputs of the multiplexers IC12 . . . IC14 9-41 9-42 . 1 ©— i7pmmr 'o opo g o gd ■W t 0 8 WHW 00 W> Diretttrj 2 ) Crate i ita fill 3 > Ckeue t fill mi 9 ) Oiltlt fill (ru (iitelte 5 ) Crate ilui Uu iiitette 6 ) Creete kite (ittette »itk files 3 ) Crate leffer sate fir itu files 8 > Siisle er till list (rive eerier 9 > Eiter 0S-65D sistea Tire tke inker if inr select i it n4 Repress RETURIt ? | because of the time that elapses between an address being supplied to the RAM and the appearance of the dot information at the outputs of the EPROM. The delay time is a few hundred nanoseconds, and that would mean that the cursor and display enable signals would appear too early relative to the dot signal. To alleviate the problem, the DEN and CUR signals are delayed by the two whole character times before being mixed with the dot signal. The links at pin 12 of N33 enable the user to select a bright (lit) or dark cursor on the screen. This in effect means that the whole image on the screen can be either normal or ‘negative’ (in the photographic sense of the word), because if we want to use a dark cursor then all the dot signals on the screen are also inverted by N34. Link ‘T’ is used for a normal image (dark background) and using link 'S’ gives an inverted image (light background). N15, N25, N28 and N29 make up the Z80 interface. These gates ensure that the signals supplied by the Z80 are compatible with the R/W and enable signals from the 6502. If using a Z80, links U-V and X-Y must be used. The dotted lin k at pi n 13 of N28 is made if the refresh (RFSH) of the Z80 is used, or alternatively an external refresh signal can be supplied to this pin. For 6502 and 6800 family processors U-W and X-Z must be linked. Construction Any hobbyist who has already constructed other computer projects (for the Junior Computer, for example) will have no prob- lem building the video card, especially if the Elektor printed circuit board as shown in figure 5 is used. This figure only shows the component overlay for this double sided It is recommended that all the ICs should be mounted in good quality sockets. This is quite important for IC3 and IC20 but these ICs should preferably be soldered directly to the printed circuit board as they deal with high frequency signals. T1 is given in the parts list as BSX 20 but a BC 547B is also suitable. It is important to remember to connect the various wire links (in the Z80 interface and the one to select normal or inverted image), and the same applies for the address decoder connections. If a crystal is used in the oscillator then LI, C 1 and C2 can be omitted from the board. Three EPROMs are needed if the VDU card is to be used with the expanded Junior. These are one 2732 containing the character generator and two 2716s, TMV and PMV, with the video routines. These last two replace the TM and PME EPROMs and, as they contain the TM and PM software, the Junior is none the worse for it. With the DOS Junior a 2732 with the character generator and one 2716 containing the video routines (DOSVT) are used. The 2716 is mounted in the socket for 1C5 on the interface card. A CMOS RAM 6116 is also needed for the DOS Junior and is put in the IC4 socket on the interface card. This interface card requires a few modifications 944 for correct operation with the VDU card, - pin 18 of IC4 is joined to pin 20 - the following connections are made: M-J, G-I, I'-G’, J’-L’, O’-M’. The DOS Junior (unlike the expanded JC) requires a few software changes in order to work correctly with the VDU card. For this a V 3.3 diskette suitable for the Junior and an Elekterminal or another serial I/O device are needed. First of all a copy of the diskette is made via Utility 8 and this copy is placed in drive A. Now the modifications given in table 1 are made and the following is entered on the Junior keyboard: A2C0 and the bootstrap modifications from table 2 are given. This is followed by: A311 FFFF (video output 1) FFFF (video output 2) A2FE (serial output 1) E1F3 (Centronics output 1) and then carry on with table 3. When that is done we then have a new V 3.3 diskette adapted to the VDU card. If there is sufficient interest, we will possibly publish a Paperware to deal with this subject in greater depth, especially as regards the Table 2. 0 , A200 : A9 01 A210 : FE 20 A220 : F8 8C A230 : EA EA A240 : EA A9 A250: 61 27 A260 : 49 4F A270 : 2E 30 A280 : 42 59 A290 : A9 FF A2A0: E6 2A 2 3 4 5 6 8D 5E 26 20 BC 67 29 20 79 2E 00 23 A2 01 8E EA EA EA EA EA 00 8D F7 EF 8D 20 73 2D 0D 0A 52 20 43 4F 4D 2A 0D 0A 0A 43 20 45 4C 45 48 8D 7D FA A9 00 AX CA 8288-39,1 - DISKETTE UTILITIES - II COMPAR 2) TRACK 9 READ/WRITE - TRACK ZERO READ/WRITE UTILITY - COMMANDS: Rnnnn - READ INTO LOCATION nnnn Wnnnn/9999 P - WRITE FROM nnnn FOR pPAGES WITH 9999 AS THE LOAD VECTOR 3 — EXIT TO OS-65D COMMAND: RA 200 -TRACK ZERO READ/WRITE UTILITY E - EXIT TO OS-65D COMMAND? E AXCA AA09-81.1 7 8 9 26 A9 2A A0 BF 20 C6 2A 4C EA EA EA D2 EF 20 0A 2A 44 50 55 54 4F 50 59 54 4F 52 8D 7 A FA ABC 85 FF 20 EC 22 F0 41 22 EA EA EA EA 35 F4 20 4F 53 20 45 52 20 52 49 47 00 A9 2E A9 FC 8D D E F 54 27 86 03 88 D0 EA EA EA EA EA EA 30 F3 20 4A 55 4E 20 56 32 48 54 20 8D 7C FA 7B FA 4C operation of the CRTC and the associated software. The EPROMs are available as a pre-pro- grammed set from Technomatic Ltd-ESS 522 is for the expanded Junior and ESS 521 for the Junior with DOS. The circuit works from a single supply of 5 V and draws a current of about 450 mA. When the power is switched on the system must be initialized by pressing the reset button. To set PI and P2, these two presets are first put to their mid positions. Then they are adjusted to get a clear image on the screen. If a TV set is used instead of a monitor the contrast control must be turned back completely as the bandwidth is gene- rally too large. Trimmers Cl and C2 are used to set the frequency so that the image remains stable on the screen. If a 15 MHz crystal is used in the oscillator this last adjustment is unnecessary. M Table 3. AXG0 9299 - DISKETTE UTILITIES - SELECT ONE: 11 COMPAR 21 TRACK 9 REAO/WRITE - TRACK ZERO REAO/WRITE UTILITY - COMMANDS: Rnnnn - READ INTO LOCATION nnnn. Wnnnn/9999. P - WRITE F ROM nnnn FOR p PAGES WITH 9999 AS THE LOAD VECTOR E - EXIT TO OS-65D COMMAND? W A 299/2298,8 - TRACK ZERO READ/WRITE UTILITY - COMMANDS: Rnnnn - READ INTO LOCATION nnnn. Wnnnn/9999.P - WRITE FROM nnnn FOR p PAGES WITH 9999 AS THE LOAD VECTOR COMMAND? E VDU card elektor September 1983 Table 1. This is how track 0 of the floppy disk is transferred to the RAM memory starting at address SA200 and track 1 to RAM starting at address SAA00. Table 2. This is the data needed to modify the the modified bootstrap floppy disk. 9-45 Manufacturers are always interested in miniaturising receiver circuits and they keep pushing the limits further and further. In a normal receiver set-up extreme integration is to be avoided especially as regards tuning coils, ceramic filters, band filters, and trimmers. Coils especially are a problem. Certainly they could be replaced by gyrator circuits, but because of their complexity these also have certain disadvantages at high frequencies, such as low Q factor, limited dynamic range and fairly high current con- sumption. So Philips set out to develop a receiver that was less sensitive to the various problems posed by IC technology itself. And they succeeded with an 18 pin chip that needs only an oscillator and a few small capacitors to form an FM receiver. Everything else is internal, from the aerial input right through to the IF filters and demodulator! The break through came when they decided to aban- don accepted practice and chose to use an FLL system (a type of feedback PLL). This system works with a low enough IF (inter- mediate frequency) so that the IF selectivity can be realised with RC filters which, unlike LC filters, can be miniaturised successfully. Moreover, the disadvantages inherent in this low IF were suppressed by using a clever muting system. Figure 1 shows the block diagram of the IC, complete with the components needed for a bog-standard radio. A very simple affair! We will not go any further into this block diagram at the moment as we will concen- trate on how this circuit is expanded into something more interesting. Micro or mini We are always interested in new ICs and how they can be used and this is the case with the TDA 7000. Now that we’ve decided we want personal FM miniature high quality FM receiver The relatively new TDA 7000 from Philips is an IC that forms the basis of a complete FM receiver just by adding a few passive components. This IC could be described as an 'aerial signal in — low frequency signal out' sort of chip. However, not being satisfied with that, we expanded a little on the basic theme by adding a bit here and there, designed a printed circuit board, and ended up with a high quality mono FM receiver that is quite literally pocket sized! to use it as the basis for a radio receiver we have to decide what sort of receiver it is going to be. Should it be a normal small FM radio? Or maybe something extremely small? Should the accent be not so much on small dimensions as quality . . .? The charac- ter of the IC is an invitation to make a micro radio . . . but that’s easier said than done! A real micro design does not seem so interesting. There are limits to how small it can be made if it is to be put on a printed circuit board and we would not seriously consider anything else. So what we want is a ‘bigger than micro’ design with somewhat higher quality and without the disadvantages of the ‘as small as possible’ design. It must have a suitable low frequency amplifier included and the complete unit must all be contained on one printed circuit board so that only a battery, headphones and, pos- sibly, an aerial have to be connected to it. The circuit diagram Let us start by saying that, no matter what type of receiver is designed around the TDA7000, a large part of it will always be the same. Almost everything is included in the IC so there is very little designing to be done with external components, and the receiver design cannot really be changed. The similarities between the design of figure 2 and that in figure 1 are clear enough personal FM elektor September 1 983 C19andC20). There are a few qualities of the basic design that we were not entirely happy about. In the first case it was found that the sensitivity of about 7 nV is a bit on the low side for a personal FM receiver. If you walk around with that sort of radio receiver the aerial is not always in the most ideal position and the chances are that the station that you are tuned in to will continually disappear under the squelch. Therefore we decided to include a HF pre- amplifier (Tl). This preamplifier stage is very easy to set up, not at all critical and ensures that the sensitivity is always under 1 pV. As the circuit diagram shows, its input is connected to one side of the headphones so that the lead can act as an aerial. The L4/C21 network has two functions. Apart from suppressing any spurious components but there are also a few differences, princi- pally in the input stage and the oscillator. Also the more advanced design (figure 2) includes power supply stabilization and the LF amplifier mentioned before. Although in principle a small loudspeaker can be used for the output of the radio, it is intended, initially, that small personal cassette type headphones should be used. A secondary advantage of headphones is that the lead can act as an aerial. To avoid making the receiver any bigger and more complicated than absolutely necessary we used a readily available amplifier IC (the LM 386 from National) for the headphone amplifier. This chip supplies very good sound quality and, for a small loudspeaker or headphones, its power output of 0.5 watt is quite sufficient! Furthermore the LM 386 needs only three external components (R4, Resistors: R1.R8- 18k R2- 1k8 R3 = 2k2 R4 = 47 k R5 = 68 k R6.R9 = 10 k R7 - 100k RIO- ion PI - 10 k ten turn pot P2 = 22 k log pot Capacitors: C1.C2 - 68 p ceramic C3 = 4n7 ceramic C4.CS.C20 * 10 n ceramic C6 - 1 p/6 V C7.C19- 47 n ceramic C8 - 2n2 C9.C12 = 3n3 Cl 0,C1 3 * 1 80 p ceramic Cl 1 ,C1 5 = 330 p ceramic C14 = 100 n C16- 220 p C17- 150 n C18 - 220 n C21 = 10 p/6 V C22 - 220 p/10 V C23- 100 p/6 V Semiconductors: 01 - BB 105 02- AA119 Tl = BF 494 T2- BC640 T3.T4 = BC 549C IC1 - TDA7000 supplier: Technomatic Ltd. IC2- LM386 L1.L2 = 0.22 pH (coil on L3-E526HNA100114 L4 - inductance made Miscellaneous: Leightweigt headphones, at least 8 n impedance )-48 of the output signal from IC2, it also acts as a decoupling circuit between the LF out- put and the HF input. There are also a few details about the oscil- lator which should be changed. First of all the coil. To alleviate supply difficulties we used a standard off-the-shelf Toko coil. There are two problems with using a tuning capacitor for this circuit: availability is often a problem and some sort of mechanical gearing must be used in order to make tuning easier. We decided to kill two birds with one stone and used a varicap diode (Dl) in combination with a 10- turn poten- tiometer (PI) for the control voltage. Because the tuning voltage must remain very stable, some form of voltage stabilization must be used. In order to spare the (small) battery as much as possible, the losses (vol- tage drop and current consumption) of the stabilizer should be small. This explains the use of a discrete circuit here (T2, T3 and T4) in preference to an 1C. Even if the battery voltage drops to 5.5 V this stabilizer still supplies a constant 4.5 V. And that is the whole circuit. Note that pin 3 of the TDA 7000 is left unconnected because it was considered that using squelch suppression with artificial noise is going a bit too far. For anybody who wants to use this built in noise generator, a 22 nF capacitor can be connected between pin 3 and the positive supply. The printed circuit board Although it was not intended as a micro cir- cuit, the 50 x 50 mm dimensions of the double sided printed circuit board shown in figure 3 still make it very diminutive for a complete FM receiver. Even when the 9 V battery is included the end result can justly be called a personal receiver. In the case of the HF stage there are abso- lutely no problems with construction. The worst thing is trying to remember the type number of the oscillator coil, L3. It is an E 526 HNA - 100114 from Toko, and that’s quite a mouthful for ‘the morning after the night before’. However, L4 is not so difficult as it is already etched onto the printed cir- cuit board. The input and oscillator stages should ideally not be able to 'see' each other. Therefore the area around T1 should be screened, prefer- ably with mu-metal or copper. Space has been left on the board for these screens and their locations are indicated. The four pieces of screen are soldered into a box and then soldered to the upper side of the printed circuit board. Most of this upper side (or component side) of the board is an ‘earth plane'. Therefore, all points which should be connected to earth are soldered to the top of the board and the rest simply connect to the under side. These latter (non-earth) points are of course the copper 'islands’. When construction of the printed circuit board is completed, only the tuning and volume potentiometers (PI and P2 respect- ively) have to be connected, not forgetting the battery and headphones of course. The connection points are clearly marked. Adjustment Normally quite a large section of an article describing the construction of an FM receiver would be devoted to setting up, but that is hardly necessary with the TDA 7000. The simple adjustment of L3 to ensure the correct receiver range (87.5 . . . 104 MHz) is all that is required. That can be done with a frequency counter of course but the simple method is to compare it with another receiver! One final point. Even though it is extremely handy to use the headphone lead as an aerial, it is much better to use a 60 cm (or even 30 cm!) aerial. And that does not apply only for this receiver, but also for any other personal radio. If an aerial is used it should be connected to the junction of Ll/Cl (aerial input) and the headphones between the LF input and ground. We have spent hours listening to our FM receiver (mainly before the morning coffee break? Ed.) and it must be said that it gives a very good account of itself. The sensi- tivity is reasonable and the quality of the sound is actually very good. The only ‘but’ is that the TDA 7000 is only a mono receiver. But you can’t have everything and who knows, maybe it is only a matter of time before we get a pin compatible version suitable for stereo. In the meantime we have a trick up our sleeve that may be just as good but that will have to wait until - maybe the next issue! M 9-49 Even today, looking for simple electronic components can give you quite a headache. Take, for example, a simple voltage divider for a voltmeter: when you try to buy the necessary high-stab resistors, the likelihood is that you're told in shop after shop: 'Sorry, we don't stock those'. precision voltage elektor September 1 983 precision voltage divider . . . for home construction In the construction of measuring equipment, you normally require a number of precision components. Particularly voltage and current dividers need resistors of 1% tolerance. The simple four-way voltage divider shown in figure 1 has a total resistance of 1 Mfl and requires four resistors: 900 kS2, 90 kfl, 9 kfi and 1 kS2. And that’s where your troubles are likely to start. If you’re not lucky enough to find a complete divider somewhere, forget about buying the indivi- dual resistors. It’s extremely unlikely that you'll find the above four values in the high-stab range in one shop. Parallel connections Fortunately, it is possible to make a pre- cision voltage divider with an input im- pedance of 1 Mil from standard value resistors. The solution lies in connecting two high-stab resistors in parallel to obtain the required value as shown in figure 2. If a shop stocks high-stab resistors, it’s pretty certain that it has standard values of 1 Mfi, 100 kf2, and so on. And that’s what the divider of figure 2 depends on! The resulting resistances are 909.09 kS2, 90.909 kft, 9.09 kfi, and 1.01 kfl. The deviation from the ideally required divide factors is smaller than 0.01% so that in practice the variations are entirely dependent upon the tolerances of the resistors used. In parallel connections as used in figure 2, not all resistors need be 1% types. Because each combination consists of two resistors of which one has ten times the value of the other, the larger one has a much smaller effect on the result than the smaller one. As a consequence, the tolerance of the larger resistor is of much less importance than that of the smaller one. Even if 5% types are used for the larger resistors in the parallel branches, the overall stability will be suf- ficient. The same is true of R7 because this is pretty small compared with R8. As an example of the above: if R2 deviates exactly 5% from its nominal value, the variation of the resultant value of R1/R2 is only 0.4%. You might say that the tolerance of the larger resistor improves roughly by a factor equal to the ratio of the two resistors. Parallel connections have a further advan- tage: statistically there is only a very small probability that two resistors in a parallel branch both deviate in the same direction. In other words: there is a good chance that the network of figure 2 is more precise than the one constructed from 1% resistors as shown in figure 1. All in all, the above gives enough reasons to use parallel-connected resistors. Figure 3 gives an alternative which uses fewer re- sistors. However, its theoretical stability is rather worse than that of figure 2: 0.01% instead of 0.001%. M 9-50 alarm extension... The garden party is in full swing . . . Amidst all the happy noises and chatter it is difficult to hear when the telephone rings or a late guest rings the front-door bell. The alarm extension described here will enable you to hear the phone ringing wherever you are, provided there is a mains socket close at hand. . . . over the mains The principle is well-known: an intercom which uses the mains wiring as the trans- mission channel. This is a very handy gadget which can be used wherever a mains socket is available. Speech facility is not provided: the receiver merely indicates that the trans- mitter has ‘detected’ a certain sound, which may come from the telephone bell or from another source. General principles The transmitter and receiver contained in the alarm extension are shown in block form in figure 1. The signal detected by the transmitter is amplified, rectified, passed through a high-pass filter, and then used to switch an astable multivibrator (AMV). This stage generates a 22 Hz square-wave signal which is used to phase-modulate a second AMV. This astable operates at 178 kHz. The output of the modulator is taken via a limiter to a low-pass filter which removes the last traces of any spurious frequencies, so that a ‘clean’ signal is fed to the mains via a suitable transformer. The receiver is even simpler than the trans- mitter. The ‘telesignal’ is recovered from the mains by means of a suitable trans- former. A diode limiter ensures that any high-voltage spikes do not damage the (following) phase discriminator, a phase- locked loop (PLL) with digital and analogue output. The digital output lights an LED to provide an indication when the input signal is locked to the discriminator. The demo- dulated 22 Hz signal at the analogue output is ‘recognized’ by a tone decoder which acknowledges receipt of the signal by causing a second LED to light and a buzzer to operate. The circuit diagram The transmitter (see figure 2) The input signal is taken from a telephone adapter coil or simple microphone. A coil does not pick up ambient noise and will therefore give better results . The amplifier, rectifier, and high-pass filter mentioned are shown at the top lefthand of figure 2. They are followed by comparator 9-51 elektor September 1 IC4, the threshold of which is set by PI. The output of IC4 is used to switch the astable multivibrator formed by IC1. This AMV can be fed simultaneously with a square-wave signal to provide a facility for the remote control of an external equip- ment connected to the receiver. Details of this will be featured in a future issue. The second of the 555 timers is also connec- ted as an astable multivibrator. With values shown, IC2 oscillates at around 178 kHz and IC1 at about 22 Hz. Oscillator IC1 is started by a logic 1 at the output of IC4. The output of IC2 is phase-modulated with relatively good linearity. Any spurious frequencies produced during the on and off switching of IC1 are filtered out by R3/C9. The network around diodes D6 and D7 prevents any mains-bom interference from reaching the output of IC2. The filter network L2/L3/C5 removes any harmonics from the phase-modulated signal to ensure that a ‘clean’ signal is applied to the mains via transformer LI. The power supply for the transmitter is provided by the usual 5 V voltage regulator IC. The supply transformer must be capable of providing 9 V at 100 mA. The receiver (see figure 3) The receiver draws the phase-modulated signal from the mains via Cl and trans- former LI, which is identical to LI in the transmitter. Diodes D1 and D2 protect the demodulator circuit against interference which may be present on the mains voltage. The phase-modulated signal is applied to phase discriminator IC2 via C3. Apart from a phase-locked loop, IC2 in- cludes a phase detector, a voltage-controlled oscillator (V.C.O.), an output filter (with C8), and a comparator. The frequency of the V.C.O. is preset to 178 kHz by means of PI. The input signal at pin 3 is, as usual in a PLL, compared with the oscillator output by the phase discriminator. If the input signal is phase- modulated, the difference between it and the oscillator frequency, that is 22 Hz, appears at pin 2. The internal resistance, together with C7, forms a smoothing circuit for the output signal. When the PLL is locked to a signal at pin 3, the signals at the inputs of the phase detec- tor are in phase. The consequent output of the detector is a constant-voltage signal, which is applied to the non -inverting input of the comparator. This stage compares the signal with an internally set reference level and switches its output (pin 8) to logic 0. LED D7 then lights, indicating that IC2 has ‘received’ the 178 kHz carrier. The 22 Hz signal is amplified in T1 and applied to tone decoder IC3. On receipt of this 22 Hz signal, the output at pin 8 switches on the LED D8 and the buzzer. The receiver power supply unit is identical to that of the transmitter. Construction and adjustment Construction of the alarm extension should present no real problems if our two specially designed printed circuit boards are used. The transmitter board is shown in figure 4, that for the receiver in figure 5. As no special components are used, the construction needs no further explanation. One thing must be borne in mind, how- ever: capacitor Cl in both transmitter and receiver MUST BE 600 V types! On the receiver board a thin metal screen must be soldered to the appropriate soldering points: the screen is shown in the diagram as a dotted line. )-52 Each transformer LI is made by winding 10 turns evenly spaced onto a toroidal suppressor choke (as commonly used in triac circuits). For this purpose enamelled copper wire SWG 18 may be used, but better performance is obtained by the use of insulated stranded wire. The ad- ditional winding is connected to mains live: you have been warned! When the construction has been completed, set all presets to their mid-position. Connect the LEDs, buzzer, and transformers tempor- arily. Before connecting the coupling trans- formers to the mains, read the following setting-up instructions. Setting up the transmitter ■ Connect the mains transformer to the mains and check the supply voltages. ■ Connect a good voltmeter or an oscillo- scope to the output of IC4. ■ Attach the telephone adapter-coil or microphone to the transmitter input, and adjust PI for maximum deflection on the voltmeter or oscilloscope with the telephone ringing. If the deflection is small, the coil or microphone is located in the wrong place. Better resolution can be achieved by connecting an oscilloscope across C13. The coil can then be placed in a position which gives the greatest amplitude. ■ Connect LI also to the mains. ■ Connect ‘S' to +5 V by means of a jump Setting up the receiver ■ Connect the mains transformer to the mains and check the supply voltages. 9-54 ■ Connect the coupling transformer LI to the mains. ■ Adjust PI till LED D7 lights brightly. This LED will already light, but a pos- ition of PI should be sought where it lights twice as brightly as normal! ■ Adjust P2 till LED D8 lights brightly. Same remarks as for LED D7 apply. ■ Remove the jump wire from ‘S’. ■ Finally, with the telephone ringing, check the entire alarm extension for satisfactory operation. Final notes ■ If the sound of the small buzzer is too feeble for your purpose, a relay can be connected (via an isolating diode) in its place. The tone decoder can deliver up to 100mA output current. The relay can be used to switch on a bright light, a siren, or a similar optical or acoustical device. ■ Although a Government Health Warning is not printed on every mains socket, bear in mind that both Lla windings are at mains potential. Therefore, use extreme care when handling the printed circuit boards with the mains supply switched on. Please, gentle reader, do not become a statistic! M toil side of the receiver printed circuit board. The coupling coil is made exactly as that for the 9-55 Nothing generates quite so much interest in computers by raw beginners as a computer that makes noises. This is particularly true with children and especially if the computer can actually play its own tune on command. It can encourage them to take a serious interest in programming and/or computers in general. for Synthesizer makp \/DI I r When a flood of new musical instruments - appeared that could be controlled by a computer pley microprocessor, some of the many Junior y q y p Computer owners must certainly have com- y . bined the two ideas. Actually this computer faVOUrite tunes lends itself quite readily to controlling an analogue synthesizer. However, some people have probably not yet taught their computer to play music and so to make it easier we have written a program to turn your Junior Computer into a Junior Synthesizer. A singing display The only ‘hardware’ needed for this JC to JS conversion is a 100 loudspeaker that is connected between one of the display driver outputs of IC11 and ground. No other special interface is needed as the only com- ponent used is connected directly to the existing circuit. The audio signal that feeds the loudspeaker is produced by the 6532 on the main board of the computer, and con- sists of a series of pulses whose frequency is determined by the software. The tune to be played is memorized in page $0300 and is made up of a series of bytes, two of which are needed for each note to be played. The first is placed in an even address and corres- ponds to the pitch of the note; the second, corresponding to the duration of the note, is placed in the next odd address. The pitch depends on the frequency of the pulses, and the duration depends on how long the signal lasts. 9-56 There are four values of duration possible: minim, equal to two crotchets, each equal to two quavers which in turn are each equal to two semi-quavers. The durations are calculated from the computer clock which has a frequency of 1 MHz. For example, the note 'A' at 440 Hz has a pulselength of 2.28 ms. With a symmetrical waveform, the space lasts 1.14 ms. There is already a timing stage available in the computer (DELAY). So for our ‘A’, this delay has to be executed 81 times before inverting the logic level (81 x 14 ps * 1.14 ms). Thus the hexa- decimal value of the pitch of this note is $51 (81 in decimal). Because the program is very simple, only the $0300 page (up to $03FF) can be used to memorize a melody, so it can only have 127 notes at most. The tempo is fixed by the contents of location MULT ($0002) which can be changed to increase or decrease the speed of play. The rhythm is determined by the magnitude of the bytes in the uneven addresses, although, of course, the value of the durations also varies with the pitch of the notes. When the processor finds the value $00 in an even address (pitch), it is silent for a certain length of time which is normally determined by the contents of the immediately follow- ing uneven address. If on the other hand, the value $00 is in an uneven address the tune is stopped and starts again from the beginning. In the example given here, the Junior plays the Menuet du Bourgeois Gentilhomme by J. B. Lully, but with a little experimentation you can probably make it play 'Chopsticks' as well! M JUNIOR HEXDUMP: 0 0200: A9 0210: 85 0220: 20 0230: 50 0240: CA 0250: A6 200, 25D 12 3 7F 8D 81 02 A6 00 50 02 A6 02 C6 01 EA EA EA 00 BC 00 4 5 6 1A A9 08 BD 01 03 00 BC 00 D0 E5 C6 D0 FA 4C 03 A2 02 7 8 9 8D 82 1A 85 01 F0 03 F 0 08 02 D0 D8 0E 02 00 CA D0 FD ABC A9 00 85 E5 A9 40 A9 BF 8D E6 00 E6 00 00 00 88 D0 F8 D E F 00 A9 02 8D 80 1A 80 1A 20 00 A2 FF 00 00 00 60 JUNIOR M HEXDUMP: 0 0300: 51 0310: 61 0320: 3D 0330: 61 0340: 56 0350: 3D 0360: 61 300.36B 12 3 58 3D EA 4 A 5B 4E 75 36 84 94 79 3A 53 51 B 0 75 3D 75 4A 5B 4E 4 5 6 41 DE 3D 6C 84 61 51 58 48 61 94 5B 51 58 3D 48 63 41 6C 84 79 7 8 9 75 36 84 94 79 3A 63 5B 9C 4E 51 B0 EA 48 63 DE 3D 75 74 00 70 ABC 51 58 48 51 58 3D 61 4A 5B 51 58 48 41 6F 41 51 58 48 00 00 D E F 63 5B 9C EA 41 DE 4E 6C 84 63 48 63 6F 51 58 63 5B 9C Table 1 . The codes for the pitch and duration of the notes shown here can make the Junior Computer play your favourite tune. Table 2. This is the program which uses the 6532 and the display signal that is heard through the loudspeaker. No Table 3. The sequence re- produced here corresponds the Menuet du Bourgeois Gentilhomme by Lully. The even addresses contain of the notes. Note that in some cases the durations are not exactly minims. The see at $e36B acts as that the piece is to be replayed from the start. 9-57 All home constructors are constantly looking for simple ways of checking whether electronic components they have in stock are fit for use. This is particularly so in the case of the more expensive transistors, such as the power metal-oxide field -effect transis- tors, or simply power MOSFETS, as used, for example, in the Crescendo amplifier featured in our December 1982 issue. Although the complete electrical testing of such devices requires complicated, expensive test gear, it is perfectly feasible to check them with a multimeter. The tests described refer to n-channel devices; by reversing the rest leads indicated in the text, p-channel types can also be checked. With the multimeter set to highest resistance range (x lOMfl or x 100 MQ) check that the resistance between gate and source is infinite. Reverse the test leads and check again. simple MOSFET ■ Set the multimeter to the lowest resist- ance range. ■ Connect the (red) lead from the + ter- minal to the source, and the (black) lead from the terminal to the gate. The gate is now forward biased . ■ Move the black lead from the gate and connect it to the drain. The multimeter should now indicate zero ohms (see figure la) ■ Connect the (black) lead from the terminal to the source and the (red) one from the + terminal to the gate. The gate is now reverse biased. ■ Connect the - lead to the drain and the positive one to the source (see figure lb). The meter should not deflect be- cause of the equivalent diode between drain and source. If now the + lead is con- nected to the drain and the negative one to the source, the meter should deflect. ■ If the above checks are satisfactory, the device is perfectly fit for use. As many months of experience with, for instance, the 2SK135 and 2SJ50 MOSFETs has shown that these devices are very reliable, a negative result of the above checks is very unlikely. M 9-58 Simple phase shifter for bridge circuit The question is often raised regarding the possibility of obtaining more output power with two identical power amplifiers According to the basic principle, two ampli- fiers connected in a bridge circuit theor- power of a single amplifier at the same supply voltage. The loudspeaker in the bridge is provided with twice the voltage. However, this also means that the power amplifiers must supply twice the output current. A normal, properly rated output When a bridge circuit is used, therefore, the result is not necessarily four times the power, but a somewhat lower figure (de- pending on the maximum output current of the amplifier). If the amplifier is not equipped with a current limiting circuit, there is also a risk of overloading the output transistors. Now let us examine the question of drive. The two amplifiers must be driven in phase-opposition; the loudspeaker is then connected between the two amplifier outputs. A suitable phase shifter consists of a transistor stage with emitter and collector resistors of the same value. The signal at the collector is then identical with that at the emitter, but shifted by 180°. This is exactly what we need to drive two amplifiers in a bridge configur- ation. Thanks to the relatively high col- lector current of the BD135, the output impedance of the phase shifter described input impedance of only 1 k can be con- nected without problems. On the other hand, the 20 k input impedance of the phase shifter is high enough to allow the usual preamplifiers to be connected. car PDM amplifier (Summer circuits '83 page 7-36) We regret that one illustration of the double-plated printed-circuit board of this amplifier was omitted from the Summer Circuits ’83 issue. At the same time, the foil-side was omitted from the PC board pages. Both omissions are put right in the PC board pages in this issue. morse converter (may 1983 page 5-52) Owing to an error in our master EPROM, the hexdump (table 4 - page 5-58) needs should be amended to OB. Readers who have an erroneously coded EPROM can carry out the amendment quite simply, because the RAM of the expanded Junior lies at address EB6C. The following should be typed in: EB6C 4C EB6D 6C EB6E OB JMP 0B6C After the program has been copied to address 4000 and following, EA must be entered at addresses 4032 . . . 4034. These amendments do NOT apply to the DOS Junior. floppy-disk interface for the Junior (December 1982 page 12-48) Our attention has been drawn to a small omission in the December 1982 article on the DOS Junior. In the 3.3 version of the DOS Junior there is an Extended Monitor which permits, among other things, BREAK points to be placed in a program. Some readers who tried this discovered it was not quite possible. This is because the BREAK vector is not monitor, to place the following data into the adresses indicated. SFA7E S25 SFA7F SIB Thus, the BREAK vector points to the routine which controls the BREAK points. elektor infocard 55 The formulas for the gain of both the Wien-Robinson bridge and twin-T filters Wien-Robinson , _ ni G p 3V<1— P’)’ + 90 ’ where 0 * f/f m Twin-T filters 1 - fl 3 - G = -- -- •J (1 -0 1 ) 1 + 16 0 1 where 0 = f/f m elektor infocard 70 We regret that several errors and omissions crept into infocard 70. The value of capacitors Cl . . . C16 * 1 50 pF. FF2 does not have a pin 16: this should be pin 14. The divider/counters are not type 4013 but type 401 7. Finally, an RC combination and diode were omitted: the connection between FF1 and the MK 50398 should be as shown below. coming soon... Central heating controller Basicode Simple anemometer . . . and many more! (itch is available with a choice of red, een, orange and yellow LEDs, with ^responding diffuser caps (plus a clear switches can be stacked on a standard 2.54 mm p.c.b. pitch. Switching capability extends from 1 pA to 1 A up to a maxi- is typically 20 mJi, and insulation re- sistance 100 Gfi. Erg Components, Luton Road, Dunstable, Bedfordshire LU5 4LJ. Telephone: 0582.62241 J Brynberth Industrie! Estat Rhayader, Powys LD6 SEN. Telephone: 0597.81071 1 Power booster amplifiers In addition to their existing 15 Watt (Rmsl mono power booster amplifier ILP introduce the NEW low priced STEREO 1 5 Watt (Rmsl per channel version. rnarrcsa . Rugged calculator in factories, offices i Lawco HD calculators loped and perfected o\ years and feature a ui Protecting the calculat its shell, the hinged pi firmly locked by six hooks, yet folds back t to microprocessors. A number of useful for the practising and aspiring designer of digital circuits alike. jurs of daily use Telephone: 051-227.1212 •king documents and notebooks. Ruislip, Middlesex, have introduced a new "Z' Series to their range of Multiswitch thumbwheel switches. Designed as a more compact version of the well established 'D' switch, the 'Z' Multiswitch is a step index. 10 position switch with BCD or decimal output codes. Its size: 15 mm 9-61 The cases are manufactured in plastic coated metal which is antistatic with high insulation and screening properties, end cheeks are in textured high impact re- sistant polystyrene. E lines Products Limited, Lyon Works, Capel Street, Sheffield S6 2NL, Telephone: 0742.339774 Digital plotter drawing (viewport), and to scale drawings up or down as required, are possible. While manual entry and control are via a membrane keyboard, a built in RS 232C allows for interface with most current computers. An extensive self test and diagnostic repertoire enable the operator quickly and easily to determine the plotter n during it colour plots is drive system. Reliable, quiet and accurate stepper motors, controlled by dedicated microprocessors, drive both pen and drum. With both axes plotting in in- refined by Houston Instruments c years to provide highly reliable op generating repeatable plots of p defined resolution and high accurac Quiswood L imited, 30 Lancaster Road, St. Albans, Hertfordshire AL I 4ET, Telephone: 0799.24922 readership survey first results! drum plotter from Houston Instruments. The DMP 40 occupies a space of little more than one square foot yet combines sophisticated firmware options, plotting precision, speed, rugged reliability and ease of operation. Sizes up to and including A4 and A3 perforated or special sheets are not re- quired. Plots, maps, formulae, graphs, script, block letters, drawings, geometric patterns and charts are all available, mistake-free, on ordinary bond paper, drafting vellum, acetate and mylar from frame computer, or by both novice and experienced operators. Routines within DM/PL 111 can automatically generate size. Eleven different line types (solid, dotted or dashed) are provided. Straight and slanted (Italic) characters can be drawn at any of 360 possible angles and 255 sizes. Aspect control, in which one axis may be lengthened, as well as the capacity to plot only a portion of a We are still busily counting and evaluating the response to the readership survey in our July/ August edition. Although this work is by no means completed, some findings are already obvious. In the first place, some 80 per cent of the replies express a genuine interest in the results, while only a few per cent consider it ‘a waste of paper’. Several readers remarked that ‘the competition should be interested, too!’ True enough, and most of them have a free subscription. So here's something for them to chew on. We printed the PC board layouts on special pages (mirror image, with the reverse side blank) as an exper- iment. We thought this would make life easier for everyone who repro- duces the boards with photosensitive material. Apparently, we scored a hit: over 30 per cent of our readers ticked the box ‘Those special pages are a great help’! As of now, those pages are no longer an ‘experiment’ - they are a standard Elektor fea- ture! One reader even described how he had been using a similar technique for years. Evidently, he erases the printing on the reverse side with emery paper (‘very carefully’), and uses sewing-machine oil to make the paper transparent. He sent us a board he had produced in this way and, believe it or not, it proved to be extremely good! The other results? It’s early days yet: we haven't completed the evaluation. But we will publish them as soon as they’re available - pos- sibly even next month. Just one more is worth noting: against ‘Edi- torial introduction/opinion?’, most readers ticked ‘I’m neutral’. So, this is not an introduction, nor is it an opinion. 9-62 ■ In view of the enthusiastic response from our readers, we have decided to continue the experimental pro- vision of the special PC board pages. We will, however, review their inclusion from time to time on the basis of readers’ interest. The pages contain the mirror images of the track layout of the printed circuit boards (excluding double-plated ones as these are very tricky to make at home) relating to projects featured in this issue to enable you to make, that is, etch, your own boards. ■ To do this, you require: an aerosol of ‘ISOdraft’ trans- parentizer (available from your local drawing office suppliers; distributors for the UK: Cannon & Wrin), an ultraviolet lamp, etching sodium, ferric chloride, positive photo-sensitive board material (which can be either bought or home made by applying a film of photo-copying lacquer to normal board material). ■ Wet the photo-sensitive (track) side of the board thoroughly with the transparent spray. ■ Lay the layout cut from the relevant page of this magazine with its printed side onto the wet board. Remove any air bubbles by carefully ‘ironing’ the cut-out with some tissue paper. ■ The whole can now be exposed to ultra-violet light. Use a glass plate for holding the layout in place only for long exposure times, as normally the spray ensures that the paper sticks to the board. Bear in mind that normal plate glass (but not crystal glass or perspex) absorbs some of the ultra violet light so that the exposure time has to be in- creased slightly. ■ The exposure time is dependent upon the ultra-violet lamp used, the distance of the lamp from the board, and the photo-sensitive board. If you use a 300 watt UV lamp at a distance of about 40 cm from the board and a sheet of perspex, an exposure time of 4 ... 8 minutes should normally be sufficient. ■ After exposure, remove the layout sheet (which can be used again), and rinse the board thoroughly under running water. ■ After die photo-sensitive film has been developed in sodium lye (about 9 grammes of etching sodium to one litre of water), the board can be etched in ferric chlo- ride (500 grammes of Fe3Cl2 to one litre of water). Then rinse the board (and your hands! ) thoroughly under running water. ■ Remove the photo-sensitive film from the copper tracks with wire wool and drill the holes. 9-63 9-65 BBC Microc omputer System FOR RELIABILITY SEIKOSHA AND TEAC SLIMLINE DISK DRIVES Akhter Instruments Limited DEPT. EK, EXECUTIVE HOUSE, SOUTH RD.. T EMPLEFIELDS, HARLOW, ESSEX CM20 2BZ. UK. TEL: HARLOW (0279) 443521 OR 412639 TELEX 995801 REF elektor September 1983 advertisement Now open in Newcast^ =? THE BEST IN ELECTRONIC COMPONENTS TEST EQUIPMENT AND ACCESSORIES Marlborough Electronic Components 15, Waterloo Street Newcastle NE1 4DE Tel: 618377 Open 9am-6pm Mon-Sat Easy Parking STOCKISTS OF TRANSISTORS RESISTORS CAPACITORS I.C. DIODES ELECTRONIC BOOKS Etc. ■Mtw yrtouai bu REPAIRS UNDERTAKEN microprocessor Are you looking for a terminal for your micro- processor . . ? Or maybe a memory extension? Is your cassette interface too slow or just not good enough? Computer capacity underestimated? How do you program your (E)PROMs? All these and many other questions are answered in this micro- processor hardware book in clear and easy-to-under- stand language. The heart of every personal computer is the micro- processor and only a limited number of these are in common use. This book describes a range of peri- pheral equipment which can be used with an assort- ment of personal computers using the 6502, 6809, Z80, or 8080 microprocessor. This is obviously not an easy matter, but the book explains all that is necessary to enable the systems to be applied with the minimum number of circuit modifications. Price C7.50 + 50p postage & packing. To order please use the postage paid order CIRCUIT DIAGRAM or hand- book for Leak 1*0101 One" — TL 10" Power Amplifier (valve). Christopher Smith, 34 High Leys Drive, Leics. LE2 52L. Tel. 713942. WANTED, nearly new Daisywheel typewriter with RS232 Interface. Details to P.H. Smallwood, Lr. Triffleton. Haverfordwest. STROBE LIGHT - £25 o.n.o. Also stereo disco mixer module inc. controls, autofade, etc. — £30. Tel. Nick on 0706 50223 (evenings). 8 MINIATURE microphones £1 each. Please include SAE. Also some projects and components. D. Martin, 29 St. Johns Close, Leatherhead, Surrey. RAMS, set of 8. 4116, £5. EPROMS. 5 V, 2716, 2532, 2 of each, all for £7. 6502 CPU. 6522 PIA, both for £4. Bench meter 6" scale. £20. Mr R. Mlnchin, 51 Thurleigh Road, London SW1 2 8TZ. WANTED, circuit and pinout of SN 76489. Want to make contact with friendly Elektor readers for corresponding on electronics and computing. Write me soon. Hamid-Reza-Tajzadeh, 4th floor, no. 11, Street no. 3, Noarmack, Tehran 16479, Iran. ACORN ATOM fully expanded 5V7A PSU. Twin A/D. Fully proportional joystick. All in custom teak cabinet, £200 o.nx>. Tel. 0264 54748 (Andover). TELETEXT DECODER - full spec GMT design. Cased with ultrasonic remote control. £75 Hutchinson. 18 The^StreeL Ovington, Norfolk. Tel. 0953 883879. ELEKTERMINAL £35. cassette interface £1 . 0.56 key keyboard £25. Ferranti vdu. faulty clock c/w 65-key keyboard. Offers D. Roddis, 59 Hendon Rise, NOTTINGHAM NG3 3AN COMMODORE PET 8k RAM, basic3. Lots of S/W including invaders, golf and database. £200 tel. 0934 24856. P.S.U. Lambra 5 V 3A ± 12V - 15V. !4A. £25. High resolution TV monitor, data or picture, £45. Phone Bishop's Stortford (0279) 504212. WILLIAM STUART'S Big Ears speech recognition system for UK101. Sprbd, Nascom, Atom. Complete with software, access, new, £35. K.Y. Chang. 70, 1-up, Ashley Street, Glasgow G3 6HW. NASOM 1 + Buffer Brd. + PSU + Transformer + Documents, £150. Will sell separate. Mr W.K. Ip, 46 Burnley Road East, Waterfoot, Lancs. BB4 9AF. WANTED: Scope Tube DG7/32 or DB7/32. M. Rymenans, P. Coudenberglaan 21 . 2520 Edegem, Belgium. KSR TELETYPE and stand, work- ing order with manual. Ideal for computer printer or RTTY. Only £60. Phone Davis 01 399 5487. HELP! Need instructions to build 'CY - ENDFIELD' Micro-writer. 8. Schlatter, Shin-ogawa-Machi 6-18, Edogawa-Apato 56, 162 Tokyo, Japan. WANTED: ZX - Spectrum cir- cuit diagram, advise TMS4532 — 20NL4 DRAM equivalent re- placement. Uri Sela, Kibutz Lehavot-Habashan, 12125 Israel. WANTED: Circuit diagram and workshop info, for Leak Stereo 30 amplifier. Your price or borrow for copying. Philip West, 2/26 Stirling Road, Birmingham B16 9BG. STEREO DISCO MIXER-2 mag- netic p.u.'s + aux +micautofade. deck switches etc. great sound £50. o.n.o. Tel, Rochdale 0706 50223 TEKTRONIX STORAGE os- cilloscopes plus 4 input modules order. £400. complete o.n.o. Steven Bush, 37 North Croft, Woodburn Green, Bucks. Tel. Bourne End 25311 SWAP-2 PR super speakers No. 7 AVO (needs repair) NEAL 4 channel resolver (and others), want computer, add onsl p.s.u. etc. W.h.y, Mel Saunders. 7 Drumcliff Rd.. Thurnby Lodge, Leicester, LE5 2LH ^PROBLEMS WITH THAT PROJECT?^ We will - * BUILD * TEST * REPAIR All your Electronic Kits and projects. Prices from only £5.00 *Call us now for a quote.* WEB Logic Systems Ltd 15 High Street, Harpenden, Herts. V 05827-62119 / elektor September 1983 advertisement elektor switchboard dent 2000 required, must WANTED: Circuit diagrams for od condition, unfinished TRD 622 Reel-to-reel tape and idered. £56. Mr C. Fyson. pre-amplifier unit. Will pay cost hener Road, Hampton and postage. D. Jones. 60 Sutton Juthampton, Hampshire Lane. Belle Vue. Shrewsbury, Shropshire SY3 7QQ. Tel. Shrews- IX probes, two XI bury 59932. TELETEXT TV Adapter with remote control unit, woth £150 - only £85. Tel. day Gerry 629 3758, eve. 554 7267. Ilford area, collect. COMPLEX Pulse Generator, TV to 'scope converter + frequency meter for sale. All in same port- able case. £47. Inquiries to Declan Quinn. St. Judes. Patricks- well, Co. Limerick, Ireland. INFORMATION wanted on satel- lite TV, anything from rec- commended reading to circuit dia- greatly welcomed. Richard mpson, 1 Seymour Close, . Redcar. Cleveland TS11 HELP to supply or locate source for push button telephone 1C, no. CIC910 IE. Will appreciate by gifts. Iftikhar Ahmad, P616-A, Angatpura, Rawalpindi, Pakistan. DISK DRIVES, Double density, double sided. MPI # B52. Use with IBM, TRS80, etc. 90 days factory guaranteed. Only $230. David Jadid, 1 162 - 52nd Street, Brooklyn. NY 1 1 21 9, U.S.A. (21 2) 436 5261 . WANTED: Triac Pulse trans- formers and information on Hart- "T436 Scope. P. Walsh, ford St - • • FREE I enclose a valid switchboard voucher. AIR-MAIL COPY with a MAPUN MODEM KIT Exchange program* with friend*, leave or read menage* from the various Billboard services, talk to computer bureaux, or place orders and check stock levels on Maplin's Cashtel service A Maplin Modem will bring a whole new world to your computer and vastly increase its potential Now you can exchange data with any other computer using a 300 baud European standard (CCITT) modem and because the Maplm Modem uses this standard, you could talk to any one of tens of thousands of existing users Some computers need an interface and we have kits for the ZX81. VIC20/Commodore 64. Dragon and shortly Spectrum and Atari, whilst the BBC needs only a short program which is listed in Protects A Maplin Modem will add a new dimension to your hobby Order As LW99H (Modem Kit) excluding case Price £39 96 YK62S [Modem Case) Price £9.95 Full construction details in Projects Book 5 Maplin’s Fanti CiMK Wflft, -r— stic Projects NEW MAPLIN STORE OPENS IN MANCHESTER ing the full range of Maplin's electronic components, compu- ters and software will be opening 16th August. 1983 Part of the around and choose the parts you want Counter service will be available as well Upstairs you will find our computer demonstration Full details in our protect books Price 70p each In Book 1 (XA01BI 12CW rms MOSFET Combo Amplifier • Universal Timer with 18 pro- gram times and 4 outputs • Temperature Gauge • Six Vero Protects In Book 2 (XA02C) Home Security System • Tram Con- troller lor 14 trains on one circuit Miles -per-Galkm f hundreds Manchester s Oxford Road station if different soft- and about five minutes walk from for Atari. BBC. the city centre There is excellent Commodore 64, Dragon. Sord M5, parking on meters in the ad|acent Spectrum and VIC20 sideroads and we re about five You will Find us at 8. Oxford Road minutes drive straight in from opposite the BBC. between Piece (unction 1 0 on the M63 at the start dilly and the University complex of the M56 We re just a lew steps from Call in and see us soon 1 In Book 3 (XA03D) ZX81 Keyboard with electronics • Stereo 25W MOSFET Ampli her • Doppler Radar Intruder Detector • Remote Control for Tram Controller In Book 4 (XA04E) Tele- phone Exchange for 16 exten- lOHt to 600 MHr • Ultrasonic Intruder Detector • I/O Port for ZX81 • Car Burglar Alarm • Remote Control for 25W Stereo In Book 5 (XA06F) Modem to European standard • 100W 240V AC Inverter • Sounds Generator for ZX81 • Central Heating Controller • Panic But ton for Home Security System • Model Train Protects • Timer for External Sounder In Book 6 (XA06G) Speech Synthesiser for ZX81 & V1C20 • Module to Bridge two of our MOSFET amps to make a 350W Amp • ZX81 Sound on your TV • Scratch Filter • Damp Meter • Four Simple Protects In Book 7 (XA07H) Modem (RS232) Interface for ZX81 VIC 20 • Digital Enlarger Timer- Controller • DXers Audio F>ro- cessor • Sweep Oscillator • CMOS Crystal Calibrator In Book 8' (XA08J) Modem (RS232) Interface for Dragon • VIC Extendiboard • Synchime • Electronic lock • Minilab Power Supply • Logic Probe • Door- bell for the Deaf • Projects for Book 8 were in an advanced state at the time of writing, but contents may change prior to publication (due 13th August 19831 Great Projects From E&MM * 1983 * ^CATALOGUE LEARN ROBOTICS Our new book "Best of E8.MM Protects Vol. 1" brings together 21 fascinating and novel pro- jects from fJMMi first year Protects include Harmony Gen- erator, Guitar Tuner, Hexadrum. Syntom, Auto Swell. Partyfite. Car Aerial Booster. MOS FET Amp and other musical, hi-fi and car protects Order A* XH61R Price £1 £ - with Hero 1 . the new robot who sees, hears, speaks and detects movement I This remarkable microprocessor con - trolled robot is the perfect robotics training system tor industry, home and schools Hero 1 can see. hear speak detect moving and stationary all branches ^ J of WH Smith Price £1.26 Or send £1 50 (including p&p) to our mail-order address i superbly documented Order As HK20W (Robot Kit) Price £1.599 95