incorporating movement detector an ibm for alarms compatible micro auto service timer Volume 3-Number 7 EDITOR: SURENDRA IYER PUBLISHER: C.R. CHANDARANA ADMINISTRATION: J DHAS PRODUCTION: C N MITHAGARI ADVERTISING & SUBSCRIPTIONS: eIeIs cuurilb Uie important to note that the first sine wave Sin© W0V6S starts, and that the eighth sine wave ends, at a zero crossing. Fourier analysis shows that the complete signal contains integral multiples and submultiples of the fun- damental sine wave. In tests, a tone burst may be considered as a combination of a continuous sine wave and a stepped signal. This makes it possible for two parameters of a system to be measured: the sinusoidal response and the switching behaviour. It is illuminating to test an audio filter with a tone burst: it gives a new insight into the operation and quality of the filter. As stated, tone bursts are used in testing loudspeaker systems. A tone burst and a measuring microphone make possible the precise observation of diaphragm vibrations. They also facilitate the measur- ing of the dynamic range of a loud- speaker (this is the region in which the cone, i.e., the diaphragm, reacts linearly to the applied input voltage). This can be a risky test without a tone burst, because the applied power may be so great that the loudspeaker breaks down. With a Circuit description The sine waves are produced by a stan- dard sine wave generator or a function generator. The circuit shown in figure 2 monitors the zero crossing of the sine waves and uses this information to deter- mine whether the waves should be passed on to the output or not. This arrangement meets two requirements: the tone burst starts and ends at exactly a zero crossing; and the number of periods is constant irrespective of the sine wave frequency. The input stage, IC,, compares the input voltage with the potential at the wiper of preset Pj. Its output is a rectangular signal, the frequency of which is identical to that of the input signal. The off-set of the device, and the effects of a not quite symmetrical supply voltage, may be com- pensated with P,. The 22 k resistor to the + 9 V line is required because of the open collector output of the LM311. The quadrangular pulses are applied to the clock input of counter IC 2 . The logic level at the O3 output of this counter changes state every eighth period, and tone burst, this danger does not arise, because power is then applied to the loudspeaker for short periods of time ' that at the Q 4 output every sixteenth period. Both outputs are applied to NAND gate N,, so that the output of this gate is logic 1 for twenty-four periods, and logic 0 for eight periods. This signal is sub- sequently inverted by N 2 . The wave forms at the various output terminals are shown in figure 3. The outputs of N, and N 2 drive two elec- tronic switches, ES, and ESg. Because the control signal for ES, is inverted with respect to that for ES^ these switches work in opposition. When ES, is closed (and ES>2 is open), the input signal is passed to the output. When ES, is open, the input signal is no longer passed to the output, while ES 2 , which is closed, earthes the output. Resistors R 3 and i? 5 ensure that neither the input resistance nor the output resistance is too high when ES, or ES 2 is open. The circuit needs a symmetrical supply of ± 9 V, which must be well regulated, and is required to deliver a current of only 5 mA. It is important that the voltage does not exceed ± 9 V, because the CMOS ICs can stand only 18 V. 3 R 1 .R 2 = ic R3.R5 = 4; Ri = 22 k Semiconductors: ICi = LM311 IC 2 = 4024 IC 3 = 4011 IC 4 = 4066 ;s Sources See Page 7-78 Construction and setting up The tone burst generator is best built on the printed circuit board shown in figure 3. Only potentiometer P, needs to be preset, for which an oscilloscope is required. Connect the generator to a ± 9 V power supply, the sine wave oscillator, and the oscilloscope. Set the output of the oscil- lator to 1 V pp at a frequency of 1 kHz. Adjust P, so that the last sinusoidal cycle stops exactly at the zero crossing. If it stops too early, this is visible on the screen as a vertical line towards the zero crossing. If it stops too late, the sine wave will continue in a positive direction after the zero crossing. Once this point has been set correctly, the tone burst will also start exactly at a zero crossing. Finally. . . Input capacitor C x blocks any direct voltage components that may be present in the sine wave generator output. When tone burst frequencies below 100 Hz are required, it is advisable to increase the value of the capacitor to 1 \S. The signal to no-signal ratio of 8:24 in the present circuit may be altered by coup- ling different 0 outputs of IC 2 to N,. For instance, a ratio of 8:8 is obtained by disconnecting pin 5 of IC 2 (Q,) from pin 9 of N, and connecting the latter to the +9 V line. M 7.17 ^ The detector described in this article reacts to fast temperature variations caused by the movement of people or animals in an enclosed space. All mammals radiate a certain amount of heat, and it is this that causes local variations in temperature. The radiant heat energy occupies the electromagnetic spectrum between light and radio waves, i.e., 0.74. . .300 ^m, which is usually called the infra-red region. The radiant energy is picked I up by a Fresnel lens, at the focus of which is a double differential pyroelectric sensor. The detector is largely unaffected by other electrical radiation. Also, it does not react to movement outside the guarded space. infra-red movement detector for use in intruder alarms The Fresnel lens is named after the physicist A J Fresnel (1788-18271 The space to be monitored is divided by the lens into a number of zones as illustrated in figure 1. The number of zones depends on the number of segments of which the lens is composed. When somebody moves from one zone into another, there is a change in tempera- ture which is collected by the lens as a variation in radiant energy. At the focus of the lens is a pyroelectric sensor which reacts to such a change by generating a | small electric signal. That signal is pro- cessed and used to actuate the alarm installation. Lens or reflector t So far, we have spoken of the lens, but it | is equally possible to use a Fresnel reflec- tor, which is, however, much more difficult to obtain. A Fresnel lens is composed of a number j of smaller lenses so arranged that they give a very short focal length. Such lenses are used in headlights, spotlights, camera viewfinders, to name but a few. Pyroelectric sensor Pyroelectricity is the property of certain I crystals, such as lithium sulphate, of developing (opposing) electric charges on opposite faces when the crystals are heated. Infra-red intruder alarms invariably use dual element (= crystal) sensors. The elements, each measuring about 2 x 1 mm, are connected in series and in reverse polarity to each other at c. 1 mm intervals. These crystals are represented by two capacitors connected in opposition as shown in figure 4 — IR,. Any incident energy that crosses two elements sequentially causes positive and negative signals to be generated. The out- put signal will, therefore, vary over a wide range of peak to peak voltages. Since the two crystals are of reverse polarity, any simultaneous incident energy on both elements causes no output signal, because the generated voltages negate one another. Dual element sensors therefore: ■ prevent spurious operation caused by vibration; ■ are highly resistant to variable environmental temperatures; ■ prevent incorrect operation caused by external light sources, such as sun Apart from the two crystals, the sensor contains an n-channel field-effect transistor Figure 4. Circuit diagram ot the infra-red movement detector. coupled to the non-inverting input of IC, via capacitor C x . This capacitor prevents signals with a frequency of about 0.3 Hz or less from reaching the input of IC,. This opamp has an amplification of about 40 dB and cuts off frequencies above 10 Hz. Resistors R u X 2 , R 3 , and /? 6 in the feed- back network are all metal film types to ensure that the low noise factor of IC] is not negated. The second amplifier, IC 2 , is also con- figured to cut off frequencies above 10 Hz. and has an amplification of about 27 dB. As the amplifiers are operated from an asymmetrical supply, an auxiliary direct voltage is required for setting the correct operating point. This direct voltage of 3.2 V is provided by divider R B —R 2 o- The inverting input of IC, is earthed via 7?, so that the output of the opamp is always a few hundred millivolts more positive than the negative terminal of C 3 . The signal from IC 2 is fed to Schmitt trig- ger IC 3 , whose threshold is set by P,. The trigger stage is followed by a diode pump consisting of 7? n , C 5 , C 6 , D,, and D 2 . Every time the output of IC 3 goes high ( + 12 V), capacitor C 6 is charged via /?„ and D 2 , and at the same time discharged slowly via 7? 15 . The charging current through C 6 is, therefore, shaped as shown for i/ C6 in figure 6. If IC 3 generates so many pulses that the voltage across C 6 exceeds the level preset by P 2 , IC 4 toggles and its output goes low. Transistor T, then switches on and D 4 lights to indi- cate that there has been a movement. The alarm may be actuated in two ways. If wire link a-b is closed, the low output of IC 4 cuts off transistor T 2 , so that the relay is not energized. If, however, wire link c-b is closed, T 2 is switched on via T, and D 4 , so that the relay is energized. It is, therefore, possible to have an open circuit or a short circuit at terminals D-E for set- ting off the alarm. The circuit requires an operating voltage of 11 ... 15 V: our prototype worked from 12 V. Current consumption is 25 ... 30 mA, ignoring the relay and the LED, and some 80 mA with the relay energized and the LED fit. 7.20 eleklof India july 1985 Construction The circuit is best built on the printed cir- cuit board shown in figure 5, which has been designed to provide the lens holder. First, cut the board as shown in photo- graph 1 — taking care that the copper tracks are cut cleanly. The first cut should be made along the dotted line. Next, the small rectangular piece should be cut out, and then cut into two. Finally, the half- round sections should be cut out, which is best done with a fretsaw. The four sec- tions of the board are then soldered together as shown in photograph 2. This is facilitated by the small bars etched into the copper on the larger sections adjacent to the half-round parts. These bars indi- cate the exact position of the sections. Care should be taken during the cutting of the board not to saw into these bars! At a later stage, the lens is fitted into the resulting lens holder. Next, the board can be wired up; first, of course, those components that are soldered at both sides of the board: Jt t , *18. *20. c e- C* Cio. C ||, C, 2 , and D,. Then, the sensor should be fitted. These devices, like transistors, have a metal lip. When the SS02-CHK1 or the E002SX4 is used, this lip must point in the direction of IC 3 ; when the RPY94 or RPY95 is used, the lip should point to the 6 of i? 6 . Both situations are illustrated in figure 5. Soldering in of the sensor should be done quickly, because the device is heat sensi- tive. The sensor should be positioned roughly S mm above the board. Before the lens is fitted, apply 12 V to the circuit and check that there is a direct voltage of about 3.2 V between the output of IC 2 and earth. This voltage should vary by ± 1 V when you move your hand close in front of the sensor. The time has now come to fit the lens into place. First, solder four soldering pins into the four remaining free holes on the board. Then, slide the lens holder between the soldering pins into a position where the whole of the top of the sensor is visible through the centrally drilled holes in the sides of the holder. The lens holder is then soldered squarely onto the soldering pins. Finally, the lens is mounted into the holder with the line of segments pointing toward IC 5 . If this has been done correctly, the lens is set at the proper angle. The complete circuit should now be fitted into a small case, preferably of the type as indicated in the parts list. Before this is done, however, a hole the size of the lens should be drilled in the appropriate pos- ition in the lid of the case; this hole should be covered on the inside with a small piece (about 80 x 60 mm) of infra-red translucent window material. Also, two holes for adjusting the potentiometers and one for cable entry should be drilled in the appropriate places. Finally, the pcb is fitted into the case on two 15 mm insulated spacers. Calibration As already explained, IC 3 must deliver a number of pulses to ensure that C 6 is charged sufficiently to enable the alarm to be set off. How many pulses are required in a certain period of time depends on eleklor India july 1985 7.21 the setting of P 2 and on the value of /? 15 . The higher this value, the slower C e discharges: it keeps its charge longer and thus functions as a kind of energy store. With the value of 7? 15 as in figure 4, is., 4M7, the time constant, r=22 s. In this case, P 2 may be adjusted so that the alarm only goes off when at least five pulses are provided within fifteen seconds. If you find that the circuit reacts too slowly, ie., it is not sensitive enough, set P 2 to a lower value At the same time, reduce the value of 7? ls , but this should not be taken below 470 k. The setting of P, and P 2 , as well as the value of 7? ls , is largely a matter of personal preference, but P 2 should not be set to its minimum value to avoid the alarm being set off by any small pulse. The diode pump ensures that no false alarms can be given. installation The detector is best placed at a height of about 2 m (6 ft 6 in) at a downward angle of 14° from the vertical in a comer of the space to be guarded. It should not be placed in direct sunlight, nor above heating appliances. Our prototype has a reliable range of up to 12 m (39 ft). Remember also that the detector is not really suitable for use in open spaces. M Ri* = see IRi R2*.Rs*.Rii = 100 k R 3 = 10 k R4 ,Ris = 4M7 R5*.R9 = ' M R 7 = 2M2 R8,Rl2,R20* = 1 k Rio = 120 k R,3 = 33 k Rm = 150 k Ris = 15 k R,7.R2! = 2k 2 Ris = 560 a Capacitors: C1.C3.C8 = V7/25 V tantalum C 2 = 15 n C4 = 8n2 C 5 = 470 n C 7 = 330 n C8- - -Cio = 100 n Cn = 10 p/16 V C12 = 100 p/25 V 7.22 i july 1986 7.23 m | ' ■ ST compatible micro for home construction As announced last month, we now publish the details of how to build yourself a first class personal computer. Note, however, that this is a project that should be tackled only if you have a fair amount of I experience in electronics construction. The Megaboard kit produced by DTC of Texas is available with: DYNALOG MICRO-SYSTEMS 14. Hanuman Terrace. Tara Temple Lane. Lamington Road. Bombay - 400 007. Our prototype is built partly from the Megaboard construction kit. produced by DTC (Display Telecommunication Corpor- ation) of Dallas, Texas, USA, which is available from a number of specialist retailers. It is advisable to strictly follow the assembly instructions supplied with the Megaboard kit. In addition, note the fol- lowing points. 1) As the board is relatively expensive, it is wise to use IC sockets of prime quality. 2) A number of components are difficult to obtain; improvisation in some instances is, therefore, unavoidable. For instance, ■ trimmer C 8 is a two-terminal type: it may be necessary to use a three- terminal type of which one of the two rotor terminals must be cut off; ■ the resistance networks may be replaced by ''bW resistors: in our proto- type RN X was replaced by 3 x 4k7, RN 2 by 5 x 4k7, JtN e by 7 x 33 Q, and RN 7 by 7x33 Q. ■ delay line TD 2 has such a short delay time (7 ns) that we just replaced it by a wire link; ■ some of the jumper connections for the EPROM selection are angled: these may be made from a piece of double-pole connector strip; ■ jumper connection 1-3 is wrong — this jumper should interconnect terminals 2 and 3. 3) We found the instruction on how to place the shorting plugs for the EPROM 7.24 decoding somewhat vague; note, therefore, that the stated connections only apply to 2764 type EPROMs. Wire link 5-6 at E 8 is superfluous, as is 5-7 at E 9 . Also at E 9 , wire link 13-14 should read 14-15. 4) When the board is wired up, but before the ICs are inserted into the relevant sockets, it is best to check it with a 5 V supply and a voltmeter for any short cir- cuits or missing connections. 5) At ths stage, the ICs can be placed into the appropriate sockets. Most ICs are fairly conventional types, but the PROM, U 43 , the 100 ns delay line, TD,, and U 47 are not often encountered. 6) If you are using the Megaboard kit, you either have a ready-programmed PROM, or you do not need one (in case of the Super XT/PC Board to which we will revert later). If you are doing your own programming, note that Toshiba's 24S10 may be replaced by Harris's HM7611, MMI's 9301-1, or Fairchild’s 93427. The hex- dump of the program can be found on page 20 of the IBM PC manual, the RAM sub-system is described on page 18, and on page 19 is shown which wire links must be placed at E„ for the various RAM ranges (these are not stated in the assembly instructions). What has to be done at E 12 can only be seen at the track side of the board, which (not shown on the circuit diagram) has already been provided with the appropriate connections. A wire link has to be placed across ter- minals 1-2 of E n : here again, this is not mentioned anywhere. Delay line TD, is best replaced by the auxiliary circuit of figure 2, in which all eight driver stages have been cascaded, so that the propagation delay times of the gates provide the required delay. The encircled figures on the periphery corre- spond to the pins of TD,; the others are the pin numbers of the 74LS241. The prac- tical construction of the circuit is illustrated in figure 3. Although the measured delay time is a little shorter than theoretically predicted, our prototype functioned without a hitch. If you have difficulties obtaining the 75477 for the U 47 position, you can use a field- effect transistor type BS 170 or VN10KM, connected as shown in dotted lines. Power supply For convenience's sake, we have used the microcomputer power supply previously published in the August/September 1984 issue of Elektor — p. 8-46. This design can be modified as shown in figure 5: the —5 V can be omitted because the DRAMs do not need a symmetrical supply. As the 12 V section can provide up to 3 A, it is possible to use extension boards equipped with internal 5 V reaulators. Adequate cooling of the power transistors is imperative; we have mounted them on a generous heat sink, so that thermal prob- lems will not be encountered. Furthermore, we have added the micro- computer power supply protection circuit originally published in the August/Sep- tember 1984 issue of Elektor — p. 8-87 in somewhat modified form as shown in figure 7. The modification consists of S2 being replaced by a wire link and placing a push button switch in series with a 1 k resistance across D 3 . The function of the new switch is to ensure that the 12 V line is always switched off before the 5 V line, so that the read/write head of the drives can never be loaded uncontrolled at switch off. This measure is not strictly necessary with modem drives, because these are normally already provided with this protection. However, if you are not sure, or you have an older drive mechan- ism, it is safest to fit the switch! The original printed circuit board of both the power supply (84477) and the protecti- on circuit (84408) can be used without modification. Intermediate test The EPROM containing the BIOS (basic input output system) also has some self- test routines with which the operation of the mother board can be checked. First, however, we advise you to thoroughly test the power supply before connecting it to the mother board: we tested ours with resistive loads for 15 hours, but in your case, two hours should do nicely. Once that has been completed satisfactorily, the supply can be connected to the board. Then, contacts SW , and SW 2 of the DIL switch on the board should be closed ( = on = logic 0), which indicates to the MEGA BIOS that there is no arithmetic processor present, and that a RAM test need not be carried out. If the latter were omitted, the test program would try to test the RAM on the video card, and, of course, there is no RAM as yet. If everything is in order, the loudspeaker should emit a short high frequency tone some seconds after the supply has been switched on, and also when the reset switch is pressed. After that, it is best to follow the Testing and Debugging instructions. However, in our experience, neither a 100 MHz oscillo- scope, nor a logic analyser is necessary; a 10 MHz scope is perfectly adequate. Figure 4. The type 75477 1C in the U 47 position may be replaced by a MOSFET as shown. 7.26 5 Video/floppy controller card There are several video/floppy controller cards on the market, either in kit form or ready made. We have chosen a black and white video controller that was provided with a printer interface. Construction of this kit was simplicity itself, but its IBM compatibility raised a problem: IBM uses a line frequency of 18 432 MHz instead of the usual 15 750 MHz. This meant we could not use a normal monitor without some modification. This modification is an interface between the card and the moni- tor as shown in figure 8. The printer inter- face will be reverted to later. There is not much to say about the floppy controller card, other than that it is used with the Shugart bus. Only when it is con- nected to external drives is it necessary to make a connection between the drive(s) and the D connector specially provided for this purpose on the card. Connections are shown in figure 9. Case Be careful when buying the case: there are at least four versions of the mother board and each has its own case. The four cases are not interchangeable. Final test Connect the monitor, open SW,, and switch on the mains. If everything is in order, the loudspeaker, as before, should emit a high frequency tone. During the self-test procedure, the words TESTING 7.27 Figure 6. The: photographs Cards, cards. . . We received virgin as well as fully con- structed boards from a number of sup- pliers, so that we had ample opportunity to assess and compare the different MEMORY appear on the screen, followed by an alternately left and right slanting line as shown in table la. After the tone has been emitted by the loudspeaker, the content of table lb should appear on the screen, followed by the content of lc. At this stage, we ran a series of programs on our prototype: PC-DOS 2.0; PC-DOS 2.1; the entire commercial program of our accounts department (who use an IBM PC); an IBM word processor program; and an IBM flight simulator program. All these presented no problems at all. MS-DOS programs may, however, give trouble, because these are often adapted to the slightly deviating hardware of other computers. One problem we encountered here is that BASIC ROMs are not available from IBM, so that ROMs, or EPROMs, of other manufacture had to be used. Fortunately, these proved to be 99 per cent compat- ible. If you want full compatibility, it is possible to load an independent BASIC, for instance. GWBASIC. from a floppy disk. The original Mega board is of high quality and can be recognized by the inscription DTC. The copies we received were of similar quality, so they should prove per- fectly usable. But find out what documen- tation is provided with the copied boards! The Super XT/PC board appears to be of very good quality, and is cheaper and smaller than the Mega board. We have not yfet been able to test this fully, though. This board can accommodate eight EPROMs against only five on the Mega board. Moreover, just one IC is sufficient to determine which EPROMs can be selected. Figure 10 clearly shows the dif- ference in size between the two boards. With the Mega board, it is simple to choose between 64 K DRAMs ( = 256 Kbyte on the mother board), and 256 K DRAMs MEGA BIOS lications 'GOD 7.28 ele (=1 Mbyte on the mother board). It worked first time without any hitch. The appears that this can also be done with most important of these extension cards the Super XT/PC board, but nowhere in were: the documentation is it stated how. ■ black and white video card with printer In general terms, the documentation sup- interface; plied with the Super XT/PC board is con- ■ graphics colour video card with printer siderably less detailed than that of the interface; Mega board. So much so, that on quite a ■ multi-function card (memory extension few occasions we were glad to have the — clock — calendar — cartridge IBM PC manual to hand! adapter — and so on); The connections to the extension cards on ■ hard disk controller, both types of mother board are identical Other cards available include digitizers, to those provided in the IBM PC, so that digital to analogue converters, and others, all extension cards, including the hard A selection of these cards (by no means disk controller of Western Digital, could all) are shown in figure 11. be tested at once. Every one of them 1 Figure 9. Connections to g j the external floppy drives. 7.29 IBM compatible micro Figure 10. This photo- graph clearly shows the difference in size between, at the left, the Mega board and the Super XT/PC board. Peripheral devices To use a computer to the full, a number of peripheral units, such as a monitor, keyboard, printer, drive, and so on is required. We have already discussed the monitor. We have tested three different keyboards which are shown in figure 12. The Staff K4 was the least expensive, and its connec- tions are virtually the same as those of the IBM PC. The Preh Commander PCI has rather more keys, and can also be con- nected without any problems. We found the arrangement of the keys better than on the K4 and the IBM PC. The RAFI keyboard 3.94000.022 has not only the longest type number but also the greatest number of keys. In fact, there are so many that on a first glance one doubts whether they all have a purposeful func- tion: they have! It is, however, also the most expensive of the three. The best keyboard of the three? Our designers could not agree on the best compromise between performance, price, and convenience. It really is a matter of personal preference and taste. Another important peripheral is a printer. If you do not yet possess one, we can only advise you, if you can possibly afford it. to get an IBM PC compatible type. This is because the IBM PC — and the present compatible micro — offers many graphics and special characters. If you use a nor- mal printer with Centronics interface, you can, of course, print all the usual characters, so that BASIC and similar listings present no problems. The connec- tions of the relevant D connector are shown in figure 13. There are also specially modified printers available that have the IBM graphics and special characters in a PROM or EPROM. 7.30 Summary As we stated at the beginning, this project can be tackled by anyone with a fair amount of experience in electronics con- struction. The parts and components are available from specialist suppliers and. other than the few difficulties stated in the text, we had no trouble in getting them. Building this compatible yourself is cheaper than buying the ready made article only if you already have a number of the required parts, such as the power supply, drives, and so on. If you start from scratch, doing it yourself works out at about the same expense as buying an IBM PC! But, of course, when you build it yourself, you will know the machine inside out, and gain a lot of valuable experience in computer technology. And that is worth a great deal, too! H ototype RAM used as EPROM s As long ago as December 1981, we acquainted you with an easily programmed replacement for the 2716 EPROM: the IPROM. In October 1984, we introduced you to MOSTEK's 48Z02, which is compatible to both the 6116 RAM and the 2716 EPROM. It is now time to make you familiar with a replacement for the widely used type 2732 EPROM, consisting of two battery buffered 2 Kbyte RAMs type 6116, which can simply be inserted into the available EPROM socket. With a small additional extension, the circuit can also be used as a substitute for the less common type 2532 EPROM. pseudo 2732 The principle of the circuit is quite simple: instead of in a 4 Kbyte type 2732 EPROM, the data is stored in two 2.2 Kbyte type 6116 RAMs. The 6116s are mounted on a small board which can be inserted into the socket intended for the 2732. When the power to the computer is switched off, batteries take over the supply of the two RAMs. As the current consumption of the 6116s is very small, the stored data can be retained in this way for over a year. The circuit behaves, therefore, as an EPROM that may be programmed like a RAM. The circuit The circuit diagram in figure 1 shows that a total of twenty lines are simply intercon- nected: the complete data bus, the address bus up to terminal A n of the EPROM socket, and the OE (output enable) terminal. Each of these lines has been provided with a pull-up resistor to ensure uniform signal levels. These twenty lines do not further concern us here, as their function is the same as with an EPROM or a normal static RAM. As regards terminals A u and OS of the EPROM socket, it is essential that the cor- rect pin of both 6116s is connected to these, and this is ensured by a 2-bit binary decoder in 1C 3 . Pin 3 of IC 3 is at earth potential when the power to the computer is on. and this enables the decoder. The truth table for this situation is given in table 1. Of interest are the situations in which the CS line goes low. If address line A n is also logic low, output J0 becomes logic 0, and this results in 1C 2 being selected. If, however. A„ is logic 1, output J2 goes low, and IC, is enabled. Pull-up resistors R 2 i and /?22 ensure uniform signal levels. The NWDS (negative write data strobe) signal is applied to the WE (write enable) input of both 6116s via WP (write protect). This signal has quite different desig- nations (WR, R/W combined with 2 .. . .) in different computers, but is available in all of them: it is just a question of finding the line which, when logic low, enables loading the memory. If link WP is not closed, writing into the memory is not possible, and the stored data are then pro- tected. Resistor R- a is the pull-up resistor for this line. The necessary change-over to the back-up battery has been kept as simple as poss- ible: when the supply from the computer is present, D 2 conducts, and when it is not, D! conducts. As the cathodes of these diodes are connected in opposition, and either the supply from the computer is higher than the battery voltage, or vice versa, there is virtually no change-over If a NiCd battery is used, this is charged via 7?24 when the computer supply is present. • When the supply from the computer is present, D 3 lights, and T, is on. The G pin of IC 3 is then connected to earth and the .n decoder in IC 3 is enabled. Diode D 3 should be a red LED: the different resist- ance of LEDs of another colour would shift the switch-on point of TY It is clear from the above why IC 3 should be an HC or HCT type: the decoder It is theoretically possible that the circuit malfunctions, but only through a fault of the computer. It may happen that for some reason the supply voltage in the computer rises relatively slowly after switch on. The power-on reset is then actuated relatively long after switch on, and in the interval spurious pulses may cause erroneous writing into the RAMs. This can be prevented by connecting X 23 to the junction of D, and D 2 instead of to the computer supply as shown in figure 1. needs power even when the supply from the computer is off. This power is. however, very small: in stand by operation, the current consumption is less than 10 jiA. 7.33 5 2532 extension To enable 2532 EPROMs also to be replaced, it is necessary to construct an adapter plug from two 24-pin 1C sockets: the interconnections are shown in figure 5, The 2732 socket must be the higher one of the combination. This adapter plug can also be used to substitute a 2732 EPROM for a 2532 type in an existing circuit (but not during programming!). A tip It may be beneficial to reread the article universal memory card in the March 1983 issue of Elektor (UK), which contains some fundamental and important information regarding CMOS RAMs, particularly the 6116. It also explains the necessity of pull- up resistors. H 7.34 elaktor indi. interval timer service One hundred years ago the horseless carriage was born, and what a birth that was, for the motor car, after a timed youth, has now become an indispensable part of our modern way of life. A century of development has, of course, brought about much improvement, fortunately so, as even a short quarter-century ago there were plenty of cars needing servicing every 500 or 1000 miles. Now the service interval for many cars is 12 000 miles. Ideal though this might seem, it is not faultless. Twelve thousand miles is more than six months driving for most people and it is easy to forget whether the last service was at 16 934 or 19 364 miles. Furthermore, mileage is only one of the factors that should be taken into account in considering when a car should be serviced. The speed and temperature at which the engine is run also play an important part. A few (expensive) cars today provide the driver with an indication of how close the vehicle is to needing a service. Our circuit is modelled on these and bases its judgement on the three factors we have already mentioned. It then provides an indication by five LEDs, three green 'nothing to worry about', one yellow 'service not yet needed', and one red 'time for a service'. warns to have your car serviced Few and far between are the cars that today require any service attention at intervals shorter than every 6000 miles and even that is usually little more than an oil change. Service intervals are still, how- ever, stated as if the distance covered was the only important factor. This is, of course, not so. The engine requires regular attention but how often is a func- tion of how hard it is used. Car manufac- turers play it safe and specify a conservative service interval although they, more than anyone, know that neither hours of service nor distance covered is an infallible indication as to the engine's condition. 7.35 One car maker in particular, BMW, has questioned its customers extensively about how they use the car. A number of distinct types of journey were identified: short trips, starting from cold, long trips, consistently high-revolution running, and economical driving. A distinction could then be made of the most important fac- tors affecting significant engine com- ponents. The studies revealed four factors that are of primary importance: ■ the temperature at the start of a trip; ■ the engine speed; ■ the engine temperature; and ■ the distance covered since the last service. We will look at these in turn. The initial temperature This is of vital importance to an engine's health. At our latitudes the winter is not necessarily warm (like last winter, for example). The lower the ambient tempera- ture, the longer it takes a car to reach cor- rect operating temperature. For the sake of our circuit, we have not made a point about measuring the engine's temperature but have just divided it into two ranges: above and below 50°C. Engine speed In general, there is a point at which a car's fuel consumption increases noticeably. This occurs about half-way between the torque peak and maximum power. Every car is different, of course, but we have taken 4500 rev/min as an acceptable value. Operating temperature Every engine has a specific operating 1 temperature at which it works best. If the actual temperature is lower than this ideal, the engine suffers. Distance covered This has, until now, been the only factor quoted with reference to service intervals. As we know that just distance is not enough, we add the other factors stated and arrive at the following formula for effective distance: D, = [D(l + P, + P,)/R a ]km where D, = effective distance in km; D = measured distance in km; P t = tempera- ture penalty; P, = rev/min penalty; and R a = average engine speed for the journey. We picked the brains of the automobile industry for the values in the formula. For engine speeds above 4500 rev/min P, has a value of 0.5; below this point P, is 0. If the engine temperature is less than 50°C P, is 1; above 50°C P, is 0. What all this means for our circuit we will now see. Block diagram The block diagram of figure 1 shows that this circuit contains three sensors: number of wheel revolutions = distance; tempera- ture above or below 50°C; and engine speed above or below 4500 rev/min. It also has a section that makes a correction for the size of the wheels and this is con- nected to a divider and a display. We will look at each section in turn. The distance sensor gives one pulse for every revolution of the car's wheels, which is translated into a certain number of pulses per kilometre (or mile). We con- sider this to be a better idea than an 7.36 ,i. 7.37 in Elektor before (in September 1984, to be exact). It takes the pulses provided by the car’s contact-breaker (c.b.) points and shapes them into a useable form. It out- puts a train of regular pulses that is applied to monostable MMV, which, in combination with MMV 2 , forms a fre- quency detector. The 0 output of MMV , remains high for about 6.6 ms (determined by T=jf 6 C 3 which corresponds to 4500 rev/min in a 4-stroke 4-cylinder engine. The actual frequency detected is 150 Hz, given by 4500/60 x 2 (rev/min divided by 60 times 2 pulses per engine revolution). Below 4500 rev/min, MMV,'s Q output is pulsed; above this value, the monostable is retriggered so the output is constantly high. The Q output of MMV 2 is therefore permanently high and so also is input P, of synchronous decimal counter IC 6 the output of which is therefore either logic 1 or 0. The detector (a VDO pulse generator. Hall-effect device such as Siemens' HKZ101, or a reed relay and magnet arrangement) is connected to the revol- ution counter input. We will return to the set-up with a VDO sensor later in this article. Every time the wheel makes a complete revolution, the TR input of monostable multivibrator IC 10 receives a pulse and then outputs a pulse whose duration is given by T=2 48 RC. In our cir- cuit this works out at about 30 ms so that bounce in the detector will have no effect. A Hall-effect sensor is, of course, bounce- free. The 0 output of this MMV then pro- vides the clock signal for IC 6 . Four NAND gates, N 5 . . .N 8 , together form an XOR gate which combines the different signals provided by the temperature and engine speed sensors. If both of these factors are 'unfavourable' a logic 0 is applied to input P 0 . The three parallel inputs of the 40160, P 0 , . ,P 2 , accept a 3-bit binary word that can be 000, Oil, 101, or 110. These corre- spond to decimal values of 0, 3, 5, and 6 and represent no penalty; a temperature penalty; rev/min penalty; and a combi- nation of both, respectively. The 40160 counts from this input value up to 10. The relation between all the factors in question is shown in table 1, where we see the penalty in each case, the binary word input to IC 6 , and the count needed. This latter is always the quotient of the number 10 divided by the penalty factor. At optimal operating conditions, output pin 15 of IC 6 gives one pulse per ten wheel revolutions. This CARRY OUT signal is applied to the LD terminal via inverter N 9 so the IC starts counting again from the input value. Two programmable syn- chronous down-counters, IC 3 and IC 4 , form a 16-bit programmable divider, in which every rising edge of the clock signal decrements the count starting from the value applied to inputs .J 7 . When the count reaches zero the CO/ZD output becomes active (logic 0). The values that should be fed to the J inputs are shown in table 2 and the circuit is thus tuned to the size of the wheel at which the sensor is. This is done by links a. . ,k. As for the remaining links, 1 is linked to + 5 V and m. . ,p to earth. This gives us a range of divisors between 2048 and 4096, but we are only interested in those between 2169 and 3236. The circumference of the wheel is taken to be the theoretical value; perfectionists may consider measuring the actual circumference but that is not really necessary. As we have already hinted, the VDO pulse generator is a special case as it is already present on some cars' odometers (distance meters). The magnetic sensor generates six pulses for every rotation made by the speedometer cable. Where this sensor is fitted (on many Volvos, Mercedes', Opels, VWs eto.) a number between 542 and 975 is inscribed on the case. If the sensor is numbered 700, for instance, the cable makes 700 rotations per kilometre and the sensor outputs 700x6 = 4200 pulses in this period. For our circuit we want to reduce this to a single pulse per fifty kilometres so we multiply this number by 50 and then divide it by 10. This gives us the desired divisor of 21 000, from which we subtract 1 and con- vert the result (20 999) to the binary number indicating the straps must be set. This procedure is clarified by the example in the margin here. What we achieve by all this is that the 5PE output provides one pulse for a 'real' distance of 50 km. Another programmable synchronous down-counter, IC 5 , is used to define the number of 50 km intervals counted before sending one pulse to decimal up/down couhter IC U . Keeping things metric, we have assumed that the service interval is 10 000 km so the distance between the lighting of suc- cessive LEDs is 2500 km. The divisor of IC S is then 50. The actual programmed divisor is 49 as we must always subtract 1 from the desired value. The resulting binary value of 110001 is fed to inputs ] 0 . . J 7 of IC 5 . Straps v, u, and q are tied to + 5 V and r, s, t, w, and x to earth. Each pulse provided by the ZD output increments ICn, making the next output I active and lighting the next LED via | inverters N ]3 . . . N The final (red) LED is j made to flash by the multivibrator con- ‘ sisting of NAND gates N 3 and N 4 to draw | the driver’s attention to the fact that a ser- | • vice is due. J Two sections of the circuit have not yet been described, the first of which is 7.38 called RST (reset). This consists of a pair of contacts connected to N 2 . When the car has been serviced, these two contacts are closed briefly and the whole circuit is At the lower right-hand comer of the cir- cuit we see a NiCd 4.8 V battery that is kept charged via R, 9 . The charging cur- rent is taken as i/as of the nominal current which is 20 mA in this case. The car bat- tery voltage and Ohm’s law (R=U/I) give the resistance. For a 12 V car battery R, 9 will be about 600 Q. Construction The printed circuit board shown in figure 3 reduces construction to a matter of correct and careful soldering. First, however, the board must be cut into two. As usual, make sure that semiconductors and electrolytic capacitors are fitted with correct polarity and we recommend that good quality sockets be used for the CMOS ICs. Check that all the links are fit- ted as there are a full dozen, not including those needed for programming. Nine short lengths of flexible cable are needed to interconnect the two boards. When you are sure the circuit is working correctly, the two boards can be fixed together like a sandwich, with the components in the middle. The LEDs must be mounted such that they all face forward. For the sake of aesthetics, rectangular LEDs can be used but if the red LED is not striking enough, a round version will give a better indi- Connections The temperature detector The vast majority of modem cars have a water temperature gauge and the simplest solution for our circuit is to tap the wire leading from sensor to meter and feed it to the circuit at point T. Then preset P, is adjusted (with the car at operating tem- perature) so that the output of IC 2 is low. A separate temperature sensor, used pure- ly for the service interval timer, could be fitted. If this is necessary, it is important 7.39 »»»• that the sensor gives an output voltage directly proportional to the temperature, certainly in the range that is of interest to us. Such a sensor might also have to be earthed separately instead of using the single central earth that is sufficient for our circuit. The distance sensor We have already talked about the special situation presented by the VDO pulse generator. This, of course, requires no mounting as it is a standard fitting in some cars. All that is needed is to link its output to terminal D of the PCB. Failing this, either a Hall-effect sensor or a reed relay plus magnet can be mounted to give one pulse per wheel rotation. The reed relay/magnet solution requires care to avoid having the result corrupted by other magnetic effects in the car. Magnetism holds no fears for the Hall-effect sensor but, as figure 4 shows, the mounting pos- I ition of this sensor is rather exposed. The engine speed sensor The engine speed measurement is based on the pulses provided by the c.b. points. All you need to do therefore is to connect terminal D to the line from the coil to the c.b. points. Programming the dividers The fitting of links a. . x depends on the programming factors chosen. Start by inserting a. . .k to suit the size of the car’s wheels. For a normal 13 inch wheel, for example (165/13, 155/13, etc.) the links must form the binary value 01001 0101 1001. It is clear from the printed circuit board itself how to program a logic 0 or a 1. Next you have to program the distance. During the description of the circuit we have taken a distance factor of one pulse per 50 km. This was chosen for sim- plicity's sake (and not through some zeal to' banish the good old mile), but if a dif- ferent value is chosen the programming is different. Actually it is far better to accept this one pulse per 50 km and add the cor- rection you want in the next stage. In the text we have assumed a service interval of 10 000 km, corresponding to one pulse per 2500 km for the stage in question. Your car owner’s manual probably states the service interval both in miles and kilometres but should this not be so or if the interval is not 10 000 km, IC 5 must be programmed accordingly. A service inter- val of 15 000 km gives a divisor of 15000/4x50 = 75 resulting in a binary value of 100101ft The circuit can cater for ser- vice intervals up to 51 000 km and if you dare go that far without visiting a garage, don't expect any sympathy from us if you have problems. Fitting the circuit The circuit should be mounted so that the driver sees the LEDs when they light and then the various connections must be made. It may also be fitted under the car bonnet where it will be seen when check- ing the oil or water. The circuit is reset by bridging the RST contacts and the first LED should then light. All that then remains is to check that the other LEDs light at the right times (about every 2500 km in our example). In most cases, this will be 5 to 10 per cent less than the theoretical distance (between 2250 and 2375 for a theoretical value of 2500). Assuming again that we expect the LEDs to light at 2500 km intervals, the red LED can be expected at 9000. . .9500 km. This circuit is no intended to supplant all other forms of car maintenance. It remains just as important to check the oil and water regularly but the service interval timer will give you an idea of how mechanically sympathetic you are. Then you can plan your servicing more sen- sibly, and that is certainly laudable in these days of ever-increasing garage charges. M Literature: Automonitor Eiektor May 1985 For Components Sources See Page 7-78 7.41 -itograph electronic pantograph for use with a computer A pantograph is an instrument with jointed rods for copying plans, drawings, etc., on any scale; the electronic version described in this article does so in graphics form on the monitor of a computer. It may also be used for drawing or writing direct onto the screen. The instrument is connected to two analogue to digital (A/D) converters, which translate the coordinates into digital signals. Figure 1. This diagram illustrates the operation of the pantograph. Co- angles a and It according to the following formulas x, = /?lcosUf-] +■ sin,;] At the point of origin in figure 1 is a potentiometer to the spindle of which one of the rods of the pantograph, of length R, is connected. When that rod is moved, the potentiometer setting is changed. If the potentiometer is positioned such that it is at zero when the rod coincides with the negative x-axis, its angle of rotation in figure 1 is o. At the end of the rod is a second potentiometer, to whose spindle a second rod is connected, also of length R. The connection between the second potentiometer and second rod is such that the potentiometer is at zero when the two rods coincide. The angle of rotation of the second rod, and consequently the second potentiometer, with respect to the first rod is p. The coordinates of the end of the second rod, are calculated from the length, R, of the two rods, and the angles a and p. Since the potentiometers are potential dividers, the voltage at their wipers is directly proportional to their angle of ro- tation. These voltages are translated by analogue to digital converters into binary digits (=bits) from which the computer can calculate the x and y coordinates. As the total reach of the pantograph is 2 R, the drawing area should be a square with sides 1.414/? or a rectangle with a long diagonal of 2 R. Note that the pantograph is intended for use in the first and fourth quadrants of a polar diagram; our proto- type is for the first quadrant only. The electronics The electronics required for the transfer of the analogue output of the poten- tiometers to the A/D converters is minimal, as shown in figure 2 for one potentiometer. The signal from pantograph potentiometer P, is applied to the non- inverting input of operational amplifier IC,. The inverting input of IC, is con- nected to P 2 which serves to set the point of origin (i.e., compensates for the offset of the opamp). 7.42 elaktor in A second operational amplifier. IC 2 , pro- vides direct voltage amplification as required; the gain may be set between 0 dB and 21 dB with P 3 . The output of IC 2 is fed to the A/D converter. Each pantograph requires two circuits as shown in figure 2: one for each of its potentiometers. The power supply for the circuits must be well regulated: its current consumption amounts to only a few milliamperes. The A/D converters may be constructed as described in digitizer in the May 1985 issue of Elektor. If you use this, you need only one because it has switched inputs. The mechanics The mechanical part of the pantograph is fairly simple and will not be described in detail, because the construction depends largely on the materials used. It is import- ant to use good quality potentiometers; we found the best linear behaviour in ten-tum wire-wound types. The rod connected to the potentiometer in the point of origin must be mounted so that it can move freely between the negative and positive y axes. The second rod must be fixed to the / gives the number of clock periods for which a specific digit is on (5 bit word) Display-Data ASClI-Charat Display-Data ASCII-Ch 01000001 01000010 01000011 01000100 01000101 01000110 01000111 01001000 01001001 01001010 0100101 1 01001100 01001101 01001110 01001111 01010000 01010001 01010010 01010011 01010100 01010101 01010110 01010111 01011000 01011001 01011010 01011011 01011100 01011101 01011110 01011111 00100000 00100001 00100010 00100011 00100100 00100101 00100110 00100111 00101000 00101001 00101010 00101011 00101100 00101101 00101110 00101111 00110000 00110001 00110010 00110011 00110100 00110101 00110110 00110111 00111000 00111001 00111010 00111011 00111100 00111101 00111110 00111111 this byte. The left-most display in the diagram is number 1. Below 0 the count continues downwards from 16 so digit 1 has a decimal value of IS and digit 2 a value of 0. The Load Digit Counter code is normally used in initialising to indicate the number of digits used. The multiplexer frequency is then modified to suit the number of active digits. For 16 digits the code used is 0. Load Duty Cycle determines for how long the display is switched on and off and in this way the brightness can be set. Each digit has 32 clock periods available and can be switched on for a maximum of 31 of these. They must be off for at least one clock cycle out of every 32. After a reset pulse (which is always a consequence of switching on the supply voltage) the following occurs: ■ the digit and segment drivers are all switched off ■ the Load Duty Cycle 'on' time is set to 0 ■ the Digit Counter is set to 16 (bit code 0) ■ the Load Buffer Pointer is set to 15 (= digit 1). After this the desired control information must first be provided. The order is not important: Load Duty Cycle Load Digit Counter Load Buffer Pointer Then come the ASCII codes. The buffer pointer is automatically incremented after each data word, except in the case of decimal points and commas. After digit 16 the pointer jumps to digit 1. If the digit counter is programmed so that not all the digits are used the duty cycle must be carefully chosen. If the number of digits used is 8, for example, the duty cycle must not be higher than 16, with 4 digits it is 8, and so on. If this is not done there is a danger of the display burning out. There are a number of points to bear in mind when programming the processor. The clock and data line must be reset to zero immediately after switch-on or the circuit will act strangely. Timing also requires a certain amount of care. There must be at least 40 ps between the end of one data word and the start of the next. There must also be at least 120 ps between the start of one data word and the start of the next one (this is shown in figure 3). The display module has certain power requirements. It needs + 5 V (supplied by the computer system), —24 V d.c. (with respect to the processor system’s ground line) and an a.c. supply of 6 V. The information in this article should be sufficient for you to write a program to show the desired characters on the display. Further information on the theory and background of the actual display can be found in the applicator on page 6-58 of the July 1983 issue of Elektor. M Literature: Rockwell datasheet — 10937 alphanumeric display controller. Elektor July 1983 — applicator, page 6-58. 7.54 elekto While here on earth we discuss, seemingly ad infinitum, the pros and cons of alternative energy sources, there is not far from us — a mere 90.5 million miles (149.5 million kilometres) — a nuclear plant that has been going for the best part of 5000 million years and is estimated to go on for another 10000 million years. The amount of energy this factory releases through nuclear fusion each second (it converts 600 million tons of hydrogen into helium at a temperature of 15 million degrees Celsius every second) is enough to meet our earthly needs for energy for a million years. That factory is, of course, our sun. solar battery Although we know that the sun radiates all that energy into space — only an infinitesimally small part of it is absorbed by the earth and other planets in our solar system — we do not really know how to harness it on a large scale. How can we convert the solar energy falling onto earth into electric energy for powering our industries, transport, heating and lighting systems, and others? Heat and electricity Who has not tried to set fire to a piece of paper with a magnifying glass? This is one of the oldest methods of converting solar energy. Archimedes used it suc- cessfully — with the aid of a parabolic mirror — in the defence of Syracuse. In a parabolic mirror, the energy falling onto a large area is optically concentrated in one point, called the focus. This leads to very high temperatures at the focus, which may, for instance, heat the water in the boiler of a steam engine that is used to drive an electric generator. A second method of gaining heat from solar energy has come about in the last decade: large solar collectors placed in south-facing roofs of buildings. In these, there is no focusing of energy; instead, water Dows through the longest possible path just under the surface of such collec- tors and is heated direct. This method is based on the principle of the heat exchanger. A third method of using solar energy lies in the direct conversion of solar energy into electric current, and it is with this method that the present article is con- cerned. However, do not think that it will be possible to make use of a large part of the radiation released by the converting of hydrogen to helium at the core of the sun, as some simple arithmetic shows. The sun radiates equally in all directions. As the average distance from sun to earth is about 150 million kilometres, the (electro- magnetic) radiation takes about 8 minutes to reach the earth. In those eight minutes, the total energy radiated by the sun has spread over the inside of a sphere of sur- face area 3 x 10 17 km 2 . The total surface area of the earth that is being fit by the sun at any one time amounts to only 113 x 10 6 km 2 . Even if we were able to cover that whole area with solar cells, we would receive only 3 tenthousandmillionth parts of the totally radiated energy. The rest (virtually all) is lost in the universe. However, the situation is not as hopeless as at first sight it may look, because only 1 the answer to our energy problems? india jul* 1985 7.55 2 1N4148 19 000 km 2 of solar cells would receive enough energy to meet the estimated world demand for the year 2000. Construction and operation of a solar cell After the astronomical figures of the last section, we return to earth and the microscopic dimension of the cross sec- tion of a solar cell. The thickness of the cell shown schematically in figure 1 has been highly exaggerated in comparison with the surface dimensions. A solar cell uses the photovoltaic effect to convert radiation from the sun into elec- trical energy. The photovoltaic effect arises when a junction between a metal and a semiconductor or two opposite polarity semiconductors is exposed to electromagnetic radiation, usually in the range near-ultraviolet to infra-red. A for- ward voltage appears across the illuminated junction and power can be delivered from it to an external circuit. The p-n junction of which the cell consists has a relatively large surface area and relatively high efficiency (10 . . . 15 per cent). Solar cells are fabricated mainly from silicon, gallium arsenide, selenium- cadmium sulphide, and thin-film cadmium sulphide. As part of the radiation is reflected by the surface of the cell, an anti-reflect layer is incorporated to minimize reflection. The absorption coef- ficient is large for short wavelengths, and smaller for longer wavelengths. The efficiency of solar cells reduces by about one half per cent for each degree centigrade rise in their body temperature, so that most cells must be suitably cooled. 3 Note, however, that this depends to a large extent on the material; gallium arsenide/gallium phosphide, for instance, has optimum efficiency at well over 100°C. The spectral response curve of a silicon cell indicates a useful range of wavelengths between 0.5 |im and 1.0 ^m, peaking at about 800 |im. Angle of incidence and atmospheric absorption Placing the cells at right angles to the sun ensures that the highest possible amount of radiation falls onto the cell surface. It should, however, be noted that at our latitudes it is never possible to equal the amount of radiation that can be received in regions between the tropics of Cancer and Capricorn. The reason for this is that the distance the radiation travels through the atmosphere is shorter in these regions than at more northerly or southerly latitudes. Solar battery charger The circuit of a solar battery charger, designed and tested by us, is shown in figure 2. It consists of twenty single solar cells connected in series. In the calcu- lation of the required charging voltage, allowance must be made for the 0.6 V drop across diode Dl. This diode is necessary to prevent the electrical battery discharging through the solar cells. Specifications and technical data supplied by the manufacturers of solar cells must be treated with caution as they normally refer to optimum incidence of radiation, which, owing to climatological and geographical factors, cannot always be realized. It is true that even under moderate light conditions the no-load voltage of a cell is about O.S V. However, the current produced by the cell is a func- tion of the incident light radiation: this is shown schematically in figure 5 where the voltage/current characteristic of a cell moves further and further to the right with increasing radiation. The characteristic in figure 4 shows the voltage/current relation of our solar bat- tery charger. Measurements for this curve were taken on a sunny November day, in mid afternoon, at a latitude of about 51°N. Note that the maximum current is just about 20 mA, which is sufficient to charge a small electric battery. Increasing the load caused a voltage breakdown. It is clear that the optimum operating point is at the knee of the curve with the Electricity Board. This is because for the generation of one kilowatt of power a solar battery with a surface area of 10 m 2 is required. As prices are still around 50p per square centimetre, that one kilowatt of power would be very expensive indeed — certainly compared with the few pence charged by the Elec- tricity Board. None the less, solar cells have become, and will remain, the most important long-duration power supply for satellites and space vehicles. H Construction of the solar battery The fragile solar cells are connected together with thin, flexible stranded wire. Solder one end of the short length of wire to the front ohmic contact (positive ter- minal) of one cell and the other end to the underside (contact plate) of the next cell as shown in figure 3. Where the solar bat- tery is placed in the open, it is advisable to protect it from the environment by, for instance, housing it in a transparent or translucent case. Economics of solar cells Although solar cells provide a promising alternative source of energy, the time is not yet ripe for terminating your contract 7.57 To put your mind at rest: the title does not imply that the circuit described here enables a computer to see. But if you want to use your computer for controlling external equipment without connecting this direct to the computer, the proposed circuit will 'keep an eye' on certain output signals of the computer and on that basis switch the equipment on and off. In other words, it provides an optical coupling between the computer and the equipment to be controlled. This does imply, of course, that a monitor screen is available and that the computer has some graphics facilities. Otherwise there would not be much to see for the eye! computer eye control by monitor screen The circuit is based on an opto-electronic comparator as shown in figure 1. The ‘eye’ proper is formed by two light-dependent resistors — LDRs — R1 and R2. The voltage level at their junction is applied to the inverting input of the comparator, IC1, via R4. The non-inverting input of IC1 is held at a fixed reference voltage. The comparator toggles when the level at its pin 2 is lower than the reference voltage. Transistor T1 is then on, and the relay is actuated. At the same time, T2 conducts, so that the LED, Dl, lights to indicate the state of the circuit visually. When the level at the inverting input of the comparator is higher than the refer- ence voltage, the relay is not energized, and Dl is out. The idea is that the control program includes instructions which cause two light areas to appear on the monitor screen as required. The intensity of one of these areas should be constant, while that of the second should be either low or high (dark or light). The preferred mode of operation is for the second area to be dark when the external equipment should be switched on, and bright when it is to be. switched off. The LDRs should be attached to the moni- tor screen where the two light areas appear. The voltage (about 2 V pp ) at the junction of these resistois is a measure of the difference in brightness between the two light areas on the screen. Super- imposed on this voltage is, of course, the sawtooth voltage produced by the 50 Hz line scan oscillator. Resistor R4 and capacitor Cl, and to some extent PI, ensure that this sawtooth voltage does not 7.58 1 affect the correct operation of the com- parator. Construction of the circuit is not critical: all components, except the LDRs, are fit- ted on a small prototyping board. The LDRs are connected to this board by suffi- ciently long pieces of stranded equipment wire. It is recommended to fit them in suitable shrink sleeves or swathe them in insulating tape in such a way that only the light of the two areas on the screen falls onto them (see photograph). They can be attached to the screen with some self- adhesive tape. If the equipment to be con- trolled is switched on when it should be switched off, and vice versa, simply inter- change the LDRs. Presetting of the comparator is not critical as long as the change-over frequency of the two light areas is of the order of 1 Hz. In that case, PI is simply set so that the relay is actuated and de-energized in rhythm with the change-over frequency. When that frequency is higher, e.g. when the circuit is used for data transfer, the presetting of PI becomes more critical. The maximum allowable change-over fre- quency depends on the cut-off frequency of the low-pass filter, R4/C1, which here is less than 10 Hz. Optimum setting of PI is then best achieved by applying a square- wave voltage at a frequency of about 8 Hz to the comparator input. Measure the out- put at pin 6 with an analogue voltmeter (10 V d.c. range) and adjust PI so that this level is half the value of the supply voltage. Although the pointer of the voltmeter quivers somewhat, the setting can be carried out without any trouble. If you have an oscilloscope, it is, of course, preferable to use that for the presetting. Note that the current through the relay coil should not be too high: when a BC 547 is used for Tl, it should not exceed 100 mA. That means that the resistance of the coil should be not less than 50 Q for a supply voltage of 5 V, and not less than 90 Q at 9 V. The rating of the relay contacts depends on the equipment to be con- trolled. Current consumption of the circuit amounts to only a few mA plus the current drawn by the relay coil. For data transfer operation only, the relay is not required: the signals are then taken direct from the collector of Tl. M Did you know. . .? Robot has come to mean an intelligent and obedient but impersonal machine; it is derived from the Czech robota — forced labour. The word robot was first used in Karel Capek's play Rossum's Universal Robots (1920). (OED) Gain is a ratio, normally expressed in dB. For an amplifier it is the ratio of output power to input power; for an aerial, it is the ratio of the voltage produced by a signal entering along the path of greatest sensitivity to that produced by the same signal entering an omnidirectional aerial. Although often used as such, it is not synonymous with amplification, which is a number indicating by how many times an electronic device increases an electrical signal. Gain is, therefore, 10 or 20 times the logarithm of the amplification, depen- ding on whether that refers to a power or a voltage increase. M i July 1985 7.59 m Soldering Techniques Soldering is the most common method of connecting electronic components and conductors together to construct a circuit. The technique of soldering is briefly introduced here. Soldering Iron and Solder Wire. I * A 15 or 25 W soldering iron is the most convenient for soldering work involved in SELEX projects. It can be purchased from any good electronics shop. • Good solder wire consisting of 60% tin and 40% lead should always be used for good results. The core of the solder wire is made of flux which melts and evaporates while soldering and prevents oxidation. 1 mm thick solder wire should be preferably used. • A stand for the soldering iron can easily be constructed or purchased. • Soldering fluids/pastes etc. should be avoided. This may cause the soldered joints to corrode in future. Preparation for soldering. • The leads of components which are to be soldered must be clean and free from oily & greasy substances. They may be cleaned with spirit if necessary. • All the components should be properly positioned and the leads should be slightly bent on the track side of the PCB after inserting them through the holes. • Soldering iron should be turned on. and its tip should be cleaned after it becomes hot with a piece of cloth or moist sponge to remove all oxidation residue before starting the work. • Tip of the new soldering iron must be tinned at first. This is done as follows: The tip is heated sufficiently so that the solder wire quickly melts over it. The molten solder is wiped off and new solder wire is applied once again. This is repeated till the tip gets a uniform tin coating. • The tip of the soldering iron should never be cleaned with chemicals or files etc. Soldering • Both the surfaces to be soldered together are heated with the soldering iron tip. • Solder wire is now applied. The molten solder must easily "Flow''. Supplying the correct quantity is a matter of practice. • The tip of the soldering iron is withdrawn within 1 or 2 seconds, and the soldered joint is allowed to cool. During this period there should be no movement at the joint, since it develops fine cracks in the soldered joint. • A good soldered joint should look like the one shown in figure 3 (1st Sketch). * The components and conductors should not become too hot during soldering. This is particularly very important in case of semiconductors The lead can be held with forceps to dessipate some of the heat. Conclusion * The lead ends which are jutting out can be snipped off at the soldered joints, with small cutting pliers. While cutting these bits of wire fly like small missiles. take care that none of these hit your eyes. * To prolong the life of the soldering iron tip; it must be wiped clean and switched off after the soldering work is over, or in case you are going to stop for more than 1 5 minutes. * Dabs of soldering materials can be cleaned with petrol or nailpolish-remover. These solvents should be sparingly used as they can also dissolve the printed component layout on the PCB. Digi-Course Chapter : 3 More about 'GATES' The last chapter of this series dealt with NAND and NOR gates. Both have originated form the logical functions AND and OR respectively by adding negation (interchanging "I" and "0"). Figure 1 shows the symbol for NAND gate and its truth table. The truth table shows how the output of the gate behaves in response to the two inputs. The output and inputs are characterised by "1" and "0" where "1" means that the voltage at the corresponding connection is 5V and "0" means it is at OV. On the Digilex Board, the input values of "0" or "1 " are introduced by connecting the input terminal either to the OV line or the 5V line. The output states can be observed using one of the Red LEDS, by connecting the output of the gate to one of the pins A H, The truth table for the AND operation is also included with the NAND truth table for comparison, in figure 1 2 Figure 2 shows the symbol and the truth table for the NOR gate. The symbols and tables naturally remain abstract theory, so long as no concrete informations are attributed to the logic states. Let us take a small example. Consider the sentence: "Mr. OUT goes to work on the bicycle, when it NEITHER storms NOR rains.” The sentence includes the same logical condition as that in the NOR gate. Now if we denote storm by ”1 ” and no storm by "0" and feed this information at input A, and denote rain by "1" and no rain by "0" and feed this information at input B, then the output shows, whether Mr. OUT can go to work on his bicycle ("1") or not ("0"). The NAND, NOR gates are very universal. By connecting their two inputs together, they behave like NOT gates (inverters), and by connecting these inverters to the NAND, NOR gates we can get back the original gates AND and ORI 7.62 elektor India July 1985 °' 7.64 Transformers Unfortunately, the large power requirements of household and commercial appliances cannot be supplied by the dry cells. For such requirements we must turn to another source of power-namely the mains supply. The mains supply voltage is 230 Volts and is perilous to life! Considering the battery prices, sooner or later, one has to turn to the mains supply as a cheap power source. However, we do not always need such a high voltage as 230 V. A device used for changing this level to the desired level is called a Transformer. The mains voltage is an alternating voltage. A transformer can either increase or decrease the voltage level and depending on this function it is either called a step-up or step-down transformer. Transformers can work only with alternting voltages. The simplest transformer has two input and two output connections, (so called primary and secondary sides) The input (primary side) is connected directly across the mains supply of 230 Volts. The output connections (secondary side) provide a lower voltage in case of a step down transformer. Such a simple transformer is illustrated in figure 1. 7.65 recast The voltage available at the secondary side is very safe, as its level is low, and moreover, it is completely isolated from the mains supply as there is no interconnection between the input and output terminals. The output terminals, which have 9 Volts in this case, can be touched without any risk. The secondary voltage level depends entirely upon the design of primary and secondary windings and need not always be 9 volts. Hence, before purchasing a transformer one must know the value of secondary voltage required. (Secondary voltages above 42 V are not safe for touchingl) Figure 2. Transformer with two independent secondary voltages Transformer with multiple outputs. Mains Voltage Some rules to observe. A list of rules to be observed during construction and testing jobs on circuits which carry mains voltage is given below for ready reference: 1 . Construction ■ All conductors carrying mains voltage must be insulated in such a manner, that they cannot be touched when the enclosure is closed, not even with the help of a long thin rod or wire. ■ All metalic parts which are accessible from outside, must be earthed. Even a master switch with metalic handle must be earthed though it may be installed in a plastic casing. ■ The mains cord must be brought out through a securety fixed insulating grommet on the enclosure, in case the supply is not through a socket on the apparatus. ■ The three cores of the mains cord must be fixed in a mechanically stable manner, and not by soldering alone. ■ The green earthing wire must be longer than the other two wires, so that it is the last one to release itself in case of an accidental tearing of the mains cord. ■ There must be a distance of at least 3mm between the non insulated current carrying parts, and bare conductors. 2. Testing ■ All jobs like assembly, soldering repairing etc. inside the open apparatus must be carried out only when the mains plug is removed. Switching off is not sufficient. ■ Before starting the operation, check whether all the parts carrying current are fixed in a stable manner. Inspect the non-conductive contacts for insulation or short circuits with multimeter. ■ While testing any part of circuit carrying current, the test leads must be clamped with insulated clips and the mains plug should be inserted and the power turned on. The clips should be released only after disconnecting the plug. ■ While testing the low voltage sections of the circuit, all current carrying parts must be insulated in order to eliminate unintentional touching or shorting with other current carrying parts. Some hints for good desoldering: * Remove excess solder by heating the soldered joint, while the PCB is held with component side on top, the molten solder flows on the tip of the soldering iron. Tap the PCB lightly so that the molten solder flows down completely. * In difficult situations, solder sucking stranded wire is used, (Also known as solder sucking wick). Place the stranded wire on the joint to be desoldered and heat both with the soldering iron. The stranded wire sucks the molten solder. Lift the soldering iron and stranded wire simultaneously. * In case the holes are still blocked by solder after desoldering, heat the area with soldering iron and prick the molten solder with a pencil point to clear open the hole. * Solder bridges shorting two tracks can also be cleared with a pencil point. However, pencil lines on the board must be carefully erased, since graphite is conductive. Components Resistors Resistors are designated with R. The coloured bands on the body of the resistors indicate the value of. the resistance. © Condensers (Capacitors) These are charge accumulators, which allow the AC signals to pass through and prevent the flow of DC currents, when a DC voltage is imposed across a capacitor, it accumulates enough charge so as to develop an equal voltage across its terminals. This charge accumulating capacity is measured in Farads (F). Besides the capacity, the dieletric strength is also important. It should be at least 20% above the operating voltage. Examples of capacitor values: 1n5 = 1.5 nF lOOp = 100 pF 30n = 30nF = 0.03pF = u03 Foil type or ceramic type capacitors are generally available from IpF to 1 >jF. Example of reading the resistance values from the coloured bands: brown — red — brown — silver = 1 20n 1 0% yellow — violet— orange — silver = 47 K n 10% (In SELEX projects the notation followed is slightly different; 47K n is written as 47K, 4.7 K n is written as 4K7, 1 ,5M n is written as 1 M5 and so on. The tolerance values are assumed to be 5% or 10% unless otherwise mentioned) Potentiometers These are special resistors with adjustable sliding contact. The sliding contact serves as the tapping point of the potential divider formed by the resistance. In addition to the spindle & knob type potentiometers, small presettable potentiometers are also available. These are to be set by using a screw driver. Electrolytic Capacitors The Electrolytic capacitors have a high capacity, and are generally available from luF. They are polarised and their terminals cannot be interchanged. The terminals are clearly marked as + and— or sometimes only the — terminal is marked. In case of small sized Tantalum capacitors the + pole is additionally emphasised with a longer wire. -HIP- = * c 7.67 PTH PCB Platetch Circuits now offer a modern manufacturing facility exclusively for manufacturing PTH PCBs. These are provided with bright acid tin plating, roller tinning and gold plating. Solder masking and legend printing can also be provided. PCB designs with fine lines and high density are manufactured with excel- lent line sharpness and hole centering. Complete jobs starting from lay-out, artwork, photography and PCB fabrica- tion are executed with short delivery For further information, write to: Platetch Circuits 1 10, Nirmal Industrial Estate, Near Sion Fort, Sion (East) Bombay 400 022 DIGITAL 1C TESTER R.C. Digital 1C tester 4016 is a microprocessor based instrument de- signed to perform functional testing of TTL, RTL, HTL, DTL, CMOS and MOS ICs of 74/54/40/74 C series ICs in 14/16 pin versions. Preprogrammed software for about 200 most commonly used ICs is stored in the memory and is expandable to another 200 ICs through expansion boards. The testing procedure is completely automatic and messages like good/bad, 1C Number etc. are displayed on a seven segment LED display. THERMOCOUPLE TEST SET Vaisheshika 4 ? digits thermocouple test set and calibrator type 7709 is a versatile instrument for calibrating pyrometers, potentiometric recorders, platinum resistance thermometers temperature controllers etc. The instru- ment can also be used as thermocouple simulator with an accuracy of * 0.02%. A stable potential source with a range of 0 to * 100 mV and a resolution of 10 pV is provided with the test set. A standard Wheatstone bridge is also provided with the test set. Resistances ranging from 0.1 ohm to 1 K ohms can be measured or simulated with an accuracy of * 0.1%. The bridge can also be used as standard decade resistance substitution box with an accuracy of ± 0 . 1 %. For further information, write to: Vaisheshika Electron Devices Near Allahabad Bank Ambala Cantt. 133 001 LOGIC CUP Alfa Products Company have intro- duced their new Logic Clip LCU-16. This is a small troubleshooting instru- ment which fits directly on to DIP ICs and instantly displays the logic states of all the pins of the 1C and under test. It can test 14 or 16 pin ICs with equal ease. The clip has its own gating logic which locates the power supply pins of the 1C under test and derives its supply from the circuit directly thus eliminating the need for an additional power supply for the clip. The built in buffered inputs reduce circuit loading. These logic clips are compatible with almost all the logic families and are claimed to be truly universal. For further information, write to : Alfa Products Company FF-11, Baja) House. 97, Nehru Place, New Delhi 110 019 CHARGED BODY DETECTOR Monroe Electronics Inc. have intro- duced a novel instrument called the Charged Body Detector/Alarm Annun- ciator'. The charged body detector is basically an electrometer utilising a special multilayer tape sensor which sets up a capacitance field between the static source and the tape coupled to the charged body detector's input. The tape probe detects the electric field from a moving charged object. ' The sensitivity may be set from 10V to 1000V. The instrument has capability of additional features like remote alarm outputs, event counter and alarm latch. The event counter keeps track of the number of electrostatic discharges or intrusions of charged objects into the protected area. For further information write to: Swadeep Instrumentation 101, Vishnu Villa, 10th Road, Khar, Bombay 400 052. THUMB WHEEL SWITCHES Elcom have introduced the new TC series subminiature Thumb wheel switches which can be snap fitted onto the panel. These are ideally suited for Test and Measuring Instruments and Industrial Control systems. These are available in the following variations: One pole ten way, two poles five way, BCD, with or without limit stop, with or without extended boards and coloured wheels. Subminiature DPDT snap fitting toggle switches moulded in polyamide have also been recently introduced. These are available for both low and high current applications. ELCOM 103, Jaygopal Industrial Estate, B. Parulekar Marg, Dadar, Bombay 400 028 DIGITAL TACHOMETER Beacon Digital Tachometer LDM-5004 is a versatile, compact RPM indicator, with a range of 30 to 9999 RPM and accuracy of ± 1 RPM. The instrument can also be supplied to read linear speeds in terms of Mts/min/ or Ft/min. The instrument works from 5V DC but can be provided with optional power supply unit for mains operation. Various types of pick ups like magnetic, optical pick ups or proximity switches can be used with the LDM-5004 T achometer. For further information, write to : Beacon Industrial Electronics Pvt. Ltd. 13- A, Shri Ram Industrial Estate, Katrak Road, Wadala, Bombay 400 031 WIPER CONTROL msM Penguin Electronics have developed a wiper control unit tor four wheelers. This unit can operate the wipers intermittantly in a preprogrammed manner. Two delay settings and two sweep settings are provided in addition to the normal operation, the delay and sweep settings are independant of each other. The controller is suitable for vehicles of both positive and negative ground systems, and is fully protected against overcurrent, reverse polarity, vibrations and temperature variations. Fitting procedure is claimed to be very easy. For lurther information, write to: Penguin Electroncis D-105, 1st Main Road, Annanagar (East), Madras 600 102. POCKET VDU G.R. Electronics, U K. offer a hand held Video Display Unit with 2 'lines * 40 characters capacity. All memory con- tents are displayable for editing by cursor. The display has the capability of displaying all 128 characters of the ASCII set. Both conversational as well as block modes are possible. 20 mA loop, RS232C or RS422 interfaces are available and the baud rates are selectable from 50 to 9600 in thirteen steps. Spare PROM capacity is available for OEM software. The VDU is powered by rechargable Ni/Cd battery. POCKET MDU For further information, write to: MRO-INDIA Systems No. 3, 1st B' Main Road. Gangenhalli Extension, Bangalore 5 60 032. COILS FOR COMPUTERS AND CTV ABC Taiwan Electronics Corporation offer a wide range of coils for computers and CTV. The range consists of fixed coils, adjustable coils. IFTs, EMI/RMI filters, power chokes, trans- formers, noise suppressors and surge stoppers. The coils are made to customers specifications. « • * gn WAS* w *fV For further information, write to: Shilpa International 107, Parklane, Secunderabad 500 003. ALL PURPOSE MARKERS Tiger Management Services offer all purpose markers which eliminate cum- bersome processes of marking on all types of surfaces. The marking is instant drying and is non-messy. These markers are available in Red. Black, Violet, Golden and Silver colours. Inks for refilling the markers are also available. For further information, write to: Tiger Management Services, No. 10, Apparsamy Koil street, Mylapore. Madras 600 004. POWER SAVER FOR INDUCTION MOTOR Advance Industries have developed a new inexpensive solid state power saver for single phase induction motors. The unit is claimed to be useful for reducing the inefficiencies in the motors used in refrigerators, air- conditioners. pumps, washing machines, cleaners, and industrial sewing machines etc. The manufa- cturers estimate of reduction in no load power wastage is by a factor of 2 to 3. Considerable power savings can be achieved also when the motor is lightly running or is intermittently loaded. For further information, wri Advance Industries 11. Tinwaia Building, Tribhuvan Road, Near Dreamland Cinema, Bombay 400 004. FREQUENCY STABILISERS Spectron manufactures a wide range of frequency stabilisers. The systems consist of stable frequency oscillators and power amplifiers. The power derived from mains is converted to D.C. using rectifiers and capacitors and then used to drive the oscillators and amplifiers. A constant output voltage is maintained with help of feedback circuits. These systems find applica- tions in synchronous drives and com- puter systems. For lurther information, write to: Spectron Sales & Services Pvt. Lid. 63. Bharatkunj No. 2, Erandavane Pune 411 038. DPM WITH CRYSTAL CLOCK Lascar Electronics, U.K. have intro- duced a new LCD DPM which employs direct chip bonding technique to reduce the size. The DPM 300 has a crystal controlled clock and a tempera- ture compensated display drive. Some of the salient features include Auto- zero, Auto-polarity, Underrange and Overrange signals, Programmable decimal point and easy rescaling. For further information, write to: Electronics India Co. 3749, Hill Road, Ambala Cantt. 133 001. Industrial Electronic & Allied Products AN INTRODUCTION TO BASIC THE BASIC PRINCIPLE WITH EVERY NEW SUBSCRIPTION A BOOKLET FOR BEGINNERS A copy o-f the booklet THE BASIC PRINCIPLE Grant Road (East) , Bombay-400 007. Desoldered With Dinm nnn Diam ond ■ Desolders thoroughly. Distributors: prVCiOUS Corporation Chhotani Building 52C. Proctor Road Grant Road (E). Bombay-400 007. 1423, Shukrawar Peth, Off. Bajirao Road, POONA 41 1 002, India. Phone: 446241, Gram: SEFOTAKE. ■ Sturdy construction ■ Replaceable Teflon Nozzle ■ Largest selling in India ■ Widely accepted in CJ.K., CJ.SA, West Germany and Singapore. Export Enquiries Welcome 7.74 DIGITAL MULTIMETERS THAT GIVE YOU THE GREATEST NUMBER OF RANGES, HIGHEST RESOLUTION, BEST ACCURACY, MODEL MIC 6000 Z precious Electronics Corporation CHHOTANI BUILDING, 52C, PROCTOR ROAD, GRANT ROAD (E), BOMBAY-400 007. PHONE - 367459. 369478. TESTICA T-3 Rsl 70/- THE ONLY MULTIMETER WITH PROMPT SERVICE AFTER SALES ACCURATE! ROBUST! ECONOMICAL! AVAILABLE AT ALL COMPONENT SHOPS MANUFACTURERS : ELECTRICAL INSTRUMENT LABORATORIES, 339/68. RAJESH BUILDING, LAMINGTON ROAD. BOMBAY-400 007 PHONE-36 07 49. LOW COST HIGH QUALITY Eagleman 7.75 GOOD REASONS FOR SUBSCRIBING TO The SCiefltiFiC HM 312 increases its functions to match your requirements. Already a bestseller in the 20MHz range, the dual trace HM 312 now brings you two additions that puts it ahead of the others. 1. BUILT-IN SINGLE TOUCH COMPONENT TESTER 2. Z-MODULATION PLUS 3. REDUCTION IN COST OTHER SPECIFICATIONS: • Bandwidth (-3 db) : 20MHz 5mV g (-6 db) : 28 MHz 5 mV • Triggering : 30 MHz • Risetime : 17.5nS • Timebase : 40nS-200nS So we have brought you single touch component testing in the 20MHz range We have shown that EXTRA features need not mean extra price. That's Service and Satisfaction from scientiFic SCIENTIFIC SALES 7.76 ulekiof i WE OFFER FROM STOCK l.c.'s : ttl. CMOS, MOS, LSI, Microproccessor. Micro computer etc. Zener Diodes : 400 mw & 1 Watt LED's • Red, Green, Yellow in 5mm and 3mm dia IC Sockets : SMK & Memorex make Trimpots : Multiturn Bourn's, VRN & Beckman make Single Turn cermets : EC as well as imported Floppy Discs : 8" as well as mini floppy of memorex, & dyson make How electronics can be childs play for your son! 7.77 Advertisers Index classified ads. CONDITIONS OF ACCEPTANCE OF CLASSIFIED ADVERTISEMENTS 1 ) Advertisements are accepted subject to the conditions appearing on our current rate card and on the express understanding that the Advertiser warrants that the advertisement does not contravene any trade act inforce in the country. 2) The Publishers reserve the right to refuse or withdraw any advertisement. 3) Although every care is taken, ihe Publishers shall not be liable for clerical or printer's errors or their consequences. 4) The Advertiser's full name and address must accompany each advertisement submitted. The prepaid rate for classified advertisement is Rs. 2.00 per word (minimum 24 words). Semi Display panels of 3 cms by 1 column. Rs. 150.00 per panel. All cheques, money orders, etc. to be made payable to Elektor Electronics Pvt. Ltd. Advertisements, together with remittance, should be sent to The Classified Advertisement Manager. For outstation cheques please add Rs. 2.50 Wanted Engineers and Technicians for quality control & production of Televisions and Video Cassette Recorders Manufncturing Unit. Apply to: 'TOSHNIWAL' Post Box No. 56, H-5/12, M.I.D.C. Chikalthana, Aurangabad - 431 210. We can send application notes or data sheet for any electronic component. Minimum charges Rs. 15/- Write to: DATA BANK Plot No 16. Bldg. No 3. Flat No. 17. Bhavani Nagar, Marol Maroshi Road. Andheri (E). Bombay-59. 7.10 BALAJI 7.04 COMPONENT TECHNIQUE 7 04 COSMIC 7 80 DANNIES ELECTRONICS 7 10 DOMINATION RADIOS 7 06 DYNALOG 707 EAGLEMAN ENTERPRISES 7 75 ELCIAR 7 10 ELCOM 7.06 ELECTRICAL INSTRUMENT CO 7 72 IEAP 7 74 JETKING 7 77 KAYTEE ENTERPRISE 7 70 LUXCO 7 71 M C ENGINEERING 7 11 OSWAL ELECTRONICS CO 7 72 PADMA 7 70 PRECIOUS 7 75 PULSECO 7 72 SCIENTIFIC SALES 7 76 SAINI ELECTRONICS 7 04 SIEMENS 7 08 7 09 TECHNOMATIC LTD 7 02 7 05 TESTICA 7 75 TEXONIC 7 70 VASAVI 7 06 VISHA 7 79 ZODIAC 7 77 mfsJn^ Components are normally available with the following companies: VISHA ELECTRONICS a new keyboard for Spectrum (April 1 985. pags 4-38) The circuit diagram in figure 3 oncorrectly gives the value of R 35 as 4k7: this should be 47 k. P.C.B s For SELEX & DIGILEX Will be announced next month in our E.P.S. Page 1 7. Kalpana Building, 349. Lamington Road Bombay - 400 007 Phone: 362650 DYNALOG MICRO SYSTEMS 14. Hanuman Terrace, Tara Temple Lane, Lamington Road Bombay - 400 007. Phone: 353029. 362421 ELECTROKITS 20, Narasingapuram Street (First Floor) Mount Road Madras 600 002 INTEGRATED ELECTRONICS INSTRUMENTS &2174 Red Cross Road Secunderabad 500 003 Phone: 72040 7.78 R.N. No. 39881/83 MH/BYW-228 LIC. No. 91 OH Tulsi Pipe Road. It* ,ir BomMy 400 052 )