INDIA Introducing the most advanced front-line Speaker Systems. Sonodyne SX 500, 600, 900— the only Speakers in India with original Japanese Woofers, Tweeters* and Midrange. The Woofers are Japanese. The Cone Tweeters are Japanese. The Midrange is Japanese. No Indian Speaker System could Among the outstanding characteristics of Sonodyne 'SX' Speakers: a unique bass-reflex with twin port design. An immaculate stereo presentation within the full frequency range. Sonodyne SX' Woofers These cone-type high efficiency woofers. 200 to 250 mm in Sonodyne SX' Tweeters guaranteeing an unmatched musical reproduction and a highly sensitive bass response. We can go on and on about the SX' Series advancements. SX’ 500/600/900 having an input 'SX' 500, 600 having a 2-way, 2 speaker system. Or the SX' 900 having a 3-way, 3 speaker system. But we'll just say that Sonodyne Speaker Systems, are the perfect without distortion. Low harmonic frequency transducer and delivers answer for people with a ear for content giving music a life-like crisp, clear reproduction. Free music and a head for money, quality. Competitively priced, yet from coloration/phase errors. Listen to them at vour nearest incorporating superb features and Sonodvne dpaipr tndavi Japanese components, yet to be Sonodyne 'SX' Bass Reflex ^ ^ found in a single Indian Speaker with Twin Port Design System! A special crossover network ‘Cone tweeters only. Sonodyne SX’ Bass Reflex with Twin Port Design A special crossover network § SONODYNE — The name that’s music to your ears. j Volume 3-Number 5 EDITOR: SURENDRA IYER PUBLISHER: C. R CHANDARANA PRODUCTION: C N MITHAGARI ADVERTISING & SUBSCRIPTIONS e1eI(TOR ElECTRONiCS pVT lid. Chotani Building I 52 C, Proctor Road Grant Road (E) Bombay- 400 007. news, views, people 5-13 selektor 5-16 The changing face of communications light-powered radio 5-18 A small portable receiver that is not dependent on conventional batteries. revolution counter 5-20 This unique instrument displays the torque characteristic of your car over the useful [ X-Y plotter 5-24 A computer peripheral that gives a new meaning to 'a picture paints a thousand DISTRIBUTORS: INDIA BOOK HOUSE PRINTED AT: TRUPTI OFFSET 103, Vasan Udyog Bhavan. Off Tulsi Pipe Road, Lower Parel, BOMBAY- 400 013. I 1 Elektor India is published monthly under agreement with Elektuur B V Holland. August/September is a double issue SUBSCRIPTION INLAND 1 YrRs. 75/- 2YrsRs.140/ 3YrsRs.200/ FOREIGN One year Only Surface mail Rs. 1 25/- Air mail Rs. 21 0/ the first cuckoo in spring 5-35 Continues our tradition of regularly presenting a sound-effect project. long interval timet 5-38 voltage frequency converter 5-38 10 A power supply 5 39 Provides a fixed output voltage between 1.2 V and 32 V at a current of up to 10 A. stepping motors 5-42 applicator 5-48 New transistors for use in satellite TV or UHF broadband receiving systems. capacicoupling reading in bed limiter . market switchboard missing link index of advertisers 5-50 .5-53 5-62 .5-65 . 5-74 5-74 5-54 INTERNATIONAL EDITIONS EDITOR: P HOLMES 5-03 Software development. Computer hardware. 5-04 eMaor indi. m.y 1985 Elektor— India takes you behind the scene, where enc :, -^rs design, develop and tes ; ects at the ultra modern Etek stories in Holland. A view of the laboratories. As we move into the future we find that electronics is increasingly becoming a part of our daily life. It appears that everything will ultimately function with the aid of electronics. In fact, electronics is already present in most of what is going on around us today— few people are aware of this. It is high time the average individual is periodically enlightened on the significant role electronics is continuously playing in his/her life. And we believe that anyone who is interested and has access to an excellent introduction can understand electronics very easily. Our new section SELEX (Simple Electronic Experiments) is designed to provide this introduction in addition to teaching the fundamentals of the subject. Our team of engineers and technical editors at Holland (see opposite page) have prepared programme "SELEX" which will be a regular feature in elektor- India —starting with this issue. A final word— SELEX is an additional section to the existing magazine. This means more pages— thus the reader gets his usual editorial plus SELEX. — Editor m 1 ^ - • For further details write to: THE MOTWANE MANUFAC- TURING COMPANY PVT. LTD.. MOTWANE llflOl B "“ a ' N ° Bik Tel.: 86297/86084 Telex: 752-247 MMPL IN Grams: MOTWANE or Gyan Ghar. Plot 434 A 1 4th Road. Khar, Bombay-400 052. Grams- : MOTESTEM. SELL ADS.MMC. EES ■n tiCs « ~;f * j mm 6 -6 o 1 bB IP* W *•«•-• “ r — *"*,1 l THE AUTO LOGIC MONITOR ! llQGICUP 1LC-H6 Works effectively on single/double • sided PC Boards. Powerful vacuum time-proven ranse of HM Series Oscilloscopes: HM 203 and HM 204 Dual Trace 20 MHz Oscilloscopes. These sleek new low-line portables incorporate the latest in international product design and features: a 140 mm rectangular flat-face CRT with illuminated internal graticule, 8 x 10 cm display, high 2 mV sensitivity and 20 MHz bandwidth, HF triggering up to 50 MHz, single touch component tester, sweep delay, and many more features never before available in this price range. Dependable performance. Assured results. Two New Numbers to Remember ! HM 203 HM204 scientiFic portables ! Manufactured by: SCIENTIFIC MES-TECHNIK PVT. LTD. ormerlv known as: SCIENTIFIC INSTRUMENTS (INDORE) PVT. LTD. 5-12 The changing face of communications The modernization of the world's sixth largest national telecommuni- cations network has been substan- tially accelerated with the introduc- tion of System X. This range of micro-electronic digital exchanges was designed and developed by British Telecom and a number of telecommunications manufacturers, and is made jointly by Plessey Telecommunications and GEC Telecommunications. The first production System X exchange came into operation last year in Coventry in the English midlands. Within three years British Telecom plans to install at least 30 System X trunk exchanges and 1200 local exchanges. The latter will be made up of some 300 large systems, with 900 local connector units used to extend System X services to much wider areas than the localities served directly by the main local exchanges. Despite the fact that the British net- work is already fully automatic, with direct national and international customer dialling to 158 countries, it shares with many other national telecommunications networks a number of serious constraints. Two wire switching It is dominated by two wire switching and by signalling associated with the connection path established for each call. This affects network transmission efficiency, severely restricts customer facilities, and makes centralized supervision of the network difficult. At the same time, numerous types of Checking System X with the aid of a visual display terminal. signalling system are used and, because these have to work together, this limits the capacity to convey information about the call and caller. Connection times are long for calls routed through several exchanges, and calls are subject to variable transmission losses, noise, and distortion. In addition, Strowger switches are prone to wear and require expensive maintenance. There is limited scope for further evolution and development of new facilities. The equipment has no potential for miniaturization to minimize the cost of accommodation in expensive city centre sites. Although many telecommunications experts argue that computer control is at least as important as the method chosen for routing signals through a telephone exchange's switching matrix, digital switching techniques offer real economic and operational advantages. Fully digital exchanges are very reliable, economical to build and maintain, and much more compact than their electromechanical counterparts. Digital operation also makes for great flexibility in the use of the network by enabling different services - data, text, graphics and pictures, as well as speech - to be sent more cheaply over the same carrier, whether copper cable, optical fibre, microwave radio beam or satellite. When allied to a digital transmission system the arguments for the technology become irresistible. The major advantage of customer-to- customer digital operation is that once voice signals are converted from analogue to digital form they can be routed without further con- version over the whole network. This is a cheaper process, with simplified control, improved transmission qual- ity. and reduced error rates. The result is an integrated network capable of supporting every modern telecommunications task and service. The forerunner of British Telecom (BT) — when the operation was part of the Post Office — first attempted to switch traffic telephone digitally in the mid-1960s. Due to the time required to move from a small scale experiment to a fully developed pro- duction system, an interim system had to be found. The authority thus took an evolutionary approach to the technology, with reed switched elec- tronic exchanges such as Plessey's TXE 2 and STC's TXE 4 being introduced in large numbers in the late 1960s and the 1970s. The 1800 or so of these now in service will form a bridge to a fully digital network. The United Kingdom has been criticized for not making a serious commitment to digital technology earlier than it did; after all, the first pre-production System X machines did not appear in the national net- work until 1980. In fact, there are a number of reasons why this approach was preferred, if not inevitable. Changing over from a very diversified national network primarily based on electromechanical exchanges of dif- ferent types is a difficult, time con- suming and intricate task. While digital technology, of a very early generation, could have been bought from overseas, the perpetuation of a viable British supply industry was considered to be in the best interest of the country as a whole. And the BT strategy had one inestimable technical advantage in that it allowed the United Kingdom to overtake developments in other countries. The evolutionary nature of digital technology in Britain is matched by an evolutionary approach to its implementation. Wholesale substi tution of new technology for old in more than 6000 exchanges is not in any case feasible because of the need to maintain uniform service and amortize existing plant. BT has ident- ified a number of implementation strategies. One can be termed augmentation. Under this concept, network nodes are progressively extended with digital switching. This has the advan- tage that disruption to the existing network is minimal, but has the dis- advantage of requiring a large quan- tity of interface equipment. Another strategy is simple replacement of older equipment by digital exchanges. A third is to create an overlay, in which a digital network is built up side by side with an existing network and is linked to it in a con- trolled fashion. The last is basically the strategy adopted by BT in the majority of circumstances and will result in the most rapid penetration of new customer facilities. In essence, this overlay strategy allows digital elements to be fitted into existing analogue networks with minimal changes and, at the same time, provides a simple means of expanding the digital network. The component parts of a System X exchange can be envisaged as building blocks that interact to pro- vide the total function. 5-16 The eight major blocks are: * The concentrator accepts customers' calls and concentrates them on to high traffic channels. * The distributor switches calls to other destinations. " Signal interworking enables System X to work with the analogue exchanges. * The testing unit makes possible maintenance checks on customers' lines and on interconnecting circuits to other exchanges. * Inter-processor signalling sets up calls and "talks" to other System X exchanges using an internationally agreed standard. * The man-machine interface enables staff to monitor, control and main- tain an exchange. * The processor is the "brain" that provides instructions to other sub- systems. It contains a number of software packages controlling such exchange functions as call process- ing and accounting, management statistics, overload, and maintenance control. Starting with the Spires exchange in Coventry, the production versions of System X use a new pro- cessor which is up to ten times as powerful as the original. This gives these exchanges a very large traffic handling capacity, and up to 500 000 calls an hour can be carried with the new processor. * Automatic announcements guide the subscriber through the use of the sophisticated exchange facilities. The existing analogue exchanges use a wide variety of signalling systems in which control signals are sent over the same channels as the conver- sation. System X rationalizes this in a radical fashion. Currently, analogue telephone net- works employ a range of direct cur- rent (short distance), alternating current (long distance), and multi- frequency tone (transit network) signalling systems. In present pulse code modulation systems, transmission technology time slot 16 is used for signalling for the 30 speech channels and is the first stage of a migration away from what is known as channel associated signalling to separate channel signall- ing. The latter is a feature of System A separate System X data link of 64 kbit/s capacity puts virtually no constraint on the number of signals that can be used. Signals are trans- mitted rapidly to set up and clear down calls, and, most important, the data link permits signalling to con- tinue during the call without inter- ference. This feature is important both for data communication and for utilizing the new range of System X facilities. Network signalling will be reduced by System X to two basic systems. The first is the direct access signalling system (DASS), which signals between the customer and the local System X exchange for the integrated services digital network (ISDN). In essence, the ISDN con- verges all customer services — voice, data and text — through encoding and multiplexing equipment into a common digital network. This is CCITT Signalling System 7, which deals with national and international network operation. Star services Ultimately, the success of System X will be determined by its popularity with users. In addition to the oper- ational advantages already outlined, System X will offer what are termed as 'star services'. These are accessed by the subscriber using a push- button telephone in conjunction with automatic voice guidance from the exchange. Included among those services are: ■ Abbreviated dialling. ' Call diversion to an alternate number. ■ Three way conversations. ‘ Alternation between an existing call and new one. ■ Repetition of last number dialled. ’ Reminder call. ' Call barring. ‘ Charge advice. Among the additional voice services being considered by BT is ringback, which involves getting the exchange to keep trying an engaged number and calling the subscriber when it is free; voice 'mail'; and charging calls made from other telephones to a personal account. Other innovations System X is only one of the many innovations for both business and domestic customers that British Telecom is introducing. Known as SatStream, a commercial service provides private high speed digital communications between Britain and mainland Europe for companies using small dish satellite earth terminals. It provides integrated speech, data transmission, facsimile, teleconferencing and remote printing services. International packet switching is now available to more than 50 networks and a 24 hour public electronic mail service is run by Telecom Gold, an independent company backed by BT. Radio pagers with alphanumeric displays, which show the number to be called or provide coded infor- mation, were introduced last year, and the first public telephone on a high speed train was recently unveiled. And, on the simplest level, the tra- ditionally limited range of telephones available to subscribers has given way to a wide choice of shapes and styles and colours. British Telecom is also one of the main parties in the development of cellular radio. Together with Securicor, the private security company, it has won one of two licences granted to operate cellular radio in Britain. The other went to the Racal Millicom consortium. Under the cellular radio system, for mobile users of radio-telephone, a country is divided into areas and areas into small cells, each with a low power radio transmitter operating at different frequency from others in the area. A computer tracks the subscriber automatically and changes frequency when the user moves from one cell to another so that uninter rupted communications are main- tained. With this wealth of experience, BT along with the UK's telecommuni- cations industry is expecting to gain significant business from other countries which are faced with the problems of modernizing their telephone systems, and require similar solutions to those in the UK. (LPS) for a System X com- light- powered radio. . . .saves on batteries All portable receivers, large and small alike, share a big drawback: their batteries! Those energy sources seem to know when that cricket match is getting really interesting, or when the play you are listening to is coming to its climax, ghost. Our tiny receiver works from less likely to let you down at those long as it is not too dark . . . Rising costs and our endeavours to save energy mean that solar energy is in! Large solar panels are already in extensive use for the provision of heat and other energy in domestic and industrial buildings. And, of course, what can be done on a large scale can be done on a small scale, so that in almost every High Street you can find clocks, watches, and calculators that are powered by small solar cells. So, we thought, why not design a little radio that works from solar cells? Little, because that keeps the size of the required cells down, and makes it easy to slip the receiver in your pocket or handbag. Circuit description To keep the design simple and easy to build, we decided on a straight medium- It is then that they give up the solar cells and is therefore far exciting moments, at least, as wave receiver, because this lends itself par excellence to our requirements. The circuit is based on a Ferranti ZN416. This IC is a welcome addition to the range that already includes the popular ZN414 and the ZN41S (descriptions of these appeared in the May 1982 issue of Elektor UK and the December 1983 issue of Elektor India). The ZN416 contains a complete AM receiver with enough audio output to drive headphones direct. It covers the fre- quency range 150 kHz. . .3 MHz which includes the medium and long wave broadcast bands. The ag.c. characteristic shows an increase of less than 7 dB in AF output for an increase of more than 30 dB in RF input. Due to the high input impedance of more than 4 MQ, selectivity is pretty good: 8 kHz bandwidth at —6 dB A number of external components is required to complete the design, as can be seen in figure 1. The input circuit can be tuned over the range 450 kHz ... 2.2 MHz, which amply covers the MW band. Inductor LI serves also as aerial. Capacitors C2 . . .C5 ensure optimization of the on-chip circuits. The impedance of the headphones should be greater than 32 ohms. The power supply requirements of 1.5 ... 2.0 V at 10 ... 15 mA are met by four solar cells, each measuring 20 x 10 mm. Such cells can provide 0.5 V at up to 45 mA in good bright light. Their output current decreases with reducing ambient light. The current drawn by the ZN416 depends on the input signal and the out- put load, and normally varies from about 5 to 8 mA. The current consumption drops appreciably when high-impedance head- phones (>2000 Q) are used. For instance, when the output impedance is 4000 2, the current consumption drops to some 1.5 mA. Capacitor C6 smoothes fluctuations in the supply voltage caused by varying light incidence onto the solar cells. If you do not want to be dependent on light energy, it is, of course, possible to replace the solar cells by a 1.5 V Ull battery. Construction The receiver is most conveniently built on the pcb shown in figure 2. Make sure that the rotor, and not the stator, of Cl is con- nected to pin 8 of the ZN416. This may mean reversing the connections of this capacitor to the pcb. Inductor LI consists of a single layer of 60 turns of SWG36 enamelled copper wire close wound onto a 50 x 10 mm ferrite rod. Before winding the coil, stick a few layers of sellotape onto the ferrite rod. The turns may be fixed in place with nail varnish or quick drying glue. If you can get it, use litz wire instead of enamelled copper wire as this will result in a higher Q factor. The completed inductor should be fitted to the pcb with nylon thread or similar, but not with metal wire as this will reduce the Q factor to less than useful! The completed board should be installed in a small man-made-fibre case. The on/off switch and the headphone connector are best fitted at the side of the case as shown in the photograph at the beginning of this article. The cells should be fixed with double-sided sticky tape as shown in the same photograph. They must be con- nected in series: their polarity is easily determined with a multimeter. Connec- tions should be made with thin, flexible wire. Soldering should be done quickly: solar cells do not like heat! Performance If the radio has been constructed cor- rectly, it should receive a number of MW stations, although this depends, to some extent, on your location. Note that solar cells can also convert energy contained in bright artificial light into electrical energy. If the receiver generates whistles, this may be obviated by interchanging the connections of LI. Finally, it is possible, if you want to use the radio predominantly in moderate light conditions, either to connect four addi- tional solar cells in parallel with the existing ones, or to use larger cells. M revolution counter A standard revolution counter tells us only what the number of revolutions per unit of time is. It is, however, more important to know the moment (torque), because an engine develops maximum moment at a certain number of revolutions and it is then that it works at its most efficient. The natural consequence of this is the unit presented here which shows both the number of revolutions per minute and the moment. revolution counter. . . . . with torque indication Any revolution counter may be used to economize on fuel consumption, as long as you know the relation between the number of revolutions and the moment of your car. That relation for a modem petrol engine is illustrated in figure 1. This shows that the maximum moment is available at 4000 rev/min, so that the engine then works at its most efficient. The curve also shows that this particular engine is most economically used over the range 3300 . . . 4S00 rev/min. The method we have devised of showing the driver at a glance in which range of revolutions the car engine is working is based on a LED bar indicator that has the shape of the revolutions vs moment curve of the engine. A schematic representation of such a bar, based on the curve of figure 1, is shown in figure 2. For the range below 3300 rev/min. yellow LEDs are used; for the optimum range of 3300. . .4500 rev/ min, green LEDs; and for the range above 4500 rev/min, red LEDs. 1 2 i i ▼ ▼ ▼ i Circuit description To cover the useful range of revolutions, a total of thirty LEDs are proposed to ensure a reasonable resolution. All the circuit has to do is to arrange for the appropriate LED to light at any given number of revolutions. This can be done as shown schematically in figure 3: the ignition fre- quency, which is proportional to the number of revolutions, is taken from a point between the coil and the contact breaker and fed to a frequency-to-direct- voltage converter. The output of this con- verter is applied to the LED control cir- cuits which arrange for the relevant LED to light. The complete circuit is shown in figure 4. Resistor Rll, diode D35, and capacitor C5 shape the ignition pulses which is then applied to NAND Schmitt trigger Nl. Gates Nl and N2, together with C6, R12, and P3, form a monostable multivibrator, the output pulses of which are buffered by N3 and N4. Low-pass filter R13. . .R15/C7. . .C9 converts the output pulses of the monostable into a frequency- proportional DC voltage. The input of the LED control circuit is formed by preset P2. The control circuit proper consists of two cascaded ICs type UAA170. As they are cascaded, and not all outputs are used for controlling LEDs, the transfer from one UAA170 to the other can be set with PI. Light-dependent resistor R9 controls the brightness of the LEDs; when it gets dark, the brightness is automati- cally reduced. A small power supply, incorporating a type 78L05 voltage regulator, ensures a stable +9 V supply to the circuit. Construction Building the purely electronic part of the counter on the printed circuit shown in figure 5 is a piece of cake. The real diffi- culty lies in the construction of the LED indicator, because its shape differs from car to car, and we cannot, therefore, offer you a ready made design. The first thing to do is, of course, to find out the shape of the relevant curve for your car; this is nor- mally given in the workshop manual. If you have not got this book, your local library is bound to have it — otherwise, you will have to ask your local car dealer. 5-20, Once you have the curve, you have to enlarge it until it is 75 mm wide. Now, not everybody will have a pantograph to hand, but many of you may remember from your school-days how you can enlarge draw- ings by parallel projection (ruler and triangle). If you are still stumped, you can have it done by your local photographer — but that is a rather more expensive way! The printed circuit board shown in figure 5 should be cut into two. The enlarged curve is now transferred to transparent paper. Then lay a sheet of copy paper on the copper side of the blank part of the pcb, put the transparent paper face downward on the carbon paper and trace the curve firmly. Where the curve crosses the copper track, care- fully remove the copper, i.e., cut the track. At the centre of each copper island immediately below and above the cut drill a 0.8 mm diameter hole. The terminals of each LED are passed through the two holes from the front of the pcb and soldered to the copper. Remember to do this with correct polarity! 4 Calibration A function generator with accurate fre- quency scale is needed for the cali- bration. If the frequency scale is not very accurate, you need an oscilloscope or a frequency counter as well. The frequency .5-21 of the pulse train emanating from the con- tact breaker is related to the number of revolutions as follows: f = NAB where f is the pulse rate; N is the number of revolutions per second; A is the number of cylinders; and B is the number of ignition pulses per cylinder and revol- ution. In almost all engines (notable exception: the Citroen 2CV) each cylinder is ignited at every second revolution. In the case of a four-stroke engine, B is therefore '/z. In the following calibration procedure, we have assumed a four-cylinder four-stroke engine with a minimum number of revol- utions of 2000 per minute and maximum 6000 rev/min. At minimum revolutions, f = 2000/60 x 4xl4 = 66.67 Hz. At maximum revolutions, f = 6000/60 x 4 x Vi = 200 Hz. Before commencing the calibration, set PI ... P3 to about the centre of their travel, and set the function generator output to about 130 Hz. Next, adjust P2 and P3 until an LED somewhere in the centre of the curve lights. Then, adjust PI so that chang- ing the frequency very slightly causes a smooth transfer of lighting from the lighted LED to the immediately adjacent LED at its left or right. Next, adjust P2 and P3 alternately so that at frequencies of 66.67 Hz and 200 Hz 5-22 LEDs D1 and D30 light respectively. Fi- nally, starting at 66.67 Hz, increase the fre- quency in steps of about 4.5 Hz and make sure that, from pi onwards, all LEDs light in smooth succession. Note that only one LED should light a< a time. If necessary, readjust PI slightly. Different minimum anjd maximum numbers of revolution give, of course, different fre- quencies. And, of course, your car may be a five or six cylinder model; here again, this makes a difference to the frequency. The principle of calibration remains the same, however. Installation Installation into the car and connecting the revolution counter to the contact breaker terminals depends very largely on the type of car and we must leave these, therefore, to your own ingenuity. We have deliberately made the top of the indicator pcb black, so that it can be used as the front panel of the revolution counter with the other pcb mounted behind it. The whole may then be housed in a small suitable case A piece of perspex over the front panel gives the unit a very pleasing appearance. H 5-23 Most of us would never even consider the idea of building an X-Y plotter or a matrix printer with a Centronics input. That, however, is exactly what this article proposes: a combined X-Y plotter and matrix printer. Probably the most important point is that you do not have to be a genius with your hands to construct the mechanical section. Not only that, but the electronics is straightforward and the cost of the design is not prohibitive. The concept of this d.i.y. project is made possible by the availability of the entire printer mechanism, complete with two bi-directional motors that drive a thermal print-head. All that remains is to fix all this in place with four small bolts. The circuit is quite simple, consisting of the Centronics interface, an input data buffer, and a character generator. The software included provides the means of drawing vectors point-to-point with a high resolution. X-Y graphic plotter an elegant solution to the problem of how to make your own graphics printer This project is very original, even by Elektor standards. It is a complete matrix printer and high-resolution X-Y plotter, affordable enough to be a solution for the 'impoverished' but at the same time it is a very interesting design in its own right. The idea of making an X-Y plotter is by no means new but to achieve a good result there is one essential prerequisite, namely a very precise mechanical section. A realistic compromise Designing the circuit and writing the necessary software for this project comes easily to the Elektor designers. The mechanical part is a different matter, however. You cannot expect to be good at everything, after all. However, just as with our mini-printer published in the December 1984 issue, Seiko supply a com- plete X-Y plotter (minus electronics). This is shown in photo 1. We used the STP411 printer mechanism for our prototype but we must stress that the electronics and the software could also be used with dif- ferent mechanical modules. This leaves plenty of options open for those fortunate readers who are skilled in the arts of sal- vaging or even making the whole unit. Before becoming involved with the details of this project we have to define what we mean by a matrix printer and X-Y plotter. Most commercial matrix printers (Epson, Seikosha, Nec, etc.) have a (pseudo) graphics mode to enable them to print designs. The resident software, however, does not enable them to handle the co- ordinates of a vector on a cartesian (X-Y) grid direct, as happens with a drawing table. What these printers do is produce a hard copy of a memory (generally the screen or video memory) in which the design to be traced is stored. Just as the design exists pixel by pixel on the screen, 5-24 dimensions: 153 x 45 x 20 mm weight: 135 g expected lifespan: 500 000 lines 11 expected print-head lifespan: 300 000 lir AC supply: 5 V/5 A (max.) it exists bit by bit in the memory. By send- ing the contents of the memory one byte at a time to the matrix printer (which must be in graphics mode), it is possible to obtain a copy of the design on paper. It is, however, impossible to trace the design directly on the printer based on the vec- tor coordinates. That is exactly what the plotter proposed here can do. The procedure used is quite simple. We start by sending the ESC character to the printer via the Centronics port. This signi- fies that the following ASCII codes are not characters for printing but the co-ordi- nates of a vector that has to be traced. The coordinates of the vector are then sent, separated by ASCII character 7" and beginning with the origin of the vector. For example, the vector starts at X = 2, Y = 6, and finishes at X = 15, Y = 12 (see figure 1). The sequence of instructions needed to print the vector is: PRINT CHR$(27); 7”; ’2’; ’6’; 7”; ’IS’; T2’; 7" It is worth noting at this point that most BASIC interpreters accept the PRINT instruction without the semi-colons between strings of characters (which are in quotes) and variables (which are not enclosed by quotes). If the end-point of a vector is the same as its origin a single dot is printed. The para- meters needed to trace vectors are as follows: (ESC)/OX/OY/EX/EY/(CR) Photo 2. The prii ,5-25 Figure 3. The dimens of the two types of printer. STP411 256 01 STP411-320. are differ where OX and OY define the origin of the vector and EX and EY signify its end. That all seems very simply but the desired result is achieved only if electronics, mechanics, and software are perfectly co- ordinated. The printer mechanism The sketch in figure 2 shows the printer , mechanism with its two bi-directional step- ping motors, worm-drive shaft, and ther- mal print-head. We will not deal with this mechanism in any great detail. As photo 2 shows, it is a fine example of precision engineering but, because it has been kept as simple as possible, it is pleasantly inex- pensive. The horizontal motor is connec- ted direct to the drive shaft; every pulse to the motor causes the head to move one step to either the left or the right. The horizontal resolution is 256 or 320 dots depending on the type of mechanism chosen and the size of step is 0.35 mm in 7-8 the former and 0.28 mm in the latter case ' ~ (see figure 3). The manufacturer indicates yes that there is a ‘dead’ angle of two or three no dots according to the type of mechanism ves used. This means that nothing happens for ™ 2 or 3 pulses after the head changes n0 direction. The software that drives the yes printer must take this into account. Like the head movement, the paper feed- ing occurs in steps, which are the same size as the steps the head makes. In this case the motor is not directly coupled to the paperdrum. A miniature 'gearbox’ is used that gives a reduction factor of 4 : 1. This means that the motor has to receive four pulses for the paper to move by one This reduction (illustrated in figure 3) is also subject to a ‘dead’ period every time the motor direction is changed. If uncor- rected, this would, of course, make rub- bish of any design that is being drawn. Unfortunately, Seiko, did not mention this detail in their data sheet for the STP411, which caused a few headaches for our designers. They were, of course, very reluctant to modify the otherwise excel- lent mechanics to cure the problem. As it happens, this was not necessary: the soft- ware was made clever enough to iron out this little difficulty. Our final comment about the motors is to note that each has a maximum current consumption of 500 mA at 5.5 V. Photo 3. The gearing STP411. 6821/IC4 Port A Centronics interface CA1 linl STROBE CA2 (out) BUSY PA0 1 We have already mentioned that there are two different printer mechanisms available. The main difference between them is in the print head. The 2S6 dot version has 8 thermal elements while the 320 dot type has 9. The sketch in figure 3 shows how the size of the dots consequently varies. The current applied to the heating el- ements is corrected to compensate for changes in the ambient temperature. This current regulation is achieved by varying the frequency of the signal applied to the print head. The maximum current drain is 3.5 A when all the thermal elements are on simultaneously. The final feature of the printer mechanism we will mention is the ’home’ detector. This is a micro-switch which is open when the print head is at the extreme left. As our designers were not fully satisfied with this arrangement, they added a further precaution. After receiving a ‘head-home’ indication, the head is first moved several steps to the right, then brought left until ‘home’ is again detected, and finally moved three steps to the right. This is then taken to be the initial position for the head. This precaution ensures that the head's ‘home’ position is always correct even if the mechanism is moved or stopped accidentally by hand. So much for the mechanics of the printer, now for the electronics. CB2 (outl BUSY indicator Motor for paper feeding A complete microcomputer The electronics section of this project is no less than a complete microcomputer, as the block diagram of figure 4 shows. It has a CPU (6502), random access memory (2K or 8K), read-only memory (4K or 8K), input and output ports (18 lines), a clock, and the ‘home’ detector already men- tioned. The layout requires no comment. There are, however, some points in the SEIKO diagram of specific importance to this project. There is a select switch to turn the plotter on and off, a manual paper- feed switch, the Centronics interface, the transistorized power stages, the clock used to control the head-current based on the ambient temperature (dot timer), and a timer (FIFO timer) that determines the printing speed for characters received via the input buffer. At the right-hand side of figure 4 we see the printer sections: two motors (one for the paper, one for the head), the head itself, and the ‘home’ Once you have seen the block diagram, the actual circuit (shown in figure 5) holds few surprises. On power-up the circuit is reset by R28 and C8. The 4 MHz clock sig- nal generated by N13 and N14 is reduced to 1 MHz by FF1 and FF2. 'A RAM R/W 5-29 examines the Centronics interface: if a new character has appeared it is loaded into the buffer and reception continues until the end of the pulse; if there is no new character to receive, the program continues to print the lines of characters already received until the buffer is empty or the timing pulse supplied by the 5SS This cycle continues indefinitely. The soft- ware constantly examines the buffer pointer to avoid a skip that would result in an irreparable loss of data. The oscillator based on N6. . .N9 is also an essential timing element during print- ing. Its frequency determines the cyclic relationship of the pulses applied via T12 . . .T20 to the print-head elements. The energy applied to these elements is scru- tinized closely as the current cannot be 5-30 1 1 .QQOQaaaooooooaoi t q qqqqq qqq q q qqq qqq TW Y" O O UUOU I 0-0 o — o . 00 . 0000000000,00 ? l q qqqq qq q qq q qqq » tooqooouo o oe oo ooo a ogg iq q oo o oo og oo oooeoo i constantly present or it would cause a bum-out. Compensation for changes in ambient temperature is achieved with pre- set PI, whose wiper is connected to the base of transistor Tl. Moving the wiper of PI changes the biasing on Tl and thereby increases or decreases the frequency of the associated multivibrator. This section of the circuit also enables the electronics for the printer to be tuned to the different types of thermal elements that Seiko mount in the mechanism. The suffix used (A, B or C) designates the resistance of the print head. The exact value is unimportant as PI compensates for it in any Case. The smaller the resist- ance of the thermal elements the lower the multivibrator oscillating frequency (upon which the current directly depends). i 5-3 1 The stepping motors are controlled via two groups of four transistors (T4 . . .T7 and T8. . .Til), each fitted with a diode circuit as a protection against any reverse induc- tive charges the motors may generate. An article is dedicated to this sort of motor elsewhere in this issue so we will not duplicate any of the details here. Before moving on from figure 5 we would like to point out the power supply section based on IC7. This provides power for the processor and its peripherals, of course, but also for the motors and thermal el- ements. Because of that is dissipates a lot of heat. During printing the peak current consumption is actually about 4.5 A. this way, there is a line free either at the left or at the right of the female connector. The Seiko version leaves the empty line at the left (pin 15 in table 4), but in our design we have moved the space to the extreme right (pin 24). This change is eas- ily made: carefully extract the female con- nector from the chassis, move it one step to the left, and re-insert k. Do not use any sharp (or toothed) tools for this — it is far better to just use your fingers. If the wiper of PI is turned fully clock- wise, this electroru'co-mechanicaJ assembly is now ready for the baptism of Small, but. . . Of no little merit is the fact that this printer/plotter is small in size. The layout of the printed circuit board is seen in . gu- re 6. The four comers of the printer mech- anism are bolted to this board at the positions provided. Connecting the mech- anism to the board is a matter of making 24 direct links between the two, on a one- to-one basis. Before doing this, however, it is wise to test the power supply (without the other components), and then the clock, anti-bounce flip-flops, and oscillator N6. . . N9. After mounting PI on the printed circuit board, its wiper should be turned fully to the right. In this position the printing contrast is minimal and there is no danger of burning out the print-head elements. Initialize (reset) the circuit and check that the logic level at the bases of T12 . . T20 is high. These transistors are then switched off so no current can flow through the thermal elements. The 'electronics' can now be connected to the ‘mechanics'. If an STP411-320 is used, make links 1 ... 24 as indicated. If the lower-resolution STP4U-256 is chosen, make all the links except 23 and then solder pins 23 and 24 together at the printer mechanism (not on the printed cir- cuit board). The mechanism of the STP4 11-256 must also be modified slightly. As table 4 shows, pins 15 ... 23 are offset on the '256' compared to the '320'. Rather than correct this by software, we prefer to move the internal connector on the printer block. The print head is connected to the chassis by a small piece of flexible printed circuit board (this can be seen in photo 4). The ‘320’ version uses all of the ten available tracks, whereas with the '256' only nine of the lines in the female con- nector are used by the male connector. In The software The program stored in EPROM IC3 cannot be properly dealt with in this article so we will only describe it in a very general way. The software is the same no matter Table 6 Important addresses Owing to lack of space, we are not able to give you the complete source listing: the hex dump of the EPROM in the plotter is given instead. Vector NMI in FFFAhex and FFFBhex points to the origin of a test routine in FB41hex- The remainder of the EPROM content is divided into two: the routines for receiving and printing lalphanumericallyl with the character generator, and the routines for plotting the vectors. Table 6 gives the principal addresses in hexadecimal. F000 . . F02C : internal jump table F02D . . F034: stepper look up tables F039: delay subroutine F041: SIGMA initialisation t. reset vector) F092: turn paper feed stepper right F0AC: turn paper feed stepper left F0BC: step print head left F0D6: step print head right F0E6: feed paper and increment F10D: eat paper and increment F13B: head right and increment F144: head left and decrement F154: home head F194: print character in A F308: print line buffer F384: load head F393: receive a character F41A: printer main program F586: character generator F936: graphic sigma F976: plot origin FA4F: graphic handler FB41 : test program Ih/MI vector ) FB90: vector plotter 5-32 I coordinate of the origin on the Y-axis I coordinate of the end on the X-axis ■ coordinate of the end on the Y-axis ■ 7" If none of these parameters is left out or if there is an error in the syntax the com- plete instruction is simply ignored. Be especially careful not to forget the last "/” after the end Y coordinate. Before starting to trace a design the pointers and timers for the plotter program must be initialized. This is achieved with the CTL-D (CHR$4) command. It will now be apparent just how easy this printer is to use in either mode. It is also a simple matter to combine alphanumeric characters and graphic traces. Lines are traced using an algorithm that makes successive approximations for the coordinates of all points between the ori- gin and the end of the vector (table S). In theory this algorithm allows vectors to be 32768 dots. If the vectors end coordinates are lower than the origin (on one axis or both), the X-Y plotter itself automatically reverses the direction of the plot. In printer mode the CTL-I (CHR$9) instruc- tion flips a ‘switch' in the program: all characters received after this command are printed in white on a black back- ground. The inversion continues until anot- her CTL-I is received. Note that an ASCII LF (line feed) is not needed after CR (carriage return) but it does not affect the operation of the printer. On the other hand, the characters fed into the buffer are dealt with one line at a time so the program can determine the position of the print head when the CR arrives. This infor- mation is then used to decide whether the next line will be printed from left to right or right to left. This so-called ‘bi-direc tional logical seek' simply looks at which choice requires the least head movement. Printer This printer/plotter can be tested even without a Centronics interface. An auto- matic test program included in EPROM IC3 takes care of this. The test draws a three-dimensional pyramid and is started by a short negative pulse on the 6502’s NMI (non maskable interrupt) input. A push-button can be connected from pin 6 of IC1 to ground for this. The printing contrast is increased by moving the wiper of PI left-ward. The con- trast changes very gradually only. There may be a noticeable drift at the cor- ners of the test pyramid's base. If this is the case, insert the link between pins 7 and 8 of PL4 and give another NMI pulse. The drift is then reduced by one step. If this is not enough, insert the next link. Continue like this, following table 2, until the pyramid is as perfect as possible. When this correction is made, the push- button can be removed. Now all the printer/tracer needs is to be put into a suitable case. Final note If the power-on reset does not always work error-free, this may be remedied by (a) replacing the 74LS04 in the IC12 pos- ition by a 74LS14, or (b) connecting an additional pull-up resistor of 1 k between the +5 V line and pin 10 of 1C 12 (output of N16). M • 5-34 eleklor india It is one of our traditions that we regularly publish some sort of sound-effect project, and what better at this time of the year than a cuckoo? It is, of course, not our intention to replace the real cuckoo, because however fascinating electronics may be, it cannot ever take the place of nature! the first cuckoo in spring* With reference to the circuit diagram in figure 1, integrator A1 and trigger A2 form a triangular-pulse generator. Diodes DI and D2 chop the apex of the pulses, so that the input to A3 looks like a distorted sine wave. Oscillator A3 produces the voice of the cuckoo which is amplified by T2 and T3. The remainder of the circuit serves to control the frequency and volume of the output. Counter/divider IC2, with its associated gates, determines the duration of each of the two syllables of 'cuckoo', and when oscillator A3 should be switched off. The design is such that even after trip switch S2 has been opened a complete cry of 'cuckoo' is produced. After all, no cuckoo worth its salt stops in mid call! Random number generator IC3, with its associated gates N2 and N5 . . . N7, is not necessarily involved in the synthesis of ... makes you I forget the long winter 5-35 ure 2. The various tim- diagrams facilitate an erstanding of the ction of the circuit It finding. 2 •> m m » ®- } used as the interface between the | triac controller shown in figure 1 and the ‘outside world’. The tap sensors control a set/reset 1 flipflop constructed from two C-MOS I NAND gates and a few resistors. To prevent this FF from assuming an indeterminate state when the power is switched on, the FF is preset to the off state by Cl. This can be particularly useful in areas where power cuts are frequent . . . At a certain age, children are often packed off to bed with the final admonition: 'All right, you can read in bed for a quarter of an hour, but then you must turn off the light and go to sleep'. However, as most parents will know, the children tend to suddenly loose all sense of time in this situation . . . When a member of the Elektor design team was faced with this problem, he started looking for an electronic solution. The final circuit, as published here, has proved extremely effective. In the situation outlined above, what is really required is a unit that will auto- matically turn off the bedside reading lamp after the specified time has elapsed. This time switch must have a few special - It should only be possible for the parent(s) to switch on the lamp. This ' Figure 1. Complete circuit of the reading-in- bed limiter. SI must be a key-switch that can only be operated by the parents. ■K&e* Bar-Code "Have you read about these new cash registers?" "Which ones?" "The ones with the bar code system , One day in the future, these cash registers will be seen in all the departmental stores and large shops. When you buy anything, say. a pair of jeans, the sales girl at the counter will just move an electronic pencil over the price tag and immediately the cash memo will come out from the cash register." "What’s morel not only the price will be printed on the cash memo, but even the article number and the size of jeans!" "How do these new cash registers manage all this?" "Where these cash registers are being used, the price tags on the articles have a zebra strip pattern. You must have noticed this strip pattern on many foreign products, even books and magazines." "Yes I have seen this patternl" "This zebra strip pattern is called a Bar-Code. All figures and letters for the article number, size, price etc. are hidden in this Bar-Code. The pencil which the sales girl at the counter moves over the price tag can read this Bar-Code." "Read the Bar-Code? You mean a small man is sitting inside the pencil and counting the strips? ' "Not quite so, in the tip of the pencil there is a source of light, which illuminates the Bar-Code. The white paper reflects the light back into the pencil. The black strips don't. The pencil thus recognises the black strips and informs the cash register about this through the cable connecting the pencil to the cash register. "But what does the cash register do with this information of ’Black' and ’White' coming from the pencil?" "The cash register sees this Black’ and White’ as binary numbers ’V and ’O’. Sometimes the broad black strips are read as 1 and narrow black strips as O. There are several possibilities.” "Nowl You are really making up storiesl Can you tell me how the cash register can read JEANS. SIZE 108. Rs. 98.75 from the ones and zeros?" "Take it easy! Have you ever heard about digital technology?" "No.” 0&3C "The digital technology manages with only two numbers, 0 and 1 . This number system is called the binary system. When you need larger numbers, you simply put together several binary numbers. I'll now show you how it is done. Let us write down the numbers 1 to 10 as binary numbers. So far both are same. z 1 o "That's right! This is Digital Technology! With an extra lamp and some wire, you can even transmit the numbers somewhere else." For number 2, there is no single binary number, so we need a second digit. "By the way, we mostly use 5V in digital technology." "Just a minute, I need four switches if I want to reach upto 10" v3 9 1 1 1 0 O For the number 4 even two digits are not enough, so we add a third." s 9 10 10 1 1 1 o 111 100 0 10 07 10 10 "Four digits for a simple 101 That’s rather elaborate." "That's right! But the practical aspect of this is that we can substitute these 0 and 1 easily through something else, like 'White' and 'Black' in the Bar- Code, or a lamp lighted or extinguished, or a voltage switched on or off and so on." "In that case I can even generate numbers with a battery and a switch." 4 5-56 elehtor india mav 1985 "Would it not simplify matters, just by using two wires and different voltages to represent different numbers? For instance, OV for 0, IV for 1 and so on upto 10V for 10?" "Naturally, you would save the wire but then it would be quite difficult to see from the lamp how many volts are applied. Moreover, when there are voltage fluctuations in the power supply, it can spell disaster! A drop in voltage by 1 V means 9 will be read as 8" "And the jeans will cost only Rs. 87.64 instead of Rs. 98.75! Special discount by virtue of the voltage fluctuations!" Digi-Course Chapter 1 : AND, OR, NOT We have already seen how digital technology works, when we looked at the Bar-Code in the previous pages. At first we may find it a bit odd to denote two mutually exclusive quantities by 1 and 0 and then build a complete technology on it. However this simple basic rule of digital technology makes it so much versatile and all powerful. It is equally simple to work with binary numbers, and to link them logically. There are three basic operations that can be carried out with binary numbers. —the AND operation — the OR operation —the NOT operation (Negation) These operations are quite simple compared to the fundamental mathematical calculations like addition, subtraction etc. Within the scope of this course we shall focus our attention on the practical applications of this system of logic. For the practical implementation of these operations it is always necessary that we clearly define the logic states of the circuit, for example. 5V/OV or Switch closed/open states should be clearly attributed to the binary numbers "1" and "0” 1 . The AND operation Figure 1. shows two switches in AND configuration. The functional description of this circuit is: When switch A AND switch B are dosed, the tamp is lighted. s a Se This logic function can be described in form of a table. This is called the truth table of the particular function. This covers all possible combinations of the switch positions. Table 1 SA SB closed La tinguished tinguished tinguished lighted For the switches as well as lamp, there are only two states possible. A switch can be eithe'r open or closed and the lamp can either be lighted or extinguished. This is ideally suited for our application to binary numbers as these are the only two mutually exclusive states possible for the switches and lamps. By attributing numbers 1 and 0 to these states as follows: Switch closed 1 Switch open 0 Lamp lighted 1 Lamp extinguished 0 We obtain the new version of our truth table. Table 2. Now, a question that naturally follows is "What this switch and lamp configuration and its mathematical abstraction has to do with modern digital technology?" Certainly nothingl as long as no concrete meaning is attributed to the switch positions. Let us examine the following statement: "Only the person who informs us his address on the order card AND pays the subscription, shall receive Elektor magazine" This statement contains two conditions, which are linked by AND, therefore, this sentence fits the description of the circuit of figure 1. The two conditions can be attributed to the two switches SA and SB. Suscription is paid: switch SA closed. Address was informed: switch SB closed. Lamp lighted: Magazine shall be sent. "False" and ’True" in table 3 now correspond to "0" and "1" in table 2. false false false ,5-57 0£3C Although this electronic "Calculation" of the logical connection between these statements is realistic, the program of the subscription computer cannot make use of this switch and lamp configeration. In the digital technology, the so-called "Gates" implement these functions. The AND Gate has the following symbol: (See table 5.) The output OUT of the second AND Gate becomes TRUE only when all the three conditions are fulfilled. The "False" and "True” in the table can easily be replaced by "OV" and "5V" or simply "0” and "1" Figure 2. The power supply lines are not shown, as all the gates in the TTL series work with 5V supply. The voltage for logic 1 is also same, i.e. 5V. whereas the logic 0 is OV. Unconnected inputs of the gate behave as logic 1. Table 4 gives the AND Gate truth-table in form of these voltage levels at input and output. Table 4. Inputs Output A I B I OUT 0 V 0 V OV 5 V OV OV 0 V . 5 V OV 5 V 5 V | 5 V The combination of two AND Gate in figure 4 can be replaced by a single symbol with 3 inputs or a more generalised symbol as shown in figure 5. The input voltages can be applied from a voltage source through switches and the output voltage can be indicated by means of an LED. (Light Emitting Diode) 3D— The real utility of these gates is because of the fact that the output of one gate can become an input of another gate. Figure 4 shows two AND Gates connected in such a way that the output of first AND Gate becomes an input to the second AND Gate. Now a further information can be fed at the third input, for "A new issue of Elektor has come out" Because of the third input, the total number of possible combinations is considerably increased. 2. The OR operation The OR operation can also be demonstrated with two switches and a lamp. When SA OR SB is closed, the lamp is lighted. Figure 6. Table 6. SA S8 closed closed extinguished The symbol for the OR Gate is as shown in figure 7. The OR Gate gives a 5V output when any one of the inputs A OR B is at 5V. 83619X7 Table 7. Inputs Output A | 3 1 OUT OV OV 0 V 5 V OV 5 V OV 5 V 5 V 5 V 5 V 5 V For better understanding of the OR operation, let us go back to our example of Elektor subscription. Examine the statement: "The subscri ption can be paid by Demand Draft OR The truth table for this statement can be written as follows: Table 8. Surprisingly, there are three instances in which the magazine is supplied, because the OUTPUT shows a "1” The last two lines of the table say that somebody has paid his subscription twice. Although this is very improbable in reality; in principle it can be thought of and since our subscription department works honestly, the circuit must be extended once more. (See figure 9.) Figure 9. A B Demand Draft Cheque false false The OR Gate output indicates whether the subscription is paid or not, so it can be placed at the input B of our earlier subscription data processing circuit which now becomes a circuit with four inputs, and can handle 16 different input combinations. Table 9 shows all different combinations. The added AND Gate picks out the double payments and reports them with a logical "1 " at output 2. 3. The NOT operation The NOT Gate is also called an inverter; because its output is exactly opposite of the input. "1" at the input gives a "0" at the output, and vice versa. This inversion is marked by a bar above the input letter. Our subscription data processing could also use an inverter. It prevents that the issues are delivered even when the cheque is not honoured by the bank. "... AND the cheque was NOT returned. Is the additional function which is realised by an AND Gate and a NOT Gate at the input C. Figure 11. The input E is fed with a "1 " if the cheque is not honoured. This gives an output ”0" irrespective of the input C. The truth table for this circuit now becomes very extensive with 32 input combinations. Why 32? With every additional input the number of probable input combinations is doubled; because for every input combination already covered, the new input can be "0" or "1 " | Table 11 Number of . Number of inputs Combinations 0 1 1 2 3 8 4 16 5 32 The figures in the right column are the basic numbers of the binary system. (See Bar-Code) Bicycle Siren Just imagine, you are walking down the street and suddenly behind you, you hear the famous Police "What have I done to attract the Police? "you are shocked and look back just to find a harmless cyclist who has constructed himself a Bicycle Siren. The circuit is quite simple. 1C 2 together with R2, R3, P2 and C3 forms an oscillator. A circuit which produces an A.C. output with a frequency in the audio range. However, as the output of the 1C 2 is not sufficient to drive the loudspeaker. Transistor T1 is used to amplify the signal at the output of 1C 2. Transistor T1 is used in the emitter follower configuration and produces a large emitter current proportional to the base current provided by the output of 1C 2. The oscillations produced by 1C 2 are controlled by the setting of potentiometer P2 as well as the voltage on Pin 5 of 1C 2. The voltage of Pin 5 is supplied by another oscillator circuit formed by 1C 1 . 1C 1 produces a slowly rising and falling voltage signal at its output pin 7. which is applied to Pin 5 of 1C 2 through R5. Corresponding to rise and fall in voltage at Pin 5 of 1C 2, the pitch of the siren also rises and falls, producing the exact effect of a Police Siren. This entire circuit is powered by the dynamo of the bicycle itself, and no battery supply is required. (Quite a saving on energy!) Since a dynamo is an A.C. generator, its voltage is rectified by the bridge rectifier B1. The electrolytic capacitor Cl serves as a filter to smooth out the rectified D.C. voltage. Construction Details: All components used in the circuit are standard components. These are assembled on a small SELEX PCB (Size 1.). The 1C socket, jumper wires and resistors are soldered first. Then the three capacitors and finally the semiconductors are soldered. A cooling fin is slid over the transistor T1 to prevent it from getting hot. The orientation of ICs should be as shown in figure 2. Three small 8 ohm speakers are connected in series for optimum sound level, but to economise on speaker cost and to make the unit compact, even a single 8 ohm speaker will do. However it should be protected by a 47 ohm resistor in series as shown in the circuit diagram. The design of enclosure is left to the imagination of the constructor. The push switch SI should be fixed on the bicycle handle. An additional switch for switching off the lamp will also be needed. Potentiometer P2 is used for adjusting for frequency of the siren and PI is used for adjusting the rise and fall cycle of the siren. Regular potentiometers with spindle and knobs can also be used for PI and P2 instead of the small preset pots shown in the figure 2. 1C 1 and 1C 2 The versatile timer 1C 555 used in the circuit as oscillators (Astable miltivibrators ). The resistors R1 and PI charge the capacitor C2, and the voltage across C2 rises slowly. When it reaches 2/3 of the supply voltage, the 1C discharges capacitor C2 and 5-60 Circuit diagram of the Bicycle Siren. Figure 2: Component layout. 1 /3 of the supply voltage, at this value the discharge is stopped and charging cycle begins again. Thus the output voltage at Pin 7 of 1C 1 oscillates between 1 /3 and 2/3 of the supply voltage. 1C 2 also functions as an astable multivibrator. However its output is controlled by voltage on Pin 5. The control voltage on Pin 5 decides the upper limit for the capacitor charging voltage and higher the upper limit, longer is the period of charging cycle. Caution: This siren should not be used in place of the bicycle bell, and should never be used in normal trafficl Components: ibeM W/W POTENTIOMETERS Technocrat Components have intro- duced BHS-3 wire wound potentio- meters with 3 watts rating. They are housed in bakelite moulded body and the sealing is claimed to be almost hermetic. resistance values of 100 E, 500 E, 1 K, 2 K, 5 K, 10 K, 15 K, 20 K and 25 K. Non standard shaft lengths and resistance values are available only against specific bulk order. For further information, write to: Technocrat Components Post Box No. 930, Madras 600 020 EMERGENCY LIGHT Elsonic Santo have introduced ‘Nite- sun’ emergency light with a beam type reflector. The unit has seperate battery compartment which houses a chloride 3EV9 plastic encased wet battery or an equivalent rechargable dry battery. The battery needs topping up once in 45 to 60 days. A solid state device is used for switching to avoid faults in switching with relays. For further information, write to: Elsonic Santo Corporation 8/1. Palmgrove Road, Bangalore 560 047. HIGH VOLTAGE TEST PROBE Equilab have developed a new high voltage TV test probe and meter. This is available in two series— HT 200 and HT 300. These are suitable for mono- chrome as well as colour TVs. The series HT 200 has a sensitivity of IOuA/KV and the series HT 300 has a sensitivity of 2 uA/KV. Accuracy avai- lable is * 3% to * 5% depending on the individual models. For further information, write to: Electronic Instrument Labs. 339/68. Rajesh Building, Dr. Bhadkamkar Marg. Bombay 400 007. TWILIGHT SWITCH Otronic have developed an automatic light control switch which can switch the lights ON and OFF at a predeter- mined intensity of ambient light. The circuit is based on a Light Dependant Resistor and needs only one setting. The unit consumes 10 VA power and has a switching capacity of 10 Amps. It works directly on mains supply ULTRA VIOLET LIGHT SOURCE Professional Electronic Products offer a compact UV light source for erasing EPROMS like 2708, 2716, 2758, 8755, 8748 etc. The source can erase eight EPROMs at a time. A O to 60 minutes timer is provided to set the time of erasure. The unit is claimed to be completely safe due to the low wattage lamp and a safety interlock system. Power consumption is about 20 Watts. For turther information, write to: Professional Electronic Products, Post Box 316, Delhi Road, Meerut 25 0 002. 16 PIN 1C CLIP Comlech have introduced their T-16 1C clip for 16 pin DIL packages. It provides easy access to ICs through non- shorting electrical contacts with posi- tive mechanical clamping. Selectively gold plated spring brass contacts are designed for wiping action. The con- tact-comb with its insulating barriers provides easy positioning and prvents accidental shorting of adjecent leads. TV DEFLECTION COMPONENTS Selectronics (Gujarat) Pvt. Ltd. have introduced their new TV deflection components— a set consisting of Defle- ction Yoke, Line Output Transformer and Linearity Coil. The components are tested according to international standards specifications and are claimed to give perfect picture quality. For turther information, write to: Selectronics f Gujarat) Pvt. Ltd. 5, Ruxmani Park, Kankaria, Ahmedabad 380 022 For further information, write to: Otronic Lawyers Chambers-Ground floor. 18, Picket Cross Road, Bombay 400 002. For further information, write to: Component Technique 8. Orion Apartments. 29/a. Lallubhai Park Road. Andheri (West), Bombay 400 058. NON CONTACT VOLTMETER Swadeep Instrumentation have marke- ted a new 20 KV Nor. contact electro- static voltmeter manufactured by Mon- roe Electronics Inc. of U S A. The electrostatic voltmeter permits mea- surement of Electrostatic surface potentials upto 20 KV without physical contact to the surface under test, with an accuracy of better than 0.1% Response is better than 35 milliseconds to 20 KV and the drift is less than 2V/hour non cumulative. The instru- ment is available against actual users import licence. For further information, write to: Swadeep Instrumentation 101, Vishnu Villa, 10th Road, Khar, Bombay 400 052. BEFORE YOU BUY A juP Training / Development Kit Make sure you are getting all that you need. O Powerful hardware and software features to meet all your requirements. # Most comprehensive, easy to understand courseware documentation. Complete with data sheets of ICs used. % Instant service back up from expert engineers. Series gives you ail that you need MICROFRIEND-I: 8085 CPU, 4K Firmware. 2K RAM. Expandable to 24K ROM or 1 2K RAM EPROM Programmer lor 2716. 2732 and 48016. 46 PIO lines. TTY-20 mA. RS232C l/F. Audio cassette IF. 8155 Timer. 6 digit display and keypad. STD Bus for expansion. MICROFRIEND-Z: Z80 A CPU with specifications same as Microfriend-I. MICROFRIEND-68: 6802 CPU with specifications same as Microfriend-I. MICROFRIEND-II: 8085 A CPU, 4K Firmware, 2K RAM. Expandable to 24K ROM or 12K RAM. 48 PIO lines, TTY-20 mA. RS232C l/F, Audio cassette l/F, 8253 Timer, 6 digit display and keypad. 50 Pin buffered Bus for expansion. MICROFRIEND-III: 8085 A CPU. 8K Firmware with Editor Assembler. 2K RAM. Expandable to 52K RAM or ROM EPROM Programmer for 2716, 2732, 2764, 27128 and 27256, 48 PIO lines, 80 x 24 Video Controller using MC 6845. ASCII Keyboard l/F, Centronics Printer and Audio cassette l/F. RS232C l/F using 825 1 . 8253 Timer. 32 Key Keypad and 6 digit display. STD Bus for expansion. MICROFRIEND-ZLC: Z80 A CPU, 4K Firmware. 2K RAM. Expandable to 8K ROM or RAM 16 PIO lines. Audio cassette and Serial l/F, EPROM Programmer for 2716 to 27128, 280 CTC Timer, 6 digit display and keypad. MICROFRIEND-65: 6502 CPU. 4K Firmware. 2K CMOS RAM 64K DRAM Memory expandable to additional 1 6K, EPROM Programmer for 27 1 6 to 27 1 28, RS232C Serial l/F. Audio cassette l/F. 8253 Timer. 6 digit display and keypad. STD Bus for expansion. MICROFRIEND-86: 8086 CPU, 1 6K Firmware. 4K RAM Expandable to 48K RAM or ROM 128K DRAM EPROM Programmer for 271 6 to 27128, RS232C Serial l/F. Audio cassette l/F. 8253 Timer. 72 PIO lines, 8 digit display and keypad. MULTIBUS for expansion. MICROFRIEND-8678: 8086 CPU, Socket for optional 8087 and 8088 CPU. 1 6K Firmware. 4K RAM Expandable to 48K RAM. or ROM EPROM Programmer for 2716 to 27128, 72 PIO lines, RS232C Serial l/F. Audio cassette PF. 8253 Timer. 8 digit display and keypad. 50 Pin Buffered Bus for expansion. MICROFRIEND-68K: 68000 CPU, 20K Firmware, Single line Assembler and Disassembler, 32K DRAM, Expandable to 256K. EPROM Programmer for 27 1 6 to 27128, 80 x 24 Video Controller using MC 6845. RS232C Serial port with complete baud rate control. Centronics compatible printer port plus one more PIO port. Audio cassette l/F. ASCII keyboard l/F. PLUS A WIDE RANGE OF OPTIONAL ATTACHMENTS TO EXPAND THE SYSTEM. Dynalog Micro-Systems TECHNICS 4731/21 Dayanand Marg, Daryaganj, New Delhi 1 10 002 Tel : 276988, 270832 14. Hanuman Terrace. Tara Temple Lamington Road. Bombay 400 007 Setting the standards in juP based technology. 5-67 'Cable Faults' break the life line of your Telephone Resurrection of the dead phones involves time consuming operations like detecting fault in several kilometers of underground cable pair and a lot of trial and error digging. P & T guys had to toil really hard until APLAB 3039 Cable fault locator arrived on the scene Now within minutes and with an unprecedented accuracy of one metre in kilometres, one can pin point the fault location, dig at the right place and give back to you your life line. Aplab 3039 was bom out of its extensive R&D. Germans. French. Americans. Belgians and Austrians used over 1000 units of APLAB 3039 as a standard PTT field kit. Today Indian P & T also serves you faster with our assistance- with 3039 1 'APLAB HOUSE' A - 5/6, WAGLE INDUSTRIAL ESTATE, THANE PHONE : 59 18 61 - 2 - 3 TELEX : 01 1 - 71979 APEL IN ■ . - 1 Luxco car stereo speakers bring concert hall performance to you —crystal clear Hi-Fi stereo, well above the wind and traffic noise. Make driving a pleasure with car stereo LUXCO speakers 5-73 igcosmic IS COLOURVISION R ChWKterana. 2. Kouman. MthARoadKh