INDIA mmmtmmim EQU mcv January 1985 function generator soldering-iron regulator Ni Cad-charger tinier 7 watt IC amplifier 7400-siren light dimmer | o , o i) 7 V. Volume 3-Number 1 EDITOR: SURENDRA IYER PUBLISHER: C R. CHANDARANA PRODUCTION: C- N. MITHAGARI ADVERTISING & SUBSCRIPTIONS ElEkTOR ElECTRONiCS pVT Hd Chotanl Building 52 C. Proctor Road Grant Road (E) Bombay- 400 007 DISTRIBUTORS: INDIA BOOK HOUSE PRINTED AT: TRUPTI OFFSET 103, Vasan Udyog Bhavan. Off Tulsi Pipe Road, Lower Parel, BOMBAY- 400 013. the XR2206 in the function generator Why this old 1C is still the one to use for a new function generator. This article shows how we have capitalised on the XR2206's good points and negated its drawbacks to provide a simple, but very effective, new function generator. shorthand BASIC Many computers provide a sort of shorthand to simplify and speed up the process of typing in BASIC programs. Here we provide the same facility for the Junior Computer and other 6502-based machines. function generator Made-to-measure sine, square and triangle waves are very useful for testing cir- cuits. This new function generator can provide them all but is neither expensive nor difficult to construct. 1-20 1-23 1-26 time switch Adds a touch of sophistication and user-friendliness to 1-32 cheap battery chargers. cumulative index 1984 1-35 with a pencil point ■ • • Simple effective desol dering aid. give your soldering tip a longer life 1-39 A modern economy circuit that may increase the life expectancy of your soldering computer-controlled slide fader 1-42 This circuit not only enables slide pictures to fade into each other on the screen but can also be used for controlling the gating angle of other electrical appliances 7 watt 1C audio amplifier 1-53 toroidal transformers 1-54 The article discusses the excellent electrical qualities and advantages of the toroidal transformer over the conventional types microprocessor-controlled frequency meter (part 0) . . 1-56 A look at the features of this sophisticated menu-driven frequency counter. The constructional details will be featured in next month's issue. 7400-siren 1-58 light dimmer 1-58 market 1-59 appointments 1-61 switchboard 1-65 INTERNATIONAL EDITIONS EDITOR: P HOLMES COPYRIGHT C ELEKTUUR B V — THE NETHERLANDS 1984 index of advertisers 1-70 1.03 A fine design belongs on a ISRO, BHEL, OEN, ITI, NGEF. Of fine Circuit Board. Keltron is course, there are good reasons, uniquely equipped to supply The best equipped factory, superior service on prototype with the largest camera in boards. Our totally India— for photographing the self-contained plant is presently biggest artworks devoted eolely to tdeir ln|(a ., ed full WM( . m to menofeotore. Our success has rs) | 0 „ in so|d „ encouraged us to up-date our _ , . technology to produce Quall, V control to ensure that multi-layer boards in the near every board exhibits full f uture electrical integrity before The cotteot expeosion will compon.nts ,r * m0 “"“ d make Keltron the largest place producer of Circuit Boards in u . _ _ _ India. Our clients include Keltron r.C.B.s high-tech organisations like guarantee reliability. THE FINE ART OF ELECTRONICS: P C B s BY KELTRON SintLI l 985 ative index 1984 cumulative i multi-channel analog to digital converter . parallel/serial converter power switches for pPs programming the 6845 RS232 analyser RS232/Centronics converter RS232/V24: the signals RS423 interface audio, video and sound generation active crossover filter amplification selector analytical video display audio preamp buffer audio signal embellsher audio sleuth at work digital band pass filter dynamic pre-amplifier guitar preamplifier gyrophone infra red headphones, receiver infra-red headphones: transmitter., metronome extension mini crescendo real-time analyser (part 1) real time analyser Ipart 21 real-time analyser (part 31 scratch and rumble filter screen noise killer 70/90 watt amplifier small high power amplifier stereo balance indicator stereo doorbell tape contents detector the QL: first impressions three-state indicator tnac control board 2716 versus 2708 twin RS232 2 x 2716 = 2732 UHF video and audio modulator use your TV receiver as a monitor 280 EPROM programmer Z80 CPU simulator ZX81 cassette pulse cleaner ZX extensions dynamic RAM power supply 64 way 2 dimensional bus board banking program domestic alarm timer automatic cloakroom light automatic reserve warning light battery meter blown fuse indicator burglar detenent central -heating monitor coffee temperature indicator Elabynnth electronic mousetrap energy-saving porch light flashing telephone light fridge alarm from thermometer to thermostat how accurate is your watch kilowatt dimmer musical doorbell portable distress signal programmable disco light display rain indicator single button code lock sonic deterrent super-simple bell extension switch-on delay sync separator the story of valves touch- pad potentiometer valve amplifier versatile audio peak meter video colour inverter video combiner video sync box voltage-controlled audio switch vidio amplifier disco phaser sound generator computers and microprocessors address decoding Basicode-2 for Junior plus VDU card . controlling the floppy-disk drive motor CPU clock generator daisywheel typewriter printer interface . data communication by telephone digital cassette recorder digital cassette recorder revisited digital cassette recorder with the ZX81 direct -coupled modem DIRPUT eiektermmal bell EPROM copier EPROM eraser fast analog to digital converter floppy expander floppy tester GET and GO IDUST intelligent EPROM eraser loystick interface level indicator lightpen memory timing merging BASIC programs pP infra red interface mini signal cleaner telephone amplifier how to recycle dry cell batteries Frost warning device LEO ornaments temperature reading on a multimeter . tnac control boaro twin doorbell 2N3055 sun switch wind direction indicator generators and oscillators .35 dex 1984 cumulative index 19 pulse generator pulse generator sawtooth generator . . Wien bridge oscillator 5-24 varistor protection circuits 8-37 World's smallest microcomputer (selektorl . 8-99 circuit boards and soldering 8-78 the Bf 494 NOVRAM data storage without batteries ( i measuring and test equipment a 63 amplification selector 615 analytical video display 6 )6 audible ohmmeter 8 23 capacitance meter „ 54 combining 4017 counters 8-73 , , 8 digitester with a difference frequency meter from thermometer to thermostat hi lo pulse rate discriminator 8 29 LC meter 8 26 LED current sensor 6 36 level indicator 3 18 PARSER . 10-35 pulse generator 7 50 pulse generator 8 69 real time analyser (part 1) 10-30 real-time analyser Ipart 2) 8 28 real time analyser (part 3) 8 78 three-state TTL logic probe 8 17 transistor polarity tester 4 15 VHP dipper 8-42 window' LEDs . 3-34 signal injector . 8 44 analog frequency meter 8 45 h I logic teter . 8 16 8 70 miscellaneous 3-57 aviary illumination 1 -54 bird imitator blown-fuse indicator economical motor driving circuit 6 46 electronic key set 1 o 46 event counter 2 39 lunny bird 76488. home-made low-cost wiring probe 3 b2 'ead-acid battery charger .486 one armed bandit maximum and minimum memory 10-18 photoelectromc relay 10 52 l ,or, able distress signal s , 7 programmable crystal oscillator (applicator) ,, , , SCART adapter 1 3 14 single chip colour decoder - the TDA1365 (applicator) g jg switch indicator 7 1 6 switching delay 3 38 ,nac coPtroi board 5,5 universal active filter 12 18 ualve simulator 5 i a varistor protection circuits 2 gg versatile timer 12 ,4 voltage controlled audio switch 8 .59 flashing badge 4 , g universal NiCad charger 10-16 balancing transformers EM pocket radio noise squelch short-wave pocket radio time signal receiver VHP /AM air-band converter VHP converter MF HP USB marine receiver hobby and car alarm clock for cars automatic reserve warning light aviary illumination diesel tachometer digital tachometer echo sounder fatigue tester flash meter guitar preamplifier "lights on" warning pace counter petrol saver remote shutter release reversing buzzer revolution counter self-switching battery charger speed regulator for disco lights stroboscope automatic battery charger locomotive headlamp reverser A new memory 1C from Mostek 6116 + 2716 = 48Z02 (applicator) universal active filter using the pulse generator disco drum guitar preamplifier musical doorbell . . 1.36 84 cumulative index 1984 cui frequency meter 3.49 IJuly/August 1984, page 8-38 a 49 how accurate is your watch’ 8 M (January 1984. page 2 16 7 39 mfocatd 97 8 91 May 1984 19831 8/9 infocard 102 8 46 j u iy 1984 8 87 lamp saver 8 40 (September 1984. page 10 48 . 9 01 mating logic families 8 74 (February 1984, page 3 38 8 - 55 maximum and minimum memory 8 27 (June 1984. page 7 37 6 24 merging BASIC programs 8 70 (June 1984. page 7 48 5-62 musical doorbell 7-42 (July/August 1984. page 8 80 1 -52 power controller for model railways 1_26 (November 1983, page 12-18 Prelude (part 31 (April 1983, page 5-34 programmable disco light display 9 ,4 (February 1984, page 3-21 pulse generator 10 74 (Aphi 1984, page 5-24 VDU card 9- 14 (October 1983 page 10.38 musical doorbell 1074 (Aug/Sept 1984 page 8.80 circuit 77 triac control board 4-74 (March 1984, page 4-18 universal active filter 12-70 ( January 1984, page 2 36 power supplies constant voltage source dissipation limiter high power op-amp supply lead acid battery charger linear opto-coupier low-power switching regulator microcomputer power supply microcomputer power supply protection NiCad charger overvoltage protection power supply considerations power supply for computers power supply monitor switching power supply transformerless mams power Supply variable a c power supply PSUs on PCBs bus extension symmetrical power supply missing link analytical video display (May 1984, page 6-29 capacitance meter (February 1984, page 3 42 CPU card (November 1983, page 12-24 daisywheel typewriter printer interface (June 1984, page 7 32 digital cassette recorder (January 1984, page 2 23 direct-coupled modem (October 1984, page 11-34. . elektcF Wishes its readers a happy new year! 1 .37 with a pencil point W. Schmidt Willi a pencil point Many electronics enthusiasts look on solder removing as a loathsome job. This is especially true of printed circuit boards with narrowly-spaced conductors. Things which often happen when one is trying to desolder are: - The solder forms bridges between the conductors. Blobs of solder drop off the board. De-soldering tools or wicks are available commercially, but there is no need to lay out that kind of money. Any work- shop toolbox should yield a really cheap device which will do the trick - a pencil. Propelling pencils with long leads of 2B or B hardness are particularly suitable (e.g. clutch pencils). To remove solder from a hole, the solder must be heated with a soldering iron until it melts (figure 1). The next step is to stick the pencil point in the hole, and take away the iron (figure 2). Where the pencil lead touches molten solder, the solder ‘jumps’ away, because of its surface tension, and the hole is cleared of solder (figure 3). A similar method can be used for get- ting rid of bridges of solder between tracks. To do this, the pencil point is laid flat on the molten solder between the tracks. 1.38 elektot india tanuary 1985 give your soldering tip a longer life The life expectancy of the tip of a soldering iron may be increased substantially by heating the iron to full capacity only during actual use. To accomplish this, the input power to the iron is reduced during the periods the iron is resting on its stand. This is achieved by using only one half of each cycle of the mains voltage during the rest period. with this economy circuit Heating of the iron during half cycles of the mains voltage only is effected by con- necting a suitable diode in series with the "live" mains conductor as shown diagram- matically in figure 1. A suitable actual arrangement of this is shown in figure 2. When the iron is suspended at rest, the spring-loaded switch is open, and the diode passes only one half of each mains voltage cycle. When the iron is lifted for use, the draw spring causes the switch to be closed by the aluminium strip: the diode is then short-circuited and full mains power is applied once more to the The fuse in series with the diode protects it during the transient caused by the clos- ing of the switch. The neon lamp indicates when only half power is being supplied to the iron. This type of arrangement has the advan- tage that it is suitable for use with any soldering iron, but it is almost twenty years old. Nowadays, pulse control instead of half-wave control us used. In pulse control, the soldering iron is heated for only 50. . .90 per cent of the time the mains is on. The relation of the control pulses (Q) to time is shown diagrammatically in figure 3: at the top the mains voltage, 240 V/50 Hz, under this the clock pulses derived from the mains, then the 0 pulses which switch the heating element, next the voltage across time determining capacitor C2, and finally the part of the mains voltage actually used for heating. Circuit description The circuit of the soldering iron regulator, figure 4, is quite uncomplicated. In the following, the description is on the basis of figure 3. soldering irons of 15 . . . 1500 watts. It is also possible to control other resistive heating elements, such as immersion heaters, with the circuit. If, however, the circuit is used for the control of heating elements combined with a fan, such as hair dryers or fen-forced heaters, it becomes necessary to connect a 220-ohm resistor in series with a 47 nF/400 V capacitor across the triac. No calibration is required: it is only necessary to set one potentiometer for the required power during the rest periods, and the other for the required power dur- ing use. Inevitably, this means that some compromise between the two require- ments has to be found as on the one hand the power during the rest periods should not be so low that it takes too long for the iron to reach normal heat after being picked up for use, and on the other, that this power should not be so high that the tip of the iron overheats during the rest periods. As already stated, switch SI may be arranged as shown in figure 1. M elektoi India January 1985 1.41 The use of two slide projectors and this computer-controlled slide fader enables the pictures to fade into each other on the screen at a variety of speeds. The fader is a versatile circuit that can be used for a number of applications other than the control of slide projectors. It allows the gating angle of two devices, such as lamps or motors, to be arranged by computer: the angle may be increased or reduced automatically at up to sixty-three different speeds. Within a given program, the circuit also provides for the independent actuating of up to four relays. Moreover, it provides an eight-bit input for data from equipment connected to it. computer-controlled slide fader. . . . . .can also be used for phase gating other devices Figure 1. This bli diagram gives a clear view of the fund*" - the complete cirt The circuit came into being from a desire to design an easy-to-use slide fader that could be controlled by a computer - any computer - and which would fade slides smoothly. This necessitated filed address decoding and automatic control of the switch-on and fading of the projector lamps. Moreover, it was thought desirable for the projectors to be switched forward and backward independently of each other. To make this possible, it was found necessary for the circuit to be able to actuate four relays independently of one another. When all this had been incor- porated, we had an interface that was clearly also usable for purposes other than the control of slide projectors. It seemed therefore logical to add an eight- bit input port via which messages from equipment connected to the interface could be read. Block diagrams A schematic view of the complete circuit is shown in figure 1. The complete address bus, A0. . .A15, and the required control bus connections are taken direct 1 .42 ele«(c to the address decoder. Examples of the decoding with the ZX81, ZX Spectrum. Commodore C64, and the Junior (with extension bus) are given later in this article. The address decoder generates four CS signals which select eight-bit memory units: three output and one input. Writing into the output memories and reading the contents of the input memory takes place via the data bus. The four relays are controlled via two lines of two output ports; all other lines of the output ports are used for the program- ming of the two counters. These counters, synchronized with the mains frequency by a zero crossing detector, are the real heart of the circuit in that they provide the desired phase shift and generate the trig- ger pulses for the triacs. A special output stage enables these triacs to fire very close to the zero crossing of the mains fre- quency. The triac output stages are electrically isolated from the control stages by opto- coupler. They have been arranged so that they may be connected to different ax:. supplies. The two supplies must, of course, be in phase or anti-phase. The schematic in figure 2 shows the counters in more detail. It should be noted that the terms "fading", "coming on”, and "fading speed” used in the following apply, strictly speaking, to lamps only: in the case of motors, these should be "reducing speed”, "increasing speed”, and "rate of reduction, or increase, of speed" respectively. In proper technical terminology, we should have used "increasing, or decreasing, gating angle", but that might have become too con- fusing. Counter 1 is loaded with the fading speed by the computer, and counts downwards. When counter position ”0” is reached, a clock pulse is given to counters 2 and 3 via the time lapse control stage, while counter 1 is loaded again with the content of the memory unit (which makes it poss- ible for the fading speed to be altered during fading or coming on). Counters 2 and 3, both type 4S16, are connected in cascade and thus form a composite counter. The direction of counting is reversed via U/D . During the coming on period of the lamp, the counter is loaded by a pulse on PE with bit pattern 1111 1111, and switched to downward counting via U/I). During fading, counter 2/3 is reset to 0000 0000 by a pulse at RST and switched to upward counting via U/D . Counter 4 is triggered by the zero- crossing detector, loaded with the actual content of counter 2/3, and then counts downward from that content. As soon as counter position ”0” has been reached, the ZD (zero detect) output is actuated, and this causes the trigger generator to impart a pulse to the triac. At the same time, the clock output is disabled. On the next pulse from the zero crossing detec- tor, this process repeats itself, and so on. Figure 2. The counter units in figure 1 consil three interconnected counters the function which is represented i this diagram. pnrng Ebisbiiim connected variety of c The content of counter 2/3 keeps on changing, of course, as this counter is clocked by counter 1. Summarizing, counter 1 functions as pro- grammable clock generator for counter 2/3, while the content of counter 2/3 is loaded into counter 4 to determine the phase gating angle. The time lapse control stage ensures that the lamp stays on after coming on, and remains out after fading, until a new pro- gram is used, and that at the onset of fading the lamp does not prematurely extinguish. Circuit diagrams The circuit of the control board is shown in figure 3, that of the triac board in figure 4. Starting with figure 3, the address decoder for the various computers will be discussed a little later on. Integrated cir- cuit 17 is an input port which is actuated by CS4. The three output ports are formed by IC1. . .IC3: the number of the port cor- responds with that of the IC. Outputs Q6 and Q7 of IC1 and IC3 serve to control the relays. Outputs Qft . .Q5 of the same ICs are used for programming the fading speeds of counter 1 and counter 2 respectively. The arrangement of the remainder of the stages in figure 3 as compared with the block diagram of figure 2 is as follows (counter 2 in brackets): counter 1 = IC4 (IC5); counter 2/3 = IC8/IC9 (IC10/IC11); counter 4 = IC6 (IC7); time lapse control = Nl. . .N3, Dl, D2, R2, R3, C2 (N10. . N12, D3, D4, R4, R8, C4); trigger generator = NS, RS, C3 (N7, R6, CS), clock oscillator 1 = N4, Rl, PI, Cl; clock oscillator 2 = N9, R7, P2, C6. Control of counters 1 and 2 is provided by IC2: Qft . .03 for the former and Q7. . ,Q4 for the latter (the single port lines are shown in figure 2). Note that the 0° line in figure 2 becomes logic 0 when the desired gating angle is 0° (maximum power): the output of N5 (N7) is consequently logic 1 during the entire following half cycle. On the triac board shown in figure 4, Dl, D2, D7, D8, Cl, C2, C4, R4, and R5 form the power supply for the zero crossing detector. This detector itself consists of Nl. . .N4, Rl. . .R3, and C3, and drives Figure 4. Apart from the triacs and associated components, the power circuit also contains the zero crossing detector and the four relays with their drivers. This board may be cut into parts. opto-coupler IC2, which provides the required electrical isolation, via T1 and R6. The output signal of IC2 is shaped into a clean low-active pulse for the counters by T2, T3, R7 . . . R9, and D9. The power supply for the two triac stages, which — like the counters — are identical, is formed by D3. . .D6 and CS. Opto- couplers IC4 and IC4’ are driven by T4 (T5) and RIO (Rll). The trigger pulse at the output of the opto-coupler is regenerated by T6 (T6') and R13. . .R17 (R13’. . .R17’) and then applied to the gate of the triac. The triacs used are of medium heavy duty type TIC 263C, enabling lamps of up to 400 W (at 24 V) to be switched: maximum permissible current (with resistive loads) lT(rms) = 25 A - The triacs are protected against spurious surge currents by C7 and R12 (C7' and R12'). When the triacs are used to switch 240 V lamps, a suppressor choke of 30. . .50 (jH should be connected in series with the lamps. The relays, controlled via gates N5. . .N8, are of the DIL type, and are protected by free-wheeling diodes D10 . . . D13. Completion of the two printed circuits shown in figures 9 and 10 is straightfor- ward and is, of course, to some extent dependent upon the application of the cir- cuit. The triac board may be suitably div- ided as shown in figure 10. In any case, the parts of the boards where mains voltage is present should be insulated by, for instance, a layer of glue applied with a glue gun. Addressing The address decoder consists of two 8-bit comparators type 74LS688 (IC14 and IC15), a 2-bit binary decoder and demultiplexer type 74LS155 (IC16), a number of wire bridges, a . . .s, and sixteen switches, SI. . .S16, contained in two 8-way DIL packages. The two 74LS688s compare the information set by the switches with the bit pattern at their inputs 00. . .07. If th e two sets of data are identical, output P = 0 (pin 19) becomes logic low. The two ICs may be cascaded by closing wire bridge "r” to give a 16-bit comparator. If wire bridge "s" is closed, only IC15 is active (as 8-bit comparator). The output (pin 19) of IC15 provides the strobe signal for IC16. Two-bit information is applied to data inputs P and Q of IC16. Switch-over of the on-board data dividers is effected via the R/W line: if the line is logic high, and the information at P and Q "If’, CS4 becomes active (writing); if the R/W line is logic low, CSl is actuated when the information at P and Q is "00”, CS2 when the infor- mation is "10”, and CS3 when the infor- mation is ”01”. Tables 1 and 2 give the state of the wire bridges and switches respectively for use with the Junior computer. If the Extended Junior is used, the control board can be plugged direct into the extension bus. We have taken the Junior as an example for the addressing and will deal with the 1 .46 eletoor india januarv ’S Table 1. other three computers further on. necessitates the closing of switches S13 The two lowest-value address lines are and S14. All this results in the decoding of connected to the data inputs of IC16 via ■ CSl by address E200 (decimal 57 856); bridges ”m" and ”q”. Bridge ”r” enables ■ CS2 by address E201 (decimal 57 857); IC14 and IC15 to be combined into a 18-bit ■ CS 3 by address E202 (decimal 57 858); comparator. Address lines A2, A6, and A7 ■ CS4 by address E203 (decimal 57 859). are connected to the comparator via A caution here: if, in the Junior, you have bridges ”f”, ”j”, and ”i” respectively. placed RAM in block E (addresses Inputs Q6 and Q7 of IC15 are connected E000. . .EFFF), this RAM must be to earth via bridges ”c” and ”e”, which deselected to avoid double addressing. Table 1. bridges computi SPECTRUM Elektorbus The three other computers (with the poss- ible exception of the ZX81 — see below) require a simple adapter to interface their extension connection ("User Port”) with the Elektor bus. This adapter is made from a plug which fits the User Port of the relevant computer, a 64-way female con- nector, and a small Veroboard. The board should be cut to the correct size to enable the plug and socket to be soldered to it. Appropriate connections are then made between the plug and socket with short lengths of insulated wire. The photograph in figure 5 shows our prototype adapter for the ZX Spec- trum. The two long pieces of wire are for connections to an external +5 V supply. Depending on the rating of the power supply in the computer, it may be poss- ible to draw the required power from this supply. Figures 6, 7, and 8 show the pin out of the user port, the required connections between the plug and socket, the pin out of the Elektor bus (64-way female connec- tor), the wiring of the bridges, and the switch positions for the C64, ZX81, and ZX Spectrum respectively. If a C64 without floppy disk drive is used, it is possible with the change-over switch in the a dapt er to choo se between output signals I/Ol and 1/02, and consequently between addresses DE00. . . DE03 and DF00. . .DF03. If a floppy disk drive is fit- ted, the switch must be set to 1/01, and only address DE00. . DE03 are then available. It is in that case, of course, poss- ible to replace the switch by a fixed wire bridge. If a ZX81 is used, the bus buffer described in the July 1984 issue of Elektor India (page 7-22) may be used instead of the adapter. Terminals 31a and 29c of the buf- 1 .48 eteklc fer board should then be interconnected. Finally, the adapter shown in figures 6, 7, and 8 may, of course, also be used to con- nect other Elektor bus boards to the respective computers. Programming The primary task of the programming is the writing of the data into IC2: this deter- mines the operation of the two counters. The bit on data line D0 matches that at the IC output Qfi that on D1 matches that at 01, and so on. The significance of the single bits is (counter 2 lines in brackets): ■ D0 (D7): if this line is logic high, automatic fading is selected; if it is low, the prevailing fading state is retained; ■ D1 (D6): the state of this line determines whether the relevant lamp is coming on (logic 0) or fading (logic 1); ■ D2 (D5): if this line is logic high, com- posite counter 2/3 is reset; ■ D3 (D4): when this line is logic 1, com- posite counter 2/3 is loaded with bit pattern "1111 1111”. The slide control program contains the bit patterns of the only four practical 1.49 iiIbi Table 3. Bit patterns of the only four practical operating states of each Table 4. The bit patterns of table 3 may form six- teen data words for pro- gramming the fading and coming on behaviour of the two lamps. A off. B coming o A on, B coming oi A coming on, B oi A fading, B off A fading, B on A fading, B comi Table 3. Table 4. operating states of each lamp: on, off, coming on, lading: these patterns are given in table 3. The complete circuit (that is, two lamps) therefore offers sixteen possible combinations which are listed in table 4. Our master programs have been so arranged that no confusion is likely to arise. If you design your own program, take care that it runs sensibly. You may, for instance, want to interrupt during fading, or reverse the direction during fading or coming on, or something similar. Such operations have not been catered for in our programs to keep them to a reasonable length. An example, using the Junior it is required that lamp A comes on and that lamp B is and stays off. It is then necessary to write bit pattern 1001 0001 (= decimal 145) into IC2, address E201 (= decimal 57857). The instruction for this POKE 57857, 145 In the case of the C64, this command would be: POKE 57089, 145 or POKE 56833, 145 When programming the fading speed and actuation of the relays, bear in mind that these are arranged in one IC (IC4 or IC5). If the relays are not needed, matters are .50 simple: you write with a POKE command a decimal number between 1 and 63 into IC1 (IC3). Examples: Junior computer, lamp A, medium fading POKE 57856, 31 C64, lamp B, maximum fading speed: POKE 57090, 1 ZX Spectrum, lamp A, minimum fading OUT 65342, 63 As you see, the smaller the number, the higher the speed. Note, however, that the command POKE nnnnn, 0 is not possible, because counter 1 — see figure 2 — then cannot operate. The two highest-value bits are always logic 0 for decimal numbers between 0 and 63. Table 6 shows how the relays may" - be controlled: when it is required that relay A (IC1) or relay C (IC3) be actuated, a decimal number between 129 and 191 should be selected. The correct number is calculated by adding 128 to the value of the wanted fading speed. The instruction in the first of the above examples would POKE 57856, 159 If only relay B is to be actuated, add 64 to relay A (Cl relay B ID) the value of the required fading speed. If both B and D are to operate, add 192 to the value of the fading speed. In all cases, decimal numbers 0, 64, 128, and 192 are not permitted, because bits 0. . .5 are logic low so that the clock generator is disabled. Table 6 shows a menu-controlled program for the Junior and C64 which enables the reading or programming of the collective functions of the circuit by entering code numbers. The program as printed is cor- rect for the Junior, for the C64, line 2050 should be altered as shown in table 7. Lines 10. . . 1900 are explained in the foregoing: the remainder of the lines arrange for the automatic control of the relays, so do not again program them! Tables 8 and 9 give a short sample pro- gram for the ZX81 and ZX Spectrum respectively, and have been added to make clear the difference in the program- ming of these computers in comparison with table 6. Like that in table 6, these two programs are also menu controlled, a small menu in the case of the ZX81 and two small ones for the ZX Spectrum. Lines 20. . .80 in the ZX81 enable the "poking” of a machine language routine into the memory in the range of the REM line (line 10 which is therefore changed after the first program run). Lines 20 ... 40 load accumulator A of the processor with the content of address decimal 16 516. Lines 50. . .60 arrange for this content to be car- ried onto the data bus, and lines 70. . .80 contain the RETURN command. Note that the user function is explained in chapter 26 of the BASIC handbook of the ZX81, and the OUT command in chapter 23 of the BASIC manual of the Spectrum. Final remarks Before taking the circuit into use, set presets PI and P2 to the centre of their travel. Testing of the circuit should initially be carried with resistive loads only, even if you later want to control motors, that is, inductive loads. The fading speed is set with PI and this is a matter of personal taste. Preset P2 should be set with the aid of a frequency counter or oscilloscope so that oscillator N9 operates at 25.6 kHz (50 Hz mains only: for other values, the oscillator frequency should be calculated from fo = H*. where f 0 is the oscillator frequency and f m the mains frequency. The preset may also be adjusted ‘visually’ so that a fading lamp is only really ‘out' when the fading process is at an end. When the circuit is subsequently used for the control of motors, it may be necessary to readjust P2 slightly. If it is impossible to adjust P2 for the stated frequencies, this is probably due to differences in trigger threshold between various makes of IC: the remedy is to increase or reduce, by trial and error, the value of C6. With the information given in this article, it should be possible to use the circuit with current computers other than the ones mentioned here by carefully study- ing their documentation. You need four free addresses and the pin-out of the extension connector, programming may be carried out with the aid of the pro- gramming hints given in this article. M .52 elekic 7 watt 1C audio amplifier -i' production for several years, and by now the price has dropped to a very reasonable level. It has built in thermal and short-circuit protection circuits, so it should have a reasonable life expectancy. Without any additional cooling, the 1C can deliver 1 Watt into a 4 J2 load with a 6 V supply. With a sufficiently large cooling fin and a 16 V supply it can deliver up to 7 W into 4 SI, the input sensitivity in this case is 240 mV. If 8 SI loudspeakers are used, the maximum output power is about half. The input impedance is practically determined by PI (1 M), so it is possible to connect a crystal cartridge direct to the input. If this high input impedance is not required, the value of PI can be reduced. There are two versions of the TBA810: the ‘S' and the ‘AS', with differently shaped cooling fins. The additional fin shown in the drawing is suitable for the ‘S’ version, but it will need some slight modifications to fit the ‘AS’ type. The frequency response is ±3 dB from 40 Hz to 18 kHz. The voltages shown in the circuit were measured when the unit was powered with a 16 V power supply. Note that the pin numbers in the circuit do not take account of the cooling fin; the 1C has a total of 1 2 pins. & ^>1 LA ’ >1 1.53 toroidal transfornwv the best transformers . . . around! Ring core or toroidal transformers are becoming fashionable. Thin is beautiful? As their name implies, they are 'round' and low in profile, allowing the home constructor and manufacturer, to build highly compact circuits. This seems to be necessary in order to satiate the public's appetite for any equipment that looks like a permanent 'Weight-Watcher'. Seriously, they do have excellent 'electrical' qualities, and advantages over the conventional transformer, other than looks. Unfortunately good taste is always relatively expensive. The toroidal transformer has a ring core formed by a tightly bound metal lami- nated band. Copper windings are simply placed on the core without the use of bobbins. The wire is wound over the complete surface of the core and this considerably aids the dissipation of heat. Due to the round shape, there is good 'concen- tration' of the magnetic flux lines in the core, thereby reducing the 'stray' fields. It requires less wire than the conven- tional transformer for the equivalent number of windings, thus reducing the ohmic resistance, and the chance of overheating. So far so good. But why is the ring core transformer in most cases more expensive to buy than the conven- tional type? After all, they use less copper wire, no bobbins etcetera! Good question. The answer is that they take a lot longer to manufacture than conven- tional transformers, and today more than ever, time is money. The core is formed as a complete ring without an air gap. It is made from a strip of high grade sheet steel, which is rolled up very tightly. The end of the strip is then welded, to prevent it un- winding. This form of construction helps to concentrate the lines of flux within the core and keeps losses to a minimum. An added advantage is its lack of buzz; due to the very tight 'lami- nations', which are completely enclosed by the winding. The result: an inbuilt disability for the production of noise. Mains toroidal transformers are readily available in the 15 to 680 VA range, and up to 5000 VA types are supplied by some manufacturers. Most are available with two secondary windings, of be- tween 6-60 V. Winding toroidal transformers The manufacture of toroidal trans- formers may present something of a question mark to the inquisitive reader. As in most things of this nature, the answer is quite simple; once you know how! Figure 1 illustrates, what, in simple terms, actually occurs. The complete core is loaded onto a machine that is able to hold and, rotate it. A ring, that is about three times the diameter of the core, is linked onto the core in much the same way as two links of a chain. This ring is called, not un- reasonably, a shuttle and can also be rotated. While doing so, an amount of wire equalling one complete winding is fed onto it. And now we come to the 'trick' that makes it all so simple. The end of the wire is turned through 180° around a guide wheel on the shuttle, and held onto the outer edge of the core. The shuttle then reverses direction and lays the wire onto the core as one winding. The core is of course rotated slowly as this happens, so that the winding is evenly spread around it. Tension of the wire is easily controlled. Mechanically this method is both simple and quick, and in fact takes just three minutes per winding. The Lord of the Rings (Transformers) The equivalent conventional trans- former is in most cases 2 to 3 times heavier. The same ratio in size also holds true. The ring core transformer's 'iron losses', (when compared with the 'standard' conventional type), are only 10%. The advantage of the ring type are clearly noticeable when comparing 'stray fields'. In a no-load situation the conventional field is at a maximum and the ring core at a minimum. With an increasing load the 'stray field' of the conventional decreases and the ring core's field in- creases in strength. No matter what the situation, the stray *ield of the ring core type is always considerably smaller. Therefore using a toroidal transformer reduces the risk of unwanted noise being generated in any power supply circuit. Quality costs money? Toroidal transformers up to power ratings of 200 VA are more expensive to buy than conventional types. Above 200 VA and up to 500 VA this situation is reversed. A reasonably priced, com- pact, transformer above 200 VA is cer- tainly useful, especially when building high power amplifiers. Final remarks Compared to the ordinary standard transformer, the high-grade core ma- terial of the toroidal type will cause a higher initial surge current; A slow-blow fuse on the primary winding is there- fore necessary. A fuse having approxi- mately double the value normally used with an equivalent conventional trans- former should do the trick. Even so, do not be alarmed if the whole neighbourhood is 'blacked out' the moment you switch on your new 2 x 50000 . . . W amplifier (with multiple toroidal transformers). This is a normal occu ranee! H 1.55 microprocessor- controlled frequency meter (part 0) Next month we will be publishing all the constructional details for a frequency meter. This is no ordinary meter, however, as it is small, very simple to use and at the same time quite easy to build yourself. All that is made possible by the microprocessor that controls the circuit. What exactly the microprocessor does you can find out in four weeks' time but just to whet your appetite have a look at the features listed here. an introduction to an exceptional project featured next month. The circuit for the new Elektor frequency meter is very unusual and because of this it deserves special attention. Tbtally unlike any other d.i.y. frequency meter, it is, of course, part of our range of test instruments. We will look at it in functional sections, starting with the most unusual part of the circuit: the frequency measuring section. ‘Normal’ frequency meters make use of a crystal-controlled time base supplying an exact measuring time of 1 second, for example. During this ‘gate time’ the number of incoming cycles of the signal that is being measured are counted (see figure la). An accurate measurement is taken by using a measuring time long enough to enable a large number of cycles to be counted. Low frequency signals require a long measuring time but at high frequencies the time can be shorter. In 1 second only 10 cycles of a 10 Hz signal can be counted, for instance, so the read-out can only indicate a value of 10 plus or minus 1 Hz. If any figures are shown after the decimal point they are totally useless. In this case a measuring time of 10 s or longer is needed to give a reasonable degree of accuracy. The new Elektor frequency meter uses a principle that is also used in modem pro- fessional instruments (see figure lb). Once again a time base (providing a 10 MHz signal) and a counter are used. The signal to be measured goes first to a program- mable divider. A microprocessor sets the division factor such that the counter is ‘filled’ as much as possible with pulses from the time base. This is exactly the opposite to the previous situation as in this case the gate time is supplied by the signal that is measured. The frequency of this signal is calculated by the micro- processor based on the division factor and the contents of the counter. The great 1.56 advantage of this method is that the instru- ment is always working at full accuracy and the measuring time is virtually cons- tant, irrespective of the frequency measured. The microprocessor makes the calculations so fast that the user does not even have time to think about it. An extra divider stage may be included to raise the upper limit of the frequency range from the standard 100 MHz to 1.2 GHz. The meter has three different inputs: one for analogue signals up to 10 MHz (with pre-settable sensitivity), one for digital signals up to 10 MHz and a high frequency input for signals above 10 MHz. The user can select a resolution of six or seven digits, giving average measuring times of 0.15 and 1.5 s respectively. Using a microprocessor in this frequency meter also allows a number of other interesting features to be incorporated. The method of calculation chosen means that automatic range changing is a simple matter. 'User friendliness’ is also a feature of the meter. The alphanumeric display shows the user in plain language what options are available and selection is a matter of pressing the ‘yes' or the 'no' but- ton. Pressing another button calls up the menu (the instrument then shows what its modes of use are), there is a ‘last’ button to recall the previous choice and the 'hold/reset button is used to freeze or reset the display. The only ‘normal’ switch in this whole instrument is that for the main power. The various different possible modes that can be chosen are shown in figure 2, which surely requires no further comment. We could carry on listing all the wonder- ful features of this new frequency meter but that is not really necessary. One thing we will say, however, is that in spite of having some very expensive test equip- ment in our labs at Elektor this microprocessor-controlled frequency microprocessor controlled meter is probably the fastest and easiest frequency meter (part 0) to use. This is because hidden inside a mini case is a giant instrument. Can you afford to miss an offer like that? M la 2 Figure 2. This is the fre- Any of these options can be selected using just two buttons. What could be simpler? 1.57 7400 siren M. Mergel The electronic siren described here is easy and cheap to build. The circuit consists of two astable multivibrators, N1/N2 and N3/N4. The 0.2 Hz square-wave signal from the latter oscillator is integrated by R3 and C3; this voltage swings the frequency of the other AMV (N1/N2) up and down at 0.2 Hz, The output level is about 2 Vp.p, sufficient to drive a power amplifier directly. 14 Parts list R1.R2 - 4k7 R3- 10 k R4 - preset potentiometer 4k7 R5 - 5k6 R6- 1 k Capacitors: C1.C2 ■ 1000 fl/6 V C3 - 500 /t/6 V C4.C5 - 470 n C6 = 1 50 n Semiconductor: N1 . . . N4 - 7400 light dimmer This simple triac dimmer can be used to control incandescent filament lamps up to 1 500 W. The circuit operates on the phase-control principle. The main con- trol is provided by P2. This determines the rate at which C2 charges and hence the point along the mains waveform at which the voltage on C2 reaches the breakdown voltage of the diac, which is when the triac is triggered. PI, in con- junction with R1 and Cl determines the minimum brightness level, or alterna- tively may be used as a fine brightness control, interference suppression is provided by R2 and C3. Construction The printed circuit board is very com- pact and can easily be accommodated inside the modern, square type of flush- mounting switch panel, or in a small box for portable applications. The following safety points should be noted. No part of the circuit should be access- ible from the outside. The case should preferably be made of plastic or other insulating material, and fixing screws for the board should be nylon. If a metal case is used the board must be ad- equately insulated from it and the case should be earthed. The potentiometer should have a plastic spindle. H maim SOLDER PASTES Electro Science Laboratories Inc. U.S.A have announced the availability of large particle pastes. These pastes make reflow soldering more reliable by inhibiting solder balls. As the solder paste flux melts before the alloy melts, very fine solder particles flow with it. away from the main mass of alloy, and become isolated. Fine particle powders also have more surface area for oxidation that can form a barrier to the main solder mass. ESL's large particle solder pastes inhibit these causes of solder balls. SINGLE PHASING PREVENTER ALTEK SYSTEMS introduce the Reliance PLG— single phasing preven- ter cum water level guard unit. This unit is used for protecting the motors of submersible pumps from single phasing and dry running. The single phasing preventer operates by sensing the negative sequence voltage and the water level guard operates by sensing the conductivity. The unit is available with housing or in open form to suit the requirement of control panel manu- facturers. For further information. Safari Industries 11. Tribhuvan Road. Bombay 400 004. GEARED SYNCHRONOUS MOTORS VISHAL Electromag Industries have developed geared synchronous motors which are sturdy and compact. These motors can operate on 110V or For further information, write 220/240 V AC at 50Hz and consume 2.5 or 5 watts depending on the model. Out put speeds are available from 1 Sec./Rev. to 24Hrs./Rev. These motors are basically unidirectional and can be used directly for recorders, time- totalisers time switches, timers, maximum demand meters, action displays, oscillating grills in air conditioners and fans etc. The motors can also be made available as reversibel synchronous motors for potentiometers or servo voltage stabilisers. For further information, writ Eltecks Corporation C-314, Industrial Estate Peenya, Bangalore 560 058. ULTRASONIC LEVEL INDICATORS ELTRONICA have developed non- contact type ultrasonic level indicator/ controller-Model VUL-8 which can sense level by ultrasonic waves The material can be liquid . powder or in form of lumps. The level is measured instantaneously and hence even dynamic level indication and control is possible. Measurement is fairly independent of temperature upto 70°C. The digital display is directly calibrated in mm or cm and BCD outputs are provided for control or printout. TEMPERATURE CONTROLLER ESD— 90/ESD-92 is the digital tem- perature indicator/controller introd- uced by Electronics Systems and Devices. A wide selection of measure- ment ranges is available to suit Thermocouple as well as RTDs. Large bright LEDs are used in the digital display of temperature being moni- tored. Ambient temperature compen- sation and thermocouple break protection are incorporated in the circuit. Input linearisation is also provided. The measurement is claimed to be unaffected by mechanical vibrations or mounting position of the instrument. For further information, write to: Eltronica 98. Kaliyammankoil Street. Verugambakkam, Madras 600 092. For further information, write to : Vishal Electromag Industries D-202. Bonanza Industrial Estate. 2nd floor Ashok Chakarvarti Road. Kandivli (East). Bombay 400 101. For further information, write to : Electronics Systems and Devices 38-39/7, Hadapsar Industrial Estate, Pune 411 013. maim: routing of Cable Harnesses while forming a neat, protective bundle. It twists on easily and quickly and allows lead-outs at any point. When Spirap is installed, it may be gapped for greater economy and flexibility or it may be butted tightly for maximum abrasion resistance, insulation protection and greater rigidity. RAIL TESTER Vibronics Pvt. Ltd. have developed the ultrasonic rail tester equipmentto meet the exacting standards set by RDSO. The equipment comprises of a portable flaw detector— model FD-301 A. with 5 sets of probes controlled through a junction box. The position of the probes can be raised or lowered as required The applications consist of fatigue testing on rail head, testing of cracks on core bolt holes, cracks on T/C SCANNER The WAHL Data Force dual micro- processor controlled 40-channel temperature scanner computes, auto- matically measures and linearises upto 40 thermocouples every 2.5 seconds. The input channels accept any standard thermocouple types and are linearised to 0.005°C. The unit has 4 multiplex cards, each having 10 T/C input channels, with interchannel isolation of 300 V DC. Temperature readings are displayed with the 0.01°C resolution and the accuracy is * 0.2°C. Calculator functions such as weighted average, delta T. computed max/min. deviation, polynomial linearisation, cross channel computation etc. are also available. °OBQq BDI]aa • j For further information, write to : Novoflex Cable Care Systems Post Box No. 9159 Calcutta 700 016. For further information, write to: Jost's Engineering Co. Ltd- 60. Sir Phirozeshah Mehta Road, Bombay 400 001. MINI TOGGLE SWITCH Switchcraft now offer a miniature D.P.D.T. toggle switch rated for 250V AC at 2A. This switch is suitable for use as ON-OFF switch for electrical and electronic instruments. It is housed in a deep drawn brass casing which pro- tects the inside mechanism from dust and moisture. The switch has a transfer moulded base with terminals moulded in it. The contacts are silver plated. Dimensions behind the panel are 13 (L) • 12 (W).* 18.5 (H) mm. CURRENT TRANSFORMER MECO Instruments Pvt. Ltd. have added a DIN type plastic moulded current transformer in four different models. The material of the moulded case is ABS and a cap is supplied for sealing the secondary terminals and to make the CT tamperproof These can be mounted either on base plates or directly on bus-bars and are claimed to be unaffected by highly corrosive and dusty atmosphere. For further information, Vibronics Pvt. Ltd. Masrani Estate Near Halav Bridge Kurla. Bombay 400 070. UPS SYSTEM JAYANT Electric & Radio Corpn. have introduced an uninteruptible power supply system to overcome the pro- blems of transients, brownouts and blackouts. Various models are avail- able ranging from 200 VAto5 KVA. The system is mounted on a trolly with a battery and incorporates automatic electronic switching, dual function voltage stabiliser, battery charger with automatic trickle and boost charging etc. Output is 230 V ± 5% AC, single phase sine or square wave. Input can be 12 V to 110 V DC depending on the required capacity. Frequency of opera- tion is 50 Hz ±1%. For further information, write to: Switchcraft 54/55 Crescent Mansion Gamdevi Road Bombay 400 007. TUBE LIGHT INVERTER SBAJ tube light inverters are specially designed for the Bus body builders. They are completely solid state in design and use ferrite core trans- formers. 40% more efficient is claimed over the old lamination type trans- former designs. The inverters are For further information, write Meco Instruments Pvt. Ltd. Bharat Industrial Estate T.J. Road. Sewree, Bombay • For further informatiori write to: Jayant Electric & Radio Corporation 5 B, Naigaum X-Road P.B. 7129 Wadala, Bombay 400 031. For further information, write t Sbaj Electronics 19. Mother Gift Building Opp. Novelty Cinema Grant Road. Bombay 400 007. CABLE BINDING NOVOFLEX offers Spirap cable binding system which permits flexible RIR RECTIFIES YOUR RATINGS Appointments Appointments .61 NOW THE LATEST BOOKS-KITS ARE AVAILABLE WITH US DATA BOOKS : SHjnntics nc/i INTERSIL FAIRCHILD ZILOG - - GE' - ANALOG DEVICES SIEMENS -INTEL SGS. ATES SILICONIX - TELEDYNE COOK BOOKS OSAORNE BOOKS SYBEX BOOKS - TAB BOOKS SAMS BOOKS - TOWERS BOOKS AND APPLE COMPUTER BOOKS PLEASE WRITE FOR DETAILS ELTEK ■■ - BOOKS-N-KITS ellSK 6. RITCHIE STREET, 1ST FLOOR. MOUNT R O AD, MADRAS- 60 0 002 We also stock ELEKTOR INDIA kits & back issues. IMPORTANT SUBSCRIPTION RENEWALS ARE ON! HAVE YOU RENEWED YOURS? * To use the card in this issue * To quote your subscription number * To mention that it is a renewal ‘ To send your renewal at least one month in advance * Timely renewal ensures continuous receipt of issues without irritating breaks ele kte E electronics PCB Drafting Aids ' Tapes • Donuts • 1C Patterns • Connectors • Targets • Alphabets • Component Legends. I Available as Stickers or Transfers. E IZUMIYA 1C INC Free Catalogue. _ ’ Sole Representatives For India : eIeIuting Computer Lights Use your ZX 81 /Spectrum to control Lights, Small electric motors, Heaters etc. ON/OFF, Brightness, Speed controls of 8 gadgets individually, using BASIC or Machine Code. Rs. 850.00 SPCCTAUM Effects Box Atack, Delay, Sustain, Echo, Rs. 300.00 SPECTRUM Amplifier Improves sound output of the Spectrum. Rs. 410.00 VHF/UHF Modulator Connect your computer to any domestic TV set. Connect your VCR to any Black & White TV. Rs. 400.00 Products announced under Computer corner will be supplied only in assembled and tested form. ^ TERMS: ■ Goods by return post subject to availability. ■ Special prices for volume order. ■ Minimum outstation orders Rs. 50.00 ■ All orders must carry a minimum advance of 50%. balance payment by VPP or through Bank. (No cheque payment.) ■ Prices are subject to change without any prior notice, will be charged as prevailing on date o of despatch of goods. ~ ■ All prices are exclusive of M.S.T. and Postage.