Electronic maze EZSEim 1 •im; L £ Volume - 4 Number - 5 May 1986 Satellite loudspeakers are not a separate category ol sound reproducing equipment; any loudspeaker whose bass performance should be improved could be classified as a satellite. So-called bookcase loudspeaker $ ire invariably satellites, because their modest dimensions prohibit proper reproduction of frequencies below about 100 Hz. The article follows on the Active subwoofer and deals with the satellite loudspeakers that complement the subwoofer to give complete coverage of the audio spectrum. projects 5-18 5-26 5-29 5-32 5-36 Junior Computer 5-42 Satellite loudspeakers 5-46 information News and views 5-16 Noiai , | | IiilIJ 5-59 guide lines Switchboard 5-67 5-74 Index of advertisers 5-74 selex 1 2 Digi-Course II (chapter 6) Mini Amplifier Z- Diode tester 5-51 5-52 5-55 5.03 A YABASU PCB Drafting Aids now made in India. V • Tapes in black, red & blue. All widths in inch or metric measure available ex-stock. • 1C Patterns and Donuts to be introduced soon. Write to precious' ELECTRONICS CORPORATION 52-C, Chhotani Building, Proctor Road, Grant Road (E), Bombay-400 007. Dealers wanted all over India Video in decline? Now the semiconductor markets are beginning to show signs ot a slow revival, it seems to be the turn of video revenues (and therefore profits) to start declining. The reason for this is that some forty per cent of households in the industrialized world already have a VCR (video cassette recorder). To retain their share of the consequently declining market, the 20-odd Japanese (and some other Asian) manufacturers have become engaged in a price war that is hotting up. What they are all hoping for is a miraculous expansion of the market, or a new market. But that is pie in the sky, because market observers believe that such an expan- sion or new market will only occur if a technically new, yet lasting and exciting, equipment is introduced. Moreover, such equipment must be relatively inexpensive, easy to operate, and offer a high degree of standard- ization. The only equipment that seems to meet most of these requirements is Sony's new 8 mm video system. But since this is not compatible with the 100-odd million half-inch VCRs already in use it has a long, hard slog ahead of it. In the mean time the video market is likely to go on declining at an increasing rate. As guarded estimates suggest that nearly a fifth of Japanese electronics sales consists of VCRs and their components, some sectors of the Japanese industry are in for a leaner time than they have experienced for years. The question is: what are they going to do about it? Copyright S 1986 Elektuur B.V The Netherlands 5.05 A complete REFERENCE GUIDE for your file. LOW POWER TRANSISTOR COOLERS • Cool Transistors & ICs PLUGS & SOCKETS 4, 6. 8. 12. ' & 33 PIN Smooth insertion/withtlraw (Specially profiled contact No scratches onPCB platir TRANSISTOR COVERS Transistors AFCO INDUSTRIAL & CHEMICAL LTD. Kanjuimatg (East). Bombay 400 078. Phone 582164. 582978 • Telex : 01 1 -71478 • Grams TUTELA' DEALERS. BRANCHES (PHONESI BOMBAY National (316713). Cresta (457230). BANGALORE Amar (220547) Afco (22565 7). DELHI Synthetic 1511436). Atco (513537). PUNE Universal (445729). BARODA .layman (5(5 :811. SECUNDERABAD: Shilpa (73792). Telrrama (551379). MADRAS: Texonrc (844405). CALCUTTA Primed (452091). TRIVANDRUM: Bhuvanesh (61719). JAIPUR: PM Electro (77492) aafrm/Afco/1 ' ,We have a chip. Are you a designer? Do you enjoy playing around with microprocessors? 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Bcrr»», *00001 5.15 The subwoofer described in this article can be used to extend any existing loudspeaker system, tt has been designed to obtain a frequency response within ±i dB over the frequency range 30-100 Hz with an enclosure volume of only 85 litres ACTIVE SUBWOOFER The faithful reproduction of very low on the length. /, of the room: | such large boxes required for a audio frequencies in normal living j stereo installation are often unaccep- rooms poses a number of problems t-dil [Hz| 1 table in a normal living room. The first is that the lowest frequency, | Fortunately, there is an alternative f. that can be reproduced depends where c is the velocity of sound , which offers much the same bass waves in metres per second at nor- performance and has a much more mal atmospheric pressure and at modest space requirement. It uses j only one enclosure for the low fre- In a 6-metre long room, therefore. , quencies. even in stereo operation, the lowest frequency that can be For the middle and high fre- reproduced without distortion is ; quencies. one loudspeaker system 1 about 28 Hz. In practice, other prob- : per channel remains required. I lems, such as the vibrating of doors, j The alternative solution is made windows, cupboards, glassware, J possible by the human ear having and so on. become evident long | virtually no sense of direction at fre- before this frequency has been j quencies below about 200 Hz. This leached. ! means that if frequencies below, A more important problem concerns say, 100 Hz, are reproduced by one the dimensions of the enclosure. For j central subwoofer, and the re- a reasonably faithful reproduction at mainder of the audio spectrum by 30 Hz and full volume, the enclosure j so-called satellite loudspeakers, should normally have a volume of i there is no discernible impairment not less than 100 litres, and j of the stereo effect. Note that the preferably about 200 litres. Two I satellite speakers can be kept small Table 1. Some prominent types ' of loudspeaker » system and their' most important properties. this type depend to a large extent on its specific design, which can be ap- proached from different directions. The questions that immediately crop up are: "how low should the —3 dB point be?", and "what are the ac- ceptable dimensions of the enclos- ure?". The lower the frequency at the —3 dB point for a certain volume, or the smaller the dimensions for a given —3 dB point, the more elec- tronic correction will be necessary. inability to reproduce very low audio frequencies when its volume is modest to small. The bass reflex and transmission-line types are superior in this respect, but these suffer from an inferior frequency response characteristic and a much worse step response. The horn and transmission-line types are, further- more, rather difficult to build. This leaves, in practical terms, the active closed box. The properties of because they are required to reproduce frequencies above 100 Hz only. The design and con- struction of these satellite loudspeakers will be described in Fig. la. Fre- quency response characteristic of the Dynaudio 30W54 drive unit in an 80-litre closed box with- out any filtering. Table 1 shows some types of loud- speaker system and their most im- portant characteristics. It is clear that the closed box generally offers the best performance, were it not for its Fig. lb. Fre- quency response characteristic of the Dynaudio 30WS4 drive unit in an 80-litre closed box with electronic crossover net- work and correc- tion filter Sensitivity la o X 0 " X 1 O wa M* GD CD CZ1 ...... O © 1 \ Subwoofer 4 - - \ \ , A. . ■ ■■■■•SI . l 13-oi'K 1 1 5.19 But this correcting cannot be taken too far, otherwise the sensitivity as well as the step response will suffer; also, distortion will increase and power handling will be reduced. The present system was designed to give a reasonable performance with- out any electronic help first, and then some electronic circuits were added to extend the frequency range downwards. The frequency response of the sub- woofer in an 80 1 enclosure is given in fig. !: lb clearly shows the effect of the added filters, particularly the lowering of the -3 dB point from about SO Hz to 30 Hz. Set-up The system is arranged as shown schematically in Fig, 2, and is seen to consist of the loudspeaker in its enclosure, an output amplifier, and an electronic circuit. The output amplifier will not be discussed here, because any good type may be used, as long as it is capable of delivering at least 50 W into 8 ohms. The enclosure is simple to build as described under Construction. The loudspeaker used in the prototype was a Dynaudio (Denmark) type 30W54 —see Fig. 3. This is a robust I 300 mm drive unit on a light metal | frame with high peak power hand- [ ling capability, good step response, and a suitable frequency response (see Fig. la). Dynaudio 30WS4 The electronic circuit consists of two drive unit. parts: the filters and the output 3 limiter. There are three filters: a steep-skirted anti-rumble type with its change-over point at 20 Hz; a cor- rection filter for the very low audio frequencies from 50 Hz downwards; and a crossover filter with change- over point at 100 Hz and a slope of 24 dB/octave. The combination of these filters results in the frequency response shown in Fig. lb. The output limiter is, strictly speak- ing, not essential but very useful, particularly where full volume is used habitually. It has been added to allow for the decreasing power handling capability of the drive unit below 50 Hz. The coming into oper- ation of the limiter is indicated by the lighting of an LED. Subwoofer and satellite speakers In principle, the subwoofer can be used as an addition to any loud- speaker system that has unsatisfac- tory performance at low fre- quencies. If, however, a new loud- speaker system is planned, the design of the satellite speakers should take account of the sub- woofer. These units need reproduce frequencies above 100 Hz only, so that the volume of their enclosures can be kept to about 10 litres. The various units should be intercon- nected as shown in Fig. 4. The simplest and least expensive way is shown in Fig. 4a: the subwoofer system, including the output ampli- fier and filters is simply connected to the loudspeaker terminals of the existing amplifier. Capacitors C form a 6 dB filter to protect the satellite speakers high low-frequency output power. The necessary level match- ing between the subwoofer and the satellite speakers may be effected with a preset on the filter PCB. Where the pre-amplifier an output amplifier are separate units, inter- connections may be made as il- lustrated in Fig. 4b. In this way, each loudspeaker has its own output amplifier, so that filtering can take place between the pre-amplifier and the output amplifiers. The set-up in Fig. 4b is preferable to that in Fig. 4a. The question may be asked why the satellite speakers are filtered at only 6 dB/octave from 100 Hz, whereas the subwoofer has a skirt roll-off of 24 dB/octave. The answer is that the satellite speakers (in a closed box) have an inherent fall-off of about 12 dB/octave. Together with the ad- ditional filtering, this works out at 18 dB/octave, which is ample in this combination. The value of capacitors C is deter- mined from C= 10 6 /2nZ/r | m F] where Z is either the impedance of the satellite speaker (Fig. 4a), or the 5.20 elelto 0 ' Fig. 5. The cir- cuit diagram of the three filters and output power limiter. Diode D; should be mounted so that it can be seen from the outside, since it serves as overload indicator. input impedance of the relevant out- | f put amplifier (Fig. 4b) in ohms, and U ! is the roll-off frequency in hertz. I If, therefore, in Fig. 4a the satellite I speaker impedance is 8 ohms, and I | the roll-off frequency is 100 Hz, the j series capacitor should have a value ' | of 200 mF. It is recommended to shunt j j such large bipolar electrolytic ! capacitors by a foil capacitor of 1 yF. which improves the properties of the | | filter. Since the input impedance of the I I output amplifiers in Fig. 4b is con- siderably higher than the loud- | | speaker impedance, the value of the | filter capacitor is much smaller. For j instance, an input impedance of, say, 20 k gives a value of C=80 nF (use I 68 nF or 0.01 M F). Electronic circuits The circuit diagram of the three j filters and the active output limiter is | given in Fig. 5. After the two input signals have been summed in amplifier A,, they are applied to a complex rumble filter formed by A2. This elliptical or Cauer (high-pass) filter provides an attenuation of 0 dB at 23 Hz, —3 dB at 20 Hz, and 40 dB at 10 Hz. Note that some resistors and capacitors are connected in parallel to obviate the need for non-standard 1 per cent components. The rumble filter is followed by the correction filter, which, covering a range of only 3-6 dB, is a fairly simple circuit. It is formed by A3 and the frequency-determining components are Rs6 and C46 . The third filter is the actual crossover network and is constructed around A4 and As. It is a fourth-order Bessel type which provides an even phase shift and very good step response. The remainder of the circuit is the active output power limiter. The filtered signal at pin 7 of As is I applied to a metering circuit formed by As and Aio. Network Rsi-Rss-Rsi- I RsrCso-Cs. ensures that the input to [ As is large at low frequencies j (against which the system needs pro- 1 tection) and small at high fre- quencies. The rectified signal is compared in Aio with a reference voltage. If the signal becomes too large, the comparator toggles, Ti is switched on, and Di lights. At the sa- me time, T2 is switched off and the control loop of attenuator 1C« is actuated. The voltage-controlled attenuator (VCA) was described in Design Ideas in the February 1986 issue of Elektoi India Opamps As and A? provide buffering of the input and output of the VCA respectively. The buffered signal at pin 14 of ki is passed via low-pass filter R40-R41-R42 -R54-R58-R59-C24-C26-C44 to active rec- tifier An. This low-pass filter serves to adapt the control characteristics to the frequency-dependent power curve of the loudspeaker. Note that the signal is passed to An only when T2 is switched off. The output of the rectifier is applied to the control input of the VCA via integrator A 12. As long as the signal level at pin 6 of Aio remains below that of the refer- ence voltage at pin 5. T2 remains on. The control loop of the attenuator is then inactive and the VCA merely passes all signals applied to it. This arrangement ensures effective limiting of the output signal. The power supply is a fairly standard circuit. Diodes D12 and D13 prevent a temporary reversal of the supply voltages on switch-off: the ICs can- not then accidentally be put into an undefined state. Construction I electronic ! circuits) It is best to complete the electronic part first on the PCB shown in Fig. 6. Most if this work is pretty straightfor- ward, except for the heat sink of regulators ICs and IC6. This should be made from a 25 x 100 mm strip of 1 mm thick tin or tinned copper. Bend this lengthwise into an L of 70x30 mm. Drill two holes in a suitable position in the short leg to receive the ICs. Place the heat sink onto the PCB along the indicated fat line and solder it in place with the aid of two pins mounted as shown. The regulators are then fitted to the heat sink: the 7815 without, and the 7915 with, insulating washers. If the arrangement of Fig. 4b is used, the values of resistors Ri and Rz should be as shown in the parts list. With the set-up of Fig. 4a, their value should be increased to about 560 k. Some trial and error may be necessary to find the correct value that gives a satisfactory control range of Pi. The (mono) output amplifier required should, as already stated, be rated at not less than 50 W for satisfactory performance. Tbgether with the filter PCB and mains trans- former, it can then be fitted in a suitable case. | Connections between the filter i board and output amplifier should \ be made in screened audio cable. The amplifier and subwoofer drive | unit may be interconnected by any j twin cable with a cross-sectional I core diameter of 2.5 mm 2 for lengths up to 7 metres. Construction (enclosure) The enclosure is, simply, a rec- tangular box that must be really solid and have a net volume of about 85 litres. A suitable construction is shown in Fig. 7, but it should be noted that the dimensions stated may be varied by +30 per cent, as long as the net volume remains about 85 jlol a yfpfij or F=l, or FdB = OdB (3) Unfortunately, no electronic device has been developed as yet for use in the ideal preamplifier, nor will it ever be developed, due to some basic laws of physics. However, modern SHF transistors are now readily available with noise figures as low as 1.5 dB at 1000 MHz, while Gallium j Arsenide (Ga-As) FETfe have been de- I | signed to achieve 2.8 dB at 12 GHz; i j however, the cost and circuit design complexity of these devices puts them well beyond the reach of the average home constructor. The importance of a low preamph- j tier noise figure is evident after a ' comparison of Figures lb and lc; while its signal gain (amplification | factor) is still ndB, the amplifier of Fig. lc has a noise figure improved by 4 dB, which enables reception of signals that were inaudible with the | F- 6 dB amplifier of Fig. lb. We may. ] therefore, establish the general rule that reception is improved with a lower preamplifier noise figure. Thus, designing for low noise should be a high priority issue So far, only the active device in the preamplifier has been held respon- sible for the noise addition, but it should be pointed out that this device can only attain its minimum noise contribution when supported by passive components that ensure thermal stability and low signal in- I sertion loss at the amplifier input. It I will stand to reason that any mismatch at the booster input will | adversely affect (i.e. increase) the 1 transistor noise figure as given in the manufacturer's data sheets. No preamplifier stage, however low its noise figure, will be capable of reception improvement if the signals at the target frequency have been considerably attenuated before be- ing applied to the first active device, either by downlead cable losses or a severe mismatch at the booster in- j put. As the above mentioned article pointed out, however, the preampli- fier input necessarily consists of a low-loss filter, which serves the dual function of an out-of-band signal at- tenuator and signal source to transis- tor input impedance transformer (source matching). It should be fairly obvious by now that the actual gain of the booster is far less important than its noise figure; if the former is some 10 dB higher than the down- lead cable attenuation, adequate results are usually obtained; a gain of 15 ... 20 dB is common for a single- transistor preamplifier stage. Practical circuit The circuit diagram of the present i VHF preamplifier is shown in Fig. 2. I The RF signal at the input is passed to the base of Ti by a capaci- I tance-tuned, inductive top-coupled, low insertion loss and source match- | ing bandpass input filter with a —2 dB bandwidth of 20 MHz (88.. .108 MHz). This is quite a mouthful for a basically simple filter that per- forms the functions outlined above. I Note the taps on Li and La to obtain j impedance matching of the cable and the transistor respectively. Any of the listed transistor types may be | ! used in the circuit, but the Type ] BFQ69 is preferable because of its I extremely low noise figure. Since | this transistor has been introduced | only quite recently, however, it may prove difficult to get hold of. J The amplifier is fed by the receiver power supply over the downlead coax cable; the parts to the right of the dotted line are, therefore, mounted in the FM tuner. Decoup- ling parts Ls and Ci ensure that no RF signal is lost in the power supply. The amplifier bias setting is effected with Pi; depending on the transistor in use, this preset may be adjusted to I find the right compromise between 5.33 Fig 3 Curves optimum noise figure (low current the novel BFQ69, a collector current | BFR34A and BFR96S will also ensure showing the | or maximum amplification with ac- of IS mA appears to be suitable for a a noise figure that is usually far better characteristics of [ ceptable intermodulation response minimum noise figure of about 1 dB, | than the average FM tuner specifi- the new BFQ69 \ (high current). For further details or, which will bring the total noise fig- cation in this respect. transistor. Note j the bias setting of RF preamplifier | ure of the present design in the j The coils and chokes for the present that the curves in transistors, refer to Eiektor Elec 12 dB range with a Type BFQ69 design are wound as follows: Figures 3b and I ironies (UK), February 1980 issue fitted and the filter tuned to optimum j Li = 4 turns 20SWG (4 1 mm) enam- frequency of 500 MHz and not to the design fre- quency of the present pre- amplifier. (Siemens) Fig. 4. This RF design is also fit- Fig. 3 shows three curves relevant to input matching. However, the Types 4 elled wire, close wound on dia. 6 mm, tap at 1.5 turns from earth. La = identical to Li, but tap at 2.5 turns from earth. L3 = 11 turns 20SWG enamelled wire on toroid core Type T50-12 (Amidon). I* Lb = 4.5 turns 30SWG (4 0.3 mm) enamelled wire through 3x3 mm ferrite bead. For more information on inductor calculations and specifications, refer to last month’s issue of Eiektor Elec- tronics. Construction and alignment The present amplifier is fitted on the universal RF board 85000 as shown in Fig. 4; not shown are the bias setting parts, since these are mounted in the receiver. After completion, the unit may be tested by tuning the receiver to a weak transmission at about 95 MHz and adjusting Ci and Cz for optimum reception. The collector current setting should be fairly un- critical; its precise effect on the amplifier performance can only be judged when a very stable and yet sufficiently weak transmission is be- ing received and the input filter has already been correctly tuned. Fi- nally, the preamplifier may be fitted in a suitable water-resistant case for masthead mounting, equipped with suitable coaxial sockets, and fixed to the aerial mast. JBJB 5.34 .i. REAL-TIME CLOCK A good many highly interesting computer applications will no doubt have been cancelled for tack of a programmable time keeping device. This article, however, | offers a truly up-to-date RTC extension board to program dates with data! Fig. I Internal organization of the Type ICM7170 chip. an all-CMOS and microprocessor compatible real- time clock (RTC) controller. I With the presentation of the univer- sal I/O bus in the June 1985 issue of j | Elekior mdia the peripheral handling capabilities of the popular I C64 computer, as well as other per- | sonal micros, have been consider- ably enhanced, since the I/O bus board allows a number of extension boards to be inserted in a neat and versatile arrangement. The present design enables the user to program real-time software drivers without the need for critical and cumbersome machine language wait loops. Time and data can now be read from and written to I/O ad- dresses, in the very same manner as customary with peripheral control ports; the time updating process is autonomously controlled by a dedi- cated low-power chip: the Type ICM 7170 manufactured by Intersil. In order to be useful for many owners of personal micros currently on the market, the present add-on RTC board has been designed to operate in both 6S02- and Z80-based systems equipped with Elektor's universal I/O bus. However, there is one important restriction for use with the Z80 processor: since the I/O bus was originally intended for the 65XX series of microprocessors as used in Commodore machin es, no bus line is left over for the Z80 NMI or INT in- put; this means th?t the alarm and periodic interrupt facilities offered by the RTC chip can not be put to use in conjunction with the Zilog CPU. None the less, the time and calendar features of the ICM7170 will also be fully functional with the Z80. inside the RTC chip Since the real-time clock controller (RTC) Type ICM7170 is an all-CMOS device with extremely low power consumption, it may conveniently be operated from a back-up battery to keep the internal oscillator and i counter sections working when the | I computer supply voltage is off, or j when a mains failure occurs, j The main features of the RTC chip in ] the proposed circuit may be sum- marized as follows: • full compatibility with 8-bit micro- processor types that have either a fully decoded or multiplexed ad- dress bus; • time registers supply binary coded data to simplify software; • faultless RTC register-to-CPU data transfer thanks to intermediary buffer section; • calendar with automatic leap year correction; • chip switches automatically to back-up supply; • chip access time less than 300 ns; • software selection of one of four crystal frequencies; • data buffering after any read of 10 millisecond register (l/100th part of a second); • programmable alarm with mem- ory function; • CPU interrupt requests generated by alarm section or by one of six selectable periodic signals; • 2 mA typical standby current at 3V and oscillator frequency of 32 kHz. The internal organization of the ICM7170 RTC controller is shown in Fig. 1. The chip has a low-power Pierce-type CMOS oscillator which only requires two external capaci- tors and a quartz crystal to obtain an accurate frequency standard for the present RTC extension board. One of the capacitors is an adjustable type for precise alignment of the crystal frequency, which is divided down to 4 kHz by a programmable prescaler section. By virtue of this prescaler, four crystal frequencies may be used with the on-chip oscil- 5.36 elekto COMMAND REGISTER AODRESS 110001b. HR' WRITE J + = not present in interrupt-mask register, MSB in interrupt-status register. — = not used. * = AM/PM in 12-hour indication mode; (AM = 0, PM = 1). M = alarm time is compared with corresponding counter time when this bit is programmed low (0) Note that addresses 10010 up to and including 11111 (i.e. 12hex. . . lFhex) are noi the RTC chip. INTERRUPT MASK REGISTER ADDRESS 110000b. II INTERRUPT STATUS REGISTER ADDRESS 111 Table 1. RTC command register organization. Table 2. Pro- gramming func- : of bits .D s inthe command register at ad- dress U hex . Table 3. Address organization for the RTC counter sections and their RAM counterparts. lator: 4.194304 MHz, 2.097152 MHz, 1.048576 MHz, or 32.786 kHz. As can be seen from Tables 1 and 2, two bits, Do and Di in the RTC command register at address llhex (10001?) sel- ect the appropriate prescale divisor for the crystal in use. Databit Da allows selection between 12- or 24-hour mode operation. The 4 kHz signal is next divided down to 100 Hz for use as a central clock input to the ripple counter stages. The time and calendar data are available from eight sequentially arranged and programmable coun- ter sections: 10 milliseconds, se- conds, minutes, hours, day of the week, date, month, and year. The in- formation is binary coded and basi- cally consists of eight bits per section, as can be seen from Table 3 . However, since a maximum indi- cation of 31 is sufficient for the date counter, 59 for the seconds counter, and so on, eight bits are never re- quired (2* = 256): the unused ones are kept logic low (0) during a read, while they are not observed (‘don't care') in the case of a write operation. Also inside the chip is a 51-bit RAM memory area to hold the alarm time and date as programmed by the user; these registers are loaded in exactly the same way as the updated counter sections. When set to the alarm mode, the RTC chip will gen- erate an interrupt request signal when the current (updated) time matches the preprogrammed alarm time. ie. the updated counter sec- tions are constantly compared on a byte-by-byte basis to their RAM counterparts after every counter step. If a certain counter section is to be ignored in this continuous com- parison, the user may set the M (mask) bit in the relevant RAM byte, | which will prevent an interrupt from ! being generated if the updated ; counter contents match those of the | corresponding alarm register. | The RTC chip interrupt request out- ! put may be programmed to supply I any one of the following periodic Table 4. Organization of the internal RTC interrupt mask and interrupt status registers at address Whey. Fig. 2 By virtue of the high number of func- tional sections contained in ICi the final circuit of the RTC exten- sion board is fnn'v si'::;.;, Note that it is not possible to use the RTC chip in- terrupt facilities in Z80-based systems, since this would re- digital signals: 100 Hz. 10 Hz, 1 pulse/second, 1 pulse/minute. 1 pulse/hour, or 1 pulse/day. Provi- sion has been made for both simul- taneous and independent interrupt operation of the alarm and periodic signal circuitry. Both the alarm and periodic inter- rupts are under the control of the interrupt-mask register (IMR) and interrupt-status 'register (ISR), the bit assignments of which are shown in Table 4. Selection of the desired in- terrupt signal is effected by setting the relevant bit in the IMR. By reading ISR, the CPU is informed about the nature of the interrupt re- quest; ISR is automatically cleared by the falling edge of the CPU read pulse. Whatever the source of the interrupt request signal, it may or may not be passed to the 6502 IRQ line depend- ing on the logic level of the interrupt enable bit in the RTC command register (see Table 1). This bit con- trols an on-chip output FET which j has its drain connected to the INT | terminal (pin 12) and its source to the INTERRUPT-SOURCE terminal (pin 11). This arrangement allows the ; INT output to be used in an existing WIRED-OR interrupt request bus configuration, together with other , devices that may supply interrupts to I the CPU. If an interrupt is generated by the RTC chip, the INT output will I be at near interrupt-source potential, since the FET is switched on intern- ally; this may occur both in the stand- by and in the power-down (battery back-up) mode If, as in the proposed circuit, the RTC supply voltage is connected to the Vdd and Vss terminals, and the interrupt-source connection also to Vss, the INT output can only be ac- tive (i.e. logic low with respect to Vss) in the presence of a sufficiently high chip supply voltage; that is, when the computer has been switched on (RTC fully operational). In case the user wishes to pass inter- rupts in the power-down mode only, pin 11 should be connected to the negative terminal of the battery at the Vbackup pin. This arrangement may be useful to activate a computer wake-up circuit after a predeter- mined time has elapsed since system power-down. When the voltage between the Vbackup and Vss terminals drops below 1 V, the RTC chip switches to the power-down mode with only the internal clock ^nd interrupt sections active; all other functions are dis- abled to ensure minimum power consumption from the back-up bat- tery. Chip terminals Ao...Ai, De. . .Dr, ALE, WR, RD, and CS are internally connected to Vdd with a single 50 kQ resistor. In case a bat- tery back-up supply voltage can be dispensed with, Vaa may be connec- ted to Vbackup. Practical circuit The proposed circuit of the real-time clock extension board for the univer- sal I/O bus is shown in Fig. 2. Note that very few components are re- quired to make a functional unit with the ICM7170 RTC chip in a 6502- or Z80-based system. To select be- tween these two types of micropro- cessor, the user need merely fit the appropriate wire links; connection to the I/O bus is through a standard 21-way PCB connector. The ready-made PCB for this project is fitted with the necessary parts as shown in the mounting plan of Fig. 3. Note that the battery is an integral part of the completed RTC board; it may be charged from the computer +5V supply by means of D. and Ri. Since it was considered a waste of available I/O address space to re- serve 17 memory locations or I/O channels for the RTC registers, ICi and IC2 latch the RTC register number which must be supplied as a databyte with a POKE or OUT in- struction to an address within the slot that has a 0 for address line As; the contents of the RTC chip registers are next read from or written to an address within the same slot with An [3 high (1). Since every slot offers four I/O addresses (see the article on the universal bus, Elektor Electronics. June 1985), both the latch and the RTC chip appear two times within the slot occupied by the present extension board. Finally, Z80 pro- grammers are referred to the first article in the series on MSX exten- sions in the February 1986 issue of Elekioi India to find details on modification of the universal I/O bus as required for this CPU. Setting up As can be seen from Table 1, the real-time clock may be stopped and started by programming bit Di in the command register; this bit controls the 100 Hz clock input to the counter sections. To stop the clock in order to synchronize it with an available time standard, Da must be set low (0). The desired start time for the RTC is next loaded into the time registers, the correct data is also supplied, and the RTC may be started at the de- sired time by setting Di again (1). To enable the CPU to read glitch-free and therefore absolutely stable time data from the RTC chip, time register data are passed through a buffer sec- tion before being transferred to the CPU databus during a read cycle. However, this buffer is only loaded when the 10 ms register is read, and I programmers are advised to start any j time reading from the RTC chip with a read of this latching register to en- sure that time data are stable and ac- curate. The command register comprises a TEST bit (Ds) to apply the internal I 100 Hz signal to the seconds counter; | this will cause the clock to run a hun- dred times faster than normal, which may be useful for test purposes. I It will be evident that the accuracy I of the present RTC board depends j solely on crystal stability and correct | frequency setting of the oscillator. Outlined below is a preferred align- t ment method using a penod counter 1 such as the one featured in Elektor ! India Febr uary 1985. To pre- | vent the RTC INT output from actual- ly generating an interrupt pulse in I the computer during the alignment I session, temporarily disconnect the I wire at pin 12 of ICi First, write all zeros to the 1MR. Next, load the command register with j decimal values 24 or 28 (18 or 1C \ hexadecimal respectively) to run the clock in either the 12- or 24-hour mode with interrupts enabled. Now set Di in the IMR to generate | periodic interrupts with a frequency of 1 Hz. Adjust capacitor Cj for an in- | dication of exactly 1.000 second on the period counter which should be | connected to the RTC chip INT out- | put (pin 12). For this measurement, the period counter should be set to trigger on the falling edge of the digital input signal. Reset ISR by Fig. 3 Compo- nent mounting plan for the RTC Note the on- board NiCd bat- tery and the wire links to accom- modate either the 6502 or the Z80 processor in the host com- puter. connected in series PCB 86017 Listing I. The essentials of MSX real-time clock program- ming. Although the present RTC hardware does not support inter- rupts with the Z80, provision has been made to set the RTC alarm function. For this purpose, the subroutines at lines 1000 and be called with N=8 and U$= 'ALARM". Note that the register latch is at OUT 113. the RTC proper at INP/OUT 112. 5 CLS:PRINT-***« MSX REAL-TIME CLOCK «**.“ 7 OUT 1 1 3 , 17:0UT I12,4:REM STOP CLOCK 9 REM GO GET TIME&OATE INFO 10 N=0 :US=" SYNCHRO ' :60SUB 1000 20 CLS: PRINT "SET 'iUS;“DATE = " iA ;A 1020 INPUT-MONTH * I -12 )“ i At N+4 > 1030 INPUT"DATE * : 1-31 )-;A(N+5) 1040 INPUT-DAY OF THE WEEK * < 0-6 ) " i A( Nt7 ) 1050 INPUT "HOURS » ( 0 - 2 3 > ' t A ( N+ 1 ) 1060 INPUT "MINUTES - < 0-59 )" i A( N+2 ) 1070 INPUT -SECONOS = < 0-S9 ) _ i A< N+3 ) 1080 INPUT 10 MILLI-SECONOS * (0-99)" iA(N) 1090 RETURN 2000 REM LOAD RTC REGISTERS 2005 FOR N-N TO N+7 2010 OUT 1 13 ,N:REM POINT LATCH 2020 OUT 1 1 2 ,A( N ): REM LOAO RTC 2030 NEXT N 2040 RETURN reading it; this will also deactivate the INT output (logic 1). The outlined method should be programmed as an instruction loop to obtain maxi- mum clock accuracy. Where a period counter is not readily available, use may be made of another time reference signal with known accuracy, such as the BBC time signals on radio and TV. Ob- viously, this method costs more time and requires a good deal of patience before the target accuracy is reached. RTC programming Hardware needs software support and vice versa. To complete this article, two sample programs are of- fered to guide in further program- ming explorations, which will, no doubt, lead to more complex and sophisticated time-keeping software once the basics of RTC control have been mastered. Programmers should be well aware of the essential difference in I/O mapping between the Commodore type of computer and Z80-based micros, such as the MSX series. Gen- erally speaking, the former use memory locations for I/O byte transfer, the latter have 256 I/O chan- nels available which are under con- trol of IN md OUT instructions, whereas the 65XX-based computers work with PEEKs and POKES for this purpose. However, the basic method of RTC control remains the same for both computer types: first the inter- nal RTC register is specified with an appropriate instruction, then data may be read from or written to that register by addressing the RTC MSX users may key in the program of Listing 1 which displays a digital clock in the top left-hand comer of the screen. Obviously, the screen formatting and graphics features of this computer type allow the user to 'brush up’ this little program to his heart's content. Note that line 100 reads the 10 ms register before the actual time reading is performed in a loop. Experienced programmers may have a go at writing a routine that prints time and date on every printer sheet prior to a listing or any other draft copy. Note that, once the clock has been synchronized, time display is simply effected with GOTO 90. However, some provision will have to be made to exit the time display loop and resume the main program. The sample program listed for the Commodore 64 and 128 model com- puters is somewhat lengthier than the MSX version, and, therefore, of- fers more programming functions; among these are selection of video polarity and word-based input of days and njpnths — see Listing 2. HS.CS 5.40 10 REM * COMMODORE 64 REAL-TIME CLOCK CONTROL » 20 DIM A$( 1 2 ) ,B$< 7 ) 30 RESTORE 40 FOR Q=1 TO 12:READ A$(Q):NEXT Q 50 DATA "JANUARY" ."FEBRUARY" ."MARCH" , "APRIL" ."MAY" , "JUNE" ."JULY" ."AUGUST" 60 DATA "SEPTEMBER" ."OCTOBER" ."NOVEMBER" ."DECEMBER " 70 FOR 0=1 TO 7: REAO 8$:PRINT:PRINT“— COMMODORE 64 REAL-TIME CLOCK CONTROL—" 100 PRINT :PRINT :PRINT : 110 INPUT “CLOCK SETTING (Y/N)"-,U$ 120 IF U$=“N" THEN 365 130 PRINTCHR$( 1 47 > 140 REM CLOCK SETTING 150 INPUT " ENTER HOURS " f H:PRINT : PRINT 160 INPUT " ENTER MINUTES “ iM:PRINT :PRINT 170 INPUT “ ENTER SECONDS " iS:PRINT:PRINT 180 INPUT " ENTER MONTH “ ;M$:PRINT :PRINT 190 FOR 0=1 TO 12: IF M$=A$(Q) THEN R=Q 200 NEXT 0 210 INPUT " ENTER DATE “ iO:PRINT :PRINT 220 INPUT " ENTER YEAR “ iF:PRINT :PRINT 230 F I =INT( F/ 1 00 ) :F2=INT( FI / 1 0 ) :F3=F I - 1 0*F2 : Y=F-F 1*100 240 INPUT ” ENTER DAY OF THE WEEK “ iW$:PRINT:PRINT 250 FOR 0=1 TO 7: IF W$=B$ “;P$: IF P$="R" THEN C=128 280 POKE 5§832 . 1 7 : POKE 56833. 4:REM 24 HOURS-MODE SELECT 290 POKE 56832,1 :POKE 56833 ,H:REM SET HOUR 300 POKE 56832, 2:P0KE 56833, M:REM SET MINUTES 310 POKE 56832 ,3:P0KE 56833, S:REM SET SECONDS 320 POKE 56832, 4:P0KE 56833, R:REM SET MONTH 330 POKE 56832 ,5:P0KE 56833,0: REM SET DATE 340 POKE 56832 ,6 :POKE 56833, Y:REM SET YEAR 350 POKE 56832 ,7 :POK£ 56833 ,E: REM SET DAY OF THE WEEK 360 POKE 56832, 17:P0KE 56833, 12:REM ACTIVATE CLOCK 365 PRINT CHR$( 147) 370 POKE 56832 ,0:REM PUT TIME IN LATCH 380 POKE 56832,1 :H=PEEK< 56833): REM REAO HOUR 390 POKE 56832 ,2 : M=PEEK < 56833 ) : REM READ MINUTES 400 POKE 56832 ,3 :S=PEEK< 56833 ) :REM READ SECONDS 410 OH=INT(H/I0 ):UH=H-DH*I0+C:DH=OH+C:REM PRINT HELP HOURS 420 DM* I NT ( M/ 1 0 > :UM=M-DM* 1 0+C :DM=DM+C :REM PRINT HELP MINUTES 430 DS-INT :UY=Y-DY* 1 0 :REM PRINT HELP YEAR 490 POKE 56832, 7:E=PEEK( 56833 ):REM READ DAY OF THE WEEK 500 KL=S4272:REM PRINT TIME WITH COLOUR HELP 510 POKE 105 1 ,0H+48 : POKE 1 05 1 +KL , 1 4 520 POKE 1 052 ,UH+48 : POKE 1 052+KL , 1 4 530 POKE1053 ,58+C:POKEI053+KL , 14 540 POKE 1 054 ,DM+4S : POKE 1 0S4+KL , 1 4 550 POKE 1 055 ,UM+48 : POKE 1 055+KL . 1 4 560 POKE1056 ,58+C:POKE!056+KL , 14 570 POKE 1057 ,DS+48 :P0KE1 0S7+KL , I 4 530 POKE 1 058 ,US+48 : POKE 1 058+KL , 1 4 590 PRINT :PRINT TAB( 27 > ; 8S( E ) 600 POKE) 171 ,0D+48:P0KE1 1 71 +KL , 1 4 S10 POKE I I 72 ,UD+48 :POKEI 172+KL , 1 4 620 PRINTTAB1 30 > i A$< R ) j 530 PRINT “ " : :REM CURSOR 3 LINES UP 540 POKE 1 2 1 1 ,49: POKE 1 2 1 1 +KL , 1 4 650 POKEI 21 2 ,57: POKE 1 2 1 2+KL , 1 4 S60 POKE 1213 ,DY+48:P0KEI21 3+KL , 1 4 S70 POKEI 2 1 4 ,UY+48:P0KEI 2 1 4+KL , 1 4 j 680 GOTO 370 Listing 2. Com- modore 64 and 128 users may enter this BASIC program, in- tended as a guide to further experiments with the real-time clock board as described in this article. Note the PEEK and POKE in- structions to ac- cess the RTC registers at lo- cations 56832io (RTC) and 56833io (latch). junior computer The cost and complexity of home computers is a serious I deterrent to the newcomer to computer operating and programming. We know of many readers who would like to ' build their own' but who lack the necessary I technical knowledge. The Junior Computer has been designed (for just this reason) as an attempt to 'open j the door’ to those readers who need a push in the right direction. I It should be emphasized that, although simple to construct, the Junior Computer is not a 'toy' but a fully workable computer system with the capability for future expansion. It has been designed for use by amateurs or experts. The purpose of this article is to give a general description of the operation of the Junior Computer It has been decided to publish a more detailed description | in book form. The arrival of 'The Junior Computer' Books 1 and 2 on the market will be announced shortly. This, however, is a preview intended to give the reader an idea of what the computer entails. There are many readers who would like to know more about | home computers but who may | not be technically minded or j who consider them too complicated to understand. These two reasons, coupled with cost, tend to prevent many people from 'taking the plunge'. To help overcome these problems we have designed the Junior Computer (JC>. Do not be misled by the term 'Junior' - this computer provides the first step to understanding large and powerful systems. When fully expanded the Junior Computer can work with higher level languages. It uses a simplified method of operation and has the advantage of various expansion possibilities. The heart of the JC occupies no more than a single printed circuit board which should dispel any fears produced by large and complicated systems. The inten- tion of this article is to encourage readers to take the intitial steps towards constructing and operating their own personal compute'. Extensive and precise details will not be dealt with here but will be published in depth in book form - the Junior Computer Books 1 and 2. We can however whet the appetite and set the ball rolling. Specific data concerning the computer are given in Table 1 , this is intended for readers who are already familiar with computers. Block diagram The fundamental features of the Junior Computer are shown in the simplified block diagram of fi- gure 1. The heart of any compu- ter system is the CPU, or central processing unit. In this particular case it is a 6502 microprocessor, a 40 pin chip that you can hold in the palm of your hand - but shouldn't! Its purpose is to con- trol communications between the various units inside the com- puter in accordance with the in- structions of the program. A clock generator (oscillator) serves as a 'pacemaker' for the processor. A certain amount of memory is required by the microprocessor to store programs and data. In the JC it consists of two sections. The first one for storing perma- nent data and the monitor prog- rame The monitor program cont-' tains a number of routines which perform such chores as program loading, debugging and general housekeeping. The second sec- tion of memory is used for stor- ing temporary data and program instructions. The block marked I/O (input/out- put) maintains contact between the computer and the outside world including the keyboard and display. In the circuit the I/O appears as the PIA, or peripheral interface adapter. It takes care of the data transfer in two direc- tions and can (temporarily) store data. The operator communi- cates with the computer via the keyboard and display. Computers are not as 'intelligent' as some television programmes would have us believe. In fact, they merely carry out (program- med) instructions in a certain (programmable) order. There are three sets of parallel interconnec- tions (called buses) which carry the various data and control sig- nals. First of all there is the data bus to consider. It is made up of a number of lines along which data travels from block to block. The processor must also be able to in- | dicate the memory location j where data is to be stored or re- moved. This is performed by the ; second bus, the adress bus. Last, but by no means least, is the con- trol bus which ensures that the CPU is able to control the internal status, for instance the nature and direction of datatransfer and the progress of successive prog- ram sections. This then very briefly covers the various blocks, tbeir functions and their interconnections. We can now move on to look at the circuit in greater detail. Circuit diagram The circuit diagram of the entire Junior Computer (except for the power supply) is shown in figure 2. Now that the block diagram has been examined, each section should be easily recognisable. The 6502 microprocessor is IC1. Below it is clock generator formed by N1, R1, D1, Cl and the 1 MHz crystal. The system uses a two-phase clock, shown in the circuit diagram as signals 01 and - 2 . The memory is constituted by IC2, IC4, IC5 and part of IC3. The monitor program is stored in IC2, which is an EPROM (Erasa- ble Programmable Read-Only- Memory). This is the basic prog- ram in the computer (not to be confused with BASIC - a high level computer language). The RAMs (Random Access Memory) IC4 and IC5 serve as user mem- ory and together have a capacity of 1024 bytes. In the PIA, IC3, there are another 1 28 bytes of RAM. The PIA consti- tutesadata buffer which controls all the data transfer passing in either direction between the computer and ports A and B. The port lines are fed out to a 31 pin connector. IC3 also contains a programmable interval timer. The displays (Dpi ... Dp6) and keys (SI ... S23) are at the bottom of the circuit diagram. Of these keys, sixteen are for the purpose of entering data and addresses in hexadecimal form and the re- maining seven have various con- trol functions. Data to the dis- plays and from the keyboard is transferred across seven lines from port A. The information on the displays is controlled by the software in the monitor program, which also ensures that key func- tion signals are recognized. IC7 multiplexes the displays and periodically checks the state of the rows of keys to see which one, if any, is being depressed. With the aid of switch S24 the dis- play may be switched off. The display may be used in two different ways. Usually, the four left hand displays will indicate an address and the two right hand ones will indicate the data in the address location concerned. As a second possibility, the two left hand displays can show the (hexadecimal code of an instruc- tion while the others display the address of the data correspond- ing to this instruction. This makes program entry much The address decoder, IC6, pro- vides chip select signals for each of the various memory blocks. These appear as K7, K6 and K . ' for the EPROM, PIA and the RAMs respectively. The other five selection signals are availa- ble externally for memory expan- sion. The RAMs also require a R W (read/write) signal. This is made available via gate N6 and is generated by a combination of the R/W signal in the 6502 and the 72 clock pulse (02 data bus ena- ble) Another control signal is the reset signal RES. which places the microprocessor and the PIA in the correct initial condition for the monitor program. A reset is generated when key RST (SI) is pressed and half of a 556 timer (IC8) is used to suppress any con- act bounce this key might produce. 5.43 f Table 1 General information on the Junior Computer - single board computer , - programmable in machine i language (hexadecimal) I - microprocessor type 6502 - 1 MHz crystal - 1024 bytes of monitor in EPROM - PIA type 6532 with two I/O ports.128 bytes of RAM and a programmable interval timer - six digit seven segment display - hexadecimal keyboard with 23 keys: 16 'alpha' keys and 7 double function control keys Control keys (normal mode) + : increment address on display by one DA : enter data AD : enter address PC : call up contents of current program counter position GO : start program from address on display ] ST : interrupt program by way of NMI RST : call up monitor i STEP : step by step run through programe Control keys (editor mode via ST) insert : insert program step before address shown on display input : insert program step after address shown on display skip : jump to next op-code search : search for a certain label delete : delete row of characters on display Possibilities debugging hex editor hex assembler : all internal registers may be shown on display : label identifiction hexadecimal figures JMP JSR, branch instructions operate with label : conversion of label numbers displacement values for real address : calculate address offset for jump instructions Applications - can be used as a basis for many expansions - can be used as a 6502 CPU card - educational computer for beginners - can be expanded with: elekterminal cassette interface video interface matrix printer assembler disassembler ] There are two ways in which a program bieng run can be inter- rupted by means of the NMI I (non-maskable interrupt). The I first one is provided by the STOP key S2 (which uses the other half | of IC8 for contact bounce sup- J pression) and the second is | provided by the STEP switch S24 when this is in the 'ON' posi- tion. When the output of N5 then I changes from high to low, the IRQ (interrupt request) connec- tion causes the program being I run to be interrupted, for in- I stance by programming the in- I terval timer in IC3. Also present I on the control bus are the two clock signals 01 and 02 which control the PIA and the RAM R W signals. These determine the di- I rection of data transfer. Finally, lines RDY, SO and EX provide possibilities for future expan- | Ail the address, data and control | signals are fed to a 64 pin expan- sion connector which, as its j name suggests, is meant for the [ purpose of expanding the sys- ! tern futher at a later stage. Figure 3 shows the power supply for the I Junior Computer. This produces I +5V for all the ICs and the dis- j plays. A few remarks ] Before work is begun on the con- [ structionofthe JuniorComputer, two more aspects have yet to be | considered. The entire system is built up on three printed circuit I boards of which one is double j sided with plated through holes, j It is advisable to check all the through connections with an | ohmmetertomakesurethatboth sides of the circuit are well con- j nected. This will avoid problems, j for after soldering it is very dif- ficult to trace any breaks. How to build the Junior Computer ! Construction of the Junior Com- puter is not difficult by any stan- dards. If it is assembled carefully (paying particular attention to | solder connections) and the in- j structions are followed to the let- I ter, very little can go wrong. The three sections of the JC are each constructed on a separate printed circuit board: the main ! board (including keyboard) the ] display board and the power sup- | ply. Detailed instructions for con- j struction will be given in Book 1. The 6502 (CPU) is available from M/s Semiconductor Complex Ltd. See page No. 5.11 SATELLITE LOUDSPEAKERS This article deals with the satellite loudspeakers that complement the subwoofer featured elsewhere in this issue, to give complete coverage of the audio spectrum. These satellite are, however, also perfectly suitable for independent use. Satellite loudspeakers are not a | separate category of sound i reproducing equipment; any loud- speaker whose bass performance should be improved could be classified as a satellite. So-called bookcase speakers are invariably satellites, because their modest di- mensions prohibit proper repro- duction of frequencies below about 100 Hz. If you are planning a new loud- speaker system, you could do worse than to opt for a subwoofer-satellites system. It is then, of course, best right from the start to design the satellites for optimum performance with the subwoofer and vice versa. It is on this basis that the present article has come about: the results are very satisfactory, indeed. Even those who are not terribly in- terested in the subwoofer will find that the bass performance of the satellite speakers (— 3dB point at 65 Hz) is perfectly adequate for their requirements. Although the design of a loud- speaker enclosure is never an easy task, the one proposed here pre- sents the constructor with relatively few difficulties. This is, of course, I largely due to there being no need of paying much attention to the bass reproduction. A response down to 100 Hz would be perfectly adequate; true, an octave further down would be very nice, but is. in this case, not necessary. , This immediately removes the prob- ] lem of choosing the right shape and j size of enclosure and deciding how many "ways” the system should have. The enclosure decided on is a nor- | mal closed box, while it was felt that I a two-way system would be perfectly I acceptable, provided that the chosen drive units would allow this. | The latter aspect also requires less arithmetic and fewer measurements than, e.g., a three-way system. These considerations have resulted in a very satisfactory practical realization, both as regards the enclosure and the number of drive units. As a bonus, the bass perform- ance measured is considerable bet- ter than that aimed at. In short, the proposed design is compact, easy to build, not expensive, and, even with- out a subwoofer, gives an excellent overall performance. The drive units As said, the design is based on two I drive units. Since the majority of Fig. 1. The Dynaudio Type 17W75 was used as the bass and middle fre- quency drive unit in the proto- type system. j Noteworthy aspects of this unit are the centre magnet and the PH A (phase homogenous area) propylene cone. I Fig. 2. The tweeter is a Dynaudio Type D-28AF, which was specialty de- signed for use with 6 dB/octave cross-over filters. middle-frequency units are not really satisfactory above about 2000 to 2500 Hz, which causes problems in the choice of tweeter, Dynaudio units were used for the prototypes. These units did not only meet the re- quirements for the present design better than most; they also offer the advantage of an excellent match with the subwoofer (which also uses a Dynaudio drive unit). The units are the Type 17W75, a 170 mm bass and middle-frequency unit, and the Type D-28 AF tweeter. The 17W75, shown in Fig. 1, is a drive unit with a relatively large voice coil (75 mm) in hexacoil technique, which, in conjunction with the unusual shape of the one-piece cone, gives an ideal transfer of the acceleration force from the coil to 1 the PHA (phase homogeneous area) j cone. Another advantage of the big j voice coil is the short rise time (fast transient response) of 50 ms. Very low distortion and excellent phase | characteristics are a result of the total | concave shape of the cone. The D-28 AF, shown in Fig. 2, is a 28 mm soft dome tweeter. The voice coil is coupled with the aid of ferro fluid. The unit has a noteworthy fast transient response (short rise time) of | 12 ns. It offers the great advantage of j having been designed specifically | for use with 6 dB/octave filters; not many dome tweeters have! Cross-over filter Cross-over filters (or networks) are, unfortunately, necessary, because there is not a drive unit that can reproduce the entire audio range satisfactorily. As long as these filters are not to steep-skirted, they do not cause too much harm, but with in- creasing skirt steepness the flaws they introduce become more and more serious. Steep-skirted filters have particularly bad transient I response characteristics. The design of a cross-over network should therefore be based on 6 dB/octave slopes, provided the drive units used allow this. This is so | in the present design as can be seen from the diagram in Fig. 3. Strictly | speaking, this circuit contains only two true filter components: Li and C2. The remainder of the compo- nents perform the correcting func- tions that are always necessary for good filter operation. Network Ri-Ci serves to counteract the impedance of the 17W75, which increases with rising frequency. This carefully de- signed network ensures that the overall impedance of the drive unit remains constant above its reson- ance frequency. Only because of this can the filter perform as re- Resistive divider Rj-Rj serves a twofold function. In the first place, it ensures level matching of the tweeter, whose efficiency is somewhat higher than that of the 17W75. Then, the value of R? may be varied between zero ohms and 2.2 ohms without the necessity of chang- ing the value of C. A value of 0 ohms corresponds to a 0.5 dB correction for the tweeter, while 2.2 ohms gives a — 1.5 dB correction. Moreover, R3 smoothes out a small uneveness in the tweeter characteristic: its value must, therefore, not be changed under any circumstances. The characteristic in Fig. 4 represents the output voltage of the filter, measured across the two drive units. Note that the cross-over point only appears to be at —5 dB; it is ac- tually at the customary —3 dB. The characteristic of the 17W75 has a slight peak at the cross-over fre- quency, and this has been corrected by a slightly earlier action of the filter. Acoustically, everything is, therefore, as it should be. Construction of the filter should not Fig. 3. The 6 dB/ give any difficulties if the PCB (Type octave cross-over 86016) shown in Fig. 5 is used. Note, network is however, that Li should be fastened typified by its with glue or a brass/nylon bolt: a simplicity. Fig. 4. Character- istic curve of the output voltage of the cross-over filter measured with the drive units connected. steel fastening would affect the value of the inductor. Also, observe cor- rect polarity when the drive units are connected to the board. The PCB may be conveniently mounted —on spacers- on the bottom lid or against the back panel of the enclosure. Although theoretical considerations point to a somewhat larger volume, in practice the manufacturer’s recommendations proved to be cor- rect. In a damped closed box of ex- actly 10 litres volume, the bass performance of the 17W75 was sur- prisingly good. The difference be- tween a box with, and one without, a variovent is slight. The variovent only serves to attenuate the resonance peak, and this results in a somewhat more rigid performance at low fre- quencies. Although some photographs accom- panying this article show a beauti- fully styled pentagonal, pyramid- shaped prototype enclosure (cour- tesy Dynaudio), the proposed enclosure has been kept rather simpler. Note, however, that the pen- tagonal enclosure is available from Dynaudio as a kit: it is acoustically excellent, but quite difficult to build. Our own proposal, shown in Fig. 6, offers similar advantages as the Dynaudio design: no parallel side panels; leaning backwards; upward tapering front panel; but does not demand the craft of a furniture maker. The material is 18 mm fine-chip board; plywood may, of course, also be used, but is rather more expens- ive. The front, back, and side panels have exactly the same dimensions. If these are sawn very carefully, all four can be glued together in one go. The bottom and top lid must be sawn very carefully to ensure a good, tight fit onto the leaning vertical panels. The top lid may be glued in place, but the bottom panel is best fitted with screws and sealing tape so that access is possible at a later stage, if required. Next, the holes for the drive units, the variovent, and the connector terminals should be cut. The variovent should be glued into Fig. 5. The printed-circuit board for the cross-over net- work (Type 86016 — available through our Readers' Services). According to the manufacturer’s data, the 17W75 is best housed in a 10 to 15 litre closed box, which has been provided with a so-called variovent (acoustic resistance). Ci - 22 (i bipolar electrolytic or polyester Cr = 10 p polyester Ri = 5 Q;5 W Ri - 0.47 0;5 w R. - 22 Q;5 W Dynaudio Type 17W75 Dynaudio Type D-28 . board or plywood, place, while the drive units should be screwed on. Afterwards, the gap between the rim of the drive units and the front panel should be sealed with suitable tape. The beste place to fit the cross-over filter is at the back panel between the variovent and the connector ter- minals. Panel resonance is further prevented by gluing strips of rubber-backed floor covering at the inside of all panels and then covering these with 30 mm thick rock-wool. If this material is amply cut, the strips will be push-fitt, obviating the need for gluing them into place. The finish of the exterior of the enclosure is left to your own taste and preference. Performance It is. of course, easy (and tempting) for a designer to sing his own praises, so the performance of the system can be gauged from the measured impedance and fre- quency response characteristics illustrated in Figures 7 and 8 respect- ively. The smooth impedance curve should not present any problems to a good output amplifier. The frequency response curve was measured with Ra=0.47 ohms. When this is increased to 2.2 ohms, the characteristic shifts down by about 2 dB above 2 kHz. Response at low frequencies was ascertained by close-proximity (20 mm) measure- Fig. 6. Construc- tion details of the proposed enclosure. The material may be 18 mm plywood or good quality chip board. ments. The acoustics of the test room has such an effect that measure- ments at greater distances give no meaningful information as to the behaviour of the system at low fre- quencies. For measurements at middle and high frequencies, the test microphone was placed at a distance of about 2 metres at roughly the height of the acoustic centre of the enclosure. Fig 7. Character- istic impedance curve of the completed satellite system. Fig. 8. Fre- quency response curve of the completed satellite system. selex 12 We have seen so far how divider and counter circuit can be constructed using cascaded Flipflops. In this chapter, we shall see another practical application of the cascaded Flipflops; the 'Shift Register' 1 connected to the inputs J and K of the next Flipflop. The clock inputs of all four Flipflops are connected together. A 'NAND' gate inverter is inserted at the input of. the first Flipflop so that the possibility of having J/K = 1/1 or 0/0 is eliminated. The state of input SE is thus taken as a single input to the cascade and travels to the next Flipflop on occurance of a clock pulse at the clock input. If we sent the in put SE = "1 " at the first clock pulse and then reset it to "0" before the second clock pulse, we can observe that this ”1 " will travel to the next Flipflop on every subsequent clock pulse. On the fifth clock pulse the "1 " gets out of the last Flipflop and as the output of the last Flipflop is floating, it is lost from the cascade. The clock pulses are generated by alternately connecting the R and S inputs to the ground line. The NAND gate Flipflop consisting of gates T and U switches states on each transition and the clock is ''debounced'' As the circuit described in Figure 1 is used to shift the data at the input forward to the next Flipflop on every clock pulse, it is called a 'Shift Register'. For proper functioning of the circuit, all unused inputs of 1C 6 and 1C 7 must be connected to "1 " Figure 2 shows how we can prevent the "1" from getting lost on the fifth pulse. Digi-Course II Chapter 6 Here the Q output of the- last Flipflop is connected back to the input of the first Flipflop. through the OR gate obtained by using a NAND gate. A NAND gate functions as an OR gate with inverted inputs. In the circuit of figure 2, SE must always be held at "1” and taken to "0" only at . the first clock pulse, so that a "1 " is entered into the Shift I Register At the fifth pulse when QD switches from "V to "0". QD switches from ”0'' to "1" and this ''0” being shifted out of the FF 4 appears at the input Sg of the NAND gate S. This in turn appears as a "1 " at the output pin S8 and enters Flipflop FF 1 on the fifth clock pulse This "1 " again travels through the cascade for next four clock pulses, and appears at the QA output of FF 1 on the 9th clock pulse. This operation continues as long as we provide the clock pulses. This modified circuit is called the Ring Counter, j As the Flipflops can assume any state when power is [ switched on for the first time, we must initially Reset all the Flipflops to ”0'' before starting the clock pulses, otherwise the initial condition of the Flipflops will keep on rotating through the Ring-Counter The circuit of figure 2 has only four Flipflops; and can count only four clock pulses. If we want to construct a I Decimal Ring Counter we need 10 Flipflops. This will have its feedback line which activates after every 10 pulses. Another Decimal Ring Counter can be operated from this feedback pulse used as a clock pulse. Practically, such circuit are not constructed using individual Flipflop ICs. Fully integrated Shift Register or Ring Counter ICs are available for these applications. Shift registers are often used in Computer Technology, and rather than entering 1 bit, a series of bits is entered. For example, a bit sequence of 1001 can be entered into a Shift Register using clear and preset inputs and shifted out bit by bit. This will represent a serial transmission of the binary number 1001 (Decimal 9) If the sequence 1001 is entered bit by bit into a shift register on 4 clock pulses, we have the combination 1001 at the outputs Qa. Qb.Qc and Qo at the end of the fourth clock pulse, thus representing a serial input of the binary number 1001 into the 4 bit Shift Register, which gives a parallel output 1001 at the end of the 4th Clock pulse. In the first case when we set the 4 Flipflop outputs to 1001 before giving the clock pulses, it can be described as uarallel input/serial output operation. In the second case, where we had all Flipflops set to zero, and entered the sequence 1001 bit by bit at every clock pulse, it can be described as serial input/parallel output operation. Data transmission between two devices can either be serial or parallel Serial transmission requires only two lines, one data line and one ground line. Parallel transmission requires one line for each bit and an additional ground line. For 8 bit data transmission in parallel mode, we would thus require a 9 core cable. However, as the parallel transmission can take place in one shot, it takes much less time than in case of serial transmission. An 8 bit data to be transmitted serially will require minimum 8 clock pulses, whereas if it is transmitted parallely it will take only one clock pulse, (almost 8 times faster! ) You can try the serial and parallel data transmission using two Digilex Boards The internal block diagram of a 4 bit Shift Register 1C 74 LSI 94 is shown in Figure 3. OUTPUTS :ular 1C can operate as Shift Left or Shift Right The direction of Shift is decided by the on at the inputs SO and SI a 01 combination t Left and a 10 combination gives a Shift Right A 1 1 combination allows parallel entry of data input is blocked by the 00 combination. CLEAR sed to reset all the outputs to "O" and DSL are used as the data input pins during t and Shift Left operations. Mini Amplifier Only a few passive components (resistors and capacitors) are necessary to complete the amplifier The input signal is given to the 1C through capacitor Cl This is amplified by the 1C A small amplifier circuit is described here for the readers who are always looking for a practical project. The description 'Mini' does not apply to the performance of the amplifier, it applies to the size, and number of components required. A full fledged amplifier generally consists of two main stages, a pre amplifier to amplify the signal coming from the signal source like a Tuner, Cassette-player or a record-player, and the power amplifier which amplifies the signal further and delivers the driving power to the loud speaker The circuit's presented here takes care of the second function. It raises the signal level coming from the pre amplifier and delivers the driving power to the loudspeaker. It can give a maximum of 10 Watts to a suitable loudspeaker. It is built around a single 1C and a few additional passive components. The Circuit The main component of tl circuit illustrated in figure is the amplifier 1C TDA 2003 (which can also be substituted by another 1C I TOA 2002 without affectin the performance) It is a compact integrated low frequency amplifier suitable for output capacities upto 1 0 Watts. 5.52 selex supply. Il Is a simple battery eliminator circuit with a 12V/1.5A transformer, a bridge rectifier consisting of 4 diodes of the type 1 N 4002 and an electrolytic filter capacitor of 1000 uF/25 V. This gives a no load voltage of about 16V. The supply voltage to the 1C should not be more than 1 8V in any case. Though the 1C can tolerate upto 28V without any damange, the performance of the amplifier is affected beyond 18V and the volume Construction The component layout of SELEX PCB is shown in figure 4. The layout is very simple and everything except the loudspeaker and the battery eliminator fits on the PCB. The assembly should be carried out in the usual sequence - jumper wires, resistors, capacitors and semiconductors. The fully assembled PCB is shown in photograph 1, which clearly shows the construction details. It also shows how the heatsink is fitted to the PCB and the 1C cooling fin. the cooling fin of the 1C is internally connected to pin 3 which is externally connected to the ground line. No mica washers are therefore necessary between the 1C and the heat sink. Care should be taken while mounting the heatsink that the mounting screws on the PCB do not short the heat sink with any , other tracks, because the heat sink is connected to the ground line through pin 3 of the 1C. There should be a gap of about 2 to 3 mm between heat sink and the PCB. 5.53 not make any sound. (Because the input is connected to the ground line.) If one or both of these immediately switch the power off. Check the PCB for faulty connections or then remove the multimeter from the supply line and connect the output of the eliminator directly to the amplifier PCB Now you can check all the DC voltages marketed in the circuit diagram of figure 2. If these are all as per the specified values, you are ready to operate vour amplifier. The short circuit between the input and ground can now be removed and the input can be connected to the output of a preamplifier | preamplifier output required to drive the amplifier at full load is about 45 mV. A 50 mA signal is required if the loudspeaker has an impedance of 41! or 80. If you expect the preamplifier to deliver a higher output signal, then a potentiometer must be used in the input circuit as shown in figure 6. The connection between the preamplifier and the power amplifier must be through a shielded cable, with the shield connected to the ground and the core connected to the signal. This precaution reduces the hum pick ups by the amplifier. It is generally very difficult to obtain 211 loudspeakers, and a simple solution to this problem is to use two 41! , loudspeakers in parallel The battery eliminator circuit must be constructed separately as it has no space on the main P(?B. The output of the battery connected through a cable to the amplifier PCB at the terminals marked + ad 0. Testing When the assembly is complete, the first test can be carried out. The input is connected to the ground line, and a suitable loudspeaker is connected at the output. A multimeter is inserted in the supply line to measure the no load current. The measuring range is set to 100 mA. As The Digilex-PCB is now available! Price: Rs. 85.00 + Maharashtra Sales Tax. Delivery charges extra: Rs. 6.00 Send full amount by DD/MO/PO. Available from: precious e ELECTRONICS CORPORATION Journal Division 11. Shamroo Vithol Marg (Kiln Lane) Off Lamington Road. Bombay-400 007. 5.54 selex Z-Diode Tester Right at the beginning, let have called it a Z-Diode Tester and not a Zener Diode Tester as you might be expecting. A little bit of hair splitting is necessary to understand this. To be very precise. Zener Diodes are available only for the voltages between 2.7 and 5V. Ony these are the genuine Zener Diodes, based on the effect inverted by Mrs. Zenerl The so-called Zener Diodes available for higher voltages are really 'Avalanche- Diodes' which are based on the Avalanche effect. Zener Diodes for voltages less then 2.7 V are also not true Zener diodes but they are just the combinations of two or three ordinary silicon diodes in senes packaged in a single glass body. Precisely for this reason, we have not used the name Zener Diode Tester The name Z-Diode is used to cover all the three types of diodes. The Z- Diode teter described here can be used for all types of Z-diodes. as well as for ordinary diodes. The tester can be used to test a function, how well it can function and how high is the Z-Voltage. Normally the Z-voltage is marked on the body itself. For example, "4 V 7" or "'5 V 6" means a Z-Voltage of 4.7V or 5.6V. However, there are some Z-Diodes which have code numbers only and no Z-Voltage markings. In case of these diodes, one must either consult the manufacturers data book or use the Z- Diode Tester to find out more about the diode. Sometimes when using components removed from old circuit boards, one may come across a diode with illegible markings. In such a case, firstly we want to find oux \\ w \% a Z-Ovotie at att, and if it is . then we must find out the Z-Voltage. How well a Z-Diode functions depends upon its V-l characterisistics. The V-l characteristics if ab udeak Z-Diode and a practical Z- Diode are shown in figure 2a and 2b. In case of an ideal Z-Diode, the diode is non conducting till the voltage reaches the Z- Voltage value. As soon as the Z-Voltage is reached, current flows through the diode and the diode behaves like a short circuit. The voltage remains clamped at the Z-Voltage value and remains independent of the amount of current flowig through the diode. The characteristic curve goes up vertically towards infinity. If we operate such a diode with a series resistance as show in figure 3. the voltage across the diode remains clamped at the Z- Voltage and only current changes with change in UB This property is very useful in designing stabilised power supplies. A practical Z-Diode does not function as effectively as an ideal Z-Diode. The characteristic curve of a practical Z-Diode is shown in fugure 2b. 5.55 selex 2b The curve does not rise vertically upwards, but does so at an angle. Due to this slightly slanted curve, the voltage across the Z-Diode does not remain fully independent of the diode current. How well the Z- Diode functions can be seen from how steeply the curve rises. The Z-Diode tester described here has a facility to measure the Z-Voltage at seven different currents flowing through the Z- Diode. The Circuit The principle of our Z-Diode Tester is similar to the circuit shown in figure 3 A DC voltage, a series When the voltage is more than the Z-Voltage, a current flows through the circuit. Value of the current is decided by the series resistance ^nd the Z- Voltage of the diode. With a 9 V DC supply, a resistance of IK and a Z- Voltage of 4.7V, the voltage across the resistor is 4.3V and current flowing through the circuit is 4.3 mA. Now if we replace the Z- diode by another one with a Z-Voltage of 6.8V. then the voltage across the resistance is only 2.2 V and the current through the circuit is only 2.2 mA. From the above observations, we can draw a conclusion that just a series resistance is not enough if we want to test different Z-diodes at the same current. We need a constant current source for this, preferably one with different current settings available. Figure 4 shows the practical circuit of the Z-Diode Tester with a constant current source and three switches to set the constant current value. Transistors T1 and T2 together function as a constant current source. These are connected in such a way that the colletor current of T1 always remains constant and depends on the resistance across the Base-Emitter of transistor T2; which can be varied in seven steps by setting the switches SI, S2 and S3 in different combinations. To understand the functioning of the circuit, assume that switch SI is closed. With the power supply connected across© and(o)various currents will flow in the circuit. The collector current of T1 also flows through the Z- Diode and through the resistance R1. However, as the resistance R1 is directly connected between the base and emitter of transistor T2, voltage across R1 cannot exceed 0.6V which is the Base-Emitter voltage of T2. When voltage across R1 tries to cross 0.6V, T2 goes into conduction and its collector current flowing through R4 increases. With increased current through R4, the voltage on the base of T1 reduces. A drop in base voltage of T1 means a drop in its collector current; which is nothing but the Z- Diode current. These two actions balance each other across R1 in not allowed to rise beyond 0.6V and in effect the collector current which is also the Z-Diode current remains constant. By changing the switch settings in various combinations, we can obtain seven different values of the diode current for our tester. The three switches give three independent settings, three combinations of two switches closed simultaneously and one combination where all three are closed simultaneously. When more than one switches are closed simultaneously it results into a parallel combination of resistances. Table 1 gives all the seven combinations, and the values of currents produced by them with a 24 V power supply. 5.56 flek.o' i 5.57 Now if the diode polaritv is reversed and switch S2 is closed, the voltage measured by the multimeter should be about 0.6 to 0.7V for Germanium and 0.2 to 0.4V for silicon diodes If this voltage is less than 0.2 volts, it means that the Testing with the Tester. battery packs as the power supply of your Z-Diode Tester, it will be suitable for testing Z-Diodes from 1.5 to 15V and the normal silicon diodes like 1N4148, 1N4001 etc. (With a supply voltage of 24V, you can test Z- Diodes upto 21 V.) For testing, the Z-Diode is connected with the two crocodile clips, and the multimeter is connected through the banana plugs. The measuring range to be set on the multimeter is 20V D.C. Switch S2 is now pressed and you can directly read theZ-Voltage on the multimeter. Switch S2 is used because it gives approximately 5 mA current through the Z-Diode. and the rated Z-Voltage is generally specified at 5 mA operating current. This is true for almost all 0.4W Z- Diodes. In case of 1 W Z- Diodes, keep all three switches pressed to give the maximum test current of about 28 mA when measuring the Z-Voltage. The find out how well the Z- Diode functions, measure the Z-Voltage at every switch combination of table 1 . The varioation in Z- Voltage with increase in current will tell you how steeply the characteristic curve rises. A 5.6V/0.4W Z- Diode may give a variation of about 0.2V in the Z- Voltage over the current range of 5mA to 28mA. The smaller this variation, the better is the Z-Diode. In case of a good Z-Diode which showed the Z-Voltage equal to the supply voltage, it should show a voltage of about 0.7 when its polarity Z-Diode) will always show the Z-Voltage to be almost equal to the supply voltage when connected in the blocking direction. If during the test, the multimeter shows a Z- Voltage comparable to the supply voltage itself, this can mean the following: 1 . The Z-Voltage is beyond the measuring range of our tester. 2. The Z-Diode is open. 3. This is not a Z-Diode but it may be just an ordinary germanium or silicon 0.1 ohms resolution, and ohms, 20 K ohms, 200 K ohms and 2 M ohms. For further details contact M/s A RUN ELECTRONICS PRIVATE LIMITED B 125 126 Ansa Industrial CENTURY INSTRUMENTS PVT. LTD. SCO 289, 1st floor. Sector 35 D CHANDIGARH ■ 160 036 of 18 gauge M S. Steel nished in oven baked el paint The Total height I trolley is 32" from floor COMPONENT TECHNIQUE 8. Orion Apartment 29 A Lallubhai Park Road. DIGITAL BOARD TESTING COURSE TEKNIS U.S.A. offers a court ;ar burglar alarm ADVANCE’’ has inlrodL CABLE MARKERS MICROSIGN Chevr MICROSIGN PRODUCTS Mehta Terrace. Satyan ELCOM >03. Jay WNAGAR 364 001. THICK FILM VOLTAGE REGULATOR INSTANT Servo Contr. Line Voltage Regulators AC DRIVE SYSTEM SPECTRON . PVT. LTD. Now you can Learn Electronics Through Exciting Experiments The Electronics Fever Is On! So hurry up, write to: Dynatron Electronics 3, Chunam Lane, Bombay 400 007. Q: Who wi!l show the way? A: Dynatron! Q: What else does he require? A: An excellent introduction and some confidence! Q:Can a beginner hope to become an expert in electronics? A: Certainly! Q:How? A: By experimenting! An Industrial TWO-in-ONE Digital Relative Humidity & Dry Bulb Temperature Indicator Impact Extruded Capacitor Housings Automated mass oroductic cost and quick delivery Special rectangular & oval ^Two latest, indispensable aids for' the industry— FULLY ELECTRONIC OTA j H digital MULTI METER 1 J I & • Large LCD (or easy rea 3 mECO insTRumEnTs pr ding. VATE LTD. Bharal Industrial Estate. T.J. Road. Sewree, Bombay-400 015 1 Phones 413-7423. 413-2435. 413-0747 Telex 011-71001 MECO IN J L 'TnECD for Precision, Accuracy & Reliability. 1 TEXONIC x TEXONIC 71 /a. LCD DMM DM 1 4B1 THAKOR ESTATE. KURLA KIROL ROAD, VIDYAVIHAR (W), BOMBAY 400 086. PHONES: □ 5132668 □ 5132667 • Duties & Taxes Extra BOOKS ON DATA- HARDWARE - SOFTWARE A WIDE RANGE OF COMPREHENSIVE LITERATURE • NATIONAL SEMICONDUCTORS INTERFACE BIPOIAR LSI BIPOLAR MEMORy PROGRAMMABLE LOGIC DATA BOOK 300-00 SERIES/80 8.L.C. 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A complete reference source for all Fairchild Semiconductor SSI/MSI HI products 20000 • THE APPLE II CIRCUIT DESCRIPTION This book is a detailed Circuit description of the Apple II computer. 7500 Send full advance by M.O./D.D. only Available at: precious ELECTRONICS CORPORATION Journal Division 1 1, Kiln Lane (Shamrao Vithal Marg) Bombay-400007. 5.73 classified ads. CONDITIONS OF ACCEPTANCE OF CLASSIFIED ADVERTISEMENTS 1 ) Advertisements are accepted subject to the conditions appearing on our current rate card and on the express understanding that the Advertiser warrants that the advertisement does not contravene any trade act inforce in the country. 2) The Publishers reserve the right to refuse or withdraw any advertisement. 3) Although every care is taken, ihe Publishers shall not be liable for clerical or printer's errors or their consequences. 4) The Advertiser's full name and address must accompany each advertisement submitted. The prepaid rate for classified advertisement is Rs. 2.00 per word (minimum 24 words). Semi Display panels of 3 cms by 1 column Rs. 150.00 per panel. All cheques, money orders, etc. to be made payable to Elektor Electronics Pvt. Ltd. Advertisements, together with remittance, should be sent to The Classified Advertisement Manager. For outstation cheques please add Rs. 2J&Q lease 1000 S. ft. with power. < phone. Indeal for light Electronic I try. Reply Box No 0586. Elektor 52, C Proctor Road, Grant Ro Bombay-400 007 EPROM programmer, power supply, 2K CMOS/RAM with dry cell back up expandable to 8 K. 1 2 K user EPROM installed Rs. 2975/-. All inclusive EPROM Eraser Rs. 500/-. Contact: NEW AGE ELECTRONICS, Third Floor. Laxmi Mahal. Near Vandana Cinema. Agra Road. Thane - 400 607 Unassembled Assembled kits. 1 1 MW Transmitter 1 50 meter range for Rs 90/-. 2) 12 Melodies horn for vehicles Rs 80/- Kits price list Re 1/-. (50% Advance for VPP) PERFECT ELECTRONICS 453. Ganpati All, Wai 41 2 803 (Satara) 18, Ranganathan Street. Nehru nac Chromepet, Madras 600 044 (All In Jniversal Electronics Club FREE wiemt CORRECTIONS MSX Extensions — 3 (April 1986) The caption to Fig. 5 should have read: "For slot signal functions see Infocard Active subwoofer in this issue Owing to a printers' error. Advertisers Index ACTRON ADVANI OERLIKON AFCO I & C LTD APEX APLAB COMPONENT TECHNIQUE CTR DEVICE DYNALOG MICRO SYSTEMS DYNATRON ECONOMY ENGINEERING ELECTRON SYSTEM . . IEAP INSTRUMENT CONTROL INSTRUMENT RESEARCH ION ELECTRICALS JUNIOR COMPUTER . . . KAYCEE ELECTRONICS . KEJRIWAL KLAS ENGINEERING . . . LEADER ELECTRONICS MECO INSTRUMENTS . . MODI ELECTRONICS MOTWANE MURGAPPA ELECTRONICS OSWAL ELECTRONICS . . . PIONEER ELECTRONICS PLA PRECIOUS KITS RAJASTHAN ELECTRONICS SAINI ELECTRONICS SEMICONDUCTOR COMPLEX .... S.S. INDUSTRIES SUCHA ASSOCIATE TESTICA TEXONIC UNLIMITED VALIANTELECTRO VASAVI ! VISHA ; YABASU | ZODIAC 5.09 5.66 5.06 5.10 5.07 5.65 5.76 5.61 5.12 5.70 5.10 5.62 5.14 5.62 5.06 5.63 5.13 5.02 5.08 5.73 5.71 5.02 5.70 5.64 5.64 5 73 5.64 5.75 5.04 5.66 RF Circuit Design — 2 (April 1986) The value of f in Fig. 4b should read 65.0 MHr, not 5.74 Tel: 362421 , 353029 Telex: 01 1-75614 SEVK IN Gram: ELMADEVICE Branches and representatives at: Pune. Bangalore. New Delhi, Hyderabad and Chandigarh r-yy-r-, Jynalog Micro-Systems I II ) k 4 14, Hanuman Terrace. Tara Temple Lane, L A-Tut-h — ) Lamington Road, Bombay 400 007 ELECTRONICS HOBBYISTS How long will you continue to play with simple projects and obsolete technologies? Electronics Hobbyists all over the world are experimenting with Microprocessors and their most exciting applications. Now Dynalog makes it possible even for you to get into the exciting world of Microprocessors. Dynalog has specially designed two LOW COST Microprocessor Trainers based on the popular chips 8085A and Z80A. Advanced Hobbyists. Students and Beginners can use them initially for learning and then for experimenting with Microprocessor Applications. Write today for more details: