up-to-date electronics for lab and leisure m.p.g indicator ignition timing strobe car service meter windscreen wip eigte rev counter 9-02 — Elektor September 1976 elektor decoder What is a TUN? What is 10 n? What is the EPS service? What is the TQ service? What is a missing link? Semiconductor types Very often, a large number of equivalent semiconductors exist with different type numbers. For this reason, 'abbreviated' type numbers are used in Elektor wherever possible: - '741' stands for pA741, LM741, MC741, MIC741, RM741. SN72741, etc. - 'TUP'or 'TUN' (Transistor, Universal, PNP or NPN respectively) stands for any low frequency silicon transistor that meets the specifications listed in Table 1 . Some examples are listed below. - 'DUS' or 'DUG' (Diode, Universal, Silicon or Germanium respectively) stands for any diode that meets the specifications listed in Table 2. - 'BC107B', 'BC237B', ‘BC547B’ all refer to the same 'family' of almost identical better-quality silicon transistors. In general, any other member of the same family can be used instead. (See below.) For further information, see 'TUP, TUN, DUG, DUS', Elektor 17. p. 948. Table 1. Minimum specifications for TUP (PNP) and TUN (NPN). 20V 100 mA 100 100 mW fT.m'in 100 MHz Some 'TUN's are: BC107, BC108 and BC109 families; 2N3856A, 2N3859, 2N3860, 2N3904, 2N3947, 2N4124. Some TUP's are: BC177 and BC178 families; BC179 family with the possible exception of BC1 59 and BC179; 2N2412, 2N3251, 2N3906, 2N4126, 2N4291 . Table 2. Minimum specifications for DUS (silicon) and DUG (germanium). DUS DUG v R,max 'F.max lR,max P,o, max C D .mex 25V 100mA IpA 250mW 5pF 20V 35mA lOOpA 250mW lOpF Some 'DUS's are: BA127, BA217, BA218, BA221, BA222, BA317, BA318, BAX13, BAY61 , 1N914, 1N4148. Some 'DUG's are: OA85, OA91, OA95, AA116. BC107 (-8, -9) families: BC107 (-8,-9), BC147 (-8,-9), BC207 (-8, -9), BC237 (-8. -9), BC317 (-8, -9), BC347 (-8, -9). BC547 (-8,-9), BC171 (-2,-3), BC182 (-3. -4). BC382 (-3, -4). BC437 (-8,-9), BC414 BC177 (-8. -9) families: BC177 (-8. -9), BC157 (-8, -9). BC204 (-5, -6), BC307 (-8, -9). BC320 (-1 . -2), BC350 (-1, -2), BC557 (-8, -9). BC251 (-2. -3), BC212 (-3. -4), BC512 (-3, -4). BC261 (-2, -3I.BC416. Resistor and capacitor values When giving component values, decimal points and large numbers of zeros are avoided wherever possible. The decimal point is usually replaced by one of the following international abbreviations: P (pico-) * 10' IJ n (nano-) = 10"* M (micro-) = 10' 6 m (milli-) - 10** k (kilo-) = 10 s M (mega-) = 10‘ G (giga-) = 10* A few examples: Resistance value 2k7: this is 2.7 kn, or 2700 n. Resistance value 470: this is 470 n. Capacitance value 4p7: this is 4.7 pF. or 0.000 000 000 004 7 F . . . Capacitance value 10 n: this is the international way of writing 10,000 pF or .01 pF, since 1 n is 10~’ farads or 1000 pF. Mains voltages No mains (power line) voltages are listed in Elektor circuits. It is assumed that our readers know what voltage is standard in their part of the world! Readers in countries that use 60 Hz should note that Elektor circuits are designed for 50 Hz operation. This will not normally be a problem; however, in cases where the mains frequency is used for synchronisation some modification may be required. Technical services to readers — EPS service. Many Elektor articles include a lay-out for a printed circuit board. Some — but not all - of these boards are available ready-etched and predrilled. The 'EPS print service list' in the current issue always gives a complete list of available — Technical queries. Members of the technical staff are available to answer technical queries (relating to articles published in Elektor) by telephone on Mondays from 14.00 to 16.30. Letters with technical queries should be addressed to: Dept. TQ. Please enclose a stamped, self addressed envelope; readers outside U.K. please enclose an IRC instead of stamps. — Missing link. Any important modifications to, additions to, improvements on or corrections in Elektor circuits are generally listed under the heading ’Missing Link' at the earliest opportunity. ELEHTOr 17 Volume 2 Number 9 Editor Deputy editor Technical editors : Art editor Drawing office Subscriptions W. van der Horst P. Holmes J. Barendrecht G.H.K. Dam E. Krempelsauer G.H. Nachbar Fr. Scheel *K.S.M. Walraven C. Sinke L. Martin Mrs. A. van Meyel UK editorial offices, administration and advertising 6 Stour Street. Canterbury CT 1 2XZ. Tel. Canterbury (0227) - 54430. Telex: 965504. Assistant Manager and Advertising : Elektor is published monthly on the third Friday of each month, price 40 pence. Please note that number 15/16 (July/August) is a double issue, 'Summer Circuits', price 80 pence. Single copies (including back issues) are available by post from our Canterbury office to UK addresses and to all countries by surface mail at £ 0.55. Single copies by air mail to all countries are £ 0.90. Subscriptions for 1976 (January to December inclus.-.# to UK addresses and to all countries by surface mail £ 6.25. to all countries by air mail £11,-. Subscriptions for 1976 (October to December inchjs~» to UK addresses and to all countries by surface mar) £ 1 60. All prices include p & p. Subscribers are requested to notify a change of address four weeks in advance and to return envelope bearrg previous address. Letters should be addressed to the department eoncer-ee TQ = Technical Queries; ADV = Advertisements. SUB “ Subscriptions; ADM =■ Administration; ED “ Editorial (articles submitted for publication etc. EPS « Elektor printed circuit board service. For technical queries, please enclose a stamped, addrenao The circuits published are for domestic use only. The submission of designs or articles to Elektor implies permission to the publishers to alter and translate the aw and design, and to use the contents in other Elektor publications and activities. The publishers cannot guarantee to return any material submitted to them. All drawings, photographs, printed circuit boards aid articles published in Elektor are copyright and me> nor be reproduced or imitated in whole or part without or o- written permission of the publishers. Patent protection may exist in respect of circuits, deans, components etc. described in this magazine. The publishers do not accept responsibility for faring id identify such patent or other protection. Distribution: Spotlight Magazine Distributors Ltd.. Spotlight House 1. Bentwell road, Holloway, London N7 7AX. Copyright © 1976 Elektor publishers Ltd — C Printed in the Netherlands. selektor quadrille The ideas behind the (quadrophonic) systems. I Music of the spheres 910 Several tools have been proposed for evaluating and comparing quadrophonic matrix systems. For those of us who are not gifted mathematicians, but who like to 'see' wh8t is happening, the 'energy sphere' approach suggested by P. Scheiber can be quite useful. Tachometer • 916 This Tachometer adapter was primarily designed to be used in conjunction with the UAA 170 LED meter (Elektor 12, April 1976, p. 441) and will give a clear 'analogue' indication of the number of revolutions made by the car engine. Rev counter and dwell meter — C. Wiinsche 921 A rev counter and dwell meter is a useful service aid when setting up the ignition timing of a car. The instru- ment described here will indicate dwell angle as a percentage of the complete timing cycle and will measure , 7 engine r.p.m. in two ranges that are selected automatically depending on engine speed. Windscreen wiper delay circuits and how to install them — AJ. Cartwright 924 H Servotape — R. Hardcastle , Miles-per-gallon indicator . A fuel consumption meter indicating From stereo to SQ — B. Bauer In Elektor 8 (December 1975) we published a background article on CD 4 and a construction project for a CD-4 demodulator, both sent to us by JVC. At the time, we stated in an editorial note that we wished to give the proponents of the other three systems an equal opportunity. CBS has responded by sending us two articles on SQ. As with the previous articles, we have decided to publish them in full. SQL-200 SQ decoder - D.W. Gravereaux The SQL-200 is a 'free-standing' SQ decoder with its own power supply, intended for converting stereo re- ceiver/preamplifiers to SQ quadrophony. The unit is of full logic with variable-blend type. Ignition timing stroboscope There are several ways of adjusting the ignition of a car engine. One of the quickest and best is to use a strobo- scope. Transistors, TUP/TUN/DUG/DUS, ICs . Advertisers index 957 Elektor September 1976 - 9-07 AN ENTRY BELOW TYPE THAT ENTRY ABBREVIATION ■> CONSUMER Semiconductors: T1 = TUP T2 . . . T4 = TUN IC1 = 7413 IC2,IC3 = 74121 IC4 = 7400 IC5 = LM 309KC (5 V, 1 A) D1,D2= DUS D3 = 1 N4001 D4 = LED Miscellaneous: SI = 3-pole 3-way switch Ml = meter, 1 mA f.s.d. them both across the car battery and selecting R9/R10 so that the voltmeter reading corresponds with the multi- meter reading. If a multimeter is not available then simply use a 15 k 2% resistor in place of R8 when the full- scale deflection of the voltmeter will be about 15 V. H 9-24- Elektor September 1976 wind screen wiper delay circuits and how to install them (e)@[)0^ eOffetyfe scto tow to 0(n)stoOO to@® When driving in a very light rain one finds that the wipers have to be continually switched on and off to remove the small quantity of water on the windscreen. This is usually accomplished in one or two sweeps and then the wiper blades proceed to grate and screech, obviously not good for the wiper blades or the windscreen itself. The obvious answer is to find some way to automatically switch on the wipers every once in a while. This article describes two good 'delay' circuits and the way to connect them into a car. (This article is based in part on an article sub- mitted by Mr. A.J. Cartwright). Many articles have been published de- scribing the ‘end-all’ windscreen wiper delay circuit. Often these circuits are capable of doing a good job. In fact, everything usually goes well until the constructor gets to his car. There, a large and bewildering bundle of wires connects what was thought to be a simple on-off switch, to what was thought to be a simple motor. A quick glance at figure 1 shows where some confusion comes from. There are many different wiper systems, using a wide variety of switching configurations. However, an investigation of figure 1 will show that all electrical wiper systems have common operating ideas. It can be seen that all systems have a switch (designated ‘H’ in figure 1) that is coupled to the motor. This is a cam operated micro-switch which is used to ‘self-park’ the wipers after they have been switched off at the dashboard. To this end, power is maintained via H until the wipers are in the correct position to stop. Further analysis of figure 1, confining the discussion to the first column for the moment, will show that there are two basic wiper circuits. Figures A1 and B1 show the simplest type, used mostly in older cars: a simple on-off switch connected in parallel with the self-park micro-switch. The other basic circuit (figures Cl, Dl, El, FI, G1 and HI) is more complex, and is used in newer cars. When the motor reaches the desired ‘ofP position, the power is switched off and a short circuit is connected across the motor. In this way, the back EMF of the motor is used as a brake. Without this type of braking, the wipers would overshoot the self-park position and begin another wipe cycle. Figure 1C1 shows the simplest form of the shorting system. First, let us assume that the wipers are turned on. (Contacts Sa are closed and Sb are open). When the dashboard control is switched off, contacts Sa open and Sb close. Power to the motor is maintained via micro- switch H until the wipers reach the self-park position. At that moment the micro-switch removes the power from the motor and connects the short instead via Sb. The other circuits (figure 1D1 to 1 HI ) are all variants on the same principle. The other circuits shown in figure 1 are all easily derived from the basic circuits already described. The top two rows are all variants on the simple basic circuits (figures A1 and Bl); the rest are all variants on the more complex shorting system. In each case, the first column shows the one speed system with the switching taking place in the positive lead. The second column is the same one speed system, but with the switching in the negative lead. Column three is the two speed wiper with positive switching while column four is two speeds with negative switching. Column five shows one possible place to connect the delay circuits. If an electrical diagram of the car is not available the first thing to be done is to make a trip to the car, taking along a multimeter. Making voltage measure- ments to the wiper switch and com- paring the findings with figure 1, it should be possible to determine which type of system is used. Once it is known what wiper system is in the car, a suitable delay system can be chosen. For the simple wiper system all that is needed is an on-off device. For the more complex system this will not be sufficient: if the power is applied before the short is removed, sparks will fly. Therefore, the short must be either removed or altered in some way before applying power. The fifth column in figure 1 shows the basic principle of where to add additional (automatic) switches, driven from the delay circuit. Figure 1: Survey of possible wiper switching arrangements. The first column gives the basic circuits; columns 2, 3 and 4 show variants on the basic circuits and column 5 shows where to connect the additional ‘switches' that form part of the delay circuit. 9-26 — Elektor September 1976 i wiper delay circuits A simple practical circuit If the original wiper circuit corresponds to one of the circuits shown in figure 1 A or IB, the simplest delay cir- cuit shown in figure 2 can be used. This is a straightforward circuit that gives very satisfactory results. It is possible to use this circuit on either 6 or 12 V cars with no modifications. After power has been applied, the R-C time constant of R2 . . . R5 and Cl determines the delay before turning on a UJT. This in turn fires the SCR, which allows current to flow to the motor. When the motor starts to turn, the self- park micro-switch shorts across the SCR. This resets the circuit. Connection to the original wiper circuit in the car is very simple: connect point X (figure 2) to point X (figure 1), and point Y to point Y. This simple circuit may also be used I with most of the complex wiper systems, I provided a high wattage car headlamp is I added in series with the shorting lead. I The lamp lends itself to this job because I of its positive temperature coefficient I (PTC). When the lamp is cool (passing no current) its resistance is very low, a j good short. However, when warmed the I resistance goes up. This means that I when the SCR is first turned on it must deliver a heavy current into the lamp and the motor, connected in parallel. The SCR should have an adequate maximum current rating. However, the lamp will heat up rapidly so that its resistance rises and the power dissipated in the SCR will drop rapidly. Once the Elektor September 1976 — 9-27 motor starts to turn the short is re- moved by the self-park micro-switch. The lamp goes out and its resistance goes down to the low ‘cold’ resistance. When the short is needed at the end of the wipe, it’s there and the wipers will stop. A not-so-simple circuit For those who wish to build an all- solid-state system, not using the head- lamp trick, figure 3 would do the job. In figure 3, a thyristor is used for the on-off function and a transistor (T4) is used for the short. The extensive logic circuitry is mainly required to ensure that the SCR and T4 can never be turned on simultaneously. However, it is apparent from the number of com- ponents that this circuit will be expens- Figure 2a: SCR wiper delay. Figure 2b: Lamp with connecting points Figure 3. All solid state delay system. Figure 4 The best wiper delay circuit using a 555 for the timing and relay driver. Figure 5 Component layout and p.c. board for figure 2. (eps9474 — 1) Figure 6: Component layout and p.c. board for figure 3. 9-28 — Elektor September 1976 ive to construct. An alternative circuit, with a reduced component count, is called for. A more practical circuit An alternative solution to the lamp and the transistors is a relay. A multi- contact relay lends itself to any switching situation which might occur. Figure 4 shows a simple circuit using a 555 timer. The maximum output current of this IC is 200 mA, so it can drive the relay direct. This circuit will operate on 6 or 12 volt cars. The only circuit change is the relay (12 V relay for a 12 V car, 6 V car 6 V relay). Most circuits using the 555 don’t give a wipe immediately after being switched on. To cure this, R1 is included. This resistor keeps the timing capacitor (C2) charged, so that the relay is activated as soon as the delay circuit is turned on. A further improvement of this circuit over the simple SCR unit (figure 2) is the possibility of having the wipers sweep twice between delays. This multi-wipe function is adjusted with PI. Connection to the original wiper circuit As stated earlier, column 5 in figure 1 shows where to include the additional switches required for a delay circuit. So as not to become too redundant only connections to the first example of each type are shown, i.e.: connection to figure 1A1 is shown in figure 1A5; figure 1E1 in figure lES.etc. For wiper systems like figure 1A and figure IB, the SCR circuit (figure 2) is adequate. It should be connected across the self-park micro-switch. The delay using the 555 can be used with all wiper systems. The normally open contacts X and Y of the relay are connected across one set of dashboard contacts, and the normally closed relay contacts W and V are connected in series with the shorting lead. For safety reasons, it is advisable to connect the relay into the original wiring in the car in such a way that the dashboard switch will maintain its original function. Then in case of electronics failure the wipers will still work. The circuits shown in figure 1 (fifth column) all meet this requirement. M Figure 7: Component layout and p.c. board for figure 4. (eps 9474 - 2) From time to time, the avid home con- structor is confronted with the problem of how to mount printed circuit boards into a case. By using a product known as Servo-tape, the mounting of small p.c. boards can be made much simpler and neater. Servo-tape (also sold as ‘Tesa-tape’) is a foam plastic tape with a self-adhesive layer on both sides, and comes in two thicknesses: 1/8 and 3/16 inches. It is sold at model shops and is usea ior mounting servo modules and the like into model aircraft and boats. If the thicker tape is used, it should provide sufficient clearance for the solder joints on the underside of a p.c. board. The tape is trimmed into squares about lcm across. One of these pads is stuck onto each corner of the p.c. board, after which the board is ready for mounting into the box. No bolts, no holes. The appearance of the case is not marred by bolt heads in odd places. As stated previously, the thicker type of tape should provide enough clearance for most solder joints. However, to pro- vide more space when needed, servo- tape can be stuck to both the top and bottom of a small block of wood as illustrated in the drawing. T Elektor September 1976 — 9-29 miles-per -gallon indicator (MiOILdS 0 P@K<=> d^MLCLOOD 0GM)(Mr®(B A fuel consumption meter indi- cating 'miles per gallon' is a useful instrument for economy- minded motorists. By making one minor modification to an existing petrol flow meter made by ABM, the long wished for MPG indicator can become a reality. There are several special items needed for the construction of a fuel consump- tion meter. The most important is a sensor that is capable of measuring the fuel flow rate. This type of sensor is not readily available at a ‘reasonable price’, and it is even harder to make. However, a simple fuel consumption meter has recently been introduced, comprising a flow sensor, a readout device and some electronics in between. This meter, made by ABM-Electronic, is marketed in several countries by ITT Hobbykit Centre for about £ 20. It indicates the fuel consumption in litres per hour. Although such an indication is better than nothing, some further calculation is required to work out the mileage per gallon from the information avail- able. And since miles per gallon (MPG) is in fact what we want to know, it is not at all unlikely that the motorist will be concentrating on mental arith- metic more than on driving. Obviously, road safety could be better served if the meter could be extended by an auxiliary circuit that will do the arithmetic and give a direct reading in ‘miles per gallon’. In practice, this modification requires a speed sensor and some additional circuitry. The speed sensor is an ordi- nary telephone pick-up coil, of the type used for ‘loudspeaking’ telephones or for taping telephone conversations. The original fuel consumption meter Figure 1 shows the ABM fuel consump- tion meter. Sensor X is the specially designed fuel flow sensor, which must be incorporated in the fuel line between the fuel pump and the carburettor. It produces a pulse signal with a frequency corresponding to the flow rate of the petrol. This signal is amplified to a suitable level by the TAA861. Pulse shaping is performed by a simple one-shot (T A /Tb), after which the pulses are fed to an integrator built around Tc* The emitter of Tc drives the meter (M) which is calibrated in litres per hour. Figure 1. The original litres-per-hour' meter. 'X' is the fuel flow sensor. 9-30 — Elektor September 1976 miles-per-gallon indicator The instrument can be calibrated with the two 1 k preset potentiometers; how- ever, this setting is best left alone for the moment because the instrument has already been properly adjusted in the factory. The point marked ‘A’ in the diagram is important in view of the extension circuit now to be described. Extension of existing meter If the ‘litres per hour’ meter, shown in figure 1, is to be extended to a ‘miles per gallon’ indicator, some sort of miles-per-hour information will be needed. This information will have to be mixed in a suitable way with the orig- inal ‘fuel flow’ signal at point ‘A’ of the ‘litres per hour’ meter. The new pulse signal, containing both the ‘litres per hour’ and the ‘miles per hour’ infor- mation, can then be integrated (Tc) and used to drive the meter. This can now be calibrated to read ‘miles-per-gallon’. The block diagram of figure 2 shows how all this can be achieved with only one change to the original circuit: it is split up into two parts (at point A in figure 1 ) in such a manner that the inte- grator (block C) is separated from the rest. Blocks B, D, and E are added. The output signal from the flow sensor (X) is first amplified and shaped in block A - exactly as in the original litres-per-hour meter. The output signal from block A is brought out and fed to block B. This is part of the extension circuit. It generates a saw-tooth signal, the amplitude of which decreases as the repetition frequency of the pulses increases. In short, after detection, block B produces a DC output voltage which is inversely proportional to the fuel consumption. Sensor Y and blocks D and E are also part of the extension circuit. Since prac- tically all speedometers operate on the eddy current (magnetic friction) prin- ciple, a pulse signal can be obtained by means of a simple pick-up coil (Y) in the vicinity of the speedometer. The pulse frequency then corresponds to road speed. Parts list for figure 3 Resistors: R1 = 1 k R2.R3= 12 k R4= ioon R5=3M3 R6.R13 = 47 k R7,R8,R15,R17 = 10 k R9 = 5k6 R10,R12,R20= 1k5 R11 = 33D R 1 4 = 470 k R16 = 33017 (see text) R18 = 2M2 R19 = 220 SI R21 = 3k3 Capacitors: Cl = 220 m/16 V C2 = 2m2/4 V C3 = 220 m/4 V C4.C5.C8 = 22 m/16 V C6 = 3m3/16 V C7 = 470 n C9 = 2m2/16V C10= 1000 m/2.5 V Semiconductors: T1 . . . T5.T7.T8 = BC107B, 2N3904 T6 ■ BC177B, 2N3906 D1 . . . D6 - DUS IC1 - 741 Miscellaneous Y “ telephone pick-up coil PI .P2- 10 k (preset) SI * two-position switch, single pole (SPDT) The upper part of the circuit is the fuel consumption meter by ABM-Elektronik GmbH, 8500 Niirnberg 15, Postfach 150568, West Germany. It includes the flow sensor X, the meter M and the electronics shown in figure 1 . We have been advised that H B- elec- tronics now intend to stock these units. See their advertisement elsewhere in this issue for address and telephone number. The output signal of this pick-up is amplified (block D) and clipped, after which a pulse shaper (E) produces pulses of a constant width. The (DC) output of block B is chopped by the pulse signal from block E. The ‘height’ (voltage level) of the resulting pulses now contains information con- cerning the fuel consumption in litres per hour, whilst the frequency (and duty cycle) contains information con- cerning the speed in miles per hour. After integration (block C) the meter will indicate MPG. The circuit When designing the extension circuit, the main objective was that it should involve the minimum amount of modifi- cation to the original instrument. Figure 3 shows the complete diagram of the modified fuel consumption meter. The uppper part of the diagram is the original meter as shown in fig- ure 1. Switch SI is connected between the output of pulse shaper Ta/Tb ( point A) and the input of integrator Tc (point A'). With SI in the position shown the circuit functions as the MPG indicator; with SI in the other position only the original litres-per-hour meter is in operation. Block B of the diagram of figure 2 is formed by the circuit around T4 . . . T7. Electrolytic capacitor C8 is continu- ously charged by current source T6. Each pulse from the flow sensor (point A) turns on transistor T4 briefly, discharging C8. The result is a sawtooth waveform with a peak voltage level that is inversely proportional to the petrol flow: a high fuel consumption rate corresponds to a large number of pulses per second, so that capacitor C8 will be discharged at very short intervals, and hence the amplitude of the sawtooth will remain small; at low fuel consumption rates, on the other hand, the voltage across C8 will rise to a considerable value during the longer intervals between two suc- cessive pulses. illon indicator Elektor September 1976 - 9-31 This sawtooth voltage is then rectified (D6, C9), producing a DC output from emitter follower T7. The DC-voltage at this point is related directly to the fuel flow rate. In the above discussion of this part of the circuit, T5 has been intention- ally ‘forgotten’ for the time being, li is an offset control which will be dealt with further on. As explained, the ‘miles-per-hour’ infor- mation is derived from the speedometer by means of a telephone pick-up coil (Y). This produces a pulse signal with a frequency which is proportional to the speed of the car. This signal is first pre-amplified in opamp 1C1 and then squared’ by trigger T1/T2. transistor U serves as the one-shot pulse shaper (block E in figure 2); the output pulse length is set with PI. The switch function between the outputs of blocks B and E in figure 2 is also carried out by transistor T3. Since this transis- Figure 2. Block diagram of the miles-per- gallon meter. Figure 3. The complete circuit diagram of the modified fuel consumption meter. The upper part of the circuit is the original meter. 'Y' is the speed sensor coil. Figure 4. The input signal of the integrator. "V' is inversely proportional to the gallons of fuel consumed per hour, whereas T' is inversely proportional to the speed (miles- per-hour). tor opens and closes in -the rhythm of the miles-per-hour pulses, the fuel-flow dependent voltage at the output of T7 is sampled, as it were, by switch T3. The resulting signal is shown in figure 4. The frequency of this pulse signal corresponds to the number of miles per hour, and so period T is inversely proportional to it. V is inversely pro- portional to the fuel consumption in litres per hour. The pulse width r is a constant which depends on the setting of PI in the pulse shaper stage T3. Summarizing, it will be obvious that after integration (Tc), the meter M receives a voltage that will be higher as the number of pulses from the pick-up X per unit time (fuel flow) is lower, and also as the number of pulses from Y (speed) is higher. In other words: both a decreasing flow rate of the fuel and an increasing speed of the car will cause the output voltage of integrator Tc to rise, so that the meter 9-32 - Elektor September 1976 miles-per -gallon indicator will indicate a higher value, and thus a more economic fuel consumption. Offset control When detecting the sawtooth voltage which is derived from the litres-per-hour pulses, a small voltage drop occurs across D6 and emitter follower T7. At fairly high levels (= low fuel con- sumption) the resulting error is small. In the case of high fuel consumption, however, this voltage drop will give rise to a considerable measuring error. To compensate for this, an offset- control is included (TS). The offset voltage (set with P2) is added, as it were, to the sawtooth voltage across C8. Adjustment There are two ways to calibrate this unit. If we assume that the original litres- per-hour meter is properly calibrated, a new scale reading gallons-per-hour can be glued over the original one. The con- version factor for this new scale is 4.546 litres per gallon for the UK and anywhere else using gallons, except the USA with 3.785 liters per gallon. This means that in the UK the original full scale deflection will now correspond to 4.40 gallons, which is possibly not the most useful scale. The other method is a bit more com- plex, but should prove to be more suitable. With the aid of an audio signal generator connected to the flow sensor terminals, the basic ABM unit can be calibrated to read 5 gallons per hour (f.s.d.). The AF generator should be set for an output frequency of 50 Hz (41.6 Hz for USA) after which the 1 k pot in series with the meter in the basic ABM unit is adjusted until the meter gives a full scale reading. Once the basic unit has been re-calibrated and/or re-scaled, the Elektor unit can be con- nected to it. Then the completed MPG indicator can be installed in the car. This is discussed in greater detail further on. Calibration now proceeds as follows. - drive at such a speed that it can be safely assumed that fuel consumption is low, say 30 mph. The fuel flow should preferably be one gallon per hour or less. (NB. See ‘final notes’!); - switch the unit to the gallons-per- hour position and read off the fuel consumption. Divide this reading in to your speed, to obtain the correct MPG indication; - switch to the miles-per-gallon pos- ition and adjust PI so the meter reads properly; - drive faster, to cause an increase in fuel flow (preferably three gallons per hour or more). Check the GPH, compute the new MPG and adjust P2 to obtain a correct reading. This procedure is repeated several times, until no further improvement can be obtained. Figure 7. Photograph of the p.c.b. of the ABM meter. The points A and A' are obtained by interrupting the copper track at the place indicated by the arrow. Range Obviously, the range of the fuel con- sumption meter has certain limits. When measuring the flow rate of the fuel, for example, the phenomenon occurs that at a very low pulse fre- quency from sensor X the voltage across C8 is limited by the supply voltage. Lower flow rates cannot be measured. Similarly, at a certain speed the duty cycle of pulse shaper T3 will reach its maximum (50%). Any further increase of speed will have no effect. For the component values shown in figure 3 the lowest fuel consumption that can be measured is about ‘A gallon per hour; the maximum speed at which the unit will work is about 95 mph. Reducing the value of R16 will shorten the charge time of capacitor C8. Correct calibration now corresponds to a different setting of PI, which in turn corresponds to an increased maximum measurable speed. At the same time the minimum number of litres per hour that can be measured shifts higher up the scale. For really fast drivers a suitable value for R16 might be about 220 f2. The maximum speed at which measure- ment is still reliable then lies around 140 mph (but who is still interested in fuel consumption at that speed?). Usually the value of 330 £2 as given in the diagram will give the best results for the ABM meter; if different flow sensors are available giving other frequencies per gallon, the value of R16 will have to be modified accordingly.* Construction The entire extension circuit - i.e. the circuit of figure 3 except the orig- inal (upper) part — is mounted on one p.c.b. Figure 5 shows the p.c. board, and figure 6 the component layout. Although the supply voltage terminals of the original litres-per-hour meter can, of course, be simply connected to the battery as shown in the instruc- tions, the point in question can also be connected to point ‘B’ of the extension board to improve interference sup- pression. The supply voltage for the entire circuit is best obtained from the ‘accessories’ position of the ignition lock. The instruction leaflet supplied with the litres-per-hour meter gives sufficient information on how to install the flow sensor (X). The speed sensor (Y) can be attached to the speedometer by means of its rubber suction pad or, better still, with some suitable glue. The best position will be found by experiment; this will usually be close to the drive cable. This telephone coil must be connected to the points C and D on the p.c.b. by means of a two-core screened lead. Once switch SI is wired, the last remain- ing ‘obstacle’ is the connection to points A and A’. In practice this is not too difficult, as shown in figure 7. This is a photograph of the p.c.b. of the orig- inal litres-per-hour meter. At the place indicated by the arrow, the copper track forming the connection between the •For instance, for the recently introduced 'Spacekom' digital flow sensor, giving 3200 pulses per gallon, R16 would probably have to be increased to 3k3. At the same .•me, C9 would have to be increased to about 10 *i. Note that we have not tried this! Figure 5. The p.c.b. layout for the exten- sion circuit. Figure 6. Component layout on the p.c.b. The supply of the original meter can be connected to point 'B'. collector of transistor Tg and the 39 k resistor must be interrupted. Two wires are (carefully!) soldered on, one on each side of the break, and connected to points A and A' on the extension p.c.b. Even the less experienced will probably have little difficulty building the rela- tively simple circuit on the p.c.b. Final notes Nobody will doubt that a fuel consump- tion meter is a useful instrument. It will persuade many to drive more ‘economically’, thus contributing towards the general drive to save energy. However, a word of warning is justified: Under no condition should use of the fuel consumption meter be allowed to endanger road safety. The driver’s attention should in principle always be on the traffic, and only when traffic conditions allow will a quick glance at his instrument panel be justified. An instrument like this fuel consumption meter will be an extremely interesting eye-catcher, which involves the risk that it might ‘steal the show’ by drawing attention from more important matters. Furthermore, drivers should be careful not to develop such an ‘economic’ style of driving that road safety is adversely affected. One might, for example, easily be startled by a sharp drop of the meter indication when accelerating to overtake other road users; however, seeing this brief higher fuel consumption should not lead the driver to take it easy and spend a dangerously long time in the wrong lane. To conclude, a remark that should really not be necessary : it is just asking for trouble if the same person combines driving the car and adjusting the fuel consumption meter. This calls for the undivided attention of two people! H 9-34 - Elektor September 1976 stereo to SQ too B® B. Bauer Recent developments in quadraphonic sound were very much in evidence both at the 53rd Meeting of the Audio Engineering Society, in Zurich, where CBS showed its latest SQ decoders and records, and at the Festival du Son, in Paris, where no less than 16 manufacturers of high-fidelity equipment displayed receivers and players embodying the SQ* system — by far the most popular quadraphonic system on the market today. Ideas were shared at the meetings with outstanding recording engineers and high- fidelity enthusiasts. One fact stood out with complete certainty: those who had experienced quadraphony in their own homes were the quadrophiles who expressed total satisfaction and commitment and declared that they would never go back to stereo. Those who had not experienced quadraphony were the quadrophobes who, nevertheless, were interested and willing to discuss their concerns with the quadrophiles. Some conclusions stemming from these interactions are reported here for the interest of those planning to experiment with quadraphony. It became evident during the course of the discussions that much of the existing quadrophobic folklore had made quadraphony appear as a for- bidding extravagance which obsoleted one’s existing stereo investment. But the facts, of course, are otherwise. Quadraphony - especially SQ quadraphony — is a relatively simple but necessary step toward better fidelity of sound reproduction, which actually en- hances the user’s present high-fidelity equipment and records. And, further- more, it is attainable at modest cost, well within the means of most hi-fi enthusiasts, especially those willing to construct some of their own equipment. What they say First, let’s listen to the quadrophobes. Some complain about the cost of decoders and the expensive duplication of amplifiers and loudspeakers. Others are troubled by the problem of quadraphonic loudspeaker arrange- ments. (‘My wife will never put up with them.’) Others are worried about the fate of their stereo record collections. And a few are opposed to quadraphony in principle, with the argument, ‘I have only two ears - why should I listen to four sources?’ What came to mind in discussing these matters was the slow and patient process of education and demonstration that had been required during the introduction of stereo a decade and a half ago. We believe that history is bound to repeat itself with quadraphony. The two ear . . . four loudspeaker paradox Let us dispose of the ‘two-ear’ argument first by pointing out that its logical conclusion would be to listen only to duets because each performer in a symphony orchestra is a separate source of sound. Nevertheless, there is a serious aspect to this otherwise fatuous argu- ment since it gives us an opportunity to answer the question of why quadraphony - not stereo - provides true high fidelity and, in addition, why four, not three, loudspeakers are necessary for effective reproduction of . the auditory space. Consider a listener in a concert hall, j depicted in figure 1 . He first hears the direct sounds of the performers and soon they are followed by sounds I reflected from the walls, floor, and ceiling. All these reflections build up into the spatial reverberant energy which gives the concert hall its charac- teristic ambiance surrounding the listener. Let us assume that both the direct and reverberant sounds are picked up with four microphones shown in the illustration, and that the resulting signals are properly mixed so as to produce a stereo record which is repro- duced over a stereo system, shown in figure 2. It is clear that regardless of how skillfully the direct and the reverberant sounds have been mixed for stereo, they emerge from stereo’s two loudspeakers, which tends to confuse the direct sounds. But, if the orchestral sounds are reproduced over the front loudspeakers and the ambiance sounds | over the four loudspeakers, as shown in figure 3, then it is possible to closely approximate the sound field of the real concert hall. Conclusion: quadraphony produces spatial high fidelity; stereo does not. But why four loudspeakers? A facile answer is that four loudspeakers are used because rooms are square, not tri- angular; but there is a more fundamen- tal reason which is to be found in the way human hearing responds to a sound field. Listen to the center solo of a stereo record over the two loudspeakers. As you approach the line connecting the two speakers, the center image rises, and on the centre line it appears to be directly overhead! From this itj follows that for a good periphonic: capability we need four loudspeakers,! because a rectangle in addition to connecting lines on the periphery also has connecting diagonals, therefore giving the listener an opportunity to be Elektor September 1976 — 9-35 Editioral note In Elektor 8 (December 1975) we published a background article on CD-4 and a construction project for a CD-4 demodulator, both sent to us by JVC. At the time, we stated in an editorial note that we wished to give the proponents of the other three systems an equal opportunity. CBS, in the person of Mr. B.B. Bauer (Vice President and General Manager of the CBS Technology Center), has responded by sending us two articles on SQ. As with the previous articles, we have decided to publish them in full. Our own thoughts on the subject of quadrophony at the present moment are outlined in a separate article elsewhere in this issue. Figure 1. Stylized representation of a listener n a concert hall, and the production of a starao program. The performers' sounds are grown in heavy arrows and the ambiance Bunds are shown by curved wavefronts. s igure 2. Stereo's two loudspeakers cannot srovide a true representation of a concert hall secause the ambiance sounds arrive from the lame direction as the performer's sounds. figure 3. To properly reproduce the concert- *all experience four loudspeakers are needed, die front ones carrying the performer's nunds and the back ones cooperating with die front ones to reproduce the ambiance. Bifficiently near a connecting line to tear elevated sounds, when they are present, anywhere within the listening area. The marvelous feeling of rever- beration which rises to the top of the live of the Freiburg Cathedral, in the • Power Biggs recording of the Four Toccatas and Fugues of Bach, could not lave readily been achieved with but ±ree loudspeakers. Quadraphonic loudspeaker arrangements While, undeniably, space and cost permitting, identical loudspeakers are ideal for quadraphony, many quadra- philes have concluded that in practice it is not necessary for the back loud- speakers to be as large and costly as the front ones. This does not mean, of course, that back loudspeakers of low quality are consistent with good quadraphony — but only that if the front loudspeakers have ample low fre- quency response then the back ones need not go quite as far ‘down’ as the front ones in the bass region. This is understandable because the nature of disc recording encourages the producer to place the heavy bass sounds near 9-36 — Elektor September 1976 from stereo to SQ « i / \ / \ / center front, and, anyway, the direction of bass sounds is not readily perceived. Therefore, excellent but quite small loudspeakers responding, say, down to 60 Hz will be quite suitable for back channels while the front ones normally should provide full bass response. Small loudspeakers can be placed inobtrus- ively on lamp tables, bookshelves, or mantelpieces, eliminating much oppo- sition which may arise from the mistress of the house to four large loudspeakers. Considerable experimentation since the early days of quadraphony has been going on with loudspeaker arrange- ments. Many experienced listeners have concluded that it is equally effective and often much more convenient to use the trapezoidal arrangement shown in figure 4 in place of a square array. Here, the back loudspeakers have been shifted 20-30° forward, in this manner producing an arc of sound in part surrounding the listener. The trapezoidal arrangement is especially convenient for a rectangular living room and it often is more pleasing than the square format to a listener venturing into quadraphony for the first time. The back loud- speakers can be placed conveniently at either side of the main seating area, preferably at the ear level of a standing person. In this manner several seated listeners can hear the back loudspeakers unimpeded and with relatively good sonic balance. Ambiance vs surround sound Some quadraphobes say they wish to hear only frontal sounds — but we found this to be merely a stereo-induced habit. Once the historical context of surround sound is understood, oppo- sition to it fades away. In the real world of music the composer and the conduc- tor always have enjoyed the spatial freedom to surround the audience with sounds. We already have mentioned the Freiburg Cathedral (where an organist plays four spaced-apart organs simul- taneously or antiphonally from a central console) - but other examples abound. In the 14th century, Gabrieli placed his choirs on four balconies of San Marco’s in Venice. Berlioz staged his ‘Requiem’ in the liglise des Invalides in Paris in surround sound using an enormous symphony orchestra and chorus aug- mented by four brass orchestras on the balconies and four pairs of kettledrums thundering from various placings. Stravinsky placed trumpets and tubas offstage in the ‘Firebird’ ballet. During the inaugural performance of his cel- ebrated ‘Mass’, Bernstein surrounded the audience with four sources. Opera, musical comedy, and the rock group all offer great excitement in a surround- sound arrangement. For too many years, alas, stereo’s two- only loudspeakers have deprived the high-fidelity enthusiasts of hearing marvelous surround-sound performances with full spatial fidelity. Quadraphony breathes life into them. And the SQ record holds for the listener the best of the possible worlds — realistic ambiance performance for the classical music lover, exciting surround sound for the more adventuresome hi-fi enthusiast, and standard stereo performance for the listener who has not, as yet, converted to quadraphony. Because of SQ’s excellent compatibility many records today are issued as ‘stereo-compatible’ with only a small note on the back of the jacket identi- fying them as being quadraphonic. The SQ system revisted The SQ system employs a special matrix to encode a stereo record or tape with four (or more) directional signals. Those signals which should appear over the front loudspeakers (and which normally include the front stage sounds) are applied to the SQ record in precisely the same manner as they are to a con- ventional stereo record. (This is the Figure 4. Modified quadraphonic loud- speaker arrangement in which the back loud- speakers have been moved forward (as shown by curved arrows) to conform to the g* ometry of a rectangular living room. If thi front loudspeakers have ample bass response the back loudspeakers can be smaller unit] than the front pair. Figure 5. Transformation of a stereo program to simulated quad after SQ synthesis. Figure 6. Converting an existing stereo inst# lation to a quadraphonic system by adding ■ SQ decoder, a stereo power amplifier, and two back loudspeakers. Elektor September 1976 - 9-37 STEREO POWER AMPLIFIER reason why an SQ record or tape is so uniquely compatible with any stereo record system - the front channel sounds of SQ fill completely the space between the stereo loudspeakers just as any stereo record does.) The back channels are contained in both the stereo channels in quadrature, in such a manner that the left-back channel signal leads in the left channel of the record and the right-back channel signal jeads in the right channel of the record, in the stereo mode, these back-channel annals (which might represent reverber- ation in the ambiance format or discrete sounds in the surround-sound format) are reproduced at full level at either side of the center and appear to be some- shat spread in space thus simulating a feeling of depth. And if the SQ record is reproduced in mono (as often happens when broadcast, since many receivers are monophonic), the listener '.ears all these sounds at appropriate levels, precisely as in the case of a stereo record. Because of these characteristics the SQ record can be considered a fully stereo- and mono-compatible record suitable for broadcasting as well as home use. While the SQ record can be used in all existing mono or stereo equipment as my stereo record, its ‘raison d’etre’, of course, is quadraphonic reproduction. For this purpose a suitable decoder is needed, as well as the additional ampli- fiers and loudspeakers. Although a ample matrix decoder will provide pleasing ambiance decoding, the best SQ decoders are of the so-called ‘logic’ type. Elsewhere in this issue a construc- tion project for a logic-type decoder is described. SQ stereo record enhancement There are currently available sizable catalogues of SQ records on some of the world’s most respected labels. But, what about the existing stereo records? These can be played on SQ equipment ai the normal manner, appearing mainly on front loudspeakers, with some of the random sounds spilling over to the back and resulting in a delightful synthetic ambiance. Nevertheless, many radio d broadcasters and listeners have won- dered if their present stereo records can '"be endowed with a more pronounced * quadraphonic perspective. Such a seem- , mgly impossible feat of ‘quadraphonic tl synthesis’ turns out to be quite simple when an SQ encoder is at hand. To synthesize qaudro from stereo, the m record is played in the normal manner, but its output signals are connected equally to the respective front and * hack channels of the SQ encoder. When ^this is done, the results are as follows: the monophonic listener hears no change whatsoever in the sound and the stereo listener perceives a slight change e channel separation; but the quadra- phonic listener receives a pleasing surprise - the stereo orchestra is no fcmger located mainly in the front chan- nels but is aurally ‘bent’ in an arc (figure 5) around the listening room. In effect, the listener is placed on the conductor’s podium - a brand new concept in Spatial High Fidelity! And, this quadraphonic transformation does not, in any way, upset the sub- carrier/baseband level balance or the area coverage of the FM station, another unique advantage of the SQ system. The above SQ synthesis or ‘stereo enhance’ circuit obviously can be pro- vided either in the transmitter or the receiver. For the listener’s convenience, it has been included (and made sel- ectable at the turn of a knob) in the SQ decoder described in the companion construction project article. The listener will enjoy the new dimension which it provides to his existing records or stereo broadcasts. Many FM stereo stations in the U.S.A. currently use one or more of the SQ broadcasting techniques: (1) direct playing of SQ records or encoded tapes, (2) quadraphonic synthesis of stereo records or tapes using an SQ encoder, and (3) live broadcasting of local musical events using an SQ encoder. As a result of these resources, some stations have been able to announce tljat they are broadcasting fully compatible quadraphonic programs 24 hours a day. How to convert to SQ quadraphony in the home The task of constructing an SQ decoder is made relatively simple through the use of IC’s manufactured especially for this purpose by Motorola Inc. The Motorola SQ IC’s are the MC1312 (matrix), MCI 3 14 (control circuit), and MC1315 (logic circuit). A decoder using these IC’s can be assembled by any skilled hi-fi enthusiast with reason- able ease. The circuitry shown in the 9-38 - Elektor September 1976 SQL-200 SO decoder companion construction project is for an advanced full-logic decoder using what is known as a ‘variable blend’ cir- Once a decoder has been assembled according to the instructions, the existing stereo system is readily con- verted to quadraphony. Connect the decoder input terminals to the tape- recorder ‘output’ terminals of the receiver/preamplifier as shown in figure 6. Next, connect the ‘front’ output terminals of the decoder to the corresponding receiver ‘tape input’ terminals and switch the receiver mode switch to ‘phono’ and ‘tape monitor’. This connects the two decoded front channels to the original stereo ampli- fiers and loudspeakers. The ‘back’ output channels are connected through an added stereo amplifier to the two loudspeakers at the back of the room. The turntable, pickup, and stylus remain unchanged from those used currently with stereo records. After the equipment has been assembled in the specified manner, the four channels are balanced for pleasing listening. An SQT-1100 test record or any suitable SQ record such as ‘Chase’ (‘Epic’ EQ-30472), which begins with trumpets playing in succession around the room, will be found helpful for the achievement of acoustical balance between the front and the back loud- speakers. Once a pleasing balance has been achieved the volume level is controlled with the decoder’s volume control knob which adjusts the four channels simul- taneously. With the equipment arranged as in figure 6, the SQ broadcasts originating from any FM stereo station are repro- duced quadraphonically, and any stereo programs are heard conventionally, with or without enhancement as may be desired. Therefore, many SQ listeners leave the equipment connected as in figure 6 for the reproduction of all their records and broadcast programs - stereo and quadraphonic. Conclusion The existing notion that quadraphony is a forbidding extravagance has been shown to be nothing but quadraphobic folklore. Quadraphony is a giant ad- vance in the hi-fi arts because it brings with it Spatial Fidelity, or fidelity in space as well as in time. With an ad- vanced SQ decoder built according to the companion construction project plus two amplifiers and two good but modest loudspeakers, any component stereo system can readily be converted to a high-performance quadraphonic system and its owner will discover a new level of enjoyment not only with new SQ records he might purchase but also with his present stereo records. This is why so many former quadraphobes have joined the ranks of the quadrophiles! M D. W. Gravereaux ©M§GD® @ (EJeeQ^so’ The SQL-200 is a 'free-standing' SQ decoder with its own power supply, intended for converting stereo receiver/preamplifiers to SQ quadrophony with the addition of another power amplifier and back loudspeakers. The unit is of full logic with variable-blend type. A stereo-to- quadrophonic enhancement mode as well as a stereo mode are also included. The complete circuit is shown in fig- ure 1 . The two inputs (LT and RT) are at the left and the four outputs (LF, RF, RB and LB) are at the right of the diagram. T1 and T2 are input amplifiers providing 8 dB of gain. Closing switch S2 reduces the gain of this stage to -6 dB for high level studio use, when the audio level is 1 volt. 1C1 (Motorola MC1312) is the SQ Matrix Decoder integrated circuit. The two networks connected to pins 1 , 4 and 5, and 9, 10 and 13, are the phase- shift components. The phase shifters cover a frequency range of 200 Hz to 20 kHz with an accuracy of ±7°. This is sufficient for a separation between the left-back and right-back channels of more than 26 dB over this frequency range. T3 through T5 comprise the stereo enhancement circuit, which will be discussed later. The four matrix outputs from IC1 (L'F, L'B, R’F and R’B) connect to the mode switch, SI. SI is a five-pole three- position switch to select ‘SQ Quadra- phonic’, ‘Stereo Enhancement’, or ‘Ste- reo’ modes. When in the SQ quadra- phonic mode, the four outputs of IC1 are applied to emitter followers, T7 through T10. These emitter followers' provide isolation so that the following circuits do not influence the decoder’s frequency response or levels. Proceeding from the emitter followers, the four matrix-decoded audio signals drive both the Logic integrated circuits, IC2 (MC1315) and the Voltage Con-| trolled Amplifier IC3 (MCI 3 14). The| audio signals going to the Logic IC are equalized for optimum logic perform-j ance by three RC circuits (C27/28, R43; C33/34, R58; C35/36, R64). The Logic IC, IC2, develops control signals corresponding to the dominant! sounds contained either in the front or back corners of the quadraphonic pro- gram. These control signals, from pins 3j and 5, drive the VC A (Voltage Con-, trolled Amplifier) IC3, causing the four amplifiers within this IC to vary in gain in order to increase the quadraphonic separation. When the dominant sounds are center-front or center-back, the Logic IC (IC2) develops center-front/ center-back signals on pins 7 and 8, which are used to actuate the variable- blend FET, Til. T13 through T15 comprise the driving circuit for the FET. T13 and T15 are a rectifying differential amplifier; T14 is an adjustable constant current source, used to set the variable-blend operating, point and gain; and T12 is a saturating amplifier used to ‘switch’ the FET, (Til). Upon command from the center-front/I center-back logic, Til blends the back, channels, Lg and Rg, in order to cancel, the CF (out-of-phase) sound from ths rear channels. Also connected to the VC A integrated circuit (IC3) are the three balance con-i trols and the master volume. Note that only a single-section potentiometer is needed for each of these functions. Four output amplifiers follow the VCA, SQL-200 SQ decoder Elektor September 1976 - 9-39 supplying added gain (9 dB) and low output impedance. These amplifiers may be omitted unless the decoder is re- quired to drive studio lines or very long cables. Stereo enhancer Return now to transistors T3 through T6. This circuit makes up the stereo en- gineer. T3 is an inverting adder; T4, T5 iad T6 make up a subtracting circuit. These circuits rearrange the stereo signal ato a quadraphonic format. The ’Left’ stereo signal is changed to Lg', the ■Right’ stereo signal is changed to Rg\ the stereo center appears as center front ' «n quad. The Logic and variable-blend farther increase the quadraphonic sep- aration; just as in the SQ mode. Stereo For stereo operation the audio signals tor the left and right channels are taken from the two front matrix outputs, Lf - tad Rp', and applied to the VCA (IC3) nputs. The Logic IC (IC2) is made in- active by grounding the ‘dimension’ I control, R68. The volume and balance j controls are left operative, and decoder s output appears only from the Lp and j Rp terminals. Power Supply •A fully regulated current-limited power s sipply is included in the SQL-200 de- s sgn. If a split-primary power trans- ■fcemer is used as shown, operation is e possible on either 90-125 volt or 180- 6250 volt AC-mains. A voltage regulator "1C. IC6 (MC1723C) controls the base of •> series-pass transistor, T16. R105 adjusts fee DC output to 20 volts. t Construction r Hw printed circuit board (figure 2) has ' »een designed for mounting standard 3 4ectronic parts, as well as some specific ‘■joraponents, such as the printed circuit ,r «itch and the power transformer. The n Jjc. board can, of course, be modified c br different components. However, it is s aggested that the general layout be e Min tained in order to avoid any unfore- een problems. ’!he layout of the power supply is fairly : 'ntical. The negative terminal of the i.OOO pF filter capacitor, C56, must g »nnect physically as close as possible a e the transformer center-tap. This s osures that the ‘charging-pulses’ do not e rsate a voltage drop along a ground 8 tad, introducing hum into the audio. A ®mall heat sink must be used with the enes-pass transistor, T16. lie power transformer (2 x 20 volts, /'.25 m A) can be mounted on the de- coder’s case if desired, with its leads ! oldered directly to the p.c. board. If e he transformer used is different from k< one specified, it is important to d enfy that the secondary voltage is be- >-»een 20 and 40 volts per section. (Re- d •ember to tie the capacitor, C56, nega- is he lead to the point where the trans- : er center-tap connects.) Lfer power supply voltage should be adjusted to 20 volts DC before plugging in the MC1312, MC1314 and MC1315 integrated circuits. This is extremely im- portant because the maximum supply ratings on these integrated circuits is 24 volts DC! SI is a 5-pole, 3-position, switch; prefer- ably make-before-break. It should be mounted close to the p.c. board so that the leads are kept short. Care must be observed in keeping track of the 14 wires needed! All five potentiometers (volume, three balance and dimension) operate on DC control signals. (There is no audio on them.) Therefore, the controls may be located at any reasonable distance from the decoder itself. A remote control center could be utilized provided cable can be obtained with a sufficient number of cores. Also, for the mechanically ingenious, a ‘joy-stick’ control could be devised for the three balance potentio- meters. Bypass capacitors may be re- quired near the MCI 3 14 IC to bypass AC picked up on the control lines from stray fields if the lines are very long. The four output amplifiers (two MC1458, dual operational amplifiers) may be omitted for the home decoder. In this case, just connect the output sides of C47, C48, C49 and C50 directly to the respective output jacks on the de- coder case. Variable-Blend Adjustment R73 sets the point at which the FET, Til, blends the signals in Lg' and Rg' during a center-front sound source. Adjustment is quite simple. Apply audio (from either the preamplifier output or sinewave oscillator) to one channel input of the decoder and drive the same signal, attenuated by a specific amount, to the other channel. Then rotate R73 until the gate of Til drops close to ground, turning on the FET and thus blending the back channels. Specifically, connect a high impedance voltmeter (> 10 MS2) 1 between the positive lead of C29 and supply com- mon. Connect the appropriate resistive network shown in figure 3 to Lj and Rp. Drive a constant 2 music signal, or a 1 kHz sinewave into the network. While the audio is applied, note that if R73 is rotated from one end to the other end, the voltage of C29 varies from around +1 8 down to almost 0 volts. This indi- cates the correct performance. Now, set the potentiometer so that C29’s voltage just reaches the lowest value. You will find this setting to be very sensitive . . . this is because you are setting the threshold at which the FET switches (when T12 drops to near 0 volts) and the gain of T1 2 is very high. Checkout A complete functional check of the logic portion of the decoder can be per- formed with an SQ test record, the SQT- 1 1 00. Users’ instructions are included with this record. If the record is not available, perform- ance can be verified quite well by using 1 We fail to see why it is essential to use such a high impedance voltmeter for this adjust- ment. A universal meter with a sensitivity of 20 k«/V, and used in the 25 V f.s.d. range, should be adequate. The only difference is that the '+18V' mentioned further on will then be +9 V — Ed. 1 It is best to use a loud busy music selection, such as a full chorus, fortissimo, or loud continuous rock music. , SQL-200 SQ decoder Elaktor September 1976 — 9-41 2 single audio source, such as the output of the phono preamplifier or tuner, or a I kHz oscillator. To check the SQ mode for Lf, Rf and Cf logic operation, proceed as follows: First, turn the di- mension control fully clockwise, center the balance controls, switch to SQ logic, and adjust the volume control for a reasonable level. Then apply the audio sgnal to Lj (0.25 volts from the oscil- lator, or high level ‘busy’ music from the phono preamplifier or tuner output). Observe that the output appears from Lp, no audio from Rp and that the sound is attenuated at the Lb and Rb outputs (approximately 15 dB below Lf). Repeat for Rj and observe that Lp now has no output and that the back channels are similar to the previous Lj test. For a center-front signal, drive the same audio signal into both Lj and Rj; observe equal outputs on Lf and Rf, and observe attenuated outputs on Lb ind Rb (approximately 15 dB below Lp and Rp). To check the back logic, switch the decoder to ‘enhance’. Drive audio into Ly and observe that output signal appears on Lb, with very little output on all other channels (15 dB below Lb). Repeat for Rj and observe output on RB, with low output on the other chan- nels (approximately 15 dB below Rb). If both Lp and Rt are driven together with the same signals, Lp and Rp should have the same output, whereas the two backs should be attenuated « 15 dB below either Lp or Rp). Fgure 1. Complete circuit of the SQ logic •ecoder. Fgure 2. Component layout and p.c. board hr the decoder. Fgure 3A. Network for variable-blend adjust- ment when using a 1 kHz sine-wave . The out- puts from this network are fed to the L-p and ■p inputs of the decoder. Fgure 3B. Network for variable-blend adjust- a*nt when using a music source. tqure 4. This brass shield should be mounted s>- the p.c. board between the mains trans- _e»mer and the output amplifiers. 3b Operating Suggestions The SQL-200 decoder is intended for operation at an input level of 250 milli- volts (1.0 volt if switch S2 is closed). Operation with audio signals consider- ably below this value will yield poor separation. Similarly, operation above 250 millivolts average level could cause audio distortion. Fortunately, most equipment in the home operates around the E1A recommended standard of 250 millivolts. Some suggestions on how to incorporate the decoder into the existing hifi system are given in the companion article ‘From Stereo to SQ’. Volume If the decoder is used with a quadra- phonic receiver, it is desirable to set the SQL-200 volume to an appropriate pos- ition and then make all listening level adjustments with the receiver master volume. A method of adjusting volume is to play an FM station directly. Then switch to the decoder (‘Tape Monitor’ on the receiver) and adjust the decoder volume for equal output level. When the decoder is used with a stereo receiver, the volume control on the receiver should be used to adjust the program volume. Channel Balance Best SQ performance is obtained when the entire decoder, amplifier, and speaker are balanced for the preferred listening position or area. An SQ test record, the SQT-1100, is available for setting SQ decoder balance. If this record is not on hand, the adjust- ment can be made using any SQ record which contains a solo vocal or lead instrument and instrumental music in all four channels. Before adjusting the balance controls, set all three to mid- position. Stand between the front loud- speakers to observe an apparent sound image of the solo directly in front of you. If the image is not centered, adjust the ‘front balance’ control to achieve the centered image. Next, while playing the same selection portion, stand be- tween the two back speakers. Adjust the ‘back balance’ for equally loud instru- ments in both back speakers. Finally, adjust the ‘F/B (front-back) balance’ for the desired level of the two back speakers relative to the front pair. In general, pop or rock type music is recorded in ‘surround sound’ wherein the accompanying instruments are placed around the listener in a balanced or interplaying orchestration. This type of music is helpful for checking the acoustical balance of the decoder. A record like ‘Chase’ (‘Epic’ No. EQ 30472) in which trumpets are played in success- ive channels around the room is excel- lent for this purpose. Dimension Control This knob adjusts the amount of logic enhancement for corner-channel sounds ■in both the ‘SQ’ and ‘stereo enhance’ modes. In conventional listening areas, such as a living room with light drapes and some overstuffed furniture, the ‘dimension’ control should be set about 3/4 clockwise. However, if there are many pieces of furniture, drapes, and carpet, then a lower setting of this con- trol may provide a more pleasing quadra- phonic performance. References B. B. Bauer, R. G. Allen, G, A. Budel- man, and D. W. Gravereaux, 'Quadra- phonic Matrix Perspective - Advances in SQ Encoding and Decoding Tech- nology’, J. Audio Eng. Soc., vol. 21, pp. 342-349 (June 1973). B. B. Bauer, G. A. Budelman, and D. W. Gravereaux, ‘Recording Tech- niques for SQ Matrix Quadraphonic Discs', J. Audio Eng. Soc., vol. 21, pp. 19-26 (Jan. /Feb. 1973). B. B. Bauer, D. W. Gravereaux, and A. J. Gust, 'A Compatible Stereo- Quadraphonic (SQ) Record System’, J. Audio Eng. Soc., vol. 19, pp. 638- 646 (Sept. 1971). 9-42 — Elektor September 9-44 - Elektor September 1976 ignition timing stroboscope 0g(n)8G6@(n) WCD© There are several ways of adjusting the ignition timing of a car engine. One of the quickest and best is to use a stroboscope. The stroboscope timing aid described in this article is a self-contained unit for easy adjustment of the car's ignition. It can also be used for running a fluorescent lamp off the car bat- tery and with a few modifications it will operate as an electronic flasher for photographic use. The equipment differs from most commercially available stroboscopes in that it has its own high tension power supply. There is no need to interfere with the car’s existing high tension wiring, except for the link to the ig- nition system required for triggering the flash. The unit only draws an extremely small amount of energy from the power intended for the spark. ‘Simplicity’ was the catch word main- tained during the design of the circuit. The critical component in the unit is formed by a transformer having a centre-tapped secondary (2 x 6 V) and a 220 . . . 245 V primary. For those who remember the ‘good old days’ of valves: a heater transformer. The secondary winding is used in a balanced oscillator with T 1 , T2 as active elements. The transformer character- istics along with the resistors in the circuit determine the frequency the unit will oscillate at. In this case it will be about 100 Hz. The transformer primary (which is used as the secondary in this unit) will supply about 325 V (AC) which results in approximately 450 V (DC) after rec- tification (off load). With an 8 mA load, the voltage drops to about 300 V. The DC voltage is used to power the strobe light. The current for the fluor- escent lamp comes direct from the transformer winding. A small readily available 8 W fluor- escent lamp is used with this unit. This will slightly overload the circuit, causing saturation of the transformer core. This in turn leads to an increase of the oscillator frequency which improves the lighting efficiency of the fluor- escent lamp. Admittedly, the lamp will not emit its normal amount of light, but it should prove to be a suitable and economical battery-powered camping light. There is little risk of the car battery running down in the course of the evening, since the current de- mand does not exceed 750 mA. spark plug clip Elektor September 1976 - 9-45 The unit can also be used as a photo- grapher's electronic flash. However, several circuit changes will be necessary. Capacitor C2 must be increased to at least 250 /iF (an electronic flash capaci- tor) and the trigger pulse must be applied via a pulse transformer actuated by the flash contacts on the camera. Stroboscope The diagram of figure 1 shows that only a small capacitor is connected *:ross the flash tube when the device s used as a stroboscope. At a working voltage of 300 to 400 volts, the energy stored will be approximately 0.5 Ws. This energy is sufficient to produce a flash which is visible for about 50 cm <20 inches), depending of course on the ambient lighting conditions. On the other hand, the energy is not so high b to require a particular type of flash tube; any commercially available type capable of handling 20 Ws can be used. ; Since the ignition voltage of the flash tube is rather high it can be connected 1 permanently across the capacitor with- ’ out risk of spontaneous discharge. The ‘ rube must then be triggered in such a ; way that the flashes are synchronised to the ignition timing. It is standard ’ practice to trigger a flash tube via a : pulse transformer producing pulses of some 10 or 20 kV. However, since the ’ pulses at the spark plug are already at this voltage, there is no need for such a : transformer in this case. The trigger a pulses can be derived straight from the ' spark plug electrode. This can be done s fcy using a well insulated wire of suf- ’ Scient length fitted with an adequately I msulated alligator clip. i § Using the unit r The timing reference is usually the firing e of the spark plug in the number 1 " cylinder. As the flash is triggered at the instant i the plug fires, the engine is illuminated at the same moment. The flash should make the rotating parts of the motor [teem stationary. Somewhere on the 'engine there are special timing marks, usually one on the flywheel or a pulley on the crankshaft, and the other on the Mock. When the unit has been correctly | booked up to the engine (plus and | minus to the car battery and the trigger wire to the correct plug) these marks (will both appear stationary. The timing | adjustment is carried out by rotating i rie entire distributor housing until ■ lie marks are correctly aligned, k is best to consult the car service manual or other service notes. They rtiould contain the location of the timing marks and the correct alignment position of the marks. There may be other points to be noted, for instance, tie vacuum advance and centrifugal advance may have to be disabled before tming can be carried out. A good motto is: ‘If in doubt, don’t; contact jour garage or the A A or RAC for ..farther information’. 9-46 — Elektor September 1976 ignition timing stroboscope Construction The actual construction, although simple, must be carried out with care. All components except the flash tube and the fluorescent lamp are mounted on one printed circuit board, which should be mounted in an insulated case. Bear in mind that the voltage generated will rise to about 350 V and could become dangerous in the circum- stances under which the equipment is being used! It is a good idea to mount the flash tube in a separate shell (well insulated!) as it is rather awkward to ‘aim’ a box containing all the electronics . ... A re- flector mounted in the shell will im- prove the brightness of the flash. Photograph 2 shows the U-shaped flash tube fitted in its small case. It also shows how the triggering cable is arranged: the wire is wound around both ends of the flash tube. The high tension pulses from the spark plug ionise the gas inside the tube causing the gas to become conductive, in- itiating the flash. The prototype unit used a U-shaped flash tube, but prac- tically any tube, whatever the shape and size, will be suitable. H Resistors: R1,R4 = 33 n R3.R4 = 220 «, 1/2 W Capacitors: Cl = 220 p/16 V C2 - 8 *i/350 V Semiconductors: T1.T2- BD 139. 2N4923 01 ,D2 - 33 V/1 W zener diode B1 ■ bridge rectifier B400 C50 Miscellaneous: Trl = 220 . . . 245 V prim. 2 x 6 V, 0.3 A sec. SI £2 = on/off switch. Flash tube. (0 O £ >_ o o (0 0) E o Q CO CO C0 0 k_ n CO c CO L— CO > D E c n o CO 0 o E E 1— 0 ■C o ■*— > f— c -C L_ CO (0 o o 3 (0 T3 C ra > l- © © © © © © CO c 'l— o o CO o CO l_ 0 r~ i— 0 O CO CO E ® £ s ^ CD O) Q. 0J *■* .ts W > ,S> 3 r T) ® C -Cr -£> 9-48 - Elektor September 1976 tup-tun-dufl-du» TUP TUP run uus Wherever possible in Elektor circuits, transis- tors and diodes are simply marked 'TUP" (Transistor, Universal PNP), 'TUN' (Transistor, Universal NPN), 'DUG' (Diode, Universal Ger- manium) or 'DUS' (Diode, Universal Silicon). This indicates that a large group of similar devices can be used, provided they meet the minimum specifications listed in tables la and Elektor September 1976 - 9-49 fm*/ bim Elektor September 1976 — 9-51 9-58 — Elektor September 1976 WHO and WHERE A directory of electronic component suppliers to Elektor readers IF THERE IS A COMPONENTSHOP IN YOUR AREA NOT LISTED BELOW PLEASE LET US KNOW THE RADIO SHOP 16 Cherry Lane, Bristol, BS1 3NG, Tel. Bristol 421 196, S.T.D. Code 0272 CAMBRIDGE B. BAMBER ELECTRONICS 5 Station Road, Littleport, Cambs., CB6 1QE, Tel. ELY (0353) 860185 Electronics Mart 370 Charminster Road, Bournemouth, BH8 9RX, Tel. Bournemouth 516565 ml 25 High Street, Brentwood, Essex, Tel. (0277) 216029, Telex: 995194 222-224 West Road, Westcliff -on-Sea, Essex SS0 9DE, Tel. Southend-on-Sea 46344 HARRINGTON COLORVISION 9 Queen Street, Colchester, Essex, Tel. Colchester 47503 [W1 m Phoenix Electronics ISdentl Limited WM. B. PEAT & COMPANY L 25/26 Parnel Street, Dublin 1, Ireland, Tel. 749973/4 Custom electronic controls 45, Picardy Road, Belvedere, Kent. DA17 5QH, Tel. Erith 34476 LEICESTERSHIRE S&cAonicO 112 Groby Road, Glenfield, Leicester. Tel. Leicester 871522 LRS ELECTRONIC SUPPLIES 3 Clivesway, Hinckley, Leicestershire m