video biofeedback get to grips with microprocessors by 'experimenting with the SC/MP' elektor november 1977 — E 5 The electrometer will indicate the presence of an electric field, and fluctuations in its field strength. This may prove useful when investigating psychic phenomena . . . The video biofeedback system consists of an alpha-wave detector and a visual display generator. The display consists of a white square on a TV screen; the size of this square increases as a higher level of alpha- activity is registered. The practical construc- tion of the racing cars for the slotless model car track is discussed in this (final) article in the series. A large number of electronic and electro- mechanical components must be mounted within the cramped confines of a model car . . . Experimenting with the SC/MP is a good way to get the feel of micro- processors. The first step is to build the (very basic) operational unit shown on this month's cover. selektor E14 microprocessors - can you afford not to understand them? 11-01 experimenting with the SC/MP (1) 11-02 H. Huschitt By far the best way to gain a clear understanding of the com- plexities of microprocessors is through the practical experi- ence of actually constructing and learning to operate one of these 'microcomputers'. fields : 11-13 electrometer 11-14 ejektor 11-17 relaxation generator ccir tv pattern generator (3) 11-18 Having completed those sections of the circuit that produce the CCIR standard sync, signal, attention is now given to the design of the pattern generator module, which will turn the instrument into a versatile aid to TV adjustment and servicing. poltergeist 11 -22 The title of this article should really be 'remote-controlled poltergeist-imitator'. By operating a miniature ultrasonic transmitter concealed for example in one’s jacket pocket, a receiver hidden somewhere in the room will simulate the sound of a poltergeist loose in the house. video biofeedback 11-24 In recent years the use of biofeedback techniques to achieve conscious control of brain activity has become extremely popular. Of particular interest is 'alpha feedback' which, by stimulating the production of alpha-waves, promotes relax- ation. magnetiser 11-32 Recent medical experiments have lent weight to the idea that magnetic fields are of therapeutic value in the treatment of psychosomatic complaints and rheumatic ailments. The fol- lowing article, which is preceded by details of a controlled experiment into the efficacy of this method of treatment, describes a device which will produce an alternating magnetic field of the type suitable for medical use. slotless model car track (6) 11-34 This final article in the series on the slotless car track dis- cusses the remaining electronic circuits, namely the power supplies for the car, track and infra-red transmitter, before describing the mechanical construction of the car and testing of the complete system. formant — the Elektor music synthesiser (5) . 11-41 C. Chapman Last month's article dealt with the theoretical circuits used in the VCO. This month's contribution covers the selection of components for, and the practical construction of, the VCO module, after which testing and adjustment of the VCO are described. market E15 advertisers index E26 ®e»- series regulator transistor T4. The 5.6 V supply is This final article in the series on the slotless car track discusses the remaining electronic circuits, namely the power supplies for the car, track and infra-red transmitter, before describing the mechanical construction of the car and testing of the complete system. derived from the 9 V rail by a shunt regulator comprising R7, D12 and CIS. As is apparent from the circuit, the various supply rails are isolated from the input contacts and from each other by diodes, and are extensively filtered using chokes and capacitors. This is necessary because of the high sensitivity of the receiver and MPX decoder, the operation of which could be upset by interference pulses on the supply lines. The receiver must also be mounted as far as possible from the pickup contacts and motor, to avoid radiated r.f. interference caused by contact arcing. The power supply circuits are accomo- dated on the printed circuit board shown in figure 3, which also forms the chassis of the racing car. The chassis shape must be cut out using a fret saw, and assembly of the p.c. board must be delayed until this has been done, as will be explained in the assembly instruc- tions. Transmitter Power Supply The power supply for the infra-red transmitter is shown in figure 4a. This is simply a stabilised supply based on an IC voltage regulator - a design which has previously been used in Elektor. A printed circuit board and component layout for the power supply are given in figure 4b; in this application diode Dl, shown on the board, is not required and is replaced by a wire link. Track Power Supply Power to the track is obtained from a simple, unregulated 15 V supply, the circuit of which is shown in figure 5. The current rating of the transformer should be about 1.5 A for each car that is to be used, and one 4700 n reservoir capacitor should be added for each car. Thus if, say, four cars are to be run simultaneously, the transformer rating should be 6 A and the total capacitance should be about 18800 /r. Of course, it is not necessary to use individual 4700 n capacitors if other values are to hand. For example, two 10000 /J or one 22000 H capacitor(s) would be quite acceptable for a four-car power supply. Fuse FI in the transformer primary circuit should be a slow-blow type, and slotless model car track elektor november 1977 — 11-35 the current rating should be chosen to suit the power rating of the transformer: where I is the fuse rating in amps, P is the transformer power in watts and V is the mains voltage in volts. Mechanical Construction The first step in the mechanical con- struction is to cut out the chassis p.c.b. using a fret saw. Some of the car suspension and steering components are provided on the p.c. board, namely the two rear suspension mounts, which are to be found on the left of the board in figure 3, two control horns, which are on the right of the board, and the track rod, which is at the top of the board. These components should be cut out very carefully and should be worked to the correct shape using a file and emery paper. Front Suspension The front suspension and steering mechanism of the car is the most critical part of the mechanical construction since, it if is not satisfactory the car will not perform well. The experienced model builder who has access to a lathe can easily construct a steering mech- anism without assistance, but for the less experienced constructor the assembly must be easy to make using readily available parts and simple tools. Apart from simple handtools such as 1 Figure 1. Since a large number of components must be crammed into the racing car, the normal type of chassis supplied with model cars is too wasteful of space, as can be seen by comparison with the servo. A special chassis, which also doubles as a p.c. board, is therefore used. Figure 2. Circuit of the car power supplies, which are mounted on the p.c. board/chassis. screwdrivers, spanners, centre punch, file and hacksaw,; the only slightly less common tools recited are an electric drill mounted in a'y.erticql drill stand, a tap wrench and ’-ad' M-3(_tap, or similar B.A. size (4 B.A. or Jj-Tj.#- would do). The suspension and steering system is based on ready available electronic hardware such as threaded hexagonal spacers and bits of alloy heatsinks. Figure 8a shows an exploded diagram of the complete front suspension system. The suspension bearers (12) and (23) are U sections cut Virgin an aluminium heatsink. The suspSteifon legs (4) and (20) are internaUy,^jjj&f?fled hexagonal spacers, down the^cpntrjj? of which are lengths of threatftifgiiod to act as pivots (5) and (28). Two control horns (15) and (19) joined by a track rod (16) operate the steering mechanism. The offside control horn is linked to the servo by a wire link (24). Construction of 4 the frpnt suspension should begin jij^^abricating the suspension bearejfej/and legs. The suspension bearers,’, affrjmade from U section heatsink in accordance with the dimensions given in figure 8b. A drill stand must be used when boring the holes to ensure that they are true and, to avoid bending the U section while drilling, it is best to cut the heatsink to length after the holes are drilled. To avoid the risk of injury the heatsink should be securely held in a vice or pliers while drilling' t not in the fingers! After drilling and-ctfStting to length the U sections should- be deburred with a fine file. 2 D1...D10=1N4004 D13=1N4148 BC 547B E300 1-36 — elektor slotless model slotless model car track elektor november 1977 — 11-37 4a Parts list to figures 4a and 4b: Capacitors: Cl - 2200 p/40 V C2,C4 ■ lOOn C3 = 470 p/16 V Semiconductors: IC1 =7815 8 = 4x1 N4004 Miscellaneous: Transformer with 24 V/1 A secondary. B1 = 4 x 15A-Si- Diode Figure 3. The p.c. board/chassis and its com- ponent layout. Some of the steering and suspension components are also provided on this board. (EPS 9850). Figure 4a. Stabilised power supply for the infra-red transmitter. Figure 4b. Printed circuit board and com- ponent layout for the transmitter power supply. (EPS 9218) Figure 5. Unstabilised power supply for the racetrack. An additional 4700 p of reservoir capacitance is required for each additional racing car, and the transformer must be uprated by 1 .5 A for each extra car. Figure 6. Photograph of an early prototype of the racing car — which is somewhat of a Next, take a 10 mm long hexagonal spacer and check it for fit between the faces of the U section. If it is too long then file one end until it is a clearance fit. Repeat this with the other U section and another spacer. The hole for the stub axle must now be drilled and tapped in one face of the spacer. Mark the centre of one flat face of the spacer and dot with a centre punch. Drill a 2.5 mm hole right through the spacer and tap with a 3mm tap. Repeat with the other spacer. Finally, drill out the front wheel hubs to 3 mm, holding them in combination pliers as shown in figure 9, and cut two 28 mm lengths of 3 mm threaded brass rod. Assembly of the front suspension may now commence. The nearside and offside suspension bearers are secured to the chassis using M3 nuts, bolts and lockwashers (8, 9, 10, 11 and similar for the offside). The suspension legs are then inserted between the faces of the bearers and are secured by threading the lengths of threaded rod through them. A plain washer and two nuts (6, 7, 21 and 22) are put onto the bottom of 1-38 — elektor november 1977 slotless model track 7 Figure 7. Drive motors and rear axle sets similar to these can be obtained from most model shops. Figure 8a. Exploded view of the front sus- pension and steering, which is built from readily obtainable components. Figure 8b. Dimensions of the suspension bearers and suspension legs. Figure 8c. The 'raw materials' used in the front suspension and steering assembly. Key to Figure 8a 1 .Stub axle — M3 screw. 2. Nearside roadwheel. 3. Tapped hole for stub axle. 4. Suspension leg 5. Threaded rod 6. M3 nut. 7. M3 nut. 8. M3 screw. 9. Lockwasher. 10. Lockwasher. 11. M3 nut. 12. Suspension bearer. 13. M3 nut. 14. M3 nut. 15. Control horn. 16. Track rod. 17. M3 nut. 18. M3 nut. 19. Control horn. 20. Suspension leg. 21. M3 nut. 22. M3 nut. 23. Suspension bearer. 24. Piano wire control link. 25.Stub axle - M3 screw. 26. Track rod pivot - terminal pin. 27. Track rod pivot — terminal pin. 28. Threaded rod. each rod and the nuts are locked together. M3 screws (1 and 25) are now passed through the wheel hubs into the threaded holes in the suspension legs and are tightened until they bite into the threaded rods running down the suspension legs, thus locking the suspen- sion legs to the threaded rods. At this stage the wheel should be free to rotate and the suspension should be free to pivot. A plain washer is now placed over the top of each threaded rod and an M3 nut (13 and 18) is run down lightly onto the washer. The control horns (15 and 19) are then placed over the rods and are locked in placed by two nuts (14 and 17). Again check that the suspension is free to pivot and is not binding - if it is the nuts will have to be repositioned slightly. The two control horns can now be linked by the track rod. Two ordinary p.c. terminal pins are pushed through the holes in the track rod and soldered. The pins are then pushed through the appropriate holes in the control horns and the track rod is secured by soldering a small washer to the head of each pin. At this stage the steering assembly should again be checked for freedom of movement. The servo is now secured to the chassis using double-sided adhesive ‘Servotape’. With the steering centred and the control horns on the servo central, the dimensions of the control link (24) can be measured up and the link bent from piano wire. The dimensions of the link will depend on the type of servo used and its exact position. The link can now be inserted into the holes in the servo and steering control horns and can be secured in a manner similar to that used to secure the track rod. In order to maintain correct steering geometry it is essential that when the servo control horns are central, the track rod is central and the roadwheels are in a straight ahead position. For this reason the wire control link must be made accurately. It is no good using a link which is the wrong length and trying to correct the resulting offset in the steering by adjusting the roadwheels, as this would spoil the steering geometry and cause poor cornering. slotless model car track elektor november 1977 — 11-39 Figure 9. The wheel hubs should be held in combination pliers while drilling out the axle Figure 10. General layout of the rear sus- pension and drive unit, also showing the mounting of the multiplex decoder, speed controller and servo amplifier. Figure 11. If a more powerful motor is used, which draws a current in excess of one amp, then Til of the drive controller should be replaced by a BO 139 or BD 241 B. Rear Suspension and Motor Gearing Rear axle assemblies and drive motors for model cars are available from model shops (figure 7). Assembly of the rear suspension system is extremely simple. The two rear suspension mounts are soldered into the slots provided and a fillet of epoxy adhesive is added to give extra strength. The axle assembly is dismantled and the axle is passed through the holes in the suspension mounts. The motor is then mounted on the chassis so that the motor pinion meshes with the axle gear, and the motor is then fixed in this position. Power can then be applied briefly to the motor to ensure that the roadwheels turn satis- factorily. Electrical Assembly Once the basic mechanical assembly of the chassis is complete, the electrical components may be mounted in ac- cordance with the component layout, after which power may be applied from the 15V track supply to any pair of the contacts XI to X4 and the various supply voltages checked. PI should be adjusted so that output U4 is 9.5 V. The multiplex decoder, servo amplifier and speed controller may now be mounted. These three boards are ar- ranged on the chassis around the motor, as shown in figure 1 0. First, secure the speed controller to the top of the motor with a piece of 'Servotape' then, to provide more support, solder two stiff wire links between the spare holes provided in the left side of the chassis and the holes in the two left corners of the speed controller board. Solder in the motor suppression components, Cl 6, and the supply connections U2 and U4 to the speed controller and motor. Next, mount the servo amplifier (L) behind the motor, securing it by stiff wire links to the supply connections U1 and U5, and between the spare hole in the chassis and the corner hole of the servo amplifier board. The last board to be mounted on the chassis is the MPX decoder board, which is mounted in front of the motor. The infra-red receiver must be kept well away from sources of interference, so it is mounted inside the roof of the car body shell. The photodiode is mounted on top of the car roof and is wired to the receiver through holes drilled in the roof to accomodate the leads. Once all the boards have been mounted in their respective positions they can be interwired in accordance with the wiring diagram of figure 12. Note that the link shown between the servo amplifier and the servo actually represents the five wires that join these two units. Wiring is probably best carried out using light-duty ribbon cable. Figures 14-16 show photographs of various stages of the construction. Testing and adjustment The principal adjustments to be made are tuning of the transmitter and receiver frequencies, and for this an oscilloscope is required. The adjustment procedure is as follows: 1. Temporarily disconnect the motor supply U4 (to avoid the car zooming away!) and connect the 15 V track supply to any pair of the contacts XI to X4. 2. Switch on the 1R transmitter and set its frequency adjustment preset PI to the mid-position. 3. Half mesh the vanes of the receiver tuning capacitor Cl, and place the car about 5 metres from the IR LED array. 4. Set the oscilloscope to 200 mV/div and monitor the receiver output. Adjust PI on the transmitter board until the MPX signal at the receiver output has maximum amplitude and is noise-free. 5. Turn the IR LED array away from the receiver until noise again appears on the MPX signal, and readjust PI for minimum noise. 6. Finally, adjust the receiver supply voltage U3 by means of PI on the chassis p.c.b. for maximum amplitude of the MPX signal. 7. Once the optimum transmitter fre- quency has been found for the first car, the transmitter frequency should 11-40 - elektor november 1977 slotless model car not be altered. To tune in other cars adjust the receiver trimmer Cl and adjust the receiver supply voltage as above. Final Remarks Due to tolerances in the receiver input FETT1, it may be found that the receiver is insensitive. With the receiver supply voltage set to 9.5 V the drain voltage of T1 should be nominally 5 V. However, if the drain voltage is less than 4.5 V it will be necessary to increase the source resistor R4 to, say, 8k2. If the drain voltage is greater than 6.2 V then R4 should be reduced to, say, 5k6. With more powerful types of motor that draw currents much greater than one amp, it will be necessary to replace T1 1 on the motor speed controller with a BD139 or BD241B. However, since it should not be necessary to fit a heatsink to these types of transistor they take up little extra space on the board, as can be seen from figure 1 1 . In some cases it has been found that the input impedance of the servo amplifier is too low to be driven by the MPX decoder, and that the threshold voltage is in excess of 2.5 V. A useful modification therefore, is to change the components of the servo amplifier input attenuator to R1 = 47 kand R2 = 150 k. Figure 12. Interconnection diagram for the car electronics. Figure 13. The component layout of the servo amplifier given in part 3 (fig. 13) was unfor- tunately not very clear, so it is here reproduced twice full size. Figures 14 to 16. Showing various stages in the construction of the racing car. Note that this is the 'Mk. II' prototype, which differs in some slight details from the final version. forinncrir Hne dW ifor music syrHneslser=i6 Care must be taken in the choice of components for, and in the construction of, the VCO, if reliable performance is to be obtained. The same general com- ments apply that were made earlier with regard to component quality. In addition, the following points should be noted: 1 . Capacitor C2 should be a low leakage type preferably MKM or equival- ent. 2. Transistor T1 to T3 should be tested, as will be explained later. 3. Diodes D3 and D4 should be a matched pair. It is important that the reset transistor T1 in the CCO section should be selec- ted for low leakage current, as excessive leakage current means current lost from C2 and non-linearity of the CCO at low frequencies. The test setup for T 1 is shown in figure 1 . The PNP transistor T8 can be used as the second transistor in the circuit, or any similar transistor can be used. The meter can be a multimeter set to the 1 mA range. The base of T8 is initially left open-circuit to check that it is not leaky. The meter should read zero. The base of T8 is then connected to the 0 V rail via a 1 00 k resistor to check that it has adequate current gain. The meter should read at least 1 mA (i.e. full-scale). The base of T8 is then connected to the collector of Tl. Any leakage current through Tl will be amplified by the current gain of T8 to give a deflection on the meter. Only if the meter reads zero is the leakage current of Tl suf- ficiently low. Finally, the current gain of Tl can be checked by connecting its base to +5 V through a 2k2 resistor, when the meter should again show full-scale deflection. FETs T2 and T3 can be tested using the circuit given in part 3 for testing the FETs in the keyboard interface. Unlike the keyboard interface circuit, FETs which show a U s in the test circuit of less than 0.5 V are not suitable for the VCO. However, FETs that have been rejected for the keyboard interface because their U s value was too high, can be used in the VCO if the value of U s lies between 1.6 V and 2 V. For FETs with U s values between 0.5 and 1.5 V the source resistors R17 and R20 should Last month's article dealt with the theoretical circuits used in the VCO. This month's contribution covers the selection of components for, and the practical construction of, the VCO module, after which testing and adjustment of the VCO are described. Since the quality of the VCO ultimately determines the performance of the synthesiser, it is worth spending a not inconsiderable amount of time and effort on this module. (C. Chapman) be selected from table 1 in part 3. For FETs having a U s value between 1.6 V and 2 V. R17 and R20 should be 4k7. Diodes D3 and D4 should be purchased as a matched pair or, if several diodes of the correct type are to hand, a reason- ably matched pair may be selected by measuring the forward voltage drop versus forward current characteristics of the diodes and selecting the pair that are most similar. Construction Once these critical components have been selected, construction of the VCO may commence. On the printed circuit board the VCO is split into two func- tional sections: the exponential converter and CCO, the complete circuit of which is given in figure 2a, and the curve shaper section, the complete circuit of which is given in figure 2b. These two circuits are the combination of all the partial circuits discussed last month. Printed circuit board and component layouts for the VCO are given in figure 4. The oscillator section occupies the top third of the board, whilst the remainder of the board contains the curve shaper circuits. To avoid interac- tion between the two sections of the circuit they each have separate supply and ground connections. The only link between them is at the source of T3, which is the CCO output (point A in figures 2a and 2b). Assembly of the board poses no particular problems, the only point to note being that at this stage C13, R26, R27, R42, R43, R54, and the link joining pin 4 of IC3 to the gate of T2, are omitted for test purposes. Test and adjustment The first test is to check that the CCO is functioning, and for this purpose a 1 M resistor is connected between the gate of T2 and - 1 5 V to act as a current source for the CCO. The CCO output can be monitored with an oscilloscope at point A. Should the oscillator fail to start then P10 can be adjusted until it does. It will probably be found that the oscillator stops as the slider of P10 approaches its two extreme positions, and P10 should 11-42 — elektor november 1977 be set midway between the positions at which oscillation ceases. At this stage, the frequency of the oscillator should be around 1 kHz, and the waveform will not be a perfect sawtooth, but will exhibit an exponential curvature due to the 1 M resistor being used in place of a constant current source. Once the CCO has been checked the 1 M resistor can be removed and the CCO connected to the exponential converter by soldering in the link between pin 4 of IC3 and the gate of T2. With the sliders of P2, P3 and P8 turned to zero volts and the KOV input grounded, it should now be possible to vary the VCO frequency by adjusting PI . If the exponential converter is operating correctly the waveform at point A should be a perfect sawtooth. It may be found that at low frequencies the VCO will not oscillate reliably, in which case the adjustment of P10 will require further attention. Once the VCO functions reliably over the entire audible range, PI should be turned completely anticlockwise and the offset potentiometer P8 adjusted until the lower frequency limit (with no control voltage other than from P8) is around 1 5 Hz. This adjustment does not need to be extremely accurate. Curve shaper section Adjustment of the curve shaper begins with the spaced sawtooth converter section. PI 1 adjusts the clamp level of Figure 1 . Simple test circuit for selecting transistor T1 of the VCO. Figures 2a and 2b. These two circuits consti- tute the complete VCO, and combine into two functional groups the partial circuits discussed last month. formant elektor november 1977 — 11-43 this circuit and hence the ‘spikness’ of the waveform, which affects the tonal quality. The adjustment is a matter of taste, but as a guideline the peak-to- peak amplitude of the waveform, viewed at point S3a, should be about 3 V. Next, the triangle converter (T4, T5) can be adjusted. The symmetry of the triangle waveform is determined by the matching of diodes D3 and D4. PI 2 can compensate for slight mismatches in these diodes, but if the degree of mismatch is large the only answer is a better matched pair of diodes. The output waveform should be monitored at point S5a with PI 2 in its mid- position, and PI 2 should then be turned one way or the other to obtain a sym- metrical triangular waveform. If notches are apparent at the peaks of the triangle waveform (especially noticeable at high frequencies) then capacitor Cl 3 should be added . The value of 1 n is given as a guideline, but C13 should preferably be chosen experimentally to give the best compromise between elimination of the notches and attenuation of the signal at high frequencies. Once the triangle waveform is satisfac- tory the sine converter may be adjusted. Ideally, diodes D5 and D6 should also be a matched pair in order to ensure symmetry of the sine waveform. However, a random pair of lN4148s or lN914s will usually prove to be a sufficiently close match in practice. The purity of the sinewave is adjusted visually by monitoring the waveform at point S6a and varying the resistance of PI 3 for best results. The sine converter output can be compared with the sine output of a signal generator, if available, or with a sine curve plotted on graph paper. The purists may like to adjust for minimum distortion using a distortion meter, though the simpler adjustment procedure is adequate from a musical point of view. The final section of the circuit to be adjusted is the pulse-width modulated squarewave generator. The aim of this adjustment is to set trimmers PI 4 and PI 5 so that the adjustment range of P5 varies the duty-cycle from 1% to 99%. The setting-up procedure is as follows: 2b 11-44 — elektor november 1977 formant 1) Adjust P14 until its wiper voltage is —5.5 V, and adjust PI 5 to maximum resistance. 2) Connect the voltmeter to the output of IC6 and monitor the PWM signal at point S2a with an oscilloscope. 3) Adjust P5 to give first maximum (approx. 99%) and then minimum pulse width (approx. 1%) of the PWM signal, and note the output voltage of IC6 for these two con- ditions thus: - V ma x = voltage for minimum pulse width, V m in = voltage for maximum pulse width. 4) Turn the wiper of P14 to zero volts and the wiper of P5 to maximum voltage. Now used PI 5 to adjust the output voltage of IC6 so that it is equal to the difference between the two previously noted values V max and V m in i.e. V 0 ,IC6 = ^min * v max- The output voltage of IC6 will be negative since it is connected as an inverting amplifier. 5) Adjust P14 to give maximum pulse- width (99% duty-cycle) of the output signal. When the wiper of P5 is now turned to zero volts the pulse width should be minimum (1% duty-cycle). This completes the adjustment of the PWM stage. Oscillograms of all the waveforms are shown in photos 1 to 7. Output adder Once the various sections of the curve shaper have been adjusted the input resistors of the output adder may be selected (R26, R27, R42, R43 and R54). A 250 k potentiometer is connec- ted in place of each resistor in turn, and the peak-to-peak amplitude of the relevant waveform is adjusted to about 2.5 V at output EOS. The resistance of the pot is then measured and it is replaced by a fixed resistor of the nearest preferred value from the E24 range. Front panel A front panel layout for the VCO is given in figure 3. The three inputs, FM, ECV and PWM are at the top of the panel, with the switch (SI) to select between ECV and KOV mounted below. Potentiometer P3, which controls the FM modulation depth, is mounted below the FM input socket, while P4 and P5, which control the pulse width modulation depth and duty-cycle re- spectively, are mounted below the PWM input socket. The coarse and fine tuning controls (PI and P2) are also grouped together, on the left of the panel, while the output level control (P6) is grouped with the waveform selection switches (S2 to S6) and the output socket. Module construction It is essential that the VCO module should be screened to avoid any inter- ference pickup. To provide this screening, and to make the module elektor november 1977 - 11-45 ECV = External Control Voltage, i.e. front-panel input to VCO. KOV - Keyboard Output Voltage, i.e. permanently wired input to VCO from inter- face receiver. FM = Frequency Modulation input PWM = Pulse Width Modulation EOS = External Output Signal from VCO (front panel output) VCO/IOS = Internal Output Signal from VCO, will be perma- nently wired to one VCF Figure 3. Suggested front panel layout for the VCO. Photos 1 to 7. These oscillograms give an indication of the waveforms that should be available at the curve shaper outputs: 1. Sawtooth 2. Spaced sawtooth 3. Triangle 4. Sinewave 5. Squarewave, minimum duty- cycle 6. Squarewave, 50% duty-cycle 7. Squarewave, maximum duty-cycle. mechanically rigid, the p.c. board is mounted on a carrier made from 16 or 18 SWG aluminium. The dimensions of the carrier are those of a large Eurocard (165 mm x 210 mm) so that the module will fit a Euro-standard card frame. A right-angle bend at the front edge of the carrier allows it to be secured to the front panel by means of the poten- tiometer mounting bushes. The p.c. board is mounted on the carrier using M3 screws and spacers. Photo 8 shows the completed module. Octaves/Volt adjustment The most critical adjustment made to the entire synthesiser is the setting up of the octaves/volt characteristic of the VCOs, as this adjustment determines the accuracy of the synthesiser tuning. There are two methods of adjusting the VCO. The simpler method requires the use of a frequency counter and digital voltmeter, while the second method requires an audio signal generator with a calibrated frequency scale. Before commencing the adjustment procedure power should be applied to the VCO for several minutes to allow the temperature (especially of 1C3) to stabilise. To adjust the VCO using frequency counter and DVM, all inputs and controls of the VCO input adder are set to zero volts and P9 is set in its centre position. The frequency counter is con- nected to the VCO output and the DVM to the wiper of PI. With PI turned fully anticlockwise the frequency counter will read around 15 Hz, which was set previously by means of P8. PI is now turned slowly clockwise until the DVM reads 1 V, when the VCO frequency should be twice what it was with PI set to zero, e.g. if the zero frequency was exactly 15 Hz the frequency should now be exactly 30 Hz. Of course, initially this will not be the case, and some adjustment of P7 will be required. PI is then turned until its wiper voltage is exactly 2 V, when the VCO frequency should be four times the zero voltage frequency, e.g. 60 Hz. This procedure is repeated at 1 V steps over the entire range of PI, checking that the correct frequency is obtained at each step. Thus if 0 V = 1 5 Hz, then 1 V = 30 Hz, 2 V = 60 Hz, 3 V = 1 20 Hz etc. P7 is adjusted to obtain the best accuracy possible over the widest frequency range. At high frequencies (greater than 3 kHz) P9 can be used to correct any deviations from the 1 octave/volt characteristic. To adjust the VCO using the beat note method, the outputs of an audio oscillator and the VCO must be fed into the left- and right-channels of a stereo amplifier, or via an audio mixer into a mono amplifier, so that the beat notes can be heard via the loudspeakers. The VCO is connected to the KOV output of the previously calibrated keyboard. The audio oscillator is set to a frequency between 400 and 500 Hz, and the main tuning of the keyboard is switched off. elektdr n^verhbei 1977 — 11 b. Carbon P12= 10k P13,P14,P15 =100 k Potentiometers: PI = 100 k lin b. Carbon P2,P4 = 100 k lin P3 = 50 k log. P5 = 10 k lin. P6 = 4k7 (5 kl log. Capacitors: Cl = 1 n C2 = 3n3 (MKM) C3.C4.C5.C6.C7, C8.C12 = 680 n C9 = 47 p/16 V Cl 0/C1 1 = 1 00 m/ 25 V Cl 3= 1 n (see text) Semiconductors: T1 = BC109C T2.T3 = BF 245A, B T4 . . . T7 = BC107C T8 = BC 1 77C D3.D4 = OA91, OA95, D1.D2.D5. D6.D7 = 1 N4148, or 1N914 D8= LED. TIL209 or IC1 = 7413 IC2,IC4,IC5,IC6,IC7,IC8, IC9.IC10.IC11 = mA 741 C or MCI 741 CPI (MINI DIP) IC3 = mA 726C (Fairchild, TO package) Miscellaneous: 31 pin (DIN 41617) connector SI . . . S6 = SPDT Figure 4. Printed circuit board and i AA1 1 8.AA1 1 9, or 1N34A ponent layout for the Formant VCO The top note of the keyboard is then depressed, and the VCO tuning controls PI and P2 are adjusted until the audio oscillator and VCO are in tune with zero beat. Next, the key an octave lower is de- pressed, when a dissonance or very rapid beat note will be heard. P7 is then adjusted until zero beat is obtained between the audio oscillator and the VCO note one octave lower. The top key is again depressed, when it will be found that, due to the adjust- ment of P7, a beat note is again heard. Using the VCO tuning controls, readjust for zero beat, then depress the key an octave lower, which will now be slightly out of tune due to adjusting the VCO tuning controls. P7 must therefore be readjusted to obtain a zero beat. This procedure is repeated several times until the oscillator is perfectly in tune with both the top note and the note an octave lower. The tuning is then checked two octaves and three octaves below top C, and if necessary P7 is readjusted to obtain the best tuning over the entire keyboard range. The higher ranges of the VCO must now be adjusted using P9. For this purpose the audio oscillator is tuned to around 2 kHz, the bottom note of the keyboard is depressed, and the coarse and fine tuning controls of the VCO are adjusted for zero beat. The key an octave higher is then depressed, and P9 is adjusted for zero beat using the same technique as for the previous adjustment procedure using P7. The tuning is then checked two octaves and three octaves above bottom C. This completes the adjustment of the VCO. Next month’s article will describe the circuit of the voltage-controlled filter (VCF). This is an exponential voltage controlled, multimode filter with four functions and variable Q-factor. M market elektor november 1977 — E 15 Microprocessor 'Hands-on' development system Designed around the National Semiconductor SC/MP, eight-bit microprocessor, this development system - SCRUMPI - which has been designed and developed by Bywood Electronics Ltd., provides a self-contained low-cost system for the engineer or student who whishes to obtain ‘hands-on’ experience of using and designing with microprocessors. Mounted on a single printed-circuit board, the system costs only £ 55 which, it is claimed, is more than price- competitive with any other similar system. Microprocessor addressing In ‘Scrumpi’, the states of the 12 address lines and the eight data lines are displayed in binary form on light-emitting diodes driven by C.M.O.S. buffers. The data lines can be taken to ground by eight programming switches. The memory consists of two 256 x 4 bit memory chips, providing 256 words of read/write memory. Two four-bit latches act as an eight-bit I/O port in which each set of four can be wired as either inputs or outputs. The various functions of the kit are controlled by a flip/flop, a 555 timer and NAND gates, which are selected by eight toggle switches: RESET; SLOW; STEP; RUN/HALT; PROTECT; SENSE-A; SENSE-B; and LOAD. Scrumpi is programmed by stepping or running the micro- processor to the required address, putting the eight data switches to the required eight-bit binary value, and then operating the load switch. This switch puts the memory chips into read mode and so loads the value on the data bus into the memory location. All parts are supplied in the kit including sockets for all ICs. The switches are soldered to the board by their terminals. The circuit needs a power supply of +5 and - 7 volts and these can be derived from a single 12 volt supply with a five volt Zener diode. Comprehensive instructions and operating data are provided with Scrumpi along with operating details for the SC/MP micro- processor. Bywood Electronics Ltd., 68 Ebherns Road, Heme I Hempstead, Herts, HP3 9QR, England (571 M) 8085 Design kit Intel have just announced a new design kit based on their recently announced 8-bit microcomputer, the 8085. Known as the SDK-85, the prime purpose of the kit is to provide a means for engineers to evaluate and become familiar with the 8085 microcomputer. It is also very useful for building prototype systems and for one-off applications. Since the SDK-85 is a complete system incorporating on-card 24-key keyboard input and a 6-digit 7-segment LED display output, it will also be popular with computer exper- imenters and hobbyists. The kit (see block diagram) contains a 1.3 nsec cycle time 8085 epu; an 8355 providing 2 K bytes of program memory (containing the system monitor) and two programmable I/O ports; and an 8155 which, in addition to providing 256 bytes of read/ write memory, also adds a pro- grammable 14-bit timer and a further two programmable I/O ports. A new chip, 8279, is used in conjunction with two 8205 1 of 8 decoders to provide direct interface to the on-card keyboard and display. As supplied, therefore, the SDK-85 has 2 K bytes of PROM, 256 bytes of program memory and no fewer than 38 general- purpose TTL level parallel I/O lines. A serial port is implemented using the SID and SOD lines of the 8085 with software generated timing. This is set for 20 mA current loop and 110 baud enabling direct connection to a standard teletype, although the system can be operated without a teletype. The SDK-85 has been designed with user expansion in mind; not only has a large (45 sq.in.) wire wrap area been provided, but the circuit provides for a number of additional chips if required. An extra 8155 and 8355 can be added to double the on-card program memory, read/write memory and parallel I/O capa- bility. There is also space for 8212 and 8216 bus drivers, should it become necessary to provide off-card bus driving capability. The keyboard has 16 hexadecimal keys, four of which serve a dual purpose, and eight special- function keys such as vectored interrupt, single-step, go, substitute memory and examine memory. The on-card monitor provides a number of general- purpose utilities and supports the keyboard/LED I/O in addition to a teletypewriter, using standard Intel monitor commands. INTEL Corporation (UK) Ltd., 4 Between Towns Road, Cowley, Oxford OX4 3NB, England (572 M) Versatile data cassette terminal The Model MFE5000 cassette terminal, which is now available from Data Dynamics, is manu- factured in America by the MFE Corporation of New Hampshire. It is an ex- tremely reliable unit that has been designed to fit into a wide variety of data processing and data capture systems. As with any system employing a combination of electronic and mechanical components, it is usually the mechanical side that is the most prone to failure. To combat this, and to ensure that the MFE 5000 performs reliably in the field, a tried and tested tape transport system has been used. This is the Model MFE 250b, of which more than 20,000 units have been sold worldwide. Much of the reliability of the tape transport mechanism is due to the complete absence of any pulleys or belt drives. The internal microprocessor controls the cassette transport and implements all commands to the system. In addition to forcing the operator to perform only legal operational sequences, it also implements all the internal self- checking such as parity, read- after-write and cyclic redundancy check (CRC). The Model 5000 can be switched for either an 86 or 138 character block length and is totally ANSI and ECMA compatible. Interface to the system can either be CCITT V24 (EIA RS-232C) or TTY current loop, so that the unit can either function as a terminal replacement or can be connected directly to a terminal for off-line data preparation. Communications rate is switch selectable to any one of six speeds from 1 10 to 2400 baud. Charac- ter length is 1 1 bits at 1 10 baud and 1 0 bits at all other speeds. Transmission can be either half or full duplex and is asynchro- nous serial bit-by-bit character. Each 300 ft. long cassette will store up to 221,000 characters which are recorderd at 800 bits per inch using a single track and phase encoding to ANSI/ECMA specifications. Operator controls are provided for read, write, initialize, fast forward, rewind, auto-program search and edit. There are also thirteen remote control functions which arc implemented by ASCII control characters; these are: start and stop read, start and stop write, erase, rewind, load point, search, status, skip, back- space, reset and cancel. There are many other functions that can also be implemented if desired. Other features in the compre- hensive specification for this unit include adjustable carriage return delay, automatic source control, binary data read, and front panel indicators for ready, busy, end of tape and ‘data’ (illuminates when data is either being sent or received). Data Dynamics Ltd., Data House, Springfield Road, Hayes, Middlesex, England BLOCK DIAGRAM OR THE I NTEL S0K-8S ■ Jifil: (573 M) 0 0 ® Greenway Electronic Components