December 1976 40p B £ a Ifc "T' i B | ^ 12-02 — elektor december 1976 elektor decoder What is a TUN? What is 10 n? What is the EPS se 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: - '74V 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 - THJSr'or 'DUGMDiode, Universal, Silicon or Germanium respectively) stands for any diode that listed in Table 2. - 'BC107B', 'BC237B', 'BC547B' all refer to the same 'family' of almost identical better-quality general, any other member of the same family can be used instead. (See below.) For further information, see 'TUP, TUN, DUG, DUS'. Elektor 20. p. 1234. Table 1. Minimum specifications for TUP (PNP) and TUN (NPN). v CEO,m 'C,max hfe.min p tot,ma> 20V Some 'TUN s are: BC107, BC108 and BC109 families; 2N3856A, 2N3859, 2N3860, 2N3904, 2N3947, 2N4124. Some 'TUP'S are: BC1 77 and BC178 families; BC179 family with the possible exception of BC1 59 and BC179; 2N2412, 2N3251, 2N3906, 2N4126, 2N4291 , Table 2. Minimum specif ications for DUS (silicon) and DUG (germanium). DUS DUG VR,max If, max p tot,max 25V 100mA IpA 250mW 5pF 20V 35mA 100p a 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.-3). 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"” n (nano-) « 10"* M (micro-)- 10"* m (milli-l = 10" 5 k (kilo-) - 10 3 M (mega-) * 10* G (giga-) = 10 9 A few examples: Resistance value 2k 7: this is 2.7 kn. or 2700 S2. Resistance value 470: this is 470 n. Capacitance value 4p7: this is 4.7 pF, or 0.000 000000 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 circuits are generally listed under the heading 'Missing Link' at the earliest opportunity. ei.eHTor - Volume 2 BBBB Number 12 Editor Deputy editor Technical editors Art editor 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 Mrs. A. van Meyel UK editorial offices, administration and advertising: 6 Stour Street. Canterbury CT1 2XZ. Tel. Canterbury (02271 - 54430. Telex: 965504. Bank: Midland Bank Ltd Canterbury A/C no. 11014587, Sorting code 40 16-11, giro. no. 3154254. Assistant Manager and Advertising : R.G. Knapp Editorial : T. Emmens 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 to all countries by surface mail at £ 0.55. Single copies by air mail to all countries are £ 0.90. Subscriptions for 1977 (January to December inclusive): to UK addresses and to all countries by surface mail: £ 6.25, to all countries by air mail £11,—. All prices include p 8i p. Change of address. Please allow at least six weeks for change of address. Include your old address, enclosing, if possible, an address label from a recent issue. Letters should be addressed to the department concerned. 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, addressed envelope. 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 text 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 and articles published in Elektor are copyright and may not be reproduced or imitated in whole or part without prior written permission of the publishers. Patent protection may exist in respect of circuits, devices, components etc. described in this magazine. The publishers do not accept responsibility for failing to identify such patent or other protection. National advertising rates for the English edition of Elektor and/or international advertising rates for advertising at the same time in the English, Dutch and German issues are available on request. Distribution: Spotlight Magazine Distributors Ltd. Spotlight House 1, Bentwell Road, Holloway, London N7 7AX. Copyright © 1976 Elektor publishers Ltd — Canterbury. Printed in the Netherlands. contents selektor 1 209 thermometer 1212 If one is to keep up with the Joneses — or, better still, beat them to itl - now is the time to install a digital thermometer in the living room. Preferably one using seven-segment LED displays. missing link 1218 snooze-alarm-radio-clock 1219 Although most readers of technical magazines will have had a surfeit of digital clocks by now, we feel that the design given here may still be of interest. The integrated circuit (Fairchild type 381 7 D) is quite cheap, and it can be used as (snooze) alarm clock, radio alarm clock, stopwatch or time switch, to name a few possibilities. All the components will fit on a single small printed circuit board. parking meter alarm — J. Schmitz 1224 in most large towns and cities the parking meter is a very familiar sight. If one is careful parking is still relatively cheap, but if one forgets to get back to the 'mechanical wonder' before it gets hungry again, one runs the risk of making a large donation to the city treasury. By letting you know when your time is just about up. the little unit described here can pay for itself in one go. ejektor 1226 Class-B output stages without quiescent current (adjustment). drill control 1228 There are two basic types of speed control for electric drills. The most common type simply reduces the power to the drill to obtain a lower speed; this has the disadvantage that the speed of the drill depends on the load. A more sophisticated type uses some form of feedback to hold the speed more or less constant at the required number of revs. The control described here is of the latter type. transistors (data) 1231 cumulative index '76' 1232 tup/tun/dug/dus (data) 1234 seven-segment to BCD converter 1235 phasing and vibrato 1236 In this article some applications of the analogue shift register type TDA 1022 are described, including a phasing and vibrato unit. Elektorscope (part 1) 1244 The Elektorscope is a dual-trace general purpose oscilloscope for the home constructor. In this design the accent has been placed on reliability, ease of construction and simplicity of operation, rather than on elaborate facilities that will rarely be used and extremely high performance circuits that the home constructor has not the equipment to calibrate. To simplify wiring, the oscilloscope is of modular construction, with Y amplifiers and timebase that plug into a motherboard containing most of the interwiring. sirens 1254 Sound effects are always popular. One of the most popular effects for ’livening up' disco-shows, films, etc., is the (police) siren. The crime series on TV have taught practically everybody the difference between the European two-tone siren and the banshee wail of the American version. The circuit described here can produce either sound. market 1256 12-12 — elektor december 1976 thermometer VlUMiliUlAIlL Digital displays are becoming quite popular — even though they sometimes consist of little more than numbers painted on a rotating drum. . . This particular type of display is beneath the dignity of the electronics enthusiast, of course. If one is to keep up with the Joneses — or, better still, beat them to it! — now is the time to install a digital thermometer in the living room. Preferably one using seven-segment LED displays. The next step is to convert this voltage into a corresponding number of pulses in a ‘voltage-to-frequency convertor’ (block B). An even better description might be *voltage-to-pulse-train con- vertor’. Finally, these pulses are counted and the number of pulses is displayed on two seven-segment LED displays (block C). Temperature-to-voltage Either a normal silicon diode or a silicon transistor can be used as temperature sensor. The transistor should be wired as shown in figure 2. In both cases, the voltage drop across the device depends on the temperature. When a constant current is passed through either device, It is not at all surprising that digital displays are becoming increasingly popular. Admittedly, there is a certain element of novelty; but the main reason is that they provide a clearly legible display. The thermometer described here is a good example of this: it is much easier to read than the conven- tional mercury type! The temperature is displayed in whole numbers of degrees, so the maximum error is ± 0.5°. Originally, the unit was intended for measuring in degrees Centigrade and the measuring range was chosen to suit the domestic environ- ment: 5° . . . 50°C (41° . . . 1 22°F). However, it is a relatively simple matter to convert it to the Fahrenheit tempera- ture scale. This has the additional advantage that it will then measure to below the freezing point (measuring range 5° . . . 99°F), so that it can also be used for measuring the outside temperature. The temperature sensor can be connected to the display unit via almost any length of cable. The basic principle The unit consists of three distinct sections (figure 1 ). The first is the temperature sensor proper ( a silicon diode) with some associated electronics. This is what could be called a ‘temperature-to- voltage converter’ (block A). thermometer elektor december 1976 - 12-13 Figure 1. Block diagram of the thermometer. The temperature sensor is a normal silicon Figure 2. It is also possible to use a silicon transistor as temperature sensor, connected as shown here. If the connection to the rest of the circuit is longer than 2 ft. (50 cm), twin-core screened cable should be used. Figure 3. The temperature-to-voltage con- vertor. The determining factor for the re- liability of the thermometer is the stability of the reference voltage V re f. This voltage (7.1 V) is derived from the very stable voltage reference source in the 1C in the power supply. Figure 4. Conversion characteristic of the temperature-to-voltage convertor. The lower limit of the output voltage is determined by the characteristics of the opamps; it cannot go much below 100 mV. Photo 1. The prototype temperature sensor consisted of a transistor glued into the end of a length of plastic tubing. This makes the unit sufficiently water-tight for use in aquaria or out-of-doors. the voltage drop varies almost linearly with (absolute) temperature. This means that if the voltage drop corresponding to the first 273 K is subtracted from the total drop, the resulting voltage is proportional to the temperature in degrees Centigrade. Just what the doctor ordered! This part of the circuit is shown in fig- ure 3. D4 is the sensor - this can be either a diode or a transistor, as men- tioned above. As stated earlier, a con- stant current must be passed through this diode. The first opamp (Al) and transistor T3 are used as a constant current source. A reference voltage is applied to the non-inverting input of the opamp and the voltage at the emitter of T3 is applied to the inverting input. The circuit will now maintain a constant voltage at the latter point, and since this voltage appears across a constant resist- ance (R8), the current through the resistor must also be constant. With the component values shown, this current - which also flows through the diode - is fixed at approximately 0.5 mA. The other three opamps together form a high-performance differential amplifier, the gain of which can be preset with P3. The sensor diode D4 is connected to one input (pin 5 of A3); a constant L scember 1976 - 12-15 7 voltage, set with P2, is applied to the other input (pin 10 of A2). This second voltage is the drop which corresponds to the first 273 Kelvin. It is now possible to set P2 so that freezing point corre- sponds to 0 V at the output. If the gain of the opamp is set correctly, a tempera- ture variation of 50°C will correspond to an output voltage variation of 10 V, as shown in figure 4. Vo Itage-to-pu Ise-train This part of the circuit is shown in figure 5. Its function is to produce a series of pulses, whereby the number of pulses correspond to the output voltage from the preceding circuit. Each measuring cycle is initiated by a reset pulse from A5. This opamp produces one pulse every 2 seconds, so the final temperature reading is up- dated at two-second intervals. If re- quired, a different interval can be set by changing the value of Cl . For a proper understanding of the circuit, it is essential to realise that the integrated circuit used here (the LM3900) contains four Norton-type opamps. The input stages of these opamps can be considered as transistors with the emitter connected to supply common. This means that they must be current- driven, and so a resistor is included in series with all the inputs in this circuit. Each measuring cycle now proceeds as follows. At the moment that the output from A5 becomes ‘high’, current Hows through R9 and D4 into the inverting input of A7, causing its output voltage to drop to almost 0 V. C3 is discharged. Since the output of A7 is now practi- cally zero, the current through R 1 1 will be less than the current through R12 and the output of A8 will also drop to 0 V. This output is used for blanking the display during the reset and count cycle. After a very short time (5 ms), the output of A5 becomes ‘low’. Diodes D2 and D3 are both blocked now, so the second oscillator (A6) is enabled. This multivibrator produces short positive pulses at two-millisecond intervals. The width of the pulses can be set with PI ; they will normally be approximately 25 ns ‘wide’. Each positive pulse from A6 causes a fixed current to flow through RIO for the duration of the pulse. Opamp A7 will drive an identical current through C3 during this period. A fixed current flowing into a capacitor for a fixed period corresponds to a specific voltage rise across the capacitor. This means that the output of A7 will increase in a series of steps: each rise from one level to the next corresponds to one output pulse from A 6 (see figure 8). When the output from A7 rises above the DC voltage applied to input ‘A’, the output of opamp A8 will change from zero to almost full supply voltage.This voltage is passed through diode D2 to block the multivibrator. The result of all this is that a series of pulses appears at the ‘Hz' output, the number of pulses being proportional to the voltage at the ‘A’ input. This pulse train is repeated once every two 2 seconds .These pulses can be counted and displayed as ‘temperature’. Pu Ise-trai n-to-d isplay The counter and display unit is shown in figure 6. This is a standard TTL circuit. The only unusual feature is the interface: the 15 V outputs from the preceding stage must be converted to the standard 5 V level for TTL. This function is performed by a single CMOS integrated circuit, type CD4050. It contains six buffer stages that are ideal for the purpose, and it has the added advantage that it only requires a single supply voltage (5 volts). The reset pulse that starts the count cycle in the preceding stage is also used to reset the counters (IC3 and IC4). At the same time, the blanking pulse turns off the display until after the count is completed. Construction and adjustment The design itself is not at all critical, so ’Ml 't&L J 12-16 — elektor december 1976 thermometer Parts list for figure 9 R2.R9.R1 1 = 1k5 R3 = 4k7 R4 = 1 k2 R5-i n R6.R7.R8 = 6k8 RIO = 18 k R12 . . . R17 = 100 k R18 = 2k2 P1,P3 = 1 k (preset! P2 = 470 n (preset) Capacitors: Cl ,C2,C4 = 100 p/16 V C3 = 1000 p/16 V C5 = 470 p C x — 1 0 n Semiconductors: D1 ,D2 = 1N4001 D3 = 15 V/1 W zener diode D4 = 1 N4148 or TUN (see text) T1 = BC547B, BC107B T2 = BD135 T3 = BC109C IC1 = 723 (DILI IC2 = LM324 Sundries: FI =100 mA fuse, slow blow Trl = 9 . . . 1 2 V/700 mA trafo B1 = 40 V/400 mA bridge rectifier cooling fin for T2 the components can be mounted on the board without need for any special precautions. If the whole unit, including the j temperature sensor, is built into a box, care must be taken to ensure that all components that get warm (trans- former, power supply and displays) are kept well away from the sensor. However, the sensor does not have to be mounted inside the box. For distances up to one or two feet, twisted wires can be used for the connection; if the distance Ls greater, twin-core screened cable should be used as illustrated in figure 2. It is advisable to mount a contrast- enhancing filter in front of the displays. In spite of its long name, this is nothing more than a small sheet of red plastic. To calibrate the unit, it is best to use a (cheap) multimeter. The procedure is then as follows: elektor december 1976 - 12-17 thermometer Resistors: R1,R6 - 2M2 R2,R6,R1 1 ,R12 = 1 M R3.R7 - 150 k R4 - 10 k R8 - 2k2 R9 = 1k2 RIO -22 k R13.R14 = 1 k R1 5 . . . R28 - 180 n PI - 10 k (preset) maim Capacitors: Cl = 10 p/16 V C2,C X = 10 n C3= 100 n (see text) C4 = 10 p/10 \/ Semiconductors: D1 . . . D5 - 1N4148, DUS I Cl = 3900 IC2 = CD4050 IC3.IC4 = 7490 IC5,IC6 = 7447 DPI ,DP2 = common-anode seven-segment display, such as HP5082/7750. For pin- compatible equivalents see Elektor 3, page 451 . Figure 8. This simplified timing diagram I illustrates the operation of the voltage-to- pulse-train convertor. Note that neither the output voltages of the opamps nor the time scale are shown in true proportion: the diagram has been 'distorted' for the sake of Figure 9. Printed circuit board and com- ponent layout for the temperature-to-voltage convertor and the power supply (figures 3 and 7). (EPS 9755-11. Figure 10. Printed circuit board and com- ponent layout for the voltage-to-pulse-train convertor and the counter/display unit I figures 5 and 6). (EPS 9755-2). - before switching on for the first time, it is advisable to remove all ICs except IC1 from the circuit. Failing this, start with PI in the power supply in the mid-position. - adjust the TTL supply voltage (pin 3 of IC1) to 5 V, using PI. Switch off again, and plug in the other ICs. - connect the multimeter to the output of A4. Submerge the (insulated!) temperature sensor in a glass containing a mixture of water and ice cubes. Adjust P2 so that the meter just reaches its lowest reading (approximately 0.1 V). The idea is that this adjustment is “just on the verge’: turning P2 even a fraction anti-clockwise should cause a sudden increase of the voltage, whereas turning P2 clockwise should have little or no effect. - let the temperature sensor warm up to a much higher temperature — preferably warm water at 50 C. Adjust P3 until the corresponding voltage is measured: for 50 C this should be 10 V, or for room temperature (20°. . .22°C) it should be 4.0. . .4.4 V. This adjustment is not particularly critical - any error will be compensated for further on. - finally, adjust PI on the display board (not the power supply!) so that the display registers the correct temperature. If no multimeter is available, it is still possible to calibrate the unit as follows: - Before swiching on, set PI in the power supply to the mid-position. This should be sufficiently accurate. — submerge the sensor in a glass containing a mixture of ice and water, and adjust P2 so that the display just reaches its lowest count (this will usually be either ‘1’ or ‘2’). — v/ith P3 in the mid-position, adjust 12-18 - elektor december 1976 lissing link PI on the display board so that a higher temperature is correctly indicated. - the measuring range should now be from just above freezing point to approximately 70°C. If the upper limit differs widely from this (if it is, say, 55°C or 100°C) P3 should be adjusted to a different setting; after the display has been readjusted with PI, the upper limit can be checked again. Repeat this until the upper limit is somewhere between 60 C and 80°C. If a temperature indication in degrees Fahrenheit is required, the adjustment procedure is rather more complicated: - first set the TTL supply voltage at 5 V, according to one of the procedures described above. - increase the value of C3 in the voltage-to-pulse convertor (i.e. near A7) to 150 nor 180 n. - set P3 in the mid-position and P2 somewhat anti-clockwise from the mid-position. Place the temperature sensor alternately in a glass with ice water and a glass of warm water (at a temperature of 70° . . . 90°F). Allow the reading to stabilise properly after each change of tem- perature and adjust PI on the display board until the temperature differ- ence is correctly indicated. For instance, with the ice water at a temperature of 32°F and the warm water at 82° F, the temperature difference is 50°F. If the indication in the ice water is, say, •45°F’, PI should be adjusted until the reading in the warm water is *95°F’. - place the sensor in the glass containing a mixture of water and ice, and adjust P2 until the display reads 32°F. - if a multimeter is available, check that the output voltage of A4 is now somewhere between 3 V and 4.5 V (with the sensor still submerged in ice water). If this is not the case, try a different setting of P3 and repeat the whole procedure. - alternatively, if no multimeter is available, check that the maximum temperature that can be displayed with reasonable accuracy is some- where between 105° and 125 F. Note that the first d^it is not dis- played. of course:' 110 ’, is displayed as ‘10 . If the maximum tempera- ture is well outside either of these limits, try a different setting of P3 and repeat the whole procedure. H Modifications to Additions to I mprovements on Corrections in Circuits published in Elektor Albar Novem ber 1 976, E 1 9, page 1110 While testing the Albar with several different types of US transducers, it was discovered that by making several minor circuit changes the unit’s overall sensiti- vity can be greatly improved. Therefore the following changes should be made: R12 = short circuit connection D1 = deleted R3 = 4k7 R4 = 2k2 R6 = becomes a 3.3 mH coil (Toko 0812-332) RS = lk2 for Murata transducers and 2k7 for Valvo units. PI = replaced by a 1 k (lin) pot, moun- ted on the back panel of the Albar. R 1 = changed to a 220 k or 250 k preset pot. Adjustments: Set R1 to mid-range, adjust PI so there is 2.6 V DC on the emitter of T3. Monitor this voltage for a few minutes, if it drops away or becomes unstable, lower the resestance of Rl. Repeat this process until this voltage is stable. Pocketronics In many of the ‘pocketronics’ projects in both past and future issues of Elek- tor, there is a need for a small audio transducer. The Sennheiser HM35, which is usually specified, works very well but it may be just a little expensive for some people. An alternative transducer is a cheap ear- phone of the type usually supplied with inexpensive transistor radios. Due to the shape of the air passage these devices don't give much audio power output, however, and if the top is pried off all the pieces fall out. The solution is to apply a small amount of glue to four spots around the outside of the diaphragm. This keeps everything in place and the unit will have a fair audio output. The idea is illustrated in the drawing. A further point is the impedance re- quired. In the various circuits, several different values are given. In practice any value between about 500 £2 and 1 k will be suitable; in some circuits lower values are also permissible. Sensitive metal detector November 1976, El 9, page 1116. It has been discovered that the Murata , filter (FL1 = SFD455) can be installed in two different directions on the pcb. 1 Only one way is correct. For correct I positioning, Murata put a small ‘dot’ or I bump on the top of the filter’s plastic I case. This dot should be located at the I end of the filter nearest to Cl . Transistor T3 is shown reversed in I figure 4. For proper connection, the transistor should be rotated 180°. The p.c. boards supplied by the EPS I service are correct. It has also been brought to our atten- 1 tion that a license is required when using heterodyne metal detectors inside I the UK. Almost every metal detector, including the Elektor design is of the heterodyne type. Furthermore, operation of metal detec- tors in the UK is restricted to frequen- cies between 16 kHz and 150 kHz. This means that the VFO in this design must operate between 45.5 and 136.5 kHz. The search coil dimensions should be , adjusted accordingly: the number of ' K turns will have to be drastically increased. License applications should made to: | The Home Office Radio Regulatory Dept Waterloo Bridge House Waterloo Road London SE1. Pinning BF494 The transistor list in El 7, p.947 shows I the pinning for the BF494 according to I the ‘official’ Pro-Electron publication. I This has proved to be incorrect: the correct pinning is shown in the list on I page 1231 in this issue. Although most readers of technical magazines will have had a surfeit of digital clocks by now, we feel that the design given here may still be of interest. The integrated circuit (Fairchild type 381 7 D) is quite cheap, and it can be used as (snooze) alarm clock, radio alarm clock, stop- watch or time switch, to name a few possi- bilities. All the components will fit on a single small printed circuit board. The 3817 D has the major advantage that it can drive the display direct - no buffer transistors are required. Either LED or liquid crystal displays can be used; in the design described here, 7-segment LED displays are used, since they are more rugged. Since the basic principles of a digital clock have already been described many times, this article will only deal with the construction and possible applications of the clock. The connections to the IC are shown in ' figure 1 , and figure 2 gives the complete circuit diagram. The 50 Hz (or 60 Hz) mains frequency is passed through a simple interference filter (Rl/Cl) to drive the clock. For 50 Hz operation, pin 36 must be connected to the positive supply; for 60 Hz operation this pin is left floating — an internal \zm Wi"' : '•-••>£3 r ’ i> 12-20 — elektor decern ber 1976 snooze-alarm- radio-clock Figure 1. Pinning of the 381 7D. Figure 6. Printed circuit board and com- ponent layouts for the clock IEPS 9500). Figures 6a and 6b: copper layout; figures 6c and 6d: 12-hour version with Fairchild FND500 display; figures 6e and 6f: 24-hour version with Hewlett Packard HP5082-7760 display. Note that either type of display can be used for either version. ‘pull-down’ resistor then holds it at ‘low’ logic level. The power supply for the displays is connected to a seperate pin on the chip (pin 23). For normal operation, this pin can simply be connected to the same supply as pin 28. However, care must be taken to ensure that the display drivers cannot be overloaded. The maximum dissipation per output is 25 mW and the maximum current is 8 mA. A simple and adequate solution is to drop the excess voltage across a simulated zener diode (Tl/Dl) in the common cathode return. Pin 37 can be used for display blanking. The displays are ‘on’ when this pin is connected to the supply. In this case, there is no ‘pull-down’ resistor on the chip, so R2 has to be added if the blanking option is required. This option can be useful if the clock is to be run on batteries: the wire link on the board between pin 37 and positive supply is replaced by a pushbutton. Of course it will be necessary to add a crystal timebase or something similar if battery operation is considered. The clock can be set to run in either a 12-hour or a 24-hour mode. The 12-hours mode is selected by omitting the wire link between pin 38 and the positive supply .The difference between !~b elektor december 1976 - 12-21 Parts list. Resistors: R1 = 100 k R2 = 100 k (only if blanking is required) R3 = 4k7 R4 = 33 k R5 = 390S2 (see text) R6 = 4k7 (24-hour version only) R7 = 27012 (24-hour version only) Capacitors: Cl - 10 n C2= 1 000 m/25 V Semiconductors: T1 = BC141. 2N3553 T2, T3 - TUN T4 • TUP (24-hour version only) 01 - 12 V/IOOmW zener 02 = IN4002 D3. D4= LED (3mm) D5, D6 « DUS (24-hour version only) B = bridge rectifier BY164 DPI . . . DP4 = HP5082-7760 or FND500 IC1 = 381 7D Sundries: Cooling fin for T1 Tr = transformer, 12 V/300 mA secondary Re = relay, 1 2 V, >60012 SI . . . S4 = single-pole pushbutton 55 = selector switch, 5-way 56 = change-over switch 57 = single-pole switch the two modes will be discussed later. As the circuit diagram shows, all displays are driven individually - the segment drive outputs are not multi- plexed. This will often prove to be an advantage. However, since the maxi- mum drive current per segment output is only 8 mA, even this continuous operation will not produce a particu- larly bright display. High-efficiency LED displays are advisable, and the Hewlett Packard types proved to be the most suitable. The Fairchild displays are shown as an alternative, since the 1C is sometimes supplied complete with these displays. The printed circuit board is designed to accomodate both alternatives. The connections to the left-hand display (tens of hours) are rather unusual. For operation in the 12-hour mode, this display is connected as shown in figure 4. The ‘b + c’ output causes the two right-hand segments to light for 10, 11 and 12 o’clock. The upper left-hand segment (‘f’, see figure 3) lights to indicate ‘AM’, and the lower left-hand segment (‘e’) indicates ‘PM’. For operation in the 24-hour mode, the first display is connected as shown in figure 5. The ‘1Hz’, ‘AM’, ‘PM’ and ‘b + c’ outputs now produce a ‘O’, ‘1’ or ‘2’ as required. elektor december 1976 snooze-alar m-radio-clock Leds D3 and D4 are connected to the positive supply in the 24-hour mode. The value of R5 may have to be altered slightly to obtain the correct brightness. In the 12-hour mode it is also possible (not essential!) to connect these LEDs to the T Hz' output so that they flash on and off in a 1 Hz rhythm. The value of R5 should not be less than 270S2 in that case, however. Operation With switches S 1 . . . S4 all open and S5 in position 1 , the clock is in the normal time-keeping mode. Switches SI and S2 are for slow and fast setting of the clock. S5 is used for selecting the display mode. As stated above, position 1 is the normal mode where the time is dis- played in hours and minutes. In position 2, the units of minutes are displayed on DP2 and the seconds on DP3 and DP4. Position 3 of S5 is used for setting the alarm. The alarm time is displayed in hours and minutes; it is set in the same way as the clock itself, using SI and S2. The alarm can be reset to 12.00 hrs. (12-hour mode) or 00.00 hrs. (24-hours mode) by operating SI and S2 simul- taneously. After setting the alarm, S5 is returned to position 1. When the alarm time is reached, a DC buzzer can be turned on via T2. Alternatively, with S6 in the other position, T3 operates a relay which can be used to switch on a radio. ^ The alarm can be turned off by pushing either S3 or S4. S4 turns it off com- pletely; S3 is the ‘snooze’ position: if , the alarm is silenced with this button, it will sound again after 1 0 minutes. In the week-end, for instance, the alarm can be put out of action entirely by setting SS to position 5. This does not alter the | setting of the alarm time. The radio can be switched on by operating S7, for music-while-you-make- the-bed ... It can also be used as an alternative to sleeping pills. For this, S5 is set to position 4 and SI and S2 are used to set the number of minutes that the radio is to stay on. S5 can then be snooze-alarm-radio- clock elektor decern ber 1976 — 12-23 switched back to position 1 . The radio will now be turned off automatically after the alotted time; if it becomes desirable for some reason (a change of program, for instance) to switch it off sooner, S3 can be operated briefly. Table 1 summarises the various possible operating modes. Construction A double-sided printed circuit board is used (figure 6). There are several differences between the 1 2-hour and the 24-hour version, but these are clearly marked on the component layout and in the parts list. It is advisable to use a socket for the 1C. In any case, it should be the last component that is mounted on the board. The buzzer should be suitable for operation on 15 V DC, and it should not draw more than 100 mA. T1 must be adequately cooled. If the radio is mains operated, the relay should be mounted inside the radio as shown in figure 7. If it is battery operated, the relay can be mounted inside the clock as shown in figure 8. Obviously, the relay contacts should be suitable for the currents and voltages that it will have to switch. Figure 2. Complete circuit of the clock. Figure 3. The seven segments of a display are indicated by the letters a . . . g. iXiliiLlXLL; LiLT.Ul LlUiliil J. Schmitz In most large towns and cities (for that matter, in many small ones as well!), the parking meter is a very familiar sight. Installed in both likely and unlikely places in an attempt to alleviate the problem of insufficient parking spaces and at the same time, as profitable (?) sideline, to raise a little money which can then be spent on more 'no-parking' signs, the parking meter seems to be becoming a status symbol for progressive communities. If one is careful parking is still relatively cheap, but if one forgets to get back to the 'mechanical wonder' before it gets hungry again, one runs the risk of making a much larger donation to the city treasury. By letting you know when your time is just about up, the little unit described here can pay for itself in one go. The device is programmed by three switches which set the time interval between 15 and 105 minutes, and it will sound an alarm when the preset time has elapsed. The alarm sounds for about 2 minutes and consists of a series of beeps and a flashing LED. The circuit To minimise power consumption, MOS ICs were used. Gate N2 and inverter N9 are used as the clock pulse generator circuit. This oscillator must be adjusted to an output frequency of about 2.5 Hz. This signal is then divided by a 14 stage binary counter (CD4020). The binary division outputs 2 12 , ,2 13 and 2 are available on pins 1, 2 and 3 respectively. These outputs are connected to NAND gate N1 via the three time program switches. parking meter alarm p Parts list for figures 1 and 2. Resistors: R1,R4= 1 M R2= 2M2 R3 = 220 k R5 = 68 k R6 = 1 00 PI = 250 k preset Capacitors: Cl = 1 n If C2 = 470 n Ip C3 = 3n3 Semiconductors: D1.D2 = DUS D3 = LED I Cl = CD4023 IC2 = CD4049 IC3 = CD4020 Sundries: SI . . . S4 = miniature SPOT switches Audio transducer = modified 1 k* earphone or a Sennheiser HM35 microphone capsule. Battery = 3 x 1 .2 V miniature mercury. * See this month's 'missing link'. When the unit is first switched on a I short reset pulse is applied to the: CD4020, resetting all the outputs to zero. If the switches are set as shown in| j the circuit diagram, pins 2 and 8 of gate N 1 are held high and the third input to U N1 is connected to the binary 2 13 out- 1] put. When this output goes high the alarm 1 ) | will sound. The time (T) required for this pin to go high depends on the clock frequency (f)| as follows: For f = 2.5 Hz, the time is approxi- mately 820 seconds, or 13 minutes] i 40 seconds. The times for various switch settings are! given in table 1 . Once this pin is high, and since the, i other two were already high, the output, j of gate N1 is low. Therefore the output elektor december 2' 7 CD4020 IC3 N3=CD4023 •N9=CD4049 e 1. Circuit of the 'pocketronics' parking r alarm. An audible and visual warning is after a programmable preset interval. layout for the alarm. (EPS 94911. of N4 is high, and this enables gate N3. The other two inputs of N3 are the clock frequency and a tone source (gate N3 and inverter N6). Once gate N3 is enabled this tone is gated on and off by the clock frequency. This gated signal is fed to two inverter amplifiers, N7 and N8. They are used to drive a LED and a small audio transducer. A discrete AND gate (D1,D2 and R4)is used to switch off the alarm after a short time. The parking meter timer can be reset by switching the main on-off switch (S3) to the off position and then back to on. When the unit is not in use it should be switched off. To test and adjust the circuit, the three time program switches should first be put in the up position (connected to the battery). This should cause the alarm to sound and the LED to flash for just under 2 minutes. PI is used to adjust the clock pulse frequency, which should be set at 2.5 Hz. This frequency is important, and a small error in adjustment can cause large timing inaccuracies. If no frequency counter is available, the program switches should all be set in the ‘up’ position, so that the alarm sounds as soon as the unit is activated. The alarm should sound for 1 minute and 42 seconds. If not, PI should be ad- justed for that time. K 12-26 - elektor december 1976 Class-B output stages without quiescent current (udjustment) It is not so easy to dream up a circuit for a high-quality class-B output stage without quiescent current. As a compromise, one could consider a circuit where the quiescent current does not have to be accurately adjusted. However, this should not adversely affect the quality of the amplifier (crossover distortion). And this is where the difficulty lies. In Elektor 8 (december 1975, p. 1220) the 'current dumping’ principle pro- posed by Quad was discussed. This prin- ciple is illustrated schematically in figure 1. Basically, there are two amplifiers A and B to drive the load. Amplifier A supplies a current 1(A) to fill the ‘dead zone’ where amplifier B refuses to do any work (1(B) = 0). If required, A can also be used to drive B, but that is not essen- tial to the principle. If angle 0 of figure I can be reduced to (almost) zero, A will only have to supply current in the dead zone. The transistors T1 and T2 in figure 2 form amplifier B. Amplifier A is the differential amplifier which amplifies the base-emitter voltage Vbe by a factor one. The amplifiers are connected to the load Rl via the resistors Rg and Ra, respectively. Let us assume now that a drive voltage Vj is applied between the bases of T 1 / T2 and junction P of figure 2*. As a function of Vj, the currents 1(A), 1(B), and II vary as follows (see figures 1 and 2 ): The current supplied by amplifier B is: KB) = V ‘ p Vbe for |Vj| > |VdI. and K B 1(B) = 0 for -Vd < Vj < Vq (for Vp see figure 1 ). Since the output voltage of A equals Vj), its output current is: If Ra = Rb = R, the total current into the load becomes: IL = 1(A) + 1(B) = . (Note that in the dead zone 1(B) = 0, so Vbe = Vj!). This means that the output current, and thus the output voltage V u , has become independent of Vbe: the nasty charac- teristics of TI /T2 have no further effect. The principle on which the above set-up is based is known as 'adding what is lacking’. For further information see the list of literature. lis is the condition if 'bootstrapping' is . It is not an essential condition, how- it is also possible to refer the drive volt- o supply common. There is, however, a pitfall. Differential amplifier A of figure 2 must operate in Class-A for small signals. So quiescent current is needed after all!! (Remember the fundamental Law of Conservation of Misery . . . ). However, it must be possible to arrive at a circuit which can do without quiescent current adjustment in spite of spreads in diode and base- emitter voltages. An alternative The circuit of figure 3 is similar in some ways to the one already discussed. It is I actually an extension of the circuit I '1/ "U -V_D elektor december 1976 - 12-27 principle used in the Edwin amplifier (Elektor 6, September 1975, p. 910). The output stage comprising T1 . . . T4 must be driven between input and ground, not between input and output, so it is connected as an emitter follower. In this circuit the fact that the IL-Vj- characteristic of an emitter follower is highly dependent on the load resistance Rl_ is used to good advantage. Transistors T1/T2 form amplifier B. The dead zone is halved by including D3. Transistors T3 and T4 are the ‘adding’ amplifier A. D1 and D2 cause a quiesc- ent current to flow through T3 and T4. The sum of the voltage drops across the two resistors R equals the threshold voltage Vd of one diode. For very low signal levels (Vi), only T3 1 and T4 supply current into the load. However, as soon as the input voltage exceeds ± 14Vd T1 and T2 also start to conduct alternately. As the level of the input signal is increased further, T1 and T2 supply more and more current into the load. Under these conditions the current supplied by T3 and T4 does not increase, however: it is limited to approximately Vd/R. This circuit differs from the first sugges- I tion in that both amplifiers (A and B) ; now operate in Class-B. s Since the output stage works as an t . emitter follower, the slope of the I characteristic in the dead zone equals I about — — — . Outside the dead zone, (RL + R) with T1 and T2 conducting, T3 and T4 can be considered as supplying a DC current into the load. The slope is then determined by amplifier B (T1 and T2), so it is about , where S is the Rl + 7T L S slope (mutual conductance) of T1/T2. Both R and ^ can be made much smaller than Rl. This means that the slope of the overall characteristic is practically constant and depends only on Rl. Any remaining imperfections can be ironed out by using overall feedback. Why not? An entirely different approach to the J problem can also be considered. The magnetization curve of recording tape also has a dead zone. It has been , found that h.f. ‘bias' is one method of ‘ reducing the distortion caused by this. (In the early days of recording, DC bias was also tried - but it didn’t work very well . . . ). This might also apply to output stages with a dead zone. Anybody who has heard the sounds coming out of oscil- lating power amplifiers with the quiesc- ent current set to zero will know that they may sound awful — but there is no cross-over distortion! This approach has already been tried in a ‘low-fi’ appli- cation, with good results (‘Loud-mouth’, Elektor 18, October 1976, page 1048). Literature 1. Quadi Complementary, Elektor 8, December 1975, p. 1220. 2. Equin ( 1 ), Elektor 12, April 1976, p. 448. 3. The loud mouth, Elektor 18, October 1976, p. 1048. 4. Precision Electronics (G. Klein and J.J. Zaalberg van Zelst), Chapter 27. (Philips Technical Library). I 12-28 — elektor december 1976 HULL UULtldlL There are two basic types of speed control for electric drills. The most common type simply reduces the power to the drill to obtain a lower speed; this has the disadvantage that the speed of the drill depends on the load. A more sophisticated type uses some form of feedback to hold the speed more or less constant at the required number of revs. The control described here is of the latter type. It is suitable for most electric drills, no matter what their power rating is, although some minor modifi- cations will be required for really high-power drills. be required (T 2 ). The operating point will therefore slide down the curve to point Aj , corresponding to speed n 2 . To keep the speed constant under most load conditions, some form of feedback is required. In the ideal case, the result could be as shown in figure 2. Three curves are shown here, corresponding to three different values of motor current, but there are actually an infinite number of curves between zero and maximum current. Once again we can assume that A i is the off-load operating point. If the load increases, a higher torque is required (T 2 ). Instead of sliding down the 1 1 curve, the operating point is now shifted to the I 2 curve to a point which corresponds to the higher torque at the same speed (A 2 ). In other words, the motor current is increased in such a way that the speed remains constant. A normal electric drill works on alter- nating current. This means that some way must be found to alter the average value of an alternating current. The standard solution is to full-wave rectify it and pass it through a thyristor chop- per. For optimum results, the speed of a drill should be chosen to suit the type of material and the diameter of the drill. For ease of operation, it is desirable that the speed should remain more or less constant independent of the load. Both of these requirements can be fulfilled by using a sophisticated electronic speed control. This has the additional advantage that the drill will always run smoothly, even at low speeds. The existing motor. If a normal electric drill motor is driven with constant current, the torque varies with speed as shown in figure 1 . This is approximately the situation when it is driven either directly from the mains or through a simple drill speed control unit. (Note, however, thet the current does not stay constant in either of those cases: if the speed decreases, the current will increase. This reduces the effect of the load to some extent.) Off-load, the drill will run, say, at speed ni and deliver torque T ( ; this corre- sponds to point Ai on the curve. If the load is now increased more torque will elektor decern be r 1976 — 12-29 I he thyristor is turned on at a specuic point after every zero-crossing, as shown in figure 3. Since the ‘specific point’ corresponds to a certain phase angle, this is called ‘phase angle control’. In the example shown, the average current increases from l! to I 3 as the phase angle decreases from ISO 0 to 45°. It will be obvious that 1 80° corresponds to no current, whereas 0° would correspond to full drive. Motor drive The complete circuit of the motor control unit is shown in figure 4. It consists of a fairly standard thyristor control unit with an extra feedback loop. The basic control unit works as follows. A full-wave rectifier (Dl. . .D4) is connected in series with the motor. This has the advantage that a thyristor can be used for full-wave control. The alterna- tive would have been to use a triac, of course, but this is jnore expensive in the long run. The full-wave rectified AC voltage is passed through R1 to a bridge circuit. This consists of a capacitive branch R2/P1/C1 and a resistive branch R5/P2/R7. The capacitor introduces a phase lag in the first branch; the phase shift depends on the setting of PI . The Darlington transistors T1 and T2 are connected between the two legs of the bridge. When Cl has charged to the point where the voltage on the emitter of T1 is 1.2 V higher than the voltage on its base, this transistor is turned on. This causes both T1 and T2 to go into saturation, triggering the thyristor and discharging Cl. This circuit has the advantages that the hysteresis is very small and that the phase angle can be varied over almost 180°. The portion of the circuit described so far is quite a good drive unit in its own right. However, it is not a control unit in the true sense: it does not maintain a constant speed independent of the load. To achieve this a feedback loop must be added. Motor control A current sensing resistor R8 is included in series with the thyristor. The voltage drop across this resistor is proportional to the current through the motor. This voltage is rectified by D5 and C2, and used to drive T3 through P3, R9 and D6. The simplest way to understand the operation of this part of the circuit is to think of T3 as a voltage-controlled re- sistance. As the load on the drill increases, its speed tends to drop. This causes the current through the motor to increase (the back EMF decreases with the speed), so the voltage across R8 in- creases. This, in turn, causes the base drive to T3 to increase so that the 0 tf V r\ -*W ■ 14 *.- - 12-30 — elektor december 1976 drill control Parti list Resistors: R1 =68 k R2 = 6k8 R3, R5, R7 = 4k7 R4 = 47 k R6 = 1 k R8 = 1 .50 /1 5 W (see text) R9 = 12 k PI = 100 k lin potentiometer, with plastic shaft. P2, P3 = 5 k (preset) Capacitors: Cl = 100 n/100 V C2 = 10 m/25 V Semiconductors: T1 = BC 516 T2. T3 = BC 517 D1 . . ,D4 = 400 V/3A (see text) D5. D6 = DUS Thl = 400 V/3A thyristor (see text) Sundries: SI = single-pole switch. Figure 4. Complete circuit diagram. Figure 5. Printed circuit board and com- ponent layout (EPS 9484). ‘resistance’ of T3 decreases. Provided SI is closed, this decreases the voltage on the base of T1 , causing the thyristor to be triggered sooner. The average current through the motor increases still further, offsetting the tendency for the speed to drop. Note that this system really works with positive feedback! With the component values shown, and provided the alignment procedure is carried out correctly, this will not lead to oscil- lation. However, it can have a slightly disconcerting tendency to over- compensate: under some conditions, increasing the load will cause the motor to speed up! The control loop can be put out of action by opening SI. The circuit will then operate like any normal speed control: the speed can be varied, but it will depend on the load to a much greater extent. Alignment Warning : The alignment procedure 1 should be carried out with due care and J using an insulated screwdriver! The ; entire circuit is connected to the mains. Alignment now proceeds as follows: — Open switch SI: set PI to the maximum resistance. — Adjust P2 until the drill runs at the lowest speed that will be required. Check whether the motor starts I without any problems when it is switched on; if not, readjust P2 slightly until it does. - Turn the slider of P3 to the negative end of C2 and close S 1 . - Turn up P3 slowly until the speed of the drill just starts to increase. This completes the alignment pro- cedure. P3 can now -be used to set the speed of the drill as required. The component values shown will be suitable for motors up to 400 W. For more powerful motors, diodes Dl. . . D4 and the thyristor will have to be replaced by suitably up-rated types. Allow an adequate safety margin to cope with the heavy currents during switch-on. It will also be necessary to * decrease the value of R8 accordingly. Construction As noted earlier, the entire unit is connected to the mains. Since it may well be used in damp surroundings, due care must be taken when building the unit and it must be built into a well- insulated box. For the same reasons, PI must be a type with an insulated ' (plastic) shaft. The mains connections should be good quality mains cable (three-core), with a rubber grommet and a cable clamp where it enters the box. A mains outlet can be mounted on the box for the connection to the drill. H ' 12-32 — elektor december 1976 cumulative index 1976 LULtliLaUUli Ui.iiLlL l/Lli. Ittlr contents for Elektor Volume 2 Audio a LOG I Cal replacement for the carbon-track pot 1 147 class A amplifier re considered 739 dynamic noise limiter 341 equin (1) 448 equin (2) 525 Hafler circuit for quasi-quadrophony .... 757 Hl-Z stereo amplifier for headphones .... 716 infra-redphone 762 peak indicator 744 piano tuner 742 phasing and vibrato 1236 preco(l) 416 preco (2) 516 rain synthesizer 714 simple headphone amplifier 725 speech processor 225 SQL-200 (1) 938 SQL-200 (2) 1030 stereo indicator 763 super-bootstrap RC oscillator 764 symmetrical power amp 758 the LOUD mouth 1048 three channel mixer 735 triangular wave oscillator 728 variable slope filter 723 variable stereo width mixing stage 710 wien bridge oscillator 726 7 watt 1C audio amplifier 755 Cars ignition key reminder 734 ignition timing stroboscope 944 miles-per-gallon indicator 929 motorphone 711 parking meter alarm 1224 rev counter and dwell meter 921 rev counter for diesels 721 seat belt reminder 730 tachometer 916 voltage regulator for motorbikes 760 windscreen wiper delay circuits and how to install them 924 Displays digits on TV 1034 homemade display 514 led fm scale 134 led light show 634 led meters 441 read-out brightness regulator 756 stereo led level meter 143 7 segment to BCD converter 1235 Domestic albar 1110 a.m. mains intercom 618 bird-bell 757 capacicoupling 1142 DEW line 1121 digibell 638 drill control 1228 high security burglar alarm sensor 149 intercom 1128 kettlestat 715 molestation 716 optical-lock 122 porch lighter 727 refrigerator alarm 1141 sensitive metal detector 1116 signal horn 1130 sixpence detector 123 tap doorbell 735 tapped code lock 726 thermometer 1212 touch activated dimmer 752 wireless bell extender 738 Games a steady hand 714 battleships 131 lap counter 728 pin the tail on the donkey 139 poker 741 racing car control 128 score on screen for TV games (TV tennis) 1008 to drive or not to drive 119 TV tennis extensions (1) 318 TV tennis extensions (2) 453 TV tennis extensions (3) 544 Information articles driving lessons 238 ejektor 625 and 1226 from stereo to SQ 934 image width control 523 missing link: link 75 624 music of the spheres 910 quadrille 910 servotape 928 supply decoupling 535 vertical fets 628 vhf fm reception 613 Music digital master oscillator (1) 144 digital master oscillator (2) 241 hand-effect organ 760 ic rhythm generator 420 tremolo 745 Miscellaneous AMV without R and C 736 aquastat 716 battery indicator 722 capacity relay 138 i mulative index 1976 elektor december 1976 — 12-33 UlLlil urn ittir contents for Elektor Volume 2 cricket 1133 dark room aid 722 digital speed readout for turntables 748 driving LEDs from TTL 748 electronic voting system 750 film slave 1135 frequency doubler using 4011 719 light sensitive astable multivibrator 710 liquid level indicator 723 min-max temperature indicator 718 MMV for ACG 744 moisture indicator 764 MOS monostable 732 on-off TAP 742 one shot 745 opto coupler with two LEDs 729 quiz selector 761 schmitt trigger 741 sirens 1254 solarstat 718 sound effects generator 754 speech shifter 742 spike monoflop 733 triac control 617 triac relay 331 VCO with 74123 734 voltage-to-time converter 1131 wind machine 727 Power Supplies battery charger 756 cascode current source 746 current source 726 dissipation dumper 754 dual voltage regulators 1040 improved current source 1052 integrated voltage regulators (1) 348 integrated voltage regulators (2) 436 power supply for varicap tuner 340 quad symmetrical supply 765 regulated + and - power supply 728 symmetrical regulated supply 763 TTL insurance 724 variable regulated supply 748 0-30 V/1 A stabilised 739 Radio aerial booster 723 automatic call-sign generator 212 aircraft communication receiver 736 alignment squeaker 1029 DSSC generator 756 feedback PLL for fm 110 FM on 1 1 meters 1013 integrated indoor fm aerial 510 masthead preamp 550 mini mw 130 morse decoder 218 morse typewriter 226 pll-ic stereo decoder 150 preset aerial amplifier 765 sample/hold synthesiser 747 simple front-end for vhf fm 746 simple mw receiver 140 single sideband adapter 747 super-plam 310 squelch 754 ssb adapter 731 ssb exciter with hf compressor 766 ssb receiver 324 trawler band converter 767 tv modulator 739 tv sound — in brief 332 tv sound front-end adapter 334 wide band frequency doubler 722 200 MHz sample/hold adapter 760 Test Equipment acoustic logic probe 717 active oscilloscope probe 724 audioscope 752 autoranger for dfm 1018 channel quadrupler 610 digisplay 538 fet front 620 function generator ic 2206 124 linear scale ohmmeter 758 measuring pencil 612 microammeter 731 minivolt 1132 pip meter 750 polarity indicator 715 pulse generator 1138 elektorscope (1) 1244 simple pulse generator 720 sine-square-triangle generator 712 single transistor sawtooth generator 739 stylus balance 447 test logic 718 transistor tester 752 versatile logic probe 553 voltage to frequency converter 711 Time Related alarm 135 calendar 1124 car clock using watch ic 734 crystal timebase for synchronous clocks . . 721 digital wrist watch 231 egg-timer-with-a-difference 1119 handy dark room timer 750 perpetual solar clock 732 Polaroid timer 434 reading-in-bed limiter 1145 time on tv 1022 snooze-alarm-radio-clock 1219 UUla DUS r 1 uuG tors and diodes are simply marked ‘TUP 1 (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 1b. Table 6. Various equivalents for the BC107, -108, . . . families. The data are those given by the Pro-Electron standard; individual manu- facturers will sometimes give better specifi- cations for their own products. NPN PNP Case Remarks BC 107 BC 108 BC 109 BC 177 BC 178 BC 179 BC 147 BC 148 BC 149 BC 157 BC 158 BC 159 •g Pmax = 250 mW BC 207 BC 208 BC 209 BC 204 BC 205 BC 206 •© BC 237 BC 238 BC 239 BC 307 BC 308 BC 309 •€) BC 317 BC 318 BC 319 BC 320 BC 321 BC 322 : x5 sv 3 C>o speed of 100 ns/cm. VO. 6 ° \ k( O 3 ( J «0 ]*i DG7-32 W ,V\, '°o L ”»fs O "o£ VO , / DIO— 160 GH IC\0 X O Vv D13-480GH £ O operating in the chopped mode. This prevents a trace appearing on the screen as the beam switches between the two Y channels. The final function of the blanking amplifier is to provide an input for external Z modulation. The blanking amplifier is, of course, not a linear amplifier but a pulse amplifier. The input from the timebase is normally at a positive potential, transistor T1 is turned on and so is T2. During the flyback period the input from the timebase goes low, turning off T1 and T2, which provides a negative-going pulse to the grid of the CRT via C2. Diode D1 in the CRT bias circuit acts as a clamp to prevent the grid potential exceeding the potential set by the brightness control when the output of the blanking amplifier is positive-going, as this would otherwise cause a bright-up of the trace. When the oscilloscope is operating in the chopped mode a pulse is fed to the blanking amplifier on each positive and negative-going edge of the chopping waveform to blank out the trace during switching. However, during the flyback period this is overridden by the flyback. This will be dicussed in greater detail when the timebase, trigger and switching circuits are described. iktorscope (1) elektor december 1976 - 12-53 Figures 11 and 12. 2 kV and 1 kV high volt- age boards. Each board can be laid out for either type of supply, but if the smaller board is used for a 2 kV supply then (rare) 2 kV capacitors must be used. The component layout shown in figure 11 corresponds to the 2 kV supply (figure 8), whereas the layout in figure 12 is for the 1 kV supply (figure 7). Construction The blanking amplifier is mounted on the same p.c. board as the EHT supply and CRT bias circuits. Two alternative board layouts are given. Figure 1 1 is intended for use with 13 cm CRTs and the arrangement of the potentiometers matches the layout of the faceplate for a 1 3 cm tube, which will be available from the EPS service. The board layout of figure 1 2 is intended for use with 7 cm tubes, and again the layout matches the faceplate which will be available. However, for the benefit of the exper- imenter provision has been made in the layout for each board to have either a 1 kV or 2 kV EHT supply, and it is essential that the board should be wired up to suit the tube to be used. Since 7 cm tubes will generally be used with a 1 kV supply no provision has been made on the smaller board for series connec- tion of capacitors Cl to C3 to obtain a higher voltage rating. If this board is used for a 2 kV supply then capacitors with a 2 kV rating must be obtained. The highest voltage across any poten- tiometer in the bias chain is less than 200 volts, and any ordinary poten- tiometer of reasonable quality will withstand this voltage. However, in view of the high voltages at which the poten- tiometers operate with respect to ground, only types with plastic spindles should be used. (to be continued) Note All component lists will be given in the final part of this article. M 12-54 — elektor december 1976 Sound effects are always popular. One of the most popular effects for 'livening up' disco- shows, films, etc., is the (police) siren. The crime series on TV have taught practically everybody the difference between the European two-tone siren and the banshee wail of the American version. The circuit described here can produce either sound. The basic principle of the siren is shown in the block diagram (figure 1 ). The first section is an oscillator (Astable Multivibrator, or AMV). For the European siren, the square-wave output from this oscillator is fed direct to the control input of a Voltage Controlled Oscillator (VCO). This causes the VCO to switch to and fro between two fre- quencies. For the American siren, the output from the AMV is first passed through an integrating low-pass filter. The output from this stage is something mid-way between a sinewave and a triangular wave. When the VCO is driven by this signal, the result is a close approxi- mation to the noise made by the American cops. The complete circuit is shown in fig- ure 2. Transistors T1 and T2 are the active elements in the AMV. With SI in position ‘E’ (for European) the time- I determining elements are PI, R2, R3 | and C2; PI sets the ‘switching fre- quency’. The time-determining elements for the American siren are P2, R3 and C2; P2 sets the ‘wailing speed’. Any number of additional preset potentio- meters can be added if further siren effects are required. The main components of the integrator are P3, RIO, C5 and T3. P3 sets the amplitude of the output signal from this stage, so it is used to set the difference between the highest and lowest fre- quency of the American siren. Transistors T4 . . . T7 are the active elements in the VCO. The voltage at the control input (base of T6) determines the output frequency. For the American siren, the control voltage is the output from the integrator. Since this voltage swings up and down in the rhythm of the AMV, the output from the VCO will swing up and down in the same rhythm. The centre frequency of this wailing siren is set with P6. For the European siren, the square-wave output from the AMV is fed direct to the VCO, causing the latter to produce two frequencies alternately. P5 sets the lower of the two, and P4 sets the differ- ence between them - so it can be used to set the higher frequency. The adjustment procedures for the two sirens are quite simple. For the European siren, first set the desired switching frequency with PI. Then set the lower frequency with P5; finally, set the upper frequency with P4. The American siren is slightly more difficult to adjust. First set the ‘wail speed’ with P2. Then adjust P5 and P6 to get the desired effect. Note that P3 will need readjustment if the setting of P2 is altered. If more than one American siren is to be preset, an extra switch will be required between C3 and P3, so that it becomes possible to switch in several different presets for P3. Alternatively, normal potentiometers can be used with a calibrated scale. An almost infinite number of different sirens can then be ‘dialed in’. H Figure 1. Block diagram of the siren. Figure 2. Circuit diagram of the complete unit. The three switches can be coupled for ease of switching between the American and European type of siren. Figure 3. Printed circuit board and compo- | nent layout. Resistors: R1 ,R16,R17 = 2k2 R2,R3,R5,R20 = 100 k R4,R7,R10 = 10 k R6,R8,R9,R1 1 ,R12,R13,R14 » 1 k | R1 5 = 3k3 1 R18 = 22 k R19= 12k P1.P2- 470 k (preset) P3 = 100 k (preset) P4 = 22 k (preset) P5.P6 - 4k7 (preset) | Capacitors: Cl - 22 p/6 V C2 = 1p5/63 V C3.C6 ■ 47 p/16 V C4 = 470 p/6 V C5.C8 = 4p7/16 V C7 = 680 n Semiconductors: T1 ,T3,T8 = TUN T2 = TUP T4 ... T7 = BC547B, BC107B or equ. D1 ... D4 = 1N4148 Z1 = 4.7 V/250 mW zener Sundries: j SI ... S3 = 3-pole, 2-way (see text) rrOH \^h _n_ri A E f C1 f C2 alektor december 1976 - 12-57 Variable persistance/ storage oscilloscope A new variable persistance/storage oscilloscope from Hewlett- Packard includes a number of features not normally found in instruments in this price range. This new product is part of a line of low-cost scopes (the 1220 series) entirely developed and manufactured at Hewlett- Packard’s European Instrument Division in Boeblingen, Germany. The model 1223A includes a burn-resistant CRT and automatic storage control to make it easy to capture low rep-rate and single- shot waveforms for stored dis- play. The 15-MHz bandwidth and 2 mV sensitivity make it ideal in education, medical, electro- mechanical, and many other applications. The 1223 A combines the advan- tages of variable persistance, to integrate very-low-frequency or low-duty-cycle traces into clear displays, with the advantages of storage for single-shot events. Maximum stored writing speed is 1 cm/ps in the storage mode. The 1223A auto-erase mode provides repetitive single-shot dis- plays for recurrent viewing of traces while also making it easy to set up the instrument for captur- ing single-shot events. An auto- store mode allows the scope to wait for an event and capture it when it occurs for a total of at least two hours. A variable con- trol for brightness of stored traces is included so a setting can almost always be found for optimum trace to background contrast. The 1223A is suited for vibration and shock analysis (electromech- anical), ECG/EEG/muscIe reac- tion analysis (medical), machine design and service (X-Ray and numerical control), as well as the design of low frequency filters and circuits for integrating and differentiating (research and edu- cation). The 1223A also includes TV sync, variable trigger holdoff, A + B modes, calibrated X-Y display, and selectable chop/alternatc sweep operation. The instrument is supplied in an entirely closed metal cabinet. Hewlett Packard, P.O. Box 349, CH-121 7 Meyrin 1 Geneva, Switzerland Green response photocells A new scries of green response silicon photocells has been added to the Spectra-Band series of photovoltaic devices available from International Rectifier Corporation. The new units, called Green Blaze Photocells, are specially designed for spectral response which is greatest in the green portion of \ the visible spectrum. The spectral response of the units resembles a broadened photopic curve, with a maximum response in the vicinity of 556 nanometers. Applications of the Green Blaze units are chiefly in photographic, photometer and visible band insolation measurement equip- ment. Temperature coefficient in the short circuit current operating mode is 0.2 percent per degree C, and operating temperatures for the new units are between -40 and +125 degrees C. I The new photocells are designed for long term stability to ensure j less than ± 2 percent drift in current response over a period of two years. Units are available in standard optoelectronic cases or in custom packaging or assemblies at the customer’s option. Price for standard 1 cm x 1 cm Green Blaze Photocells is about | S 3.25 in quantities of 1 ,000. International Rectifier Corp., 233 Kansas Street, El Segundo, California 90245, U.S.A. Digital clock A miniaturized electronic digital I clock movement with a bright LED display showing numerals .84 inch high is now available in | quantity from National Semi- | conductor. The model "MAI 010" series elec- tronic clock modules, which in- clude a large-scale monolithic MOS integrated circuit, power supply and other discrete compo- nents on a single printed circuit board feature a four-digit .84 inch Light Emitting Diode (LED) dis- play. According to national, this represents a larger numeric dis- play than on any digital clock module previously manufactured. Another important factor is that the size of the entire module is not much larger than its display. "It's ideal for those manufac- turers who want a large numeric display but only have limited space for a clock movement. The user only needs to add a transformer and switches to con- struct a pre-tested digital clock for application in a clock radio, digital alarm clock or instrument panel clock. The module is also suitable for use in communi- cations and CB base radio stations, TV and stereo systems and medical instruments. Time-keeping may be done from inputs of either 50 or 60 hertz. Display formats of 12 and 24 hours are available. Direct, non-multiplexed drive for the LED display eliminates RF interference, which makes the module easy and economical to use in clock radios and hi-fi systems. Features include indicators for "alarm on" and "p.m.", a blink- ing colon to indicate interruption of power, "sleep” and "snooze” timers, and capability for a vari- able-brightness controL Time- setting is made easy for the user by providing "fast” and "slow” scanning controls. Alarm clock options include a transistor oscillator circuit that is capable of driving an 8 ohm loud- speaker, or may be used with an inexpensive earphone tye audio transducer. National Semiconductor GmbH Industriestrafie 10 D 8080 Fiirstenfeldbruck West Germany K, '0/ects section '"eludes complete s&; ftSSS 8 'o'-cornpteu. NAME ADDRESS ay in completion of lai g rehouse. catalogue will I The new Maplin Catalogue is no ordinary catalogue... I !*(***<>* ' \ I II highPUohW' ,tW ' F ' J ^ r \ Catalogue includes a very wide range of components: hundreds of different capacitors; resistors; transistors; I.C.’s; diodes; wires and cables; discotheque equipment; organ components; musical effects units; microphones; turntables; cartridges; style test equipment; boxes and instrument cases, knobs, plugs and sockets; audio leads; switches; loudspeakers; books; tools - AND MANY MANY MORE. ■ Please rusn ^ Qnl lf | a m comply i receip 1 ,nst 0 nc "• '= I SOP ^ 14 I Our bi-monthly newsletter keeps you up to date with latest 1 guaranteed prices - our latest special offers (they save you — I pounds) - details of new projects and new lines. Send 30p ■ for the nest six issues (5p discount voucher with each copy). ffliipyim ELECTRONIC SUPPLIES delayed by up to tour weeks - ho there's still time to order before publication and get your pack ot ten super special offer coupons, giving big discounts on ten different popular items YOU COULD SAVE POUNDS! - SO DON'T DELAY - Fll I IN AND POST COUPON NOW! P.O. BOX 3, RAYLEIGH, ESSEX SS6 8LR Shop: 284. London Road. Westcliff-on-Sea. Essex (Closed on Monday) Telephone: Southend (0702) 44101