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ELEITO gp-to-date'electronies for lab and ldifuro 9-04 — elektor september 1977 decoder elektor Editor : W. van der Horst Deputy editor : P. Holmes Technical editors : J. Barendrecht G.H.K. Dam E. Krempelsauer G.H. Nachbar A. Nachtmann Fr. Scheel K.S.M. Walraven Art editor : C. Sinke Subscriptions Mrs. A. van Meyel U.K. editorial offices, administration and advertising: Elektor Publishers Ltd., Elektor House, 10 Longport Street, Canterbury CT1 1PE, Kent, U.K. Tel.: Canterbury (0227)-54430. Telex: 965504. Please make all cheques payable to Elektor Publishers Ltd. at the above address. Bank: 1. Midland Bank Ltd., Canterbury, A/C no. 11014587, Sorting code 40-16-11, Giro no. 3154254. 2. U.S.A. and Canada: c/o World Way Postal Center P.0. Box 80689, Los Angeles, Cal. 90080, A/C no. 12350-04207. Assistant Manager and Advertising Editorial Elektor is published monthly on the third friday of each month. 1. U.K. and all countries except the U.S.A. and Cananda: Cover price £ 0.45. Number 27/28 (July/ August), is a double issue, 'Summer Circuits”, price £ 0.90. Single copies (incl. back issues) are available by post from our Canterbury office, at £ 0.60 (surface mail) or £ 0.95 (air mail). Subscriptions for 1977, January to December incl. £ 6.25 (surface mail) or £ 11. (air mail). Do a from October to December 1977 £1.60 (surface mail). 2. For the U.S.A. and Canada. 50. : R.G. Knapp : T. Emmens Cover price $ 1 ate 27/28 (uly/ August), is a double issue, “Summer Circuits”, price $3. Single co; (incl. back issues) $ 1.50 (surface mail) or $ 2.25 (air mail). Subscriptions for 1977, January to December incl., $ 18.— (surface mail) or $ 27.— (air mail). Subscriptions from October to December 1977 $4.50 (surface mail). All prices include post & packing. Change of address. Please allow at least six weeks for change of address. iddress label from a Include your old adi 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. ss, enclosing, if possible, For technical queries, please enclosa a stamped, addressad envelope. designs or articles to Elektor implies permission to the publ alter and tran: ing, 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 O 1977 Elektor publishers Ltd — Canterbury. Printed in the Netherlands. What is a TUN? What is 10 n? What is the EPS service? What is the TQ service? What is a missing link? Semiconductor types Very often, a large number of equivalent semiconductors exist with different type numbers. For this reason, 'abbreviated' type numbers are used in Elektor wherever possible: 741" stand for vATA!, LM741, MC641, MIC741, RM741, SN72741, etc. *'TUP' or 'TUN' (Transistor, Universal, PNP or NPN respect- ively) stand for any low fre- quency silicon transistor that meets the following specifi- cations: UCEO, max 1C, max hfe, min Prot, max fT, min “Some *TUN's are: BC107, BC108 and BC109 families; 2N3856A, 2N3859, 2N3860, 2N3904, 2N3947, 2N4124. Some 'TUP's are: BC177 and BC178 families; BC179 family with the possible exeption of BC159 and BC179; 2N2412, 2N3251, 2N3906, 2N4126, 2N4291. *'DUS' or 'DUG: (Diode Univer- sal, Silicon or Germanium respectively) stands for any diode that meets the following specifications: DUS DUG UR,max |25V 20V TF, max 100mA — |35mA IR, max 14A 100 uA Prot,max |250mW | |250mW! CD max |5pF 10pF, Some 'DUS's are: BA127, BA217, BA218, BA221, BA222, BA317, BA318, BAX13, BAY61, IN914, 1N4148. Some 'DUG's are: OAB5, 0A91, OA95, AA116. *'BC107B', 'BC237B', 'BC547B' all refer to the same 'family' of almost identical better-quality silicon transistors. In general, any other member of the same family can be used instead. BC107 (8, BC107 (-8, BC207 (8, BC317 (-8 BC547 (8 BC182 (3, BC437 (8, BC177 (8, BC177 (8, BC204 (-5, BC320 (1, BC557 (8 BC212 (3, BC261 (2, -9) familios: 9), BC147 (8, 9), -9), BC237 (8, 9), -9), BC347 (8, 9), 9), BC171 (2,23); 4), BC382 (-3, 4), -9), BC414 -9) families: -9), BC157 (8, -9), -6), BC307 (-8, -9), -2), BC350 (11, -2), -9), BC251 (-2, -3), 4), BC512 (3, 4), -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 abbreviations: p (pico) = 1012 n (nano) = 10º u (micro)= 108 m (milli) = 107 k (kilo-) 10º M (mega-) 108 G (giga) = 10º A few examples: Resistance value 2k7: 2700 92. Resistance value 470: 470 2. Capacitance value 4p7: 4.7 pF, or 0.000 000 000 004 7 F... Capacitance value 10n: this is the international way of writing 10,000 pF or .01 uF, since 1 nis 107? farads or 1000 pF. Resistors are X Watt 5% carbon types, unless otherwise specified. The DC working voltage of capacitors (other than electro- Iytics) is normally assumed to be at least 60 V. As a rule of thumb, a safe value is usually approxi- mately twice the DC supply voltage. Test voltages The DC test voltages shown are measured with a 20 kS92/V instru- ment, unless otherwise specified. U, not V The international letter symbol “U' for voltage is often used instead of the ambiguous 'V”. *V"is normally reserved for “volts” For instance: Up = 10 V, not Vb = 10 V. 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 modifi- cation may be required. Technical services to readers e EPS service. Many Elektor articles include a lay-out for a printed circuit board. Some — but not all — of these boards are avail- able ready-etched and predrilled. The 'EPS print service list” in the current issue always gives a com- plete list of available boards. e 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. e Missing link. Any important modifications to, additions to, improvements on or corrections in Elektor circuits are generally listed under the heading Missing Link at the earliest opportunity. 9-12 — elektor september 1977 selektor % AS e) Where are those buses? Coras Iompair Eireann (CIE), Ireland's national transport company, are installing a fully automatic vehicle monitoring (AVM) system for Dublin City Bus Services” entire fleet of some 900 buses which carry over 216 million passengers and operate over 32 million miles each year. Storno Limited of Camberley, Surrey are the main suppliers for the system which will enable the entire fleet to be monitored by Control Inspectors from seven garages. The system is based on a dual computer arrangement which auto- matically collects location data from each bus on a route. The results are pre- sented on visual display units (VDU's) so that Control Inspectors in each garage can see at a glance the actual, and scheduled, position on all buses on a particular route. Garage no 7] Although the collection of location data is automatic, and does not require the driver to answer queries, normal speech contact between driver and Control Inspector is also provided in this com- plete radio communications system. This system will enable CIE to provide improved services for passengers by reducing bus waiting times, operating services on time, and by having the facility to summon aid in cases of emergency, or passenger illness. Significant benefits are also being provided for the CIE management and 4,000 workforce. Of the utmost importance, the system generates valuable statistical information which is available within 24 hours and forms the basis of a comprehensive management information service for the scheduling, maintenance and operating departments. The Control Inspectors, who are now being removed from often unpleasant outdoor work, are achieving a re-newed sense of job satisfaction and involve- ment from being able to control a full bus route, or group of routes without assistance, or interference. Improved morale has been achieved for the operating staff who will now be responsible to a single Control Inspector instead of reporting to several Control Inspectors located at different parts of their route. The greater control achieved with radio is providing an equalisation of workload between crews, enabling them to take their mealbreaks at correct times, and providing immediate assistance in the event of assault, or vandalism. Dublin Bus Services first started experimenting with radio telephones in 1970. Tests proved so satisfactory that there are now 740 radio equipped buses in service using 14 voice channels. Due to the limited availability of VHF channels, expansion to the remainder of the fleet could only be achieved through higher utilisation of existing allocation, and the solution appeared to lie in the automation of the existing scheme. Major trials took place in 1975 on all aspects of automatic vehicle monitoring on 100 buses from the Phibsborough garage. The buses were fitted with Stornophone CQM612 semi-duplex VHF FM mobile radio telephones, designed to facilitate data transmission. A telemetry unit stored the data message and facilitated transmission when interrogated by the computer located at the CIE headquarters in O"Connell Street. Results were presented on two VDU?s at the Phibsborough garage. A printer provided hard copies of specific information. The data link comprised a base station at the computer site, and a station at Three Rock Mountain, approximately seven miles away to relay the intor- mation from the computer to the mobile bus units and vice versa. These comprehensive tests included location accuracy, facilities tests, tests on voice communications, computer system and display responses, equip- ment reliability, Control Inspectors' and operatives” reactions. The results obtained paved the way for the complete AVM system now being installed and due to be in full operation Storno Radio Data Link for = E THREE ROCK MOUNTAIN SITE STORNO COF6IZ dock up. Dublin City Bus Services ecenars channel 12 1 Spesen channel control ton 2 Spesch channel contro! bos 1 E = Garage no 2 STORNO CoMeIz [ERAM Er Garage no 1 ) EE em Line modems %e other | gorages 59 O'CONNELL STREET STORNO COF SG? UHE Link Trenemitter 4 recenver with deck up Computers POP 11/10 20» 1/70 Tema 4 Equipment PIT telephone “lines [ Gs S selektor elektor september 1977 — 9-13 by mid 1979. When fully operational a “front end” PDP 11/10 computer will interrogate ch busin turn at the rate of 900 buses/ minute via a fully duplicated radio system. It will also handle requests to speak. Once verified the bus replies are fed into a larger PDP 11/70 machine | which presents the results as actual and scheduled positions of the buses on | “individual routes on 2000 character screen VDU?s — a number of which with a printer are being located at each of the seven garages. This will enable Control Inspectors in each garage to see at a glance the positions of all buses on a particular route so that they get an accurate picture of the situation as it is, and as it should be, to allow them to accurately make any changes that may be necessary to maintain, or improve services. Additionally, as part of the improve- ment of control techniques a number of closed circuit television cameras | | (CCTV's) are being installed at city centre points. These will provide “ontrol Inspectors with an awareness of traffic conditions and build-up of passenger queues. Route Control Inspectors can operate the CCTV's which incorporate low light level lenses for night operation together with pan, tilt, zoom and focus facilities. The bus radio is being modified to accept and transmit the computer data and this, together with a bus data unit and control head comprises the bus equipment. The control head provides the means of establishing voice communications between the driver and the Control Inspector and also feeding in the odometer reading at commencement of each journey to identify its precise location. Thereafter, location identifi- cation is automatic as the odometer is fitted to the final drive in parallel with | the normal speedometer drive unit and generates pulses to the data unit at 44 yard intervals. The control head also incorporates an input for emergencies. The computer can also make direct inputs to the odometer. The bus data unit stores the location of the bus and passenger loading. It also incorporates facilities to record up to O oO The Storno bus data control head provides the means of feeding in the three-digit code odometer reading at commencement of each journey to identify the precise location of the bus, Thereafter, location identi automatic. When the driver wishes to speak he uses the RTS button which informs the Control Inspector through a VDU of his request. Up to eight such requests may be displayed at any one time. Every 20 seconds a general call is sent to all Storno bus data units searching for an “alarm! condition. Should any bus have its “alarm” button depressed it will respond by causing its number and location to flash continuously on the Control Inspectors VDU. At the same time the computer automatically switches the bus to the speech mode thus giving drivers speech contact with their respective Control Inspectors on average within ten seconds of pressing the “alarm' button. Ei o o Me e . Close-up of typical map shown on the VDU's and up-dated automatically at least every two minutes. The route is shown as two hori- zontal lines — one for each direction of travel. The scheduled positions for the buses oper- ating on the route are shown on the inside of the diagram. Actual positions are plotted on the outside of the diagram and are represented by the duty number of the bus concerned. deemed to be under the first character of the duty number. Time and route numbers are shown on the first line of the screen. Driver “alarm” calls are flashed on and off on the first line until answered by the Control Inspectors. Requests to speak by bus crews appear on the last line and again will remain there until cleared by the Control Inspectors. Columns on the right-hand side of the screen give additional information on buses being monitored. toa 17 BELFO DBRCH OVERFLOW:X 03,094,08,17 COMMAND? COMMAND LINE PRINTER LINE TIME 10:58 05 -APR-77 ROUTE 10 ALARMIO/19 CHECK40/01 Fx SET ODO ISA 1015 0411 o7A “005 1093 18 ta 2a RA 18 GARAGE o41o 4011 1009 1021 ANARD PHXPK ocost STPET 094» NO REPLY 15 20 06 17 1219 ISA INVALID 01 18 16 132207 REQUEST TO SPEAK:10/02 10/03 10/18 4/01 40/15 selektor elektor september 1977 — 9-15 % AS vç) tu Optical waveguides used in Air Force's data-carrying cable Optical waveguides made by Corning are an essential part of a cable installed at the U.S. Air Force Arnold Engineering Development Center in Tennessee. The glass waveguides are contained in a custom-made cable of the General Cable Corporation that connects rocket engine test sites with a central data processing facility. The cable contains six waveguides, along with several copper conductors. Each waveguide may be employed independently for transmitting, at high- speed, data signals or any other infor- mation, including voice and video signals. The waveguides transmit data from the engine test sites to the base computer center, located approximately two kilometers away. The optical waveguides were chosen for the installation because of their large data-carrying capability, and because they are immune to hostile environments, particularly electro- magnetic interference. Measuring about 0.005-inch (0.127 mm) in diameter, or about the thickness of a human hair, the waveguides are well protected by other cable components. Because the cable is buried for most of its 7,000-foot (2,100-meter) length, special steps were taken to make it suitable for such an environment. The cable consists of a welded tubular aluminium sheath surrounding the fibers and their support structure, a polyethylene inner jacket, a corrugated steel wrapping and a polyethylene outer jacket. The cable is suitable for instal- lation in ducts or can be buried directly in the ground. The installation at the Arnold Center is particularly significant because it is intended as an operational system, not an experimental one. The complete system is expected to be in service by mid-1977, when installation of other elements of the system is complete. The graded-index optical waveguides used in this cable system were made by a patented Corning doped deposited silica process. In this process, carefully controlled materials that raise the refractive index of the core glass are introduced during deposition of the core. Freedom from electromagnetic inter- ference is a characteristic of optical waveguides that is particularly desirable in the Arnold Center installation, where accurate data transmission is essential. The characteristics are particularly important because real-time trans- mission reduces opportunities for error correction. Neither natural inter- ference, such as lightning, nor man- made interference, such as that created by adjacent electromechanical equip- ment or cross-talk between fibers in the same cable, affects signals carried in optical waveguides. Also, waveguides do not radiate energy that might inter- fere with other equipment. The practical application of waveguides on a demanding installation such as that at the Arnold Centre has only been possible recently. Six years ago the purest glass fibers of one- kilometer length could deliver only one per cent of the light introduced into them. However, steady improvement has been made, so that today as much as 80 per cent transmission has been achieved in the best optical waveguides of comparable length. (2058) Optical fibers are branching out The purpose of telecommunication systems is to transmit information and data to specific destinations. For certain transmission applications, optical fibers are well on the way to competing effectively with conventional metal conductors. Viable methods of optical distribution of communications are also being established, and Siemens is now presenting a branching unit for optical waveguides, developed with the support of the Federal Department of Research and Technology. In an optical-fiber communication network, definite light components have to be branched off from the main optical waveguide. Since optical fibers do not readily lend themselves to branching, it was necessary to find a suitable optical distributor. Using a planar thick-film technology, research engineers at Siemens succeeded in realizing novel branching structures for optical fibers, based on the use of a light-sensitive plastic foil with a thickness of approximately 0.1 mm, correspond- ing to the diameter of the fibers. Any desired structure can be etched into this foil by photolithographic processes. The structure required for the wave- guide branch is such that the two ends of the cut fiber meet with a slight offset. The light component escaping at the interface enters the foil and is guided along a curvature to a branching fiber. The amount of optical power coupled out depends on the offset of the ends of the main waveguide at the interface. The advantage of the described technology is that the light- guiding structure in the foil, and the guiding channels for the fibers, can be produced in a single operation. This fabrication method is very simple, while at the same time fulfilling the stringent requirements specified with respect to the accuracy of fiber alignment (tolerances of approximately £ 3 um). (2045) Alternating current flow can be detected and indicated using only four components. How? See the inside of this month's mailing wrapper! 9-16 — elektor september 1977 introducing microprocessors (1) infroducino) micropprocessors! ||) A microprocessor is simply an extremely small processor, and a pro- cessor is part of a computer or other data processing system, so before delving into the intricacies of micro- processors it is first necessary to under- stand the operating principles of com- puters, and the function of a processor in a computer system. A computer is basically a machine for processing data. The data to be pro- cessed is fed into the computer, and the results of the data processing are obtained at the output. The operations that are to be performed on the data are contained in a sequence of instruc- tions known as the programme. Apart from complexity, the major difference between a computer and say a simple pocket calculator lies in the programming. A calculator possesses a number of pre-programmed mathemat- ical functions that can be called up at the push of a button, e.g. cosx, yX, log x, as well as the basic arithmetic functions +, —, x, +. A computer, how- ever, possesses only basic arithmetic and manipulative logic functions “if xy, then...', and these must be written into the programme step by step. How- ever, this makes a computer infinitely more versatile than a calculator. A caleulator is limited in its operation to the mathematical functions available on its keyboard, whereas (within reason) any desired manipulation of data or complex mathematical operation may be performed by a computer by building the correct sequence of instruc- tions into the programme. A typical computer system might consist of four units. 1. A separate (or sometimes peripheral) unit for preparation (and sometimes even verification) of programmes. This might consist of a teletype or visual display unit (VDU) and punched tape or card equipment. 2. A peripheral input/output unit such as tape/card reader to read in the programme and data, and tape/card punch to output the results. The programme preparation and input/ output units may frequently be com- bined, especially in applications where the computer and the user interact directly, e.g. by means of light pens, Over the past two decades increasing miniaturisation, and in particular the advent of integrated circuits, has revolutionised the electronics industry. Nowhere is this more true than in the field of digital electronics, especially in the area of data processing and calculating machines, where large- scale integration (LSI) has made possible low price units of a small size and high performance unheard of even ten years ago. Currently, microprocessors are the “in thing”, so this series of articles is intended to provide a simple introduction to these extremely versatile devices. voice recognition units etc. 3. A memory unit to store the data and programme instructions. The same memory may be used to store both data and programme, especially in small computers, or there may be separate programme and data memories. 4. A central processing unit (CPU). This carries out arithmetic operations, data comparison, manipulation and move- ment in accordance with the programme instructions. Many readers will have seen photographs of early computers built using valves, and may have marvelled at their apparent complexity and wondered just why they were so complex. The answer is really very simple. After a few initial attempts to build computers operating in decimal notation it was quickly realied that to represent decimal numbers O to 9 electronically was not a very practical proposition when applied to a large computer system. It soon became apparent that it was much simpler to make computers operate in the binary number system, since this system uses only digits 1 and Q (“Q" is used instead of “0' for the digit, to clearly distinguish it from the letter '0”), which can be represented electronically by “on” and “off” conditions. A computer system must be able to handle and store large amounts of information (i.e. numbers), and to store one digit of a binary number requires an electronic circuit that can be set in one state or another depending on whether the digit is Q or 1. Such a cir- cuit is the common flip-flop. To store and handle many large numbers requires a correspondingly large number of flip- flops, and when one considers that in the days of valves each flip-flop would require one double-triode valve, it is not difficult to see why valve computers were so bulky. In those days each of the four units of a computer might have occupied a room to itself, depending on the complexity of the computer system. The introdue- tion of transistors made possible much smaller computers, and after the intro- duction of TTL and later MOS inte- grated circuits the size of computers could be reduced even further. Finally, with the perfection of LSI MOS tech- 9-18 — elektor september 1977 FM — mains intercom A design for a simple mains intercom has already been published in the June *76 issue of Elektor. It was stated then that a future issue would contain a design for an improved version, which in a number of respects, would “offer considerably better performance. The original design was for an AM- system with roughly the same charac- terístics as most commercially available (AM-) devices. However, since there is very little that can be done to alleviate the problem of mains interference with such a system, it is often the case that users soon revert back to “normal” intercom-installations. The superior performance of the mains intercom described here is due almost entirely to its reduced sensitivity to interference. This is achieved by using an FM system. The advantages of using an EM- as opposed to an AM-trans- mission system... were extensively discussed in the article “modulation systems” which appeared in the February "75 issue of Elektor. Although the system does in fact employ a transmitter and a receiver, it is somewhat uncommon to use these terms when talking of an intercom system since it is the mains wiring which is being used as the medium to carry the signals. An intercom system is used in the first instance for the transmission of the spoken word, so that high fidelity reproduction is not required. This means that narrowband FM will give sufficient intelligibility for spoken signals. The use of a very narrow bandwidth has the advantage that, if the transmission and reception frequency is made adjustable over a reasonable range, then the number of available channels is thereby greatly increased. The system described here takes advantage of this possibility, since increasing the number of channels reduces the chance of one frequency overlapping with another and producing interference or “splatter”. The transmitting power of the intercom has to be fairly high to take account of the potentially very severe mains inter- ference. However, under normal circum- stances the output power (which may be varied) will be kept to a fairly low level in order to prevent the transmitter FIM-moins infercom The disadvantage of conventional AM-mains intercoms is that they are subject to the often highly disruptive effect of mains interference. The system described in this article however, obviates this problem by employing FM; in addition, by reducing the bandwidth to a minimum, the number of available channels is thereby greatly increased, so that there is little chance of interference ('splatter”) between different intercom systems caused by channel overlap. ) (a being picked up outside the building. The construction of the intercom is simplified by the fact that a complete station, consisting of a transmitter, a receiver and a supply section, can be mounted on one printed circuit board. In addition the circuit is simplicity itself as far as tuning is concerned. Design Figure 1 shows the block diagram for a complete intercom station. The trans- mitter and receiver sections inter- connect at point B, so that the mains connection functions as both the in- and output of the station. The transmitter section is shown on the upper half of the diagram. The signal from the microphone is first amplified, limited and filtered, then used to fre- quency modulate an oscillator. After being amplified, the resulting FM-signal is fed into the mains via an isolation transformer. Signals transmitted from other stations are picked up by the transformer and fed to the receiver section. After being amplified and limited, the received signal is demodulated and fed, via a simple audio-amplifier, to a loudspeaker. Switching between “speak” and “listen”, ie. between transmit and receive, is accomplished by switching the supply voltage between the output stage of the transmitter and the AF-amplifier of the receiver. The Transmitter Figure 2 shows a more detailed block diagram of the transmitter section of the intercom. The circuit diagram for the first three blocks is reproduced in figure 3a, whilst figure 3b shows the circuit diagram for the rest of the transmitter. As is apparent from the block diagram, the signal from the microphone is first amplified by the stage round Tl, In order to reduce the bandwidth of the transmitted signal to a minimum approx. 10 kHz in this case), TI is followed by a clipper, consisting of the differential stage round T2/T3 Although the signal is severely clipped, the intelligibility of the audio signal is virtually unaffected. The clipper is FM — mains intercom elektor september 1977 — 9-19 Figure 1. Block diagram of a complete station of the mains intercom. The station, together with the supply section, can be mounted on a single circuit board. Er vco [+ PA Figure 2. Block diagram of the transmitter. After being clipped and filtered, the micro- phone signal is used to modulate the frequency = of a VCO. The resulting FM-signal is then amplified and fed to the mains via an isolation FM- transformer. cemodu- LF Itor Figure 3a. The iagram of the micro- phone preamplifier, clipper and lowpass filter. Figure 3b. The circuit diagram of the VCO and the output stage of the transmitter. 24v e D— D Clipper vco PA é i | E 8 ER rw S si 24v sa E —E)sv “E no a fon. Ho Aa 2x1N4148 ter CO] E: E éav Pi | 100n O 1000V] | IO) 1900V D3..D8=1N4001 saso 20 O) EM — mains intercom elektor september 1977 — 9-21 5b Figure 4. Block diagram of the receiver. After it has been amplified and limited, the received signal is demodulated in a PLL with “lock squelch'. The demodulated signal is fed to the loudspeaker via a low-frequency amplifier. Figure 5a. The circuit diagram of the high- frequency section of the receiver. IC1 contains a PLL FM-demodulator. The output transistor of the IC, together with T14, forms the lock squelch. Figure 5b. The low-frequency amplifier of the receiver. Figure 6. Internal block diagram of the tone decoder IC, type number 567. Figure 7. The supply, which, along with the receiver and transmitter is mounted on the circuit board. OM ER [E B30C2200 ev 15a 53557 and Exar under type number 567) is a tone decoder, and contains a PLL, a phase detector, a comparator/amplifier and a driver amplifier with open collector. When the received signal is within the capture range of the PLL, the PLL locks on to the input signal. The built-in detector functions as a “lock- indicator”; when the PLL is locked in, there is a sharp increase in DC-output voltage of the detector. This voltage is converted by the amplifier and output driver transistor into a logic state. In the quiescent state pin 8 of the IC is high, whilst during lock, the logic state at this pin is low. The EM-input signal is demodulated by taking as the LF-signal the control voltage for the PLL-VCO present at pin The lowpass filter which is connected to this pin is formed by C31 (see figure Sa) together with a resistor in the IC. The LF-signal is fed via R41 and C30 to the base of transistor TI4. However the DC-bias voltage of thus transistor is determined by the logic state at pin 8 of the IC. The transistor will tum on only when the PLL is in lock and pin 8 is low. If the input frequency band is outside the capture range of the PLL, the latter will not lock in, and the low frequency signal at the output will be suppressed, hence the term “lock squelch-. By means of P4 the free running frequency of the PLL-VCO can be tuned to the centre frequency of the transmission. The range of the PLL- VCO is roughly the same as that of the VCO of the transmitter. The LF-signal is fed to the power amplifier via preset potentiometer PS, which functions as a volume control. PS may be replaced by a normal pot. if a manual volume control is required. As figure Sb makes clear, the power amplifier is of a very simple design, given the fact that there is no need for hi-fi reproduction. In the absence of a signal no quiescent current flows through the output stage; with a supply voltage of 24V the circuit will deliver S watts to an 8 ohm loudspeaker. The Supply I will have become clear from the foregoing that two separate supply voltages are needed for the intercom. Most of the circuit operates at 7.5 V, but for the output stage of the trans- mitter and the LF-amplifier in the receiver, a 24 V supply is necessary. The 24V supply is switched between the transmitter-output stage and the-LF- amplifier by means of transmit/receive switch SI. For ease of construction, the supply for the entire intercom is also mounted on the printed circuit board. Figure 7 shows the circuit diagram for the supply section, which although fairly simple, is perfectly satisfactory for this appli- cation. The 24 V supply is taken direct from a rectifier circuit, whilst the 7.5 V supply is obtained using a simple regulator, consisting of a transistor and a zener diode. Supply transformer Tr2, which of course cannot be mounted on the p.cb., should have a secondary voltage of 18 V and supply a current of fESCAS Construction Figure 8 shows the component layout and copper side of the printed circuit board. The construction of the intercom should present few difficulties, providing the listed component values are adhered to. The only problem may be the isolation transformer Trl, which has to be selfwound. A pot core without an air gap, 30 mm in diameter and 19 mm high, should be used. The primary winding consists of 48 turns of enamelled copper wire 0.3 mm thick; 24 windings of the same wire will suffice for the secondary 9-22 — el tor september 1977 FM — mains intercom Parts list for figure 8: a complete station (figures 3a, 3b, 5a, 5b and 7) Resistors: R1=1M R2,R3,R6,R12,R13,R32, R45,R46 = 47 k R4,R52,R55 = 150 2 R5,R39,R44,R48 = 10k R7,R40,R47 = 220 k R8 = 330 k R9,R37 = 1k5 R29,R54 = 3k3 R10,R28,R30,R34, | R31,R35,R36=1Kk R50 = 4k7 R49,R53 = 10 2 R11,R33,R41 R51 = 680 2 R14,R15,R38 P1,P2 = 4k7 preset R16,R17 = 100 9 P3=470 9/5 W 330 2 P4=22k preset 20 2 P5 = 100 k preset 270 92 R21,R24,R43 = 220 92 R22,R23, R42 = 1k2 R25,R26 = 560 2 R27=229/5W Capacitors: C1,C30,C36,C41 = 100 n c5=180n C6=18n C7 = 5n6 C8,C24,C28,C39 = 47 n C9=10u/M0V C10,C33 = 3n3 C11 = 447/63 V C12,C13= 242/40 V C14=33p C15,C16=4n7 C17,C18 = 242/63 V C19,C20 = 100 n/1000 V C21,C22,C26=1n C23=145/6V C25,C43 = 100 4/0 V C27 = 680 p C29 = 4u7/3 V C31=15n c32=1n5 c34 =220n C35 = 224/16 V c37=27p C38 = 100 u/16 V C4O = 220 1/16 V C42 = 4700 u/35 V Semiconductors: T1 = BC549C T2... T9,T12= BC547 = BC557 TM = BD241 T14=BC557B T18= BD138 T19 = BC140 D1,D2,D10...D16= 1N4148 «.. D8 = 1N4001 D17 = BZX79-C 8V2 (or equ. 8V2 zener) 1C1 = 567 Miscellaneous: L1 = choke 15uH Trl = pot core tranformer (see text) Tr2 = supply transformer 18V/1.5 A B = bridge rectifier B30C2200 S1 = SPDT switch g 9-24 — elektor september 1977 EM — mains intercom 9359 9a. Sb In Conclusion If, as is shown in figure 9a, a multi-way switch, along with a number of fixed resistors connected in series with preset potentiometers, is used to replace P2, then the result is a true multichannel transmitter. A similar alteration to the frequency-determining section of the receiver (figure 9b) thus converts the system into a complete mains-trans- ceiver. Should difficulties occur with the 5 W wirewound potentiometer (P3 in figure 3b) used to regulate the trans- mitting power, an alternative arrange- ment is shown in figure 10. The replace- ment circuit, shown on the right of the diagram, employs a more conventional type of potentiometer and a power transistor, which should of course be fitted with a heat sink. Babyphone extension A large number of mains intercoms are used as babyphones or baby-alarms. It is important that, before an intercom is used for this purpose, it be fitted with a voice-operated control. If this is omitted, the result is that a continuous, more or less unmodulated carrier signal is being transmitted, which, in the case of widespread use, will soon lead to channel congestion. In addition, those present in the same room as the receiver station will be subject to a variety of background noises produced by the intercom. For this reason the following add-on circuit (see figure 11) offers a baby- phone extension for the mains intercom, which will ensure that the intercom is only switched on when the alarm has been actuated. The signal from the microphone is first amplified by Al and A2. The latter amplifier stage can also be used to amplify the signals from up to three separate alarm-signal sources of the type described in Elektor 19, November 1976, p. 1121 and 1141. A3, together with D2 and D3, functions as a 24v 24v 2N3055.1 To de 3x IN4148 2x1N4001 os a sasa-10 Figure 9. Extension to switchable multi- channel transceiver. Figure 9a shows the necessary alterations to the frequency-determining section of the transmitter VCO; figure 9b shows the alter- ations to the VCO frequency in the PLL of the receiver. Figure 10. On the left is the original circuit, whilst an alternative method of regulating the power of the transmitter is shown on the right (ef. figure 3b). Figure 11. Circuit diagram of babyphone extension for mains intercom. - ai 1 5 1€1 f ax o CE ca = “lê Remo | 16v Ru E [och WA 22 e a E ns D2 D3 ms Ai AT 4 nor] ed DI...D3=1N4148 213055] a É mi Pan E 1 o on [ton [| ai A4g-ICI=LM324 H FO PRE DE CEE e SR INTERCOM Eee FM — mains intercom elektor september 1977 — 9-25 rectifier, and feeds a DC voltage to A4, which operates as a trigger, the threshold voltage of which may be adjusted by means of P2. With a sufficiently large input signal, the output of A4 is pulled low, causing T1 and T2 to turn on and switch the supply voltage to the intercom. The value of R14 is such that the maximum current through T2 is 1A, which should prove sufficient in the majority of cases. The adjustment procedure is as follows: the slider of P2 is turned fully towards the anode of Dl and P1 is used to adjust the circuit to the desired sensi- tivity. If the circuit fails to trigger with Pi set for maximum sensitivity, then the trigger threshold can be lowered by means of P2. In addition to its use with a mains intercom, the circuit can be adapted for radio ham applications, since: *the circuit functions with supply voltages equal to or greater than 6 V *the circuit offers the possibility of VOX (Voice operated transmission) *Al and A2 can be used as microphone amp and clipper. K A a =) Multipurpose time switch Summer Circuits 1977 (E27/28), circuit no. 6. The operation of this circuit is such that only half of the mains period is multipled to obtain the required timing period. The maximum timing interval is therefore 0.01 x 2? seconds, or approximately 46.6 hours. In the example given for a 24-hour timer, an extra nought should be added at the end of the binary number. It will be noted that the Al...A8, Bl...B4 and Ci... C4 connections shown in the cir- cuit diagram are correct for this appli- cation. The last paragraph is perhaps mis- leading. The CMOS NAND gates men- tioned are actually N8 and Ná in the circuit. Automatic NiCad charger Summer Circuits 1977 (E27/28), circuit no. 13. In the diagram, two resistors are shown as Ré. The one in the top left hand corner should be R4 = 330 2. Furthermore, it should be noted that although S1 is shown on the p.c.board, only one pushbutton is required for any number of boards as shown in the circuit diagram. 0... 10V supply Summer Circuits 1977 (E27/28), circuit no. 24. A resistor Rx is shown on the component layout for the printed cir- cuit board. If a wire link is used here, the circuit shown in figure 1 is obtained. Alternatively, a fixed resistor at this point can be used to reduce the maxi- mum output voltage obtainable to any desired value. Spot-frequency sinewave generator Summer Circuits 1977 (E27/28), circuit no. 25. The input pinning of IC2 and IC3 are shown incorrectly. In both cases, the inverting input should be pin 2 and the non-inverting input should be pin 3. Stereo pan pot Summer Circuits 1977 (E27/28), circuit no. 35. The value of PI/PI” is not shown in the diagram. This should be a twin 10 k lin potentiometer. Reaction speed tester Summer Circuits 1977 (E27/28), circuit no. 54. Very little remains of the identification of the preset potentio- meter between pins 6 and 7 of ICI... This is PI, and the value is 100 k. If desired, C1 can be reduced to 390 n and P1 can be readjusted until clock pulses are produced every 10 ms. Shortwave converter Summer Circuits 1977 (E27/28), circuit no. 64. In the text, for BFO read VFO (variable frequency oscillator). Phaser Summer Circuits 1977 (E27/28), circuit no. 70. Tl... T6 are given in the cir- cuit as BC245Cs. This should have read BF245C. Voltage controlled monostable Summer Circuits 1977 (E27/28), circuit no. 82. The positive end of the electro- Iytic should be connected to pin 11 of the IC, the negative end to pin 10. Drill speed control Summer Circuits 1977 (E27/28), circuit no. 104. A better position for LI is in series with the connection between the top of CI and the top of RI — Cl is then connected direct across the mains. RI should be a 1 Watt type 34% digit DVM Summer Circuits 1977 (E27/28), circuit no. 105. T6 is shown as an E300. Although this FET will work in the circuit shown, its pinning does not correspond with the p.c.board layout. The correct type for use on the p.e.board is a BF245. (F é working perspex. elektor september 1977 — 9-27 should be around 80 watts, and for safety reasons the secondary voltage should not exceed about 24V. The resistance of the wire can easily be calculated from the equation: v2 R= where R = resistance V = transformer voltage P = transformer power The length of wire required can then be found by dividing the required resist- ance by the specific resistance (ohms per metre) of the wire. For example, if the transformer secondary is 24V at 2 80 W then R = EE = 2.81 92 If the specific resistance of the wire is 2.5 Q/m then the length required is 281 or l.12m. Alternatively, if a particular length of wire is required, for example to fit a certain bench, then the required specific resistance can be obtained by dividing the resistance by the length required. Obviously the wire gauge chosen should not be so thin that it will quickly burn out in use, but there is obviously much scope for individual ingenuity in con- structing a bending jig. The basic circuit of the bender is shown in figure la. The heating effect may be controlled by driving the transformer from a 100 VA Variac as shown in figure 1b, or by driving the heater direct from an isolating Variac as shown in figure lc. On no account should the heater be driven direct from a normal Variac, however, as this is not isolated from the mains. To use the bender the bend line is placed directly over the heater and the heater is switched on for about thirty seconds, after which the acrylic sheet should bend easily. Care should be taken not to bend at too low a tempera- ture as this can cause stress lines and cracks. When making a right angle bend it is best to bend the sheet just past ninety degress as it will tend to “unfold” as the material cools. With a little prac- tice bends with very clean, straight edges can easily be achieved. Bending is best carried out after all drilling operations have been completed, as otherwise the sheet cannot easily be supported while drilling. The only exception to this rule is if a large hole is to be cut very close to a bend. This should be cut after bending, as other- wise the bending operation may distort the hole. Cabinets may be constructed from a single sheet in “wrap-around” form with two endplates, as shown in the accompanying photograph. In this case only one seam is required on the main part of the box, and from an appearance point of view it is best to place this at the base of the cabinet. The end cheeks can be made of acrylic sheet or, for a contrasting appearance, wood. Wood also has the advantage that it can easily be grooved to accept the edges of the box. A transparent acrylic box with >sova gray 3799 14 sova 979918 9798 1€ wooden end cheeks can make an attract- ive housing for an instrument such as a digital clock, allowing all the *works” to be seen. Another useful method of construction is to make three sides of the cabinet in a *U” shape from a single acrylic sheet. The other three sides are also made in the form of a *“U* which mates with the first U”. The advantage of this method is that one part of the cabinet can form the front panel, base and back panel with components mounted on it, while the other part is simply a lift off lid. Seams and joints may be made using acrylic adhesive which is available from suppliers of acrylic sheet. Lettering Acrylic cabinets, like any other cabinet, can be attractively labelled using instant dry transfer lettering. After rubbing down the letters firmly they can be sprayed with protective lacquer to prevent damage. The lacquer should be of a type that dries to a hard gloss finish, as the matt types of lacquer supplied for use with instant lettering tend to attract dirt very quickly. TM-Perspex and Plexiglas are registered trade marks. Figure 1. Construction of a simple bending jig for acrylic sheet work. Figure 2. Three possible methods of powering the heater for the bending jig. Photo. An almost complete acrylic sheet cabinet, showing the main assembly and the RES Ee o ma CEM, - aan oo go e two end cheeks. sc e E guess a Ma — ES RER -28 — elektor september 1977 logarithmic darkroom timer oojoriiinmic ddiroom Linear or Logarithmic When taking a photograph, the exposure of the film can be varied in two ways, by altering the shutter speed and by altering the aperture setting of the camera. Opening the aperture by one stop doubles the amount of light falling on the film, ie. the aperture setting is calibrated logarithmically. In the darkroom, when printing or enlarging, the exposure of the photo- graphic paper is varied by altering the time for which the lamp is switched on. Here again, a logarithmic scale is appro- priate. For example, consider a timer with a linear scale calibrated from O to 100 seconds in intervals of five seconds. The first “stop”, from 5 to 10 seconds, will double the exposure time. However, at the top end of the scale a change of exposure time from 95 to 100 seconds would have little effect on the final print, as this last stop represents only a 5% change in exposure time. This means that: a) the timing scale is too finely calibrated at the upper end, but is probably too coarsely calibrated at the lower end, and b) the range of such a timer is limited, since to extend it to say 200 seconds would require a 40-way switch! This objection could admittedly be overcome by building a digital timer programmed by thumbwheel decade switches, but there would still remain the basic difficulty of having to estimate how much to increase or decrease the exposure time in order to obtain a lighter or darker print. In the circuit given here, each increment of the timing switch doubles the exposure time, so each switch position will have the same effect on the density of the final print. If a finer increment is required a “halfstop' position is provided that increases the exposure time by a factor of 2. A block diagram of the timer is given in figure 1. Pulses from a 10 Hz clock generator are divided by a counter whose division ratio can be set to either 5 or 7 by means of Sla. This means that with Sla in the *x 1.4” position the period of the output pulse is 7/5 (= 1.4) times the period of the output waveform with Sla in the divide-by-five Although there is no shortage of designs for darkroom timers, many of these suffer from the twin drawbacks of a linear timing scale and inconvenient controls that leave the user fumbling about in the dark. The design presented here overcomes these disadvantages by having a logarithmic timing scale and ergonomically designed controls. ) ImMer —) position. Since 1.4 is a reasonable approximation to 2, the timing interval with Sla in the 'x 1.4” position is /2 times the timing interval with Sla in the *x 1º position. The divided-down clock frequency is then fed to the start/stop switching circuit, and also to a 12-bit binary counter. The start/stop circuit is provided with Q and Q outputs, and in the quiescent state the Q output is high, holding the binary counter in a reset condition. When the start button is pressed the Q output goes high on the next positive- going edge of the clock pulse. This removes the inhibition on the counter which begins to count the clock pulses. S2 is used to select the particular output of the counter at which the timing interval is to stop. When that output goes high the Q output of the start/stop circuit goes low and the Q output goes high, which stops the count and resets the counter. A manual stop button is also provided for resetting the timer on initial switch-on, or for manual termination of the timing interval. As each stage of the binary counter divides the output frequency of the previous stage by two, the output, period of each stage is twice that of the, preceding stage, and this is how the logarithmic timing scale is obtained. The Q and Q outputs can be used to drive a relay or relays to switch on the enlarger/printer lamp during the timing interval and, if required, to switch off the darkroom safelight. The complete circuit of the timer is given in figure 2. The clock generator is an astable multivibrator built around two NAND gates N1 and N2. The clock frequency is divided down by ICI, a 4017 decade counter. Depending on the position of Sla this counter will count to 5 or 7 before, resetting itself via N3 and N4. The) divided down clock pulses are available: at the output of N3. The start/stop circuit comprises two) D-flip-flops FFl and FF2. In the quiescent state, for example when the stop button has been pressed, both these flip-flops will be in the reset state. The Q output of FF1 will hold the rese: input of the binary counter IC3 high, 
