MEMBER General Interest PROJECT: Fuel economiser 8.24 PROJECT: Door bell memory 8.46 New Computer System enhances textile production 8.54 PROJECT: Proximity detector 8.56 Radio & Television PROJECT Chrominance locked clock generator 8.20 PROJECT Microprocessor controlled radio synthesi7e> - Part 1 8 28 PROJECT: Direct-conversion receiver for 80 metres 8.38 PROJfcCI Frequency read-out for short-wave receiver 8.41 PROJECT Reception and transmission of radio teletype 8 47 Test 8i Measurement PROJECT: Electrometer 8.35 Information Telecommunication news 8 16 Electronics news 8.17 New products 8.62 Corrections a 73 Guide lines Classified advertisements 8.74 Index of advertisers 8.74 Selex-37 Battery operated tube light 8.59 Printed at : T rupti Offset Bombay - 400 013 Ph. 4923261,4921354 Copyright ® 1988 Elektuur B.V. 1 8.03 TELECOMMUNICATION NEWS • TELECOM Optic Fibre Lab The quality assurance circle of the De- partment of Telecommunications will set up a Rs. 6 crore optic fibre and sys- tems laboratory in Bangalore during 1988- 89. Two quality assurance centres are prop- osed to be set up at Bangalore and Bhopal where production of optical fibres will begin shortly. The 1TI and Hindustan Cables Ltd. , will set up a pro- ject in the joint sector at Naini for pro- duction of optical fibre cables. This pro- ject will be in collaboration with the Danish firm NKP. The Madhya Pradesh State Electronics Corporation will set up a Rs. 50 crore unit at Bhopal for the manufacture of both optical fibre cables and systems in collaboration with the Japanese firms Fujitsa and Furokowa. The first phase of production is scheduled to begin in 1989- 90. To develop expertise in handling the sophisticated equipment, the Interna- tional Telecommunication Union and the United Nations Development Prog- ramme are sponsoring training prog- rammes, according to Mr. U.R.G. Acharya, general manager, Telecom QA circle. In 1987-88, the Telecom QA circle had evaluated telephone instruments pro- duced by six manufaeturers in the pri- vate sector-Swede India Tetronics, Ban- galore, Rajasthan Telephone Industries Ltd., GCEL, Ahmedabad, Keltron Telephone Instruments Ltd, Telematics Systems Ltd., and Bharat Telecom Ltd. About 66,000 instruments, mostly pro- duced by the first three firms, had been approved. Reviewing the circle’s achievements in 1987-88, Mr Acharya said that more than 700 cases of prototype approval had been processed and finalised. About 25 publications for helping Tele- com QA personnel and telecom indus- tries had been brought out, which in- cluded 16 quality manuals. New QA test centres have been established at Goa and Mysore, while additional centres will be opened shortly at Madras and Hyderabad. Testing facilities in all test centres, par- ticularly at the Components Approval Centre for Telecommunication and the Telecom Testing Laboratory, both in Bangalore, would be augmented. As per the agreement with the ITU and UNDP, telecom experts from the de- veloped countries would organise prog- rammes for Indian participants and senior Indian telecom officials would be trained abroad in latest telecom technologies. Telecom Plan To provide telephone connection to anyone on demand by the year 2000, five more electronic switching factories, in addition to the existing one. are needed. According to a perspective plan drawn up by the Department of Telecommuni- cations for 1990-2000, an investment of Rs. 47,700 crores should be made during these 10 years if the targes are to be achieved. The targets are provisions of telephone on demand, a public tele- phone in every village, and installation of eight lakh voice and data communica- tion circuits to meet the demands of the business and industry. In the seventh plan, 1985-90, the ex- pected expenditure on telecommunica- tions is Rs. 8,100 crores. The perspec- tive plan requires at least six times this investment in the next 10 years. According to Mr Satya Pal, secretary to the Department of Telecommunications the department had spent Rs. 3000 crores in 1985-88, installed 10.23 lakh lines of local switching capacity, 1.81 lakh lines for replacement and 9.04 lakh lines of direct exchange lines, besides providing STD facilities for 107 district headquarters. During the last three years, the depart- ment, established 2000 rural exchanges, 16 trunk automatic exchanges, 5,085 long distance public telephones and 60 telephone exchanges. Besides providing 11,356 telex connections, the depart- ment set up 36 satellite earth stations. The department has been authorised to spend Rs. 1700 crores for the current fi- nancial year, 1988-89 though its demand was for Rs. 2400 crores. According to a DOT review, against the seventh plan target of creating 21 lakh lines of local switching capacity, 4.81 lakh lines for replacement and 16 lakh direct exchange lines, it could create only 10.23 lakh lines, 4.81 lakh lines and 9.04 lakh lines respectively in 1985-88. The department hopes to fulfill the target in the remaining two years. The DOT has engineered remote area satellite network with a capacity of 1000 subscribers and has invested Rs. 15 crores. The system, likely to be opera- tional by 1989, will provide the users with their own microwave earth sta- tions. Over 300 industrial units have re- gistered with the department for this facility. On the Cellular or car telephone system, Mr Pal said, in Bombay 1200 car tele- phones would be installed in the first phase and 5000 more would be installed in the second phase. The categories of telephone would include those fixed in cars, hand-held apparatus and trans- portable units. Initially some imports would be made and later they would be manufactured locally, even in the pri- vate sector. Kiss Phone Telephones are undergoing a lot of change in their names, appearance and action. No wonder, some manufacturers catalogue their telephone instruments as “Telemoon" and “Kiss Phone”, thus making the phone more of a personal fashion piece. Japanese stores display over 500 types of telephone instruments making it dif- ficult for shoppers to make a simple choice. Telemoon and Kiss Phones are meant for personal use rather than for the whole family. Telephone answering machine is in- creasingly gaining popularity. This machine tapes messages from callers when there is no one at home to answer the phone. Today’s telephones come with a variety of features - phone number pre-setting; one-touch dialling; automatic redialling; call waiting; call rejection; screen display of dialled number for confirmation; volume and tone adjustment and so on. Most of the high-tech phones are push button types. Push button phones and dial phones differ in the way dialled numbers are transmitted. In the dial phone, each number is represented by a series of current breaks that is transmit- ted to the switchboard. In push button phones, each number signal is transmit- ted as a pair of audio frequencies one of which is the same for four horizontal rows of buttons and the other same for three vertical rows. TELECOMMUNICATION NEWS • TELECOM Cordless phone is another item becom- ing popular. Using this, a person can carry on the conversation staying within 20 metres of the main set. A wireless handset functions as a cordless phone. The phone is made up of a built-in mini- ature transreceiver, with a wireless base unit. It uses weak electrical signals for communication. The negative feature of the cordless phone is that only a limited range of frequencies is available for this facility. If all houses use the cordless phone, there is a likelihood of mixed transmissions and “wave tapping”. Mobile phone or car phone is another type of cordless phone. It paves way for a two-way communication. They are basically powered by car battery. Mobile phones are also known as cellu- lar phones. This name is derived from the fact that many cell-like zones, each with a radius of two to 10 kilometres, are marked off for mobile phone service. In each zone, a radio base station is con- structed to send voice signals over elec- tric waves of certain frequencies through a dedicated base station. When a car moves from zone A to zone B, the fre- quency of the transmission is automati- cally switched. The key station controls this change of frequency while tracking the target car. Radio paging is another popular form of one-way communication. This system makes use of “beepers” which are car- ried by construction supervisors, sales- men and doctors so that they can be notified when someone is trying to reach. New paging devices are appearing in the market. One new pager, the size of a pack of cigarettes, is capable of display- ing numerals on its liquid crystal display. During operation, the caller is able to use a push-button phone to send a code indicating his own number which the holder of the page is to call. The system can also be used to transmit simple coded messages. Improvements in the messagcs-receiv- ing functions of pagers have prompted many new service companies to provide real-time information on foreign ex- change rates, stock prices and other ap- plications for customers who need up to the minute data. Though these gadgets have come on the Japanese scene, like many other technologies and services, it won’t be long before they invade the Indian market. ELECTRONICS NEWS • ELECTRONICS NEW Face Competition The Electronics Commission has suggested that the electronics industry should be exposed to international com- petition to bring down prices. The commission at a meeting held re- cently discussed the high prices of com- puter peripherals such as floppy drives, terminals and printers and noted that despite concessions such as steep cut in the customs duty on the imported in- puts, the industry had failed to bring down prices. Domestic prices of these items were still three to four times higher than the world prices. The slight drop in prices was not in proportion to the concessions given to the industry. The commission has asked the Depart- ment of Electronics to conduct systema- tic studies on cost-price structure of the items. If the industry failed to cut pro- duction costs due to inefficiency, the sol- ution should be to allow imports of these items and expose the local industry to world competition. If the problem was traced to disproportionate marketing costs or the smaller units facing a severe marketing constraint, the department should take remedial measures. It has been suggested that an organisation like the ET & T should make bulk purchases and sell the items at fixed price through- out the country. The public sector units engaged in the manufacture of defence electronics had gained strength in several areas and all out efforts should be made to exploit the potential. India has massive deposits of ferrites in Madhya Pradesh and the commission felt that the studies relating to the ex- port potential ferrites should be taken up. Schemes should be developed to Make Madhya Pradesh a “Ferrite Val- ley” like the Silicon Valley. The thrust of the commission's last meeting was on how to increase the use of electronics in improving the standard of living of the people, to increase its use in the industrial sector, and to improve reliability and quality of the Indian products. Matkem Silicon The Department of Non-convcntional Energy Sources has sanctioned Rs. 1 crore to Matkem Silicon Ltd., for its proposed research and development centre. A further soft loan of Rs. 50 lakhs is extended for upgrading the existing plant and equipment. Efforts are underway to scale up the plant technology to bring down the pro- duction cost of indigenously produced silicon wafers. The company is now wholly owned by Mcttur Chemicals Ltd, a private sector firm. Negotiations are in progress to provide equity to the gov- ernment in this plant. The quality of polysilicon produced at Matkem was satisfactory and was meet- ing international standards, according to Mr Maheshwar Dayal, secretary to the department. The 25-tonne plant was now meeting the demands of the coun- try. The production can be scaled up to 150 tonnes per annum. Polysilicon crystals and wafers had a growing market with the increased utili- sation of photovoltaic cells. Currently, Matkem is supplying polysilicon wafers to the BHEL and the Central Elec- tronics Ltd. The government has set a target of one megawatt power to be pro- duced annually through photovoltaic cells. The primary technological goal of Matkem would be to reduce the cost. of production by cutting down energy 1 8.17 ELECTRONICS NEWS • ELECTRONICS NEW By June, 1989, a pilot plant for the man- ufacture of amorphous silicon would be ready near Delhi. Seven research groups in the country were studying this mate- rial and developing the production technology. Amorphous silicon has a potential to reduce the costs of photo- voltaic cells. A new financing body called Indian Re- newable Energy Development Agency has been set up recently to finance both producing and purchase of renewable energy sources. An expert panel on photovoltaics has been set up with representatives fro^n leading research institutions and indus- tries to review the development of this technology in the country. The DNES has submitted a proposal to set up a chain of solar energy stations of 30 MW capacity each and the proposal is under the consideration of the planning commission. Shortfall of Silicon A latest report of the Department of Electronics on the industrial promotion and research and development in silicon has found that there is a gap of about 1.5 million silicon wafers between de- mand and supply for photovoltaic applications. Apart from Metkem, two other indigen- ous companies, Super Semiconductors private limited, Calcutta and Siltronics, Bangalore, are in the silicon business. They buy polysilicon from the market, pull single crystals and slice wafers from When all the expansion plans of the three companies come through, the total installed capacity for conversion of polysilicon into wafers, would be over one million wafers which is equivalent to 20 tonnes of polysilicon. The existing shortfall is expected to be made up Within one year. The DOE does not feel the need to invest in creating additional capacities immediately. The three manufacturers, in the current year, are slated to supply 640,000 wafers, of which the share of Metkem is 480,000. Photovoltaic industry uses only 10 cm diameter wafers and until last year the total watering capacity was 300,000 against the total consumption of 1.4 million wafers, corresponding to a total poly consumption of six tonnes. Though Metkem’s annual poly production could yield close to 1.25 million wafers, lack of adequate pulling and wafering capacity resulted in shortage of indigenous wafers. The solar cell manufacturers, the CEL and the BHEL, expect to create a higher total capacity of 1.6 MW peak solar power in 1988-89 to meet the additional markets generated outside the require- ment of the DNES. From this, the DOE has projected a demand of two million wafers for 1988-89 for the PV industry. The CEL alone has recently floated global tenders for 1.7 million wafers. Taking the indigenous supply position, then the shortfall may be around 1.3 million. Thus, there is actually a de- mand for more than 25 tonne per annum of poly if enough wafering capacities can be created. Till then, wafers will con- tinue to be imported. For semiconductors, hardly any supply is being made by local suppliers. Sub- stantial import of silicon is taking place in the form of diffused wafers and chips. In 1987, close to 3000 kg of undiffused wafers were imported. About 50 per cent of semiconductor devices are pro- duced on indigenous diffusion. If all the devices were to be made with indigen- ous diffusion, the estimate for silicon consumption for the semiconductor in- dustry would be around 6000 kg. Computer Hacker A 24-year old man in West Germany gained access to over 50 military and in- dustrial computers in the United States and Japan, using a home computer and a telephone, thus creating a sensation in the history of computer crimes. Sitting in Hanover, the hacker who is called David Keller (not his real name) operated the national computer security centre in Fort Mead, Maryland, which is a data protection facility; the SRI net- work information centre in Nebraska; an air force control system in California; a naval coastal system command centre; the Optimus data base of the Pentagon; the gas turbine laboratory in Pasadena; the Boeing security computer in Seattle; the Anniston army depot in Alabama; and a system at the Fort Buckner American army base in Okinawa, Japan, to name a few. The story of the discovery, the investiga- tion and the identification of the Hanover hacker illustrates both com- plexity and susceptibility of the high- tech world as well as the clashing in- terests of the main players. In August, 1986, Cliff Stoll, a 37 year- old systems manager at the Lawrence Berkley Laboratory in California disco- vered that an unknown person was using his laboratory computer. His laboratory is associated with the Star Wars project of the Lawrence Livermore Laboratory, Stoll is also processing nuclear arms information. Computer systems of Livermore and Berkley labs, in addition to the compu- ter systems of many universities and re- search institutions in many parts of the world, are interconnected. Berkley is also connected to Milnet, which is linked to military and a. naments computers. Stoll’s surveillance showed that Keller hacked into about 450 different military computers. In one system, he got through a security hole which gave him the status of a super user, a privilege which got him access to all stored data which he could then either read or alter. Stoll followed the hacker day and night and the pursuit through the computers remained a secret. The hunted hacker used the trial and error method, like walking along a street, pressing every door bell, without using force. If the front door did not open, the attempt was made at the back door or side window and then he moved onto the next house. The hacker was present only for a few minutes and it posed a problem in trac- ing him. But, false information was lured before him and more details about him were gathered. The hacker was in- terested in catchwards like nuclear and SDI, Strategic Defence Initiative. A breakthrough came in the investiga- tion when the hacker was traced across the Atlantic in a German post office net- work. He was using the Bremen univer- sity computer as a springboard to America. The FBI alerted the German authorities and the hacker was being watched both from America and Ger- many. Then a lure was dangled in the form of a false Star War project and the hacker got hooked to it. He remained at the screen until he was traced through the Bremen computer to his home at Hanover. A few months later, the laboratory re- ceived a request for more information about the decoy project from an arms dealer in Pittsburgh who was known to ELECTRONICS NEWS • ELECTRONICS NEW have ties with Saudi Arabia. It is not known how he got the information about the project. In June, 1987, the hackers home and of- fice were searched. His machine was confiscated. But, hacking alone was not an offence and the evidence was insuffi- cient to prosecute him under West Ger- man law. The legal committee of the government said hackers who simply burrowed their way into systems and did not obtain data illegally should not be prosecuted. The FBI maintained a news blackout. Stoll wrote an article about the episode in a computer magazine in May, 1988 and the news appeared everwhere. Time magazine and New York Times began a research in this case. A lot remains unknown. What, for example, are the chances of foreign powers getting information through their secret services hacking into compu- ter systems? Though claims were made that the hacker had not seen any secret material, the problem is that no one knows exactly which data the Hanover hacker had seen or not seen. Clifford Stoll emerged as a victorius hacker hunter. But the question re- mains: How many hackers, apart from the Hanover hacker, have gained entry to strategically important computer sys- tems? Have hackers altered program- mes without anyone knowing? How near is this episode to the film “War Games” in which a young hacker set in action the war programme in the Penta- gon computer just to impress his girlfriend? The Chaos Computer Club, a hacker club in Hamburg, sees the world as being more and more automised and controlled by strange forces through machines, computers and robots. It has become necessary to analyse the work of hackers to improve computer security. Meanwhile, the Hanover hacker has been offered a new job with double pay. Mega Bubbles Incredibly small magnetic bubbles are emerging as the new generation, ultra- dense memory storage systems. These systems are rugged, resistant to radia- tion and non-volatile. They retain the data when the power is switched off and they need few moving parts. Bubble-memory devices in which the presence or absence of bubbles denotes the Is and Os of computer language al- ready exist. They arc used in robot memories, portable instruments, specialised computers and many more places where ruggedness and reliability are needed. But the bubbles in these systems are elephantine in size com- pared with the bubbles now under study in the laboratories of Carnegie Mellon, USA, Japan’s Hitachi and Fujitsu and a US firm, Mem Tech. The shrinking bubbles, ten times smaller than the ones used today, combined with modern technologies like ion im- plantation may enable developers in less than a decade to cram as many as a bill- ion bits of information on a chip of the size of a thumbnail. Today’s state of the art bubble chips and silicon semiconduc- tors chips hold four million bits. These super-high density bubbles, as a result of the price drop, will find appli- cations in areas where bubble memory is now too expensive. These include ordi- nary personal computers, automobiles that remember your destination, digital audio players with no moving parts and filmless cameras. Before bubble technology reaches store shelves, however, specialists say that more basic research is needed. The sta- bility of bubbles in new devices must be evaluated, faster ways of moving the bubbles around inside chips must be found, and the bulky electronic compo- nents for detecting bubbles need to be more compact. In bubble-memory systems, as in semiconductor memories, information must be written, moved around, re- trieved and read. The underlying differ- ence is that in bubble-memories, infor- mation is represented by tiny magnetic regions, or bubbles. The bubbles are formed on the surface of a garnet crystal made up of magnetic domains pointing in opposite directions. As a magnetic field is applied perpendicularly to the crystal surface, those domains pointing in the direction opposite to the field begin to shrink into snakelike patterns and eventually, into smaller circular spots or bubbles. MICRON TECHNOLOGY The Electronics Commission has cleared the import of 1.5 micron technology from the US. The 1.5 micron technology will be used for the manufacture of telecommunica- tion equipment. This will enable India upgrade its existing miniaturisation of the integrated circuits. The Semicon- ductor Complex Ltd., Chandigarh and the Bharat Electronics Ltd. have the capabilities to manufacture these mic- ron chips. SCL is working towards achieving two microns capability before the end of the year. One micron is ten-thousandth of a cen- timetre and 1.5 micron technology im- plies that at this level of integration of circuits on the silicon chip, each compo- nent will have dimensions roughly of this order. Such high level integration corresponds to somewhat beyond what is termed as Very Large Scale Integ- rated circuits. The VLSI regime begins at two microns: VLSI corresponds to in- tegration of close to about a million components on a standard size semicon- ductor chip. The Indian Telephone Industries has sought transfer of technology from an American firm, VLSI Technology, California, for the 1.5 micron technol- ogy. When the technology becomes av- ailable, ITI will be able to fabricate de- vices for defence applications, digital for cipher codes and echo canceliors for telecommunication and so on. Microelectronics production in India forms hardly 0.6 per cent of the total electronics production in the country or it is worth Rs. 7 crores. The target set for 1995 is Rs. 1000 crores. The Application Specific Integrated Cir- cuits arc the fastest growing segment of the microelectronics family which are ideal for low volume production and known for their competetive edge in cost and functions. India has just made entry in the production of VLSI ASICs. Production for 1988 has been estimated at Rs. 50 lakhs whereas it should be around Rs. 2.50 crores for an electronics systems market of Rs. 75 crores. SCL has approached the AMI of USA for upgrading its two micron technology into three micron technology. Ulti- mately, SCL may transfer this technol- ogy to the ITI. However, ITI seems to have preferred a collaboration with the VLSI Technology Inc. CHROMINANCE LOCKED CLOCK GENERATOR A remarkably simple solution is offered to a problem almost any constructor of a test card or callsign generator, logomat, graphics card, or any other video equipment must have been faced with at some time: phase synchronicity between clock pulses in the system and the chrominance subcarrier. A PLL circuit is described that enables deriving the TV line and field frequency, and a number of other useful signals, from the chrominance frequency, 4.433 MHz. A mystery unravelled! by J. C. Stekelenburg PE1FYZ In video equipment, the beneficial ef- fects of phase-locking the central clock oscillator to the chrominance subcarrier are mainly the elimination of annoying digital interference and colour cross- patterning. The improvement can be noticed in the well-known colour bar test chart, in which colour transitions be- come sharply defined rather than blur- red with bands of spurious lines and ran- . domly moving coloured spots while longer lines are moving slowly and diagonally or horizontally across the screen. In professional video systems and studios, complex equipment is available to ensure that all TV synchronization signals have a fixed phase relationship with the chrominance frequency, as set forth in the relevant CCIR- specifica- tions. This article demonstrates how some thinking on the technical background of the PAL ( Phase Alternation Line ) and NTSC ( National Television System Committee) TV systems, and a com- parison between these in respect of poss- ible interference, leads up to simple computer-assisted arithmetic and, fi- nally, the design of a circuit that achieves the above objective of providing chrominance-locked, standard clock fre- quencies for digital video generators. Choice of the chrominance subcarrier frequency The PAL TV system is based on double- sideband modulation of the picture colour information onto a subcarrier of 4.433 MHz. This system is basically similar to that used for NTSC TV. The Y (luminance) signal is obtained by adding the three primary colours, red (R), green (G) and blue (B), in proportion, as Y=0.3R+0.59G+0.11B The degree of luminance of each in- dividual pixel determines its brilliance, black corresponding to minimum, and white to maximum luminance. For a monochrome TV set, the luminance signal is sufficient for producing a pic- ture. A colour receiver, however, needs the three primary colours for mixing to give each pixel on the screen the correct colour. The colour receiver finds two modulated signals, R-Y and B-Y ad- jacent to the 4.433 MHz subcarrier. From these, the R, G and B signals are obtained by means of a number of simple operations involving subtraction and addition. The R-Y and B-Y signals are quadrature-modulated on the 4.433 MHz carrier, so that the instantaneous phase provides a measure for the colour of a pixel, and the amplitude for the colour saturation. Since the colour sub- carrier is found within the luminance band (0 ... 5 MHz), its sidebands will be- come visible as a pattern of thin lines. In the NTSC TV system, this undesirable effect is minimized by using a colour subcarrier frequency that is an odd multiple of the line frequency. This gives rise to a dot pattern which is far less con- spicuous and annoying than the line pat- tern that would be formed in the PAL picture (see Fig. 1). In the PAL system, the phase of the modulated R-Y signal is inverted for every line in the picture. This causes two sidebands adjacent to the 4.433 MHz subcarrier, at an offset corresponding to half the line frequency. When the sub- carrier frequency is chosen such that it is an odd-numbered multiple of half the line frequency, B-Y information will result in a dot pattern, and R-Y infor- mation in a line pattern. To avoid this, the chrominance subcarrier frequency is an odd multiple of the line frequency divided by four ( quarter-offset ). Time- averaging of the remaining interference on a raster-by-raster basis is further achieved by adding 25 Hz (raster fre- quency) to the colour subcarrier, so that cross-interference between luminance and chrominance is least noticed. Sum- marizing the above, the optimum fre- quency of the chrominance subcarier, fciir, becomes: /'ch,=(15,625/4)-U35+25 = 4,433,618.75 Hz corresponding to the line frequency multiplied by 283.7516. The deriving of the line frequency from the chrominance frequency would, therefore, require dividing this by 283.7516. This is imposs- ible by electronic means, which only Table 1. 1 REM chrominance-locked clock generator 5 REM successive approximation of clock divisors 10 K=44336l8.75 20 INPUT 1 'Enter output frequency ",F 30 H=K/F 40 P=H/(H-1) 50 B=1 60 FOR X=1 TO 1000 70 Y=P*X 80 A=ABS(Y-RND(Y,-1)/X 90 IF A>=B; NEXT X 100 IF A from pin 4 of Nj. This enables checking the operation of the 4 MHz oscillator with the aid of an external tuning voltage obtained from the wiper of a po- 2 Fig. 2. Block diagram of the chrominance- locked clock generator for video systems. Resistors (±5%l: Ri = 10M R2=120K R3;R7;R1 1;R12 = 10K R4;R6= TOOK R5 = 560K R8 = 12K R9= 1K0 Capacitors: Ci = 100p C2=40p trimmer C3=220n C4;C5;Ca;Cto;Ci3=47p C6 = 68p C7;Ce:Cii = 100p Ci2= InO Ct4;Ci5” lOOn Inductors: Li = winding details are given in the text. Neosid Type 7A0 INeosid Limited • Icknield Way West • LETCHWORTH SG6 4AS. Tele- phone: 104621 481000. Telex: 826405. Con- tact Mr. E. Adcott). Neosid inductors are also available from C-l Electronics. L2= 13pH with centre tap (see text). L3 = 7/iH with centre tap (see text). Semiconductors: Di. . .Dll incl. = 1N4148 Di2 = BB105 Dt3;Dl4 = AA1 19 ICl =4093 IC2 = 4001 IC3;IC4 = 4040 IC5 = 4013 ICe = 4516 Ti;T2 = BF199 Miscellaneous: Xi = quartz crystal 4.433 MHz. It is regretted that a printed-circuit board for 3 Fig. 3. The clock generator is essentially a discrete phase-locked loop. Fig. 4. Oscillograms showing Ihe operation of the XNOR phase comparator. tentiometer connected between +12 V and ground. To begin with, adjust Li so that oscillation is achieved around 4 MHz. Check that the oscillator can be tuned with the potentiometer. The out- put of Nj should supply CMOS- compatible clock pulses. It is essential that these pulses have the full CMOS swing of about 12 V PP when the oscil- lator is tuned around 4 MHz. Do not add too much capacitance to the parallel tuned circuit when its resonance fre- quency is found to be too high: instead, ensure more inductance by increasing the number of turns on Li. Next, adjust trimmer capacitor C: to give 4.43362 MHz at the buffered out- put. Measure the frequency at pin 2 of Nj - this should be 4.8721085 kHz. Similarly, measure the frequency at pin 1 of N2 to check the operation of IG1-FF2. Tune the oscillator to obtain about 4.8 kFIz here. When these tests check out, it is time to close the loop by removing the poten- tiometer, and connecting IC to the out- put of Nj. Connect the frequency meter to the 4 MHz output. Some re- adjustment of Li may be required to get the PLL to lock. The oscilloscope photographs of Fig. 4 may be used as guidance if difficulties are encountered in the setting up. The upper two traces show the 4.8 kHz signals at the inputs of the phase com- parator, i.e., pins 1 and 2 of N2 (or Ns), the lower trace the phase comparator output (pin 4 of Nj). Although the lat- ter signal is different in the photographs, the PLL was locked in both conditions, with only Li set differently within the hold range of the oscillator. It is clearly seen that the phase comparator is essen- tially an exclusive NOR function: the output goes low only when the two input signals are different. The operation of the PLL can be check- ed by carefully adjusting Li while monitoring the phase comparator out- put with an oscilloscope. It will be found that the PLL loses lock when the pulses become significantly narrower than those in the lower trace of Fig. 4b. When the PLL is locked, Li can be adjusted over a small span while the output fre- quency remains stable at 4.000002 MHz (7-digit resolution). Finally, switch the power to the circuit on and off a few times to verify that the PLL starts and locks properly. All drift on the 4 MHz output is, of course, caus- ed by drift of the quartz crystal fre- quency. It is, therefore, recommended to make the final adjustment of C2 and Li after a warming-up period of about 10 minutes. Multiplier for TEA1002 The circuit described is used by the author as part of a digital test chart and call-sign generator for amateur tele- vision. The system incorporates a TEA1002 colour generator chip (Ref. '") which requires an input signal of 8.86 MHz. The circuit of Fig. 5 multiplies the buffered crystal oscillator output of the chrominance oscillator by two to obtain this frequency. The multiplier is essen- tially a double-phase rectifier with a parallel-resonant L-C output filter. Suggested diode types are AA119 or OA95 (in any case, germanium types should be used). L2 and Lj are wound as 30 and 20 turns respectively of 0.2 mm dia. enamelled copper wire, with a centre tap. It is also possible to use ready-made inductors provided they are known to have a centre tap and the cor- rect inductance (use a grid-dipper to check the in-circuit resonance fre- quency). Both L2 and Lj are simply peaked for maximum amplitude of the 8.86 MHz output signal. Bu Reference: <» Video combiner. Eleklor India, March 1984. For further reading: Principles of PAL Colour Television. H. V. Sims, London Iliffe Books Ltd. 1969. Phase-lock techniques. F. M. Gardner, John Wiley & Sons Inc. 1966. eleklor india august 1988 8.23 an R.P.M. indicator as an economy guide. Although an r.p.m. counter is a useful instrument, it is not very helpful in terms of saving petrol. If it was to be used for this purpose it would have to be watched far too carefully to be effective and this would be too demanding on the driver. The circuit described here does not provide a complete r.p.m. indication but rather an indication of when to change gear in order to keep the engine speed at its most efficient. It also gives a warning when the maximum engine speed is approached and would therefore be of use to drivers of high performance cars as well. The circuit has been designed to demand as little attention as possible (in 4 economiser A car engine is at its most efficient when the amount of energy it produces is closest to the amount consumed. This occurs at an engine speed that produces the maximum torque output. Outside of this quite small speed range energy is wasted. The fuel economiser provides both an optical and an acoustical guide to enable the driver to change gear at the optimum time and thereby keep the engine within its most efficient range. from the driver. As well as giving a visual indication in the form of coloured LED's, it is able to produce an audible indication of the correct gear chance How an r.p.m. counter can help save fuel. It is often underestimated how much a person's driving style will affect fuel consumption. Figure 1 shows the factors which are involved. The con- sumption of a car without any technical defects has been set at 100%. The 'extra's' piled onto that block should be avoided, and it is the 'driving style' section which depends exclusively on the driver. As far as driving economically is concerned, this is easier said than done. Usually, we drive 'by ear' which is not always an objective mehtod. An r.p.m. counter is highly objective and can help break some bad habits. The amount of energy consumed by the engine is largely dependent on the engine speed and the torque. Figure 2 shows the torque/revs curve of a typical engine with the energy consumption as a function of the r.p.m. The engine will produce the maximum amount of torque at a certain number of revs. (The ■ exact amount will of course depend on the engine). At this speed, the engine will be running at its highest efficiency. When engine speed is increased signifi- cantly above this figure however, much more fuel will be consumed, with a progressive decrease in actual power output per 100 r.p.m. From the graph the following guidelines for an econ- omical driving style may be deduced: When accelerating (particularly in town traffic) the engine speed in every gear should reach the point at which the maximum torque occurs. As soon as this speed is exceeded, the driver should change gear. • When accelerating depress the accel- erator smoothly and not too quickly. • The key to success is to accelerate smoothly and change gear on time. When the car is not accelerating, it will be apparent that the higher the gear, the lower the fuel consumption. (For in a high gear the number of revs will be lower and as figure 2 shows, fuel consumption is at a minimum at low engine speeds). The number of revs should not exceed the level at which the maximum amount of torque is produced. Unfortunately, prevailing these measures will be affected by traffic conditions. Flowever, any attempt at saving fuel and whenever possible must be better than no attempt at all. This is where the Fuel Economiser becomes realy effective. Which r.p.m. counter? Of course any r.p.m. counter can be used to save energy. Unfortunately, as mentioned previously, the 'ordinary' type using a dial or, even worse, a digital display demand too much of the driver's attention. An r.p.m. counter which is meant to save fuel should only provide relevant information when required and not in such a way that the driver is distracted. It is better for it to indicate ranges rather than exact values. In the Fuel Economiser these are indicated by LED's in the following manner; yellow: engine speed lower than at maximum torque green: engine speed about right for maximum torque red: engine speed higher than maximum torque Figure 3. The fuel economiser does not indicate the exact number of revs, but gives a general idea of whether they are too low. too high or just right. 4 red flashing: maximum permisible engine speed reached Figure 3 shows how the display works in relation to the torque/rev curve. Three LED's are sufficient. An extra acoustic signal means you don't have to keep your eye on the LED's continu- ously. A short tone signals the transition from the green to the red range and indicates it is time to change gear. When the maximum number of revs is exceeded an intermittent warning note will be produced. The fuel economiser itself: The block diagram shows a frequency- to-voltage converter at the input to convert the contact breaker frequency into a linear, proportional DC voltage level. This is fed to three comparators which are used to switch the corre- sponding LED on when the measured engine speed complies with the preset threshold value. When the light switches from green to red, the monoflop MF sends a pulse to the tone oscillator AMV2, which then produces an acoustic signal with the aid of a loud- When the threshold value for the maximum number of revs is reached AMV1 is triggered and produces the flashing frequency for the red LED. At the same time this signal is used to switch the output of the tone oscillator via an OR gate. As can be seen in the circuit diagram (figure 5), the frequency-to-voltage converter is a fairly simple circuit. Transistor T1 acts as a pulse shaper and IC1 is a 555 timer 1C in a monoflop configuration. By integrating its output with the two RC networks R7/C6 and R8/C7, a DC voltage level that is proportional to the pulse frequency is obtained. This DC level will arrive at the non-inverting inputs of op-amps < A1 . . . A3. These three op-amps are used as comparators and are, together with A4, combined in a single LM324 1C. The voltages to be compared are adjustable with preset potentiometers P2 . . . P4. Until one of the threshold values is reached, (the number of revs being below the economical value) the outputs of the three comparators will be low. In this condition the yellow LED D7 will light and the others will remain unlit. When the first threshold is reached (lowest limit of the maximum torque range) the output of A1 will be at the positive supply voltage (about 12V); causing the green LED (D8) to light and D7 to go out. At the second threshold A2 will switch, the green LED will go out and the red LED's D9 and DIO indicate that the torque output is falling. The positive edge of this signal triggers the tone oscillator. Integration through C11 and R19 causes a tone with a descending pitch to be produced. This is to advise the driver to change to a higher gear. When the engine speed reaches the value set by P2, comparator A3 will switch on the astable multivibrator A4. This will cause the red LED's D9 and DIO to flash once every second and modulates the tone oscillator IC3 via D4 to give an intermittent warning signal. IC3 controls an 8 (2/0.2 W loudspeaker. If a greater volume is required, a piezo tweeter can be used instead. If the volume is too loud, R21 can be increased. To enable the fuel economiser to work efficiently in the car a voltage stabiliser is needed and this consists of zener diode D6 and transistor T2. Diode Dll, resistor R12 and capacitor C5 serve to suppress transients. Construction and setting up Thanks to the printed circuit board shown in figure 6, construction should pose no problems. It is advisable to use sockets for the three IC's. It is also an advantage to use tantalum electrolytical capacitors for C7, CIO and if possible for C14 and C11 too. Setting up requires a multimeter, a small transformer and a bridge rectifier. In addition, the following engine data should be obtained: 1 . The highest acceptable engine speed in r.p.m. (n max ). This can usually be found in the car manual but if in doubt, 5,500 r.p.m. will be close enough. To save the engine a slightly lower figure should be taken, say about 5,250. 2. The lowest (nl) and highest (n2) limits of engine speed are derived from the engine torque/rev curve (see figure 3). If this is not given in the manual, you should ask your car dealer. 3. The number of revs at a contact breaker frequency of 100 Hz. The following ratio exists between frequency f (Hz), number of revs ° ^iT^n* an< ^ ,he number °* cylinders Z: f=^2^ (for 4-stroke engines) and f = n gQ^ (for 2-stroke engines). From this it follows that for 100 Hz in a 4-cycle engine nioo Hz = — ^°° is required. Once these r.p.m. values have been calculated, the voltage value can be preset for n max at 5 V with P2 measured either at the rotor or at pin 9 of IC2). The following voltage for n2 is then preset at the rotor of P3: Up,,5V-=2- n max Analoguous to this the voltage for nl is preset at the wiper of P3: Up 4 = 5 V • ^1- Finally, the frequency-to-voltage converter will have to be adjusted to the engine's r.p.m. For this the 100 Hz generator (figure 7) is connected to the rev counter and PI is set so that the following DC level is measured at capacitor C7: U C7 = ill 00 Hz The value of Cl is calculated for the maximum revs per minute (4 cylinder 4-stroke). That covers regulation. Now for a practical example. Engine data: 4cylihder 4-stroke, maxi- mum torque 101 Nm at 3800-4600 r.p.m., maximum power at 5800 r.p.m. and maximum r.p.m. 6600. Since the greatest power is already reached at 5800 revs, the maximum number of revs (5 V at P2) is set at 6000 r.p.m. Therefore Up3 should have a voltage of 3.8 V and Up 4 3.1 V. With 100 Hz at the input PI is adjusted to a voltage of 2.5 V across C7. Hints for building the circuit into the car The circuit can be mounted in a standard plastic or aluminium case. The connection of the positive supply voltage is made at a convenient point on the ignition switch or the fuse box. The negative supply voltage (ground) is connected to the closest earth point (in cars with the negative of the battery to earth). The input of the circuit will be connected to the contact breaker side of the coil. In cars where the connecting pins are according to the DIN 72552 standards, the positive supply voltage is derived from pin 15, the earth from pin 31 and the contact breaker from pin 1 . To avoid interference from radio, the connection between the contact breaker and the rev counter should be laid close to metal parts of the bodywork. Even better would be to use a cable with an earth shield. Make sure that the wiring does not touch any 'hot parts' of the engine. If after fitting the display should 'jump' and the circuit shows a false alarm once or twice, the value of R1 may be 8.26 lowered to a minimum of 4k7. It is also possible that PI is incorrectly preset and so has to be readjusted. Guarantee for economy It is difficult to determine how much fuel an economiser circuit could save, because the consumption does not depend on the circuit, but on the driver. The circuit will merely give a helping hand. If the driver is prepared to be 'advised' then some reduction in consumption is bound to be achieved. Naturally, a driver who is converted from a 'quick-off-the-mark' speeder to an energy-heeder will save a great deal more than someone who drives econ- omically anyway. In any case, much Figure 7. A vary simple ‘100 Hz generator'. more will be saved in town traffic than on the motorway. One guarantee can be given for certain and that is that it is considerably cheaper to use a fuel economiser than the 'on-board computer' with which cars are likely to the equipped in the near future and which serves exactly the same purpose. sources: Dr. E. Spoerer, W. Thieme, ' The technique to drive economically' VDO Vertriebsgesellschaft mbH, Postfach 2220, 6232 Bad Soden 2. N 1988 8.27 MICROPROCESSOR-CONTROLLED RADIO SYNTHESIZER — 1 The addition of a microprocessor-controlled synthesizer to a continuously-tuned receiver greatly improves tuning accuracy and provides several additional facilities that have become available in recent years. The versatile synthesizer described has a 6-digit LCD or LED display and a 16-position keyboard which allows direct frequency entry, channel or frequency increment or decrement, as well as the storing and recalling of 30 frequencies. The MW, SW and FM band are covered each with a choice of IF offsets. by P. Topping Most recently designed quality radios employ synthesized local oscillators con- trolled by a microprocessor. These com- plex designs should not discourage the advanced home constructor, however, as components are currently available which enable similar facilities to be either incorporated in individual designs, or added to existing radios. Synthesis of the local oscillator (LO) in a superheterodyne receiver provides many advantages over the more tra- ditional mechanical tuning. The main benefits are improved tuning accuracy, stability and the possibility to store often used frequencies. Accuracy and stability result from the fact that the local oscil- lator is phase-locked to a reference crystal oscillator. Before synthesizers became available, crystals were used to obtain a good degree of accuracy. This has the disadvantage of requiring a separate crystal for each frequency. Using a phase-locked loop (PLL) syn- thesizer, similar performance can be achieved at an unlimited number of fre- quencies from only one crystal. Ac- curate, drift-free, tuning is particularly important for stand-by use of a receiver when nobody is on hand to provide fine tuning. A synthesizer can be incorporated into almost any receiver simply by replacing the tuning capacitor with a variable capacitance diode (varicap) as shown in Fig. 1. The voltage biasing this varicap is supplied by the synthesizer, which thus takes over the RF tuning. A simpler solution is to retain the RF function of the existing tuning control as a preselec- tor to avoid tracking problems in multi- band designs. The current trend is to eliminate front-end tuning altogether, and employ only a wideband filter be- tween the RF input and the first mixer. Synthesizer MC145157 The Type MC145157 CMOS synthesizer from Motorola is one of a series offering a variety of options including serial or parallel interfacing, and single or dual modulus prescaling. In the synthesizer described here, only single modulus MULTIBAND RF SYNTHESIZER Features: ■ Coverage of MW, SW and VHF FM ■ Variable step size in accordance with station spacing. ■ CMOS design allows battery back-up while minimizing power consumption and RF interference. ■ il switch-selected bands with a var- iety of IF offsets, including nought. ■ Power-down mode for display and processor. ■ Easy to operate keyboard. ■ RIT (receiver incremental tuning) control provided. ■ Choice of three 6-digit displays: 7- segment LED, static LCD or multiplexed LCD. ■ Memory function for up to 30 often- used frequencies. ■ Last used frequency automatically recalled at receiver power-on. ■ Simple to incorporate in almost any general-purpose receiver. ■ Direct synthesis up to 16 MHz with- out prescalers. ■ Prescalers for up to 60 MHz and up to 150 MHz. ■ IF offset can be customized to indivual requirement. Fig. 1. A local-oscillator synthesizer can easily replace mechanical tuning to provide crystal- controlled accuracy and many other improvements in performance and convenience. 8.28 eleklor India augusl 1988 1'iR. 2. The MC145I57 synthesizer includes two 14-bit shift registers, one each for the refer- ence divider (top) and the variable (IX)) divider. Their loading is controlled by the value of a trailing 15th bit. The outputs of these dividers are compared in respect of phase to control the frequency of the local oscillator. Fig. 3. The synthesizer module contains the MC145I57 phase-locked loop chip and its opamp-hased active low-pass filter. It also includes a RIT control and a microprocessor reset circuit, which makes it possible to resend the last used frequency in stand-by applications. prescaling is used. Serial interfacing was chosen to minimize the number of inter- connections between the synthesizer and the microprocessor. The block diagram of the MC145157 is shown in Fig. 2. There are two 14-bit long counters, which are loaded by shift registers, starting with the most signifi- cant bit (MSB). After loading the 14 databits, a 15th control bit is loaded, and the information is transferred to the selected latch using LE (latch enable). If the control bit is a logic one, the refer- ence divider latch is loaded; if it is a logic zero, the variable (LO) divider latch is loaded. The reference counter divides the crystal oscillator down to the reference fre- quency (in this case 1 kHz), at which the comparison is made with the (also div- ided down) local oscillator frequency. The error signal from the phase com- parator is filtered, and forms the tuning voltage for the local oscillator. The numbers chosen as the divide ratios determine the frequency at which this oscillator stabilizes. The equation below shows the relationship between the various frequencies, where P is the LO prescaler, N is the reference divider ratio, and Q is the LO divider ratio. The re- ceived frequency can be changed by altering the LO divide ratio. The micro- processor lakes care of the decimal to binary conversion, IF offset, and the other required arithmetic. fLo=RF+ IF =P(fWNX? The practical application of the MC145I57 is shown in the circuit diagram of Fig. 3. The output signal of the synthesizer’s 10 MHz crystal oscil- lator is divided down by 10,000 to obtain the reference frequency at which the phase comparator operates. A com- promise is required when deciding on this frequency. Filter design is relaxed by choosing a high reference frequency, but the disadvantage is that the minimum step size of the synthesizer is determined by the reference frequency, as the smallest change which can be made results from a change of 1 on the LO div- ide ratio (see the above equation). A ref- erence of 1 kHz is a reasonable com- promise for most broadcast receivers. The MC145157 is specified to operate up to 20 MHz, so presealing is required on FM (VHF) and SW. Shortwave band divide-by-5 prescaling is used, and for FM divide-by-10. This increases the minimum step size to 10 kHz on FM, which is ideal for this band, and to 5 kHz on SW, which is suitable for most broadcast receivers but too large for some shortwave applications. Fortunate- ly, however, this can be alleviated by the use of an RIT (receiver incremental tun- ing) control, formed by external poten- tiometer Pi. The low-IF (455, 468 and 470 kHz) SW bands do not use prescal- Fig. 4. Circuit diagram of the microprocessor-based controller and the keyboard. ing, and thus have a step of 1 kHz, but a maximum frequency of just under 16 MHz. (2 ,4 -IF). Complex multiple loops are used in some commercial designs to achieve bet- ter resolution, but this can also be achieved with the previously mentioned RIT control. With reference to Fig. 3, the adjustment is made by slightly changing the synthesizer’s reference fre- quency. This can be accomplished by re- placing the usual combination of a fixed and a trimming capacitor on the crystal pins of the MC145157 with varicap diodes (D1-D2). Adjustment is thus by a direct voltage, taken from the wiper of potentiometer Pi, which can be fitted remote from the synthesizer. This type of adjustment necessarily gives a control range which depends on the tuned frequency, but the relatively high IF ensures that this is not too significant. For instance, using an IF of 10.7 MHz, the circuit shown gives the required range of ±2.5 kHz at the lower end of the SW band (1.6 MHz), and just over twice this range at about 15 MHz. If an RIT control is not required, pins 1 and 2 should have a 47 pF capacitor and a 30 pF trimmer to ground respectively, the trimmer being adjusted to provide a ref- erence of 1 kHz. If a frequency meter is not available, this adjustment can easily be made by tuning into a strong broad- cast of known frequency, and adjusting for optimum reception and symmetric off-channel response. An important part of any phase-locked loop is the loop (low-pass) filter. The ac- tive filter set up around opamp IC2 is driven from the double-ended phase detector output of the MC145157. An active filter has the advantage of increas- ing the available voltage swing beyond the supply rail (5 V) of the synthesizer chip. The supply voltage on the active filter determines the maximum voltage available to the varicap diodes in the RIT circuit — 10 V is suitable for the Type KV1235 triple varicap from Toko. The 10 V supply is conveniently taken from the receiver which incorporates the synthesizer. The combination of active filter and double-ended phase detector outputs makes it simple to select the correct rela- tionship between voltage and LO fre- quency. Usually, one side of the varicap diode is grounded, so that increasing the reverse voltage on it increases the fre- quency of the local oscillator. In some oscillator designs, however, the fixed side may be taken to the supply rail, so that increasing the tuning voltage decreases the frequency. With the filter design shown, the choice can be made simply by interchanging the connections to pins 15 and 16 on the MC145157. Resistors Rt. . .Rio incl. may need to be adjusted empirically to stabilize the loop and eliminate any trace of the reference frequency from the output of the radio (remember that LO phase noise is demodulated together with the wanted signal). Microprocessor and keyboard The next module in the synthesizer is the microprocessor circuit — see Fig. 4. The microprocessor used is the CMOS Type MC146805E2 from Motorola, which of- fers powerful bit manipulation instruc- tions, useful for this type of application. It also has a stand-by (power-down ) mode in which the clock is stopped. This has the double advantage of saving power in battery applications, and eliminating interference problems with the radio. When a key is pressed, the mi- croprocessor ’wakes’, performs the re- quired function, and then goes back into the stand-by mode. The MC146805E2 has a multiplexed bus for data and low-order addresses. This arrangement saves pins but requires an external address latch, IC4, to interface with the system EPROM, ICs. This is a CMOS Type 27C64 so that the whole system consumes only a few milliwatts when active, and a few microwatts in stand-by. Although the control program in the EPROM could have been accom- modated in a 27C16 (2Kx8) with room to spare, an 8 Kbyte EPROM was chosen because this is currently less expensive and generally better obtainable; the 2716, and its CMOS version, 27C16, is now rapidly becoming obsolete. After performing the initialization routine at power-on, or following a reset, the microprocessor is programmed to switch lines PA4 . . . PA7 of port A to output, and PA0. . . PA3 to input. The output lines are set logic low before the CPU is software-switched to the power- down state. Any subsequent action on one of the keys Si. . .Si* inch driv es the processor’s interrupt request (IRQ) line logic low, ending the power-down state. Instructions in the EPROM cause the CPU to start scanning the keyboard with the aid of outputs PA4 . . . PA7 and in- puts PA0. . . PA3, to determine which key was pressed, execute the appropriate command or load the pressed number on the keyboard, write serial data to the synthesizer via PBft PB1 and PB2, and update the display read-out via PB3- PA7, PB0-PB2, or PB1-PB3-PA7 (the port lines used depend on the display type — this will be discussed later). The EPROM-resident control program is located in address range 1800 h to IFFFh. This is the top of the CPU’s ad- dress space (it can address 8 Kbyte of memory), and includes the reset and in- terrupt vectors. These vectors reside be- tween 1FF6 h and IFFFh with the program itself starting at 1800 m. The MC146805E2 microprocessor has a 112- byte on-chip RAM area in page zero. The CPU bus is demultiplexed by octal latch ICj using the address strobe (AS) pulse. The 5 V supply to the controller should not be switched off if the station memories are to survive. The supply does not need to be regulated, and four 1.5 V zinc-carbon or Ni-Cd batteries will do. With the static LCD on, the current drawn in stand-by is about 50 /iA, with- out it, less than 1 fiA. Eight 100 kQ pull- down resistors on the multiplexed bus lines of the CPU are used for ensuring minimum stand-by power dissipation. When the display is switched on, it will show random data, but will be written to when any key is pressed (use of the ex- ecute key restores the display to its previous data), or automatically by the reset circuit shown in Fig. 3. Using the keyboard The 16-key keypad performs the follow- ing functions: 0-9 These keys are used for both direct frequency entry and recalling (or stor- ing) the ten frequencies available in each band. UP Increment by one channel (5 KHz SW; 9 kHz MW; 50 kHz FM) or 1 kHz (10 kHz on FM, not applicable to 10.7 MHz SW). DOWN Decrement by one channel (5 KHz SW, 9 kHz MW, 50 kHz FM) or 1 kHz (10 kHz on FM, not applicable to 10.7 MHz SW). STORE Next key (0-9) stores current frequency at that key (indicated by a decimal point on the left-most digit). CLEAR Clear display (direct frequency entry). Also toggles between channel steps and 1 kHz steps (indicated by a decimal point on the second digit from the right). MODE Change between frequency and station mode. EXECUTE Go to frequency, but stay in current mode. The leftmost digit in the display in- dicates which mode is current: • Display blank: direct frequency entry mode ; • Number: last station stored or recall- ed — station mode; • Small square (LC display) or a single lit horizontal centre segment (LED Fig. 5. Six-digit multiplexed LED display. Fig. 6. Static liquid crystal display for the synthesizer. display): the current frequency has not been written into or recalled from mem- ory. A choice of two modes permits the minimum number of keystrokes regardless of method of use. In the station mode, previously memorized stations can be recalled by pressing only the required key — there is no recall key. Storing a frequency requires two key actions, viz. store (indicated by a decimal point on the left-most digit) fol- lowed by the memory number. If direct frequency entry is required, mode is pressed followed by the fre- quency. There is now a choice: press mode again to jump to the new fre- quency, and return to the station mode. Alternatively, press execute to jump to the selected frequency but stay in the fre- quency mode — new frequencies can then be selected with only the execute key required after each new frequency entered. The store facility also works in the frequency mode. If it is desired to change back from fre- quency mode to station mode without retuning the radio, press store, then mode, and to display current frequency press execute. In station mode, ex- ecute updates the synthesizer and the display with the current frequency. This can be used when the receiver is newly switched on to retune the frequency which was in use when it was switched off, even if that frequency was not stored. Returning to the circuit diagram of Fig. 3, it is seen that this is achieved by T i resetting the microprocessor when the radio is switched on — when the 10 V supply rises, Ti momentarily pulls the CPU's reset input low. Bands and IP' offsets Port B lines PB4. , .PB7 inch are used for providing band selection infor- mation to the CPU. These lines can be tied to the appropriate logic level if only one band is required (one band can con- stitute all the bands which use the same oscillator, but select frequency range by switching inductors). If, however, more than one oscillator has to be tuned, or the step size has to be changed (e.g. be- tween MW and SW), the port lines can be set to the appropriate logic level by means of a set of switches (as shown in the circuit diagram), or, if available, spare contacts on the band selection switch in the receiver. Additionally, the local oscillator feed to the MC145157 synthesizer may need to be switched with the aid of RF relays or PIN diodes. The direct tuning voltage will not normally need to be switched as it can be fed to all varicaps in parallel. The relationship between the bit combi- nations on the four MS lines of Port B and the selected band plus IF offset is shown in Table 1. • Bands 0, 1 and 2: single-conversion SW receivers; • Band 3: dual-conversion SW receivers (external prescaler P= 5); • Band 4: ’oscillator-low’ FM receivers or front ends such as the LP1186 (ex- ternal prescaler P = 10); • Band 5: FM band without IF offset; intended for seeing the actual oscil- lator frequency on display in experimen- tal configurations using a purpose-built test oscillator (external prescaler P = 10; no prescaler in band 13); • Band 6: low IF (70 kHz) FM radio ICs (e.g. TDA7000); • Band 7: ’oscillator-high' FM receivers or front ends such as the Toko 5803/4 or 5402, or Larsholt 8319 or 7254; • Bands 8, 9 and 10: single-conversion MW receivers (9 kHz steps); • Band 11: dual-conversion SW receivers (external prescaler P = 5). It is seen that bit combination 01 h in PB6, PB5 and PB4 will select 10.7 MHz IF shortwave regardless of the state of line PB7, so two banks (1 and 3) of memory giving a total of 20 stations can be used, provided that the third bank is not being used for medium wave. A front-panel button connected to PB7 is required to utilize this feature. This will also work for the low-IF shortwave op- tions in which the raising of PB7 selects medium wave with the same IF offset. The IF offsets can be modified in EPROM if required. They are in 6-digit unpacked BCD format, starting at mem- ory address 1E05 h with negative offsets appearing in 10-complement form. FM offsets are in tens of kHz, all others in kHz. For medium wave, starting at band 8, the same series of offsets is used again starting at band 0’s 455 kHz. Only the first three are meaningful for medium wave, and at band 11 the software auto- matically repeats a selection of band 3 as described above. Beyond this there are no useful bands except, perhaps, band 13 which, like band 5, has a zero IF off- The software does not include any restrictions on the frequencies which can be used in each band. This maximizes Table 2. Hexadecimal dump of the EPROM contents. EPROM address range 0430 h to the versatility of the synthesizer. For 07 EFii is purposely not shown because it is left unprogrammed (addresses read FFh), just as example, the shortwave bands can be the remaining 6 Kbyte in the EPROM (0800ii— IFFF ii). used for MW in the USA where the Table 2 0000 : 2E 01 80 cd 0010: 0E B7 2E D6 0020: 5C 5C 20 EF 0030: A6 0F B7 05 0040: B7 2E CD 19 0050: 24 12 B7 00 0060: 06 2E FA 99 0070: 81 EE CC 18 0080: B1 BE CC 18 0090: B1 7D CC 18 00A0: 3D E7 CC 19 00B0: 05 9F 44 44 00C0: 2F CD 1A C2 00D0: F8 B6 24 F7 00E0 : 01 04 AB 14 00F0: B6 30 E7 30 0100: 31 B7 31 20 0110: 20 51 AD 0D 0120: 42 AE 02 02 0130: 02 AE 12 81 0140: CD 19 B6 AE 0150: AE 10 BF 2C 0160: CD 1A 0B CD 0170: BF 2C AE 16 0180: AE 10 CD 1A 0190: 42 06 2F 02 01A0: 2F 81 00 2F 01B0: 02 13 2F 17 01C0: 05 B7 23 A6 01D0: E7 15 3A 2A 01E0: 05 00 00 00 01F0: 07 00 00 09 0200: 09 09 09 09 0210: B6 30 48 B7 0220: 48 39 31 BB 0230: BB 30 B7 30 0240: 31 81 BF 26 0250: 5 A 3A 2A 26 0260: 06 B7 2A BE 0270: 24 BE 25 EB 0280: 05 3A 26 3A 0290: 81 B6 31 B7 02A0: 21 AD IF A6 02B0: 06 AE 10 BF 02C0 : EA 81 AE 10 02D0: 60 C7 E5 6C 02E0: 23 81 AD F5 02F0 : F6 27 F8 5A 0300: D6 1A CF BE 0310: 0D 01 05 0E 0320: 2F 02 A A 10 0330: 18 20 AE 05 0340: 00 16 01 17 0350: FF B7 IF B7 0360: B7 22 CD 1C 0370: 14 26 04 B6 0380: 22 B7 21 A3 0390: 11 26 06 A4 03A0 : 23 B7 20 5A 03B0: 01 2F 0E B6 03C0: 20 07 2F 02 03D0: IE ID A6 FF 03E0: AD 28 B6 30 03F0 : IE BE 24 5C 0400: 14 01 3F 01 0410: 08 48 24 02 0420: FF FF FF FF 07F0 : FF FF'FF FF 0800: 00 18 4D 24 23 5F B7 18 71 B1 28 27 0A 5C DD 18 71 CD 1A 3F 01 3F 00 3F 2F 63 10 2F CD 1A E2 2F F9 98 B6 00 AD 3F 00 81 AE FF 21 B1 DE CC 18 B1 DD B1 BD CC 18 B1 BB B1 7B CC 18 B1 ED 12 EB CC 19 A2 B7 00 2F IE 06 2F IB CD 1A D9 BE 22 E6 81 97 B7 2E D6 1A 20 05 0D 01 02 AB B6 31 E7 31 17 2F 5E AD 1A 3C 30 26 3D 30 26 02 3A 31 2F 0D AD 0C A1 03 B6 01 A4 70 44 44 10 BF 2B CD 1A 5B CD 1A 5B AE 05 E6 1A 91 AD CC A1 03 CD 1A 5B AE 16 BF 5B CD 19 B6 AE 10 AD A 7 17 2F 01 2F 05 CD 1A C2 20 09 2F 81 CD 19 34 48 06 B7 2A BE 23 D6 26 FI AE 16 BF 2C 04 06 08 00 00 00 09 08 09 03 00 00 03 00 00 01 00 07 22 39 31 B6 31 B7 22 B7 30 B6 31 B9 4F B9 31 B7 31 A3 BE 2C A6 06 B7 2A F5 3F 29 3C 29 20 2B BF 24 BE 2C BF 05 3A 25 BB 29 3F 2A 26 E4 81 A0 0A 23 B6 30 B7 22 AE 0E B7 27 34 23 36 2C AD A4 AE 1C BF A6 06 B7 2A 7F 5C AD AF E0 EF ED A6 AE 1C AD DC BE 22 BF 27 A6 05 B7 25 25 E7 1C 3A 25 BE 01 02 18 IF B6 1C B7 1C CD 19 34 A1 E6 1C BF 24 IF 00 01 IF 00 5A 26 F2 20 B7 21 A6 0F B7 05 B7 23 A3 15 26 22 B7 ID B6 21 A3 12 26 06 A4 0F BB F0 BB 22 B7 20 A3 B3 27 26 B7 0D 01 20 A4 0F B7 20 E-6 16 IF CD 19 34 A1 AD 39 A6 FF AD 35 AD 29 14 01 15 01 A3 05 25 F3 A6 4E 81 48 48 48 48 81 12 01 11 01 10 01 FF FF FF FF FF FF FF FF 18 2C 18 2C 28 A6 27 B7 2D A6 A1 77 27 0D 5C 5C E2 80 A6 F0 B7 04 A6 27 B7 2D A6 0E 8E 20 FD A6 F7 48 0C 2F 07 2E FE AD FE 21 FE 5A 26 F9 CC 18 B1 DB CC 18 CC 18 B1 7E CC 18 CC 19 91 D7 CC 19 16 2F 81 77 CC 19 B7 24 05 2F 05 15 01 F7 5C B3 23 26 CF B7 2D 9F 4C 0F 0A 48 97 07 2F 0B 81 E6 30 B7 30 E6 02 3C 31 5A 26 F7 3A 30 5A 26 F5 20 27 07 AE 0A 0F 01 44 44 81 00 2F 23 AD E8 A1 03 26 10 0F E7 10 5A 26 F9 26 19 AE 10 BF 2B 2B AE 10 CD 1A 5B BF 2B 14 2F CC 1A 04 11 2F 20 06 10 02 2F 04 12 2F 20 B7 22 48 BB 22 AB 19 DB 3A 23 BE 2A 81 00 00 00 04 05 04 07 00 00 01 00 00 00 00 00 00 09 00 3F 30 3F 31 5F 23 B6 22 48 39 31 23 B7 31 5C E6 10 05 26 D3 38 30 39 A6 09 E0 05 E7 05 04 3F 29 BF 26 A6 25 BE 24 E6 05 3A 29 AD 0F BE 26 E7 3C 29 A1 0A 24 F8 1C BF 2B AD 25 3C 22 34 23 36 22 24 2C AD 9E 3A 27 26 3A 2A 26 FA 81 EB 10 B7 22 AB 05 B7 5A 5C B3 23 27 03 BE 23 F6 BF 26 97 26 5A B3 27 26 EC 01 2F 02 B6 2D 07 03 £7 05 03 2F 02 AE 08 44 24 02 IE BE 24 5A 2A E5 A6 ID 3F IF BE 23 F6 04 B6 23 B7 IE A3 13 26 06 A4 F0 BB 23 B7 21 B6 20 A3 10 26 06 A4 0F BB 05 0E 01 02 10 IF 2E AD 48 BB 20 B7 03 27 05 03 2F 02 A6 FF AD 31 B6 31 5F E6 ID BF 24 AD AD 0E A6 21 AD 0F 48 AE 07 20 02 AE 13 01 5A 26 F2 81 FF FF FF FF FF FF 18 00 18 2C 18 2C 880120 channel spacing of 10 kHz means that the SW step size of 5 kHz is more useful than the 9 kHz provided on MW for use in Europe. Select your display The display indicates the current fre- quency and memory number, and assists with the entry of commands and new frequencies. The user is offered a choice of three types of 6-digit display for the synthesizer: 1. LED display; this has the advantage of probably being the least expensive thanks to the use of common 7-segment LED displays. The disadvantage of this circuit is its relatively high current con- sumption. 2. Static liquid crystal display. 3. Multiplexed liquid crystal display. All three displays are driven with only two or three lines from the processor board to simplify wiring, and they work without any change in the software. It is, of course, possible to omit the display altogether, or use two displays simul- taneously. The multiplexed LCD is definitely the most elegant of the three options available, since it enables building a compact display unit with only one driver chip and few connections between this and the LCD. Unfortunately, how- ever, the display required in this appli- cation proved very difficult to obtain, and it was, therefore, decided not to sup- port this option with a printed-circuit board. The circuit diagram will, how- ever, be discussed below. LED display The circuit diagram is given in Fig. 5. In line with the rest of the design, the LED display driver is also based on low-power CMOS LSI chips from Motorola, in this case two Type MC14499 display decoders/drivers set up in a multiplexed circuit with four and two common- cathode 7-segment LED displays. The anode resistors, Rj 3 . . . R« incl. and R41 R« incl. should be dimensioned to give the required compromise between brightness and power consumption. IC? and IC* share their clock and latch en- able (LE) lines with the synthesizer (ICi), and receive their data from its shift register (S/R) output, pin 12. As the current consumption of the LED display unit is of the order of 100 mA using 270 Q anode resistors, the module cannot be left on with the microproces- sor in battery-backed up applications, but should be switched off with the re- ceiver. As the data to the drivers is sup- plied by the MC145157, the display should not be switched off while the MC145157 is still powered, unless the data line (SR) from this is also discon- nected by opening S22. Static LC display 6-digit static displays are currently available with standard pin-outs from a number of manufacturers, with only minor differences in the use of colons and other signs, which are not used here. Figure 6 shows the circuit diagram of the static LC display unit set up around drivers Type MC144115P. The suggested display from Philips Components (for- merly Mullard/Videlec) gives good con- trast while requiring very little power — the total current consumption of this display module is about 50 Non- used segments in the display are tied to the backplane. Multiplexed LC display The software can control a display unit composed of a 6-digit multiplexed LCD and a single driver chip as shown in Fig. 7. The benefits of a multi-plane display are immediately apparent from a com- parison of the number lines between the controller and the display in this circuit diagram and that of Fig. 6. The con- troller, a Type MC145000, is fed serially with 48 bits corresponding to 6 digits of 8 segments, including the decimal point. It formats this data into the four backplane and 12 front-plane waveforms required to drive the LCD. Preset P2 is used for setting the contrast. To avoid in- terference with the radio owing to multiplexing pulses, the complete dis- play module should be fitted in a metal enclosure. Part 2 of this article will deal with the prescalers and the construction of the synthesizer. It should be noted at the outset that this instrument is not intended to give a quantitative measurement of field strength, but only to indicate the pres- ence, and fluctuations in the strength, of an electric field. It should also be noted that other factors such as mag- netic fields may influence the instru- Principle of operation When a body acquires an electric charge, then an electric field and a potential difference exist between it and earth and indeed between it and other (charged) objects. The geometry and strength of the electric field depend on the shape of the charged object, the potential difference, and the distance between the object and earth (or another object). For example, consider the electric field between two large, flat parallel, con- ducting plates. The potential falls uniformly across the space between one plate and the other. It is possible to detect (or even measure) this so-called ‘potential gradient’ by inserting a pair of electrodes into the field and measuring the voltage difference between them. Of course all this takes place in an insulating (dielectric) medium such as air, which has a very high resistivity, so any instrument used to measure the potential difference must have an extremely high input impedance. It is no use waving about the probes on one’s multimeter and expecting to get a reading! The input stage of the electrometer must therefore consist of a pair of elec- trodes feeding into an amplifier with a very high input impedance (figure 1). The amplifier output drives some form of indicator. As the present electro- meter design is intended to give only a qualitative indication of field strength, it was felt that the expense of a meter was not justified, so an audible indi- cation is provided. The electrodes, which are etched on a piece of printed circuit board, are con- nected to the differential inputs of a FET input operational amplifier. The output voltage of the amplifier is used to control the frequency of a voltage- controlled oscillator (VCO), which Researchers into psychic matters believe that electric fields often accompany or are the cause of unusual phenomena. For example, it has been conjectured that buildings having certain geometrical shapes, such as pyramids, have the ability to concentrate electric fields and thus preserve organic tissues (mummification). This claim seems partly to be borne out by recent experiments in the USSR, where strong electric fields have been used to preserve vegatables and sharpen razor-blades. It is also believed that electric fields accompany psychic manifestations. An instrument that will indicate the presence of an electric field is thus of con- siderable use when investigating such phenomena, and this is what the electrometer is designed to do. drives a loudspeaker. The VCO fre- quency is an indication of the field strength. The smaller electrode between the two main electrodes serves as a balance elec- trode and a discharge path. Since the input impedance of the amplifier must be extremely high, it is not possible to reference the two inputs to zero or supply voltage by any resistive network. The input terminals are thus floating DC-wise with respect to the supply terminals, and it is possible that the common-mode range of the amplifier could be exceeded, even if the differ- ential input voltage was quite small. The balance electrode is thus connected to half supply potential to provide a reference. The balance electrode also serves as a discharge path for any static charges that may build up on the main elec- trodes. When using the electrometer the main electrodes should periodically be connected to the balance electrode to discharge them. Bridging the three con- tacts with a finger-tip will do the trick! Complete circuit The circuit of the electrometer is given in figure 2. The input amplifier is a CA3140 FET op-amp. Negative feed- back to define the closed-loop gain is provided to one of the offset inputs via R3. (Providing feedback to the inputs, as is more usual, would lower the input impedance!). Cl provides high-fre- quency rolloff to maintain stability and prevent any high-frequency pickup. The VCO is built around a 741 op-amp. This is connected as a voltage compara- tor, with the reference voltage on the non-inverting input determined by R5, R6, R7 and the output voltage of IC1. When the voltage on pin 2 is higher than the voltage on pin 3 the output will go low and C3 will discharge through R8. When C3 has discharged to such an extent that the voltage on pin 3 exceeds that on pin 2 then the output will go high and C3 will charge rapidly through Dl. The output voltage will then go low and the cycle will repeat. The output waveform of the VCO is thus a series of pulses having a very small duty-cycle, which keeps the cur- >8.35 1 3 rent consumption low and allows a 9 V The electrometer can now be used to transistor power pack battery to be used investigate electric fields around other as the supply. bodies. Potentiometer PI in series with the The electrometer may also be modified loudspeaker provides some adjustment to indicate voltages generated during of the volume. For an 8 H loudspeaker physiological changes such as muscle PI should be adjusted until the total contraction, or the voltages generated resistance (P 1 + R9) is around 390 H. by plants. These modifications are. The current consumption of the circuit detailed in figure 3. The electrode plate will then be around 5 m A. is dispensed with and 10 M input Printed circuit board and component resistors are connected into the circuit layouts for the circuit and the sensor as shown. New electrodes, preferably of electrodes are given in figures 4 and 5. silver, are attached to the subject and . j i- - connected via screened leads. In this Testing and applications case the centre electrode is optional, but When the electrometer is switched on, if connected to the subject midway in the absence of an electric field, the between the other two it will reduce the instrument will produce a fixed tone, susceptibility to common-mode inter- If an insulator such as an ebonite rod or ference. To use the instrument, P2 is piece of acrylic (which has been charged first adjusted until the output of IC 1 is by rubbing on fur or other material) is at half supply. The electrodes are then brought close to the electrodes the pitch connected to the subject, either by will change. taping to the skin over a muscle when 3.36 eleklor India august 1988 Figure 1. Block diagram of the electrometer, which consists of two sensor electrodes, a high input impedance differential amplifier, a VCO and a loudspeaker. Figure 2. Complete circuit of the electrometer. Figure 3. The input stage can be modified to monitor voltages generated by physiological changes such as muscle contraction. CA3140 741 1N4148 monitoring muscle contractions, or by taping to the leaves or stem of a plant. When the muscle is flexed the pitch of the VCO will change, or in the case of plants there may be a response to stimuli such as light, heat or even sound. Whatever application the. electrometer is used in, it should be remembered that the instrument is fairly sensitive and. has a high input impedance, and is thus very susceptible to interference such as mains hum. It should therefore preferably be used well away from such sources of interference. M i8.37 DIRECT-CONVERSION RECEIVER FOR 80 METRES What better occasion to present an ultra- simple 80 m receiver than this month’s issue devoted to amateur radio and TV? An ideal project for the holidays, this CW/RTTY/SSB receiver is inexpensive, yet has good sensitivity and selectivity. You will have it ready in no time, and it only requires headphones, a set of bat- teries and a long-wire aerial to bring in the 80 metres band, popular among hams around the world for its reliable propagation characteristics. The tuning range of the receiver dis- cussed here is about 3.5 to 4.0 MHz, a section of which is assigned to licenced radio amateurs. In most areas in the world, the 80 m amateur band extends from 3.5 MHz to 3.8 MHz. Predominant modulation methods are single-sideband (SSB), continuous wave (CW) and FSK RTTY (radioteletype based on frequency shift keying, using an SSB transmitter). The 80 m band has some interesting properties as regards propagation. Daytime range is usually of the order of a few hundred kilometres, while in the evening and at night field-strength in- creases, and stations up to 2,000 kilometres away can be heard. Occasion- ally, American stations are received in Europe in the early hours of the morn- ing. Direct-conversion receiver The operating principle of the direct- conversion (or homodyne) receiver is simple: the received signal is mixed with that of a local oscillator to give a beat note, which is at once the AF output (see Fig. 1). In a direct-conversion receiver, the degree of selectivity is determined almost exclusively by the AF low-pass filter. The present design uses an active mixer which doubles as a linear detector, obviating the need for a prestage and providing the necessary high audio am- 8.38 dektor india august 1983 plification thanks to a special feedback circuit. The practical circuit of the receiver is shown in Fig. 2. The circuit looks rela- tively complex at first, but is basically not very different from the block diagram. The aerial signal is fed via coupling ca- pacitor Ci, to a parallel tuned circuit, L1-C2-C3-C4-D1. This band-pass filter can be tuned by applying a direct voltage to variable capacitance diode (varicap) Di. Coupling capacitor C< feeds signals passed by the filter to operational transconductance amplifier (OTA) ICi, a Type CA3080. An OTA differs from an operational amplifier in supplying an output current rather than an output voltage. In the present application, am- plification of the CA3080 is controlled by the feedback circuit and the voltage on pin 5, which is provided by the local oscillator, to achieve the desired mixing effect. The feedback network is com- posed of Cs, Cm, Cn, Ti, Ra, Rt, R4 and C<,. It is a relatively complex circuit because it functions as a current-to- voltage converter in conjunction with FET T 1, and at the same time as a low- pass filter whose roll-off frequency is de- termined mainly by the capacitance across Ra, i.e., Cm (lOOnF; CW/RTTY) or C11 + C12 (570nF; phone). The oscillator set up around T2 is a varactor-tuned Clapp type with polystyrene capacitors to ensure opti- Fig. 2. Circuit diagram of the direct-conversion receiver for the 80 metres band. mum stability. The common tuning voltage for the oscillator and the input bandfilter is obtained from multiturn potentiometer P2. Presets Pi and Pj form part of a potential divider, and en- able accurate setting of the receiver’s tuning range. Since the capacitance of a varicap is inversely proportional to the reverse voltage across it, the received fre- quency increases with the voltage on the wiper of P2. With this in mind, it is readily seen that Pi and Pj set the upper and lower band limit respectively. Construction The direct-conversion receiver is con- structed on the double-sided, but not through-plated, printed circuit board shown in Fig. 3. The component side of this board is left largely unetched to en- able it to function as a ground plane. Commence the construction with soldering 15 mm high tin plate or brass screens onto the component side — the locations are shown in dashed lines on the overlay. Use soldering pins at the corners to aid in positioning and, if necessary, bending the screens. Drill holes to ensure access to the spindles of multiturn presets Pi and P3 later. Inductors Li and L2 are home-made and identical. They are composed of 20 turns of 0.2 mm dia. enamelled copper wire wound on the plastic former of a Type 7A1S inductor assembly from Neosid. Remove the three pins on one side of the base, and use the remaining two pins for connecting the winding. Scratch off the enamel coating with a pen-knife, pretin the wire end, remove solder flux by scratching again, and then wind the wire end two times around the pin. Tighten the winding and move it up towards the base to prevent a short- circuit with the ground plane. Solder fast to prevent the base melting and the pin being dislocated. Now close-wind 20 turns of the wire upwards on to the former, right up to the rim. Adjustment of the inductor is facilitated when the grounded (‘cold’) end of the inductor is near the rim on the former. Secure the winding with a few drops of glue or wax, and check continuity at the pins. Carefully mount the inductor on the board, and solder the pins at the track side. Fit the ferrite cup, and insert the core. Finally, mount the screening can, and solder the tabs to ground at both sides of the PCB. The mounting of the remaining compo- nents on the board is a matter of routine. One terminal of the following compo- nents is soldered to ground at both sides of the PCB: R2, Rs, Rio, C2, Cs, C«, Cs, Cu, Cis, Ci», C20, Di, D2, P 4 and Si. The two rotor terminals of foil trimmer Ct, C3=470p C4=40p trimmer C6;Cii;C2O=100n Ce=4p7; 16 V C7«1n0 Cs=390p Ce;Ci2=470n Cio=1n5 Cl3”47n Cu;Ci8=470p + Ci5=220p* Cie=1p5 MKT Cl7=270p + Cl9=1n5 + * polystYrene (Siemens: styroflex* ) capacitor 5% (available from Cricklewood Electronics). Inductors: Li;L2 = Neosid assembly 7A1S: winding details are given in the text. Neosid pert no. 06956500. Neosid Limited e Icknleld Way West e LETCHWORTH SG6 4AS. Telephone: (0462) 481000. Telex: 826405. Fax: (0462) 481008 (contact Mr. E. Adcott). Neosid inductor assemblies are also available from C-l Electronics e P.0. Box 22089 e 6360 AB Nuth e The Netherlands. Semiconductors: Di ;02 = BB21 2 ICirkit stock no. 12-02045) Tl = BF256B T2-BF494 ICi =CA3080E Miscellaneous: St - miniature SPST switch. PCB Type 886034X 1 and the two ground pins (supply and AF output), are soldered likewise. In the case of the trimmer, take care not to damage the PTFE material by overheating it with the iron. Unfortunately, there is a small error on the ready-made PCB for this project: facing the flat side of varicap Di (BB212), the right-hand side terminal of the device should not be inserted in the hole provided. Instead, it is soldered direct to the ground surface. PCBs sup- plied through our Readers Services are accompanied by a note advising of this design error. Capacitor Cis is preferably an MKT type. When this is not available, a low- leakage electrolytic type may be used in- stead. The photograph of Fig. 4 shows a prototype of the receiver. Note that a number of ceramic capacitors are fitted in positions that should have polystyrene types. Unfortunately, these were not available when the photograph was taken. The previously mentioned grounded terminal of Di is clearly vis- ible to the left of the device. It is essen- tial that the receiver is Fitted in a metal enclosure. Figure 5 shows a suggested front-panel layout. Setting up The following items are required for set- elektor india august 1988 8.39 Fig. S. Suggcsled layout of the front panel. Prototype of the receiver board. ting up the receiver: a nylon trimming tool, a multimeter and a frequency meter (or a good-quality 80 m receiver). Temporarily power the completed re- ceiver from a regulated 12 V supply. Connect the AF output to an amplifier. Him Pi to the centre of its travel, and measure the voltage at the wiper. Adjust Pi and Pi to obtain 4 V. Connect the frequency meter to the emitter of Ti, and use the nylon trimming tool to ad- just the core in Li until the oscillator produces 3.65 MHz. Turn P: fully counter-clockwise, and check that the oscillator frequency decreases. Exchange the wires to the outer connections of the potentiometer if the frequency increases. Adjust P; until the frequency meter reads 3.4 MHz. Turn P2 fully clockwise, and adjust Pi for an oscillator fre- quency of 3.9 MHz. Turn P: to the centre of its travel, and check that the os- cillator frequency is about 3.4 MHz. If necessary, re-do the adjustments of Pi and Pj until Pi covers the full tuning range of 3.4 MHz to 3.9 MHz. As a matter of course, the function of the frequency meter can be taken over by a calibrated 80 m receiver, which should have no difficulty picking up stray radi- ation from Ti. The oscillator frequency can then be read from the dial -of the auxiliary receiver. Connect the aerial to the input of the direct conversion receiver. Tune to a weak transmission at the lower band edge (3.4 MHz), and peak Cj for opti- mum reception. Then tune to a station at about 3.9 MHz and similarly adjust the core in Li. Repeat the adjustment of Cj and Li to optimize sensitivity across the band. Power supply: beware of adaptors The receiver is preferably fed from a well-regulated 12 V supply, or a set of batteries that gives the same voltage. In many cases, however, it will be con- venient to power the receiver from an available 12 VDC mains adaptor. When this is used, it is likely to cause hum in the receiver, a problem which can often be solved by fitting an additional smoothing capacitor of 470 or 1000 //F across the adaptor’s output terminals. If hum persists, it is probably caused by capacitive coupling of the receiver and the mains. When the rectifier diodes in the adaptor are reverse-biased, they behave as capacitors. This is not nor- mally a problem, but the oscillator signal, via the supply wires, can thus Find a path to these diodes, which cause amplitude modulation of 50 (60) Hz (single-phase rectifier) or 100 (120) Hz (double-phase rectifier). This modulated signal is radiated by the mains wires, and is picked up again by the receiver. In this, the oscillator frequency equals the re- ceived frequency, so that hum is pro- duced as the AF output signal. The supply connections of the receiver should be decoupled by fitting chokes between the terminals of the 12 VDC in- put socket and the relevant soldering pins on the board. Both socket terminals are decoupled to ground with a 100 nF capacitor. The L-C networks prevent the oscillator signal being superimposed onto the supply lines. If hum still per- sists, try winding the supply wires through a ferrite ring core, or around a ferrite rod. A Final tip is to solder a 100 nF capacitor across each rectifier in the mains adapter. B FREQUENCY READ-OUT FOR SW RECEIVER Although the circuit described here was designed as a frequency read-out for a short-wave receiver, it can also be used as a universal counter. The text of this article will be described on the basis of the ‘SSB receiver for 20 and 80 metres’ (l) . The block schematic of the unit is shown in Fig. 1. The signal to be measured is first fed to a variable-gain amplifier and then applied to an up/down counter via a NAND gate. The value at which count- ing starts depends on the setting of a number of preset switches. The final count depends on the setting of the up/down switch and may be larger or smaller than the preset value. To obtain a stable read-out, a latch has been in- troduced between the counter and the LED display, which stores the outcome of the measurement. The timing section serves to ensure that the other sections operate in time and with the required ac- curacy. The block schematic of relevant sections of the receiver is given in Fig. 2 to show how the read-out unit transfers the infor- mation to the display. The signal whose frequency is to be measured is the output of the oscillator in the receiver, which is available at test point 2. To display the received frequency, the counter must start from 900,000, i.e., the IF of the re- ceiver. Note that the counter counts in steps of 10 Hz. That value is set with the preset switches. Whether the counter is to count up or down depends on whether the received frequency lies above or under the IF. In the 20-m band, the IF is lower than the received fre- quency, and the counter must then count up from 900,000. In the 80-m band, the IF is higher than the received frequency, and the counter must then count down. Technical Data Bandwidth of input amplifier Input sensitivity Max. counter input frequency Counter resolution Gate time Number of Number of digits Current drawn 1 kHz to 50 MHz £25 mV 25 MHz 10 Hz 0.1 s Preamplifier and timing section The circuit of the input and timing sec- tions is shown in Fig. 3. The preampli- fier ensures that the oscillator in the re- ceiver is not loaded unduly and raises the oscillator signal to a level of about 1 V PP at the collector of Tj. Preset Pi serves to set the gain so that the counter operates in a stable manner, and also that Tj does not go into saturation. The amplified signal is fed to a Schmitt trigger, Nj, via C>. Since the input of the trigger is at half the supply voltage level (Rj-Rj), the gate toggles readily at an input of 1 V PP . Whether the output of Nj is passed to the counter via clock N.j is determined by the timing circuit, formed by ICi, IC:, and IC3. Circuit ICi contains an oscillator and a 14-bit divider. The oscillator frequency is determined by crystal Xi (6.5536 MHz). The oscillator output is divided in ICi and IC: by 2 17 to 50 Hz. This signal is divided by 10 in Johnson counter ICj. The shape of the final 5 Hz signal is shown in Fig. 6, together with that of the signals at the other outputs of ICj : and the outputs of Ni and Ns. The Johnson counter produces from each 50 Hz pulse five symmetrical square waves that have a PRF of 5 Hz and are separated from one another by 20 ms spaces. After the first clock pulse, Qi goes high, and as long as it remains so (for 100 ms), the signal to be measured is passed from ! Nj to the counter. Then Ni transmits a ! pulse which ensures that the contents of the counter are passed to the latch, and thus to the display. To prepare the coun- J ter for the next measurement. Ns ] transmits a pulse which is used to reset j the counter, and this terminates the i count cycle. Fig. 3. Circuit diagram of the preamplifier and the timing section. Discrete counting The counter is constructed from discrete counter elements and display drivers (with built-in latch), as shown in Fig. 4. Each of the seven identical sections con- sists of four preset switches with pull- down resistors, a BCD counter, a BCD- to-seven-segment decoder/driver with latch, seven biasing resistors, and a seven-segment LED display. Preset switches Si to S7 set the BCD code to a value at which the counter starts counting. The pull-down resistors 8.44 elektor India august 1988 ensure that the preset inputs of the coun- ter are provided with a 0 if the switch is open. Counters ICs to ICi; inch are coupled asynchronously. This has the advantage that only the first counter (IC») is sup- plied with a high clock frequency. The result of the measurement is stored in latches ICn to ICi» incl. These ICs ensure that the measuring result is made visible on the display, because they also have the BCD-to-seven-segment-decoder and a display driver on board. The pos- ition of the decimal point is determined by the location of R93. If this is in the position shown solid, the display reads in kHz; in the position shown in dashed lines, the read-out is in MHz. Construction The three printed circuits are housed on one board, as shown in Fig. 5. The three sections should be cut off as required. The circuits are single-sided, which gives rise to a fair number of wire links. These Fig. 6. Output signals of ICs, Ni, and Ns. are, of course, best put in place first. Construction is facilitated by Fig. 7, which shows the layout of the prototype. Several types of switch may be used for Si to S7. First, there are DIL switches, which are set according to the BCD code in Table 2. Note that the least significant bit is located at the left-hand side of the switch viewed from the display. Another, rather more luxurious, type is a BCD thumb-wheel switch: rather expensive, but very useful if the switches are set often. If the switches are used only once, they may be replaced by wire links. Resistors Ri6 to R43 and DIL switches Si to Si are then, of course, not required. Where a preset input must be 1, the wire link is fitted in place of the switch; if the preset input must be 0, the wire link takes the place of the relevant resistor. Take care that each preset input gets only one wire link — no more, no fewer. The calibration of the read-out is carried out by turning Pi so that its wiper is at ground potential, and then turning it un- til a stable read-out appears on the dis- play. Take care that Tj does not go into saturation with differing input signals at high frequency, because this will affect the bandwidth which may lead to er- roneous measurements. Once Pi has been adjusted correctly, the frequency of the crystal oscillator must be set with the aid of C2. This is done most con- veniently by tuning the receiver to a strong station whose frequency is known accurately: C2 is then rotated until that frequency is displayed. Accuracy The accuracy of the read-out unit is de- termined mainly by crystal Xi. Without special precautions, the frequency of the received signal is measured with an accu- racy of within 200 to 300 Hz. The short- term accuracy may be improved by placing the crystal in polystyrene foam and tuning the oscillator (before any measurement) with the aid of a reference oscillator. This will guarantee good ac- curacy for up to an hour. If greater accuracy and stability are re- quired, a crystal with a temperature coefficient of 20 to 30 ppm should be used. Bear in mind that the effect of temperature becomes greater at high fre- quencies. Finally The read-out lends itself readily to ex- perimenting. It is, for instance, possible to use an external and very stable fre- quency source, such as the ‘Intelligent Time Standard’ 121 to enable measure- ments to be made with a resolution of 1 Hz. The (divided) external oscillator signal is connected across pins 6 and 8 (ground) of the socket for IC2 (ICi and IC2 and associated components are, of course, nor required and may be omitted or removed). The frequency, f , of the (divided) external signal is determined by fi = 5/T m , where Tm is the measuring time (=1 s for a frequency of 1 Hz). With these changes in the timing section, it may, of course, happen that it is no longer possible to place the decimal point at its correct position with R»j. In that case, the resistor will have to be mounted on the display PCB (track side) between the +5 V track and pin 5 of the relevant display module. Speed is another aspect with which may be experimented. The maximum fre- quency the counter can handle is deter- mined by the highest clock frequency to which ICs can react. The first thing to do is to try each of the seven modules in the IC6 position: in the prototype one or two of the modules worked satisfac- torily up to 25 MHz, although the data sheet indicated 17 MHz (Type 74190). The modules shown in Fig. 4 (Types 74HC190) can operate with clocks of up to 40 MHz. If even higher speeds are re- quired, use a Type 74F190 in the IGs position, which is intended for operation with clock frequencies of around 90 MHz. The other ICs can remain HC types, because they need not work at these high frequencies. It is also possible to use HCT types: these are essential, by the way, if it is required to drive the counter from a TTL circuit. It should be noted that the design of the counter circuit with discrete components is deliberate: a multiplexed integrated display unit is a source of noise and in- terference, which in a sensitive receiver is, of course, the last thing you want. None the less, it is still advisable to mount the read-out in a properly screened enclosure. References: Elektor India, December 1987 121 Elektor India, March 1988. doorbell memory On occasion it may be useful to know when a visitor has called in your absence. This is especially true in the case of an enforced absence when a visitor is expected. Confusion reigns supreme on these occasions. The circuit here helps to rectify the situation by providing a ‘memory' for the doorbell. On your return a LED will advise you whether or not a visitor called. The circuit is powered by the bell transformer via diode D1 and capacitor Cl. This provides a d.c. voltage level sufficient for the 'memory'. Under normal conditions (with no one ringing the doorbell) transistor T1 will be switched off and T2 will be conduc- ting to provide a form of latch for T1. Obviously LED D3 will never light under these conditions! Now our visitor arrives! With a joyful cry of 'Avon calling' they press the doorbell — only to lapse into total embarrasment when there is no answer! However our circuit now leaps into action. Via D2 and R1, the doorbell switch SI provides a base drive current to T1 which switches off T2 and, in passing, LED D3 on. Now the transistor 'latch' (T2) swings the other way and T1 is held on by the current path to the positive supply through S2 (normally closed) R5 and R6. The unfortunate visitor goes away totally deflated but the LED will indicate his 'past presence'! On your return the LED will be noted and the circuit 'reset'. This is carried out by simply pressing S2 which breaks the base currents path holding T1 on causing this transistor to switch off. In doing so the LED will be switched off and T2 will be switched on. The 'latch' will be back in the original position where T1 is held off by the fact that R5 is effectively in parallel with R2. A further refinement would be to provide an automatic reset when the front door is opened. In this case S2 is a switch operated by the opening door. However the LED must then be mounted outside the door (poss- ibly in the doorbell switch housing) or the LED will be off by the time you get into the house to look! On the other hand a second circuit could be built as a 'memory' for the 'automatic' memory and then it would be no problem to open the door! This second circuit will of course require a reset switch! M RECEPTION AND TRANSMISSION OF RADIOTELETYPE The results of our recent Readership Survey have confirmed the popularity of construction projects and informative articles on every aspect of modern telecommunications. In particular, RTTY is a well-liked subject; and for good reasons, because the combination of simple circuits and a computer offers many advantages over the mechanical telex machine. In addition to a low-cost telex converter plus tuning aid and powerful decoding software, we present a precision, phase- synchronous, AFSK generator for radio amateurs in possession of a licence to transmit RTTY. If you have never worked with telex for fear of complex circuits, this is the time to take the decisive step into the fascinating world of long-distance com- munication where messages originate from press bureaus, radio amateurs, navigational, meteorological and utility stations in the shortwave bands. In this article it is assumed that the reader is familiar with the concept of RTTY, but just for convenience a short recapitu- lation is offered on the structure of the serial data format. Baudot code and FSK RTTY information is composed of characters that are transmitted sequen- tially to the format shown in Fig. 1. One dataword is composed of 7 bits: • 1 start bit, which is always low; • 5 data bits, which represent the character; • 1 stop bit, which has a duration 1.5T rather than T used for the start and data bits. Five databits offer 32 (2 5 ) possible com- binations. There are, however, 26 letters in the alphabet, 10 numbers, and a num- ber of punctuation marks and symbols, so that 32 positions would appear too few. A solution to this problem is offered by the Baudot system, which reserves a special code for distinguishing between letters on the one hand and figures, punctuation marks or signs on the other. This means that a number of available databit combinations can represent either a letter or a number, depending on the group selection code, which is trans- mitted after pressing the Ltrs or Figs key Fig. I. Serial transmission of an RTTY character. on the teletype machine (cp the caps lock function on a typewriter). The bit combinations in the Baudot sys- tem are listed in Table 1 for reference. It should be noted that there exist many other systems and standards for RTTY, with variations in transmission formats, pulse duration and bit combinations. The majority of telex stations, however, use the Baudot code. The speed of the RTTY transmission is called the baud rale. This is defined as the number of bits transmitted per sec- ond. For instance, a 75 baud station can transmit nearly 11 characters per second. On the shortwave bands, the modulation used for RTTY transmission is usually frequency shift keying (FSK) — depend- ing on the logic level of the bit (mark or space), frequency f\ or h is transmitted. The difference between these frequencies is called shift . Figure 2 summarizes the above by show- ing the units required for over-air trans- mission of a telex message. This article will deal with the construction of the RTTY converter, AFSK generator and Fig. 2. Transmission and reception of ruiliixclctype. printer. The latter function is assumed by a computer running an advanced program that enables decoding RTTY at a number of standardized baud rates. PLI^based RTTY converter and tuning aid The function of the RTTY converter is to translate the mark and space notes re- ceived into the appropriate logic levels. To keep the circuit as simple as possible without compromising versatily, it was decided to set it up around an integrated phase-locked loop, the Type XR2211 from Exar. The operation of the converter is best ex- plained with reference to the internal cir- cuit of the XR22I1 shown in Fig. 4, and the circuit diagram in Fig. 5. Note that the small circles and numbers in Fig. 4 are the pins of the chip — the resistors and capacitors are external components. Basically, a phase-locked loop will at- tempt to make the frequency of the inter- nal voltage-controlled oscillator (VCO) equal to that of the input signal. The two frequencies are compared by the quad and/or loop detector, and the error signal produced by one of these is used for controlling (i.e., tuning) the VCO un- til the difference between VCO fre- quency and input frquency is nought. The VCO control signal is, therefore, a measure of the frequency of the input signal provided by the shortwave receiver tuned to an RTTY transmission. In the present application of the XR2211, the on-board quad detector is not used. The circuit diagram of the converter is very similar to the block diagram of the XR2211. The input signal enters the IC via R-C network R1-C1-C2, and is fed to an amplifier driving the loop detector, whose output signal is used for controll- ing the VCO via potential divider Rt-Rk, and driving comparator 1 via R*-C». The comparator uses the input voltage to decide whether the received frequency is f< or h (mark or space). Its output signal needs filtering, however, because the PLL is so fast that it also responds to interference in the input signal. Com- parator 2, in combination with low-pass R--Cj, ensures a filtered, rectangular output signal. The amplitude of the out- put signal of comparator 1 (fed to pin 3 via R.'-Cj) is much greater than that supplied by the quad detector, which is thus rendered ineffective. Comparator_2 has complementary outputs Q and Q, which are useful for selecting between stations transmitting standard and in- verted RTTY signals (logic high = fo; logic low = f<). This selection is ac- complished by toggle switch Si. It will be clear that the mark and space tones can only be decoded correctly when the receiver is accurately tuned to the telex transmitter. Figure 6 shows the circuit diagram of a bar-graph tuning in- dicator which will prove indispensable for RTTY reception. Based on a VU- meter IC, it indicates centre tuning as well as shift employed by the transmitter. The display indicates frequency of the 1 2 3 4 5 figures 110 0 0 A _ 10 0 11 B 0 1110 c 10 0 10 D 1 0 0 0 0 E 10 110 F 0 10 11 G optional 0 0 10 1 H optional 0 110 0 1 8 110 10 bell 11110 0 10 0 1 L ) 0 0 111 M 0 0 110 N 0 0 0 11 0 0 110 1 0 1110 1 Q 1 0 10 10 R 10 10 0 0 0 0 0 1 T 5 1110 0 u 7 0 1111 V m 110 0 1 2 10 111 X / 10 10 1 Y 10 0 0 1 z 0 0 0 1 0 carriage return 0 10 0 0 ne feed 11111 etters 110 11 figures 0 0 0 0 0 0 0 0 0 0 backspace mark and space tones by means of LEDs to the right and left of the centre, re- spectively. The centre two LEDs are il- luminated when the input signal from the converter has a frequency of 1500 Hz. When the receiver is correctly tuned, LEDs at equal distance from the centre will be seen to flash rapidly. The distance between the illuminated LEDs is a measure of the shift employed by the RTTY transmitter. Fig. 5. Circuit diagram of Ihe RTTY decoder. Fig. 6. Circuit diagram of the optional RTTY tuning aid, which is essentially a I.KD-based shift and tuning indicator. Power supply and computer interface It will be noted that the supply voltage for the RTTY converter is 5 V, whereas that for the display unit is 12 V. The lat- ter is optional, so that the converter may be fed from the computer’s built-in 5 V power supply. When the display is used in conjunction with the converter and a computer, it is essential that the con- verter is fed from 12 V rather than 5 V. This can be done with impunity using the power supply of Fig. 7 and the simple computer interface of Fig. 8 (the latter reduces the converter’s output voltage swing of 12 V rP to 5 V PP ). The serial bitstream from the converter is applied to the computer’s joystick port as shown in Fig. 9. To prevent Fig. 7. Suggested power supply for the RTTY converter and tuning aid. Fig. 8. Resistor-diode attenuator for reduc- ing the logic swing at the output of the decoder from 12 V PP to 5 V PP . Fig. 9. Connection of the RTTY decoder to joystick connector #2 on an MSX I or MSX2 computer. Fig. 10. Interference from Ihe computer can be suppressed by winding the serial data and supply cables onto a ferrite ring core. 1 8.49 Fig. 12. Printed circuit board for the RTTY tuning aid and power supply. digital interference from the computer entering the converter circuit, it is rec- ommended to wind the cable between the converter and the computer onto a medium-size ferrite ring core as shown in Fig. 10. Setting up Apply the output signal of a sine wave generator to the converter. Adjust the generator between 1 and 2 kHz, and use a scope or a voltmeter to find the fre- quency at which the output of the con- verter toggles. Leave the'generator set to this frequency, and adjust P2 and Pj in the display circuit until the two centre LEDs light. Then correct the settings un- til 1 kHz corresponds to the leftmost LED, and 2 kHz to the right-most LED. The preset adjustments will be found to interact, and care should be taken not to shift the centre frequency indication away from Dto-Du. If necessary, repeat the adjustments. When a sine wave generator is not available, connect the converter to the re- ceiver, and tune to a station that transmits an unmodulated carrier. Switch to SSB, and tune the receiver un- til the output of the converter toggles. The note produced by the receiver then has a frequency of about 1500 Hz, and P2-P3 may be adjusted such that the centre LEDs light. Table 2 lists a number of meteorological services that use a shift of 1 kHz, enabling the maximum shift indication of the display to be set as discussed above. Enter the computer An RTTY decoder program was written for MSX1 and MSX2 computers with a disk drive running under MSXDOS. This program can be obtained through the Readers Services by sending in a for- matted 3 Zi -inch diskette that contains MSXDOS.SYS and COMMAND.COM. The program has its own video drivers because those available under standard MSX software proved too slow to ensure correct interrupt servicing and picture scrolling given the speed of the pulses supplied by the RTTY converter. Further, the program boots up automati- cally when the disk is inserted in the machine at power-on. After some time, the main menu will appear, and the user is prompted to enter the required parameters — see Fig. 13. Although the menu is mostly self- explanatory, a short discussion will be given of the various options available. ■ ASCII: when this mode is selected, the computer switches to decoding 8 databits and 2 stop bits. Since this is a non-standard format, the mode is called ASCII rather than ASCII. It can be tried by tuning to the news bulletin of radio amateur station W1AW on 14.095 MHz in the 20 m band. This North- American station transmits at 110 baud, and is one of very few not to use the Baudot code. ■ Shift: It was already noted that the Baudot code has two special characters for switching between letters (Ltrs) and figures/punctuation marks/signs (Figs). When shift normal is selected from the menu, switching be- tween these character sets takes place when the relevant code is received. When, owing to interference, the com- puter does not receive one of these codes, it will produce illegible text. To prevent this, select Unshift On Space (UOS), to automatically switch to letters following the reception of a space character. This is particularly useful for stations that transmit mainly text, e.g. press bureaus. The reverse is also poss- ible: Shift On Space (SOS) causes the ‘figures’ set to be selected following a space, aiding in the reception of, for in- stance, meteorological data, which is mainly clusters of figures and signs. ■ Invert data: this is the software equivalent of operating the polarity switch. Si, on the RTTY converter. ■ Baud rate selection: available speeds are arranged in order of frequency of use. ■ Read Text buffer: text read by the computer is stored in memory. When the computer is in the RX (receive) mode, the memory contents can be examined and, if required, sent to a printer. The text buffer mode is selected by pressing m on the keyboard. Decoding of incoming data is inhibited in this mode, which can be left by pressing r. User-selected parameters are loaded by pressing the space bar to enter the re- ceive (RX) mode. When the settings are correct, and the converter is properly aligned, text will appear on the screen. If there appears no text, or only garbled data, the parameters must be changed by 13 RX BAUDOT AT 50 BAUD NORM Fig. 13. Menu screen shown by the RTTY decoding program for MSX computers. returning to the menu — press return. An interesting feature of the MSX RTTY software is its ability to decode Russian stations using an extended version of the Baudot code. A number of additional shift characters are used in this to enable using the Cyrillic alphabet, which has more than 26 letters. The software translates these in characters that are relatively little used on computers. For instance, the ampersand sign, &, represents the sound /sj/ (Sa&a), while the exclamation mark, !, stands for /e/ (llektrik). There are more replacement signs, but a discussion of all of these is beyond the scope of this article. Actually receiving Russian stations is the best way of getting accustomed to the special signs, since their sound and meaning can be learned fairly rapidly by deduction from the context. Recommended fre- quencies are around 8,350 kHz (evenings and night) and 12,500 kHz (daytime). Other useful frequency allocations are given in Table 3. Finally, it will be understood that usable results are only obtained by using a good-quality SSB receiver connected to an outdoor aerial. Everything possible must be done to eliminate sources of in- terference, since these give rise to decoding errors even when the telex station received has sufficient field- strength locally. the relevant RTTY standard. As a result, a poor signal-to-noise ratio is obtained, and there are station operators who at- tempt to cure this by switching over to AMTOR or other error-correcting systems, while the trouble originates clearly from their poorly designed AFSK generator. The circuit described here is simple to build from a handful of fairly common parts, and can produce virtually any fre- quency used for AFSK at a resolution of a few hertz. put, but is first applied to a :64 divider. When, owing to the switching at its in- put, the :64 divider receives one pulse too many or too few, the toggling of the output will be delayed or speeded up by only l/64th part of the period of the signal applied. This results in negligible pulse-width distortion whilst ensuring that the output signals of the divider are phase-synchronous. After filtering in a low-pass, an RTTY signal is obtained that is much cleaner than one produced by a PLL-based generator. AFSK generator for VHF RTTY Contrary to a good many other designs, the audio frequency shift keying (AFSK) generator described here is not only quartz-controlled, but also phase- synchronous, ensuring very high signal quality and accurate definition of the tone frequencies. Most AFSK generators used by radio amateurs incorporate R-C or L-C oscillators, which often suffer from poor stability and accuracy. Many PLL-based and computer-driven AFSK generators are also remarkable for their low signal quality and deviation from the prescribed mark and space fre- quencies, making it impossible to achieve proper decoding when the re- ceiving station uses filters that are known to be accurately dimensioned to AFSK generator: principle of operation The block diagram of Fig. 14 shows that a quartz-controlled 10 MHz oscillator clocks two counters/dividers, whose div- ide ratio can be preset to any value be- tween 1 and 256. The counters are, of course, configured to give signals of dif- ferent output frequency, which are ap- plied to an electronic toggle switch com- posed of NAND gates. The position of this switch is controlled by the logic level of the signal applied to the TTL input. The frequency of the signal at the output of the electronic switch changes with every change in the logic level of the signal at the digital input. In this ar- rangement, phase disturbance will occur because of the abrupt switching between the output frequencies. The result is an annoying click, which is particularly troublesome when SSB is used, because it easily causes sideband splatter. These switching problems are also frequently encountered in PLL-based AFSK generators, where the oscillator is con- stantly on the verge of losing lock owing to the fast changing AFSK frequency. The present generator offers an elegant way round the above difficulties. The output signal of the electronic toggle switch is not fed direct to the circuit out- 14 Fig. 14. Block diagram of the crystal-controlled AFSK generator. 8.52 elektorindia august 1988 AFSK generator: circuit description. The practical circuit diagram is shown in Fig. 15. The 10 MHz clock oscillator is set up around Ti, which drives counters ICi and ICt. The divisor of each of these can be set by means of Sia. . . Sih and S 2 a . . . Sjh respectively. The user is left free to use either (DIP-) switches or wire links in these positions. The previously mentioned NAND gates that form the electronic toggle switch are found in ICt, while ICj is the :64 div- ider. The circuit around T 2 and T 3 forms an interface between the TTL in- put and ICj. TTL signals are limited by Di and inverted by T:. Tj once more in- verts the signal. Switch Sj allows selec- ting normal or reverse signal polarity. Harmonics and interference at the out- put of divider ICj are eliminated in low- pass filter Li-L:-Cj-Cs- 0-C». The am- plitude of the AFSK signal can be set with Pi. Construclion and use The AFSK generator is relatively easy to construct on Veroboard. In practice, it will be found that a number of con- figuration switches may be omitted because a fixed set of AFSK frequencies often suffices. Standard AFSK frequencies and associ- ated shifts are listed in Fig. 16. It is seen that the step size is 85 Hz. Formerly very popular frequencies were 2125 Hz and 2975 Hz. These multiples of 425 Hz, and those of 170 Hz, were long used by American telegraph companies. Dividing these frequencies reveals that they are all multiples of 17 Hz, which is important to remember for accurately setting the AFSK generator. The need for the new AFSK frequencies in Fig. 16 arose from the fact that amateur radio receivers incorporated AF filters too nar- row to pass 2975 Hz, so that many RTTY hams were forced to use lower fre- quencies. It should be noted that some stations use shifts other than those shown, e.g. 85 Hz or even shifts which are not a multiple of 17 Hz (70 and 240 Hz). When the AFSK generator is used with an SSB trans- mitter, the absolute frequencies are not important, only the shift. For FM 15 transmitters (VHF), however, it is desired to approach standardized AFSK fre- quencies as closely as possible. This can be achieved by setting ICi and ICj to the highest possible divisor, so that the output frequencies can be altered in small steps, and having ICj divide by 32 instead of 64 at the cost of a small in- crease in pulsewidth deviation. The following example shows how to set the DIP switches in the AFSK generator to obtain mark/space frequencies of 1200 and 2400 Hz. Arithmetically, it makes no difference which of the divisors is defined first. To begin with, there is the fixed divisor at the output (IC4): 10 MHz divided by 64 equals 156,250 Hz. This, in turn, must be div- ided down, with divisors between 1 and 256 available (ICi; IC2). For instance, in (8.53 the case of ICi, the result should be as close as possible to 2400 Hz. Dividing 156,250 by 2400 gives 65.1042, which is rounded off to 65. Due to the internal structure of the 74HCT40103, the set divisor becomes 64 instead of 65. This m'eans that binary code 0100 0000 is ap- plied to inputs J0...J7 inch (Jo=LSB, J?=MSB). In other words, only J« is held logic high. The decimal values with Jo, Ji, J2, J3, J4, Js, Jo and J? are 1, 2, 4, 8, 16, 32, 64 and 128 respectively. Any divisor be- tween 1 and 256 can, therefore, be set by closing one or more switches. B NEW COMPUTER SYSTEM ENHANCES TEXTILE PRODUCTION by Anna Kochan, BEng An integrated computer system that can warn of production bottlenecks a year ahead and can be used by an operator with no experience of data processing has been on the market since late last year. Made by McGuffie Brunton North- ern" 1 , the first installation is at the nor- theast England textile manufacturing mill of the J.H. Walker Company, which collaborated in the design. Walker specializes in sliver pile fabric and jersey fleece. McGuffie started as a partnership in 1981, became a limited company two years later and developed an annual turnover of £1.8 million by 1986. Its first products were the Trader 25 and Jobber 25 software packages for the wholesale and distribution industries, and make- to-order, finish-to-order and jobbing manufacture, respectively. These are now installed in more than 250 businesses in the United Kingdom. The new package has evolved from these two earlier versions to suit the requirements of weavers, spinners, dyers, yarn ex- truders and finishers. For the past years the firm has been li- censed to sell certain ICL computers and it is the ICL System 25 range of business minicomputers that the new package for the textile industry has been chosen to Textile 25, as the new integrated company management control system is known, covers the needs of production control and costing, stock sales order' and financial accounting with com- prehensive management reporting. Total control The system is modular and can be in- stalled progressively from a modest be ginning. The modules are designed in such a way that they can be used by an inexperienced operator and the pro- grams lead the operator through the systems by means of conversational English screen prompting. Whithin the Textile 25 system, 27 differ- ent modules are included and they fall into six broad categories as follows: * Sales order control: sales order pro- specially adapted to handle the many thousands of quality and colour combi- nations that are possible without the need to store each one. Production batches can be planned and allocated to orders well in advance of start. The re- quirements planning module highlights potential bottlenecks and material short- ages for up to one year ahead, allowing timely action to be taken to rectify the situation. As work on a production batch is started, it is booked on to a knitting machine. Pieces coming off the machine are then weighed and measured. The sys- tem assigns a piece number and prints a bar-coded ticket immediately to identify the piece and accompany it around the factory. As operations are completed, the piece bar code is read and comple- tion of the operation automatically recorded. Accurate information At the final inspection, extra infor- mation such as quality, net weight and net length are entered via the factory ter- minal, and a new bar code roll card is printed to accompany the completed piece into store. Customer despatches are carefully con- trolled by the system. Each roll card be- ing despatched is bar-code read and checked to be of the correct quality, shade and so on, for the order. Despatch documentation is printed instantly giv- ing the customer full details of roll lengths. Invoicing then follows auto- matically, quickly and accurately. At any time the firm can view the current state of a production batch and customer order. Reports highlight over- production and under-production or potential late delivery situations. Com- prehensive yield analysis and raw material location control monitors costs and minimises waste. The system has enabled Walker to im- prove its customer service levels in terms of meeting delivery deadlines and ac- curate despatches. Usage of raw materials stocks has been improved and stock holding has been reduced. The sys- tem operates 24 hours a day, six days a week and is proving to be reliable and resilient. In the future, Walker plans to introduce enhancements to its system to cover fibre blending, time and attendance recording and automatic machine motoring. References: 1. J.H. Walker Ltd, Ravensthorpe Mills, Calder Road, DEWSBURY WFl'3 3SJ. 2. McGuffie Brunton Northern, The Granary, 50 Barton Road, Worsley, MANCHESTER M28 4PB. cessing, telephone selling option, order intake analysis, production batch-to-sales allocation, despatch control and invoicing. * Stock control: stock recording, batch control and location control, stock movement audit, stock management and demand forecasting. * Production control: job and batch estimating, works order documen tation, batch costing and labo- analysis, production piece tracking, blending and recipe management, bill-off-resource management and re- quirements planning. sk Buying control: buyer’s information database and purchase order process- ing. sk Financial control: sales ledger, sales analysis, purchase ledger, nominal ledger, fixed ledger, fixed assets, payroll and BACS (bankers automatic clearance system) link. =k Data and security link: menu system and data management system. Avoiding bottlenecks J.H. Walker uses this new system in the manufacture of a range of high-quality knitted fashion fabrics for the clothing and upholstery trade. The company’s two major manufacturing ranges are a jersey and a sliver fabric. The jersey fabric is knitted and stored in a ‘grege’ (natural) state, and then dyed and fin- ished to individual customer orders. The sliver fabric is knitted and finished in one pass to individual customer re- quirements. This involves special fibre blending and very precise quality con- trol. So far, Walker has implemented the first phase of Textile 25 for production, order control and tracking system. A network of factory data collection terminals distributed throughout the production area and connected to the ICL system 25 minicomputer has been installed for this purpose. As customers’ orders are received they are entered on to the computer. The Tex- tile 25 order processing module is Before production begins, work is booked to specific knitting machines. proximity detector There are many methods of detecting the presence of a person within a specified area, for example by using ultrasonic or microwave Doppler techniques, which are the methods frequently employed in intruder alarms. The approach adopted in this article is based on the fact that a person moving about in a room alters the geometry and strength of the electric field that invariably exists. The circuit detects changes in the electric field and produces an audible warning. Figure 1. Block diagram of the proximity Natural and artifical electric fields exist practically everywhere. Their geometry and strength is influenced by the pres- ence of objects, particularly conductors, that are in the field, but in a static situation, i.e. with no moving objects, field patterns will change only slowly, over a period of some hours. If a large conducting object such as a human body moves through an electric field then it will distort the field pattern. Due to the electric charges generated on clothing by friction these variations in the electric field can be very large. In a carpeted room, particularly if the car- pets are of man-made fibre, the changes can be even more pronounced. An electric field can be monitored by a sensor electrode connected to the input of a high impedance amplifier. The elec- trode will acquire a potential which is dependent on the field strength at the point where the electrode is mounted. Changes in field strength can also be detected very easily by using an ana- logue voltage comparator. If the output of the sensor electrode amplifier is connected to one input of a comparator then the voltage at that input will consist of that due to the normal electric field with a changing voltage due to any variations in the field superimposed upon it. If the same signal is connected to the second input of the comparator via a lowpass filter with a very low cutoff frequency (~ 0.2 Hz) then the signal appearing at this input will consist only of the voltage due to the static component of the electric field. Whilst it can follow slow changes due to natural variations in the field over a period of time it will be unable to follow voltage changes due to objects moving in the field. The voltage on the second input of the comparator thus provides a reference against which to measure changes in the field. Normally the voltage on both inputs of the com- parator will be the same, but if the field changes then the voltage on the first input of the comparator will vary and the comparator output will change Two problems must be solved before a practical field variation proximity detec- tor can be built. The first is caused by the 50 Hz AC field which is invariably present in any building where there is mains wiring, and which the sensor would see as a rapid change in field strength. This problem can be overcome by using a second lowpass filter to remove the 50 Hz component from the signal picked up by the sensor plate. The cutoff frequency of the filter (1.8 Hz) is chosen so that the 50 Hz component is completely suppressed, but is still sufficiently high to pass the somewhat slower changes in voltage caused by movements in the field. The second problem is that, since the amplifier connected to the sensor plate has a high input impedance (which it must have to detect electric fields) the voltage on the sensor plate cannot dis- charge. The sensor plate will therefore simply charge up to the highest voltage that it sees and any drop in voltage will not register. This problem is solved by periodically discharging the sensor plate through an (electronic) switch. To avoid possible spurious signals caused by beating between the 50 Hz AC voltage and the signal that controls the dis- charge switch, it is essential that the plate should be discharged in synchron- ism with the mains frequency. This is achieved simply by having a 50 Hz mains signal control the switch. Block diagram Figure 1 shows a block diagram of the proximity switch. The sensor plate is connected to the input of a high impedance buffer amplifier. This is fol- lowed by a lowpass filter, which con- sists of two sections. The first is the 50 Hz filter; the output of this section connects to the first input of the com- parator, i.e. the ‘signal’ input. A second filter section with a much lower cutoff frequency precedes the second input to the comparator, the ‘reference’ input. The signal arriving at the signal input of the comparator will thus consist of the total voltage picked up by the sensor plate, i.e. the static reference plus any variations caused by objects moving in the field, whilst only the (practically) unchanging reference volt- tage will get through the second filter section to the reference input of the comparator. At the output of the comparator are connected two monostable multi- vibrators, one of which is positive- triggered and the other negative- triggered, so that either positive- or negative-going transitions of the com- parator output can be detected. The outputs of the two monostables are used to control an astable multivibrator, which drives a loudspeaker to give an audible warning. By using the output of the comparator to vary the frequency of the astable a two-tone signal is provided, the frequency depending upon whether the comparator output is high or low. Complete circuit The complete circuit of the proximity detector is given in figure 2. The sensor plate is connected to the gate of Tl, which is a FET connected as a source follower. This stage has an extremely high input impedance and a low output impedance. The gain is slightly less than unity. Resistors R3 to R7 and their associated capacitors form the lowpass filter which removes 50 Hz signals. The output of this filter is connected to the non-inverting input of the comparator, a 741 op-amp, via R9 and Cl. A lowpass filter section with a very long time con- stant (R8-C6, approximately 800 ms) removes all but very slow variations from the voltage applied to the inverting input of IC1. To obtain clean switching of the com- parator output a small degree of hyster- esis is introduced by applying positive feedback to one of the offset inputs via R10. Negative-going transitions or the comparator output cause the input of N1 to be pulled low via C8. The output of N 1 therefore goes high and the out- put of N2 goes low. Positive-going tran- sitions of the comparator output take the input of N2 high via C9, so that in this case also the output of N2 goes low. The length of time for which the output of N 2 remains low depends on the time constant C8-R1 1 (or C9-R13). N3 and N4 are connected as an astable multi- vibrator, which drives a small audio amplifier consisting of T4 and T5. When Figure 2. Complete circuit of the proximity detector. Fi*ire3. Printed circuit board and com- ponent leyout for the proximity detector (EPS 9974). >8.57 the output of N2 is low the multi- vibrator will oscillate. An input to the multivibrator from the comparator, via R 1 2, alters the multivibrator frequency depending on whether the comparator output is high or low. The sensor plate is discharged every 20 ms by FET T2. Transistor T3 turns off at each negative- going zero-crossing of the mains wave- form, at which point T2 conducts briefly and discharges the sensor elec- trode. Power supply Power for the circuit is obtained from a mains transformer with a 1 5 V or 1 8 V secondary rated at 1 00 m A or greater. The output voltage of the transformer is half-wave rectified by D2 and smoothed by C14 before being fed to a 12 V IC regulator. The mains transformer also provides the 50 Hz signal to switch T3 and T2. For optimum sensitivity the 0 V rail of the circuit must be connected to an earth point such as mains earth or a metal water pipe. If no such earth is available then an ‘artifical earth’ must be used consisting of a second electrode connected to a negative supply voltage as shown in figure 2. However, if a true earth is used then R25, R26, C16 and D3 can be omitted. Construction and use A printed circuit board and component layout for the proximity detector are given in figure 3. All the components, with the exception of the loudspeaker and mains transformer, are mounted on this board. The electrode(s) may be made from copper laminate board approximately 1 5 cm square. If two electrodes are used, they should be mounted about 1 metre apart. The sensor plate must be well-insulated from surrounding objects. Probably (he best method is to mount it on the out- side of the box in which the circuit is housed using nylon spacers. The unit should function immediately when switched on, and the only adjustments required are to vary PI for the best sensitivity and to set the volume of the audible warning using P2. Although intended mainly as demon- stration of the principle, the circuit can also be used for practical applications such as intruder alarms, provided its limitations are known. The proximity detector is much less prone to false alarms than ultrasonic or microwave Doppler alarms, which can be triggered by flapping curtains or rattling doors and windows. However, the circuit may be falsely triggered by changes in field strength caused by switching on and off of electrical equipment. This is not such a problem if the unit is intended to protect unoccupied premises, provided care is taken not to mount it in the vicinity of equipment that switches on and off automatically, such as a refriger- To trigger an external alarm or other circuit the signal from point (A) may be used. This is normally high, but when the audible warning sounds point (A) goes alternately high and low at the same frequency. M 8.58 selex-37 Battery Operated Tube Light Many of you must have faced this situation when you would have liked to have a tube light operated from a car battery. The reasons for this need may be numerous, but the solution is one, and it appears here as a simple electronic circuit which can light up a small tube light from a 12 V car battery. At the heart of the circuit is the voltage converter. A block schematic diagram is given in figure 1. Just one look at the diagram will make the operating principle clear. The 12 V DC voltage from the car battery is given to an astable multivibrator, which produces rectangular pulses - and converts the DC voltage to an AC voltage. Though it is not an AC sine wave, it will serve our purpose. Only one difficulty with this AC square wave is that it's amplitude can never be more than 12 V, because of the battery voltage. This difficulty is overcome by stepping up the voltage through a transformer. Also, as the current requirements is high we must use power transistors to boost the current output before feeding the 12 V square wave to the transformer. This task is accomplished by the block shown just before the transformer. The transformer is just a common stepdown transformer of 12-0-12 V/1A rating used in reverse direction so as to make it a step up transformer. By connecting the 12 V Ac square wave to the transformer, we can now get about 230 V AC at the output, under no-load condition. The voltage may drop to about 100 V after connecting the tube light, but this is sufficient to operate the small tube light. Just four transistors and a few passive components are enough to construct the circuit, which is shown in figure 2. Transistors T1 and T2 form the astable multivibrator which produces the square wave. The frequency of this squarewave depends on R2, R3 and PI as well as the capacitors Cl and C2. The frequency in the given circuit is about 220 Hz, with the potentiometer PI on zero. The wave shape is a square wave with this combination. By increasing PI, the frequency can be reduced to about 125 Hz. The on/off ratio or the duty cycle of the wave will also change with this. The change in duty cycle affects the brightness of the glow and thus PI can be used to control theh brightness level. The dim light of this fluorescent lamp can perhaps substitute the romantic atmosphere of a mild moon light.... The transistors T1 and T2 are too weak to deliver the required output current necessary to drive the tube light. Hence two power transistors are used to handle this current level. These are the transistors T3 and T4 which feed the current through the transformer Trl. This is a stepdown transformer used in reverse way to serve as a step up transformer. It finally provides the high AC voltage required by the tube light. The transformer used here is a 1 0-0-10 V or 1 2-0-12 V transformer which has either two different windings on the lower voltage side or a center tapped winding. The center tap is connected to the + 12 V DC from the battery, and the two ends of the winding are connected to the power transistors. The wave forms on the transformer are represented schematically in figure 3. The common terminal is connected to + 12 V. At terminals 1 and 3, the voltage is opposite of each other. If 1 is on 12 V, 3 is on 0 V and if 1 is on 0 V then 3 is on 12 V. These Voltage levels change in rhythm of the square wave delivered ■ by the astable multivibrator. This drives the current once selex 8.60 ole the heat sinks. The terminals of the power transistors can be connected to the PCB through flexible wires. The screws used for fitting the power transistors must not have contact with the heat sink and you must use insulating bushes with these screws. In case the screws come in contact with the heat sink, both the collectors of T3 and T4 will be shorted together through the heat sink. After properly assembling the circuit and checking the circuit connections visually as well as with a multimeter, power can be applied to the circuit. Make sure that the collectors of T3 and T4 are not short circuited. If you want to be very sure about the functioning of the circuit, do not connect the transformer first. Use a 9 V battery in place of 12 V and check the voltages on collectors of T1 and T2. The collector voltage of T1 should be around 3 to 4.5 V and that of T2 around 4 to 6 V. Some deviation can be expected depending upon the position of PI. If this check is as desired, then you can be certain about the functioning of the The fluorescent light is fed from an AC square wave in this case and requires higher power than in case it was driven by an AC sine wave. The current consumption in this case is aproximately 2 A. If the power is reduced and current restricted to about 1.2 A then an additional resistance of 4.7 fi /10 W must be introduced in the collector lines of T3 and T4. We must also mention an undesired side effect here, the circuit makes a fuzzing sound— which can of course be interpreted as if a fly was humming around our lamp! The component layout is shown in figure 4 as usual and is very simple to follow. All components can be accomodated on a small SELEX PCB of size 1, except for the transformer and the power transistors. The standard procedure for soldering must be followed, that is, first the Jumper wires, then resistors, diodes, capacitors, transistors etc. Even if-you can find space to accommodate the power transistors on the PCB, do not mount them on the PCB as they must be mounted on a suitable heat sink. Do not forget to use the mica insulation and heat sink compound while mounting the transistors on > 8.61 NEW PRODUCTS • NEW PRODUCTS • NEW Insulation Testers. Meco Instruments have introduced the new “FUSO” Hand driven, generator type Insulation Testers. These testers are housed in light weight ABS Plastic cases. The constant voltage AC generator is hand - driven via nylon gears. Cross coil ratio meters are used throughout the range. All models incorporate spring loaded terminals, and are supplied complete with test leads. Meco Instruments Pvt Ltd • Bharat Industrial Estate • T J Road • Sewrce • Bombay-400 015. Tin Plating ‘Tinglo’ process is a method of high speed bright acid Tin plating which gives bright uniform tin deposits. Besides, it gives better ductility, conductivity, strength, corrosion protection, bright- ness and does not tarnish or stain as com- pared to other methods of plating. ‘Tinglo’ is recommended for smooth ductile plating in the Electronics Indus- try for Terminals, Tags, Lugs, Semi-con- ductor devices, Electrical connectors and contacts, PCBs and other Electrical/ Electronic components, due to its low contact resistance properties. The ‘Tinglo’ process is simple to operate and maintain. The bath make-up in- cludes Tinglo salt. Sulphuric acid C.P. (Sp. Gr: 1.84), Tinglo brightener “A" and Tinglo Brightener “B". Typical operating instructions and guidelines for the process are provided to the user. Various package sizes of the salt and brightness are available. Dawlat International • 167 A to Z Industrial Estate • Lower Parel • Bombay 400 013. Milli Ohmmeter This Digital Ohm Meter features 3V5 digit, 7 segment RED LED Display. 5 ranges with lowest range of 200 milli ohm with 0. 1 milli ohm resoultion and highest range of 2 K ohm with 1 ohm resolution. Other ranges are 2 ohm, 20 ohm, 200 ohm. Selection is by interlocked push button switches. 4 wire measurement av- oids lead resistance error. Economy Electronics • 15 Sweet Home • Plot No. 442 • 2nd floor • Pitamber lane • Off Tulsi Pipe Road • Mahim • Bom- bay 400 016. Test Terminal Blocks ‘Nelster Welcon' Test Terminal Blocks, are available in 3-phase 3-wires and 3- phase 4-wires for front or rear connec- tion. Housed in a black moulding these brass terminals are of high current carry- ing capacity and have 0 5 mm holes for cable. Brass shorting links/screws pro- vide easy and positive operation. All metal parts are nickel plated. Nelster Welcon • 6 Laxmi Woolen Mills Compound • Shakti Mills Lane • Qff Dr. E Moses Road • Mahalaxmi • Bombay- 400 Oil. Time Totalizer M/s. Controls & Equipments have re- cently introduced new Mini Time To- talizer series 622 having 6 digits counter with a range of 0 to 99999.9 hours or 0 to 9999.99 hours. This is also offered with- out Re-set facility sp that the counter cannot be manually re-set to zero thereby ruling out any possility of tam- pering with the recorded time. M/s. Sai Electronics • (A Div. of Starch & Allied Industries) • Thakor Estate • Kurla Kirol Road • Vidyavihar (West) • Bombay-400 086. Telephone-5136601. 8.62 NEW PRODUCTS • NEW PRODUCTS • NEW Static Eliminator CIRCUIT AIDS INC offers indigen- ously developed Static Area Eliminators having an effective area coverage of 0.75 Mtrs. The instrument works on a princi- ple of high voltage corona generation through gold plated pins. The gold plat- ing of pins ensure that no ozone is gener- ated. Throws ionised air using a built-in propeller. The instrument is portable and weighs 2.75 Kgs. Rated for continu- ous use, the instrument consumes 30 watts of power. The areas of applications of the instru- ment are Clean Rooms, Antistatic Work Stations, Semiconductor Manufactur- ers, Lens manufacturers. Pharmaceuti- cal manufacturers etc. Block • Rajajinagar • Bangalore- 560 010 (Karnataka). Liquid Dispensing System The I & J” Model LD1000B is a fully au- tomatic dispensing system that allows a wide variety of dispensing applications to be performed such as solder mask and solder paste dispensing onto printed cir- cuit boards, SMT chip bonding adhesive or solder paste dispensing onto SMT boards and one or two part epoxy encap- sulation of electrical components. In ad- dition, other materials such as form-in- place gasket material, conformal coat- ing, cyanoacrylate, grease and other liquids can easily be dispensed. Typical applications include dispensing a UV cure material to seal switches, dis- pensing a solder paste or SMT adhesive onto surface mount boards or to auto- mate any application that requires accu- rate liquid dispensing and precision parts positioning. I & J Fisnar Inc. • 2-07 Banta Place • Fair Lawn • NJ 07410 • USA. Screwless Terminal Blocks Wago Kontakkechaik GMBH manufac- ture rail mounted terminal blocks of var- ious types and sizes for use in power plants, telecommunication equipment, and applications requiring interconnec- tion of power supplies. These are suitable for all copper conduc- tors from AWG 26 upto AWG 2. The product range includes: PCB termi- nal blocks, connectors, electronic rail mounted terminal blocks, plug-in-mod- ules, screw clamp connecting systems, terminals blocks, multicore connectors, of various types an assortment of side entry connectors, marker strips, and card connectors. M/s. Arun Electronics Pvt. Ltd. • 2E, Court Chambers • 35 New Marine Lines Bombay 400 020 • Tel: 252160/259207. High Voltage Op Amp Handles ± 45 4V Burr-Brown's new OPA445 monolithic operational amplifier operates from power suppplies up to ± 45V with minimum 15mA output current. Its com- pact size and voltage-handling ability make it an excellent choice for a broad range of applications, including ATE pin drivers, power supplies, power control- lers, and other programmable power sources. OPA445 has FET input circuitry, and it’s input bias current is only 50pA max at room temperature. The device is unity gain stable and re- quires no external compensation compo- nents. The new op amp is available in TO-99 and 8-pin plastic DIP packages with standard industry pin-outs. Oriole Services & Consultants Pvt. Ltd. • Post Box No. 9275 • 4 Kurla Industrial Estate • Ghatkopar • Bombay-400 086. High Power Alternistor Silicon Power Electronics, manufactur- ers of Power Semiconductors have intro- duced 80 Amp. Alternistor, a bidirecti- ional device, used for application in reac- tive circuits and in high frequency instru- ments. The 80 Amp. Alternistor will be useful in control panels, servo systems, mag- netisors, variable speed controls etc. 29/3, D-2 Block, M I D C Telco Road • Chinchwad • Pune 411 019. NEW PRODUCTS • NEW PRODUCTS • N Timer Multi - Controls have developed an elec- tronic timer for control of varied proces- ses which require time related control. The timer is offered in two types viz.: (1) Industry Standard Flush Panel Type and (2) Plug - in Type. The Plug - in feature provides ease of maintenance and replacement. It is ac- comodated in a standard 8 pin/ll pin relay base. The timing range offered is 1 sec to 60 minutes in nine different forms. The operating voltages could be 12. 24. 110, 230, 440. AC/DC. All standard timer modes such as, "ON DELAY". "OFF DELAY", are offered. Multi Controls • Shantarani Jagtap Building • Hingne Khurd • Vitthalwadi • Pune-411 009. Burnishing Machine M/s. O.R.T. of Italy have developed an external burnishing machine for finish- ing the external diameters of soft, cylin- drical components. This process is suitable for a wide variety of components, including fanshafts; pis- ton-rods of shock-absorbers; crankshafts of compressors; needle-bar and presser- bar of sewing machines; etc. The bur- nished surface accepts electroplating as a finishing process. Burnishing machines canbe imported under O.G.L. by Actual-Users, and the import-duty is concessional. M/s. O.R.T. are participating in the India International Trade Fair at New Delhi in Nov. 87. Precision International • P.O. Box 3041 • New Delhi- 1 10 003. Modular Computer The Unit comes comppletc with two 5 1/ 4" Floppy Drive. Video monitor alongwith keyboard is all that is required to complete the system. This is available in standard 19" Rack with all Eurobus boards. A printer of required capacity and specification can be connected to the Rack. Additional 3 Slots are provided for user defined expansion, such a sys- tem can be used as development system for programme development and debug- ging- Arun Electronics Pvt. Limited • B/125- 126 Ansa Industrial Estate • Saki Vihar Road • Bombay 400 072. Tel: 58 33 54/ 58 71 01. Illuminometer Upto India has introduced a very sensi- tive. portable, compact IL- LUMINOMETER for measurement of light levels. This is suitable for all photo- metric measurements in science and re- search as well as quality testing labs. Its response meets with internationally ac- cepted standard CIE observe 's curve (equivalent to average human eye re- sponse) with cosine correction : The ranges of the instrument is 0-3, 0-10, 0-30, 0-100. 0-300. Agrawal Sales Enterprises • 34 Ganesh Bazar • Jhansi-284 002. Cabinet Cooler Electronics Consumer Durables Pvt. Ltd. has introduced a solid state cabinet Cooler - Elektra-Staykool. Elcktra-Staykool operates on solid state thermoelectric technology, witha closed- loop cooling system. The cabinet cooler can be easily installed by screwing it onto the cabinet. It has a modular construction, is light-weight and compact. Operating costs are low due to low power consumption. This product has wide applications - It is useful manufacturers of electronic con- trol panels, electronic systems, and CNC controllers. It is also widely used in the field of defence, where, among other factors, high reliability, portability, and silent operation, are often prerequisites. Elektra-Staykool is available for Rs. 2.500 plus taxes. Electronica Consumer Durables Pvt. Ltd. • 12 Kaka Halwai Industrial Estate • Pune-Satara Road • Pune- 411 009. NEW PRODUCTS • NEW PRODUCTS • N Multiple Coil Winding Machine Taga Manufacturing Co of Japan intro- duce single spindle type multiple au- tomatic coil winding machine model 2085. This machine winds multiple number of coils simultaneously on one spindle. This model is most suitable for production of thin wire coils and with thin insulating paper. With this coil win- der, ignition coils, vertical transformers, coils for cross bar switches, relay coils, choke coils, neon transformer coils etc. can be produced. Murugappa Electronics Limited • Agency Division • ‘Parry House' • 3rd floor • 43 Moore Street • Madras 600 001 • Phone: 21019. 21003, 27531. Darlington Module SGS has added a new silicon to its TO240 family for high power D.C. applications. This high gain SC.S 100DA0250 Dar- lington module can sustain I00A of con- tinuous current in circuits which operate from up to 250V supply lines. Applca- tions include high power regulated D.C. supplies, and D.C. motor control. SGS Semiconductors (Pte) Ltd • 28 Ang Ko Kio Industrial Park-2 • Singapore- 2056. Controller The GPC 02 card is a control and govern- ing module in the standard Europe 100 x 160 mm size. It operates on the ABACO (R) 16 bit BUS and exploits the wide outfit of in- dustrial peripheries and intelligent mod- ules of said bus. ABACO (R) BUS is compatible with SC 84 BUS. The card operates through and is assem- bled with the CPU Intel 51 family in its different version with/without internal ROM/EPROM including the BASIC masked model. The development and setup of program- mes for this card can just start from the single GPC 02. since it is already pro- vided with the minimum outfit necessary for a first approach, including the built- in EPROM programmer. The completeness of GPC 02 card makes it suitable to meet on its own. control re- quirements of medium-complex units or automations. Where a more complex as- sembly is required, the performance are easy to increase using suitable cards to be assembled on the powerful ABACO (R) BUS. On the contrary, when cost saving is re- quired alongwith a card optimization, just beginning from small series, it is pos- sible to order cards depleted from un- necessary functions. Grifo Di Damino S. & C. S.N.C. * 40016 San Giorgio di piano (bologna) • Italy • Via Dante 1 • Temperature Controller Radix introduces LSC 260 featuring two to eight independently programmable set-points for a single input channel. This microprocessor based controller accepts B. E, J. K, R, S or T thermocouple and Pt 100 inputs. The instrument is housed in a 96 (H) x 192 (W) x 260 (D) mm, DIN size panel mounting case. M/s. Radix Elecrosystems. • A/22, Bonanza Indl. Estate • Kandivli (E) • Bombay- 400 101. • Phone: 69 95 89. Rotary Wire Stripper Ajit Engineers, Bangalore have de- veloped a semi-automatic Rotary wire stripper-cum-twister. It is ideal for use with PVC hook up wires, shielded wires, automobile cable and Industrial panel Wiring etc. It uses a unique, simple rug- ged stripping-cum-twisting mechanism which can be set for any desired wire diameter and strip length within sec- onds. It can strip lengths upto 75 mm and wires from 1 .5 mm to 5 mm 0 . The waste is collected in a bag leaving stripped and twisted wires ready for tin- ning. soldering and crimping operations. Ajit Engineers • 70 S S I Area • Rajajinagar • Bangalore-560 010. 8.70 elektcf electronics SPECIAL SUPPLEMENT ON ELECTRONICS INDIA 88 EXHIBITION The International Exhibition on Electronics being organised by the Trade Fair Authority of India at Pragati Maidan New Delhi RN No 39881/83 o Dual In-line 1C Sockets, o Single In-line 1C Sockets, o Pin Grid Array Sockets, o Socket Adaptors, o Cage Jacks. Champion £l£ctrai?iz!s Pi/t LM S-17. M l. DC Bhosan. Pune 411 026. India (0212) 82S82, 83791 Cable CHAMPION Your Bight Connection ft The Champion Connectors!