U.K. 50 p U.S.A./CAN. $ 1.50 S, 33 F 55 Kr. 9 F. 7 DM, 3 80 DFL. 3.25 Kr, 9 Kr. 9 incl. moms F . 4.40 Austria Belgium Denmark France Germany Netherlands Norway Sweden Switzerland on LEDs CMOS function generator development timer " • r infra-red light gate E 4 — elektor february 1978 decoder elektor 34 Volume 4 Number 2 Editor Deputy editor Technical editors Subscriptions W. van der Horst P, Holmes J. Barendrecht G.H.K. Dam E. Krempelsauer G.H. Nachbar A, Nachtmann K. S.M, Walraven Mrs, A. van Meyel International head offices: Elektuur B.V. P.O, Box 75 Beek (L), Netherlands Telex: 56617 Etekt NL U.K. editorial offices, administration and advertising: Elektor Publishers Ltd., Elektor House, 10 Longport Street, Canterbury CTT 1PE, Kent, U,K. TeL: Canterbury (0227)54430. Telex: 965504. Please make alt cheques payahle to Elektor Publishers Ltd, at the above address. Bank: 1, Midland Bank Ltd., Canterbury, A/C no, 11014587 Sorting code 40-16-11, Giro no. 3154254. 2, U.S.A. only: Bank of America, c/a World Way Postal Center, P.Q. Box 80689, Los Angeles, Cal. 90080, A/C no. 12350-04207. Assistant Manager and Advertising Editorial R.G, Knapp T, Emmens ELEKTOR IS PUBLISHED MONTHLY on the third Friday of each month, 1- U.K. and all countries except the U.S.A. and Canada: Cover price £ 0,50. Number 39/40 (July/August), is a double issue, 'Summer Circuits', price £ 1 , — Single copies {inch back issues} are available by post from our Canterbury office, at £ 0.60 (surface mail} or £ 0.95 (air mail). Subscriptions for 1978, January to December inch, £6.75 (surface mail) or £ 12,00 lair mail}, 2. For the U.S.A. and Canada: Cover price $ 1.50. Number 39/40 (July/August), is a double issue, 'Summer Circuits', price S 3.—. Single copies (incL back issues) $ 1.50 {surface mail) or $ 2.25 (air mail). Subscriptions for 1978, January to December inc!., $ 18. — (surface mail) or $ 27.- — {air mail). All prices include post & packing, CHANGE OF ADDRESS. Please allow at least six weeks for change of address. Include your old address, enclosing, if possible, an address label from a recent issue. LETTERS SHOU LD BE ADDRESSED TO the department concerned : TQ ~ Technical Queries; ADV = Advertisements; SUB - Subscriptions, ADM = Administration; ED = Editorial (articles submitted for publication etc J; EPS = Elektor printed circuit board service. For technical queries, please enclose a stamped, addressed envelope or a self-addressed envelope plus an IRC. THE CIRCUITS PUBLISHED ARE FOR domestic use only. The sub- mission of designs or articles to Elektor implies permission to the publishers to alter and translate the text and design, and to use the contents in other Elektor publications and activities. The publishers cannot guarantee to return any material submitted to them. Alt drawings, photographs, printed circuit boards and articles published in Elektor are copyright and may not be reproduced or imitated in whole or part without prior written permission of the publishers. PATENT PROTECTION MAY EXIST in respect of circuits, devices, components etc. described in this magazine. The publishers do not accept responsibility for failing to identify such patent or other protection. National ADVERTISING RATES for the English language edition of Elektor and/or international advertising rates for advertising at the same time in the English, Dutch and German issues are available on request. DISTRIBUTION in U.K.: Spotlight Magazine Distributors Ltd., Spotlight House 1, Bentwell Road, Holloway, London N7 7AX. DISTRIBUTION in CANADA: Gordon and Gotch (Can.) Ltd., 55 York Street, Toronto, Ontario, M5J 1S4. Copyright ©1978 Elektor publishers Ltd — Canterbury. Printed in the Netherlands, decoder What is a TUN? What is 10 n? What is the EPS service? What is the TQ service? What is a missing link? Semiconductor types Very often, a large number of equivalent semiconductors exist with different type numbers. For this reason, ’abbreviated' type numbers are used in Elektor wherever possible: • 741 J stand for ^A741 , LM741, MC641, MIC741, RM741, SN72741 , etc. * TUP' or H TUN H (Transistor, Universal, PNPor NPN respect- ively) stand for any tow fre- quency silicon transistor that meets the following specifi- cations: UCEQ, max 20V 1C, max 100 mA hfe, min 100 p tot, max 100 mW fT, min 100 MHz Some 'TUN's are: BC1Q7, BC108 and BC109 families; 2N3856A, 2 N 3859, 2N3860, 2N3904, 2 N 394 7, 2N4124. Some TUP's are: BC 177 and BC1 78 famil ies; BC179 family with the possible exeption of BC1 59 and BC179; 2N2412, 2N3251, 2N39G6, 2N4126, 2N4291. • OUS' or 'DUG F (Diode Univer- sal, Silicon or Germanium respectively) stands for any diode that meets the following specifications: ■ □ US 0UG UR, max IF, max IR, max Plot, max Cp, max 25V 1 00mA 1/jtA 250mW 5pF 20 V 35mA 100 250 mW 10pF Some 'DUS's are: BA127, 8A217, BA218, BA221 , BA222, BA317, BA318, BAX13 BAY61,lN9t4, 1N414S. Some 4 DUG'S are: OA85, OA91 , OA95, A A 116, *'BC107B\ 'BC237B', 'BC547B' all refer to the same 'family' of almost identical better-quality silicon transistors. In general, any other member of the same family can be used instead. BC107 ( 8, -9) families: BC 107 (-8, -9), BC 147 (-8, -9) BC207 (-8, -9), BC237 (-8, -9) BC317 1-8, -91, BC347 {-8, -9) BC547 (-8, -9), BC171 (-2, 3} BC182 1-3, -4), BC382 (-3, 4), BC437 (-8, -91, BC414 BC177 (-8, -9) families: BC177 {-8, -9), BC 1 57 \-8 r -9), BC2G4 (-5,-6), BC307 {-8, -9), BC320 (-1,-2), PC350 M, -2), BC557 (-8, -9), BC251 (-2, 3), BC212 1-3, 4), BC512 {-3, 4), BC261 (-2, -3), BC416. Resistor and capacitor values When giving component values, decimal points and large numbers of zeros are avoided wherever possible. The decimal point is usually replaced by one of the following abbreviations: p f pi co- ) - IQ" 12 n (nano-) - 10 9 M (micro) = 1Q” e m (mi Hi-) = 10“ 3 k (kilo) = ID 3 M (mega-) - 10 6 G (ciga-) = 10* A few examples: Resistance value 2k7: 2700 12. Resistance value 470: 470 n. Capacitance value 4p7: 4,7 pF, or 0.000 000 000 004 7 F . . . Capacitance value 10n: this is the international way of writing 10.000 pF or .01 juF, since 1 n is 10" 5 farads or 1000 pF. Resistors are % Watt 5% carbon types, unless otherwise specified. The DC working voltage of capacitors (other than elect ro- lytics) is normally assumed to be at least 60 V. As a rule of thumb, a safe value is usually approxi- mately twice the DC supply voltage. Test voltages The DC test voltages shown are measured with a 20 kH/V instru- ment, unless otherwise specified. U, not V The international letter symbol 'U' for voltage is often used instead of the ambiguous V'. V' Is normally reserved for Volts'. For instance: - 10 V, not Vp - 10 V. Mains voltages No mains (power line) voltages are listed in Elektor circuits. It is assumed that our readers know what voltage is standard in their part of the world ! Readers in countries that use 60 Hz should note that Elektor circuits are designed for 50 Hz operation. This will not normally be a problem; however, in cases where the mains frequency is used for synchronisation some modifi- cation may be required. Technical services to readers • EPS service, Muny Elektor articles include a lay-out for a printed circuit board. Some - but not all — of these boards are avail- able ready-etched Bind predrilled. The EPS print service list' in the current issue always gives a com- plete list of available boards. • Technical queries. Members of the technical staff are available to answer technical queries (relating to articles published in Elektor) by telephone on Mondays from 14.00 to 16.30. Letters with technical queries should be addressed to: Dept. TQ* Please enclose a stamped, self addressed envelope; readers outside U.K. please enclose an I RC instead of stamps, • Missing link. Any important modifications to, additions to, improvements on or corrections in Elektor circuits are generally listed under the heading Missing Link' at the earliest opportunity. elektor february 1978 — E-5 contents The infra-red light gate can be used in a wide variety of applications ranging from intruder alarms to automatic garage door openers. When the light beam from the infra-red source is interrupted, the receiver circuit detects this and energises a relay. 'Throwing some light on LEDs' aims to dispel some of the mystery sur- rounding LEDs, so that the constructor can choose the most suitable type for his requirements, and calculate the operating conditions. Using only one inexpensive CMOS 1C and a handful of discrete components, it is possible to build a versa- tile CMOS function generator that will provide a choice of three waveforms over the entire audio spectrum and beyond. The reason why LED dis- plays are becoming ever more popular is obvious: they look so neat! Quite apart from being reliable and requiring relatively little power. infra-red light gate ...... Z-\jZ throwing some light on LEDs 2-06 formant — the elektor music synthesiser (8) * . 2-10 C, Chapman This article continues the discussion of the tone-forming cir- cuits with a description of The Dual VCA module,, which can be used in conjunction with the envelope shaper for dynamic control of signal amplitude, and also for periodic amplitude modulation of the signal waveform (tremolo). slow on/off ........... - < 2-17 The slow on/off fader circuit will fade the lighting up and down slowly, rather than switching it on and off abruptly. CMOS function generator , 2-20 zener tester . 2-22 This simple fester provides a reliable means of measuring zener voltages and of plotting the variation of zener voltage with zener current. development timer - . . - . 2-24 Developing photographic films can he something of a chore. Not only is it necessary to measure the total development time, but it is also necessary to agitate the development tank at frequent intervals to ensure even development of the film. This means that the clock must he watched continuously. The development timer described in this article overcomes these problems by measuring the intervals at which and the length of time for which the tank must be agitated , as well as the total development time. experimenting with the SC/MP (4) ......... 2-28 H. Kampschulte, H. Huschitt By abolishing the restriction of having to work exclusively in binary code, the hexadecimal input/output unit described in this article considerably increases the ease and speed with which the user can communicate with the SC/MP — providing, of course, that he has a thorough grasp of the relevant soft- ware. market . . * 2-39 advertiser's index E-16 selector elektor february 1978 — 2-01 Conference on microprocessors The advent of the microprocessor, coupled with the availability of in- expensive high density memory devices is resulting in a development of singular importance in the stale of the art of electronics. This development, which provides inexpensive and reliable intelligence to the widest possible variety of equipment, ranging from toys and washing machines to supersonic aircraft and space probes, could revolutionise society. The Institution of Electronic and Radio Engineers conference on Micro- processors in Automation and Control at the University of Kent at Canterbury, in September 1978, will provide a forum for recent advances in the application of the latest technology on microprocessors through the medium of original technical papers and debate. The following list outlines the scope of the conference and shows the topics on which papers are solicited. The list is meant to be a guide and the organ- izing commitee is prepared to consider papers in other areas which are appro- priate to the general theme of the conference. Industrial Automation, Tele- communication Systems. Interfaces, Commercial Applications, Social, Psychological and Financial Implications, Consumer and Entertainment Applications, Transport Systems, Security Applications, Medical Equipment. Military Systems, Tductionai and Instructional Uses, Software, System Simulation, Design and Development Aids, Energy Conservation, Systems Reliability and Maintenance and New Dcvel opm en Ls, A 1 1 en qu i rie s to th e Co n fe re n ce Secre tar ia t , The Inst i tu t io n of Electronic and Radio Engineers, 9 v G o wer S i ree t, London, WC2 (259 5) Computer aid for IEA 78 visitors and exhibitors One of the many special facilities provided for exhibitors and visitors at IEA 78 — the I 2th Instruments, Electronics and Automation Exhibition at the National Exhibition Centre, Birmingham, 13-17 March 1978 will be a computerised visitor registration and enquiry system, operating in four languages. The system will enable visitors to obtain specific-interest information on product categories, companies exhibiting, stand locations and so on. The system will provide an excellent two-way information service ben- efiting visitors and exhibitors alike. Some 300 companies and organisations from i he UK ami countries in Europe, America and Asia have already reserved stand space for IEA 78. The international influence of IEA 78 will be illustrated by exhibits from at least I 7 overseas countries to date these are Belgium, Canada, Czechoslavakia, Finland, France, East Germany, West Germany, Holland, Ireland, Japan, Monaco, Norway, Poland, Sweden, Switzerland, ESA, IEA 78 will occupy the largest hall at the NEC 1 and will have three sections — for Electronic Components, Process Control Instrumentation and a General classification. Products on show will include professional and industrial electronics, active and passive com- ponents, process control and scientific instrumentation, machine tool control and automation, computer techniques and data handling. The show will be the only recognised trade fair in 1978 covering the electronic and instruments industries in the United Kingdom. It will again be held alongside ELECTREX, the 19th International Electrical Exhibition, following the most successful coming together of the two shows in 1976 at the NEC. For further information contact In du s t ria l an d 1 ra d e Fa irs L i m i te d, R ad cliff e House , Blenheim Court, Solihull West Midlands, 89 1 28 G (257 S) Cable testers use pulse 'radar' technique The Tektronix I 502 and 1 503 cable festers are small, portable, rugged, battery-powered instruments designed for locating and identifying faults and discontinuities in any type of cable. The testers use a system known as time-domain reflectometry, based on 'radar' type techniques of sending pulses down the cable and examining the characteristic shape and timing of the reflected pulse. The two testers cover the entire range of cable types from simple electrical connections to coaxial systems. The Tektronix 1 502 is a high-resolution instrument designed to locate faults to within I Vi centimetres over distances up to 600 m, and is ideal for checking coaxial and other cables in aircraft, ships and radar systems. The ] 503, on the other hand, is designed for long- range applications (up to I 5 000 m) with a resolution of 1 rn, and is appropriate for testing long runs of coaxial or twisted-pair cables in telephone and other communications applications. Both festers arc designed for use as field maintenance tools, and each weighs less than 8 kg. The units can operate for more than 5h on their internal batteries before recharging is required. A built-in cathode-ray tube provides facilities for direct visual observation and photography. An optional plug-in Y- l chart recorder is available to provide a self-contained hard-copy capability, A plug-in X-Y output module can drive an external X-Y recorder. The model 1502 high- resolution tester is directly calibrated in reflection coefficient (The) and distance, and is thus very simple to operate. It uses 110 ps step- type excitation signals, and provides fault resolution to within l .5 cm. The tester is matched to 50 Cl cables, but may be used on other cables by adjusting a front-panel gain control or using optional impedance adaptors. Because the limited bandwidth and relatively high losses of long cables require special high-energy, controlled bandwidth test signals, the Tektronix I 503 provides 1 0 V, half- sine wave shaped pulses, and is calibrated in decibels for direct readings of return loss. Impedance levels of 50, 75, 93 and 1 25 il are pushbutton- selected. Tektronix G.K. Ltd., Beaverton House, T O. Box 69, Harpenden , Herts. (258 Si 2-02 — efektor february 1978 infra-red light gate infra-red light gate The use of an infra-red light source is an obvious choice for this type of application. In the first place, for intruder alarm applications the light beam must be invisible, which limits the choice to infra-red or ultra-violet lighl. Ultra-violet light can cause visible fluorescence of certain materials, which makes it less suitable than infra-red. In the second place, relatively powerful solid-state int’ra-red sources, and infra- red sensors, arc available at modest cost, whereas there arc no solid-state UV sources commercially available, the circuit described here uses the Siemens LI) 241 infra-red emitter and BPW34 IR photodiode. Although these devices are not exorbi- tantly priced, neither are they inex- pensive, so in order to minimise the number of iR emitters necessary to achieve a given range the transmission system should be as efficient as possible. Since the light level received at several metres distance from the transmitter will be very low, the receiver must have a high gain, '[’his immediately excludes the simpler types of photoelectric switch that use a continuous light beam and a DC '-coupled receiver, since a high- gain DC’ coupled receiver amplifier would be prone to offsets, temperature drift and other effects that could lead to poor sensitivity on the one hand, or false triggering on the other. The choice therefore falls on an AC modulated light beam and AC-coupled receiver, since a high AC gain can be achieved without offset problems. Such a system can be either narrowband or wideband. The advantages of a narrow- band system are a higher signal-to-noise ratio and less susceptibility to ex- traneous interference, either in the form of ambient light or transients on the supply lines. The disadvantage of a narrowband system is that the trans- mitter and receiver frequencies have to be accurately aligned, in a wideband system, the light source is simply pulsed on and off, and the amplification stages of the receiver have a fairly large bandwidth. The advantages of this system are simplicity and ease of alignment, but the disadvantages are poor signal-to-noise ratio and suscepti- bility to interference. However, advan- This article describes an infra- red light source and detector, which can be used in a wide variety of applications ranging from intruder alarms to automatic garage door openers. When the light beam from the infra-red source is interrupted, the receiver circuit detects this and energises a relay. Lage may be taken of the fact that the infra-red emitting diode will withstand a peak current that is much larger than the average current (1 A peak as against I 00 mA continuous). Small duty-cycle, high-power pulses may thus be trans- mitted., which will give an improved signal-to-noise ratio over a larger duty- cycle transmission of the same average power, Fhe effects of external sources of inter- ference may be reduced by careful attention to constructional layout, mounting the unit in a screened box, and suppression of the supply lines. With these precautions a wideband system can give quite acceptable per- formance and was thus chosen because of its other advantages. Transmitter circuit The simple transmitter circuit, is shown in figure I. It consists of a 555 timer connected as an a stable multivibrator, driving an output transistor which switches the IR emitter on and off. The duration of the transmitted light pulses is about 10 and (he repetition rate is just less than 1 kHz. The average current drawn by the circuit is about 12 mA and the peak current through the IR diode is around 700 in A. The LD241 is available in three versions, LD 241/1, LD 241/11 and LD 241 /III, which have different radiant intensities. For the same forward current, the light output of the LD 241/11 is typi- cally Wi times, and the light output of the LD 241/111 typically 2 ] /z times, that of the LD 241 /l. The power supply for the transmitter is not critical provided the output voltage is no greater than 6 V, as this could result in the maximum current rating of fhe LD241 being exceeded. A suitable circuit is given in figure 2 and can be built up on the board for the "Local Radio’ power supply (Llektor 22, February 1977). Note that the component values for this circuit differ from those of the original circuit (see parts list) and that the following components are omitted: R5, C2 (replaced by R6), Dl, D2, T 3 (base and emitter connections linked on the p.c.b.L nfra-red light gate elektor february 1978 — 2-03 iNV COlVr' Figure 1. Circuit of the infra red transmitter Figure 2. The 'Local Radio' power supply may be modified to provide a 5 V supply for the IR transmitter. Since the average current is only 12 mA, The external transistor T1 may be omitted. Figure 3, Circuit of the infra-red receiver BPW34 BC64/A T - pro r-j o J£. (N — i — cJ T 2 _ Receiver circuit The receiver circuit is shown in figure 3. A BPW 34 infra-red photodiode is opened in the reverse-bias mode. The leakage current of this diode varies with the light received from the transmitter, which causes a varying voltage to appear across resistor R2* the gale resistor of the Ft T source-follower i I. The signal appearing at the source of T1 is fed to IC], which is used as an ampli- fier and limiter, PI varies the sensitivity by altering the reverse bias voltage of the diode* When light pulses are being received from the transmitter, a negative-going pulse train with an amplitude in excess of 1 V peak-to-peak appears at the output of IC] (pin 8), This turns T2 on and off continually, charging up Cll. T3 is thus always turned on, 14 is turned off and relay Re is not ener- gised. When then light beam between the transmitter and receiver is interrupted, the amplitude of the pulse train from the output of IC’ 1 will fall. F2 will be cut off, Cl 1 will discharge, T3 will turn oft and T4 will turn on, pulling in the relay. Once the light beam is re- stored the relay will, of course, drop out again, but can be made to hold in for several seconds after the light beam lias been restored by adding the com- ponents shown dotted, R12 should be infra-red light gate Parts iist for figure 5 Resistors; R1 ~150 k R2 = 1 k5 R3, R4 - 47 n R5 - 3H3 Capacitors; Cl .= 10 r> 02 = 100 o C3 = 100 p/6 V tantalum Semiconductors; I C 1 = 555 timer T 1 = BO 136 D1 - L D 241 /1,/M or/IH 2-04 — elektor february 1978 Figure 4* The power supply for the receiver is simply a 12 V version of the 'Local Radio' power supply. Figure 5. Printed circuit and component layout for the transmitter. ( EPS 9862- 1 ), FigureO. Printed circuit board and com- ponent layout for the receiver (EPS 9862*2). Figure 7. Printed circuit board and com- ponent layout for the power supplies (EPS 9499-2). Vr; V UUt — comr f v. v ■ I W * T * * ’•ammmmsi ill 1 9 m ss m m ■ ■ ■ 4k 7 and Cl 2 can be from 10 fjt to 1 00 ju, depending or the desired hold -in Lurie. Alternatively a latching arrangement may be used that will hold the relay in until a reset button is pressed* Power supply A power supply for the receiver circuit is shown in figure 4. This is virtually identical to the power supply for the Local Radio 7 and may be built on the same board. Construction Printed circuit board and component layouts for the transmitter and receiver are given in figures 5 and 6. C onstruc- tion of the transmitter should present no problems. When constructing the receiver, great care must be taken with the layout due to the high sensitivity and targe band’ width. The leads to the BPW34 photo- diode must be as short as possible, as otherwise they may pickup interference. The relay should preferably not be housed in the same box as the receiver, as the magnetic field set up when it is energised may completely saturate the sensitive receiver input stage, causing the relay to drop out immediately. The receiver will then begin to function again, the relay will pull in and the whole process will repeat. If the relay must be mounted in the same box as the receiver, then it should be mounted as far as possible from the receiver input stage, and must be magnetically and electrically screened. The receiver itself should be mounted in a metal box for screening, the only holes in the box being for relay and supply leads, an adjustment hole for access to Pi and a hole for the photo- diode. Since the photodiode is sensi- tive to visible as well as infra-red light, it must be fitted with an infra-red filter (obtainable from photographic suppliers) if the unit is to be used in daylight. Even with the infra-red filter, direct sunlight should not be allowed to fall on the photodiode, since its large infra- red content could affect the diode biasing and hence the receiver sensi- tivity. Some kind of hood or tube to screen the diode may be necessary in such circumstances. Adjustment The transmitter diode and receiver diode should be aligned with one another, although the radiation pattern of the one and the acceptance angle of the other are so wide that a slight misalignment will have little effect (but remember that a screening hood or tube on the photodiode will reduce the acceptance angle). The circuit is then cheeked for reliable operation at close range by breaking the infra-red light beam, after which the transmitter and receiver are moved progressively further and further apart, whilst PI is adjusted to obtain the maximum range. If the photodiode is well screened from ambient light, this adjustment will have little effect and the wiper of PI can simply be turned fully clockwise. As it stands, the circuit will function at distances of up to 6 meters between the transmitter and receiver, if lenses are used to concentrate the transmitted light into a much narrower beam and to focus the received light on the photodiode then much greater ranges can be achieved. However, the physical infra-red light gate elektor february 1978 — 2-05 Parts list for figure 6 Resistors: R1 ,R8 - 4k7 R2 r RlO = 100 k R3,R4,R6 = 2k 2 R5,R1 1 = 1 k R7 - 22 k R9 = 120 H R1 2 - see text Capacitors: Cl - 4^7/16 V C2,C6,C7,CS,C1 0 - 100 n C3 - 1 0 ju/1 6 V C4,C5 = 470 n C9 - 10 n Cl 1 - 2^2/16 V Cl 2 - see text Semiconductors: IC1 = TBA 120 T1 = E 300 T2 - TUP T3 - TUN T4 - BC 547A,BC107A D1 = BPW34 IR photodiode D2,D3 P D4 - 1 N41 48 Miscellaneous : PI = 10k preset Re = relay with 12 V/100 mAl'max) coil Parts list for figure 7 , for circuit Parts list for figure 7 r for circuit shown in figure 2 : shown in figure 4: Resistors: Resistors: R1 = 2k2 R 1 - 390 n R2 = 10 ft R 2 = 1 ft R3 - 470 ft R3 = 320 ft R4 = 1 k5 R4 = 680 ft R5 - omitted R6 = 5k6 (replaces C2 on p.c.b.) R5 = 1 k Capacitors: Capacitors: Cl = 1000 m/25 V Cl - 470 m/ 16 V (tantalum) C2 - 47 m/10 V C2 - replaced by R6 C3 = 100 p C3 = 1 00 p C4..C5 = 6n3 C4 r C5 = 6n8 Semiconductors: Semico nducto rs: T1 = BC 140 T 1 = omitted 101 = 723 ICt = 723 D1 ,D2 - 1N4148 01 ,02 = omitted D3 - LED D3 = LED D4 . . r D7 - 4 x 1N4002 or □4 , 07 = 4 x 1N4002, or 20 V 500 mA bridge rectifier 40 V/500 mA bridge rectifier Miscellaneous: M seel aneous: T r ar-£' r ornner = 9 V 50 mA sec. Transformer = 15 V/25G mA sec. alignment of the transmitter and receiver will then be much more critical. Notes on the TBA 120 The TBA 120 is produced by several manufacturers, and several different versions arc available. All of these should function satisfactorily in the receiver circuit. However, in some cases it may be necessary to omit R6 (sec figure 3) or connect it to ground instead of +Uh, to obtain the best sign alto-noise ratio. To check this the output of the K should be monitored,, either on an oscilloscope, or by con- necting a pair of high impedance (> 500 £2) headphones between pin 8 of the 1C and +U|> When receiving a signal from the transmitter a 1 kHz signal should be heard (or seen). The effect of omitting R6, or connecting it to ground, can thus be investigated, l he optimum result is indicated by the loudest (highest amplitude) signal, (.’are should be taken when altering R6 not to disturb the relative positions of the receiver and transmitter, as this could give false results, M Light emitting diodes were first made in 1954. when it was discovered that a point -contact diode made with gallium phosphide (tiaP) as the base material emitted red light when forward biased. Although it was realised that this material offered the prospect of making a commercial solid-state light source, the physics of light emission from semiconductors was poorly understood, the technology to make the material was difficult, involving high tempera- tures and pressures, and it was some time before commercial devices appeared. Early LEDs were packaged in metal TO- 18 type transistor housings, with a glass or plastic end window or lens, and costs were initially very high; furthermore, one could have any colour, provided it was red, Efficiency (Le, light output for a given power input) was also very low. When the phenomenon of semi- conductor light emission was better understood, it was realised that the red emission of early GaP diodes was due to zinc and oxygen impurities in the GaP material. LEDs made with purer GaP produce a green light. Various exotic semiconductor materials for LEDs have now been developed, but the most common compound used is gallium arsenide phosphide (GaAsP). The advantage of this material is that the colour of light emitted can be varied by altering the proportions of arsenic and phosphorus in the material, from infra-red radiation, obtained with pure GaAs, to green radiation, obtained with pure GaP. At present there is no commercially available LED that emits blue light. The most popular colour for LEDs is still red, using GaAsP material with the formula GaAso^^o .4 (i.e + the ratio As:P is 6:4). LEDs using this material are easiest (and hence cheapest) to produce, and have the highest efficiency. Green LEDs are the least efficient, but this disadvantage is offset to some extent by the fact that the human eye is more sensitive to green light than to red light. LEDs are now commonly available in four colours; red, orange, yellow and green. An important factor to be considered when choosing the colour of Light-emitting diode (LED) lamps are replacing incandescent filament lamps in a variety of indicator applications, as they offer improved reliability and performance at a comparable price, A bewildering variety of LEDs of different shapes, sizes, colours and prices is now available, and the amateur constructor may find it difficult to choose a device for a particular project, especially if the parts list simply says that a 'LED 1 should be used, with no indication of type. This article aims to dispel some of the mystery surrounding LEDs, so that the constructor can choose the most suitable type for his requirements, and calculate the operating conditions. a LED is the proposed application. For example, red is conventionally used for warning lights, but green and yellow may be aesthetically more pleasing for other purposes. Cost is always an important consider- ation. Green and yellow LHDs may be up to twice as expensive as red LEDs, as well as being less efficient. This inefficiency is not necessarily a disad- vantage, provided low-current (e,g. battery) operation is not required. For comparable light output from a green LED it may be necessary to run it at twice the current of a red LED, but if a mains power supply is available this is no great problem, provided the ratings of the LED are not exceeded. In general, it is true to say that, in terms of efficiency, ( yer gets what yer pays for’ with LEDs. The high-efficiency, "state- of-the-art' devices now appearing on the market are considerably more costly than the less efficient second generation devices that are commonly available to the amateur contructor, since the technology required to make high- efficiency LEDs is considerably more difficult, and development costs still have to be recouped. Packaging The high cost of the early LEDs was partly due to the expensive metal-can package, which is still used for some military and industrial devices. Modern consumer LEDs utilise a much cheaper form of encapsulation, the semi- conductor wafer and its leadouts simply being encapsulated in a moulded epoxy resin housing. A typical selection of modem, epoxy-encapsulated LEDs is shown in photo 1 . Although the diode junction is essen- tially a point source of radiation, the encapsulation can have a profound effect upon the radiation pattern of the LED. For example, it the epoxy encapsulation is transparent then the LED functions as a point source, with the emitted light being confined to a relatively small angle, as shown in figure la. If the epoxy material is translucent, then the light produced by the LED is diffused over a much wider throwing some light on LEDs elektor february 1 97B — 2-07 angle, as shown in figure i h. For a given light output, from the LED chip, the point source LED will appear brighter, when viewed on axis, than the diffuse LED. However, off axis the brightness of the point source LED falls off rapidly, while the diffuse LED provides even illumination over a much wider viewing angle. The shape of the encapsulation also has a marked effect on the radiation pattern, since it acts as a lens. For example, a LED in a cylindrical encapsulation with a domed end produces a radiation pattern as shown in figure 2a, whereas one with a parabolic cross-section produces the radiation pattern in figure 2b. It is apparent that the radiation pattern of figure 2b would produce much more even illumination of a plane surface placed at right-angles to the axis of the LED, As well as being transparent or translucent, the LED encapsulation may be either clear or coloured. Of course, a coloured encapsulation does not influence the colour of light emitted by the LED, this is determined by the semiconductor material. If a coloured encapsulant. is used it must be the same colour as the light emitted by the LED, otherwise the light output will be seriously attenuated. Special packages Most commonly available LEDs have a circular cross-section, for the simple reason that, for panel mounting purposes, round holes arc easiest to Figure la. A point source LED produces a fairly narrow beam of light. Figure 1b, A diffuse LED produces a much more even radiation pattern, and has a wider viewing angle. Figures 2a and 2b, The LED encapsulation acts as a lens, the shape of which has a marked effect on the radiation pattern. Photo 1* A typical selection of commonly available LEDs, 2'08 — elektor february 1978 drill. However, with the demand for types of LED display other than single panel lamps (e.g. bar graph type displays), different types of package have appeared. Photo 2 shows a LED which has a flat rectangular cross* section with a rounded top. The dimensions of this type of LED (2.5 x 5 mm cross-section) allow it to be stacked on a standard 2,54 mm (0.1'’) pitch, to form arrays for such appli- cations as audio level meters. Another interesting shape is shown in photo 3. This type of LED has a transparent plastic case fitted with a flat diffuser screen, which makes it particu- larly suitable for backlighting of legends. In fact, press-on lettering or transfers can be applied direct to the diffuser screen. Integrated LED arrays, housed in dual- in-line packages, are also becoming quite popular. Such an array of 10 LEDs is shown in photo 4. Electrical characteristics of LEDs Electrically, LEDs behave like normal semiconductor diodes, which is not surprising, since they consists of a single PN junction. However, the forward voltage drop of LEDs is considerably greater than that of, say, a silicon diode. Furthermore, this forward voltage drop is not the same for all LEDs: it depends on the type anti colour. Earlier types of LED had forward voltages varying from around 1.6 V for red, to around 2.4 V for green. However, modern high-efficiency LEDs tend to have forward voltages around the 2 V mark, irrespective of colour. As with normal diodes, the forward resistance of LEDs is very low, which means that once the forward voltage is exceeded the current through it will increase very rapidly for only a very small increase in voltage. This makes it essential to use an external, series, current-limiting resistor If the LED is to 9852 2 4 be connected to a voltage source. Eor DC operation, the required series resistor is found from the equation: „ U s -Uf . R = ~ 2 , where U s = supply voltage Uf = LED forward voltage l - required current throwing some light on LED. If data on a LED is unobtainable (e.g. unmarked, untested types) then as a rule of thumb, most LEDs will withstand a forward current of up to 40 mA (many will withstand more and only a few types will withstand less). Using 2 V as a value for the forward voltage drop will also not be far out. However, if a LED is to be used with a low supply voltage then extra care must be taken not to operate the LED too near its maximum current, since a small variation in the supply voltage could lead to a large increase in current. Care should also always be taken to connect LEDs the correct way round, since they have a very low reverse- breakdown voltage (typically 4 V) and are easily destroyed by excessive reverse voltages. For this reason great care should always be taken when trying to identify the leadouts of an unknown LED, A 3 V supply with a 150 Li series resistor should be fairly safe. However, most manufacturers identify the leadouts of LEDs in one of two ways. T he cathode, which is connected to the more negative supply voltage, has a shorter leadout than the anode (which is connected to the more positive supply voltage), or else the LED package has a flat side next to the cathode leadout (this only applies to circular cross- section LEDs). These identification marks are shown in figure 3. AC operation LEDs can be used to replace low-voltage incandescent, lamps where only an AC supply voltage is available. The LED conducts only on one half cycle of the AC waveforms and is reverse biased on the other half cycle. The LED must therefore be protected from excessive reverse voltages. This can be done by connecting a diode in reverse parallel with the LED, as shown in figure 4a. The diode conducts on the negative half-cycle of the waveform and this limits the reverse bias on the LED to the diode forward voltage drop. Another method is to connect a diode with a high breakdown voltage (greater than peak supply) in series with the LED, as shown in figure 4b. The first method has the advantage that the diode need not have a high reverse breakdown voltage, since it is protected by the LED. However, it has the disad- vantage that current flows through the series resistor during the whole cycle, so the resistor dissipates twice as much power as in the second circuit, where the resistor conducts only on positive half-cycles of the waveform. In either case, when calculating the resistor value it is important to remember that the LED is conducting for only half the time, so the average LED current will be only half that expected from the calculated resistor value. To allow for this the approximate required resistor value is obtained from the equation; ih r owing some light on LEDs elaktor febrtiary 1978 — 2*09 angle) than a comparable diffuse LED, If high light output and/or low power consumption are prime considerations, then it is worth considering a high- efficiency LED from a reputable manu- facturer, though this wall inevitably be more expensive. For special applications, such as bar- graph type displays, interesting possi- bilities are offered by the integrated LED arrays and the new shapes of LED packages now available. Readers wishing to pursue the subject further are recommended to read the ‘Optoelectronics Applications Handbook' from Hewlett-Packard . M Figure 3. The leadouts of a LED may be identified by a shorter lead for the cathode, or a flat on the package next to the cathode. Figures 4a and 4b, Two methods of con necting a LED for AC operation. URMS -Uf Conclusion To sum up, the choice of a LTD for a particular application should be based on several criteria. For general indicator lamp applications in mains powered equipment, most LEDs are adequate, and the choice can be made on the basis of cost and the required colour. If a narrow viewing angle is acceptable, then a point-source LED will give greater apparent brightness ( within its viewing where Photo 2. LEDs are also available in a rectangu- lar package with a half-round end, specifically for use in arrays. URMS - AC supply voltage Uf - forward voltage of diode(s) I - required average current The protecting diode must have a current rating greater than L Photo 3. These LEDs are fitted with a flat diffuser screen, and are ideal for back illumi- nation of legends. Lifetime of LEDs Early LEDs had problems with copper contaminants poisoning the diode unction, which caused a reduction in brightness after only a few hundred operating hours. Modern LEDs, however, if properly treated, should have an operating life of at least 1 00,000 hours, and possibly up to 1,000,000 hours (defined as the time taken for the light output to fall to 50%). For the constructor, ensuring that a LED has a long life starts with careful handling of the device. The leads of a LED should never be bent closer than about 2 mm from the encapsulation; pliers should always be used to relieve :he strain, otherwise the package could "re damaged, resulting at best in the -gress of moisture, and at worst in ; r mplete disintegration of the package. When soldering LEDs the junction temperature should never be allowed to exceed 1 25° C\ so a heat shunt should be used on the leads. LEDs should not be operated at excessive temperatures. A LED rL-7±::ng at a temperature of 75 C pre duces only half the light output that :i does ' 15 C and also has a shorter hte I be rule is far as the constructor is ■ ztTTit : - thus to keep LEDs away from hot spots in equipment, and not to operate their, too near their maximum current rating. Photo 4. An array of 10 LEDs boosed in a dual-in-line package. 2 10 — elektor february 1978 formarr The voltage controlled amplifier module is called a ‘Dual VC A’ because it contains two cascaded , but in depen- dently controlled, amplifiers. The gain of the first amplifier is voltage controlled via an exponential converter, and is used for envelope shaping. The second has a linear gain-control input and is used for periodic modulation of signal amplitude (tremolo). The VGA is provided with a modulation indicator, which allows the best compromise to be obtained between sign a l- to- noise ratio and overload margin. This article continues the discussion of the tone-forming circuits with a description of the Dual VGA module, which can be used in conjunction with the envelope shaper for dynamic control of signal amplitude, and also for periodic amplitude modulation of the signal waveform (tremolo). Connection of the VGA in the synthesiser system Figure 1 illustrates how the VGA fits mio the synthesiser system. The VGA takes its input from the output of the VCF, which in turn takes its input signal from the VC Os, The VCF and VGA can both be controlled by the ADSR envelope shapers, so allowing dynamic variation of tone colour and amplitude during the playing of a note. However, the VCF has a KOV input from the keyboard to allow it to function as a tracking filter, but the VGA lacks this, since there is no pitch related control of signal amplitude. C. Chapman Using the VCA and the VCF It may be interesting at this point to spend a little time comparing and contrasting the effects produced by the VGA and VCF, and discussing how they are used to complement one another in the synthesiser system. As an example, consider the case where the VGA and VCF are both controlled by the same waveform from the envelope shaper, consisting of a rapid attack and a relatively slow exponential decay, as shown in figure 2a, and are fed with a 440 Hz sawtooth waveform. If the VCF is used alone in the lowpass mode and the cutoff frequency of the filter is initially set very low, the input signal will be completely suppressed. However, during the attack phase of the envelope control waveform the cutoff frequency of the filter will rise very rapidly, and the amplitude and harmonic content of the note will both increase as first the fundamental, then the harmonics, are passed. During the s)ow r decay phase the note will die away slowly as the cutoff frequency falls, starling with the higher harmonics, then the lower harmonics, and finally the fundamental, The variation in turnover frequency of the filter is illustrated in figure 2b, j 1 tie tone thus produced is not unlike that of a clavichord, or of a piano which has had drawing pins stuck into the hammers to produce a jangly, honky- tonk effect. if the same signal and control waveforms are fed to the VGA, the signal amplitude will rise rapidly as the gain increases during the attack phase, and will fall away slowly during the decay phase. However, the harmonic content of the signal will remain unaltered. The sound thus produced is similar to that of percussion instruments such as the piano and xylophone. By varying the attack and decay times of the envelope shapers a wide variety of tone colour and amplitude dynamics can be produced using the VCF and VGA in conjunction. VCA design considerations The dual VCA contains two amplifiers whose gains are independently voltage- controllable, and the design of the VCA poses certain problems, the principal one being that of obtaining adequate dynamic range, as is illustrated in figures 3a to 3d, Figure 3a shows a control contour froir the envelope shaper. At the peak of the control contour the VCA must have i finite maximum gain, which, for the purposes of the discussion, it will bt assumed is unity, or 0 dB. At the beginning and end of the note the signal must be inaudible, which means that the gain of the amplifier should ideally be infinitesimally small at these moments in time. In practice, if the gain is around 70 dB then this will be adequate. What happens if the dynamic range is inadequate is shown in figure 3b, Suppose the gain of the amplifier can be varied by a range of only 40 dB or so. and is set to 0 dB on the peak of the control contour. At the start and end of the note the signal will only be 40 dB formant elektor february 1978 — 2-1 1 Figure 1. Block diagram illustrating how the VGA fits into the Formant synthesiser system. Figure 2. Envelope control of the VCF and VGA. The attack-decay contour of figure 2a, when applied to the VCF, varies the turnover frequency of the filter, which provides dynamic alteration in the tone colour of the sound (figure 2b). When applied to the VGA, the envelope contour alters the gain of the VGA and thus the amplitude of the sound (figure 2c). down, and if the note is being played fortissimo then this residual signal will stilt be quire audible. Another fault of badly-designed VC As is illustrated in figure 3c. In this example, the VC A cuts off completely below a certain level of control voltage, and so misses part of the attack and decay period of the note. This might be said to be the opposite fault to that of figure 3b, though it is not directly related to dynamic range, but rather to extreme non-linearity of the control characteristic. Returning to the example of the VC A with only 40 dR dynamic range, if the gain is adjusted so that the signal is inaudible at the beginning and end of the note (i.e. some 70 dB down), it will only be able to increase by 40 dB when the control voltage is applied, instead of the 70 dB required to reach the 0 dB level. The result is an amplitude plateau, as shown In figure 3d, As mentioned briefly earlier in the article, control of the envelope shaping section of the VC A is carried out exponentially. This is to compensate for the logarithmic loudness response of the human ear. On the other hand control of the periodic amplitude modulation section (tremolo) is linear, since this gives the 'softest 5 and "sweetest" sound lo the tremolo effect. Principle of the Formant VGA The VGA in Formant uses the C A3 080 OTA as the controllable amplifier, as in the VCF, and to refresh Their memories with regard to the operation of the OTA, readers ire referred back to part 6 in the December 1977 issue. The principle of the Formant VC A is illustrated in figured. The input voltage Uj is converted to a proportional output current Tq - g m ■ Up However, since we are interested in voltage amplification ' > Hd pul current must be converted mt : an output voltage, and this is done simph by feeding the current through a load resistor Rl to produce an output voltage U 0 = g m - Ui • Rl- The transconductance of the amplifier, g m , may of course be varied by a control current I ABC* as explained in part 6, and the gain of the VGA may VCGl VC 02 VC03 KOV GATE OUT R 2 external input/output internally wired Input/output signal path control signal path Sa i Avi • + 5- + 0b- 2-12 — elektor -February 1978 formar Figures 3a to 3d. Some typical faults of badly designed or badly-adjusted VCAs are illus- trated here. None of the amplitude envelopes in figures 3b to 3d follows the control contour of figure 3a. in figure 3b there is feedthrough of the signal finishes; in figure 3c the signal is still cut off for some time after the control contour starts and cuts off again before it finishes; in figure 3d the VGA has insufficent headroom and limits causing a 'plateau" on top of the envelope curve. Figure 4. The principle of the Formant VGA is illustrated here. The OTA produces an output current proportional to the product of the input voltage and the control current I^BC- This causes a voltage drop across the load resistor Rj_, and the output is buffered by an op-amp voltage follower. The input attenuator is necessary to avoid overloading the OTA. Figure 5, Complete circuit of the Formant Dual VGA. This contains two, cascaded, voltage-controlled amplifiers with independent control inputs; exponential control for envel ope shaping and linear control for amplitude modulation (tremolo). thus be controlled — although at. this stage of course it is a CCAf The output of the OTA may not drive any external load in addition to Rl, as this would lower the load impedance and alter the gain, so the output of the OTA is connected to a voltage follower/buffer with a high Input impedance. Both sections of the VC A operate on the same principle. However, only the output of the second OTA is buffered, since it is this output that is connected to any external loads. As the output of the first OTA has no external connection it is simply connected to the input of the second OTA. Hie OTA has one disadvantage that cannot be ignored. As mentioned last month, its linearity Is good only for small input signals (typically ± 10 mV) which is why a large degree of input signal attenuation is required. This means that the signal-to-noise ratio is not exceptionally good, and for this reason it is best to use the VGA with the largest possible input signal consistent with low distortion, A modulation indicator is provided, which allows the best compromise to be obtained between excessive noise, at low r input levels, and distortion at high input levels. formant elektor february 1978 — 2-13 AM 1.5 V 15 V eann ■© -015V I Cl - C A3 034 IC2 ICS. ICS y A741C r MC1741CPl (MINI DIP) ICG ... IC7 - CA30&0(AI (MINI DIP'i Dt DA = OA91, AA119, AAU3 R 14 K13 H rja lOOfc 100* '00k 'S Oo — II H16 ■ixiCy 60 IC5) are enabled (via address logic gates N4 . . . N"9) by the address decoder of the CPU card. The keyboard will respond to any address between 17x8 and 17 x F, where 'x' can be any value (i.e, 'don't care 7 ). Alternatively, as described in part 3 ( £ p age-ad dress struc- ture 7 ), the address can be located on the first memory page between 07 x 8 and 07 x F, Hexadecimal output Figure 2 shows the circuit diagram of the hexadecimal output. Basically, this is a relatively self-contained unit that can store eight hexadecimal digits (and several other symbols) and display them on eight seven-segment LED displays. Each of the LED displays has its own address, so that the output unit actually has a total of eight (groups of) addresses: 17x0.., 17x7 (or 07 x 0 , . . 07 x 7), where V again stands for 'don't care 7 . The last three bits of the address indi- cate the particular seven-segment dis- play. Thus the address ending . . , 000 will indicate display 0. In the circuit, these last three bits- are applied to the input of a multiplexer 1C (1C 14). When entering new data, this information is passed to the address inputs of a 16x8 bit 'scratch-pad' memory (IC15 and IC 16). 8 bytes of this memory are used to store the data for the 8 displays, as present on the data bus, during the Negative Write Data Strobe (NWDS). Having stored the information, the next step is to display it, A clock generator (N36) drives a 4-bit binary counter (1C 18), three outputs of which are actually used. These three outputs are connected to the 'A 7 input of the multi- plexer (1C 14); when this input is selec- ted (in the display mode) the memory will be scanned continuously and the data for the 8 displays will appear sequentially at its output. At the same time, the three outputs of the counter are decoded by a BCD to Decimal decoder-driver ( IC 17) and used to enable each of the 8 displays in turn. The data appearing at the memory out- put are buffered by the open-collector buffer/drivers N20 . . . N27 and used to enable the segments of the displays. Each bit corresponds to one of the seg- elektor february 1978 — 2-29 experimenting with the SC/MP (4) IC1.IC2.IC3 -3 .74148 IC4.ICS - 2 . 74125 N1 N4 IC6 - 7400 | N5.N7.N16 ’ 4049 N6.N15 MC9 - V, 74137 N8.N12.N13.N14 - ICIO 7400j N9.N10.N I I N17 - x 7416 1 IC13- 7474 14IC13 .7474 DATA BUS NIB N2B N35 IC7.IC8 VA . 4049 N19.N36 ’4*IC9 N20 N27IC11 IC14 74157 IC15.IC16 7489 IC»7 - 7414- IC»8 7493 74137 DATA BUS i|ijs= ™s E B H! 1! HI Vi^S mm MT'yW' ^ C H u J FSgSf > my 2-30 - elektor february 1073 experimenting with the SC/MP (4) Figure 3. This figure shows which display seg- ments are enabled by which bits of the data byte. Figure 4. This figure shows the track patterns and component layouts of the top {4a and 4b} and bottom (4c and 4d| sides of the HEX I/O printed circuit board (EPS 9393 L merits , as shown in figure 3, so no further decoding is required. If, for example, data bit 00 is a T, then seg- ment V lights up. The d aia-byte 01110110 would enable segments b, c, e, f and g, resulting in the letter 4 H’ being displayed (note that the binary number should be 'read’ from right to left, so that the extreme right-hand digit corresponds to segment V!), In this way any desired symbol can be rep- resented on the displays. Whilst data is being written into the experimenting with the SC/MP (4) elektor february 1978 — 2-31 scratch-pad memory the display is randomised. This is due to the fact that the clocked counter (1C 18) has no halt facility s thus when the B inputs of the multiplexer (1C 14) are enabled, the digit enable is no longer synchronised with the segment drive. However the write- cycle is so short that this effect should he scarcely perceptible. The printed circuit board Ail the components (including the key- board and display) for both the input and output circuits are mounted on the same board. As may be seen from fig- ure 1 , this board also accomodates the NR ST and Halt-reset switches, which means that the SC/MP system can be built without the RAM I/O card. If the RAM I/O card is retained however, then t h e switches an d f 1 ip-flops f o r the above functions can naturally be omitted from the HF.X I/O board. The relevant com- ponents are: S25, S26, R3, R4, R5. R39, R40, R41 , D 1 , IC 1 3. To keep its size down to reasonable pro- Parts list to figure 4b. Displays 0 ... 7 * HP-7750 D1 - LED in S26 SI ... S25 - Schadow digitast SPOT S26 = Schadow digitast SPDT + LED I « m m N «$ n : ■: m MW \ m rw I m I k i | 'M i 1 m \ I ? m | I i !■ r : c cU"4j ‘ I 1 I 2-32 — elektor lebruary 1978 experimenting with the SC/ 11 "? (4} portions, the board is double-sided with plated through boles. Figures 4a and 4b show the track pattern and component layout on the upper side of the board; figures 4c and 4d show the underside. The design of the board takes into ac- count the possibility of mounting the input/output unit in a console or plinth. To this end the upper side of the board (see figure 4b) contains only the key- board switches, the connector and the displays. Ideally, the displays should then be soldered direct to the board, i.e. without using connector sockets. The board can be covered with a sheet of red perspex, with a section cut out to allow' access to the keyboard. All the remain- ing components are mounted on the underside of the board (see figure 4d). Ail connections to and from the HEX I/O board (including those to the busbourd) are made via connectors. Figure 5 shows the details of the wiring between the HEX I/O board and the bus board. The connections shown as dotted lines should only be made if the RAM I/O card is omitted. Power supply Before starting on the software, it is important to make sure that all hard- ware is operating satisfactorily. This will not always be the case if the supply voltages are not accurately maintained. All supply voltages should be within 59b of the nominal values, and this is par- ticularly the case if SC/MP II is used (V cc " 5 V i 5%). Note that this voltage should be present at the pins of the IC! experimenting with the SC/MP {4) elektor february 1978 — 2-33 Even if the output of the power supply itself is within the tolerance, a voltage drop in (excessively) long supply lines may just be sufficient to reduce the voltage at the IC to below the minimum required for reliable performance. In case of doubt, it is advised to check the supply voltages at the pins of the ICs. Next month we hope to publish a suit- able power supply for the SC/MP. I/O software In contrast to the RAM I/O card, the Parts list to f igure 4d. C7 . . . CIO = 100 ... 150 n IC1 7 - 74141 C6 ^ 100 m/ 0 V (tantalum) [CIS = 7493 Resistors: T1 . * /T8 = BC 177 or equ. m = i k Sem [conductors: R2 . . . R5, R4G . . , R42 - 4k7 IC1 . . . IC3 - 74148 R6 . . . R9, R13 . * * R21 - 2k2 IC4JC5 = 74125 RIO . . . R17 = 82 n* 1 C 6 r 1 C 1 0 - 7400 R22 . , . R29 = 820 H IC7JC8 = 4049 R30 . . . R37 - 470 n IC9 - 74132 R3S, R39 = 330 ll Id 1JC12 - 7416 (7406) 47 If greater display bright- Id 3 = 7474 ness is required, the value Capacitors: IC1 4 = 74157 of R10. . . R1 7 may be Cl _ . C5, 1 C 1 5 r I C 1 6 ~ 7489 reduced to 47 fl. 2-34 — elektor february 1978 experimenting with the SC/MP 14! v 0600 07 FF ADOS HEX ■ I/O- AD03 AD0O DB07 o DB00 4AA6 4 A 46 1A .1C 1A4C 2 A 2 A 2?C 2b A 25 A 25C 25 C 26 A 26 A 2£j C 26 f; IDA 1 0 A lflt ijQC Ta - |9C 9C.I 3 A a a bC SC 7A 7 A T£ fC !L A 5 A MC 1 ' © 30 A 3 DA 3 1 A 31A -12V J- +5 V + 5 V ENIN 0600-07 FF N HOLD (1600 17FFI AD 10 AD08 AD03 AD00 DB07 o DB00 Q NRST CONT NADS ^ NWDS BUS BOARD with CPU card and memory- extension- card AD00 DB 07 0 OB 00 l nrst{] cont(] NAOS^ NWDS^ CE RAM I/O ^ 3A.3C 4A.4C 8A4C. Mfl 5 C SIC 12V BV 0 © © 1 _ 1 23A 23 C 24 A 246 25A 25 C 2bA 26C tO A IOC QA 9C BA ec 1A 7C 5A 116 30A 31 A T7A + 5V AD 10 0 AD 00 DB 07 0 DB00 ^ NRST ^ CONT [) NADS \\ NWDS 0 CE RAM - I/O - 9363 b Table la. Bit 07 06 05 04 03 02 01 00 - 1 U3t3 (0-F) — I Command (0-7) — (Key (0,1) Table 1b. Code 01110000 (701 Command 3 1 1000000 (CO) Data C 11111100 (FC) Table 2, START - 0000 0000 08 NOP 0001 C417 LDI 1 7 ; load PTR 1 with address 0003 35 XPAH 1 ; of output 0004 C400 LDI 00 ; load data for display 5 0006 C905 ST 5 (1) ; Into display memory 0008 C454 LDI 54 ; load letter 'n' for 000A C907 ST 7 11 ) ; display 7 000C C45C LDI 5C ; load letter 'o' for 000 E C906 ST 6 (1 ) ; display 6 and 0010 C901 ST 1 (1) ; display 1 0012 C479 LDI 79 ; 'E'for 0014 C904 ST 4 {11 ; display 4 0016 C450 LDI 50 ; etc. 0018 C900 ST 0 (1) 001 A C902 ST 2 ( 1 ) 001 C C903 ST 3 (1 ) 001 E 00 HALT • END hexadecimal input/output requires the assistance of a certain amount of soft- ware to perform its task. As far as the output section is concerned, this is rela- tively simple. To transfer the required data to a particular display a ‘STORE" instruction is used. The displacement value of this instruction determines which display is addressed. In the example shown in figure 6, the letter ‘P 1 is to be displayed on display 3. In this case the effective address is cal- culated using indexed addressing via PTR 1. Table 2 lists a programme which will also test the hardware involved. This programme, which must be loaded into the RAM of the RAM I/O card, will display the words "no Error’. A second example programme which will display a well-known name is listed in table 3 . The software required to interrogate the keyboard is somewhat more compli- cated. Figure 7 shows the flow -diagram for the simplest possible programme which allows the state of the 16 data keys to be tested. After the start of the programme, the 8 bits of keyboard data are loaded into the AC. This continues until bit f)7 is T ", thereby indicating that a key has been pressed. Before the keyboard data is further processed, a delay instruction is executed to ensure the data is valid (I.e, allow for contact bounce). experimenting with the SC/MP (4} elektor february 1978 — 2-35 J • * •' ' • ffin III* n l lljUi: U>« . t* «*fc H®! w i ^ | iiii’ff * .f ** & *£§ ■ 111* I 1 !' M#il MU ' iSiiSstifli f-^4 S i [ l My T ill I I I I I* i " m^tpB ® 4- II' #np§t£ **h mmmm •vr%r*t* i '4i ■ ; - «*i #*4r«tiw * . ***«»*«« T » * . . •*. * «#*««*« '« ' ■■■■ ■'■■ ■■■■;:>: ■ . •;. ‘ '■■■"■ w-x-:-. _ ' ■i* :¥c¥;.». .-. i ItIHill •« «*%*•*** • « mm mm. «***#***:» *•<««♦ UI«Nft Since only the state of the data keys is to be tested, the AC is first masked by 0F, after which the new contents of the AC are stored in memory. The state of data-bit 07 is tested once more, and so on until it is *0' (the key is released), upon which a second delay instruction follows. The cycle may then be repeated if so desired. A slightly more complicated demon- stration programme which will display the contents of the data keys on the readout is listed in table 4, Once the programme has been loaded into the RAM on the RAM I/O card and started by operating the NRST switch, pressing one of the data keys, e..g. key A, will result in the letter A appearing on dis- play 0, It then key B is pressed, the letter B will appear on the next display, and so on until all 8 displays are enabled. The programme can then be repeated by operating the NRST. The above programme is simply in- tended to demonstrate the HEX I/O, and cannot in fact do anything apart from display the 'contents 5 of a data key. The programme which enables the key- board to perform its true function, i.e. modify the contents of the memory, is given in table 5 (see figure 8 for the How-diagram). This involves investing a certain amount of time, since the pro- gramme, which is 200 bytes long, must be written into RAM using the data switches. Table 1 # This table shows the formats of the 8'bit code generated by the keyboard. Table 2. This programme will cause the words 'no Error' to appear on the displays. Table 3. A 'surprise' programme. Figure 5. The connections between the HEX I/O board and the bus board. The con- nections which are shown as dotted lines are made only if the NRST and Ha It -reset func* tions on the RAM I/O card are no longer being used. Table 3, 0000 08 0001 C41 7 0003 35 0004 C450 0006 C900 0008 C45C 000 A C901 000C C478 000 E C902 0010 C475 0012 C903 0014 C470 0016 C904 001 8 C906 001 A C438 001 C C905 001 £ C400 0020 C907 0022 00 Once the programme is started (by pressing the NRST key), the display will show lE00xx, where l xx’ are the con- tents of 'address' 1 K00. I h e command key which generates the code 10000000 (i.e. key C0) is Lhe 'NEXT' key. Pressing this key results in 1 H0 1 yy appearing on. the displays, where s yy’ represent the contents of address 1 E01 . In this way if is possible to read out the contents of every location of the same page in mem- ory. After 1FFF the displays show 1000 since there is no carry to the 4 most sig- nificant address bits. In order to modify the contents of a memory location, the new data is entered at the desired address by means of the data keys. For example, pressing key A twice, will result in 'A A' being written into the desired address. If the 'user's programme 5 is to com- mence at a start address other than 1F00, then the loader programme should be modified accordingly. Using the data switches, the lower-order byte of the desired start address is loaded into address 0009 and the higher-order byte into address 000C. Once the user's programme has been loaded into memory, one would nor- mally expect to start it by operating the NRST key. However, since the loader programme precedes the user’s pro- gramme in the memory, the loader pro- gramme must first be modified: it wilt have to start with an instruction ‘jump 2-36 — elektor february 1978 experimenting with the SC/MP (4) Figure 6. An example of how a particular symbol p in this case the letter P, is presented on a specific display. Figure 7. The flow diagram for a simple key- board routine. Table 4. The fisting for the HEX I/O demon- stration programme, TableS. The listing for the HEX I/O loader programme. \-i T am r Delay I AC I \ OF I AC I i r» Memary Delay Table 4 i START = 0000 0000 08 NOP mm C403 LDI L (KB) 000 3 31 XPAL 1 load PTR 1 with 000 4 C417 LDI H (KB) EA of 'KB' 0006 35 XPAH 1 0007 C40G LDI L (DISPL) 0009 32 XPAL 2 000 A C41 7 LDI H (DISPL) load PTR 2 with 000C 36 XPAH 2 EA of 'DISPL' LABEL 1 ; 000 D Cl 00 LD 0(1) load keyboard 000 F 94 FC JP LABEL 1 bit 7 - 0, no key pressed 001 1 D40F AN1 0F mask bits 0 - 3 0013 01 XAE in E , indirect addressing 0014 C427 LDI L (TAB) 001 6 33 XPAL 3 'TAB' to PTR 3 (higher byte - 00) 0017 C380 LD'1 28 (3) addressing via E 0019 CE01 ST@ 1 (2) display 7 -segment 'code' 001 B 8F0A DLY 0A delay approx 10 msec. LABEL 2 001 D Cl 00 LD 0 (1) wait until key is released 001 F 9402 JP DLY 0021 90 FA JMP LABE L 2 0023 8F0A DLY 0A delay approx. 10 msec. 0025 90E5 JMP LABEL 1 TAB: Table with 7-segment code. 0027 3F » BYTE 3F h 06 r 5B, 4F r 66, 6D r 7D, 07 0028 06 0029 5B 002 A 4F 002 B 66 002C 6D 002 D 7D 002E 07 002 F 7F * BYTE 7F, 6F, 77, 7C, 58, 5E, 79, 71 0030 6F 0031 77 0032 7C 0033 58 0034 5E 0035 79 0036 71 • END LDi 73 C473 •IPTR 1 ) - \im Address display 3 = 17x3 C903 ST3 Mi experimenting with the SC/MP (4) elektor fefaruary 1978 — 2-37 Table 5. 0075 0501 LD @ 1 (1) 0077 909B JMP $1 HEX I/O LOADER RAM: 0000 08 NOP 0079 00 * BYTE 00 0001 9005 JMP START ; programme start KBOARD: 0003 08 NOP 007 A 00 ■ BYTE 00 0004 03 NOP ; space for start routine PI L: 0005 08 NOP ; of user's programme 0078 00 • BYTE 00 0006 08 NOP PI H: 0007 08 NOP 007 C 00 • BYTE 00 START: COUNT: 0008 C400 LDl L (ADR) 007 D 00 * BYTE 00 000A 31 XPAL 1 ; load PTR 1 with start address SEGM 7: 0006 C41E LD1 H (ADR) 007 E 00 # BYTE 00 00 0D 35 XPAH 1 S4: 000E C402 LDl L (D1SPL) 007 F C0FE LO SEGM 7 0010 32 XPAL 2 ; load PTR 2 with EA of display 0081 CAFF ST - 1 (2) 0011 041 7 LDl H (DISPU ; digit 2 0083 40 LDE 0013 36 XPAH 2 0084 C3F4 ST RAM $1 : 0086 C4A2 LDl L (LDKB) ©014 0402 LDl ©2 0083 33 XPAL 3 0016 0866 ST COUNT ; load cycle counter 0089 €400 LDl H (LDKB) 0018 C4C9 LDl L (TAB) 0038 37 XPAH 3 001 A 33 XPAL 3 ; load PTR 3 with EA of table 003C 3F XPPC 3 001 B C400 LDl H (TAB) ; for converting binary to 008 D CAFE ST - 2 (2) 001 D 37 XPAH 3 ; 7-segment 'code' 008 F C0E9 LD RAM 001 E 31 XPAL 1 0091 IE RR 001 F 0859 ST RAM ; fetch lower byte of 'adr' 0092 IE RR 0021 31 XPAL 1 0093 IE RR $2: 0094 IE RR 0022 040 F LDl 0F 0095 53 ORE 0024 D054 AND RAM ; mask bits 0 - 3 0096 01 XAE 0026 01 XAE ; load E for indirect addressing 0097 C0E3 LD PI L 0027 C380 LD - 1 28 (3) ; fetch 7-segment J code' and 0099 31 XPAL 1 00 29 CE01 ST @ 1 (2) ; store in display , digit 2 009 A C0E1 LD PIN 0026 C04D LD RAM 009C 35 XPAH 1 002 D 1C SR ; bits 4 - 7 of lower byte of 009 D 40 LDE 002E 1C SR ; PTR 1 (higher byte in second 00 9 E C900 ST 0 (1 ! 002 F 1C SR ; cycle) = 'adr', are shifted 00A0 3F XPPC 0030 VC SR ; into bits 0 - 3 00A1 90CC JMP SI 1 0031 01 XAE LDKB: 0032 C3S0 LD - 128 (3) ; fetch 7 -segment code 00 A 3 C40S LDl L (KB) 0034 CE01 ST @ 1 (2) 00A5 31 XPAL 1 0036 6846 DLD COUNT 00A6 C4i ; LDl H (KB) 0038 9308 JZ $3 ; 2 cycles completed? 00A8 35 XPAH 1 003A 35 XPAH 1 $5: 0036 C83D ST RAM ; fetch higher 'adr' byte 00A9 Cl 00 LD 0 U ) 003D 35 XPAH 1 00 A B 94 FC JP $5 003E 90E2 JMP $2 ; jump for second cycle 00 AD 03 CC ST KBOARD $3: 00 A F D40F AMI 0F 0040 C400 LDl 00 00B1 01 XAE 0042 CE01 ST @ 1 (2) ; clear displays 6 and 7 $6: 0044 CE01 ST @ 1 (2) 00 B2 3F0A DLY 0A 0046 C6FA LD@ —6 (2) ; reset PTR 2 00B4 Cl 00 LD0 (1) 0048 Cl 00 LD 0 (1) ; load contents of 'adr' 00B6 9402 JP $7 004A D40F AN1 0F 00B8 90 FA JMP $6 004C 01 XAE $7: 004D C330 LD - 123 (3) ; fetch 7 -segment code 00 BA 3F0A DLY 0A 004 F CAFE ST - 2 (2) ; store in display J 0' 00 BC C4C3 LDl L (TAB] 0051 Cl 00 LD 0 U) 00 BE 31 XPAL 1 0053 1C SR ; shift (adr) 4 bits to the right 00BF 0400 LDl H (TAB) 0054 1C SR 00C1 35 XPAH 1 0055 1C SR 00C2 Cl 30 LD 128(1) 0056 1C SR 00C4 C8B9 ST SEGM 7 0057 01 XAE 00C6 3F XPPC 3 0058 0380 LD - 123 (3) ; fetch 7-segment code 00C7 90 DA JMP LDKB 00 5 A CAFF ST - 1 (2) ■ store in display J V TAB: 005C 31 XPAL 1 00C9 3F • BYTE 3F, 06, 005D C81D ST PI L ; store (PTR 1 ) 00CA 06 00 5 F 35 XPAH 1 00CB 5B 0060 CS1E ST PIN 00CC 4F 0062 C4A2 LDl L (LDKB) 1 00CD 66 0064 33 XPAL 3 00CE 6D 0065 C400 LDl H (LDKB) ; start 'LDKB' ( - keyboard 000 F 7 D 0067 37 XPAH 3 ; routine) 00D0 07 0063 3F XPPC 3 00D1 7F * BYTE 7F, 6F, 0069 C010 LO KBOARD 00D2 6F 006B £480 XRI X r 80 00D3 77 006D 9C10 JNZ $4 00D4 7C SI 1 00D5 58 006F C00B LD P1L 00 D6 5E 0071 31 XPAL 1 ; reload PTR 1 00 D7 79 0072 C009 LO PI H 00 D8 71 0074 35 XPAH 1 • END ; increment PTR 1 ; jump back without loading ; into 'adr' ; memory storage for keyboard ; data ; 2 bytes for (PTR 1 ) ; RAM-byte for 7-segment code data to display '1 ' 1 ■ to keyboard routine ; data to display J 0 r ; reload PTR 1 with ■ previous contents ; in 'LDKB r wai t for key = '1 r ; load keyboard routine ■ load PTR 1 with EA of keyboard ; wait for key to be pressed ; keyboard code to memory ; mask bits 0-3 ; delay approx, 10 msec, ; wait until key is released ; delay approx, 10 msec, ; load PTR 1 with EA of Tab" ; fetch 7 -segment code ; jump back for ; new start 58, 4F, 66, 6P, IQ, 07 77 r 70, 58, 5E, 79, 71 2’38 — elektor february 1978 experimenting with the SC/MP (4) Figure 8, The flow-diagram for the HEX I/O loader programme. See table 5. Table 6, The start routine Table 6 0000 08 0001 C400 0003 33 0004 C4 1 E 0006 37 0007 3F NOP LDf 00 XPAL 3 LOi X J 1E XPAH 3 XPPC 3 to user’s programme’, A suitable start routine is shown in table 6; this routine must be entered (using the data switches) before operating the NRST key to start the user’s programme. If a start address other than IE 00 is used, the start routine must be modified accordingly. In order to be able to use the HEX I/O loader programme again, the beginning of this programme must restored to its original state. It must be admitted that the start pro- cedure for the user’s programme is slightly awkward. However the alterna- tive would involve further lengthening of the 200-byte loader programme, and without a cassette interface this is not really practical. Once ibe system is equipped with a cassette interface how- ever, a programme of this length need be keyed into memory once only, since it can then be stored permanently on tape. Details of the cassette interface for the SC/MP will follow in a subsequent article. M '-:AUS HF* I/O loader di&p ay ADR i ! ADR l in ere -Tie m ADR NF XT key preswd f Missing link Experience has shown that the SC/MP II will not always work re- liably in combination with the RAM I/O card. The reason is that the SC/MP II has a lower fan-out than the older SC/MP, for which the system was originally designed. The problem can usually be solved by replacing IC4, IC5 and 10 1 4 on the RAM I/O card by their low- power’ equivalents: 74LS75 for IC4 and ICS , and 74LS00 for IC 1 4, If the problem persists after this modification, several ICs on the CPU card can also be replaced by their low-power equivalents: IC7 = 74LS00 and IC9 . . IC 12 — 74LS1 25. higher-order he* digir from key uoflrrt to display lo^r-o^dei hex- digi: from keyboard to display write digits irllp ADM increment ADR An extra decoupling capacitor, C7, has been added on the memory card (EPS 9863) — as can be seen in the top right-hand corner of the component layout shown in figures (part 3). The value should be 1 50 n. key pressed? 9703 S SW8/MOD elektor february 1978 — 2-39 market indicator cases are produced in a total of over twenty different types. Large stocks are held of standard models, whilst pro- duction quantities with customised scales are produced quickly to special order. Componex Limited 48/56 , Bay ham Place London NWI OEV diameter, the BZX 85 series covers voltage ratings from 3.3 to 33 V. Maximum dynamic impedance ranges from 35 1 1 at 8 mA for the 33 V version down to 3 a at 35 mA for the 7.5 V diode. I he diodes are designed for oper- ation over the temperature range 55 a C to +]75"C. SASCO, PO Box 2000 Crawley Sussex , RtilQ 2RU (641 M) High-speed error measurement system At a time when high speed digital transmission is beginning to be commercially exploited, Hewlett- Packard has introduced a new 1 5 0Mb /s bit error rate measure- ment system. The 3762A Data Generator and 3763 A Error Detector arc specifically designed for field evaluation, com- missioning and maintenance of digital line and radio equipment. The measurements performed by the system are: • binary bit-by-bit error detec- tion on binary and coded signals. * • clock f req uen cy offset gener- ation and measurement. The 3762A/3763A system strikes i fine balance between dedication and flexibility. Thanks to a wide variety of options available, it can be configured to meet the specialised requirements of existing systems such as cable and radio. At the same time, flexi- bility is retained to meet the developing needs of new systems such as optical fibre. Choices of internal clock frequencies, data formats, interface levels and impedances are available. Key ncw r features of the 3762A/ 3763A include a 2 2 M PRBS test pattern and new interface code for high speed systems, input equalisation for interconnecting cable loss, and zero block injec- tion to check the pattern depen- dance of systems. Burst gating inputs allow 7 the 3762A/3763A to operate in burst mode for TDM A satellite applications. To extend the capability further, outputs from the 3763A to an external counter, printer and pen recorder allow unattended long term measurements and error distri- bution analyses to be made. Hewlett-Packard Limited King Street Lane Win n ersh . Wo kingha m Berksh ire R G 1 J 5AR Analog shift registers for electronic music applications AMI have expanded further their broad line of customer and stan- dard MGS/ LSI devices for the electronic music field, with the introduction of two new analog shift registers. Designated the Si 01 10 and the S10I 1 1 , these new analog shift registers use analog delay elements to provide 185-bit delays. Among the effects achiev- able with the devices are delaying audio signals, adding an electronic chorus, vibrato or string ensemble, providing reverberation or simulating speaker rotation. The SI 0110 is the only second- sourced analog shift register avail- able: it is a replacement for the ITT TCA 350. It requires a two- phase symmetrical clock input, and the amount of signal delay depends upon the clock fre- quency. Similarly, the $101 1 1 imposes a delay dependent upon the clock frequency. It is designed to save outboard circuitry by requiring only a one-phase clock input. AMl Microsystems Ltd , 108 A Commercial Road Swindon, Wii tsh ire England (642 Ml Phase-locked oscillators Now available from Ferranti Limited is their new range of solid-state Phase-locked Oscil- lators covering the hand from 0.5 to 1 8 GHz* The Solid State Microwave Group has produced the VPO and VPM series of signal sources designed for telecommunication, radar, telemetry and instrumentation system applications. The VPO series is tuneable over 0.5 to 4.93 GHz and the VPM series over the range 4.8 to 18 GHz, with an output pow r er range of up to 750 mW and a maximum load VSWRof 1.5 : 1. Features of this range of oscil- lators include high spectral purity, extremely low AM and FM noise characteristics, high reliability, and ease of field tuning by two simple adjustments using only a VOM, When locked to an external refer- ence such as a primary standard or synthesizer, the stability of the oscillator is the same as the refer- ence: when using the internal crystal oscillator, the stability can be up to a best of ± 0.00036%. The many options available for this range of phase-locked oscil- lators include the capability to meet the requirements of MIL-STD-461 , high or low fre- quency modulation options, a mggedised construction, lock, limit alarm, and a non-translating tuning shaft. Ferranti Limited Solid State Microwave Group Microwave House Lee stone Road Manchester M2 2 4RN United Kingdom (640 M) Low cost mini-meters Componex mini-meters are low cost miniature moving coil indicators designed for use on a w 7 ide range of industrial and consumer electronic products. They lend themselves to many applications which require analogue indication, but do not justify the cost of a conventional panel meter. The meters are com- pact, have a low current drain (from 200 microamps) and incor- porate rugged movements which make them suitable for use on portable equipment. Round, rectangular, square and edgewise Low -cost zener diodes A new range of miniature glass- encapsulated zener diodes, the I R BZX 85 series, is available from SASCO Ltd. The new silicon regulator diodes, which combine a large voltage range with low dynamic impedance at low r cost, have a maximum power dissi- pation of 1.3 W at 25°C. Measuring only 5 mm in length (excluding leads) by 2.7 mm in 2-40 — elektor february 1978 market mapping feature allows the memory functions to be trans- ferred, block by block, from the Microprocessor Lab to the proto- type as the designer's confidence grows in the input/output portion of the prototype and in the program* An additional option is the real- time prototype analyser, which allows the program to run in real time while the memory of the Microprocessor Lab captures the data associated with each instruc- tion, together with eight external channels acquired through a separate test probe. The data for the 128 instructions prior to the breakpoint are available for examination. The designer can set breakpoints based on complex conditions involving micropro- cessor signal lines and external signal lines. Also available as an option is built in PROM (programmable -read- only-memory) programming; this option saves time and effort by eliminating the need to transfer the program to another piece of equ ipment. The flexibility of the 8000 series Microprocessor Labs to accommodate different micro- processor types results from the use of a multiple -processor archi- tecture. One emulator processor can be replaced by another at any time to accommodate additional microprocessor types, and no additional hardware reconfigur- ation is required to switch from one development project to another, Tektronix UK Ltd . Beaverton Home P.O. Box 69 llarpenden , Herts England. ... is available with alternative two- hole fixing, illuminated rockers or complementary pilot lights. This new facility extends even further the versatility of this popular series of ‘snap-in' switches rated at 10 A 250 V AC (15 A 125 VAC) and limited DC capability. Arrow- Hart ( Europe J Ltd '. Ply m bridge Road. Estover Plymouth, PL 6 VPN England (639 M) The 8002 is a complete system for developing software and for rapid and convenient integration of the software with the hardware prototype. Interactive entry and editing of the control program is via a visual-display terminal such as the Tektronix CT8 1 00 or CT8 IQ1 . The 8002 assembles the sources code into object code for the microprocessor chosen for the design. Lor the designer of micropro- cessor systems who already has the facility for software develop- ment, the 8001 provides a test bed for hardware checkout and for integration of software and hardware. For use of the 8001 , programs developed on external stand-alone or time-sharing systems can be downloaded to the 8001 via a RS-232C source. The key to the versatility of the 8000 series Microprocessor Labs is the in-prototype emulation mode in which the designer runs his program. The emulation sub- system employs the emulated microprocessor type itself, and therefore works exactly like the microprocessor will in (he proto- type circuit. Slep-by-step checkout of the soft- ware /hard ware combination is available under debug control via a prototype control probe con- nected between the Micropro- cessor Lab and the micropro- cessor socket of the prototype. The checkout sequence makes use of the Microprocessor Lab's memory resources. A memory General-purpose micro- processor development system Tektronix U.K.. Ltd, announces the availability of a universal microprocessor development system which greatly eases the integration of software and hard- ware at the prototype stage. Known as the 8000 series Micro- processor Development Lab,, the new system is designed for use with several commonly used microprocessors, including the 8080, 6800, Z-80, 9900 and 8085; emulation of other types will follow, and support for new microprocessors will be added as they are introduced, 1 he availability of a general- purpose microprocessor develop- ment tool means that the system designer has only one micro- processor development system to purchase and learn rather than having to purchase one for each type of microprocessor or being committed to a single micro- processor at an early stage. Because the cost of supporting additional microprocessors is minimised, the designer can feel free to choose the micropro- cessor best suited to his system requ ire ments. The Tektronix 8000 series is avail- able in two forms: the 8002 Microprocessor Lab, which is a complete stand-alone system; and the 8001 Microprocessor Lab, for users who already have software development capability* 65k CCD digital memory Thought to be the first 65k-bit Charge Coupled Device (C CD ) digital memory on the market, the L464 from Fairchild is offered at a per bit 1 priee that is lower than any other yet avail- able, Further significant price reductions are predicted for the future. The l 464 is a 65,536-bit dynamic serial memory organised as sixteen 4096-bit ‘Serial Parallel Serial 1 blocks in which one bit from any one of the sixteen blocks can be addressed. The company's double-poly IN -channel Isoplanar process is used in its fabrication. Features of the F464 include TTL compatibility on addresses, data input, wore enable, chip select and data output. Its organisation is such that the device can be packaged in a standard I 6-pin dual-in-line package. The device operates from 1 MHz to 4 MHz over a temperature range of 0-55 'C, whilst power consump- tion is lo w ; 1c ss t han 4 u W / bit at 4 MHz active and less than 1 pW/bit at 1 MHz, standby mode. Data is shifted through the memory by four low capacitance clocks. Three -st ate output is a feature. Output drive capability of the memory is 1 00 pF and 3,5 mA into a 100 pF load, Fairchild Camera £ Instrument (UK) Ltd , Sem [conductor Division 230 High Street, Potters Bar Herts, EN6 5BU Spade/solder lug for Arrow switch The Arrow 93 Senes of rocker lever switches is now available with 3/16" spade terminals with solder fixing capability. With their "positive 1 slow.' make and break action and inter- national approvals, the 93 Series market elektor february 1978 — E-15 Programmable Time and Amplitude Test Set An unusual programmable time and amplitude test set, the portable 6125C by Ballatitjne combines four instruments in one package and offers programma- bility on all front panel functions. The 6 I 25C is a voltage calibrator; a sweep/ delay-time or frequency calibrator; a risetime calibrator; and an error indicator. As an oscilloscope calibrator, the user can programme functions such as ranges; divisions of vertical amplitude; marker frequency and the number of All programming for the 6125C is done with TIL logic or connections to ground. In the programming function, two modes of remote operation are provided. In the first, the programme has full control and cannot be overridden by the panel controls. In the second mode the programme can be overridden locally by the operator via the front panel controls, if the operator wants to repeat or change a test. Then the operator has the option of returning to the programme sequence by re-setting the dials to the remote indication. An adapter card to interface the markers displayed; deviation in terms of direct percentage of error in decimals; the rep rate of the fast square used for risetime checks; and either of two modes of remote operation. Retailing at £ 3,160 in the UK, the Ballantinc 6125C can check oscilloscopes rated to 500 MHz as well as slow speed scopes, and is also highly suitable for calibrating counters, voltmeters, simple multimeters, panel meters, timers, signal generators and spectrum analysers. The 6l25's arrangement of controls and large arror display makes the nstrument useful for non-tcchni- caliy trained staff calibration :hecks - particularly at speed - in engineering laboratories, ;a!ibration houses, factory test nes, and inspection benches. 6125C to the ILC bus will be available shortly. No calculations are necessary when testing whether an instrument meets specification limits since the large 3 -14 digit LED readout in the centre of the 6 1 25C panel displays the error of the tested instrument directly, in percentage, with a resolution of 0.01% over a + 10% range. Other features of the instrument include its ability to select square wave amplitude outputs at any frequency from 10 Hz to I 0 kHz in decade steps; ability to test high speed scopes with the up to 500 MHz timing stimuli; and the availability of fast square waves with more than 1 nanosecond risetimes at selectable rep rates from 100 nanoseconds to 1 s. As a voltage calibrator the 6 1 251’ provides square waves at four different frequencies: 10, 100. 1000 and 10,000 Hz, crystal derived and accurate to within ± ,01%. Amplitudes arc adjustable in steps over an absolute range from 30 microvolts to. 220 volts in a 1-2-5 sequence and a nine- position multiplier sw-itch selects whether L 2, 3, 4, 5, 6, 7, ft or 10 divisions high are displayed on the scope screen. Accuracy of the amplitude calibration is better than ± 0.25%, Principal applications are calibration of oscilloscopes and other instruments or as a quick performance checker. The 6 I 25C needs only 30 watts at any frequency from 50 to 400 Hz and can be operated from any of the following AC line voltages; 100, 120, 220 or 240 V rms ± 1 0%, The instrument is easily portable with dimensions of 16.375 inches x 5.25 inches x 12 inches. Weight is 18 lbs, Du iron Sales l Am tied Pen mark House Wood bridge Meado ws, Cm! dfo rd Surrey GUI l BA, England (651 Mi High-speed fuses for semiconductor protection Now available from SASCO Ltd., the 1R range of high-speed fuses is specifically designed for the protection of semiconductor devices such as thyristors. Unlike conventional fuses, which incorporate a plain fusible wire element, the high-speed fuses depend for their operation on a pure silver element formed with a series of 'necks' and embedded in silica sand. The result is that when an overload situation does occur the clement breaks very quickly, and there is no likelihood of the joint reforming and welding together. Fuses are available with r.m.s, voltage ratings from 130 V to 700 V over a wide range of r.m.s, currents. Typical maximum l 2 t ratings at 250 V range from 26 A 2 s for a 7 A, 250 V fuse to 1.6 x 10^ A 1 s for an 800 A, 600 V type. SASCO, PO Box 2000 Crawley Sussex, R1I10 2 RU England (648 M} Additions to F4000 CMOS family Two further parts have recently been added to Fairchild’s F400G series of CMOS logic, a family which utilizes the advanced isoplan at C process. These are the F453 1 , a 1 3-input parity checker/ generator and the f - 45 32, an 8-input priority encoder. The parity checker, F4531, can handle words of variable length. Outputs are fully buffered (active high) and inputs are of the parity type, also active high. With the F4532 priority encoder data is accepted on the priority inputs. The binary code corre- sponding to the highest Priority Input which is High is generated on the Address Outputs if the Enable Input is High. Both devices are fully ca scad able and comply with the new r Jedec Industry Standard 4 R Scries CMOS specifications. Immediate delivery is available in both plastic and ceramic D1L packages (commercial temperature range) and ceramic OIL packages and Flatpak (military temperature range). Fairchild Camera & Instrument (UK) Ltd., Sem ^conductor Di v is ion, 230 High Street, Potters Bar, Herts, EN6 5BU, England (650 M) 7400 7401 740? 740 1 7404 7405 7400 7407 740H 74tJ9 74 If) 7411 74 V/ TIL. 74 1.C.'s By TEXAS, NATIONAL, ITT FAIRCHILD Etc. 14p 74 1 30p 74 {? 2Sp 7454 ISp 7430 35p 74121 2Sp 74139 lOOp 74156 70p 74174 lOOp 74 1 H'-t 350p 14p /4 14 60p 74‘i / ?5p / 450 15p 7401 7Sp 741?? 40p 74141 60p 74157 70p 74175 75p 74190 UOp 14p /41b 30p 7438 25p 74 70 30p 7487 4Sp 74123 60p 74142 2 7 Op 74160 90p 74’76 lOOp 74191 UOp 14p /4 1 7 30p 7440 ISp 74/7 ?5p 749 : 40p 7412S SOp 74143 270p 74161 90 p 7417/ lOOp 74’9? 120p 14p 7470 ISp /441 b5p 74/3 30p 7405 GOp 74176 SOp 74144 270o 74162 90p 741 ?e UOp 91 1 93 1?0p Up /4?? 20p 744? 65 u 74 74 30p 749b 70p 74 1 30 1 30p 74145 75p 74163 90p 74179 UOp 74 - 54 loop 40p 74? 5 ?5p 7445 80 p 74 7S 30p 74103 95p 74 T 31 i00o 7414/ ?30p 74164 125p 74130 lOOp 74195 7 So 40p 7425 ?5p /44h H5p 74/6 3 tip 74104 40p 7413? 65p 74148 160o 74165 12Sp 74181 200p 74196 lOOp 20p 7475 2Sp 744 7 75p 748* 85p 74105 40p 741 3S lOOp 74150 120p 74166 125p 7418? 75p 74197 lOOp ?0p /4?7 ?5p /448 /Op 7485 lOOp 74107 30p 74136 80 p 7415’ 65p 74167 325p 74184 150p 74198 16Sp ISp 74?« 40p 745f 15p 7486 30p 74100 SOp 74137 lOOp 74153 65p 74170 200p 74 • 85 ISOp 74199 lB5p 20p 74 ffj ISp 7451 ISp 7480 2S0p 74118 90p 74138 125p 74154 120p 741/3 ISOp 741 SB 350p 20o 7453 15p 74170 99p 74155 70p SEMICONDUCTORS by MULLARD.TEXAS, MOTOROLA, SIEMENS, ITT, RCA. A A 11 j lOp KAI1H 16p BCIbHH AA 144 lOp BA 148 16p HC168C AA/1 / 30p HA1S4 12p BC 1 690 AC121 30p HA157 ISp HCI71 AC 176 19p I1A 1/3 15p MCI 720 AC127 19p HA71I. 18p HOI 78A AC 127/01 25p HA316 16p 11018? AC 178 IHp HA/ 1 1 5p BC182L AC15I 25p HA/ 1b 5p MCI 83 ACIS3K 40p BB105A 3b P MCI 8 11 AC 1 /6 20p HB1 10 45p B0 184 ACiVI / :»5 P MC107 lOp HC184L AC V?| 30p IlC 108 lOp HC18H AD 149 bOp BC10BC ISp HO 70S A0 161 40p HCT09 lOp H021? A016? 40p Mf 1109C Up HC212L AD161/2M8 90 p MCI 13 12p HC213L Ar 114 22p HCU7 19p HO? 14 AF 115 22p BC125 20p HO? Ul AF116 22p BC1?b ISp 8C258 AF 11/ 22p HCUb 1?p BC294 Af 1 18 50p BC147 lOp HC303 Al 175 ?5p 110148 lOp HC31 / AT 139 35p lie uw. Up BC373 AF2J9 4Sp HCU9 lOp HC326 ASYTf. 40p HC157 10p BC338 RAII4 9p B0 158 lOp HCS16 BA121 9p H0 1 SO lOp IlCSl 7 I1C16/A i?p : 1 BC64 7H HC548 Up MC548C Up BF 123 4Sp 15p BC549H 13p OF 125 4Sp ISp I1C5490 Up BF 127 SOp 1?p BC557 13p HFlbb 30p 12p HOY 34 SOp BF 167 25p 16p BCY70 I5p HF 1 73 2Sp 10p HCY71 20p HI 1 79 3Sp »?P. BCY/7 15p 8F179C 40p lOp BD1?l 85p M *• 130 30p 12p BD»23 lOOp HI 181 3Sp lOp I1D174 85p BF 18? 30p l?p HD 131 3b p BF183 30p 34p BDU? 39p BF 186 25p Up BD133 4Sp BF 194 lOp lip BD13S 40p BF19S lOp 12p HD 13b 40 p HF 196 10p 1?p HOU/ 40p BF 197 lOp 13p BDI39 38p BF 198 2Sp Up BDUO 40p BF199 25p 13p BD181 80p BF 200 30p 3Sp ■ 80p BF224 20p SSp HD70/ 70p BF22S 70p 15p BU2 t’J SOp HI 741 16p GOp BD263 6Sp HI 744 0 35p 13p 8DY10 lOOp BF257 2bp 12e BDYb2/0l 90p BF258 26p bOp HF 170 SOp BF259 lOp 65p 1?P 13p BF 171 4Sp BF2/4 BF 324 15p 30p I2e HF336 3Sp BY 164 SOp OCUO BF 337 3Sp HYX94 8p OC1/1 BF 368 GOp Cl 120 30p 00200 8F594 30p 01 164 20p 0RP12 BFW5H ?0p E 100 42p TIP29 RFX29 30p E201 50 0 TIP29A 8FX31 lOOp E204 4Sp TIP29C HFX84 ?5p E300 47p TIP30 BFX85 30p E310 60p TIP30A BFX87 2Sp E4?0 180p TIP308 BFX88 ?Sp E430 125p TIP30C BF Y60 20p VUE 340 45p TIP31 BFY51 20p MP5A06 ?5o TIP31A BFYS2 20o OAIO 40p TIP31B BFY90 125p OA4/ 15p TIP31C on 101 35p 1 6p TIP3? 8RY39 35p OA91 6p TIP32A BR V 58 35p OA202 8p TIP328 HSX20 20p 0023 200p TIP32C HSY40 25p 0025 lOOp TIP33 HSY95 20p OC23 7S P TIP33A BT 100 A 80p OC35 75p TIP33B BLM05 150p OC42 35p TIP33C BU133 7Sp 0043 35p TIP34 HU 708 220p OC45 35p TIP34A BY1UO 20 p OC/1 25p TIP34B ft Y 1 76 15p 0072 30p TIP35 BY127 15p OC7S 30p BY133 22p 0081 30p OC810 25p OC83 50p OC84 SOp ISOp TIP3SA 230p 2N1305 30p 40p TIP35C 260p 2N1036 38p 80p TIP36A 3S0p 2N1308 50p 70p TIP41A 70p 2N1711 22p 45p TIP41B 75p 2N2219A 2Sp 47p TIP41C 80p 2K 2483 30p 75p TIP42A 80p 2N2906 16p S5p TIP42B 8Sp 2N2 907 20p 58p TIP29SS 7 Op 2N3053 20p 6Sp TIP3055 55p 2 43054 50p BOp TIS90 25p 243055 60p 55p TIS91 25p 2N3439 SOp SSp IN914 5p 7N3702 1 1p 65p IN3754 10p -.N3703 12p 70p IN4001 Sp N 1 1 lip bOp IN4002 5p 2N370S 12p 65p IN4003 5p 2N3 706 lip 8Sp IN4004 5p 7N3711 12p 90p IN4005 &P 2N3715 300p 1 00 p IN4006 6p 2N1772 1 75p 105p IN4007 ?P 3N3819 25p 11Sp IN4148 4p 2N3866 9Sp 150p IS44 4p IN3904 15p 115p 2N456A 90 p 2N4C62 14p 118p 2N607 15p 2N4126 20p U5p 2N929 20p 2*45081 35p 225p 2N930 20 p 2NS163 3Sp 2N1307 25p 2N6027 SOp 2SD234 50p B2Y 88 400 mW Zeners 0V7 2V4 2V7 3 VO 3V3 3V6 3V9 4V7 5V1 5V6 6V2 6V8 7V5 8V2 9V1 10V 11V 12V 13V 15V 18V 20V 22V 27V 30V 33V ALL ONE PRICE 1 0p each 100 mix £8.50 BF 257 IQfot £1.50 RCA SCR TO 3 case 100 V 12.5 A £2.00 MULLARD BTY87 100R 100 V 8.5 A £1.00 each Linear Integrated Circuits CA 30 76 200p CA 3085 85p CA 3088 190p CA 3090 A Q 400 P CA 31 30 . lOOp 1 M 300 TOb . 1 7 Op LM 301 AN . . 65p LM30/N ... 6 bp LM 308 TO 5 . 1 30p LM 308 DIL 1 30p LM309K . . I80p LM 310 TO 5 . 16 Op LM 31 1 TO 5 . . 260p LM317K 325p LM324N 350p LM348N . . 200p LM380N lOOp LM 555 3Sp LM 701 TO 5 . 60p LM 710 OIL . . 65p LM 723 TO 5 75p LM 723 DIL 75p LM 748 . 45p LM 1303N 155p LM 1468 lOOp LM 3900 N 90p MC 1310P . l8Sp ML 741 14 PIN 30p MM 5314 450p MM5316 550p NE 529K 1 50p Nt 555 35p NE 556 ... lOOp NE 5628 . 400p SN 760 13N I80p SN 7601 3ND 125p SN 76023N 180p SN 76023NO 12Sp SN 76227N 160p SN 76228N 180p SN 76666N lOOp T A A 300 1 50p 1 A A 350 190p T AA 550 50p TAA661B UOp T AA 700 390p TAD 100 . 160p T AD 1 10 1 30p I BA 120S 80p TBA 1 20 T 125p TBA 520Q 240p TBA 530Q 21 5p ELECTROLYTIC CAPACITORS SPECIAL OFFERS uF/V 4 7/?5 Sp 1/16 Sp 1/75 5p 1/50 5p 2 2/25 Sp 7 7/35 Sp 3 3/75 5p 4 7/10 Sp 4 7/16 Sp 4 7/76 Sp 4 7/50 5p 6.8/2S Sp 10/10 Sp 10/16 5p 10/7S Sp 10/3S Sp 10/50 5p 22/6V3 Sp 22/10 Sp 77716 Sp 22/75 Sp 22/35 5p 77/50 6p 3376V3 Sp 33/16 6p 33/2S 6p 33/40 6p 33/50 7p 47/10 bp 4 7716 bp 4 7/2S 6p 4 7/35 bp 4 7/50 75p 100/10 6p 100/16 bp 100/76 bp 100/50 bp 100/63 lOp 125/15 6p 770/ lb lOp 220/25 1?p 220/50 20 p pE/V 330/25 I5p 330/35 16p 330/50 18p 470/10 12p 470/25 . 16p 470/35 . 18p 470/50 22p 1000/16 25p 1000/35 26p 2200/10 28p 2200/16 35p 2200/63 75p 2200/100 1 20p 3300/16 . 40p 3300/25 . 42p 3300/63 80p 4700/25 45p 4/00.40 5 Op 4700/63 I20p POLYESTER CAPACITORS Mullard or Erie pF/V .001 Sp .0022 Sp 0033 5p .0047 5p 0068 Sp .01 Sp .077 Sp .033 5p .047 Sp 1 bp t»p .4/ 12p 1 00 20p » 7 2Sp 4 7 35p 6 3 40p BC147 BC148 100 BC149 ASSOR BC157 TED BC158 FOR HC159 t7.50p BF 194 8F195 BF196 BF 197 IN4148 100 I O' ISOp TEXAS TIS88A V.H F FET 10 lor £ 2.30 100 lor £20.00 555 TIMER 10 lor . £2.80 741 OP.AMP. lOlor . £2.00 BYX94 DIODES 1250 FIV1 Amo. 100 lor £6.00 BD607/608 COMP POWER £1.50 pair SPECIAL OFFER DL 707 DISPLAYS 65 p EACH XEROZA RADIO 306, ST. PAULS ROAD, HIGHBURY CORNER, LONDON, N1 Telephone 01-226-1489 Easy access to Highbury via Victoria Line (London Transport) British Rail RESISTORS CARBON FILM 5% .2 S W 2.2 4 ?m ?p 5 W 2.2 - 4 7M 2.5p 1.W 2 2 10 MEG 3.5p POTENTIO- METERS 1 K Lin 30p 5 K Lin 30p 10 K L.n 30p 25 K Lin 30p 50 K Lin 30p 100 K Lm 30p 250 K Lm 30 p 500 K Lm 30p 1 Meg Lm 30p ? Mrg Lm 30p 5 K Log 30 p 10 K Log 30p 26 K Log 30p 50 K Log 30p 100 K Log 30p 250 K Log 30c 500 K Log 30p 1 Meg Log 30p 2 Meg Log 30p ROTARY SWITCHES BY LORLIN 1 P 1 2W 40p 2P 6W 4 Op 3P 4W 4 Op 4P 3W 40p 1200 mE 63V . .2 for £1.00 2200 mF 63V .2 for £1.50 3300 mF 63V .2 for £1.60 MULLARD C280 0.01 mF 100 for £2.50 LATE EXTRA Linear IC's TBA 540 . . . . 230p TBA 5400 . . 240p TBA 550Q ... 33Sp TBA 560C . 33 5p TBA 64-1 A12 250p TBA 720 250p TBA 800 110p TBA 81 OS 110p TBA 990 280p TCA 270Q 250p ZN 414 120p CMOS 4000 20p 4001 20p 4023 400? 20p 4024 4006 120p 4025 4007 20p 4026 4009 70p 4027 4011 20p 4028 401? 20p 4029 4013 55p 4030 4015 90p 4037 4016 55p 4043 4017 nop 4048 4018 250p 404 7 4020 UOp 4049 407? 180p 4050 4054 20p 4 OSS UOp lOOp 4056 U5p 20 p 4060 130p 200p 4066 SSp 85p 4069 30p ISSp 4071 30p 130p 4072 30 p GOp 4081 20p 150p 4082 30p 220p 4510 145p ISOp 4511 200p 1 15p 4516 UOp 70p 4518 UOp SOp 4528 130p 130p T.T.L. OFFERS 7410 . 10 for lOOp 7412 . 10 for 150p 7420 . 10 for 100p 7430 10 for lOOp 7432 1 0 for 200p 7442 10 for 350p 7474. 1 0 for 200p 7476 10 for 250p 7483 10 for 700p 7493 1 0 for 250p 7496 1 0 for 450p 74107 1 0 for 200p 74121 10 for 250p 74153 1 0 for 400p 74161 1 0 for 800p LEDS RED 17S GREEN 125 /ELLOW 17S TIED 2 GREEN .2 YELLOW 2 DL 747 Duplay 200p DIL SOCKETS 8 Pin 1 3p 14 Pin 14p '6 Pm 15p BRIDGE RECTI FIERS OCTAL VALVE HOLDERS 10 for £1.50 1 A SOV ?5p 1A 100V 30p 1 A ?00V 30p l A 400V 35p 8D 144 . . 160p •A 600V 40p R 201 OB 250p 2 A SOV 35p BU 205 . 220p 2A 100V 50p BDX32 250p ?A 200V SSp AU 110 I80p 2 A 400V 60p R 2008B 2 1 0p 15p 25p 25p 15p 25p 25p PLEASE NOTE ALL PRICES INCLUDE POSTAGE AND V.A.T. AT 8 OR 12%% AS APPROPRIATE LARGE STOCKS OF NEONS, NUMICATOR TUBES. 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