London EN5 1 ED Editor: Len Seymour Elektuur B.V. Peter Treckpoelstraat 2-4 6191 VK Beek - the Netherlands Editor: PEL Kersemakers Elektor sari Route Nationale; Le Seau; B.P. 53 59270 Bailleul - France Editors: D R S Meyer; G C P Raedersdorf Elektor Verlag GmbH Susterfeld-StraBe 25 100 Aachen, — West Germany Editor: E J A Krempelsauer Elektor EPE Karaiskaki 14 electronics technology Loudspeaker impedance correction Computers and health care Electronics and temperature control Magnetic-field sensors Early detection of electronic failures A million frames hold the new Domesday Pioneering nuclear power for peaceful purposes Design ideas : LC displays 16673 Voula - Athens - Greece Editor: E Xanthoulis projects Portable mixer -1 Flashing colours Simple auto slide changer Versatile stereo amplifier information New products . Readers services guide lines Switchboard Appointments .... Classified ads .... Index of advertisers selex-13 Digi-Course II (chapter 7) . . The Oscilloscope TV Antenna signal distributor Tips for selex PCB 6.28 6.31 6.33 6.38 6.42 j 6.43 6.44 ; 6.46 j 6.18 6.26 6.35 6.40 6.49 6.63 6.71 6.54 6.56 6.60 6.61 6.03 m@ta 0 0 0 component tester in our oscilloscopes is altogether different from other’s. In addition to all Oscilloscope funtions component tester provision can test all components passive and active, in circuit and out of circuit. ONLY OUR SCOPES CAN recognise NPN/PNP. Distinguish HIGH/LOW Gain, Distinguish AUDIO, R.F., SWITCHING transistors. MULTI FUNCTION OSCILLATOR rus~LA/ * Pure Sine wave output. » Amplitude settable with ease down to millivolts. X 1. X 1/10 and X 1/100 attenuated outputs available. * No amplitude bounce when trequency varied. J VASAVI ELECTRONICS 630, Alkarim Trade Centre Ranigunj SECUNDERABAD-500 003. ph: 70995 PCB Drafting Aids now made in India. Motwane has its measure SELL ADS.MMC. | EH 1 I ' ' \ . 1 l % If 5: 0 or- M * -F-" ^ ~':~" : fo l 1 Device offers til) ELECTRONIC EDUCATIONAL & TESTING DEVICES We stock: elektef Magazines ic IZUMIYA 1C INC. P.C.B. Drafting Aids TELEDYNE RELAYS I1CJ1 Semiconductors KONTAKT omSmis Cleaners FAIRCHILD Semiconductors Texas Instruments Semiconductors VPN T " mmin9 jrJ-MI Potentiometers Ribbon Cable Connector Panels as Semiconductors RS 232 Connector Panels SPECIAL EX STOCK OFFER E-Prom D-RAM 4116 41256 4164 42128 Regulators 7805 - 24 7905 - 24 SCR/Triacs 4 amp - 40 amp 400 V - 600 V TTL/CMOS 74 LS00 - 629 4001 - 40257 2716 27128 2732 27256 2764 Bulk importers and users in India may Kindly forward their specific enquiries © OBi'iae EleatroiiQs Pta. ltd. 101 Kitchener Road. ‘02-04, Singapore Electrical, Electronics and Hardware Centre, Singapore 0820. Telex : DEVICE RS 33250 FOR ENQUIRIES CALL: 298 6455 (4 lines) 6.11 Today BESTAVISI0N are in the news 6.13 BESTAVISION ELECTRONICS LTD CMOS Technology RCA 1802 Microprocessor Based Micro Computer and Control Systems, for DEFENSE APPLICATIONS, FIELD DATA LOGGING, Electroplating Process Control and other Industrial Applications. 5 avia pc i and R* can be ascertained precisely for any in- dividual power unit by replacing them by two 5 k preset poten- tiometers. Adjust these presets until the output of the relevant regulator is 18.1 V. Switch off, remove the presets, and carefully measure their values with an ohmmeter. Fixed resistors with values so found should then be soldered in the R3 and R« positions (this may, of course, entail making up a parallel combination to obtain the correct value). Check that the output voltages of the regulators are still ±18 V. MIC-LINE module Although the number of presets'may give the impression of complexly, the circuit in Fig. 3 shows thafmifc would be misleading. Operational amplifiers Ai, A2, and A3 form an in- strument amplifier that provides properly balanced inputs. f' The sensitivity of the microphone in-" put is about 20 dB higher than that of the line input. Fig. I. The front panels of (a) the MIC-LINE module ; (b) the stereo module ; and (c) the power unit. Fig gl&fcu. n diagfjhi of the To keep the overall noise level down, Ai and A 2 are low-noise types, while Ri to R13 incl. are high-stability (1%) metal film resistors. Gain control Pi, which enables set- ting the gain between 20 dB and 60 dB, must be a high-quality type, because it is located in a noise- and scratch-sensitive position. The peak indicator is formed by tran- sistors Ti and T2. The threshold of operation is fixed at 9 V PP or 3 Vims by voltage divider Ris-Ris. These levels correspond to a microphone input of 3 rnVims at maximum amplifi- cation. Reservoir capacitor Ci en- sures that short-duration overloads are also clearly indicated. Coupling capacitor C< prevents any DC reaching the potentiometers and connects the amplified input to the three-way active (A*) tone control. Ef- fects control P2 , of course, precedes Uauone control stage. lWtentiometer Ps sets the wanted monitor output level. Stereo slide potentiometer P7 is the fade control. Since a signal to drive a multi-track ■ recorder is also required, slide con- trol Pi —the fader— is a stereo type to prevent any feedback between the stereo channel and the multi- track outputs. An alternative to this arrangement is to provide each channel with a PFL (pre-fade listen- ing) facility; Cij-Rm can then be omit- ted, Pi can be a single track control, and S> and R« are fitted externally. Stereo input module The stereo input module —see Fig. 7— has no balanced input: in- stead. it is provided with an equaliz- ing pre-amplifier, formed by Ai and ht (Ai' and hi), for use with variable- reluctance pick-ups. Input selection is effected by Si: pos- ition 1 is for variable-reluctance pick- ups; position 2 for high-level inputs, such as from tape recorders; and position 3 for mono signals. Position 3 is for use when the MIC- LINE module is not available, or, for instance, when more equipment is to be connected than was originally foreseen. Note, however, that only line signal sources can be connec- ted: not microphones. The (un- balanced) signal is then taken from the right-hand AUX input, and amplified in Ai and hi by a factor 3. Stereo potentiometer Pi provides a monophone effects signal, but is ar- ranged such that its input and output resistance are equal, whatever the position of the wipers. The active tone control is followed by the controls for the monitor out- put (Ps), the channel output (Ps), and the balance (P?). With Si in position 3 (LINE), the balance control functions as panorama control. The pre-fade listening facility is con- structed with (external) components R9, Rio, and S2. A multi-track output is not necessary in this module, because the unit is normally fed from a multi-track tape machine. If the MD input is not required, the operation if Ai (Ai’) can be made lin- ear by omitting C< and Cs (C<’ and Cs’), and replacing R« and Rs (R«’ and Rs') by R* (Rx’). The value of the new resistor may be calculated from Rx=R 3 (o-l) [Q] where a is the amplification of the amplifier. If the amplification is large, Rx=Rs. S10k250 complete ■ Fig. 3. The printed-circuit board for the power unit. s - 1 sfv ups n m U Capacitor Ci (Ci') may be adapted to match the output impedance of the tape machine used. Construction Before buying any new components, it is wise to determine how many modules are required. Prepare the printed-circuit boards shown in Fig. 5, Fig. 8, and Fig. 9; note that the board in Fig. 8 consists of two parts, which must be separated before any components are fitted. The dimensions of the front panels are given in Fig. 10: 10a is that for the M1C-LINE module; 10b that for the stereo module; and 10c that for the power supply. The overall length will, of course, depend on the cases used. The prototype was built in one aluminium case with compartments for the various modules. The con- struction of this will be described in next month’s issue. In the mean time, the completed modules may be tested by connect- ing their outputs to the TUNER or 5 >« , O 9&°G*l So.' Tn°“©S «1N4148 Di = LEO: red Ti;T? = BC557B ICi.lCr = NE5532 or LM833 ICrilCr' = TL072 ICa = XR4195 (see fig. XLR Cannon-type 3-pin Fig. 10. Drilling plans for the front panals: (a) the MIC-LINE module; (b) the stereo module; and (c) the power unit. Many high-resolution graphics images may be considerably embellished by highlighting and enlivening effects such as controlled colour flashing and inversion, since the degree of screen animation seems to be proportional to the interest viewers take in watching the image. FLASHING COLOURS The proposed circuit has been de- signed for insertion between the digital RGBfl) outputs of the Elektor high-resolution colour system and a RGB(I) monitor, see Elektor India. issues from October 1985 onward. The colour inversion and flashing ef- fects are entirely under software control (BASIC); they are easily brought about by writing appropri- ate data to a specific memory lo- cation, as will be explained further on in this article. Since the proposed design of the flash/invert extension is fairly universal, other graphics col- our systems may also incorporate it, provided the necessary control signals are available. Colour inversion One of the fundamental operations in Boolean algebra is refened to as the exclusive-OR (EXOR) bit manipu- lation method, which is a means for controlling the digital polarity (in- verted/non-inverted) of an operand A when this is applied to either one input of an EXOR type logic gate, the other input being driven by a logic level (0 or 1) PROG. Depending on the logic level assigned to PROG, operand A will appear either in the non-inverted form (B = A; PROG = 0 ) , or the inverted form (B=A; PROG = I) at the EXOR gate output; see the diagram opposite this text illustrating the logic function of this program- mable inverter gate. In the present add-on circuit, gates Nit to N20 receive the RGB1 signals and a common control level COLOR which is obtained by latching the Da databit from the host processor bus during a memory write operation to I/O map location XX67 — see Fig. 1. Fig. 1. A few SSI gates, a dual counter, a latch, and two diodes constitute a pro- grammable flash /invert add- on circuit for the high-resolution graphics card. AH signals at the left of the figure come from the existing main and colour ex- tension board. Application of HCCD type ICs is preferred for ICs and ICs, although stan- dard LS equiv- alent types will also do. 6.26 ele 0 = bit at logic lew level. 1 = bit at logic high level. X = bit level irrelevant to listed effect. — = bit is low or high as required for c Table 1. Every bit in the byte written (POKEd) to XX67hex specifies a func- tion in the flash/ invert ex- tension; the examples listed in this table serve to illustrate some of the poss- ible program- ming configura- tions with their resultant effects on the RGBI monitor. Thus, by setting and resetting this bit at the indicated memory location, the user is in control of simultaneous colour inversion of all picture elements. Since there happened to be an EXNOR gate left over in ICa, this wasjjut to good use as an ad- ditional 1’ output along with I'. Flashing colours The colour flash circuitry is a bit more complicated than the combi- nation of gates to effect colour inver- sion since, as opposed to the overall effect of the latter, the flash circuit section operates specific to any of the colours red, green, or blue. To start with, some slow, periodic switching signal is required to deter- mine the flash rate. The present design enables software selection of two flash rates, fast or slow, as selected by the logic level of Da writ- ten to XX67. In order to ensure the necessary fixed phase relationship between picture scan and flash pulse, the vertical blanking pulse (VB) is applied to the CK1 input of a dual 4-bit counter Type 74LS393. The outputs 2QA and 2QB of the second counter section in this IC have been selected to supply two flash fre- quency rates to selection gate net- work Ns-Nu-Ns and the two diodes in OR configuration. Fast or slow flashing is now under control of the F/S signal; in other words, D7 at XX67. Note that proper operation of the diode OR simulator may only be achieved with the use of HC(T) types for IC3, and ICs, which must feature good high and low level definition to compensate for the inevitable voltage drop across the silicon diodes. However, where these new types are not yet available, the use of 74LS equivalent types may be resorted to. The function of the other logic gates in the circuit is best elucidated by starting at the output side of the pro- posed design, establishing, for in- stance, the order in which the red (R) signal is processed. When pin 2 of Nu is permantently at high logic level, the red bit is simply passed by this gate; if, however, the logic level at this pin is arranged to toggle along with the flash signal, the red output bit will also flash, whether or not in- verted by N17. Gate N