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Search the history of over billion web pages on the Internet. Full text of ” Elektor – Circuits ” See other formats I practical electronic circuits for the home constructor J introduction circuits The book follows the theme, and is a contirtuation of our popular and very succe sfut circuits publication.

It is composed of assorted circuits ranging from the simple to the more complex designs described and explained in straightforward language. An ideal basis for constructional projects and a comprehensive source of ideas for anyone interested in 310 tronics. In a nutshell something to please everybody.

No part of this publication may be reproduced or transmitted in any form or by any means, including photocopying and recording, without the prior written permission of the publishers. Such written permission must also be obtained before any part of this book is stored in a retrieval system of any nature.

The circuits and other diagrams contained in this book are for domestic use only. Patent protection may exist with respect to circuits, devices, components, etc, described in this book, The publishers do not accept responsi- bility for falling to identify such patent or other protection. Reprinted in India by Elektor Electronics Pvt.

India Under agreement with Elektuur B. Seek The Netherlands Price Rs. For this reason, ‘abbrevia ted’ type numbers are used in Elektor wherever possible: UCEO, max 20 V! In general, any other member of the same family can be used instead. 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: Resistance value 2k 7: Capacitance value 1 0 n: The DC working voltage of capacitors other than electrolytics is normally assumed to be at least 60 V. As a rule of thumb, a safe value is usually approximately twice” the DC supply voltage.

U, not V The international letter sym- bol ‘U ‘ for voltage is often used instead of the ambiguous ‘V’. Mains voltages No mains power line volt- ages 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.

Automatic mono stereo switch. Simple CMOS square wave generator. Improved supply Square wave-staircase converter HF current gain tester. Car ammeter Timebase scaler Model railway lighting Frequency synthesiser controller Squarewave oscillator Temperature -com pen sated Scope calibrator Electronic open fire Common-base virtual-earth mixer FSK modem Voltage trend meter.

When the mains supply drops out, the light- ing is switched on automatically. The circuit of the unit is extremely simple.

Trl, D1 and Cl provide a halfwave rectified and smoothed DC supply of approx. The voltage drop across D2 reverse-biases the base-emitter junction of Tl, so that this transis- tor is turned off and the lamps are not lit.

When the mains supply fails, however, TI is supplied with base current via R2; the transistor therefore turns on and the lamps are lit. An obvious example is in that infamous dark cupboard under the stairs, so that, should a fuse blow, a replacement can be easily found and fitted. A transformer with a slightly higher secondary voltage can be used, provided that R1 is uprated to limit the current through this resistor to mA. Pseudo random running lamp V If a number of the outputs of a shift register are fed back in a certain fashion via an EXQR gate to the data input, then the Q outputs of the regis- ter will run through the maximum possible num- ber of mutually different logic states.


N4 back to pin 7, the data in- put, of the register.

The clock signal is provided by ICl. The clock frequency, and hence the speed of the running light, can be altered by means of PL R The circuit can be extended for use as a light or- gan.

The LEDs are replaced by opto-couplers which, via the necessary hardware triac etc. The phase-shift is dependent on the relative values of R eleltor C and on the input frequency. The complete circuit of a phasing unit using all- pass filters is shown in figure 2.

The use of a total of ten op- amps in the eleltor may seem rather excessive, but as eight of these are LM quad op-amps the total package count is only four ICs.

The direct and phase-shifted signals are summed by IC2d. The proportion of phase-shifted signal and hence the depth of phasing can be adjusted by means of P4.

Elektor – Circuits

This may be con- trolled either manually by means of P3 or may be swept up and down automatically by the out- put of the triangular wave generator consisting of IC3 and IC4. As the gate voltage of the FETs must always be elekor the output of this oscil- lator swings bet ween ” 2 and – 6 V. The oscillator frequency may be varied by means of PIand the best phasing effect occurs at fre- T70DI 1 quencies between 0. The reference voltage output is fed to the two threshold inputs via presets PI and P2, which are used to calibrate the circuit.

The lowest acceptable voltage for a 12 V car bat- tery is about If the battery voltage rises above P2 is therefore adjusted so that D3 is lit for input voltages eleotor It will be noticed that the LEDs do not light and extinguish at exactly the same voltage. Eldktor is due to a hysteresis of 60 mV which is incorpor- ated into the 1C to prevent the LEDs flickering when the battery voltage is close to the threshold levels. The novel feature of this circuit is that it requires only one touch contact.

N1 and N2 form a flip-flop bistable multivibra- tor. The inputs of N2 elekgor thus high, which satisfies the criterion for the output to be low, which was the original assump- tion. Cl is charged to logic high through R3 from the high output of NL If the touch con- tacts are now bridged by a finger, the logic high on Cl will be applied to the inputs of Nl through R1 and the skin resistance.

Once the finger is removed, Cl will discharge through R3 into the low output of NL If the touch contacts are subsequently bridged, the in- puts of Nl will be pulled low by Cl since it is now discharged. The output of Nl will thus go high and the output of N2 low, which will hold the inputs of Nl low even after the finger has been removed. The TAP is now reset to its orig- inal state. Cl will charge to logic high through R3 from the output of Nl, ready for the elektorr to elrktor touched again.

Elektor – 301 Circuits

The only constraint on the operation of the cir- cuit is that the interval between successive oper- ations of the switch must eektor at least half a sec- ond to allow Cl time to charge and discharge. CMOS function generator Using only one inexpensive CMOS IC and a handful of discrete components, it is possible to build a versatile function generator that will pro- vide a choice of three waveforms over the entire audio spectrum and beyond.


The aim of this project was to produce a simple, cost-effective, general purpose audio generator, which was easy to build and use. The positive- and negative-going sweeps of the integrator output make up a triangular wave- form, whose amplitude is determined by the hysteresis of the Schmitt trigger i.

The triangle output is fed through a buffer amplifier to a diode shaper, which ’rounds elekgor the peaks and troughs of the triangle to produce an approximation to a si new ave signal.

Any one oF the three waveforms may then be selected by a three-position switch and fed to an output buffer amplifier. The frequency of all three signals is varied by altering the Integrator time constant, which changes the rate at which the integrator ramps, and hence the signal fre- quency.

The voltage drop across Cl thus increases lin- early, so the output voltage of Nl falls linearly until the lower threshold voltage of the Schmitt trigger is reached, when the output of the Schmitt trigger goes low. To ensure symmetry of the triangle waveform he. Assume for ihe moment that R — is connected to the positive 1 14 Figure 1.

Block diagram of the CMOS func- tion generator. Complete circuit of the function generator. Photos, Rlektor three output waveforms pro- duced by the function generator. However, when the output of N3 is low, R4 and P2 form a potential divider so that a voltage from 0 V to 3 V can be fed back to PI, depending on the wiper setting of P2. Of course, the adjustment of P2 must be carried out to suit each individual function generator, owing to the tolerance in the value of U t.

Elektor – – [PDF Document]

Fine frequency control is pro- vided by PI which varies the charge and dis- charge current of Cl or C2 and hence the rate at which the integrator ramps up and down. The triangle output is taken through a buffer amplifier N4, and thence through the 3001 switch to the out- put buffer amplifier.

Up to about plus or minus 0. The sine output is fed via C 5 and RIO to the output amplifier. Sine purity is adjusted by P4, which varies the gain of N4 and thus the amplitude of the triangle signal fed to the sine shaper. Too low a signal level, and the triangle amplitude will be below the diode threshold voltage, so that it will pass without alteration; too high a signal level, and the peaks and troughs will be clipped severely, thus not giving a good sine wave.

The input resistors to the output buffer amplifier are chosen so that all three waveforms have a peak to peak output voltage of about 1. The elekttor level can be adjusted by P3. Adjustment procedure The adjustment procedure consists simply of ad- justing the triangle symmetry and sine purity. In cases where the symmetry improves as the wiper of P2 is turned down towards the output of N3 but exact sym- metry cannot be obtained, the top of R4 should be connected in the alternative position.

Elektor – 301 Circuits.pdf

Since the supply voltage alters the output voltage of the various waveforms, and hence the sine pu- rity, the circuit should be operated from a stable 6 V supply. If batteries are used they should never be allowed to run down too far. Ekektor ICs used as linear circuits draw more cur- rent than when used in the normal switching mode, and the supply voltage should not be greater than 6 V, otherwise the IC may overheat due to excessive power dissipation.

Performance The quality of the waveforms can be judged from the oscilloscope photographs. In many cases the breakdown voltage of a zener diode is printed, fairly clearly, on the case.