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It is a useful item of test gear, especially for calibrating other instruments that are designed to measure duty-cycles in one form or another – dwell meters, fop instance. This simple signal injector should find many uses in trouble shooting and alignment appli- cations.

The disadvantage is that bat- teries of ceils cannot be charged. Press- ing SI, 32 or S3 In various combinations feeds a choice of seven different constant currents through the zener and the zener voltage Is measured with a multimeter.

This type of resistor has quite a high self- inductance, but since the usual applications of high-power wirewound resistors are DC or low- frequency AC this is not important. If the oscillator eoektor generates the clock pulses is set 96 j so that a pulse is produced say, every 20 ms, then the reaction time of the players can be calculated quite simply by observing which LED remains lit, A new game can be started after pressing the re- set button. The sine output is fed via C 5 and RIO to the output amplifier.

For this reason a start button SI is included which, when pressed, takes the input of Nl low. This is sufficiently long for the indication to be seen. Circuit of the calibrator Figure 2.

The pulse stretcher is a one-shot multivibrator with an output pulse period of approximately ms.

It is advisable to use 1 resistors, and PI and P2 should preferably by high-quality preset poten- tiometers. The counter output is used to switch transistor Eelktor on and off, and the collector signal of Leektor is fed to the output amplifier A4, Since the collec- tor resistor of Ti receives its supply from the output of the envelope follower, the amplitude of the collector signal, and hence of the output signal, varies in sympathy with the amplitude of the original input signal.


Elektor – Circuits

Eldktor is connected in parallel with N1 to increase the fan- out of the circuit. Firstly, care must be taken not to exceed the common-mode input rating of the op-amp used, especially with a single-ended asymmetric sup- ply. Also, short single pulses will be missed comple- tely. There surely cannot be many meters with a sensitivity lower than that, if one ele,tor a separate moving coil milliameter avail- able, it can be fitted with a series resistor that makes its internal resistance up to the value re- quired of a voltmeter giving f.

This is particularly a problem in areas of fringe reception. A constant current of – thus flows through R2. Wirewound resistors are available with high power ratings, but unfortunately such resistors are rarely wound so as to minimise self- inductance.

N1 and N2 are Schmitt triggers connected to form a monostab ie multivibrator with a period of about 15 ms. The triac must also be able to withstand the peak mains voltage i. The fre- quency band from Thus an oscilloscope will fre- quently agree with itself between different Y sen- sitivity elektr timebase ranges, even though the calibration may be wildly inaccurate with refer- ence to an externa] standard.

Elektor – 301 Circuits

This ensures that when the relay drops out due to the lamp being switched off the LED does not light, since its supply is also disconnected. The built-in preamplifier boosts the output level to several hundred milli- volts, which allows the signal to be fed direct to the ‘auxiliary’ or ‘line 1 inputs of amplifiers or tape decks.

For example, the type number of the zener family is often printed, together with the zener voltage, so a BZY88 6V8 would be a 6,8 V zener from the BZY88 family.

The divided down output is available at pin 1 of the IC. So that the resistance of the zener does not affect the output voltage the zener current must be fairly constant. The circuit diagram elekttor the servo polarity changer.

The value of inductance thereby obtained h equal to the product of the values of R2, R3 and C2 i. This can be used to calibrate the oscilloscope time- base. Elekyor most cases a value of 1 k should prove sufficient. The duty-cycle at the output is de- termined by the division ratio. However, with supply voltages greater than 10 V this should not be a problem.


The ac- companying figure shows a circuit diagram of a simple and reliable FSK modulator which has the advantage of requiring no calibration. Tl in turn will tend to turn off and the supply voltage will fall. This contrasts with con- ventional circuits where the bases of T 1 and T2 are connected to one another by means of a diode network. When the input of N1 is taken low by bridging the lower pair of touch contacts with a finger, the output of N1 goes low.

The direct and phase-shifted signals are summed by IC2d. Block diagram of the Eletkor func- tion generator. N1 to N4 form a 5-input OR gate, but the number of inputs can easily be increased by add- ing extra gates.

Elektor – Circuits : Free Download, Borrow, and Streaming : Internet Archive

The input impedance of the circuit that the compressor output feeds should be as high as possible. D1 and D2 are included to stabilise the reference voltage. The Table lists frequency ranges for a few capacitor values. 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. When constructing the circuit par- ticular care should be taken to ensure that the 0 V rail is of low resistance heavy gauge wire or wide p.

The latter choise of course implies that every reading will require a little mental gymnastics! The supply failure indicator described here will sense the interruption of the power supply and will light a LED when the supply is restored, thus informing the microprocessor user that the information stored in RAM is garbage and must be re-entered, and telling the digital clock owner that his clock must be reset to the correct time.

These counters are set in the decimal down-count mode.