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This is particularly a problem in areas of fringe reception. Cl now discharges through R4 into the output of IC 1 until its voltage falls below that on the non- inverting input, when the output of IC1 again swings positive and the cycle repeats. The opamp is used as a comparator. Single contact operation is possible using a ca- pacitive pickup of mains hum, but this is not very reliable, and will not work at all with bat- tery powered equipment!
A slight modification to the circuit, shown in fig- ure 2allows recording from disc while listening to a different source. The circuit pre- sented here can measure both voltages and cur- rents. Supply failure indicator — S 12V When the supply is interrupted all voltages, of course, fall to zero. There seems to be something soothing in watching the flames flicker and play about the coals. The complete circuit of the voltmeter uses only this 1C and a handful of other components, since the 1C will drive the LEDs directly.
N1 and N2 form a flip-flop bistable multivibra- tor. Since there is a 0. The decimal point is usually replaced by one of the following abbreviations: This can be achieved by pro- viding the resistor with a centre tap and connec- ting it as shown in figure 1Current flows in op- posite directions in each half of the resistor, so the magnetic fields produced in each half and hence the self-inductances tend to cancel out. When a squarewave is fed to the dock input the circuit will count up until the counter reacheswhen the carry output will go low and clock FF1.
D1 and D2 are included to stabilise the reference voltage. This invariably means resistor values in excess of I MO, which can give timing errors due to stray leakage resistance in the circuit, or large electrolytic capacitors, which again can introduce timing errors due to their leakage resistance. An example of 4 random voltage levels displayed simultaneously on the ‘scope. The switching circuit is shown in figure 1.
Hence the following circuit, which is intended to reduce power dissipation when the is used with an external transistor, should prove very popular.
When the generator is being aligned, switch SI should be open, thereby 75 preventing modulation of the output signal.
There are two possi- bilities: The output thus goes low, taking the inputs of all NTs low and inhibiting the elektod buttons so that no other flip-flop may be set. To make a really professional job the output of the preamp can be taken via a Cannon XLR or locking DIN connector socket mounted in the base of the housing.
This is achieved by feeding the zener via Ri from the output of the op-amp. This is done by decreasing the value of R7. The circuit is based on the wellknown 1C regulator. 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.
The value of R5 is dependent on the supply volt- age used and should be 33 ohms for voltages between 9 V and 15 V, 68 ohms for 15 V to 25 V and ohms for 25 V to 35 V.
This is due to a de- cision by the BBC to transmit the 19 kHz pilot tone with all programmes, ostensibly to elim- inate annoying clicks that occur when switching 22 1 stereo decoder 6. IC1 functions as a voltage controlled multivibrator.
Simple transistor tester This simple elekror checks the functioning and measures the current gain hf? The same pulse is fed to one input of the PLL, where it is compared with the reference frequency. When the thief cuts this wire to remove the equipment then the alarm will sound.
Elektor – 301 Circuits
With S3 in its centre position a signal can be taken from the source to the record inputs of both tape re- corders. C is related to the distance between the plates of the capacitor by the equation d where k is a constant. The signal level is increased until distortion be- comes apparent, whereupon PI is adjusted to minimise distortion. Since D 5 and D6 receive their bias from the output of the supply, R5, R6 and D7 epektor be included to make the circuit self-starting. Via D6 the input of N4 goes high.
Fur- thermore, a choice of seven different zener cur- rents is provided, which allows the zener voltage to be plotted against current.
Since C2 is charging and discharging exponen- tially it follows that the higher the analogue 1 44 I 2 input voltage the longer will be the charge periods of C2 and the smaller will be the dis- charge periods.
Thus, if the carriage lighting consists of two lamps, then the capacitor in series with these two lamps should have a value of approx. The proportion of phase-shifted signal and hence the depth of phasing can be adjusted by means of P4.
The output level can be adjusted by P3. Figure 3, In order to set the servo In the neu- tral position rlektor pulse duration of 1.