Telephone dialer (CB21268E)

This circuit was found in Electronics Now. With it the dialing signals of a telephone are generated, reproduced in a buzzer.

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Alternating Flash 555 (CB25533E)
This circuit was found in the November 1992 Radio Electronics magazine. The resistor in series with...
Impedance Match (CB493)
The input impedance of this circuit is about 700 k ohm and the output impedance is about 1 k ohm....
Variable Oscillator (CB23970E)
This 1-transistor Hartley oscillator generates an audio signal that is dependent on capacitor C1....