With this circuit it is possible to modulate pulses from a pulsating input signal. The PNP transistor can be the BC558 and the power must be supplied with 5 V.
To obtain variable frequency signals, the circuit in the figure is recommended. In this circuit, the...
This circuit was found in old English documentation. It can be improved by using resistors of...
This circuit was published in a 1979 magazine, but it can still be easily assembled as the...