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.
This circuit was found in a 1992 documentation and has excellent sensitivity, using components that...
This practical idea from a 1992 documentation shows how to count the turns of a winder using a...
In this circuit from the 60s, the power supply is made with 22.5 V, which is the voltage of the...