Found in an 80's Elektor, this circuit can use any equivalent optical coupler. The buzzer is of the Sonalert type with included oscillator.
This circuit was obtained in a documentation from the 80's. The components used are of the time,...
Obtained in a 90s Radio Electronics, this configuration appears with variations in other points of...
This circuit was obtained in a 90s EDN. The components used are from that time. The voltage...