Found in a 1980s documentation, this circuit uses transistors from that time. Modern equivalents can be used. The alarm is a piezoelectric buzzer with na included oscillator.
We found this control circuit for three-phase motors used in the control of doors and gates in a...
This extremely slow circuit produces one pulse per month and can be used in a timer. We found it...
This circuit is from an American publication of 1977. The tunnel diode admits equivalents and the...