We found this circuit in the June 1992 issue of Radio Electronics magazine. The sensor is a common diode. The circuit is powered by the power grid from a 12 V transformer.
This circuit is from 1999 documentation. However, it can still be easily assembled, as all...
This circuit, obtained from the component manual used, has an ultra narrow 1 kHz range given by...
The zener diode determines the triggering of the circuit and R3 must be a resistor that will be...