This circuit was obtained from an American 1980s documentation. The frequency depends on the crystal and the circuit may be a PNP that reaches the generated frequency.
When the sensor is activated the relay turns on powering na external load such as a buzzer siren...
This circuit has a 200 kHz bandwidth and a low input current. The circuit is from the 80's, but...
This circuit makes use of a commercial type current transformer. The circuit is from a 2005 Linear...