Found in American documentation from the 90s, this circuit uses a high voltage relay and has no grid isolation. The high values of R1 and R2 prevent the shock when it touches the sensors.
This circuit was found in a 90s Popular Electronics. It generates tones given by the oscillators and...
We find this ultra-simple transmitter circuit that is nothing more than a very short range RF...
This is a high efficiency version with the MC723 which is the Motorola version for this well-known...