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 is from a publication of the 70s, but it can be easily assembled with the BC548. The...
This very low frequency amplifier has a gain of 1,000 and was found in a 1967 documentation. The circuit is...
This transmitter was found in a 1993 documentation, but it can be assembled with operators like...