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 intended to reinforce old car radios, having been found in 1997. At that time,...
The Sample and Hold circuit shown in the figure was found in a 1994 Linear Applications Handbook by...
Found in a 1980s documentation, this circuit detects when the voltage drops below 11 V. Other...