This circuit was found in a 1967 Japanese documentation. It consists of a touch control system with two transistors from the time. The circuit uses a power source and sensitive relays.
This circuit detects smoke by changing the light falling on the sensor. The circuit was found in...
This circuit uses an unusual operational amplifier nowadays and has a very low consumption. The...
This very high voltage circuit was found in the 1990 special issue of Radio Electronics...