This circuit is from old documentation, using a component that cannot be found easily today. The indicator is a galvanometer, and the input voltage is in the order of 1 V.
This circuit triggers a relay when it gets dark, thus enabling the lighting of fluorescent lamps, which...
This mechanical option touch switch was found in an old English documentation. Transistors may be...
Found in a 1980s manufacturer documentation, this circuit can be used as an optical shield. The...