This 1977 circuit only allows the solenoid to energize if the right combination of switch positions is selected. The relay is 6 or 12 V depending on the low voltage supply used.
This small unregulated variable power supply was found in an American book from the 60's. The...
This circuit indicates when the voltage of a 12 V battery is low. With changes, for example, the...
This basic circuit is from 1984 documentation. This circuit can be used as an efficient burglar alarm...