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.
By connecting several photocells in series, we can directly activate a sensitive relay, as shown in...
The purpose of this circuit is to provide a constant current to an experimental electromagnet. The...
Found in Linear Technology documentation from the 90s, this circuit uses components from that...