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 circuit is from Popular Electronics of the 90's. It makes use of NO and NC sensors. The relay...
Based on TTL logic this circuit can vary both the frequency and the pulse width of a rectangular signal....
This circuit was found in an old English publication. The circuit makes use of general-purpose transistors....