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 two-channel wired intercom was found in the April 1990 issue of Radio Electronics magazine....
The voltage of this symmetrical power supply depends on the regulating integrated circuits, which...
A staircase signal is produced by this circuit using a TTL IC and an operational amplifier. The...