This wired intercom circuit was found in an English publication from the 80's. The integrated circuit can be replaced by an equivalent, just like the transistor which is a general-purpose type.
Found in an 80's Elektor, this circuit can use any equivalent optical coupler. The buzzer is of the...
We found this circuit in a 1986 documentation. It is based on TTL integrated circuits that can be...
This small battery-powered high-voltage generator was found in Radio Electronics magazine from...