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.
This circuit was suggested by National Semiconductor and is present elsewhere on this site. The...
This configuration, well known, was obtained in a publication in 1976. The unijunction transistor can be...
This circuit consists of a touch switch with optical isolation, using CMOS integrated circuits. The...