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 of a few tens of milliwatts of power requires a single source. We found it in a Radio...
This interesting circuit is from a 1988 documentation. It is a matrix of diodes that converts...
Found in older Signetics documentation, this circuit generates signals from 30 Hz to 25 kHz....