We found this circuit in the Encyclopedia of Electronic Circuits Volume 5 from 1995. It uses a 3-terminal transducer from the time. The circuit is triggered by light.
The presented differential amplifier, indicated for instrumentation, was obtained in the 1994...
This circuit provides a signal when dialing occurs. The circuit is powered by the telephone line...
This circuit uses two TTL trigger inverters to generate signals that can be adjusted at R1. The...