This circuit that we found in a 1990 documentation uses an LED as a sensor. The operational amplifier is equivalent to the 741 and the trigger adjustment is made in the potentiometer.
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...