This is the receiver for the previous transmitter. The microphone is of the high impedance ultrasonic type. The circuit activates a relay. The operational amplifier supports equivalent.
We find this circuit in the 80's own component manual itself. The characteristics of the circuit...
We found this amplifier with high input impedance and low capacitance, using FET, in a...
This circuit was obtained in a 1979 magazine, but it can be easily assembled today, as the...