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.
This amplifier with differential input uses two old op amps but can be implemented with modern op amps....
The main feature of this circuit is that it provides a sine waveform signal. In this circuit, the...
The HA2620 integrated circuit used in this comparator is from the 80's, but the setting can be...