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 found this circuit in old American documentation. It can be implemented with more modern...
The purpose of this circuit is to control the high and low light of a car, detecting when a...
This powerful transmitter for the 27 MHz band was found in a Japanese publication from 1961. The...