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 mains-powered switch circuit in Electronics Now magazine from July 1994. It could be...
This 80's circuit can be made with current comparators. Rectification accuracy is 1% DC up to 100...
When the light falling on the sensor is cut off, the SCR fires, powering the lamp. Remember that...