Found in a 1980s telecommunications documentation, the circuit presented acts as a product detector. The modulator or mixer in the square may be that of the previous circuit.
We found this circuit in an old American documentation from years 80. The diode determines the frequency...
The slope of an object causes the sensor, a mercury switch to be triggered. The circuit activates...
I found this simple circuit in an English magazine from 1984. The circuit can be assembled easily...