Found in a 1980s documentation, this amplifier uses an integrated circuit that is not easy to obtain now as it is of the era. The circuit is intended for FI ceramic filter circuits.
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...