Found in a 1968 American documentation, this circuit uses an operational amplifier that is uncommon today. The feed must be symmetrical. The gain is 40 dB.
This circuit was obtained from an 80's Electronic Engineering. The circuit detects ice formation...
This circuit is from the Motorola Linear Databook published in 1990. The circuit for 1 kHz can be...
In the fist circuit the alarm triggers on when any sensor is CUT. In the second circuit the alarm...