This current switch was found in a Radio Electronics from November 1957. It triggers the current determined by the electromechanical sensor, a polarized relay of the time.
This circuit is from a 2005 Linear Technology manual. The circuit is powered by 3.3 V but can...
This circuit uses two operational amplifiers, which can be of the type 741, in a full wave...
This simple circuit for an audio link uses a lamp, which has a very poor frequency response, but...