This circuit was found in a Popular Electronics from the 80s. It is possible to control a relay from a video signal. The circuit was used in video recorders of the time.
We found this circuit in an Electronic Design from the 80's. The generated tone can be changed as well...
This basic tone control circuit employs a Philips NE5538 operational amplifier, but can be adapted to work...
This two-phase stepper motor circuit was found in an old documentation using an operational amplifier...