Poptronics recommends this circuit for use in the car when the headlights are left on. The circuit uses a sensitive relay with contact current according to the headlights.
This circuit was originally intended for reading movie soundtracks. The circuit is from 1967 and...
This circuit was obtained in an old magazine from the 1970s. The circuit can still be assembled with...
This circuit recognizes a tone determined by the tuned input circuit (R3 / R4 / C2). The circuit...