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 variable filter circuit was found in July 1975 Radio Electronics magazine. The circuit uses 3...
This Hughes circuit is from 1968. Equivalent modern components can be used. The input impedance is...
This circuit emits a warning sound when night falls. The circuit is from a Hands On Electronics from...