This circuit was found in February 1976, Radio Electronics magazine. The circuit is quite sophisticated using a fast-acting (thermometric) sensor and analog indicator.
This simple sensitive circuit was suggested in a July 1992 Radio Electronics issue. The relay is a...
Found in an old English publication and in other parts of this website in different versions, this...
This circuit can keep a set of lamps on for up to 1 minute, time given by C2 and R2 that can be...