This untuned (aperiodic) amplifier circuit was found in the August 1974 Radio Electronics magazine. The transistors are period, and the board layout is critical.
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...