This circuit turns off a relay after a time determined by C1. The circuit was found in the December 1974 Radio Electronics magazine. The relay is rated according to the supply voltage.
This filter has a factor Q = 10 (selectivity), and its frequency can be changed as shown in the...
I found this circuit in a Popular Electronics from 1992. The circuit shows how we can modulate a lamp...
The circuit shown in the figure shuts off a load when the voltage drops below the value determined...