This simple sensitive circuit was suggested in a July 1992 Radio Electronics issue. The relay is a double-contact changeover relay. Sensitivity adjustment is made at R2.
The circuit in the figure is from a source with the possibility to adjust the output voltage from...
We found this circuit in an old magazine 73 of 1974. The circuit must be powered by a continuous voltage...
This circuit is from a 1987 American publication called Electronics Handbook. The circuit can be...