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 operational amplifier used in this configuration is uncommon today, but more modern types can...
This is a circuit that appears several times in this section and in articles. It is a preamplifier for...
We found this circuit in the August 1994 issue of Electronics Now. The 4046 is unusual today. The...