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.
This TTL circuit is from a Radio Electronics magazine from February 1973. The circuit must be...
Common operational amplifiers like the TL series, CA3140 and others can be used in this circuit...
This circuit uses only two common transistors and provides good audio power in a speaker. Readers who...