This circuit was found in the September 1971 Radio Electronics magazine. The buzzer can be replaced by a relay according to the supply voltage. R1 adjusts the sensitivity.
This circuit provides a pulse train of 4 MHz or at another frequency determined by the crystal during...
This instrument was obtained in a documentation for radio amateurs of 1976. The circuit measures...
This circuit was found in a publication by Gernsback from 1960. The circuit generates signals from...