This two-tube circuit, one being a double, was found in Radio Electronics magazine from July 1958. The distance to the microphone depends on noise and losses. The cable must be shielded.
This circuit was found in the July 1992 issue of Radio Electronics magazine. The circuit is based...
This timer activates a relay after a time interval of up to 15 minutes has elapsed, starting from...
The circuit presented is based on a mechanical tuning fork. The circuit is suggested by National...