We found this circuit in a technical documentation for the National Semiconductor LM3909. The circuit consists of a low consumption continuity tester powered by a single battery.
The circuit suggested by National Semiconductor mows signals from a peak determined by the...
This 90's project shows how to use an old cassette recorder to practice telegraphy. In position A of the...
This circuit from Radio Electronics magazine, March 1994 edition uses two LM388 bridged, providing a 4...