This circuit, from a 303 Circuits from the 90s, uses a telephone pickup coil as a sensor to capture power grid noise, thus making it possible to locate electrical wiring.
This experimental short-range transmitter came out in a 1972 publication and was designed to...
This circuit, from a 2001 documentation, appears elsewhere on this site. Its purpose is to obtain a...
This 1980s documentation circuit uses a 741 in a different high-speed comparator configuration. The feed...