This circuit is from a July 1970 Radio Electronics magazine. The sensors are metal probes. The 18 V power source must be isolated from the mains.
August 2017 - Mouser Electronics is announcing the availability of TDK ICS-52000 microphones with...
This circuit, which can be used as a shield or in other applications, can be found elsewhere on...
This crystal or galena radio was found in documentation from the 1990s. The earpiece must be a...