This circuit lets through the 300 Hz to 3kHz range that corresponds to the human voice. We found it in the Radio Electronics magazine of February 1990. The circuit uses both parts of the LM381.
Critical components of this project are the Geiger tube and the 300V battery. The battery can be...
The instrument is a common multimeter on the lower voltage scale. The FET can be BF245 or MPF102. The...
Suggested by National Semiconductor in a documentation of the 90s, this circuit uses a power...