This circuit was found in a 90s Popular Electronics. The sensors can be common speakers that reach from 15k to 25 kHz, such as piezoelectric tweeters.
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...