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.
The integrated circuit used is not common today. The circuit is from the SGS linear integrated circuits...
This circuit includes the power supply from the power grid. We found it in Radio Electronics from...
This circuit was found in the April 1998 issue of Electronics Now magazine. The circuit uses...