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.
We found this circuit in a 1967 Electronics World. It analyzes a transistor by determining its...
This circuit monitors the output level of an amplifier. The circuit is set to R4 and can be...
Originally designed for an incandescent lamp, this flasher or pulser can be adapted to operate with...