This circuit was found in a Popular Electronics from the 90s. The circuit uses an ultrasonic microphone. The indicator is dual with LED and Buzzer.
This circuit is from the 1977 RCA Linear Integrated Circuits Manual. The circuit has a...
This circuit was found in 1980's Radio Electronics. The circuit produces a 1500 Hz modulate 35 kHz....
The maximum power of the controlled load depends on the triac used. The circuit is from a Radio...