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 basic oscillator with tunnel diode generates a 100 kHz signal with 1 uW output power. The...
This amplifier for medium or high impedance magnetic headsets (above 200 ohms) was found in an...
This circuit provides precise signals of three frequencies, using CMOS technology. The integrated...