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.
We found this simple transistor tester in a French publication in 1981. It uses a common analog...
Who is faster? or reaction game are other names for this circuit that we find in old...
This circuit is from an 80's component manual. The components are from the time, but the circuit...