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 was found in an English publication from 1967. The circuit is for listening on a...
This circuit allows you to use a digital multimeter as a thermometer. The sensor is mounted in a...
This configuration, which appears in other articles on this website, was found in a European...