Originally, this circuit was created to monitor the liquid level in the reservoir of a car's windshield wiper. The circuit is from documentation from the 90s.
This audio circuit was published in a Rado Electronics issue from October 1963. The transistors are from...
This circuit was published in a 1981 magazine, but it can be easily assembled using a BC548 paraQ1...
September 2016 - can already be purchased at Mouser Electronics the Robot Scribbler S3 from...