We found this circuit in a Hands-On Electronics from the 90s. The circuit must be connected to an external amplifier. Frequency control is capacitive, using an antenna for this purpose
The idea of this circuit from a 1960 publication is simple: we can switch the transistor being...
Using a small speaker as a microphone, this 10-LED circuit was found in the March 1992 issue of...
We found this circuit in a 1977 documentation. The National Semiconductor's LM380 is no longer...