Designed for the audio track, this circuit was found in a Popular Electronics from the 90's. Other operational can be used and R7 can be 470 k. The frequency is 1 kHz.
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...