This circuit for audio signals was found in the March 1990 Radio Electronics magazine. The circuit uses a unusual optocoupler that can be replaced with an equivalent one.
This circuit can be used as a rhythmic light or as a control shield for incandescent lamps from...
We found this circuit in a European publication from the 1990s. Transistors are still common types...
Settings like this can be found in this section and on this website, but from different sources of...