This series LED circuit was found in the February 1992 issue of Radio Electronics magazine. The effect's speed is dependent on C1 and adjusted by R3.
The circuit shown is from an old European publication. In it we have the way to activate a relay...
We found this circuit in a European publication from the 1990s. Transistors are still common types...
This circuit was found in an American documentation and can be added to common amplifiers of any...