This circuit makes use of a stroboscopic tube, a component that no longer exists today. The circuit is from the 70's and can be adapted to use mains voltage.
The circuit shown by the figure below can produce signals in the range between 20 kHz and 30 kHz....
This circuit was found in the March 1992 issue of Radio Electronics magazine. The 10-LED circuit has...
We found this circuit in an early American 80's documentation. We note that the first gate of the...