The LED frequency flashes depends on the value of the capacitor tested according to the table. We found this circuit in a Popular Electronics from the 80s.
This circuit is from an Electronics World of 1964. The circuit can be made with modern...
The Variable Frequency Oscillator (VFO) or Variable Frequency Oscillator shown in the figure can...
This guitar effect circuit was found in a 2002 documentation. The circuit can be powered by a 9 V...