This circuit was obtained from an American documentation from 1976. The circuit has a dynamic range of 100 kHz. FETs may be replaced by current equivalents.
This 2004 circuit is based on the ionization effect that occurs in old incandescent lamps with...
This circuit memorizes through an LED indicator if your phone was used during your absence. The...
Found in a 1969 Electronics World, this circuit generates low frequency signals with two...