This grounding test circuit was found in an American 80's documentation. The circuit is for the 110 V power grid but can be changed to the 220 V power grid.
This JFET amplification stage was found in the April 1993 issue of Electronics Now. The input...
This circuit with TTL output was found in a 1968 EEE. The transistor can be of general use. The...
Using a piezoelectric sensor of the time, this circuit was found in the February 1994 issue of...