This circuit is part of an article published in the March 1990 issue of Radio Electronics magazine. The sensor consists of a grid-shaped electrode shown in the figure.
This circuit uses a CA3140, an operational amplifier with FETs in the input stages. Equivalent can be...
Found in a Popular Electronics from the 90s, this circuit has a configuration that has been widely...
This circuit was found in an American 80s circuit manual. The components used are unusual. The...