This circuit can detect static charges or extremely low voltages. The circuit was found in ancient American documentation and makes use of a JFET. A BF245 which is a more modern transistor can be used.
This very simple circuit uses a phototransistor and a very sensitive relay (reed type) being used...
We found this circuit in Radio Electronics magazine from January 1958. It uses a neon lamp as the...
The integrated circuits in this application are not very common today. One consists of an A / D...