We found this circuit in the Linear Applications Handbook of the National Semiconductor of 1994. The circuit can be adapted to use other operational amplifiers and the power supply must be symmetrical.
This 1964 Electronic Design circuit uses a photo-FET as a sensor. The component is rare today. |...
Operational amplifiers or comparators like those in the LM139 series can be used on this circuit,...
This sensitive electrostatic charge detector uses only common discrete components. The circuit can be...