This circuit was found in Radio Electronics from the 90s. It converts capacitance into frequency in order to obtain a proportional voltage that can be measured in a common multimeter.
The integrated circuit used in this project is not common today, but it can be implemented with more...
Found in an American publication from 1969, this circuit can be adapted to be used as a shield....
This current meter with many scales was found in a 80s American documentation. The operational amplifier...