We found this circuit in the May 1989 Radio Electronics magazine. The circuit can have its values changed to operate at other frequencies and the power supply must be symmetrical.
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...