Found in the May 1971 Radio Electronics magazine, this is the circuit for a commercial high-impedance instrument. The circuit uses 4 transistors and is powered by 2 9 V batteries.
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...