This circuit is from an American manual from 1975. The transistors are types of the time, but equivalents can be used, as well as the relay that can be according to the supply voltage.
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...