The operational amplifier and the sensor used in this National Semiconductor circuit are not common today, but the configuration can be adapted to use current components.
Suggested by Amperex in a 1968 documentation, this circuit is based on TAA370, an integrated circuit...
Found in American documentation from the 90s, this circuit uses a high voltage relay and has no...
This circuit is from a Popular Electronics from 1993. The magazine is no longer printed, but the...