This circuit was found in an English publication from the 70s, an article that teaches how to calculate instruments. The circuit is still current and can be built with an analog indicator of 100 uA.
This amplifier for automotive use is suggested by the Philips Databook of 1990. The integrated circuit...
This circuit is used in transceivers, enabling input selection by diode switching through polarity...
Suitable for operation with high impedance microphones, this circuit was found in American...