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.
July 2017 - Microchip's new MCP39F511 demonstration and development boards, which consist of...
This circuit, which controls both the temperature and the level of a liquid in a reservoir, was...
This circuit provides a constant current of 1 mA, stabilized by an LED, which can be equivalent to that...