This humidity sensor indicates the different levels of conduction of the sensors through an LED bar. The circuit is from Popular Electronics and must be powered by cells or battery.
This ohmmeter can be made with a scrap milliammeter used for continuity tests or even resistance...
This circuit was found in the November 1992 issue of Radio Electronics magazine. The circuit has...
Found in an English Maplin documentation from 1983, this circuit generates separate frequency...