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 circuit, with an operational amplifier, was found in the Motorola Dataar Linear of 1990. The...
Found in a 90s nHands On Electronics, this circuit triggers a relay that shuts off the load when...
This 100 kHz crystal oscillator was found in American documentation from the 1980s. The JFET can...