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.
We found this source with the CI 723, common at the time, in a 1989 paper. Power transistors must be...
Found in an American 80's documentation, this circuit can use common FETs like the BF245 and cover...
This simple passage alarm is powered by the power grid using an LDR as a sensor. The circuit is...