This circuit is from an article about operations in a Radio Electronics magazine from around 1968. The transistors are types of the time and the power is not the greatest.
The operational amplifier is old. The circuit is from an 80's documentation but can be designed...
This configuration, explored in other applications of this section and website, was found in a 90s...
The sensors can be screens having porous tissue between them. When the water moistens them, the...