This unijunction transistor circuit was found in Radio Electronics magazine from July 1968. The circuit operates up to approximately 100 kHz depending on C1.
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...