We found this simple toy organ circuit in the February 1968 issue of Radio Electronics magazine. The transistors were common at the time and the transformer was from a transistor radio output.
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...