This organ, played by a probe was found in no old documentation, but it can be easily implemented these days. The integrated circuits are 555. The trimpot allows individual tuning of the keys.
In this circuit of a 1991 publication, we can use the 2N2646 unijunction transistor and the sensor...
Measuring capacitances and resistance this simple instrument was found in Radio Electronics...
Found in a 90’s 303 Circuits, this circuit uses components that are still common and has a common...