Here is a little demo of an instrument which I have just finished. I have spent quite some time getting this thing to work.
The magnetic cello has a similar size, shape, and playing style of an acoustic cello. However, instead of a horsehair bow, the player uses a magnetic rod (the "bow") to induce a voltage in a coil (the "bridge"). This voltage is used to control the volume of the signal. The pitch of the instrument is controlled by resistive ribbons (the "strings") which control a second voltage. Note that this creation does not use a microcontroller or digital circuity--just capacitors, resistors, and the occasional IC, like in a simple radio.
Once I start college (I am studying electrical engineering) I will be able to improve the tone, playability, ect. of this instrument. Sub to get the updates! Thanks for reading all of this.