Dana’s excellent hamemade Ondes Martenot ring controller uses a multiturn potentiometer + pulleys making possible quite a lovely version of “When You Wish Upon a Star”. The note-marker indentations on the fingerboard are a nice touch likely improving note accuracy by far.

Here is part two of my progress, building an Ondes Martenot-style controller for my modular synthesizer.
Feel free to use my ideas, but no, I will not be building one for you! ;)
I built this around my beloved DX-7, but it only uses that keyboard for visual reference, while playing the ring controller. You could use ANY keyboard for your own reference.

[via Synthtopia]