I've been working on a few other Arduino/Pi/MIDI projects recently, such as my Guitar effects Pedal and a Drum Module, and it's given me a real spark to get all my music based projects finished.
This one was really taking shape for the 2018 contest until changing jobs threw me off track a bit. I've now started to rethink this one and definitely reckon I can complete it after my other two projects are wrapped up.
The Slide mechanism was always something I never figured out fully, but I think I have a plan for it. I want to build the frame out of aluminium extrusion (20x20 perhaps). Rather than having an extending slide I'll just have a handle on runners inside the frame, and use am encoder to track position. I'll have an endswitch at the fully open (7th position) and fully closed (1st position) for calibration, and on powering on require the user to return the slide to the home position.
I've done a fair bit of work using python on a Pi to simulate a midi device, so ideally I'd like to follow that pattern and connect all switches direct to the gpio of the Pi. For the analog stuff I have an analog Pi HAT which i could use to read the air pressure sensor and any pots that end up being used.