For a variety of reasons I decided to create my own dedicated MIDI controller.
I was previously using an expensive Softstep2 5x2, and a cheap Akai MPD218 4x4 drum pad, on the floor to control my iPad rig.
Additionally I had an expensive AudioFront 3 channel "expression to USB midi" convertor dohicky. I use four expressiona pedals and I plugged one of them into the Softstep, 3 into the AudioFront, and then had the 3 USB outputs go to a USB router which goes to the iPad.
A while ago I learned that the AudioFront is actually, more or less, just a teensy, and I've learned a lot since I bought that back in 2018.
So I decided to replace all three of those devices with one integrated MIDI controller. It sits on the floor and the buttons have to be big enough to hit with my toes.
I decided to make it "tiered" as eperience has shown me that it is hard to "reach over" buttons on the floor (on the drum pad) without accidentally hitting them. Also neither the Softstep or the Akai had RGB addressable leds, and that seems really useful.
I also decided to have a small display, so I threw in the 3.5" touch screen. I added the rotary controllers because it seemed practical and I have them, but I've never really used them, although I have verified that the work and there is framework code for them.
Perhaps what was most revelatory about this project was discovering, and making use of the USB Host port included on the Teensy 3.6.
That got me back on the track of reverse engineering the Fishman FTP pickup, and I finally made some substantial progress at that, which is encapsulated in this project.
Finally, I need a non-USB controller for another project (the "Bare Metal rPi Looper" as yet to be revealed) and so I also added a 1/8" audio jack over which serial data can be sent and received. It can be used as a debugging port, or, as envisioned, as a "midi over serial" at 115kbaud to the other project.
For the time being, I'm gonna ask you to have a look at the github project at https://github.com/phorton1/Arduino-teensyExpression and hopefully I will update this page with some more "hackery" details at some point.