I had a lot of work this year... Not enough time left for this project.
Now, I'm stuck home for two weeks now, because of the virus. First of all, I really hope that you and your famillies are ok. I hope that the worl will sort this out as soon as possible !
I rediscovered the primal way to hack : I mean without the the help of Amazon or Aliexpress ;-) Funny how you can find things if you really dig in your house. As an example, I found pieces of wood under some furnitures in my living room. They were here for like 5 or 6 years....
I also had arced buttons laying around (the arcade box is built, but I wanted a better quality button set).
Video is better than words :
Hardware : I already had the tft screen working on the celtic version. I added a physical switch (pedal / celtic) and a set of 14 arcade (foot) switch. Everything is wired in pullup mode on the mega 2560 analog inputs (digital are used by the TFT).
A semi-fail : 2560 + TFT is a I2C master for the 5 aduino DUEs slaves (each one sense the string tension variation and produce the midi event). To prevent another wire mess, I planed to add an arduino nano on the pedals, so only I2c wire would be running along the frame (instead 14 + ground). It was late, I was a bit lazy and , sometimes, the simpler is the better (even if it involves another mess of wire on my prototype). The truth is that I think that my I2c configuration is close to the breakdown (Due and 2560 don't work at the same logic level (I realised that monthes after), no pull up resistors)... It works, I don't know how but I feared that if I added one more arduino, it would ruin all.
Software : No major problem here. Just played a little bit with UTFT. I2C is stable so ther is no feedback needed from Due's (i.e. if I switch to Re b on the master, I assume that Due's are always receiving the information). The only problem is that when I reboot the master, notes are not matching with the Due's ones (I only have to switch up or down every notes on the master once, and everything's fine). This is not meant to happen in normal use as master and slaves are switched on and off from the same power supply.
Next step is to improve "pedals". The harp player needs a position feedback (i.e. he needs to know if the pedal is down/middle/up just touching it with feet), and he/she also needs to prepare the action by puting her/his foot on the pedal but without fire it up (i.e. it needs a minimum force to be applied).