I’ve been slowly working on this MIDI concertina. The last burst of energy I put into this resulted in a 3D printed prototype that could be used to see if it felt right:
It felt pretty good, so the next step was getting a Printed Circuit Board (PCB).
Starting the PCB
I hate doing PCB design: I don’t understand KiCAD very well; and iterations are expensive and slow, requiring some factory in China to make 10 of your board and mail them to you. But I’d waited around long enough, and it was time for a version 1, so I got to designing it.
These switches are a tight fit, and are going to be closer together than is usual for a keyboard. I found a reversible hot swap PCB footprint, which I’m hoping will save me from needing to buy twice as many wrong-but-i-don’t-know-how-yet PCBs.
The program needs to know if you are pushing the sides together or pulling them apart, like an accordion, if you know how those work. For this I’ve decided I’m going to make 3D printable handrest models that mount with M3 screws. The screws will make contact with a big copper pool on each side. When the screws on one side touch the big copper pool on the other side, that will make an electrical connection. So the entire instrument is going to be a great big switch that I’ll hold open with some springs or styrofoam packing peanuts or whatever else gives the right feel and isn’t conductive. It will only detect push, and if you’re not pushing, that will count as pull. We’ll see if this is good enough for the player.
I’ve added a second thumb button to basically mean “Fn”, and an OLED display so the firmware can communicate what mode you’re in (like, change volume, remap keys, etc)
Things I still have to do:
- Add the MIDI chip (I’m going to mount a whole board to make my life easier)
- Put diodes all over the place so the grid can handle multi-press
- Figure out how I’m going to wire the two halves together
- Model the wrist rests and tiny thumb rests
- Figure out how to mount straps: probably I’ll just screw them into the wrist rests
- Connect everything with traces
- Add screw holes for the wrist and thumb rests
- …