Midi instrument with velocity - beginner looking for advices

[piwicode]

Hi there,

I’m working on midi keyboard wit the shape of a bandoneon 4.
All the design are free to use here https://github.com/piwicode/bandoneon

It works well on a breadboard, and I would like to share with you the current state of the design. This is my first PCB board, and I’m looking for feedback on schematics and mostly on the PCB. More eyes see more. If you want to share something, try to provide explanation, a link some documentation or calculation so that I can ramp up.

Here is a viewer for the PCB: https://kicanvas.org/?github=https%3A%2F%2Fgithub.com%2Fpiwicode%2Fbandoneon%2Ftree%2Fmain%2Fboards%2Fbandoneon

Here we go:

The instrument has 71 keys
I want to measure velocity and avoid manufacturing pushbuttons, hence I use magnetic keyboard push buttons 2
- The position is measured by 71 hall effect sensor SS39ET
- The analog signal is converted by 9 MCP 3008
- I use an Adafruit Feather M4 to bitbang 9 SPI buses in parallel
- The bus frequency is 2 Mhz the voltage is 3.3V.
- The PCB uses 2 layers. Maybe that is a mistake, but I would like to use 2 layers if this can works

I put ground fill on two faces: the one on the back is for return current, the one on the front is to avoid wrapping.

I have no idea of what I’m doing with regard to return current, crosstalk and track size. Please let me know if you know more.

Thank you to everyone who take a look.