[floren]

Well done, shame about the ergo problems! Hopefully with some iteration, it could be more comfortable. My recommendation: don't be afraid to take up more desk space :) I'd try something which put the button caps in an upward-facing orientation instead of facing out.

When I built my mouse (https://jfloren.net/bellwether.html) I found that in the past there were these neat modules which packaged a sensor and a microcontroller on 1 chip, and you basically just had to wire it up to USB -- but those don't seem to exist any more! So I picked essentially the same Pixart sensor as you, used the same leaked datasheets, and built my own. I do wonder why the all-in-one devices disappeared, though.

[fragmede]

Is a micro with a PLC (or just a fast enough adc+CPU these days) connected to a photodiode fast enough to do it in software?

Actually it seems modern devices use a CCD and then process the image.

[convolvatron]

i think you'd have a hard time determining the direction from just one sample

[fragmede]

for the photodiode you'd use to perpendicular sensors

[xythobuz]

Awesome project!

Yes, I've also thought about mounting the switches vertically. And more surface should also provide more grip on the table.