FYI - if you make another iteration (or build it into your keyboard), strongly recommend moving the sensor away from directly below the ball. For reasonable ergonomics - you want the top of the ball as close to the desk surface as possible. The 5 ~ 10 mm you need to fit the sensor package makes a big difference. When prototyping the Expert Mouse, we found that offset angles as high as 20 degrees weren't really noticeable, and that allowed the ball to sit just barely clearing the bottom plastic case. (That and use the smaller 51 mm billiard ball instead of the American 2.25" ball)
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.<p>When I built my mouse (<a href="https://jfloren.net/bellwether.html" rel="nofollow">https://jfloren.net/bellwether.html</a>) I found that in the <i>past</i> 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 <i>do</i> wonder why the all-in-one devices disappeared, though.
Overall, I'm impressed. Very much.<p>Now, I'd love to see a picture of how a hand is supposed to sit above or around this trackball because I can't picture how fingers can comfortably reach the 4 buttons just by looking at their location on the device.<p>Which leads me to the personal opinion: I think I prefer the design of the testbed over the final iteration. Buttons are missing, I know, but... Here I stand nonetheless.
I would like to make custom trackballs, and pool balls are a great idea. I would want a scroll ring like my Kensington Expert mice (<a href="https://duckduckgo.com/?q=kensington+expert+mouse&t=fpas&iax=images&ia=images" rel="nofollow">https://duckduckgo.com/?q=kensington+expert+mouse&t=fpas&iax...</a>). Any idea how to make such a thing?
Server is currently hugged to death and timing out for me.<p>In the meantime, enjoy the sweet nectar of an archive.org snapshot link (collected yesterday):<p><a href="https://web.archive.org/web/20230217104641/https://www.xythobuz.de/trackball_v1.html" rel="nofollow">https://web.archive.org/web/20230217104641/https://www.xytho...</a>