I am glad there is interest in my idea of building a trackball into the DodoHand, I really think this will be a good option. I am more than happy to post my progress to this thread as I see it as a prototype option for the DodoHand rather than an upgrade to the obsolete DataHand. I will also release all details and code publicly in case anyone else is interested in cannibalizing a DH200 in the same way but I must stress that it is far from trivial and would be easier to start from the DodoHand components when they are complete.
I have been using the right-hand unit as a trackball for a week now and find it surprisingly comfortable and convenient. In mouse-mode I have mapped the thumb down key as the left mouse button, the second level down switch and left double-click, the thumb pad key as the middle mouse button and the thumb nail key as the right mouse button. This arrangement feels similar to Logitech TrackMan Marble FX which I used from the late 90s until I fitted a Kensington Slimblade ball unit into the middle of my Kinesis Advantage keyboard. While this is a good arrangement and saves on arm movement the original Logitech TrackMan is the best trackball I have used and I am hoping the trackball fitted into the DodoHand will be even better.
One minor issue I have with the current hardware I am using is that the Kicklighter breakout board for the ADNS9800 laser sensor:https://www.kickstarter.com/projects/1034145369/high-speed-laser-optical-sensorhttps://www.tindie.com/products/jkicklighter/adns-9800-optical-laser-sensor/
is quite large and needs to be mounted opposite the point at which the fingers move the ball which is hard to achieve as it hits the base of the case. However John Kicklighter has a smaller version of the breakout board which if he releases would solve this problem completely.