Found an article within a PDF of the Status Newsletter on archive.org. It explained how to rewire a CX-22 Trackball for use as an ST-mouse for an A8-Diamond GOS based system or the ST. I have been using a mouse from Best Electronics (model CBM1) for quite some time and should have a backup. I made the modifications to my CX-22 as explained in the article and it worked the first time. Diamond has been configured to use STMOUSE2.DRV for the mouse driver and worked just as well with the modified trackball.
Arnold, Blake, "Trackball to Mouse", Status Newsletter v7i4, 1988, Page 13-14.
The article is well written and contains all the information you'll need. I took pictures as I made the modifications in case I wanted to revert back to the trackball and to explain how I made them.
The next six photos are of the track ball before modifications.
Remove 4 screws.
Notice the posts to the north and south of ball. The top has pins that are inserted in these and they are friction fit. Care should be taken so that these pins are not broken while pulling the top off.
Wiring on Left side of unit
Wiring Right side trigger.
Separated parts. The wiring could be unplugged without damage and was put aside for safe keeping.
Making the Mods.
Since the case was apart, it was placed in the dishwasher for cleaning. The chips are all socketed , so they were removed and the pins were cleaned, then reinserted. The LM339 was set aside until after the soldering on the board was completed.
When you look at the photos don't use the wire colors for reference. I happen to have a couple of old cords out of a Sega(?) or was it a Genesis( ?) joystick. (been a long time). I know the cords had 9 pin plugs and 9 wires. Both Blake and I recommend mapping the wire colors to the pins before you start soldering.
I made the connections on the bottom of the board. I also reminded myself several times were the #1 pin of the chip was as the board was flipped over. This allowed the wires to be run safely under the board.
The board was put back into place and the LM 339 chip reinserted.
Holes were drilled through the button boards for the wires. Wires were then soldered directly to the boards. I've never had much luck with those push on connector thingies.
The 5volt and ground wires were connected using the female ends of a couple of jumper wires. This way I didn't have to solder the wires directly to the power pins. Its an option I had sitting in my Arduino kit.
The ball is in place and the wiring doesn't look like it will interfere with the rotational sensors. Time to put the top back and tighten the last 4 screws.
The 130XE was booted up with Diamond and the Best Electronic's ST Mouse as usual. The mouse was unplugged and the trackball plugged in. The pointer moved as would be expected and the system responded to the left button presses, although sometimes rather sluggish. I can't remember ever having to use the right mouse button for Diamond GOS so it wasn't tested. (I'm not getting out the ST, so am assuming the right button will work.)
While I had the trackball apart I considered replacing the spring caps with micro switches. I didn't want to take the time to figure out if there was enough room for a micro switch and put it off for another time. In use not every button click was registered and if I were going to make the trackball my mouse of choice this would have to be fixed.