I wanted a trackball on my arcade cabinet, mostly so I could play missile command but I know my mom likes centipede and I’ve always wanted to try marble madness. Trackballs are common, lots of people put them on arcade machines so it should be cheap and easy to interface with. Wrong. Or, somewhat wrong. This all depends on your level of cheap. For me I thought the big trackballs were too expensive, and the ones that connect to a computer were even more. If you think differently just remember this was a few years ago. If you still think differently pretend it was a long long time ago when my point would be valid even to you.
I came across a trackball on ebay available for purchase. It was 2.25″ across (boo), about $25 (yay!) and ps/2 (…good enough!). It had three sets of wires for left right and middle click as well as a ps/2 cable coming out of it. I have put a picture of it above. If you’ll notice there’s no convenient way to flush-mount this in a wood and acrylic control panel. My solution involves a 2×4, some brackets, and shims to bring it to the right height. As imprecise as this method is, I prefer it to a ‘trackball mounting plate’. Those are ugly. They also make highball versions that can be mounted like I want to, but they are more expensive.
Over time I came to find that the trackball didn’t work anymore. I attribute it to me plugging the non-polarized harness in backward and frying the chip on board. It turns out that all that’s needed these days to make a ps/2 mouse is one monolithic chip, some ir beam break sensors and some buttons. I reverse engineered it and found that the circuit was as simple as one of these ps/2 mice I got at black friday a long long time ago. They were $0.50 at abc warehouse so I bought 20 or some stupid number like that, I figured with a fleet of identical ones I could use them in projects… just like this!
Now, I’ve tried before to mod trackballs with a different controller but I wasn’t able to make the new IC like the old sensors so I gave up and stuck an optical mouse sensor under it (and flipped the axes). That led to some skipping because of the mechanical advantage I had over the mouse now that it was a trackball, so I actually prefer this method of modifying it.
I recognize that it’s stupid to hold out for a ps/2 trackball and then replace the controller anyway, but that’s all I had at the time and since it worked I will accept no criticism on it. I will concede the point that the original PCB is un-needed and I probably could have removed the chip and dead-bugged it, but this was a bit easier and I’m more confident in it.
There you go, no code, no real difficult parts. If you have an old ball mouse there’s a good chance you can use it as a trackball controller.