I was motivated by more than idle curiosity when I took apart my old Logitech M570 wireless trackball. I also wanted to use it to prototype an idea. Years of computer use has taken its toll on my body, one of them being RSI (repetitive stress injury) to my wrists. Clicking a mouse button with my index finger is an action that quickly leads to a tingling sensation and if I continue, pain. This was part of the reason I prefer trackballs that let me click with my thumb, but what I really want to do is transfer that workload to an entirely different part of my body.
Which is where the retired wireless trackball came into the picture. The ergonomics of this design preserved the use of index finger for button clicks, something I explicitly did not want. But it is still a perfectly functional computer pointing device, so I took it apart hoping to find electrical contacts I could utilize for different mouse click options. I was happy to find that the primary (left click) and secondary (right click) buttons were large through-hole Omron switches, with easily solderable pins accessible from the bottom of the circuit board. Probing with my meter found their “Common” pin are both connected in parallel. I see traces going to their center pin, which is Normally Open. The third pin is Normally Closed (with Common) and appears unused in this device.
To experiment with different ways to left- and right-click, I soldered three wires: red wire went to the common pin shared between both switches. Blue wire went to the left-click button’s “Normally Open” pin, and yellow went to the right-click button’s Normally Open pin.
Powering the device back up, I confirmed that connecting blue to red wire would result in a left-click, and connecting yellow wire to red would result in a right-click. I closed the trackball back up, routing these wires through the hole left by removing the physical plastic pieces for left- and right-clicks. These three wires were crimped into a JST-SM wire-to-wire connector (*) so I could experiment with different button implementations.
The first prototype is to mount large durable arcade machine style buttons to the left and right legs of my chair. This picture shows the right side, with a yellow button corresponding to right-click yellow wire. This allows me to perform mouse clicks by using my legs, pressing my calf against the button. I have no idea how well this would work (if at all) so I used cardboard to hold the button in this first draft. And thanks to the fact this trackball is wireless, I could still move the chair around without worry of tangling or damaging a wire.
The first few attempts to use this felt really strange, but that’s fine. Clicking a mouse button is such a habitual task that I expect a period of acclimation even in the best of circumstances. And this doesn’t really get in the way of anything, because I could continue using my desktop trackball. I will leave it installed for a few weeks to see if I’ll adapt to it over time. One thing is sure, though, moving my legs to click these buttons would not put any stress my wrist.