Extra Mouse Button

by Phil Stewart

A while back, while searching for a cheap USB hub, I happened across a sale on an "upgrade package" which included hub, mouse, and mousepad. I had no particular use for another mouse or mousepad, but the package was about as much as the cheapest hub alone, so I went for it. The USB hub is now serving its intended purpose, the mousepad wound up in use after a few got lost in a move, but the mouse has remained an orphan. It's not a terrible mouse, but not an improvement over anything we already had. One night, while watching TV, I found both mouse and screwdriver within arm's reach, and made an interesting discovery.

The mouse is a USB mouse, made by microConnectors, model number OK-520. Immediately above is the mouse before modification. Its biggest flaw was always the fact that it had only a single button. One button may be enough for Steve Jobs, but I've been spoiled by two buttons for too long to go back. Well, when I opened it up, and discovered markings on the circuitboard for three buttons, labeled SWL, SWM, and SWR. Only SWM has anything connected to it, that being the one button. However, it seemed obvious that the mouse was at least intended to have multiple buttons at some point. I'm guessing they stand for Switch Left, Switch Middle, and Switch Right.

I looked at the tracings on the back. The top terminal on SWM ran to the black ground wires on the USB cable, as did the top terminals on SWL and SWR. The button terminal on SWM ran to a pin on the little integrated circuit, while SWL and SWR's lower terminals didn't connect to anything. I noticed two unused pins on the chip next to the one for the button, and I got the idea that these might actually be intended for other buttons.

Of course, I had no driver to support these things, but luckily OS X supports two buttons on it's own, so, feeling daring, I plugged the disassembled mouse into my iBook, and bridge the second pin over to the ground. To my delight, a little contextual menu popped up. I'd found the connection for the second button!

I soldered a wire to SWR (and, I must admit, to SWL ,before I realized what I was doing and that I'd probably want the button on the other side) Soldering on the chip was a little too scary for me, given my limited skills with such fine work, so I simply made a little loop with the end of the wire, and wrapped it around the appropriate pin with the help of some very small needlenose pliers. I attached a little switch I bought at Radio Shack to the leads. I'd wanted a much nicer, larger, flatter switch, but when it came right down to it, I had to use what would fit, and this was all I could find that would worked. Below is a close-up diagram of what I did:

I cut the large single button in half, being sure to leave the entire hinge portion attached to the left hand part, leaving the left side attached as it was before and able to be used normally. Into the right part, I drilled a hole, and put the switch through. It didn't quite line up with the opening in the plastic below it, so I brutally tore at the edge of the white plastic with vise-grips until the button could go through. Then I superglued the piece into place, leveling it slightly with a scrap of plastic to keep it in line with the rest of the button.

The button, while not what I'd intended, works great. My only complaint, really the only thing I'd do differently, is that there's no 'click' to the button, so if you're using it in some way in which there's no visual cue, it's hard to tell if you've pushed it in far enough.

I assume it's possible that with the correct driver (probably a generic driver, like USB Overdrive, would work just fine) one could also use the third button by grounding the third pin from the left on the pin, but, alas, I was unable to test that idea, but I'd be interested if some one tries it. It's also possible it might work as a scroll wheel, but I think if the mouse had been intended to have one, then that would have been the middle switch, rather than the single button, which amounts to a left click.