Originally when I was working on the Wiimote part of my touch table, I was tired of needing a mouse. I wondered if I could harvest a touch pad from an old laptop to mount on the edge of the table, and as it turns out, yes!
However, I ended up using the laptop and needing the touch pad again, only now I might need it for both projects. So, I wanted it modular and USB. Apparently some old laptops use PS/2 to communicate with the touchpad. I discovered that information here, which is also the source for most of the knowledge needed to do this mod.
According to the Sparktronics blog, my touch pad IS one of the ones that works via PS/2. It is a Synaptics T1004. You can’t see that on my chip in the photo, nor can I see it with my eyes now, but it was visible before I started messing with it.
I was able to follow the wires inside the cables back to the chip as shown on the Sparktronics blog, and they did in fact match up.
I cut the male end off of an old keyboard, pried out the metal connector, and soldered some wires to the BACK side of it. You can see how the end result will plug into a PS/2 port. It is possible my wire colors are not appropriate, so if you are doing this I would not use them as a reference.
I also soldered the appropriate wires to the PS/2 connector on the touchpad – the connector by which it was plugged into my laptop’s motherboard.
There are some other diagrams available on the Sparktronics blog, but ultimately it came down to this:
Now to conver to USB – it is easy to use a USB mouse on a PS/2 port and the adapters are fairly standardized, but to go the other direction and use a PS/2 mouse in a USB port requires hardware translation. I think I have read it is only a matter of the clock having to be translated, but either way it needs to be converted. Some keyboards and mice supposedly already contain this clock conversion hardware and it can be used as necessary, so any cheap adapter will work, but in this case I am certain my device was never intended to work over USB. So, I ordered an adapter that was sure to convert the clock. Still a cheapy from MonoPrice, but it does the job.
Once everything is wired up, the end result looks like this:
At this point I had previously tested the concept and used it for another project, minus the USB conversion though, so I was still curious if that would work. Windows did find the adapter, and following that it found the pad itself.
After the devices were found, everything worked. The only down side is that the Synaptics software that came with the laptop cannot find the device over USB. This means I cannot customize what the buttons do using that software, but that is not a huge problem because AutoHotKey can be used to do that anyway, and in a much more powerful way. Check out the test video: