I'll admit I was a little discouraged with your reply, Mowcius. I was pretty clear about the first project I was considering doing with one or more of them. I've been scouring thrift and pawn shops in my area, but there are no old touchpads available. The PC recycling places near me don't recycle them and generally don't have old laptops. It's become my white whale to find one to play with. I can see a lot of uses for this sort of input device and clearly the arduino platform makes it easy to hook up any old ps/2 device.
And absolute positioning for them, per synaptics (old, 2001) data sheet is easy to achieve. There are even some threads on this forum describing how to do it.
But still, my problem lies in the fact that there is no handy guide to which model numbers are which sizes, and where to get them. They can be found as low as $5 US, and in bulk, but there's no way of knowing what size one is. It's very hard to go "well, I'll get a laptop replacement assembly for XXXX laptop and hope it will work out."
So I've taken to keeping a spreadsheet for whenever someone mentions a synaptics model number when building a project. Hopefully I'll be able to discern a pattern and make a more informed choice before picking one up. But here's what I've found out by doing so:
TM41xx134 Standard TouchPad 47.1 × 32.3
TM41xx156 Mini module 44.0 × 24.5
TM41xx180 Super module 70.2 × 52.4
(discontinued) Flexible pad
TM41xx220 Ultra-thin module 47.1 × 32.3
TW41xx230 Wide pad module 54.8 × 31.7
TM41xx240 Stamp pad module 21.4 × 17.9
TM41xx140 SubMini module 32.8 × 18.2
TBD MultiSwitch module
TM41xx301 Advanced Technology Pad
TM41xx221 Ultra-thin module, connector reversed
That's some of the data from the "holy grail" of using these devices, http://www.synaptics.com/sites/default/files/ACF126.pdf?q=decaf/utilities/ACF126.pdf Those are sizes of the the actual touch surface, in mm. The document even lists the SENSITIVITY of the different models!
But that document was last updated in 2001!
The more modern update of that document, http://www.synaptics.com/sites/default/files/511-000275-01rA.pdf does not contain any model information at all. And it seems the model numbers carry a different format.
Newer ones have model numbers like
And I don't know the specs on them, or what these different model numbers mean. I've got an email into Synaptics and I'll post here with what I find out. If anyone knows of a good place online to get parts cheaply, please let me know.