Synaptics trackpads/touchpads- where to get them?

I'm seeing a lot of threads describing using old laptop touchpads as interface devices. I'm interested in seeing if I can hook 4 of them up to an Arduino Mega. I want to make a project similar to the Touchpad midi on the forums here.

They look like a great input solution. Simple to wire up ps/2 interface, absolute positioning and z-index (pressure) sensing -- and according to the documentation I'm seeing from the pdf on Synaptics' site it's possible for them to have up to 11 buttons.

I'm seeing that replacement for laptop boards go for very cheap (as low as $5us) but I haven't found a site that really spells out the specs of each. Which is what I'm looking for here.

Does anyone know of a good source for these things? Any site that lists the pros and cons or features of these PS/2 Synaptics touchpads?

I'd welcome any experience or advice on using these. I wouldn't mind using a laptop replacement assembly (including buttons) with them. I just have no source to get them from that really shows me what I'm getting.

Thanks!

Well what do you want to do with them?

The arduino library for PS2 is not kitted out to do much more than motion and clicks.

Pretty much any touchpad will do that.

Ebay might be a good source. I have 3 (maybe 4 if I can find my other one) which came out of old laptops. All the same... Trying to think of a use for them ;)

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

TM41PDA306 TM42PUZ307 TM41PNG301

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.

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.

Yeah now I think of it, I have also seen that mentioned somewhere.

Yeah the info on them is always the issue. It took me a long time to find the pinout of mine. I ended up finding a picture of a very similar model which someone else had worked out the pinout on and then working mine out from there.

Mowcius