Wednesday, May 23, 2012

Laptop touchpad/mouse pad salvaging

I was recently given a very old, dead laptop. I soon took it apart to see what parts I could salvage, what parts I could reuse in my projects.

Among the numerous parts there was one that I was interested the most: the mouse pad or touchpad. I was wondering how it is interfaced with the motherboard and if there is a way to use it on its own, like an ordinary PS/2 mouse.
This is the salvaged touchpad, back side. The other side is the actual pad that one touches.


After opening the laptop I found that the touchpad was not directly connected to the motherboard but through another flexible board that handled some of the buttons around the touchpad, i.e. left, and right click and some other, custom buttons. I got rid of all the extra buttons and the flexible PCB since I wanted to focus on the touchpad only.
Here I still have the flexible PCB for the buttons - not interesting, just for show.

On the back of the mouse pad I found a small circuit that was built around a Synaptics T1004 0406 chip. For days I was researching this controller, but found very little information on it. The only place where there was a good bit of info on touchpads is http://sparktronics.blogspot.com/2008/05/synaptics-t1004-based-touchpad-to-ps2.html. This page doesn’t have information for my particular controller or touchpad, but it had enough information that got me started. Using the information on this page I started to poke around the PCB with a multimeter and an oscilloscope.

There are a number of test points on the PCB so I started to check them first. I quickly found the power lines and using the oscilloscope I was able to identify the Data and Clock lines:

Test point #
IC pin
Description
20
44
Vcc
15
46
Gnd
10
3
PS/2 clock
11
2
PS/2 data
6
7
Right button (active low)
7
6
Left button (active low)

I salvaged a mouse cable from a dead mouse and soldered the four wires to the test points previously identified.
All four cables soldered in place. some hot glue was used to keep the assebly in place.

The experiment was a success: when I plugged the PS/2 connector into a PC I was able to use the touchpad as expected. The touchpad is ready to start a new life embedded in some custom project!

 

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