Thursday, 18 April 2013

Hacks: Reuse a Laptop trackpad

A few months ago I scrapped a Toshiba's Satellite P25-S507. It was actually a rather nice laptop which had died prematurely. 
With a 17" screen size and an aluminium deck it was aimed more at the desktop replacement market. All I saved was the Aluminium deck which included the Trackpad and the LCD screen which, I will save for another project.

It occurred to me that the track pad could be put to some use!
Enter the CHOP SHOP !

Most older laptop track pads use the legacy PS2 protocol to transmit the data, this particular laptop was of 2004 vintage.

I must admit, in this day and age, PS2 devices are not particularly useful, but I decided to continue as such a device is easily interfaced for use with micro controllers such as the Arduino ETC and often a static track pad is better than a mouse which would take up extra space in a project.

After alot of searching on Google, no info or a data sheet could be found for the 1CA017A Chip. I do not think the part was Synapse, as they usually have custom branding on the chip. After 30 minutes I decided to wing it and look at the PCB traces.
As usual the Ground and Power tracks were easily identified with a multimeter. The two buttons were wired through separate tracks, on the flat flex connector, so they were easily identified. When it came to the PS2 Data and Clock signals, I was left with a 50% chance of getting it correct. Not having access to an oscilloscope, I decided to pull out the Arduino and load the PS2 Arduino library and examples. This proved a safe way to debug the remaining traces!

Being aluminium and having a non ferrous blade in my table saw, I proceeded to cut out the track pad.

I then found a suitable PS2 lead from my parts bin.

A word of warning here... always double check the pin outs against the wire colours ! It would seem in the manufacture of cables, the pin out versus the colour of wire for each connection can be quite random. The lead I chose for instance, you would expect Red to be +V and GND to be black, however, in this case GND was actually RED !!! and Black DATA. So do not assume anything!!

I managed to find some aluminium L Section in the workshop, after a little trimming, it fit the backside rather well.

 The Gallery :)