A friend gave me a broken HP Pavilion laptop. With just a little work, you can remove the trackpad and connect to a PS/2 or 9-pin Serial port . Connect to your PC and use as a simple mouse, or even wire to an Arduino for a unique interface for your project. You can make this project entirely from recycled parts you may just have lying around.
What you need:
-trackpad (I used a Synaptics TM41PUZ307)
-male PS/2 connector with cable (or a 9-pin serial)
Step 1: Remove Trackpad From Laptop
Unscrew all the parts to the trackpad. Gently pry up any plastic. I used a hair dryer to help loosen the glue that held the pad to the laptop palm rest.
Step 2: Salvage a PS/2 Cable
I removed the PS/2 cable from an old broken keyboard. Alternatively, you can also wire to a 9-pin Serial cable.
Step 3: Cofirm Pinout of PS/2 Cable
Use a multimeter to confirm what the pinout of the PS/2 cable is.
Your wire colors may differ, mine where as follows:
pin1 = DATA = Red
pin3 = GND = Grey
pin4 = +5V = Brown
pin5 = CLK = Yellow
Or, you can wire to a 9-pin Serial port old school mouse style. This is also nice idea to use on a desktop as a secondary mouse.
pin4 = DATA
pin5 = GND
pin7 = CLK
pin8 = +5V
*You could even wire to an AT keyboard.
Step 4: Find Pinout for Trackpad.
Use the Internet and search for the pinout of your pad. Or you could use your multimeter again.
Synaptics has a great resource for helping you determine the pinouts of many of their models HERE.
My Synaptics TM41PUZ307 wasn't on the list, but an internet search turned up this:
pin5/6 = GND
pin7/8 = CLK
pin9/10 = DATA
pin11/12 = +5V
Step 5: Solder
I used a razor blade to carefully cut the ribbon cable to connect the 4 wires from the PS/2 cable. A quick dab of some cooling solder (too hot and you'll destroy the cable) and some electrical tape to reinforce.
Step 6: Mount
Ok, you'll want to test first. Just plug it in quickly and the standard windows mouse driver should work just fine. Without installing any drivers, I was able to navigate the mouse, left click, and use the mouse scroll wheel. I mounted it on my keyboard for now. But I plan on eventually using it in an Arduino project. Details on interfacing a trackpad to an Arduino can be found HERE
If you wish to use with USB, you must purchase a "PS/2 to USB Keyboard and Mouse Converter."