A monthago I posted an instructable over recycling a Laptop webcam (https://www.instructables.com/id/Laptoprecycling-Webcam/), three weeks ago I posted a second instructable over reusing the Bluetooth module of the Laptop (https://www.instructables.com/id/Laptoprecycling-Bluetooth/)now I’m back with the third instructable over recycling the parts of a broken laptop. This time I choose the Touchpad.
A Synaptics Touchpad or TrackPoint
A PS2 plug with cable from mouse or keyboard or a RS232 plug
Optional: PS2/USB Converter
Optional: Two or more buttons if they are not on the PCB.
Optional: A mouse pad with a plastic surface (mine was a cheap advisement present)
Optional: Something to large up the button heads like ICs
Optional: a wooden plate
An exactor knife
Some rubbing alcohol
Optional: a hairdryer
Optional: A drill
Optional: a pen
Step 1: Get a Touchpad
The first step if you are working with CMOS is to ground yourself, specifically if you have a carpet floor like I do. I use an antistatic wristband, but if you haven’t one you can also touch a radiator or a grounded case before you start working. OTHERVISE YOU MAY DEMAGE SOMETHING!!! In my case the touchpad was integrated into the case. It was glued to its back and after heading it with the hairdryer and a bit of bending it around it came of easily. On the PCB there was some glue who can be cleaned away with some rubbing alcohol.
Step 2: Identify Your Touchpad
Synaptics Touchpads do always have their model name at the same schema as it is shown in picture 2.
Product class: Type of sensor. TM for Capacitive touchpads, TS for TrackPoint’s
ASIC type: Shortcut for the processor type
Host protocol: Type of Connection Interface. Now this is very important! There should be written a P, because that means PS/2. This solution only works with PS/2 Touchpad! Other Letters can be B for a PS/2-Serial combination, I’m not Sure if this works too, but I think it should. S means Serial only, You could try to Use T11 like TX and T10 like RX, but I’m not guaranteeing that it will work. A means ADB, what is a transmission protocol invented by apple for their keyboards and mice. If you like to use that you need an apple pc with a ADB interface or you can try This: https://trmm.net/ADB_to_USB or this: https://geekhack.org/index.php?topic=14290.msg277407 T10 would be the ADB Signal, and T6 the Button. The Last possible letter is a T. T means TTL. To use it connect it like a Serial only touchpad, but with a Serial-TTL or TTL-USB Converter IC like the good old MAX232 between Touchpad and PC.
Orientation: Says which side X+, X-, Y+ and Y- is. This can be U for Up, D for Down and P for Portrait.
Color code: Color of the Touchpad PCB.
Auxiliary Feature: Letter for Extra Features like More Buttons, Customized firmware…
Board type: Size and Resolution of the Touchpad. The possible numbers are listed in picture 3
Revision: Optional for Version
Step 3: Test the Touchpad
The touchpad was connected with a 12 pin ribbon cable, but not every touchpad has the same pin out, so I searched for an alternative way to connect the touchpad, and found it: on the back of the PCB there are some solder pads, who are named with a T and then a number. After a little bit of reverse engineering I had the pin out: T22 is 5V (CTS on RS232), T23 is GND (GND on RS232), T10 is Clock (RTS on RS232) and T11 is Data (DTR on RS232). Don’t look at the colors of the wires, they are not normed and the position of the solderpads can be also different on each model. All the other pins aren’t used yet. Now it’s time for the first test, therefore I used a second plug without isolation to see the pin out and soldered it in the correct way to the solder pads on the touchpad. I plugged it over a PS2/USB converter to the pc and checked the function.
Step 4: Buttons
On my notebook the buttons were on the Motherboard and not on the touchpad, so I had to add external buttons. After finding the correct pins by following the conductor patch, I added two buttons between T6 and ground and for the left button T7 and ground for the right button (Sometimes the pin T2 and T6 are flipped around). If you need the “mouse wheel” too you can see the pin out on picture 1, but notice that may not every button works on each touchpad. Reconnect it to your pc and test the buttons.
Step 5: New Wire
My plan is to put the touchpad into a mouse pad, therefore I drill a hole into my table to fit the cable trough. I placed the mouse pad over the hole and marked the hole to the back of the mouse pad. After fitting the new wire thought the hole and verifying the pinout of that wire with my multimeter I soldered it to the touchpad. Now the new buttons: I desoldered the original SMD pushbuttons from the mainboard and ad some wire. Because they only have a small head I decided to make them larger, otherwise you always have to search for the buttons. Therefore I used two ram ICs from a broken graphic card. Add a very small drop of superglue to the button head and stick the IC over it.
Step 6: Housing
Now we are going to modify the mouse pad to fit the touchpad in. Lay the touchpad and the buttons to about the middle on the back of the mouse pad, Double-check that the touchpad is not flipped around and mark the position with a pen, you can also mark the position of the wire. Now start by cutting out the marked rubber and look if under there is a plastic foil or paper. If there is paper you can’t use superglue, because it goes inside the paper and makes it transparent. In my case fortunately there was a plastic surface. Lay the touchpad inside its hole and check if everything fit, otherwise large the cut.
Step 7: Installation
After cleaning the touchpad and the hole with some rubbing alcohol apply some superglue to the touchpad and punch it inside the hole. Don’t safe at the superglue, otherwise the touchpad may don’t work perfectly. If your fingers look like mine in picture 3 and 4 you took enough superglue :-). Repeat it with the buttons (and the wire). Now solder the wires of the buttons to the solder pads if you removed them. It’s nearly finished, Test it, and you can glue it to your table or a wooden plate.
Step 8: Software and Other Variants
The very last step is to get the driver software, you can download it from the manufacture’s website of your laptop or directly from Synaptics (http:www.synaptics.com/en/drivers.php). The driver normally isn’t need, but it gives you a few extra setting possibilities like scrolling and zooming (if it is supported by your touchpad). If you haven’t got a touchpad you can also use a TrackPoint. It has the same pin out like the touchpad. You can also add it to an Arduino or a Raspberry Pi. There’s only one more thing I have to say: it is not very precise, for designing a PCB I prefer to use a normal mouse. But for easy movements, like opening files an surfing it is a great solution, specially if you only have a little space around.
I also added a short video, where you can see that it actually works!
Thanks for reading my third Laptop recycling project, more of it will may come soon!