Laptop touchpad as a standalone peripheral

[Viktor] is working on salvaging parts from a dead laptop. In his eyes the biggest gem to be had is the touchpad, so he set out to see if he could make the touchpad a standalone device. You might be envisioning the many hells of interfacing this with a microcontroller and writing firmware to measure and translate the input to HID compatible commands. The good news is it’s quite a bit simpler than that, with just one gotcha.

He looked around to see what he could find about the chip that drives the touchpad. He couldn’t locate an exact match, but a datasheet from a similar family of controllers make him think that there should be a PS/2 data and clock output from the chip. After probing the test points on the board he found them, as well as the voltage and ground rails. Above you can see he soldered an old mouse cable to the board and it works when plugged in.

But we did mention the gotcha. There doesn’t seem to be any support for the right and left buttons. Those were housed on a flexible PCB which attached to the white connector seen above. That PCB also connected to the computer so we don’t know if they will work with this hack or not.

47 thoughts on “Laptop touchpad as a standalone peripheral

  1. Old hack, done that 10 years ago. I’ve yet to scrap a computer that uses a USB-based Touchpad – all i have tried so far is PS/2-based. He can use the buttons for sure! – The FFC cable routes the buttons to the touchpad controller and the PS/2 signals from the touchpad to the motherboard….

    1. About 3 years back I gutted an old Mac laptop of some kind and wired up the touchpad to a USB cable and plugged it in to a PC. It was recognised as a USB device, but couldn’t find a driver for it.

      1. I did exactly this four or five years ago with the top shell of a Macbook that I got off eBay for $15. Power and ground test points were easy to find by trace inspection; I then identified the data lines by attaching each test point in turn to D- with the cable plugged into a Windows machine and waiting to hear the ‘failed enumeration’ noise (as pulling D- high indicates a low-speed device is connected). Once I had D- correct D+ was easy to find by the same process. The trackpad had test points for all of these signals so splicing on a USB-A port was easy.

        It enumerated as a composite device and the keyboard worked immediately, though the trackpad was more of a mixed bag since its button was non-functional and the Boot Camp drivers of the time didn’t support tap-click. From a cursory Google search it appears Boot Camp 3.0 (came with Snow Leopard) does support this now so I may dig it back out of the scrapheap :-)

  2. once again, hackaday ignores one of my video from waaaaaaaay back when I originally submitted it.

    follow the links in the description of the video to see the revisions.

    1. Ever consider it might be because of the annotations obstructing the view, shaky handheld low quality recording, excessive noise, bad muffled music, commercials, and complete lack of a description of what you’re really doing or how you did it within the video?

  3. That’s a nice way to make use of a dead laptop, any plans for the rest of the parts?

    Though I wonder, since the buttons don’t (currently) work, does tapping the touchpad work?

    1. Just to add this 2 years later…

      Mice in Windows AFAIK work in parallel. So connect up another mouse to a USB hub and use it’s buttons. You could cannibalise some of the very cheap mechanical mice they still make, for the buttons. Case it all accordingly.

  4. I have one laying around in my scrap projects bin. Works flawlessly on a PS/2 interface and was a matter of about an hour, with most of it hunting down a datasheet and verifying the pinout.
    And the buttons even work.

    It’s certainly nice for him he got that working and I appreciate it if people salvage parts instead of just throwing them away. This is also a great beginner’s project as it is overseeable and provides a quick return in success.
    But on the hackaday homepage it really stands out as trivial among most anything else.

    Maybe you could make a category with hacks that would be great for beginners. Ones that don’t require too much knowledge, time, equipment and can be had cheaply.

  5. Does it interpret taps and 2-finger taps as clicks like most any modern pad? Hopefully that chip will interpret that and send it down PS/2!

    1. I found with mine, that if I connected it directly to a real PS/2 port, then I could use multitouch capability (two finger scroll, three finger right click), but if I went through a USB converter I couldn’t. I assume that the multi-touch signals were unknown to the USB converter, and so it just ignored them.

      1. USB converters converts the PS/2 protocol to USB HID. As there’s no way to directly communicate with the PS/2 touchpad it will stay in mouse emulation mode which (on the devices I’ve tested) doesn’t support any multitouch gestures. Single taps and side scrolling tend to work at least on more modern pads.

  6. I had a touchpad that I had saved to be able to do a hack like this at some point in time, but now that I go looking for it I can’t seem to find it. I must have tossed it out :(

      1. LOL. I just found the touchpad. Too bad I can’t find a datasheet for this 1CA022A IC that is on it, so it kinda leaves me stuck :(

  7. This is one vary old hack, made mine 8 years ago from a synaptics touchpad out of a dell and i would be using it now if any of my computers still had a PS/2 port.

    Don’t worry if you cant find any documentation for a particular model touchpad, PS/2 is only 4 wires so its easy enough to guess the pinout through trial and error.

  8. im suprised.

    everyone have the same exact chip in all different laptops ???

    or do they *ALL* just use regular ps/2 protocol inside the laptop ???

    what im asking is does the chip have dualprotocol/dualport ?

    1. Makes sense doesn’t it? Basically all chipsets will have a PS/2 controller, no point in reinventing the wheel! Synaptics make the vast majority of touchpads, and all are very similar.

      I would’ve thought newer ones might connect via USB (internally), but like mentioned above, I’ve not stripped down a new enough machine

  9. I’ve done this myself at least 2 times previously;P… the really nice thing about the touch pads is that ps/2 is fairly solid(on older boards anyway) and so even without datasheets, long as you find the power traces/contacts the rest can usually be guessed without frying anything…tips: usually the lead with the thickest trace on pcb going to the zif header is positive and the biggest piece solid copper on pcb is grounding / negative…. have dmm near by and guess at your own risk; use an older box you can afford to throw out:P…

      1. You know the biggest problem I’ve had with a touchpad is getting it to stay put on my desk – I can imagine it being soooo hard to get a nipple to be fixed enough to be useful!

        Incidentally, anyone got any good ideas for how to keep a very lightweight touchpad from moving?

      2. A squishy and slightly tacky pad of silicone rubber stuck on the underside should work. The only problem with that sort of thing is that they will get lots of dust stuck to them if you are always shifting its position.

      3. Yeah… I’ve being trying stuff like that. Unfortunately the state my bench is in, it gets dirty and slippy pretty quickly

        Maybe I just have to stop living like a pig

  10. It makes sense that the more modern touch pad controllers would be compatible with both USB and PS2, there are the same number of pins and they both run off 5V. There are already tons of mice and keyboards that are dual protocol, they simply need a pin adapter to work with either.

    I have been thinking of doing this with a trackpoint, i just need to make a wireless PS2 bridge first. My plans are to make something that looks like a joystick handle with the trackpoint in the top and 2-3 buttons on the side.

  11. Someone needs to make a USB to PS2 converter, maybe use one of the low end micros such as the 16F628?
    This has been done, its not like it needs USB V2.0 for such a low powered device.

  12. @ deadlyfoez -> I was disassembling Yesterday my Notebook HP Pavilion zv5000 (PP2200). I found a Touchpad with an ALPS Controller 1ca022a on the PCB.
    With try and a little error i found the Pinout for this IC. You can find the pinout description on this url:

    I’ve soldered an old PS2 Mouse Wire on this IC and now i have an Stand alone Touchpad.

      1. Sorry, but you’re right. It’s Hosted by a free Web Space with a quota of 1 GB. If the website unreachable the traffic volume is consumed.At the next month it reachable again.

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