A Bluetooth trackpad from a resistive touchscreen

touch

If you’ve checked out your favorite online retailer of absurdly inexpensive Chinese electronics, you’ll find a whole bunch of replacement parts. Phone parts are especially common, with high-resolution LCDs available for just a few dollars. There are also a few touchscreen kits – resistive touchscreen digitizers that can easily be read with a microcontroller. [Vinod] got his hands on one of these touchscreen digitizers, and with the help of an 8-pin micocontroller turned it into a Bluetooth trackpad.

The clear plastic touchpad is a relatively simple device. By reading a pair of analog values, it’s easy to find the coordinates of a finger or stylus on the touchpad. [Vinod] programmed an ATtiny13 to read these values and turn them in to x y coordinates, but he needed something useful to do with this data.

By connecting a small bluetooth module to his microcontroller, [Vinod] could send these coordinates to his computer. The result is a homebrew touchpad, able to move a cursor around, left and right click, and emulate a scroll wheel.

Comments

  1. Galane says:

    Nifty. Next step, put a color LCD under it with a button to turn on a keyboard mode.

  2. I love it, I have all the parts even the Bluetooth Module. I could see a homebrew light switch or a tiny home automaton control platform. All and all, nice build.

  3. Terrapisces says:

    Any ideas on the part number for the digitizer?

  4. Whats the link for the “absurdly inexpensive Chinese electronics” website?

  5. xorpunk says:

    something I learned from doing thing a long time ago: division on x,y for scaling resolution with driver or service, multiplication on x,y for using homebrew touchpads with pressure sensors or electrodes…

    • Ren says:

      Okay, let me see if I’m following you on this, [I'll] need to divide the x.y coordinates for better resolution or multiply them for what? Please explain in a less cryptic manner.
      Thanks

  6. indiantinker says:

    Great Build!

  7. HLL says:

    I’m trying to convert the CSR BC4 Chip to do just this, but using BT-HID Profile, if anyone has any references, post it here, thanks.

  8. Robwasab says:

    really cool, liked the bit banged uart code, will have to implement that. Is it easier on the 13 bc of its 9.6 MHz oscillator?

  9. Would there be a way to use a cheap BT headset to do this, as these sometimes have an undocumented serial port for “diagnostics” that even shows up in Windows..

  10. James says:

    If anybody is looking for these resistive digitizers to have a play with, on ebay, searching for “resistive touch screen digitizer 4 wire” seems to turn up a few around the $10 US mark.

    And this is the best simplified Chinese search I could come up with thanks to google (hope this comes through in the HAD comments…)
    触摸屏数字化仪,电阻
    there is a seller on taobao selling laptop touch-pad sized ones for half a yuan (that’s 8 US cents each), not sure if there is a minimum quantity (it’s often hard to work out if there is a minimum in an taobao advert) – of course, add agent fee, domestic china, and international shipping, still if a hackerspace wanted to get a box full to play with it could be worth it. I used taobaofocus as an agent for a recent box if stuff from a seller there and have no complaints, but make sure you record the price you expect to pay per item in the order, the taobaofocus order process rounds up to the nearest yuan unless you specifically enter in the correct amount.

  11. Heska says:

    How this work in the pc side? Is it need especial software?

  12. really interested in this project, could you make it so a 4 wire resistive usb controlled touchscreen for an in-dash monitor can be controlled by bluetooth, sending video to an in-dash monitor from my phone is easy however using its touchscreen is another matter and this would solve that problem

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