Paper touchpad

If you don’t mind getting your fingers a little dirty you can replace your mouse with a piece of paper. [Dr. West] made this touchpad himself, which measures signals at the corners of the paper using four voltage dividers. The paper has been completely covered with graphite from a pencil (which we see in hacks from time to time), making it conductive. The user wears an anti-static strap that grounds their hand, allowing an Arduino to calculate contact points on two axes when a finger completes the circuit. See this controlling a cursor in the video after the break.

34 thoughts on “Paper touchpad

  1. if you dont mind having silver fingers this is nice XD

    quite smart idea and if you can find a material that is as conductive as graphite and does not rub off its quite pricital(sp?)

    i dont suppose multitouch would work … will it?

  2. You could also use:
    Window screen (or upside down paper+graphite)
    (Conductive metal surface as ground) Like sheet metal or foil.

    That is so you don’t need a wrist strap for ground.

  3. The hard part is keeping layers spaced apart while allowing them to contact without much pressure. Commercial resistive screens use closely spaced arrays of tiny silicone dots. I’d say the approach above is pretty much the limit of what’s reasonably possible without special materials.

  4. @BiOzZ @Gdogg A thought that springs to mind for a bit of cheapo multitouch on the cheapo touchpad…

    Seeing as you’re grounding your hand, rig a glove with conductive tips, and then scan/switch through which finger pad is connected to the ground, then you have positioning for each finger.

  5. Just so everyone knows, this hack was kind of a joke. I thought it would be funny to make a ghetto touchpad out of just a pencil and a piece of paper lol. I’m currently working on a slightly more sophisticated version using a rigid surface and dry graphite lubricant as the resistive coating, which doesn’t rub off on your finger.


  6. @Dr. West – So many things i do are for my own personal enjoyment and have no practical use (kazoo controlled mouse , i’m lookin at you). These projects prove their worth for both education, reference, and as inspiration for bigger and better things. Keep it up!

  7. if he had it attached to a rigid surface, then had some buttons for click)like a laptop trackpad), then the user would be able o ground by just resting a finger or two on the buttons.

  8. @jentulman That is a good idea. Adds a lot of complexity and removes the simplicity of it (since we need a smart touchpad, as always, but also a glove that can tri-state and toggle between ground and high impedance.)

  9. Now that I think how this is done, electrostatic foam one finds IC’s packed in should work as well.

    It’s measuring a exponential drop in resistance across 4 outputs, so the material has to me kind-of conducive. Metal foil or like would not work. And the foam could be worked so that you could work multiple sides (say in a 2 monitor compiz setup).

  10. This was already in my notebook months ago! This is the first time a hack has been posted which I devised but never went through with…

    Someday I’ll have to actually do some of the things in my notebook…

  11. @Josh C

    I’ve got a piece of electrostatic foam, and it does work on a trackpad.

    Granted, laptop trackpads are usually capacitive, but I think it would work on a resistive trackpad like this hack.

  12. Correction: use a metal top foil and a graphite bottom foil with a uniform resistance, so you can use the same method as this one to calculate where the finger is.

    If both foils are metal, then all you’ll know is how hard the user pushes.

  13. Well, the way I see it all you need is one metal-insulator-resistor sandwich.

    Because the stack lets through a certain amount of current when it’s idle, so there’s your no touch baseline. When you press on it, the capacitance changes and the current obviously increases.

    The current is measured from four terminals at the corners, and seeing how much current is going to each terminal in proportion to the others you can calculate the position of the finger.

    Then, knowing how much current on average is going through the stack, you know how hard it is pressed, or how big an object is pressing it. (Both would have the same effect of increasing the overall current.)

  14. When you have announced that Korg Monotron released it’s schematics i’ve been looking for some know-how to make the resistive ribbon 1-dimension touchpad and this seems nice:

    i think we can use knowledge from both these projects to make something even better. i just wonder if there is some cheap material that changes it’s resistance when pressed, i just don’t like the idea that there is nothing between two layers of ribbon. i would like to see something flexible so i can be sure that ribbon will not get stucked in contact after few weeks…

  15. Along the lines of the foil-graphite-foil sandwich, you should be able to modify Plusea’s work (soft circuits over on Instructables) for this: replace the graphite with a sheet of Velostat and add a layer of grounded foil (or two sheets of Velostat, maybe: one with the four measurement points and one that is connected to ground). You should be able to get both position (by the relative voltages at each pin) and pressure (by comparing those voltages to an idle baseline).

    By using two sheets of Velostat and establishing a baseline idle profile, I believe you can eliminate the need for additional spacers.

  16. Building a variable resistor using a thin film of graphite really is very old technology. But the interface between the Arduino and the PC is interesting and useful. Tell us more about that.

  17. Oh man I was making the almost exact same thing 2 years ago I just wasn’t good enough with electronics and microcontrollers at the time. I was gonna use a screw for the ground (cause im cheap and wanted it quick) but a empty ball point pen if you could ground the tip should work (didn’t want to smudge things but its pretty cool idea with the antistatic strap). I even was gonna use a atmega 168 for the job but I just couldn’t get it to work. I wanted to make something cheaper than buying one of those bamboo tablets that are pretty pricey for drawing stuff. Congrats man and I just wish I would have beat you to it.

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