Two input devices made with common items

Here’s two input devices you can easily build with materials you already have on hand.

To the left, [John] built a 3×3 keypad matrix from paper and tinfoil. The rows and columns are made up of strips of tin foil on the front and back layers of paper. The layers are separated by spongy double-stick tape. A ‘keypress’ results when the gap between the conductors is compressed with your finger.

In much the same way, [Dave Fletcher] built a touch potentiometer. He made two resistance plates by scribbling pencil lead on sheets of paper. When the two plates face each other, separated by the same type of foam tape as before, they can be pressed together to form a circuit with a variable resistance. This results in a crude version of the SparkFun softpot.

Comments

  1. therian says:

    and this keypad will last for full phone number or two, capacity keys are as cheap but much more durable

  2. JTaylor says:

    @therian

    Yes, but I need a input device NOW! Sometimes just having the part when you need it is valuable as well. I also suspect that it would last for more than 2 or 3 phone numbers. Most basic keyboards are built in much the same way…2 layers of conductive traces separated by an air gap.

  3. Targen says:

    Neat. I just started working on a strip of paper with graphite just like this last night for use as a linear position indicator for some mobile part in a robot. Doing some preliminary research I ran into this link that does a bit of comparison between a few ways of making a linear potentiometer: http://itp.nyu.edu/physcomp/sensors/Reports/HomeMade

    I haven’t found a suitable magnetic tape yet, but it does seem like the best solution. Paper can get rather weak after scratching all that graphite onto it; perhaps some sort of cardboard might work better.

  4. Osgeld says:

    It wont last super long, but it will last long enough for you to decide if ordering a proper part is worth while, or if you had your fun but want to move on

    good job

  5. googfan says:

    i’ve built one of those paper keypads before. NNot very reliable.

  6. threepointone says:

    I have too. And it lasts for probably at most 2-3 phone numbers. Seriously.

    This may be similar to how actual buttons are made, but all the materials are wrong! The biggest problem is the Al foil–if you look at the stress-strain curves, when you press your finger that far into the foil, you definitely exceed the region where it’s elastic. In other words, you permanently deform the foil (i.e. it wrinkles up) and you eventually get a permanently on button. If you could make the separator thinner (and more resilient to compression) and increase the conductor size somewhat (or better yet, use spring steel or similar), it’d work better.

    Great for prototyping, though!

  7. TJ says:

    I was hoping one of the common items was going to be a hammer…

  8. Will says:

    The keypad doesn’t have a 0.

  9. Rocks25 says:

    “The keypad doesn’t have a 0.” That made my day.

  10. Haku says:

    The build method used to make the numpad keypad is great for making a rudimentary under-carpet sensor that’s triggered when you unwittingly step on it, I made one using this method some 20+ years ago which was hooked up to a doorbell alarm when I was a kid.

  11. DST says:

    I’ve made similar keyboards using plastic laminate. The neat thing is that you can print any design on the paper and laminate it, these are actually very durable, and as the plastic laminate will not get worn, and always return to it’s original shape.

  12. John Warren says:

    whoot i’m on hackaday lol… the keypad does work for a good period of time. it is glued to the paper which makes it more durable thus allowing for it to separate. It’s meant more for a keypad that you are not afraid of losing i.e your door in a college residence (drunk kids rip up everything). with better materials like more durable paper or transparencies, silicone caulking spacers, etc. you can get a very reliable keypad. it was more for showing the concept and it’s up to you to make it what you will

  13. M4CGYV3R says:

    I can’t say this loud enough, but FUCK Instructables. Their website is just pure crap, and they try to charge you to see build pictures other people posted. The BugMeNot logins don’t work anymore.

    If H-A-D still has any shred of self-respect they won’t post that payola garbage anymore. It can die in the same fire as the Arduino.

  14. Haku says:

    I can view all steps on one page and download the PDF, but I haven’t paid anything to become a ‘pro’ member (and never will), though often I have to go through the login sequence more than once before I can view all steps on one page.

  15. walt says:

    i was going to read this entire article but a gigantic ad took over my screen. oh well. that site wont let me see all of the images anyhow. instructables strikes again. boooo!

  16. Maave says:

    Wasn’t this on Instructables? lol

  17. J Harton says:

    @M4CGYV3R I don’t what they’re doing now, but I signed up before this pay thing and I have yet to have an issue with viewing bigger pictures, showing all steps on one page, or getting pdfs. So either previous members automatically have access to all, or we’re going to get that removed and be forced to pay.

    In either case, I believe it’s perfectly ridiculous to charge for turning images and text into pdfs, in other words the site can make money off of those who’d like pdfs of someone else’s instructable.

  18. J Harton says:

    Oh and by the way, M4CGYV3R, self-respect and respect of you are two entirely different things. That and I can’t understand what issue you have with a product like arduino that gets people interested in doing interesting things with electronics.

  19. mk says:

    “I recalled that putting 12 volts across the lead of a pencil caused it to glow brightly red [...] So I knew that it would conduct and that it has resistance.”

    Wouldn’t the paper that is sandwiching the graphite burn after some time?

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