Conjuring Capacitive Touch Sensors From Paper And Aluminum Foil

Stumbling around YouTube, we found what has to be the lowest-tech method of producing a touchpad to make a capacitive touch keyboard, and we just had to share it with you. If you’re afraid of spoilers, skip down to the video below the break now.

[James Eckert] got his hands on a Freescale MPR121 capacitive touch sensor. The chip in question speaks I2C and senses up to twelve simultaneous capacitive sense electrodes; break-out boards are available in all of the usual places. It’s a sweet little part.

So [James] had to make a twelve-key capacitive keyboard on the quick. He printed out a key template on paper — something that he does often in his woodwork — and spray-glued aluminum foil on the back side. The video doesn’t say how many hours he spent with the razor blade tracing it all out, but the result is a paper, foil, and packing tape keyboard that seems to work just fine.

A pin-header was affixed to the foil with conductive paint and more tape. If you’ve ever tried soldering directly to aluminum foil, you’d know why. (And if you’ve got any other good tips for connecting electrically to aluminum foil, we’d love to hear them.)

When we get stranded on a desert island, aluminum foil is one of the things we’d love to have along. Between making your own high-voltage capacitors with it, and making more complicated pressure-sensing keyboards, whenever you need something super-thin and conductive, aluminum foil has your back. (OK, it’s also good for cooking.)

25 thoughts on “Conjuring Capacitive Touch Sensors From Paper And Aluminum Foil

    1. G.K. Chesterton and several other literary figures were once asked what book they would prefer to have with them if they were stranded on a desert island.

      “The complete works of Shakespeare,” said one writer without hesitation.

      “I choose the Bible,” said another.

      “How about you?” they asked Chesterton.

      “I would choose Thomas’ Guide to Practical Shipbuilding,” replied Chesterton.

  1. I did a similar thing for a uni project, but created a slider using aluminium foil tape, FR-4 and some logic chips. For connecting to the foil tape I resorted to alligator clips which worked but was less than ideal. For the final board I used the copper on the board as 1 electrode with the FR-4 as the dielectric. Here’s a photo of my finished board with the captouch slider on the left.

      1. As part of the the assessment I did do a writeup. I’ve put it in my dropbox for ease of access. I will say right off the bat though that there are issues that I know of a need to fix, but have been busy with other projects. Compared with other projects in the course, the left hand section would have been more than enough, but I wanted to stretch my legs a little.

        1. Thanks a lot! I never expected such a fine PDF. It will be a pleasure to read and source inspiration from. Kudos to your homebrew PCB fabrication skills. That touch input principle is also super tasty. Well done, I hope your university will appreciate your talent!

          1. You’re most welcome. While I did do the layout, I have to admit that the electronics workshop at uni did the PCB fabrication. Apparently everyone was avoiding my board, particularly for the drilling of the 700+ holes. If was to do it again, I would certainly go with SMD components.

  2. The particular touch sensor controller was released in probably 2010 – or at least first revision of appnotes is from that year – and now, in 2015 it is not longer manufactured and unavailable. How typical for Freescale.

    1. As the company that I work for just found out, it’s microcontrollers are now powerful enough that the overhead of taking touch readings and calculating touches isn’t really a big deal anymore. We’re going to switch from using a touch asic, to just doing it on-board the arm that we’re using.

      1. I am not sure I get the “magic staff” reference…

        On reading my question again, I have realized one important detail: there would be a feet in the sock to bang away on the plates… Of course, I am thinking about DIY Dance Dance Revolution/Stepmania pad…

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