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.)

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HDTV antenna that can hang in a window

We can’t wait to give this one a try. We’ve got a DIY HDTV antenna hanging out in the attic which was made from some scrap wood and eight metal coat hangers. It works great but it’s pretty ugly and not everyone has an attic to hide it in (not to mention the signal drop caused by the roof shingles). This is a fractal antenna anchored to some clear plastic so you can just hang it in the window and start picking up the over-the-air channels without much effort.

The pattern was modeled in SketchUp then printed out on two pieces of paper. One piece had it printed on both sides, which makes it easy to glue on a sheet of aluminum foil, then follow the pattern on the opposite side to cut out the important parts. The other template was used as an aligment guide when gluing the foil to the clear plastic. A coaxial adapter was then attached using nuts and machine screws. If you build it, let us know how it comes out!

Roll your own capacitors – high voltage edition

[Grenadier] tipped us off about his method for building your own high-voltage capacitors. He thought the paper and foil capacitor project was a nice introduction to the concepts, but at the same time he knew he could produce a much more powerful device.

For the dielectric he is using acetate film. This is the material from which overhead transparency sheets are made. He stuck with aluminum foil for the two plates. Just roll the foil flat with a rolling-pin, use thin wire to minimize the air that will be trapped between the dielectric layers, and make sure the foil plates are at least 4cm shorter than the acetate film on each end to prevent leakage. After rolling and securing the capacitor with zip ties you’ll be ready for the 3nF worth of fun seen in the video after the break. [Grenadier] mentions that this can be improved further if you were to vacuum impregnate the device with beeswax.

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