LED Coaster
I've had the pleasure to work with and learn from bunnie Huang for over a year. He knows a lot about how to make things, and it shows in the Chibitronics project, a recent collaboration he's embarked on with MIT Ph.D. student Jie Qi. There's a lot of neat stuff involved in producing flexible circuit stickers and the work that's lead to their creation is worth reading about. I've been excited to try these LED stickers out since hearing about them, so I was ecstatic when bunnie and Jie finally sent me a few to play with.


I exhausted a few stickers on little experiments with copper tape and paper, building a few simple circuits and a paper switch. Depending on the surface you stick these guys to, it is possible to peel them up and reuse them a few times before the conductive tape starts to wear. Peeling them from paper is a lot more difficult than peeling from 3D Printed PLA, like any normal sticker. To me, one of the most exciting thing about these stickers is their extremely low profile, so I wanted to take advantage of that with this project.



The original plan was to place copper tape around the bottom surface of my coffee mug and set up the circuit in such a way that placing the mug in the correct spot would complete it and light up the LEDs. This turned out to be way harder than I thought it would be, so I ended up changing direction. More on that soon.

In order to hide the CR2032 battery from the rest of the circuit, I planned to mill out a cavity in the top of the Zombie Hunter's head and pass the wiring through to the other side. Here are a few build photos up to that point, along with other tests I did prior to the main build:

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As you may have gathered from the slideshow, there were a few major flaws with this method:
1. The mug had to be in a very precise spot in order to complete the circuit.
2. I had copper tape on the bottom of my mug, and who wants that? Although it was surprisingly durable (stood up to multiple washes in the sink).
3. Physical connections between copper tape are not reliable. Solder helps if you're trying to complete a circuit with physical contact.

With these in mind, I changed the plan, now working towards a pressure-sensitive solution. And so I began testing different ways to complete the circuit with combinations of bent paper, copper tape and blobs of solder. I found blobs of solder to be unreliable and searched for a more springy solution. After using a small piece of stripped hookup wire to test the circuit for days, I finally realized that it may have the perfect springy-ness to act as a simple pressure-sensitive switch, and it did! Here are a few additional photos of finishing off the build:

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This actually turned out to work much better than I thought it would. I simply glued the piece of wire to a piece of paper and lined it up with the two contacts on the coaster. I then cut a circle out of a tape container, sanded it to help diffuse the light, and taped it on top of everything else. Done!

There are a few things that can still be improved here, like using something less obtrusive than a piece of hookup wire for the switch - although it works well, it does put the container on the coaster at a slight angle. I'd also like to add in one of the fading effect stickers as soon as I can get my hands on one :)

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