Soft Circuit Swatches with Surface Mount LED

Creating small electronics out of uncommon materials is a hobby of mine. I think it’s fun to show that electronics isn’t limited to circuit boards, and computers don’t have to be stuffed inside boxes. Especially when FabLab is exhibiting for school age kids who might change their minds about whether they’re interested in CS and ECE, I’m happy to show off a wide variety of computers, usually various arduino-powered objects.

Aside from having interesting widgets to show off, I mostly enjoy the challenge of building something with materials I haven’t seen used before. Instead of sewing LEDs on top of fabric, I wanted to integrate the LEDs into the fabric, so I used a hand loom to make a patch of fabric, using stainless steel thread as my weft. Knots have never made sense to me, so setting up the loom was especially challenging.

I really can’t think of anything to do with this, so for now it’s just a tech-demo. I’d love to hear your ideas.

I really appreciate what Adafruit and Sparkfun do to make small electronics available in sew-able packages (such as the Flora and Gemma microprocessors from Adafruit, and the Lilypad from Sparkfun), but I never really liked that the components were still bonded to a chunk of fiberglass circuitboard — it limits the flexibility of the fabric where it’s sewn and it looks bulky. With that and the extra expense of those products in mind, I wanted to come up with a strategy that allows surface mount components be embedded into a flexible material. SMD is the cheapest package for many parts — we order these 1206 size LEDs at 2 or 3 cents apiece on eBay.

Stranded copper soldered directly to these LEDs are sewn into leather which was lasered to punch holes and provide guides for the wire. This is just a test swatch, I have it in mind that lasering the holes and traces like this would provide a way to wire fairly complex 2-layer circuits (since traces could cross to opposite sides of the leather to avoid intersecting). The parts can sit flush with the surface of the leather, and the leather can flex without dislodging the parts — they aren’t bonded to the substrate, just pulled against it by the copper stitches. This also makes it surprisingly repairable. At one point I melted an LED after stitching everything together, and it only took a minute to un-solder and drop in a fresh LED.

For the leather circuits, I’m looking forward to trying to do 7-segment displays with the same LEDs, but embedded the microcontroller and battery holder directly into the material. I’m imagining interesting tabletop radios and clocks that exhibit their circuitry on their surface.

A quick demonstration of both circuits: