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I first got interested in making a wearable television for
Burning Man in 2009. I had a pile of surplus red LED 8x8 displays,
and wanted to put them to use. They cost about a penny a pixel - a gonga!
So I built Satanvision. While I was designing the world's worst wearable television, I kept thinking how great it would be to design the world's best wearable television. Hmmm... that would take about a gazillion dollars' worth of LEDs. It would also require some kind of flexible sub-panel arrangement so that it would wrap around my torso. I let the idea drop, and built SatanVision, and had fun with it. But it weighed 50 lbs., and was very uncomfortable to carry around on the shoulders of my wife and myself. So it lives as a wall hanging instead of a wearable video display. Fast forward to January 2011, when Burning Man tickets went on sale. I placed the order in the early afternoon, and the pile-on was so huge this year that I ended up having to wait about 8 hours to complete the ordering process. So I figured I'd pass the time by coming up with my Burning Man art project. I thought about covering the car in LED displays, but realized that I'd be buying $100,000 worth of LEDs. No, it's got to be something smaller, and doable. I decided that a suit covered in LEDs would work. I thought about separate pants and coat, but realized that would it be difficult to cover the thighs in LEDs, due to the nature of the curves in that region of the body. So I settled on a jacket. I spread out my big 1940s coat on the dining table, measured it, and came up with the dimensions of 4 feet wide by 3 feet tall. This could be done in the same dot pitch as Satanvision, with a slightly higher resolution of 160x120 pixels, at 0.3" per pixel. That pixel count is exactly half of the screen size of an iPod. The display circuit boards presented a challenge. I could use the method employed by Moritz Waldemeyer and Hussein Chalayan in their Video Dress, but that looked too heavy for my taste. I realized that I'd have to use narrow, vertical strips of circuit boards, preferably flexible, to get the desired draped effect without weighing me down. I also had to figure out how to scan the LEDs, and make circuit boards that would hold the scanning chips and LEDs on that tight dot pitch, yet be manufacturable. The chip selection was easy. A high-school friend works in Las Vegas at a sign company, and he gave my brother a surplus LED billboard circuit board, which he passed on to me. I saw that Allegro made the LED driver chips. I found a tiny, modern version of that chip in a 4mm square package. This chip is so small that I could put it on the front of the board in between the pixels! I quickly did some sketches and concluded that I could make a circuit board in two layers that would have all the necessary signal traces. I hemmed and hawed a while about using either very thin FR-4 rigid PC boards, or using flex boards made of Kapton film. The Kapton flex boards won out, due to their ability to be made with flexible and stiffened regions. The concern is that any flexure of the board near the IC pads would crack the delicate copper traces. I also had to figure out how to get the video into the LED display boards. I basically copied the SatanVision method of pulse-width modulation using programmable gate arrays (FPGAs). However, I had to do something fancier in the input circuit to get the color signal from the yellow RCA plug chopped up into red, green and blue signals. fortunately, there are chips that do that job. The only one i could find that also would scale the image down to the desired 160x120 pixel resolution is a TI TVP5154A quad video processor made for security cameras. I use one fourth of the chip. It requires a microcontroller to load its registers, so I added a little PIC18F4523 since I had some lying around from my underwater robot project of last year. |
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