When I first learned of the awesome SpokePOV project put together by MIT engineering wonder Limor Fried, I just had to get some of the boards together to try it out.
I ordered the Triple SpokePOV Kit that came with two neodymium magnets as well as a useful parallel programming dongle. I also decided to splurge a little on the bright blue LEDs and a 4Kb EEPROM for each. With shipping and all, it came out to a smashing $132.05; a pretty good deal for what I was getting. Shipping took a couple days, but came soon enough. I was so giddy to get everything once it came, and was able to put together the first board, program it, and try it out in about an hour.
Programming the actual images proved to be a bit more trouble than I was hoping. The python program that Limor put together was pretty good for a hack, but it leaves some things to be desired. The rendering while drawing pixes is a little slow, and it unfortunately choked with getting pyParallel working on my Linux machine. I had to resort to programming the boards on Windows. Ick.
And it looked awesome. With only one board going, I ended up needing to have the wheel zipping along pretty quick in order to attain a full image. But, once I got three going on one wheel, I got full-image POV without having to race down the street.
In all, it’s a pretty robust little kit with some nice touches. The only thing I might change is the length of the board for bigger wheels on cruisers (maybe a homebrew hack for the future). I’m not sure if it was counting error, but I got an extra LED in two of the kits. Those could come in handy if something happens to any of the running ones. And above it all, the crumpled up Digi-Key catalog pages for padding was an extra nice touch.
For future additions, the platform seems pretty hackable. I’ve already got a couple of ideas brewing to fix it up to be a more robust system. Here’s what I’m thinking so far:
- The addition of a pad for an external power connector makes it easy to add batteries (balancing the wheel might be hard), or a generating hub to either charge batteries, or run everything directly.
- Syncing the hall effect sensors on each board so that all the microcontrollers gets the same pulse. I’m thinking that it would make syncing animations that stay on the boards easier. I’d have to fiddle with the offset timing to make it work.
- Having a tiny external computer like a gumstix machine under the seat barf out SPI data to the latches on the board for longer animations. Longer clips with sound could be stored on an MMC card on a gumstix machine.
- Getting a SPI stream into a moving wheel might be kind of hard. My initial idea was to use a brush on the wheel’s conductive frame, but I’m guessing it would be too noisy. I might have to opt for something wireless.
- And if I wanted to make it extra fancy, I could use some wireless networking to the gumstix with either a cell phone or permiscuous 802.11x detection to get images that people could submit over the Internet to be displayed. Kind of like a mobile blinkenlights setup.
Here’s a video of the whole three-board setup on one wheel. It’s currently setup with four images and it cycles through each every 100 hall effect sensor pulses (rotations past the magnet).From the video, images of an alien head, Commodore logo, dragon, and Tux head can all be clearly made out. The camera doesn’t really do it justice though. Viewed with the naked eye, the image blurs together much more nicely. And the bonus is when you stop; the whole setup looks like the “flux capacitor” from Back to The Future.
SpokePOV in Action
