Carl Sagan, Immortalized in SpokePOV
Cross posted from Skepchick. Post by Rebecca Watson.
OK, maybe “immortalized” isn’t exactly the right word for a portrait in LEDs that only appears when in motion, but it’s close enough.
SpokePOV is a kit you can build that will let you program images that appear on your bicycle’s wheel when you ride at a certain speed. The “POV” stands for “persistence of vision,” which in a colloquial sense refers to the optical illusion in which still images can appear to be moving, as when you watch a film, and a moving object can display a static image, as in SpokePOV. SpokePOV uses lines of LEDs on a circuit board with a small computer attached. The circuit board is strapped to the spokes of your bike wheel and a magnet is attached to the bike so that the computer can tell when to flash the LEDs. When the wheel is spinning fast enough, people watching will see an LED image on your bike wheel as you fly past.
An interesting side note: the phrase “persistence of vision” comes from the idea that an image remains on your retina for a brief period of time, even after the image itself has changed. An early hypothesis suggested that this is why we perceive films as fluid motion, but that hypothesis has been disproved. These researchers would like to replace it with the phrase “short range apparent motion,” but I’m unsure of where that leaves illusions like SpokePOV or these novelty clocks, since they aren’t creating apparent motion but apparent static images. Beta movement also doesn’t seem to fit, nor does phi phenomenon. Any psychologists in the audience, please feel free to weigh in, here.
Anyway, SpokePOV is a fun project and fairly easy to put together, though I’m lucky that I have a partner who honestly loves to solder. We got three circuit board kits, since the more circuit boards on each wheel, the stronger the image will show at slower speeds. We got blue, which requires a bit more power than red, yellow, or green, but is so super awesome and bright. Plus it matches my handlebar tape and shoes.
We used a serial-to-USB converter to be able to upload images to the computers, each of which has enough space for four different images, allowing us to create animations or just to display a rotating set of images.
For my first go, I tried a portrait of Carl Sagan. Because we only have one color, I had to find a simple portrait that was easy to reduce to a single color. I found this one on Google Images, and turned it into this:
And because I could animate it, I decided to make Carl give a sassy little wink:
I uploaded the images and spun the wheel, and here’s what it looked like:
Okay, probably not a likeness that is immediately recognizable for most people on the street (or, maybe, for anyone) but I’m still pleased with it, and regardless of what image is showing, the LEDs are so bright that drivers should be able to spot me from a mile away on a dark and otherwise dangerous night.
I’ve already designed a new image of an old school atom that looks pretty amazing, though I don’t have a good photo of it on the bike just yet – I’ll probably Tweet it when I do have one. I’d love to get a pic of the bike in motion, but my photographer partner tells me that’s going to be very, very difficult, so in the meanwhile we have to go with the upside-down stationary bike. Also, in the future I may pick up some more kits to light up the front wheel as well, at which point I’d like to experiment with images that “jump” from one wheel to the other.
If you have SpokePOV or want to try it and would like a winking Sagan face on your bike, here are the .dat files, which you can edit as you please! Also, let me know what other dorky images you think would work on a bike wheel and maybe I’ll try them out.