Monthly Archives: May 2014

Cheap bicycle wheel LED sign (POV)

Due to finances, about the only form of recreation I have these days is riding my bike. I like to take casual rides on the many trails here in Des Moines (Iowa is famous for it’s massive bike trail network).

A few years ago, I came across this neat LED display that attaches to a bike wheel and created images using persistence of image (i.e. lights flashing real fast as the wheel rotates, which the eye sees as a complete, though flickering, image):

http://www.ladyada.net/make/spokepov/

Go there and look at the pictures and watch the videos. It is able to display full color and even animate images (I love the Pac-Man and Ghost images they show). It works by having a row of LEDs that flicker on and off as the wheel spins. The wheel has to spin very fast to show an image, so they sell kits with multiple circuit boards of LEDs. The more on the wheel, the slower it has to turn to show an image.

It looked really cool, but it came in a kit, and I am not really that capable of an electronics person. Plus, the kit with three circuit boards was $113.

A found similar (much cheaper) devices on Amazon, though most of them just did preset patterns and didn’t let you load your own. You can find some simple LED wheel lights at Amazon for around $13 that can display short text messages:

http://www.amazon.com/Trademark-Games-Spoke-Message-Light-14/dp/B007VYZP6M/ref=sr_1_7?ie=UTF8&qid=1397281675&sr=8-7&keywords=spoke+led

Do some searching and you will find all kinds of cheap POV displays for bike wheels. I even found one for around $12 that was programmable via USB:

http://www.amazon.com/Docooler-Programmable-Colorful-Bicycle-32-pattern/dp/B00FOIZFNK/ref=sr_1_1?ie=UTF8&qid=1397281771&sr=8-1&keywords=spoke+led+programmable

None of these are anywhere near as cool as the Adafruit SPOKEPOV kit, but they might be pretty neat for the money.

Then, I came across this one on from an e-Bay store:

http://www.ebay.com/itm/PC-Programmable-Wireless-LED-Custom-Message-Bike-Wheel-Lights-/400354534043?pt=LH_DefaultDomain_0&hash=item5d36fd629b

It had two rows of LEDs and could attach to the hub of the bike and display messages or graphics. At the time I found it, there was a seller auctioning them off, and I picked one up for $6 (shipped from the US, even). Unfortunately, the device was not like the pictures show — it was not in color, just blue (the description says this, but all the listings, including Amazon, use pictures showing one with color).

Also, the device would not fit the hub of my bike (the bolts were too short), nor the sensor on the frame (the bracket was too small). I am not sure what tiny little bikes these were made for, but my old 1998 Trek wasn’t one of them.

However, with a bit of rigging, it was easy to attach the device to the spokes of my bike (rather than clamping it around the hub) using some tape, and then I could do some quick experiments.

If I get time, I would like to experiment with a very low-cost version of this, using an Arduino-style device and a strip of the high speed LPN8806 addressable LEDs. An Arduino in a plastic enclosure with batteries could easily power two segments of 32 LEDs (wider spacing than the commercial units, though) and do full color. The only other hardware would be a magnet and a sensor so the device can tell when the led strips circle around.

Sound fun? More to come… (I already have created JavaScript code that lets me load in an image in a web browser and convert it to the format that this device would need to display it.)