LED ShiftBar Pumpkins
Jason was talking to one of our distributors recently (Paul at Pololu.com). He mentioned that he wasn't going to be at home this year to try putting some ShiftBrites in pumpkins. That sounded like such a good idea, we decided to run with it!
We had a bunch of high brightness LED arrays left over from a recent project, and decided to use those to replace the candles in some pumpkins. Each array has 10 five-chip 100mA LEDs: four red, three green, and three blue. The extra red LED was added because they tend to be a little dimmer than the blue and green LEDs. Since the ShiftBar can't control more than 150mA per channel, the LEDs are arranged in series for a higher forward voltage, to approach 4.5W total. The light output is about the same as 15 ShiftBrites, with 5 extra ShiftBrites thrown in for the red channel.
Naturally, we had to start with some pumpkins. I got eight of them from Safeway and set them up in the back yard. Our friends Ethan and Karly were coming over for a barbecue, so we added pumpkin carving to the list of activities. They were happy to help carve pumpkins...and also brought food and grilled it for us! The bison burgers were delicious. The pumpkin carving went as usual...disgusting pumpkin guts clinging to everything, etc.
Here's where the fun stuff begins! We made a control board for eight pumpkins, using eight ShiftBars, 50mm cables, a Seeeduino, a ShiftBrite Shield, and a 12V power supply. The ShiftBar potentiometers were adjusted to deliver about 100mA to each of the 24 LED channels. We wired the LED array boards to the control board using cheap 4-wire telephone station cable from Home Depot. An old cat litter bucket made a good semi-waterproof enclosure.
Once everything was wired up, we brought in the pumpkins and installed the LED arrays. To seal them against the disgusting pumpkin insides, we ziptied small plastic bags over the arrays and cable ends. Then we used some heavy copper wire sort of bent into staples to hold the LEDs on the bottoms of the pumpkins. A little last minute coding on the front fence and they were ready to glow!
You might notice in the last photo, I appear to be wearing late 60's style mutton chops. This is completely ironic and is an intermediate step to shaving my beard. I would never actually wear them in public.
The LED arrays light up the pumpkins very well. You can actually see light glowing through the skin of the pumpkin, not just the holes. I wrote Arduino code to cycle through a few patterns; a chaser, random strobe, a wavering green glow, lightning, and candle flicker simulation.
Of course, we took some video of the whole thing. Check it out below!
Submitted by Garrett on Sun, 10/18/2009 - 02:29.