It takes too long to update the board via the arduino. I need to pump 576 bits per 4 pixel x 4 pixel board to light it. To get 24 frames a second I need to be able to transfer 1.7Kbps per board. I found that the arduino can pump out about 30 fps for one board, which means adding a second will bring me down to 15fps which isn't much. To overcome this I got a gumstix computer which should be faster. However, I will probably redesign the whole thing to operate more like the similar project that Sparkfun put together for the Makers Faire.
The gumstix computer I got is great. Its tiny even with the WiFi card attached. However the breakout board that I have with it doesn't come with headers. I don't want to solder wire directly to the breakout since I don't know how I'll use it yet, but the holes aren't the standard 0.100" apart. They seem to be 0.049". Looking around I found these connectors from Hirose, and I can probably make my own cables with those, but it'd be nice to see them first. (sometimes pictures just don't prepare you for what you end up getting).
Each board sucks up about 300mA of power. With two boards its almost 700mA. If my goal was to have a total of 16 of these, I'm going to need a way to deliver about 5A of power to the whole system. Most of the power supplies I've seen that deliver 5A and up cost too much and I can't figure out what I'm getting. I feel like I have an advantage in that I don't necessarily need 5A all in one place, I can deliver power to each of the 300mA boards independently, but I can't figure out how to do that. Just as a test I got a $2 voltage regulator (Fixed 5V) at Radio Shack and ran a 12V 600mA wall wart to it.
I found that it powered my board but then when into thermal shutdown after about 5 minutes of operation. I found that I could stop this from happening by using a lower voltage via a different wall wart (6V) but it didn't deliver as many mA so I could only power one board. I'm still looking for good ways to power this...
A single board costs too much. Each board requires 3 TLC5940 chips @ $4.50 a pop. Thats $13.50 a board and $216 if I want to make an array of 4x4 boards. Each board uses 48 LEDs which are about .50 or .60 each, and with the 4x4 array thats, 768 LEDs at $384. The only other materials are about 9 analog components per board (< $1), some connectors (< $1) and the board itself. So in addition to whatever the cost of fabricating 16 of these boards, I'm paying at least $620 total on this project.
I was really impressed by the similar project by Spark Fun at the Maker Faire, but also a little depressed that they had done it so much better. Still there are ways I can use some of their ideas to bring down the cost. Rather than using the expensive Ti chips that I'm using, they have a single ATMEGA8 chip that does everything at $2 a chip. It can't offer 4095 levels of brightness per LED, but my setup doesn't really take advantage of that anyway.
They also use tri-color LEDs rather than 3 discrete LEDs at $1.60 a pop. This may be slightly cheaper, and definitely simpler. I'm having problems finding suppliers however.