I had several 8x8 LED matrices with a MAX7219 driver board lying around for a clock/message board project i'm working on. I'm heading to RobotFest in MD this weekend with my kid and thought it'd be fun to make a wearable message board to clip on my backpack since I had the parts lying around.
Time to build: 4-6 hrs
Cost: $20-$30 depending on parts and how much stuff you have laying around and if you want to make it bluetooth enabled.
I am using a bluetooth module I have for another robotics project that was very simple to integrate, and I wanted to build my first stand-alone ATmega328 project instead of doing everything on an arduino all the time.
This project is fairly simple and inexpensive. The "MAX7219 8x8 LED matrix kit" boards can be found on ebay for as low as $2.70 with free shipping, ATmega's with the arduino bootloader are about $4, the capacitors and oscillators are only a 10-50 cents per part if you buy a bunch at a time. The bluetooth module is more expensive but i am using a much more expensive model than what is really required for the project. You can do the same thing with a cheaper version that is only around $8. Or leave out the bluetooth all together and just run a pre-set series of animations or text.
(estimated costs in USD)
1 x ATmega328P-PU ($4)
1 x 28 Pin DIP IC Socket ($0.20)
1 x 16Mhz Crystal Oscillator ($0.50)
2 x 22 pF capacitors ($0.20)
1 x Bluetooth Module ($8-30)
1 x 8x8 MAX7219 LED Matrix board kit ($3)
1 x 3AA Battery Holder ($2.50)
3 x AA batteries ($3)
1 x piece of breadboard ($2.50)
Total: $24 - $46
Various header pins (male and female), hookup wire, solder, some kind of enclosure, Arduino for programming the ATmega328
Soldering iron, dremel for enclosure