You can now program the firmware into the microcontroller.
I use the USBtinyISP by ladyada.
I also designed this POV to be compatible with the Arduino. You just have to use the FTDI USB-TTL232 cable. But don't take my word for it, test it! (because I didn't).
There is also a TLC5940 library for the arduino by Alex Leone
Currently in this version of firmware you can only display one image, but you can easily tweak it. Also, the image data is read from program memory.
In the future I plan to try a SPI EEPROM connected to the serial port. This way I am able to store tons of images and animations!
In this version there is also a small section of feedback control loop, to synchronize the image to the velocity of the wheel.How much space do I need for my image?
Depends on the level of detail you desire. With level of detail, I mean the number of divisions of your wheel.
If want to use 100 divisions, you'll divide the circle in lines with 3.6 deg. The greater the number of divisions, the narrower the lines.
For one image of 100 lines:
192 bits for each colour * 3 colours for line = 576 bits / 72 bytes for each line
72 bytes/line * 100 lines = 7200 bytes/image, ~7kBytes/image