In a moment of irrational exuberance I volunteered to make an edible LED matrix for the upcoming SHHH. It will basically be 64 jello cups backlit by the LEDs. The panel is now wired and assembled, it uses an Arduino Uno in combination with a MAX7219 to power the display. I am not much of a programmer so all it does right now is sideways scrolling text. Maybe some other functions can be added but I probably don’t have time to figure out anything more. The dimensions are based on some 2 oz. plastic cups I found at the dollar store, the overall outer dimension is about 26" x 26" square.
Unfortunately the resolution is so low and the spacing is a bit too wide so that it is difficult to make out the text from up close. It might help to mount it at a slight angle and observe from a few feet away. I will try it out with jello later this week to see how it actually looks.
The LED8x8 code linked above uses all the output pins to drive the matrix directly. I read that this gives inconsistent brightness because each cathode line will be sinking the current for up to 8 LEDs but is limited to 40mA max without external circuitry. This means about 5mA per LED when a whole row is lit.
The MAX7219 has constant current outputs so each LED is always driven with the same current. I was concerned about getting absolute maximum brightness without exceeding the limits of the Arduino. I might have time to try your circuit this weekend so I can utilize your Tetris game.
