An attempt at re-creating Grumpy Mike's 4x4 matrix sans push buttons.

I'm attempting to ultimately create a 7x7 RGB LED matrix via multiplexing with an Arduino and 3 TLC5940 LED drivers.

I'm trying to start by building a 4x4 matrix with the instructions from

So far, I've been able to get whole columns to light up individually but am trying to get individual LED's to fire independently.