I'm having trouble with my LED matrix setup. This is relevant part of schematic:
So, rows are controlled by MOSFETs. LR1, LR2.... LR6 are connected to ATmega32u4. Those pins are set as outputs. When one of the outputs is low, MOSFET is active, and voltage on row is VCC (5V). Yes, I realize those row resistors are low, but user is supposed to add additional external resistor - irrelevant for this discussion. When I set output to high, MOSFET is off and voltage on row is 0V. This part is okay and it works.
Second part of matrix is controlled by decoder and ULN2803 sink (LED columns). For testing, I am not switching columns at all - only the first output from decoder is active which activates first column (I've checked this - Y0 really is set to 5V, rest of the outputs are 0V). Now, when I connect positive side of LED to any LED row (all are activated - 5V on each) and negative side to first column connected to ULN, LED should be on, but it's not. I'm struggling to find out why. Am I missing something obvious here?
LED works if I connect anode to any active row and cathode to any GND pin - it won't work if cathode is connected to any ULN-connected column though.