I wonder if it makes a difference if I use 1 resistor on the common anode pin
what is the best method to keep difference in brightness at minimum
They're actually off by a lot for columns with 8 LEDs lit compared to one LED lit.
And for the one digit I want to control with the arduino, do I write a HIGH to turn it off and LOW to turn it on?
I need a resistor, but I would have to add it on on the cathode side, is that okay?