I want to build a honkin' big 7-segment display using a bunch of 20mm LEDs, get close to 10" high digit. They all have built in resistor and are meant to be used at 12v so naturally I'd need optoisolator to keep Arduino running at safe 3.3v and MOSFET to drive the display.
One: what are the best way to wire them all? I was planning to use 5 LED per segment. Do I wire them all to anode segment, common cathode or cathode segment and common anode? Second, whatever drives the common may have to handle up to 1A (7 segment lit for number 8, 5 LED per segment (35 total) approximately 30mA so around 1050mA.
And lastly, would I still need MOSFET for segment (about 150mA per segment per active digit) or can I leave that to optoisolator?
Very rough schematic for the LED display if it helps get you an idea:
Imgur: The magic of the Internet (this one is anode segment, common cathode configuration)
(I noticed no isolation on 4 digits line. I didn't check if I used right transistor (PNP vs NPN) or MOSFET (N vs P channel)