AllenPitts:
If the LEDS each use 20 mA (i think this is a maximum and they actually
use about half that but will use 20mA for design purpose) then
256 would require 5120 mA or a little over five amps.
The MAX7219 drives an 8*8 matrix, so only eight of the 64 LEDs are on at a given time.
If... the MAX is set for 20mA (resistor), then one MAX only draws ~160mA.
AllenPitts:
A seven volt 10 amp power source has been acquired...
You should have ordered a 5volt supply. Now you have to drop it further to 5volt.
AllenPitts:
Whats the best to provide power to the three systems?
Any regulated 5volt supply with enough current capability,
connected to the 5volt pin of the Arduino, the MAX chips, and the PIR.
Share all grounds.
Leo..