LED Drivers MAX7219 or MAX7221

I am currently in the process of building an Aruinome and am confused on which LED driver[integrated circuit resistor] to use.
How would I figure out which is my best choice the MAX7219 or the MAX7221

http://arduino.cc/playground/Main/MAX72XXHardware#SelectProduct

yes I have gone to that page.does it then matter what type of LED and/or amount of LEDs (64 being the max) I use?

you need common cathode LEDs. 20ma per LED seems good. read the last few paragraphs there, they talk about power comnsumption

Right on, thanks your very much for the help sirbow2

Sirbow2 you mentioned common cathode LEDs. How does that apply to single color LEDs that have both a cathode and an anode lead? In comparison to RGB LEDs that you can either get in common cathode or anode. sorry if I am asking beginner questions this is my first project.

dunno really, but i just know that if its common cathode, you connect the cathode to ground, and then you need a resistor and 5v or whatever on (all) the anode(s). common anode, you hook the anode to 5v, and then use a resistor on each of the cathodes to ground.

just to clarify as CrossRoads says below; this is just for a single LED and is no way related to using a 7219

If you are buying a 8x8 LED Matrix to use with a 7219/7221, you should use a common cathode matrix.
If you are buying discrete LEDs, it doesn't matter. And current is controlled by a single resistor on a 7219/7221 pin.

sirbow2's description is not correct for using parts with the 7219/7221, where the chip controls both the anode and the cathode of the LEDs.

CrossRoads
I am trying to build an 8x8 LED matrix to use with the 7219/7221, and am trying to figure out what type of LEDs to purchase as well as which integrated circuit resistor to use.

Purchase the color & brightness you want. You can get 20mA LEDs that are 30mCd and you can get 20mA LEDs that are 15,000mCd.

The resistor you use will depend on the max current you want to flow in the LEDs.

The 7219/7221 has a variable that you can set to change brightness also, from 1/16 to 15/16 I think (need to check the spec on that).

Forward voltage
ISeg 1.5V 2.0V 2.5V 3.0V 3.5V
40mA 12.2k? 11.8k? 11.0k? 10.6k? 9.69k?
30mA 17.8k? 17.1k? 15.8k? 15.0k? 14.0k?
20mA 29.8k? 28.0k? 25.9k? 24.5k? 22.6k?
10mA 66.7k? 63.7k? 59.3k? 55.4k? 51.2k?

this chart helps you select the resistor

So get a 10K resistor and wire it in series with a 50K trim pot, will let you cover the range of current you can dial in. And then adjust brightness further with software commands.

IMHO.. 'my' tests/results.. using a 10K resistor makes the leds VERY dim..

Im not sure if its because of the multiplexing or what.. but I couldnt get a comparable brightness to a normally powered, matching led unless I used a 1k resistor.. (not saying it correct/safe to use..just posting MY results.)

Also the MAX7219 & MAX7221 chips differ slightly.. in that the MAX7221 supports PIS and the MAX7219 does not..
if this effects your project or not.. no clue on how you plan on communicating with them/library of choice you want to use.

but there are (some new) SPI libraries out there this is that is your route.

MAXIM will also send you free samples of these chips.. (as well as a VERY cheap supplier on ebay for these.).. beats paying $10 per chip!!!!

while Im not doing a 'cube' I still have matrix 'wiring' to control my 120+ led strip/ladder.. (individually addressable)

In contrast to xl97, driving 4 digits of a 7-segment display off a '7219 I found to be insanely bright with a 10K to the extent that running at brightness level "0" (which is 1/32 on the '7219) was barely dim enough for indoors and I had to adopt the 10K + trim-pot approach to give myself a sensible range.

As LED drivers I think these are both equally suitable for your purpose. It's really the interface that makes the difference. I also found '7219 to be hugely cheaper - of the order of 30p per chip off e-bay.