I want to control multiple 10-segment led bargraph displays with my Arduino NG using the multiplexing capabilities of the MAX7221: http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1339
Ultimately I will have 8 7221's running 512 LEDs. I have found the library for programming the arduino to work with the 7221 (http://www.wayoda.org/arduino/ledcontrol/index.html), and have read about running 64 leds from one 7221. On page 13 of the datasheet they show 2 7221's multiplexed - this is what I'm using as a guide.
I am very close to understanding how it's all going to work, but I'm stuck on the actual wiring bit due to my limited electronics knowledge.
On my breadboard I have a bargraph (10 leds) and a single 7221. I did an earlier test adjusting the brightness of an led directly using a potentiometer, as well as blinking the led with a program via the arduino, and that all worked great. Now I want to wire the leds to the 7221.
This is how I currently have it wired - I have not put power to it as I suspect I'm doing something wrong:
On the breadboard I have a +5v rail and a ground rail I have a wire from the +5v rail over to a pad that has: - a 10k resistor running to [ISET], and - a 0.1uF cap running to the ground rail, and - a wire running to [V+]
I have wires from both [GND]s to the ground rail
so far I have wired 4 leds to the 7221 as follows: [DIG0] to the + of led 1, - to the ground rail [DIG1] to the + of led 2, - to the ground rail [SEGA] to the + of led 3, - to the ground rail [SEGB] to the + of led 4, - to the ground rail
I'm pretty sure this is wrong, since this is just a 1 to 1 correlation which even if it works will only give me 16 leds. I'm pretty sure I need to wire it differently to get the matrix behavior described in the datasheet and code articles, but the matrix diagrams are not translating into actual wiring for me.
Once I have this right I'll wire the [LOAD] [CLOCK] and [DIN] to the arduino and I should be ready to program, right?
Can anyone get me on the right track here? I am in way over my head and loving it. Please forgive any aspect of this question which seems completely stupid as I am a total amateur but learning fast now that I have my hands on the parts. :)