recently i could get many led matrix (8x8) displays, so i bought 16! with in my mind an idea to build a large supercool display, with a total of 1024 PIXELS!
but how do i connect them to the arduino? i read something about the MAX7221, an IC to control a 8x8 display that can be daisychained (that's what it's called right?)
but is it possible to daisychain 16 MAX7221 and then easly control it with 1 arduino? (i'm a bit of an beginner with the arduino.
is there maybe another way to connect multiple matrixes to the arduino?
There are lots of ways to connect LED matrix display to the Arduino! Have you looked at all the examples on the Arduino web-site? It would help us to advise you if you could say what you've done already, with the Arduino. Are you confident to connect, say, a single MAX7221 or MAX7219 top the Arduino? Have you done anything with other shift-registers, like the 74HC595?
i think i can connect 1 max7221, but i is it possible connect 16? (2x8 led array)
Just to be clear,
MAX7221 = $4 ~ $9 each
74HC595 = $0.40 ~ $0.90 each
These assume a single 8x8 display. Mostly just multiply for larger displays.
MAX approach:
one MAX for red, one MAX for green, one MAX for blue
memory contents updated by serial only when display must change
chips refresh displays from the internal memory without help
chips have constant-current gates so no external resistors
no PWM per pixel
74HC595 approach:
one 595 for red, one 595 for green, one 595 for blue, one 595 for anodes
no memory for refreshing image (processor must always help)
no constant-current gates so you need 8 resistors for red, ...
no PWM per pixel
I would really like to see what it would take to finish out a 74HC595 solution that uses a local serial command port, a RAM package, a local clock, and a couple of octal counters to drive the display. I think the cheapest approach becomes a dedicated ATmega*8 per display to handle all this. At the prices of MAX parts, this might be comparable.
halley,
Very nice job of comparing the two approaches. 
I would just like to add one caveat - regarding the MAX approach, I have not confirmed that anyone has successfully driven a 3 color matrix with the MAX. (2 or 3 were very close but "disappeared" before they confirmed success.) Two colors, is no problem.
Lately, I've been asking myself (and this scares me a little : ) what's the point of driving a 3 color display without PWM? I mean, if you are going to the trouble and expense, it seems a shame to be stuck with only 7 colors.
I might be mistaken, but I thought I heard of a chip that might enable RGB PWM ? (the Holy Grail!).
It amazes me that with all the LED signs in the world, we don't seem to have an elegant solution for this problem.
Hello world, I want 8x8 RGB PWM for under $25 without a lot of supporting do do going on in the MCU!
Lately, I've been asking myself (and this scares me a little Roll Eyes ) what's the point of driving a 3 color display without PWM? I mean, if you are going to the trouble and expense, it seems a shame to be stuck with only 7 colors.
Would this little gem be of any help?
about the max7221 ic's, i sampled them ( i know it's bad)
my led matrix displays are one color, red and i don't need pwm.
just a minute ago i read this
he uses an HEF4794 , apparently that's an shift register, but with the power to drive many led's (am i right?)
is this an better solution?
koyaanisqatsi - thanks for the link. That's the chip I couldn't remember during my rant. I couldn't tell if it can be applied to an 8x8 matrix. I'll look into it more.
oddish2211 - I'd say if you have 1 color and the MAX chip already, that is the way to go. Check out the Playground for examples and libraries (LedControl) that make it easy to use. With the MAX your sketch can concentrate more on what it needs to do.
(Personally, I don't think there is anything wrong with free samples - I'll always feel the proper guilt and indebtedness to Maxim - and in my next life . . .)
i sampled them, but i don't have them yet.
about this page
http://www.arduino.cc/playground/Main/LedControl
it's in my bookmarks, but this library can control a maximum of 8 display's. is it possbile to run the software twice so it can control 2 rows of max7221?
nr. 1 does the upper 8 panels and nr 2 does the lower 8 panels.
about the sampels, i know almost certain i'm gonna do something in electronics, so i'l let my future boss know i need to buy 10.000 max7221's 
From the page you reference. . .
If you need to control more than 8 MAX72XX, you can always create another LedControl-variable that uses 3 different pins on your arduino-board. The only thing you have to do is to initialize another LedControl
So yes, it seems possible. (But you may be the first to try it! 8-))
and how do i initialize another LedControl? do you know that?
RTFM! - i.e. It's all covered in the Playground article you referred to.
Hi guys,
I got a lot of 4021 and some darlington divers : the UDN 2981.
So, my question seems to be, is there a way to drive a RG matrix, 16x16, with pwm, using these parts, or transistor gates in worst case.
I do not really catch the difference between the 4021s and the commonly used 74HC595.
Thanks