more LEDs than a single MAX72XX can handle

Forum 2005-2010 (read only) Hardware Interfacing
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Hi. I'm new here. I'm also fairly new to circuit design. I've made a few things, but never with a PIC, arduino, or anything like that.

My plan is to wire up a bunch of LEDs in a grid somewhere between 5x16 and 6x17. I'll know my size constraints once something arrives in the mail. Anyways, with one MAX72xx I can (read: will fail to) wire up 64 LEDs, and the datasheet says that more MAX72XXs can be cascaded through DOut->DIn. Does this mean that I can individually control up to 128 LEDs with two MAX72XXs, brightness and all? Or does it just mean that [u]this[/u] wiring of two MAX72XXs is achievable, so that each group of up to 64 LEDs behaves identically?

Also, since this thread might attract people knowledgable in similar areas, I have two more questions: 1) Regular LEDs arranged in a grid are big...do smaller LEDs that can be densely packed exist that won't break my budget? 2) Know of a cheaper place than [u]this[/u] to buy the 7219 (cheap already, I know, but worth a shot.)?

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Hi,

Does this mean that I can individually control up to 128 LEDs with two MAX72XXs, brightness and all?

With the LedControl-lib
http://www.arduino.cc/playground/Main/LedControl
you can drive up to 8 MAX72XX, so this is good for 8x64=512 Leds

You can switch each one of the 512 Leds on and off individually, but brightness can only be set for all the 64 Leds controlled by a single MAX72XX. If you need individual brightness for each Led, the MAX72XX can't do this.

(You didn't ask for this, but it is one of the common questions with this chip:)
The other problem with the MAX72XX is that it wasn't made to control RGB-Leds, or more general : Leds of different color connected to a single MAX72XX.
If you're fine with all 64 Leds having the same color the MAX72XX is great .

  1. Know of a cheaper place than this to buy the 7219 (cheap already, I know, but worth a shot.)?

There is a company from austria that produces a much cheaper replacement for the MAX7221:

There was a posting somewhere on the Arduino-forums that said it worked fine with the LedControl-Lib.

Eberhard

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I can answer both of your questions...
Firstly I was also looking for cheap LED matrixs' a few months ago, ebay is a great place to look.
http://cgi.ebay.com/10-pcs-8-8-Dot-Matrix-1-9mm-dia-LED-Display_W0QQitemZ250504999770QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item3a5342f35a&_trksid=p3286.c0.m14
these are cheap and work great. There are also Bi color and RGB available.

Secondly, I too was not willing to pay around $10 per max72XX chips. You can get several for free if you request samples from the Maxim website. I bought AS1107 chips from Newark, and also requested some samples from austriamicrosystems. These work fine with the Led Control and matrix libraries already available for the Max72XX chips.

These 24 X 16 displays by Sure Electronics on eBay are also a great place to start.
http://cgi.ebay.com/24-16-2416-Dot-Matrix-Red-Display-information-Board_W0QQitemZ350258244594QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item518d04abf2&_trksid=p3286.c0.m14
There is a thread already on here explaining everything you need to get started with it.
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1225239439/all