8x8 LED Board Driver

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nocnotcaught
Posts: 3
Joined: Sat Jan 10, 2009 10:45 am

8x8 LED Board Driver

Post by nocnotcaught » Sat Jan 10, 2009 2:04 pm

Hi Paul

I want to thank you for allowing me to join your forum. The content and mode of discussion seems very positive and constructive.
You mentioned that you had found a pin for pin replacement for the STP16C596 chips used in your 8x8 LED Display Board. Can you tell me what that new chip is? I have also noticed that the 596 chips are fast becoming extinct. Another question that I have based on the constant references to memory limitations of the various RAM and EEPROM portions of the microcontrollers like 14k flash, 1k RAM, and 512 bits EEPROM for the Atmega 168 chip - Is it possible to add any sort of external memory chips or possibly double or triple-up on the microcontrollers themselves to extend the memory? This is probably a really dumb question but I had to ask.
Thanks.

paul
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Joined: Mon May 12, 2008 4:19 pm

Re: 8x8 LED Board Driver

Post by paul » Sun Jan 11, 2009 5:09 pm

Here are two chips, both available that appear to work - they seem to be pin compatible but I haven't tested either yet. On the todo list though.

A6279EA-T
Allegro A6276A

As to external memory, it certainly can be done. See Lady Ada's Wave shield and just steal the memory part of the circuit (and code!).
The important thing about using the Atmega168 though is that you need to get your storage into program memory with PROGMEM. That buys you 14K instead of 1k - not a great deal of storage but still a very large improvement.

I wrote some docs on PROGMEM when I first engineered the 8x8 - David Mellis, the chief Arduino honcho, in his ever impenetrable style, recently deleted the docs or moved them somewhere. He believes Arduino users should be shielded from all the same AVR code that makes Arduino useful apparently. I could go on about this but I'd start ranting insensibly.

In any case you might have to search the Arduino site for PROGMEME. Google "site:Arduino.cc PROBMEM" and you'll get the idea - you can also check my demo code for the scrolling sign which I believe used PROGMEM.

As to other solutions: The Atmega128 chip comes to mind (Wiring Board - although overpriced IMHO). You could check specs on Sanguino - I haven't done so thoroughly yet.

Paul

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