[dorkbotpdx-blabber] Advice on large LED matrix

[Donald Delmar Davis]

Dallas,

Because you have indicated that brightness is a priority then you are  
going to be looking at driving them in a row column fashion and the  
number of columns is going to be limited by the need for brightness.  
For around $13 per 8x8 array maxim puts out a pretty clean solution  
which will do a lot of the work well. In the most people can afford it  
range you will be looking at shift registers and transistors sourcing  
the current and depending on the current of each led something  
standard sinking them like a 74x595/6 or a high current version of  
something standard like the tpic series of chips from ti. The need for  
light also more or less negates the other obvious solution which is to  
directly drive (through current limiting resisters) an array directly  
using the xxduino. The avr can source sink over 10ma  per pin but  
there is a cumulative limit which is in the electrical characteristics  
section of the fine datasheet.

I have purchased the parts to experiment with a circuit that was in  
Circuit Cellar a few months ago but I haven't had much time to lay out  
the boards so It wont be this year. In the interest of killing the  
thought you might look at several of the open source "products" out  
there for guidance..

Again we missed you yesterday.

Don.

On Dec 9, 2008, at 10:37 AM, dan p wrote:

> There is a way called Charlieplexing, the problem for your project  
> might be brightness. The downside is that due to strobing the  
> brightness is divided. If you need max brightness this sort of  
> multiplexing isn't the way to go.
>
> On Tue, Dec 9, 2008 at 10:05 AM, Mykle Hansen <mykle at mykle.com> wrote:
> i'm interested in this question as well.  i've been told
> that N shift-registers, combined with an arduino, can
> control N^N or so LEDs.  but then a friend sent me this
> article about how to control a small LED array with no
> shift registers.  it only lets you strobe the LEDs one
> at a time, but due to POV it can work, at least up
> to some limiting size of grid.
>
> http://www.instructables.com/id/How-to-drive-a-lot-of-LEDs-from-a-few-microcontrol/
>
> i think someone actually showed me this at a dorkbot meeting
> a month ago, and i recall staring at it and not getting
> it at all.  but now i do.  a handy trick, for sure.
>
> (there's another instructable linked from that one which
> goes into the theory of this -- calling it "charlieplexing"
> -- and it's a pretty easy read, for electronics:
>
> http://www.instructables.com/id/Charlieplexing-LEDs--The-theory/
> )
>
> at any rate, controlling N output lines from one arduino
> will be a recurring need for humanity.  if there are
> other classic approaches with pros and cons, i'd love to
> read a summary.
>
> -m-
>
>
> On Dec 9, 2008, at 12:16 AMTuesday, dalas v. wrote:
>
> I'm thinking of building a matrix of RGB LEDs. Brightness is a  
> priority. Size would be maybe 1 or 2 square feet. Battery power  
> would be preferred, but if there is a need for AC power, I'd need to  
> use a prebuilt power supply, because I don't want to attempt making  
> one. Minimum control would be 32 color options (preferably more),  
> maybe you can program 8 - 12 sequences and switch between them?
>
> It seems like the arduino might be able to handle this? It would be  
> my first arduino project. I know that it can control LED matrices  
> and sequences, how would it be for a large matrix and how big /  
> bright can I get?
>
> I'm in the really early stages with this, so any advice or links to  
> kits would be appreciated.
>
> -dalas
>
>
>
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