[Noisebridge-discuss] Sanity check on LED matrix design.

Daniel Pitts Daniel at coloraura.com
Sun May 20 20:19:28 UTC 2012

On 5/20/12 9:40 AM, John Adams wrote:
> On Sun, May 20, 2012 at 9:18 AM, Daniel Pitts <Daniel at coloraura.com 
> <mailto:Daniel at coloraura.com>> wrote:
>     I'm going to try to make a simple LED matrix display powered by an
>     Arduino, and wanted to validate my approach with the more
>     experienced people here.
> Lag time on that chip is proportional with temperature. On a good day, 
> at room temp (+25C), it'll pass an input to an output at 15nS or so. 
> Get the chip hot and it'll get really bad.
> Given the Arduino's speed and the small size of your display you could 
> probably just clock the entire display as a gigantic shift register. 
> This is what commercial LED displays like the Translux data wall do, 
> and do well.
> Use a 74HS164, tie one pin to clock from the Arduino, and another for 
> data. Tie all of the reset lines together and tie that to another 
> arduino pin. The operation at that point is reset -> clock data 
> through -> rinse -> repeat.  Vary the on-durations in the bitstream to 
> change display brightness.
> As your display gets larger and larger you'll have to increase the 
> update frequency of the clock. Eventually you'll exceed the clock 
> speed you can output from the arduino's pins and you'll have to take 
> other approaches like outboard memory, etc.
> The beauty of the shift-register approach is that you can scale for 
> larger displays just by adding more LEDs and changing the clock 
> frequency. Adding color is stupidly easy too. Just add more shift 
> registers.
> -john
I *almost* see what you're talking about here.  The I found the 
datasheet for74HC164 (not the HS?),  It appears to be an 8bit shift 
register. I'm not sure how that'll be useful for powering an 8x8 
display, unless you meant one per row, or unless you mean for me to find 
a shift register with larger capacity.

I do see however how a shift register in general will be a helpful tool 
to have in my toolbox.
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