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On 5/20/12 9:40 AM, John Adams wrote:
<blockquote
cite="mid:CAO9uaO1yCinzGJRoVvqNX_d+6P4JmhG-m=Db6WykEEsMeL0mYw@mail.gmail.com"
type="cite">On Sun, May 20, 2012 at 9:18 AM, Daniel Pitts <span
dir="ltr"><<a moz-do-not-send="true"
href="mailto:Daniel@coloraura.com" target="_blank">Daniel@coloraura.com</a>></span>
wrote:<br>
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<div style="font-family:-moz-fixed;font-size:12px"
lang="x-western">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. <br>
</div>
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</blockquote>
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<div>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. </div>
<div><br>
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<div>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. </div>
<div><br>
</div>
<div>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.</div>
<div><br>
</div>
<div>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.</div>
<div><br>
</div>
<div>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.</div>
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<div>-john</div>
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</blockquote>
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. <br>
<br>
I do see however how a shift register in general will be a helpful
tool to have in my toolbox. <br>
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