Sanity check on LED matrix design idea.

[Daniel Pitts]

Hello,

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.

My goal is to have something that will allow several "brightness" values
for each LED. In other words, I'd like each LED to be able to be
independently one of: full bright, 3/4 bright, 1/2 bright, 1/4 bright,
full dark.

The design has 3 of the Arduino outputs connected to a 74HCT138, to
decode the "column", and then 8 other pins connected to each of the
"row" (with appropriate resisters).

The software part of this would run through each column, and enable the
appropriate rows. I'm hoping to put this process on a 4ms timer, so
that I can interleave on/off states depending on the desired brightness,
and still have the entire matrix update at around 50hz

Does this seem like a reasonable approach, or is it likely to cause too
much flicker? Does anyone know if the 74HCT138 can keep up with this
pace? How about the Arduino? I'll be doing more than just the display
part of course, since I'll have to actually create something worth
displaying.

Thanks,
Daniel.

 

[Rich Webb]

On Sun, 20 May 2012 09:12:38 -0700, Daniel Pitts
<newsgroup.nospam@virtualinfinity.net> wrote:

The software part of this would run through each column, and enable the
appropriate rows. I'm hoping to put this process on a 4ms timer, so
that I can interleave on/off states depending on the desired brightness,
and still have the entire matrix update at around 50hz

Does this seem like a reasonable approach, or is it likely to cause too
much flicker?

50 Hz may be visible, especially at lower brightness levels, although
some people seem to be more affected than others. Try making the scan
rate a "tunable parameter" just to see whether, and how much, you're
affected. After all, that's the benefit of playing with real components.

Does anyone know if the 74HCT138 can keep up with this
pace?

Easily, but read the datasheet!

How about the Arduino? I'll be doing more than just the display
part of course, since I'll have to actually create something worth
displaying.

It depends on how you get there and what else is going on but probably
yes.

--
Rich Webb Norfolk, VA

 

[Jasen Betts]

On 2012-05-20, Daniel Pitts <newsgroup.nospam@virtualinfinity.net> wrote:

The software part of this would run through each column, and enable the
appropriate rows. I'm hoping to put this process on a 4ms timer, so
that I can interleave on/off states depending on the desired brightness,
and still have the entire matrix update at around 50hz

50hz refresh is typical of digital alarm clocks where I live.

Does this seem like a reasonable approach, or is it likely to cause too
much flicker? Does anyone know if the 74HCT138 can keep up with this
pace?

74HCT138 is good upto several megahertz.

How about the Arduino? I'll be doing more than just the display
part of course, since I'll have to actually create something worth
displaying.

Should not be a problem I saw a video on youtube of a few thousand
LEDs being driven with a video signal by an arduino,

--
⚂⚃ 100% natural

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