MAX Number of DMD

The Dot Matrix Display (DMD) is a 32x16 array of high-brightness LEDs for visually striking effects. [Product Page]
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JammerJar
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MAX Number of DMD

Post by JammerJar » Sun Feb 28, 2016 5:49 am

I don't seem to be able to find a definitive answer to this simple question.

Whats the maximum number of DMD that I can daisy chain and run of one Arduino?

I have done four but can you do 8, 16, 32?

Cheers

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stryker
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Re: MAX Number of DMD

Post by stryker » Sun Feb 28, 2016 8:53 am

I've driven 6 after tweaking the SPI divider value in the DMD library so I've used that as a rule of thumb for ATmega328 based boards. With the standard settings I don't think you get past 4. To be fair though I haven't tried the same tests with the new DMD2 library.

andrew
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Re: MAX Number of DMD

Post by andrew » Tue Mar 01, 2016 4:56 am

Stryker is spot on, six is the usable limit.

pitas
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Re: MAX Number of DMD

Post by pitas » Mon Mar 21, 2016 10:36 am

Hi, just found out about DMD library, and it looks great.

I found out trying to get ideas to build a very large scoreboard, around 20 DMD's panel's, i realised very quickly that's not possible because of refresh rates on an AVR arduino.

So the question is, it would be possible to drive them all with an arduino DUE? being it an ARM at 84Mhz?

If not could i use slave AVR's to drive each row (4 panel's for row)? If so how do you drive the slave AVR's? I mean, imagine drawing a text message bigger than one row, you have to break the information for the upper and below row's and send them do the slave's!!!

Sorry for the noob question's!

Regards.

andrew
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Re: MAX Number of DMD

Post by andrew » Mon Mar 21, 2016 10:53 am

To run 20 ... falls outside the scope of the display ecosystem with Arduino/AVR/SAM etc.
You would really want fewer number of large panels and a dedicated control board - a more commercial situation.

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stryker
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Re: MAX Number of DMD

Post by stryker » Mon Mar 21, 2016 11:13 am

pitas wrote:If not could i use slave AVR's to drive each row (4 panel's for row)? If so how do you drive the slave AVR's? I mean, imagine drawing a text message bigger than one row, you have to break the information for the upper and below row's and send them do the slave's!!!
I'm currently working on a digital scoreboard with 32x DMD panels (refined down from 59 since I made that original concept post). I'm doing something similar to your slave suggestion, but rather than per-row my approach has been to have an ATmega328p per display element (score, quarter, game clock, team name etc) where each of those has up to 6 DMD only. That way I can use a 2xDMD tall font, and a group of 2x2 DMD can display 4 digits.

As you suggest, if you were to control the scoreboard row by row you'd need some way of breaking up the displayed content.

Geoff
Last edited by stryker on Mon Mar 21, 2016 11:20 am, edited 1 time in total.

pitas
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Re: MAX Number of DMD

Post by pitas » Mon Mar 21, 2016 11:17 am

Thanks Andrew, i did look for some commercial control boards, but they have their own software to update the data for the display, and what i want is to write a program in C that updates the display data and i can't find a controller to do that!

Do you know of any controller that you can write data directly to it?

Thanks.

pitas
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Re: MAX Number of DMD

Post by pitas » Mon Mar 21, 2016 11:27 am

stryker wrote:I'm currently working on a digital scoreboard with 32x DMD panels (refined down from 59 since I made that original concept post). I'm doing something similar to your slave suggestion, but rather than per-row my approach has been to have an ATmega328p per display element (score, quarter, game clock, team name etc) where each of those has up to 6 DMD only. That way I can use a 2xDMD tall font, and a group of 2x2 DMD can display 4 digits.

As you suggest, if you were to control the scoreboard row by row you'd need some way of breaking up the displayed content.

Geoff
Thanks stryker, initially i was planing on using 8x8 font, that way i could have 2 lines of text per row and everything would be fine, cause i could drive each independently, but then i realised that font was too small for what i wanted, and a 16px font is to big, so i ended up with the problem of using a font with 10px or 12px height, the second line of text falls into the row below.

I guess i could try to drive 2 rows of 4 DMD's each, but that's outside the maximum of 6 DMD's panels either.

Thanks for your info.

pitas
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Re: MAX Number of DMD

Post by pitas » Mon Mar 21, 2016 5:10 pm

Another quick question!

I've seen 2 kinds of daisy chain connection, one like this:
http://www.adebenham.com/2012/02/freetronics-dmd-games/

where every odd row is upside down to allow connecting a small cable (Good for high speeds transmission).

and another one with a "cross" pattern.

What is the actual connection in the DMD/DMD2 official library?

Thanks for the help!

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