Driving 48 panels

The Dot Matrix Display (DMD) is a 32x16 array of high-brightness LEDs for visually striking effects. [Product Page]
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tommy_ent
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Joined: Mon Apr 29, 2019 7:51 pm

Driving 48 panels

Post by tommy_ent » Mon Apr 29, 2019 8:17 pm

Hi There,

I need to run a large number of panels (48, to be exact), and I need them to have one large scrolling RSS feed. From what I read, 6 panels is about the maximum that one arduino uno can handle.

Does anyone have any advice on how to go about this? I've looked into commercial solutions but so far nothing useful that doesn't cost a fortune. I'm think my best bet is to have every 6 panels have it's own sub controller, and have one master controller send data to the 8 subs. Unfortunately, I have no clue how to go about this.

I would really appreciate any guidance!

Brissieboy
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Re: Driving 48 panels

Post by Brissieboy » Mon Apr 29, 2019 11:22 pm

I suspect you will have a trouble achieving your goal with unos.
You are correct with the basic limit of 6 DMDs on a single uno, so you would have to set up a master/slave configuration. However I doubt a single uno as master could handle enough slaves.
And you would not be able to achieve any acceptable scrolling in that sort of configuration.
#stryker has had good success with master/slave uno setups on static (non-scrolling) scoreboard type displays so he might be able to offer more help.

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stryker
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Re: Driving 48 panels

Post by stryker » Tue Apr 30, 2019 12:09 pm

Hi Tommy

That's a really fine challenge. I never did try to scroll with the scoreboard so while I can confirm the master/slave idea tested fine it wasn't for this.

Thinking aloud though I expect you could setup each slave with the same string and using some pretty slick timing kick off the marquees delayed so that it appears to scroll from the left of one into the right of the next adjacent one. If you can imagine, the marquee effect starts with the DMDs blank and the text scrolls in from the right so as it vanishes "off the left" of the 6th DMD on the first (rightmost) slave you'd start it on the next one. If all hardware is equal, timing will be just a matter of maths.

As a sideline, I've yet to try driving DMD with ESP8266 based boards, but I've recently been using UDP over wifi to communicate between a bunch of NodeMCU for another project and if I was redoing the scoreboard today I'd try something like that rather than the spaghetti tangle of wires the scoreboard prototype featured for coordinating the slave boards. YMMV of course.

All the best with your project, and do keep us posted.
Geoff

tommy_ent
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Re: Driving 48 panels

Post by tommy_ent » Tue Apr 30, 2019 5:11 pm

Thanks guys, that's a good idea! I suppose that I don't need to break up the scroll if I can just have a bunch of different scrolls appear to be one. If you can't do something the right way, might as well do it the long way!

If I went the arduino route, what should I use to control the eight sub-unos? And how should I connect them? Maybe a CAN bus type system?

I don't have any experience with ESP8266 boards, but I'll do some googling and see what I can come up with. I've always been more of a mechanical guy but I'm quickly learning my way through the electronics side of things!

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stryker
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Re: Driving 48 panels

Post by stryker » Tue Apr 30, 2019 8:22 pm

The "master" or coordinator of this is actually less of a processor intensive task than driving the panels, so another ATmega328 based Uno will well cover that. Canbus is a bit of overkill I think for what you need - I used Serial, with software Serial to have each board controller in a daisy chain, and each controller had an ID so it would know to act on some messages not just pass them along. I used this retransmission to ensure the messages could get to every board regardless of distance. I initially thought about I2C but discounted it due to distance. There are chips that can help with extending I2C too but I didn't go that way at the time.

FWIW the 8266 idea is just to simplify the comms and cabling, but I've not used them on a DMD so it might be a dead end. You can program them as an Arduino just the same. You will need to do your own wiring though as the DMDcon ribbon interface board won't be compatible.

tommy_ent
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Re: Driving 48 panels

Post by tommy_ent » Tue Apr 30, 2019 11:34 pm

Good to know about the distance of I2C! I had been reading about that option but didn't realize it was only good for a meter or so.

I'll look into the software serial option a little more. Do you have a write up anywhere on how you did it?

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stryker
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Re: Driving 48 panels

Post by stryker » Wed May 01, 2019 4:25 am

Because our club didn't end up progressing this I've not published the code as it is, nor done a write up other than the posts in this forum. I actually pulled the test board apart about a month ago and threw out most of the custom PCBs etc. In hindsight they'd have been perfect for what you're chasing too.

I'll see what I've got, cut out the serial comms parts, add some comments as needed and send it your way. Hoping it's helpful though as it will be far more complex than you need as yours won't (necessarily in any case) require an address for each module as they'll all receive and display the same content.

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