A question regarding power (4 DMDs + eleven)

The Dot Matrix Display (DMD) is a 32x16 array of high-brightness LEDs for visually striking effects. [Product Page]
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A question regarding power (4 DMDs + eleven)

Post by Ragnarokandroll » Fri Sep 19, 2014 7:24 am

Hey all,

I'm eyeing the DMD for a project I want to do. It would involve daisy-chaining 4 DMDs vertically and using an Eleven board.

I'm 100% new at this and only have an extraordinarily rudimentary understanding of Electrical Engineering.

I did some forum searching, and I *think* I understand what the power needs would be, but I thought it might be best to ask directly anyway since none of the posts I found really directly answer my question(s). Be warned: some of them are probably going to sound comically stupid to you guys...

- I understand that to power 1 board at maximum brightness, I'd need a 5v, 4a power supply of some kind, powered separately from the Eleven / Arduino. The number of amps needed = # of DMDs x 4. So for my intents and purposes I'd need at least 16amps...right?

- Can the eleven board be powered as well by the same supply in some way, so that the thing I'm making ends up having one plug that goes into the wall as opposed to two (or more)?

- If I use an ATX power supply as some suggest, is there an easy way of finding out which of the 45 billion wires is 5 v ? Does one need to string a different wire to each DMD, or are they supposed to be daisy chained? I understand you're supposed to connect all the grounds to one another...I think?

- Another forum post mentioned each DMD can only have 1/4 of its LEDs lit up at any one time. Yet I see in the demo this is not true as the entire board lights up. What's the deal with that?

- Will the DMD's LEDs wear out over time if some LEDs are left on (static)?

I'm sorry for these hideously dumb questions. I'm just trying to avoid injury, death, or worse: wasted money. :mrgreen:

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Re: A question regarding power (4 DMDs + eleven)

Post by Palomar » Sat Sep 20, 2014 3:54 am

Hi Ragna,
I'm no expert as I'm also developing my first project using DMD hardware. However, I can offer a few observations...
>I have six 32x16 panels which I believe are essentially the same as the red DMD units sold by Freetronics, connected to an Aduino Nano, with juice provided by a cheap 300 watt ATX power supply. It runs fine with a 5 amp fuse on the 5V line, but it will blow a 2 amp fuse.
>I can turn on all 6 panels at full brightness via the dmd.clearScreen command, no problem. Of course, only 4 rows in each panel are actually lighted at any moment, but the driver circuit cycles thru the rows so fast they just APPEAR to be all on. It's a trick that fools the human eye, but it does not fool a video camera.
>Assuming that the Eleven board is basically an Aduino clone, you can run it on the same 5V line that powers the LED panels. By the way, beginners (like me) tend to hook the wrong wire to the wrong thing and -- $!*%#! -- that's the end of the microprocessor. That's why I'm using cheap (mini-USB) Arduinos like this http://www.ebay.com/itm/Mini-USB-Nano-V ... 1297932221 or http://www.ebay.com/itm/Mini-USB-Nano-V ... 4ad72f2666 For that price, you can order a half dozen.
>On the ATX power supply, you can use any red wire for 5V and any black wire for ground. Note that you must connect the lone green wire to any black wire in order to turn the power supply on. I have a mini on/off toggle switch between green and black for this purpose.
>I don't think that LED's "wear out" over time, but I would shut it off when not in use.
>For more info, see http://forum.arduino.cc/index.php?topic=260320.0
>And a photo of my R&D rig using two panels...http://i351.photobucket.com/albums/q452 ... _4620x.jpg

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Re: A question regarding power (4 DMDs + eleven)

Post by stryker » Sat Sep 20, 2014 7:42 am


Additional to the good advice above I can confirm I'm also using 6x DMDs with a scavenged ATX power supply and while we use a custom board I do a lot of debugging with an eleven. On the custom board the power is shared on the 5V rail of the ATX supply so that works fine. But for the debugging eleven I use the 12V rail into the 2.1mm power jack. There's no science behind that, it's a choice purely based on convenience. I'm just using the dangerous prototypes breakout for the ATX supply when debugging, and it only has 1x 5V, 1x 12V but 2xGND.


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Re: A question regarding power (4 DMDs + eleven)

Post by Palomar » Mon Oct 27, 2014 11:02 pm

Just for the record, I should update my comments above, now that my project is fully operational.

As mentioned above, I'm using 16x32 monochrome (red) dot matrix panels for a total of 12 now. As the project progressed, I found I needed more and more power to maintain voltage, along with heavier wiring. I now have a 40 amp power supply using two short 12-gauge wires to get the juice to the DMD panels. The PS is dialed back to 4V, and I estimate I'm running 30 amps.

On the 12 panels there are a total of 6144 LEDs. The way I use my displays, a max of 2400 LEDs are turned on. But due to multiplexing, only 1/4 of those are lighted at any one time. So 600 LEDs are using some 30 amps at 4 volts, i.e., 120 watts.

To light all 6000 LEDs without multiplexing would require about 1200 watts. With 1/4 multiplexing, it would be about 300 watts.

For more info and photos, see http://forum.arduino.cc/index.php?topic=260320.0

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