10`x 6` LED matrix 96x56 Resolution

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kodyaudette

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Hello everyone! I'm really glad I stumbled upon this forum, I've been looking for a method to build a large LED display to serve as a backdrop for a band, and I think I've finally found a good way to do it. I needed a way to show video clips (albeit at very low resolution) for ease of making animations for a live show and it seems like using a pair of Teensy boards with the OctoWS2811 Library and the Processing movie2serial Program would be a fairly solid approach.

I have a couple questions for you before I start ordering parts though, as this will be a fairly expensive project and I don't want to run into any avoidable issues.

Here are my design targets, most of which are flexible based on ease of build and practicality:

Overall screen dimensions: ~10' wide x 6' tall, or in metric, around 317cm wide x 125cm tall.

LED pitch: 30 LEDs/meter, or 3.3cm. I was initially looking at some pre-strung LEDs at 5cm pitch, but after drawing out a grid on the floor, I don't think that would really work too well without some sort of diffuser,and I think that the 3.3cm spacing of the 30 LED/m strings should work fine without diffusion, the viewing distance for this screen will be 5+ meters and it's acceptable for people to see the individual pixels, not to mention that fog/haze on stage will help to diffuse things a little anyway.

So as far as pixel resolution, that equates to roughly 96x56. These numbers are flexible in both dimensions if it makes more sense to group the strings differently, etc. but that's the approximate number I'm moving forward with. This means a total of ~5376 LEDs. As far as I can tell, two Teensy 3.2 boards should be adequate to control this many LEDs at very acceptable speeds, correct? I see that for a 3.0, a limit of 1000 is recommended, but that a 3.1 can handle 4000. Am I mistaken here? That would be 16 banks of 336 LEDs each. I know that power distribution can be a concern with such long strings of LEDs, however each vertical column of LEDs will be 56 LEDs and I will apply power to each column, while every 6 columns will comprise one "Bank" as far as Data goes. I estimate around 1300w of power draw at full white brightness and will be providing plenty of extra power supply and wire guage headroom to handle the currents required for so much power.

My total budget for this project around $1000, though I was really hoping to target closer to $800. The biggest costs are the LEDs, the wire, and the power supplies. Now I have received a quote for 180m of the 30 LED/m strip for two different voltages, 12v and 5v. Now I can see that it would be simpler to use all 5v since the Teensy Boards are happy with 5v, as is a Raspberry Pi which I am considering eventually using as the video source, but the difference in price between equivalent amounts of the 5v and 12v LEDs is substantial when buying this amount. I was quoted $504 shipped for the 12v and $792 for the same amount of 5v LEDs. Both are individually addressable WS2812, I assume the 12v ones just distribute the power in groups of 3 LEDs, but the Data signal should have the same voltage requirements as the 5v LED strings, correct?

After specing out the rest of the parts necessary, the difference in total approximate project cost would be ~$795 for the 12v strings, or around $1100 for the 5v Strings.

So my biggest question is, do you see any issues with running the Teensy boards off of USB power from a laptop, then getting an appropriate number/wattage of 12v supplies for the LEDs? If this works, it would have the added benefit of lowering the current on each of the power wires which would lower wire cost a bit and also give me the warm and fuzzies about being able to overspec my wire gauge.

Thanks for any help you can provide! I will definitely be documenting this whole process, and since it will be used as a backdrop for a band, there will be plenty of photos and footage of it in action.

Sorry for the long post, but I figure it's much better to be thorough!
 
I see that for a 3.0, a limit of 1000 is recommended, but that a 3.1 can handle 4000.

Confirmed. We built and documented a 4320 LED project last year. Worked great.

https://community.arm.com/groups/embedded/blog/2014/05/23/led-video-panel-at-maker-faire-2014

It also worked fine with movie2serial, even though all the documentation is showing it running stand-alone playing from a SD card.

I know that power distribution can be a concern with such long strings of LEDs, however each vertical column of LEDs will be 56 LEDs and I will apply power to each column, while every 6 columns will comprise one "Bank" as far as Data goes.

Power delivery is a hardest part of these big LED projects. Do not assume the LED strips are good conductors. Test with all LEDs fully on and measure the voltage drop. You can find prior conversations here and on other forums where someone wired up a huge panel and the LEDs towards the end of the strip were pink, due to voltage loss.

Remember, you're buying Chinese LED products at rock-bottom prices. Expect cheapness!

My total budget for this project around $1000, though I was really hoping to target closer to $800. The biggest costs are the LEDs, the wire, and the power supplies.

You may be greatly underestimating the practical realities of making a rugged product that can survive repeatedly being transported and set up on stages in less than ideal conditions.

Here's an article about a similar project, done a year before the lower cost WS2812s appeared on the market.

http://dorkbotpdx.org/blog/armatronix/led_video_wall

I was quoted $504 shipped for the 12v and $792 for the same amount of 5v LEDs. Both are individually addressable WS2812, I assume the 12v ones just distribute the power in groups of 3 LEDs, but the Data signal should have the same voltage requirements as the 5v LED strings, correct?

Don't assume ANYTHING. Buy a small quantity of each and test them yourself. You'll probably have some discovery about how the 12V ones really work. Do your homework!


So my biggest question is, do you see any issues with running the Teensy boards off of USB power from a laptop, then getting an appropriate number/wattage of 12v supplies for the LEDs?

That should work fine, if the grounds are connected properly. I'm personally run my 1920 LED test panel many times from its own power and the Teensy from USB power.
 
Paul, thank you very much for your swift reply!

It's good to hear that two Teensys should handle it just fine, also that it won't be a problem to use movie2serial.

I did indeed read examples of people getting color effects from poor power distribution. I'm definitely prepared to have to apply power at both ends of each column. I'm hoping that it wouldn't be necessary to add a power point in the middle of each string, but it could certainly be done.

Thank you very much for sharing the article about the similar project for the band STRFKR. The substrate that they mounted theirs in is great! One of the remaining issues I had been wrestling with was how I could keep everything both durable and break-down-able for transportation, I really like that they were able to mount the strips inside protective channels. I will definitely look into that as an option. I do understand that there will be substantial costs to this project that I'm not yet accounting for, that's the biggest reason I want to approach the issues I do know with a mind for keeping costs low. It's one thing going into a project with $800-900 of cost and expecting a couple hundred dollars more of surprises, but another still to go into it planning for $1200 and then getting another few hundred in surprises.

Thanks for your help thus far! Now that you've confirmed that my basic premise is fine I can order some small quantities and start testing. I'll also definitely look into the polycarbonate panels used in the project you mentioned. I think that may be the thing that makes a big difference in the overall reliability of this project. I will provide updates as I make any progress!

Kody
 
Well, I have found suppliers for the Polycarbonate panels, though the shipping costs may be prohibitive for the small order size I am looking at. I'm looking for a local supplier. If I can find that, then my plan moving forward will be:

1) Order one Teensy 3.2 board and OctoWS2811 adapter.
2) Order two meters of the 12v LEDs from the supplier I have been working with.
3) Order one of the 12v 30A power supplies I have Speced out.

This way I can verify:

1) I am able to successfully control the 12v LEDs with the data signal from the Teensy.
2) The power supply has sufficient and appropriate voltage.
3) I can determine whether the voltage drop over 2 meters (60 LEDs, the maximum length used in this project) of LEDs results in color shift, and whether I will need to supply multiple power connections.
4) I can verify that the LED strips I ordered fit into the cavities in the Polycarbonate sheets as expected.

After reviewing the successful project you linked to, I have adjusted a few parameters based on things they learned, so I will be doing 8 panels, organized as they did theirs. I will also use the bus wire concept for +V and Gnd to simplify wiring. I will not be using 32 smaller power supplies that would be mounted on each panel like they did, instead I will use four 12v 30A power supplies, each of which will power two of the eight panels. Because these power supplies are a bit larger than the laptop sized power supplies they used, and I would like to still be able to fold the panel up for transportation, I need the power supplies to be separate from the panel, but able to connect easily during set up, so I am planning for each of the four power supplies to have two sets of plugs that will connect to the bus wires on each panel.

My concern about this set up is that I need to establish a connector that cannot be confused with any other connection. This connection should only supply 12v DC, but with a 15A suitable gauge wire. I don't want to use standard 3 prong household style plug, because someone who is "trying to help" may connect it to 120v AC. I considered making cables with standard XLR connectors, which would work great, except for the possibility of someone trying to use a standard microphone cable in a pinch and trying to pull 14A across some 22 Gauge wire. I'd love to find some kind of connector that locks, for safety and durability reasons. Ideally it would not be the kind of connector that anyone could plug something incorrect into. Any suggestions?

I'd like to make as much of this project "idiot proof" as possible. I'm also planning to limit the output of the LEDs to help make sure that I'm not pushing the limits of anything in the system. I'm pretty sure that 5000+ LEDs will be plenty bright without being pushed to full power. The majority of the situations this will be used in are dimly lit stages.

Another thought on design that I had is that since I'm designing this such that there are no connections between the individual panels, I can design it so that the panel can be broken into two separate pieces for more stage options. Then I can set up different video schemes, etc. based on whether it's set up as one large screen or two separate screens.
 
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