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Thread: Large Scale WS2811 Build, Need driving advice

  1. #1
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    Large Scale WS2811 Build, Need driving advice

    Hey Guys, I need some help

    Here is the project thus far:
    Me and my club are working to build a 120x64 LED matrix capable of displaying video. The current plan is to have 4 panels that attach together. Each panel will host 2 teensy 3.0s, each driving 8 horizontal lines of 120 WS2811 LEDs. So in total each panel will host 120x16 LEDs. These will be powered by 2 300W power supplies on the back of each panel, so 8x300W = 2400W total. ~20A at 120V, so we will plug into two different line supplies (It is hard to come by a 220V plug around here). The panels then interconnect to form the full matrix. Currently we are working on getting all of the parts together to build the matrix itself. It will end up being 2 meters wide by 1 meter tall (not including the stand).

    The plan then is to test out the OctoWS2811 code with Paul's video display program running on a PC with a USB hub to connect the 8 teensys running the panels. If that works just fine I want to find a better way to drive the display. As in, a way that doesn't need my computer driving the whole thing. Currently I am thinking the BeagleBone Black(BBB) seems like a pretty good option. I saw Paul's post about using the BBB to display .gifs at his makerfair booth and streaming a web cam to his display. (http://www.dorkbotpdx.org/blog/paul/maker_faire_2013) I would like to do something similar here.

    The real question is, will the BBB be able to output to all 8 teensys without any hickups? Could I modify the code that was posted for that maker fair display to stream the webcam video to the display? And the ultimate goal would be to use one of these: http://www.amazon.com/StarTech-SVID2.../dp/B000O5RIWO to get frames from an outside source and play them on the LED display. This way we would be able to plug in a gaming system and play off of that. Although, now that I think about it I could just use an emulator on the BBB and find some way to output to the LED display. I personally am a Linux noob so that may be a bit of a long shot.

    If anybody has some advice it would be much appreciated.

    Also, side note, how to get audio out of a BBB with it is running the display. I am thinking a DAC on a few of the pins would work?

  2. #2
    Senior Member PaulStoffregen's Avatar
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    Quote Originally Posted by Intrinsic_Eb View Post
    The real question is, will the BBB be able to output to all 8 teensys without any hickups?
    I saw about 20% to 30% CPU usage on the Beaglebone Black, so I'd say the odds are good you can scale it up to a 4X larger display. Some of that CPU usage is probably fixed, some probably will scale 4X. You might end up close to 100%. You'll just have to give it a try and find out.

    When I talked with Jason Kridner (the Beaglebone guy from Texas Instruments) at Maker Faire, he mentioned more efficient USB drivers were in beta testing. That was back in May, only a couple weeks after the first BBBs were available, so I was running on the earliest publicly released version. Maybe those more efficient drivers are now standard? If they are, it will probably help quite a bit. I know lots of other stuff on the BBB software has improved since then.

    Again, you'll probably just have to hook it up and try it. OctoWS2811 doesn't know or care if LEDs are actually connected, so you could pretty easily do a "dry run" with code on the BBB and 8 Teensy3s connected, without any actual LEDs.


    Could I modify the code that was posted for that maker fair display to stream the webcam video to the display?
    It already does that. I used it with a Logitech 9000 webcam.

    But it doesn't do any gamma correction or other processing on the video, other than a very simple crop and scale down to the lower LED resolution.

    And the ultimate goal would be to use one of these: http://www.amazon.com/StarTech-SVID2.../dp/B000O5RIWO to get frames from an outside source and play them on the LED display.
    The code I published uses the v4l2 library, so pretty much any v4l compatible video device ought to work. I hard-coded the input resolution to 320x240, so using my code as-is, it will only work with sources that support scaling to that resolution. But you could probably edit the code if you have reasonable skill in C programming.
    Last edited by PaulStoffregen; 10-17-2013 at 07:27 PM.

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