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Thread: Software Question: Controlling LEDs

  1. #1

    Software Question: Controlling LEDs

    Does anybody have software suggestions for controlling an array of 70k WS2812 LEDs? I have used Paul's movie2serial script and Glediator on some smaller displays I have built but I am having trouble scaling them up. Is there software that could allow me to display pictures, movies or camera feeds on that large of an array?

  2. #2
    Senior Member+ MichaelMeissner's Avatar
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    According to the Octows2811 page (https://www.pjrc.com/store/octo28_adaptor.html) if you go past 4,416 LEDs, you can no longer do 60Hz refresh rate (due to the required communication rate for the WS2812's). If you go past 8,832 LEDs you can no longer do a 30Hz refresh rate. I suspect you probably want to break it down into smaller chunks and multiple Teensies, as you no longer have moving pictures if it is less than 30Hz.

  3. #3
    Thanks @MichaelMeissner. Yes, I would need to use multiple Teensys. I didn't realize that limitation existed because of the Teensy itself. Maybe my problem is the hardware and not the software but I thought the Teensy could handle many thousands of LEDs. I that just for static pictures and pre-programmed effects? I guess you are saying that I need about 17 Teensys if I want a 60Hz refresh rate.

  4. #4
    Also, are those refresh rates still true for the 3.5 and 3.6? I am using a 3.2 right now.

  5. #5
    Senior Member+ MichaelMeissner's Avatar
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    As I understand it, the WS2812's have a mandated period of time for each LED before passing the remaining signals to the next LED down the chain. Even if the Teensy is infinitely fast, that communication penalty will get to you with really long strands of LEDs (plus all of the fun things like powering 70k LEDs, and maintaining the signals). You need to find somebody who has done some of the big walls. I'm out of my depth.

  6. #6
    The strips are organized in rows of up to 300 each. I was definitely planning to use more than one Teensy but, you raise a good question, how many LEDs can be on one Teensy and still have a good refresh rate. Also, does anybody have a suggestion on what software to use?

  7. #7
    Senior Member PaulStoffregen's Avatar
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    The main number to keep in mind for the length of your LED strips is 30 us per LED. If a strip is 500 LEDs long, it will take 15 ms, which is still what most people consider "good" refresh rate (assuming all the other code is fast enough to deliver all the data every 15 ms).

  8. #8
    That is good to know. That sounds like the strips can handle a 60Hz refresh rate. Does the Teensy itself have any limitation in that regard? Do you know of any software that can handle that setup?

  9. #9
    Senior Member PaulStoffregen's Avatar
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    Many people have built displays in the 10,000 LED scale running at 60 Hz refresh using OctoWS2811. It will probably scale up higher, but so few people build much larger displays and the small number who do usually have corporate funding that limits their ability to share feedback, so there just isn't a lot of experience beyond "ought to work" and we've seen some bigger projects but don't know if they managed full 60 Hz.

  10. #10
    How many LEDs do those people put on each Teensy to preserve a 60Hz refresh rate? Do they just use a USB hub to expand the number of ports to communicate with or does that create bottlenecks as well?

  11. #11
    Senior Member PaulStoffregen's Avatar
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    Quote Originally Posted by BuffaloFan32 View Post
    How many LEDs do those people put on each Teensy to preserve a 60Hz refresh rate?
    No more than 4000 LEDs (8 strips of 500) per Teensy.

    You'll need a Multi-TT USB hub to sustain full 60 Hz refresh to multiple boards. A cheap Single-TT hub won't do.

  12. #12
    This is helpful, thank you! Sorry to be a pain but how do I limit the refresh rate in the software? So far, I have mostly been using the movie2serial program that you wrote in Processing. Isn't that just spitting out strings as fast as my computer can process them? I have noticed that the array works for a lot more LEDs when it is running something simple like the rainbow or fire example programs but crashes when I try to scale up anything having to do with video fed from my computer.

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