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Thread: Teensy 3.6 + Octo LED Performance

  1. #1

    Teensy 3.6 + Octo LED Performance

    I am experimenting with my new 3.6 and a very large array of LEDs (using the Octo shield). When I upload the Rainbow script from the Octo library example files, everything seems to freeze when I get to about 10,400 LEDs. For the Movie2Serial + Video Display script, it happens around 9,600. Is this what you guys would expect with the new Teensy or should I be troubleshooting something else? It seems to freeze at the same point even when I turn the brightness on the LEDs way down via the code.

  2. #2
    Senior Member PaulStoffregen's Avatar
    Join Date
    Nov 2012
    Yes, there does seem to be some sort of bug when more than 1365 LEDs per pin are used. I've put this one my list of issues to investigate.

    But even when this limitation is fixed, you still won't be able to use this many LEDs with VideoDisplay using 30 Hz video files, at least not with a single Teensy. There are 2 important hardware limits which no amount of software can solve.

    First, each LED requires 30 us, because it has 24 bits of data transmitted at 800 kbit/sec. To update the LEDs, 1100 per pin is the absolute maximum number of LEDs you can use and still achieve 30 Hz update.

    12 Mbit/sec USB is the other limit. 1100 LEDs per pin requires 26400 bytes of data per frame. That's 792 kbytes/sec to sustain 30 Hz. The best case scenario for 12 Mbit/sec USB is approx 1.1 Mbyte/sec. In practice, running over about 70% to 80% of the possible bandwidth risks all sorts of issues.

    I will work on fixing the 1365/pin limit. But when it's fixed, that many LEDs per pin will only really be usable when the animation is done locally on the Teensy, and only at slower refresh rates due to the 800 kHz data rate.

  3. #3
    I was just thinking about this problem again. Let's forget about all other issues besides the 12Mbit/sec USB limit. If my computer has 4 USB ports, does that mean all I can ever hope for is 4x1100x8 LEDs? If I use one of those ports to run a multi USB hub with ten ports does that mean I now have capacity for 4x1100x17 LEDs? If so, is there a limit to how many hubs I can connect (sorry this is probably a really stupid question to you guys)?

  4. #4
    sorry, i think that second estimate should have been 13x1100x8

  5. #5
    Anybody out there?

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