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Thread: Best way to drive huge LED Matrix Display

  1. #1
    Junior Member
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    Best way to drive huge LED Matrix Display

    Hi everybody,

    This is my first time writing in this forum.

    I want to build a long line of flexible LEDs with 8 rows of LEDs x (approximately) 10 meters long.
    If I use 144 LEDs / meter, that would result in 1440 LEDs x 8 lines = 11520 LEDs
    and finally play some animation on them (art project).

    I though about using neopixel LEDs originally.
    Adafruit NeoPixel Digital RGB LED Strip 144 LED

    then I noticed the LED matrix and to put them one after another:
    Flexible 8x32 NeoPixel RGB LED Matrix

    Since I have used Teensy, in the past I would like to continue to do so.
    My first candidate is to use the Teensy 3.5 together with the OctoWS2811 Adaptor board.

    • Do you think that is a good choice of micro-controller, is it even possible to drive so many LEDs with one Teensy 3.5 or do I need more than one?

    • Also should I use rows of strips or LED matrix and put them next to each other?

    • Does the OctoWS2811 LED Library handle the case of a display built with multiple LED matrix? or am I limited to use LED strips only?

    • I have also notices that there is a 144 LEDs/meter RGBW strip available now! Can I use the library with those strip (SK6812RGBW Datasheet) ?


    Any help is appreciated as I have not dealt with such huge number of LEDs previously.

  2. #2
    Hi,

    that's an interesting project. Therefore I had a look into the referenced adafruit pages (https://learn.adafruit.com/adafruit-neopixel-uberguide). Because you referenced it, I guess you did it too.

    The adafruit link contains notes on usage (suitable applications and not recommended ones) and offers code for Arduino Uno, etc.. A Teensy 3.5 is much more faster but you want to drive 10x8 RGBW strips which is a lot.

    In the end it depends what you really want to do where update rate is an essential point.

    Good luck and success

    NikoTeen

  3. #3
    Senior Member
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    See notes in the side bar for interaction of RAM and refresh rate at pixel counts increase
    https://www.pjrc.com/store/octo28_adaptor.html
    See power supply notes down the bottom of
    https://www.pjrc.com/teensy/td_libs_OctoWS2811.html
    OctoWS library doesn't currently support the white LED strips, I believe fastLED does but have not actually checked.

    OctoWS has several alternate layouts listed on those two pages but it's not particuarly hard to remap if you are after alternate option.

    As always with these things, before starting a project with thousands of pixels strongly suggest getting a couple of Teensys, ~40 pixels and doing some playing (few enough pixels that you can power from USB). all pixel strips can be feed more data than they have pixels on the strip without a problem, so you can write and test code for massive numbers of pixels and get a feel for memory use and timeing before spending massive amounts of $. Note that there are lots of build logs around, and a great many ways for projects like this to go wrong on physical reasons. You will need to test and expirment to work out how the practical elements of the build will work, and that design process will take at least as long as the code design. And don't order the final build list until you have built a couple of sub elements and added up how much time it takes to build AND test them and multiplied up. This is an expensive build but the man hours gluing, soldering and fault finding can dwarf the hardware price, especially if this needs to be portable or waterproof.

  4. #4
    Senior Member PaulStoffregen's Avatar
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    You should put some thought into how you're going to power 11520 LEDs. A tremendous amount of power will be needed.

    If you budget 65 mA per LED (the norm is 50 mA for RGB... presumably with 4 elements you ought to plan for 15 to 20 mA per internal LED), that adds up to 750 amps at 5 volts. You're going to need a lot of 5V power supplies!

    You will also need a lot fairly heavy gauge wires from those many supplies to the LED strips. A build strategy that distributes the power supplies evenly behind the display to keep the LED power wires short will really help. Inadequate power wiring is the most common failure of large DIY LED projects. Placing the power supplies away from the LEDs or using thin wires or not feeding strips in < 250 LED segments from both ends almost always results in terrible flickering problems due to poor power delivery.

    The other issue is this adds up to about 3750 watts. If you use cheap power supplies which are (hopefully) about 70% efficient, that translates to about 5350 watts drawn from the AC mains, if you light them all up a maximum white brightness. If you're in the USA, that's more than you can get from a standard 120 volt outlet with a 15A or 20A circuit breaker. With 220 volts AC, the max current draw ought to be about 24 amps, so you still might have issues if plugged into a service with only a 20 amp breaker.

    Cheap power supplies also tend to have pretty high inrush current, during the first half AC cycle when you switch them on. Better quality ones have power factor correction and other fancy input protect to play nice on the AC power line. But cheap ones have pretty much just a diode rectifier feeding a huge capacitor (or 2 in series), and maybe some minimal RF noise suppression. We built a display with 4320 RGB LEDs a few years ago as a test and managed to get away with six cheap 240 watt supplies without any sort of inrush current limiting. But if you scale up to much larger, you might need power up sequencing or some other technique to prevent all those power supplies from drawing a large inrush power up current at the same moment.
    Last edited by PaulStoffregen; 09-26-2017 at 09:23 AM.

  5. #5
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    Thanks for all the replies.
    I have access to pretty good power supply units. I have purchased a couple of these. Which can deliver 60 amps. Have a look at the datasheet and you will see that those are pretty much protected against any type of abuse. (I also don't plan to run them at full brightness at least not for more than milli seconds).

    My main concern at this point is that I need to use SK6812 RGBW Leds instead of the usual RGB WS2811 (or equal ones) since both fastLed and OctoWS library at the moment only support RGB Leds.
    I know that fastLEDs creator is planning to support RGBW in the future.
    Are there any plans to update the OctoWS library to support RGBW Leds?

    So I am forced to use the adafruit library to create the animation.
    just for testing, I am currently using Teensy 3.5 and the adafruit neopixel library to control a 500 LEDs and running some very basic animation. but the refresh rate is way to low.

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