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Thread: Various problems with an LED display I've made

  1. #1
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    Various problems with an LED display I've made

    Hi there,

    This is precisely what I've built:



    It is wired in the exact same manner, using the same LED strips and the same transformers. The problems I'm experiencing are as follows:

    - The transformers occasionally (but not always) make a worrying buzzing noise. This problem does not always occur immediately after plugging it in. When using less than 1% power (all LEDs set to 1/255 on their respective RGB channels), the problem is far less likely to occur.
    - I'm also getting odd data glitches (again, more frequent on full brightness), but can occur under any situation. Large sections (or sometimes an entire strip) can flash full brightness for a fraction of a second, some LEDs can flicker between different colours, things like this. I'd say 9/10 of the updates are displaying things correctly but the constant glitches are rendering the display unusable.

    Any ideas what may be causing these faults or how to fix it? It almost seems as if there's some kind of interference or short somewhere but I can't find any.

  2. #2
    Senior Member Wozzy's Avatar
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    What is the power rating of the power supplies?
    With 12 strips of 145 pixels and assuming around 50mA for a full white pixel, you can be drawing up to 87A (435W) per 5 V power supply
    https://www.pjrc.com/how-much-curren...ds-really-use/

  3. #3
    Senior Member PaulStoffregen's Avatar
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    Quote Originally Posted by j.biscuit View Post
    - The transformers occasionally (but not always) make a worrying buzzing noise.
    Is there an AC voltage selection switch on the side of those power supplies? (like 110V vs 220V) Is it set correctly?

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    Quote Originally Posted by Wozzy View Post
    What is the power rating of the power supplies?
    With 12 strips of 145 pixels and assuming around 50mA for a full white pixel, you can be drawing up to 87A (435W) per 5 V power supply
    https://www.pjrc.com/how-much-curren...ds-really-use/
    Hi there, thanks for your reply.

    I should clarify, the wiring diagram I posted shows (almost) the precise wiring and hardware setup I'm using. Everything is the same except I'm actually using slightly less LEDs. 18 strips of 120 LEDs each (9 strips per transformer).
    Ethernet port 1: 3 strips on cable 1, 2 strips on cable 2, 2 strips on cable 3, 2 strips on cable 4
    Ethernet port 2: 3 strips on cable 1, 2 strips on cable 2, 2 strips on cable 3, 2 strips on cable 4

    I used a test meter to measure the current being drawn on a full 120 LED strip on full white and it was pulling just under 4A.
    This also coincides with the information on the link you provided. It appears I have the type A LEDs as 33.5 * 120 = 4.02A.
    Each transformer is rated for 40A and I believe on full power I should be using 36.18A (72.36A for the entire display).

    Quote Originally Posted by PaulStoffregen View Post
    Is there an AC voltage selection switch on the side of those power supplies? (like 110V vs 220V) Is it set correctly?
    Hi there, once again thanks and sorry for the delay in replying.

    Yes there is a voltage selection switch. It's set to 220V on both transformers.

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    Have you confirmed your power supplies can actually handle your 36A load? I didn't see a brand/part number, but a lot of those style units are optimistically rated. Also, how clean is the output at that load?

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    Quote Originally Posted by Spitko View Post
    Have you confirmed your power supplies can actually handle your 36A load? I didn't see a brand/part number, but a lot of those style units are optimistically rated. Also, how clean is the output at that load?
    Hi,

    Well, the problems still exist under a low load, albeit to a lesser degree. Saying that though, I'm not actually sure how to test how clean the DC output is - do you have any advice on how I might go about doing that?

    Also, what would you recommend to look for when buying transformers for this kind of job?

  7. #7
    Senior Member Wozzy's Avatar
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    How are you supplying power to the Teensy?
    Are the power supply grounds and the Teensy ground all connected together?
    Some photos of your actual setup and the Code you are running would be helpful to help others help you troubleshoot.

  8. #8
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    Quote Originally Posted by Wozzy View Post
    How are you supplying power to the Teensy?
    Are the power supply grounds and the Teensy ground all connected together?
    Some photos of your actual setup and the Code you are running would be helpful to help others help you troubleshoot.
    Unfortunately I'm not near the display at this moment to take some photos, but I will at my earliest opportunity.

    I've tried powering the Teensy via 3 different methods, they all have the same results:
    1. Powered via USB from a PC
    2. Powered via USB from a charger
    3. Powered via one of the transformers (in this case, the Teensy and power supply grounds were connected. I cut the USB cable and connected the +5V and GND lines directly to the transformer)

    The code I'm using is pretty rudimentary. It's nothing more than a slow cycle through various intensities of red, blue, green and white for testing. Again, I don't have access to the code at the moment from this machine, however I'm sure it's not an issue as the code works perfectly fine on a smaller display I assembled.

    Can you provide feedback on your earlier question regarding how clean the DC output is? How would I go about testing that?

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