1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

RPi + Other Software APA102 Power issue - White showing as reddish

Discussion in 'Hardware Support' started by gazm2k5, 15 March 2020.

  1. gazm2k5

    gazm2k5 New Member

    Messages:
    7
    Hardware:
    RPi1/Zero
    If my screen is red, the LEDs are red. Blue, blue, green green. BUT if I show a full white screen, some of the end LEDs show as reddish. The further away from the power line they are, the redder they get.

    At 0.4 Luminance gain, they were okay.

    So I added a ground and power connector to the end of the strip too, which helped a bit, but still not able to go above 0.5 luminance gain without the corner furthers from power source showing as reddish. At 1 luminance gain they are fully red when meant to be showing white.

    I have APA102 LEDs connected to the 5V line of a molex power connector on my PC. From a quick google it should be able to deliver 11A.

    I have 103 LEDs, (60 LED/m) and at 2.8 A/m power requirement, this should need no more than 6A.

    The raspberry Pi and APA102 LEDs have a common ground, but the Raspberry Pi has its own micro USB power input which is not delivered to the LEDs.

    Is this a current issue? Perhaps my ATX PSU is not delivering the full 11A that I think it is... unfortunately I don't have a multimeter.
     
  2. Cosmicbase

    Cosmicbase Member

    Messages:
    315
    Hardware:
    RPi3, +Arduino
    You have to connect your power supply from all 2 sides.
    Otherwise an even power supply is not guaranteed.
     
  3. gazm2k5

    gazm2k5 New Member

    Messages:
    7
    Hardware:
    RPi1/Zero
    I have wired up the 2 corners now, but the issue still persists.
     
  4. Blokmeister

    Blokmeister Member

    Messages:
    31
    Hardware:
    RPi2, 32/64bit, +AtmoOrb
    For such high currents, the voltage might drop quite significantly. If you have a multimeter, you should measure the voltage across the 5V - 0V lines. I saw a drop in voltage of roughly one volt across my 200 LED strip, even when I connect from both sides. I have now also run a thick copper wire from one corner to the other. Now the effect is still there, but barely noticeable. I think the voltage drop is now around 0,5 V. I have also increased the voltage output from my power supply from 5V to around 5,5V to compensate.
     
  5. Blokmeister

    Blokmeister Member

    Messages:
    31
    Hardware:
    RPi2, 32/64bit, +AtmoOrb
    For such high currents, the voltage might drop quite significantly. If you have a multimeter, you should measure the voltage across the 5V - 0V lines. I saw a drop in voltage of roughly one volt across my 200 LED strip, even when I connect from both sides. I have now also run a thick copper wire from one corner to the other. Now the effect is still there, but barely noticeable. I think the voltage drop is now around 0,5 V. I have also increased the voltage output from my power supply from 5V to around 5,5V to compensate.