Greetings, I just installed a 4 meter WS2812B strip (120 LEDs) and for some

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1

Greetings,

I just installed a 4 meter WS2812B strip (120 LEDs) and for some reason, any FastLED library that I have tried simply doesn’t work.

Here’s what they look like when I try to load a simple rainbow wave pattern: https://i.imgur.com/yMdscdf.jpg

They start going crazy with flickering and half of the strip is white.

I have no problem with an Adafruit Neopixel library.

  • Connected to an Arduino Nano
  • They’re powered by a 5v 8a adapter.
  • I use a 470 ohm resistor between the arduino and the data pin.
  • I use a 1000 uf capacitor between the positive and negative.
  • Wiring: 18 AWG wiring. There’s about 5 meter distance between the arduino and the WS2812B strip. I soldered dupont wires between the Arduino and the long 18 awg cable.

This is the code that I tried: https://github.com/atuline/FastLED-Demos/blob/master/rainbow_march/rainbow_march.ino

One last thing to note, I have another 1 meter strip (30 LEDs) that uses the same code and it doesn’t have any issues. However, that 1 meter strip doesn’t have any resistor or capacitor.

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Do you have any way to measure the voltage at the start of the led strip? Some 5v power supplies actually push out 5.3 or 5.4v and I’ve found that can mess with the timings. Also - what happens if you try dropping the max brightness to 64? Also - just sanity checking - you have ground shared between the power supply, the nano, and the leds, right? And is your 5 meter of wiring twisted pair or just straight wire?

3

Thanks for the reply.

  1. I don’t have such tool unfortunately

  2. Just tested with brightness set to 64, still broken.

  3. Here’s an image of how I soldered everything: https://i.imgur.com/HqjiI7E.jpg

4

I’d try a shorter wire first. You seem to have thought about common ground, right?

5

I will try using shorter wires tomorrow.

I am not too sure if my ground wiring is good. Should I split the ground cable directly from the “GND” on the strip or it can be split midway of the ground cable like I did? Sorry, completely new to this.

6

Either way will work for the ground.

7

The resistor should be at end closest to led strip data pin, iirc

8

This might help…connect +ve and-ve to both ends of the strip

9

My guess is that the voltage drop is getting you. According to https://www.pololu.com/product/2550 the current per led is 50ma on max. With 120 leds, that’s 6A. If we assume the strip wiring is equivalent to the 18ga, and that it’s failing about half way you have 5m + 2m (4meters/2) = 7 meters. Using a voltage drop calculator found here (http://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=20.95&voltage=5&phase=dc&noofconductor=1&distance=7&distanceunit=meters&amperes=6&x=105&y=28) you get a predicted voltage drop of 1.76 volts. This is going to cause problems (and is why @Simon_Hyde pointed out the Adafruit wiring suggestion). The Pololu page has some additional recommendations.

By the way, a simple multimeter can be used to measure the voltage. You say you don’t have one. You can get one for <$10 suitable for projects like this, and possibly even a lot less. They are a must when doing projects like this.

10

I finally fixed it. My cabling was really long. I cut it in half and re-soldered everything.

Thank you so much guys.

11

@Flower_Style ​, as far as I can tell FastLED drives the LEDs faster than other libraries.

Faster data can show up minor wiring problems. This is why the other library worked with longer wires and FastLED didn’t.

Glad you got it sorted :slight_smile: