I'm using FastLEDs builtin fill_rainbow function for generating a rainbow spectrum on an LED strip. The issue is, I get a random red pixel midway through the yellow region. I've tried it on 3 different Arduino nano's, and two different LED-strips. Here's the code:

#include <FastLED.h>

#define DATA_PIN 2
#define NUM_LEDS 114

uint8_t hue = 0;

void setup() {
  FastLED.addLeds<WS2812B, DATA_PIN, GRB>(leds, NUM_LEDS);

  fill_rainbow( leds, NUM_LEDS, hue, 1);
  for(int i=0; i<NUM_LEDS; i++) {
    Serial.print(' ');
    Serial.print(' ');
    Serial.print(' ');

  CHSV hsv;
  CRGB rgb;
  //rgb = hsv;

void loop() {
  fill_rainbow( leds, NUM_LEDS, hue, 1);

Here pixel number 60 gets the rgb code 160, 0, 0. When it should have something like 160, 150, 0.

The strangest part of all is that I can get rid of the problem in two ways, either by uncommenting the line rgb = hsv;, or by commenting out the fill_rainbow function in the loop function. This strange behavior leads me to believe im somehow messing up a pointer or misusing a FastLED feature. Additionally the fill_rainbow function is very simple and relies on FastLEDs hsv to rgb typecasting, which is another reason to believe I'm doing something wrong.

So help me out here, am i doing something silly, or have I discovered a bug with FastLEDs hsv to rgb converter?

  • Issues with a specific third-party library are best raised with the author of the library. Raise an issue here. – Majenko Oct 9 '18 at 21:59
  • @Majenko Sure, but the reason for posting the question is i suspect i made a mistake, as explained in the latter part of the question. I'm hoping to get some feedback on weather I have made a mistake before posting an issue at the developer. – Tehanu Oct 10 '18 at 6:45

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