Simple FastLED example to fade a WS2816B LED by using two virtual WS2812Bs / NeoPixels

ws2816bTest.ino

#include <FastLED.h>

// Not tested with more then one LED!

#define NUM_LEDS 2
#define DATA_PIN D4

CRGB leds[NUM_LEDS];

void setup() { 
    FastLED.addLeds<NEOPIXEL, DATA_PIN>(leds, NUM_LEDS);  // GRB ordering is assumed
}

void loop() { 
  for(int i=0; i<65535; i+=32){
    float v = i / 65535.0; // map to 0 - 1
    v = sin(v * 3.1415 * 2) * 0.5 + 0.5; // Sine wave from 0.0 - 1.0

    uint16_t val = v * 65535; // map to range of uint16_t
    char split[2];
    memcpy(split, &val, 2); 
   
    leds[0] = CRGB(split[0], split[1], split[1]); 
    leds[1] = CRGB(split[1],split[0],split[0]);
    FastLED.show();
    delay(1); // Crashes without delay()
  }
}