#include "FastLED.h"
#define NUM_LEDS 16
#define LED_TYPE WS2812
#define LED_PIN 2
#define BRIGHTNESS 255
#define DX 1
CRGB leds[NUM_LEDS];
int j;
int k=0;
unsigned long tempTime;

void setup() {
  FastLED.addLeds<LED_TYPE, LED_PIN, GRB>(leds, NUM_LEDS).setCorrection( TypicalLEDStrip );
  FastLED.setBrightness(BRIGHTNESS);
}

void loop() {
  if (millis() - tempTime >= 200){
    tempTime = millis();
    rainbow();
  }
}

void rainbow(){
  for (int i = 0; i < NUM_LEDS; i++ ) {
    j = i + k;
    if (j >= NUM_LEDS) j = j - NUM_LEDS;
    leds[j] = CHSV(i * 255 / NUM_LEDS, 255, 255);
  }
  FastLED.show(); 
  k+=DX; 
  if (k >= NUM_LEDS) k = k - NUM_LEDS;
}