#include <FastLED.h>

#define LED_PIN 7
#define NUM_LEDS 16

#define LED_SPACING 4
#define LED_ON 255, 0, 0
#define LED_OFF 0, 0, 0
#define STEP_DELAY 100

CRGB leds[NUM_LEDS];

void setup()
{
    FastLED.addLeds<WS2812, LED_PIN, GRB>(leds, NUM_LEDS);
}

void loop()
{
    for (int i = 0; i < LED_SPACING; i++)
    {
        for (int j = 0; j < NUM_LEDS / LED_SPACING; j++) {
          leds[i+j*LED_SPACING] = CRGB(LED_ON);
          leds[i+j*LED_SPACING - 1] = CRGB(LED_OFF);
          if (i == 0) leds[NUM_LEDS-1] = CRGB(LED_OFF);
        }
      FastLED.show();
      delay(STEP_DELAY);
    }
}