#include <Adafruit_NeoPixel.h>

Adafruit_NeoPixel neo(16, 12, NEO_GRB + NEO_KHZ800);

volatile int amount = 0;

int del;

bool red = true;

void setup() {
  Serial.begin(9600);
  neo.begin();
  pinMode(2, INPUT_PULLUP);
  attachInterrupt(digitalPinToInterrupt(2), my_func, FALLING);
}

void loop() {
  if (del + 500 < millis()) {
    if (red) {
      red != red;
      for(int i = 0; i < amount; i++) {
        neo.setPixelColor(i, neo.Color(0,0,255));
      }
    }
    else {
      red != red;
      for(int i = 0; i < amount; i++) {
        neo.setPixelColor(i, neo.Color(255,0,0));
      }
    }
    neo.show();
  }
  Serial.println(del);
}

void my_func() {
  if (amount < 16) {
    amount++;
  } else {
    amount = 0;
    neo.clear();
  }
}