#define led_pin 9
#define btn_pin 2

volatile long long last_mod_ledv = millis();
volatile int cont = 0, last_cont = 0;
long long led_interval = 5000;

void handleSW () {
  digitalWrite(led_pin, HIGH);
  last_mod_ledv = millis();
  cont++;
}

void setup () {
  Serial.begin(9600);
  pinMode(led_pin, OUTPUT);
  pinMode(btn_pin, INPUT_PULLUP);
  attachInterrupt(INT0, handleSW, CHANGE);
}

void loop () {
  if (cont != last_cont) {
    Serial.print("interr: ");
    Serial.println(cont);
  }
  if (millis() - last_mod_ledv > led_interval)
    digitalWrite(led_pin, LOW);
  last_cont = cont;
}