#define btn_pin 13
#define led_pin 9

#define PCICR_ B00000001

#define PCMSKx_ PCMSK0
#define PCMSK_ B00100000
#define PCINTx_vect PCINT0_vect

int counter = 0;
bool led_value = LOW;
long long last_mod_ledv = 0;
long long led_interval = 5000;

void setup() {
  Serial.begin(9600);
  pinMode(btn_pin, INPUT_PULLUP);
  pinMode(led_pin, OUTPUT);
  PCICR |= PCICR_; // Habilita IRQ na porta PB
  PCMSKx_|= PCMSK_; // Habilita IRQ em D13
  long long last_mod_ledv = millis();
  
}

int last_value = 0;

void loop() {
  Serial.println((int)last_mod_ledv);
  Serial.print("counter: ");
  Serial.println(counter);
  delay(100);
  digitalWrite(led_pin, led_value);
  
  if (led_value && millis() - last_mod_ledv > led_interval)
   led_value = LOW;

  last_value = 0;
}

ISR (PCINTx_vect) {
  led_value = HIGH;
  counter++;
  last_mod_ledv = millis();
}