void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200); //bits por segundo
  pinMode(6, OUTPUT);
  pinMode(9, INPUT_PULLUP); //conectado a 5v, o sino a tierra 0
}

void loop() {
  // put your main code here, to run repeatedly:
  if(digitalRead(9)==LOW)
  {
    Serial.println("Hello world");
    digitalWrite(6, HIGH);
    delay(500);
    digitalWrite(6, LOW);
    delay(1000);
  }
  // else 
  // {
  //   digitalWrite(6, LOW);
  // }
}