void setup() {
  // put your setup code here, to run once:
  //Serial.begin(115200);
  //Serial.println("Hello, ESP32!");
  pinMode(D4, HIGH);
}

void loop() {
  // put your main code here, to run repeatedly:
  digitalWrite(D4, HIGH);
  delay(10); // this speeds up the simulation
  digitalWrite(D4, LOW);
  delay(10);
}