void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  Serial.println("Hello, ESP32!");
  pinMode(2, OUTPUT);
}
long last = 0;
void loop() {
  // put your main code here, to run repeatedly:
  if(millis()-last>=500){
    digitalWrite(2,!digitalRead(2));
    last = millis();
  }
}