An Arduino sample running with buzzer

buzzer.ino

#define BUZZER D6

void setup() {
  Serial.begin(115200);
  Serial.println("setup");
  
  pinMode(BUZZER, OUTPUT);
  digitalWrite(BUZZER,HIGH);
}

void loop() {
  buzzer_Di();
}

void buzzer_Di() {
  Serial.println("Bi..");
  digitalWrite(BUZZER,LOW);
  delay(300);
  digitalWrite(BUZZER,HIGH);
  delay(300);
 }