int tri= 15;
int echo= 14;
int buzzer = 16;
void setup() {
  Serial1.begin(115200);
  Serial1.println("Hello, Raspberry Pi Pico!");
  pinMode(tri, OUTPUT);
  pinMode(echo, INPUT);
  pinMode(buzzer, OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
// Start a new measurement:
  digitalWrite(tri, LOW);
  delayMicroseconds(2); 
  digitalWrite(tri, HIGH);
  delayMicroseconds(10);
  digitalWrite(echo, LOW);

  // Read the result:
  int duration = pulseIn(echo, HIGH);
  Serial.print("Distance in CM: ");
  Serial.println(duration / 58);
  if((duration/58) <30){
  for (int i = 0; i < 3; i++) {
        tone(buzzer, 1000); // Phát âm thanh tần số 1000Hz
        delay(200);            // Kêu 200ms
        noTone(buzzer);     // Tắt còi
        delay(300);            // Nghỉ 300ms
      }
  }else if((duration/58) >= 30){
    noTone(buzzer);
  }
  delay(100);
}