#include <Wire.h>

void setup() {
  Serial.begin(9600);
}

float ultrasonic(int Trig, int Echo) {
  pinMode(Trig, OUTPUT);
  pinMode(Echo, INPUT);
  digitalWrite(Trig, LOW);   delayMicroseconds(2);
  digitalWrite(Trig, HIGH);  delayMicroseconds(10);
  digitalWrite(Trig, LOW);
  float dist = pulseIn(Echo, HIGH) / 58;  // 由HIGH轉LOW所需時間
  Serial.println(dist);
  return dist;
}

void alarm() {
  int i = 200;
  while (i < 800) {
    i += 20;
    tone(8, i);    // tone(pin, frequency, duration)
    delay(5);
  }
  delay(100);
  noTone(8);
}

void loop() {
  float d = ultrasonic(3, 2); // Trig發動, Echo收回
  if (d<10) alarm();
  delay(250);
}