const int TrigPin = 4;
const int EchoPin = 3;
const int BELLPin = 11;

int AudioVoice = 678; //音频范围为0~1023

boolean CtrlFlag = false;
float distance;

void setup()
{
  Serial.begin(115200);
  pinMode(TrigPin, OUTPUT);
  pinMode(EchoPin, INPUT);
  pinMode(BELLPin, OUTPUT);
  noTone(BELLPin);
}
void loop()
{
  digitalWrite(TrigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(TrigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(TrigPin, LOW);
  distance = pulseIn(EchoPin, HIGH) / 58.0;
  Serial.println(distance);
  if (distance < 50)
  {
    CtrlFlag = true;
    tone(BELLPin, AudioVoice);
  }
  else
  {
    CtrlFlag = false;
    noTone(BELLPin);
  }

}