#define LED 12
#define TRG 9
#define ECH 8
#define SPK 11
#define Sp 340 //音速(m/sec)
#define DS 100 //接近距離(cm)
#define frq 2000 //ブザー周波数

void setup() {
  pinMode(LED,OUTPUT);
  pinMode(SPK,OUTPUT);
  pinMode(TRG,OUTPUT);
  pinMode(ECH,INPUT);
  Serial.begin(115200);
  Serial.println("OK");
}

void loop() {
  double dist;
  dist=getDis();
  if(dist>=0 && dist<=DS){
    digitalWrite(LED,HIGH);
    tone(SPK,frq);
  }else{
    digitalWrite(LED,LOW);
    noTone(SPK);
  }
  Serial.print(dist);
  Serial.println("cm");
  delay(100);
}

double getDis(void){
  double dis;
  digitalWrite(TRG,LOW);
  delayMicroseconds(2);
  digitalWrite(TRG,HIGH);
  delayMicroseconds(10);
  digitalWrite(TRG,LOW);
  dis=pulseIn(ECH,HIGH);
  if(dis>0){
    dis=(dis/2)*Sp*0.0001;
    return dis;
  }
  return -1;
}