// MCU BASIC: https://www.basic4mcu.com
// DateTime : 2018-09-20 오후 12:11:02
// by Ok-Hyun Park
//
#include <SoftwareSerial.h>
#define BT_RXD 8
#define BT_TXD 7
SoftwareSerial bluetooth(BT_RXD,BT_TXD);
//
const int TRIG=9,ECHO=10,LED=6,SPEAKER=12;
//
long duration;
int distance,note;
//
void setup(){
  pinMode(TRIG,OUTPUT); pinMode(ECHO,INPUT);
  pinMode(LED,OUTPUT);  pinMode(SPEAKER,OUTPUT);
  Serial.begin(9600);
  bluetooth.begin(9600);
}
//
void loop(){
  digitalWrite(TRIG,HIGH); delayMicroseconds(10); digitalWrite(TRIG,LOW);
  duration=pulseIn(ECHO,HIGH); distance=duration/58; // Cm 환산
  note=(100-distance+200)*10;
  Serial.print("Distance: "); Serial.print(distance); Serial.println("cm");
  //
  if     (distance>250){ bluetooth.write('0'); analogWrite(LED,  0); } //거리 2.5M 이상 LED 소등
  else if(distance>100){ bluetooth.write('1'); analogWrite(LED,128); } //거리 1~2.5M LED 반 밝기
  else                 { bluetooth.write('2'); analogWrite(LED,255); tone(SPEAKER,note,1000); } //거리 1M 이하 LED 최대 밝기
  delay(100);
  //
  if(bluetooth.available()){
    Serial.write(bluetooth.read());
  }
  if(Serial.available()){
    bluetooth.write(Serial.read());
  }
}
 
거리값에 따라서 '0'~'2'를 출력하도록 작성했습니다.