#define echo 2
#define trig 3

unsigned long echo_start; //초음파반향수신시작시간
unsigned long echo_end;  //초음파반향수신종료시간
unsigned long echo_t;  //초음파반향수신길이
unsigned long t1; //초음파센서작동주기기용
float distance; // 측정됨거리cm

void ISR_echoUP(){ //초음파반향수신시작시간
  echo_start = micros();
  attachInterrupt(digitalPinToInterrupt(echo),ISR_echoDOWN, FALLING);
  
}

void ISR_echoDOWN(){ //초음파반향수신종료시간
  echo_end = micros();
  echo_t = (echo_end - echo_start);
  //Serial.println(echo_t);
  if(echo_t>=23530 || echo_t <= 115){Serial.println("out");}//측정범위를 넘어서면
  else{distance = ((echo_t*17.0)/1000.0); Serial.println(distance,1);}//cm 
}

void Wave(){
  
  digitalWrite(trig, HIGH);
  delayMicroseconds(10);
  digitalWrite(trig, LOW);//초음파 발사 10us동안
  echo_start=0;
  echo_end =0;
  attachInterrupt(digitalPinToInterrupt(echo),ISR_echoUP, RISING);//인터럽트는 low에서 high가되면 발생
}
  

void setup() {
  
  pinMode(echo, INPUT);
  pinMode(trig, OUTPUT);
  Serial.begin(115200);
  t1=millis();
}

void loop() {  //25ms마다 초음파 거리측정(장치의 권장사양)
  
  if(millis()-t1>=25){
    Wave();
    t1=millis();
  }
}