int trig=17;
int echo=16;
int lowled=18;
int midled=19;
int highled=21;
int relay=4;
unsigned int level=0;
void setup() {
  Serial.begin(115200);
  pinMode(trig,OUTPUT);
  pinMode(echo,INPUT);
  pinMode(lowled,OUTPUT);
  pinMode(midled,OUTPUT);
  pinMode(highled,OUTPUT);
  pinMode(relay,OUTPUT);
   digitalWrite(lowled,HIGH);
  digitalWrite(midled,HIGH);
  digitalWrite(highled,HIGH);
  digitalWrite(relay,LOW);
}

void loop() {

  digitalWrite(trig,HIGH);
  delay(1000);
  digitalWrite(trig,LOW);

  int duration=pulseIn(echo,HIGH);
  Serial.print("Distance in cm:");
  Serial.println(duration/58);
  level=duration/58;
  if(level<100)
  {
    digitalWrite(lowled,LOW);
    digitalWrite(relay,HIGH);
  }
  else if(level>200 && level<400)
  {
    digitalWrite(lowled,HIGH);
    digitalWrite(midled,LOW);
  }
  else if(level>=400)
  {
  digitalWrite(lowled,HIGH);
  digitalWrite(midled,HIGH);
  digitalWrite(highled,LOW);
  digitalWrite(relay,HIGH);
  }

}