long t,d;

void setup(){
  Serial.begin(9600);
  pinMode(12,OUTPUT);
  pinMode(13,INPUT);
  pinMode(3,OUTPUT);
  pinMode(4,OUTPUT);

}

void loop(){
    digitalWrite(12,LOW);
    delayMicroseconds(2);
    digitalWrite(12,HIGH);
    delayMicroseconds(10);
    digitalWrite(12,LOW);

    if(d>20){
      digitalWrite(3,LOW);
      digitalWrite(4,LOW);

    }

    if(d>17){
      digitalWrite(3,LOW);
      digitalWrite(4,HIGH);

    }

    if(d<15){
      digitalWrite(3,HIGH);
      digitalWrite(4,HIGH);
    }



    t=pulseIn(13,HIGH);
    d=0.015*t;
    Serial.println(d);
}