int rp=2;
int gp=4;
int bp=7;
int relay_pin=8;
int trig=12;
int echo=3;
void setup() {
  Serial.begin(9600);
  pinMode(rp, OUTPUT);
  pinMode(gp, OUTPUT);
  pinMode(bp, OUTPUT);
  pinMode(relay_pin, OUTPUT);
  pinMode(trig, OUTPUT);
  pinMode(echo, INPUT);

}

void loop() {
   digitalWrite(trig, HIGH);
   delayMicroseconds(10);
   digitalWrite(trig, LOW);
   int duration=pulseIn(echo,HIGH);
   int distance=duration*0.034/2;
   Serial.println("distance is "+String(distance));
   if(distance<40 && distance>30){
    digitalWrite(gp, LOW);
    digitalWrite(bp, LOW);
    digitalWrite(relay_pin,HIGH);
    digitalWrite(rp, HIGH);
    delay(3000);
    
   }
   if(distance<30 && distance>20){

    digitalWrite(rp, LOW);
    digitalWrite(gp, LOW);
    digitalWrite(bp, HIGH);
    digitalWrite(relay_pin, HIGH);
    delay(3000);
   }
   if(distance<20){
    digitalWrite(rp, LOW);
    digitalWrite(bp, LOW);
    digitalWrite(relay_pin, LOW);
    digitalWrite(gp, HIGH);
    delay(3000);

   }

}