#define echo 2
#define tring 3
#define blue 8
#define red 9
void setup() {
  // put your setup code here, to run once:
pinMode(red, OUTPUT);
pinMode(blue, OUTPUT);
pinMode(tring, OUTPUT);
pinMode(echo, INPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
float distance= readDistanceInCm();
if(distance<20)
{
  digitalWrite(red, HIGH);
  digitalWrite(blue,LOW);
}
else
{
  digitalWrite(red, LOW);
  digitalWrite(blue,HIGH);
}
}
float readDistanceInCm()
{
  digitalWrite(tring, LOW);
  delayMicroseconds(2);
  digitalWrite(tring, HIGH);
  delayMicroseconds(10);
  digitalWrite(tring, LOW);
  
  int timeDuration = pulseIn(echo,HIGH);
  return timeDuration*0.034/2;
}