#define TRIG_PIN 22
#define ECHO_PIN 23
const int LED1 = 21, LED2 = 19;
float duration_us, distance_cm;
void setup() {
  Serial.begin (9600);
  pinMode(LED1, OUTPUT);
  pinMode(LED2, OUTPUT);
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
}
void loop() {
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);
  duration_us = pulseIn(ECHO_PIN, HIGH);
  distance_cm = 0.017 * duration_us;
  Serial.print("distance: ");
  Serial.print(distance_cm);
  Serial.println(" cm");
  delay(500);
  if(distance_cm<= 15) {
   digitalWrite(LED1, HIGH);
   digitalWrite(LED2, LOW);
  } else{
   digitalWrite(LED1, LOW);
   digitalWrite(LED2, HIGH);
  }
}