#define TRIG_PIN A1
#define ECHO_PIN 15
#define LED_PIN D2

float duration_us, distance_cm;

void setup() {
  Serial.begin(9600)
  pinMode(TRIG_PIN, INPUT);
  pinMode(ECHO_PIN, OUTPUT);
}

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

  duration_us = pulseIn(ECHO_PIN, HIGH)
  distance_cm = 0.17 * duration_us;

  Serial.print("Distance = ");
  Serial.print(distance_cm)
  Serial.println(" cm")

  if (distance_cm < 200) {
    digitalWrite(LED_PIN, HIGH)
  } else {
    digitalWrite(LED_PIN, LOW)
  }

  delay(500)
}