#define TRIG_PIN 3
#define ECHO_PIN 2

void setup() {
  Serial.begin(115200);
  pinMode(LED_BUILTIN, OUTPUT);
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
}

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

  float distance = pulseIn(ECHO_PIN, HIGH) * 0.034 / 2;
  digitalWrite(LED_BUILTIN, distance < 100);

  Serial.print("Distance: ");
  Serial.println(distance);

  delay(100);
}