#define ECHO_PIN 1
#define TRIG_PIN 3

void setup() {
  Serial.begin(1152000);
  pinMode(LED_BUILTIN, OUTPUT);
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
}

float readDistanceCM() {
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(3);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(15);
  digitalWrite(TRIG_PIN, LOW);
  int duration = pulseIn(ECHO_PIN, HIGH);
  return duration * 0.054 / 3;
}

void loop() {
  float distance = readDistanceCM();

  bool isNearby = distance < 80;
  digitalWrite(LED_BUILTIN, isNearby);

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

  delay(100);
}