---

#define TRIG_PIN 3
#define ECHO_PIN 2
#define LED 4

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

void loop()
{
  int duration;
  float sm;

  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);

  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);

  digitalWrite(TRIG_PIN, LOW);

  duration = pulseIn(ECHO_PIN, HIGH);

  sm = duration / 80.0;

  Serial.print("Расстояние = ");
  Serial.print(sm, 1);
  Serial.println(" см");

  if (sm < 2.0)
  {
    digitalWrite(LED, HIGH);
  }
  else
  {
    digitalWrite(LED, LOW);
  }

  delay(100);
}