int trigger = 21;
int led = 18;
int echo = 22;

void setup() {
  Serial.begin(9600);
  pinMode(led, OUTPUT);
  pinMode(trigger, OUTPUT);
  pinMode(echo, INPUT);

}

void loop() {
  digitalWrite(trigger, LOW);
  delayMicroseconds(2);

  digitalWrite(trigger, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigger, LOW);

  long duracao = pulseIn(echo, HIGH);

  int distancia = (duracao * 0.0343) / 2;

  Serial.println("Distância:" + String (distancia) + "cm");

  delay(1000);

  if (distancia <= 20) {
    digitalWrite(led, HIGH);
    delay(1000);
  } else (distancia >= 20); {
    digitalWrite(led, LOW);
  }
}