Le_string

//#include <SPI.h>
//#include <MFRC522.h>

//#define SS_PIN 10
//#define RST_PIN 9
//MFRC522 mfrc522(SS_PIN, RST_PIN);

//char st[20];
String comando;
//byte led = 7;
//boolean estado = LOW;
//-------------------
void setup()
{
  Serial.begin(9600);
//  pinMode(led, OUTPUT);
//  SPI.begin();
//  mfrc522.PCD_Init();
}
//-------------------
void loop()
{
  /*
  if ( ! mfrc522.PICC_IsNewCardPresent())
  {
    return;
  }
  if ( ! mfrc522.PICC_ReadCardSerial())
  {
    return;
  }
  String conteudo = "";
  byte letra;
  for (byte i = 0; i < mfrc522.uid.size; i++)
  {
    conteudo.concat(String(mfrc522.uid.uidByte[i] < 0x10 ? "0" : ""));
    conteudo.concat(String(mfrc522.uid.uidByte[i], HEX));
  }
  conteudo.toUpperCase();
  Serial.println(conteudo.substring(1));
  */
  delay(1000);
  if (Serial.available() > 0)
  {
    comando = Serial.readStringUntil('\n');
  }
  if (comando == "OK")
  {
     Serial.println("Entrei no if comando == OK maiuscula");
     Serial.println(comando);
//    digitalWrite(led, HIGH);
//    delay(3000);
//    digitalWrite(led, LOW);
    delay(100);
    comando = "";
  }
}