Le multiplo String

#include <SoftwareSerial.h>

SoftwareSerial bt(1 , 2); // TX RX
String str ;
String inString = "";
int portao = 3; // a
int rele1 = 4; // b


void setup() {
  bt.begin(9600);
  pinMode(portao, OUTPUT); // a
  bt.begin(9600);
  pinMode(rele1, OUTPUT); // b
  bt.begin(9600);

}

void loop() {
  if (bt.available()>0)
  {
     str = bt.readStringUntil('\n');
     inString = inString + str;

    if (inString == "aa") {
      digitalWrite(portao, HIGH); // a
      bt.println("OK, port A/F.");
    }
    if (inString == "AA") {
      digitalWrite(portao, LOW);
      bt.println("OK, port a/f.");
    }
    if (inString == "bb") {
      digitalWrite(rele1, HIGH);
      bt.println("OK, rele1 ligad."); // b
    }
    if (inString == "BB") {
      digitalWrite(rele1, LOW);
      bt.println("OK, rele1 deslig.");

    }
  }
}