code i'm using

void setup() {
  // put your setup code here, to run once:
  int test_send = 12;
  pinMode(13, OUTPUT);
  pinMode(13, LOW);
  delay(5000);
  pinMode(13, HIGH);
  Serial.begin(9600);
  Serial.println("AT$SF=12");
  Serial.print("...");
  Serial.print("AT$SF=");
  Serial.println(test_send, HEX);
  pinMode(13, LOW);
}

void loop() {
  // put your main code here, to run repeatedly:

}