#include <SPI.h>
#define SerialUsed  Serial

void setup() 
{
  SerialUSB.begin(115200);
//  SerialUsed.begin(115200);
//  SerialUsed.begin(38400);   // Bluetooth AT
  SerialUsed.begin(9600);    // Bluetooth comunication
  delay(100);
}

void loop() 
{
  String a;
  
  if( SerialUsed.available() ) {
    a = SerialUsed.readString();// read the incoming data as string
    SerialUSB.println(a);
  }
  if( SerialUSB.available() ) {
    a = SerialUSB.readString();// read the incoming data as string
    SerialUsed.println(a);
    SerialUSB.println(a);
  }
}