Arduino Mega 2560 with SIM808 module I have a SIM808 module like this: https://www.banggood.com/SIM808-Module-GPS-GSM-GPRS-Quad-band-Development-Board-For-Arduino-p-1063106.html

The output header has 5 pins: GND/RX/GND/TX/VCC and I connected them as: 

GND/VCC to a LiPo battery, 7.4V@1000mAh

RX->pin 14 (written on it TX3)

GND->to arduino GND

TX->pin 15 (written on it RX3)

and uploaded this code

#include &lt;SoftwareSerial.h&gt;


SoftwareSerial GSMSerial(15,14);    // RX, TX

void setup()
{

  GSMSerial.begin(19200);
  Serial.begin(19200);
  Serial.println("START");
}

void loop()
{
  if(Serial.available())
    GSMSerial.print((char)Serial.read());
  else  if(GSMSerial.available())
    Serial.print((char)GSMSerial.read());
}


But I'm not getting anything on it (when sending "AT" or anything else). 

Any help is appreciated. 

Thank you!
Don't use SoftwareSerial on the HardwareSerial pins.  Instead of this:

#include &lt;SoftwareSerial.h&gt;
SoftwareSerial GSMSerial(15,14);    // RX, TX


Just do this:

#define GSMSerial Serial3