how send sms by Arduino Nano and Sim900a

Question

I try to use Arduino GSM library for sending sms.I have an Arduino Nano Board And an sim900 module and that connect together by serial port.but can't send sms. also for testing I use this example code in Arduino website:

#include <GSM.h>

#define PINNUMBER ""

// initialize the library instance
GSM gsmAccess;
GSM_SMS sms;

void setup()
{
  // initialize serial communications and wait for port to open:
  Serial.begin(9600);
  while (!Serial) {
    ; // wait for serial port to connect. Needed for Leonardo only
  }

  Serial.println("SMS Messages Sender");

  // connection state
  boolean notConnected = true;

  // Start GSM shield
  // If your SIM has PIN, pass it as a parameter of begin() in quotes
  while (notConnected)
  {
    if (gsmAccess.begin(PINNUMBER) == GSM_READY)
      notConnected = false;
    else
    {
      Serial.println("Not connected");
      delay(1000);
    }
  }

  Serial.println("GSM initialized");
}

void loop()
{

  Serial.print("Enter a mobile number: ");
  char remoteNum[20];  // telephone number to send sms
  readSerial(remoteNum);
  Serial.println(remoteNum);

  // sms text
  Serial.print("Now, enter SMS content: ");
  char txtMsg[200];
  readSerial(txtMsg);
  Serial.println("SENDING");
  Serial.println();
  Serial.println("Message:");
  Serial.println(txtMsg);

  // send the message
  sms.beginSMS(remoteNum);
  sms.print(txtMsg);
  sms.endSMS();
  Serial.println("\nCOMPLETE!\n");
}

/*
  Read input serial
 */
int readSerial(char result[])
{
  int i = 0;
  while (1)
  {
    while (Serial.available() > 0)
    {
      char inChar = Serial.read();
      if (inChar == '\n')
      {
        result[i] = '\0';
        Serial.flush();
        return 0;
      }
      if (inChar != '\r')
      {
        result[i] = inChar;
        i++;
      }
    }
  }

Answer 1

It seems you are having issues using the GSM libraries that come with Arduino as they use soft serial

You can then use GSM arduino library provided by GROUND LAB

This library gives you option to select the serial port. check the documentation on wiki

/*First you have to make the gsmSMS object, the arguments are in order
*GsmSMS (#1 Name of the serial port connected to GSM (your choice),#2 the address of millis function(just copy whats there) )*/
gsmSMS  myGsmSMS(Serial3,&millis,&Serial);        //gsmSMS TELIT SMS

This library mentions that it is for Telit but it works for sim900 as well