/*
 Voltaat learn (http://learn.voltaat.com)
 Link for full tutorial:

 Tutorial: Control an LED from anywhere via your phone!

 The function of this code is to control a small LED
 by sending messages from your phone and receiving them through
 the Arduino with the help of the SIM900 GSM shield.

 Connections from the Arduino to the breadboard:
 • Arduino pin GND → Breadboard ground line
 • Arduino pin 5V → Breadboard 5V line

 Connections from the sim900 GSM module:
 • TWO GND pin→ Breadboard ground line
 • TXD pin → Arduino pin 7
 • RXD pin → Arduino pin 8

 Connections from the LED:
 • Negative pin→ Breadboard ground line
 • Positive pin→ Arduino pin 2
*/

//Allows serial communication on other digital pins of an Arduino board
#include "SoftwareSerial.h"

//Configure software serial port with digital pins 7,8
SoftwareSerial SIM900(7, 8);

//Define the variable led to digital Pin 2
const int led = 2;

//Define the variable mySMS with String data type
String mySMS;

//Commands inside void setup run once
void setup() {

 //Arduino communicates with SIM900 GSM shield at a baud rate of 9600 (9600 bits per second)
 SIM900.begin(9600);

 //Start the serial monitor at 9600 baud rate (9600 bits per second)
 Serial.begin(9600);

 //Delay for 100 milliseconds
 delay(100);

 // Set module to send SMS data to serial out upon receipt
 SIM900.println("AT+CNMI=2,2,0,0,0");

 //Delay for one second
 delay(1000);

 //led is defined as an output
 pinMode(led, OUTPUT);

 //Turn LED off
 digitalWrite(led, LOW);

}

//Commands inside void loop run forever
void loop()
{

 if (SIM900.available() > 0)
 {
   //Read string data from SIM900
   mySMS = SIM900.readString();

   //Print mySMS value to serial monitor
   Serial.println(mySMS);
 }
 //Check if the SMS contains "ON"
 if (mySMS.indexOf("ON") > -1)
 {
   //Print "LED ON" to serial monitor
   Serial.println("LED ON");

   //Turn LED ON
   digitalWrite(led, HIGH);
 }
 //Check if the SMS contains "OFF"
 else if (mySMS.indexOf("OFF") > -1)
 {
   //Print "LED OFF" to serial monitor
   Serial.println("LED OFF");

   //Turn LED OFF
   digitalWrite(led, LOW);
 }
 //Delay for 10 milliseconds
 delay(10);
}