How to read an SMS from Arduino and get LED to switch on or off

Question

#include <SoftwareSerial.h>
char inchar; //Will hold the incoming character from the serial port.
SoftwareSerial cell(2,3); //Create a 'fake' serial port. Pin 2 is the Rx pin, pin 3 is the Tx pin.

 int led1 = A2;

 void setup()
 {
     // Prepare the digital output pins
     pinMode(led1, OUTPUT);
     digitalWrite(led1, HIGH);

     //Initialize GSM module serial port for communication.
     cell.begin(19200);
     delay(30000); // Give time for GSM module to register on network, etc.
     cell.println("AT+CMGF=1"); // Set SMS mode to text
     delay(200);
     cell.println("AT+CNMI=3,3,0,0"); // Set module to send SMS data to serial out upon receipt 
     delay(200);
 }

 void loop() 
 {
     //If a character comes in from the cellular module...
     if(cell.available() >0)
     {
         delay(10);
         inchar=cell.read(); 
         if (inchar=='a')
         {
             delay(10);
             inchar=cell.read();
             if (inchar=='0')
             {
                 digitalWrite(led1, LOW);
             } 
             else if (inchar=='1')
             {
                 digitalWrite(led1, HIGH);
             }
             delay(10);
             delay(10);
         }
         cell.println("AT+CMGD=1,4"); // Delete all SMS
     }
 }

This is the code for receiving SMSes from the cellular network. I am using the Arduino Gboard with SIM900. There is no error in the code, but the LED on the board doesn't switch on or off in response to an SMS.

Why?

Solution 1

Here's a fully functional code for sending a command thru SMS using Arduino and GSM, it will also reply the state of the light.

#include <SoftwareSerial.h>
SoftwareSerial GPRS(10, 11);
String textMessage;
String lampState;
const int relay = 12; //If you're using a relay to switch, if not reverse all HIGH and LOW on the code

void setup() {  
  pinMode(relay, OUTPUT);
  digitalWrite(relay, HIGH); // The current state of the light is ON

  Serial.begin(9600); 
  GPRS.begin(9600);
  delay(5000);
  Serial.print("GPRS ready...\r\n");
  GPRS.print("AT+CMGF=1\r\n"); 
  delay(1000);
  GPRS.print("AT+CNMI=2,2,0,0,0\r\n");
  delay(1000);
}

void loop(){
  if(GPRS.available()>0){
    textMessage = GPRS.readString();
    Serial.print(textMessage);    
    delay(10);
  } 
  if(textMessage.indexOf("ON")>=0){ //If you sent "ON" the lights will turn on
    // Turn on relay and save current state
    digitalWrite(relay, HIGH);
    lampState = "ON";
    Serial.println("Lamp set to ON\r\n");  
    textMessage = "";
    GPRS.println("AT+CMGS=\"[phone]\""); // RECEIVER: change the phone number here with international code
    delay(500);
    GPRS.print("Lamp was finally switched ON.\r");
    GPRS.write( 0x1a );
    delay(1000);
  }
  if(textMessage.indexOf("OFF")>=0){
    // Turn off relay and save current state
    digitalWrite(relay, LOW);
    lampState = "OFF"; 
    Serial.println("Lamp set to OFF\r\n");
    textMessage = "";
    GPRS.println("AT+CMGS=\"[phone]\""); /// RECEIVER: change the phone number here with international code
    delay(500);
    GPRS.print("Lamp was finally switched OFF.\r");
    GPRS.write( 0x1a );
    delay(1000);
  }
  if(textMessage.indexOf("STATUS")>=0){
    String message = "Lamp is " + lampState;
    GPRS.print("AT+CMGF=1"); 
    delay(1000);
    Serial.println("Lamp state resquest");
    textMessage = "";
    GPRS.println("AT+CMGS=\"[phone]\""); // RECEIVER: change the phone number here with international code
    delay(500);
    GPRS.print("Lamp is currently ");
    GPRS.println(lampState ? "ON" : "OFF"); // This is to show if the light is currently switched on or off
    GPRS.write( 0x1a );
    delay(1000);
  }
}

Solution 2

Change

AT+CNMI=3,3,0,0

to:

AT+CNMI=2,2,0,0,0

Solution 3

The simplest way is the best way.

// if You use SoftwareSerial lib, declare object for GSM
SoftwareSerial gsm(8,9); // TX, RX
void setup(){
     // initialise UART and GSM communication between Arduino and modem
     Serial.begin(115200);
     gsm.begin(115200);
     // wait 5-10sec. for modem whitch must connect to the network
     delay(5000);
     // configure modem - remember! modem didn't remeber Your's configuration!
     gsm.print("at+cmgf=1\r"); // use full functionality (calls, sms, gprs) - see app note
     gsm.print("at+clip=1\r"); // enable presentation number
     gsm.print("at+cscs=\"GSM\"\r"); // configure sms as standard text messages
     gsm.print("at+cnmi=1,2,0,0,0\r"); // show received sms and store in sim (probobly, I don't compre this settings with app note but it's working :)
}
void loop(){
     String response = gsmAnswer();
    if(response.indexOf("+CMT:") > 0 ) { // SMS arrived
    // Now You can parse Your Message, if You wont controll only LED, just write
       if(response.indexOf("LED ON") > 0) {
          digitalWrite(LED_PIN, HIGH); // enable it
       }else if(response.indexOf("LED OFF") > 0) {
          digitalWrite(LED_PIN, LOW); // turn off
       }
       delay(1000);
    }
}


String gsmAnswer(){
   String answer;
   while(!gsm.available());
   while(gsm.available()){
     delay(5);
     if(Serial.available() > 0){
       char s = (char)gsm.read();
       answer += s;
     }
  }
  return answer;
}

One think more, incomming sms has the following format:

+CMT: "+48xxxxxxxxx","","17/07/07,21:57:04+08"
Test of arrived messages

Comments

[mehmet]

hi, GPRS.print("AT+CMGF=1\r\n"); or GPRS.print("AT+CMGF=1\r"); why did you use \n, is that necessary.