Arduino Uno + GSM Shield + StarHub Sim Card : Send / Recv SMS

2013101801.c

#include <GSM.h>

// the gsm library instances
GSM gsmAccess ;
GSM_SMS sms ;

void setup() {
  
  // initialize serial communications
  Serial.begin( 9600 ) ;
  
  // start gsm shield
  Serial.println( "GSM is initializing" ) ;
  boolean notConnected = true ;
  while ( notConnected ) {
    if ( gsmAccess.begin() == GSM_READY ) {
      notConnected = false ;
    } else {
      Serial.println( "GSM is not connected" ) ;
      delay( 1000 ) ;
    }
  }
  Serial.println( "GSM is initialized" ) ;
  
}

void loop() {
  
  // when there is new sms arrived it will raised sms.available() as true
  if ( sms.available() ) {

    // read the mobile number
    char mobileNumber[20] ;
    sms.remoteNumber( mobileNumber , 20 ) ;

    // read the message text
    char ch ;
    String st = String( "" ) ;
    while ( ch = sms.read() ) {
      st += ch ;
    }
    sms.flush() ;    
    int lenText = st.length() + 1 ;
    char messageText[ lenText ] ;
    st.toCharArray( messageText , lenText ) ;
    
    // display it
    Serial.print( mobileNumber ) ;
    Serial.print( " > " ) ;
    Serial.println( messageText ) ;
    
    // send the reply sms back with prefix RE:
    sms.beginSMS( &mobileNumber[1] ) ;
    sms.print( "RE: " ) ;
    sms.print( messageText ) ;
    sms.endSMS() ;
    
    delay( 1000 ) ;
    
  } // if ( sms.available() )
  
}