File content as of revision 1:d20ef536050e:

//It is the code of the GPRS communication by the use of the Sim800 module.
//This code has work is "to upload data on data.sparkfun.com in every 5 seconds.
//To check the uploaded data the URL is "data.sparkfun.com/streams/roYVdJgWrXUpxVpDYJpA".

#include "mbed.h"
#include <string> 

Serial sim800(D8,D2);                                   //Serial communication of the sim800 and pc.
Serial pc(USBTX,USBRX);

Ticker t_SendData;

char x[300],y[30],z[30],l[30],m[30];;
float nilai = 44 ;

void SendData();
int main()
{

    pc.baud(9600);
    sim800.baud(9600);

    pc.printf("*******GPRS TEST*******\r\n");

    sim800.printf("ATE0\r\n");                              //Command for the TURN OFF the repated terms(ECHO).
        sim800.scanf("%s",x);                               //Take response in string x given by the "sim800".
        pc.printf("%s\r\n",x);
       
        sim800.printf("AT+CGATT?\r\n");                     //To check the GPRS is attached or not.
            sim800.scanf("%s%s",x,y);
            pc.printf("%s   %s\r\n",x,y);
        
        sim800.printf("AT+CIPSHUT\r\n");                    //To reset the IP session if any.
            sim800.scanf("%s%s",x,y);
            pc.printf("%s   %s\r\n",x,y);
    
        sim800.printf("AT+SAPBR=3,1,Contype,GPRS\r\n");     //To Set the connection type to GPRS.
            sim800.scanf("%s",x);
            pc.printf("%s\r\n",x);
        
        sim800.printf("AT+SAPBR=3,1,APN,internet\r\n");          //To Set the APN to to "www" , It might be different for you, and depends on the network.
            sim800.scanf("%s",x);
            pc.printf("%s\r\n",x);
        
        sim800.printf("AT+SAPBR =1,1\r\n");                 //To Enable the GPRS.
            sim800.scanf("%s",x);
            pc.printf("%s\r\n",x);
        
        sim800.printf("AT+SAPBR =2,1\r\n");                 //To get the IP address.
            sim800.scanf("%s%s%s",x,y,z);
            pc.printf("%s   %s  %s\r\n",x,y,z); 
        
        
        sim800.printf("AT+HTTPINIT\r\n");                   //To enable the HTTP mode.
            sim800.scanf("%s",x);
            pc.printf("%s\r\n",x);
        
        sim800.printf("AT+HTTPPARA=CID,1\r\n");             //To sets up HTTP parameters for the HTTP call.
            sim800.scanf("%s",x);
            pc.printf("%s\r\n",x);
            
        t_SendData.attach(&SendData, 20);
        while(true)
        {
            //nilai = nilai + 1;
//            pc.printf("loop nilai : %f\r\n",nilai);
//        
//            sim800.printf("AT+HTTPPARA=URL,api.thingspeak.com/update?api_key=9R927S4HY3F10GRQ&field2=%0.2f\r\n",nilai);
//                                                            //The above command is for "To Set the url to the address of the webpage you want to access".
//                sim800.scanf("%s",x);
//                pc.printf("%s\r\n",x);
//            
//            sim800.printf("AT+HTTPACTION=0\r\n");           //To Start the HTTP GET session, by giving this command.
//                sim800.scanf("%s%s%s",x,y,z);
//                pc.printf("%s   %s  %s\r\n",x,y,z);
//        
//            //sim800.printf("AT+HTTPREAD\r\n");               //To read the received data.
////                sim800.scanf("%s%s%s%s%s",x,y,z,l,m);
////                pc.printf("%s   %s  %s  %s  %s\r\n",x,y,z,l,m);
////            
//            wait(10000);
        }
}

void SendData() {
    
    nilai = nilai + 1;
    pc.printf("loop nilai : %f\r\n",nilai);
        
    sim800.printf("AT+HTTPPARA=URL,api.thingspeak.com/update?api_key=9R927S4HY3F10GRQ&field3=%0.2f\r\n",nilai);
                                                            //The above command is for "To Set the url to the address of the webpage you want to access".
    sim800.scanf("%s",x);
    pc.printf("%s\r\n",x);
            
    sim800.printf("AT+HTTPACTION=0\r\n");           //To Start the HTTP GET session, by giving this command.
    sim800.scanf("%s%s%s",x,y,z);
    pc.printf("%s   %s  %s\r\n",x,y,z);
        
            //sim800.printf("AT+HTTPREAD\r\n");               //To read the received data.
//                sim800.scanf("%s%s%s%s%s",x,y,z,l,m);
//                pc.printf("%s   %s  %s  %s  %s\r\n",x,y,z,l,m);
    
}