Interfacing of GSM SIM908 and 89v51rd2

[Amit Raijade]

Hello frnds..

 

I m doing a small project on sending SMS through above mentioned modules

I m using 8051 development board made by nskelectronics.

 

My hardware connections:-

 

RX of 908 to TX of Controller. and vice versa.

 

My Queries:-

 

1>  Is there more connection to do?

2> Should i bypass max232 IC from board?

3> How to check OK response after every AT command?

 

My code:-

 

#include <reg51.h>

#include <stdio.h>

 

sbit BIT1 = P0^0;

sbit BIT2 = P0^1;

 

char phone_number1[13]= “+9197xxxxxxxx”;        

char phone_number2[13]= “+9197xxxxxxxx”;

char msg1[10] = “HELLO”

char msg2[10] = “SYSTEM”;

 

 

char aux_string[20];

void delay_ms(unsigned int);

void send_sms(char[],char[]);

 

 

void serial_init() {

SCON=0x50; //setup for 8-bit data

TMOD=0x20; //setup timer 1 for auto-reload

TH1=0xfd; //Baud Rate 9600

TR1=1; //turn on timer 1

//TI=1; //indicate ready to transmit

}

 

void send_serial(unsigned char *s){

while (*s != 0x0){

 

SBUF = *s;

while (!TI){

 

}

TI = 0;

s++;

}

}

 

void main(){

BIT1 = 1;

     BIT2 = 1;

delay_ms(800);

serial_init(); //Initialize Serial port.

 

if(BIT1 == 1){

 

send_sms(phone_number1,msg1);

}

 

else if(BIT2 == 1){

 

send_sms(phone_number2, msg2);

}

else{

send_serial(“check pin statusn”);

}

}

 

void delay_ms(unsigned int iTime){

unsigned int i,j;

for(i = 0 ; i < iTime ; i++)

for(j = 0 ; j < 1275 ; j++);

}

 

void send_sms(char phone_number[],char msg[]){

send_serial(“ATr”);

delay_ms(2000);

 send_serial(“AT+CREG=1r”);

delay_ms(2000);

 send_serial(“AT+CMGF=1r”);

delay_ms(2000);

sprintf(aux_string,”AT+CMGS=”%s””, phone_number);

 send_serial(aux_string);

 send_serial(“r”);

delay_ms(2000);

send_serial(msg);

 send_serial(“r”);

delay_ms(2000);

send_serial(“0x1Ar”);

delay_ms(3000);

}

 

 

 

[AJISH ALFRED]

Hi Amit,

 

1>  Is there more connection to do?

Connect the ground lines together.

 

2> Should i bypass max232 IC from board?

If you are connecting the gsm module through db9 connector then you must use max232 at the microcontroller end.

 

3> How to check OK response after every AT command?

 

Take this piece of code,

send_serial(“ATr”);

delay_ms(2000);

 

Instead of using a delay, try something like this;

 

while ( strcmp( “OK” == receive_serial_string () ) );

 

where, “receive_serial_string ()” is a function which you have to write, that can read a string from the serial port. The statement will loop there itself until the received string matches with the required sting “OK”

[Amit Raijade]

thank you Ajish..

[Author]

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