gsm interfacing with mcu

[abhishek dhiman]

guys i need help.....how to connect gsm module with 89c51.

means do i should connect 89c51 via max232 with gsm module
or
should i directly connect Rxd and Txd pin og mcu to Txd and Rxd pin of gsm module

 

[Inti Innovations]

I'd bypass max232 and connect it directly.

 

[abhishek dhiman]

I'd bypass max232 and connect it directly.

thanks for reply

 

[Twisted_transistor]

hey abhishek.. r u using any other pins besides RX and TX? coz I'm trying to interface a GSM module with LPC2148 & its just not working..
Pls check my latest thread..

 

[abhishek dhiman]

hey abhishek.. r u using any other pins besides RX and TX? coz I'm trying to interface a GSM module with LPC2148 & its just not working..
Pls check my latest thread..

i am using only Gnd,Rxd n Txd pins... even i was able send sms twice...but i forgot pin configuration of that time.......that was just hit trial...from then onwards im still struggling :???:

 

[Twisted_transistor]

Oh man.. my code runs fine withot the GSM module connected.. But wen I connect the GSM it just hangs.. wonder wots wrong?

 

[abhishek dhiman]

same here code working in hyperterminal.......tested n verified,,,,,,,,,but now nothing....... can u help me,,,,,,,,, like i am using 8051..... it is ttl compatible,,,,,,there r three o/p in gsm module that are ttl o/p(Rxd, Txd n Gnd).
to connect it with 8051 should i use ttl pins or 2nd or 3rd pin of db9 connector.

luk at image which i have attached above.........plz help if u can

 

[irfan ahmad]

connect gsm rx to mcu tx
and gsm tx to mcu rx.
dont connect max232.
apply 4.2v to gsm.

 

[abhishek dhiman]

connect gsm rx to mcu tx
and gsm tx to mcu rx.
dont connect max232.
apply 4.2v to gsm.

thanks irfan.......i was really confused here,,,,,,,,thanks alot

 

[abhishek dhiman]

thanks irfan.......i was really confused here,,,,,,,,thanks alot

@irfan ahmad bro its again not working..... mcu is sending proper response to hyperterminal but not sending sms via gsm module....................

plz chk out my code

#include<stdio.h>
#include<reg51.h>

//Function to initialize RS232 Serial Port
void serial_init()
{
SCON=0x50; //setup for 8-bit data
TMOD=0x20; //setup timer 1 for auto-reload
TL1=0xFd; //setup for 9600 baud
TH1=0xfd; //Baud Rate 9600
TR1=1;
}



//This function displays a null-terminated string on the RS232 port
void send_serial(unsigned char *s)
{
while(*s!=0x0)
{
SBUF=*s;
while(!TI)
{
}
TI=0;
s++;
}
}

int i;
//Start of Main Program
void delay_ms(unsigned int);


main()
{
delay_ms(400);
serial_init(); //Initialize Serial port.
for(i=1;i<=2;i++)
{delay_ms(400);
send_serial("AT\r\n");
delay_ms(400);
send_serial("AT+CMGF=1\r\n");
delay_ms(400);
send_serial("AT+CMGS=\"7696240117\"\r\n");//my mob number here
delay_ms(400);
send_serial("gsm working\r\n");
delay_ms(400);
send_serial("0x1A\r\n");
delay_ms(400);delay_ms(400);delay_ms(400);delay_ms(400);


//send_serial("\"com test\"\r\n");
}
}


//generates delay in milli seconds
void delay_ms(unsigned int i)
{
unsigned int j;
while(i-->0)
{
for(j=0;j<500;j++)
{
;
}
}
}

if possible kindly test it......................
waiting 4 ur reply

 

[irfan ahmad]

TRY THIS.

 

[abhishek dhiman]

TRY THIS.

thanks irfan,,,,,this was really useful to me.... as per this post..... i have to connect 3rd pin of db9 to 11pin of mcu n 2nd pin of mcu to 10th pin......am i right????????????

- - - Updated - - -

can anybody tell gsm module is ttl compatible??????????????? bcz if it ttl compatible we do nt require max232 to connect it with gsm module.............

 

[irfan ahmad]

are you using sim900??????

you do not need max232 to communicate mcu with gsm. i already have mentioned it .
this is ttl compatable.
apply 4.2v to gsm.

 

[abhishek dhiman]

problem solved thanks frnd

 

[irfan ahmad]

my pleasure