Problems with a Program to send a text message from PIC16 using GSM module

Ian Rogers said:

What pic pins are you using for Txd and Rxd?? I think that the line

Code:

#use rs232 (baud = 9600, xmit=PIN_B0,rcv=PIN_B1,stream=GSM)

is messing you up...

In C you put characters in single quotes ie.. transmit('A'); If you put it in double quotes.. C will append the string with a 0.

There is a serial example in C in my tutorials... The link in my signature.. tutorial 7_7..

There doesn't seem to be ANY difference between transmit() and transmitn()...

Click to expand...

#include<htc.h>
#define _XTAL_FREQ 20000000
__CONFIG(0x37F2);
#use rs232 (baud = 9600, xmit=PIN_B0,rcv=PIN_B1,stream=GSM)


void transmit(unsigned char data);      //for transmitting ascii characters

{
TRISC=0b10000000;
SPBRG = 0x81;	 //Baud=9600 at 20 MHz
TXSTA = 0x24;	 
RCSTA = 0x90;


transmit('A');
transmit('T');
transmit('+');
transmit('C');
transmit('M');
transmit('G');
transmit('F');
transmit('=');
transmit('\"');

transmit('9');
transmit('8');
transmit('4');
transmit('6');
transmit('0');
transmit('5');
transmit('1');
transmit('2');
transmit('5');
transmit('6');
transmit('\"');

transmit('\r');

transmit('h');
transmit('e');
transmit('l');
transmit('l');
transmit('o');
transmit(0x1a);
}


void transmit(unsigned char data)
{
while(!TXIF);
TXREG = data;
}

Diver300 said:

I think that you need to send
AT+CMGF=1
to get the GSM module into text mode.

Then you need to send
AT+CMGS=”+nnnnnnnnnnnn” (where nnnnnnnn is the number you want it sent to)

and when the GSM module replies with
>
you can send the message followed by a return.

I would suggest that you connect a terminal emulator to the module, so that you can type the commands by hand to check that they work. It is a good idea to have a test setup that allows the terminal emulator to see what the processor sends to the GSM module, and what the GSM module sends to the processor. That makes it much easier to see what is actually happening.

Click to expand...

Diver300 said:

I don't quite understand your setup. A diagram might help. Here are a few suggestions in no particular order.

You don't want a MAX232 to connect a PIC to the GSM module as both use the same voltage levels.

The output of the PIC should go to the RXD input of the GSM module. As that is an input, it shouldn't affect any voltages on it so you should be able to see the commands being sent from the PIC when the GSM module is connected.

If you put a 1 kΩ resistor between the PIC and the GSM module, you should get the same signal at both ends of the resistor. If not you have got two outputs fighting.

If you get the PIC to send once a second:-
OK[LF][CR]
(where [LF] is the line feed character and [CR] is carriage return)
then the GSM module will reply with

OK

Keep the baud rate low, say 4800 or 9600, at least to start with.

Some GSM modules are very fussy about how precise the timing of the serial data is.

Click to expand...