How to interface GSM Module with PIC18F4550 Microcontroller- (Part 17/25)




The Global System for Mobile (GSM) communication is the Second Generation of mobile technology. Although the world is moving towards Third and Fourth generation but GSM has been the most successful and widespread technology in the communication sector. GSM technology paved a new way for mobile communication.
This project explains the interfacing of a GSM Module with a PIC microcontroller. It also covers a way to dial a particular GSM mobile number as well as send a message to it using AT Commands with the help of PIC18F4550.
 
As explained earlier (refer GSM interfacing with 8051), a line converter MAX232 is employed to convert the RS232 logic data of GSM Module to TTL logic so that it can be processed by the microcontroller. In this project, instead of RS232 logic data, TTL logic output has been taken and thus PIC18F4550 has been directly connected with GSM Modem without any line converter in between. The following diagram shows the TTL input and output of GSM modem used.
 
How to interface GSM Module with PIC18F4550 Microcontroller- (Part 17 25)

Objectives:

This project has following objectives which are fulfilled using AT Commands:

1.      Test the simple AT Command.
2.      Find out the IMEI number of the GSM Modem.
3.      Connect a call to a GSM mobile number (Dial a number).
4.      Send a text message to a mobile number.
 
The provision of these four operations has been provided by means of four tactile switches. Each switch corresponds to each of the above functions. AT Commands used to perform the above operations have been given below along with their output. (For complete list of AT Commands supported by GSM Modem, refer the list in tutorial on AT Commands.

1. Test the simple AT Command.
AT     (Enter)
 
OK
 
2. Find out the IMEI number of the GSM modem.

AT+GSN     (Enter)
xxxxxxxxxxxxxxx(15- digit unique IMEI number) 
 
OK
 
3. Dial a number.
ATDXXXXXXXXXX;     (Enter) (10-digit mobile number)
 
OK
 
4. Send a text message.
AT+CMGS= “XXXXXXXXXX”     (Enter) (10-digit mobile number)
>Hello ^z                    (Enter message after ‘>’ and use Ctrl+z to terminate the message)

 
The program for the controller is written in a manner so that when a particular switch is pressed, its corresponding command will be called to execute. LCD is also interfaced with PIC18F4550 to display the results. The circuit connections of GSM module, LCD and switches with controller are shown in the circuit diagram tab. Check the video for the execution of this project.
 
Programming Steps:
1. Store all AT commands into strings.
2. Set the baud rate of microcontroller to 9600bps.
3. Enable serial port. (Refer USART with PIC)
4. Enable the global and peripheral interrupt bits of the INTCON register.
5. Configure Port D as input port.
6. Use if condition to detect the pressed switch.
7. As switch is pressed, process the corresponding AT command and transmit via USART.
8. Reception interrupt method is used to store the GSM output data into an array.
9. Display the stored value on the LCD. (Refer displaying text on LCD using PIC)
 

Project Source Code

###

//Program to interface GSM Modem with PIC18F4550 Microcontroller
//This code takes four choices as four inputs

//Choice 1 : Test the simple AT Command.
//Choice 2 : Find out the IMEI number of the GSM Modem.
//Choice 3 : Connect a call to a GSM mobile number.
//Choice 4 : Send a text message to a mobile number.

#define FREQ 12000000
#define baud 9600
#define spbrg_value (((FREQ/64)/baud)-1)
#define rs LATA.F0
#define rw LATA.F1
#define en LATA.F2
#define lcdport LATB

void tx_data(unsigned char);
unsigned char rx_data();
void lcd_ini();
void lcdcmd(unsigned char);
void lcddata(unsigned char);
void gsm_cmd(unsigned char *);
void output(void);

unsigned char value=0;
int i=0,j,k,temp,flag,choice;
unsigned char *starting_text=”Enter choice=”;
unsigned char *dial_text=”Dialing…”;
unsigned char *at_cmd=”AT”;
unsigned char *imei_cmd=”AT+GSN”;
unsigned char *call_cmd=”ATD9xxxxxxxxx;”; // Provide a 10-Digit Mobile Number
unsigned char *sms_format=”AT+CMGF=1″;
unsigned char *sms_write=”AT+CMGS=”xxxxxxxxxx””; // 10-Digit Mobile Number
unsigned char *sms=”Hello”;
unsigned char *sms_report=”SMS Sent…”;
unsigned char sms_terminate=0x1A;
unsigned char enter=0x0D;
unsigned char *data;

void main()
{
TRISB=0; // Set Port B as output port
LATB=0;
TRISA=0;
LATA=0;
TRISD=0xFF;
LATD=0;
SPBRG=spbrg_value; // Fill SPBRG register to set the baud rate
RCSTA.SPEN=1; // To activate serial port (Tx and Rx pins)
TXSTA.TXEN=1; // Activate Transmissiom
RCSTA.CREN=1; // Activate Reception
PIE1.RCIE=1; // Enable Reception interrupt
INTCON.GIE=1; // Enable Global interrupt
INTCON.PEIE=1; // Enable Peripheral interrupt

lcd_ini();
while(1)
{
k=0;
lcdcmd(0x80);
while(starting_text[k]!=”)
{
lcddata(starting_text[k]);
k++;
}

//Check inputs

//Choice 1
if(PORTD.F0)
{
gsm_cmd(at_cmd);
output();
Delay_ms(1000);
}

//Choice 2
if(PORTD.F1)
{
gsm_cmd(imei_cmd);
output();
Delay_ms(1000);
}

//Choice 3
if(PORTD.F2)
{
gsm_cmd(call_cmd);
output();
Delay_ms(1000);
}

//Choice 4
if(PORTD.F3)
{
gsm_cmd(sms_format);
output();
Delay_ms(1000);

gsm_cmd(sms_write);
output();
Delay_ms(1000);

gsm_cmd(sms);
output();
tx_data(0x1A);
Delay_ms(1000);
}

}

}

void gsm_cmd(unsigned char *string)
{
i=0;j=0;
while(string[i]!=”)
{
temp=0;
if(string[i]==0x5C) // Not to send ” cahracter
i++;
tx_data(string[i]); // Send by serial communication
i++;
while(temp!=1);
}
temp=0;
tx_data(enter); // Send ASCII code for ‘Enter’ key
while(temp!=1);
}

void output(void) // To print data on LCD
{
lcdcmd(0x01);
i=-1;flag=0;
while(i<j)
{
if(flag>1)
{
flag=0;
Delay_ms(500);
lcdcmd(0x01);
lcdcmd(0x80);
}
if(data[i]==0x0A) // This condition is to avoid double Enter




// during execution of a command
{
flag++;
lcdcmd(0xc0);
}
if(data[i]==’>’||data[i]=='”‘) // Not to print this character
{
i++;
lcdcmd(0xc0);
}
if(data[i]!=0x0D&&data[i]!=0x0A&&data[i]!=0x1A) // Condition to print the data
// except ‘Enter’,’New line’ and ‘Submit’

{
lcddata(data[i]);
i++;
}
else
i++;
Delay_ms(300);
}
lcdcmd(0x01);
}

void tx_data(unsigned char serial_data) // Transmit data function
{
TXREG=serial_data;
while(PIR1.TXIF==0);
}

void interrupt()
{
data[j]=RCREG; // Store the data into array when Reception interrupt occurs
value=RCREG;
j++;
temp=1;
}

void lcd_ini()
{
lcdcmd(0x38); // Configure the LCD in 8-bit mode, 2 line and 5×7 font
lcdcmd(0x0C); // Display On and Cursor Off
lcdcmd(0x01); // Clear display screen
lcdcmd(0x06); // Increment cursor
lcdcmd(0x80); // Set cursor position to 1st line, 1st column
}

void lcdcmd(unsigned char cmdout)
{
lcdport=cmdout; //Send command to lcdport=PORTB
rs=0;
rw=0;
en=1;
Delay_ms(10);
en=0;
}

void lcddata(unsigned char dataout)
{
lcdport=dataout; //Send data to lcdport=PORTB
rs=1;
rw=0;
en=1;
Delay_ms(10);
en=0;
}

###




Source: How to interface GSM Module with PIC18F4550 Microcontroller- (Part 17/25)




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