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Gsm presentation

  1. 1. Interfacing GSM Modem With Microcontroller By: Gaurav Arora
  2. 2. Building a Embeded system with ability to Send Sms using an GSM modem. Objective
  3. 3. WORK FLOW <ul><li>Initialize system to set parameters for transmission and interrupt </li></ul><ul><li>System waits to be triggred using a sensor or an manual External interrupt like Switch. </li></ul><ul><li>Detecting interrupt Atmega 16 Checks availability of modem and tries to send SMS using GSM Modem using AT Commands. </li></ul>
  4. 4. Defining Modules <ul><li>System Consist of three modules: </li></ul><ul><li>> Interrupt Detection. </li></ul><ul><li>> Activating USART module Transmitting and Receving Data. </li></ul><ul><li>> Sending AT commands to GSM Modem. </li></ul>
  5. 5. GSM MODEM <ul><li>A GSM modem is a wireless modem that works with a GSM wireless network. </li></ul><ul><li>AT commands are used to control modems. </li></ul><ul><li>Operations Performed by GSM Modem. </li></ul><ul><li>Reading, writing and deleting SMS messages. </li></ul><ul><li>Sending SMS messages. </li></ul><ul><li>Reading, writing and searching phone book entries. </li></ul><ul><li>GSM Modem Datasheet : 1122_datasheet.pdf in your kit </li></ul>
  6. 6. Confiuring GSM Modem <ul><li>· Insert SIM card : Press the yellow pin to remove the tray from the SIM cardholder. insert SIM card </li></ul><ul><li>Connect RS232 Cable : (Cable provided for RS232 communication) Default baud rate is 9600(using 2400) </li></ul><ul><li>with 8-N-1, no hardware handshaking. </li></ul><ul><li>o Pin 2 is RS232 level TX out </li></ul><ul><li>o Pin 3 is RS232 level RX in </li></ul><ul><li>o Pin 5 is Ground </li></ul><ul><li>Send AT commands. </li></ul>
  7. 7. Some Terms <ul><li>BAUD RATE-A baud Rate is the measurement of the number of times per second a signal in a communications channel changes. bps = baud per second x the number of bit per baud </li></ul><ul><li>8-N-1 – this config means 8 databits,no parity bit,1 stop bit. </li></ul><ul><li>RS232 - RS-232 (Recommended Standard 232) is a standard for serial binary single-ended data and control signals connecting . It is commonly used in computer serial ports. </li></ul>
  8. 8. AT commands <ul><li>AT is the abbreviation of ATtention. </li></ul><ul><li>AT commands are instructions used to control a modem. </li></ul><ul><li>AT commands used to send SMS </li></ul><ul><li>AT ; -To check if the device is available </li></ul><ul><li>AT+CMGF=1; - select the operating mode GSM or mobile using 0 and 1(GSM) </li></ul><ul><li>AT+CMGS=”mobile no.”<CR>Text Message<Ctrl+Z>; -AT commands +CMGS can be used to send SMS messages </li></ul><ul><li>All AT commands are available in 1122_at_AT_Commands.pdf in your kit </li></ul>
  9. 9. Interfacing Modem with Microcontroller
  10. 10. Output of hyper-terminal for AT commands to modem
  11. 11. USART <ul><li>USART - Universal synchronous and asynchronous receiver and transmitter. </li></ul><ul><li>Main Registers – UCSRA,UCSRB,UCSRC,UBRR,UDR </li></ul><ul><li>UCSRx – USART Control and Status Register A,B,C. </li></ul><ul><li>UBRR – USART Baud rate Register </li></ul><ul><li>UDR – USART Data Register. </li></ul><ul><li>Two UDR USART register to transmit and receive to provide full duplex mode. </li></ul><ul><li>Must Read Status Bits before receiving or transmitting Data (most important) </li></ul><ul><li>TXC and RXC flags. </li></ul>
  12. 12. Initializing USART module
  13. 13. Activating USART module(1) <ul><li>we have to enable the UART Receiver and Transmitter using bit RXEN and TXEN in UCSRB register </li></ul>
  14. 14. Activating USART module(2) <ul><li>Bit 3 – TXEN: Transmitter Enable </li></ul><ul><li>Writing this bit to one enables the USART Transmitter. The Transmitter will override nor-mal port operation for the TxD pin when enabled. The disabling of the Transmitter </li></ul><ul><li>In UCSRC register UPM1:0: bit are used to set parity bits to 0,Bit 3 – USBS:to select Stop bits, Bit 2:1 – UCSZ1:0: to select character size to 8 bits. </li></ul>
  15. 15. Activating USART module(3) <ul><li>Setting Baud Rate: </li></ul><ul><li>Set values of UBRR -USART Baud rate register according to table: </li></ul>
  16. 16. USART initialization code <ul><li>UBRRH=0x00; </li></ul><ul><li>UBRRL = (unsigned char)BaudRate; /* Set the baud rate */ </li></ul><ul><li>UCSRB = 0b00011000; // enable transmitter and reciever </li></ul><ul><li>UCSRC = 0b10000110; // 8 bit data, no parity bit, 1 stop bit. </li></ul>
  17. 17. USART Transmission <ul><li>In UCSRA register Bit 5 – UDRE: USART Data Register Empty </li></ul><ul><li>The UDRE flag indicates if the transmit buffer (UDR) is ready to receive new data. If </li></ul><ul><li>UDRE is one, the buffer is empty, and therefore ready to be written. </li></ul><ul><li>If UDRE is one put data in the buffer. </li></ul>
  18. 18. Problem with Baud rates <ul><li>GSM modem supports a wide range of baud rates 1120-12000 </li></ul><ul><li>We cannot send data using higher baud rate while transmitting USART as higher baud rate require higher clock speed which is not available on board </li></ul><ul><li>4800 and 9600 baud rates are not supported with 1MHz oscillator. </li></ul>
  19. 19. USART RECEPTION <ul><li>In UCSRA register bit 7:• Bit 7 – RXC: USART Receive Complete </li></ul><ul><li>This flag bit is set when there are unread data in the receive buffer and cleared when thereceive buffer is empty (i.e., does not contain any unread data). </li></ul>
  20. 20. Interrupt Detection <ul><li>Code sniplets used to set Interrupt. </li></ul><ul><li>GICR = 0x40; // enable external interrupt 0 </li></ul><ul><li>MCUCR = 0x02; // activate external interrupt0 (on pin16) it recognizes rising edge </li></ul><ul><li>sei();//set enable interrupts. </li></ul><ul><li>If externel interrupts is provided to system then control goes to interrupt handler and set a flag variable to one. </li></ul><ul><li>And send the required Sms. </li></ul>
  21. 21. Have a look on code!! Any Questions??
  22. 22. Thank You!