CODEWITHSUNDEEP
echoresponseavrat-commandsim900
STILL_Lok4
STILL_Lok4

Reputation: 31

Sim900 only echos back the commands- No response

I'm using Atmega32 and sim900 for a project. I keep sending "AT" command and wait for the "OK" response, but all I am getting is AT\r\n. I've checked and rechecked wiring and my baud rate, but still getting no where. Whatever I send to sim900 I only get echoed back of the same transmitted string.

Can anyone help me please? I'd really appreciate it.

I'm posting my code here:

int sim900_init(void)
{   
    while(1)
    {
    sim_command("AT");
    _delay_ms(2000);
    }
return 0;
}

void usart_init(void)
{
/************ENABLE USART***************/
    UBRRH=(uint8_t)(MYUBRR>>8);
    UBRRL=(uint8_t)(MYUBRR);                         //set baud rate
    UCSRB=(1<<TXEN)|(1<<RXEN);             //enable receiver and transmitter
    UCSRC=(1<<UCSZ0)|(1<<UCSZ1)|(1<<URSEL);  // 8bit data format

    UCSRB |= (1 << RXCIE); // Enable the USART Recieve Complete interrupt (USART_RXC)

/***************FLUSH ALL PRIVIOUS ACTIVITIES********************/

    flush_usart();

/*********APPOINT POINTERS TO ARRAYS********************/

    command=commandArray;       // Assigning the pointer to array
    response=responseArray;     //Assigning the pointer to array

/*****************ENABLE INTRUPT***************************/
sei();                          //Enabling intrupts for receving characters
}


void flush_usart(void)
{
    response_full=FALSE;        //We have not yet received the  
}

void transmit_char(unsigned char value)
{
    while (!( UCSRA & (1<<UDRE)));            // wait while register is free
    UDR = value; 
}

void sim_command(char *cmd)
{
    int j=0;
    strcpy(command,cmd);
    while(*(cmd+j)!='\0')
    {
         transmit_char(*(cmd+j)); 
         j++;
    }
     transmit_char(0x0D);   // \r                   // after all the at commands we should send \r\n so, we send it here after the string
     transmit_char(0x0A);   // \n

}

unsigned char recieve_char(void)
{   
    char temp;
    while(!(UCSRA) & (1<<RXC));           // wait while data is being received
    temp=UDR;
    LCDdata(lcdchar,temp);
    return temp;
}

void recive_sim900_response(void)
{
    static int i=0;
    char temp;
    temp=recieve_char();

    if(temp!='\n' && temp!='\r')        // We dont want \r \n that will be send from Sim so we dont store them
    *(response+i)=temp;

        if(i==8)                    //when null char is sent means the string is finished- so we have full response
        {                               //we use them later in WaitForResponse function. we wait until the full response is received
            i=0;                                    
            response_full=TRUE;
        }
        else
            i++;
}

Upvotes: 3

Views: 2809

Answers (2)

HallMark
HallMark

Reputation: 101

By default GSM module is in echo back ON mode. And you need to change your command.

sim_command("AT");

you need Enter=CR/LF after Command so modify your code like this and give a try

sim_command("AT\r");

And in case you want to turn off echo back of command you send then you should send this command once you have OK response back for AT command.

sim_command("ATE0\r"); //Echo back OFF
sim_command("ATE1\r"); //Echo back ON

Upvotes: 0

Felix Scheinost
Felix Scheinost

Reputation: 473

You were the only one who had exactly the same problem as I.

Somehow the library from gsmlib.org worked but entering AT commands directly using the Arduino serial monitor using the Arduino as a bridge or just an FTDI didn't.

The reason is that apparently the SIM900 expects commands to end with an '\r' character. I found this by trying GTKTerm which worked.

If typing "AT" and pressing enter in GTKTerm what is actually sent is "AT" followed by twice '\r' (0x0d) and one 0x0a

Upvotes: 1

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