In the previous post I explained how to make a connection and send data via TCP connection on SIM900 and similar modems. This post is going to be about FTP connection. FTP stands for “file transfer protocol.” FTP powers one of the fundamental Internet functions and is the prescribed method for the transfer of files between computers. It is also the easiest and most secure way to exchange files over the Internet.

Without going into much details I would show the related AT commands and brief description. Later I would include sample code for FTP upload/download using arduino and SIM900

Make sure you have a server and note the ftp port, we would consider using the default port 21. Switch on your modem and make sure pin code is disabled or properly entered and that GPRS connection is available.

1. Configure GPRS by sending AT+SAPBR=3,1,”Contype”,”GPRS”r  .
2. Set APN by sending   AT+SAPBR=3,1,”APN”,”your apn”r  .replace your apn with APN for your network.
3. Now set the username and password for the apn (replace username and password with correct values )
   AT+SAPBR=3,1,”USER”,”username”r  .
   AT+SAPBR=3,1,”PASS”,”password”r
4. Connect to GPRS connection by sending AT+SAPBR=1,1r, when connected Modem will respond with OK
5. Now select profile 1 for FTP by sending AT+FTPCID=1r
6. Now set FTP server domain or ip using the command AT+FTPSERV=ftp.yourserver.comr
7. Set FTP port by AT+FTPPORT=21r
8. Now send FTP credentials using AT+FTPUN=user_namer and AT+FTPPW=”password”r
9. To get a file from FTP send AT+FTPGETNAME=file_namer
10.  Now set the path of the file AT+FTPGETPATH=/path/r
11. Now send AT+FTPGET=1r and wait for response from server, which starts with +FTPGET:1,1
12. To upload a file to FTP server send AT+FTPPUTNAME=file_namer
13. Now set path AT+FTPPUTPATH=/pathr
14. Now send AT+FTPPUT=1 and wait for +FTPPUT:1,1 after which you need to send the content of file to be uploaded.

int8_t answer;
int onModulePin = 2;
char aux_str[30];

char incoming_data[120];

char test_str[ ]= "0000000011111111222222223333333344444444555555556666666677777777000000001111111122222222333333334444";

int data_size, aux;


void setup(){

    pinMode(onModulePin, OUTPUT);
    Serial.begin(115200);


    Serial.println("Starting...");
    power_on();

    delay(5000);

    Serial.println("Connecting to the network...");

    while( (sendATcommand("AT+CREG?", "+CREG: 0,1", 500)
            || sendATcommand("AT+CREG?", "+CREG: 0,5", 500)) == 0 );

    configure_FTP();

    uploadFTP();

    downloadFTP();

    Serial.print("Incoming data: ");
    Serial.println(incoming_data);
}


void loop(){

}


void configure_FTP(){

    sendATcommand("AT+SAPBR=3,1,"Contype","GPRS"", "OK", 2000);
    sendATcommand("AT+SAPBR=3,1,"APN","APN"", "OK", 2000);
    sendATcommand("AT+SAPBR=3,1,"USER","user_name"", "OK", 2000);
    sendATcommand("AT+SAPBR=3,1,"PWD","password"", "OK", 2000);

    while (sendATcommand("AT+SAPBR=1,1", "OK", 20000) != 1);
    sendATcommand("AT+FTPCID=1", "OK", 2000);
    sendATcommand("AT+FTPSERV="ftp.yourserver.com"", "OK", 2000);
    sendATcommand("AT+FTPPORT=21", "OK", 2000);
    sendATcommand("AT+FTPUN="user_name"", "OK", 2000);
    sendATcommand("AT+FTPPW="password"", "OK", 2000);

}


void uploadFTP(){

    sendATcommand("AT+FTPPUTNAME="file_name"", "OK", 2000);
    sendATcommand("AT+FTPPUTPATH="/path"", "OK", 2000);
    if (sendATcommand("AT+FTPPUT=1", "+FTPPUT:1,1,", 30000) == 1)
    {
        data_size = 0;
        while(Serial.available()==0);
        aux = Serial.read();
        do{
            data_size *= 10;
            data_size += (aux-0x30);
            while(Serial.available()==0);
            aux = Serial.read();
        }
        while(aux != 0x0D);

        if (data_size >= 100)
        {
            if (sendATcommand("AT+FTPPUT=2,100", "+FTPPUT:2,100", 30000) == 1)
            {
                Serial.println(sendATcommand(test_str, "+FTPPUT:1,1", 30000), DEC);
                Serial.println(sendATcommand("AT+FTPPUT=2,0", "+FTPPUT:1,0", 30000), DEC);
                Serial.println("Upload done!!");
            }
            else
            {
                sendATcommand("AT+FTPPUT=2,0", "OK", 30000);
            }
        }
        else
        {
            sendATcommand("AT+FTPPUT=2,0", "OK", 30000);
        }
    }
    else
    {
        Serial.println("Error openning the FTP session");
    }
}

void downloadFTP(){

    int x = 0;

    sendATcommand("AT+FTPGETNAME="file_name"", "OK", 2000);
    sendATcommand("AT+FTPGETPATH="/path"", "OK", 2000);
    if (sendATcommand("AT+FTPGET=1 ", "+FTPGET:1,1", 30000) == 1)
    {
        do{
            if (sendATcommand2("AT+FTPGET=2,50", "+FTPGET:2,", "+FTPGET:1,", 30000) == 1)
            {
                data_size = 0;
                while(Serial.available()==0);
                aux = Serial.read();
                do{
                    data_size *= 10;
                    data_size += (aux-0x30);
                    while(Serial.available()==0);
                    aux = Serial.read();
                }while(aux != 0x0D);

                Serial.print("Data received: ");
                Serial.println(data_size);

                if (data_size > 0)
                {
                    while(Serial.available() < data_size);
                    Serial.read();

                    for (int y = 0; y < data_size; y++)
                    {
                        incoming_data[x] = Serial.read();
                        x++;
                    }
                    incoming_data[x] = '';
                }
                else
                {
                    Serial.println("Download finished");
                }
            }
            else if (answer == 2)
            {
                Serial.println("Error from FTP");
            }
            else
            {
                Serial.println("Error getting the file");
                data_size = 0;
            }
        }while (data_size > 0);
    }
    else
    {
        Serial.println("Error openning the FTP session");
    }
}




void power_on(){

    uint8_t answer=0;

    // checks if the module is started
    answer = sendATcommand("AT", "OK", 2000);
    if (answer == 0)
    {
        digitalWrite(onModulePin,HIGH);
        delay(3000);
        digitalWrite(onModulePin,LOW);

        while(answer == 0){     // Send AT every two seconds and wait for the answer
            answer = sendATcommand("AT", "OK", 2000);
        }
    }
}


int8_t sendATcommand(char* ATcommand, char* expected_answer, unsigned int timeout){

    uint8_t x=0,  answer=0;
    char response[100];
    unsigned long previous;

    memset(response, '', 100);    // Initialize the string

    delay(100);

    while( Serial.available() > 0) Serial.read();    // Clean the input buffer

    Serial.println(ATcommand);    // Send the AT command


        x = 0;
    previous = millis();

    // this loop waits for the answer
    do{
        if(Serial.available() != 0){
            // if there are data in the UART input buffer, reads it and checks for the asnwer
            response[x] = Serial.read();
            //Serial.print(response[x]);
            x++;
            // check if the desired answer  is in the response of the module
            if (strstr(response, expected_answer) != NULL)
            {
                answer = 1;
            }
        }
    }
    // Waits for the asnwer with time out
    while((answer == 0) && ((millis() - previous) < timeout));

        return answer;
}

int8_t sendATcommand2(char* ATcommand, char* expected_answer1,
            char* expected_answer2, unsigned int timeout){

    uint8_t x=0,  answer=0;
    char response[100];
    unsigned long previous;

    memset(response, '', 100);    // Initialize the string

    delay(100);

    while( Serial.available() > 0) Serial.read();    // Clean the input buffer

    Serial.println(ATcommand);    // Send the AT command


        x = 0;
    previous = millis();

    // this loop waits for the answer
    do{
        // if there are data in the UART input buffer, reads it and checks for the asnwer
        if(Serial.available() != 0){
            response[x] = Serial.read();
            x++;
            // check if the desired answer 1 is in the response of the module
            if (strstr(response, expected_answer1) != NULL)
            {
                answer = 1;
            }
            // check if the desired answer 2 is in the response of the module
            if (strstr(response, expected_answer2) != NULL)
            {
                answer = 2;
            }
        }
        // Waits for the asnwer with time out
    }while((answer == 0) && ((millis() - previous) < timeout));

        return answer;
}