Sim900 + Blynk via gprs

hello all, I have this idea. We can use sim900 + Blynk to make our boards more flexible than Wifi and ethernet are. Maybe, we can select one of them. It mean that we have got wifi and gprs, we use wifi and we havent got wifi we use gprs. I try to modify some function in library to do this. I wana get some advice from you. Did you ?

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You can use User_Defined_Connection example to achieve this and code all the needed logics…

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Thank you so much ! @vhymanskyy

I am also trying to do the same for a while now and I am failing wonderfully. I keep coming back to the few pages that talk about gprs and blynk and there is no updates. This is what I have so far. I can get to where it’s connected to my blynk server by tcp.

I run netstat -an 1 | find “8442” and it shows when the tcp goes from listening to established. All I see after that is blynk consistently sending my auth code in serial.

Any help would be greatly appreciated.

Serial output:

 Powering on GPRS Shield.
 SIM900 started
 Connected to the home cell network
 Attaching to Packet Service
 Attached to Packet Service
 Setting APN
 APN Set
 Starting GPRS Connection
 GPRS Connection Established
 Establishing TCP Connection
 Connected to server

Here is what I’m working with right now.

#include <BlynkSimpleUserDefined.h>
#include <SoftwareSerial.h>

// SIM900 Shield Serial Pins
SoftwareSerial SIM900(7, 8);

// You should get Auth Token in the Blynk App.
// Go to the Project Settings (nut icon).
char auth[] = "4fadeMYTOKENee6cc96eded52d";
#define ip_address "AT+CIPSTART=\"TCP\",\"\",\"8442\""

bool connected = false;

// This function is used by Blynk to receive data
size_t BlynkStreamRead(void* buf, size_t len)
  return Serial.readBytes((byte*)buf, len);

// This function is used by Blynk to send data
size_t BlynkStreamWrite(const void* buf, size_t len)
  return Serial.write((byte*)buf, len);

void setup()
  // Setup your connection here.
  pinMode(9, OUTPUT);
  Serial.begin(19200); // for serial monitor
  Serial.println("Powering on GPRS Shield.");
  SIM900.begin(19200); // Serial for GSM shield
  SIM900poweron();  // turn on shield
  sendCommand("AT", "OK", 1000);     //Wake up modem with an AT command
  if(sendCommand("AT", "OK", 1000) == 1){
    Serial.println("SIM900 started");

  do {
    connected = Blynk.connect();
  } while (!connected);

void loop()
    // Make sure that is called
  // only when the connection is established
  if (connected) {
    // Okay, handle Blynk protocol
    bool hasIncomingData = (Serial.available() > 0);
    // Tell Blynk if it has incoming data
    // (this allows to skip unneeded BlynkStreamRead calls)
    if (! {
      // Error happened. No action for serial.

void gprs()
  //Wake up modem with two AT commands
  sendCommand("AT", "OK", 1000);
  sendCommand("AT", "OK", 2000);
  sendCommand("AT+CIPSHUT", "SHUT OK", 2000);
  // Check if it's currently registered network
  if(sendCommand("AT+CREG?","+CREG: 0,1",2000)){ 
    Serial.println("Connected to the home cell network");
    Serial.println("Not connected to home cell network");
  Serial.println("Attaching to Packet Service");
    Serial.println("Attached to Packet Service");
    Serial.println("Unable to attach to Packet Service");
Serial.println("Setting APN");
    Serial.println("APN Set");
    Serial.println("Unable to set APN");
Serial.println("Starting GPRS Connection");
    Serial.println("GPRS Connection Established");
    sendCommand("AT+CIFSR", "OK", 1000);
    Serial.println("Unable to start GPRS connection");
 Serial.println("Establishing TCP Connection");

 Serial.println("Connected to server");

void SIM900poweron()
// Software equivalent of pressing the GSM shield "power" button
  //Wake up modem with an AT command
  sendCommand("AT", "OK", 1000);
  if(sendCommand("AT", "OK", 2000) == 0){
    digitalWrite(9, HIGH);
    digitalWrite(9, LOW);


int sendCommand(char* ATcommand, char* expected_answer, unsigned int timeout){

    int answer=0;
    int responsePos=0;
    char response[100];
    unsigned long previous;

    memset(response, '\0', 100);    // Clears array


    while( SIM900.available() > 0);    // Clean the input buffer

    SIM900.println(ATcommand);    // Send the AT command 

    responsePos = 0;
    previous = millis();

    // this loop waits for the answer
        // if there are data in the UART input buffer, reads it and checks for the asnwer
        if(SIM900.available() != 0){    
            response[responsePos] =;
            // 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;

I’m tring to get your code woring…
Don’t we have to add some AT+CIPSEND commands into BlynkStreamWrite and BlynkStreamRead fnctions, so Blynk lib knows how to talk?
Any help from @vshymanskyy?:grin:

For GSM/GPRS we recommend using HTTP API - it consumes much less data plan, and is easier to implement low power modes…