Getting Error on AT+CSTT and AT+CIFSR

Question

I'm completely new to Arduino, so please forgive me if something I ask here sounds stupid. So I have this Arduino UNO & Arduino compatible GSM-GPRS-GPS Simcomm SIM808 module that I'm working with. I want it to communicate with a Web server, but I can't even get it to start.

Following is my Arduino code:

#include<SoftwareSerial.h>

SoftwareSerial mySerial(2,3);




void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  mySerial.begin(9600);
}

void loop() {
  // put your main code here, to run repeatedly:
  Serial.println("Starting GSM...");
  mySerial.println("AT");
  Serial.println(getResponse());
  mySerial.println("AT+CSTT=\"TATA.DOCOMO.INTERNET\",\"\",\"\"");
  Serial.println(getResponse());
  mySerial.println("AT+CIFSR");
  Serial.println(getResponse());
}

String getResponse(){
  while(!mySerial.available()>0);
  return mySerial.readString();
}

And this is what I'm getting:

Starting GSM...
AT

OK

AT+CSTT="TATA.DGCOMO.INTERNET","",""

ERROR
ÿ
AT+CIFSR

ERROR

Starting GSM...
AT

OK

AT+CSTT="TATA.DOCOMO.INTERNET","",""

ERROR

AT+CIFSR

ERROR

Starting GSM...
AT

OK

AT+CSTT="TATA.DOCOMO.INTERNET","",""

ERROR

AT+CIFSR

ERROR
ÿÿÿÿ
Starting GSM...
AT

OK
ÿ
AT+CSTT="TATA.DOCOMO.INTERNET","",""

ERROR

AT+CIFSR

ERROR

I have no clue why it's happening & why I'm getting those ÿÿ in the result.

Take a look at this, it might help you: github.com/helmutkemper/__old_ArduinoRobot/blob/master/Codigos/… — Rasmus Friis Kjeldsen
While I cannot say why AT+CSTT fails, I can give some tip on how to fix your response handling (which at least is present, good start). Using while(!mySerial.available()>0) will never work reliably; it is doomed to fail on you sooner or later. You must change to parse the response from the modem on a strict line by line basis. If the modem only sends you half a line you should block until the complete line is received. See this answer for details. — hlovdal
You might get some useful details in the error responses by running AT+CMEE=2, although be aware that sometimes they are not that accurately describing the core problem and must be taken with a grain of salt. — hlovdal
What is firmware version of SIM808? how about putting some delay between AT commands and serial response? — Studuino

Abhishek Kumar Abhishek Kumar · Accepted Answer · 2018-06-25T10:43:14

ÿÿÿÿ This string appears when you restarts the SIM modem since you are getting it in the middle of your program, it is probably caused by insufficient power supply.

Getting Error on AT+CSTT and AT+CIFSR

2 Answers