Strange characters after typing an AT command in serial monitor

Projects Programming
1

I'm trying to test AT commands (I am working with an Arduino Uno and a GSM/GPRS SIM900 shield; my system is ubuntu 14.10) . Yesterday when I was testing , all ran well.. For example after typing AT+SAPBR=3,1,"APN","ooredoo" in the serial monitor it showed me OK.. but But now it shows me strange characters.

this is mys GSM/GPRS SIM900

This is my code

#include <SoftwareSerial.h>
    SoftwareSerial GPRS(2,3);


void setup() {
  // put your setup code here, to run once:
 GPRS.begin(9600);
  Serial.begin(9600);
 Serial.write("start");

}

void loop() {

  // put your main code here, to run repeatedly:
     while(GPRS.available()) 
     Serial.write(GPRS.read()); 

  while(Serial.available())
    GPRS.write(Serial.read());  


}

And this it is the result of AT+SAPBR=3,1,"APN","ooredoo" typed in the serial monitor(see below :attachment)

Thank you for helping me

er.png
er.png762×304 15.3 KB

2

try changing the software serial setup to the following in your code:

SoftwareSerial GPRS(7, 8);

Source for determining change:
http://www.geeetech.com/wiki/index.php/Arduino_GPRS_Shield
Z

3

try changing the software serial setup to the following in your code:

Given that "Yesterday when I was testing , all ran well.", it seem highly unlikely that changing the pins is somehow magically going to help.

OP: I suspect that you changed the baud rate that the device is communicating at, and have not changed the code to reflect the new baud rate. "Yesterday when I was testing..." tells us nothing about what you did.

4

thank to reply... i understand what you are saying...the led of NET always blink after 3 seconds normally...i don't change the connection pin on the Shield or code source...the only thing i did is to reset Arduino Uno board While it was connected to the Shield . the baud on serial monitor has always been 9600 ...i supect that the communication between ARDUINO UNO and my GSM/GPSR Shield Does not go well...if i change SoftwareSerial GPRS(2, 3); nothing will work..

5

the baud on serial monitor has always been 9600

The speed that the Arduino uses to talk to the PC has nothing to do with the speed it uses to talk to the GSM shield.

In both cases, though, the speed must match what the other device expects.

6

Thank you paul ...you are the best...

 GPRS.begin(2400);
  Serial.begin(9600);

i change the GPRS speed to 2400 and it work perfectly ...since 3 long days i was worry to this