Strange characters after typing an AT command in serial monitor 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 my code

    #include &lt;SoftwareSerial.h&gt;
    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



Thank you for helping me
for those who have this issue, i resolve this by changing the speed baud of my GPRS Shield :

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


and if you want to test AT command directly on the serial monitor you must use 2400 anywhere 

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


and don't forget to change also  the speed on the serial monitor to 2400
I hope this will help someone