user30272: 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 <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

Thank you for helping me

user30272: 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

30272: <p>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.</p>

<p>This is my code</p>

<pre><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());  


}
</code></pre>

<p>And this it is the result of AT+SAPBR=3,1,"APN","ooredoo" typed in the serial monitor</p>

<p><a href="https://i.stack.imgur.com/IaJie.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/IaJie.png" alt="enter image description here"></a></p>

<p>Thank you for helping me</p>
 30272: <p>for those who have this issue, i resolve this by changing the speed baud of my GPRS Shield :</p>

<pre><code>GPRS.begin(2400); 
Serial.begin(9600);
</code></pre>

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

<pre><code>GPRS.begin(2400); 
    Serial.begin(2400);
</code></pre>

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