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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

enter image description here

Thank you for helping me

  • Did you select the right baud rate? I get these strange characters when I have set it wrong. – Juergen Jan 23 '17 at 16:55
  • i didn't change anything...it worked like this yesterday,but now i have this strange characters...what can be the problem? – EL General Jan 23 '17 at 21:16
  • You haven't changed any settings, but have you knocked a wire. It could be a loose connection or a bad ground connection. – Code Gorilla Jan 24 '17 at 8:37
  • bad connection? i don't know..but the shield work normaly..the red led is on, the station led is also on and the net led blind every 3 seconds – EL General Jan 24 '17 at 12:27
1

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

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