Sim908 Serial Communication not working

Projects Networking, Protocols, and Devices
1

Hi, i need you help. Yesterday I buy a SIM908 Shield. I can't read AT commands and only see strange characters.

The Shield

1200×1200 22 KB

I connect pin 10 and 11 to RX and TX

The Code

#include <SoftwareSerial.h>
#include <String.h>

int TX = 10;
int RX = 11;
int modGSM = 8;
int modGPS = 7;
int baud = 9600;
SoftwareSerial mySerial(RX,TX);
int x =0;
char rep[100];
String inData;
byte byteRead;
void setup() {
    pinMode(TX,OUTPUT);
    pinMode(RX,INPUT);
    pinMode(modGSM, OUTPUT);
    pinMode(modGPS, OUTPUT);
    
    Serial.begin(baud);
    mySerial.begin(9600);
    delay(2000);
    
    delay(300);
    Serial.println("Initializing...");
    delay(300);

    mySerial.println("A");
    delay(300);

    mySerial.print("AT\r");
    delay(300);
    

  if(mySerial.available() > 0)
    {
        Serial.println("Sim908 available");
        delay(300);
        Serial.write(mySerial.read());
          
    }
    else
    {
         Serial.println("SIM908 not available");
    }    
}

void loop() {
  mySerial.print("AT\r");
  delay(300);
    if (mySerial.available() > 0) {
       
          /* read the most recent byte */
          byteRead = mySerial.read();
          /*ECHO the value that was read, back to the serial port. */
          Serial.write(byteRead);      
          }           
    }
    
}

Serial Display

Initializing...
SIM908 available
                    þ                                           þ

Only show space and strange characters. I test change serial baud 9600,19200,115200 but not change anything.

2

Did you connect Gnd to Gnd and power to power (3.3V or 5V) ?