One blink every three seconds or so indicates the device is connected to the network and ready to use - so far so good...
What happens if you use a simple passthrough code like this>
//Serial Relay - Arduino will patch a
//serial link between the computer and the GPRS Shield
//at 19200 bps 8-N-1
//Computer is connected to Hardware UART
//GPRS Shield is connected to the Software UART
#include <NewSoftSerial.h>
NewSoftSerial mySerial(7, 8); // You must change these port numbers to reflect the serial pins you're using
void setup()
{
mySerial.begin(19200); // the GPRS baud rate
Serial.begin(19200); // the GPRS baud rate
Serial.println("Turning on");
}
void loop()
{
if(Serial.available())
{
mySerial.print((unsigned char)Serial.read());
}
else if(mySerial.available())
{
Serial.print((unsigned char)mySerial.read());
}
}
If you load this code then you should be able to communicate with the modem froam a terminal program
It can be recommended not to use use the built-in terminal program in Arduino, as this have problems passing the and signals through, use the bray terminal instead
If you cannot make this work you could try different (slower) baudrates. The SIM900 module most likely will be set to 'autobauding', so it should adapt by itself - at least in theory 