Some issue with Adruino Mini Pro and a SIM900 module

Dear All,

Actually I am working with a

  • Arduino Mini pro
  • A GSM module SIM900
  • A power adaptator to 4V to power the GSM module

See picture of my project

And here is the pin definition of my SIM900 GSM module

and I am using that library

I am a bit confused because it does not work and I always have that message

GSM Shield testing.
Trying to force the baud-rate to 9600

ERROR: SIM900 doesn't answer. Check power and serial pins in GSM.cpp


Second suprising think; I never can call the SIM GSM module. It like if it is not powered or switched off. However, there is green led flashin

I have no experience with the SIM900 module that you can see in the first module and may be I have not wired it correctely.

Someone has an experience with that componment?
Could you check my wire connection and let me know your advises?

Many thank for your great help. It will really help me


what is the baud rate that the gsm is set to.
have your tried a pass through sketch

look at this

different setup but it might shed some light

But it seams to be at 9600.
but what do you means by

have your tried a pass through sketch

Trying to force the baud-rate to 9600

using a pass through sketch you can use Serial monitor to send commands to the gsm module and get feedback from the gsm module to see what settings it uses. But you get more info
if you can use Terminal services. The link i sent you has a pass through sketch to do this. Not sure how you arduino board will work with it, you might have to edit some pins ect.

You should have a manual for the Gsm with the relevant AT commands you issue to the gsm module to find the relevant info.

I believe my frist issue is the pin1 of the SIM900 module.
I should not put a 4V put a pulse of 2sec.
But event if I add this in my setup() loop
in order to have a pulse

  digitalWrite(9, HIGH);
  digitalWrite(9, LOW);

it does not work

Someone has an idea about my issue?
I think my major issue is how to poser the GSM shield.
There is a pin1 where I am supposed to send a pulse of 2sec.
I did this but it did not work

void setup()

  digitalWrite(9, HIGH);
  digitalWrite(9, LOW);
  Serial.println("GSM Shield testing.");
  if (gsm.begin(2400)){
  else Serial.println("\nstatus=IDLE");
//if (inet.attachGPRS("internet.wind","", ""))
    if (inet.attachGPRS("internet","", ""))
    else Serial.println("status=ERROR");
    numdata=inet.httpGET("", 80, "/", msg, 50);
    Serial.println("\nNumero d'octet recu:");
    Serial.println("\nData recived:");
void loop()

Thank for helping

How do I send this pulse if I don't have the shield, rather just the module?