Pls i need help with my GSM/GPRS Shield

Hi all guys,
I’m new in this forum and aleready i need help :(.
I bought a Shield for my arduino mega(This one: and now i’m stuck D:
Because i’m trying to use the GSM part (SIM900) but I don’t know which one of the 6 RX/TX pins are the right ones and even which pins are the essentials for making SIM part works.

I tried it in differents combinatoins with this sketch but i receive no respond:

#include “SIM900.h”
#include <SoftwareSerial.h>
#include “sms.h”
#include “string.h”
SoftwareSerial cell(10,11);
int numdata;
boolean started=false;
char smsbuffer[160];
char n[20];
int led1= 13;
int led2= 12;
int led3= 11;
int lastsmsbuffer;
int inchar;

void setup()
//Serial connection.
Serial.println(“GSM Shield testing.”);
//Start configuration of shield with baudrate.
//For http uses is raccomanded to use 4800 or slower.
if (gsm.begin(2400)){
else Serial.println("\nstatus=IDLE");

/* if(started){
Enable this two lines if you want to send an SMS.
if (sms.SendSMS(“3388296822”, “Arduino SMS”))
Serial.println("\nSMS sent OK");


void loop()
//Read if there are messages on SIM card and print them.
if(gsm.readSMS(smsbuffer, 160, n, 20))

Does anyone know how this module works and where i’m wrong? Ty for any help.

You have a Mega. Do NOT use SoftwareSerial on the Mega!

You have the TX and RX pins of the shield connected to some pins on the Mega - there are a total of 8 RX and TX pins on the Mega, two for each of the 4 hardware serial ports. Which pins is the shield connected to?

Dear PaulS, Ty for reply. Now, as u said i'm wrong from the start, so i decided to start all over. now, I've just plugged in my Shield on Arduino (Essentials Vcc and GND), na d even insert my SIM card into the shield. Now all the status LE are on but now i'm stuck. There are those 6 pins (3 RX and 3 TX) on the shield (Right corner) and i don't know what to do...

From the website you provided: Question: Do you have documentation for this product? Answer:

: Yes, we have, you can send us an email to ask for the documents and we will send it to you

So I would start by asking for those documents. It also looks like the yellow headers need two jumpers installed - from the middle to the left pins to use D0/D1, or from the middle to the right pins to use D7/D8. If you want to use hardware serial on the mega, then connect mega pins D7/D8 to whichever pins are used for Serial1, Serial2, or Serial3.

Dear CrossRoads,
I’ve done as u said: i’ve tried to contact the product customer for receive some datasheets of the shield…but they delet my request 3 times!! :confused:
So, i decided to follow your suggestion and i’ve putted 2 jumpers on center-right to enable D8 and D7, then I’ve connected them to Serial1 of Arduino MEGA (Pin 18 and 19).
now i want to test if it works…can u make 3/4 lines of program to make me test it? (sry for all these questions but this is my first time on a GSM /GPRS Shield an i really need it works because i have to create a project for my maturity exam). :slight_smile: