Sim900 and Arduino Ethetnet

Hi guys!

I have a little project where need to read some sms messages form a sim900 and pass throught an Arduino Ethernet in order to strore the info into a Mysql DB via PHP.

The think is that the sim900 is working ok by itself.
The Arduino Ethernet is working ok by itself.

But when I try to combine both of then, it get stuck between the sim900 and arduino ethernet.

Attached the code and where it get stucked.

Any ideas???



#include “SIM900.h”
#include <SoftwareSerial.h>
#include <Ethernet.h>
#include <SPI.h>
#include “sms.h”

byte mac = { 0x00, 0xAA, 0xBB, 0xCC, 0xDE, 0x01 }; // RESERVED MAC ADDRESS
EthernetClient client;

String t = “var1”; // TEMPERATURE VAR
String h = “var2”; // HUMIDITY VAR
String data;

int numdata;
boolean started=false;
char smsbuffer[160];
char n[20];

void setup()

//Serial connection.
Serial.println(“GSM Shield testing.”);

if (gsm.begin(2400)) {
} else Serial.println("\nstatus=IDLE");

if(started) {


// IF I ENABLE THE “gsm.begin…” code the program get stuck right here at the “If (Ethernet.begin…” sentence with no message at the serial console.
// IF I DISABLE THE “gsm.begin…” the program continue with no problems.

if (Ethernet.begin(mac) == 0) {

Serial.println(“Failed to configure Ethernet using DHCP”);


data = “”;


void loop()



I am guessing that the two shields are trying to access the same pins.

String  t = "var1";  // TEMPERATURE VAR
String h = "var2";  // HUMIDITY VAR

How are those anything remotely like reasonable initial values?

What pins ARE the two shields using? We know that the Ethernet shield is an SPI device, do it uses pins 10, 11, 12, 13, and 4. But, we don't know what pins the GSM modem uses.