I'd like to set up a CAN network of multiple nodes using Arduino Pro Minis and MCP2515 cards. But I can't get the Receive to work.
#include <mcp_can.h>
#include <SPI.h>
long unsigned int rxId;
unsigned char len = 0;
unsigned char rxBuf[8];
char msgString[128];
#define CAN0_INT 2 // Set INT to pin 2
MCP_CAN CAN0(10); // Set CS to pin 10
void setup() {
Serial.begin(115200);
// Initialize MCP2515 running at 8MHz with a baudrate of 125kb/s
// and the masks and filters disabled.
while (CAN_OK != CAN0.begin(MCP_ANY, CAN_125KBPS, MCP_8MHZ)) {
Serial.println("CAN BUS Module Failed to Initialize.");
}
Serial.println("MCP2515 Initialized Successfully!");
CAN0.setMode(MCP_NORMAL);
pinMode(CAN0_INT, INPUT); // Configuring pin for /INT input
}
void loop() {
if(!digitalRead(CAN0_INT)) { // If CAN0_INT is low, read receive buffer
CAN0.readMsgBuf(&rxId, &len, rxBuf); // Read data: len = data length, buf = data byte(s)
if((rxId & 0x80000000) == 0x80000000) // Is ID standard (11 bits) or extended (29 bits)?
sprintf(msgString, "Extended ID: 0x%.8lX DLC: %1d Data:", (rxId & 0x1FFFFFFF), len);
else
sprintf(msgString, "Standard ID: 0x%.3lX DLC: %1d Data:", rxId, len);
Serial.print(msgString);
if((rxId & 0x40000000) == 0x40000000) { // Is message a remote request frame?
sprintf(msgString, " REMOTE REQUEST FRAME");
Serial.print(msgString);
} else {
for(byte i = 0; i<len; i++) {
sprintf(msgString, " 0x%.2X", rxBuf[i]);
Serial.print(msgString);
}
}
Serial.println();
}
}
However, all I get out are the error messages, including this:
Entering Configuration Mode Failure
What am I missing here?
I got the circuit to work. The 2-node CAN Bus is communicating.
I found this site and made a couple of changes:
My Arduino ProMini MISI, MISO pins were not aligned with the SI, SO pins on the MCP2515s.
I used the CAN_BUS_Shield library.
Related
I'm trying to get the following project running:
https://github.com/kalanda/esp8266-sniffer
The project is about Probe Frame / Probe Request. It let's a simple ESP8266 act like a WLAN Router, and collect all incoming Probe Frames. Every Probe Frame should include the MAC address of the device, and one SSID of it's saved networks. That's it.
I have copied the code of the project on my ESP8266.
I have 3 different smartphones laying around.
So now, when I look in the Serial Monitor, I should see all the packages from my 3 smartphones, every package should include the MAC address of the smartphone, and also one of the saved SSID's, which it was connected to in the past.
I see everything, except for the SSID's.
I can see the Probe Frames, coming from my different smartphones, but the SSID's are just blank.
Anyone has a idea?
Here is the complete code of the project.
Also, I have attached a screenshot of my Serial Monitor output. I have just painted the MAC addresses of my smartphones green. So as you can see, no SSIDs.
I'm very thankful for EVERY help or idea!
Thanks in advance,
EMHA.
SCREENSHOT OF SERIAL MONITOR OUTPUT
#include <Arduino.h>
extern "C" {
#include <user_interface.h>
}
#define DATA_LENGTH 112
#define TYPE_MANAGEMENT 0x00
#define TYPE_CONTROL 0x01
#define TYPE_DATA 0x02
#define SUBTYPE_PROBE_REQUEST 0x04
struct RxControl {
signed rssi:8; // signal intensity of packet
unsigned rate:4;
unsigned is_group:1;
unsigned:1;
unsigned sig_mode:2; // 0:is 11n packet; 1:is not 11n packet;
unsigned legacy_length:12; // if not 11n packet, shows length of packet.
unsigned damatch0:1;
unsigned damatch1:1;
unsigned bssidmatch0:1;
unsigned bssidmatch1:1;
unsigned MCS:7; // if is 11n packet, shows the modulation and code used (range from 0 to 76)
unsigned CWB:1; // if is 11n packet, shows if is HT40 packet or not
unsigned HT_length:16;// if is 11n packet, shows length of packet.
unsigned Smoothing:1;
unsigned Not_Sounding:1;
unsigned:1;
unsigned Aggregation:1;
unsigned STBC:2;
unsigned FEC_CODING:1; // if is 11n packet, shows if is LDPC packet or not.
unsigned SGI:1;
unsigned rxend_state:8;
unsigned ampdu_cnt:8;
unsigned channel:4; //which channel this packet in.
unsigned:12;
};
struct SnifferPacket{
struct RxControl rx_ctrl;
uint8_t data[DATA_LENGTH];
uint16_t cnt;
uint16_t len;
};
// Declare each custom function (excluding built-in, such as setup and loop) before it will be called.
// https://docs.platformio.org/en/latest/faq.html#convert-arduino-file-to-c-manually
static void showMetadata(SnifferPacket *snifferPacket);
static void ICACHE_FLASH_ATTR sniffer_callback(uint8_t *buffer, uint16_t length);
static void printDataSpan(uint16_t start, uint16_t size, uint8_t* data);
static void getMAC(char *addr, uint8_t* data, uint16_t offset);
void channelHop();
static void showMetadata(SnifferPacket *snifferPacket) {
unsigned int frameControl = ((unsigned int)snifferPacket->data[1] << 8) + snifferPacket->data[0];
uint8_t version = (frameControl & 0b0000000000000011) >> 0;
uint8_t frameType = (frameControl & 0b0000000000001100) >> 2;
uint8_t frameSubType = (frameControl & 0b0000000011110000) >> 4;
uint8_t toDS = (frameControl & 0b0000000100000000) >> 8;
uint8_t fromDS = (frameControl & 0b0000001000000000) >> 9;
// Only look for probe request packets
if (frameType != TYPE_MANAGEMENT ||
frameSubType != SUBTYPE_PROBE_REQUEST)
return;
Serial.print("RSSI: ");
Serial.print(snifferPacket->rx_ctrl.rssi, DEC);
Serial.print(" Ch: ");
Serial.print(wifi_get_channel());
char addr[] = "00:00:00:00:00:00";
getMAC(addr, snifferPacket->data, 10);
Serial.print(" Peer MAC: ");
Serial.print(addr);
uint8_t SSID_length = snifferPacket->data[25];
Serial.print(" SSID: ");
printDataSpan(26, SSID_length, snifferPacket->data);
Serial.println();
}
/**
* Callback for promiscuous mode
*/
static void ICACHE_FLASH_ATTR sniffer_callback(uint8_t *buffer, uint16_t length) {
struct SnifferPacket *snifferPacket = (struct SnifferPacket*) buffer;
showMetadata(snifferPacket);
}
static void printDataSpan(uint16_t start, uint16_t size, uint8_t* data) {
for(uint16_t i = start; i < DATA_LENGTH && i < start+size; i++) {
Serial.write(data[i]);
}
}
static void getMAC(char *addr, uint8_t* data, uint16_t offset) {
sprintf(addr, "%02x:%02x:%02x:%02x:%02x:%02x", data[offset+0], data[offset+1], data[offset+2], data[offset+3], data[offset+4], data[offset+5]);
}
#define CHANNEL_HOP_INTERVAL_MS 1000
static os_timer_t channelHop_timer;
/**
* Callback for channel hoping
*/
void channelHop()
{
// hoping channels 1-13
uint8 new_channel = wifi_get_channel() + 1;
if (new_channel > 13) {
new_channel = 1;
}
wifi_set_channel(new_channel);
}
#define DISABLE 0
#define ENABLE 1
void setup() {
// set the WiFi chip to "promiscuous" mode aka monitor mode
Serial.begin(115200);
delay(10);
wifi_set_opmode(STATION_MODE);
wifi_set_channel(1);
wifi_promiscuous_enable(DISABLE);
delay(10);
wifi_set_promiscuous_rx_cb(sniffer_callback);
delay(10);
wifi_promiscuous_enable(ENABLE);
// setup the channel hoping callback timer
os_timer_disarm(&channelHop_timer);
os_timer_setfn(&channelHop_timer, (os_timer_func_t *) channelHop, NULL);
os_timer_arm(&channelHop_timer, CHANNEL_HOP_INTERVAL_MS, 1);
}
void loop() {
delay(10);
}
The probe requests that you are recording most probably do not even contain an SSID.
Directed probes (targetting a specific SSID) came somewhat out of fashion, mainly for privacy reasons (clients are revealing the SSID they are looking for). What you are seeing are broadcast probe requests. Basically the same thing, but difference is that they do contain an SSID. All access points that receive such probe request frames reply with a probe response, this way allowing the client to aggregate a list of networks in range.
Directed probe requests nowadays are only sent just right before a (re-) connection is established. So maybe it helps if you disconnect/reconnect some clients from the Wi-Fi network to test your code?
I have bought a "APDS-9930" ambient light sensor, which communicates over I2C (TWI) protocol. I intend to read the the ambient light level from it, using ARDUINO Mega2560 development board. As I searched the net, I found a modified ARDUINO library, based on APDS-9960, which claims to work with APDS-9930 on ARDUINO UNO. However, when used with Mega2560, It gives me "Error initializing" error. Does anyone here know how to handle this error?
I have already used "Wire.h" library in many ways, to read "CH0 ADC data register" with address 0x14, which holds the ambient level value (according to datasheet). The code is as follows:
#define DUMP_REGS
#include <Wire.h>
#include <APDS9930.h>
// Global Variables
APDS9930 apds = APDS9930();
float ambient_light = 0; // can also be an unsigned long
uint16_t ch0 = 0;
uint16_t ch1 = 1;
void setup() {
//analogReference(EXTERNAL);
// Initialize Serial port
Serial.begin(9600);
Serial.println();
Serial.println(F("--------------------------------"));
Serial.println(F("APDS-9930 - Ambient light sensor"));
Serial.println(F("--------------------------------"));
// Initialize APDS-9930 (configure I2C and initial values)
//if ( apds.init() ) {
// Serial.println(F("APDS-9930 initialization complete"));
//} else {
// Serial.println(F("Something went wrong during APDS-9930 init!"));
// }
// Start running the APDS-9930 light sensor (no interrupts)
//if ( apds.enableLightSensor(false) ) {
// Serial.println(F("Light sensor is now running"));
// } else {
// Serial.println(F("Something went wrong during light sensor init!"));
// }
#ifdef DUMP_REGS
/* Register dump */
uint8_t reg;
uint8_t val;
for(reg = 0x00; reg <= 0x19; reg++) {
if( (reg != 0x10) && \
(reg != 0x11) )
{
apds.wireReadDataByte(reg, val);
Serial.print(reg, HEX);
Serial.print(": 0x");
Serial.println(val, HEX);
}
}
apds.wireReadDataByte(0x1E, val);
Serial.print(0x1E, HEX);
Serial.print(": 0x");
Serial.println(val, HEX);
#endif
// Wait for initialization and calibration to finish
delay(500);
}
void loop() {
// Read the light levels (ambient, red, green, blue)
if ( !apds.readAmbientLightLux(ambient_light) ||
!apds.readCh0Light(ch0) ||
!apds.readCh1Light(ch1) ) {
Serial.println(F("Error reading light values"));
} else {
Serial.print(F("Ambient: "));
Serial.print(ambient_light);
Serial.print(F(" Ch0: "));
Serial.print(ch0);
Serial.print(F(" Ch1: "));
Serial.println(ch1);
}
// Wait 1 second before next reading
delay(1000);
}
As discussed in the comments above, the issue is hardware related.
On the Arduino Mega 2560 board there are two resistances tying lines SDA and SCK (pins 20 and 21 on the connector) to +5V.
With those pull-up resistances, it's not possible to interface with sensors working at 3.3V directly.
The solution is to add a level shifter or remove the resistances on the board and install them externally connecting them to 5V or 3.3V as necessary depending on the sensor you want to interface to.
I'm trying to get VGM CAN message out of a Reachstacker 42-45 tonnes
where I am using an arduino MEGA 2560 with a CAN-BUS shield
this my current code:
#include <SPI.h>
#include "mcp_can.h"
// the cs pin of the version after v1.1 is default to D9
// v0.9b and v1.0 is default D10
const int SPI_CS_PIN = 9;
MCP_CAN CAN(SPI_CS_PIN); // Set CS pin
void setup()
{
Serial.begin(115200);
START_INIT:
if(CAN_OK == CAN.begin(CAN_500KBPS)) // init can bus : baudrate = 500k
{
Serial.println("CAN BUS Shield init ok!");
}
else
{
Serial.println("CAN BUS Shield init fail");
Serial.println("Init CAN BUS Shield again");
delay(100);
goto START_INIT;
}
}
void loop()
{
unsigned char len = 0;
unsigned char buf[8];
if(CAN_MSGAVAIL == CAN.checkReceive()) // check if data coming
{
CAN.readMsgBuf(&len, buf); // read data, len: data length, buf: data buf
unsigned char canId = CAN.getCanId();
Serial.println("-----------------------------");
Serial.println("get data from ID: ");
Serial.println(canId);
for(int i = 0; i<len; i++) // print the data
{
Serial.print(buf[i]);
Serial.print("\t");
}
Serial.println();
}
}
this was the result at the time of doing the test, the problem that I do not understand the result
according to the documentation should have a result like this :
this is another part of the documentation :
If someone needs more information or does not understand what I'm looking for, you can request what you need to help me
Send data:
// demo: CAN-BUS Shield, send data
#include <mcp_can.h>
#include <SPI.h>
// the cs pin of the version after v1.1 is default to D9
// v0.9b and v1.0 is default D10
const int SPI_CS_PIN = 9;
MCP_CAN CAN(SPI_CS_PIN); // Set CS pin
void setup()
{
Serial.begin(115200);
START_INIT:
if(CAN_OK == CAN.begin(CAN_500KBPS)) // init can bus : baudrate = 500k
{
Serial.println("CAN BUS Shield init ok!");
}
else
{
Serial.println("CAN BUS Shield init fail");
Serial.println("Init CAN BUS Shield again");
delay(100);
goto START_INIT;
}
}
unsigned char stmp[8] = {0, 1, 2, 3, 4, 5, 6, 7};
void loop()
{
// send data: id = 0x00, standrad frame, data len = 8, stmp: data buf
CAN.sendMsgBuf(0x00, 0, 8, stmp);
delay(100); // send data per 100ms
}
You have two pieces that do not fit between your documentation and the output you are generating:
The data payload
The ID of the CAN frames
For the data payload it is simply a matter of formatting. You print each byte as integer value, whereas in the documentation it is printed as hexadecimal values. Use
Serial.print(buf[i], HEX)
to get the payload printed as hexadecimal characters.
For the ID of the CAN frames, you see from the documentation that they do not fit inside an unsigned char, as already mentioned in the comment by #Guille. Actually those are 29-bit identifiers, which you should ideally store in an appropriately sized variable. Ideally use an unsigned long:
unsigned long canId = CAN.getCanId();
In the documentation the CAN ID is also printed in hexadecimal, so also here use:
Serial.println(canId, HEX);
I have written below code for Arduino Uno to scan an RFID card using a RC522 module and an ESP8266 module to connect to my router.
Now when I scan any card it should read the card number and send a request to my server's IP address and get the response.
But after successfully reading the RFID card, the connection to the server via TCP does not work:
esp.println("AT+CIPSTART=\"TCP\",\"" + server + "\",80");//start a TCP connection.
So I am not able to send a request to my server.
But when I remove the RC522 code (for testing) it is working!
What is the problem using the RC522 and the ESP8266 together?
#include <SPI.h>
#include <MFRC522.h>
#include "SoftwareSerial.h"
#include <Wire.h>
#include <LiquidCrystal_I2C.h>
//I2C pins declaration
LiquidCrystal_I2C lcd(0x3F, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE);
#define SS_PIN 9
#define RST_PIN 7
#define mainLock 2
String ssid = "MYSSID";
String password = "PASSWORD";
SoftwareSerial esp(2, 3);// RX, TX
String server = "192.168.1.102"; //Your Host
String uri = "/get_data.php?rfid_key=";
//#define LED_G 4 //define green LED pin
//#define LED_R 5 //define red LED
#define BUZZER 6 //buzzer pin
MFRC522 mfrc522(SS_PIN, RST_PIN); // Create MFRC522 instance.
String rfidUid = "";
#define DEBUG true
void setup()
{
// Serial.begin(9600); // Initiate a serial communication
esp.begin(9600);
Serial.begin(9600);
SPI.begin(); // Initiate SPI bus
mfrc522.PCD_Init(); // Initiate MFRC522
connectWifi();
httpget();
delay(1000);
Serial.println("Put your card to the reader...");
Serial.println();
pinMode(mainLock, OUTPUT);
lcd.begin(16, 2); //Defining 16 columns and 2 rows of lcd display
lcd.backlight();//To Power ON the back light
}
void connectWifi() {
sendData("AT+RST\r\n", 2000, DEBUG); //This command will reset module to default
sendData("AT+CWMODE=3\r\n", 1000, DEBUG);
String cmd = "AT+CWJAP=\"" + ssid + "\",\"" + password + "\"";
esp.println(cmd);
delay(4000);
if (esp.find("OK")) {
Serial.println("Connected!");
}
else {
Serial.println("Cannot connect to wifi ! Connecting again...");
connectWifi();
}
}
/////////////////////////////GET METHOD///////////////////////////////
void httpget() {
// // Look for new cards
if ( ! mfrc522.PICC_IsNewCardPresent())
{
return;
}
// Select one of the cards
if ( ! mfrc522.PICC_ReadCardSerial())
{
return;
}
//Show UID on serial monitor
Serial.print("UID tag :");
String content = "";
byte letter;
rfidUid = "";
for (byte i = 0; i < mfrc522.uid.size; i++)
{
Serial.print(mfrc522.uid.uidByte < 0x10 ? " 0" : " ");
Serial.print(mfrc522.uid.uidByte, HEX);
content.concat(String(mfrc522.uid.uidByte < 0x10 ? " 0" : " "));
content.concat(String(mfrc522.uid.uidByte, HEX));
rfidUid += String(mfrc522.uid.uidByte < 0x10 ? "0" : "");
rfidUid += String(mfrc522.uid.uidByte, HEX);
}
Serial.println();
content.toUpperCase();
lcd.clear();
lcd.setCursor(0, 0);
lcd.print(rfidUid);
esp.println("AT+CIPSTART=\"TCP\",\"" + server + "\",80");//start a TCP connection.
if ( esp.find("OK")) {
Serial.println("TCP connection ready");
} delay(1000);
if ( esp.find("OK")) {
Serial.println("TCP connection ready");
} delay(1000);
String getRequest =
"GET " + uri + rfidUid + " HTTP/1.0\r\n" +
"Host: " + server + "\r\n" +
"Accept: *" + "/" + "*\r\n" +
"Content-Type: text/plain\r\n" +
"\r\n";
String sendCmd = "AT+CIPSEND=";
esp.print(sendCmd);
esp.println(getRequest.length());
delay(500);
if (esp.find(">")) {
Serial.println("Sending..");
esp.print(getRequest);
if (esp.find("SEND OK")) {
Serial.println("Packet sent");
while (esp.available()) {
String response = esp.readString();
Serial.println("response.." + response);
}
esp.println("AT+CIPCLOSE");
}
}
}
void loop()
{
httpget();
}
String sendData(String command, const int timeout, boolean debug) // Function to send the data to the esp8266
{
String response = "";
esp.print(command); // Send the command to the ESP8266
long int time = millis();
while ( (time + timeout) > millis()) // ESP8266 will wait for some time for the data to receive
{
while (esp.available()) // Checking whether ESP8266 has received the data or not
{
char c = esp.read(); // Read the next character.
response += c; // Storing the response from the ESP8266
}
}
if (debug)
{
Serial.print(response); // Printing the response of the ESP8266 on the serial monitor.
}
return response;
}
Forum link - https://forum.arduino.cc/index.php?topic=538180.0
Unfortunately you are not showing the differences between the code that is working (partially, TCP connection) and the one that is not (at all, or just the TCP connection?).
when i remove the Rc522 code testing then it is working !
Just try to describe what is working and what isn't a little more in detail. You could also provide your debug output and add some comments.
Also I'd try removing more non-essential code (like the display) to help narrow down the cause. This might already get you on the right track to fix it yourself, but it would also make your code here easier to read (also see How to create a Minimal, Complete, and Verifiable example though I doubt many will have the exact parts to reproduce your problem - but you might get lucky).
But, from the code you've provided, here's just a guess:
The Arduino might not be receiving data from the ESP8266 module because you are reconfiguring the RX pin as output (but you're not using it!?):
#define mainLock 2
...
pinMode(mainLock, OUTPUT);
conflicts with
SoftwareSerial esp(2, 3);// RX, TX
So I'd recommend double-checking your pin use and connections (also, providing this information would increase your chances of somebody spotting an error).
I'm using I2C to communicate a Master Arduino to 4 Slaves Arduinos, and an Shield (OULIMEX Shield LCD 16x2) on every Arduino slave.
I send Data from the master to slaves using I2C. So I use this code in the master :
#include <Wire.h>
#include <math.h>
#include <floatToString.h>
double incomingData;
void setup()
{
Wire.begin();
Serial.begin(9600);
incomingData = Serial.parseFloat(); //read incoming data
}
void loop()
{
delay (1000);
if (Serial.available())
{
incomingData = Serial.parseFloat(); //read incoming data
Wire.beginTransmission(8); // transmit to device #8
if ((M==0) || (M==1) || (M==2))
Wire.beginTransmission(8); // transmit to device #8 *****************************************************************
else
Wire.beginTransmission(7); // transmit to device #7 *****************************************************************
M++;
if (M==5)
M=0;
String a = "";
a = floatToString(test,incomingData,3,5,true);
for(i=0; a[i]!='\0'; ++i); // length of the string
Wire.write(i);
Wire.write(floatToString(test,incomingData,3,5,true)); // sends one byte
Wire.endTransmission(); // stop transmitting
}
}
I wanted the Data to be printed on the Shield, but I'm connecting all slaves with the same way with the master. For that I have two problems :
1- The global data I'm using to print value is always printed as 0, and not giving the real value;
2- All Shields print the same thing : For exemple, I print "hello" in the first Shield, and I print "hi" in the second Shield, but bouth are printing the same thing (hello or hi).
The code using for the first slave is :
#include <LCD16x2.h>
#include <Wire.h>
LCD16x2 lcd;
int buttons;
int sensorPin = A0; // select the input pin for the potentiometer
int sensorValue = 0; // variable to store the value coming from the sensor
float numOut;
int comp=1 ;
String wordd = "";
int M =0;
void setup()
{
Wire.begin(8); // join i2c bus with address #8
Wire.onReceive(receiveEvent); // register event
Serial.begin(9600); // start serial for output
}
void loop()
{
delay(500);
}
// function that executes whenever data is received from master
// this function is registered as an event, see setup()
void receiveEvent(int howMany) {
wordd = "";
int x = Wire.read();
for (int i=0; i<=x; i++)
{
char c = Wire.read();
wordd += c;
}
numOut = wordd.toFloat();
Serial.println(numOut,3); // print the integer
}
Thank you in advance !!
I think it's due to a poor program structure in master shield.
This block selects the slave but on the first line you already select #8
I think this is confusing for the slaves.
Wire.beginTransmission(8); // transmit to device #8
if ((M==0) || (M==1) || (M==2))
Wire.beginTransmission(8); // transmit to device #8
else
Wire.beginTransmission(7); // transmit to device #7
This block should be at the end of the function
M++;
if (M==5)
M=0;
Then you parse the value in a string.
But leave out the first char because you write ++i instead of i++
Moreover you close the loop with ; so it does nothing
String a = "";
a = floatToString(test,incomingData,3,5,true);
for(i=0; a[i]!='\0'; ++i); // length of the string
Finally you write the ordinal number of the byte
And then again the Whole string
So you should get "0" (or "1" because of ++i)
followed by your number if Wire.write() supports it
Wire.write(i);
Wire.write(floatToString(test,incomingData,3,5,true)); // sends one byte
Wire.endTransmission(); // stop transmitting
}
Your sketch should be:
if (Serial.available())
{
incomingData = Serial.parseFloat(); //read incoming data
String a = "";
a = floatToString(test,incomingData,3,5,true);
if ((M==0) || (M==1) || (M==2))
Wire.beginTransmission(8); // transmit to device #8
else
Wire.beginTransmission(7); // transmit to device #7
for(i=0; a[i]!='\0'; ++i) // length of the string
Wire.write(a[i]); // write one byte
Wire.endTransmission(); // stop transmitting
M++;
if (M==5) M=0;
}
Let me know if this works.
I already ask this question but I think I have the answer of it. A global variable have to be diclared befor the void setup, and the void loop too, like that :
type YourGlobalVariable;
void setup()
{
}
void loop()
{
}
So, it is exactly how I did already. The reason it didn't work for me, it was cause of I used this function :
void receiveEvent(int howMany) {}
I don't really know what are the properties of it that let it not work for a global variables, but It works like I sayd already.
Thank you all