Not able to establish an I2C connection

Projects Networking, Protocols, and Devices
1

Hi guys,
I tried for several days now to make an I2C connection between an Arduino UNO R4 Wifi and an Arduino UNO R3. I tried programming it myself first, but it didn't work so I tried examples online with the same outcome. Here the example(https://www.instructables.com/I2C-between-Arduinos/): Master:

// Chapter 7 - Communications
// I2C Master
// By Cornel Amariei for Packt Publishing

// Include the required Wire library for I2C
#include <Wire.h>

int x = 0;

void setup() {
  // Start the I2C Bus as Master
  Wire.begin(); 
}

void loop() {
  Wire.beginTransmission(9); // transmit to device #9
  Wire.write(x);              // sends x 
  Wire.endTransmission();    // stop transmitting
 
  x++; // Increment x
  if (x > 5) x = 0; // `reset x once it gets 6
  
  delay(500);
}

Slave:

// Chapter 7 - Communications
// I2C Slave
// By Cornel Amariei for Packt Publishing

// Include the required Wire library for I2C
#include <Wire.h>

int LED = 13;
int x = 0;

void setup() {
  // Define the LED pin as Output
  pinMode (LED, OUTPUT);
  // Start the I2C Bus as Slave on address 9
  Wire.begin(9); 
  // Attach a function to trigger when something is received.
  Wire.onReceive(receiveEvent);
}

void receiveEvent(int bytes) {
  x = Wire.read();    // read one character from the I2C
}

void loop() {
  //If value received is 0 blink LED for 200 ms
  if (x == '0') {
    digitalWrite(LED, HIGH);
    delay(200);
    digitalWrite(LED, LOW);
    delay(200);
  }
  //If value received is 3 blink LED for 400 ms
  if (x == '3') {
    digitalWrite(LED, HIGH);
    delay(400);
    digitalWrite(LED, LOW);
    delay(400);
  }
}

Thank you for helping

2

Your Slave sketch s revised as follows:

#include <Wire.h>

int LED = 13;
byte x = 0;     //I2C network handles data byte by byte
volatile bool flag = false;

void setup() 
{
  // Define the LED pin as Output
  pinMode (LED, OUTPUT);
  // Start the I2C Bus as Slave on address 9
  Wire.begin(9); 
  // Attach a function to trigger when something is received.
  Wire.onReceive(receiveEvent);
}

void loop() 
{
  //If value received is 0 blink LED for 200 ms
  if(flag == true)
  {  
     if (x == 0x00)   //'0' is equal to 0x30
     {
        digitalWrite(LED, HIGH);
        delay(200);
        digitalWrite(LED, LOW);
        delay(200);
     }
     //If value received is 3 blink LED for 400 ms
     if (x == 0x03)   //'3' is equal to 0x33
     {
       digitalWrite(LED, HIGH);
       delay(400);
       digitalWrite(LED, LOW);
       delay(400);
     }
     flag = false;
  }
}

void receiveEvent(int bytes) 
{
  x = Wire.read();    // read one character from the I2C
  flag =  true;   //to tell loop() function that data has arrived from Master
}
3

I see no 4.7K pullup resistors to VCC in the schematic you refer to. There should be on the SDA and SCL line.

4

You send 2 bytes but receive only 1.

Please note the difference between char and int. The slave cannot react because it will never receive any of the coded characters.