Arduino sketch for bridging the I2C and USB serial interfaces

i2c-to-serial-bridge.ino

/*
 * Title: I2C <-> USB serial bridge
 * Board: Arduino Pro-Micro (ATMega32U4)
 * Author: Luigi Di Fraia
 *
 * Note: This example is provided as a guideline only, without any warranty!
 */

#include <Wire.h>

const byte addressSlave = 8;    // slave's address

void setup() {
  Wire.begin(addressSlave);     // join i2c bus as slave with chosen address
  Wire.onReceive(receiveEvent); // register receive event
  Wire.onRequest(requestEvent); // register request event
  Serial.begin(9600);           // configure USB serial (always 12 Mbit/sec)
}

void loop() {
  delay(100);
}

void receiveEvent (int numBytes)
{
  while (numBytes--) {          // loop through all bytes
    byte c = Wire.read();       // receive byte on i2c bus
    Serial.write(c);            // output byte to USB serial
  }
}

void requestEvent (void)
{
  while (Serial.available()) {  // loop through all bytes
    byte c = Serial.read();     // receive byte on USB serial
    Wire.write(c);              // output byte to i2c bus
  }
}