Three or more Arduino slaves sending bytes to 2 different I2C devices

Question

I'm trying to connect 3 Arduinos with this scheme: Arduino1 Master, Arduino2 Slave, Arduino3 Slave. The slave devices need to communicate with each other and I'm trying to programming Arduino2 and transmit bytes to the other slave device Arduino3 and Master Arduino1 at the same time. Is that possible?

Master CODE:

#include <Wire.h>

void setup() {
  Wire.begin();
}

void loop() {
  Wire.requestFrom(0x04, 2);
  while (Wire.available()) {
    var1 = Wire.read();
    var2 = Wire.read();
  }
}

Arduino1 Slave:

#include <Wire.h>

void setup() {
  Wire.begin(0x05);
  Wire.onReceive(receiveEvent);
}

void loop() {
}

void receiveEvent(int howMany) {
  var1 = Wire.read();
  Serial.print("VAR1 is : ");
  Serial.println(var1);
}

Adrduino2 Slave code:(Where I think I'm wrong)

#include <Wire.h>
int var = 123;
int var2 = 123;
int var3 = 123;

void setup() {
  Wire.begin(0x04);
  Wire.onRequest(requestEvent);
}

void loop() {
  Wire.beginTransmission(0x05);
  Wire.write(var);
  Wire.endTransmission();
}

void requestEvent() {
  Wire.write(var1);
  Wire.write(var2);
}

Is this the correct way to make the Arduino2 send to 2 devices?

Answer 1

As soon as an Arduino starts writing data, it is a Master. Do you use Arduino Mega 2560 and Arduino Uno and Nano boards ? In theory those ATmega microcontrollers can handle collisions in a multi-Master bus, and in theory the Wire library handles collisions as well. However, everyone tries to avoid that, because it causes a lot of problems. You would even have to program a complete new layer in the code to re-transmit data until it was received without collision.

Select one Arduino board as Master, and use the Master to read and write data. If you want to transfer data from one Slave to the other Slave, then use Master to read the data from one Slave and write the data to the other Slave.

It is possible to use other busses between the two Slave Arduino boards.