#include <Wire.h>

void setup() {
  pinMode(2, OUTPUT);  // Setup the built-in LED
  Wire.begin();        // Begin I2C as master
  Serial.begin(115200);
}

void loop() {
  digitalWrite(2, HIGH);   // Turn on local LED
  delay(1000);             // Keep LED on for 1 second

  Wire.beginTransmission(0x04); // Address of first slave
  Wire.write(1);                // Command to turn on LED
  Wire.endTransmission();
  delay(1000);                  // Wait for 1 second

  Wire.beginTransmission(0x05); // Address of second slave
  Wire.write(1);                // Command to turn on LED
  Wire.endTransmission();
  delay(1000);                  // Wait for 1 second

  digitalWrite(2, LOW);    // Turn off local LED
  delay(1000);             // Keep LED off for 1 second

  // Repeat cycle
}