Example of I2C communication between Raspberry Pi and Arduino

I2CPiArduino.ino

#include <Wire.h>

#define SLAVE_ADD 0x08 // Set Arduino I2C address
#define NOTE_C5 523
#define NOTE_E5 659
#define NOTE_G5 784
#define BUTTON 2
#define BUZZER 8

int pin;
int ledArrayHigh;
int ledArrayLow;
volatile int mode = 0;
int prevMode = 0;
boolean buttonPressed = false;

void setup()
{
  pinMode(BUTTON, INPUT_PULLUP);
  for (pin = 3; pin < 14; pin++) {
    pinMode(pin, OUTPUT);
  }

  Wire.begin(SLAVE_ADD);
  Wire.onReceive(receiveEvent);
  Wire.onRequest(requestEvent);
}

// Where the Magic Happens
void loop()
{
  if (digitalRead(BUTTON) == LOW &&
      buttonPressed == false) {
    buttonPressed = true;
  }
  else if (digitalRead(BUTTON) == HIGH &&
           buttonPressed == true) {
    buttonPressed = false;
  }

  if (mode != prevMode) {
    prevMode = mode;
    pin = 0;
    if (mode == 1) {
      tone(BUZZER, NOTE_C5, 100);
      delay(100);
      tone(BUZZER, NOTE_G5, 100);
      delay(100);
      noTone(BUZZER);
    }
    else if (mode == 2) {
      tone(BUZZER, NOTE_G5, 100);
      delay(100);
      tone(BUZZER, NOTE_C5, 100);
      delay(100);
      noTone(BUZZER);
    }
  }

  for (pin = 0; pin < 5; pin++) {
    if (mode == 1) {
      ledArrayHigh = 13 - pin;
      ledArrayLow = 7 - pin;
    }
    else if (mode == 2) {
      ledArrayHigh = 9 + pin;
      ledArrayLow = 3 + pin;
    }
    else if (mode == 3) {
      digitalWrite(ledArrayHigh, LOW);
      digitalWrite(ledArrayLow, LOW);
      continue;
    }
    digitalWrite(ledArrayHigh, HIGH);
    digitalWrite(ledArrayLow, HIGH);
    delay(100);
    digitalWrite(ledArrayHigh, LOW);
    digitalWrite(ledArrayLow, LOW);
    if (pin == 4) delay(100);
  }
}

// function that executes whenever data is received from master
// this function is registered as an event, see setup()
void receiveEvent(int howMany)
{
  int inData = Wire.read(); // receive byte as an integer
  Serial.println(inData); // print the integer
  mode = inData;
}

// function that executes whenever data is requested by master
// this function is registered as an event, see setup()
void requestEvent()
{
  if (buttonPressed) {
    Wire.write(4);
  }
  else {
    Wire.write(5);
  }
}

I2CPiArduino.py

from gpiozero import LED, Button, Buzzer
import smbus
from time import sleep

LED1 = LED(17)
LED2 = LED(18)
LED3 = LED(27)
LED4 = LED(22)
LED5 = LED(5)
LED6 = LED(12)
LED7 = LED(13)
LED8 = LED(19)

SW1 = Button(21)
SW2 = Button(16)
SW3 = Button(20)

BUZZER = Buzzer(26)

i2c = smbus.SMBus(1)
I2C_ADD = 0x08 # Arduino I2C address

def beep(times, delay):
  for x in range(times):
    BUZZER.on()
    sleep(delay)
    BUZZER.off()
    sleep(delay)

def writeI2C(data):
  i2c.write_byte(I2C_ADD, data)

def readI2C():
  inData = i2c.read_byte(I2C_ADD)
  return inData

prevI2CData = 0
beep(2, 0.07)

try:
  while True:
    if SW1.is_pressed:
      writeI2C(1)
      SW1.wait_for_release()

    elif SW2.is_pressed:
      writeI2C(2)
      SW2.wait_for_release()

    elif SW3.is_pressed:
      writeI2C(3)
      SW3.wait_for_release()

    I2Cdata = readI2C()
    if I2Cdata != prevI2CData:
      prevI2CData = I2Cdata
      if I2Cdata == 4:
        LED1.off()
        LED2.off()
        LED3.off()
        LED4.off()
        LED5.on()
        LED6.on()
        LED7.on()
        LED8.on()
        beep(1, 0.07)
                
      elif I2Cdata == 5:
        LED1.on()
        LED2.on()
        LED3.on()
        LED4.on()
        LED5.off()
        LED6.off()
        LED7.off()
        LED8.off()

      sleep(0.1)

except KeyboardInterrupt:
  GPIO.cleanup()