I created a 3.3V side to my build.  It has my Raspberry Pi 4B and Arduino Giga R1 Wifi.  RPi_I2C_driver_27.py is the file for the I2C LCD on address 27.   As I add I2C LCD screens, this file will be copied and address and name changed to match up to the new screen.  I2cBus is 1 on the Raspberry Pi 4B.  2f is the Arduino Giga R1 Wifi.  Raspberry Pi 4B is the Master on I2C.

sudo i2cdetect -y 1
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: — — — — — — — —
10: — — — — — — — — — — — — — — — —
20: — — — — — — — 27 — — — — — — — 2f
30: — — — — — — — — — — — — — — — —
40: — — — — — — — — — — — — — — — —
50: — — — — — — — — — — — — — — — —
60: — — — — — — — — — — — — — — — —
70: — — — — — — — —

RPi_I2C_driver_27.py

# -*- coding: utf-8 -*-
# Original code found at:
# https://gist.github.com/DenisFromHR/cc863375a6e19dce359d

"""
Compiled, mashed and generally mutilated 2014-2015 by Denis Pleic
Made available under GNU GENERAL PUBLIC LICENSE

# Modified Python I2C library for Raspberry Pi
# as found on http://www.recantha.co.uk/blog/?p=4849
# Joined existing 'i2c_lib.py' and 'lcddriver.py' into a single library
# added bits and pieces from various sources
# By DenisFromHR (Denis Pleic)
# 2015-02-10, ver 0.1

"""

# i2c bus (0 -- original Pi, 1 -- Rev 2 Pi)
I2CBUS = 1

# LCD Address
ADDRESS = 0x27

import smbus
from time import sleep

class i2c_device:
def __init__(self, addr, port=I2CBUS):
self.addr = addr
self.bus = smbus.SMBus(port)

# Write a single command
def write_cmd(self, cmd):
self.bus.write_byte(self.addr, cmd)
sleep(0.0001)

# Write a command and argument
def write_cmd_arg(self, cmd, data):
self.bus.write_byte_data(self.addr, cmd, data)
sleep(0.0001)

# Write a block of data
def write_block_data(self, cmd, data):
self.bus.write_block_data(self.addr, cmd, data)
sleep(0.0001)

# Read a single byte
def read(self):
return self.bus.read_byte(self.addr)

# Read
def read_data(self, cmd):
return self.bus.read_byte_data(self.addr, cmd)

# Read a block of data
def read_block_data(self, cmd):
return self.bus.read_block_data(self.addr, cmd)


# commands
LCD_CLEARDISPLAY = 0x01
LCD_RETURNHOME = 0x02
LCD_ENTRYMODESET = 0x04
LCD_DISPLAYCONTROL = 0x08
LCD_CURSORSHIFT = 0x10
LCD_FUNCTIONSET = 0x20
LCD_SETCGRAMADDR = 0x40
LCD_SETDDRAMADDR = 0x80

# flags for display entry mode
LCD_ENTRYRIGHT = 0x00
LCD_ENTRYLEFT = 0x02
LCD_ENTRYSHIFTINCREMENT = 0x01
LCD_ENTRYSHIFTDECREMENT = 0x00

# flags for display on/off control
LCD_DISPLAYON = 0x04
LCD_DISPLAYOFF = 0x00
LCD_CURSORON = 0x02
LCD_CURSOROFF = 0x00
LCD_BLINKON = 0x01
LCD_BLINKOFF = 0x00

# flags for display/cursor shift
LCD_DISPLAYMOVE = 0x08
LCD_CURSORMOVE = 0x00
LCD_MOVERIGHT = 0x04
LCD_MOVELEFT = 0x00

# flags for function set
LCD_8BITMODE = 0x10
LCD_4BITMODE = 0x00
LCD_2LINE = 0x08
LCD_1LINE = 0x00
LCD_5x10DOTS = 0x04
LCD_5x8DOTS = 0x00

# flags for backlight control
LCD_BACKLIGHT = 0x08
LCD_NOBACKLIGHT = 0x00

En = 0b00000100 # Enable bit
Rw = 0b00000010 # Read/Write bit
Rs = 0b00000001 # Register select bit

class lcd:
#initializes objects and lcd
def __init__(self):
self.lcd_device = i2c_device(ADDRESS)

self.lcd_write(0x03)
self.lcd_write(0x03)
self.lcd_write(0x03)
self.lcd_write(0x02)

self.lcd_write(LCD_FUNCTIONSET | LCD_2LINE | LCD_5x8DOTS | LCD_4BITMODE)
self.lcd_write(LCD_DISPLAYCONTROL | LCD_DISPLAYON)
self.lcd_write(LCD_CLEARDISPLAY)
self.lcd_write(LCD_ENTRYMODESET | LCD_ENTRYLEFT)
sleep(0.2)


# clocks EN to latch command
def lcd_strobe(self, data):
self.lcd_device.write_cmd(data | En | LCD_BACKLIGHT)
sleep(.0005)
self.lcd_device.write_cmd(((data & ~En) | LCD_BACKLIGHT))
sleep(.0001)

def lcd_write_four_bits(self, data):
self.lcd_device.write_cmd(data | LCD_BACKLIGHT)
self.lcd_strobe(data)

# write a command to lcd
def lcd_write(self, cmd, mode=0):
self.lcd_write_four_bits(mode | (cmd & 0xF0))
self.lcd_write_four_bits(mode | ((cmd << 4) & 0xF0))

# write a character to lcd (or character rom) 0x09: backlight | RS=DR<
# works!
def lcd_write_char(self, charvalue, mode=1):
self.lcd_write_four_bits(mode | (charvalue & 0xF0))
self.lcd_write_four_bits(mode | ((charvalue << 4) & 0xF0))

# put string function with optional char positioning
def lcd_display_string(self, string, line=1, pos=0):
if line == 1:
pos_new = pos
elif line == 2:
pos_new = 0x40 + pos
elif line == 3:
pos_new = 0x14 + pos
elif line == 4:
pos_new = 0x54 + pos

self.lcd_write(0x80 + pos_new)

for char in string:
self.lcd_write(ord(char), Rs)

# clear lcd and set to home
def lcd_clear(self):
self.lcd_write(LCD_CLEARDISPLAY)
self.lcd_write(LCD_RETURNHOME)

# define backlight on/off (lcd.backlight(1); off= lcd.backlight(0)
def backlight(self, state): # for state, 1 = on, 0 = off
if state == 1:
self.lcd_device.write_cmd(LCD_BACKLIGHT)
elif state == 0:
self.lcd_device.write_cmd(LCD_NOBACKLIGHT)

# add custom characters (0 - 7)
def lcd_load_custom_chars(self, fontdata):
self.lcd_write(0x40);
for char in fontdata:
for line in char:
self.lcd_write_char(line)

example.py

import RPi_I2C_driver_27
from time import *

mylcd = RPi_I2C_driver_27.lcd()

mylcd.lcd_display_string("Hello World!", 1)