diff --git a/lib/lcd_api.py b/lib/lcd_api.py
new file mode 100644
index 0000000..5512b3d
--- /dev/null
+++ b/lib/lcd_api.py
@@ -0,0 +1,212 @@
+"""Provides an API for talking to HD44780 compatible character LCDs."""
+
+import time
+
+class LcdApi:
+    """Implements the API for talking with HD44780 compatible character LCDs.
+    This class only knows what commands to send to the LCD, and not how to get
+    them to the LCD.
+
+    It is expected that a derived class will implement the hal_xxx functions.
+    """
+
+    # The following constant names were lifted from the avrlib lcd.h
+    # header file, however, I changed the definitions from bit numbers
+    # to bit masks.
+    #
+    # HD44780 LCD controller command set
+
+    LCD_CLR = 0x01              # DB0: clear display
+    LCD_HOME = 0x02             # DB1: return to home position
+
+    LCD_ENTRY_MODE = 0x04       # DB2: set entry mode
+    LCD_ENTRY_INC = 0x02        # --DB1: increment
+    LCD_ENTRY_SHIFT = 0x01      # --DB0: shift
+
+    LCD_ON_CTRL = 0x08          # DB3: turn lcd/cursor on
+    LCD_ON_DISPLAY = 0x04       # --DB2: turn display on
+    LCD_ON_CURSOR = 0x02        # --DB1: turn cursor on
+    LCD_ON_BLINK = 0x01         # --DB0: blinking cursor
+
+    LCD_MOVE = 0x10             # DB4: move cursor/display
+    LCD_MOVE_DISP = 0x08        # --DB3: move display (0-> move cursor)
+    LCD_MOVE_RIGHT = 0x04       # --DB2: move right (0-> left)
+
+    LCD_FUNCTION = 0x20         # DB5: function set
+    LCD_FUNCTION_8BIT = 0x10    # --DB4: set 8BIT mode (0->4BIT mode)
+    LCD_FUNCTION_2LINES = 0x08  # --DB3: two lines (0->one line)
+    LCD_FUNCTION_10DOTS = 0x04  # --DB2: 5x10 font (0->5x7 font)
+    LCD_FUNCTION_RESET = 0x30   # See "Initializing by Instruction" section
+
+    LCD_CGRAM = 0x40            # DB6: set CG RAM address
+    LCD_DDRAM = 0x80            # DB7: set DD RAM address
+
+    LCD_RS_CMD = 0
+    LCD_RS_DATA = 1
+
+    LCD_RW_WRITE = 0
+    LCD_RW_READ = 1
+
+    def __init__(self, num_lines, num_columns):
+        self.num_lines = num_lines
+        if self.num_lines > 4:
+            self.num_lines = 4
+        self.num_columns = num_columns
+        if self.num_columns > 40:
+            self.num_columns = 40
+        self.cursor_x = 0
+        self.cursor_y = 0
+        self.implied_newline = False
+        self.backlight = True
+        self.display_off()
+        self.backlight_on()
+        self.clear()
+        self.hal_write_command(self.LCD_ENTRY_MODE | self.LCD_ENTRY_INC)
+        self.hide_cursor()
+        self.display_on()
+
+    def clear(self):
+        """Clears the LCD display and moves the cursor to the top left
+        corner.
+        """
+        self.hal_write_command(self.LCD_CLR)
+        self.hal_write_command(self.LCD_HOME)
+        self.cursor_x = 0
+        self.cursor_y = 0
+
+    def show_cursor(self):
+        """Causes the cursor to be made visible."""
+        self.hal_write_command(self.LCD_ON_CTRL | self.LCD_ON_DISPLAY |
+                               self.LCD_ON_CURSOR)
+
+    def hide_cursor(self):
+        """Causes the cursor to be hidden."""
+        self.hal_write_command(self.LCD_ON_CTRL | self.LCD_ON_DISPLAY)
+
+    def blink_cursor_on(self):
+        """Turns on the cursor, and makes it blink."""
+        self.hal_write_command(self.LCD_ON_CTRL | self.LCD_ON_DISPLAY |
+                               self.LCD_ON_CURSOR | self.LCD_ON_BLINK)
+
+    def blink_cursor_off(self):
+        """Turns on the cursor, and makes it no blink (i.e. be solid)."""
+        self.hal_write_command(self.LCD_ON_CTRL | self.LCD_ON_DISPLAY |
+                               self.LCD_ON_CURSOR)
+
+    def display_on(self):
+        """Turns on (i.e. unblanks) the LCD."""
+        self.hal_write_command(self.LCD_ON_CTRL | self.LCD_ON_DISPLAY)
+
+    def display_off(self):
+        """Turns off (i.e. blanks) the LCD."""
+        self.hal_write_command(self.LCD_ON_CTRL)
+
+    def backlight_on(self):
+        """Turns the backlight on.
+
+        This isn't really an LCD command, but some modules have backlight
+        controls, so this allows the hal to pass through the command.
+        """
+        self.backlight = True
+        self.hal_backlight_on()
+
+    def backlight_off(self):
+        """Turns the backlight off.
+
+        This isn't really an LCD command, but some modules have backlight
+        controls, so this allows the hal to pass through the command.
+        """
+        self.backlight = False
+        self.hal_backlight_off()
+
+    def move_to(self, cursor_x, cursor_y):
+        """Moves the cursor position to the indicated position. The cursor
+        position is zero based (i.e. cursor_x == 0 indicates first column).
+        """
+        self.cursor_x = cursor_x
+        self.cursor_y = cursor_y
+        addr = cursor_x & 0x3f
+        if cursor_y & 1:
+            addr += 0x40    # Lines 1 & 3 add 0x40
+        if cursor_y & 2:    # Lines 2 & 3 add number of columns
+            addr += self.num_columns
+        self.hal_write_command(self.LCD_DDRAM | addr)
+
+    def putchar(self, char):
+        """Writes the indicated character to the LCD at the current cursor
+        position, and advances the cursor by one position.
+        """
+        if char == '\n':
+            if self.implied_newline:
+                # self.implied_newline means we advanced due to a wraparound,
+                # so if we get a newline right after that we ignore it.
+                self.implied_newline = False
+            else:
+                self.cursor_x = self.num_columns
+        else:
+            self.hal_write_data(ord(char))
+            self.cursor_x += 1
+        if self.cursor_x >= self.num_columns:
+            self.cursor_x = 0
+            self.cursor_y += 1
+            self.implied_newline = (char != '\n')
+        if self.cursor_y >= self.num_lines:
+            self.cursor_y = 0
+        self.move_to(self.cursor_x, self.cursor_y)
+
+    def putstr(self, string):
+        """Write the indicated string to the LCD at the current cursor
+        position and advances the cursor position appropriately.
+        """
+        for char in string:
+            self.putchar(char)
+
+    def custom_char(self, location, charmap):
+        """Write a character to one of the 8 CGRAM locations, available
+        as chr(0) through chr(7).
+        """
+        location &= 0x7
+        self.hal_write_command(self.LCD_CGRAM | (location << 3))
+        self.hal_sleep_us(40)
+        for i in range(8):
+            self.hal_write_data(charmap[i])
+            self.hal_sleep_us(40)
+        self.move_to(self.cursor_x, self.cursor_y)
+
+    def hal_backlight_on(self):
+        """Allows the hal layer to turn the backlight on.
+
+        If desired, a derived HAL class will implement this function.
+        """
+        pass
+
+    def hal_backlight_off(self):
+        """Allows the hal layer to turn the backlight off.
+
+        If desired, a derived HAL class will implement this function.
+        """
+        pass
+
+    def hal_write_command(self, cmd):
+        """Write a command to the LCD.
+
+        It is expected that a derived HAL class will implement this
+        function.
+        """
+        raise NotImplementedError
+
+    def hal_write_data(self, data):
+        """Write data to the LCD.
+
+        It is expected that a derived HAL class will implement this
+        function.
+        """
+        raise NotImplementedError
+
+    # This is a default implementation of hal_sleep_us which is suitable
+    # for most micropython implementations. For platforms which don't
+    # support `time.sleep_us()` they should provide their own implementation
+    # of hal_sleep_us in their hal layer and it will be used instead.
+    def hal_sleep_us(self, usecs):
+        """Sleep for some time (given in microseconds)."""
+        time.sleep_us(usecs)  # NOTE this is not part of Standard Python library, specific hal layers will need to override this
diff --git a/lib/machine_i2c_lcd.py b/lib/machine_i2c_lcd.py
new file mode 100644
index 0000000..6d4ac2c
--- /dev/null
+++ b/lib/machine_i2c_lcd.py
@@ -0,0 +1,82 @@
+"""Implements a HD44780 character LCD connected via PCF8574 on I2C.
+   This was tested with: https://www.wemos.cc/product/d1-mini.html"""
+
+from lcd_api import LcdApi
+from time import sleep_ms
+
+# The PCF8574 has a jumper selectable address: 0x20 - 0x27
+DEFAULT_I2C_ADDR = 0x27
+
+# Defines shifts or masks for the various LCD line attached to the PCF8574
+
+MASK_RS = 0x01
+MASK_RW = 0x02
+MASK_E = 0x04
+SHIFT_BACKLIGHT = 3
+SHIFT_DATA = 4
+
+
+class I2cLcd(LcdApi):
+    """Implements a HD44780 character LCD connected via PCF8574 on I2C."""
+
+    def __init__(self, i2c, i2c_addr, num_lines, num_columns):
+        self.i2c = i2c
+        self.i2c_addr = i2c_addr
+        self.i2c.writeto(self.i2c_addr, bytearray([0]))
+        sleep_ms(20)   # Allow LCD time to powerup
+        # Send reset 3 times
+        self.hal_write_init_nibble(self.LCD_FUNCTION_RESET)
+        sleep_ms(5)    # need to delay at least 4.1 msec
+        self.hal_write_init_nibble(self.LCD_FUNCTION_RESET)
+        sleep_ms(1)
+        self.hal_write_init_nibble(self.LCD_FUNCTION_RESET)
+        sleep_ms(1)
+        # Put LCD into 4 bit mode
+        self.hal_write_init_nibble(self.LCD_FUNCTION)
+        sleep_ms(1)
+        LcdApi.__init__(self, num_lines, num_columns)
+        cmd = self.LCD_FUNCTION
+        if num_lines > 1:
+            cmd |= self.LCD_FUNCTION_2LINES
+        self.hal_write_command(cmd)
+
+    def hal_write_init_nibble(self, nibble):
+        """Writes an initialization nibble to the LCD.
+
+        This particular function is only used during initialization.
+        """
+        byte = ((nibble >> 4) & 0x0f) << SHIFT_DATA
+        self.i2c.writeto(self.i2c_addr, bytearray([byte | MASK_E]))
+        self.i2c.writeto(self.i2c_addr, bytearray([byte]))
+
+    def hal_backlight_on(self):
+        """Allows the hal layer to turn the backlight on."""
+        self.i2c.writeto(self.i2c_addr, bytearray([1 << SHIFT_BACKLIGHT]))
+
+    def hal_backlight_off(self):
+        """Allows the hal layer to turn the backlight off."""
+        self.i2c.writeto(self.i2c_addr, bytearray([0]))
+
+    def hal_write_command(self, cmd):
+        """Writes a command to the LCD.
+
+        Data is latched on the falling edge of E.
+        """
+        byte = ((self.backlight << SHIFT_BACKLIGHT) | (((cmd >> 4) & 0x0f) << SHIFT_DATA))
+        self.i2c.writeto(self.i2c_addr, bytearray([byte | MASK_E]))
+        self.i2c.writeto(self.i2c_addr, bytearray([byte]))
+        byte = ((self.backlight << SHIFT_BACKLIGHT) | ((cmd & 0x0f) << SHIFT_DATA))
+        self.i2c.writeto(self.i2c_addr, bytearray([byte | MASK_E]))
+        self.i2c.writeto(self.i2c_addr, bytearray([byte]))
+        if cmd <= 3:
+            # The home and clear commands require a worst case delay of 4.1 msec
+            sleep_ms(5)
+
+    def hal_write_data(self, data):
+        """Write data to the LCD."""
+        byte = (MASK_RS | (self.backlight << SHIFT_BACKLIGHT) | (((data >> 4) & 0x0f) << SHIFT_DATA))
+        self.i2c.writeto(self.i2c_addr, bytearray([byte | MASK_E]))
+        self.i2c.writeto(self.i2c_addr, bytearray([byte]))
+        byte = (MASK_RS | (self.backlight << SHIFT_BACKLIGHT) | ((data & 0x0f) << SHIFT_DATA))
+        self.i2c.writeto(self.i2c_addr, bytearray([byte | MASK_E]))
+        self.i2c.writeto(self.i2c_addr, bytearray([byte]))
diff --git a/lib/pico_i2c_lcd.py b/lib/pico_i2c_lcd.py
new file mode 100644
index 0000000..fd83b8b
--- /dev/null
+++ b/lib/pico_i2c_lcd.py
@@ -0,0 +1,86 @@
+import utime
+import gc
+
+from lcd_api import LcdApi
+from machine import I2C
+
+# PCF8574 pin definitions
+MASK_RS = 0x01       # P0
+MASK_RW = 0x02       # P1
+MASK_E  = 0x04       # P2
+
+SHIFT_BACKLIGHT = 3  # P3
+SHIFT_DATA      = 4  # P4-P7
+
+class I2cLcd(LcdApi):
+    
+    #Implements a HD44780 character LCD connected via PCF8574 on I2C
+
+    def __init__(self, i2c, i2c_addr, num_lines, num_columns):
+        self.i2c = i2c
+        self.i2c_addr = i2c_addr
+        self.i2c.writeto(self.i2c_addr, bytes([0]))
+        utime.sleep_ms(20)   # Allow LCD time to powerup
+        # Send reset 3 times
+        self.hal_write_init_nibble(self.LCD_FUNCTION_RESET)
+        utime.sleep_ms(5)    # Need to delay at least 4.1 msec
+        self.hal_write_init_nibble(self.LCD_FUNCTION_RESET)
+        utime.sleep_ms(1)
+        self.hal_write_init_nibble(self.LCD_FUNCTION_RESET)
+        utime.sleep_ms(1)
+        # Put LCD into 4-bit mode
+        self.hal_write_init_nibble(self.LCD_FUNCTION)
+        utime.sleep_ms(1)
+        LcdApi.__init__(self, num_lines, num_columns)
+        cmd = self.LCD_FUNCTION
+        if num_lines > 1:
+            cmd |= self.LCD_FUNCTION_2LINES
+        self.hal_write_command(cmd)
+        gc.collect()
+
+    def hal_write_init_nibble(self, nibble):
+        # Writes an initialization nibble to the LCD.
+        # This particular function is only used during initialization.
+        byte = ((nibble >> 4) & 0x0f) << SHIFT_DATA
+        self.i2c.writeto(self.i2c_addr, bytes([byte | MASK_E]))
+        self.i2c.writeto(self.i2c_addr, bytes([byte]))
+        gc.collect()
+        
+    def hal_backlight_on(self):
+        # Allows the hal layer to turn the backlight on
+        self.i2c.writeto(self.i2c_addr, bytes([1 << SHIFT_BACKLIGHT]))
+        gc.collect()
+        
+    def hal_backlight_off(self):
+        #Allows the hal layer to turn the backlight off
+        self.i2c.writeto(self.i2c_addr, bytes([0]))
+        gc.collect()
+        
+    def hal_write_command(self, cmd):
+        # Write a command to the LCD. Data is latched on the falling edge of E.
+        byte = ((self.backlight << SHIFT_BACKLIGHT) |
+                (((cmd >> 4) & 0x0f) << SHIFT_DATA))
+        self.i2c.writeto(self.i2c_addr, bytes([byte | MASK_E]))
+        self.i2c.writeto(self.i2c_addr, bytes([byte]))
+        byte = ((self.backlight << SHIFT_BACKLIGHT) |
+                ((cmd & 0x0f) << SHIFT_DATA))
+        self.i2c.writeto(self.i2c_addr, bytes([byte | MASK_E]))
+        self.i2c.writeto(self.i2c_addr, bytes([byte]))
+        if cmd <= 3:
+            # The home and clear commands require a worst case delay of 4.1 msec
+            utime.sleep_ms(5)
+        gc.collect()
+
+    def hal_write_data(self, data):
+        # Write data to the LCD. Data is latched on the falling edge of E.
+        byte = (MASK_RS |
+                (self.backlight << SHIFT_BACKLIGHT) |
+                (((data >> 4) & 0x0f) << SHIFT_DATA))
+        self.i2c.writeto(self.i2c_addr, bytes([byte | MASK_E]))
+        self.i2c.writeto(self.i2c_addr, bytes([byte]))
+        byte = (MASK_RS |
+                (self.backlight << SHIFT_BACKLIGHT) |
+                ((data & 0x0f) << SHIFT_DATA))      
+        self.i2c.writeto(self.i2c_addr, bytes([byte | MASK_E]))
+        self.i2c.writeto(self.i2c_addr, bytes([byte]))
+        gc.collect()