from machine import Pin, I2C
import utime
from lcd_api import LcdApi
from pico_i2c_lcd import I2cLcd
from dht import DHT11, InvalidChecksum
I2C_ADDR     = 39
I2C_NUM_ROWS = 2
I2C_NUM_COLS = 16

i2c = I2C(0, sda=machine.Pin(0), scl=machine.Pin(1), freq=400000)
lcd = I2cLcd(i2c, I2C_ADDR, I2C_NUM_ROWS, I2C_NUM_COLS)


lcd.move_to(0,0)
lcd.putstr("Custom Character")





main.py

diagram.json

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()


pico_i2c_lcd.py

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,
    # with bit numbers changed 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.
                pass
            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

    def hal_sleep_us(self, usecs):
        # Sleep for some time (given in microseconds)
        time.sleep_us(usecs)


lcd_api.py

import array
import micropython
import utime
from machine import Pin
from micropython import const
 
class InvalidChecksum(Exception):
    pass
 
class InvalidPulseCount(Exception):
    pass
 
MAX_UNCHANGED = const(100)
MIN_INTERVAL_US = const(200000)
HIGH_LEVEL = const(50)
EXPECTED_PULSES = const(84)
 
class DHT11:
    _temperature: float
    _humidity: float
 
    def __init__(self, pin):
        self._pin = pin
        self._last_measure = utime.ticks_us()
        self._temperature = -1
        self._humidity = -1
 
    def measure(self):
        current_ticks = utime.ticks_us()
        if utime.ticks_diff(current_ticks, self._last_measure) < MIN_INTERVAL_US and (
            self._temperature > -1 or self._humidity > -1
        ):
            # Less than a second since last read, which is too soon according
            # to the datasheet
            return
 
        self._send_init_signal()
        pulses = self._capture_pulses()
        buffer = self._convert_pulses_to_buffer(pulses)
        self._verify_checksum(buffer)
 
        self._humidity = buffer[0] + buffer[1] / 10
        self._temperature = buffer[2] + buffer[3] / 10
        self._last_measure = utime.ticks_us()
 
    @property
    def humidity(self):
        self.measure()
        return self._humidity
 
    @property
    def temperature(self):
        self.measure()
        return self._temperature
 
    def _send_init_signal(self):
        self._pin.init(Pin.OUT, Pin.PULL_DOWN)
        self._pin.value(1)
        utime.sleep_ms(50)
        self._pin.value(0)
        utime.sleep_ms(18)
 
    @micropython.native
    def _capture_pulses(self):
        pin = self._pin
        pin.init(Pin.IN, Pin.PULL_UP)
 
        val = 1
        idx = 0
        transitions = bytearray(EXPECTED_PULSES)
        unchanged = 0
        timestamp = utime.ticks_us()
 
        while unchanged < MAX_UNCHANGED:
            if val != pin.value():
                if idx >= EXPECTED_PULSES:
                    raise InvalidPulseCount(
                        "Got more than {} pulses".format(EXPECTED_PULSES)
                    )
                now = utime.ticks_us()
                transitions[idx] = now - timestamp
                timestamp = now
                idx += 1
 
                val = 1 - val
                unchanged = 0
            else:
                unchanged += 1
        pin.init(Pin.OUT, Pin.PULL_DOWN)
        if idx != EXPECTED_PULSES:
            raise InvalidPulseCount(
                "Expected {} but got {} pulses".format(EXPECTED_PULSES, idx)
            )
        return transitions[4:]
 
    def _convert_pulses_to_buffer(self, pulses):
        """Convert a list of 80 pulses into a 5 byte buffer
        The resulting 5 bytes in the buffer will be:
            0: Integral relative humidity data
            1: Decimal relative humidity data
            2: Integral temperature data
            3: Decimal temperature data
            4: Checksum
        """
        # Convert the pulses to 40 bits
        binary = 0
        for idx in range(0, len(pulses), 2):
            binary = binary << 1 | int(pulses[idx] > HIGH_LEVEL)
 
        # Split into 5 bytes
        buffer = array.array("B")
        for shift in range(4, -1, -1):
            buffer.append(binary >> shift * 8 & 0xFF)
        return buffer
 
    def _verify_checksum(self, buffer):
        # Calculate checksum
        checksum = 0
        for buf in buffer[0:4]:
            checksum += buf
        if checksum & 0xFF != buffer[4]:
            raise InvalidChecksum()