Raspberry Pi Pico si afisajul LCD 20x04 cu interfata I2C

In acest articol vom vedea cum se poate folosi un afisaj LCD uzual si foarte raspandit de genul 16x02, 16x04 sau 20x04. Aceste tipuri de afisaje se pot folosi impreuna cu un adaptor I2C pentru a simplifica legatura intre display si Raspberry Pi Pico.

Pentru functionarea displayului avem nevoie de minim 3 fisiere: lcd_api.py, i2c_lcd.py si main.py.

Conexiunea se va realiza in modul urmator:

LCD       ---        Raspberry Pi Pico

VCC        -           VBUS (Pin 40)

GND        -           GND (Pin 38)

SDA         -           GPIO0 (Pin 1)

SCL         -            GPIO1 (Pin 2)

Fisierul lcd_api.py este cel de mai jos:

import time
 
class LcdApi:
 
    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)

Fiserul i2c_lcd.py este cel de mai jos:

from lcd_api import LcdApi
from machine import I2C
from time import sleep_ms
 
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 character based 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 intiialization.
        """
        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]))

Fisierul main.py este mult mai simplu si poate fi vazut mai jos:

from i2c_lcd import I2cLcd
from machine import I2C
from machine import Pin
import utime as time

i2c = I2C(id=0, scl=Pin(1), sda=Pin(0), freq = 100000)
lcd = I2cLcd(i2c, 0x27, 4, 20)

while True:
    lcd.move_to(0, 0)
    lcd.putstr('testare randul 1')
    lcd.move_to(0, 1)
    lcd.putstr('testare randul 2')
    lcd.move_to(0, 2)
    lcd.putstr('testare randul 3')
    lcd.move_to(0, 3)
    lcd.putstr('testare randul 4')
    time.sleep(1)
    lcd.clear()
    time.sleep(1)
    lcd.backlight_off()
    time.sleep(1)
    lcd.backlight_on()
    time.sleep(1)

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