i2c LCD not working properly

[codeboy66]

Hello,

since a few days, I try to get a i2c lcd display with the PCF85744AT working.
But i get this error:


I have no idea what could be wrong. And yes i've googled already and found some articles that say that the code [Errno 5] EIO hat to do something with bad wiring/connections etc.
But a i2c scanner script works without any problems and finds the correct address! I dont think it is a hardware problem. I think something with the library or the software is wrong. I also tried other displays of the same type - they produce the same error! (with an arduino they work properly). The Pico is powered via USB over the Laptop

This is my code:

Code: Select all

import utime

import machine
from machine import I2C
from lcd_api import LcdApi
from pico_i2c_lcd import I2cLcd

I2C_ADDR     = 0x27
I2C_NUM_ROWS = 2
I2C_NUM_COLS = 16

def test_main():
    #Test function for verifying basic functionality
    print("Running test_main")
    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.putstr("It Works!")
    utime.sleep(200)
    lcd.clear()

test_main()

pico_i2c_lcd

Code: Select all

"""Implements a HD44780 character LCD connected via MCP23008 on I2C.
   This was tested with: https://www.elecrow.com/crowtail-i2c-lcd-p-1494.html on a Raspberry Pi Pico.
   This code was based on pyb_i2c_adafruit_lcd.py at https://github.com/dhylands/python_lcd/blob/master/lcd/pyb_i2c_adafruit_lcd.py"""

from lcd_api import LcdApi
from machine import I2C
from utime import sleep_ms

# The MCP23008 has a jumper selectable address: 0x20 - 0x27
DEFAULT_I2C_ADDR = 0x20

# MCP23008 Registers

IODIR   = 0x00
IPOL    = 0x01
GPINTEN = 0x02
DEFVAL  = 0x03
INTCON  = 0x04
IOCON   = 0x05
GPPU    = 0x06
INTF    = 0x07
INTCAP  = 0x08
GPIO    = 0x09
OLAT    = 0x0A

# Defines shifts or masks for the various LCD line attached to the MCP23008

# GP0 - NC
# GP1 - RS
# GP2 - E
# GP3 - DB4
# GP4 - DB5
# GP5 - DB6
# GP6 - DB7
# GP7 - LITE

MASK_RS = 0x02
MASK_E = 0x04
SHIFT_DATA = 3
SHIFT_BACKLIGHT = 7


class I2cLcd(LcdApi):
    """Implements a HD44780 character LCD connected via MCP23008 on I2C."""

    def __init__(self, i2c, i2c_addr, num_lines, num_columns):
        self.i2c = i2c
        self.i2c_addr = i2c_addr
        # Send IODIR address, set IODIR to all inputs, init all other registers 0
        self.i2c.writeto(self.i2c_addr, bytearray([0x00,0xff,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00]))

        # Set pins GP1 through GP7 to output, leave GP0 as input
        self.i2c.writeto_mem(self.i2c_addr, IODIR, bytearray([0x01]))

        # Send reset 3 times
        self.hal_write_init_nibble(self.LCD_FUNCTION_RESET)
        sleep_ms(5)    # need to sleep_ms 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_mem(self.i2c_addr, GPIO, bytearray([byte | MASK_E]))
        self.i2c.writeto_mem(self.i2c_addr, GPIO, bytearray([byte]))

    def hal_backlight_on(self):
        """Allows the hal layer to turn the backlight on."""
        self.i2c.writeto_mem(self.i2c_addr, GPIO, bytearray([1 << SHIFT_BACKLIGHT]))

    def hal_backlight_off(self):
        """Allows the hal layer to turn the backlight off."""
        self.i2c.writeto_mem(self.i2c_addr, GPIO, 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_mem(self.i2c_addr, GPIO, bytearray([byte | MASK_E]))
        self.i2c.writeto_mem(self.i2c_addr, GPIO, bytearray([byte]))
        byte = ((self.backlight << SHIFT_BACKLIGHT) |
                ((cmd & 0x0f) << SHIFT_DATA))
        self.i2c.writeto_mem(self.i2c_addr, GPIO, bytearray([byte | MASK_E]))
        self.i2c.writeto_mem(self.i2c_addr, GPIO, bytearray([byte]))
        if cmd <= 3:
            # The home and clear commands require a worst
            # case sleep_ms 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_mem(self.i2c_addr, GPIO, bytearray([byte | MASK_E]))
        self.i2c.writeto_mem(self.i2c_addr, GPIO, bytearray([byte]))
        byte = (MASK_RS |
                (self.backlight << SHIFT_BACKLIGHT) |
                ((data & 0x0f) << SHIFT_DATA))
        self.i2c.writeto_mem(self.i2c_addr, GPIO, bytearray([byte | MASK_E]))
        self.i2c.writeto_mem(self.i2c_addr, GPIO, bytearray([byte]))

lcd_api

Code: Select all

"""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.
                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)

I use: v1.17 (2021-09-02) .uf2 and MicroPython v1.16 on 2021-06-18 in Thonny
Wiring:


Thanks!
and Merry Christmas from Germany

[Roberthh]

Two questions, and sorry if I ask for something obvious:
- is the I2c address 0x27 or 27? i2c.scan() returns decimal numbers.
- do the Scan test and the lcd code use the same frequency for i2c?

[codeboy66]

Thank you for your questions. No Problem.
Yes, the addresses match!
Yes - the frequency is the same.

This is the scanning code:

import machine
sda=machine.Pin(0)
scl=machine.Pin(1)
i2c=machine.I2C(0,sda=sda, scl=scl, freq=400000)

print('Scan i2c bus...')
devices = i2c.scan()

if len(devices) == 0:
print("No i2c device !")
else:
print('i2c devices found:',len(devices))

for device in devices:
print("Decimal address: ",device," | Hexa address: ",hex(device))

It works correctly and gives me the address,

[Roberthh]

It could still be timing problem. Sensing a larger amount of data is different to scan() which just sends the address. For verification you could try a substantially lower frequency, like 10000.

[drymaestro]

Did you solve it?

I was having this problem when I noticed a blue thingy (sorry, I'm sort of new) with a '+' sign. That works as a contrast control in the LCD, have you tried moving it from one side to the other?

[scruss]

[Errno 5] EIO tends to be a timing issue. Roberthh's advice is very sound: these devices aren't very fast, so there's no need to set a high frequency for the I2C port. Sometimes you need to tweak the internal delays in the library itself: I'm finding with Cytron's 3V3 I2C and SPI 1602 Serial Character LCD you have to extend the command delays quite a bit (effectively doubling them) to make it reliable. But even then it'll sometimes fail.

The logic-level converter is optional for these boards. While they need the 5 V supply to power the backlight, their logic runs at 3.3 V-safe levels. You can tell the boards that need 5 V by looking at the back of the PCB: if there's an unpopulated section at the back (typically marked 'U3') they won't run on 3.3 V power.

Once you stop getting errors from talking to the board, drymasestro's tip about the blue thingy with the + sign is handy. You almost always have to change the contrast setting to make these LCDs legible.

[Roberthh]

The MCP23008 chip itself should be fast enough. It is specified for 100kHz and 400 kHz and 1.7Mhz. But that requires proper wiring and Pull-Up resistors.