I2C LCD Library... Help!

Discuss development of drivers for external hardware and components, such as LCD screens, sensors, motor drivers, etc.
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sequel
Posts: 12
Joined: Wed Aug 03, 2016 1:52 pm

Re: I2C LCD Library... Help!

Postby sequel » Thu Aug 04, 2016 6:10 pm

OK, i was finally able to print something on the LCD.

As stated in my first post, i was fiddling with the LiquidCrystal code on arduino to intercept what was sent on the I2C bus.

With those values, using bytearray, and with this code :

Code: Select all

from machine import Pin, I2C
from time import sleep_ms, sleep_us
i2c = I2C(scl=Pin(5), sda=Pin(4), freq=100000)

values=[0,52,48,52,48,52,48,36,32,36,32,132,128,4,0,196,192,4,0,20,16,4,0,100,96,8,8,140,136,12,8,77,73,29,25]

for value in values:
    sleep_ms(5)
    buf=bytearray(1)
    buf[0]=value
    i2c.writeto(0x27, buf)


I was able to print capital A on my LCD.

Will now try to implement bytearray in pyb_i2c_lcd.py

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dhylands
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Location: Shuswap, BC, Canada
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Re: I2C LCD Library... Help!

Postby dhylands » Thu Aug 04, 2016 6:44 pm

You can also use bytes([1, 2, 3]) to create a bytes object.

bytearrays are mutable, whereas bytes are not.

If you're sending constant data, then b'\x01\x02\x03' is equivalent to bytes([1, 2, 3])

sequel
Posts: 12
Joined: Wed Aug 03, 2016 1:52 pm

Re: I2C LCD Library... Help!

Postby sequel » Thu Aug 04, 2016 7:36 pm

Cool! Thank you so much for the tip!

I have now a second, cleaner, working version!


Thanks again!

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dhylands
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Re: I2C LCD Library... Help!

Postby dhylands » Thu Aug 04, 2016 7:56 pm

One more tip. If you did want to use a bytearray, then I'd rewrite your code:

Code: Select all

for value in values:
    sleep_ms(5)
    buf=bytearray(1)
    buf[0]=value
    i2c.writeto(0x27, buf)
to look like this instead:

Code: Select all

buf = bytearray(1)
for value in values:
    sleep_ms(5)
    buf[0]=value
    i2c.writeto(0x27, buf)
That way you're only allocating a single bytearray object, rather than a new bytearray object for each iteration of the loop.

sequel
Posts: 12
Joined: Wed Aug 03, 2016 1:52 pm

Re: I2C LCD Library... Help!

Postby sequel » Fri Aug 05, 2016 7:33 pm

Yeah i was exactly thinking about this while i was at my second attempt to modify pyb_i2c_lcd.py but finally i took your advise and used bytes() in the end, which makes the code more cleaner i think.


Thanks again!

Electra
Posts: 4
Joined: Thu Sep 29, 2016 9:01 am

Re: I2C LCD Library... Help!

Postby Electra » Thu Sep 29, 2016 9:08 am

sequel,
Could you please post your rewritten library?
I'm trying to get much the same thing going and your example 'A' code works fine, but if you have already rewritten dhylands's code, I'd rather use it than reimplementing it all myself.

Thank you.

sequel
Posts: 12
Joined: Wed Aug 03, 2016 1:52 pm

Re: I2C LCD Library... Help!

Postby sequel » Sat Oct 01, 2016 2:36 am

Hi Electra,

So sorry for the late reply.

Here is the code,

esp8266_i2c_lcd.py :

Code: Select all

"""Implements a character based lcd connected via PCF8574 on i2c."""

from lcd 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, bytes([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, bytes([byte | MASK_E]))
        self.i2c.writeto(self.i2c_addr, bytes([byte]))

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

    def hal_backlight_off(self):
        """Allows the hal layer to turn the backlight off."""
        self.i2c.writeto(self.i2c_addr, bytes([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, 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 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(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]))



lcd.py :

Code: Select all

"""Provides an API for talking to HD44780 style character LCDs."""


class LcdApi(object):
    """Implements the API for talking with n LCD. This class only knows what
    commands to send to the LCD, and not how t 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.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:
            addr += 0x14    # Lines 2 & 3 add 0x14
        self.hal_write_command(self.LCD_DDRAM | addr)

    def putchar(self, char):
        """Writes the indicated charcter to the LCD at the current cursor
        position, and advances the cursor by one position.
        """
        if self.cursor_x >= self.num_columns or char == '\n':
            self.cursor_x = 0
            self.cursor_y += 1
            if self.cursor_y >= self.num_lines:
                self.cursor_y = 0
            self.move_to(self.cursor_x, self.cursor_y)
        if char != '\n':
            self.hal_write_data(ord(char))
            self.cursor_x += 1

    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 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

Electra
Posts: 4
Joined: Thu Sep 29, 2016 9:01 am

Re: I2C LCD Library... Help!

Postby Electra » Thu Oct 06, 2016 4:17 am

It was quite a fast reply, so no problems at all!
Thank you, your library worked perfectly.

Here's proof: https://lh3.googleusercontent.com/6tkrQ ... 66-h630-no
(Couldn't find out how to attach the image through the forum)

Electra
Posts: 4
Joined: Thu Sep 29, 2016 9:01 am

Re: I2C LCD Library... Help!

Postby Electra » Thu Oct 06, 2016 12:52 pm

Or if the previous link is broken: https://goo.gl/photos/BcBiHddBxG2194kW6
(May not always work, but hopefully it gets the point across. :)

sequel
Posts: 12
Joined: Wed Aug 03, 2016 1:52 pm

Re: I2C LCD Library... Help!

Postby sequel » Thu Oct 06, 2016 1:42 pm

Hi Electra,

Thank you so much for your kind (LCD) message!

You just made my day :D


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