Python I2C LCD 驱动程序显示奇怪的字符

Question

我有一个带有 I2C 背负式适配器的 2 x 16 LCD 显示器。作为一个简单的开始，我只是显示编码器值。但是，当我转动编码器时，我会在不同区域的液晶显示屏上看到奇怪的文字。有时显示会恢复并仅显示“编码器:X”，第二行为空:

代码

#!/usr/bin/python3 -u

import time

import RPi.GPIO as GPIO

import lcd_i2c
from encoder import Encoder

GPIO.setmode(GPIO.BCM)

switch_pin = 13
encoder_down_pin = 6
encoder_up_pin = 5

GPIO.setup(switch_pin, GPIO.IN, pull_up_down=GPIO.PUD_UP)

encoder_value = 0

mylcd = lcd_i2c.lcd()


def valueChanged(value):
    encoder_value = value
    print(encoder_value)

    mylcd.lcd_clear()
    mylcd.lcd_display_string(f"Encoder: {encoder_value}", 1)


e1 = Encoder(encoder_down_pin, encoder_up_pin, callback=valueChanged)
while True:
    time.sleep(60)

# lcd_i2c.py
# -*- coding: utf-8 -*-
# Original code found at:
# https://gist.github.com/DenisFromHR/cc863375a6e19dce359d

"""
Compiled, mashed and generally mutilated 2014-2015 by Denis Pleic
Made available under GNU GENERAL PUBLIC LICENSE

# Modified Python I2C library for Raspberry Pi
# as found on http://www.recantha.co.uk/blog/?p=4849
# Joined existing 'i2c_lib.py' and 'lcddriver.py' into a single library
# added bits and pieces from various sources
# By DenisFromHR (Denis Pleic)
# 2015-02-10, ver 0.1

"""

# i2c bus (0 -- original Pi, 1 -- Rev 2 Pi)
I2CBUS = 1

# LCD Address
ADDRESS = 0x27

import smbus
from time import sleep

class i2c_device:
   def __init__(self, addr, port=I2CBUS):
      self.addr = addr
      self.bus = smbus.SMBus(port)

# Write a single command
   def write_cmd(self, cmd):
      self.bus.write_byte(self.addr, cmd)
      sleep(0.0001)

# Write a command and argument
   def write_cmd_arg(self, cmd, data):
      self.bus.write_byte_data(self.addr, cmd, data)
      sleep(0.0001)

# Write a block of data
   def write_block_data(self, cmd, data):
      self.bus.write_block_data(self.addr, cmd, data)
      sleep(0.0001)

# Read a single byte
   def read(self):
      return self.bus.read_byte(self.addr)

# Read
   def read_data(self, cmd):
      return self.bus.read_byte_data(self.addr, cmd)

# Read a block of data
   def read_block_data(self, cmd):
      return self.bus.read_block_data(self.addr, cmd)


# commands
LCD_CLEARDISPLAY = 0x01
LCD_RETURNHOME = 0x02
LCD_ENTRYMODESET = 0x04
LCD_DISPLAYCONTROL = 0x08
LCD_CURSORSHIFT = 0x10
LCD_FUNCTIONSET = 0x20
LCD_SETCGRAMADDR = 0x40
LCD_SETDDRAMADDR = 0x80

# flags for display entry mode
LCD_ENTRYRIGHT = 0x00
LCD_ENTRYLEFT = 0x02
LCD_ENTRYSHIFTINCREMENT = 0x01
LCD_ENTRYSHIFTDECREMENT = 0x00

# flags for display on/off control
LCD_DISPLAYON = 0x04
LCD_DISPLAYOFF = 0x00
LCD_CURSORON = 0x02
LCD_CURSOROFF = 0x00
LCD_BLINKON = 0x01
LCD_BLINKOFF = 0x00

# flags for display/cursor shift
LCD_DISPLAYMOVE = 0x08
LCD_CURSORMOVE = 0x00
LCD_MOVERIGHT = 0x04
LCD_MOVELEFT = 0x00

# flags for function set
LCD_8BITMODE = 0x10
LCD_4BITMODE = 0x00
LCD_2LINE = 0x08
LCD_1LINE = 0x00
LCD_5x10DOTS = 0x04
LCD_5x8DOTS = 0x00

# flags for backlight control
LCD_BACKLIGHT = 0x08
LCD_NOBACKLIGHT = 0x00

En = 0b00000100 # Enable bit
Rw = 0b00000010 # Read/Write bit
Rs = 0b00000001 # Register select bit

class lcd:
   #initializes objects and lcd
   def __init__(self):
      self.lcd_device = i2c_device(ADDRESS)

      self.lcd_write(0x03)
      self.lcd_write(0x03)
      self.lcd_write(0x03)
      self.lcd_write(0x02)

      self.lcd_write(LCD_FUNCTIONSET | LCD_2LINE | LCD_5x8DOTS | LCD_4BITMODE)
      self.lcd_write(LCD_DISPLAYCONTROL | LCD_DISPLAYON)
      self.lcd_write(LCD_CLEARDISPLAY)
      self.lcd_write(LCD_ENTRYMODESET | LCD_ENTRYLEFT)
      sleep(0.2)


   # clocks EN to latch command
   def lcd_strobe(self, data):
      self.lcd_device.write_cmd(data | En | LCD_BACKLIGHT)
      sleep(.0005)
      self.lcd_device.write_cmd(((data & ~En) | LCD_BACKLIGHT))
      sleep(.0001)

   def lcd_write_four_bits(self, data):
      self.lcd_device.write_cmd(data | LCD_BACKLIGHT)
      self.lcd_strobe(data)

   # write a command to lcd
   def lcd_write(self, cmd, mode=0):
      self.lcd_write_four_bits(mode | (cmd & 0xF0))
      self.lcd_write_four_bits(mode | ((cmd << 4) & 0xF0))

   # write a character to lcd (or character rom) 0x09: backlight | RS=DR<
   # works!
   def lcd_write_char(self, charvalue, mode=1):
      self.lcd_write_four_bits(mode | (charvalue & 0xF0))
      self.lcd_write_four_bits(mode | ((charvalue << 4) & 0xF0))

   # put string function with optional char positioning
   def lcd_display_string(self, string, line=1, pos=0):
    if line == 1:
      pos_new = pos
    elif line == 2:
      pos_new = 0x40 + pos
    elif line == 3:
      pos_new = 0x14 + pos
    elif line == 4:
      pos_new = 0x54 + pos

    self.lcd_write(0x80 + pos_new)

    for char in string:
      self.lcd_write(ord(char), Rs)

   # clear lcd and set to home
   def lcd_clear(self):
      self.lcd_write(LCD_CLEARDISPLAY)
      self.lcd_write(LCD_RETURNHOME)

   # define backlight on/off (lcd.backlight(1); off= lcd.backlight(0)
   def backlight(self, state): # for state, 1 = on, 0 = off
      if state == 1:
         self.lcd_device.write_cmd(LCD_BACKLIGHT)
      elif state == 0:
         self.lcd_device.write_cmd(LCD_NOBACKLIGHT)

   # add custom characters (0 - 7)
   def lcd_load_custom_chars(self, fontdata):
      self.lcd_write(0x40);
      for char in fontdata:
         for line in char:
            self.lcd_write_char(line)

# encoder.py
# Class to monitor a rotary encoder and update a value.  You can either read the value when you need it, by calling getValue(), or
# you can configure a callback which will be called whenever the value changes.

import RPi.GPIO as GPIO

class Encoder:

    def __init__(self, leftPin, rightPin, callback=None):
        self.leftPin = leftPin
        self.rightPin = rightPin
        self.value = 0
        self.state = '00'
        self.direction = None
        self.callback = callback
        GPIO.setup(self.leftPin, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)
        GPIO.setup(self.rightPin, GPIO.IN, pull_up_down=GPIO.PUD_DOWN)
        GPIO.add_event_detect(self.leftPin, GPIO.BOTH, callback=self.transitionOccurred)
        GPIO.add_event_detect(self.rightPin, GPIO.BOTH, callback=self.transitionOccurred)

    def transitionOccurred(self, channel):
        p1 = GPIO.input(self.leftPin)
        p2 = GPIO.input(self.rightPin)
        newState = "{}{}".format(p1, p2)

        if self.state == "00": # Resting position
            if newState == "01": # Turned right 1
                self.direction = "R"
            elif newState == "10": # Turned left 1
                self.direction = "L"

        elif self.state == "01": # R1 or L3 position
            if newState == "11": # Turned right 1
                self.direction = "R"
            elif newState == "00": # Turned left 1
                if self.direction == "L":
                    self.value = self.value - 1
                    if self.callback is not None:
                        self.callback(self.value)

        elif self.state == "10": # R3 or L1
            if newState == "11": # Turned left 1
                self.direction = "L"
            elif newState == "00": # Turned right 1
                if self.direction == "R":
                    self.value = self.value + 1
                    if self.callback is not None:
                        self.callback(self.value)

        else: # self.state == "11"
            if newState == "01": # Turned left 1
                self.direction = "L"
            elif newState == "10": # Turned right 1
                self.direction = "R"
            elif newState == "00": # Skipped an intermediate 01 or 10 state, but if we know direction then a turn is complete
                if self.direction == "L":
                    self.value = self.value - 1
                    if self.callback is not None:
                        self.callback(self.value)
                elif self.direction == "R":
                    self.value = self.value + 1
                    if self.callback is not None:
                        self.callback(self.value)

        self.state = newState

    def getValue(self):
        return self.value

i2c lcd script 的学分去它的作者DenisFromHR

Answer 1

你的LCD模块内部使用的是4位接口(interface)模式；命令或数据的每个字节都写在两个 4 位 block 中。没有办法告诉下一个 block 是预期的，除了完全重新初始化 LCD 之外没有办法强制开始一个新字节——你只需要小心总是成对发送 block 。如果您丢失了其中一个 block ，LCD 将从该点开始显示乱码(直到另一个 block 丢失)，因为它接收的字节将由发送的两个不同字节的一半组成。

这就是正是这里出了什么问题。这是“编码器:”消息的前几个字节，以十六进制表示:

45 6E 63 6F 64 65 72 3A

这是你得到的重复垃圾字符串的开始，也是十六进制:

56 E6 36 F6 46 57 23 A2

请注意，这是完全相同的数据，只是移动了一位十六进制数。

我看不出为什么会发生这种情况的明显原因，但我首先要尝试的是将 lcd_strobe() 中的那些 sleep() 增加一个因子100 左右，以防它们的长度不足以让 LCD 模块可靠地读取 block 。