树莓派上使用 LCD1602 显示状态

手头有一块 LCD1602显示屏，于是尝试着用树莓派控制它的显示。网上直接找到现成的例子，操作成功，在此记录。

 

树莓派版本：Model 3B+

树莓派系统：Raspbian Stretch with desktop and recommended software，April 2019

参考资料：《树莓派+LCD1602实现系统监控: IP/时钟/温度/内存》。

在树莓派电源关闭时，根据参考资料中的连接方式（截图如下）连接树莓派、LCD显示屏和电位器，因为很多引脚需要连接正负极，树莓派上没有足够多的5v，所以我用了一个面包板。

连接好后如下图所示。我的线太长了，显得有些乱，大家接线的时候小心短路。

树莓派开机。

LCD 显示屏就会亮，但没有显示内容。

将参考资料中的两个 python 文件保存至树莓派中的同一文件夹下，长文件命名为1602led.py，短文件命名为1602.py。代码如下，点击+展开：

#!/usr/bin/python

#
# based on code from lrvick and LiquidCrystal
# lrvic - https://github.com/lrvick/raspi-hd44780/blob/master/hd44780.py
# LiquidCrystal - https://github.com/arduino/Arduino/blob/master/libraries/LiquidCrystal/LiquidCrystal.cpp
#

from time import sleep

class lcd1602:

    # 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

    # 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



    def __init__(self, pin_rs=14, pin_e=15, pins_db=[17, 18, 27, 22], GPIO = None):
    # Emulate the old behavior of using RPi.GPIO if we haven't been given
    # an explicit GPIO interface to use
    if not GPIO:
        import RPi.GPIO as GPIO
       self.GPIO = GPIO
        self.pin_rs = pin_rs
        self.pin_e = pin_e
        self.pins_db = pins_db

        self.GPIO.setmode(GPIO.BCM)
        self.GPIO.setwarnings(False)
        self.GPIO.setup(self.pin_e, GPIO.OUT)
        self.GPIO.setup(self.pin_rs, GPIO.OUT)
        
    for pin in self.pins_db:
            self.GPIO.setup(pin, GPIO.OUT)

    self.write4bits(0x33) # initialization
    self.write4bits(0x32) # initialization
    self.write4bits(0x28) # 2 line 5x7 matrix
    self.write4bits(0x0C) # turn cursor off 0x0E to enable cursor
    self.write4bits(0x06) # shift cursor right

    self.displaycontrol = self.LCD_DISPLAYON | self.LCD_CURSOROFF | self.LCD_BLINKOFF

    self.displayfunction = self.LCD_4BITMODE | self.LCD_1LINE | self.LCD_5x8DOTS
    self.displayfunction |= self.LCD_2LINE

    """ Initialize to default text direction (for romance languages) """
    self.displaymode =  self.LCD_ENTRYLEFT | self.LCD_ENTRYSHIFTDECREMENT
    self.write4bits(self.LCD_ENTRYMODESET | self.displaymode) #  set the entry mode

        self.clear()


    def begin(self, cols, lines):

    if (lines > 1):
        self.numlines = lines
            self.displayfunction |= self.LCD_2LINE
        self.currline = 0


    def home(self):

    self.write4bits(self.LCD_RETURNHOME) # set cursor position to zero
    self.delayMicroseconds(3000) # this command takes a long time!
    

    def clear(self):

    self.write4bits(self.LCD_CLEARDISPLAY) # command to clear display
    self.delayMicroseconds(3000)    # 3000 microsecond sleep, clearing the display takes a long time


    def setCursor(self, col, row):

    self.row_offsets = [ 0x00, 0x40, 0x14, 0x54 ]

    if ( row > self.numlines ): 
        row = self.numlines - 1 # we count rows starting w/0

    self.write4bits(self.LCD_SETDDRAMADDR | (col + self.row_offsets[row]))


    def noDisplay(self): 
    """ Turn the display off (quickly) """

    self.displaycontrol &= ~self.LCD_DISPLAYON
    self.write4bits(self.LCD_DISPLAYCONTROL | self.displaycontrol)


    def display(self):
    """ Turn the display on (quickly) """

    self.displaycontrol |= self.LCD_DISPLAYON
    self.write4bits(self.LCD_DISPLAYCONTROL | self.displaycontrol)


    def noCursor(self):
    """ Turns the underline cursor on/off """

    self.displaycontrol &= ~self.LCD_CURSORON
    self.write4bits(self.LCD_DISPLAYCONTROL | self.displaycontrol)


    def cursor(self):
    """ Cursor On """

    self.displaycontrol |= self.LCD_CURSORON
    self.write4bits(self.LCD_DISPLAYCONTROL | self.displaycontrol)


    def noBlink(self):
    """ Turn on and off the blinking cursor """

    self.displaycontrol &= ~self.LCD_BLINKON
    self.write4bits(self.LCD_DISPLAYCONTROL | self.displaycontrol)


    def noBlink(self):
    """ Turn on and off the blinking cursor """

    self.displaycontrol &= ~self.LCD_BLINKON
    self.write4bits(self.LCD_DISPLAYCONTROL | self.displaycontrol)


    def DisplayLeft(self):
    """ These commands scroll the display without changing the RAM """

    self.write4bits(self.LCD_CURSORSHIFT | self.LCD_DISPLAYMOVE | self.LCD_MOVELEFT)


    def scrollDisplayRight(self):
    """ These commands scroll the display without changing the RAM """

    self.write4bits(self.LCD_CURSORSHIFT | self.LCD_DISPLAYMOVE | self.LCD_MOVERIGHT);


    def leftToRight(self):
    """ This is for text that flows Left to Right """

    self.displaymode |= self.LCD_ENTRYLEFT
    self.write4bits(self.LCD_ENTRYMODESET | self.displaymode);


    def rightToLeft(self):
    """ This is for text that flows Right to Left """
    self.displaymode &= ~self.LCD_ENTRYLEFT
    self.write4bits(self.LCD_ENTRYMODESET | self.displaymode)


    def autoscroll(self):
    """ This will 'right justify' text from the cursor """

    self.displaymode |= self.LCD_ENTRYSHIFTINCREMENT
    self.write4bits(self.LCD_ENTRYMODESET | self.displaymode)


    def noAutoscroll(self): 
    """ This will 'left justify' text from the cursor """

    self.displaymode &= ~self.LCD_ENTRYSHIFTINCREMENT
    self.write4bits(self.LCD_ENTRYMODESET | self.displaymode)


    def write4bits(self, bits, char_mode=False):
        """ Send command to LCD """

    self.delayMicroseconds(1000) # 1000 microsecond sleep

        bits=bin(bits)[2:].zfill(8)

        self.GPIO.output(self.pin_rs, char_mode)

        for pin in self.pins_db:
            self.GPIO.output(pin, False)

        for i in range(4):
            if bits[i] == "1":
                self.GPIO.output(self.pins_db[::-1][i], True)

    self.pulseEnable()

        for pin in self.pins_db:
            self.GPIO.output(pin, False)

        for i in range(4,8):
            if bits[i] == "1":
                self.GPIO.output(self.pins_db[::-1][i-4], True)

    self.pulseEnable()


    def delayMicroseconds(self, microseconds):
    seconds = microseconds / float(1000000)    # divide microseconds by 1 million for seconds
    sleep(seconds)


    def pulseEnable(self):
    self.GPIO.output(self.pin_e, False)
    self.delayMicroseconds(1)        # 1 microsecond pause - enable pulse must be > 450ns 
    self.GPIO.output(self.pin_e, True)
    self.delayMicroseconds(1)        # 1 microsecond pause - enable pulse must be > 450ns 
    self.GPIO.output(self.pin_e, False)
    self.delayMicroseconds(1)        # commands need > 37us to settle


    def message(self, text):
        """ Send string to LCD. Newline wraps to second line"""

        for char in text:
            if char == '\n':
                self.write4bits(0xC0) # next line
            else:
                self.write4bits(ord(char),True)


if __name__ == '__main__':

    lcd = lcd1602()
    lcd.clear()
    lcd.message("hello world!")

#!/usr/bin/python
 
from lcd1602 import *
from datetime import *
import commands
 
def get_cpu_temp():
    tmp = open('/sys/class/thermal/thermal_zone0/temp')
    cpu = tmp.read()
    tmp.close()
    return '{:.2f}'.format( float(cpu)/1000 ) + ' C'
 
def get_gpu_temp():
    tmp = commands.getoutput('vcgencmd measure_temp|awk -F= \'{print $2}\'').replace('\'C','')
    gpu = float(tmp)
    return '{:.2f}'.format( gpu ) + ' C'
 
def get_time_now():
    return datetime.now().strftime('    %H:%M:%S\n   %Y-%m-%d')
 
def get_ip_info():
    return commands.getoutput('ifconfig wlan0|grep inet|awk -Faddr: \'{print $2}\'|awk \'{print $1}\'')
 
def get_mem_info():
    total= commands.getoutput('free -m|grep Mem:|awk \'{print $2}\'')  
    free = commands.getoutput('free -m|grep cache:|awk \'{print $4}\'')
    return 'MEM:\n    ' + free +' / '+ total +' M'
 
lcd = lcd1602()
lcd.clear()
 
if __name__ == '__main__':
 
    while(1):
        lcd.clear()
        lcd.message( get_ip_info() )
        sleep(5)
         
        lcd.clear()
        lcd.message( get_time_now() )
        sleep(5)
         
        lcd.clear()
        lcd.message( get_mem_info() )
        sleep(5)
 
        lcd.clear()
        lcd.message( 'CPU: ' + get_cpu_temp()+'\n' )
        lcd.message( 'GPU: ' + get_gpu_temp() )
        sleep(5)

代码需用 python2.7 运行，终端进入对应的文件夹下，执行 python 1602.py ，就能发现显示屏变化了。注意，可能需要旋转电位器转轴来矫正显示屏。

运行结果：

 

该程序是无限循环的，终止程序后（control+C），显示屏会保留最后状态。

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