Raspberry Pi with 20x4 LCD - D.I.Y. Series (3) | 樹莓派加上 20x4 液晶顯示 - 自己動手系列(3)

guyverckw (70)in #cn • 7 years ago (edited)

Last time I bought couple of accessories for my Raspberry Pi3 from the bookstore in Shamshuipo.

上次在深水埗那書店買了幾件配件給我的樹莓派。

Let see what they are: First came a Lego-style box for Raspberry Pi3, look at the openings, they were customized for Pi 3.

讓我們仔細看看：先來是樂高積木款式的盒子，看看那些口子就知道這是pi 3 專用的。

Just need to align the holes on circuit board with the poles on the case, it was fairly easy to put Pi 3 in the case. This was how it looks like afterward.

只需要將電路板上的小孔對準盒中的小棒子，就可以把樹莓派安裝到盒子中。完成後就是這個樣子。

The other 2 accessories were one integrated 20x4 LCD display and some female-to-female breadboard cables.

另外兩件配件是一塊經已整合好的20x4液晶顯示板和一些麵包板連接線。

I was going to connect this LCD to Pi3 and use it for displaying of text. First of all I had to connect it to Pi3. The LCD already has a I2C LCD Controller integrated, I only need to connect the 4 pins of the controller to the GPIO pins of Pi3 using following mapping :

LCD Pin #	Pi3 GPIO Pin #
GND	PIN 6
VCC	PIN 2
SDA	PIN 3
SCL	PIN 5

我想把液晶顯示板接到樹莓派上作為顯示之用。所以我因為液晶顯示板已經整合了控制器，所以我只需根據上面的針腳配置表將它接到樹莓派的GPIO針腳上。

Then I had to enable i2c on Pi3. From Command Line type : sudo raspi-config

先要開啟在樹莓派上的i2c 支援，在命令行鍵入上面的命令

Complete following steps:

Select "Interfacing Options"
Select "I2C"
Select "Yes"
Select "Ok"
Then select "Finish" to quit raspi-config.

完成上面的步驟之後就選"Finish"去離開。

Then I have to install python i2c utilities "python-smbus" & "i2c-tools" by typing following commands in Command Line:

sudo apt-get update
sudo apt-get install -y python-smbus i2c-tools

在命令行打入上面的命令去安裝 python 應用 "python-smbus" 和 "i2c-tools"。

I tested the LCD hardware by

sudo i2cdetect -y 1

利用上面的命令去測驗液晶顯示板

This showed the LCD was connected to address 0x3f.

可以見到液晶顯示板已經連接到記憶地址0x3f。

In order to talk to the LCD, python libraries were needed. Using following to steps to create the libraries:

要用上液晶顯示板，先要有相對應的python代碼庫。利用下面的命令去建立兩個檔案：

sudo nano i2c_lib.py

type following in the file:

把下面的代碼輸入到檔案中：

import smbus
from time import *

class i2c_device:
   def __init__(self, addr, port=1):
      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)

And other file | 第二個檔案：

sudo nano lcddriver.py

Type following in the file:

把下面的代碼輸入到檔案中：

import i2c_lib
from time import *

# LCD Address
ADDRESS = 0x3f

# 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_lib.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))

   # put string function
   def lcd_display_string(self, string, line):
      if line == 1:
         self.lcd_write(0x80)
      if line == 2:
         self.lcd_write(0xC0)
      if line == 3:
         self.lcd_write(0x94)
      if line == 4:
         self.lcd_write(0xD4)

      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)

Make sure the i2C address in this file is set to #3f.

記得要把代碼中的i2c地址改成 #3f.

# LCD Address
ADDRESS = 0x3f

Finally I could use the LCD dispaly by creating a python script file:

最後就是建立python檔案來顯示文字到液晶顯示板：

sudo nano display.py

# loading the class
import lcddriver

from time import *

import time

# lcd start
lcd = lcddriver.lcd()

# this command clears the display (captain obvious)
lcd.lcd_clear()
# clock = time()

actions = ['Follow', ' Vote', ' Resteem']
action1 = ""
print ("Start : %s" % time.ctime())

# now we can display some characters (text, line)
lcd.lcd_display_string("Hello Steemit !", 1)
lcd.lcd_display_string("This is @guyverckw", 2)
lcd.lcd_display_string("   Please   ", 3)
for action in actions :
        action1 = action1 + action
        lcd.lcd_display_string(action1 , 4)
        time.sleep( 2 )

print ("End : %s" % time.ctime())

Then run the script | 執行代碼：

python display.py
Then you should able to see this:

應該就能見到這樣：

I encountered a major problem when trying to make this works, there was nothing displayed on the LCD. After checking a lot of works from others, I found that it was the contrast of the LCD was not properly set. Contrast of it can be set at the switch on the controller: