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Interfacing a 16×2 LCD with Raspberry Pi

Thursday January 29, 2015 / Ibrar Ayyub
Categories: LCD Projects
Tags: 16x2, interfacing, lcd, pi, raspberry

Hitachi HD44780 based 16×2 character LCD are very cheap and widely available, and is a essential part for any  projects that displays information. Using the I2C bus on Raspberry Pi ,PCF8574 IC, and Python characters/strings can be displayed on the LCD. The PCF8574 is an general purpose bidirectional 8 bit I/O port expander that uses the I2C protocol.
The LCD(HD44780) is connected in 4 bit mode as follows to the PCF8574:-

  1. import smbus
  2. from time import *
  4. # General i2c device class so that other devices can be added easily
  5. class i2c_device:
  6.  def __init__(self, addr, port):
  7.   self.addr = addr
  8.   self.bus = smbus.SMBus(port)
  10.  def write(self, byte):
  11.   self.bus.write_byte(self.addr, byte)
  13.  def read(self):
  14.   return self.bus.read_byte(self.addr)
  16.  def read_nbytes_data(self, data, n): # For sequential reads > 1 byte
  17.   return self.bus.read_i2c_block_data(self.addr, data, n)
  18. Interfacing a 16x2 LCD with Raspberry Pi
  19. class lcd:
  20.  #initializes objects and lcd
  21.  ”’
  22.  Reverse Codes:
  23.  0: lower 4 bits of expander are commands bits
  24.  1: top 4 bits of expander are commands bits AND P0-4 P1-5 P2-6
  25.  2: top 4 bits of expander are commands bits AND P0-6 P1-5 P2-4
  26.  ”’
  27.  def __init__(self, addr, port, reverse=0):
  28.   self.reverse = reverse
  29.   self.lcd_device = i2c_device(addr, port)
  30.   if self.reverse:
  31.    self.lcd_device.write(0x30)
  32.    self.lcd_strobe()
  33.    sleep(0.0005)
  34.    self.lcd_strobe()
  35.    sleep(0.0005)
  36.    self.lcd_strobe()
  37.    sleep(0.0005)
  38.    self.lcd_device.write(0x20)
  39.    self.lcd_strobe()
  40.    sleep(0.0005)
  41.   else:
  42.    self.lcd_device.write(0x03)
  43.    self.lcd_strobe()
  44.    sleep(0.0005)
  45.    self.lcd_strobe()
  46.    sleep(0.0005)
  47.    self.lcd_strobe()
  48.    sleep(0.0005)
  49.    self.lcd_device.write(0x02)
  50.    self.lcd_strobe()
  51.    sleep(0.0005)
  53.   self.lcd_write(0x28)
  54.   self.lcd_write(0x08)
  55.   self.lcd_write(0x01)
  56.   self.lcd_write(0x06)
  57.   self.lcd_write(0x0C)
  58.   self.lcd_write(0x0F)
  60.  # clocks EN to latch command
  61.  def lcd_strobe(self):
  62.   if self.reverse == 1:
  63.    self.lcd_device.write((self.lcd_device.read() | 0x04))
  64.    self.lcd_device.write((self.lcd_device.read() & 0xFB))
  65.   if self.reverse == 2:
  66.    self.lcd_device.write((self.lcd_device.read() | 0x01))
  67.    self.lcd_device.write((self.lcd_device.read() & 0xFE))
  68.   else:
  69.    self.lcd_device.write((self.lcd_device.read() | 0x10))
  70.    self.lcd_device.write((self.lcd_device.read() & 0xEF))
  72.  # write a command to lcd
  73.  def lcd_write(self, cmd):
  74.   if self.reverse:
  75.    self.lcd_device.write((cmd >> 4)<<4)
  76.    self.lcd_strobe()
  77.    self.lcd_device.write((cmd & 0x0F)<<4)
  78.    self.lcd_strobe()
  79.    self.lcd_device.write(0x0)
  80.   else:
  81.    self.lcd_device.write((cmd >> 4))
  82.    self.lcd_strobe()
  83.    self.lcd_device.write((cmd & 0x0F))
  84.    self.lcd_strobe()
  85.    self.lcd_device.write(0x0)
  87.  # write a character to lcd (or character rom)
  88.  def lcd_write_char(self, charvalue):
  89.   if self.reverse == 1:
  90.    self.lcd_device.write((0x01 | (charvalue >> 4)<<4))
  91.    self.lcd_strobe()
  92.    self.lcd_device.write((0x01 | (charvalue & 0x0F)<<4))
  93.    self.lcd_strobe()
  94.    self.lcd_device.write(0x0)
  95.   if self.reverse == 2:
  96.    self.lcd_device.write((0x04 | (charvalue >> 4)<<4))
  97.    self.lcd_strobe()
  98.    self.lcd_device.write((0x04 | (charvalue & 0x0F)<<4))
  99.    self.lcd_strobe()
  100.    self.lcd_device.write(0x0)
  101.   else:
  102.    self.lcd_device.write((0x40 | (charvalue >> 4)))
  103.    self.lcd_strobe()
  104.    self.lcd_device.write((0x40 | (charvalue & 0x0F)))
  105.    self.lcd_strobe()
  106.    self.lcd_device.write(0x0)
  108.  # put char function
  109.  def lcd_putc(self, char):
  110.   self.lcd_write_char(ord(char))
  112.  # put string function
  113.  def lcd_puts(self, string, line):
  114.   if line == 1:
  115.    self.lcd_write(0x80)
  116.   if line == 2:
  117.    self.lcd_write(0xC0)
  118.   if line == 3:
  119.    self.lcd_write(0x94)
  120.   if line == 4:
  121.    self.lcd_write(0xD4)
  123.   for char in string:
  124.    self.lcd_putc(char)
  126.  # clear lcd and set to home
  127.  def lcd_clear(self):
  128.   self.lcd_write(0x1)
  129.   self.lcd_write(0x2)
  131.  # add custom characters (0 – 7)
  132.  def lcd_load_custon_chars(self, fontdata):
  133.   self.lcd_device.bus.write(0x40);
  134.   for char in fontdata:
  135.    for line in char:
  136.     self.lcd_write_char(line)

Interfacing a 16x2 LCD with Raspberry Pi schematic

Main Program:-

view plainprint?
  1. import pylcdlib
  2. lcd = pylcdlib.lcd(0x21,0)
  3. lcd.lcd_puts(“Raspberry Pi”,1)  #display “Raspberry Pi” on line 1
  4. lcd.lcd_puts(”  Take a byte!”,2)  #display “Take a byte!” on line 2

Save the above code as test_lcd.py and enter sudo python test_lcd.py
My code assumes that the first 4 bits of the LCD(11,12,13,14) are connected to P0,P1,P2,P3 ports on PCF8574. The next 3 ports on PCF8574(P4,P5,P6) should be connected to 4-RS, 5-R/W, 6-E.However there are other serial backpack lcd’s with different pinouts. According to the wiring of your serial backpack LCD you can override the default mapping during initialization.There are 3 modes available-
lcd = pylcdlib.lcd(0x21,0)   lower 4 bits of expander are commands bits
lcd = pylcdlib.lcd(0x21,0,1)   top 4 bits of expander are commands bits AND   P0-4   P1-5   P2-6
lcd = pylcdlib.lcd(0x21,0,2)   top 4 bits of expander are commands bits AND   P0-6   P1-5   P2-4

(Update):- If you have a Raspberry Pi with a revision 2.0 board, you need to use I²C bus 1, not bus 0, so you will need to change the bus number used. In this case, the line lcd = pylcdlib.lcd(0x21,0) would become lcd = pylcdlib.lcd(0x21,1).

You can check that the device is present on the bus by using the i2cdetect program from the i2ctools package-
i2cdetect 0 -y  or i2cdetect 1 -y

Source: Interfacing a 16×2 LCD with Raspberry Pi


About The Author

Ibrar Ayyub

I am an experienced technical writer holding a Master's degree in computer science from BZU Multan, Pakistan University. With a background spanning various industries, particularly in home automation and engineering, I have honed my skills in crafting clear and concise content. Proficient in leveraging infographics and diagrams, I strive to simplify complex concepts for readers. My strength lies in thorough research and presenting information in a structured and logical format.

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