text: #!/usr/bin/python
  #--------------------------------------
  #    ___  ___  _ ____
  #   / _ \/ _ \(_) __/__  __ __
  #  / , _/ ___/ /\ \/ _ \/ // /
  # /_/|_/_/  /_/___/ .__/\_, /
  #                /_/   /___/
  #
  #  lcd_i2c.py
  #  LCD test script using I2C backpack.
  #  Supports 16x2 and 20x4 screens.
  #
  # Author : Matt Hawkins
  # Date   : 20/09/2015
  #
  # http://www.raspberrypi-spy.co.uk/
  #
  # Copyright 2015 Matt Hawkins
  #
  # This program is free software: you can redistribute it and/or modify
  # it under the terms of the GNU General Public License as published by
  # the Free Software Foundation, either version 3 of the License, or
  # (at your option) any later version.
  #
  # This program is distributed in the hope that it will be useful,
  # but WITHOUT ANY WARRANTY; without even the implied warranty of
  # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  # GNU General Public License for more details.
  #
  # You should have received a copy of the GNU General Public License
  # along with this program.  If not, see <http://www.gnu.org/licenses/>.
  #
  #--------------------------------------
  import smbus
  import time
  
  # Define some device parameters
  I2C_ADDR  = 0x27 # I2C device address
  LCD_WIDTH = 16   # Maximum characters per line
  
  # Define some device constants
  LCD_CHR = 1 # Mode - Sending data
  LCD_CMD = 0 # Mode - Sending command
  
  LCD_LINE_1 = 0x80 # LCD RAM address for the 1st line
  LCD_LINE_2 = 0xC0 # LCD RAM address for the 2nd line
  LCD_LINE_3 = 0x94 # LCD RAM address for the 3rd line
  LCD_LINE_4 = 0xD4 # LCD RAM address for the 4th line
  
  LCD_BACKLIGHT  = 0x08  # On
  #LCD_BACKLIGHT = 0x00  # Off
  
  ENABLE = 0b00000100 # Enable bit
  
  # Timing constants
  E_PULSE = 0.0005
  E_DELAY = 0.0005
  
  #Open I2C interface
  #bus = smbus.SMBus(0)  # Rev 1 Pi uses 0
  bus = smbus.SMBus(1) # Rev 2 Pi uses 1
  
  def lcd_init():
    # Initialise display
    lcd_byte(0x33,LCD_CMD) # 110011 Initialise
    lcd_byte(0x32,LCD_CMD) # 110010 Initialise
    lcd_byte(0x06,LCD_CMD) # 000110 Cursor move direction
    lcd_byte(0x0C,LCD_CMD) # 001100 Display On,Cursor Off, Blink Off 
    lcd_byte(0x28,LCD_CMD) # 101000 Data length, number of lines, font size
    lcd_byte(0x01,LCD_CMD) # 000001 Clear display
    time.sleep(E_DELAY)
  
  def lcd_byte(bits, mode):
    # Send byte to data pins
    # bits = the data
    # mode = 1 for data
    #        0 for command
  
    bits_high = mode | (bits & 0xF0) | LCD_BACKLIGHT
    bits_low = mode | ((bits<<4) & 0xF0) | LCD_BACKLIGHT
  
    # High bits
    bus.write_byte(I2C_ADDR, bits_high)
    lcd_toggle_enable(bits_high)
  
    # Low bits
    bus.write_byte(I2C_ADDR, bits_low)
    lcd_toggle_enable(bits_low)
  
  def lcd_toggle_enable(bits):
    # Toggle enable
    time.sleep(E_DELAY)
    bus.write_byte(I2C_ADDR, (bits | ENABLE))
    time.sleep(E_PULSE)
    bus.write_byte(I2C_ADDR,(bits & ~ENABLE))
    time.sleep(E_DELAY)
  
  def lcd_string(message,line):
    # Send string to display
  
    message = message.ljust(LCD_WIDTH," ")
  
    lcd_byte(line, LCD_CMD)
  
    for i in range(LCD_WIDTH):
      lcd_byte(ord(message[i]),LCD_CHR)
  
  def main():
    # Main program block
  
    # Initialise display
    lcd_init()
  
    while True:
  
      # Send some test
      lcd_string("RPiSpy         <",LCD_LINE_1)
      lcd_string("I2C LCD        <",LCD_LINE_2)
  
      time.sleep(3)
    
      # Send some more text
      lcd_string(">         RPiSpy",LCD_LINE_1)
      lcd_string(">        I2C LCD",LCD_LINE_2)
  
      time.sleep(3)
  
  if __name__ == '__main__':
  
    try:
      main()
    except KeyboardInterrupt:
      pass
    finally:
      lcd_byte(0x01, LCD_CMD)
  
  
  