The Python Code

The Code Running the LCD

By now you should have your Raspberry Pi and LCD running. Here we will discuss the Python code that runs the LCD display and how it works (at a top level).

The Code

On each Raspberry Pi there is a file called UMDisplay0x.py. This is the file that sends data to the LCD, it is the same on each Pi except for a setting that tells the Pi which 2 of the 8 text lines to use.

#!/usr/bin/python
#--------------------------------------
# 16x2 LCD Test Script
#
# Author : Alan Walker
# Date : 16/05/2016
#
#--------------------------------------
# The wiring for the LCD is as follows:
# 1 : GND
# 2 : 5V
# 3 : Contrast (0-5V)* - Sets the LCD Contrast
# 4 : RS (Register Select) - GPIO pin 26 - Physical pin 37
# 5 : R/W (Read Write) - GROUND THIS PIN
# 6 : Enable or Strobe - GPIO pin 19 - Physical pin 35
# 7 : Data Bit 0 - NOT USED
# 8 : Data Bit 1 - NOT USED
# 9 : Data Bit 2 - NOT USED
# 10: Data Bit 3 - NOT USED
# 11: Data Bit 4 - GPIO pin 13 - Physical pin 33
# 12: Data Bit 5 - GPIO pin 06 - Physical pin 31
# 13: Data Bit 6 - GPIO pin 05 - Physical pin 29
# 14: Data Bit 7 - GPIO pin 11 - Physical pin 23
# 15: LCD Backlight - +5V**
# 16: LCD Backlight - GND
#import
import RPi.GPIO as GPIO
import time
import socket
import fcntl
import struct
# Define GPIO to LCD mapping
LCD_RS = 26
LCD_E = 19
LCD_D4 = 13
LCD_D5 = 6
LCD_D6 = 5
LCD_D7 = 11
# Define some device constants
LCD_WIDTH = 40 # Maximum characters per line
LCD_CHR = True
LCD_CMD = False
# Do I need to change line 2 address for 40 char display?
LCD_LINE_1 = 0x80 # LCD RAM address for the 1st line
LCD_LINE_2 = 0xC0 # LCD RAM address for the 2nd line
# Timing constants
E_PULSE = 0.0005
E_DELAY = 0.0005
def main():
# Main program block
GPIO.setwarnings(False)
GPIO.setmode(GPIO.BCM) # Use BCM GPIO numbers
GPIO.setup(LCD_E, GPIO.OUT) # E
GPIO.setup(LCD_RS, GPIO.OUT) # RS
GPIO.setup(LCD_D4, GPIO.OUT) # DB4
GPIO.setup(LCD_D5, GPIO.OUT) # DB5
GPIO.setup(LCD_D6, GPIO.OUT) # DB6
GPIO.setup(LCD_D7, GPIO.OUT) # DB7
##########################################
# PROGRAM START #
##########################################
# Initialise display
lcd_init()
lcd_string(" Waiting 5 Seconds for Network Start",LCD_LINE_1) # wait 5 seconds for DHCP process to finish
time.sleep(5)
while True:
## Open the file with read only permit
f = open('/home/pi/Python/my_data.txt', "r")
## use readlines to read all the lines in the file
## The variable "lines" is a list containing all lines
# readline 400 is read in 400 chars
# replace removed the carriage return and new line
# [:40] truncates to 40 chars
line1 = f.readline(400).replace("\r\n","")[:40]
line2 = f.readline(400).replace("\r\n","")[:40]
line3 = f.readline(400).replace("\r\n","")[:40]
line4 = f.readline(400).replace("\r\n","")[:40]
line5 = f.readline(400).replace("\r\n","")[:40]
line6 = f.readline(400).replace("\r\n","")[:40]
line7 = f.readline(400).replace("\r\n","")[:40]
line8 = f.readline(400).replace("\r\n","")[:40]
## close the file after reading the lines.
f.close()
# Display the current IP Address information
# lcd_string(" lo" + " " + get_ip_address('lo'),LCD_LINE_1)
# lcd_string(" UMD 04",LCD_LINE_1)
# lcd_string(" eth0" + " " + get_ip_address('eth0'),LCD_LINE_2)
# time.sleep(2) # x second delay
# write line 1 and 2 to the LCD (Line7 and Line8 because this is UMD4)
lcd_string(" " + line1,LCD_LINE_1)
lcd_string(" " + line2,LCD_LINE_2)
time.sleep(1) # x second delay
##########################################
# CHANGE NO CODE BELOW THIS LINE #
##########################################
def get_ip_address(ifname):
s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
return socket.inet_ntoa(fcntl.ioctl(
s.fileno(),
0x8915, # SIOCGIFADDR
struct.pack('256s', ifname[:15])
)[20:24])
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 = data
# mode = True for character
# False for command
GPIO.output(LCD_RS, mode) # RS
# High bits
GPIO.output(LCD_D4, False)
GPIO.output(LCD_D5, False)
GPIO.output(LCD_D6, False)
GPIO.output(LCD_D7, False)
if bits&0x10==0x10:
GPIO.output(LCD_D4, True)
if bits&0x20==0x20:
GPIO.output(LCD_D5, True)
if bits&0x40==0x40:
GPIO.output(LCD_D6, True)
if bits&0x80==0x80:
GPIO.output(LCD_D7, True)
# Toggle 'Enable' pin
lcd_toggle_enable()
# Low bits
GPIO.output(LCD_D4, False)
GPIO.output(LCD_D5, False)
GPIO.output(LCD_D6, False)
GPIO.output(LCD_D7, False)
if bits&0x01==0x01:
GPIO.output(LCD_D4, True)
if bits&0x02==0x02:
GPIO.output(LCD_D5, True)
if bits&0x04==0x04:
GPIO.output(LCD_D6, True)
if bits&0x08==0x08:
GPIO.output(LCD_D7, True)
# Toggle 'Enable' pin
lcd_toggle_enable()
def lcd_toggle_enable():
# Toggle enable
time.sleep(E_DELAY)
GPIO.output(LCD_E, True)
time.sleep(E_PULSE)
GPIO.output(LCD_E, False)
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)
if __name__ == '__main__':
try:
main()
except KeyboardInterrupt:
pass
finally:
#lcd_byte(0x01, LCD_CMD)
#lcd_string("Goodbye!",LCD_LINE_1)
GPIO.cleanup()