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Table of Contents
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.
(This is from the Master Pi)
The File Header
This is to identify to the Linux system what this file type is, and to allow the author to add some information (anything following a hash # is just a comment)
#!/usr/bin/python #-------------------------------------- # 16x2 LCD Test Script # # Author : Alan Walker # Date : 16/05/2016 #--------------------------------------
A reminder of the pin outs
The following section is just comments, but it is a nice reminder of which GPIO pins on the Raspberry Pi that this Python code is going to try to address.
# 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 Python Libraries
Python uses standard libraries to provide standard functions, so you don't have to code everyday tasks such as printing etc. Here we are importing some standard libraries for our project.
#import import RPi.GPIO as GPIO import time import socket import fcntl import struct
Declare some Variables
Rather than referring to GPIO pin numbers in the code, we are declaring some variables that we can use to reference the GPIO pin numbers to actual functions. (So the LCD Reset that uses GPIO pin 26 can be called by using just LCD_RS for example).
The advantage of using this method is, if a pin number changes, we can change it here, and not have to hunt through the code for every occurrence of that pin number.
# Define GPIO to LCD mapping LCD_RS = 26 LCD_E = 19 LCD_D4 = 13 LCD_D5 = 6 LCD_D6 = 5 LCD_D7 = 11
Import Python Libraries
# 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()
</file>
#!/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()