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--- the_python_code [2016/12/21 15:48] – [The Code] walkeradmin
+++ the_python_code [2023/03/09 22:35] (current) – external edit 127.0.0.1
@@ Line 16: / Line 16: @@
 On each Raspberry Pi there is a file called <color red>UMDisplay0x.py</color>. 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.
 \\
+\\
+<color red>(This is from the Master Pi)</color>
+----
+==== 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)
 \\
 <file>
@@ Line 24: / Line 31: @@
 # Author : Alan Walker
 # Date   : 16/05/2016
-#
+#--------------------------------------
+</file>
+----
+==== 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.
+\\
+<file>
+# 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
+</file>
+----
+==== 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.
+\\
+<file>
+#import
+import RPi.GPIO as GPIO
+import time
+import socket
+import fcntl
+import struct
+</file>
+----
+==== Define some Constants ====
+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.
+\\
+<file>
+# Define GPIO to LCD mapping
+LCD_RS = 26
+LCD_E  = 19
+LCD_D4 = 13
+LCD_D5 = 6
+LCD_D6 = 5
+LCD_D7 = 11
+</file>
+----
+==== Import Python Libraries ====
+Below we are defining some more constants, these are to do with the LCD lines and chars, as well as the timing.
+\\
+<file>
+# Define some device constants
+LCD_WIDTH = 40    # Maximum characters per line
+LCD_CHR = True
+LCD_CMD = False
+# 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
+</file>
+----
+==== Code Start ====
+This is where the main code starts, as this program runs in a loop, anything above the line <color red>def main():</color> is only run once at program start. Anything below is run once per loop.
+\\
+\\
+<color red>GPIO.setmode(GPIO.BCM)</color> tells the Pi we are using the GPIO board numbers, not the Pin numbers.
+\\
+<file>
+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
+</file>
+----
+==== Program Start ====
+This is the main body of the code that runs the LCD, to save splitting this up I will comment in this section.
+\\
+<file>
+##########################################
+#             PROGRAM  START             #
+##########################################
+  # Initialise display
+  lcd_init()
+  # If using DHCP this is required, or code runs before network is ready.
+  lcd_string(" Waiting 5 Seconds for Network Start",LCD_LINE_1) # wait 5 seconds for DHCP process to finish
+  time.sleep(5)
+</file>
+----
+==== Read File ====
+Here we are opening the file <color red>'/home/pi/Python/my_data.txt</color> for edit (so we can read and write to it). This file contains the 8 lines of text for our LCDs.
+\\
+<file>
+  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()
+</file>
+----
+==== Set which line to write to the LCD ====
+The code below sets what lines from the 8 lines are used (so Master Pi displays lines 1&2, the fourth Pi displays Lines 7&8.
+\\
+\\
+line<color red>1</color>,LCD_LINE_<color blue>1</color>
+\\
+\\
+This above example tells the Pi to use Line <color red>1</color> from our text file, and put is on line <color blue>1</color> of our LCD
+\\
+<file>
+    # 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
+</file>
+----
+==== LCD Write Code ====
+The code below takes our text and writes it to the LCD, do not make any changes to this section.
+\\
+<file>
+##########################################
+#     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(),
+x8915,  # 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>
+\\
+----
+\\
+\\
+===== Complete Code Set =====
+\\
+Below is the complete file without any breaks, you can cut and paste this to create your own UMD LCD.
+\\
+\\
+<file>
+#!/usr/bin/python
+#--------------------------------------
+#  16x2 LCD Test Script
+#
+# Author : Alan Walker
+# Date   : 16/05/2016
 #--------------------------------------
@@ Line 120: / Line 404: @@
     ## 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)