16×2 LCD Module Control Using Python

Once you’ve played with LEDs, switches and stepper motors the next natural step is 16×2 alphanumeric LCD modules. These modules are cheap (less than $10) and easy to interface to the Raspberry Pi. They have 16 connections but you only need to use 6 GPIO pins on your Pi.

Most of the 16×2 modules available are compatible with the Hitachi HD44780 LCD controller. This allows you to buy almost any device and be sure it is going to work in much the same way as any other. There are loads to choose from on eBay with different coloured backlights. The one I purchased had a blue backlight.

LCD Module Hardware

The pinout of the module is :

1. Ground
2. VCC (Usually +5V)
3. Contrast adjustment (VO)
4. Register Select (RS).
   RS=0: Command, RS=1: Data
5. Read/Write (R/W).
   R/W=0: Write, R/W=1: Read
6. Enable
7. Bit 0 (Not required in 4-bit operation)
8. Bit 1 (Not required in 4-bit operation)
9. Bit 2 (Not required in 4-bit operation)
10. Bit 3 (Not required in 4-bit operation)
11. Bit 4
12. Bit 5
13. Bit 6
14. Bit 7
15. LED Backlight Anode (+)
16. LED Backlight Cathode (-)

Usually the device requires 8 data lines to provide data to Bits 0-7. However the device can be set to a “4 bit” mode which allows you to send data in two chunks (or nibbles) of 4 bits. This is great as it reduces the number of GPIO connections you require when interfacing with your Pi.

Here is how I wired up my LCD :

LCD Pin	Function	Pi Function	Pi Pin
01	GND	GND	P1-06
02	+5V	+5V	P1-02
03	Contrast	GND	P1-06
04	RS	GPIO7	P1-26
05	RW	GND	P1-06
06	E	GPIO8	P1-24
07	Data 0
08	Data 1
09	Data 2
10	Data 3
11	Data 4	GPIO25	P1-22
12	Data 5	GPIO24	P1-18
13	Data 6	GPIO23	P1-16
14	Data 7	GPIO18	P1-12
15	+5V via 560ohm
16	GND		P1-06

NOTE : The RW pin allows the device to be be put into read or write mode. I wanted to send data to the device but did not want it to send data to the Pi so I tied this pin to ground. The Pi can not tolerate 5V inputs on its GPIO header. Tying RW to ground makes sure the device does not attempt to pull the data lines to 5V which would damage the Pi.

In order to control the contrast you can adjust the voltage presented to Pin 3. This must be between 0 and 5V. I tied this pin to ground.

Pin 15 provides 5V to the backlight LED. It wasn’t clear on my device if this could be connected direct to 5V so I played safe and placed a 560ohm resistor in line with this pin.

Wiring Checks

Here are some sanity checks before you power up your circuit for the first time :

• Pin 1 (GND), 3 (Contrast), 5 (RW) and 16 (LED -) ( should be tied to ground.
• Pin 2 should be tied to 5V. Pin 15 should have a resistor inline to 5V to protect the backlight.
• Pin 7-10 are unconnected
• Pin 11-14 are connected to GPIO pins on the Pi

Python

You can control a HD44780 style display using any programming environment you like but my weapon of choice is Python. I use the RPi.GPIO library to provide access to the GPIO.

Here is my code :

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#!/usr/bin/python #-------------------------------------- #    ___  ___  _ ____ #   / _ \/ _ \(_) __/__  __ __ #  / , _/ ___/ /\ \/ _ \/ // / # /_/|_/_/  /_/___/ .__/\_, / #                /_/   /___/ # #  lcd_16x2.py #  16x2 LCD Test Script # # Author : Matt Hawkins # Date   : 06/04/2015 # # http://www.raspberrypi-spy.co.uk/ # #--------------------------------------   # The wiring for the LCD is as follows: # 1 : GND # 2 : 5V # 3 : Contrast (0-5V)* # 4 : RS (Register Select) # 5 : R/W (Read Write)       - GROUND THIS PIN # 6 : Enable or Strobe # 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 # 12: Data Bit 5 # 13: Data Bit 6 # 14: Data Bit 7 # 15: LCD Backlight +5V** # 16: LCD Backlight GND   #import import RPi.GPIO as GPIO import time   # Define GPIO to LCD mapping LCD_RS = 7 LCD_E  = 8 LCD_D4 = 25 LCD_D5 = 24 LCD_D6 = 23 LCD_D7 = 18   # Define some device constants LCD_WIDTH = 16    # Maximum characters per line LCD_CHR = True LCD_CMD = False   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     # Initialise display   lcd_init()     while True:       # Send some test     lcd_string("Rasbperry Pi",LCD_LINE_1)     lcd_string("16x2 LCD Test",LCD_LINE_2)       time.sleep(3) # 3 second delay       # Send some text     lcd_string("1234567890123456",LCD_LINE_1)     lcd_string("abcdefghijklmnop",LCD_LINE_2)       time.sleep(3) # 3 second delay       # Send some text     lcd_string("RaspberryPi-spy",LCD_LINE_1)     lcd_string(".co.uk",LCD_LINE_2)       time.sleep(3)       # Send some text     lcd_string("Follow me on",LCD_LINE_1)     lcd_string("Twitter @RPiSpy",LCD_LINE_2)       time.sleep(3)   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()