lcd1602gpio

Use HD44780-compatible 16x2 LCD module by Python via Raspberry Pi GPIO

Introduction

Based on RPi.GPIO, it writes instructions to a 16x2 LCD module through Raspberry Pi's GPIO pins directly.

This is not for interfacing an I2C LCD.

This module provides the following functions:

• Initialize LCD in 8-bit and 4-bit data bus modes.
• Write instructions to LCD.
• Write data to LCD's DDRAM. (Data Display RAM)
• Write custom character to LCD's CGRAM. (Character Generator RAM)
• Write a line of string and display it on LCD.
• Clear LCD display.

This module cannot:

• Read any data or address from LCD.

Synopsis

class LCD1602GPIO
|   LCD1602GPIO(rs, e,
|               db7, db6, db5, db4,
|               db3, db2, db1, db0,
|               e_pulse=0.0005,
|               e_delay=0.0005,
|               delayfunc=time.sleep) --> an 8-bit LCD controller instance

class LCD1602GPIO_4BIT(LCD1602GPIO)
|   LCD1602GPIO_4BIT(rs, e,
|                    db7, db6, db5, db4,
|                    e_pulse=0.0005,
|                    e_delay=0.0005,
|                    delayfunc=time.sleep) --> a 4-bit LCD controller instance

Arguments:

• rs: GPIO pin number to RS.
• e: GPIO pin number to E (Enable).
• db7 ~ db0: GPIO pin numbers of data bus. (set db7 ~ db4 only if you're going to use 4-bit mode.)
• e_pulse: the pulse length of E in high voltage, in seconds.
• e_delay: the delays before & after E in high voltage, in seconds.
• delayfunc: the delay function. Default to time.sleep.

Class members

• gpio_setup(): configure GPIO pins. (invoked during class initialization.)
• toggle_enable(): Toggle E (Enable) pin from HIGH to LOW in a cycle.
• _write(c): write a byte c (int) to data bus.
• command(c): send an instruction byte c (int) to LCD's instruction register (IR).
• write_char(c): write a character byte c (int) to LCD's data register (DR).
• clear_lcd(): clear the LCD display.
• initialize_lcd(): reset and initialize the LCD module. (invoked during class initialization.)
• goto_lcd_line(line, pos=0): Go to the beginning or the specified position pos (int, 0 to 15) of line line (int, 0 or 1). See table below:

• write_line(s, line): write a string s (str) to LCD line line (int, 0 or 1).
• set_cgram_char(cgram_no, bitmap): set CGRAM number cgram_no (int, 0 to 7) and write 5x8 bitmap pixels bitmap (List[int], len=8). e.g. Define a custom character “↑” (Upwards Arrow) to CGRAM number 0:

import RPi.GPIO as GPIO
import lcd1602gpio

# Disable GPIO warnings
GPIO.setwarnings(False)
# Set GPIO pin mode. RPi pins described in this example use BCM.
GPIO.setmode(GPIO.BCM)

# create an instance of LCD1602GPIO with 8-bit mode.
lcd = lcd1602gpio.LCD1602GPIO(
        rs=7,
        e=8,
        db7=18,
        db6=23,
        db5=24,
        db4=25,
        db3=6,
        db2=13,
        db1=19,
        db0=26)

# define a custom character (Upwards Arrow) to CGRAM number 0.
lcd.set_cgram_char(0, [0b00000,
                       0b00100,
                       0b01110,
                       0b10101,
                       0b00100,
                       0b00100,
                       0b00000,
                       0b00000])

# Go to the beginning of Line 0.
lcd.goto_lcd_line(0)
# Display the character at CGRAM no 0.
lcd.write_char(0)

GPIO.cleanup()

Caveats

• Since it's not for realtime applications, the clock pulse and delays are not precise. This might not work with your LCD module properly or require some tweaks on delays. Using LCD module on an Arduino will make your life easier.
• Read function is not yet implemented so it does not read Busy Flag (BF) and the default value of delay is much longer to ensure each LCD instruction can be executed in time. The performance of manipulating an LCD module will be slower than expected.

Examples

The examples are based on LCD module LMM84S019D2E (PCB: M019F REV:A) manufactured by Nan Ya Plastics, but its pin layout may be different to yours. You may need to change the wiring and adjust the delay times if your LCD doesn't work.

You may need to add a resistor to your LCD backlight's anode (if available) to protect it. You may also add a potentiometer to Contrast pin (aka V_o or V_L) to adjust your LCD contrast.

It supports both 8-bit and 4-bit data bus modes. The R/W pin is grounded because read function is not yet implemented.

8-bit mode

The configuration requires 5V power, GND, 2 GPIO pins for signaling and 8 GPIO pins for 8-bit data bus.

Import required Python modules and create an instance of LCD1602GPIO.

import RPi.GPIO as GPIO
import lcd1602gpio

# Disable GPIO warnings
GPIO.setwarnings(False)
# Set GPIO pin mode. RPi pins described in this example use BCM.
GPIO.setmode(GPIO.BCM)

# create an instance of LCD1602GPIO with 8-bit mode.
# the LCD module must be already powered on here.
# the instance initializes the LCD module immediately during init.
lcd = lcd1602gpio.LCD1602GPIO(
        rs=7,
        e=8,
        db7=18,
        db6=23,
        db5=24,
        db4=25,
        db3=6,
        db2=13,
        db1=19,
        db0=26)

# write texts to Line 0 of the LCD.
lcd.write_line("abcdefghijklmnop", 0)
# write texts to Line 1 of the LCD.
lcd.write_line("1234567890123456", 1)

# Do GPIO cleanup manually before exiting.
GPIO.cleanup()

4-bit mode

The configuration requires 5V power, GND, 2 GPIO pins for signaling and 4 GPIO pins for 4-bit data bus.

Those 4 low order data bus pins DB0 to DB3 are unconnected.

Import required Python modules and create an instance of LCD1602GPIO_4BIT.

import RPi.GPIO as GPIO
import lcd1602gpio

# Disable GPIO warnings
GPIO.setwarnings(False)
# Set GPIO pin mode. RPi pins described in this example use BCM.
GPIO.setmode(GPIO.BCM)

# create an instance of LCD1602GPIO_4BIT for 4-bit mode.
# the LCD module must be already powered on here.
# the instance initializes the LCD module immediately during init.
lcd = lcd1602gpio.LCD1602GPIO_4BIT(
        rs=7,
        e=8,
        db7=18,
        db6=23,
        db5=24,
        db4=25)

# write texts to Line 0 of the LCD.
lcd.write_line("abcdefghijklmnop", 0)
# write texts to Line 1 of the LCD.
lcd.write_line("1234567890123456", 1)

# Do GPIO cleanup manually before exiting.
GPIO.cleanup()

Reference

• HD44780U (LCD-II), (Dot Matrix Liquid Crystal Display Controller/Driver) manual