rslcd.py

#
# Python module to drive the LCD in the Recon Sentinel
# Based on example code from https://shiroku.net/robotics/using-i2c-lcd-on-raspberry-pi/
#

import time
import smbus2 as smbus

# Define some device parameters
I2C_ADDR = 0x3f     # I2C device address
LCD_WIDTH = 16      # Maximum characters per line

# Define some device constants
LCD_CHR = 1     # Mode - Sending data
LCD_CMD = 0     # Mode - Sending command

LCD_LINE_1 = 0x80   # LCD RAM address for the 1st line
LCD_LINE_2 = 0xC0   # LCD RAM address for the 2nd line

LCD_BACKLIGHT = 0x08  # On

ENABLE = 0b00000100     # Enable bit

# Timing constants
E_PULSE = 0.0005
E_DELAY = 0.0005

# Open I2C interface
bus = smbus.SMBus(1)

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 = the data
    # mode = 1 for data
    #        0 for command

    bits_high = mode | (bits & 0xF0) | LCD_BACKLIGHT
    bits_low = mode | ((bits << 4) & 0xF0) | LCD_BACKLIGHT

    # High bits
    bus.write_byte(I2C_ADDR, bits_high)
    lcd_toggle_enable(bits_high)

    # Low bits
    bus.write_byte(I2C_ADDR, bits_low)
    lcd_toggle_enable(bits_low)


def lcd_toggle_enable(bits):
    # Toggle enable
    time.sleep(E_DELAY)
    bus.write_byte(I2C_ADDR, (bits | ENABLE))
    time.sleep(E_PULSE)
    bus.write_byte(I2C_ADDR, (bits & ~ENABLE))
    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)