"""
Write a string (argv[1] if run from command line) to a HD44780
LCD module connected via a FTDI UM232R/245R module using pylibftdi
example usage:
# while true;
> do python lcd.py $( awk '{print $1}' /proc/loadavg);
> sleep 5;
> done
Copyright (c) 2010-2014 Ben Bass <benbass@codedstructure.net>
All rights reserved.
"""
from pylibftdi import BitBangDevice, Bus
[docs]class LCD:
"""
The UM232R/245R is wired to the LCD as follows:
DB0..3 to LCD D4..D7 (pin 11..pin 14)
DB6 to LCD 'RS' (pin 4)
DB7 to LCD 'E' (pin 6)
"""
data = Bus(0, 4)
rs = Bus(6)
e = Bus(7)
[docs] def __init__(self, device):
# The Bus descriptor assumes we have a 'device'
# attribute which provides a port
self.device = device
def _trigger(self):
"""generate a falling edge"""
self.e = 1
self.e = 0
[docs] def init_four_bit(self):
"""
set the LCD's 4 bit mode, since we only have
8 data lines and need at least 2 to strobe
data into the module and select between data
and commands.
"""
self.rs = 0
self.data = 3
for _ in range(3):
self._trigger()
self.data = 2
self._trigger()
def _write_raw(self, rs, x):
# rs determines whether this is a command
# or a data byte. Write the data as two
# nibbles. Ahhh... nibbles. QBasic anyone?
self.rs = rs
self.data = x >> 4
self._trigger()
self.data = x & 0x0F
self._trigger()
[docs] def write_cmd(self, x):
self._write_raw(0, x)
[docs] def write_data(self, x):
self._write_raw(1, x)
[docs]def display(string, device_id=None):
"""
Display the given string on an attached LCD
an optional `device_id` can be given.
"""
with BitBangDevice(device_id) as bb:
# These LCDs are quite slow - and the actual baudrate
# is 16x this in bitbang mode...
bb.baudrate = 60
lcd = LCD(bb)
lcd.init_four_bit()
# 001xxxxx - function set
lcd.write_cmd(0x20)
# 00000001 - clear display
lcd.write_cmd(0x01)
# 000001xx - entry mode set
# bit 1: inc(1)/dec(0)
# bit 0: shift display
lcd.write_cmd(0x06)
# 00001xxx - display config
# bit 2: display on
# bit 1: display cursor
# bit 0: blinking cursor
lcd.write_cmd(0x0C)
for i in string:
lcd.write_data(ord(i))
if __name__ == "__main__":
import sys
if len(sys.argv) == 2:
display(sys.argv[1])
else:
print("Usage: %s 'display string'")