PCA8574 Controlled HD44780 LCD library

pylcd.py

'''
Copyright (C) 2012 Matthew Skolaut

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and 
associated documentation files (the "Software"), to deal in the Software without restriction, 
including without limitation the rights to use, copy, modify, merge, publish, distribute, 
sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is 
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial
portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT
LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE 
SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
'''

import smbus
from time import *

# General i2c device class so that other devices can be added easily
class i2c_device:
	def __init__(self, addr, port):
		self.addr = addr
		self.bus = smbus.SMBus(port)

	def write(self, byte):
		self.bus.write_byte(self.addr, byte)

	def read(self):
		return self.bus.read_byte(self.addr)

	def read_nbytes_data(self, data, n): # For sequential reads > 1 byte
		return self.bus.read_i2c_block_data(self.addr, data, n)


class lcd:
	#initializes objects and lcd
	'''
	Reverse Codes:
	0: lower 4 bits of expander are commands bits
	1: top 4 bits of expander are commands bits AND P0-4 P1-5 P2-6
	2: top 4 bits of expander are commands bits AND P0-6 P1-5 P2-4
	'''
	def __init__(self, addr, port, reverse=0):
		self.reverse = reverse
		self.lcd_device = i2c_device(addr, port)
		if self.reverse:
			self.lcd_device.write(0x30)
			self.lcd_strobe()
			sleep(0.0005)
			self.lcd_strobe()
			sleep(0.0005)
			self.lcd_strobe()
			sleep(0.0005)
			self.lcd_device.write(0x20)
			self.lcd_strobe()
			sleep(0.0005)
		else:
			self.lcd_device.write(0x03)
			self.lcd_strobe()
			sleep(0.0005)
			self.lcd_strobe()
			sleep(0.0005)
			self.lcd_strobe()
			sleep(0.0005)
			self.lcd_device.write(0x02)
			self.lcd_strobe()
			sleep(0.0005)

		self.lcd_write(0x28)
		self.lcd_write(0x08)
		self.lcd_write(0x01)
		self.lcd_write(0x06)
		self.lcd_write(0x0C)
		self.lcd_write(0x0F)

	# clocks EN to latch command
	def lcd_strobe(self):
		if self.reverse == 1:
			self.lcd_device.write((self.lcd_device.read() | 0x04))
			self.lcd_device.write((self.lcd_device.read() & 0xFB))
		elif self.reverse == 2:
			self.lcd_device.write((self.lcd_device.read() | 0x01))
			self.lcd_device.write((self.lcd_device.read() & 0xFE))
		else:
			self.lcd_device.write((self.lcd_device.read() | 0x10))
			self.lcd_device.write((self.lcd_device.read() & 0xEF))

	# write a command to lcd
	def lcd_write(self, cmd):
		if self.reverse:
			self.lcd_device.write((cmd >> 4)<<4)
			self.lcd_strobe()
			self.lcd_device.write((cmd & 0x0F)<<4)
			self.lcd_strobe()
			self.lcd_device.write(0x0)
		else:
			self.lcd_device.write((cmd >> 4))
			self.lcd_strobe()
			self.lcd_device.write((cmd & 0x0F))
			self.lcd_strobe()
			self.lcd_device.write(0x0)

	# write a character to lcd (or character rom)
	def lcd_write_char(self, charvalue):
		if self.reverse == 1:
			self.lcd_device.write((0x01 | (charvalue >> 4)<<4))
			self.lcd_strobe()
			self.lcd_device.write((0x01 | (charvalue & 0x0F)<<4))
			self.lcd_strobe()
			self.lcd_device.write(0x0)
		elif self.reverse == 2:
			self.lcd_device.write((0x04 | (charvalue >> 4)<<4))
			self.lcd_strobe()
			self.lcd_device.write((0x04 | (charvalue & 0x0F)<<4))
			self.lcd_strobe()
			self.lcd_device.write(0x0)
		else:
			self.lcd_device.write((0x40 | (charvalue >> 4)))
			self.lcd_strobe()
			self.lcd_device.write((0x40 | (charvalue & 0x0F)))
			self.lcd_strobe()
			self.lcd_device.write(0x0)

	# put char function
	def lcd_putc(self, char):
		self.lcd_write_char(ord(char))

	# put string function
	def lcd_puts(self, string, line):
		if line == 1:
			self.lcd_write(0x80)
		if line == 2:
			self.lcd_write(0xC0)
		if line == 3:
			self.lcd_write(0x94)
		if line == 4:
			self.lcd_write(0xD4)

		for char in string:
			self.lcd_putc(char)

	# clear lcd and set to home
	def lcd_clear(self):
		self.lcd_write(0x1)
		self.lcd_write(0x2)

	# add custom characters (0 - 7)
	def lcd_load_custon_chars(self, fontdata):
		self.lcd_device.bus.write(0x40);
		for char in fontdata:
			for line in char:
				self.lcd_write_char(line)

class tmp102:
	def __init__(self, addr, port):
		self.sensor = i2c_device(addr, port)

	# read a register
	def read_reg(self, reg):
		return self.sensor.read_nbytes_data(reg, 2)

	# read the current temp in celsius
	def read_temp(self):
		tempraw = self.read_reg(0)
		return tempraw[0] + (tempraw[1] >> 4) * 0.0625

Hi, I want to send stuff to the lcd screen from two threads! How can I do this without crashing the i2c bus?