Raspberry Pi - Read temperature, print it to a lcd plate and indicate warnings with backlight color.

temp_with_warning.py

#!/usr/bin/python
"""
Read the temperature from the connected sensor on the w1 bus and write it
to the LCD plate. If the temperature is below TEMP_LIMIT_L the backlight
color changes to blue. If the temperature is above TEMP_LIMIT_H the
backlight color changes to red.

This script uses the Adafruit LCD Plate as output device. Documentation and
about infos for Python implementation can be found here:

http://learn.adafruit.com/adafruit-16x2-character-lcd-plus-keypad-for-raspberry-pi

As a temperature sensor a onewire sensor like the DS18B20 can be used.

"""

from Adafruit_CharLCDPlate import Adafruit_CharLCDPlate
from time import sleep

BACKLIGHT_TIME = 5
TEMP_W1_PATH = "/sys/bus/w1/devices/28-000004ac7761/w1_slave"
TEMP_LIMIT_H = 23.0
TEMP_LIMIT_L = 21.5

def read_temp():
	tfile = open(TEMP_W1_PATH) 
	text = tfile.read() 
	tfile.close() 
	secondline = text.split("\n")[1] 
	temperaturedata = secondline.split(" ")[9] 
	temperature = float(temperaturedata[2:]) 
	temperature = temperature / 1000 
	return temperature

lcd = Adafruit_CharLCDPlate()

ALL_BUTTONS = (lcd.UP, lcd.DOWN, lcd.RIGHT, lcd.LEFT, lcd.SELECT) 

lcd.numlines=2
lcd.clear()
msg = "Temperatur:"
lcd.message(msg)

c=0	#: backlight counter
backlight_color = lcd.ON
while True:
	def change_color(color):
		global c
		global backlight_color
		backlight_color = color
		c = 0
		lcd.backlight(color)

	#read current temperature
	temp = read_temp()

	#switch backlight off after BACKLIGHT_TIME
	if c >= BACKLIGHT_TIME and not (temp>TEMP_LIMIT_H or temp<TEMP_LIMIT_L):
		lcd.backlight(lcd.OFF)
	else:
		c += 1

	#switch backlight on if a button is pressed
	for b in ALL_BUTTONS:
		if lcd.buttonPressed(b):
			change_color(lcd.ON)

	#choose color acording to temperature	
	if temp < TEMP_LIMIT_L:
		change_color(lcd.BLUE)
	elif temp > TEMP_LIMIT_H:
		change_color(lcd.RED)
	else:
		if not backlight_color == lcd.ON:
			change_color(lcd.ON)	

	lcd.setCursor(0, 1)
	lcd.message("%.2f C" % temp)
	sleep(1)

anyone having problems with buttons?
i cant wake the lcd with any button
but the buttons work with adafruits lcd test