Basic Light and Temperature Sensing

Here I use two cheap analog sensors for temperature and light:
http://www.adafruit.com/products/165
http://www.adafruit.com/products/161

And convert their analog values to digital values using an Analog to Digital convertor (ADC)
http://www.adafruit.com/products/856

To make things easy I wire these up on an external breadboard connected to the Pi using a Pi cobbler:
http://www.adafruit.com/products/914

Tutorials for installing and using these components can be found on Adafruit's website and I used them heavily. I could explain the technical details of all these components but Adafruit probably does a more elegant job and has tons of documentation so please follow the links for more information. Also the temperature sensor and the ADC are used by TONS of people so a quick google search will give lots of results as well!

	import time
	import os
	import RPi.GPIO as GPIO
	# sets up GPIO pins
	GPIO.setmode(GPIO.BCM)
	GPIO.setwarnings(False)
	DEBUG = 0
	# read SPI data from MCP3008 chip, 8 possible adc's (0 thru 7)
	def readadc(adcnum, clockpin, mosipin, misopin, cspin):
	if ((adcnum > 7) or (adcnum < 0)):
	return -1
	GPIO.output(cspin, True)
	GPIO.output(clockpin, False) # start clock low
	GPIO.output(cspin, False) # bring CS low
	commandout = adcnum
	commandout |= 0x18 # start bit + single-ended bit
	commandout <<= 3 # we only need to send 5 bits here
	for i in range(5):
	if (commandout & 0x80):
	GPIO.output(mosipin, True)
	else:
	GPIO.output(mosipin, False)
	commandout <<= 1
	GPIO.output(clockpin, True)
	GPIO.output(clockpin, False)
	adcout = 0
	# read in one empty bit, one null bit and 10 ADC bits
	for i in range(12):
	GPIO.output(clockpin, True)
	GPIO.output(clockpin, False)
	adcout <<= 1
	if (GPIO.input(misopin)):
	adcout |= 0x1
	GPIO.output(cspin, True)
	adcout /= 2 # first bit is 'null' so drop it
	return adcout
	# change these as desired - they're the pins connected from the
	# SPI port on the ADC to the Cobbler
	SPICLK = 18
	SPIMISO = 23
	SPIMOSI = 24
	SPICS = 25
	# set up the SPI interface pins
	GPIO.setup(SPIMOSI, GPIO.OUT)
	GPIO.setup(SPIMISO, GPIO.IN)
	GPIO.setup(SPICLK, GPIO.OUT)
	GPIO.setup(SPICS, GPIO.OUT)
	# temperature sensor connected channel 0 of mcp3008
	adcnum = 0
	adclight = 1
	#while True:
	# read the analog pin (temperature sensor LM35)
	read_adc0 = readadc(adcnum, SPICLK, SPIMOSI, SPIMISO, SPICS)
	#convert TMP36 #1 digital reading to Celsius temperature
	c_temp0 = (((read_adc0 * ( 3300.0 / 1024.0)) - 100.0) / 10.0) - 40.0
	c_temp0 = "%.1f" % c_temp0
	read_adc1 = readadc(adclight, SPICLK, SPIMOSI, SPIMISO, SPICS)
	print 'Temp:', c_temp0, 'C'
	print 'Light level:', read_adc1
	print
	print 'ADC values:' # prints raw values
	print 'Pin 1:', read_adc0
	print 'Pin 2:', read_adc1
	if read_adc1 in range(0, 100):
	print "Time to turn on the lights!" # dark
	if read_adc1 in range(101, 250):
	print "Running our of light, might have to turn on the lights soon..." # indoor room light levels, not very bright
	if read_adc1 in range(251, 500):
	print "Plenty of light :)" # fairly bright, good growing levels
	if read_adc1 in range(501, 1023):
	print "Woah, where is the sunblock?" # Tons of light, yay!

view raw airandlight.py hosted with ❤ by GitHub

Also a quick note about the light sensor:
I use a 1K resistor to change by values a bit. This resistor gives me a nice range when the light is bright. If you use a larger resistor (say 10k) it will be better at resolving lower light level differences. Play around with it and use a resistor that gives you a nice dynamic range for the light levels you are interested in sensing.