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!
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| 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 '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! |
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.
