Temp2-Analog_TMP36.py

#!/usr/bin/env python
import time
import datetime
import os
import RPi.GPIO as GPIO

GPIO.setmode(GPIO.BCM)
DEBUG = 1
LOGGER = 1


# This code uses the MCP3008 chip to pull in analog data using 
# 10-bits of resolution to read the voltage level from the 
# analog TMP36 sensor.

# 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

while True:
        # read the analog pin (temperature sensor LM35)
        read_adc0 = readadc(adcnum, SPICLK, SPIMOSI, SPIMISO, SPICS)

        # convert analog reading to millivolts = ADC * ( 3300 / 1024 )
        millivolts = read_adc0 * ( 3300.0 / 1024.0)

        # 10 mv per degree 
        temp_C = ((millivolts - 100.0) / 10.0) - 40.0

        # convert celsius to fahrenheit 
        temp_F = ( temp_C * 9.0 / 5.0 ) + 32

        # remove decimal point from millivolts
        millivolts = "%d" % millivolts

        # show only one decimal place for temprature and voltage readings
        temp_C = "%.1f" % temp_C
        temp_F = "%.1f" % temp_F
	
	if DEBUG:
		# Print what we have gathered to the Screen!
        	print "read_adc0:\t", read_adc0
        	print "millivolts:\t", millivolts
        	print "temp_C:\t\t", temp_C
        	print "temp_F:\t\t", temp_F
        	print

        if LOGGER:
		# open a file for writing... append mode
		logtime = datetime.datetime.now()
		temphist = open('temp_hist', 'a')
		temphist.write(logtime.strftime("%Y-%m-%d %H:%M") + '\t' + 'temp_C:\t' + temp_C + '\t' + 'temp_F:' + '\t' + temp_F + '\n')

	
	# Sleep for 5 seconds... 
        time.sleep(5)

	#If you want to log this data, check out adafruit-cosm-temp.py program