# GetMAX6675.py. A pyhton routine to take 5 samples and
# return an average of a K type thermocouple Connected
# to a MAX6675 Cold junction compensated K-thermocouple to digital converter. 
# Samples are 170 ms arart, therefore rourine is approx
# 1 second. If thermocouple is open circuit, the word
# "ALARM" is returned.
# MAX6675 returns temperature in Celsius in 0.25 steps

import spidev
import time
import sys

spi = spidev.SpiDev(0,0)  #open SPI port 0, spidev controlls chip enable
spi.max_speed_hz = 1000   #select a slow speed.

samples = 5     #set routine for 5 samples
sample_delay = .170    #set samle delay to 170 ms
temperature_total = 0    #reset variable
temperature_out = 0      #reset variable
alarm = 0                #reset variable


for count in range(samples):
    bytes_in = spi.readbytes(2) #read 2 bytes form MAX6675
    if (bytes_in[1] & (1<<2)): #test for open cct thermocouple
        alarm = 1              #set alarm bit, exit loop if true
        break
    else:
        word_in = ((bytes_in[0]<<8) + bytes_in[1]) #2 bytes to word
        word_shift = ((word_in >> 3) * .25) # shift word then * 0.25
        temperature_total = word_shift + temperature_total #add total samples
        time.sleep(sample_delay) #delay to allow MAZ6675 to convert new sample
        
if (alarm):          #test form alarm bit
    print ("ALARM")  #return word "ALARM" if set
else:  #if alarm not set, return averaged temperature
    temperature_out = temperature_total / samples
    print (temperature_out)
  
spi.close()    #close SPI