Added MAX31855 support

max31855.py

@@ -0,0 +1,170 @@
+#!/usr/bin/python
+import RPi.GPIO as GPIO
+
+class MAX31855(object):
+    '''Python driver for [MAX38155 Cold-Junction Compensated Thermocouple-to-Digital Converter](http://www.maximintegrated.com/datasheet/index.mvp/id/7273)
+     Requires:
+     - The [GPIO Library](https://code.google.com/p/raspberry-gpio-python/) (Already on most Raspberry Pi OS builds)
+     - A [Raspberry Pi](http://www.raspberrypi.org/)
+
+    '''
+    def __init__(self, cs_pin, clock_pin, data_pin, units = "c", board = GPIO.BCM):
+        '''Initialize Soft (Bitbang) SPI bus
+
+        Parameters:
+        - cs_pin:    Chip Select (CS) / Slave Select (SS) pin (Any GPIO)  
+        - clock_pin: Clock (SCLK / SCK) pin (Any GPIO)
+        - data_pin:  Data input (SO / MOSI) pin (Any GPIO)
+        - units:     (optional) unit of measurement to return. ("c" (default) | "k" | "f")
+        - board:     (optional) pin numbering method as per RPi.GPIO library (GPIO.BCM (default) | GPIO.BOARD)
+
+        '''
+        self.cs_pin = cs_pin
+        self.clock_pin = clock_pin
+        self.data_pin = data_pin
+        self.units = units
+        self.data = None
+        self.board = board
+
+        # Initialize needed GPIO
+        GPIO.setmode(self.board)
+        GPIO.setup(self.cs_pin, GPIO.OUT)
+        GPIO.setup(self.clock_pin, GPIO.OUT)
+        GPIO.setup(self.data_pin, GPIO.IN)
+
+        # Pull chip select high to make chip inactive
+        GPIO.output(self.cs_pin, GPIO.HIGH)
+
+    def get(self):
+        '''Reads SPI bus and returns current value of thermocouple.'''
+        self.read()
+        self.checkErrors()
+        return getattr(self, "to_" + self.units)(self.data_to_tc_temperature())
+
+    def get_rj(self):
+        '''Reads SPI bus and returns current value of reference junction.'''
+        self.read()
+        return getattr(self, "to_" + self.units)(self.data_to_rj_temperature())
+
+    def read(self):
+        '''Reads 32 bits of the SPI bus & stores as an integer in self.data.'''
+        bytesin = 0
+        # Select the chip
+        GPIO.output(self.cs_pin, GPIO.LOW)
+        # Read in 32 bits
+        for i in range(32):
+            GPIO.output(self.clock_pin, GPIO.LOW)
+            bytesin = bytesin << 1
+            if (GPIO.input(self.data_pin)):
+                bytesin = bytesin | 1
+            GPIO.output(self.clock_pin, GPIO.HIGH)
+        # Unselect the chip
+        GPIO.output(self.cs_pin, GPIO.HIGH)
+        # Save data
+        self.data = bytesin
+
+    def checkErrors(self, data_32 = None):
+        '''Checks error bits to see if there are any SCV, SCG, or OC faults'''
+        if data_32 is None:
+            data_32 = self.data
+        anyErrors = (data_32 & 0x10000) != 0    # Fault bit, D16
+        noConnection = (data_32 & 1) != 0       # OC bit, D0
+        shortToGround = (data_32 & 2) != 0      # SCG bit, D1
+        shortToVCC = (data_32 & 4) != 0         # SCV bit, D2
+        if anyErrors:
+            if noConnection:
+                raise MAX31855Error("No Connection")
+            elif shortToGround:
+                raise MAX31855Error("Thermocouple short to ground")
+            elif shortToVCC:
+                raise MAX31855Error("Thermocouple short to VCC")
+            else:
+                # Perhaps another SPI device is trying to send data?
+                # Did you remember to initialize all other SPI devices?
+                raise MAX31855Error("Unknown Error")
+
+    def data_to_tc_temperature(self, data_32 = None):
+        '''Takes an integer and returns a thermocouple temperature in celsius.'''
+        if data_32 is None:
+            data_32 = self.data
+        tc_data = ((data_32 >> 18) & 0x3FFF)
+        return self.convert_tc_data(tc_data)
+
+    def data_to_rj_temperature(self, data_32 = None):
+        '''Takes an integer and returns a reference junction temperature in celsius.'''
+        if data_32 is None:
+            data_32 = self.data
+        rj_data = ((data_32 >> 4) & 0xFFF)
+        return self.convert_rj_data(rj_data)
+
+    def convert_tc_data(self, tc_data):
+        '''Convert thermocouple data to a useful number (celsius).'''
+        if tc_data & 0x2000:
+            # two's compliment
+            without_resolution = ~tc_data & 0x1FFF
+            without_resolution += 1
+            without_resolution *= -1
+        else:
+            without_resolution = tc_data & 0x1FFF
+        return without_resolution * 0.25
+
+    def convert_rj_data(self, rj_data):
+        '''Convert reference junction data to a useful number (celsius).'''
+        if rj_data & 0x800:
+           without_resolution = ~rj_data & 0x7FF
+           without_resolution += 1
+           without_resolution *= -1
+        else:
+             without_resolution = rj_data & 0x7FF
+        return without_resolution * 0.0625
+
+    def to_c(self, celsius):
+        '''Celsius passthrough for generic to_* method.'''
+        return celsius
+
+    def to_k(self, celsius):
+        '''Convert celsius to kelvin.'''
+        return celsius + 273.15
+
+    def to_f(self, celsius):
+        '''Convert celsius to fahrenheit.'''
+        return celsius * 9.0/5.0 + 32
+
+    def cleanup(self):
+        '''Selective GPIO cleanup'''
+        GPIO.setup(self.cs_pin, GPIO.IN)
+        GPIO.setup(self.clock_pin, GPIO.IN)
+
+class MAX31855Error(Exception):
+     def __init__(self, value):
+         self.value = value
+     def __str__(self):
+         return repr(self.value)
+
+if __name__ == "__main__":
+
+    # Multi-chip example
+    import time
+    cs_pins = [4, 17, 18, 24]
+    clock_pin = 23
+    data_pin = 22
+    units = "f"
+    thermocouples = []
+    for cs_pin in cs_pins:
+        thermocouples.append(MAX31855(cs_pin, clock_pin, data_pin, units))
+    running = True
+    while(running):
+        try:
+            for thermocouple in thermocouples:
+                rj = thermocouple.get_rj()
+                try:
+                    tc = thermocouple.get()
+                except MAX31855Error as e:
+                    tc = "Error: "+ e.value
+                    running = False
+                print("tc: {} and rj: {}".format(tc, rj))
+            time.sleep(1)
+        except KeyboardInterrupt:
+            running = False
+    for thermocouple in thermocouples:
+        thermocouple.cleanup()

oven.py

@@ -1,4 +1,5 @@
 import threading,time,random,datetime,logging
+from max31855 import MAX31855, MAX31855Error
 
 log_format = '%(asctime)s %(levelname)s %(name)s: %(message)s'
 logging.basicConfig(level = logging.INFO, format = log_format)
@@ -9,7 +10,7 @@ class Oven (threading.Thread):
     STATE_RUNNING  = "RUNNING"
     STATE_ABORT    = "ABORT"
     STATE_ERROR    = "ERROR"
-    
+
     def __init__(self):
         threading.Thread.__init__(self)
         self.profile = None
@@ -18,16 +19,16 @@ class Oven (threading.Thread):
         self.state = Oven.STATE_IDLE
         self.temp_sensor = TempSensor(self)
         self.temp_sensor.start()
-        
+
     def run_profile(self, profile):
         self.profile = profile
         self.state = Oven.STATE_RUNNING
         self.start_time = datetime.datetime.now()
         log.info("Starting")
-    
+
     def abort_run(self):
         self.state = Oven.STATE_ABORT
-    
+
     def run(self):
         while True:
             if self.state == Oven.STATE_RUNNING:
@@ -40,8 +41,8 @@ class Oven (threading.Thread):
                 self.power = 0.0
                 self.state = Oven.STATE_IDLE
             time.sleep(1)
-            
-    
+
+
     def get_state(self):
         if self.state == Oven.STATE_RUNNING:
             runtime = (datetime.datetime.now() - self.start_time).total_seconds()
@@ -55,23 +56,32 @@ class Oven (threading.Thread):
             'totaltime': 300
         }
         return state
-        
+
 class TempSensor(threading.Thread):
     def __init__(self,oven):
         threading.Thread.__init__(self)
         self.temperature = 0
         self.oven = oven
+
+        cs_pin = 27
+        clock_pin = 22
+        data_pin = 17
+        units = "c"
+        self.thermocouple = MAX31855(cs_pin, clock_pin, data_pin, units)
+
+
     def run(self):
         while True:
             time_delta = (20.0 - self.temperature)/40
             power_delta = 8.0*self.oven.power
-            
-            self.temperature += (time_delta+power_delta)
+
+            #self.temperature += (time_delta+power_delta)
+            self.temperature = self.thermocouple.get()
             time.sleep(1)
-        
-    
-    
+
+
+
 if __name__ == "__main__":
     my_oven = Oven()
     my_oven.run_profile("abc")
-    
+