added MAX6675 support

lib/max6675.py

@@ -0,0 +1,125 @@
+#!/usr/bin/python
+import RPi.GPIO as GPIO
+import time
+
+class MAX6675(object):
+    '''Python driver for [MAX6675 Cold-Junction Compensated Thermocouple-to-Digital Converter](http://www.adafruit.com/datasheets/MAX6675.pdf)
+     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 read(self):
+        '''Reads 16 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 16 bits
+        for i in range(16):
+            GPIO.output(self.clock_pin, GPIO.LOW)
+            time.sleep(0.001)
+            bytesin = bytesin << 1
+            if (GPIO.input(self.data_pin)):
+                bytesin = bytesin | 1
+            GPIO.output(self.clock_pin, GPIO.HIGH)
+        time.sleep(0.001)
+        # Unselect the chip
+        GPIO.output(self.cs_pin, GPIO.HIGH)
+        # Save data
+        self.data = bytesin
+
+    def checkErrors(self, data_16 = None):
+        '''Checks errors on bit D2'''
+        if data_16 is None:
+            data_16 = self.data
+        noConnection = (data_16 & 0x4) != 0       # tc input bit, D2
+
+        if noConnection:
+            raise MAX6675Error("No Connection") # open thermocouple
+
+    def data_to_tc_temperature(self, data_16 = None):
+        '''Takes an integer and returns a thermocouple temperature in celsius.'''
+        if data_16 is None:
+            data_16 = self.data
+        # Remove bits D0-3
+        tc_data = ((data_16 >> 3) & 0xFFF)
+        # 12-bit resolution
+        return (tc_data * 0.25)
+
+    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 MAX6675Error(Exception):
+     def __init__(self, value):
+         self.value = value
+     def __str__(self):
+         return repr(self.value)
+
+if __name__ == "__main__":
+
+    # default example
+    cs_pin = 24
+    clock_pin = 23
+    data_pin = 22
+    units = "c"
+    thermocouple = MAX6675(cs_pin, clock_pin, data_pin, units)
+    running = True
+    while(running):
+        try:            
+            try:
+                tc = thermocouple.get()        
+            except MAX6675Error as e:
+                tc = "Error: "+ e.value
+                running = False
+                print("tc: {}".format(tc))
+            time.sleep(1)
+        except KeyboardInterrupt:
+            running = False
+    thermocouple.cleanup()

lib/oven.py

@@ -10,7 +10,15 @@ import config
 log = logging.getLogger(__name__)
 
 try:
-    from max31855 import MAX31855, MAX31855Error
+    if (config.max31855 == config.max6675):
+    	log.error("choose (only) one converter IC")
+	exit()
+    if config.max31855:
+    	from max31855 import MAX31855, MAX31855Error
+    	log.info("import MAX31855")
+    if config.max6675:
+   	from max6675 import MAX6675, MAX6675Error
+    	log.info("import MAX6675")
     sensor_available = True
 except ImportError:
     log.warning("Could not initialize temperature sensor, using dummy values!")
@@ -175,7 +183,15 @@ class TempSensor(threading.Thread):
 class TempSensorReal(TempSensor):
     def __init__(self, time_step):
         TempSensor.__init__(self, time_step)
-        self.thermocouple = MAX31855(config.gpio_sensor_cs,
+        if config.max6675:
+        	log.info("init MAX6675")
+        	self.thermocouple = MAX6675(config.gpio_sensor_cs,
+                                     config.gpio_sensor_clock,
+                                     config.gpio_sensor_data,
+                                     "c")
+        if config.max31855:
+        	log.info("init MAX31855")
+        	self.thermocouple = MAX31855(config.gpio_sensor_cs,
                                      config.gpio_sensor_clock,
                                      config.gpio_sensor_data,
                                      "c")