support for kernel spi (not bitbang) MAX38155 interface

.gitignore

@@ -7,3 +7,4 @@
 thumbs.db
 storage/profiles
 config.py
+.idea/*

config.py.EXAMPLE

@@ -35,15 +35,22 @@ heater_invert = 0 # switches the polarity of the heater control
 ### Inputs
 gpio_door = 18
 
-### Thermocouple Adapter selection (MAX31855 or MAX6675)
-max31855 = 1
+### Thermocouple Adapter selection:
+#   max31855 - bitbang SPI interface
+#   max31855spi - kernel SPI interface
+#   max6675 - bitbang SPI interface
+max31855 = 0
 max6675 = 0
+max31855spi = 1
 
-### Thermocouple I2C Connection
+### Thermocouple Connection (using bitbang interfaces)
 gpio_sensor_cs = 27
 gpio_sensor_clock = 22
 gpio_sensor_data = 17
 
+### Thermocouple SPI Connection (using adafrut drivers + kernel SPI interface)
+spi_sensor_chip_id = 0
+
 
 ########################################################################
 #

lib/max31855spi.py

@@ -0,0 +1,32 @@
+#!/usr/bin/python
+from Adafruit_MAX31855 import MAX31855
+
+class MAX31855SPI(object):
+    '''Python driver for [MAX38155 Cold-Junction Compensated Thermocouple-to-Digital Converter](http://www.maximintegrated.com/datasheet/index.mvp/id/7273)
+     Requires:
+     - adafruit's MAX31855 SPI-only device library
+
+    '''
+    def __init__(self, spi_dev):
+        self.max31855 = MAX31855.MAX31855(spi=spi_dev)
+
+    def get(self):
+        '''Reads SPI bus and returns current value of thermocouple.'''
+        state = self.max31855.readState()
+        if state['openCircuit']:
+            raise MAX31855Error('Not Connected')
+        elif state['shortGND']:
+            raise MAX31855Error('Short to Ground')
+        elif state['shortVCC']:
+            raise MAX31855Error('Short to VCC')
+        elif state['fault']:
+            raise MAX31855Error('Unknown Error')
+        return self.max31855.readLinearizedTempC()
+
+
+class MAX31855SPIError(Exception):
+    def __init__(self, value):
+        self.value = value
+
+    def __str__(self):
+        return repr(self.value)

lib/oven.py

@@ -10,12 +10,16 @@ import config
 log = logging.getLogger(__name__)
 
 try:
-    if (config.max31855 == config.max6675):
+    if config.max31855 + config.max6675 + config.max31855spi > 1:
         log.error("choose (only) one converter IC")
         exit()
     if config.max31855:
         from max31855 import MAX31855, MAX31855Error
         log.info("import MAX31855")
+    if config.max31855spi:
+        import Adafruit_GPIO.SPI as SPI
+        from max6675 import MAX31855SPI, MAX31855SPIError
+        log.info("import MAX31855SPI")
     if config.max6675:
         from max6675 import MAX6675, MAX6675Error
         log.info("import MAX6675")
@@ -224,6 +228,10 @@ class TempSensorReal(TempSensor):
                                      config.gpio_sensor_data,
                                      config.temp_scale)
 
+        if config.max31855spi:
+            log.info("init MAX31855-spi")
+            self.thermocouple = MAX31855SPI(spi_dev=SPI.SpiDev(port=0, device=config.spi_sensor_chip_id))
+
     def run(self):
         while True:
             self.temperature = self.thermocouple.get()

requirements.txt

@@ -0,0 +1 @@
+Adafruit-MAX31855>=1.6.1