Merge pull request schodet#144 from dlech/nxt-temp

NXT Temperature Sensor

nxt/direct.py

@@ -156,7 +156,7 @@ def ls_write(opcode, port, tx_data, rx_bytes):
     tgram.add_u8(port)
     tgram.add_u8(len(tx_data))
     tgram.add_u8(rx_bytes)
-    tgram.add_string(len(tx_data), tx_data)
+    tgram.add_bytes(tx_data)
     return tgram
 
 def ls_read(opcode, port):

nxt/sensor/__init__.py

@@ -16,7 +16,7 @@
 from .common import *
 from .analog import BaseAnalogSensor
 from .digital import BaseDigitalSensor, find_class
-from .generic import Touch, Light, Sound, Ultrasonic, Color20
+from .generic import Touch, Light, Sound, Ultrasonic, Color20, Temperature
 from . import mindsensors
 MSSumoEyes = mindsensors.SumoEyes
 MSCompassv2 = mindsensors.Compassv2

nxt/sensor/digital.py

@@ -95,7 +95,7 @@ def _i2c_command(self, address, value, format):
         a tuple of values corresponding to the given format.
         """
         value = struct.pack(format, *value)
-        msg = chr(self.I2C_DEV) + chr(address) + value
+        msg = bytes((self.I2C_DEV, address)) + value
         now = time()
         if self.last_poll+self.poll_delay > now:
             diff = now - self.last_poll
@@ -109,7 +109,7 @@ def _i2c_query(self, address, format):
         module. See http://docs.python.org/library/struct.html#format-strings
         """
         n_bytes = struct.calcsize(format)
-        msg = chr(self.I2C_DEV) + chr(address)
+        msg = bytes((self.I2C_DEV, address))
         now = time()
         if self.last_poll+self.poll_delay > now:
             diff = now - self.last_poll

nxt/sensor/generic.py

@@ -151,3 +151,34 @@ def get_color(self):
         return self.get_input_values().scaled_value
 
     get_sample = get_color
+
+
+class Temperature(BaseDigitalSensor):
+    """Object for LEGO MINDSTORMS NXT Temperature sensors"""
+    # This is actually a TI TMP275 chip: http://www.ti.com/product/tmp275
+    I2C_DEV = 0x98
+    I2C_ADDRESS = {'raw_value': (0x00, '>h')}
+
+    def __init__(self, brick, port):
+        # This sensor does not follow the convention of having version/vendor/
+        # product at I2C registers 0x00/0x08/0x10, so check_compatible is
+        # always False
+        super(Temperature, self).__init__(brick, port, False)
+
+    def _get_raw_value(self):
+        """Returns raw unscaled value"""
+        # this is a 12-bit value
+        return self.read_value('raw_value')[0] >> 4
+
+    def get_deg_c(self):
+        """Returns the temperature in degrees C"""
+        v = self._get_raw_value()
+        # technically, 16 should be 0x7ff/128 but 16 is close enough
+        return round(v / 16, 1)
+
+    def get_deg_f(self):
+        v = self._get_raw_value()
+        # technically, 16 should be 0x7ff/128 but 16 is close enough
+        return round(9 / 5 * v / 16 + 32, 1)
+
+    get_sample = get_deg_c

nxt/telegram.py

@@ -64,6 +64,9 @@ def bytes(self):
     def is_reply(self):
         return self.typ == Telegram.TYPE_REPLY
 
+    def add_bytes(self, b):
+        self.pkt.write(pack('%ds' % len(b), b))
+
     def add_string(self, n_bytes, v):
         self.pkt.write(pack('%ds' % n_bytes, v.encode('windows-1252')))