erichiggins · June 28, 2022 07:49 · Jun 28, 2022
diff --git a/basic_scale_class.py b/basic_scale_class.py
@@ -0,0 +1,84 @@
+class BasicScale:
+    """Class for controlling a basic scale scale."""
+
+    # TODO(you): Update the default values, such as baudrate, to match your scale.
+    def __init__(self, memcache, port='/dev/ttyUSB0', baudrate=19200, timeout=0.1, _version=1, **kwargs):
+        """Controller."""
+        self._memcache = memcache
+        self._serial = serial.Serial(port=port, baudrate=baudrate, timeout=timeout, **kwargs)
+        # Set default values, which should be overwritten quickly.
+        self.raw = b''
+        # TODO(you): Change this to match the default unit of measure of your scale.
+        self.unit = Units.GRAINS
+        # TODO(you): Change this to match the resolution of your scale.
+        self.resolution = decimal.Decimal(0.02)
+        # TODO(you): Change this to match the default weight & resolution of your scale given the default unit.
+        self.weight = decimal.Decimal('0.00')
+
+        atexit.register(self._graceful_exit)
+
+    def _graceful_exit(self):
+        """Graceful exit, closes serial port."""
+        logging.debug('Closing serial port...')
+        self._serial.close()
+
+
+    def change_unit(self):
+        """Changes the unit of weight on the scale."""
+        logging.debug('changing weight unit on scale from: %r', self.unit)
+        # TODO(you): Change this to match the command that you can send to your
+        #     scale via serial connection that will change the unit of measure.
+        #     If your scale doesn't have this capability, then you can just remove
+        #     or comment out the self._serial.write line below. But, this could make
+        #     things buggy. Just make sure you start on the settings you want and don't
+        #     change the unit within the mobile app.
+        # Send Mode button command.
+        self._serial.write(b'U\r\n')
+        # Sleep 1s and wait for change to take effect.
+        time.sleep(1)
+        # Run update fn to set latest values.
+        self.update()
+
+    @property
+    def is_stable(self):
+        """Returns True if the scale is stable, otherwise False."""
+        # TODO(you): Basic scales may not include a status. Change this to just return True.
+        return self.status == self.StatusMap.STABLE
+
+    def update(self):
+        """Read from the serial port and update an instance of this class with the most recent values."""
+        # Note: The input buffer can fill up, causing latency. Clear it before reading.
+        self._serial.reset_input_buffer()
+        raw = self._serial.readline()
+        self.raw = raw
+        logging.debug(raw)
+        try:
+            line = raw.strip().decode('utf-8')
+        except UnicodeDecodeError:
+            logging.debug('Could not decode bytes to unicode.')
+        else:
+            self._stable_unstable(line)
+
+    def _stable_unstable(self, line):
+        """Update the scale when status is stable or unstable."""
+        # TODO(you): Change this line to parse the weight value, with +/-.
+        weight = line[3:12].strip()
+        self.weight = decimal.Decimal(weight)
+
+        # TODO(you): Change this line to parse the unit of measure.
+        unit = line[12:15].strip()
+        self.unit = UNIT_MAP[unit]
+
+        resolution = {}
+        # TODO(you): Change these to match the resolutions for each unit your scale supports.
+        resolution[Units.GRAINS] = decimal.Decimal(0.02)
+        resolution[Units.GRAMS] = decimal.Decimal(0.001)
+
+        self.resolution = resolution[self.unit]
+        # Update memcache values.
+        self._memcache.set(constants.SCALE_STATUS, self.status)
+        self._memcache.set(constants.SCALE_WEIGHT, self.weight)
+        self._memcache.set(constants.SCALE_UNIT, self.unit)
+        self._memcache.set(constants.SCALE_RESOLUTION, self.resolution)
+        self._memcache.set(constants.SCALE_IS_STABLE, self.is_stable)
+
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