Index: dialin/dg/load_cells.py
===================================================================
diff -u -r900f99812cee2e022fbbd46cd916b08a1397dda7 -r615852271ed083494ef644c55536c5dad1b25c83
--- dialin/dg/load_cells.py	(.../load_cells.py)	(revision 900f99812cee2e022fbbd46cd916b08a1397dda7)
+++ dialin/dg/load_cells.py	(.../load_cells.py)	(revision 615852271ed083494ef644c55536c5dad1b25c83)
@@ -29,7 +29,7 @@
     Dialysate Generator (DG) Dialin API sub-class for load cell related commands.
     """
 
-    # Pressure/Occlusion message IDs
+    # Load cell message IDs
     MSG_ID_DG_LOAD_CELL_DATA = 0x000C
     MSG_ID_DG_LOAD_CELL_OVERRIDE = 0xA005
     MSG_ID_DG_LOAD_CELL_DATA_BROADCAST_INTERVAL_OVERRIDE = 0xA00D
Index: dialin/hd/air_trap.py
===================================================================
diff -u
--- dialin/hd/air_trap.py	(revision 0)
+++ dialin/hd/air_trap.py	(revision 615852271ed083494ef644c55536c5dad1b25c83)
@@ -0,0 +1,187 @@
+###########################################################################
+#
+# Copyright (c) 2019-2020 Diality Inc. - All Rights Reserved.
+#
+# THIS CODE MAY NOT BE COPIED OR REPRODUCED IN ANY FORM, IN PART OR IN
+# WHOLE, WITHOUT THE EXPLICIT PERMISSION OF THE COPYRIGHT OWNER.
+#
+# @file air_trap.py
+#
+# @author (last) Sean
+# @date (last) 21-Sep-2020
+# @author (original) Sean
+# @date (original) 21-Sep-2020
+#
+############################################################################
+import struct
+from ..utils.conversions import integer_to_bytearray, float_to_bytearray
+from .constants import RESET,NO_RESET
+from ..protocols.CAN import (DenaliMessage,
+                             DenaliChannels)
+from ..utils.base import _AbstractSubSystem, _publish
+from logging import Logger
+
+
+class HDAirTrap(_AbstractSubSystem):
+    """
+    HDAirTrap
+
+    Hemodialysis Delivery (HD) Dialin API sub-class for air trap related commands.
+    """
+
+    # Air trap message IDs
+    MSG_ID_HD_AIR_TRAP_DATA = 0x003E
+    MSG_ID_DG_AIR_TRAP_LEVEL_SENSOR_OVERRIDE = 0x8033
+    MSG_ID_DG_AIR_TRAP_DATA_BROADCAST_INTERVAL_OVERRIDE = 0x8032
+
+    # Air trap broadcast message field positions
+    START_POS_LOWER_LEVEL = DenaliMessage.PAYLOAD_START_INDEX
+    END_POS_LOWER_LEVEL = START_POS_LOWER_LEVEL + 4
+    START_POS_UPPER_LEVEL = END_POS_LOWER_LEVEL
+    END_POS_UPPER_LEVEL = START_POS_UPPER_LEVEL + 4
+
+    # Air trap level sensor IDs
+    LOWER_LEVEL_SENSOR = 0
+    UPPER_LEVEL_SENSOR = 1
+
+    # Air trap level sensor levels
+    AIR_DETECTED_AT_LEVEL = 0
+    FLUID_DETECTED_AT_LEVEL = 1
+
+    def __init__(self, can_interface, logger: Logger):
+        """
+
+        @param can_interface: Denali Can Messenger object
+        """
+        super().__init__()
+        self.can_interface = can_interface
+        self.logger = logger
+
+        if self.can_interface is not None:
+            channel_id = DenaliChannels.hd_sync_broadcast_ch_id
+            msg_id = self.MSG_ID_HD_AIR_TRAP_DATA
+            self.can_interface.register_receiving_publication_function(channel_id, msg_id,
+                                                                       self._handler_air_trap_sync)
+
+        self.lower_level = self.AIR_DETECTED_AT_LEVEL
+        self.upper_level = self.AIR_DETECTED_AT_LEVEL
+
+    def get_air_trap_levels(self):
+        """
+        Gets the current air trap levels
+
+        @return: List containing air trap levels: [Lower, Upper]
+        """
+        return [self.lower_level, self.upper_level]
+
+    def get_air_trap_lower_level(self):
+        """
+        Gets the current air trap lower level reading
+
+        @return: 0 for air, 1 for fluid at lower level
+        """
+        return self.lower_level
+
+    def get_air_trap_upper_level(self):
+        """
+        Gets the current air trap upper level reading
+
+        @return: 0 for air, 1 for fluid at upper level
+        """
+        return self.upper_level
+
+    @_publish(["lower_level", "upper_level"])
+    def _handler_air_trap_sync(self, message):
+        """
+        Handles published air trap data messages.  Air trap data are captured
+        for reference.
+
+        @param message:  published air trap data message
+        @return: None
+        """
+
+        lower = struct.unpack('i', bytearray(
+            message['message'][self.START_POS_LOWER_LEVEL:self.END_POS_LOWER_LEVEL]))
+        upper = struct.unpack('i', bytearray(
+            message['message'][self.START_POS_UPPER_LEVEL:self.END_POS_UPPER_LEVEL]))
+
+        self.lower_level = lower[0]
+        self.upper_level = upper[0]
+
+    def cmd_air_trap_level_sensor_override(self, detected, sensor, reset=NO_RESET):
+        """
+        Constructs and sends the air trap level sensor override command
+        Constraints:
+            Must be logged into HD.
+            Given sensor must be one of the sensors listed below.
+
+        @param detected:  unsigned int - detected (0=air, 1=fluid) to override sensor with
+        @param sensor: unsigned int - sensor ID
+        @param reset:  integer - 1 to reset a previous override, 0 to override
+        @return: 1 if successful, zero otherwise
+
+        Air trap sensor IDs: \n
+            0 = Lower level \n
+            1 = Upper level \n
+        """
+
+        rst = integer_to_bytearray(reset)
+        det = float_to_bytearray(detected)
+        idx = integer_to_bytearray(sensor)
+        payload = rst + det + idx
+
+        message = DenaliMessage.build_message(channel_id=DenaliChannels.dialin_to_dg_ch_id,
+                                              message_id=self.MSG_ID_DG_AIR_TRAP_LEVEL_SENSOR_OVERRIDE,
+                                              payload=payload)
+
+        self.logger.debug("override air trap level sensor detection value for sensor " + str(sensor))
+
+        # Send message
+        received_message = self.can_interface.send(message)
+
+        # If there is content...
+        if received_message is not None:
+            # response payload is OK or not OK
+            return received_message['message'][DenaliMessage.PAYLOAD_START_INDEX]
+        else:
+            self.logger.debug("Timeout!!!!")
+            return False
+
+    def cmd_air_trap_data_broadcast_interval_override(self, ms, reset=NO_RESET):
+        """
+        Constructs and sends the air trap data broadcast interval override command
+        Constraints:
+            Must be logged into HD.
+            Given interval must be non-zero and a multiple of the HD general task interval (50 ms).
+
+        @param ms:  integer - interval (in ms) to override with
+        @param reset:  integer - 1 to reset a previous override, 0 to override
+        @return: 1 if successful, zero otherwise
+        """
+
+        rst = integer_to_bytearray(reset)
+        mis = integer_to_bytearray(ms)
+        payload = rst + mis
+
+        message = DenaliMessage.build_message(channel_id=DenaliChannels.dialin_to_dg_ch_id,
+                                              message_id=self.MSG_ID_DG_AIR_TRAP_DATA_BROADCAST_INTERVAL_OVERRIDE,
+                                              payload=payload)
+
+        self.logger.debug("override HD air trap data broadcast interval")
+
+        # Send message
+        received_message = self.can_interface.send(message)
+
+        # If there is content...
+        if received_message is not None:
+            if reset == RESET:
+                str_res = "reset back to normal: "
+            else:
+                str_res = str(ms) + " ms: "
+            self.logger.debug("Air trap data broadcast interval overridden to " + str_res +
+                  str(received_message['message'][DenaliMessage.PAYLOAD_START_INDEX]))
+            # response payload is OK or not OK
+            return received_message['message'][DenaliMessage.PAYLOAD_START_INDEX]
+        else:
+            self.logger.debug("Timeout!!!!")
+            return False