Index: leahi_dialin/dd/modules/balancing_chamber.py
===================================================================
diff -u -ra01dcb7ce7e9f929e5e5f41414ace01ce69ad051 -r9466b5c6b5867f392104a42608aa9542a7ff0358
--- leahi_dialin/dd/modules/balancing_chamber.py	(.../balancing_chamber.py)	(revision a01dcb7ce7e9f929e5e5f41414ace01ce69ad051)
+++ leahi_dialin/dd/modules/balancing_chamber.py	(.../balancing_chamber.py)	(revision 9466b5c6b5867f392104a42608aa9542a7ff0358)
@@ -54,14 +54,15 @@
         self.bal_chamber_fill_in_progress = 0
         self.current_bal_chamber_switching_counter = 0
         self.is_pressure_stabilized_during_fill = 0
+        self.bal_chamber_switch_only_state = 0
         self.dd_bal_chamber_timestamp = 0
 
     @publish(["dd_bal_chamber_timestamp",
               "execution_state", "switching_state",
               "switching_frequency",
               "switching_period", "bal_chamber_fill_in_progress",
               "current_bal_chamber_switching_counter",
-              "is_pressure_stabilized_during_fill"])
+              "is_pressure_stabilized_during_fill", "bal_chamber_switch_only_state"])
     def _handler_balancing_chamber_sync(self, message, timestamp=0.0):
         """
         Handles published balancing chamber data messages.
@@ -84,6 +85,8 @@
             message['message'][MsgFieldPositions.START_POS_FIELD_6:MsgFieldPositions.END_POS_FIELD_6]))[0]
         self.is_pressure_stabilized_during_fill = struct.unpack('I', bytearray(
             message['message'][MsgFieldPositions.START_POS_FIELD_7:MsgFieldPositions.END_POS_FIELD_7]))[0]
+        self.bal_chamber_switch_only_state = struct.unpack('I', bytearray(
+            message['message'][MsgFieldPositions.START_POS_FIELD_8:MsgFieldPositions.END_POS_FIELD_8]))[0]
 
         self.dd_bal_chamber_timestamp = timestamp
 
@@ -126,6 +129,8 @@
     def cmd_switch_frequency_override(self, frequency: float, reset: int = NO_RESET) -> int:
         """
         Constructs and sends the balancing chamber switch frequency override command
+        Constraints:
+            Must be logged into DD.
 
         @param frequency:  float - frequency value to override switch frequency with
         @param reset:  integer - 1 to reset a previous override, 0 to override
@@ -156,4 +161,35 @@
             return received_message['message'][DenaliMessage.PAYLOAD_START_INDEX]
         else:
             self.logger.error("Timeout!!!!")
+            return False
+
+    def cmd_switch_only_start_stop_override(self, start_stop: int, flow: float) -> int:
+        """
+        Constructs and sends the balancing chamber switch only start stop override command
+        Constraints:
+            Must be logged into DD.
+
+        @param start_stop:  int - value to start or stop switch ( start = 1, stop = 0
+        @param flow:  float - flow rate in ml/min
+        @return: 1 if successful, zero otherwise
+
+        """
+
+        sts = integer_to_bytearray(start_stop)
+        freq = float_to_bytearray(flow)
+        payload = sts + freq
+
+        message = DenaliMessage.build_message(channel_id=DenaliChannels.dialin_to_dd_ch_id,
+                                              message_id=MsgIds.MSG_ID_DD_BC_SWITCH_ONLY_START_STOP_OVERRIDE_REQUEST.value,
+                                              payload=payload)
+
+        # 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.error("Timeout!!!!")
             return False
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