components/actor/heater_hendi.py

@@ -4,7 +4,7 @@ from components.actor.hendiCtrl import HendiCtrl
 
 class HeaterHendi(AHeater):
 	def __init__(self, params):
-		AHeater.__init__(self)
+		AHeater.__init__(self, simulated=False)
 		self.hendi = HendiCtrl(params['port'], params['speed'])
 		self.power_set = 0
 		self.power_eff = 0
@@ -20,17 +20,35 @@ class HeaterHendi(AHeater):
 		caps = self.hendi.getCapabilties()
 		return [0] + caps['pwr_list']
 
+	def connect(self):
+		ok = self.hendi.connect()
+		self.connected = ok
+		self.firmware_version = self.hendi.sw_ver if ok else None
+		return ok
+
+	def disconnect(self):
+		self.hendi.disconnect()
+		self.connected = False
+		self.firmware_version = None
+
 	def activate(self, enable):
+		if not self.connected:
+			return
 		if enable:
 			self.hendi.remoteEnable(1)
 		else:
 			self.hendi.setSwitch(0)
 
 	def is_activated(self):
+		if not self.connected:
+			return False
 		s = self.hendi.isRemoteEnable()
 		return '1' in s
 
 	def process(self):
+		if not self.connected:
+			self.power_eff = 0
+			return
 		power = self.power_set
 		if power == 0:
 			self.hendi.setSwitch(0)
@@ -46,4 +64,4 @@ class HeaterHendi(AHeater):
 		return self.power_eff
 
 	def close(self):
-		self.hendi.close()
+		self.disconnect()

components/actor/hendiCtrl.py

@@ -12,15 +12,18 @@ class HendiException(Exception):
 class HendiCtrl:
 	def __init__(self, port, speed, debug=False):
 		self.debug = debug
-		self.ser = serial.Serial(port, speed)
-		try:
-			self.ser.open()
-		except:
-			self.ser.close()
-			self.ser.open()
-
-		self.ser.timeout = 1.000
 		self.prompt = b':'
+		self.sw_id = None
+		self.sw_ver = None
+
+		# Deferred-open pyserial idiom: the port isn't actually opened until
+		# connect() is called, so a missing/unplugged device doesn't crash
+		# the whole server at construction time (see components/actor/
+		# heater_hendi.py's HeaterHendi.connect()).
+		self.ser = serial.Serial()
+		self.ser.port = port
+		self.ser.baudrate = speed
+		self.ser.timeout = 1.000
 
 		powers = [500,  600,  700,  800,  900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900, 3000, 3100, 3200, 3300,3400, 3500]
 		digits = [4092, 3840, 3700, 3440, 3300, 3060, 3000, 2930, 2860, 2780, 2640, 2510, 2430, 2360, 2190, 2130, 2030, 1980, 1880, 1730, 1630, 1560, 1480, 1400, 1240, 1150, 1150, 1080, 920, 740, 670]
@@ -36,13 +39,28 @@ class HendiCtrl:
 		self.poly_w2d = np.polyfit(powers, digits, 5)
 		self.poly_d2w = np.polyfit(digits, powers, 5)
 
+	def is_connected(self):
+		return self.ser.is_open
+
+	def connect(self):
+		if self.ser.is_open:
+			return True
+		try:
+			self.ser.open()
+		except serial.SerialException as e:
+			print(f"HendiCtrl: connect failed: {e}")
+			return False
+		# The port itself is what "connected" means - a failed version query
+		# (e.g. the device sitting in its ungraceful-disconnect lockout, see
+		# docs/hendi_lockout_findings.md) doesn't make the link any less
+		# open, so it's reported but doesn't fail connect() overall.
 		try:
 			self.sw_id = self.getSoftwareIdentifier()
 			self.sw_ver = self.getSoftwareVersion()
 			print(f"{self.sw_id}, F/W-Version: {self.sw_ver}")
 		except HendiException:
 			print("HendiCtrl: Hendi not found")
-
+		return True
 
 	@contextmanager
 	def remote_open(self):
@@ -191,5 +209,15 @@ class HendiCtrl:
 	def getPowerWatts(self):
 		return int(self.toWatts(self.getPowerDigits()) + 0.5)
 
-	def close(self):
+	def disconnect(self):
+		if self.ser.is_open:
+			try:
 				self.remoteEnable(False)
+			except HendiException:
+				pass
+			self.ser.close()
+		self.sw_id = None
+		self.sw_ver = None
+
+	def close(self):
+		self.disconnect()

components/actor/pololu1376.py

@@ -50,17 +50,50 @@ class Varid(enum.Enum):
 
 class Pololu1376:
 	def __init__(self, serial_port):
+		# Deferred-open pyserial idiom: serial_port is constructed with no
+		# port set (see components/actor/stirrerpololu1376.py), so it isn't
+		# actually opened until connect() is called - a missing/unplugged
+		# device then doesn't crash the whole server at construction time.
 		self.ser = serial_port
-		self.ser.set_output_flow_control(False)
+		self.firmware_version = None
+
+	def is_connected(self):
+		return self.ser.is_open
+
+	def connect(self):
+		if self.ser.is_open:
+			return True
 		try:
 			self.ser.open()
 		except serial.SerialException:
+			try:
 				self.ser.close()
 				self.ser.open()
-
+			except serial.SerialException as e:
+				print(f"Pololu1376: connect failed: {e}")
+				return False
+		# set_output_flow_control() requires the port to already be open -
+		# can only happen here, after open() above, not at construction time.
+		self.ser.set_output_flow_control(False)
+		try:
 			self.stop()
+			self.firmware_version = self.get_firmware_version()
+			print("Pololu1376 F/W-Version:", self.firmware_version)
+			return True
+		except Exception as e:
+			print(f"Pololu1376: connect failed: {e}")
+			self.ser.close()
+			self.firmware_version = None
+			return False
 
-		print("Pololu1376 F/W-Version:", self.get_firmware_version())
+	def disconnect(self):
+		if self.ser.is_open:
+			try:
+				self.stop()
+			except Exception:
+				pass
+			self.ser.close()
+		self.firmware_version = None
 
 	def send(self, data):
 		self.ser.write((data + '\r\n').encode())
@@ -126,9 +159,12 @@ class Pololu1376:
 
 
 if __name__ == '__main__':
-	ser = serial.Serial("/dev/ttyACM0", 115200)
+	ser = serial.Serial()
+	ser.port = "/dev/ttyACM0"
+	ser.baudrate = 115200
 
 	drv = Pololu1376(serial_port=ser)
+	drv.connect()
 	drv.go()
 	time.sleep(1)
 	

components/actor/stirrerpololu1376.py

@@ -10,12 +10,27 @@ class StirrerPololu1376(AStirrer):
 		return "Pololu1376"
 
 	def __init__(self, dt, params):
-		AStirrer.__init__(self, dt)
+		AStirrer.__init__(self, dt, simulated=False)
 
-		ser = serial.Serial(params['port'], params['speed'])
-		ser.set_output_flow_control(False)
+		# Deferred-open pyserial idiom - see Pololu1376's own constructor
+		# comment: connect() is what actually opens params['port'] (and
+		# sets output flow control, which itself requires an open port).
+		ser = serial.Serial()
+		ser.port = params['port']
+		ser.baudrate = params['speed']
 		self.drv = Pololu1376(ser)
 
+	def connect(self):
+		ok = self.drv.connect()
+		self.connected = ok
+		self.firmware_version = self.drv.firmware_version if ok else None
+		return ok
+
+	def disconnect(self):
+		self.drv.disconnect()
+		self.connected = False
+		self.firmware_version = None
+
 	@contextmanager
 	def remote_open(self):
 		try:
@@ -30,6 +45,8 @@ class StirrerPololu1376(AStirrer):
 		return 0
 
 	def activate(self, enable):
+		if not self.connected:
+			return
 		print("activate {}".format(enable))
 		if enable:
 			self.drv.go()
@@ -37,10 +54,14 @@ class StirrerPololu1376(AStirrer):
 			self.drv.stop()
 
 	def _on_set_speed(self, speed):
+		if not self.connected:
+			return
 		self.drv.motor_forward(speed)
 		print("Set speed to {} %".format(speed))
 
 	def _on_process(self):
+		if not self.connected:
+			return
 		status = self.drv.get_variable(Varid.STATUS)
 		limit_status = self.drv.get_variable(Varid.STATUS_LIMIT_STATUS)
 		if status & 0x01 == 0x01:
@@ -51,6 +72,7 @@ class StirrerPololu1376(AStirrer):
 
 if __name__ == '__main__':
 	s = StirrerPololu1376(dt=1.0, params={'port': "/dev/ttyACM0", 'speed': 115200})
+	s.connect()
 
 	with s.remote_open():
 

components/aheater.py

@@ -1,11 +1,11 @@
 import abc
-from utils.value import AttributeChange
+from components.connectable import Connectable
 from contextlib import contextmanager
 
 
-class AHeater(AttributeChange):
-	def __init__(self):
-		AttributeChange.__init__(self)
+class AHeater(Connectable):
+	def __init__(self, simulated=True):
+		Connectable.__init__(self, simulated)
 		self.is_active = False
 
 	@abc.abstractmethod

components/astirrer.py

@@ -1,11 +1,11 @@
 import abc
-from utils.value import AttributeChange
+from components.connectable import Connectable
 from contextlib import contextmanager
 
 
-class AStirrer(AttributeChange):
-	def __init__(self, dt):
-		AttributeChange.__init__(self)
+class AStirrer(Connectable):
+	def __init__(self, dt, simulated=True):
+		Connectable.__init__(self, simulated)
 		self.dt = dt
 		self.speed = 0
 		self.cycleTime = 1

components/connectable.py

@@ -0,0 +1,22 @@
+from utils.value import AttributeChange
+
+
+class Connectable(AttributeChange):
+	"""Observable hardware-connection state shared by AHeater/AStirrer.
+
+	Simulated devices are always connected and report no firmware version;
+	real (serial) devices start disconnected and only flip once connect()
+	actually reaches the hardware.
+	"""
+
+	def __init__(self, simulated):
+		AttributeChange.__init__(self)
+		self.simulated = simulated
+		self.connected = simulated
+		self.firmware_version = None
+
+	def connect(self):
+		return self.connected
+
+	def disconnect(self):
+		pass

components/sensor/tempSensorSim.py

@@ -42,4 +42,5 @@ class TempSensorSim(ATemperatureSensor):
 			innovation = self.stirrer_sigma * np.sqrt(2.0 * alpha) * np.random.normal()
 			self._stirrer_state = (1.0 - alpha) * self._stirrer_state + innovation
 
-		return self.temp_set + self.offset + white + self._stirrer_state
+		self.temp = self.temp_set + self.offset + white + self._stirrer_state
+		return self.temp

components/sensor/tempSensor_max31865.py

@@ -47,7 +47,8 @@ class TempSensor_max31865(ATemperatureSensor):
 
 	def temperature(self):
 		digits = self.read_digits()
-		return self.temp_offset + self.to_temperature(digits)
+		self.temp = self.temp_offset + self.to_temperature(digits)
+		return self.temp
 
 	@staticmethod
 	def to_temperature(digits):

scripts/hendi_ctrl_app.py

@@ -79,6 +79,9 @@ def main():
 	args = parser.parse_args()
 
 	hendi = HendiCtrl(args.serial_port, args.baudrate, debug=args.debug)
+	if not hendi.connect():
+		print("Could not connect to Hendi - check --serial-port/--baudrate and that the device is powered on.")
+		return
 
 	if args.reset:
 		reset(hendi)

server/brewpi.py

@@ -139,9 +139,15 @@ if __name__ == '__main__':
 	forecast_estimator = SudForecastEstimator(
 		DT, theta_amb, config['TempCtrl']['pid_type'], config['TempCtrl'],
 		heater.get_powers(), sim_warp_factor, config.get('Pot', {}))
-	sud_task = SudTask(sud, tc, stirrer, pot, DT, DT_TASK, dispatcher.msgio_get("Sud"), forecast_estimator)
+	sud_task = SudTask(sud, tc, stirrer, heater, pot, DT, DT_TASK, dispatcher.msgio_get("Sud"), forecast_estimator)
 	taskmgr.add(sud_task)
 
+	# A run in progress gets force-stopped (mirrors a manual Stop) if the
+	# heater or stirrer it depends on disconnects mid-brew - see SudTask.
+	# check_connections()'s own comment for why.
+	heater_task.set_on_connected_changed(lambda connected: sud_task.check_connections())
+	stirrer_task.set_on_connected_changed(lambda connected: sud_task.check_connections())
+
 	# How often the server/sud logs checkpoint themselves to disk (in
 	# addition to always writing on their own end trigger) - so a hard
 	# crash/power loss only loses up to this much data. Config-only (no CLI
@@ -182,7 +188,7 @@ if __name__ == '__main__':
 	sud_task.set_on_end(lambda: (heater_task.shutdown(), sud_log_task.stop_run()))
 
 	# Assign temp. sensor readings to tc
-	sensor_task.set_on_changed("temp", ChangedFloat(tc.set_theta_ist, prec=2).set)
+	sensor.set_on_changed("temp", ChangedFloat(tc.set_theta_ist, prec=2).set)
 
 	heater.set_on_changed("power_set", tc.set_model_power)
 

tasks/heater.py

@@ -18,12 +18,29 @@ class HeaterTask(ATask):
 		self.closed_loop = True
 		self._on_closed_loop_changed = None
 		self.pulse_counter = 0
+		self._on_connected_changed = None
 		device.set_on_changed('power_eff', ChangedInteger(self.on_changed_power).set)
+		device.set_on_changed('connected', self.on_connected_changed)
+		device.set_on_changed('firmware_version', self.on_firmware_version_changed)
 		self.power_set_changed = ChangedInteger(self.on_changed_power_set).set
 
 	def set_on_closed_loop_changed(self, callback):
 		self._on_closed_loop_changed = callback
 
+	def set_on_connected_changed(self, callback):
+		"""Registers a callback(connected: bool) invoked whenever the
+		device's connection state changes - lets server/brewpi.py wire this
+		into SudTask's start-gating/mid-brew auto-stop."""
+		self._on_connected_changed = callback
+
+	def on_connected_changed(self, value):
+		asyncio.create_task(self.send({'Connected': value}))
+		if self._on_connected_changed:
+			self._on_connected_changed(value)
+
+	def on_firmware_version_changed(self, value):
+		asyncio.create_task(self.send({'FirmwareVersion': value}))
+
 	def shutdown(self):
 		"""Called when the brew ends (DONE/IDLE). Switches to open-loop at
 		power 0 and disables TC, mirroring what a Stop press should do."""
@@ -60,6 +77,12 @@ class HeaterTask(ATask):
 				if self._on_closed_loop_changed:
 					self._on_closed_loop_changed(self.closed_loop)
 				await self.send({'ClosedLoop': self.closed_loop})
+			elif pair[0] == 'Connect':
+				if self.device.connect():
+					self.device.activate(True)
+			elif pair[0] == 'Disconnect':
+				self.device.activate(False)
+				self.device.disconnect()
 			elif 'Power' in pair[0]:
 				self.power_soll = pair[1]
 
@@ -82,6 +105,7 @@ class HeaterTask(ATask):
 
 	async def on_process(self):
 		await self.send({'Capabilities': {'Power': {'Min': 0, 'Max': self.device.get_power_max()}}})
+		await self.send({'Simulated': self.device.simulated})
 		await self.send({'ClosedLoop': self.closed_loop})
 		if self._on_closed_loop_changed:
 			self._on_closed_loop_changed(self.closed_loop)
@@ -89,6 +113,20 @@ class HeaterTask(ATask):
 		pulse_period_s = 10
 		pulse_period_count = pulse_period_s/self.interval
 
+		# Auto-connect on startup - replaces what used to happen implicitly
+		# in the device's own constructor; a missing/unplugged device just
+		# stays disconnected instead of crashing the server (see
+		# components/actor/heater_hendi.py's connect()).
+		self.device.connect()
+		# Explicit initial push, same as Capabilities/Simulated/ClosedLoop
+		# above - a simulated device's connect() is a no-op that never
+		# reassigns self.connected (see components/connectable.py), so its
+		# set_on_changed('connected', ...) observer would otherwise never
+		# fire and a freshly-subscribed client would never learn it's
+		# connected.
+		await self.send({'Connected': self.device.connected})
+		await self.send({'FirmwareVersion': self.device.firmware_version})
+
 		with self.device.open():
 			while True:
 				# Closed-loop: TC has full control. Open-loop: direct manual power only.
@@ -113,7 +151,11 @@ class HeaterTask(ATask):
 				elif self.pulse_counter < on_count:
 					self.device.set_power(power_high)
 
+				try:
 					self.device.process()
+				except Exception as e:
+					print(f"HeaterTask: comm error, marking disconnected: {e}")
+					self.device.disconnect()
 				await asyncio.sleep(self.interval)
 
 

tasks/stirrer.py

@@ -11,9 +11,12 @@ class StirrerTask(ATask):
 		self.msg_handler = msg_handler
 		msg_handler.set_recv_handler(self.recv)
 		self.device = stirrer_device
+		self._on_connected_changed = None
 		stirrer_device.set_on_changed("speed", self.on_speed_changed)
 		stirrer_device.set_on_changed("dutyCycle", self.on_dutycycle_changed)
 		stirrer_device.set_on_changed("cycleTime", self.on_cycletime_changed)
+		stirrer_device.set_on_changed("connected", self.on_connected_changed)
+		stirrer_device.set_on_changed("firmware_version", self.on_firmware_version_changed)
 
 	def on_speed_changed(self, value):
 		asyncio.create_task(self.send({'Speed': value}))
@@ -24,20 +27,55 @@ class StirrerTask(ATask):
 	def on_cycletime_changed(self, value):
 		asyncio.create_task(self.send({'CycleTime': value}))
 
+	def set_on_connected_changed(self, callback):
+		"""Registers a callback(connected: bool) invoked whenever the
+		device's connection state changes - lets server/brewpi.py wire this
+		into SudTask's start-gating/mid-brew auto-stop."""
+		self._on_connected_changed = callback
+
+	def on_connected_changed(self, value):
+		asyncio.create_task(self.send({'Connected': value}))
+		if self._on_connected_changed:
+			self._on_connected_changed(value)
+
+	def on_firmware_version_changed(self, value):
+		asyncio.create_task(self.send({'FirmwareVersion': value}))
+
 	async def recv(self, data):
 		for pair in data.items():
-			if 'Speed' in pair[0]:
+			if pair[0] == 'Connect':
+				if self.device.connect():
+					self.device.activate(True)
+			elif pair[0] == 'Disconnect':
+				self.device.activate(False)
+				self.device.disconnect()
+			elif 'Speed' in pair[0]:
 				self.device.set_speed(pair[1])
 
 	async def send(self, data):
 		await self.msg_handler.send(data)
 
 	async def on_process(self):
+		await self.send({'Simulated': self.device.simulated})
+
 		self.device.set_speed(0.0)
 		self.device.set_cycle_time(10.0)
 		self.device.set_duty_cycle(1.0)
 
+		# Auto-connect on startup - see HeaterTask.on_process()'s own
+		# comment for why this replaces the old constructor-side connect.
+		self.device.connect()
+		# Explicit initial push - see HeaterTask.on_process()'s own comment
+		# for why a simulated device's connect() alone doesn't fire the
+		# observer.
+		await self.send({'Connected': self.device.connected})
+		await self.send({'FirmwareVersion': self.device.firmware_version})
+
 		with self.device.open():
 			while True:
+				try:
 					self.device.process()
+				except Exception as e:
+					print(f"StirrerTask: comm error, marking disconnected: {e}")
+					self.device.disconnect()
 				await asyncio.sleep(self.interval)

tasks/sud.py

@@ -3,7 +3,7 @@ import bisect
 from tasks import ATask
 from ws.message import MsgIo
 from utils.value import ChangedFloat
-from components import APid, AStirrer
+from components import APid, AStirrer, AHeater
 from components.plant import APlant
 from components.sud import Sud, SudState
 
@@ -37,12 +37,13 @@ def _downsample(t, theta, max_points=MAX_FORECAST_POINTS):
 
 
 class SudTask(ATask):
-	def __init__(self, sud: Sud, tc: APid, stirrer: AStirrer, pot: APlant, dt, interval, msg_handler: MsgIo,
+	def __init__(self, sud: Sud, tc: APid, stirrer: AStirrer, heater: AHeater, pot: APlant, dt, interval, msg_handler: MsgIo,
 			forecast_estimator=None):
 		ATask.__init__(self, interval)
 		self.sud = sud
 		self.tc = tc
 		self.stirrer = stirrer
+		self.heater = heater
 		self.pot = pot
 		# Simulated seconds per tick, vs. interval's wall-clock seconds per
 		# tick - same dt/interval split Pot/TempController/Stirrer already
@@ -255,6 +256,24 @@ class SudTask(ATask):
 	def set_on_start(self, callback):
 		self._on_start = callback
 
+	def check_connections(self):
+		"""Called whenever the heater's or stirrer's connection state
+		changes (wired up in server/brewpi.py via HeaterTask/StirrerTask's
+		set_on_connected_changed()) - force-stops a run already in progress
+		if either has dropped, since continuing to run a schedule with a
+		dead actuator is misleading. Reuses Sud.stop() (already a no-op
+		outside RAMPING/HOLDING/WAIT_USER/PAUSED), the same path a manual
+		Stop press takes, so all the usual shutdown plumbing (heater
+		shutdown, sud log stop_run - see SudTask.set_on_end()'s wiring in
+		server/brewpi.py) fires exactly as it would for Stop."""
+		if self.sud.state in (SudState.IDLE, SudState.DONE):
+			return
+		if self.heater.connected and self.stirrer.connected:
+			return
+		self.sud.stop()
+		asyncio.create_task(self.send({'Error': 'Heater/Stirrer disconnected - brew stopped.'}))
+		asyncio.create_task(self.send({'Error': None}))
+
 	def on_state_changed(self, value):
 		asyncio.create_task(self.send({'State': str(value)}))
 
@@ -473,6 +492,17 @@ class SudTask(ATask):
 	async def recv(self, data):
 		for pair in data.items():
 			if 'Start' in pair[0]:
+				# Refuse to (re)start a brew if either actuator it depends
+				# on isn't actually connected - continuing to "run" a
+				# schedule with a dead heater/stirrer is misleading. Mirrors
+				# the 'Load'-while-running refusal below: send the Error then
+				# immediately clear it, since the dispatcher has no concept of
+				# a one-shot event (see that branch's own comment).
+				missing = [name for name, device in (('heater', self.heater), ('stirrer', self.stirrer)) if not device.connected]
+				if missing:
+					await self.send({'Error': f"Cannot start - {' and '.join(missing)} not connected."})
+					await self.send({'Error': None})
+					continue
 				# A fresh start (not a resume from Pause, which keeps
 				# whatever forecast the run already established) re-
 				# anchors the forecast to the real temperature right now

tasks/tempsensor.py

@@ -12,8 +12,12 @@ class TempSensorTask(ATask):
 		self.msg_handler = msg_handler
 		msg_handler.set_recv_handler(self.recv)
 		self.sensor = sensor_device
-		self.temp = self.sensor.temperature()
-		self.set_on_changed("temp", ChangedFloat(self.on_temp_changed, prec=1).set)
+		# Prime before registering - temperature() sets self.sensor.temp,
+		# which would otherwise fire on_temp_changed() (and its
+		# asyncio.create_task()) before the event loop is running, since
+		# all tasks are built synchronously at module level in brewpi.py.
+		self.sensor.temperature()
+		self.sensor.set_on_changed("temp", ChangedFloat(self.on_temp_changed, prec=1).set)
 
 	def on_temp_changed(self, value):
 		asyncio.create_task(self.send({'Temp': value}))
@@ -26,5 +30,5 @@ class TempSensorTask(ATask):
 
 	async def on_process(self):
 		while True:
-			self.temp = self.sensor.temperature()
+			self.sensor.temperature()
 			await asyncio.sleep(self.interval)

web/app.js

@@ -41,6 +41,16 @@ let heaterMaxPower = 100;
 // Only switchable when not running; auto-reset to true on play.
 let closedLoop = true;
 
+// Hardware connection status (Heater/Stirrer channels) - simulated devices
+// are always connected and never expose Connect/Disconnect (see
+// updateDeviceStatus()).
+let heaterConnected = false;
+let heaterFirmware = null;
+let heaterSimulated = null;
+let stirrerConnected = false;
+let stirrerFirmware = null;
+let stirrerSimulated = null;
+
 // Pot hardware config from server's Pot section - used for display before
 // any sud is loaded (startup water level, status line).
 let potConfig = {};
@@ -508,15 +518,17 @@ function updateControlsEnabled() {
 	const sudRunning = RUNNING_STATES.has(sudState);
 	document.getElementById('temp-soll').disabled = !(closedLoop && !sudRunning);
 	document.getElementById('heatrate-soll').disabled = !(closedLoop && !sudRunning);
-	document.getElementById('heater-power').disabled = !(!closedLoop && !sudRunning);
-	document.getElementById('stirrer-speed').disabled = sudRunning;
+	document.getElementById('heater-power').disabled = !(!closedLoop && !sudRunning && heaterConnected);
+	document.getElementById('stirrer-speed').disabled = sudRunning || !stirrerConnected;
 	document.getElementById('closed-loop').disabled = sudRunning;
 }
 
 // Mirrors client/brewpi_gui.py's update_sud_actions(): Start also doubles
-// as Resume while paused; Stop can still abort a paused run.
+// as Resume while paused; Stop can still abort a paused run. A Sud can't be
+// (re)started unless both actuators it depends on are connected - mirrors
+// the server-side refusal in tasks/sud.py's SudTask.recv().
 function updateSudActions() {
-	const canRun = connected && !sudEmpty;
+	const canRun = connected && !sudEmpty && heaterConnected && stirrerConnected;
 	const running = canRun && RUNNING_STATES.has(sudState);
 	const paused = canRun && sudState === PAUSED_STATE;
 	document.getElementById('btn-sud-start').disabled = !(canRun && !running);
@@ -524,6 +536,23 @@ function updateSudActions() {
 	document.getElementById('btn-sud-stop').disabled = !(running || paused);
 }
 
+// Shared by onHeaterChanged/onStirrerChanged - updates the status badge,
+// firmware label, and Connect/Disconnect buttons for one device. Simulated
+// devices are always connected and have nothing to connect/disconnect, so
+// their buttons are hidden entirely rather than just disabled.
+function updateDeviceStatus(prefix, isConnected, firmware, simulated) {
+	const statusEl = document.getElementById(`${prefix}-status`);
+	statusEl.textContent = isConnected ? 'Connected' : 'Disconnected';
+	statusEl.className = isConnected ? 'status-connected' : 'status-disconnected';
+	document.getElementById(`${prefix}-firmware`).textContent = firmware ? `F/W ${firmware}` : '';
+	const connectBtn = document.getElementById(`btn-${prefix}-connect`);
+	const disconnectBtn = document.getElementById(`btn-${prefix}-disconnect`);
+	connectBtn.classList.toggle('hidden', !!simulated);
+	disconnectBtn.classList.toggle('hidden', !!simulated);
+	connectBtn.disabled = isConnected;
+	disconnectBtn.disabled = !isConnected;
+}
+
 // Mirrors client/brewpi_gui.py's show_user_message(): the Sud is already
 // blocked in WAIT_USER server-side - dismissing this dialog (OK or Escape,
 // both fire the dialog's 'close' event) is what unblocks it.
@@ -610,6 +639,17 @@ function onHeaterChanged(msg) {
 			const slider = document.getElementById('heater-power');
 			slider.min = power.Min;
 			slider.max = power.Max;
+		} else if (key === 'Connected') {
+			heaterConnected = msg.Connected;
+			updateDeviceStatus('heater', heaterConnected, heaterFirmware, heaterSimulated);
+			updateControlsEnabled();
+			updateSudActions();
+		} else if (key === 'FirmwareVersion') {
+			heaterFirmware = msg.FirmwareVersion;
+			updateDeviceStatus('heater', heaterConnected, heaterFirmware, heaterSimulated);
+		} else if (key === 'Simulated') {
+			heaterSimulated = msg.Simulated;
+			updateDeviceStatus('heater', heaterConnected, heaterFirmware, heaterSimulated);
 		}
 	}
 }
@@ -627,6 +667,17 @@ function onStirrerChanged(msg) {
 			const slider = document.getElementById('stirrer-speed');
 			slider.min = power.Min;
 			slider.max = power.Max;
+		} else if (key === 'Connected') {
+			stirrerConnected = msg.Connected;
+			updateDeviceStatus('stirrer', stirrerConnected, stirrerFirmware, stirrerSimulated);
+			updateControlsEnabled();
+			updateSudActions();
+		} else if (key === 'FirmwareVersion') {
+			stirrerFirmware = msg.FirmwareVersion;
+			updateDeviceStatus('stirrer', stirrerConnected, stirrerFirmware, stirrerSimulated);
+		} else if (key === 'Simulated') {
+			stirrerSimulated = msg.Simulated;
+			updateDeviceStatus('stirrer', stirrerConnected, stirrerFirmware, stirrerSimulated);
 		}
 	}
 }
@@ -888,6 +939,18 @@ document.getElementById('btn-connect').addEventListener('click', () => {
 document.getElementById('closed-loop').addEventListener('change', (e) => {
 	sendMsg('Heater', {ClosedLoop: e.target.checked});
 });
+document.getElementById('btn-heater-connect').addEventListener('click', () => {
+	sendMsg('Heater', {Connect: true});
+});
+document.getElementById('btn-heater-disconnect').addEventListener('click', () => {
+	sendMsg('Heater', {Disconnect: true});
+});
+document.getElementById('btn-stirrer-connect').addEventListener('click', () => {
+	sendMsg('Stirrer', {Connect: true});
+});
+document.getElementById('btn-stirrer-disconnect').addEventListener('click', () => {
+	sendMsg('Stirrer', {Disconnect: true});
+});
 document.getElementById('heater-power').addEventListener('input', (e) => {
 	document.getElementById('heater-power-readout').textContent = e.target.value;
 	sendMsg('Heater', {Power: Number(e.target.value)});

web/index.html

@@ -51,6 +51,12 @@
 		</div>
 		<div class="panel">
 			<h3>Heater</h3>
+			<div class="device-status-row">
+				<span id="heater-status" class="status-disconnected">Disconnected</span>
+				<span id="heater-firmware" class="device-firmware"></span>
+				<button id="btn-heater-connect">Connect</button>
+				<button id="btn-heater-disconnect" disabled>Disconnect</button>
+			</div>
 			<label class="checkbox-label">
 				<input type="checkbox" id="closed-loop" checked> Closed-loop
 			</label>
@@ -63,6 +69,12 @@
 		</div>
 		<div class="panel">
 			<h3>Stirrer</h3>
+			<div class="device-status-row">
+				<span id="stirrer-status" class="status-disconnected">Disconnected</span>
+				<span id="stirrer-firmware" class="device-firmware"></span>
+				<button id="btn-stirrer-connect">Connect</button>
+				<button id="btn-stirrer-disconnect" disabled>Disconnect</button>
+			</div>
 			<label>Speed [%]
 				<div class="slider-row">
 					<input type="range" id="stirrer-speed" min="0" max="100" step="1">

web/style.css

@@ -333,6 +333,16 @@ header#connection-bar {
 
 #pot-reset-row { display: flex; align-items: center; gap: 0.6em; margin: 0.4em 0; }
 
+.device-status-row {
+    display: flex;
+    align-items: center;
+    gap: 0.6em;
+    margin: 0.4em 0;
+    font-size: 0.9em;
+}
+.device-status-row button { padding: 0.15em 0.6em; font-size: 0.9em; }
+.device-firmware { color: var(--text-muted); }
+
 /* --- Hidden --- */
 .hidden { display: none !important; }