feat: add connect/disconnect status for real heater/stirrer hardware

Heater and Stirrer can be real serial hardware (hendi, Pololu1376), but
there was no connection concept at all - the constructors opened the
port and crashed the whole server if the device was missing, with no
way to see connection status or firmware version and no way to
reconnect without a restart.

Adds an observable Connectable mixin (components/connectable.py) shared
by AHeater/AStirrer; real devices defer opening the serial port to an
explicit connect(), auto-connect on server startup, and surface
Connected/FirmwareVersion/Simulated plus manual Connect/Disconnect over
the web GUI. Heating/stirring and Sud Start are all gated on connection
state, and a disconnect mid-brew force-stops the run via the same path
as a manual Stop.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YaPLuRPpyjWcwhMvCvpHCL

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

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

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

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; }