Force the heater off and show a "Cool down" indicator during a passive cooldown

A ramp step whose target is below the current actual temperature can
only be reached by ambient cooling - the heater can't actively cool.
SudTask now detects this once per ramp phase and calls the controller's
new set_cooling() override (forces y=0, bypassing the FSM) instead of
waiting for its hysteresis-based IDLE transition. The GUI shows a
blinking blue "Cool down" label in the status bar while this is active.
Progression already only advances once theta_ist matches theta_soll
regardless of direction, so no change was needed there.

client/brewpi_gui.py

@@ -227,6 +227,18 @@ class Window(QtWidgets.QMainWindow, Ui_MainWindow):
 		self.status_label_env = QtWidgets.QLabel()
 		self.statusBar().addPermanentWidget(self.status_label_env)
 		self.update_status_env_label()
+
+		# Blinking indicator for a Sud ramp step that's cooling down
+		# (target below the current temperature - the heater is forced off
+		# server-side and we just wait for ambient loss to catch up).
+		self.sud_cooling = False
+		self.status_label_cooling = QtWidgets.QLabel("Cool down")
+		self.status_label_cooling.setStyleSheet("color: blue; font-weight: bold;")
+		self.status_label_cooling.setVisible(False)
+		self.statusBar().addPermanentWidget(self.status_label_cooling)
+		self.cooling_blink_timer = QtCore.QTimer(self)
+		self.cooling_blink_timer.timeout.connect(self.on_cooling_blink)
+
 		self.update_sud_actions()
 		self.btn_connect.clicked.connect(self.on_btn_connect_clicked)
 		self.actionStart.triggered.connect(self.on_action_sud_start)
@@ -336,6 +348,7 @@ class Window(QtWidgets.QMainWindow, Ui_MainWindow):
 			self.sud_start_time = None
 			self.sud_paused_total = 0.0
 			self.sud_pause_started_at = None
+			self.set_sud_cooling(False)
 			self.update_sud_actions()
 			self.update_status_env_label()
 
@@ -361,6 +374,20 @@ class Window(QtWidgets.QMainWindow, Ui_MainWindow):
 		ambient = "{:.1f}°C".format(self.ambient_temp) if self.ambient_temp is not None else "-"
 		self.status_label_env.setText("Ambient: {}   Warp: {:.1f}x".format(ambient, self.warp_factor))
 
+	def set_sud_cooling(self, cooling):
+		if cooling == self.sud_cooling:
+			return
+		self.sud_cooling = cooling
+		if cooling:
+			self.status_label_cooling.setVisible(True)
+			self.cooling_blink_timer.start(500)
+		else:
+			self.cooling_blink_timer.stop()
+			self.status_label_cooling.setVisible(False)
+
+	def on_cooling_blink(self):
+		self.status_label_cooling.setVisible(not self.status_label_cooling.isVisible())
+
 	def on_slider_temp_soll_changed(self, value):
 		print("on_slider_temp_soll_changed {}".format(value))
 		self.msg_tempctrl.send({'Soll': {'Temp': value}})
@@ -544,6 +571,7 @@ class Window(QtWidgets.QMainWindow, Ui_MainWindow):
 					self.statusBar().showMessage("Step {}: {}".format(step.get('Index'), descr))
 				else:
 					self.statusBar().clearMessage()
+				self.set_sud_cooling(step.get('Cooling', False))
 		self.update_sud_actions()
 
 	def update_sud_forecast(self, doc):

components/pid/temp_controller_base.py

@@ -37,6 +37,12 @@ class TempControllerBase(APid):
 		self.pid_hold.set_params(params['Hold'])
 		self.pid_rate.set_params(params['Heat'])
 		self.is_startup = True
+		# Explicit override for a ramp step whose target is below the
+		# current temperature: the heater can't actively cool, so rather
+		# than wait for the FSM's own (slower, hysteresis-based) IDLE
+		# transition, force y to 0 as soon as the caller (SudTask) knows
+		# the step needs to passively cool down.
+		self.cooling = False
 
 	def on_state_entered(self, state):
 		pass
@@ -70,6 +76,9 @@ class TempControllerBase(APid):
 	def set_heatrate_soll(self, value):
 		self.heatrate_soll_set = value
 
+	def set_cooling(self, value):
+		self.cooling = value
+
 	def get_heatrate_soll(self):
 		return self.heatrate_soll
 
@@ -109,7 +118,7 @@ class TempControllerBase(APid):
 		self.pid_hold.process(theta_err, -self.theta_ist, hold_scale)
 		self.pid_rate.process(heatrate_err, -self.heatrate_ist)
 
-		if self.state == States.IDLE:
+		if self.state == States.IDLE or self.cooling:
 			self.y = 0
 		else:
 			self.y = self.pid_rate.get_y()

scripts/demos/sud/demo_sud.py

@@ -77,6 +77,15 @@ if __name__ == '__main__':
 		if step is not None:
 			ramping = sud.state == SudState.RAMPING
 			phase = step['ramp'] if ramping and 'ramp' in step else step.get('hold', {})
+
+			# A ramp step whose target is below the current temperature can
+			# only be reached by passive cooling - force the heater off,
+			# mirroring tasks/sud.py's SudTask.
+			cooling = ramping and 'ramp' in step and step['ramp']['temp'] < ctrl.get_theta_ist() - TEMP_REACHED_TOLERANCE
+			ctrl.set_cooling(cooling)
+			if cooling:
+				print("  -> cooling down to {}".format(step['ramp']['temp']))
+
 			print(f"Step {step['number']}: {step['descr']}")
 			apply_plant_params(step)
 			if ramping and 'ramp' in step:

tasks/sud.py

@@ -61,6 +61,14 @@ class SudTask(ATask):
 		ramping = self.sud.state == SudState.RAMPING
 		phase = ramp if ramping and ramp is not None else hold
 
+		# A ramp step whose target is below the current temperature can
+		# only be reached by passive cooling - force the heater off for
+		# its whole duration (decided once, here, rather than re-checked
+		# every tick) instead of relying on the controller's own FSM to
+		# notice and idle out.
+		cooling = ramping and ramp is not None and ramp['temp'] < self.tc.get_theta_ist() - TEMP_REACHED_TOLERANCE
+		self.tc.set_cooling(cooling)
+
 		if step is not None:
 			self.apply_plant_params(step)
 			if ramping and ramp is not None:
@@ -76,6 +84,7 @@ class SudTask(ATask):
 			'Rate': ramp.get('rate') if ramp else None,
 			'Duration': hold.get('duration') if (hold is not None and not ramping) else None,
 			'WaitForUser': step.get('user_wait_for_continue', False) if step else None,
+			'Cooling': cooling,
 		}}))
 
 	def on_state_changed(self, value):