diff --git a/src/App/App.cpp b/src/App/App.cpp
index ad86f40..4dae346 100644
--- a/src/App/App.cpp
+++ b/src/App/App.cpp
@@ -9,6 +9,7 @@ namespace Dough
     }
 
     App::App() : config(),
+                 ui(),
                  wifi(),
                  mqtt(
                      &wifi,
@@ -19,26 +20,30 @@ namespace Dough
                      "temperature",
                      TemperatureSensor::Instance(),
                      TEMPERATURE_AVERAGE_STORAGE,
-                     TEMPERATURE_MEASURE_INTERVAL,
-                     MINIMUM_PUBLISH_INTERVAL),
+                     TEMPERATURE_MEASURE_INTERVAL, sensorOnMeasureCallback,
+                     MINIMUM_PUBLISH_INTERVAL, sensorOnPublishCallback),
                  humiditySensor(
                      &mqtt,
                      "humidity",
                      HumiditySensor::Instance(),
                      HUMIDITY_AVERAGE_STORAGE,
-                     HUMIDITY_MEASURE_INTERVAL,
-                     MINIMUM_PUBLISH_INTERVAL),
+                     HUMIDITY_MEASURE_INTERVAL, sensorOnMeasureCallback,
+                     MINIMUM_PUBLISH_INTERVAL, sensorOnPublishCallback),
                  distanceSensor(
                      &mqtt,
                      "distance",
                      DistanceSensor::Instance(),
                      DISTANCE_AVERAGE_STORAGE,
-                     DISTANCE_MEASURE_INTERVAL,
-                     MINIMUM_PUBLISH_INTERVAL),
+                     DISTANCE_MEASURE_INTERVAL, sensorOnMeasureCallback,
+                     MINIMUM_PUBLISH_INTERVAL, sensorOnPublishCallback),
                  _logger("APP") {}
 
     void App::setup()
     {
+        ui.setup();
+        ui.onoffButton.onInterrupt(::onoffButtonInterruptCallback);
+        ui.setupButton.onInterrupt(::setupButtonInterruptCallback);
+
         wifi.setup();
         mqtt.setup();
         temperatureSensor.setup();
@@ -50,9 +55,14 @@ namespace Dough
     {
         if (config.isOk())
         {
+            // Get measurements from the sensors. Suspend the user interface
+            // interrupts in the meanwhile, to not disturb the timing-sensitive
+            // sensor readings.
+            ui.suspend();
             temperatureSensor.loop();
             humiditySensor.loop();
             distanceSensor.loop();
+            ui.resume();
         }
     }
 
@@ -89,4 +99,33 @@ void mqttOnMessageCallback(String &topic, String &payload)
     {
         callbackLogger.log("ss", "ERROR - Unhandled MQTT message, topic = ", topic.c_str());
     }
+}
+
+void onoffButtonInterruptCallback()
+{
+    Dough::App::Instance()->ui.onoffButton.handleButtonState();
+}
+
+void setupButtonInterruptCallback()
+{
+    Dough::App::Instance()->ui.setupButton.handleButtonState();
+}
+
+void sensorOnMeasureCallback()
+{
+    Dough::App::Instance()->ui.notifySensorActivity();
+}
+
+void sensorOnPublishCallback()
+{
+    Dough::App::Instance()->ui.notifyNetworkActivity();
+}
+
+// This callback is called when the TC4 timer from the UI code hits an overflow
+// interrupt. It is defined outside the Dough namespace, because TC4_Handler is
+// a hard-coded root namespace function name.
+void TC4_Handler()
+{
+    Dough::App::Instance()->ui.updateLEDs();
+    REG_TC4_INTFLAG = TC_INTFLAG_OVF; // Clear the OVF interrupt flag.
 }
\ No newline at end of file
diff --git a/src/App/App.h b/src/App/App.h
index 7597307..709318f 100644
--- a/src/App/App.h
+++ b/src/App/App.h
@@ -16,6 +16,7 @@ namespace Dough
     public:
         static App *Instance();
         Configuration config;
+        UI ui;
         WiFi wifi;
         MQTT mqtt;
         SensorController temperatureSensor;
@@ -33,7 +34,11 @@ namespace Dough
 }
 
 // Callback functions that need to live in the global namespace.
-void mqttOnConnectCallback(Dough::MQTT* mqtt);
+void mqttOnConnectCallback(Dough::MQTT *mqtt);
 void mqttOnMessageCallback(String &topic, String &payload);
+void onoffButtonInterruptCallback();
+void setupButtonInterruptCallback();
+void sensorOnMeasureCallback();
+void sensorOnPublishCallback();
 
 #endif
\ No newline at end of file
diff --git a/src/App/Configuration.cpp b/src/App/Configuration.cpp
index 4bb9217..fbd0ba8 100644
--- a/src/App/Configuration.cpp
+++ b/src/App/Configuration.cpp
@@ -2,10 +2,7 @@
 
 namespace Dough
 {
-    Configuration::Configuration() : _logger("CONFIG")
-    {
-//        _mqtt = MQTT::Instance();
-    }
+    Configuration::Configuration() : _logger("CONFIG") {}
 
     void Configuration::setup()
     {
diff --git a/src/App/Configuration.h b/src/App/Configuration.h
index 01c7a63..e4d0e32 100644
--- a/src/App/Configuration.h
+++ b/src/App/Configuration.h
@@ -2,8 +2,6 @@
 #define DOUGH_CONFIG_H
 
 #include <Arduino.h>
-//#include "App/App.h"
-#include "Network/MQTT.h"
 #include "UI/Logger.h"
 #include "Sensors/LowLevel/SensorHCSR04.h"
 
@@ -18,8 +16,6 @@ namespace Dough
     public:
         Configuration();
         void setup();
-        static void handleMqttConnect(MQTT *mqtt);
-        static void handleMqttMessage(String &key, String &value);
         void setContainerHeight(int height);
         unsigned int getContainerHeight();
         void setTemperatureOffset(int offset);
@@ -27,7 +23,6 @@ namespace Dough
         bool isOk();
 
     private:
-        MQTT *_mqtt;
         Logger _logger;
         unsigned int _containerHeight;
         bool _containerHeightSet;
diff --git a/src/Data/SensorController.cpp b/src/Data/SensorController.cpp
index 3c0abc2..8dcacdb 100644
--- a/src/Data/SensorController.cpp
+++ b/src/Data/SensorController.cpp
@@ -9,15 +9,18 @@ namespace Dough
         SensorBase *sensor,
         unsigned int storageSize,
         unsigned int minimumMeasureTime,
-        unsigned int minimumPublishTime)
+        SensorControllerCallback onMeasure,
+        unsigned int minimumPublishTime,
+        SensorControllerCallback onPublish)
     {
         _mqtt = mqtt;
         _mqttKey = mqttKey;
         _sensor = sensor;
         _storageSize = storageSize;
         _minimumMeasureTime = minimumMeasureTime;
+        _onMeasure = onMeasure;
         _minimumPublishTime = minimumPublishTime;
-        _ui = UI::Instance();
+        _onPublish = onPublish;
     }
 
     void SensorController::setup()
@@ -42,10 +45,12 @@ namespace Dough
     {
         if (_mustMeasure())
         {
+            _onMeasure();
             _measure();
         }
         if (_mustPublish())
         {
+            _onPublish();
             _publish();
         }
     }
@@ -69,19 +74,7 @@ namespace Dough
     {
         _lastMeasuredAt = millis();
         
-        // Quickly dip the LED to indicate that a measurement has started.
-        // This is done synchroneously, because we suspend the timer interrupts
-        // in the upcoming code.
-        _ui->led3.off();
-        delay(50);
-        _ui->led3.on();
-
-        // Read a measurement from the sensor. Suspend the user interface
-        // interrupts in the meanwhile, to not disturb the timing-sensitive
-        // sensor readings.
-        _ui->suspend();
         _store(_sensor->read());
-        _ui->resume();
     }
 
     bool SensorController::_mustPublish()
@@ -139,14 +132,6 @@ namespace Dough
 
     void SensorController::_publish()
     {
-        // Quickly dip the LED to indicate that a publish has started.
-        // This is done synchroneously, because the upcoming code is too
-        // fast normally to register a LED going off and on again during
-        // the operation.
-        _ui->led1.off();
-        delay(50);
-        _ui->led1.on();
-
         auto average = getAverage();
         auto last = getLast();
 
diff --git a/src/Data/SensorController.h b/src/Data/SensorController.h
index 830a2d6..316790c 100644
--- a/src/Data/SensorController.h
+++ b/src/Data/SensorController.h
@@ -9,6 +9,8 @@
 
 namespace Dough
 {
+    typedef void (*SensorControllerCallback)();
+    
     // This class is used to store measurements for a sensor and to keep
     // track of running totals for handling average computations.
     // It also provides functionality to decide when to read a measurement
@@ -32,16 +34,24 @@ namespace Dough
         // @param minimumMeasureTime
         //     The number of seconds after which to read the next measurement
         //     from the sensor.
+        // @param onMeasure
+        //     A callback function that is called right before a measurement
+        //     is taken.
         // @param minimumPublishTime
         //     The number of seconds after which to forcibly publish measurements
         //     to MQTT, even when no significant changes to measurements were seen.
+        // @param onPublish
+        //     A callback function that is called right before a measurement
+        //     is published.
         SensorController(
             MQTT *mqtt,
             const char *mqttKey,
             SensorBase *sensor,
             unsigned int storageSize,
             unsigned int minimumMeasureTime,
-            unsigned int minimumPublishTime);
+            SensorControllerCallback onMeasure,
+            unsigned int minimumPublishTime,
+            SensorControllerCallback onPublish);
         void setup();
         void loop();
         Measurement getLast();
@@ -50,7 +60,6 @@ namespace Dough
 
     private:
         MQTT *_mqtt;
-        UI *_ui;
         const char *_mqttKey;
         char *_mqttAverageKey;
         SensorBase *_sensor;
@@ -60,10 +69,12 @@ namespace Dough
         unsigned int _averageCount = 0;
         unsigned int _index = 0;
         bool _mustMeasure();
+        SensorControllerCallback _onMeasure;
         void _measure();
         unsigned int _minimumMeasureTime; 
         unsigned long _lastMeasuredAt = 0;
         bool _mustPublish();
+        SensorControllerCallback _onPublish ;
         void _publish();
         unsigned int _minimumPublishTime;
         unsigned long _lastPublishedAt = 0;
diff --git a/src/UI/UI.cpp b/src/UI/UI.cpp
index 7ae62e8..4afbd18 100644
--- a/src/UI/UI.cpp
+++ b/src/UI/UI.cpp
@@ -2,17 +2,6 @@
 
 namespace Dough
 {
-    UI *UI::_instance = nullptr;
-
-    UI *UI::Instance()
-    {
-        if (UI::_instance == nullptr)
-        {
-            UI::_instance = new UI();
-        }
-        return UI::_instance;
-    }
-
     UI::UI() : onoffButton(ONOFF_BUTTON_PIN),
                setupButton(SETUP_BUTTON_PIN),
                ledBuiltin(LED_BUILTIN),
@@ -24,9 +13,7 @@ namespace Dough
     {
         // Setup the buttons.
         onoffButton.setup();
-        onoffButton.onInterrupt(UI::onoffButtonISR);
         setupButton.setup();
-        setupButton.onInterrupt(UI::setupButtonISR);
 
         // Setup the LEDs.
         ledBuiltin.setup();
@@ -47,16 +34,6 @@ namespace Dough
         resume();
     }
 
-    void UI::onoffButtonISR()
-    {
-        UI::Instance()->onoffButton.handleButtonState();
-    }
-
-    void UI::setupButtonISR()
-    {
-        UI::Instance()->setupButton.handleButtonState();
-    }
-
     // Setup a timer interrupt for updating the GUI. Unfortunately, the standard
     // libraries that I can find for this, are not equipped to work for the
     // Arduino Nano 33 IOT architecture. Luckily, documentation and various
@@ -91,13 +68,6 @@ namespace Dough
             ; // Wait for synchronization
     }
 
-    // Disables the TC4 interrupts, suspending timed async updates to
-    // the user interface.
-    void UI::suspend()
-    {
-        NVIC_DisableIRQ(TC4_IRQn);
-    }
-
     // Enables the TC4 interrupts in the Nested Vector InterruptController (NVIC),
     // starting timed async updates for the user interface.
     void UI::resume()
@@ -106,6 +76,13 @@ namespace Dough
         NVIC_EnableIRQ(TC4_IRQn);      // Enable TC4 interrupts
     }
 
+    // Disables the TC4 interrupts, suspending timed async updates to
+    // the user interface.
+    void UI::suspend()
+    {
+        NVIC_DisableIRQ(TC4_IRQn);
+    }
+
     // Fire pending button events.
     void UI::processButtonEvents()
     {
@@ -125,7 +102,7 @@ namespace Dough
     // the timer interrupt code from above. The timer interrupt based invocation
     // makes it possible to do LED updates, while the device is busy doing
     // something else.
-    void UI::updatedLEDs()
+    void UI::updateLEDs()
     {
         ledBuiltin.loop();
         led1.loop();
@@ -133,7 +110,65 @@ namespace Dough
         led3.loop();
     }
 
-    // Flash all LEDs, one at a time.
+    void UI::notifyConnectingToWifi()
+    {
+        led1.blink()->slow();
+        led2.off();
+        led3.off();
+    }
+    
+    void UI::notifyConnectingToMQTT()
+    {
+        led1.blink()->fast();
+        led2.off();
+        led3.off();
+    }
+
+    void UI::notifyWaitingForConfiguration()
+    {
+        led1.on();
+        led2.blink()->slow();
+        led3.off();
+    }
+
+    void UI::notifyCalibrating()
+    {
+        led1.on();
+        led2.blink()->fast();
+        led3.off();
+    }
+
+    void UI::notifyMeasurementsActive()
+    {
+        led1.on();
+        led2.on();
+        led3.on();
+    }
+
+    void UI::notifyMeasurementsPaused()
+    {
+        led1.on();
+        led2.on();
+        led3.pulse();
+    }
+
+    void UI::notifySensorActivity()
+    {
+        led3.off();
+        delay(50);
+        led3.on();        
+    }
+
+    void UI::notifyNetworkActivity()
+    {
+        led1.off();
+        delay(50);
+        led1.on();        
+    }
+    
+    // Flash all LEDs, one at a time in a synchroneous manner, making
+    // this work when the UI timer interrupt is inactive. This is used
+    // as a "Hey, I'm awake!" signal from the device after booting up.
     void UI::_flash_all_leds()
     {
         ledBuiltin.on();
@@ -149,13 +184,4 @@ namespace Dough
         delay(100);
         led3.off();
     }
-} // namespace Dough
-
-// This callback is called when the TC4 timer hits an overflow interrupt.
-// Defined outside the Dough namespace, because TC4_Handler is a hard-coded
-// root namespace function name.
-void TC4_Handler()
-{
-    Dough::UI::Instance()->updatedLEDs();
-    REG_TC4_INTFLAG = TC_INTFLAG_OVF; // Clear the OVF interrupt flag.
-}
+} // namespace Dough
\ No newline at end of file
diff --git a/src/UI/UI.h b/src/UI/UI.h
index cdebc44..bfb9bd4 100644
--- a/src/UI/UI.h
+++ b/src/UI/UI.h
@@ -9,33 +9,40 @@
 
 namespace Dough
 {
-// This class groups all user interface functionality: serial logging,
-// LEDs and buttons.
-class UI
-{
-public:
-    static UI *Instance();
-    void setup();
-    static void onoffButtonISR();
-    static void setupButtonISR();
-    Button onoffButton;
-    Button setupButton;
-    LED ledBuiltin;
-    LED led1;
-    LED led2;
-    LED led3;
-    void processButtonEvents();
-    void clearButtonEvents();
-    void updatedLEDs();
-    void resume();
-    void suspend();
+    // This class groups all user interface functionality: serial logging,
+    // LEDs and buttons.
+    class UI
+    {
+    public:
+        UI();
+        void setup();
+        static void onoffButtonISR();
+        static void setupButtonISR();
+        Button onoffButton;
+        Button setupButton;
+        LED ledBuiltin;
+        LED led1;
+        LED led2;
+        LED led3;
+        void processButtonEvents();
+        void clearButtonEvents();
+        void updateLEDs();
+        void resume();
+        void suspend();
+        void notifyConnectingToWifi();
+        void notifyConnectingToMQTT();
+        void notifyWaitingForConfiguration();
+        void notifyCalibrating();
+        void notifyMeasurementsActive();
+        void notifyMeasurementsPaused();
+        void notifySensorActivity();
+        void notifyNetworkActivity();
 
-private:
-    UI();
-    void _setupTimerInterrupt();
-    static UI *_instance;
-    void _flash_all_leds();
-};
-}
+    private:
+        void _setupTimerInterrupt();
+        static UI *_instance;
+        void _flash_all_leds();
+    };
+} // namespace Dough
 
 #endif
\ No newline at end of file
diff --git a/src/main.cpp b/src/main.cpp
index e7d5113..da71482 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1,6 +1,7 @@
 #include "main.h"
 
 // TOOD: implement the calibration logic
+// TODO: don't make sensors instances
 // TODO: see what more stuff can be moved to the UI code. Maybe state to UI state translation ought to be there as well
 
 DoughBoyState state = CONFIGURING;
@@ -10,20 +11,18 @@ void setup()
 {
     Dough::Logger::setup();
     logger.log("s", "Initializing device");
-    Dough::App::Instance()->setup();
-    auto ui = Dough::UI::Instance();
-    ui->setup();
-    ui->onoffButton.onPress(handleOnoffButtonPress);
-    ui->setupButton.onPress(handleSetupButtonPress);
+    auto app = Dough::App::Instance();
+    app->setup();
+    app->ui.onoffButton.onPress(handleOnoffButtonPress);
+    app->ui.setupButton.onPress(handleSetupButtonPress);
     logger.log("s", "Initialization completed, starting device");
 }
 
 void loop()
 {
     auto app = Dough::App::Instance();
-    auto ui = Dough::UI::Instance();
 
-    ui->processButtonEvents();
+    app->ui.processButtonEvents();
 
     if (!setupNetworkConnection())
     {
@@ -66,7 +65,6 @@ bool setupNetworkConnection()
     static auto connectionState = CONNECTING_WIFI;
 
     auto app = Dough::App::Instance();
-    auto ui = Dough::UI::Instance();
 
     if (!app->wifi.isConnected())
     {
@@ -79,9 +77,7 @@ bool setupNetworkConnection()
             logger.log("s", "Connecting to the WiFi network ...");
         }
         connectionState = CONNECTING_WIFI;
-        ui->led1.blink()->slow();
-        ui->led2.off();
-        ui->led3.off();
+        app->ui.notifyConnectingToWifi();
         app->wifi.connect();
     }
     if (app->wifi.isConnected() && !app->mqtt.isConnected())
@@ -95,9 +91,7 @@ bool setupNetworkConnection()
             logger.log("s", "Connecting to the MQTT broker ...");
         }
         connectionState = CONNECTING_MQTT;
-        ui->led1.blink()->fast();
-        ui->led2.off();
-        ui->led3.off();
+        app->ui.notifyConnectingToMQTT();
         app->mqtt.connect();
         delay(1000); // purely costmetic, to make the faster LED blinking noticable
     }
@@ -106,10 +100,8 @@ bool setupNetworkConnection()
         if (connectionState != CONNECTED)
         {
             logger.log("s", "Connection to MQTT broker established");
-            ui->led1.on();
-            ui->led2.off();
-            ui->led3.off();
-            ui->clearButtonEvents();
+            app->ui.notifyConnected();
+            app->ui.clearButtonEvents();
             connectionState = CONNECTED;
             setStateToConfiguring();
         }
@@ -137,44 +129,36 @@ void handleSetupButtonPress()
 
 void setStateToConfiguring()
 {
-    auto ui = Dough::UI::Instance();
+    auto app = Dough::App::Instance();
     logger.log("s", "Waiting for configuration ...");
     state = CONFIGURING;
-    ui->led1.on();
-    ui->led2.blink()->fast();
-    ui->led3.off();
-    Dough::App::Instance()->mqtt.publish("state", "configuring");
+    app->ui.notifyWaitingForConfiguration();
+    app->mqtt.publish("state", "configuring");
 }
 
 void setStateToMeasuring()
 {
-    auto ui = Dough::UI::Instance();
+    auto app = Dough::App::Instance();
     logger.log("s", "Starting measurements");
     state = MEASURING;
-    ui->led1.on();
-    ui->led2.on();
-    ui->led3.on();
-    Dough::App::Instance()->mqtt.publish("state", "measuring");
+    app->ui.notifyMeasurementsActive();
+    app->mqtt.publish("state", "measuring");
 }
 
 void setStateToPaused()
 {
-    auto ui = Dough::UI::Instance();
+    auto app = Dough::App::Instance();
     logger.log("s", "Pausing measurements");
     state = PAUSED;
-    ui->led1.on();
-    ui->led2.on();
-    ui->led3.pulse();
-    Dough::App::Instance()->mqtt.publish("state", "paused");
+    app->ui.notifyMeasurementsPaused();
+    app->mqtt.publish("state", "paused");
 }
 
 void setStateToCalibrating()
 {
-    auto ui = Dough::UI::Instance();
+    auto app = Dough::App::Instance();
     logger.log("s", "Requested device calibration");
     state = CALIBRATING;
-    ui->led1.on();
-    ui->led2.blink()->slow();
-    ui->led3.off();
-    Dough::App::Instance()->mqtt.publish("state", "calibrating");
+    app->ui.notifyCalibrating();
+    app->mqtt.publish("state", "calibrating");
 }