Picked up the [Arduino Matter Discovery Bundle](http://amzn.itemspot.link/B0GN3T5ZK7) because it sounded interesting and I hadn't seen much written about it. Wanted to get all three Modulino sensors working in Home Assistant via Matter. Figured I'd share what I ran into because the path to getting it clean was not obvious, and most of it isn't documented anywhere.

What's in the bundle:

* Arduino Nano Matter (main board, this thing is TINY!)
* Modulino Thermo (temperature + humidity)
* Modulino Distance (time of flight, 0-1200mm)
* Modulino Latch Relay (30V DC / 5A)

Everything connects via Qwiic cables, no soldering, plug and play.

Commissioning actually just worked:

The first thing that surprised me was how smooth the initial pairing was. The Nano Matter has a Thread radio built in, and I have an Apple HomePod which acts as a Thread border router. Once I uploaded a basic sketch and opened Serial Monitor, the board printed a QR code URL. I opened it in a browser, scanned it from the Home Assistant app, and it was commissioned and online in under a minute. No manual network config, no IP addresses. That part was genuinely impressive.

The big thing nobody warned me about: ghost sensors

After commissioning I started adding more Matter sensor classes to the sketch. What showed up in HA was a mess: air quality, pressure, illuminance, EV charger controls, flow sensors, none of which exist on this hardware. It actually stalled out my HA device page to the point where I had to delete the device entirely.

Turns out the Silicon Labs board package registers a bunch of default Matter clusters regardless of what your sketch does. The fix is to only include the Matter classes you actually need, and always run a factory reset sketch before re-commissioning when you change what classes are included.

Libraries you need:  
In Arduino IDE Library Manager, install:  
Modulino by Arduino  
Matter comes bundled with the Silicon Labs board package (install "Arduino Nano Matter" in Board Manager)

Happy to answer any questions or if you're curious about anything just drop a comment.

Arduino factory **reset sketch** (run this if you need to recommission)

    #include <Modulino.h> 
    #include <Matter.h> 
    
    void setup() {
      Serial.begin(115200);
      Modulino.begin();
      Matter.begin();
    
      if (Matter.isDeviceCommissioned()) {
        Serial.println("Clearing old Matter pairing...");
        Matter.decommission();
        Serial.println("Done! Re-upload your main sketch.");
      } else {
        Serial.println("Not commissioned, no reset needed.");
      }
    }

The **final working sketch**

This gives you Temperature, Humidity, Occupancy (via distance sensor), and a relay you can toggle from HA

    #include <Modulino.h>
    #include <Matter.h>
    #include <MatterTemperature.h>
    #include <MatterHumidity.h>
    #include <MatterOccupancy.h>
    #include <MatterOnOffPluginUnit.h>
    
    ModulinoThermo        thermo;
    ModulinoDistance      distance;
    ModulinoLatchRelay    relay;
    
    MatterTemperature     matterTemp;
    MatterHumidity        matterHumidity;
    MatterOccupancy       matterOccupancy;
    MatterOnOffPluginUnit matterRelay;
    
    // Anything closer than this (mm) = occupied
    #define OCCUPIED_THRESHOLD 600
    
    void setup() {
      Serial.begin(115200);
      Modulino.begin();
      Matter.begin();
      matterTemp.begin();
      matterHumidity.begin();
      matterOccupancy.begin();
      matterRelay.begin();
    
      if (!thermo.begin())   Serial.println("Thermo not found! Check Qwiic cable.");
      if (!distance.begin()) Serial.println("Distance not found! Check Qwiic cable.");
      if (!relay.begin())    Serial.println("Relay not found! Check Qwiic cable.");
    
      if (!Matter.isDeviceCommissioned()) {
        Serial.println("Not paired yet. Use this in Home Assistant:");
        Serial.println(Matter.getOnboardingQRCodeUrl());
        Serial.println(Matter.getManualPairingCode());
      }
    
      while (!Matter.isDeviceCommissioned()) delay(200);
      while (!Matter.isDeviceThreadConnected()) delay(200);
      Serial.println("Ready.");
    }
    
    float toFahrenheit(float c) {
      return (c * 9.0 / 5.0) + 32.0;
    }
    
    void loop() {
      // Relay checked every loop for fast response to HA commands
      bool relayState = matterRelay.get_onoff();
      if (relayState) {
        relay.set();
      } else {
        relay.reset();
      }
    
      // Sensors update every 5 seconds
      static unsigned long lastUpdate = 0;
      if (millis() - lastUpdate >= 5000) {
        lastUpdate = millis();
    
        float tempC    = thermo.getTemperature();
        float humidity = thermo.getHumidity();
        matterTemp.set_measured_value_celsius(tempC);
        matterHumidity.set_measured_value(humidity);
    
        Serial.print("Temp: "); Serial.print(toFahrenheit(tempC));
        Serial.print(" F  | Humidity: "); Serial.print(humidity); Serial.print(" %");
    
        if (distance.available()) {
          int mm = distance.get();
          bool occupied = (mm > 0 && mm < OCCUPIED_THRESHOLD);
          matterOccupancy.set_occupancy(occupied);
          Serial.print("  | Distance: "); Serial.print(mm);
          Serial.print(" mm | Occupancy: ");
          Serial.print(occupied ? "OCCUPIED" : "Clear");
        }
    
        Serial.print("  | Relay: ");
        Serial.println(relayState ? "ON" : "OFF");
      }
    }Picked up the Arduino Matter Discovery Bundle because it sounded interesting and I hadn't seen much written about it. Wanted to get all three Modulino sensors working in Home Assistant via Matter. Figured I'd share what I ran into because the path to getting it clean was not obvious, and most of it isn't documented anywhere.What's in the bundle:Arduino Nano Matter (main board, this thing is TINY!)
    Modulino Thermo (temperature + humidity)
    Modulino Distance (time of flight, 0-1200mm)
    Modulino Latch Relay (30V DC / 5A)Everything connects via Qwiic cables, no soldering, plug and play.Commissioning actually just worked:The first thing that surprised me was how smooth the initial pairing was. The Nano Matter has a Thread radio built in, and I have an Apple HomePod which acts as a Thread border router. Once I uploaded a basic sketch and opened Serial Monitor, the board printed a QR code URL. I opened it in a browser, scanned it from the Home Assistant app, and it was commissioned and online in under a minute. No manual network config, no IP addresses. That part was genuinely impressive.The big thing nobody warned me about: ghost sensorsAfter commissioning I started adding more Matter sensor classes to the sketch. What showed up in HA was a mess: air quality, pressure, illuminance, EV charger controls, flow sensors, none of which exist on this hardware. It actually stalled out my HA device page to the point where I had to delete the device entirely.Turns out the Silicon Labs board package registers a bunch of default Matter clusters regardless of what your sketch does. The fix is to only include the Matter classes you actually need, and always run a factory reset sketch before re-commissioning when you change what classes are included.Libraries you need:
    In Arduino IDE Library Manager, install:
    Modulino by Arduino
    Matter comes bundled with the Silicon Labs board package (install "Arduino Nano Matter" in Board Manager)Happy to answer any questions or if you're curious about anything just drop a comment.Arduino factory reset sketch (run this if you need to recommission)#include <Modulino.h> 
    #include <Matter.h> 
    
    void setup() {
      Serial.begin(115200);
      Modulino.begin();
      Matter.begin();
    
      if (Matter.isDeviceCommissioned()) {
        Serial.println("Clearing old Matter pairing...");
        Matter.decommission();
        Serial.println("Done! Re-upload your main sketch.");
      } else {
        Serial.println("Not commissioned, no reset needed.");
      }
    }The final working sketchThis gives you Temperature, Humidity, Occupancy (via distance sensor), and a relay you can toggle from HA#include <Modulino.h>
    #include <Matter.h>
    #include <MatterTemperature.h>
    #include <MatterHumidity.h>
    #include <MatterOccupancy.h>
    #include <MatterOnOffPluginUnit.h>
    
    ModulinoThermo        thermo;
    ModulinoDistance      distance;
    ModulinoLatchRelay    relay;
    
    MatterTemperature     matterTemp;
    MatterHumidity        matterHumidity;
    MatterOccupancy       matterOccupancy;
    MatterOnOffPluginUnit matterRelay;
    
    // Anything closer than this (mm) = occupied
    #define OCCUPIED_THRESHOLD 600
    
    void setup() {
      Serial.begin(115200);
      Modulino.begin();
      Matter.begin();
      matterTemp.begin();
      matterHumidity.begin();
      matterOccupancy.begin();
      matterRelay.begin();
    
      if (!thermo.begin())   Serial.println("Thermo not found! Check Qwiic cable.");
      if (!distance.begin()) Serial.println("Distance not found! Check Qwiic cable.");
      if (!relay.begin())    Serial.println("Relay not found! Check Qwiic cable.");
    
      if (!Matter.isDeviceCommissioned()) {
        Serial.println("Not paired yet. Use this in Home Assistant:");
        Serial.println(Matter.getOnboardingQRCodeUrl());
        Serial.println(Matter.getManualPairingCode());
      }
    
      while (!Matter.isDeviceCommissioned()) delay(200);
      while (!Matter.isDeviceThreadConnected()) delay(200);
      Serial.println("Ready.");
    }
    
    float toFahrenheit(float c) {
      return (c * 9.0 / 5.0) + 32.0;
    }
    
    void loop() {
      // Relay checked every loop for fast response to HA commands
      bool relayState = matterRelay.get_onoff();
      if (relayState) {
        relay.set();
      } else {
        relay.reset();
      }
    
      // Sensors update every 5 seconds
      static unsigned long lastUpdate = 0;
      if (millis() - lastUpdate >= 5000) {
        lastUpdate = millis();
    
        float tempC    = thermo.getTemperature();
        float humidity = thermo.getHumidity();
        matterTemp.set_measured_value_celsius(tempC);
        matterHumidity.set_measured_value(humidity);
    
        Serial.print("Temp: "); Serial.print(toFahrenheit(tempC));
        Serial.print(" F  | Humidity: "); Serial.print(humidity); Serial.print(" %");
    
        if (distance.available()) {
          int mm = distance.get();
          bool occupied = (mm > 0 && mm < OCCUPIED_THRESHOLD);
          matterOccupancy.set_occupancy(occupied);
          Serial.print("  | Distance: "); Serial.print(mm);
          Serial.print(" mm | Occupancy: ");
          Serial.print(occupied ? "OCCUPIED" : "Clear");
        }
    
        Serial.print("  | Relay: ");
        Serial.println(relayState ? "ON" : "OFF");
      }
    }

Arduino Matter Discovery Bundle: working Home Assistant setup with lessons learned