Part 3: Making M5Stick Talk MQTT

Now we need to upgrade our M5Stick from just showing a blue screen to actually listening for MQTT commands and responding to them. Transforming our simple blue screen into a device that:

• Connects to WiFi
• Subscribes to MQTT topic robotinc/device/command
• Changes screen colour based on received commands
• Publishes confirmation messages back

MQTT Broker: test.mosquitto.org

We’re using test.mosquitto.org - a free public MQTT broker provided by the Eclipse Foundation. Think of it as the “hello world” of MQTT:

• Free: No signup, no configuration needed
• Public: Anyone can use it (not secure, but perfect for testing)
• Reliable: Been running for years, used by thousands of IoT developers
• Simple: Just point your device at it and start sending messages

It’s like a village notice board - you can post messages and read what others have posted. Perfect for learning MQTT basics before moving to production.

M5Stick Code

The complete code is nothing ground breaking, it’s available here: devices/m5stick/mqtt_color_control.ino

Key configuration you’ll need to update:

// WiFi credentials
const char* ssid = "YOUR_WIFI_NAME";
const char* password = "YOUR_WIFI_PASSWORD";

// MQTT settings - using public broker for simplicity
const char* mqtt_server = "test.mosquitto.org";
const char* device_id = "robotinc-m5stick-001";
const char* command_topic = "robotinc/device/command";
const char* status_topic = "robotinc/device/status";

Required Libraries

Install these in Arduino IDE:

1. PubSubClient (for MQTT)
2. ArduinoJson (for parsing commands)

Testing

Upload the code and test with any MQTT client or online tool:

To send commands:

• Topic: robotinc/device/command
• Message: {"action":"color","value":"blue"}

To see responses:

• Subscribe to: robotinc/device/status
• You’ll see: {"status":"Device screen set to blue"}

  if (color == "blue") colorCode = TFT_BLUE;
  else if (color == "red") colorCode = TFT_RED;
  else if (color == "green") colorCode = TFT_GREEN;
  else if (color == "yellow") colorCode = TFT_YELLOW;

Next Steps

Now that basic MQTT works with a public broker, we need to move to production-grade infrastructure with AWS IoT Core and proper security.

Lessons Learned

• You have so many libraries available in public libraries to inspire your projects
• AWS IOT core does have its own MQTT client, but this requires secure connections
• Spending time on colour vs colour isn’t time well spent

Part 4: Moving to AWS IoT Core with Certificates →