• MQTT is open, simple and low overhead communication protocol for sending messages between many clients which are connected to the central MQTT broker.
  • Every message contains two parts - topic and payload.
  • Topic describes content of the message.
  • Topic name contains "directory" structure - each level is divided with symbol /.
  • Topic can be bedroom/temperature or kitchen/light/set.
  • MQTT server is called the broker and clients can publish messages and subscribe to different topics.
  • The task of MQTT broker is to deliver messages from publishers to the subscribers.
  • You can use the + symbol to subscribe to all topics in the current topic (+/light/set) and # symbol to subscribe to all sub-topics (kitchen/#).

More information about MQTT topics

Mosquitto MQTT broker

BigClown is using open-source Mosquitto MQTT broker. All messages are routed through MQTT broker. This allows further expansion of BigClown system.

When you connect the Core Module or USB Dongle with connected remote node, you can display all incoming messages using mosquitto-cli package by typing:

pi@hub:~ $ mosquitto_sub -t "#" -v
node/836d19821664/thermometer/0:1/temperature 24.69
node/836d19821664/thermometer/0:1/temperature 24.94
node/836d19821664/push-button/-/event-count 5

GUI tool for MQTT messages

For debugging the communication you can use graphical tool Eclipse Paho mqtt-spy.

After installation you have to set IP adress of the MQTT broker. For example hub.local or IP adress of your Raspberry Pi

MQTT Spy tool