homieiot/convention

Homie

An MQTT Convention for IoT/M2M

Overview

Feature TCP MQTT Homie
Stream based communication
Message based communication
Publish/Subscribe
Defined topic structure
Self–describing topics
Multiple Payload types

MQTT supports easy and unrestricted message-based communication.

However, MQTT doesn’t define the structure and content of these messages and their relation. An IoT device publishes data and provides interaction possibilities but a controlling entity will need to be specifically configured to be able to interface with the device.

The Homie convention defines a standardized way of how IoT devices and services announce themselves and their data on the MQTT broker.

It is thereby a crucial aspect on top of the MQTT protocol for automatic discovery, configuration and usage of devices and services.

Example

Homies topic layout follows the pattern “homie/device/node/property”.

In this example our device has a thermostat functionality where the target temperature can be read from and written to. The thermostat function is modelled as node, the temperature is a property of that node.

The following topics are published as retained messages to the broker:

  homie / device123 / $homie → 3.0
  homie / device123 / $name → My device
  homie / device123 / $state → ready
  homie / device123 / $extensions → ''
  homie / device123 / $nodes → my_thermostat

  homie / device123 / my_thermostat / $name → My thermostat
  homie / device123 / my_thermostat / $properties → temperature

  homie / device123 / my_thermostat / temperature → 22 
  homie / device123 / my_thermostat / temperature / $name → Temperature
  homie / device123 / my_thermostat / temperature / $unit → °C
  homie / device123 / my_thermostat / temperature / $datatype → integer

Any Homie compliant controller can now find “My device” and will find out about “My thermostat” with “Temperature in °C” and that it needs to publish to “…/temperature/set” to change the temperature.

If we got your attention, head over to the specification and let all your questions being answered.