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Homie Convention - v1.5.0
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@timpur timpur released this 24 Jan 00:45
v1.5.0
5c84069

Homie logo Homie

Homie is a lightweight MQTT convention for the IoT.

You can find an implementation of the Homie convention:

Background

An instance of a physical piece of hardware (an Arduino, an ESP8266...) is called a device. A device has device properties, like the current local IP, the Wi-Fi signal, etc. A device can expose multiple nodes. For example, a weather device might expose a temperature node and an humidity node. A node can have multiple node properties. The temperature node might for example expose a temperature property containing the actual temperature, and an unit property. Properties can be settable. For example, you don't want your temperature property to be settable in case of a temperature sensor: this depends on the environment and it would not make sense to change it. However, you will want the temperature property to be settable in case of a thermostat.

Convention

Homie devices communicate through MQTT.

To efficiently parse messages, Homie defines a few rules related to topic names. The base topic you will see in the following lines will be devices/. You can customize this base topic if it fits better to your needs.

  • devices / device ID: this is the base topic name. Each device must have a unique device ID. This ID MAY be composed of lowercase letters from a to z, numbers from 0 to 9, and it MAY contain -, but MUST NOT start or end with a -.

Device properties

  • devices / device ID / $ device property: a property starting with a $ at the third level of the path is related to the device. The property MUST be one of these:
Property Direction Description Retained
$online Device → Controller true when the device is online, false when the device is offline (through LWT) Yes
$name Device → Controller Friendly name of the device Yes
$localip Device → Controller IP of the device on the local network Yes
$uptime Device → Controller Time elapsed in seconds since the boot of the device Yes
$signal Device → Controller Integer representing the Wi-Fi signal quality in percentage if applicable Yes
$fwname Device → Controller Name of the firmware running on the device. This name MAY be composed of lowercase letters from a to z, numbers from 0 to 9, and it MAY contain -, but MUST NOT start or end with a - Yes
$fwversion Device → Controller Version of the firmware running on the device Yes
$nodes Device → Controller Nodes the device has, with format id:type separated by a , if there are multiple nodes Yes
$ota Controller → Device Latest OTA version available for the device Yes or No, depending of your implementation
$ota/+ Controller → Device or Device → Controller You can use any subtopics of `$ota` for anything related to your specific OTA implementation. Yes or No, depending of your implementation
$reset Controller → Device true when the controller wants the device to reset its configuration. false otherwise. When the device receives a true, it should replace the retained message with a false before resetting Yes

For example, a device with an ID of 686f6d6965 with a temperature and an humidity sensor would send:

devices/686f6d6965/$online → true
devices/686f6d6965/$name → Bedroom temperature sensor
devices/686f6d6965/$localip → 192.168.0.10
devices/686f6d6965/$signal → 72
devices/686f6d6965/$fwname → 1.0.0
devices/686f6d6965/$fwversion → 1.0.0
devices/686f6d6965/$nodes → temperature:temperature,humidity:humidity

And it would receive:

devices/686f6d6965/$ota ← 1.0.1
devices/686f6d6965/$reset ← false

At this point, your device would understand there is an OTA update available, as $ota is different from $version.

Node properties

  • devices / device ID / node ID / property: node ID is the ID of the node, as defined in the $nodes device property. property is the property of the node that is getting updated.

For example, our 686f6d6965 above would send:

devices/686f6d6965/temperature/temperature → 12.07
devices/686f6d6965/humidity/humidity → 79
  • devices / device ID / node ID / property / set: the device can subscribe to this topic if the property is settable from the controller, in case of actuators.

Homie is state-based. You don't tell your smarlight to turn on, but you tell it to put it's on state to true. This especially fits well with MQTT, because of retained message.

For example, an homielight device exposing a light node would subscribe to devices/homielight/light/on/set and it would receive:

devices/homielight/light/on/set ← true

The device would then turn on the light, and update its on state. This provides pessimistic feedback, which is important for home automation.

devices/homielight/light/on → true

Any other topic is not part of the Homie convention.

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