How to use homie convention in openhab for auto discovery

I hope you have a basic idea about openhab installation and initial configuration so here i would like to explain my understanding about how to enable auto-discovery in openhab using homie convention

Requirements

Basic knowledge about :

What is homie convention?

Homie convention is nothing but a standardized format for communicating with MQTT broker. we know that MQTT is a messaging protocol in which each device in the network is is connected to the broker and communicates (message) through a particular channel/topic. Here, the homie convention defines some standard ways to do the same !!

“The Homie convention defines a standardized way of how IoT devices and services announce themselves and their data on the communication channel”

Openhab -Homie convention-Auto discovery

Openhab 2.4 supports homie convention 3.x(+4.x) . so it supports automatic discovery of devices that follow the "Homie convention"

Section 1 : Openhab0

1.Install and configure openhab2.4 in your raspberry pi

2. Install MQTT binding

3. Add your mosquitto* broker /create a mqtt thing*

Section 2 : ESP 32

All we need to do is - just publish mqtt messages from our device (say an esp32).

Note:-

Homies topic layout follows the pattern “homie/device/node/property”.
Retained flag must be true
Nodes in homie convention = channels in openhab

example1:

  homie/DEV_NAME/$homie → 3.0
  homie/DEV_NAME/$name → My device
  homie/DEV_NAME/$state → ready
  homie/DEV_NAME/$extensions → ''
  homie/DEV_NAME/$nodes → my_thermostat
                         ↙↙↙ ↙↙↙
  homie/DEV_NAME/my_thermostat/$name → My thermostat
  homie/DEV_NAME/my_thermostat/$properties → temperature
                                        ↙↙↙↙↙↙
  homie/DEV_NAME/my_thermostat/temperature → 22 
  homie/DEV_NAME/my_thermostat/temperature/$name → Temperature
  homie/DEV_NAME/my_thermostat/temperature/$unit → °C
  homie/DEV_NAME/my_thermostat/temperature/$datatype → integer

DEV_NAME 

It will be shown as thin line text when the device popup - on openhab inbox

eg: my home 


• homie/"DEV_NAME"/$homie : homie version (0.3/0.4)


• homie/"DEV_NAME"/$name :name of the module - Name that popup in inbox as bold letters

eg: my device


• homie/"DEV_NAME"/$state : Current state of the device 

Options :init,ready,disconnected,sleeping,lost,alert

eg:ready


• homie/"DEV_NAME"/$extensions : “ ” (future use case)

 just use " " for now 


• homie/"DEV_NAME"/$nodes : One or more nodes (light ,fan, dimmer..)

eg:homie/DEV_NAME/$nodes → my_thermostat

So here we are completed our device description,now we have a thing (my device) in openhab with one node/channel(my_thermostat)

Defining characteristics of each channel/node

• homie/"DEV_NAME"/node/$name :Node name (light12)

Just give any name (it is not necessary to use the same name that we were used in $nodes section) but in topic, the “/node/ “ must be replaced with the one we are defined in $nodes

`eg: homie/DEV_NAME/my_thermostat/$name → My thermostat`

• homie/"DEV_NAME"/node/$properties :Defining properties of the node temperature,switch or any name as you wish

`homie/DEV_NAME/my_thermostat/$properties →` `temperature`

• homie/"DEV_NAME"/node/property of node/$name : Any name is fine- It will be the channel name in openhab.
Just give any name (it is not necessary to use the same name that we were used in $properties section) but in topic, the “/property of node / “ must be replaced with the one we are defined in $properties

`homie/DEV_NAME/my_thermostat/temperature/$name → Temperature`

`So we have defined the device and its nodes now its the time to define its properties`

• homie/"DEV_NAME"/node/property of node/$settable :This topic defines 
whether the channel is editable or not , options: true /false

nb:true in our case,other wise we can’t edit the channel.



• homie/"DEV_NAME"/node /property of node/$unit :unit ,options: %,C,f

use % in case of dimmer C in temperature sensor , we can also  just

use “ “ as unit , “ ”  is also a valid unit



• homie/"DEV_NAME"/node /property of node/$datatype : datatype

options:

integer, float, boolean, string, enum, color


For RGB light and dimmer use color as data type and boolean for switch

• homie/"DEV_NAME"/node /property of node/$format :

 (use ‘0:100‘ for dimmer and

‘hsv/rgb ‘ for RGB/Hue light )

 --> normal switch doesn't require this topic👆

 This will create a thing in openhab with one channel (name : temperature)

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