Decoding JSON format from MQTT

Configuration
1

I want to build a ESP32 based device that measures flow and pressure of some sprinklers so I can calibrate a fertilizer injector. I am quite stumped decoding the JSON despite being able to do it in the template editor.
This is the JSON I settled on.

{
    "sprinkler": [
        {
            "id": "1",
            "flow": "13.6",
            "pressure": "280"
        },
        {
            "id": "2",
            "flow": "15.8",
            "pressure": "260"
        }
    ]
}

And this is what I did in the template ediitor:

{% set my_sprinklers ={
    "sprinklers":[ 
      { "id": "1", "flow": "13.6", "pressure": "280" }, 
      { "id": "2", "flow": "15.8", "pressure": "260" } 
    ] 
  } %}

sprinkler 1 = {{ my_sprinklers.sprinklers[0] }}
sprinkler 2 = {{ my_sprinklers.sprinklers[1] }}
sprinkler 1 id = {{ my_sprinklers.sprinklers[0].id }}
sprinkler 1 flow = {{ my_sprinklers.sprinklers[0].flow }} l/min
sprinkler 1 pressure = {{ my_sprinklers.sprinklers[0].pressure}} kPa

sprinkler 2 id = {{ my_sprinklers.sprinklers[1].id }}
sprinkler 2 flow = {{ my_sprinklers.sprinklers[1].flow }} l/min
sprinkler 2 pressure = {{ my_sprinklers.sprinklers[1].pressure}} kPa

I just don’t understand you to set these to values in home assistant. Any help or guidance would be appreciated. I can reformat the JSON packet as this is going to be built from scratch if there is an easier format to decode.

2

See:

e.g. in configuration.yaml

mqtt:
  sensor:
    - name: "Sprinkler 1 Flow"
      state_topic: "your/topic/here"
      value_template: "{{ my_sprinklers.sprinklers[0].flow }}"
      unit_of_measurement: L/min
      icon: mdi:waves-arrow-right

    - name: "Sprinkler 1 Pressure"
      state_topic: "your/topic/here"
      value_template: "{{ my_sprinklers.sprinklers[0].pressure }}"
      device_class: pressure 
      unit_of_measurement: kPa

    - name: "Sprinkler 2 etc...

There’s no device class for flow but there may be in future so best to use the correct unit (capital L for litres and ideally you would send L/s).

You can pick any icon you want from here: Material Design Icons - Icon Library - Pictogrammers some of the newer ones may not be added to HA yet.

3

Thanks for your help. Really helpful. I ended up with this

mqtt:
  sensor:
    - name: "Sprinkler 1 Flow"
      state_topic: "homeassistant/sprinklers"
      value_template: "{{ sprinklers[0].flow }}"
      unit_of_measurement: L/min
      icon: mdi:sprinkler

    - name: "Sprinkler 1 Pressure"
      state_topic: "homeassistant/sprinklers"
      value_template: "{{ sprinklers[0].pressure }}"
      device_class: pressure 
      unit_of_measurement: kPa
      icon: mdi:gauge

Which creates the sensors but does not create any errors but I am getting values of unknown . Do I need to use a value format?

image

4

Oops. I missed replacing an important part of the templates:

mqtt:
  sensor:
    - name: "Sprinkler 1 Flow"
      state_topic: "homeassistant/sprinklers"
      value_template: "{{ value_json.sprinklers[0].flow }}"
      unit_of_measurement: L/min
      icon: mdi:sprinkler

    - name: "Sprinkler 1 Pressure"
      state_topic: "homeassistant/sprinklers"
      value_template: "{{ value_json.sprinklers[0].pressure }}"
      device_class: pressure 
      unit_of_measurement: kPa
      icon: mdi:gauge
5

Got it! but it seems HA does not like the array, I had to change JSON to

{
    "sprinkler1": {
        "flow": 11.11,
        "pressure": 222
    },
    "sprinkler2": {
        "flow": 12.22,
        "pressure": 333
    }
}

Then it worked!

mqtt:
  sensor:
    - name: "Sprinkler 1 Flow"
      state_topic: "homeassistant/sprinklers"
      value_template: "{{ value_json.sprinkler1.flow }}"
      unit_of_measurement: L/min
      icon: mdi:sprinkler

I also tested this with mosquito_pub as working

mosquitto_pub -V mqttv311 -u homeassistant  -P Its_A_Secret -h 192.168.1.29 -p 1883 -m '{"sprinkler1":{"flow":15.11,"pressure":252},"sprinkler2":{"flow":16.66,"pressure":444}}' -t "homeassistant/sprinklers"

Thanks so much for your help.
Now I have HA set up on to some ESP32 code and some plumbing when the sensors turn up.