Modbus: Writing values / Climate control with value conversion

Configuration
1

Hi there,

I’m trying to control my water heat-pump and the temperature values require some conversion to become celcius. Like so:

Celcius = (value - 30) / 2

It looks like it’s Fahrenheit but it’s actually not so I cannot use the built-in C → F / F → C conversion.

For reading the registers i’ve already made a template function like so:\

- sensor:
  - name: water_heatpump_current_temperature_celcius
    state: "{{ (((states('sensor.water_heatpump_current_temperature') | int)-30) / 2)|round(0) }}"
    unit_of_measurement: "°C"
    device_class: temperature
    state_class: measurement
  - name: water_heatpump_target_temperature_celcius
    state: "{{ (((states('sensor.water_heatpump_target_temperature') | int)-30) / 2)|round(0) }}"
    unit_of_measurement: "°C"
    device_class: temperature
    state_class: measurement

I prefer to use a climates sensor to achieve this because of the UI but if that doesn’t work i’d like to know how to just go about writing converted values.

Thanks

2

You did not need to do that. The modbus sensor supports options you can use in the sensor definition to do the conversion.

Screenshot 2024-05-03 at 10-32-15 Modbus

So in your case just add this to your modbus sensor:

offset: -15
scale: 0.5

For writing, say you want to send the value 30

action:
  - service: modbus.write_register
    data_template:
      address: # supply this
      unit: # supply this
      hub: # supply this
      value: >
        {% set value = 30 %}
        {{ (2 * value + 30)|round(0)|int(0) }}

If you wanted to send the value of an input number or sensor:

      value: >
        {% set value = states('input_number.foobar')|float(0) %}
        {{ (2 * value + 30)|round(0)|int(0) }}

      value: >
        {% set value = states('sensor.foobar')|float(0) %}
        {{ (2 * value + 30)|round(0)|int(0) }}
3

@tom_l Thanks Tom! I missed those inline conversions! Would this also work for the climates component?

4

It has the same options: Modbus - Home Assistant It appears to be a global setting for the climate entity though.

5

@tom_l Thanks again, i got it working!

image
image1064×1568 62.6 KB

6

hey @tom_l sorry to hijack this again, but you might have an idea on this. After I added the climate component which reads the current temperature from address 113 it seems the original sensor current_temperature is showing as Unavailable.

sensors:
    - name: water_heatpump_current_temperature
      unique_id: f8c8a1a9-ef93-4764-a744-2aeeaa4ee2ca
      scan_interval: 30
      address: 113
      slave: 1
      offset: -15
      scale: 0.5
climates:
    - name: "water_heatpump_climate"
      address: 113
      slave: 1
      input_type: holding
      max_temp: 70
      min_temp: 30
      precision: 1
      target_temp_register: 2
      temp_step: 1
      temperature_unit: C
      hvac_onoff_register: 0
      write_registers: true
      offset: -15
      scale: 0.5

image
image974×142 11.9 KB

Any idea?

7

Unfortunately no I don’t. I don’t actually use the modbus integration. Perhaps trying to read the same register is causing some sort of conflict?

As an alternative you could create a template sensor from the climate device if you need the current temperature attribute somewhere that does not support attributes directly.

8

Thanks for the hint, using an entity attribute works fine! I didnt know those existed :slight_smile:

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