Kedsum temperature/humidity

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One of my neighbors uses a device which sends out a 433Mhz message eacht 5 minutes. I detected the signal with homehuino, however the device was not supported. My guess was that it was a weather sensor, which other devices would send data with such frequent interval?

So last night I was playing with rtl_433, see other topic, and this device was recognized by the software. Indeed it was a weather sensor, actually two devices matched the protocol, but since one of the devices gave a wrong humidity value I could rule out that one.

The device detected is a Kedsum temperature and humidity sensor, or a device which uses the same protocol/rebranded device.

As I don’t know which of my neighbors owns the device I can’t validate the exact make and model. However as I don’t own an outdoor temperature/humidity sensor I thought it would be interesting to implement this device in Pimatic and use it for my own benefits.

I used the rtl_433 source code for the device as a reference to implement the protocol in homeduino, and now I have the outside temperature and humidity available in pimatic.

One question I have though. In which format does pimatic expect the temperature to be delivered? The device has the temperature in Fahrenheit encoded in the signal, however some other temperature devices show the temperature in Celsius. I can’t remember I ever configured a temperature scale.

you can specify the unit for each device seperate. So you can set this device to °F and others (like CPU-temp) to °C. For pimatic they are all only numbers with units.You can also create a variable device and calculate °C from your °F readings if you want to.

Yes, of course to Pimatic it’s just numbers, but not to the user. I think it can be very confusing if some values are in Celsius and others in Fahrenheit. On top of that, in my case the interface adds °C to the temperature value, even if the device returned a value in Kelvin.

What I would propose is to have some global setting to set the preferred temperature scale. Then the device also should have a property which gives back the used temperature scale. And somewhere in Pimatic an automatic translation between scales can be done so the user always gets back the temperature in it’s preferred scale.

When I look at lib/devices.coffee I find a class TemperatureSensor:

  ###
  TemperatureSensor
  ------
  ###
  class TemperatureSensor extends Sensor
    _temperature: undefined

    attributes:
      temperature:
        description: "The measured temperature"
        type: t.number
        unit: '°C'
        acronym: 'T'

    _setTemperature: (value) ->
      @_temperature = value
      @emit 'temperature', value

    getTemperature: -> Promise.resolve(@_temperature)

    template: "temperature"

As you can see there the Celsius temperature scale is hard coded.

Is it actually possible to have Kelvin values displayed? I’m living in the Celsius part of the world, but is any Pimatic user actually using Kelvin?

@rrooggiieerr said in Kedsum temperature/humidity:

I’m living in the Celsius part of the world, but is any Pimatic user actually using Kelvin?

I believe Kelvin is not used by ordinary people for air temperature these days. It is mainly used in science and some areas of engineering and it has been established as a unit in other areas such as the characterization of light waves, known as color temperature.

I agree, the the base temperature sensor device should provide a changeable unit definition and as part of the it does not hurt to implement Kelvin, too. We have done this as part of pimatic-openweather, for example. Regarding your conversion like in your “case the interface adds °C to the temperature value, even if the device returned a value in Kelvin”, this is something which needs to be handled by device implementation. It may the case that the pimatic-homeduino does not implement it properly right now.

Regarding your new protocol for Kedsum it’ll be great if you are ready to contribute it. It needs to be implemented in coffeescript, however. See https://github.com/pimatic/rfcontroljs#adding-a-new-protocol. If coffeescript is a problem, I am happy to support you with that.

Sorry, where I said Kelvin I meant Fahrenheit. You see how confusing al those different units are, I rest my case…

When looking at the pimatic-homeduino plugin I find the following:

  class HomeduinoRFTemperature extends env.devices.TemperatureSensor
    constructor: (@config, lastState, @board) ->
      @id = @config.id
      @name = @config.name
      @_temperature = lastState?.temperature?.value
      @_humidity = lastState?.humidity?.value
      @_lowBattery = lastState?.lowBattery?.value
      @_battery = lastState?.battery?.value

      hasTemperature = false
      hasHumidity = false
      hasLowBattery = false # boolean battery indicator
      hasBattery = false # numeric battery indicator
      isFahrenheit = @config.isFahrenheit
      # skipped some code here...

      if hasTemperature
        if isFahrenheit then tempUnit = '°F'
        else tempUnit = '°C'
        @attributes.temperature = {
          description: "the measured temperature"
          type: "number"
          unit: tempUnit
          acronym: 'T'
        }

I think such functionality should be moved to the env.devices.TemperatureSensor