OH3: Generic MQTT thing - Channel Item Dimmer

Setup, Configuration and Use Beginners
1

Hello
a dimmer Item with min / max value 0 / 100 publishes values from 0 to 100…thats ok.
If min max values are different from 0 / 100 it looks like this:

Min - Max      Publish

0 - 90         0 - 81
0 - 80         0 - 64
0 - 20         0 - 4
0 - 10         0 - 1

10 - 100       19 - 100
20 - 100       36 - 100
30 - 100       51 - 100
50 - 100       75 - 100
80 - 100       96 - 100
90 - 100       99 - 100

  - id: MQTT_prozent
    channelTypeUID: mqtt:dimmer
    label: MQTT_prozent
    description: ""
    configuration:
      commandTopic: go-eCharger/000000/cmd/req
      min: 10
      formatBeforePublish: "%s"
      max: 100

I this a bug a feature or do i undestand something wrong ?

2

The Min - Max controls how the 0-100 that is stored by the Dimmer Item are translated to the range you defined. So let’s take your 0-10 example. That means I would expect the Dimmer’s values between 0-9 to be 0, values between 10-19 to be 1 and so on.

So yes, if you set the min and max to be 0-10, and you only changed the Dimmer Item to be a value between 0 and 10 you would only see 0 until you get to 10 where it becomes 1.

The Dimmer Item will always store a value between 0 and 100. What happens is that 0-100 gets translated to a number between the defined min and max before being sent. You are not constraining the values that the Dimmer Item can hold. You are defining a formula that is use to transform the Dimmer’s value to be within the range expected by the device.

publish = (((Max - Min) / 100) * DimmerItemValue) + Min
3

Don’t think you want that, it just might be interfering with scaling.

4

“…formatBeforePublish: "%s"....Don’t think you want that, it just might be interfering with scaling.”

Thats not a problem, the device also needs a prefix which works.
The device undestand the command but how to send the right values (eg 6, 7,8…14, 15,16) thats my problem.

  - id: MQTT_prozent
    channelTypeUID: mqtt:dimmer
    label: MQTT_prozent
    description: ""
    configuration:
      commandTopic: go-eCharger/021683/cmd/req
      min: 6
      formatBeforePublish: amp=%.0f
      max: 16
5

Oh right, secret settings. That makes it hard to help.

I think you might need a custom transform to do both scaling and prefix. It’s not at all clear in what order the binding will apply what you have now.

6

This is starting to look like an XY Problem. What are you controlling that only accepts values between 6 and 16?

As I tried to explain, those values will not change how the Dimmer Item behaves. It will always store a value between 0 and 100. Setting the min and max on the channel is not going to restrict the Item to only be between 6 and 16. What it will do is do the math (see above) to convert from those 100 values to a value between 6 and 16.

You probably want a String Item or a Number Item and using a selection on the sitemap or something like that.

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