Does a JS profile transformation inherit units?

[Max77 (Max)]

Hi all

I am adding my homemade air sensors into OH3 (stable release). The battery voltage is an item linked to an mqtt channel with Voltage property - it seems to work properly as the “V” unit is added.

I use a JS transformation to get the battery level

(function(voltage) {
var batt_level = (voltage - 3.5)/0.7;
return batt_level;
})(input)

and I define a dimensionless item

Question - why does the value still have the “V” unit as the parallel item linked to the same channel?

I cannot use use the %% label formatter, of course (it returns 1%).

Any explanation for this behavior?

Thanks
Max

[rossko57]

I think you have a variation of this problem

OH 3 Scale profile exception while formatting value

I don’t think it makes any difference how you create your target String type Item. Your problem does look the same as @Cybso , although you’ve not shown us the crucial part - the profile you selected for your channel link. @Cybso did not find a fix for this problem,but a circumvention (doing the transformation elsewhere) The nature of the problem appears to be that the transform profile framework attempts to use a binding supplied default state presentation format on the output of a transfo…

The OH framework is applying the default channel formatting suggested by the binding to the output of your transform profile, in this case adding " V".
It’s not yet clear if/how they’ll fix this bug.

You should be able to circumvent by removing the units from the channel, and have MQTT deal with number only.

[Max77 (Max)]

@rossko57

thanks - I will try it and post the results here.

Has the issue (bug?) already filed?

Max

[rossko57]

@Max77

Has the issue (bug?) already filed?

Yes, as referenced in the other thread that you read

Switch item with linked channel and hysteresis profile leads to error on the item

[Max77 (Max)]

Almost there!

I have now reprogrammed my (ESP-based) sensor by deleting the battery voltage unit in the source code.

I also had to clean mosquitto DB according to this tutorial

In mosquitto, I read

openhabian@openhabHost:~ $ mosquitto_sub  -v   -t homie/esp_gateway/kidsBedroomTH/battery/#
homie/esp_gateway/kidsBedroomTH/battery/$name Battery
homie/esp_gateway/kidsBedroomTH/battery/$datatype float
homie/esp_gateway/kidsBedroomTH/battery 4.08

I am now able to link this channel to the existing equipment and getting voltage (w/o unit) and battery level (in %) right.

Thanks!
Max