not a bug, but calibration on SI1145

[gnkarn]

Describe the bug

UV index calculation is offset by 0.23 points

tested on node mcu 1.0 ,

STATUS 0 OUTPUT HERE

To Reproduce
using SY1145 , wait until sun down , and the remaining uv indication is still non zero .

Expected behavior
indicate zero , on total darkness when sun is down .
Screenshots

Additional context
i will check the IR, and visible tomorrow .
(Please, remember to close the issue when the problem has been addressed)

[ascillato]

Hi,

Interesting. It should be zero? See this link

[ascillato]

Also see this https://www.allaboutcircuits.com/projects/how-to-perform-uv-monitoring-with-the-adafruit-si1145/

[ascillato]

Hi, @gnkarn

Any news about this?

[gnkarn]

?? Don’t know what you mean.
There is a problem with the values reported by the library , it is probably not a big deal as if it. Is only an offset it can be solved on the user side just by compensating with a substraction .

My intention was just a watch out .

I willl also report the visible and ir values, but it has been totally cloudy these days , so no new data so far .

[ascillato]

Hi,

I was just asking if the value of 0.23 UV Index by night need to be zero or not. In the first link, they said that by night you will have few UV due to reflection from the atmosphere, so a little UV measurement could be ok ? I'm asking.
The second link shows a display and a UV Index sensor, and it is showing 0.02 Index inside a house.

So, that is my question. 0.23 UV Index by night is not Ok ? I don't know, that's why I'm asking you.

[gnkarn]

understand , not sure about that will need more research, but my guess is that with the sensor totally covered , the reading should be zero .

on the other hand , the visible and ir light sensors are working fine , but i have no way to verify the absolute readings ( calibration)

this chart shows , the visible light evolution during the whole day against solar angle, during sunrise, and sunset , so both lines represent this difference .

[ascillato]

Hi,

Thanks for the info. Nice graphs.

About the calibration. Up to now Tasmota does not have any calibration routine for general sensors.

Mainly, the calibration is meant to be done in your home automation system, but if you need to do some value adaptation, you can use the code of the PR #2955, that adds to Tasmota Arithmetic Commands for rules.

In that case, you should read the value of the sensor on the teleperiod, scale it, and publish to mqtt. (I don't have the sensor to test, but you should check the Sensor JSON message sent on teleperiod, so as to correct the following example)

Using that PR, a example can be:

rule 1
rule on tele-SI1145#uvindex do backlog scale1 %value%,0.23,10,0,10; publish stat/sonoff/UV_cal %var1% endon

Hope this helps.

[ascillato]

Hi. Any news on this? Or we just close this issue? Thanks.

[gnkarn]

You can close it , I’m not able to compare the values against a “calibrated source”, as said in my opinion the values have an offset , that can be removed on the user side , probably is something that could be mentioned on the docs. Thanks