[hornychz]

Hi Werk_AG,
thank you for your reply.

First of all, are you testing your sensor in horizontal position?

Yes, of course, my UV sensor is in horizontal position, but now not yet in any case ...

I only see one drawback: The results are always integer numbers. I know that UV index is defined as a scale of integer numbers, but personally I like have them with one decimal place (it's better for the graphs too).

You are right, your UV Index curve looks much better then me ...

---

I would also like one another addendum:

Said that, yes, the used formula includes some correction.
Not taking in account the nonlinearity of the readings between UV index 0 and UV Index 1 (less significant part of the readings) , theoretically the formula should be: IndiceUV = ((ADC1 * 12.0) / 1023.0)

Each one may need to slightly adjust this formula according to characteristics of the material (thickness, UV transmission, etc) used to cover the sensor (it must be covered by something with good UV transmission, to protect it from natural elements).
Each person can build the Solar Radiation / UV sensor in a different manner with different materials, because of this, some final software / hardware adjustments always be required.
Nearby weather stations and Wunderground are of great help at this stage.

I think, this theoretic formula isn't correct too. Not just the non-linearity in the begining of the curve - the curve doesn't passes through the origin of the coordinate system! I think you have to add a constant to correct this problem. For example - appropriate voltages - in the first column are by datasheet, in the second by your formula IndiceUV = ADC1 * 12.0/1024.0 and in the third new approximated curve:

The resulting curves to compare:

The new formula is:

IndiceUV = (((ADC1-135) * 11.0) / 1024.0)

This formula doesn't include impact of cover, i.e everyone must verify own cover impact, if the cover is used.