I can not find "3446 5C" Not 100% sure what they used, but that type of Photo diode/Photo transistor is not cheap.
I still think being the design is several years old, there is a cheaper way to arrive at the same result.
My fear with these cheap sensors are that they might be very imprecise bacause they have a very small surface. With low angles at sunrise/sunset this could be a larger problem. The larger the surface the more precise the measurement can be potentially.
I had started a thread at: http://www.wxforum.net/index.php?topic=24761.new#new but think I will ask admin to close it and keep this one going.
This thread is about the
Davis sensor. Ask them to merge
your second with your first on the DIY subject, not this one.
In a nut shell, the sensor needs to be able to detect UV light in the 280-360 nm spectrum. It needs to out put at 150MV per UV index. The local NWS station is about an hour drive from me but does have a UV sensor on site I could use to compare to.
The dust cap on top can be just about anything as long as it does not BLOCK out UV as some glass will. Please let me know what I can do to help myself or anyone else come up with a working design.
Well, there're mainly 3 important bands for UV: A, B and C. B is the most important for humans, AFAIK. You might want to focus on that and choose an appropriate sensor. OTOH, besides spectral measurements, the cosine response is also important, and that's where diffusors come into the picture. So of you take it a little seriously, then the cover is actually pretty important. If you just want something that gives an estimate of the UVB index, then you don't need to care about these, probably.