Solar Radiation Shield

The thermometer/hygrometer need an enclosure to shield them from direct solar radiation that would otherwise skew the results during the daytime.  This shield has to allow for adequate ventilation so that the measurements are representative of the ambient air conditions, but it also needs to keep the sensors dry and protected from the elements.  Most of these shields rely on some wind for ventilation, but some (ASOS sites especially) use fans to force air across the sensors at a constant rate.  I decided that natural aspiration was good enough for now, and would keep power requirements low.

Typical naturally aspirated shield

Several companies sell products like this, but they are surprisingly expensive for something so simple. Keeping with the DIY nature of the project, I decided to make my own.  I decided that plastic bowls would be the perfect size and I found some relatively cheap at Walmart.  From there, I used a holesaw to cut 1.5" holes in the center of two of the bowls and drilled three holes in the bottoms of each to connect them together.

The two middle bowls

Since the bowls are red, I decided it would be best to paint them white in order to reflect the most sunlight. Initially, I just used generic, cheap spraypaint, but it quickly flaked off of the bowls.  I ended up having to sand them down and use Krylon "Fusion" paint, and now they look fantastic.

To finish it up, I used three threaded rods and some bits of rubber hose to connect the bowls and offset them from one another.  I decided to stick the barometer in this enclosure as well so that I don't need to make a separate one (though I will be making a more robust barometer housing in the future).  I soldered the two sensor breakouts onto a piece of perfboard and glued the entire board into the enclosure.  The sensors use 4 GPIO pins in addition to 3.3v and ground, so I used two separate runs of 4-conductor phone line to connect to the Pi.