For field-testing purposes, I hacked together some plywood “backpacks”. Each has a small lip that hangs over a laptop screen, and with a few pieces of tape or velcro, it secures nicely to the back without much trouble. Duct tape over the surface helps velcro tabs adhere, so you can velcro on a GPS logger. And you can still screw components into the 1/4″ plywood. Makes it easy to rig up a laptop for a morning’s worth of sensing.
In the process I’ve learned at least two things that could help you getter better data out of your PPD42NS:
Tip #1: The Shinyei PPD42NS has a correct orientation (expressed as “UP” on page 2 of the spec sheet). There’s a resistor at the bottom to generate a thermal updraft to move air through the sensing chamber. In the build above, I drilled three round holes into a Radio Shack enclosure, such that they line up with the exhaust port on the basic Shinyei assembly. I cut out an elongated opening near the bottom to line up with the intake port, and Dremeled out most of the enclosure to make room (hence the two absent screws). In most air sampling devices the movement of air happens through the use of a fan or pump, but this is an elegant and quiet solution. It’s not power-efficient, and it’ll be interesting to see if there’s a better way to accomplish the same goal …
Tip #2: cover the large opening to the sensing chamber. There’s also a note buried in the Shinyei docs that says to do so. Why isn’t it sealed? So the lens can be cleaned after extended use. I settled for taping a piece of stiff paper over the triangular opening (you can see this in the gallery pics below). Seems like this probably changes both the ambient light that reaches the sensor, and the airflow pattern induced by the heating element. H/T to Ajay Pillarisetti.
If you have a tip to share, please leave it in the comments!