I'm looking to deploy several copies of the Enviro hat around my garden to monitor temperature and light levels to study the optimal spots to plant new plants. How might I weatherproof the Pis without obscuring the sensors?
You've probably searched for a cover (as I just did), and didn't find anything that you could buy. That being the case, you must shift into "DIY Mode", and come up with your own solution. Before going any further, I should say that as you've not identified the "Enviro hat" hardware specifically, I will assume it's this device.
You might start by asking yourself this question: Does the RPi and the "Enviro hat" need protection from the weather? Based on limited anecdotal evidence: 1., and 2. I would venture a guess that exposure to rain is to be avoided! But, if you live in an arid climate, no chance of rain on days you wish to deploy, then maybe no protection is needed. This is something you'll have to decide for yourself.
Given that you will need rain protection, the Enviro pHat sensory functions will guide your design of the rain protector. The Enviro pHat provides the following sensory functions:
- light level,
- 3-axis motion,
- compass heading
Since you didn't specify, I will guess that temperature and light level are the only relevant functions for a garden application. If that's the case, then your rain protector must minimize its influence on those readings; i.e. it must pass light (be transparent), and it should not "trap" heat and humidity. A glass bowl might do the job (like this one from Ikea). You will place this bowl on the ground, and then drive 3 or 4 small wooden stakes in the ground such that when the glass bowl is turned upside down, it is held off the ground by the wooden stakes.
Now you have a ventilated, translucent shelter for your RPi and Enviro pHat. If you don't wish for them to lie on the ground, you could fashion a mesh sling to the bowl, and let the hardware rest in that lovely hammock.
I make enclosures mostly using snap-tight tupperware (the kind with snaps and a rubber seal) and epoxy. Although only one of them has been used in a permanent spot outdoors, it's a very adaptable approach and requires fairly minimal effort and expense,1 meaning it is easy to experiment -- if you aren't certain about your design, put some cardboard inside and leave it deployed for a while until you are satisfied it is going to keep what's inside dry. I do have a few I've left outside e.g., mostly buried in snow, for a few hours or days, and I'm pretty confident I could leave them indefinitely.
The tupperware needs some modification, of course, mostly to allow for power input. I used to use a drill, hacksaw blade, and metal files for this, until Steve Robillard (thanks Steve!) introduced me to the Dremel, aka. rotary tool. You can buy a small handheld generic (Dremel is a brand name) rotary tool online for < $50 that may or may not be great for working some material, but it handles plastic just fine. This increased my enclosure making productivity probably a 1000%.
Also potentially handy in this is duct tape. A few further thoughts:
As Ghanima hints, you probably don't want the unit completely sealed. My approach here would be to use a small tub inside a larger one with the small one secured under the top of the outer one and some ventilation holes in the bottom and then in the sides of the outer enclosure.
Measuring temperature is usually done in the shade as an enclosure exposed to direct sunlight will not provide accurate readings. This does not mean total darkness, of course, and I think no matter where you put it (including in direct sunlight), you are going to have to gauge through observation what a unit's light level readings imply about actual conditions.
- "Dollar stores" that sell both cheap epoxy and an extensive array of cheap tupperware are common where I live. I doubt any of the things I've made cost more than $5.
The Zip bag made think, so many thanks @sa_leinad. I need the Pi to be exposed to the environment and not sealed so its sensors for temperature and light and not interfered with. I then recalled you can get spray for waterproofing walking gear etc, and surprise surprise similar is available for electronics as a conformal coating which can brushed on or sprayed on. It leaves a very thin layer 25-250 μm (micrometers) thick, and together with being transparent it should not interfere with the sensors.