Note: With the breadboard design, I found that the CO2 concentration in my house was too high at various points throughout the day.  VOC's tended to peak here and there, but not into what I'd generally be concerned about.  When I added the PM2.5 sensor, I was able to correlate things like high-pollen days and air-quality notices, which gave me confidence in the data I was seeing...  Among other reasons, this was primary in helping me decide to do a PCB for the project.  Using the data I collected, I was able to adjust a number of things in our home, which in turn brought the CO2 and VOC levels much more into line with recommended levels.  Take a look here for some details about what I found and how I dealt with it.  If you're curious about my home's current indoor air-quality, this link will show you.  

As I was working on the schematic, I started wondering if maybe this could be used as more of an experimenter platform, allowing me to test out various sensors and do some code to support them both locally and in the cloud.  At that point, I decided to design the circuit/PCB in that direction.

I wanted to make it easy to build, easy to program for and flexible about what processor is used.  I also wanted to make sure there was some kind of user-input and some kind of output available in case anyone wanted to have something interactive or just needed to see what the thing is doing.

With those criteria in mind, here is a summary of the result:

I mainly used the Arduino environment for the code part.  That's certainly not required and many of the Feather modules that are available can run MicroPython or CircuitPython.  As I also mentioned, I use Adafruit.io to provide IoT cloud connectivity.  They have a great product and for what many people need, the free tier is more than sufficient.  I've tried out a variety of other offerings and for my taste and pocketbook, Adafruit is a winner.

Note: f you want to see the air-quality in my home, look here.  If you don't have an Adafruit.io account, the data won't update on its own, so you'll need to refresh the page if you want to see changes. (This is running on an Adafruit Feather Huzzah, 8266)

The schematic and printed circuit board were designed with KiCad and I used PCBWay to prototype the boards.  I've used them for a few years now and they're great.  They produce high-quality PCB's and they do it quickly, for a great price.

I made a very specific choice in naming this the "Sensor Playground".  I wanted it to be an easy, fun place to try out sensors, software, the IoT and more.  If you choose to use it for air-quality monitoring, great!  If you decide to use it for something different...great!  I'd love to hear how you end up using it.

The project files are hosted on GitHub.  Here you'll find schematics, PCB files, source code, documentation, etc.

This is an ongoing project, with new data, docs, files, etc. being added as it becomes available.