For a while now, I've been working on Air-Quality-Web, a web interface that displays air quality information. While I haven't blogged about it directly before, a number of posts (a, b, c, d) I've made here have been indirectly related.

Since the air quality data has to come from somewhere, I thought I'd blog a little about the wider infrastructure behind the air quality web interface. My web interface is actually just 1 small part of a much wider stack of software that's being developed as a group by Connected Humber.

Said stack is actually quite distributed, so let's start with a diagram:

From left to right:

• As a group we've designed a PCB (mainly thanks to @BNNorman) that acts as the base for sensor nodes themselves - though a number of people have built their own hardware.
• Multiple different pieces of software run on top of the various pieces of hardware we've developed - some people use ESP Easy, and others use custom firmware they've implemented themselves.
• Embedded devices send the data over WiFi to our MQTT broker (LoRaWAN via The Things Network is currently under development), which currently runs in a Debian Virtual Machine rented from a cloud infrastructure provider.
• Another Debian VM hosts a database loading script, which listens for MQTT messages sent to the broker. It adds the data contained within into a database, which runs on the same box.
• A final box hosts the web server, which simultaneously hosts the PHP-based HTTP API and the client-side web interface. Both of these are currently located in this repository, but later down the line I'd like to figure out how to decouple them into their own separate repositories.

We can represent the flow of data here in a flowchart, to get a better idea as to how it all fits together:

As you can see, there are many areas of the project that can be worked on independently of each other - depending on what people feel most comfortable working on. Personally, I stick mainly to the HTTP API and the main web interface with a hand in advising on database design, but there are lots of other ways to get involved if you so choose!

Sensors always need building, designing, and programming, and the data generated is available via the public HTTP API (the docs for which can be found here) - so anyone can write their own application on top of the data collected by our sensors. Want a light on your desk (or even your hat) that changes colour depending on your local air quality? Go ahead!

Found this interesting? Comment below!