Micro-service application that measures air quality together with temperature, pressure and humidity. Composed of three main services:

• tvoc: uses bme680 sensor to extract air parameters data.
  • tvoc-os: extracts data using an open source Python library from Pimoroni. See last section.
  • tvoc-bsec: extracts data using a proprietary C library from Bosch. See last section.
• mydb: saves data into a persistent database (MongoDB).
• web: shows data from mydb into the browser (flask + bootstrap + d3 v5).

The test service is used within the x86 branch for testing purposes. It substitutes the job of tvoc during development for faster iteration. It basically fills the database with fresh values when running the application on a x86 machine.

The master branch has been configured for tvoc-bsec. In order to make it work, the BSEC library needs to be downloaded and unzipped inside the /tvoc-bsec directory. This can be done from the Bosch website.

• BME680 sensor
• Raspberry Pi
• Docker, Docker-compose, Flask, D3, MongoDB, Bootstrap

In order to run the project one needs to:

1. Install docker and docker-compose
2. Run docker-compose up --build

This was my first project with a micro-services architecture and I am quite happy with the results. It allowed me to separate the different problems and tackle them in an easier and more organised way. The flexibility it offers is great too. I was able to easily switch between tvoc and test when changing the environment from the raspberry pi to my computer. On the other hand, docker containerisation is great for portability and dependencies management. Needless to say, docker-compose does a great job managing the different services making the overall work-flow much easier.

Some challenges I ran into:

• Exposing the i2c device to docker-compose network. This device is used by the sensor and needs to be accessible from the docker container.
• The armvl7 architecture and the Raspbian OS made it difficult to use MongoDB on the raspberry pi. Luckily, I found a mongodb image that uses pre-compiled 32bit ARM binaries. That is why I am not using the latest version.

-- To create a backup file of the stored data:

docker-compose exec -T mydb mongodump -u $USR -p $PASS --authenticationDatabase admin --archive --gzip --db air_data > dump.gz

-- To recover a backup file into a db:

docker-compose exec -T db mongorestore --archive --gzip < dump.gz

-- To expose a device to a docker container:

docker run -d --rm --device /dev/i2c-1 --name tvoc tvoc

To interact with the sensor, there is an open-source library from Pimoroni and a proprietary one, from Bosch, which is only available in C.

• Pimoroni
• Bosch

The air quality score calculation can be tricky since there isn't a standardized way to do it. The Pimoroni open-source algorithm uses the divergence of the gas resistance measurement from a chosen baseline. It also accounts in a simple way for the influence of humidity. I was not convinced by this approach since there aren't any clear rules for the baseline computation. If this is wrong, then all the rest would be biased. Further research on this approach is required.

Bosch, on the other hand, claims to have a complex algorithm that combines the four measurements that the BME680 sensor offers (Temperature, Pressure, Humidity and Gas Resistance). I have tested it and it seems robust. Moreover, Bosch appears to be using this same algorithm for their other commercial products. For me, this gave enough credibility to the BSEC library and that is why I decided to opt for it for my personal use.