SeptaSense - Air Quality Sensor

[acoustic scaffold]

I have been working on this ESPHome project for quite some time now. It is an air quality sensor that measures seven different things:

• Temperature (0 - 50°C ± 0.5°C)
• Humidity (0 - 100% ± 4.5%)
• VOC (1 - 500 Index ± 5 Index)
• NOx (1 - 500 Index ± 10 Index)
• Particulate Matter (0 - 1000 μg/m³ ± 10%)
• CO2 (400 - 5000 ppm ± (40 ppm + 5%))
• Pressure (300 - 1250 hPa ± 0.5 hPa)

It uses the following 3 sensors for that:

• SCD41 from Sensirion
• BMP388 from Bosch
• SEN55 from Sensirion

I have designed a special PCB that holds the first two sensors and the ESP and a "ring" of RGB LEDs to light up the top of the case depending on the air quality. It also includes a small display on the front that let's you quickly see all the sensor values. As soon as one sensor goes over the defined threshold, the LEDs turn red and the display shows what sensor it is and a graph of the last 30min of it. Everything is put in a small case and is powered with a USB-C plug at the back of it.

If I'm done with everything, I will publish all the files necessary to replicate or modify the design on GitHub. This includes the ESPHome Config, the CAD and STL files for the case and the KiCAD and Gerber files for the PCB. The link will be: https://github.com/ebrithiljonas/SeptaSense

[acoustic scaffold]

First prototype is working pretty well, except for the CO2 sensor, I must have fried it after one of the too many re-soldering I have done to it ^^ Now I only need to clean up the project files and write a small documentation and then it's ready to be published on GitHub.

[acoustic scaffold]

So i have cleaned up the project and generated all the files required to build it yourself. It is available under: https://github.com/ebrithiljonas/SeptaSense
And if someone is interested, I have a few spare PCBs, populated ones and bare ones. Just PM me if you are interested in one.

[slate mortar]

Nice! How accurate is the temperature sensor? It seems to be fairly close to a heat source (ESP32 module). Does that have any effect on temperature and humidity readings?

[acoustic scaffold]

The Temperature is measured by the SEN55 module that is located under the PCB, the BMP388 on top is only used for pressure. I just had to calibrate it because it sits inside a case and gets slightly warmer, but right now it should be quite accurate, but I will probably test it again when I can use the climate chamber at work again ^^

[slate mortar]

Oooh nice! 😄

[rotund sedge]

Nice work! @acoustic scaffold have you considered mapping the raw PM2.5/PM10 values to Air Quality Index (best to use the US format IMO, granular enough, but not overly complicated to implement), and summarising the other indexes (e.g. NOx/VOC from the SEN55 returns the US index of those air contents), before turning it into a final result to print?

It would give you a quick overview (instead of the 6-7 separate numbers on the main screen), and you could use the colour coding of the index ranges on the outer ring, instead of the three (good, warning, alert) colours used currently.