Multi-Sensor Air Quality Monitor

I have completed my project to modify a domestic air-quality monitor, ( AQM ), which retails for GBP15 in the UK, and turn it into a multi-sensor AQM. See also 5, 9 & 12 February.

The original AQM only has a Cubic PM1006 particulate matter sensor. The colour of an illuminated indicator changes, ( green, yellow or red ), with the PM2.5 ( 2.5 micron ) particle concentration in the air. I have retained this feature in my modified versions.

I fitted a 'D1 Mini ESP32' micro-controller board to read the sensors and send the measurements to a display for viewing. The display module is a 128x32 pixel OLED. The sensor types I chose are the CCS811 ( CO2 & TVOC ), (  see also 20 January ), and the AHT20 ( temperature C & relative humidity % ).

Internal view showing position of the main components

I have made two versions of the multi-sensor AQM, suited to my intended use based on which sensors I fitted and with a display to give a direct readout.. The image above shows the internal layout of the PM1006/CCS811 version.

The PM1006/CCS811 version displays data for PM1, PM2.5, PM10, CO2 & TVOC. I shall be using this version in my workshop where TVOC could occasionally be present.

The PM1006/AHT20 version displays data for PM1, PM2.5, PM10, temperature and relative humidity. I shall deploy this one in the kitchen primarily for the particulate matter measurements ( presence of smoke, flour etc ), and also the humidity.

So, in two places at least, I'll have some knowledge of how clean the air is that I'm inhaling.

I've also written software for a third version with just the PM1006, ( as in the original AQM ), only displaying data for PM1, PM2.5 and PM10. It would just be a simple matter of uploading the software to either of the other two versions.

Version PM1006/CCS811

The 'D1 Mini ESP32' micro-controller board has built-in wifi. This opens up the future possibility of integrating the multi-sensor AQM into a 'smart home' network. 

 

TVOC = Total Volatile Organic Compounds ( paint, solvents etc ).

 

 

 

 

  

  

CCS811 VOC & CO2 Gas Sensor

Until just recently I was using analogue gas sensors, ( see previous post 16 January ). I have now turned my attention to digital gas sensors, from which the measurement data are already in digital form.

I am experimenting with the CCS811 sensor which has a I2C digital interface, ( 2-wire bus, clock and data only ). The CCS811 measures the concentration of CO2 ( carbon dioxide ) and TVOC ( total volatile organic compounds, which become a gas at room temperature ) in the air in ppm and ppb respectively which would be useful in giving an indication of air-quality in a closed workshop environment.

I connected an ESP32 micro-controller development board to the CCS811 circuit board and also to a I2C 128x64px blue OLED display in the corner of an already densely populated solderless breadboard.

( top-left) Mauve coloured CCS811 circuit board

The measurement results being displayed were obtained in my basement workshop. There is an established air-quality index called the 'TVOC Index' which is derived from the TVOC ppb concentration. Ppb between 0 & 220 corresponds to a TVOC Index of between 0 & 50 and an 'Index Category' of 'Good' air quality. I am pleased as I spend a lot of time in the basement.

 

I2C = Inter Integrated Circuit

ppm/ppb = parts per million/billion