Air quality meter

Air quality meter using of-the-shelf components to measure dust particles, CO2, benzene and other nasty stuff.

Prerequisites

• Visual Studio Community
• Visual Micro
• Arduino core for ESP8266

Hardware

• Wemos D1 Mini Lite
• SDS-011 dust sensor
• 3x TM1637 4-digit display
• MQ-135 gas sensor
• breadboard
• wires, male to male and male to female
• enclosure, I used a cardboard box of 8cm x 21cm x 15cm
• power bank, with a USB cable that ends in a micro-USB connector
• stuff to attach the MQ-135 and displays to the enclosure. I used some electric wire (see photos).

Schematic

Software

1. Open AirQualityMeter.sln in Visual Studio.
2. Adjust the brightness of the digits to your liking (search for setBacklight in AirQualityMeter.ino).
3. If you're using different pins than indicated in the schematic, change the the pin definitions in AirQualityMeter.ino.
4. Select 'Wemos D1 mini Lite' in the board drop-down.
5. Select the correct COM port.
6. Build and upload. You might need to remove the D1 from the breadboard when uploading, I sometimes got a sync error with the D1 on the breadboard and everything connected.
7. Let the meter burn in for at least 24 hours. During that time the top display will alternate between the measured gas concentration en between the current Rzero*10.
8. When the Rzero*10 has stabilized after burn-in, open MQ135.h in Visual Studio and on line 27 change the value of RZERO to the displayed value / 10.
9. Open AirQualityMeter.ino and comment out the MQ135_CALIBRATION define.
10. Build and upload.
11. Each time you turn on the meter, the MQ135 needs to heat up, this may take a while (20 minutes or more).
12. You need to calibrate the MQ135, see this article.

End result

The top display shows the ppm of NH3, NOx, alcohol, Benzene, smoke and CO2. The left display shows µg/m³ of PM2.5, the right one shows µg/m³ of PM10.