ESP Air Sensor

Get air quality & CO2 data from SM300D2 & Senseair S8 with ESP32, and export as OpenMetrics (Prometheus exporter) via WiFi.

I used to have a Raspberry Pi Zero reading the SM300D2 (other's work) and an Arduino reading the Senseair S8 (my own project). Recently I got a batch of ESP32 chips, and looking for something to do with them. So I decide to combine the two using one ESP32 module, free the Raspberry Pi, and hoping all the bugs in old projects would go away.

Also, I'm migrating from Graphite to Prometheus for metrics collection.

At the time, I'm new to embedded development and C programming in general. This should be treated as a toy side project, not a serious one :)

Sensors

• SM300D2
  A cheap mulitsensor module, see the good summary at alemela/SM300D2-air-quality.

• Senseair S8
  CO2 sensor that seems more reliable. Their product page.

• LYWSD02
  Xiaomi E-Ink Display Clock w/ temperature & humidity sensors.

I use SM300D2 & Senseair S8 because I already have them on hands. But I wouldn't recommand SM300D2 due to its unreliable readings of CO2, CH2O, and TVOC. Even its temperature reading is often higher than it should be, affected by itself heat I guess. In fact, I only take the PM2.5 readings from the module alhought all data are read in this project.

LYWSD02 was added thereafter. Not like the others, it was connected via Bluetooth Low Energy.

Software

PlatformIO (the IDE) and ESP-IDF (the offical framework of ESP32) were used.

I was trying to make it modular and extensible, to facilitate adding/removing particular sensor devices.

Sturcture of source code

• components/metrics/
  Initlize Wi-Fi and HTTP server, serving OpenMetrics page.
• components/sm300d2/
  Read SM300D2 data from UART serial, put them on a queue.
• components/sense_air_s8/
  Provide functions to to read Senseair S8 data from UART serial.
• components/lywsd02/
  Read temperature & humidity data from Xiaomi clock via Bluetooth.
• src/main.c
  Keep reading data from modules and publish them as metrics.

Configure

Use pio run -t menuconfig

• Component config -> OpenMetrics Exporter
  Hostname, Wi-Fi SSID & PSK, HTTP endpoints
• Component config -> Senseair S8 CO2 Sensor
  UART port number, RX/TX pins
• Component config -> SM300D2 Air Quality Sensor
  UART port number, RX pin, aggregation period

Build

Install PlatformIO and execute pio run on terminal, or click "Build" on Visual Code with PlatformIO plugin.

Metrics

The exporter is on /metrics by default.

$ curl http://<espair-hostname>/metrics
> # UNIT espair_senseairs8_co2_ppm ppm
> # TYPE espair_senseairs8_co2_ppm gauge
> espair_senseairs8_co2_ppm{host="espair-01",mac="807d3a***"} 551
> (omitted...)
> # UNIT espair_sm300d2_humi_precent precent
> # TYPE espair_sm300d2_humi_precent gauge
> espair_sm300d2_humi_precent{host="espair-01",mac="807d3a***""} 37.00
> # EOF

Case

Files:

• case/espair_case.FCStd
  FreeCAD source of case body & ESP32 tray
• case/espair_case-Body.stl
  STL of case body
• case/espair_case-ESP.stl
  STL of ESP32 tray
• case/espair_cap.stl
  STL of rare case cover (Draw by Swin)

Printing:

• Printer: Ender-3 V2
• Filament: PLA, 1.75mm
• Resolution: 0.20mm
• Supports: yes
• Infill: no effect

The particulate matter sensor was placed outside the case, fasten along with the case body and ESP32 tray using two M2 screws & nuts.