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CO2 Meter with ESP32

Description

Messasure CO2 particles in to the air. Warns when you should ventilate the room.

You find an video documentary (in german) on my Youtube channel: https://www.youtube.com/watch?v=MKK0GAGxzaE

Features

  • Measure CO2 concentration in room
  • MQTT support (for Node-Red or Home Assistant)
  • easy integration in own WiFi network (Hotspot settings-page)
  • OLED display: can used independently thanks to the measured values shown on the display

Parts

* Affiliate Links - help to support my projects

Sketch

sketch

Wiring

CO2 sensor (MH-Z14A)

Pin on Sensor description Pin on ESP32
16 GND GND
17 Power (5V) VIN (can also used as 5V output)
18 UART RXD GPIO17 (UART 2 TX)
19 UART TXD GPIO16 (UART 2 RX)

OLED display (SSD1306)

Pin on Sensor description Pin on ESP32
GND GND GND
VCC Power (3.3V) 3V3
SCL GPIO22 (I2C SCL)
SDA GPIO21 (I2C SDA)

Setup

  • connect all parts to the ESP32
  • connect power
  • the ESP32 starting an own Wifi access point named "co2-meter-{device ID}"
  • connect to this Wifi with your smartphone
  • use waaatering for Wifi password
  • you will redirected to a config page
  • insert your Wifi and MQTT broker credentials
  • click on "save"
  • the ESP32 will restarting and connect to your MQTT broker
  • after about 60 seconds should you should see a new topic in your MQTT broker co2-meter/{device ID}/out/info with a lot of information in the payload

MQTT API

The whole module is controllable via MQTT protocol. So it's easy to integrate in existing SmartHome systems (like Home Assistant or Node-Red).

Incoming commands

Topic: co2-meter/{device ID}/in/{command}

command description payload
sleep Start deep-sleep for specific duration (in seconds!) { duration: number }
info Send info via MQTT topic co2-meter/out/info package -
display turn display on/off { on: boolean }
hard-reset Reset config with WiFi and MQTT settings and start internal hotspot to reconfigure device. -

Outcoming commands

Topic: co2-meter/{device ID}/out/{command}

command description payload
info status info complex JSON. See "info-state" chapter
sleep was send if sytem enter deep-sleep { duration: number }
wakeup was send if sytem wakeup from deep-sleep reason "timer"

Info state

field description type
version version number of module firmware string
system.deviceId Unique ID of the device. Will used also in MQTT topics. string
system.freeHeap free heap memory of CPU number
network.wifiRssi wifi signal strength (RSSI) number
network.wifiQuality quality of signal strength (value between 0 and 100%) number
network.wifiSsid SSID of connected wifi string
network.ip ip address of the module string
network.mac MAC address of the device string
co2.isPreheating TRUE if the sensor is preheated boolean
co2.temperature temperature from sensor (in °C) number
co2.ppm CO2 concentration in the air (in ppm) number

Housing

You can create a robust housing with a 3D printer or at the workbench.

I decided to make one out of plywood. It didn't turn out perfect, but it protects the components.

sketch

TODOs

  • buy sensor and ESP32
  • soldering first prototype
  • add WifiManager to easy setup
  • create sketch
  • test firmware
  • test OTA updates
  • add part list
  • add video doc
  • create housing (from wood)