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

• ESP32 Development Board *
• NDIR CO2 Sensor MH-Z14A *
• 0.96 Inch OLED Display 128*64 SSD1306 *

* Affiliate Links - help to support my projects

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.

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)