Adafruit SCD4X/SCD30 CO2 sensor for ESP32

An Arduino sketch for the Adafruit SCD4X CO2 sensor and Adafruit SCD-30 CO2 sensor running on an ESP32 with an http server returning Prometheus compatible responses, and sensor readings sent via Bluetooth BLE.

Related software:

• Prometheus/Grafana Docker containers for Raspberry Pi
• Apple HomeKit accessory for the SCD4x/SCD-30 CO2 sensor
• iOS/macOS BLE CO2 sensor
• Sensirion iOS app

Hardware

• Adafruit SCD-41 CO2 sensor
• Adafruit ESP32-C3 QT Py dev board
• Adafruit battery charger for QT Py
• Adafruit Qwiic cable
• Nokia BP-6MT 3.7V battery (any 3.7 - 4.2V battery will work)

Setup

WiFi:

• Copy the secrets file: cp secrets.tmpl.h secrets.h
• Fill in your SSID and password in secrets.h
• Note: the ESP32-C3 only connects to a 2.4 GHz network

Arduino:

• Download the latest version of Arduino from https://www.arduino.cc
• From Tools > Manage Libraries... add the library: Sensirion I2C SCD4x
• If you have an SCD-30 CO2 sensor, add the library: Adafruit SCD30
• Uncomment either #define USESCD30 or #define USESCD4X
• Install the Sensirion BLE library: cd ~/Documents/Arduino/library and then git clone https://github.com/Sensirion/arduino-ble-gadget.git
• Install the NimBLE library: cd ~/Documents/Arduino/library and then git clone https://github.com/h2zero/NimBLE-Arduino.git
• Install the Adafruit boards following their instructions
• Connect your ESP32 via USB
• Now try Upload to send the code to your ESP32

Note: As of 9th April 2024 this was the dependency versions that compiled on a Sparkfun ESP32 Thing:

• git clone git@github.com:Sensirion/arduino-ble-gadget.git into ~/Arduino/libraries and then git checkout tags/1.2.0 and add #include <string> to ByteArray.h
• git clone git@github.com:Sensirion/arduino-upt-core.git Sensirion_UPT_Core into ~/Arduino/libraries and then git checkout 919ef8b
• git clone git@github.com:h2zero/NimBLE-Arduino.git into ~/Arduino/libraries and then git checkout release/1.4
• Install the ESP32 boards library at v2.0.11

iOS/macOS Bluetooth app:

I built an iOS/macOS app so location data can be saved with CO2 reading data.

Project code: ios-ble-co2-sensor

This code also works with the standard Sensirion MyAmbience app:

• Install the Sensirion MyAmbience app: iOS/Android
• Turn on Bluetooth on your device
• The readings should update every 5 seconds

Serial monitor

If you open the Arduino serial monitor you'll see:

• The WiFi output as it attempts to connect to your WiFi network
• The SCD4X/SCD-30 CO2 readings

LEDs

While starting up the LED will light up in this sequence

• Red blink - setup is starting
• Blue slow blink - trying to connect to WiFi
• Green blink - connected

While running:

• Green pulse for an http request
• Blue pulse for a BLE reading sent

http response

Once your ESP32 has connected to your SSID, it will respond over port 80 with a Prometheus response. e.g. curl 192.168.1.100:80/metrics

# HELP ambient_temperature Ambient temperature
# TYPE ambient_temperature gauge
ambient_temperature 19.95
# HELP ambient_humidity Ambient humidity
# TYPE ambient_humidity gauge
ambient_humidity 59.20
# HELP co2 CO2
# TYPE co2 gauge
co2 1333
# HELP battery_voltage Battery voltage
# TYPE battery_voltage gauge
battery_voltage 3.15

My ESP32-C3 with the SCD-41 CO2 sensor running off of an old Nokia BP-6MT battery.

Thanks

Shoutout to Core Electronics for being so fast with their delivery of the Adafruit SCD-41.

Licenses

• My code: MIT License
• ESP32 example code SimpleWiFiServer by Jan Hendrik Berlin
• Sensirion I2C SCD4X example code exampleUsage license:

Copyright (c) 2021, Sensirion AG All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

• Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
• Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
• Neither the name of Sensirion AG nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

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