CO2 Gadget: Advanced CO2 Meter

CO2 Gadget is a firmware to create high quality CO2 meterswith optional sensors for suspended particles, temperature, humidity, atmospheric pressure and others that allow us to analyse the air quality we breathe.

In this article I am going to introduce and show you how to install and use the advanced version of CO2 Gadget, the CO2 meter with App for Android and iOS, via Bluetooth, based on the project of the Swedish sensor manufacturer Sensirion, but with several more twists and turns.

CO2 Gadget is a CO2 meter (and much more) easy to build, easy to record and easy to use.

This meter is as easy or even easier to assemble than CO2 Easy (the one from the CO2 meter tutorial of this blog). Perfect for users who just want a meter, without complicating their life, even if they have never had any contact with electronic projects. and are not technically inclined.

CO2 Gadget highlights

Who is CO2 Gadget aimed at?

The CO2 Gadget meter is aimed at everyone, although if you force me to make a distinction, I will tell you that it is aimed at two types of public:

• Users who want a quality meter, uncomplicated and affordable
• Users with technical concerns who want to start from a good basis to adapt the operation of the CO2 meter. to your taste and needs.

If you are one of the first, here below you will find all the information you will need. If you're a technical user, I'm writing an article with information to get you started, but if you have a certain level, you won't even need it: you have everything you need in the repository at CO2 Gadget on GitHub (you know, technical users only!). CO2 Gadget is Open Source.

This article is intended for users of the CO2 Gadget firmware. For any issue related to your developmentIf you have any questions, problems or requests, please contact us at CO2 Gadget repository in project on GitHub.

What do I need to build the Gadget CO2 meter?

Basically you need to three things: a board with the ESP32 chip, a CO2 sensor and the firmware. (the programme that makes it work).

This tutorial is made with a TTGO T-Display Board and a sensor Sensirion SCD30 Sensor but you can build your CO2 Gadget using many different sensors, boards and displays.as the I2C OLED display with 128*64 pixel SSH1106 driverwhich is fully supported, so that the choice is enormous.

This article is dedicated to the firmware, so I recommend you to follow one of the tutorials I have written and that you can find in this blog. For example:

This is a CO2 meter that you can build at less than an hour with only two components and four welds. I can safely say that it is the easiest to assemble CO2 meter you will ever find.

The CO2 Gadget firmware is an easy-to-use firmware, ready to write to an ESP32 board with a single click.

As it is a Open Source, open source projectYou have at your disposal all its source code so that you can analyse it, modify it, learn from it or do whatever you want with it.

A nice thing you can do is to contribute your improvements to the CO2 Gadget code so that other users can benefit from them. Did you design a new display screen because you were not happy with the ones it came with? Share it!

Use of the Gadget CO2 meter

Using the meter couldn't be easier. Just switch it on, open the free Sensirion MyAmbience App on your mobile phone and view the values. It's as simple as that.

If you have mounted one of the versions with a display, you will be able to see the measurements on the screen as soon as you switch it on, without having to do anything else.

When you first turn on CO2 Gadget it will have a default configuration consisting of:

OPTION	DEFAULT VALUE
BLE (Bluetooth Low Power)	ON
Wifi	OFF
MQTT	OFF
ESPNOW	OFF
Colour green	Up to 700 ppm
Orange colour	Up to 1000 ppm
Red colour	From 1000 ppm

This means that as soon as you turn the meter on for the first time, CO2 Gadget will be ready to display the data on your mobile or tablet without you having to do anything else.

All these values can be easily changed via the on-screen menu (or via USB) to suit your tastes, preferences or needs. Soon you will also be able to change them via a web page.

CO2 Gadget has many functionalities and options that you can use (if you want to) and I am going to tell you about each of them below.

Bluetooth operating mode

Bluetooth operation mode is the default meter mode.

In this mode, the meter sends its measurements via bluetooth to your mobile (Android or iOS) where an installed App allows you to display the values of these measurements in real time, and consult historical data.

The App also allows you to export historical data, in case you want to use them in some way (load them into Excel, for example).

This is a very interesting option if what you want is to have a user-friendly CO2 meter without the need to send data to internet or integration with other systems.

All you have to do is install the Sensirion MyAmbience App from the official Google or Apple shops (it's free), depending on your device.

Please note that on Android devices it is necessary to enable location services and grant the app the appropriate permissions. This is necessary to allow the app to continuously scan for nearby Bluetooth devices. This is a requirement of the Android operating system for Bluetooth scanning. The application itself does not use your location.

MWiF mode of operationi

This mode allows you to access the meter via a web browser to view real-time measurements.

When WiFi mode is active it is possible to access the web page generated by the meter.

At http://ip_del_medidor it displays a web page with the measurements taken by the meter in real time with graphs representing these measurements. This page is refreshed every few seconds with the updated measurements without the need to reload the page.

For the integration of the meter with other systems you have three URLs (API end points) where you can access the measurements in text format:

Latest measure of CO2 concentration:

http://ip_del_medidor/readCO2

Current temperature value:

http://ip_del_medidor/readTemperature

Current relative humidity value:

http://ip_del_medidor/readHumidity  

You will need to replace "ip_of_the_meter" with the IP address of the meter in your network. As you will see below, the easiest way to see this address is in the "Info" menu of the CO2 Gadget. For example:

http://192.168.1.201

In order to avoid having to know the IP address and to be able to access by name, CO2 Gadget implements mDNS (also known as Multicast-DNS). This way you will be able to access the meter by typing in your Host in the address bar of your browser followed by the extension .localfor example:

http://CO2-Gadget.local

You can see the Host name on the WiFi configuration screen (and also via USB at boot time).

At the moment the pages shown are very simple, but we will be working on them to improve them. If you know HTML and CSS you can help to improve them and I will be very grateful to you (and many more users, I assure you).

In the future you will also be able to view historical data and configure the meter.

MESP-NOW mode of operation

ESP-NOW is a long-range, low-power radio communications protocol.

Its inclusion allows CO2 Gadget to send its data over several hundred metres without the need for additional hardware.

If you want to know more about this protocol, I recommend you to read my article on ESP-NOW and the ESP-NOW Gateway to MQTT

Activation of ventilation equipment (relay outputs)

CO2 Gadget has three outputs that can be used to activate relays or other elements, for example, automatically activate ventilation or air filtering equipmentactivate audible or luminous alarms, etc.

The concentrations at which these outputs are activated are customisable and match those you have set as level orange and level red, in addition to green.

Both outputs turn on when the level of that colour is reached and do not turn off until the CO2 level drops at least 100 ppm below that level (hysteresis = 100ppm).

Hysteresis allows the connected device to avoid being switched on and off continuously if the concentration keeps fluctuating around that concentration).

RGB LED notifications

If you need to have a luminous indication of the CO2 concentration you can connect an RGB LED (or RGB strips) to the CO2 Gadget,

You can even use high-powered lighting using external relays - can you imagine large coloured spotlights in a discotheque indicating the CO2 level?

To connect an RGB LED, you will use the same relay outputs plus the green level output, which has a slightly different function:

The green level output turns on when the level is below the orange level and turns off when orange turns on (when operating in relay mode green stays on when orange turns on).

Note that you will have to put three resistors, one for each colour, to limit the current supplied to each LED and prevent it from burning out (or damaging the board). I recommend you try values of about 330 or 470 ohms. The RGB LEDs to be used should be common cathode.

If you use RGB strips you will have to use external circuitry (relays may work) as they will probably consume more than the ESP32 can provide directly (about 60mA per output).

Neopixel LED Notifications (WS2812B)

CO2 Gadget supports notifications via WS2812B addressable coloured LEDs (also called Neopixel). Their operation in CO2 Gadget is very similar to normal RGB LEDs.

Keep in mind that these LEDs are designed to work with 5V, so if you power them with a battery you may have problems (I recommend you to put a "step up to raise the voltage to 5V). I've done some tests at 3.3V and they worked, but I can't guarantee they will in your case.

Communication of the CO2 meter by MQTT

The support of the MQTT protocol opens up a wide range of possibilities for sending the data generated by the meter to other systems, for example, home automation systemThe data can be stored in a database or visualised.

I use it with a Mosquitto broker and Nodered, which allows me to process them, store them in an InfluxDB database and visualise and analyse them easily in Grafana, getting graphs like these:

As you can imagine the MQTT functionality needs a WiFi connection to work.

Sending measurements by MQTT

CO2 Gadget sends CO2, temperature and humidity measurements every time there is an update on the following topics:

• topic/co2Sends the CO2 concentration in PPM with the value in the message payload.
• topic/tempSends the current temperature in degrees Celsius with the value in the message payload to two decimal places.
• topic/humiSend the relative humidity with the value in the message payload as a percentage.

Receiving commands via MQTT

In addition to sending data via MQTT, CO2 Gadget is also able to receive commands. Specifically, it can receive the following two commands, which can be very useful:

• topic/calibration ppm: By sending a message with the topic "topic/calibration" and a number between 400 and 2000 in the Payload (usually 400) we can instruct CO2 Gadget to calibrate the sensor to that concentration.
• topic/ambientpressure mbar: By sending a message with the topic "topic/ambientpressure" and the value of the atmospheric pressure in millibars, the CO2 sensor will be instructed to compensate the CO2 concentration by atmospheric pressure.

Alarm sending by MQTT

CO2 Gadget sends messages via MQTT corresponding to the colour levels (green, orange, and red) configured.

The messages sent are as follows:

• topic/green: Shipped with the text "ON" in the payload when the CO2 concentration is within the configured green range. OFF" will be sent in the payload when the concentration reaches the orange level.
• topic/orange: Shipped with the text "ON" in the payload when the CO2 concentration reaches or exceeds the configured orange range. OFF" shall be sent in the payload when the concentration drops below the orange level (no "OFF" is sent when switching to red).
• topic/network: Shipped with the text "ON" in the payload when the CO2 concentration reaches the red range. OFF" shall be sent in the payload when the concentration drops below the red range.

The orange and red messages have a hysteresis of 100 ppm so that the "OFF" message is not sent until the CO2 level drops at least 100 ppm below this level. It is planned that, in a future version, this hysteresis will be configurable in the menu.

CO2 Gadget configuration

The Gadget CO2 meter is very easy to configure via the on-screen menu or the serial port (and soon the website).

On-screen menu

Navigation through the on-screen menu is done by means of the two buttons on the front of the meter as follows:

• Short press on the top button = Up
• Short press on bottom button = Down
• Long press on top button = Enter/select
• Long press on bottom button = Back/unselect

You will see that, although it has only two buttons, the menu is very easy to use and you will soon have mastered it.

If you have mounted your meter with a board without buttons, you can connect your own push buttons.

The use of buttons is optional. CO2 Gadget does not need buttons to work. You can configure all options through the USB/serial port as you will see in the next point.

Serial port menu

If you have decided to set up a meter without a display or buttons, no problem. You can use the menu through the serial port, using any terminal program, by using the following keys on the numeric keypad of your computer:

• Tecla / = top
• Key * = below
• Key – = Enter/select
• Key + = Back/deselect

In addition, you can directly use the numbers and letters on the keyboard to enter data.

The menu is exactly the same on the screen and on the serial port. What you see on one you will see on the other, and simultaneously.

In the following, I will explain each of the options in the configuration menus and I will do so in the same order in which they are displayed.

Main menu

In the main menu you can see the battery voltage (or that of the power supply or charger, if connected) and you can enter other submenus such as: Information, Calibration and Configuration. With the last option, Exit, you can leave the menu and return to the main screen with the measured data.

Information

In this menu you have useful information about the meter.

• Comp: The compilation date of the CO2 Gadget in MMM DD YYYYYY format.
• Version: The version number of the CO2 Gadget charger firmware in the meter.
• IP: The IP address of the meter, if it is connected to a WiFi network. Disconnected" will be displayed if the network is disconnected and "Disabled" will be displayed if WiFi is disabled.
• DLE Dev: The Bluetooth device code. It will be useful, if you have several meters, to differentiate one from another in the App.
• Back: Back to previous menu

Calibration

Here you can activate and deactivate the automatic calibration of the CO2 sensor, as well as perform a manual calibration.

• Auto Cal: Allows you to turn the automatic calibration of the CO2 sensor ON/OFF.
• Calibrate at 400ppm: By selecting this option with a long press you can calibrate the sensor at 400ppm.
• Custom Cal: Allows you to specify a concentration between 400 and 2000 ppm at which you want to calibrate.
• Calibrate at custom: Perform calibration at the concentration specified in "Custom Cal".
• Back: Back to previous menu

The option "Calibrate at custom ppm"is intended for advanced users. Its main utility is to be able to calibrate the CO2 sensor using another reference CO2 sensor. Not all sensors have this ability.

Configuration

In this menu, with several options and submenus, you can configure different CO2 Gadget options.

The following options and submenus are available:

• CO2 Sensor: Options related to CO2 measurement such as activation and deactivation of automatic calibration, the colours you want to use for the concentration ranges, humidity or atmospheric pressure compensation, etc.
• BLE Config: Activating and deactivating BLE (Bluetooth Low Energy) and its settings
• WIFI Config: Activating and deactivating WiFi and its settings
• MQTT Config: Activating and deactivating MQTT and its settings
• Battery Config: Battery Configuration
• Temp Config: Configuration of temperature-related parameters (temperature offset and units of measurement).
• Display Config: Display configuration options
• Neopixel config: Neopixel type LED configuration (WS2812B)
• Outputs config: Configuration of relay and RGB LED outputs
• Save preferences: Save preferences to the NVR (non-volatile memory) so that they are permanent, even if you remove power from the meter.
• Back: Back to previous menu

CO2 Sensor

In this menu you can configure everything related to the CO2 sensor installed in CO2 Gadget.

• Sensor: Here you can select the installed sensor from: Auto (for I2C sensors such as Sensirion SCD30, SCD40 and SCD41), MH-Z19, CM1106 and Senseair S8.
• Auto Cal: ON/OFF: Enables or disables automatic sensor calibration.
• Pres. Comp: Sets the pressure in millibars for pressure-dependent CO2 concentration compensation.
• Altitude: Set the height above sea level to perform pressure compensation (if you do not know the atmospheric pressure).
• Orange: CO2 concentration level in PPM above which you want the display to appear orange.
• Red: CO2 level in PPM for the colour red.
• Debug sensors: ON/OFF: Enables the output of additional sensor information via the serial (USB) port to assist in debugging the sensors.

CO2 sensor selection

To select the sensor, simply press "Enter" on the "Sensor" option (e.g. a long press on the top button of a TTGO T-Display) to access a submenu where you can choose the sensor you have connected to the CO2 Gadget.

Scroll through the available sensors (up and down keys or "/" and "+" on the serial terminal) until you select the one you want to choose and press "Enter" to select it (if you are using the serial console, in this case please do not select it by menu number).

Remember that sensors with I2C connection (Sensirion SCD30, SCD40 and SCD41) are automatically detected. Just choose "Auto" and CO2 Gadget will detect and use it automatically.

Don't forget to save the configuration when you are done and satisfied.

BLE Config

BLE (Bluetooth Low Energy) is the radio communication technology that CO2 Gadget uses to communicate with your mobile phone or tablet.

If you want to display the CO2 Gadget data in the MyAmbience App you need this option to be turned ON.

Please note that after activating or deactivating this option you will have to reset the meter (e.g. by pressing the reset button) for the changes to take effect.

WIFI Config

In this menu you will be able to activate and deactivate WiFi. Soon you will also be able to configure its parameters.

• WiFi Enable: ON/OFF: With this option you can activate and deactivate WiFi. Interesting if you are not going to use it, for example, away from home, to increase battery life.
• SSID: You must enter the SSID, the "name", of the access point you want CO2 Gadget to connect to.
• Pass: You must enter the password of your WiFi network.
• Host: The host name or hostname of CO2 Gadget on the web

MQTT Config

Here you can configure everything to do with CO2 Gadget MQTT communication.

The following options are available:

• MQTT Enable: Enables (ON) or disables (OFF) the MQTT communication functionalities of the meter.
• Topic: Topic where CO2 Gadget will send and receive messages.
• Id: The Client Id or Client Identifier that CO2 Gadget will use when connecting to the broker. This identifier must be unique (there must not be more than one device with the same identifier).
• Broker IP: This is the IP address of the MQTT broker (server) to which CO2 Gadget must connect.
• User: User name to be used for authentication with the MQTT broker.
• Pass: The authentication key with the MQTT broker.
• Back: Back to previous menu

ESP-NOW Config

This menu allows you to set the options available for using the ESP-NOW radio communications protocol in CO2 Gadget.

• ESP-NOW Enable [ON/OFF]: Enables or disables the ESP-NOW protocol.
• TX Time: Allows you to set the interval between sends using ESP-NOW between 10 and 360 seconds.

Battery Config

In this menu you can configure different aspects related to the battery.

These parameters are a bit technical and you can ignore them completely if you want. They serve to match the voltage displayed on the screen to the actual battery voltage.

• Battery: Current voltage of the battery (or external power supply if connected).
• Voltage ref: Value of the internal voltage reference.
• Bat Full (mV): Value in millivolts that matches the voltage of the battery when fully charged.
• Bat Empty (mV): Minimum value in millivolts when we assume that the battery is completely discharged (the moment when the meter shuts down due to lack of voltage or starts to give erroneous measurements due to too low a voltage).
• Back: Back to previous menu

If you don't have a voltmeter, you can do the following calibration, which is very simple and will give you a battery voltage very close to the real one: Connect the meter to a power supply or USB charger and adjust the "Voltage ref" value so that the voltage read from the battery reads approximately 5.00 volts (on the boards I have tested it on, the Voltage ref value is over 940mV).

Temp Config

Configuration of temperature-related parameters.

• Temp: Current temperature (always in degrees Celsius)
• Offset: Temperature offset (always in degrees Celsius) to adjust for possible discrepancies in temperature measurement.
• Units [Celsius/Fahrenheit]: Allows you to select the units of measurement for the display (only the display on the display, the rest is still in degrees Celsius).

Display Config

Here you have options related to the CO2 Gadget display and how it is managed.

• Brightness: Brightness of the display from 0 (off) to 255 (maximum brightness).
• Time To Off: Time in seconds without pressing a button for the screen to turn off automatically. Useful for battery saving. The screen will turn on again by briefly pressing a button. Setting it to 0 disables it (screen always on).
• Off on USB: Allows you to select whether you want the screen to turn off when CO2 Gadget is running on external power (USB, for example). In this case it may not be necessary to turn it off to save battery power, but you may want to turn it off to avoid being disturbed by the light if you have it on your bedside table.
• Orient: [Normal/Reversed]: Allows you to rotate the display 180°. This way on, for example, a TTGO T-Display board, the USB port and buttons would be on the left. The functions of the buttons are also reversed so that the operation remains normal (when rotated 180º the one on top will be on the bottom and vice versa).
• Temp: [Show/Hide]: Shows or hides the temperature measurement on the display. Useful when the meter does not have a temperature sensor (or its measurements are not valid).
• Humidity: [Show/Hide]: Shows or hides the humidity measurement on the display. Useful when the meter does not have a humidity sensor (or its measurements are not valid).
• Battery: [Show/Hide]: Allows you to choose whether to show or hide the battery data. Useful when the meter has no battery.

Outputs Config

• Neopix Bright: Allows you to choose the brightness of the Neopixel LEDs (WS2812B).
• Neopixels: Selection of the type of Neopixel used. The available options are NEO_GRB, NEO_RGB and NEO_RGBW (all at 800Khz).
• GPIO Outputs: You can select whether to connect RGB LEDs or relays to the outputs to adjust their operating mode.

CO2 Gadget Advanced Recording

Writing firmware to the board with the ESP32 is super easy. You don't have to download or install anything on your PC..

Click the button corresponding to the version you want to install, select the port where your board is connected and click "Connect". It's as simple as that, the recording of the ESP32 of the board will be done in a moment without any further complication with only two clicks..

Pins used by CO2 Gadget (GPIO)

Although in the build tutorials of the blog you will find detailed pins to use, here you have, in a more generic way, the pins used by each CO2 Gadget firmware variant.

Variant	Display	RX/TX	I2C	UP/DWN	GPIO IN	GPIO Green	GPIO Orange	GPIO Red	GPIO Battery	GPIO Neopixel
TTGO_TDISPLAY	TFT 240×135	13/12	21/22	35/0	27	25	32	33	34	26
TTGO_TDISPLAY_SANDWICH	TFT 240×135	13/12	22/21	35/0	27	25	32	33	34	26
esp32dev_OLED	SSH1106 128×64	17/16	21/22	15/0	27	25	32	33	34	26
esp32dev_OLED_OTA	SSH1106-128×64	17/16	21/22	15/0	27	25	32	33	34	26

• Variant: Name of firmware variant or flavour
• Display: Display supported by the variant.
• RX/TX: Pins (GPIO) used for the connection of sensors connected by serial port
• I2C: Pins (GPIO) corresponding to the I2C bus for connection of I2C sensors and I2C displays
• UP/DWN: Pins (GPIO) to which the "Up" and "Down" buttons are connected. These are optional, CO2 Gadget is fully functional without buttons connected.
• EN: Pin (GPIO) that supplies an ENABLE signal for switching the sensors on and off.
• GPIO Green: Pin (GPIO) corresponding to the output before reaching the orange level.
• GPIO Orange: Pin (GPIO) corresponding to the output when the orange level is reached.
• GPIO Red: Pin (GPIO) corresponding to the output when the orange level is reached.
• GPIO BatteryPin for battery reading. Note that on most boards the maximum admissible value is 1V or 3.3V, so you will have to put a resistive divider at the input.
• GPIO NeopixelPin to which you must connect the data line of the Neopixel or WS2812B LEDs.

Technical support and help

If you encounter any difficulties join the Telegram group or write your question, problem or request in the section CO2 Gadget Issues on GitHub (recommended for consultations in English).

Having problems? Meter Frequently Asked Questions (FAQ)

Although the project is very straightforward, there is always the possibility that you may have a question or a problem.

In the list below, you will find answers to the most common questions and doubts.

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This post is intended for users of the CO2 Gadget firmware. For any issue related to your developmentIf you have any questions, problems or requests, please contact us at CO2 Gadget project repository on GitHub.