A homemade CO2 meter with Wifi against the coronavirus: The CO2 Easy

Last modified 1 year


In this article I am going to explain how you can build your own homemade DIY CO2 Monitor (carbon dioxide monitor) easily and cheaply.

What I propose is a CO2 (carbon dioxide) meter with wifi, homemade, that you can build for less than 30 euros, I I can guarantee you that the result you will get will be an instrument that is the same or more precise and with many more functionalities than many commercial CO₂ meters costing several hundred euros.

The CO2 monitor CO2 Easy uses a CO2 sensor with NDIR technology and It has nothing to do with the € 60 or € 80 meters that are sold online in terms of reliability, precision and functionalities.

Don't be scared by the length of this article. Yes, it is long, but it has nothing to do with the difficulty. This article is long because I have decided to explain everything step by step, in great detail and with captures, photographs and even videos of each step. Really I could have written a much shorter article explaining how to build this CO2 meter, but it would not have been so complete.

The idea is that anyone can build this CO2 monitor, no need for prior knowledge or special equipment (except for the soldering iron, although you could even do without it).

In addition, it is fully modular, so you can easily expand it with all kinds of accessories, visual and audible alarms and even a touch screen.

However, if you don't want to build your own CO2 monitor, because you do not have time, you do not like to thinker around, or any other reason, you can access a buying guide with the best offers in commercial CO₂ monitors by clicking here.. You can buy it at a good price and have it at home in 24 hours.

Be sure to visit my new project: CO2 Gadget.

CO2 Gadget is an advanced CO2 meter with many options and supported sensors, open hardware and opensource, of which you can find all its source code on GitHub.

Is it possible to reduce the possibility of contracting Covid with a CO₂ meter of less than 30 euros?

Virtually all scientists have agreed in recent months: The virus is transmitted and contagious through the air, mainly, and one of the most effective ways to reduce the possibility of contracting Covid is to adequately ventilating spaces.

The best way to ensure that a space is properly ventilated is to measure the CO2 present in the air.

If you are still not convinced of this, and want to know more, I suggest you to read the following article:

👁️‍🗨️ Structure of the CO2 Easy Home CO₂ Meter

This CO₂ meter is a CO₂ has nothing to envy to commercial units of several hundred euros, being superior in the vast majority of cases, both for precision and for functionalities.

You will see how to make the homemade CO2 Easy meter with these main characteristics:

  • Economic. Less than € 30
  • High accuracy (50ppm +/- 3% of reading)
  • Wireless connection by Wifi
  • Portable
  • Smart (can perform many tasks based on data)
  • Web server built-in
  • Integration with home automation system
  • Publication of data to the internet
  • Support for MQTT and HTTP
  • LCD display and touch screen optional

The CO2 Easy meter is composed of only two components, low cost and easy to source:

  • Plate NodeMCU, Wemos D1 Mini or similar, with microcontroller ESP8266 with built-in Wifi
  • Sensor CO₂ MH-Z19B or Senseair S8 (there are other sensors available and supported by this project such as the MH-Z14A or the Cubic CM1106, among others).

I have chosen low cost components to build the carbon dioxide meter, in order to keep the price very low.

Buying the components in the links that I propose you on AliExpress:


Some 20 Euros for CO₂ sensor MH-Z19B on AliExpress.

See below my recommendation to use the sensor Senseair S8 LP.


Little more than 2 Euros from the plate NodeMCU with ESP8266 microcontroller in this AliExpress link.

It also has many positive reviews and if you choose AliExpress Standard Shipping, which costs less than € 2, you should receive it in a couple of weeks.


Use the CO2 sensor Senseair S8 LP.

Due to the high demand of CO2 sensors produced in recent months, there is a real avalanche of fake MH-Z19B sensors, both on AliExpress and Amazon. These sensors give fluctuating and far from reality measurements, in the best case.

I spend a lot of time checking purchase links that I put and trying to make sure, as much as possible, that they are original, but sometimes there are surprises.

If you want to play it safe, and you can afford to spend a little more, I recommend that you use the sensor Senseair S8 LP. Besides being less likely to get a fake one, it's a sensor, from a European company, of better quality and more precision than the MH-Z19B.

I leave you here the link in which I bought: Senseair S8 LP. It's original and it came to me very fast (one week):

Costs about 28 Euros here: Senseair S8 LP.

It is a store with many positive feedback and shipping is by AliExpress Standard Shipping, so you should have it at home in less than two weeks.

You can find more information about fake sensors by clicking on: MH-Z19B FALSE CO2 Sensors

If you don't want to wait that long, you have the option of buying these components on Amazon, with fast shipping. It is more expensive, but if you want it quickly, you will have it at home in 24 hours, in many cases.

A major advantage, now that there are so many fake MH-Z19B sensors, on Amazon you know what it is easy to return it, if you are not satisfied.

ICQUANZX MH-Z19 Infrared CO2 Sensor Module Carbon Dioxide Gas Sensor MH-Z19B for CO2 Monitor 0-5000ppm MH Z19B
  • This MH - Z19 C02 gas sensor has high sensitivity, high resolution.
  • Provides a variety of forms output modes, such as UART and PWM wave.
  • Anti water vapor interference, no poisoning.
  • Temperature compensated, excellent linear output.
AZDelivery NodeMCU Lolin V3 ESP8266 ESP-12F WiFi Module with CH340 2.4 GHz WiFi Development Board Arduino Compatible with E-Book Included!
  • ✅ Powerful Microcontroller: The AZ-Delivery Module is a powerful ESP8266 (ESP-12F) microcontroller with 802.11 b / g / n WLAN and integrated antenna.
  • ✅ Rapid Prototyping: It is simple to use, allowing you to easily create prototypes through simple programming through Lua code. Plus, with a motherboard-compatible design (27.5mm pin spacing).
  • ✅ Dimensions (L x W x H): 58mm x 31mm x 13mm.
  • ✅ Large storage and processing space: AZ-Delivery ESP8266 with Wi-Fi has large storage and processing space on board that allows it to integrate with application-specific sensors and devices and support minimal load during runtime. Boost your development in the fastest way combining with NodeMcu Firmware!
  • ✅ This product includes an E-Book that provides helpful information on how to get started on your project, helps with quick setup, and saves time in the setup process. We provide a series of application examples, comprehensive installation guides, and libraries.

Depending on the material you use, you probably need some cables.

You can use some cables that you have lying around. I recommend that they be from different colors, to prevent confusions.

Many people use "Dupont" connectors, which you can connect directly to the pins without soldering:

Movilideas - Dupont Bridge Connectors, 40 Male to Male Cables, 40 Female to Female Cables, 40 Male to Female Cables, 120 Cables
  • 120 jumper cables are shipped: 40 male-male, 40 male-female, 40 female-female.
  • Approximate length 20 cm
  • 0.127mm wire, 36 AWG

In case you prefer, I leave you the link where I usually buy the Dupont cables on AliExpress, which are cheaper.

Just missing a box.

As a box for CO2 Easy I propose you four options:

  • Leave it «in the air«. If it is going to be hidden, it is an inaccessible place, there should be no major problem.
  • Put it somewhere ornamental element, any adornment or accessory that is in the room and that allows to hide and protect it.
  • Buy one plastic box. I use one that I buy 10 by 10 in several similar assemblies. Simple and cheap. You can find the one I use here on AliExpress, although there are many similar ones. You can also use one of the gray boxes that are usually used in outdoor electrical installations, drilling it properly.
  • A 3d printed box. It is the solution that I used. You can find the design and tutorial in this blog, as well as others boxes that users have designed and have been made available to readers selflessly.
CO2 meter box available for download

You have to consider two important things: You have to try that the CO₂ sensor is heated as little as possible because its measurements are sensitive to temperature and you have to install it so that it receives the air from the room without problems, so do not put it in a hermetically sealed box (although it should not be given direct drafts).

CO₂ sensor MH-Z19B

The MH-Z19B carbon dioxide sensor is a general-purpose, small-size, intelligent sensor that uses the principle of non-scattered infrared (NDIR) to detect the presence of CO₂ in the air. It has good selectivity, long service life, and other characteristics, such as built-in temperature compensation.

It has simultaneous serial, analog and PWM output and is easy to use. It is a high-performance sensor that combines reliable infrared absorption gas detection technology with good design and an attractive price.

MH-Z19B sensor parameters

Gas detectedCarbon dioxide
Operating voltage4.5 ~ 5.5 V DC
Average current<60m A (@ 5V supply)
Peak current150 mA (supply @ 5V)
Interface level3.3 V (compatible with 5V)
Measuring range0 ~ 2000 ppm
0 ~ 5000 ppm
Output signalSerial (UART) - TTL level 3.3 V - PWM analog output
Preheating time3 minutes
Response timeT90<120s
Operating temperature0 ~ 50 ° C
Operating humidity0 to 90% RH (non-condensing)
Dimensions33mm × 20mm × 9mm (Length * Width * Height)
Weight5 grams
Lifetime> 5 years

MH-Z19B Features

Gold-plated gas chamber, waterproof and corrosion resistant
High sensitivity, low power consumption
Excellent stability
Temperature compensation, excellent linear output
Long duration

MH-Z19B Sensor Applications

HVAC Refrigeration Equipment
Surveillance and air quality equipment
Fresh air systems
Air purification equipment
Smart home
Schools and educational centers

You can see here his datasheet.

The module with ESP8266

The ESP8266 is a complete microcontroller on a small chip that includes Wifi and is also very cheap.

For this montage I have chosen the NodeMCU module why:
  • It's very cheap, between € 2 and € 4 depending on where you buy it (or about € 7 on Amazon)
  • Has USB so you can connect it directly to your computer by USB to record the ESP8266
  • Has all the additional components what are you going to need
  • It has many inputs and outputs for extensions

Also, you can power it with a mobile charger ordinary.
Although the video tutorial that you will find below is made with the NodeMCU Module, you can also use the small Wemos D1 Mini.

Below you will find his connection diagram, in case you decide for him.

✔️ Build the CO meter «CO2 Easy»

Enough of introduction, explanations, data and verbiage and Let's go to the mess! To construction!

You have, below, a video with the entire detailed process, to make it even easier for you. 

The construction of the CO₂ meter, the start-up and its use is very simple, I estimate that you can do this project in one or two hours. Just follow these steps to build the homemade CO₂ meter with Wifi:

  1. Write firmware to ESP8266 microcontroller with the program that I provide you
  2. Connect the CO sensor sensor using just four wires

It is a super useful and quick project for the experienced hobbyist and a excellent first project for the newcomer to electronic gadget. (Only four cables! Who gives more for less?)

Download the CO meter firmware


Burn the firmware now is even easier. From now on you will not have to download anything to your computer (you can skip the whole procedure described in the video below).

You simply have to press the "Install ESP Easy" button, select the port where you have your board connected and press "Connect".

Your browser is not supported! You have to use Windows with Microsoft Edge or Google Chrome to see the button

The first thing you have to do is download the program to your computer what then you will load in the NodeMCU or Wemos D1 Mini and that it will control the operation of the CO₂ meter.

This program is based on the fantastic project ESP Easy, that I have been using for several years with very good results.

To simplify the task as much as possible, and that you do not have to search and download the different necessary programs and files (and find which are the correct ones to use, because there are many), you can download it from here with one click and in one package that I have prepared and that it contains just what is necessary.

Below you can find the video with detailed instructions for ESP Easy recording.

It is very important that when you go to record the firmware on the board, do not have the CO2 sensor connected to the RX and TX pins (temporarily disconnect them if you already connected them). This is because the board shares these pins with the USB port and conflicts could occur.

Connect CO₂ sensor MH-Z19B

The connection of the MH-Z19B or Senseair S8 sensors (they connect exactly the same) to the NodeMCU is very easy, it only requires four connections.

There are two types of NodeMCU boards. Some that have a pin marked VU and others that do not.

If your board has a pin marked VU connect the positive of the sensor to that pin.

If your badge DOES NOT have a VU pinconnect it like this (positive of the sensor to the Vin pin):

If you are going to use the plate Wemos D1 MiniFollow the diagram below to connect the sensor:

You will need to a soldering iron, tin and a pay a little attention, but it should not take you more than 15 minutes, even if you have no previous experience.

For connection of the MH-Z19B or Senseair S8 LP sensor to the NodeMCU or Wemos D1 Mini, you can use the cable that comes with the MH-Z19B, cutting the connector at the end, as I show you in the video. If your sensor is not the version that comes with a connector, nothing happens, you will need some cables to connect it.

Just make the following connections (note that this pin numbering does not match the manufacturer's):

Pin MH-Z19BColourFunctionNodeMCU connection
1BrownAnalog outputWithout connection
2WhiteNoneWithout connection
3BlackNegative power supply (GND) Pin GND
4RedPositive feeding (Vin) Pin Vin
5blueData input (RXD)Pin TX
6GreenData output (TXD)RX pin
7YellowNoneWithout connection

In the following images you can see the assembly process, including its connections, in detail:

Cut the CO2 sensor connector

In my case, I ordered the MH-Z19B sensor version with connector.

The first thing I do is, since the cable has a connector on both sides, cut the connector on one side.

Optional: Remove unnecessary cables

The connector comes with all seven wires attached.

As we only have to connect four (Black, Red, Blue and Green), I remove the other three cables so that they do not get in the way and that the assembly is cleaner.

Stripping the wires

We strip the end of the four cables.

It is enough to peel one or two millimeters. The shorter the more "cleansed" will remain when soldered.

Solder feed

We carefully weld the sensor supply to the NodeMCU

  • Red wire (positive) to terminal marked Vin
  • Black wire (negative) to terminal marked GND

Solder the data cables

We solder the sensor data input and output cables to the NodeMCU

  • Blue wire (RXD, data input) to terminal marked TX (data output)
  • Green wire (TXD, data out) to terminal marked RX (data in)

Complete wiring

This is how the wiring will be, once we have soldered the four cables.

The finished CO2 Easy meter

All that remains is to connect the sensor to the NodeMCU, once you have recorded the firmware on the board, being careful not to put the connector upside down.

This will be how our CO2 meter will look, once the four cables are soldered and the sensor connected.

I decided to build this homemade CO2 meter with Wifi - it's super easy to make! Click to Tweet

📺 Video with the complete CO2 Meter tutorial

In this video you can see everything you need to build the CO₂ meterincluding electronics, ESPEasy recording and configuration.

Remember: it is important that when you go to record the firmware on the board, you do not have the CO2 sensor connected to the RX and TX pins (temporarily disconnect them if you already connected them).

The video has been recorded using an MH-Z19B sensor and a NodeMCU board. Remember that, if you use the Senseair S8 sensor (recommended) its connection is exactly the same (in this case see also this article I've written with the differences when using the Senseair S8).

Making these videos takes a lot of work. If you like the video, please, Don't forget to "Like" and subscribe to the channel. That It will motivate me to keep making more videos like this.

🔵 Using the CO₂ meter

Your CO₂ meter with Wifi is now finished. You just have to configure it, place it in the room you want to control and read the CO₂ concentration values from time to time.

I recommend that you see in detail the part corresponding to the configuration in the video, where it is explained in detail. However, below you have additional information.

CO₂ meter setup with Wifi

The meter needs a minimal configuration to work, which basically consists of configuring the wifi to connect it to the network of your home, office, school, etc. and tell ESPEasy which sensors you have connected (in this case only the CO2 sensor) and what to do with them.

ESP8266 Wi-Fi Configuration

As soon as you record the ESP8266, and to facilitate the configuration of the Wifi, you will see that it creates an access point called ESP-Easy.

All you have to do is connect from your computer, tablet or phone to that access point and configure the meter, in a very simple way, through a web page, thanks to the fact that the program that we have recorded in the ESP8266 includes a web server with the necessary pages for easy setup.

Normally your phone or tablet will open the configuration web page automatically as soon as it connects to the ESP-Easy access point, as you have seen in the video. If it doesn't, open a browser on your mobile or tablet (Chrome, for example), type in the address and hit enter.

The password to connect to this access point is configesp.

Configuration of the ESP8266 inputs and outputs

Through the same web page that you used to configure the Wi-Fi connection, you can now configure the inputs and outputs of the ESP8266 to tell you what's connected.

In our case, the only thing our ESP8266 has connected is the CO2 sensor and you are going to configure it so that it knows how to read the values and what to do with them.

As you will discover, it is very easy to expand the project to include other sensors and actuators as sensors temperature and humidity, LCD screens, colored LEDs, etc. (you have links to detailed tutorials below).

Reading the CO₂ data from our meter

Your CO₂ meter with Wifi is already working, reading the CO₂ concentration in the room where you have placed it and processing that data.

To read and process this data you have many possibilities that will allow you to read the CO₂ value directly and do many other things, such as: store them, create graphics, create alarms of various types when certain values are reached, send them to the internet, integrate them with your home automation system and much more.

The most basic use is see the CO₂ present in the room in real time. For that you only have to connect to the meter web page, with your web browser computer, tablet or mobile phone and access the "Devices" tab, where you will see the current value. The most recommended is save this page to your favorites, for access it easily, directly, whenever you want.

CO2 meter calibration

Both MH-Z19B and Senseair S8 LP sensors they are already factory calibrated. That does not mean that you can ignore them forever (as in any CO2 meter, commercial or not).

Over time it is usually necessary calibrate the sensor, but don't worry, it's very easy.

You can find the instructions to calibrate the sensor here: Zero Point Calibration.

Where to put the CO2 meter?

Ideally, place the meter at the point with the worst ventilation in the room, away from the wall, at head height (1.5 meters in height can be a good indication depending on whether people are usually sitting or standing) Y away from drafts.

Keep in mind that if you place the meter near a window you will be measuring a CO2 concentration that does not correspond to the real one in the room because you are measuring with that «additional ventilation«.

Benefits of CO2 Easy

There are several projects similar to this on the internet. From small basic prototypes with the minimum functionalities to obtain local CO2 measurements to complete systems that include all kinds of functionalities, its own software platform for capture and visualization, etc.

I am going to present you here what I think are the main advantages and benefits From this project of CO2 meter.

Reliability of measurements

What a CO₂ meter has to do, as obvious as it may seem, is to measure and CO₂, and do it with a certain precision (that you know how much CO₂, there is with sufficient precision), reliability (that the meter works correctly at all times) and repeatability (always measure the same thing under the same conditions).

There are many projects that promise to measure CO2 but actually use electrochemical sensors of general use for the detection of organic volatiles that do not measure only CO2, but all those gases together, so you really don't know what you are measuring.

There are, for example, many 'CO2 meters' using sensors such as the MQ-135 or CCS811, but these sensors are no useful to measure CO2. These sensors measure all organic gases together (Ammonia, Nitrogen Dioxide, Alcohol, Benzene, Carbon Dioxide and Monoxide, smoke, etc.), so if there is someone who is throwing hydroalcoholic gel or someone smoking or there is a source of combustion, such as a fireplace, the measurements will trigger without the possibility of knowing what is causing them to rise.

In case I have not made it clear: DO NOT MOUNT A METER BASED ON THE MQ-135 or CCS811 SENSORS IF YOU WANT TO MEASURE CO₂!

The project that I present here, uses an NDIR type sensor that only measures CO₂. The same sensor used in commercial meters for hundreds of euros. When you get a measure you will know that that measure it is from CO₂ and not from other gases, that surely do not interest you.

Many commercial meters that call themselves "CO₂ meters"Up to € 200 in price, they use the MQ-135 and CCS811 sensors. Run away from them if you want to measure CO₂!

In case it is not clear, the only parameter that you could obtain with sensors like the MQ-135 or the CCS811 would be: «Value in unknown units of something unknown in the air, which is not known what it is or in what quantity it is«. As you can see, something very little useful.

Ease of construction

In many projects that are online, we see that they are relatively complex to build, with many components and welds. Sometimes it is necessary to have measuring instruments to make adjustments.

This project has been designed and documented to be extraordinarily easy to build and is within reach of anyone with no knowledge of electronics. Only four connections have to be made and it does not require measuring instruments or adjustments of any kind.

There are teachers who are building this meter with children, as an activity in class. See if it's simple!

Ease of programming

Many of the projects that we find on the internet are complicated to program. It is even necessary to have programming tools, such as compilers, IDEs, or specific editors.

Also in many projects we have to edit configuration files by hand, which makes it difficult for the non-expert user.

In this project, no need to program anything. It's all pre-programmed and all you have to do is save the supplied program, which you can download from this page, on ESP8266 with a very simple process, following the video I have prepared.

Easy to set up

Many projects have very complicated configuration processes for non-experts, in which it is necessary to modify many parameters, sometimes modifying parameter files by hand or even the source code of the program before compiling and loading it into the meter.

In this project, all the configuration is done very easily, through a web page. No need to edit files by hand or modify code.

Easy to calibrate

Many projects, especially those based on sensors like the MQ-135 and the like, need tedious and very complicated calibration processes, which sometimes has to be repeated daily or every time it is going to be measured. Worse still, some don't even have the ability to calibrate the sensor.

This project does not require any type of calibration. The sensor comes already factory calibrated and then I know autor calibrate by himself, periodically.

Expandable modular design

Most of the existing CO2 meter designs on the internet have certain functionalities and these they are what they are. It is not possible to reduce or expand the design without making changes to the electronics and, above all, programming.

This project is completely modular and expandable without the need for changes in programming nor in the basic circuit. You can start with a basic CO₂ meter and later expand it, in a very simple way, with different types of screens, LEDs, additional temperature and humidity sensors, etc.

Communications and integration

That the CO2 meter can communicate with the outside and send its data (and even receive it) is very useful on many occasions. In most of the projects available on the internet, either the meter you have no possibility of communication, or your possibilities are very limited.

This project, on the contrary, has some huge communication possibilities that allows you to send data to virtually any device or system, without making any changes to your programming, supporting most of the possibilities like MQTT, HTTP, Telnet, UDP, P2P, etc.

Don't you know what all that I've put on you is? Don't worry! You don't have to know anything about it, they are just options that are there for whoever wants to use them.

Data visualization

In most projects the possibilities to consult the data are very limited. Being necessary to do major changes in your design or programming to be able to add new display options.

In this project, you can visualize the data, both in real time and historical, very easily in multiple ways: integrated web page, screens of various types, multi-color LEDs, mobile app, historical graphics on cloud platforms such as Thinkspeak, etc..

Mobile app

On many occasions it is interesting to know the CO2 concentration or historical remotely.

With most of the devices that we find on the internet this would be impossible or would require important changes in your programming.

With this project this is very simple, being able to consult from the mobile, at any time and from anywhere in the world, current and historical measurements.

Data persistence

Most projects offer real-time measurements, but do not have any data persistence system, to be able to store measurements for later analysis or integration into other systems.

This project allows, in addition to the easy use of cloud services (as Thingspeak, IFTTT and the like), databases like InfluxDB (both local and remote), etc.

Portability and mobility

Sometimes it is interesting to be able use the CO2 meter portable or on the move. Most of the existing projects on the internet do not contemplate this possibility.

This project contemplates the configuration, permanently, of two Wi-Fi networks, so that if the first is not available, the meter connects to the second automatically.

Not only that, but if we turn on the meter in a place where there is no Wi-Fi network that it has configured, It will automatically enable us a web page to which we can connect from the mobile to connect in a few seconds any other Wi-Fi network.

We can also configure the second wifi network so that use the internet connection that our mobile provides automatically.

In addition, being fed by a standard micro USB port, we can use a normal powerbank to run the meter on battery (based on my tests we can expect a autonomy of up to 48 hours, depending on the powerbank we use).

You also have a complete tutorial with a expansion to equip our rechargeable battery meter with built-in charger.

🌀 Options and Extensions of the CO2 Easy Home CO₂ Meter

The ESP8266 controller and the firmware it is based on are very powerful and you allows you to add endless possibilities.

Then you will see some of the simplest possibilities that this carbon dioxide meter allows you.

These extensions they are explained in detail in this blog and in my YouTube videos, but you can easily make many more extensions yourself.

Add an OLED screen

In the following article you can see the step-by-step tutorial to add an OLED screen to the meter, in case you prefer to see the values easily, without using your mobile or computer. It is also interesting to be able use meter without Wifi connection.

Add a custom box

A custom box is the perfect complement to your meter. It will give a more professional finish and will protect the assembly from bumps and snags.

In the following article you will find custom boxes for 3D print, both the one designed by me, and others, shared disinterestedly by users who have built this CO₂ meter.

Adding temperature, humidity and atmospheric pressure data

Add easily and for a few euros thermometer, hygrometer and barometer high precision to the CO₂ meter.

Add notices and audible alarms

You can easily add a buzzer and set alarms and warnings when certain levels of CO2 are reached.

In this article you have a complete explanation with everything you have to do prepared to copy and paste.

Creation of CO₂ evolution graph

You can create, in a very easy way, a graph with the evolution of CO₂ like this, using the free cloud service from ThingSpeak.

The ThingSpeak service allows you to store the data from your sensors in the cloud for free and consult them from your mobile, tablet or computer.

Thanks to user ManeKoYou can see quick instructions in the comments below to automatically send your CO2 meter data to ThingSpeak (press here if you want to go directly to the comment where it is explained).

Using the meter as portable / portable

Sometimes it may be convenient to use the meter in portable (in a different place than you normally have it).

This use, so convenient, is very simple and for this you have several possibilities:

Setting up a second Wi-Fi network

You can configure a second wifi network with its SSID and password, to which the CO2 meter will connect automatically if you can't find the main wifi network.

For it you only have to include the data of the second wifi (SSID and password) in the configuration tab («Config«) And you won't have to do anything else.

Set up two Wi-Fi networks

A very interesting use of this possibility is to use, when you are away from home, the access point you can create your cellphone. In this way it easily becomes a connected portable meter. Perfect for IoT solutions.

Connection to any Wi-Fi network, when neither of the two configured is available

When neither the main Wi-Fi network nor the secondary network is available, the CO₂ meter will automatically create a wifi network to which you can connect from any cell phone, tablet or computer. Just search for the "ESPEasy" network and connect to it in order to set up a new wifi network.

Equip the battery meter (portable CO2 meter)

In the following article I explain, step by step and with video, how you can equip the meter with a rechargeable battery and thus convert it into a portable CO₂ meter with sufficient autonomy to use it throughout the day.

🛒 What if I want to buy a ready-made CO2 meter?

If, for whatever reason, you don't want to build your own homemade CO2 meter, you have the option of buying a commercial one. Plug and play.

There are many models on the market, but, I must warn you that many of them are worth absolutely nothing, in order to measure the concentration of CO2, because they have a type of sensor that is affected by all types of gases and the meter is not capable of distinguishing CO2 from any other gas (and there are many gases in the air that go and they come, so you'll never know if it's measuring CO2 or something else).

Whichever meter you buy, I recommend that you buy one that has an NDIR sensor (And keep in mind that, if it doesn't wear it, it probably won't wear it).

If you want to see more models available at a good price, best sellers, best offers, etc. you have the option to visit this CO2 meter buying guide.

I, in addition to several homemade meters, have in the east room down here that has some additional things that make it a weather station:

Netatmo NWS01-EC Wireless Weather Station Indoor Outdoor With Wifi, Compatible with Amazon Alexa and Apple HomeKit, Silver, 105x45x45 cm
  • Control your indoor and outdoor environment in real time: indoor and outdoor temperature, humidity and air quality, indoor noise level, barometric pressure
  • Receive alerts in real time: with our weather station, configure indoor and outdoor alerts and receive notifications on your smartphone; you will know when to ventilate with the ventilation alert
  • Access your data remotely and with your voice: access your weather measurements with ease and at any time from your smartphone, tablet or computer, or by using your voice to interact with alexa on amazon echo or with siri thanks to the compatibility with apple homekit
  • Analyze the past: access the history of your data to observe what happens when you are not there or analyze the graphs to understand the weather trends
  • Foresee the future: check the 7-day weather forecast to adapt your clothing and your outdoor activities

📢 Do you have problems? CO2 meter faq

Although the project is really simple, there is always the possibility that you may have a question or that some kind of problem will appear.

In the list that you will see below, you have answers to solutions to a lot of things that you can ask yourself.

IMPORTANT: If you have any problem building your CO2 Easy, read this section.

The vast majority of doubts and problems that users have had are resolved in the following lines.

It is not that there are many things because of many problems (most of them are simple doubts and the problems are almost always the same, and most of the time they have to do with the charger or the USB cable), but because It has been built by hundreds of people and any little doubt that has arisen I have documented it so that if it happens to someone else it can be easily solved.

Here I leave you the Frequently asked questions that have been made by users who have been encouraged to build the CO2 meter, CO2 Easy.

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Thank you very much for collaborating with the most difficult part of this project: SHARE IT AND MAKE IT KNOWN. It is useless how much I can work on these tutorials and projects if people don't get to know them. THANK YOU SO MUCH TO EVERYONE WHO SHARES!

Just below you have some buttons that will make it easy for you to share it on Facebook, Twitter, WhatsApp and Telegram.


Be sure to visit my new project: CO2 Gadget.

CO2 Gadget is an advanced CO2 meter with many options and supported sensors, open hardware and opensource, of which you can find all its source code on GitHub.

📜 History of the eMariete CO2 meter

Here you can see the articles related to the CO₂ meter that I have published over the years (since the year 2017 when I published the first version meter).

In these articles you can find a lot of information to expand the meter with new functionalities, learn more, etc.

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305 thoughts on “Un medidor de CO2 casero con Wifi contra el coronavirus: El CO2 Easy”

  1. Hello,

    The Reply button doesn't seem to work to reply to a reply, so here's a new question.

    I successfully built a NodeMCU + OLED + Senseair 🙂

    To save even more power when using that combo off a power bank, would it be possible to provide a new firwmare that doesn't use wifi at all, or maybe use the Flash button to enable/disable wifi once the unit has been configured?

    Thank you.

  2. Good afternoon,
    I have followed all the steps and I have to say that I am surprised because my sensors work perfectly and it collects the data.
    For that part thank you very much but I have a question about Esp-easy.
    Everything is fine as long as I have the Mi Wemos connected to the laptop via USB but once disconnected I can't reconnect to the Access Point to change settings or connect it again and I don't know how to do it without having to re-run the firmware installation.
    I do not know if I have explained myself well, if something is not clear to you, do not hesitate to tell me.
    Best regards and thanks in advance.


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