PeluCO₂: A CO₂ meter on your wrist (wearable)

Last modified March 19, 2021

Do you want to always have at your fingertips the CO₂ level present in the environment? This is the perfect solution. A CO meter "Full equip" (without commitments) in a wearable that you can wear on your wrist.

This is a very special post, since it is the first post published in collaboration with a user of the eMariete blog, the user Ernesto (@ erguro1973).

It is a project, designed and built by @ erguro1973, based on EMariete CO2 meter, made with a lot of ingenuity and a lot of work. Not surprisingly, it has had to go through a number of tests and iterations of the box to get the current result.

But let it be @ erguro1973 himself who explains his motivations:

«The PeluCO₂ project was born out of the need to know the quality of the air inside the premises and in public transport, as many will already know, several studies on the spread of the SARS CoV-2 virus point to aerosols as a route of contagion , airborne infection increases its chances in poorly ventilated areas. »

«PeluCO₂ is your portable meter that will allow you to measure independently, what are the CO₂ levels in the places you visit and will warn you by means of an LED with 3 states and a screen that will show you the value in Parts Per Million of the CO concentración concentration .
For its realization, NDIR technology and sensors known and used in commercial meters have been used. "

PeluCO₂ photo gallery

We leave you some photographs of PeluCO₂ so that you can open your mouth. You can click on each of them to see them larger.

Construction of the PeluCO₂

The construction of the PeluCO₂ does not present special difficulty, beyond that of working with several elements in a small space and printing its 3D printed parts correctly.

We can divide its construction into four parts:

  1. Firmware
  2. Connections
  3. Mounting in 3D printed box
  4. Optimizations

You have all the step by step instructions, with all kinds of details and even detailed video, in the post of EMariete Homemade CO2 Meter. In that post we will tell you a duo, between Ernesto and Mariete, the differences so you can build your own PeluCO easily. starting from the main tutorial.

If you have not read it, we recommend that you do so before building the PeluCO₂.

Required components

For the construction of the PeluCO, you will need the following materials:

  1. CO₂ sensor MH-Z19B (version with pins, version with connector does not fit)
  2. Wemos D1 Mini
  3. Wemos Battery Shield
  4. OLED screen SSD1306
  5. Li-Ion 3.7V 500mAh battery
  6. PLA or PETG filament for the case and TPU for the strap

Almost all MH-Z19B sensors now on sale they are false and they work poorly. It is best to buy it at the official store of the sensor manufacturer (Winsen), in this way you will have the security of receiving the original sensor.

The problem is that the manufacturer does not sell the MH-Z19B one at a time, it has to be in pairs. So if you want to build two, or have someone who wants another, this may be a good option:

MH-Z19B2 CO₂ sensors MH-Z19B for about 38 Euros in the official manufacturer store on AliExpress.

Here you will have the sure to receive the original sensor, and not a copy.

I recommend that you order the one with a range of 5000 ppm.

Be careful not to buy the MH-Z19 sensorC (many vendors advertise the MH-Z19B and they actually ship the MH-Z19C), you may have trouble on this project.

Firmware installation

You have detailed instructions for recording the firmware, as well as for its configuration, in the main tutorial. You just have to follow them.


You can make the connections by following the diagram below:

Don't be intimidated by the mess of cables, you'll see how it's not difficult.

We will use the divide and conquer strategy to make the connections. do every step, as if there were no more components of those that we indicate in each step, and you will see how easy.

The order is not important, familiarize yourself with the whole assembly viewing the diagrams and photographs and mount it as is most comfortable for you.

We are finishing writing the tutorial, as you read this. Soon you will find more detailed descriptions of the assembly steps, photographs of each step, the files to print the parts in 3D and everything else.

Connect the MH-Z19B sensor to the Wemos D1 Mini board

You will simply have to use four cables.

Take advantage of this moment to put off the micro USB connector and the micro switch of the Wemos D1 Mini to reduce space.

Connect the WS2812B LED

You can connect the 5 volts and the GND both the SSD1306 display and the Wemos battery shield. As is most comfortable for you.

You will mount the LED "loose" without any type of plate or support, otherwise it would stumble on the screen. Put a piece of insulating tape or similar to make sure your connections they don't touch nowhere.

You will have to stick it to the box with the glue of your choice, for example, cyanoacrylate (superglue).

Connect the «Battey Shield» board to the Wemos D1 Mini

Connect the SSD1306 display to the Wemos D1 Mini

Notice that the SDA and SLC pins are used to connect them to the «sandwich» of the batteyt shield and the Wemos D1 Mini directly (match). You will connect the positive and negative to the sandwich with two cables.

Connect the battery to the «Battery Shield»

3D printed box mounting and printing

Below, you have some photographs of the assembly process that will serve as reference and source of inspiration.

@ erguro1973 is finishing some latest modifications in the design of the printed parts. Soon you will find here the STL files so you can download the pieces and print them yourself.

3 thoughts on “PeluCO₂: Un medidor de CO₂ en tu muñeca (wearable)”

  1. Thanks for sharing this interesting project. I put it together and it stays almost the same. Could you tell me how to set the battery level of the clock? Search but I can't find the solution. Thanks!

    • Hello Mariano.

      You have everything explained in great detail in the post called "Using a ModeMCU as a voltmeter" (
      For more questions about the specific implementation, I recommend that you enter the eMariete Telegram Group ( where its creator, the user Ernesto (@ erguro1973), can give you more details. In addition, you will be able to closely follow the development of the new version of PeluCO2, which is already well advanced.

      A greeting.


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