PeluCO₂: A CO₂ meter on your wrist (wearable)

Do you always want to have at your fingertips CO₂ level present in the environment? This is the perfect solution. A CO "full equipe". (no strings attached) in a wearable that you can wear on your wrist.

This is a very special post, as 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 @erguro1973on the basis of the eMariete CO2 metermade with a lot of ingenuity and hard work. Not surprisingly, it has had to go through a number of tests and iterations of the box to achieve the current result.

But let @erguro1973 himself explain his motivations:

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

"PeluCO₂ is your portable meter that will allow you to independently measure the CO₂ levels in the places you visit and will alert you with a 3-state LED and a display that will show you the value in Parts Per Million of the CO₂ concentration.
NDIR technology and sensors known and used in commercial meters have been used for its realisation".

PeluCO₂ photo gallery

Here are some pictures of PeluCO₂ to whet your appetite. You can click on each one of them to see them bigger.

PeluCO₂ construction

The construction of the PeluCO₂ is not particularly difficult, other than working with several elements in a small space and printing their 3D printed parts correctly.

We can divide its construction into four parts:

  1. Firmware
  2. Connections
  3. 3D printed box assembly
  4. Optimisations

You have all the step-by-step instructionswith all kinds of details and even detailed video, in the post of the eMariete's homemade CO2 meter. In this post we will tell you about it in duo, between Ernesto and Mariete, the differences so you can build your own PeluCO easily. starting from the main tutorial.

If you haven't read it, we recommend that you do so before building PeluCO₂.

Required components

For the construction of the PeluCO₂, you will need the following materials:

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

Nearly all MH-Z19B sensors now on sale are false and malfunctioning. It is best to buy it from the official shop of the sensor manufacturer (Winsen).This way you can be sure to receive the original sensor.

The problem is that the manufacturer does not sell the MH-Z19Bs one at a time, but has to be two by two. So, if you want to build two, or have someone who wants another one, this may be a good option:

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

Here you will have the assurance of receiving 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 sensor.C (many sellers advertise the MH-Z19B and they actually send the MH-Z19C), you may have problems with this project.

Firmware installation

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


You can make the connections by following the diagram below:

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

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

The order is not important, familiarise yourself with the whole set-up looking at the diagrams and photographs and set it up as you are most comfortable.

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

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

You will simply need to use four wires.

Take advantage of this moment to remove on micro USB connector and the micro switch of the Wemos D1 Mini to reduce space requirements.

Connect the WS2812B LED

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

The LED will be mounted "loose". without any kind of plate or support, otherwise it would trip over the screen. Put a piece of insulating tape or similar to ensure that their connections do not touch nowhere.

You will have to glue it to the box with the glue of your choice, e.g. cyanoacrylate (superglue).

Connect the "Battey Shield" board to the Wemos D1 Mini

Connects the SSD1306 display to the Wemos D1 Mini

Note that the SDA and SLC pins are used for connection to the sandwich of the batteyt shield and the Wemos D1 Mini directly (they match). Positive and negative are connected to the sandwich with two wires.

Connect the battery to the Battery Shield

3D printed box assembly and printing

Below are some photographs of the assembly process that will serve as a guide for you. reference and source of inspiration.

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

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

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


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