Exploring the Components of Gases Human Breath In and Out With SCI and Air Sensors


Do you find it hard to breathe when staying with a crowd of people in a confined space? This challenge arises due to the varying components of the air we breathe in and out. Our bodies absorb essential gases from the air and release waste gases during breathing. By conducting a fascinating science experiment using micro:bit, CO2 sensors, and O2 sensors, we can precisely visualize these differences in the air composition. Let's delve deeper into the science behind the air we inhale and exhale.



SCI DAQ Module x 1

SEN0322 Oxygen sensor x 1

SEN0536 Infrared CO2 Sensor x 1

4pin Wire x 2

Type-C Cable or Battery Holder

Small Transparent (Glass/Plastic) Bottle x 1

Sink x 1

Straw x 1



1) The diameter of the bottle top should be at least 3cm so that two sensor could be put into the bottle. It would be better if the bottle has a cap.

2) If you have no access to a suitable bottle or sink or straw, you can replace them with a small plastic bag and follow the simplified procedures of collecting the gas you breath out. The appropriate size of the plastic bag would be small enough to fill it with your one or two breathes, and big enough to contain the oxygen sensor and CO2 sensor.



1. Power the SCI module from either battery or Type-C port.

2. Connect the oxygen sensor and infrared CO2 sensor to Port 2 and Port 3 respectively. The sensors will be automatically identified and their data will be displayed on the screen.



1. Set Data Refresh Rate: 

In the previous courses we have learned that the data refresh rate can be adjusted as desired. During this experiment, where the changes of sensors indexes are accurate, we should switch to a relatively high data refresh rate, 1S.

1) Press S button to enter the setting menu.

2) Select Set Refresh Rate.

3) Select 1S and press OK to confirm.


2.  Collect the Gas You Breath In:

Fresh air is actually the gas we breath in. Open the bottle or plastic bag for 3 minutes to collect fresh air. Put the sensors into the bottle or plastic bag. Press R button and wait for 3 minutes. Press R button again to stop recording.


3. Collect the Gas You Breath Out:

You can choose one of the two presented methods to collect the gas you breath out. The standard method refers to a commonly used gas collecting method in chemical experiment, which prevents most impurities. If you have any difficulties conducting the standard procedures, feel free to switch to the simplified ones, which are less serious but do little influence to final conclusions.

Standard Procedures:

1) Fill the sink and the bottle with water. Put the bottle upside down in the sink.

2) Put one tip of the straw in the bottle, and another tip in your mouth.

3) Blow through the straw to the bottle until there is no water remain in it.Be careful not to suck in water in the bottle!

4) Seal the bottle underwater.

5) Get the sealed bottle out of water. Here is a bottle full of the gas you breath out!

Simplified Procedures:

1) Clear all the gas or liquid out of the plastic bag.

2) Blow into the plastic bag and tight it as quick as possible.

3) Here is a bag full of the gas you breath out!

4. Record the data:

1) Open the bottle or plastic bag, put the two sensor into it and then seal it. The above actions should be done as quick as possible to avoid gas exchange.

2) Press R button to start recording. Wait for 3 minutes until the data are stable.

3) Press R button again to end recording.Get out the sensors.


Please note:

1) If the module is connected to a computer via a Type-C cable, and an operation is performed in the pop-up U disk, data recording will be disabled, and the module needs to be restarted to enable it again.

2) When the REC function is enabled (meaning data recording is happening), no operations should be performed in the U-disk. If an operation is performed, it may result in data recording failure.


5. Export the Data:

The recorded data can be exported in the format of a CSV file. 

1) Connect the module to a computer using a Type-C cable, and a U-disk will appear. (Un-plug and connect again if you are using the Type-C to power the module.)

2) Open the U-disk and copy the CSV file that you need into your computer.


6. Data Analysis

Draw three line graph of O2, CO2 and humidity separately. Each line graph will show how a parameter changes before and after you put the sensor into the gas you breath out, which indicates the component differences between the gas you breath in and out. Please note that the three parameters are recorded in different measurements so that you can’t merge them into one line graph.


7. Conclusion

The graphs tell that in the gas we breath out, the levels of O2 is lower and the levels of CO2 is higher than fresh air. The humidity of the gas we breath out is also higher than fresh air, which suggests that the former contains more vapor than the later.

The energy required for all biological activity comes from breathing on the cell level, which occurs in the mitochondria of cells, the main process being the combination of O2 with stored organic matter to produce water, CO2 and energy.

Given that all sorts of living creatures consume O2 and emit CO2, why the O2 in the atmosphere haven’t been drained out? Why the air around us haven’t been filled with CO2? Thanks to plants’ photosynthesis, the components of the air have remained relatively stable. We will find out the details of photosynthesis in the later courses.


Expansion: Building a CO2 concentration indicator

When CO2 levels in the air are normal, it is not harmful. But above a certain level it can affect people's respiratory system because the concentration of carbonic acid in the blood increases, becomes more acidic, and produces acidosis. The below chart shows the effect of CO2 concentration on the human body.

By connecting the CO2 sensor to a micro-controller such as micro:bit, you can create a CO2 concentration indicator to inform you to take in fresh air when the level of CO2 is too high to do harm to your health.


Additional Materials:

micro:bit x 1

micro:bit Expansion Board x 1



1. Connect the SCI module from the I2C output port to the I2C port on the micro:bit expansion board. 

2. Power the micro:bit and SCI module using the power plug on the expansion board. 

3. Connect the micro:bit to your computer using a USB cable to begin programming.



The micro:bit will display a smiling face with the CO2 concentration lower than 700ppm, which is quite acceptable and healthy. When the CO2 concentration measures between 700ppm and 2500ppm, you may feel sleepy and a little bit uncomfortable. When the CO2 concentration reaches above 2500ppm, a sad face will appear to urge you to go outdoors for some fresh air. When CO2 concentration accumulate to more than 5000ppm, the micro:bit will ring a bell warning that it would cause irreversible damage to your body if you stay in the atmosphere for more than 8 hours.

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