Red Apple Air Quality Monitor
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42 2020-06-24 12:00:34

Long-distance driving can lead to a sharp increase in CO2 concentrations and harmful gas concentrations in vehicles when the window is closed. When we are in bad air for a long time, besides bad feelings like dizziness, dizziness, nausea, there may be anemia and even cancer. Air pollution in the car will also make the driver sluggish, restless, unable to concentrate and other phenomena, which badly affect the safety of driving. In all, keeping fresh air is closely related to our health and safety.

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Well, we are used to opening windows to breathe fresh air when we are not feeling well, but by then the air quality has already hurt our health. So, we really need a scientific data to remind the members of the car that the environment is so bad that we need to open the windows to breathe the fresh air.

In fact, air quality is the main source of reference, and the main parameters of air quality are carbon dioxide and harmful gases. So how can we make harmful gases and CO2 nowhere to hide? 

Coincidentally, a sensor, CCS811, has been discovered that can detect both harmful gas concentrations and CO2 concentrations. Isn't DIY popular now? Then let's try making our own onboard air quality tester. 

When checking the data, often see what VOC, VOCs, TVOC, IAQ, ppb, ppm or something. ??? what the hell are these? In order to save everyone's time, I have arranged this kind of knowledge. 


1. Introduction of Proper Nouns 

VOC: volatile organic compound and VOCs: volatile organic compounds 

Volatile organic compounds (VOCs) are organic chemicals that have a high vapor pressure at ordinary room temperature. Their high vapor pressure results from a low boiling point, which causes large numbers of molecules to evaporate or sublimate from the liquid or solid form of the compound and enter the surrounding air, a trait known as volatility. For example, formaldehyde, which evaporates from paint and releases from materials like resin has a boiling point of only –19 °C (–2 °F).

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TVOC: Total Volatile Organic Compounds

TVOC (ppm) is the concentration of VOCs present in the air. The TVOC index uses TVOC (ppm) to communicate the level of VOCs in your surroundings. It is mainly used for air quality monitoring. It can monitor volatile organic compounds relatively quickly. It can be used in qualitative researches, but it canot display individual test results of different groups, nor grouped filtering/traceability. 

TVOC indicator can only roughly show the amount of volatile organic compounds, but it cannot characterize the difference between various components. 


IAQ: Indoor air quality 

IAQ is the air quality within and around buildings and structures. IAQ is known to affect the health, comfort and well-being of building occupants. Poor indoor air quality has been linked to sick building syndrome, reduced productivity and impaired learning in schools. TVOC is an important polluter in IAQ), and the other four polluters are second-hand cigarette smoke, formaldehyde, mold dust, and carbon monoxide. 

Let's take a simple example to understand the relationship between VOC, VOCs, and TVOC. If there is only one kind of harmful gas in the air, like ethanol, we call it VOC. Well, if there is more than one pollution gas in the air, such as ethanol, methanol, toluene in the air. we call them VOCs. When we test the sum of all the harmful gas concentrations in the air, this "sum" refers to TVOC. 

Now, we know these special nouns, and let's look at the impact on people with different numerical ranges of them.

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We learned the corresponding professional nouns, and let’s look at the amount or concentration unit of VOC. There are two ways to represent the concentration of pollutants in the ambient atmosphere (air):

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Just like % and ‰, separate ppm ppb is not a unit. 1ppm=1000ppb, 1ppb=1000ppt

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Online ppb/ppm and mg/ m³ Converter 

http://www.aresok.org/npg/nioshdbs/calc.htm

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2. Function 

(1) Measure the equivalent harmful gas concentration (eTVOC) in the vehicle and display it on the LCD screen. 

(2) Measure the equivalent CO2 concentration in the vehicle and display it on the LCD screen. 

(3) LCD screen supporting display some other environmental parameters in the car (such as temperature) 

(4) When the CO2 concentration and the TVOC concentration exceed the set value, the LED will be ON. 


 3. Materials in Need 

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Gravity: CCS811 Air Quality Sensor can measure the eCO2 (equivalent CO2) and TVOC (Total Volatile Organic Compounds) density. Compared to conventional gas sensors, this sensor is lower power consumption, heating faster, and smaller. It is ideal for interior air quality measurement in cars. 

And the monochrome 0.96" 128x64 I2C/SPI OLED Display has a self-illuminating feature, which makes it easy for people to grasp the information displayed on the screen. Especially in the state of driving at night, self-illuminating can help drivers immediately know the air conditions inside the car. 


 4. Making Process

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Hardware Connection Figure

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Hardware Connection

We can first completely implement the application function on Leonardo, and then replace it with a Beetle. To be able to alert drivers and passengers, I added a small RGB band. When the CO2 concentration and TVOC concentration exceed the set value, the red light will be ON, reminding people in the car to ventilate in time. 

I have put the welded circuit in a 3D-printed shell, just expose the display and put other parts away (attention: the short circuit; we can wrap the bare part of wires with insulation tape). Such an air quality tester is complete.

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