Richard's Tech Reviews

Measuring PM2.5 air quality with a Raspberry Pi and Nova PM SDS011 sensor

Ryder Damen on Tom's Hardware has a straightforward project - How to make a Raspberry Pi Home Air Quality Monitor.  After a small bug fix, it worked well.

My hardware:

• Raspberry Pi 3
• Nova PM SDS011 sensor

Clean Raspberry Pi Install

Hardware:

• SanDisk microSD card
• SanDisk microSD-to-SD adapter
• Apple USB-C SD card reader

Software:

• Raspberry Pi Imager

I just followed the steps on Getting Started - Setting up your Raspberry Pi.

I downloaded the Raspberry Pi Imager, installed it on my Mac, and then installed the default Raspberry Pi OS 32 bit image on my MicroSD card.

I used the advanced options available in Imager by clicking the cogwheel in order to set the Raspberry Pi device name and a non-default username and password for the root account.

Once the MicroSD was reformatted and had the Raspberry Pi OS installed and verified on it, I safely ejected the card (actually I just powered down the Mac, which has the same effect).

Insert the MicroSD and Power Up the Pi

With a new clean install of Raspberry Pi OS ready on the MicroSD, I inserted the MicroSD into the Raspberry Pi and powered up.

I already have a keyboard and mouse on a USB hub (so a single USB-A connector) and a small HDMI monitor.

For networking I just plugged the Raspberry Pi directly into my Ethernet network.

Everything booted up fine, I disabled Bluetooth since it was unnecessary and then I opened a command line and followed the article steps.  I did everything with the root account, which is not a best practice but is the fastest way to get going for this type of single-use experiment.

Follow the Article Steps

After that I just followed the steps in the article.

https://www.tomshardware.com/how-to/raspberry-pi-air-quality-monitor

1. sudo apt-get update && sudo apt-get install -y git

2. cd ~/
   git clone https://github.com/rydercalmdown/pi_air_quality_monitor.git

3. cd pi_air_quality_monitor
   make install

4. make build

make build will take some time. It took about 15 minutes on my Raspberry Pi 3. But you only have to do it once.

5. Connect the SDS011 sensor to the USB adapter it comes with using the provided jumper cable, then
   Connect the SDS011 USB adapter to your Raspberry Pi.
6. There is a bug in the code

You need to edit the file

src/templates/index.html

and change the line (line 35)

$.getJSON('http://10.0.0.172:8000/api/', function(data) {`

to

$.getJSON('/api/', function(data) {`

You can use e.g. the built-in nano editor to do this edit.  (I have also submitted it on GitHub as a pull request - 17 Update index.html)

Otherwise without this change the hardcoded web address (IP address) will cause the web server to fail with a misleading error.

7. make run

8. Navigate to your Pi’s local IP (127.0.0.1) address on port 8000 to view the web server, and a graph of recent measurements of air quality.
   i.e.
   http://127.0.0.1:8000/

IMPORTANT NOTE: This web page does not auto-refresh.  It will start out as a blank graph underneath the text "Raspberry Pi Air Quality Monitor".  You have to manually reload the page (by e.g. clicking the circle arrow) to get the latest data.

Many people were saying their sensor or the code wasn't working, but actually all you need to do is reload the web page.

Any Port in a Particle Storm

I was worried that the four USB ports on my Pi 3 would have some unique numeric binding, but they don't.  With my keyboard and mouse on a single connection through a USB hub, and the SDS011 as the only other USB device, whichever port I plugged the SDS011 into became ttyUSB0 , so it wasn't an issue.

Testing 999

As the reading is normally just steady, I did a -- NOT RECOMMENDED AT HOME -- smoke test by intentionally burning some toast.  This set off my fire alarm and also caused my Temtop M10 PM2.5 sensor to go to its highest reading, 999. 

The on-screen readings from the Nova PM SDS011 responded as expected, so it definitely works.

I also ended up doing an unintentional smoke clearing test, which told me that it takes my air filters 40 minutes to clear the air from unsafe to safe levels.

The Raspberry Pi graph responded to the declining counts as I would expect.  The count wasn't exactly the same as the Temtop M10, but this is to be expected as the Nova PM 2.5 is reading over a shorter time interval.

Going Public

Be aware that this web server is also running on your Raspberry Pi's public IP, not just on localhost.  I solved that problem simply by pulling the Ethernet cable, but you may not have such an easy solution depending whether your Pi is on Wi-fi and what else you are doing with your device.

Conclusion

With the exception of the bug (which the code author really should fix) and the fact that the web page doesn't auto-refresh, this is a quick and easy project to get your own PM2.5 (and PM10) sensor readings.

Bug aside, thanks to Ryder Damen for making such a straightforward no-solder project possible.

Security Note

You should be mindful of the security issues that might be associated with running this as a service on port 8000 of your Pi's public IP (ideally the code should be modified to allow the option of a local service only).

Annex: Buying a Nano PM SDS011

I could only find a wide variety of vendors on Amazon.

I'm in Canada, I got my SDS011 on Amazon Canada from risingsaplings in the States for $55.  I liked that it shipped from Amazon USA, so that I had confidence there actually was a real product and that its shipping would be well tracked.

/risingsaplings-Precision-Quality-Detection-Digital/dp/B0BPQQ24ZR/

You can get much cheaper prices from Amazon Canada by going with other vendors that ship themselves from Canada.  Just search for SDS011.  I can't provide any comment on the other vendors or the reliability of their shipping, I have no idea.

if using Make Minecraft do not update Kano

UPDATE 2018-11-02: The information below is from December 2016.  It is no longer relevant to try to keep Kano at version 3.7.0  END UPDATE

I installed Kano OS 3.7.0 on a Raspberry Pi 3B

https://downloads.kano.me/public/Kanux-Beta-v3.7.0-jessie-release_noobs.zip

On first run it has several updates (to beta 3.8.0), which take a long time to run.  If you want to keep Make Minecraft DO NOT UPDATE Kano OS to 3.8.0 at this time.

The most significant update I noticed is a total replacement of Make Minecraft with Hack Minecraft.

The underlying concept of learning by using a block-based programming language remains, but the tasks are different, and there doesn't appear to be any way to easily see the Python code.  To me that was the most useful part of the exercise, to be able to show that the blocks created specific computer code.  Plus which, if you were part-way through Make Minecraft, all your tasks and progress are gone.

Also the tasks are a bit flaky.  The write your name one didn't work for me the first time I tried, and the second time it showed a black screen - I had to tab into Minecraft and look in a different direction to see the name blocks. Plus which the blocks for the letter S appear to be wrong.

It looks to me like Hack Minecraft is a replace of /usr/share/make-minecraft ; the original executable and scripting code is completely replaced with Hack Minecraft.

This is not cool to do without any warning.  You might want to backup your make-minecraft directory just in case (e.g. make a copy of it using cp -r, if you're familiar with using the command line).

I have posted on Kano World Forum asking for more information but this is probably useless as Forum is no longer maintained.  You're supposed to email [email protected] instead.

Ideally Hack Minecraft should be a separate install in /usr/share/hack-minecraft with a default to duplicate world(s) from ~/.minecraft/ (the user's home directory contains the user's Minecraft worlds)

Make Minecraft

• comes with Kano OS 3.7.0
• runs from /usr/share/make-minecraft/bin/make-minecraft
• can easily display the Python code that is being generated from the block programming interface

Hack Minecraft

• installed with an update to Kano OS 3.8.0
• runs from /usr/share/make-minecraft/www/index.html ??? (JavaScript)
• no way to see code generated from block programming interface

3.7.0 to 3.8.0

There are other differences as well.  The most significant is that instead showing just a few coding and entertainment related apps in Home (Make & Explore) and grouping everything else inside of "Kano Apps", in 3.8.0 all the apps are listed out page after page.  For young children this may not be ideal.

Kano OS beta 3.7.0 on Raspberry Pi 1B 256MB

Kano - Developers - Downloads for Kano OS beta 3.7.0 says "Runs on Raspberry Pi 1B, 2, 3 and Zero".  Which is true except there is a subtlety about the 1B.  There were actually two models of the 1B: an early model with 256MB RAM, and a later model with 512MB RAM.  This turns out to be important.

The boot config for 3.7.0 assumes the 1B has 512MB, and if you run it on the 256MB it will more or less hang once it gets to the graphics environment.  You may see a mouse pointer and nothing else, forever, or see it partly start up the graphics environment and then nothing.

I thought it might be RAM related so I looked at the config.txt

You can do this by e.g. reading the SD card on a Mac and examining config.txt on the boot partition.  (Note that you should only edit this file with a text editor such as BBEdit, not with a word processor.)

The default config.txt says

# set memory split: amount allocated to the GPU in MB.
gpu_mem=128

This is clearly way too high for a 256MB Pi 1B. I changed it to

gpu_mem=32

and then Kano OS booted up fine. top shows about 16MB free, so the capacity to run apps may be fairly limited, but you can at least see the graphic environment (GUI) and open a terminal windows etc.

You will want to wait a while for initial startup tasks to complete.  When startup is running the CPU will be close to 100%.  It should drop to around 40% once startup is completed.

Note: once you're able to actually load a terminal (e.g. K->Code->Terminal or Apps icon - CODE - Terminal) you can find config.txt in /boot/config.txt

I will do further experimentation, and see whether 32MB GPU RAM makes a usable environment or whether a 16MB allocation works better.

The OS will complain at boot time if you set GPU RAM to 16MB, but it will boot.  top will rather unsurprisingly show 32MB free rather than 16MB.

I was unsuccessful in getting Make Minecraft to run in either 32MB or 16MB configuration.  In 32MB configuration it froze, in 16MB configuration it tried to launch Minecraft but then crashed and closed.

I will make a list of what software works and what doesn't.  Development of list in progress.

Works with GPU 16MB RAM:

• Scratch

Does not work:

• Make Minecraft (crashes at Minecraft launch)