Laser cut Mylar stencils are an acceptable method of applying solder to pads if you have the means. And solder paste syringes are pricy but very, very handy if you need a little extra paste somewhere specific. Great little project! It’s been an age since I hand assembled anything like this. Makes me wish I was tooled up for more than just soldering headers.

Mylar? Most stencils I've seen are stainless steel. PCB shops will usually sell you stencils along with the board as an add-on. ($20-ish)

Yeah, they are very definitely not production grade! But we had laser cutters, mylar sheets, pots of solder paste, questionable quality spatulas and way too many different prototype PCBs. A means to an end.

Hey Phil, glad you like it. I'm just being a cheapskate with the $7 JLCPCB charges for stencils. I keep making dumb mistakes on my PCBs, so I skip the stencil and assembly to save cost.

Please can CO2 alarms become as common as smoke alarms...?

Too much CO2 has pretty clear downsides[1], and probably takes away far more productivity than people killed in fires, yet we mostly ignore it in building codes worldwide. Whereas a new building without smoke detectors would be illegal in much of the world.

[1]: http://www.aretas.ca/sites/default/files/imce_images/Indoor%...

Keeping an eye on CO2 is really interesting. I recently moved from an apartment with an electric range to one with a gas range, and CO2 gets as high as 3000ppm when I'm cooking (compared to a baseline of around 700 or 800). I don't know what the effects of this are, but the monitor reminds me to ventilate during and after cooking.

(I have my Airthings monitor bridged to HomeKit with Home Assistant and it seems severe enough for Apple to send a notification to my phone about it, by default. So I open windows and am happy to be able to notice air quality issues that most people will miss. I did turn off the notification though, I know I'm cooking ;)

Are you sure you have a CO2 monitor and not an eCO2 monitor?

A lot of cheaper CO2 sensors really detect VOCs and try to estimate CO2 from that.

I have this: https://www.airthings.com/view-plus

It ain't cheap.

Well price is no guarantee. Try the hand sanitiser test I detailed above.

The CO2 sensor in the View Plus id advertised as follows:

NDIR Sensor (Non-Dispersive Infra-Red): Measurement range 400–5000 ppm Optimum Accuracy ±50ppm ±3% within 10 – 35°C / 50 - 95°F and 0 – 80%RH after initial calibration time

Can you tell from that description whether it's a true CO2 sensor?

That's proper CO2 sensor then. The cheap ones are estimating CO2 levels from VOC levels.

Second this. It's possible that the 3000 reading is triggered by something else. They should try rubbing sanitiser on their hands and then holding the device - if it goes crazy then it's not directly sensing CO2.

I sort of did this test last night. I assume that VOCs include ethanol, so I mixed up some drinks near the monitor. VOCs went from ~60ppb to a peak of 579ppb. CO2 remained constant at about 640ppm.

I am less surprised than other people that making an open fire indoors increases CO2 levels. Where do the combustion byproducts go if not into the air.

Do you have a rangehood fan that vents outside?

You should never cook without one, even electric, but especially with gas.

If you do have one sounds like it isn’t working very well. Maybe not enough make up air coming in, it’s blocked? Not sure.

I don't think my fan vents outside, but I haven't really tested it extensively. I haven't ever seen an apartment in NYC whose range fan vents outside, but maybe I've just been unlucky.

> You should never cook without one

It's probably one of the least important thing you can act on in your day to day life when it comes to health tbh

Would you entertain the idea of stressing about CO2 levels being more harmful than elevated CO2?

Hear, hear.

Humans really are sheeple.

No.

Fair enough

To be fair, I think the fear of cognitive effects of increased CO2 concentration is overblown: https://pubmed.ncbi.nlm.nih.gov/32557862/

So some perspective;

    * 10,000 years ago, the average atmospheric CO2 was about 280ppm.
    * In 2022, the average atmospheric CO2 was about 420ppm.
    * OPs baseline indoor CO2 is 700-800ppm.
    * For a brief time when cooking, OPs indoor CO2 is 3000ppm

700-3000ppm CO2 would be catastrophic for the climate if it was the average atmospheric level (but fortunately we haven't messed up this bad yet)

But when it comes to the effect on the body, and I am not a medical professional of any kind, but normally exhaled air contains about 4.5 percent CO2 ( or 45,000ppm), so while breathing in air with 3,000ppm or 0.3% CO2 probably isn't optimal for us - our lungs are constantly dealing with much higher concentrations. So nervous shallow-breathing worrying about CO2 levels of your home probably has a similar effect to OPs cooking. ¯\_(ツ)_/¯

Levels above 1000ppm are shown to cause cognitive impairment. 3000ppm is absolutely harmful.

>our lungs are constantly dealing with much higher concentrations

After gas exchange. Not with inhaled air.

>After gas exchange. Not with inhaled air.

gas exchange is continuous, not a discrete event that only takes place just after fresh air enters the lungs.

Sitting next to someone exhaling 45,000 ppm air and breathing in, if you breathe in perhaps 5% of what they breathe out, you are still breathing in air at 2,400 ppm...

Is sitting next to someone bad for health?

It's very hard to disassociate everything from placebo effects, and I had a CO2 monitor in my bedroom plugged in for a while.

It trained me to open windows to create circulation, but unfortunately some of the reduced airflow was unsolvable short of me like... installing more ventilation into my room.

I am glad I am aware of CO2 stuff (and definitely feel like I've reduced headaches and the like from being more mindful) but sometimes you will be informed of a bad CO2 environment but be totally incapable of doing anything about it and that really sucks.

There are some pretty cool newish ventilation products that are minimally invasive (e.g. don't have to run need ducts). Lunos makes a tiny ductless HRV that can provide indoor/outdoor air exchange. There are other products, too. https://www.buildwithrise.com/stories/ductless-heat-recovery lists several.

What I'm thinking of is more two places:

- an office (fortunately not my case)

- rented apartment that would not let me drill a hole in the wall

Good info to have though! I feel like I would definitely look at setting that up in most cases

Don’t assume when someone brings up a health hyperoptimization they’re stressing out about it.

In fact, lots of people who do these sorts of things actually enjoy what amounts to a health hobby, in the same way any other hobbyist likes to geek out about their respective hobby.

Stressing out about minutiae of your own health is, in most cases, wasted effort.

However, putting that effort into fixing those small things for millions of people usually is worth it. For example, could OP contact their local building standards department and push for CO2 monitors in all new buildings? Could they do a study and publish the results to give a better scientific backing for any changes? Could they publish designs for a combined smoke and CO2 alarm?

If they are truly powerless to do anything like that, then they should just ignore the whole thing and worry about more day to day risks, like slipping on ice on their front yard.

But you're missing my point: why assume it's "stressing out"?

A similar project can be done without soldering using parts from Adafruit, including a module for the Sensiron chip. Here is a project I made using Adafruit's e-ink module and the SCD41 module they sell: https://www.printables.com/model/121265-salud-co2-monitor

I need to add price details to my blog post. The main goal of mine was low cost. The total cost for me to produce each board is $17 where $14 of that is the SCD40 sensor.

That's impressive! Mine was over $100. The SCD40 in module format is $45.

You can get SCD40s on AliExpress for under USD 15. I bought a few and around 20% did not work and some had some weird data patterns occasionaly.

I am maintaining a popular open hardware indoor air quality monitor project [1] and it's great to see more and more projects in this space. I like the small footprint and portability of this pocket CO2 monitor so congratulations on publishing this!

The SCD4x series of photo accoustic sensors from Sensirion is an excellent choice for indoor CO2 measurements and comparable to NDIR sensors. You can see a comparision of the two in a blog post I wrote some time ago [2].

The SCD4x has an built in temperature and humidity sensor and I think this project displays that data. The purpose of this humidity and temperature is to measure these parameters inside the sensor module for compensation algorithms, i.e. CO2 measurement can be affected by temperature, humidity etc. The self heating effect of the SCD is already cmpensated by Sensirion with a default offset of 4 degrees Celcius [3] but the small footprint of the device and other environmental factors, e.g. ventilation could lead to quite large deviations to the real ambient temperature and humidity.

I think in a future iteration, it would be nice if the monitor could log data, either to built in memory or through WiFi. This could give a lot more additional data, e.g. CO2 development during 24h to see the effect of ventilations and the CO2 decay curves etc.

All in all a nice project!

[1] https://www.airgradient.com/open-airgradient/kits/

[2] https://www.airgradient.com/open-airgradient/blog/co2-sensor...

[3] https://cdn.sparkfun.com/assets/d/4/9/a/d/Sensirion_CO2_Sens... see 3.6.1

The Sensirion SEN5x series is very nice to work with. I’m using the SEN55 in my own air quality monitor project. It measures Humidity, NOx, Particulate Matter, Temperature, and VOC. I’m interfacing this with a LilyGo ESP32 T-Display-S3.

I've been learning PCB design recently, and I'd like to point out that having the manufacturer do all the surface mount assembly can be surprisingly cheap and it's not all that hard to do.

I'm using Kicad and JLCPCB. Their minimum order is five boards, and if you're doing assembly the minimum is to have two of the five boards populated.

There are some extra hoops to jump through. Kicad doesn't generate the BOM or placement file correctly so you have to edit some column titles in CSV files, and apparently Kicad uses a rotation standard where pin 1 is always in a certain orientation whereas JLCPCB uses a standard where the rotation is based on how it comes off the reel (or something like that), so you have to use JLCPCB's online editor to fix the rotations manually or let JLCPCB's people do it for you.

It's aggravating, but I'd rather do that once than have to manually solder a bunch of boards -- especially if they have a lot of components.

There might be some parts they don't have or they're not in stock, so you'd have to do those manually in any case.

Some of the PCB and SMT vendors also have KiCAD plugins that in theory streamline the ordering process.

There is one for JLCPCB that generates the BOM, but you still have to manually rename the columns.

https://support.jlcpcb.com/article/84-how-to-generate-the-bo...

If you want to play with that CO2 sensor without soldering, get the evaluation kit.[1] It's $52.

[1] https://sensirion.com/products/catalog/SEK-SCD41

I just added details about the parts cost. The total for the project is $17.11 not including the vibration motor; I bought them several years ago and forgot how much I paid for them.

I recorded a video walk-through of the feathres:

https://www.youtube.com/watch?v=Kik7NmzLE-k