6 ms·

Building the Pocket CO2 Project

87 points by _Microft 3y ago

gadgetoid 3y ago
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.
- sbierwagen 3y ago
  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)
  - gadgetoid 3y ago
    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.
- bitbank 3y ago
  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.
londons_explore 3y ago
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%20Environment%20in%20Schools%20%E2%80%93%20Pupils%20Health%20%26%20Performance%20in%20Regard%20to%20CO2%20Concentrations.pdf http://www.aretas.ca/sites/default/files/imce_images/Indoor%...
- jrockway 3y ago
  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 ;)
  - alach11 3y ago
    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.
    - jrockway 3y ago
      I have this: https://www.airthings.com/view-plus https://www.airthings.com/view-plus It ain't cheap.
      - dallyo 3y ago
        Well price is no guarantee. Try the hand sanitiser test I detailed above.
        tmoertel 3y ago
        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?
        3y ago
patja 3y ago
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 https://www.printables.com/model/121265-salud-co2-monitor
- bitbank 3y ago
  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.
  - patja 3y ago
    That's impressive! Mine was over $100. The SCD40 in module format is $45.
    - ahaucnx 3y ago
      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.
ahaucnx 3y ago
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/ https://www.airgradient.com/open-airgradient/kits/ [2] https://www.airgradient.com/open-airgradient/blog/co2-sensors-photo-acoustic-vs-ndir/ https://www.airgradient.com/open-airgradient/blog/co2-sensor... [3] https://cdn.sparkfun.com/assets/d/4/9/a/d/Sensirion_CO2_Sensors_SCD4x_Datasheet.pdf https://cdn.sparkfun.com/assets/d/4/9/a/d/Sensirion_CO2_Sens... see 3.6.1
- reassembled 3y ago
  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.
elihu 3y ago
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.
- nrp 3y ago
  Some of the PCB and SMT vendors also have KiCAD plugins that in theory streamline the ordering process.
  - elihu 3y ago
    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-bom-and-centroid-file-from-kicad https://support.jlcpcb.com/article/84-how-to-generate-the-bo...
Animats 3y ago
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 https://sensirion.com/products/catalog/SEK-SCD41
bitbank 3y ago
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.
bitbank 3y ago
I recorded a video walk-through of the feathres: https://www.youtube.com/watch?v=Kik7NmzLE-k https://www.youtube.com/watch?v=Kik7NmzLE-k

87 points by _Microft 3y ago

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.

sbierwagen 3y ago
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)
- gadgetoid 3y ago
  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.
bitbank 3y ago
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.

londons_explore 3y ago

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%20Environment%20in%20Schools%20%E2%80%93%20Pupils%20Health%20%26%20Performance%20in%20Regard%20to%20CO2%20Concentrations.pdf http://www.aretas.ca/sites/default/files/imce_images/Indoor%...

jrockway 3y ago
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 ;)
- alach11 3y ago
  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.
  - jrockway 3y ago
    I have this: https://www.airthings.com/view-plus https://www.airthings.com/view-plus It ain't cheap.
    - dallyo 3y ago
      Well price is no guarantee. Try the hand sanitiser test I detailed above.
      - tmoertel 3y ago
        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?
        3y ago

patja 3y ago

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 https://www.printables.com/model/121265-salud-co2-monitor

bitbank 3y ago
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.
- patja 3y ago
  That's impressive! Mine was over $100. The SCD40 in module format is $45.
  - ahaucnx 3y ago
    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.

ahaucnx 3y ago

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/ https://www.airgradient.com/open-airgradient/kits/ [2] https://www.airgradient.com/open-airgradient/blog/co2-sensors-photo-acoustic-vs-ndir/ https://www.airgradient.com/open-airgradient/blog/co2-sensor... [3] https://cdn.sparkfun.com/assets/d/4/9/a/d/Sensirion_CO2_Sensors_SCD4x_Datasheet.pdf https://cdn.sparkfun.com/assets/d/4/9/a/d/Sensirion_CO2_Sens... see 3.6.1

reassembled 3y ago
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.

elihu 3y ago

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.

nrp 3y ago
Some of the PCB and SMT vendors also have KiCAD plugins that in theory streamline the ordering process.
- elihu 3y ago
  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-bom-and-centroid-file-from-kicad https://support.jlcpcb.com/article/84-how-to-generate-the-bo...

Animats 3y ago

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 https://sensirion.com/products/catalog/SEK-SCD41

bitbank 3y ago

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.

bitbank 3y ago

I recorded a video walk-through of the feathres: https://www.youtube.com/watch?v=Kik7NmzLE-k https://www.youtube.com/watch?v=Kik7NmzLE-k