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Show HN: I wanted to measure CO2 in my office, so I build a C++ WebServer/App

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Re: Show HN: I wanted to measure CO2 in my office, so I build a C++ WebServer/App

#21

Post by stackmad »

jamisteven wrote: post #2

No story behind the build, just a link to the git repo? yay

You can only put link + title on here. And the story is rather boring :) I wanted to measure it, I got a device from amazon, found a python script to read the data, the dependencies (pyhidapi) always sigfaulted, so I wrote my own :)

Re: Show HN: I wanted to measure CO2 in my office, so I build a C++ WebServer/App

#22

Post by wyldfire »

This device's manufacturer claims an accuracy of "± 100ppm or ± 7% of reading".

But there's a review on Amazon that describes someone getting three units and finding as much as 600ppm variation among them.

Maybe they need some kind of calibration or tuning? Or their manufacturing process is way out of control.

Re: Show HN: I wanted to measure CO2 in my office, so I build a C++ WebServer/App

#23

Post by stackmad »

ody4242 wrote: post #5

Whats wrong with this one? (it works with the same device) https://github.com/larsp/co2monitor

That looks good as well! I actually didn't know about that project. It wouldn't have worked on my specific case though since I wanted it connected to my Mac, that tool only works on Linux.

Re: Show HN: I wanted to measure CO2 in my office, so I build a C++ WebServer/App

#25

Post by AdrianB1 »

coldtea wrote: post #16
maxk42 wrote: post #8

Installed a CO2 monitor in my home two days ago. Already changed my life. It warns me when I need additional ventilation and even beeps if CO2 levels raise too high. It sounds silly but it's scary how quickly levels rise when the windows are closed.

> It sounds silly but it's scary how quickly levels rise when the windows are closed. It might be scary, but is it actually dangerous? It could just be that the levels shown, even if raised, are inconsequential. Basically wondering about the "Already changed my life" line. Are we all without one risk certain CO2 death every day, or is the parent overly worried over nothing (and opens windows without really a need for…

The "changed my life" is probably "I have one more thing to focus on for a while". As humans emit CO2 and your lungs are full of it, the danger exists if you run out of oxygen and get too much CO2, the kind of situation where you can get indoors only if you tape all your doors and windows creating an airproof seal.

Re: Show HN: I wanted to measure CO2 in my office, so I build a C++ WebServer/App

#26

Post by stackmad »

benbristow wrote: post #11

Isn't C++ a bit overkill for a web app?

Depends, this was a question I tried to answer for myself with this project. I did not easily find a good library for Python that would work on my Mac for reading the HID messages, so writing the device part in C++ was easier for me ( and an interesting excercise in c++17'ifying C code ). I thought about just having the c++ app be called from python, but wanted to try and see how hard it would be in c++ and found it extremely easy with the cpprestsdk.

Re: Show HN: I wanted to measure CO2 in my office, so I build a C++ WebServer/App

#27

Post by AdrianB1 »

maxk42 wrote: post #8

Installed a CO2 monitor in my home two days ago. Already changed my life. It warns me when I need additional ventilation and even beeps if CO2 levels raise too high. It sounds silly but it's scary how quickly levels rise when the windows are closed.

Why is it so scary? There is no danger for you to get sick or die.

Re: Show HN: I wanted to measure CO2 in my office, so I build a C++ WebServer/App

#28

Post by stackmad »

johndough wrote: post #20
jakobegger wrote: post #10

Why are there steps in the CO2 levels?

Since this is based on a reverse-engineered binary protocol and since the step sizes are reasonably close to 64 and 128, I'd guess it's a bug.

The device on its onscreen display shows the same steps, so I think its due to how the sensor works.

Re: Show HN: I wanted to measure CO2 in my office, so I build a C++ WebServer/App

#29

Post by detaro »

wyldfire wrote: post #22

This device's manufacturer claims an accuracy of "± 100ppm or ± 7% of reading". But there's a review on Amazon that describes someone getting three units and finding as much as 600ppm variation among them. Maybe they need some kind of calibration or tuning? Or their manufacturing process is way out of control.

They have a calibration feature, of course most of the reviews fail to mention if the person understood how it worked and used it. (I personally find the mechanism a bit odd, but I guess it makes some sense if you assume some things about the environment)
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