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Originally Posted by theworldtrekker
Not sure what sensor you were using for the plot, but I'd be careful to make sure you're not tracking something else like temperature or humidity with the sensor.
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I've recorded CO2 today and humidity, and RH is not moving very much... nothing like CO2. The CO2 readings I'm getting do seem to be reasonable, and when two people are here, the readings seem to make sense.
I think that one thing that makes the reading seem anomalous is that my house is small, only about 700 sq. ft. and I'm mostly living in and only conditioning a part (25%) of that area. So the respiration of one person makes a big difference, to say nothing of more than one person... which is why I want to build this HRV.
Quote:
Originally Posted by theworldtrekker
As far as building the system, I'd try to find out the necessary protocal to interface with it over a SPI bus. You have one per arduino chip (assuming not a mega) but can select which device you want to interface with via a cs pin if you're also wanting to drive say an lcd.
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This sounds like a good approach.
Do you know how to do this?
Here is some guy who was able to reverse engineer the digital interface to the sensor. He was going to build an Arduino library for this particular sensor, but he says that his computer crashed and he lost his work.
...bummer.
I don't have a logic analyzer or any experience in using one, even if I did have one.
Pin 4 of the CO2 sensor is analog out, 0 volts to 4 volts, with 0v. = 0 ppm and 4v. = 2000 ppm, linear. I thought I'd run that into an A-to-D in on the Arduino. So, I think I can figure my way through this approach.
I do think that the digital approach is more accurate, but I don't have the savvy or the pre-made Arduino library to make it happen.
I already got a couple of fans that are low current, quiet, permanent magnet ECM fans. They should do the job nicely. They are 12 V and only draw 650 ma each.
Seems to me that it will be pretty straight forward to use the data from the Arduino's A-to-D and use it to control the duty cycle of a PWM going through a transistor to the fans.
I'll have to do some experimenting when it's all together to adjust the rate.
This might even be a job for PID.
So, I know a bit about Arduino programming, actually a very little bit.
If you have any suggestions, I'd like to hear.
Oh, and here's the HRV core I got:
And I even kind of have plans for the box:
So right now, I'm in the CO2 controller design stage of the project.
I tried to buy a controller from the company in Ireland that makes these things, but their controller only works on 220v 50Hz.
Best,
-AC