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Topic: Measuring levels of carbon dioxide (Read 2 times) previous topic - next topic

dkl65

Hello!
I did not know where to put this thread, because it may not necessarily require Arduino. Maybe a moderator can move this topic to the appropriate board. At school, we were given an assignment to design a device that measures the relative amount of carbon dioxide gas. The source of carbon dioxide should be a sufficient, inexpensive source; not a person's exhaled breath. That could be something like gas coming off of a baking soda and vinegar mixture, I don't know. The measurement must also include numbers.
Quote from: Assignment Sheet

Design and build a device for detecting relative amounts of carbon dioxide (CO2) gas. Test one variable in order to increase the effectiveness of the device.
...
Which safe tests are available for demonstrating the presence of CO2?

What kind of device could be used to get a measurement of CO2 levels?


We haven't learned anything about this topic yet. I think that we have to do all the research ourselves (group project). I don't know where to start yet, so I will need some guidance on how to approach this. It could possibly involve Arduino, as long as it is inexpensive. A due date has not been announced. Any suggestions to help me start researching?
Thanks!

P.S. Please don't read this thread as "please give me a solution". I just need guidance, and steering on the right track, because I don't know where to start.

AWOL

Quote
"please give me a solution".

A solution would be ideal.
I'd use calcium hydroxide.
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

dkl65

Quote from: AWOL
A solution would be ideal.

Yes, it would be ideal. I just don't want people "yelling" at me for just asking for the solution, as I have seen before. Some one used calcium hydroxide for a science fair project to test the presence of CO2 in exhaled breath after going through a sodium hydroxide filter. He says "the solution turns milky white when it comes in contact with carbon dioxide." However, I don't know how that will generate numbers, or how to gain access to it. The assignment was only assigned today.

mykiscool

Arduino has a gas sensor that can detect many types of gasses. Try looking it up on ebay, sparkfun, or adafruit.
Proud Member of the Nighthawk Robotics Club Team 569 B

fkeel

"the solution turns milky white when it comes in contact with carbon dioxide."

you could measure the change in opacity with a photo-resistor...

dkl65

Quote from: fkeel
you could measure the change in opacity with a photo-resistor...

That is actually a good idea: shine a flashlight through the lime water in a transparent container, and use the analogRead() results of the LDR. However, getting the calcium hydroxide is a different story....

Quote from: mykiscool
Arduino has a gas sensor that can detect many types of gasses.

Here is one: http://www.parallax.com/tabid/768/txtSearch/carbon+dioxide+sensor/List/0/SortField/4/Default.aspx. Too expensive; not an option.

I will ask the teacher for more info.


AWOL

Quote
Yes, it would be ideal. I just don't want people "yelling" at me for just asking for the solution,

I'm sorry.
Was I too subtle?
Did I yell?
I didn't think I had.

What if I'd said "an aqueous mix of calcium hydroxide would be a solution"? (pun on "solution" - geddit?)
Would that have been obvious enough?

If you're going to do this optically, don't forget to put in a reference detector, to account for variations in the intensity of the light source.
Old CD or DVD drives are good sources of beam-splitters.

Remember: If you're not part of the solution, you're part of the precipitate.
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

dkl65

I was talking about people who come on the forum with a problem, and all they do is ask for a solution to their problem (e.g. code all formatted, ready to go). I didn't want to be accused like that.

Looks like we are using 0.14% lime water (0.14g of Ca(OH)2 in 100mL of water). Someone is going to bring in 7g of calcium hydroxide; enough for everyone. Lime water turns milky white when it comes into contact with CO2. The CO2 is going to come from 0.5g of baking soda in 20mL of vinegar inside a flask. The flask has an airtight lid with a tube connecting to a syringe. The lime water is inside a test tube.

Our goal is to:
1) Store CO2
2) Measure levels of CO2

Quote from: AWOL
If you're going to do this optically, don't forget to put in a reference detector, to account for variations in the intensity of the light source.
Old CD or DVD drives are good sources of beam-splitters.
What is the reference detector? What would be the best way to do the flashlight thing? I was thinking holding the test tube on top of the LDR, and shining a flashlight from the top. It will be measured against a control. I don't know how to account for anything else.

kf2qd

A reference indicator - what I understand him to mean is this - you need to have some way of monitoring the light source to determine if it has changed in intensity. The batteries run down a bit so not as much light coming out. If you don't compensate for less light from the source you will be "detecting" higher levels of CO2 with no actual change in CO2 levels because you will really just be detecting the fading bulb.

dkl65

But, if the change is so subtle, and I am only turning the flashlight on a few seconds at a time, I don't think that the LDR will pick it up, and it can be ignored. It doesn't have to be super exact. But, how can I compensate for the very subtle change in light? It sounds like it will be twice as hard as the experiment itself.

AWOL

Quote
But, if the change is so subtle, and I am only turning the flashlight on a few seconds at a time, I don't think that the LDR will pick it up, and it can be ignored.

But that's precisely why you should be using a reference; a battery may "recover" after a rest meaning the flashlight will be brighter, so to permit an absolute reading, you do need a reference detector.
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

dkl65

How do I make the reference detector? I am doing the experiment tomorrow only (Jun. 21, 2012), so I will do it if I have access to the materials.

My plan for the setup will be like this:
-An LDR with a 10k ohm pull down resistor on analog input A0, using 3.3V reference for stability.
-A black construction paper tube surrounding the LDR
-The test tube containing 2mL of lime water will go inside the tube, and a flashlight will be shined on top

westfw

The limewater hack will help you detect AMOUNT of CO2 (in particular, the amount of CO2 that you manage to put into solution, which is not quite the same thing), but I don't think it would be very good at distinguishing different concentrations.

In fact, it seems like a really hard problem, outside of "buy a CO2 detector" (which will still have problems depending on whether you're trying to measure normal atmospheric concentrations (~300ppm), the concentrations typical in exhaled breath (3-6%), or the nearly 100% CO2 from your baking soda and acid reaction.)

Aside from limewater, you could consider dissolving the CO2 in water and checking for pH (this seems to be a standard method for determining CO2 concentration in water, which is a common and important test.)  Or absorbing/reacting the CO2 with something with a strong affinity for CO2 (NaOH ?) and detecting mass changes.  (but these are both still quantity rather than concentration tests.)

Density and specific heat of CO2 are somewhat different than air.
And IIRC, the speed of sound in CO2 is different than air.  You can make sound lenses out of balloons filled with CO2...

AWOL

Quote
The limewater hack will help you detect AMOUNT of CO2 (in particular, the amount of CO2 that you manage to put into solution, which is not quite the same thing), but I don't think it would be very good at distinguishing different concentrations.

You could calculate that by metering the volume of gas passed through.
One simple way might be by measuring the volume of water displaced in a simple inverted column.

Agreed, it is a good challenge.

Perhaps you could measure the concentration by the number of polar bears it makes homeless.   :smiley-yell:
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

dkl65

#14
Jun 21, 2012, 11:26 pm Last Edit: Jun 28, 2012, 09:30 pm by dkl65 Reason: 1
Today, there was not enough time, so the experiment will be done tomorrow (Jun. 22, 2012). We don't have access to other materials other than lime water, glass flasks with airtight caps, syringes with tubes, test tubes and racks, baking soda and vinegar.


Never mind! No time today either. The experiment will be done next week.


Last week of school!  :D


Looks like we are not doing the experiment at all. Tomorrow is the last day of school!

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