CO2 sensor - The Planted Tank Forum
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post #1 of 90 (permalink) Old 11-10-2015, 03:01 AM Thread Starter
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CO2 sensor

I thought I'd give the CO2 sensor another try. This time, build the casing as water tight as I can and as cheaply as I can. Thanks goodness the CO2 sensor wasn't permanently damaged. I just had to calibrate it using CO2meter's software.


2" pvc plug with cord grip


Inside I had to thin the top off with a router.


Trap adapter for the silicone membrane.


The adapter has a washer inside which I used with the membrane and silicone for safety measure.


The hardware: Arduino, CO2 senseAir K-30 10%, 5v fan, DHT-22 humidity & temperature sensor.
The fan is for circulation, and the humidity sensor is to alert me if it's too high or if a possible leak. The membrane is porous enough for H2O molecule to pass through. If the humidity is too high, I can remove the plug.




The fit was too snug and the board broke in half so I kept it.


Final product. I'm out of the CO2 game but I'll set up a yeast reactor in a bucket to test. I'll send the data to a mysql database online. I'll post the result soon.

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post #2 of 90 (permalink) Old 11-10-2015, 09:26 AM
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Interested to see where this goes.

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post #3 of 90 (permalink) Old 11-10-2015, 06:59 PM Thread Starter
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Interested to see where this goes.
I've made an earlier version to control my CO2 solenoid. It worked really well until it leaked. This should be bullet proof. It might not be as responsive because it's bigger in volume. The fan might help in faster gas exchange. I've plugged the fan into the pwm pin so I can control the speed to test responsive rates.

Now I'm more keen on using it to measure CO2 in my dirted tanks.

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post #4 of 90 (permalink) Old 11-12-2015, 10:51 PM Thread Starter
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So here's the result of the logs



I added a 1 liter yeast diffused it a piece of chopstick and circulated with a powerhead in a 5 gallon bucket. I stopped at 60ppmw. It was recording every 7 seconds so I changed the code to record every 10 minutes instead.

CO2 is still climbing. It's at 100ppmw at last check. I pulled out the CO2 to see it tapered out. Who knew DIY CO2 can go that high. I guess it'll keep climbing if nothing consumes it or diffuse it out of the water. I guess shutting off CO2 at night is a good idea.

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post #5 of 90 (permalink) Old 11-12-2015, 10:56 PM
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I think it would be interesting if you could take a sample from water that is at equilibrium with the atmosphere, and then another sample at a 1pH drop.

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post #6 of 90 (permalink) Old 11-12-2015, 10:59 PM Thread Starter
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I think it would be interesting if you could take a sample from water that is at equilibrium with the atmosphere, and then another sample at a 1pH drop.
Ah, good idea. I was looking for an excuse to buy a pH pen.

* I just got a pH pen on amazon for 'free' . Amazon takes Amex points now.

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post #7 of 90 (permalink) Old 11-13-2015, 04:17 PM Thread Starter
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This is the log overnight. The response rate is surprisingly slow with this sensor. The rate is faster out of water. I guess the volume of air inside the encasing is too much for a fast response.

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post #8 of 90 (permalink) Old 11-14-2015, 05:12 PM Thread Starter
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So the response rate is about .005ppmw per second. It takes 7 or so hours to go from 1ppmw to 70ppmw.
I'm going to try to reduce/ seal off the area around the membrane and feed the gas in that chamber directly to the CO2 sensor via an air tube.

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post #9 of 90 (permalink) Old 11-21-2015, 02:26 PM Thread Starter
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I tried this new configuration where the cap in front seals off a section and the tubes run directly into the CO2 sensor. The fan and humidity sensor is in front.


The response rate is .003ppmw/sec. Slower that the original design.

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post #10 of 90 (permalink) Old 11-21-2015, 03:57 PM
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Don't know if this applies, but I have a buddy that builds CH2 monitors. I believe to get them to work right he has to physically pump an air sample into something like a sensor tube?? I could ask for you if you think its something that might help?

Just trying to be helpful! LOL..

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post #11 of 90 (permalink) Old 11-21-2015, 06:22 PM Thread Starter
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Don't know if this applies, but I have a buddy that builds CH2 monitors. I believe to get them to work right he has to physically pump an air sample into something like a sensor tube?? I could ask for you if you think its something that might help?

Just trying to be helpful! LOL..
Thanks. Yeah, I'm using the fan to move air around but a vacuum pump would better. I was looking around for a small cheap one.


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post #12 of 90 (permalink) Old 11-22-2015, 02:22 PM Thread Starter
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Ok, I found a used vac pump on fleabay for $2.50. It'll arrive in a few weeks from HK.

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post #13 of 90 (permalink) Old 11-23-2015, 05:50 PM Thread Starter
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I talked to the tech guy of the CO2 sensor. My current setup with the tubes in the air ports doesn't work because the entire face of the sensor has a membrane to read CO2. So I'll have to buy their adaptor.

I knew something was off from looking at the numbers. The response rate should have been faster, not slower.

Also in such high humidity environment, I should use H2O absorbing filters and materials but they're too expensive. To extend the life of the filter, it shouldn't be in water for a long period of time.

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post #14 of 90 (permalink) Old 11-23-2015, 06:18 PM
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post #15 of 90 (permalink) Old 11-23-2015, 06:40 PM Thread Starter
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