CO2 sensor for the Propeller?

Rsadeika

Since I have my QS board+sht11+RPi setup working as expected, I would now like to add a CO2 sensor to the QS board. Not even sure where to begin my research for this, first question is, who sells this sensor at a reasonable price, and has anybody done this already?

What I would like to do is have a sensor that would provide actual data, and not just a warning of a value that is too high or low. I know that Parallax sells a small adaptor board, but no CO2 sensor. I also have seen, at the Futurlec site, a CO2 sensor that might fit into the Parallax board, but not sure about that, or if it did, how it would work.

The aim for this experiment would be, is to see, from the data captured, if there is a significant change in the values at different times of the day, the season, and temperatures. Once I have something like that working as expected, then I will be setting up a monitoring station inside my living quarters. What would the human factor be, besides methane levels, in a more controlled environment. First rule of thumb for me, details, everything is in the actual detail.

Ray

Heater.

You mean like this: http://www.vernier.com/products/sensors/co2-bta/

All you need is an A to D that will handle 0-4 Volts

Not sure it that is a reasonable price though.

Heater.

Or like this http://www.futurlec.com/Gas_Sensors.shtml

CO2 sensor only 30 dollars. The output is a bit finicky 30 to 50mV for 350 10000 ppm CO2.

And you need a massively high input impedance amplifier: "the impedance of amplifier should be within 100 1000G Its testing current should be control below 1pA"

kwinn

CO2 sensors are also used in building automation. Don't have mfg/part# info with me but can look it up this evening.

Rsadeika

The Futurlec sensor is the one that I was looking at, they also have O sensor, that should be the next item on the list. Since I am not a board designer, I also need a board for the devices. This is why I mentioned the Parallax board, which I think, by design, may not be able to capture the values from the Futurlec CO2 sensor.

I am trying to stay with "off the shelf" items, and not get into special self designed and made items, my prototyping skills are not that well rounded, and I want the stuff to work correctly.

I also have seen some items in specialty gardening sites where they have CO2 devices, but there is no way to actually set them up to automatically capture data with my existing setup, QS board.

Ray

Bean

I have used this device with the propeller.

http://www.co2meter.com/collections/co2-sensors/products/k-30-ascii-co2-sensor

It's $85 and just sends ASCII serial data directly in ppM so interfacing is really easy. In fact you can connect it directly to a serial LCD.

You can also set it up with a custom prefix to make receiving data simple too.

Bean

Publison

It looks like to Parallax Gas Sensor Board will fit the sensor from Fututlec

https://www.parallax.com/product/27983

kwinn

Sorry, could not find the part number for the Honeywell sensor. Not likely to be of interest in any case. It was over $100.00 and has specs very similar to the one at Futurelec.

Rsadeika

Thanks for the information, I will now have to do a cost and use analysis to see which is the best one for what I intend to do. Although I must say that the one that Bean pointed too looks very interesting, even though it is on the high end of my price point.

Ray

Tracy Allen

Parallax used to carry a module for the MG811 CO₂ sensor (the $35 one linked to Futurlec). I don't see the document that went with it, so I'll attach it here.

It might fit physically in the Parallax gas sensor board 27983, but the circuit is not appropriate. The 27983 is designed for the gas sensors that behave essentially as resistors in a voltage divider. On the other hand, the MG811 sensor is a different beast, more like a battery or pH electrode, and it needs a very high input impedance amplifier with low bias current.

I took part in a protracted stamps-in-class thread where the goal of the "rocketeers" was to measure CO2 during a rocket flight, using the MG811. I tried to fathom how it works, a NASICON (Sodium Super Ionic Conductor). The MG811 requires individual calibration for both slope and offset and has a long stabilization time.

I've also used the COZIR, available from CO2meters.com. It draws much less current than the others. With any of them in the $100 range, treat their accuracy claims with skepticism. They are fine for a while after calibration, but the baseline drifts over the course of a day or two.

Publison

Tracy Allen wrote: »

It might fit physically in the Parallax gas sensor board 27983, but the circuit is not appropriate. The 27983 is designed for the gas sensors that behave essentially as resistors in a voltage divider. On the other hand, the MG811 sensor is a different beast, more like a battery or pH electrode, and it needs a very high input impedance amplifier with low bias current.

I

Tracy, I am now sorry that I posted that board up as reference. I have not used any of the sensors so I just assumed that they would all fit into that board. Probably why parallax is not sell the CO2 sensor, as it does not fit that board.

I should RTM more often.

Rsadeika

@Publison, I am glad that you did post, now I know for sure that the Parallax board combination will not work.

So, that kind of aims me in the direction of CO2meters.com, unless something better comes along. What concerns me now is:

They are fine for a while after calibration, but the baseline drifts over the course of a day or two.

I guess I will have to read the docs to find out exactly how the sensor gets "calibrated", is it opening up a can of Coke next to the sensor or a long deep exhale? Now if the "baseline drift" is of a consistent value, maybe the resetting could be done in the program, after a specific check point. Since the data I am aiming for is not of the critical nature, I guess a +-.01% ballpark figure would be good enough.

Now, since I will be adding an O sensor, I am wondering if I should look at the combo units, or deal with individual sensor units? I guess maybe individual units would be best, if you have to calibrate, and reset a lot of times.

Ray

Bean

The K-30 has a zero ppM calibration point and a 400ppM calibration point.
The zero can be made with nitrogen and the 400ppM is about what outside air is.

Bean

kwinn

Ray, lf you mean you will be happy that a reading of say 450ppm (.045%) is within +-100ppm (.01%) of the actual concentration then that sensor should work for your application. It should be a bit better than that.

Don't know if this will be much help for your application, but I found that the CO2 concentration of the air coming in to the buildings varied from ~400ppm to 600ppm depending on the time of day. In the early morning it would be about 400ppm, then rise to a peak of about 600ppm due to rush hour traffic. After that it would decline slowly and peak again during the evening rush. Wind speed obviously has a large effect on the peak readings. I used the readings between 4am and 5 am as the base point in verifying that the sensors were operating properly.

Rsadeika

@kwinn, interesting bit of information. I am kind of surprised at the ~400ppm to 600ppm values, considering that the level for concern is 10,000ppm, as stated in the Parallax write up. You do mention that it is the air that is coming into a building, is this conditioned air, or direct input from the outside. Not sure as to how an HVAC system would condition air, remove CO2.

I guess my +-.01% figure might be just fine, considering the concern levels(10,000ppm). Short of breathing onto a CO2 sensor, to determine the amount that a human produces (CO2), I will have to do a quick internet search.

I guess something to think about, after a major rain storm, that has high winds associated with it, would you expect the CO2 levels to increase or decrease at ground level?

Ray

kwinn

That 400-600ppm is outside air coming in to the building air handler. The air may be heated or cooled but there is no removal of CO2. The air in each room is monitored and the reading is used to control air flow to the room via motorized dampers in the ducts. I have seen room CO2 readings from classrooms as high as 2500+ppm when they were full for a long period of time.

As far as rain and winds go, rain did not seem to have much effect on the incoming air readings while strong winds tended to keep them near the 400ppm level. Hot weather with little or no air movement resulted in 700-800ppm ranges during rush hours.

Rsadeika

I am almost convinced that the K-30 module is the way to go. I think that I could probably add it to my QS + sht11 setup and have it work as expected. On my QS + sht11 setup, I think I am using three or maybe four COGs, so I could have another available COG to deal with the K-30 addition.

Later if I decide to go with the O sensor, I will still have another COG available for that. The only concern that I have now is space availability for the new unit(s), I guess another prototype enclosure will have to be developed, but maybe everything will fit in the enclosure that I have now.

Ray

Tracy Allen

The standard K30 constantly runs an algorithm that they call "ABC" (Automatic Baseline Correction). It takes the the lowest reading or an average of lowest readings over a 7.5 day window and calls that 400ppm. You can order the K30 with that feature either enabled or disabled.

The COZIR also has facility for manual or automatic recalibration, but automatic is not the default.

Both of those devices have extensive command sets for configuration, so it definitely pays to peruse the data sheets and configuration guides available at CO2meter.com.

I built up a system with multiple COZIRS that is used to measure ventilation in rooms. Several COZIRs are connected to one central Propeller . The experiment starts when all the sensors are set to the same reading, and CO2 from a cylinder is introduced into the space. The concentration profile over the next hour or so profiles the ventilation. Over that time the baseline drift is insignificant, and the baseline setting itself does not matter.

The bottom line with these it that they are very good at some things, but you'll have to have a plan and reasonable expectations.

Igor_Rast

I’m kinda late to this post , but from my experience I would say the K-30 from CO2meter is the way 2 go.
Have done quite some buying and testing out over the past time on CO2 sensing and can say

- the Taguchi type sensors are great a pain to get a steady reading from(verry weak signal wich you have to multiply), and would need constant calibration cause the readings will drift fast. So I would stay away from those.

- The NDIRA type K-30 does a pretty nice job of getting a steady reading, you just have to rx, tx it and ask for the last reading.

One thing you should do with these sensors , is turning off the standard ABC correction function it has set from factory.
This is something you can just disable with a command.
The ABC function will make the sensor auto correct itself to its lowest value (in ppm)in a week orso.
And that usualy is not a low (clean air value)the sensor is expecting to be(400ppm).resulting in fast miss calibration of the readings.

Turning it off you don’t have to worry about the sensor running up in readings.
If your really want to be accurate you can Zero calibrate it once a year orso, but there probably wont be a drift of more than 5-8% a year, at least thats my experiance.

Was bussy a few ago with 7x K-30 + 1 SHT-11, connected to a propeller + ESP8266 , sending data to an mysql database. worked out great.
https://github.com/Igor-Rast/Propeller_DB_logger
https://github.com/Igor-Rast/Propeller_DB_logger/blob/master/ESP8266.spin

here is a 2012 post on the k-30 I did


My 2 cents

I.C.E.C