ARLISS Team NH

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  • sylvie369sylvie369 Posts: 1,618
    edited 2010-06-02 - 03:41:48
    Dylan Landry said...
    Dear Andrew, Dr. Allen and Sylvie,

    If we mount the CO2 sensor so it does not connect with the stamp and only the MAWD, I believe that the only way we could collect data is in the raw form (in Millivolts).. If it is not connected to the stamp which contains the micro-controller, how will we be able to upload a formula to convert the data?

    Dylan Landry
    Dylan -

    The CO2 sensor cannot be wired directly to the MAWD. The MAWD is merely the source of the altitude data for the system. It does not have any inputs for recording or transmitting data.

    Your teammates are not talking about setting things up so that the CO2 sensor is not wired to the Stamp. They're talking about mounting it physically away from the Stamp, but still connecting it by wires to the Stamp so that the data can be converted and stored.

    ======================
    If you have the program space to do the conversion on-board, then by all means, do it that way.

    I suggest that the team members should also read the MAWD manual, available online here:

    http://www.perfectflite.com/Downloads/MAWDManual.pdf

    This is less of a priority than learning about programming and about the CO2 sensor, but it'd help to understand the setup.



    Post Edited (sylvie369) : 6/2/2010 3:50:02 AM GMT
  • Tracy AllenTracy Allen Posts: 6,514
    edited 2010-06-02 - 04:46:00
    You will have plenty of programming space on the BS2e. It has 8x the program space of the BS2 you are using now. Don't worry about having enough pins. Is the LED still taking two pins on the ASP?

    First off, though--important!--Do you have another BOE that you can use to experiment with the CO2 sensor? It is going to take experimentation. It is ALMOST ALWAYS best to make new things work and understand them separately before you combine their hardware and software into a system like the ASP. I know you have big plans, one thing at a time!!

    You as a team need to "characterize" the sensor. Right now, you don't know much about it. You don't know its "character". This is something you always have to do in science and engineering before you start on serious implementation. In my work I often have to do something called a "design review". or people do that for me. I try to find a "fatal flaw" in your design (ouch!!) or you find one in mine (ouch^2!). If not fatal, there may things that need attention. You don't want to find these things out on the launch pad. Let's say, "You have to do your homework."

    It sounds like you expect to measure ppm of CO2, not just whether or not CO2 is above or below a yes or no threshold. Is that correct?
    Homework: What is the purpose and relation to one another of the following pins on this sensor module?
    ....E1.....CNTL.....heat switch input from microcontroller, active HIGH
    ....E2.....ALM.....Alarm output to host microcontroller, active HIGH
    ....TP1.....Test Point 1+..... Buffered output of sensor (buffer/amplifier)
    ....TP3.....Test Point 3+..... Trip Level voltage set by potentiometer (R3)
    (peruse the CO2 Gas Sensor Module (#27929) instructions)

    What words in the above are unfamliar?

    What are the following attached pictures of?

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    Tracy Allen
    www.emesystems.com
    120 x 137 - 8K
    87 x 73 - 6K
  • Dylan LandryDylan Landry Posts: 235
    edited 2010-06-02 - 16:12:20
    Tracy,

    What was shown in picture #2? It was not posted. I'm as curious as they are...!

    The Rocketeers (by proxy)
  • Andrew (ARLISS)Andrew (ARLISS) Posts: 213
    edited 2010-06-02 - 21:20:58
    Mr. Kibler said...

    Andrew,

    So do you think the BS2e stamp will have enough memory for the CO2 sensor program and all the other programs...? I just checked UPS and it arrives tomorrow!


    Do you think we can replace the BS2 with the BS2e without having to write a completely new program? At the very least you will have to change "BS2" to "BS2e" at the top of the program so the program recognizes the new stamp. Yes.

    Finally, we need to find a sample/ prototype CO2 sensor program right away.

    Keep up the good dialogue,
    Mr. Kibler

    Mr. Kibler,

    Someone already stated that it should be a nearly seamless transition to the BS2e. I believe someone stated that the program would be stored in "sections" as the BS2e contains 2x8 kb "blocks" for a total of 16kb programming space. I have already posted the sample code for the CO2 sensor earlier, but let me go find it and I'll post it up right away.

    @ Dr. Allen,

    Yes, I believe we do have some spare circuit boards to experiment with only the CO2 sensor for now.

    **To other team members** Please use this advice! It will be less messy to test our CO2 portion of the program while it is completely separate from everything else -- not to mention that we can NOT risk damaging the current configuration of the ASP.

    Post Edited (Andrew (ARLISS)) : 6/2/2010 9:33:44 PM GMT
  • Mike NHMike NH Posts: 34
    edited 2010-06-02 - 21:51:59
    Will do Andrew, thanks.

    -Mike

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    "Learn to obey before you command."

    -Solon
  • Mark in NHMark in NH Posts: 447
    edited 2010-06-02 - 21:55:39
    The sample program code that was posted is for a carbon monoxide sensor, not a CO2 sensor: www.parallax.com/Portals/0/Downloads/docs/prod/sens/27931_CO_GasSensor.zip

    We're looking for·program code-- sample or otherwise-- for the carbon dioxide sensor that just arrived. The PCB's (circuit boards) for the CO and CO2 sensors are slightly different. Even though each PCB·has 4 pins, each has·slightly different electronic components on it. This begs a few questions:

    1) Are the four pins (GND, ALM, Vdd, Vss) in the same order on both (the CO and the CO2's) circuit boards?

    2) Will the CO sample code work with the CO2 sensor? Recall that when Dylan was working with the CO sensor and program code last week, "smoke came out."

    3) Should we try the CO2 sensor with the CO sample program code?

    Dr. Allen suggested yesterday that you "characterize" the CO2 sensor. What did he mean?

    Tracy, the Rocketeers have yesterday's homework assignment nearly done. A few more sentences and it will be finished; they'll post it in the morning. They wanted to post it today but I suggested that they answer your questions accurately rather than quickly so·that they really understand their answers. Thanks so much for your guidance! They're real eager-beavers this year and they've learned so much already... excellent·work for neophyte designers and programmers.
  • sylvie369sylvie369 Posts: 1,618
    edited 2010-06-02 - 21:56:06
    Team folks - I suggest that you put a little hold on working on the hardware/mounting part of things until you've very carefully thought through Tracy's questions in his most recent post. The answers are going to determine how you hook things up, and may require you to add a little additional hardware.

    Paul
  • Mark in NHMark in NH Posts: 447
    edited 2010-06-02 - 22:16:58
    Paul,

    · Agreed. What are your thoughts about starting with the CO2 sensor/ module·mounted·solo on stand-alone BOE? Also, I'm not sure what to make of what happened last week when Dylan was doing the same thing with the CO sensor and "it smoked." I didn't see smoke per se. We did get the CO program to register "alarm" on the blue screen. I'm leary of frying the CO2 sensor yet I'd like to move ahead. Like last year, the amount of time we have together as a full team is really limited. Ah, the realities of being a project manager...!

    So what new rocket (mis?)adventures have you had? When's your next big launch? How did Mad-West do at TARC this year? We couldn't go, and I haven't launched any HPR rockets since last September's ARLISS launch. I love launching big rockets to high altitude and I'm eager for this September's ARLISS launch.

    I'm curious to hear more about your high-altitude balloon project! I've considered doing a similar project for the past year or so and I'd love to hear the juicy tech-spec details. What was your "mission"? Where did you launch and recover? How long and how far was the flight (flights?) Do most high-altitude balloon flights self-terminate at 100,000 feet because of air pressure differential?

    Mark
  • edited 2010-06-03 - 00:00:56
    Mr.Kibler,

    I do not think that we should use the CO sample code on the CO2 sensor beacuse it was made for the CO sensor. We should use the CO2 sample code[noparse][[/noparse]if there is one] beacuse it is made for the CO2 sensor. Also when you used it last time with the COsensor it smoked and I don't really think we want that to happen again.

    Also, where do I find the CO2 schematics. For some reason I didn't put them in my binder

    Sean
  • Andrew (ARLISS)Andrew (ARLISS) Posts: 213
    edited 2010-06-03 - 00:05:32
    Sean from ARLISS-NH said...
    Mr.Kibler,

    I do not think that we should use the CO sample code on the CO2 sensor beacuse it was made for the CO sensor. We should use the CO2 sample code[noparse][[/noparse]if there is one] beacuse it is made for the CO2 sensor. Also when you used it last time with the COsensor it smoked and I don't really think we want that to happen again.

    Also, where do I find the CO2 schematics. For some reason I didn't put them in my binder

    Sean

    Sean,

    I'm afraid we will need to work with and learn from the CO sensor sample code. It is our only starting point at the moment. I have contacted Parallax support directly to see if they have any sample code for the CO2 sensor, as they have with previous sensors. As for the CO sensor smoking, I was not there when that happened, but that is due to improper wiring, and not programming error.

    The CO2 schematics are available on the product page. Do a search for "CO2" on the Parallax Online Store and you will find them there. E-mail me if you still can't find them.

    Andrew
  • Dylan LandryDylan Landry Posts: 235
    edited 2010-06-03 - 00:58:38
    Dear Dr. Allen, Sylvie and Mr. Kibler,

    Here are a professional written document of the questions you posted. This was a combined effort of almost EVERYONE on the team...

    1) Is the LED still taking two pins on the ASP?

    Yes, the LED uses Pins 12 and 13. Pins p3, p4, p6, p14 are available. We would like to keep the LED for these reasons. What are your thoughts?
    • When the LED lights up we know the program is running.
    • It conveys important messages in Morse code. Even though it’s programmed to say “forward and backward” in Morse code, we could re-program it to say something else. Plus we get to learn Morse code!
    • It adds “personality” to the robot (ASP)…!
    • It is useful for debugging purposes.

    2) Do you have another BOE that you can use to experiment with the CO2 sensor?

    Yes, we have two BOE’s. Neither has a MAWD attached but otherwise they both function the same as the ASP and they are all wired the same way. It is important for everyone to understand why we want a standalone board *before* making changes to the ASP.

    3) It sounds like you expect to measure ppm of CO2… Is that correct?
    Yes, that is correct. We would like the CO2 sensor to read and record CO2 concentration in ppm (not raw data) to the DataLogger, like last year’s ASP-1. That way we can correlate CO2 with altitude, temperature, and humidity like we did last year.
    Andrew said: *All the conversions* …”This can all be done, post flight, in Excel”

    4) What is the purpose and relation to one another of the following pins on this sensor module?

    • ....E1.....CNTL.....heat switch input from microcontroller, active HIGH
    • ....E2.....ALM.....Alarm output to host microcontroller, active HIGH
    • ....TP1.....Test Point 1+..... Buffered output of sensor (buffer/amplifier)
    • ....TP3.....Test Point 3+..... Trip Level voltage set by potentiometer (R3)

    5) What words in the above are unfamiliar? (Mr. Kibler interjects: What is buffered data? What is a data buffer? Why is it used?)
    • Buffered Output – Is where data is held until the device (BS2, etc.) is ready to use the data. In most simplistic form, “Buffered Output” data is data “on hold”, waiting to be used by a subroutine or another application (regards to Mike). Is this correct?
    • Buffered data is similar to the RAM (random access memory) of a standard computer -- it is a holding spot for data that is not yet stored permanently -- in this case, the data logger/flash drive. It is also important for everyone to understand that data in the buffer will be lost if the device is prematurely or improperly shut down.

    Use: You could use this term “Data Buffer” in many ways:
    • Writing in Formulas for math equations.
    • Using formulas to right in programming.
    • A device used to put data on hold for our ASP possibly.
    • People use it just in case if possibly if there data collecting has reached it threshold, they can contain the data and wait while other data is removed then it will send the data to the GUI/Flash Drive.




    6) What are the following attached pictures of? (*NOTE: Only one picture was posted to the forum “attached”.)
    • The following picture is the Pin outputs of the sensor. If you are unfamiliar with the symbols, do NOT take any guesses! Consult an electrical symbol guide such as the one I posted on the forum recently.


    Your Students,
    The Rocketeers.
  • Justin AbbottJustin Abbott Posts: 54
    edited 2010-06-03 - 01:45:18
    I don't beleive that we should use the CO sensor code with the CO2 sensor because each was designed for a different reason. If we were to try to use the CO sensor code with the CO2 sensor, it could "smoke" again or worse. If it came down to it and we couldn't find a CO2 sensor code, we would have to use the CO sensor code as a last resort only.

    It seems we have enough room to connect the CO2 sensor. When would we have the time to do a stand alone test? I know our time together as a team is very limited and we should be using that time to build. Would we have to do that test ourselves (Mr. Kibler, Mike, Dylan, I, or any of the Rocketeers) independently or would we be working as a full team? I don't know how long the test will take in case of minor or major problems that may occur.
  • Dylan LandryDylan Landry Posts: 235
    edited 2010-06-03 - 02:09:59
    Justin and Mr. Kibler,

    In terms of memory of the BS2 we do not have enough space, but in physical terms, yes. Andrew consulted someone on this matter a little bit ago in the forums. And so far Justin, you know how our searches have been going for sample code so far. Not well. We may have to resort to the CO code for a test. We could tomorrow in class consult the two documentations to see if they are similar. Andrew spoke with Parallax support and the problem with the CO sensor sample code has to be either a piece that we edited by accident or a problem with the wiring for they and others have gotten it to work with the code supplied. I will try to make a game plan for tomorrow so we don't have to spend time on," What we are going to work on".
    P.S. I was not able to get around to the questions you posted Mr. Kibler. I am sorry for this inconvenience.. I have been devoting my time to these recently posted questions. And to add to that, I got home late today. Maybe we could do a Questions and Answers session in advisory to test our current knowledge on the questions.

    Dylan Landry
  • Tracy AllenTracy Allen Posts: 6,514
    edited 2010-06-03 - 06:37:03
    • ....TP1.....Test Point 1+..... Buffered output of sensor (buffer/amplifier)

    Sorry, your definition of "buffered output" is off base for this circuit. You would be correct if this were a digital circuit, but it is not; it is analog. A different world. "Buffered" here means that the signal [noparse][[/noparse]EMF(mV)] from the Hanwei CO2 sensor passes through an amplifier before it reaches TP1. The amplifier (provided by Parallax in the 8-legged chip that you see on the printed circuit board.) both increases the mV and also gives it the capability to deliver more power, in the sense that you can attach a standard voltmeter to TP1 without "loading down" the signal. The raw EMF output of the CO2 sensor is very weak and needs to be buffered if you are going to read it accurately even with a standard voltmeter.


    Let me see if I can post the missing diagram...
    attachment.php?attachmentid=70818
    Does anyone know what it is?

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    Tracy Allen
    www.emesystems.com
    253 x 195 - 12K
    102 x 113 - 8K
  • Dylan LandryDylan Landry Posts: 235
    edited 2010-06-03 - 12:27:52
    Andrew,

    We have looked at the attached images. We have looked at schematic symbols from multiple websites and cannot seem to find this symbol inside the circle maybe the Mv symbol. We thought it might be a Test Point but that is represented by a black filled in dot. Could you help us on this or guide us on this?

    See you this weekend,
    Justin and Dylan

    Post Edited (Dylan Landry) : 6/3/2010 4:27:21 PM GMT
  • Tracy AllenTracy Allen Posts: 6,514
    edited 2010-06-03 - 18:07:10
    I wonder why you are looking at web sites to find that symbol! Find it in the instructions for the Parallax #27929 CO2 module, or on the schematic. Both documents are available on the Parallax web site. What is its part number as shown on the Parallax schematic diagram?

    What is the thing inside the symbol, three loops that runs from "H" to "H"?

    I uploaded the data sheet for the CO2 sensor. Attached. See if you can find that symbol there.

    This sensor is based on a NASICON substrate. Google that and tell what the acronym, "NASICON" stands for.

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    Tracy Allen
    www.emesystems.com
  • Andrew (ARLISS)Andrew (ARLISS) Posts: 213
    edited 2010-06-03 - 20:23:00
    Dylan Landry said...
    Justin and Mr. Kibler,

    In terms of memory of the BS2 we do not have enough space, but in physical terms, yes. Andrew consulted someone on this matter a little bit ago in the forums. And so far Justin, you know how our searches have been going for sample code so far. Not well. We may have to resort to the CO code for a test. We could tomorrow in class consult the two documentations to see if they are similar. Andrew spoke with Parallax support and the problem with the CO sensor sample code has to be either a piece that we edited by accident or a problem with the wiring for they and others have gotten it to work with the code supplied. I will try to make a game plan for tomorrow so we don't have to spend time on," What we are going to work on".
    P.S. I was not able to get around to the questions you posted Mr. Kibler. I am sorry for this inconvenience.. I have been devoting my time to these recently posted questions. And to add to that, I got home late today. Maybe we could do a Questions and Answers session in advisory to test our current knowledge on the questions.

    Dylan Landry

    Parallax does not offer sample code, we will have to work with what we know. See below.
    Dave Andreae said...

    Hello,

    There isn't a sample code due to the fact that it requires calibration depending on the gas levels. The sensor is basically a switch that is activated depending on the level of gas that the sensor is calibrated for. If you have any more questions please feel free to contact us.

    Kind regards,
    Dave
  • Mike NHMike NH Posts: 34
    edited 2010-06-03 - 21:14:14
    Andrew,

    We called the tech service today, and he gave Dylan, Mr. Kibler, and I directions in how to work it. For further info I'd ask Mr. Kibler, or call tech service.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    "Learn to obey before you command."

    -Solon
  • Mark in NHMark in NH Posts: 447
    edited 2010-06-03 - 21:15:14
    Calling All Rocketeers,

    ·· Please be certain to answer Dr. Allen's questions promptly and accurately this evening. I agree with him: some were on a wild goose chase by trying to find what the symbols mean on the internet. Search "closer to home". Use the CO2 sensor/ module documentation in your team binder and the "What's a Microcontroller?" books I got for you instead of searching the internet. Use project-specific resources to find project-specific answers.

    Dr. Allen was kind enough to upload the data sheet for the CO2 sensor for you (see his post above.) Please be sure to thank him. ·He said, "See if you can find that symbol there." You were on track earlier in the day when you started by looking in the "Microcontroller" book. But the Internet Sirens lured you too close to the rocks...! (*You should ask Mrs. Castle who the Sirens were and what the metaphor means.)

    Below is tonight's challenge; please answer Dr. Allen's questions promptly and accurately. E-mail your answers to both Andrew and Dylan first. They will check them for accuracy and post them to the forum when they are completed, and correct. I'd like to see them posted by 9 PM tonight so we can move ahead tomorrow. This sets the tone for Sunday's team practice.

    1) What is the thing inside the symbol, three loops that runs from "H" to "H"?

    2) This sensor is based on a NASICON substrate. Google that and tell what the acronym, "NASICON" stands for.


    Mr. Kibler·and the·Argonauts
  • edited 2010-06-04 - 00:27:17
    Andrew,

    Thank you for helping me find the CO2 schematics. I beleive that I found them.

    Sean
  • Dylan LandryDylan Landry Posts: 235
    edited 2010-06-04 - 00:58:46
    Dear Dr. Allen,

    Here are our Team member(s) answers to your questions. We are extremely sorry for the inconvienence of not answering accuaratly and perfesionally.

    1.)What is the thing inside the symbol, three loops that runs from "H" to "H"?

    A.) The object in the center that appears as several loops is an inductor. The swirls seem to represent what could be of a heating coil...

    2) This sensor is based on a NASICON substrate. Google that and tell what the acronym, "NASICON" stands for.

    A.) It is an acronym for "Sodium Super-ionic Conductor."that are used as coatings that are deposited on rotating molecules that enzyms act apon by co-sputtering with certian chemicals to ultimately create a chemical reaction.

    Once again we are extremely sorry for the inconvenience and difficulties.

    Awaiting your response,
    Andrew, Sean and Dylan
  • Justin AbbottJustin Abbott Posts: 54
    edited 2010-06-04 - 01:41:55
    Team,
    I apologize·I didn't get to contribute to the team's responses. I just got back to my house around 9:20 pm.

    But I do fully agree with the team's asnwers. After looking at the documentation, it does appear that Dylan is right in saying that the swirls represent a heating coil. It seems it senses the amount of heat and when the teperature gets high enough, it outputs voltage.

    NASICON does stand for Sodium Super-ionic Conductor. See the attached image, and it confirms what the rest of the team concluded.
    536 x 360 - 9K
  • Mark in NHMark in NH Posts: 447
    edited 2010-06-04 - 01:55:46
    QUESTION: This sensor is based on a NASICON substrate. Google that and tell what the acronym, "NASICON" stands for.

    ANSWER) It is an acronym for "Sodium Super-ionic Conductor."that are used as coatings that are deposited on rotating molecules that enzyms act apon by co-sputtering with certian chemicals to ultimately create a chemical reaction.
    Rocketeers,

    ·· If I'm not mistaken it's the NASICON substrate--·a "sodium·(Na) super-ionic conductor"--·that reacts with carbon dioxide. This chemical reaction creates a small amount of electricity: millivoltage! When the millivoltage is amplified (buffered?) into volts, the voltage can be measured or·converted into numbers (ppm.)

    Tomorrow we will calibrate the CO2 sensor. It's wired,·seemingly correct,·on a separate BOE (not on the ASP.) The carbon monoxide program seems to work·with the CO2 sensor module when the right pins are connected to the right inputs/ outputs. We used the schematic to figure this out. If the CO2 alarm activates (if the red LED comes on·and the word "Alarm" appears on the computer screen) we· can be fairly certain it works properly. Think about where we go and what we'll do on Sunday·if the sensor and program do work correctly tomorrow.

    What does the "H" stand for in the diagram?


    Tracy and Paul, where you suggest we go from here? What direction; what's next? I'm assuming that the CO2 sensor is up and running correctly...
    ·
  • sylvie369sylvie369 Posts: 1,618
    edited 2010-06-04 - 09:53:34
    Mark in NH said...


    Tracy and Paul, where you suggest we go from here? What direction; what's next? I'm assuming that the CO2 sensor is up and running correctly...

    It'll be good to get the CO2 sensor running as it is supposed to, triggering an alarm. Do you plan to use human exhalation (that is, breath on it) to trigger it?

    Remember that your hope is not to merely set off an alarm if you reach a certain CO2 level, but to measure the level as you fly. That means you can't just wire that alarm pin to the BS2 and expect to get what you're after. That pin only gives you "Yes/No" (are you over the alarm level?).·How will you use the CO2 sensor to measure the CO2 level? There are a few big steps you're going to have to take still. What connection are you going to have to make to the CO2 sensor to get a continuously variable reading of the CO2 level? How is the BS2 going to read that?
  • Mike NHMike NH Posts: 34
    edited 2010-06-04 - 16:07:47
    QUESTION 1 from Paul: Do you plan to use human exhalation (that is, breath on it) to trigger it?

    ANSWER: Yes, and no. The documentation says,

    YES:·"Your breath contains CO2 when you exhale. Your breath also contains moisture and potentially other particulates (cheese burger breath, etc.)· Contaminants can affect the sensor's calibration. Breathing briefly on the sensor with a single breath in a convenient way to see it react to CO2."

    NO: We also plan to borrow a can of aerosol·CO2 from the comupter tech guy. He uses it to clean computer parts. Mr. Kibler checked at the hardware stores last night but they don't seem to sell canned CO2, CO, CH4, etc. Mr. Kibler said the guy asked him, "What do you want it for anyway?" I'm sure the guy got a very detailed, technical answer!


    QUESTION·2 from Paul:

    How will you use the CO2 sensor to measure the CO2 level?

    ANSWER 2: When it reacts with the NASICON material, the CO2 sensor and converts CO2 into a small electric current through a chemical reaction (we believe. Is this correct?) The electric current (mV) is amplified (buffered) and then converted into numbers (CO2 in ppm.) Is this correct?

    You said that there are a few big steps you're going to have to take still. We agree! We hope you will help us figure out the algorithm and write a program to convert mV into ppm. We would like the data to read out on the DataLogger beside the temperature, humidity, altitude, etc.


    QUESTION·3 from Paul:

    What connection are you going to have to make to the CO2 sensor to get a continuously variable reading of the CO2 level?

    ANSWER 3: We're uncertain but we're working on this. Is it in the way the sensor module is wired to the breadboard is wired?


    QUESTION 4 from Paul: How is the BS2 going to read that?

    ANSWER 4: The BS2e will read the data using an algorith in the program. Is that right?


    Team members,

    Please file the information below in your team notebooks so you have it handy on Sunday. Mr. Kibler said that we may wire the CO2 sensor to another BOE, set up the same as the ASP, and then run the program. We have·the CO2 sensor·set up on a BOE by itself right now. Sylvie and Dr. Allen, is that a good idea?

    The ASP has these "slots" available:

    P3, P4, P6, P14

    Vdd slots·= 2

    Vin slots·= 3

    Vss slots·= 1

    From Dylan, Justin, and Derek S. who came down to lab yesterday·(and·Mr. Kibler!)



    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    "Learn to obey before you command."

    -Solon
  • sylvie369sylvie369 Posts: 1,618
    edited 2010-06-04 - 16:37:20
    Mike NH said...


    QUESTION·2 from Paul:

    How will you use the CO2 sensor to measure the CO2 level?

    ANSWER 2: When it reacts with the NASICON material, the CO2 sensor and converts CO2 into a small electric current through a chemical reaction (we believe. Is this correct?) The electric current (mV) is amplified (buffered) and then converted into numbers (CO2 in ppm.) Is this correct?
    Not quite, or at least not by the sensor. There is a test point (TP1) on the sensor whose voltage varies with the CO2 level. According to the documentation, it will have a voltage between 0V and 3.35V, and that voltage will depend upon the CO2 level. It's a voltage, and it is NOT somehow converted into numbers representing CO2 in ppm. It's just a voltage. You're going to have to do something to convert that voltage into digital numbers that can then be converted to CO2 ppm. You're going to need a connection to that test point, and it cannot be just a wire running from that point to a BS2·I/O pin, because those I/O pins can't by themselves turn variable voltages into digital numbers.

    This is going to make a difference to how you set up the hardware, so don't go too far down that road yet.

    You are correct that the BS2 will read the voltages using some kind of algorithm, but there's going to have to be something else first.

    Also in your list of available connections I notice you listed Vdd and Vss connections. You should know that you have a LOT more than that available, because you can share them with other Vdd and Vss connections in the same row of your breadboard. For example, I notice that you have a red wire from Vdd to what I believe is pin 8 of your SHT module, and there are three empty holes in that row of the breadboard. There's no reason why you couldn't connect another wire to one of those holes and use it to carry Vdd (your 5V power supply) to another device. I see three more empty holes in the row used to power the datalogger. In short, don't worry too much about the Vdd and Vss connections - you'll be fine on that part.

    Post Edited (sylvie369) : 6/4/2010 4:47:19 PM GMT
  • Tracy AllenTracy Allen Posts: 6,514
    edited 2010-06-04 - 17:25:55
    Please continue looking at the Hanwei data sheet for the MG-811 sensor, and the schematic diagram in the Parallax literature. I'll help you read it, and to read between the lines to on how to program the Stamp to read it.

    You can also download the Hanwei data sheet for the MQ-7 CO (carbon monoxide) sensor. Here, I'll attach it for comparison with the CO2 sensor.

    You will notice that the two sensors have the same schematic symbol, a squiggly line (the heater, correct) and then two blocks on each side. The two blocks represent the ends of a tiny ceramic tube that is hanging inside the enclosure that you see with the screen mesh on the top. The heater is inside the tube, and when power is applied, it makes the tube hot, really hot. like 300 degrees Celsius (?). The chemical reactions only work at high temperatures. It is like the catalytic converter in a car. Despite the similarity in the schematic symbols for the MQ-7 and the MG-811, the outside surface of the ceramic tube is quite different and the way they need to be interfaced to an external circuit is quite different. This has to do with the fact that carbon monoxide is an reactive chemical, whereas carbon dioxide is very stable. That lack of reactivity make CO2 a much harder gas to measure that CO.

    The ceramic tube in the MQ-7 carbon monoxided sensor is coated with tin dioxide.(SnO2). The CO reacts in a catalytic reaction on the surface of the (SnO2) and in the process the surface resistance changes proportional to the amount of CO present. The sensor is used like a variable resistor in the circuit for the Parallax 27931 CO module. The Parallax module has an amplifier that buffers (!) the output and turns it into an alarm signal that turns on at a certain level that you can set with the on-board control.

    Carbon dioxide, being much less reactive, uses the NASICON substrate instead of (SnO2). Correct, NASICON stands for "SodiumSuperIonicConductor". This stuff is a hot topic for research in many fields today and when you Google it you probably came up with lots of scientific papers about it in different areas as an electronic nose. I just learned about it myself, thanks to you! There is a ceramic matrix that has lots of little interior passageways, and sodium ions are free to move through those passageways. The conduction is by movement of sodium ions, not by movement of electrons as it would be in a copper wire. Now, in the CO2 sensor, there is also lithium. You can read the chemical reaction in the MG-811 data sheet. Lithium is the lightest metal, and lithium is extremely reactive. That is what makes it good for high performance batteries--all that energy potential. It also makes it useful for a CO2 sensor, because it is energetic enough to react with CO2. Again, see the reaction in the data sheet. The reaction produces a current of sodium ions that in turn produces a voltage output from the sensor. But in this sensor you can't allow a current to flow from the sensor (different from the CO sensor). The data sheet states firmly that you have to use a buffer amplifier to measure the voltage of the sensor without allowing current to flow more than one pA (10-12 Amp). {I am getting onto hazy ground now, but I think the reason for that is that the reaction is probably reversable, and allowing current to flow would quickly "poisen" the reaction by locking up the sodium.}

    Now, for the BASIC Stamp program. The MG-811 data sheet says that its heater should operate on 6.0 volts +/- 0.1 Volt, and that the heater draws 200 mA, for a power of 1.2 Watts. (This is something you will have to consider, how much battery power do you have to spare in the ASP?). You have the Parallax module 27929, and it conveniently has a 6 Volt regulator on board, so you don't have to worry about supplying exactly 6 Volts. You can supply the 27929 with 9 Volts from your battery or power supply. The 27929 also provides means for the Stamp to turn the heater on and off.

    The programming of the heater on this module is, however, going to be DIFFERENT from the CO module. On the CO module, the program has to turn the power high and low in a cycle of 60 seconds and 90 seconds respectively, and the ppm is the ratio of the two readings. In contrast, the CO2 sensor is different. The program should simply turn on the heater and leave it on. Allow the sensor to warm up. Then start to take readings. Leave the heater on continuously so long as you are taking readings. Much simpler than the CO sensor. If you are using the program for the CO sensor, it is wrong for the CO2 sensor.

    Do you have a standard voltmeter? I suggest you start with the the voltmeter connected between TP1 and TP2 on the 27929 board. Connect Vin to Vin on your BOE, and com to Vss on your BOE, and connect CNTL to p4 on your BASIC Stamp, with a 1000 Ohm resistor between p4 and CNTL. Connect the ALR to pin p3 on the Stamp, also via a 1000 Ohm resistor. Operate the BOE from a power adapter (not a 9V battery, because the power for the heater will suck down the battery really fast!) Execute the program,

    HIGH 4  ' turn on the heater.
    DO
      DEBUG BIN1 IN3  ' display the alarm status
    LOOP
    



    Now you can observe on the voltmeter (connected between TP1 and TP2) what happens when you breath on the sensor or hit it with CO2 spray or expose it to dry ice vapors. Also observe on the DEBUG screen that at some point the reading changes between 0's and 1's at the same time as the LED on the 27929 module. You can adust that alarm point with the control on the 27929 module.

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    Tracy Allen
    www.emesystems.com

    Post Edited (Tracy Allen) : 6/4/2010 5:30:29 PM GMT
  • Tracy AllenTracy Allen Posts: 6,514
    edited 2010-06-04 - 18:38:42
    As a cautionary note, don't go overboard to see how much CO2 response you can get by spraying it from the can or holding the sensor in a confined space as you breath and rebreath the air to build up CO2 concentration. Remember that the sensor is rated to respond up to 10000 ppm. You can breath "at" the sensor to bring it up into the 10000 range, but remember that exhaled air is about 4% CO2, 40000 ppm.

    It is possible that prolonged exposure to high levels could damage the sensor in some way, perhaps make it lose sensitivity at low levels (where you ultimately want to measure with the ASP). Just a caution -- the data sheet does not say anything about safe levels.

    We did talk about "saturation", what does that mean? In electronic circuits it means going beyond limits of operation, for example, the distortion that you hear when you turn up a stereo too high. In a chemical reaction, it happens when all of the chemical is used up reaches some limit. For example, there is only a certain amount of sugar or salt you can dissolve in water, the saturation point, the solubility. In the CO2 sensor there is a certain amount of lithium and sodium available to carry out the reaction, so at some level of CO2, it will be saturated. No more change in voltage with further increases in CO2.

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    Tracy Allen
    www.emesystems.com
  • edited 2010-06-04 - 20:15:50
    Mr. Allen,

    What is a voltmeter? Why do you suggest that we use it?

    Thank you all for your help,

    Sean
  • Tracy AllenTracy Allen Posts: 6,514
    edited 2010-06-04 - 21:08:17
    A voltmeter is a thing that you can purchase at your local Radio Shack or possibly hardware store. It might be called a multimeter, which is a more versatile instrument that can measure Volts, Amps, Ohms and possibly other things as well, on several different ranges of DC and AC. You can get them with either a pointer meter or with a digital display. You can also find them very cheap on the internet.

    It is really really really useful for your team to have one. You can answer a lot of questions about how the ASP is operating, the condition of the batteries, etc. etc. etc. You need one that can measure DC Volts down in the millivolt range and also up to at least 15 Volts.

    For the CO2 sensor, connect the voltmeter's two leads to TP1 and TP2. Then you can read out the voltage produced by the sensor and buffere amplifier, and convert it to ppm. Later on, we need to figure out how to make the STAMP read the Volts. But to start, a Voltmeter or multimeter is a basic tool.

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    Tracy Allen
    www.emesystems.com
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