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anemometer interface with AVR

Discussion in 'AVR' started by naz83, Jul 13, 2010.

  1. naz83

    naz83 New Member

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    thermistor circuit

    hi,

    in the circuit attached could any1 plz tell me what are these caliberation and zero pots for, what is thier purpose in the circuit?

    i did use 1k fine trim pots when i built this circuit but i dint get any result, and where should the output voltage be measured? is it at point U?

    i am not able to obtain output for any of the circuits plz if any1 has a circuit that works plz help!
     

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  2. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    The output is supposed to be where that voltmeter is drawn, between the wipers of the CAL and ZERO pots.
     
  3. naz83

    naz83 New Member

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    hi eric,
    i thought that it was the ammemeter connected between zero and cal pots.. i had connected an ammeter there coz it luks to be in series...... and also is the opamp there a comparator or acting as amplifier, i had used lm741 in place of opamp there... what is the function of the zero and cal pots and how should i set them to what readings.........
     
  4. dave

    Dave New Member

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  5. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi naz,
    I have tried to run the thermo circuit in LTpsice, using thermistor models, it will not work even as a simple circuit.
    If you look at that graph that is attached to the circuit, it indicates that the ZERO pot is set when there is no airflow and the CAL pot is set for maximum airflow.
    Note: you will never get 0V out, with no airflow for that circuit, it will always be offset by approx 3 to 4 volts.

    I am beginning to think these two circuits do not work.

    I would be interested to hear from any member who has made these circuits and say if they worked as claimed.????
     
  6. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi naz,
    This is as close as I can get with a simulation, without knowing the actual thermistor specifications.
    Note the output is from the OPA, use preset potentiometers for the CAL and ZERO pots.
    The adjustment of the two pots are interactive, so you may have to empirically find the best settings.

    Good Luck.:)
     

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  7. naz83

    naz83 New Member

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    airflow ltspice

    hi eric,

    thank u so much for the circuit, i will rig up this circuit today and will let u know how it goes....

    thanks
     
  8. naz83

    naz83 New Member

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    hi eric,

    i did rid d circuit up but no output really.... i used 2 pots 4,7k and 47k and used transistor 2n2222but the voltage was only 1.5v after setting the pots. the 1k thermistor was heated but blowing of air had no effect on it.... i connected the base of transistor to supply voltage and collector to drive the output........ but on doing reverse as ur diagram suggests the thermistor wasnt getting heated up at all...........

    i think the setting of pots is very tricky i used presets but in vain..... i am really stuggling to get an output from a simple circuit......

    any memebers if u have any circuits please suggest..

    thnx
     
  9. naz83

    naz83 New Member

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    filament anemometer

    hi, the bulb circuit is still working, it lights the led at no air flow and the led is put off when air flows over it....... any suggestions as to how to modify this circuit inorder to add ADC and then interface with an AVR...........

    at no air flow output = 0.39v
    at air flow output reaches a max of 10.75v depending on the amount/speed of air flow

    plz help.......
     

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  10. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi naz,
    Look thru these two links.

    From my reading about the two transistor circuit, its very very difficult to adjust also its not stable.!!

    Thermal anemometer

    Thermal anemometer(air flowmeter) - Circuit Diagram - Forum - SeekIC.com
     
  11. naz83

    naz83 New Member

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    hi,

    can any1 plz suggest any circuits/designs to make an anemometer using pt100/pt100 as i am giving them a try as well....

    thnx
     
  12. naz83

    naz83 New Member

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    I did experiment with pt1000s today.

    I did use two bridges each having one pt1000 as a sensor and one of the resistors was 1.2k. as a result the pt1000 was heated to reach 1.2k.

    Its like having two anemometers, one of them was subjected to air flow and the other was like a reference. and the outputs from these two was given to a differential amplifier to amplify the difference between the two. I did get it working, when no air flows the diff output is 0.13v and on air flow depending on the amount of airflow it increased to 3.0v.

    could u suggest what needs to be done further to get it to a uc and the AVR part plz....
     
  13. naz83

    naz83 New Member

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    Hi Eric,

    can you please send me the .asc file of thermair2.asc that you simulated for the air flow meter as i am trying to simulate something like it and i am new to Ltspice, i did try to simulate using proteus but i think ltspice is better to use.
    Thanks
     
  14. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi naz,
    Please find attached the LTS.asc

    Join the LTspice Yahoo users group, free, lots of info.
     

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  15. naz83

    naz83 New Member

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    .asc file

    Hi eric,

    when i open this file in ltspice it says no component for ntc and 741, and then it opens the file with the two thermistors and opamp missing. what should i do, plz suggest.

    Thanks
     
  16. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi naz,
    I have zipped all my ntc and 741 into this naz1.zip.
    Unzip and you should see 6 files.
    Unzip the zip files within naz1.zip OK.?

    Note the *.lib files should be in the same folder as the Thermair2, when you are more experienced you can move them around within the LTS main folder, follow an LTS tutorial on how to do that..
     

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    • naz1.zip
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  17. naz83

    naz83 New Member

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    Hi Eric,

    I could not unzip as it says that the archive is not valid and displays some error message. am i doing something wrong? please guide me.
    Thanks
     
  18. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    Download this free IZARC unzip.
    IZArc - Download
     
    Last edited: Aug 12, 2010
  19. naz83

    naz83 New Member

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    No graph

    Hi Eric,

    i did get all the files and could open the file with ntc and 741 but when i simulate it i dont get a graph like you have got, i just get a blank graph sheet. i have unzipped all the files but the ntc_g_temp and ntc_v_control could not be unzipped, it says extract not supported by this file type.

    also i am attching a .dsn file from proteus can u plz tell me how to create a ltspice file of the same.

    Thanks
     

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  20. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    Those two ntc_ files are LTspice 'lib' [library] files which LTS uses.
    You can read the contents of the lib files by using a text editor,,, dont change the text.!!!!

    In your Proteus sim you appear to have two identical thermistor models.?
    In my sim I used two different thermistor type, one with self heating and one without.
    As they have different resistance versus temperature characteristics their resistance values change with respect to each other.
    This gives a change in voltage at the 741 output.

    If you use two identical thermistors you must have the 'airflow' cooling only one of them so that they will have a different resistance.

    Can you post your version of the LTS asc file that gives a blank plot.???

    EDIT:
    Attached the LTS version of the posted Proteus sim.
    The circuit does not work.
     

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    Last edited: Aug 12, 2010
  21. Vizier87

    Vizier87 Active Member

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    Hi Eric, it's been a while (I depended on my sister's broadband but she's off to university, I recently graduated and I'm taking a break at home now, so my ETO-ing stops for a while ;))

    Naz, I personally built two "tranemometers" according to the one from Steve Woodward, both didn't work. Professor J. Liljencrants from his amateur report said it was diffficult to adjust and so on but it didn't work at all for me. Gary (Chemelec) said it worked nice but I'm not too sure how "nice" it was.

    Just in case you're trying to branch out and try other designs as well, the one using light bulb filament is the best according to Professor Liljencrants but it is very vulnerable. I developed a neo-anemometer, combining differential heating elements but it is very dissipative, around 2 watts I think. Here is the picture:
    [​IMG]

    It may not be better, but it works with a pretty fast time response (around a second). I heated the ambient air using light bulbs and sensed the ambient temperature using LM35s, rather than heating the sensor (usually people just tie the heating resistors to the sensor... urgh.). I'm still perfecting documentation on it (mostly on the dimensional studies) for publication. I'll write an article about it when it's finished.

    Otherwise you can also explore sonic and laser doppler anemometers as well, but they're not readily available in DIY articles yet.

    Cheers.
     
    Last edited: Aug 12, 2010

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