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pressure measuring device

Discussion in 'General Electronics Discussion' started by Achal Gupta, Sep 26, 2015.

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  1. Achal Gupta

    Achal Gupta

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    Sep 26, 2015
    please help urgently as possible
    I want a cheap digital pressuring measuring device that could be connected to aurdino,pressure is comparable to a normal human weight
     
  2. davenn

    davenn Moderator

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    Sep 5, 2009
    google load cell
     
  3. Achal Gupta

    Achal Gupta

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    Sep 26, 2015
    thanx very much for your kind and quick reply....
    but i want something more cheaper aroud 5-6 $ not very huge pressure as to be measured just comparable to an adult man standing,my budget for whole projecct is around 40$ and i need atleast 6 such pressure measuring instrument
     
    Last edited: Sep 26, 2015
  4. Old Steve

    Old Steve

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    Jul 23, 2015
    As Dave said - a load cell. They're the best way to measure a weight in the range that you want, accurately and consistently.
    I doubt that you'll find anything comparable, and especially not for $5-$6.
    There are 100kg load cells here for $5-$10 each:-
    http://www.alibaba.com/product-deta...666143.html?spm=a2700.7724857.35.1.8cSQCJ&s=p

    You'll need to add the additional circuitry, Wheatstone bridges etc, yourself though.
     
    Last edited: Sep 26, 2015
  5. GPG

    GPG

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    Sep 18, 2015
    A man standing (or sitting for that matter) is not a pressure, . Pressure is force/area eg PSI. Kg/M, Kpascals
     
    Last edited: Sep 26, 2015
  6. Martaine2005

    Martaine2005

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    It is when the mrs tells you to!!

    Martin
     
  7. Minder

    Minder

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    4 at $1.00 each.
    ebay 301695019719
    M.
     
    Arouse1973 likes this.
  8. wingnut

    wingnut

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    Aug 9, 2012
    If I could get load cells at the prices Minder pointed you to, that is all I would use.
    My robotics book suggests using conductive foam for pressure sensors. It changes conductivity when compressed. It is the sponge like stuff your electronic components (like CMOS IC's pins) arrive in. I tried it with an Ohmmeter and it works quite well if you only need to know if someone has trodden on it or not.
     
  9. Old Steve

    Old Steve

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    Jul 23, 2015
    I've done that, with the grippers on a robotic arm. Not at all practical for weight measurement unless humidity never changes.

    Minder, the ones you mentioned are fine for really small guys like me, (43kg), but not for the average body weight. Two side-by-side per body might work though. Or three for some people.

    At that price, I couldn't resist - just bought some. :)
     
  10. Martaine2005

    Martaine2005

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    May 12, 2015
    35 for some people. Still cheap though.
    [​IMG]
     
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  11. Old Steve

    Old Steve

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    Jul 23, 2015
    That's me on the right:-
    images.jpg
     
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  12. Martaine2005

    Martaine2005

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    May 12, 2015
    I am always the middle man:eek:
     
    Old Steve likes this.
  13. Achal Gupta

    Achal Gupta

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    Sep 26, 2015
    :):)thanks all of you,
    specially old steve ,I find your suggestion just want to know can I connect this to aurdino board.If yes ,then can you suggest me how could I do so..
     
    Old Steve likes this.
  14. Achal Gupta

    Achal Gupta

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    Sep 26, 2015
    Your suggestion tempts me :):),can you provide a link for the same...
    I googled it but cant find anything related
     
  15. Achal Gupta

    Achal Gupta

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    Sep 26, 2015
    :D:DWingnut can you please provide me some more details regarding it,Actually my project is based on same concept,if I am weighing two different objects,I want to check whether they are of comparable pressure or not,compression is the main logic behind it,and I think conductive foam also works on same principle..
    Can you refer me any essential robotics book regarding it..
    I googled it,then it tells me cost around 10$,is more cheaper available??
     
  16. Minder

    Minder

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    Apr 24, 2015
  17. wingnut

    wingnut

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    The robotics book is called "Robot Builder's Bonanza" Third edition by Gordon McComb and Myke Predko.
    The suggestion re. conductive foam is on page 508. The book has 733 pages of well written info covering every aspect of robot building, electronics, mechanics, sensors etc. I vaguely remember the book was around $25.

    If I were trying to do what you seem to want to do, I would sandwich conductive foam between two metal plates. From the plates, two conductors would go to the ADC pin of my controller and the ground. To measure heavier weights, I would put my pressure sensor into a bigger sandwich comprising two pieces of wood hinged together with ordinary foam stuck to the inside of both pieces of wood. The closer I place my conductive foam to the hinge, the more sensitive it would be to pressure.

    In summary, I have a sandwich of wood, ordinary foam, metal plate, conductive foam, metal plate, ordinary foam, wood, where outer planks are hinged together.
     
  18. Old Steve

    Old Steve

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    Jul 23, 2015
    As I mentioned, this is useless for measuring weight. It's a waste of time, for number of reasons, the two main ones being large variations with humidity and the fact that the foam doesn't return fully to original thickness after compression, especially with repeated use.
    If it was any good for accurate weight measurement, there wouldn't be such a thing as load cells.
     
    Arouse1973 likes this.
  19. Old Steve

    Old Steve

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    Jul 23, 2015
    You'll need to do some research on using a load cell. Have you considered Googling "load cell circuit" or similar? Even better, "load cell Wheatstone bridge" or "load cell Wheatstone bridge circuit".
    In effect, you need to use a Wheatstone bridge, with the load cell in one leg, (a 1/4 bridge configuration), and a differential op amp across the bridge to measure the bridge unbalance, then the output going to an Arduino ADC input.
    Forget the conductive foam idea, it's crude and unreliable.
     
    Last edited: Sep 27, 2015
  20. GPG

    GPG

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    Sep 18, 2015
    A lot of load cells have a resistor on the tension side and the compression side for 1/2 bridge operation. The benefit is temperature is less an effect
     
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