Pressure sensor

Discussion in 'General Electronics Chat' started by maryrose0911, Sep 10, 2014.

  1. maryrose0911

    Thread Starter New Member

    Jan 29, 2014
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    Hi. Just a quick question.

    Our design project's main problem is how to detect that a person is seated on a fixed seat (e.g. fast food seats)
    We're still thinking on what will be the best sensor (cheap yet effective) to use to detect that a human is seated there but not heavy things/load.

    Thanks and God bless!
     
  2. Sensacell

    Well-Known Member

    Jun 19, 2012
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    A capacitive proximity sensor- works right through fiberglass fast-food seats, no moving parts, cheap and reliable.
    My company makes these for decorative illumination purposes; www.sensacell.com
     
  3. sirch2

    Well-Known Member

    Jan 21, 2013
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    The sensacell product looks good but alternatives may be a strain gauge or piezo transsucer
     
  4. maryrose0911

    Thread Starter New Member

    Jan 29, 2014
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    Thanks for your response.
    How does the capacitive proximity sensor work in detecting human presence on a seat?
     
  5. maryrose0911

    Thread Starter New Member

    Jan 29, 2014
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    Hi. How does it work by the way?
    I'm just a newbie. :)
    Thanks for the response.
     
  6. Sensacell

    Well-Known Member

    Jun 19, 2012
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    Assuming the seat is made of a non-conductive material, an electrode mounted inside the seat detects changes in capacitance caused by presence / absence of a person sitting on the seat. The sensor could be very thin, multiple electrodes and some logic would help discern a person vs. a bag or other stuff placed on the seat.

    All kinds of crazy stuff happens on seats, especially in a fast food environment.
    How critical is the sensing application. i.e. what level of false trigger immunity do you need?
     
  7. maryrose0911

    Thread Starter New Member

    Jan 29, 2014
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    Our project is to detect a human presence on a seat to display on the monitoring system that the seat is occupied.. The sensor must send info that it is true once it detects ONLY human presence to consider the seat as occupied, otherwise, the seat is available at default.
     
  8. Sensacell

    Well-Known Member

    Jun 19, 2012
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    Sounds reasonable.
    To detect ONLY a human in rigorous terms is rather tricky, but I assume you would be okay if it detected a nice big dog in the seat as an 'occupied' seat?
    What about a big bag of groceries? a kids school bag? someone putting their feet up on a seat?
    To filter out these other situations you might need to layer in more technology, it could get complex and expensive.
     
  9. maryrose0911

    Thread Starter New Member

    Jan 29, 2014
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    Yup. That's one of the problems that we're considering as well. We're thinking of temperature sensor but it is quite expensive. Pressure sensor would be an alternative as they say. Thanks for all your ideas and responses. :)
     
  10. sirch2

    Well-Known Member

    Jan 21, 2013
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    What about a camera and some software to detect things that are human body shaped? All sizes of people from little kids to big guys have arms, torso and head but dogs, groceries, etc. don't.
     
  11. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Occupancy seat sensors (for airbag systems) in cars are simply triggered after a certain weight limit... (the lower limit is approximately the weight of a 24 case of beer) :)

    You need to be very specific in exactly what is occupied vs not-occupied.. if you want good suggestions on how to implement that.
    So sense a person in excess of ??? pounds
    So not detect a metallic object of "X" size or any object over "Y" pounds ?
    and on and on and in more detail.

    I assume this is not for the US as I've never seen anyone bring in 30+ pounds of steel weights with them when eating at the McDonalds nor have I even seen one with any seating problems other than the flock of yuppies into a Panera bread or Starbucks.
    To me you are adding complexity where it doesn't need to be. A hinged seat/rubber damper and simple microswitch that is tripped when the weight on the seat is in excess of 15 lbs or so is sufficient IMO to solve any occupancy problem at a fast food restaurant.
     
    wayneh likes this.
  12. wayneh

    Expert

    Sep 9, 2010
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    A fancy solution would be to use a camera and facial recognition software, like in a digital camera. It won't identify anyone but even a cheap camera is capable of finding faces in an image. But the software doesn't react to animal faces, for instance.

    But I'm with mcgyvr - keep it as simple as you can. Use an existing, tried and true solution - the seat sensor.
     
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