Choosing between capacative and FSR sensor?

Discussion in 'General Electronics Chat' started by kmuffs, Jan 18, 2014.

  1. kmuffs

    Thread Starter New Member

    Jul 14, 2011
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    Hi,

    I am trying to create a sensing device that can determine if a person is wearing a hard hat or not. This would be embedded into the hard hat itself.

    I am thinking either a pressure sensor (FSR) or a capacitive proximity sensor that is imbedded in the rim of the hat (the part which sits on a the persons head). My main concerns are that I read FSR's will be damaged if pressure is applied for a longer time period (which would be the case here). Also, the capacitive sensors are very sensitive to environmental factors — humidity in coastal/water climates can affect sensing output, so they may not be robust enough.

    Does anyone have experience with either of these sensing techniques and could provide a recommendation for this application?

    Thanks a lot!!! :)
     
  2. inwo

    Well-Known Member

    Nov 7, 2013
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    It would help to know the over all function of the sensor.

    It seems obvious to me who is wearing their hard hat.

    Will it track usage?

    Self powered?

    Must it know that it's on a head and not on say,a fence post?
     
    Last edited: Jan 18, 2014
  3. inwo

    Well-Known Member

    Nov 7, 2013
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    Capacitance seems the most straight forward.

    Motion, temperature, bio-sensing?
     
  4. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    At best, a sensor inside the helmet can tell if it is being worn or not.

    That is a different then determining if a particular person is wearing that hard hat or not.
     
  5. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Temperature was my first thought, but some industrial environments are easily at 34-35'C which is the temperature of a human head.

    I think capacitive sensing on the headband strap would be a good choice. You would need to do some tests with a sensitive capacitance meter and different sensor styles, as it needs to be comfortable and unobtrusive.
     
  6. kmuffs

    Thread Starter New Member

    Jul 14, 2011
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    Yea I thought of temperature as well, but thought that if it was either really cold or really hot it might not work. Also, if someone was wearing a tuque underneath it might mess with it. Would a tuque prevent a capacitive sensor from working? You don't need skin contact do you? What about piezoresistors? Do they have the same issue as FSR's?

    The sensor just has to be able to sense if a hat is being worn, ideally it shouldn't have false positives from being on a fence post or something similar. Low power consumption is also important.

    I could always use more than one sensor aswell. ie capacitive plus temperature.

    Thanks for the replies!
     
  7. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Not unless it's made of aluminum foil. A capaitive sensor is basically detecting the dielectric difference between air and a human brain & skull covering.

    Not sure how close that comes to a fence post.

    With any micro controller you can drive the current consumption down to the dirt, but it does need some power. Do you have anything in mind to recharge or resupply the battery?
     
  8. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    Maybe you could put a strain gauge on head band.
     
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