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Weight sensing

Discussion in 'Automotive Electronics' started by rabhishek91, Mar 27, 2013.

  1. rabhishek91

    rabhishek91 New Member

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    Hi .
    I am currently doing a project wherein i need to sense whether the person is seated or not.
    That can be done using Seat wave sensor which is used in existing automobiles, but it costly.

    Another option would be using strain gauges but its weight withstanding capability is less.

    Load cell is also a good option but it in large in size hence not feasible.

    I just need to detect whether the person is seated or not. So just a rugged switch might work (Leaf spring type).
    I am still searching for some more options.
    Please help me regarding this issue.
    Thanks in advance.:)
     
  2. Ian Rogers

    Ian Rogers Super Moderator Most Helpful Member

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    Some cars on the road today.... Use a switch to see if seated people have their seat belts on.... A micro switch with a long travel arm is all that's needed.
     
  3. rabhishek91

    rabhishek91 New Member

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    Thanks for your reply sir .
    Are these micro switches rugged? Cause it has to withstand the weight of a person .
     
  4. dave

    Dave New Member

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  5. Ian Rogers

    Ian Rogers Super Moderator Most Helpful Member

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    You just need sponge and two foil plates as a flat cushion... It only needs to touch...
     
  6. rabhishek91

    rabhishek91 New Member

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    Sir i have made a simple sketch. Can it be done like this ?
     

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  7. whylove

    whylove New Member

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    you can use a photo diode at the side of the seat
     
  8. atferrari

    atferrari Well-Known Member

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    I know of microswitches used for that.
     
  9. Norator

    Norator New Member

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    You also must not detect the weight of a package or other object so you should find the minimum weight of a vehicle occupant to some level of confidence. How bad or good are each of the last two outcomes below?

    Person correctly detected, OK
    No person correctly detected, OK
    Person incorrectly detected
    No person incorrectly detected

    Packages don't move but people do so you might want to look into a vibration/accel sensor.
     
  10. rabhishek91

    rabhishek91 New Member

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    Thank you sir. I'll go through it.
     
  11. athnylkr403

    athnylkr403 New Member

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    You place one of these at each of the four corners of your load plate. This will give you 200kg max load and an 300kg break point. Output can be run through a simple op-amp buffer to both buffer the signal and scale it to full range for the ADC you are using. A quad-op amp package would give you a single chip (plus a few resistors) solution. Add a micro with four channels of ADC. Convert the buffered voltage from each of the four sensors and then sum the results to get a weight. You will need a 10-bit ADC to get useful resolution. At 10 bits, you are looking at ~0.2kg/0.4lb minimum resolution at 200kg full scale.
    If you want temperature compensation, at a fifth cell that is passive and use its value to offset the other four appropriately.
     
  12. jase4frfa

    jase4frfa New Member

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    This load sensor is the same one found in digital bathroom scales (you know, the ones you use in January for your New Year's resolutions, and then forget about a month later). This sensor can measure up to about 110 pounds. Check the video below for a simple explanation on how these work and how to use them.
     

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