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  • Reply Summary-Fall Detection & Cheap Accelerometers

    A big *thank you* to all who responded. Here's a summary or replies so that all
    list members can benefit. My original post was

    __________ Start Original Post/Query

    I'm designing a fall detector. I need the following information

    (1) What the level of acceleration when a person falls and
    what parts of the body experience what levels?

    (2) Source of a *cheap* accelerometer to measure the
    acceleration described in (1).
    __________ End Original Post/Query

    ___________ Start Summary of Replies

    ******Part 1 of Query-Acceleration

    Reply #1---------------------------------------------------------------------

    The answer is 9.81 meters/second squared, if the person does not
    contribute to the acceleration caused by gravity by "flailing", which will
    obviously be a huge component if you are interested in the acceleration of
    the hands. I tend to think that an accelerometer mounted on the thorax
    would give you stable results. I would also stay away from the head since
    a person could jerk their head to avoid hitting it, unless of course you
    are interested in the kinetics and kinematics of the head.

    Bryan Kirking
    Research Engineer
    Department of Orthopedic Surgery
    Baylor College of Medicine
    Houston, Texas


    From Dhendry :
    1. g



    The answer to (1) is 'g' the acceleration due to gravity. This is
    9.8 m/s/s, though it varies slightly around the world.

    From: "R.E.Mayagoitia" :

    Dear Steven,
    The easiest way to calculate the acceleration and velocity at impact
    from a fall is the way presented in problem 7-24 page 197 of
    Barney Le Veau's edition (3rd) of Williams' and Lissner's
    Biomechanics of Human Motion (W. B. Saunders, 1991). It all comes
    down to how high the person falls from, how large the person's
    mass is and the length of time of impact. In this problem the center of
    mass is considered.The same method can be applied to any body
    segment. For this approach you only need high school physics.

    Ruth Mayagoitia
    Visiting Professor

    ******Part 2 of Query-Cheap Accelerometers************************************ *

    Reply #1-------------------------------------------------------------------
    From: Gary Kamen
    You may be interested in a report I recently published that describes an
    inexpensive accelerometer system for measuring balance and postural sway:

    Kamen, G. et al. An accelerometry-based system for the assessment of
    balance and postural sway. Gerontology. 44:40-45, 1998.

    A forthcoming paper will demonstrate its utility in discriminating between
    frequent fallers and healthy older adults:

    Cho, C.-Y. and G. Kamen. Detecting Balance Deficits in Frequent Fallers
    Using Clinical and Quantitative Evaluation Tools. Journal of the American
    Geriatrics Society (In Press).
    Gary Kamen
    Department of Exercise Science
    Totman 160A
    University of Massachusetts
    Amherst, MA 01003
    413-545-2906 (FAX)


    From Dhendry :
    2. any weight scale

    Seriously, what you probably want to know is the acceleration experienced by
    different parts of the body in (at the end of) a fall. Those depend on too
    many variables. You might get a suitable cheap accelerometer for ~$100, but
    the supporting equipment (amplifiers, recorders, etc) will cost ten times as

    Reply #3---------------------------------------------------------------------

    From: "Anthony J. Petrella"


    Check out Analog Devices for accelerometers in the $15-$20 range. You may
    have to do a little wiring to build a circuit, but the price is right.
    They have more expensive devices called evaluation modules that are the
    same chip as noted above but they come wired with a signal
    conditioning/amplifying circuit all in a little 3/4 x 1/2 inch block for
    about $100.


    Anthony J. Petrella
    University of Pittsburgh


    "Geoffrey.Walsh" :

    I wonder if you have the elctronics chain ,Maplin, in the US ?

    They list a small accelerometer for about 30 pounds I think.

    Their Web site is given as

    Email -

    Phone (0)131.664.3046

    64, Liberton Drive,
    EH16 6NW


    From: "A.L.HOF" :

    Analog Devices ADXL 05