lis302dl accelerometer...... help

Discussion in 'The Projects Forum' started by alexpanrui, Oct 6, 2008.

  1. alexpanrui

    Thread Starter Active Member

    Feb 25, 2008
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    0
    since the accelerometer is able to detect the acceleration.is the sensor able to detect how fast a person is running?thx
     
  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    Theoreticaly yes, since speed is integral of acceleration.
    But practicaly it is not possible, because even a small offset would lead to continuous increasing of speed and make the measurement useless.
    Also you would have to use only one axis of the accelerometer and it must be at all times in the direction of the movement.
     
  3. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
    1
    I disagree, you must use all 3-axis to perform a measurement. If you try to use only one, then a mere 1 degree tilt will completely throw off your measurements. You do the vector sum of all three axis to create a single vector with a direction and magnitude. You integrate the magnitude with respect to time, then you will obtain velocity. Then, integrate again to get position.

    Offsets will ultimately render the measurements useless. You can bound the integration in order to minimize the accumulation of error, as is often done. Realistically, you only have a short amount of time where velocity would be valid, then an even shorter amount of time that your position would be reliable.

    The only position trackers that I know of that are accurate rely on other predictable phenomena. For example, GPS units commonly read-reckon in between satellite outages. When walking, there are units that measure the time between steps to infer a position change. These can be extremely accurate over time in comparison to a double integration.

    Steve
     
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