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Measuring speed with the Parallax Ultrasonic Rangefinder — Parallax Forums

Measuring speed with the Parallax Ultrasonic Rangefinder

NoBo780NoBo780 Posts: 94
edited 2008-03-29 20:50 in BASIC Stamp
I have heard people talk before about measuring the speed of a moving object with the Ping))) sensor. Is this possible? Any ideas to where I should start?

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Giggly Googley!

Comments

  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2008-03-29 01:03
    If it's moving slowly enough, V = (x1 - x0) / t ····No Doppler capabilities, though.

    BTW, you should be able to delete your other thread before anyone else posts to it. Just click the X in the upper righthand corner.

    -Phil
  • NoBo780NoBo780 Posts: 94
    edited 2008-03-29 01:06
    Ok. IDK you could do that (delete).

    So, by slow enough, how slow are we talking here? And by Doppler, what exactly do you mean?

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    Giggly Googley!
  • NoBo780NoBo780 Posts: 94
    edited 2008-03-29 04:12
    Also, could you explain that equation...?

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    Giggly Googley!
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2008-03-29 05:54
    First, the equation: V = (x0 - x1) / t

    Assuming the object whose velocity you want to measure is coming towards you, take two distance readings. x0 is is the first one, x1 is the second one, so x0 - x1 is the distance the object moved. If the intervening time between the two readings is t, the average velocity of the object during that interval is given by the formula.

    With the right equipment, instantaneous velocity measurements could be obtained by determining the Doppler (wavelength) shift of the reflected ultrasonic wave pulse (the train whistle effect). This is the method used by police radars, except using radio waves in the GHz region instead of sound waves in the KHz range.

    -Phil
  • NoBo780NoBo780 Posts: 94
    edited 2008-03-29 19:58
    Ok. What if it is moving AWAY from you? This is starting to not seem very practical....

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    Giggly Googley!
  • Mike GreenMike Green Posts: 23,101
    edited 2008-03-29 20:50
    The same formula works with positive velocities representing motion towards the sensor and negative velocities representing motion away from the sensor (velocity is a vector quantity with a direction).
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