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Memsic 2125 Trig Formula — Parallax Forums

Memsic 2125 Trig Formula

tkcraw_NSCC12tkcraw_NSCC12 Posts: 3
edited 2013-01-03 14:41 in BASIC Stamp
Hi we are doing a college group project for measuring the amount of force impact for the memsic 2125 Accelerometer and we were wondering if anyone could help with the trig formula for determining the Gforce impact an explanation of any type would be greatly appreciated. We can measure the pulsin from the sensor we just need to be able to have the conversion to Gforce for alarming. If any additional information needed then please respond through the post or PM.

Comments

  • davejamesdavejames Posts: 4,047
    edited 2013-01-03 08:21
    Hi tkcraw_NSCC12 - welcome to the Forum!

    I'm no expert with the 2125, but I did find this over on the Parallax site, which may (?) help:

    http://www.parallax.com/Portals/0/Downloads/docs/cols/nv/vol3/col/nv92.pdf

    Regards...
  • tkcraw_NSCC12tkcraw_NSCC12 Posts: 3
    edited 2013-01-03 08:29
    Thank you for that doc and we will take a look and hopefully that will assist us in the final process of the project
  • davejamesdavejames Posts: 4,047
    edited 2013-01-03 08:37
    ...welcome. Here's the link to the Parallax 2125 store page:

    http://www.parallax.com/Store/Sensors/AccelerationTilt/tabid/172/CategoryID/47/List/0/SortField/0/Level/a/ProductID/93/Default.aspx

    There is more information available.

    Please let us know how the project progresses?
  • ercoerco Posts: 20,260
    edited 2013-01-03 10:02
    Those memsic sensors are somewhat delicate. Depending on how hard you're impacting them, you might alternatively consider a piezo sensor, which outputs a voltage spike from an impact. Cheap piezo disk speakers are useful for this. Measuring the peak voltage output would give you a number which could be calibrated to G-force.

    FWIW, I used a piezo disk to sense taps/knocks here: http://www.youtube.com/watch?v=FFLfb1kFPow
  • Duane DegnDuane Degn Posts: 10,588
    edited 2013-01-03 14:17
    Can you give more information about the impact force you want to monitor?

    The Memsic only measures up to 3g. I'm pretty sure shock forces can be much higher than that.

    When you ask for a trig formula, I assume you want to measure some angle. You can figure the angle of the force within the two dimension used by the sensor with the arctangent function. Many trig libraries have an "ATan2" fuction that takes two parameters and returns the angle made by the two parameters. A normal arctangent (ATan) only takes one number which needs to be adjusted based on the values of X and Y to get the corrected angle.

    Depending on the force you want to detect, a three axis accelerometer might be a better sensor to use than the Memsic 2125.
  • tkcraw_NSCC12tkcraw_NSCC12 Posts: 3
    edited 2013-01-03 14:41
    Well basically what we are making is an impact detection system that we are going to put into a hockey helmet to detect approximate concussion force with a warning indicator sent wirelessly depending on the severity of the hit. For example a hit that occured giving a g force rating of 85 would send a warning signal because 15% of concussions happen in around that range and the Alert signal at 90 because that is area where the majority happen in relation to hockey.

    So you seam pretty sure that the Memsic only measures 3g so i am thinking that we are going to have to find a new approach due to a 3 week deadline a new parts order may not be an option

    Thanks for the replies and info from everyone thus far
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