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Electronic project position sensor

  • 16-04-2008 9:29am
    #1
    nuig4
    Closed Accounts Posts: 14 ✭


    Hi Im starting my final year project and as part of it I need a sensor to calculate the distance from a person to a set point. The person will move in any direction so linear sensors are out. Could anyone point me in the right direction or give me any ideas? Thanks


Comments

  • #2
    DublinDilbert
    Registered Users, Registered Users 2 Posts: 5,401 ✭✭✭DublinDilbert


    nuig4 wrote: »
    Hi Im starting my final year project and as part of it I need a sensor to calculate the distance from a person to a set point. The person will move in any direction so linear sensors are out. Could anyone point me in the right direction or give me any ideas? Thanks

    What resolution do you need? are we talking centimetres or kilometres?

    Do you just need the linear distance to a point or are you looking for an x & y offset from the position?

    Is it indoors or outdoors??



    Oh so many questions :rolleyes:


  • #3
    nuig4
    Closed Accounts Posts: 14 ✭nuig4


    Sorry i should have given more details. I need to measure up to 5meters with a precision of hopefully 10cm. Its outside, and i just need the distance position is not important


  • #4
    DublinDilbert
    Registered Users, Registered Users 2 Posts: 5,401 ✭✭✭DublinDilbert


    nuig4 wrote: »
    Sorry i should have given more details. I need to measure up to 5meters with a precision of hopefully 10cm. Its outside, and i just need the distance position is not important

    You'll probably need to give us even more information.....

    Does it have to be passive? or can the person wear something / some device to help in the process??

    What sort of money would you be talking for the solution? are you think hundreds or hundreds of thousands....

    I guess ultrasonics is out, as is out doors and would be effected by wind ect... It might be hard to set up a vision system to do this also.....



    I'm sure some of the boardsie's here will pitch in a few idea's, we had great fun a few weeks back brain storming an ice sensor for a pipe!!!


  • #5
    nuig4
    Closed Accounts Posts: 14 ✭nuig4


    Thanks. The person can wear something as long as it isnt very big. hopefully it could be strapped to an arm or fit in a pocket. I have been looking at RFID but i dont think it would be accurate enough. The system can be used indoor or out so ideally it would work in both but if not inside is fine. Budget of a few hundred.


  • #6
    sharkDawg
    Registered Users, Registered Users 2 Posts: 401 ✭✭sharkDawg


    How are you only starting your final year project in April????


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  • #7
    daveyj
    Registered Users, Registered Users 2 Posts: 16 ✭daveyj


    Hi NUIG4

    Why not go with a string, tethered between the person and a drum, with rotary spring. That way you have established a linear measurable parameter (string length) for distance from the person to the drum. Put the drum on a pivot and now its good for 360 degrees. Install a rotary encoder (or other suitable sender) in the drum and connect to a DAQ card. Knowing the diameter of your drum, do the maths, make up the code to interpret the signal and you're away. Kind of like one of those extendible dog leads, stuck to a pivot, with the collar end on your test subject. The craic would be in choosing and calibrating a system to interpret whatever physical variable you choose to employ. Build the little rig yourself. It's always the simplest ideas that work in the end!

    Anyways I can't think of any wire free option that might suit. Like you said yourself linear measuring devices (laser, ultrasonics) are out. The motion capture gear they use to make video games and 3D movies is too expensive. Doppler no. GPS isn't accurate enough. DGPS is expensive and may not be feasible (you'd need a tracker dot, don't even know if they do for DGPS). So I'd recommend a more practical, simplistic, mechanical approach something like what I outlined already.

    Have a think yourself and if you reckon I could be of any help give me a shout on the PM.
    Hope you're starting this in advance of final year and not just starting it now!
    Best of luck buddy,
    Dave.


  • #8
    backboiler
    Registered Users, Registered Users 2 Posts: 368 ✭✭backboiler


    If wireless (stringless?) is required, you might consider a Wii remote. If the person carried one with them and you had three IR LEDs at known, fixed locations at and near your reference point (where you're measuring your distance from) you can use the remote's dot detection (http://www.wiili.org/index.php/Wiimote#IR_Sensor) and some basic trigonometry to figure out how far away you are from the LEDs. I think 3 LEDs would do the job for 2-D distance measurement, as long as you don't move too much in the vertical direction. Accuracy up to 5 m should be a lot better than your 10 cm requirements too.
    The project turns from being an electronic hardware problem into a mechanical and software problem, if that matters.


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