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Metal detector Help! miniature size and more — Parallax Forums

Metal detector Help! miniature size and more

wurxwurx Posts: 10
edited 2006-09-11 07:00 in BASIC Stamp
I was wondering if anyone knows how to make a DIY inductance sensor? The commercial ones seem to use 10v+ and are very expensive (50-150 per). I would like to be able to have a single coil about 1/2 inch in diameter detect a metallic object no more than 2-3 mm away. It does not have to be very accurate. I want to make a series of them and have them in a line to detect where a metallic objetct is on the line. I have used ultrasonic and photoelectric sensors in the past, but they bth have thier limitations.

Is there a way to have a BS2 run a coil with an iron center (i.e. magnet) that would be able to detect a voltage change? Very low voltage? Could that kill the BS2.

I have tried several ideas, none working.

Any help would be greatly appreciated.

Comments

  • wurxwurx Posts: 10
    edited 2006-09-10 18:29
    And yes, I saw this...

    forums.parallax.com/forums/default.aspx?f=5&m=3282&g=3395#m3282

    It is an excellect example! Just a bit over kill for my purposes, and too big.

    Thanks Beau Schwabe
  • Beau SchwabeBeau Schwabe Posts: 6,559
    edited 2006-09-10 18:34
    So use a smaller coil and a circuit similar to this...

    webpages.charter.net/schwabelove/BasicStamp/Coilread.gif

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Beau Schwabe

    IC Layout Engineer
    Parallax, Inc.
  • wurxwurx Posts: 10
    edited 2006-09-10 19:49
    That was a fast response. Thanks.
  • Beau SchwabeBeau Schwabe Posts: 6,559
    edited 2006-09-11 07:00
    wurx,

    Another method would be to have a resonate LC circuit.

    
Input >---Cap---o---> Output
                |
                |
  GND <--Coil---o



    If you supply a frequency at the input that is the same as the resonate frequency of the LC configuration, then you will see a noticeable voltage peak on the output.

    If the coil is altered in any way (add metal or subtract metal), the circuit becomes "detuned" and the output voltage will dramatically decrease. Just make sure you
    are not creating an antenna with your setup (no long wires) and that your resonate frequency is not going to interfere with any local TV, Radio, Aircraft, etc.

    Another way to "tune" the circuit would be so that the voltage peaks when the desired object that you want to detect is within "coil view". This way you don't run as
    much of a risk "transmitting" unless your object you want to detect is actually within·the range of the coil. Assuming that these are brief periods FCC would like that method better.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Beau Schwabe

    IC Layout Engineer
    Parallax, Inc.
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