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Metal Detector question.

Discussion in 'Electronic Design' started by Larry Snyder, Feb 27, 2008.

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  1. Larry Snyder

    Larry Snyder Guest

    I'm getting into metal detectors again and was wondering if I missed
    something. Here's what I have so far:
    Dual coil transmit/receive wave around thing.
    Single coil variable reluctance wave around thing.
    Blast the dirt with microwaves and look for heat with infrared imaging.
    Blast the dirt with a magnetic pulse and listen for sound and generate 3d
    image.
    I have about another month before the weather permits scrounging. Does
    anyone have a scheme for metal detecting that I missed? Thanks in advance
    Larry
     
  2. Robert Baer

    Robert Baer Guest

    "Blast" the dirt with EM wave(s) and/or pulses and do *NOT* look for
    non-existant sound; look for phase changes or pulse reflections.
     
  3. neon

    neon

    1,325
    0
    Oct 21, 2006
    blast with microwaves BLAST WITH MAGNETIC. You have no idea how it works do you ? it is a simple oscillator whereby the metal proximimity changes the freq. and you can detect that.
     
  4. Robert Baer

    Robert Baer Guest

    FM radar is nice in that one can choose the distance with a simple
    resonant-type filter.
    Seems that almost nobody knows how they work...they are all in the
    time domain paradigm.
     
  5. RFI-EMI-GUY

    RFI-EMI-GUY Guest

    Are you getting tin cans jumping out of the ground?

    What about a circuit that discharges a capacitor into a hi Q coil with
    an o'scope monitoring the coil for the primary pulse and any subsequent
    ringing or reflection? If in vicinity of conducting object could you not
    determine the relative size and distance to it?

    --
    Joe Leikhim K4SAT
    "The RFI-EMI-GUY"©

    "Treason doth never prosper: what's the reason?
    For if it prosper, none dare call it treason."

    "Follow The Money" ;-P
     
  6. Larry Snyder

    Larry Snyder Guest

    Hi Joe. That's about what I'm doing. Here's schematics(not updated lately)
    http://www.pacificsites.com/~snyder/Remotes.bmp
    http://www.pacificsites.com/~snyder/a d converter schematic2.bmp
    The idea is to put a 100kw pulse into the ground. Magnetic materials will
    be pulled toward the coil and electrically conductive materials will be
    repulsed(eddy currents). The effect is like tapping it with a hammer. The
    sounds are digitized in a 4 channel a/d converter and put in a memory. The
    waveform looks like a step with ringing after it for each thing. This is
    dumped into the laptop and processed. I'm using qbasic(qb7) for software.
    The process is stripping the step out and dumping the ring. Put the steps
    into a seperate array and match waveforms. Once matched, they are located
    in two arrays organized as right and left for a 3d display and subtracted
    from the original array. The left and right arrays set red and blue
    positions on the display. The glasses I have aren't an exact match for the
    laptop screen colors. Waiting for red and green glasses to try.
    Anyway, I would be interested in any thoughts you may have about the ground
    search radar scheme.
    Take care of yourself
    Larry
     
  7. Robert Baer

    Robert Baer Guest

    The problem with RADAR is that one has a "dead time" equal to the
    pulse width plus the TR/ATR/receiver recovery time.
    At distamces greater than that, it is OK and useable.
     
  8. Robert Baer

    Robert Baer Guest

    I have the most recent compiler M$ ever sold for BASIC; they called
    it Professional Development System 7.0 (upgraded to 7.1 if i remember
    correctly).
    Have all of the docs, etc.
    Interested?
     
  9. RFI-EMI-GUY

    RFI-EMI-GUY Guest


    TRue but its primarily a dynamic range issue that might be overcome in
    practice.

    --
    Joe Leikhim K4SAT
    "The RFI-EMI-GUY"©

    "Treason doth never prosper: what's the reason?
    For if it prosper, none dare call it treason."

    "Follow The Money" ;-P
     
  10. Larry Snyder

    Larry Snyder Guest

    Thanks for the offer but qbasic is comfortable for me. There is a speed
    problem sometimes but machine code fixes that.
    Take care of yourself
    Larry
     
  11. RFI-EMI-GUY wrote:

    The typical attenuation in the soil at radar frequencies is at the order
    of 200dB/m. Thus it is not feasible to pull out the far signal from the
    near reflections, no matter what the technology is. Ground penetrating
    radar doesn't work unless in the ideal conditions (like dry sand) and
    very shallow depth.

    Vladimir Vassilevsky
    DSP and Mixed Signal Design Consultant
    http://www.abvolt.com
     
  12. RFI-EMI-GUY

    RFI-EMI-GUY Guest

    The original poster is designing at well below microwave frequencies.

    --
    Joe Leikhim K4SAT
    "The RFI-EMI-GUY"©

    "Treason doth never prosper: what's the reason?
    For if it prosper, none dare call it treason."

    "Follow The Money" ;-P
     
  13. JosephKK

    JosephKK Guest

    I do not find them so difficult. you can even detect multiple targets
    simultaneously. The first range vs gain compensation is a
    differentiator just after the detector.
     
  14. Robert Baer

    Robert Baer Guest

    Well, practice (that is to say, real radars) have not solved the
    problems, just (partly) decreased the times involved.
     
  15. Robert Baer

    Robert Baer Guest

    Actually, if you are careful and nasty in your coding, you can
    achieve almost computer speed, as well as "optimised" ASM code after
    compiling.
    Use integers = no calls to code routines; use only single loops where
    ever possible, as the code for a second inner loop is not optimum (but
    could be hand-corrected); use COBOL fall-thru logic; use CALLs to any
    routines (get rid of spaghetti logic); use tables (internal or external)
    for complex logic.
     
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