Tiny Metal Detecting device? Magnetic Sensor?

Discussion in 'The Projects Forum' started by PaulHollingsworth, Mar 13, 2016.

  1. PaulHollingsworth

    Thread Starter New Member

    Jan 13, 2016
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    Hi All, I was wondering today if it would be at all possible to make a tiny metal detector device, no bigger than an inch squared or even smaller?

    I wouldn't know where to start in terms of the type of sensor that I would need, but it came about by an app on my iPhone, where you can utilise the magnetic sensor in the phone to turn it into a metal detector. It measures the magnetic field and alerts you when this increases to a significant value. Obviously, this isn't entirely accurate but is a good start.

    Has anybody had any past experience with certain types of sensors that might be useful for me to play around with.

    Many Thanks
     
  2. ISB123

    Well-Known Member

    May 21, 2014
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    It's doable if you use SMD.
     
  3. PaulHollingsworth

    Thread Starter New Member

    Jan 13, 2016
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    Could you elaborate on this abit more please. I'm very new to the circuit world so I'm unsure what smd is. Thank you for your advice
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Isn't metal detector and magnetic field detector two different sources?
    But you mention the sensor is already in the phone?
    (SMD is Surface Mount Technology).
    There are magnetic proximity sensors such as the miniature Honeywell SS400 series.
    Max.
     
  5. ISB123

    Well-Known Member

    May 21, 2014
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    This is THT(Through Hole Technology)
    [​IMG]

    This is SMD(Surface Mounted Device)
    [​IMG]

    Generally SMD's are smaller which makes it possible to construct smaller equipment like today's smartphones.
    You can use NE555 and a coil to build a simple metal detector.
    [​IMG]
     
  6. PaulHollingsworth

    Thread Starter New Member

    Jan 13, 2016
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    Excellent. Thanks for the info guys. This has given me something to start looking more into. I appreciate your patience to explain things to me as a noob
     
  7. Pinkamena

    New Member

    Apr 20, 2012
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    Well, magnetic field sensors (Hall Effect sensors) only detect magnetic fields, not the presence of metal itself. Metal detectors use a coil with an oscillating current passing through it, thus generating an oscillating magnetic field. When a piece of metal is introduced to this field, Eddy currents will be induced in the metal object, which then sets up its own magnetic field. It is this field that must be detected. I also believe it's possible to only use the inductor itself. When a metal object is introduced to its field, it will change its inductance. If this inductor is part of an LC circuit then the natural frequency will change, and this change can be measured. I believe this is how the "door style" metal detectors used at airports, for example, works. The benefit of this method is that you will not need the Hall Effect sensor.
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Not quite true, there are many manufacturers of industrial Hall effect sensors that will detect a ferrous metal flag, you can even get proximity sensors for non-ferrous metal.
    Others are designed to use a P.M. for detection, it is all in the design, but all are Hall effect in design.
    Max.
     
  9. ian field

    Distinguished Member

    Oct 27, 2012
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    There was one in an old copy of ETI, but I downloaded them from both americanradiohistory.com and electronicsandbooks, so I don't know which that issue came from.

    It used a single transistor and an untapped single winding inductor - but you have to use it with a pocket AM radio to pick up the disturbance in oscillation frequency.
     
  10. Pinkamena

    New Member

    Apr 20, 2012
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    Oh, that is interesting. So they come with built-in coils to generate eddy currents? I mean, it can't only be a hall effect sensor and nothing else.
     
  11. nsaspook

    AAC Fanatic!

    Aug 27, 2009
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    Yes they have an internal field generator. What's neat about them is they work at zero or very slow RPM unlike most variable reluctance sensors.
    This is a Honeywell Hall-effect based notched wheel RPM detector being used to trigger a signal to emulate (with a PIC18F1320) the original reluctance sensor output from a much higher speed motor.
    http://www.farnell.com/datasheets/1485997.pdf


    In operation:
     
    Last edited: Mar 13, 2016
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