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    The metal detector circuit shown here must represent the limits of simplicity for a metal detector, yet the design works surprisingly well. It uses just one 40106 hex Schmitt inverter IC, a capacitor and a search coil – and of course the batteries. A lead from IC1b pin 4 needs to be attached to a medium wave radio aerial, or it should be wrapped around the radio. It can be used even like those hand held metal detectors.

    As shown, the metal detector gives a respectable range for beat frequency operation (bfo) up to 90mm for a bottle-top. In fact, for the ultimate in simplicity, capacitor C1 may be omitted. In this way the author achieved am amazing 150mm range for the bottle-top. However, with the frequency then being raised to more than 4MHz, instability becomes a significant problem.

    Metal Detector circuit diagram

    metal detector diagram

    As shown, the circuit oscillates at around 230kHz. One may also experiment with the frequency by changing the value of C1. A Faraday shield may be added to reduce ground effect and capacitive coupling, and this is wired to 0V.

    Metal detector video with a funny song

    Since the inductor resists rapid changes voltage, the charging of C1 is slightly delayed as the logic level at IC1a pin 2 changes. This sets up a rapid oscillation, which is picked up by a MW radio. Any changes in the inductance of the search coil (through the presence of metal) bring about a change to the oscillator frequency. Although 230kHz is out of range of the Medium Wave band, an MW radio will clearly pick up harmonics of this frequency.

    Metal detector calibration
    The making of search coil L1 allows a lot of room for error and is far from critical. The author used seventy turns 30 s.w.g. (0,315mm) enamelled copper wire on a 120mm diameter former.
    The metal detector is set up by tuning the MW radio to pick up a whistle. Not every such harmonic works well, and the most suitable one needs to be found. The presence of metal will clearly change the tone of the whistle.

    Metal detector faq
    This is not an industrial or security metal detector and is not even close to loma or eriez metal detection products. It’s just a portable but not a hand held metal detector.

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    50 Responses to "Simple Metal Detector Circuit"

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    1. good

      Like or Dislike: Thumb up 1 Thumb down 0

    2. Nice basic circuit for a metal detector. Do you have experience with industrial level metal detectors?

      Like or Dislike: Thumb up 0 Thumb down 0

    3. Good,simple circuit pls give text book references

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    4. good but what is its range i mean whwt is the minimum disance for the metal to get detected
      actually i m plannin to use it in a problem ststement so if u can send me with its detail ill b obliged

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    5. What is the maximum range of this metal detector??
      I am looking for one with high resolution.

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    6. It is good but if there is it’s pcb design is present is more helpful for engineering student for making this project…

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    7. pls send all information about this project with including its components,component cost,it’s PCB design, it’s picture,it’s working function and it’s circuit diagram in my email id “sharifbachcha19@yahoo.in” OR “sexy2k4virus@gmail.com”.I have to make a project for electronic workshop lab,i need this .Pls reply soon…

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    8. A very good circuit, will have pleasure in making it in my spare time! ;)

      Like or Dislike: Thumb up 0 Thumb down 0

    9. Oh and Akash…im sure they have better things to do than do your college wotk for you….cheeky mare!

      Like or Dislike: Thumb up 1 Thumb down 0

    10. Akash i have completed your college course for you in my spare time and also took the liberty of completing HNC and HND for you. I will email you the details as soon as you tell me why you think people will complete you work for you.

      Like or Dislike: Thumb up 1 Thumb down 0

    11. Haha love your last post JJ :) I am actually doing my NC Electrical this year! Fancy meeting up for a drinks…and maybe more ;) x

      Like or Dislike: Thumb up 0 Thumb down 0

    12. “May you send an email to contact@electroschematics.com with your results, pictures and your review about this metal detector?”

      ….No

      Like or Dislike: Thumb up 0 Thumb down 0

    13. pls ineed a contructed circiut diagram of an automatic trash can that can be sensitive to waste or trash level which trigger off so as to stop further entry of trash. any way that circiut above is quet interesting.

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    14. J J Okacha says: on December 3, 2009 at 11:14 am

      ganiyat i think you need to plan and design the circuit yourself. You wont find shortcuts to people doing your work for you. Look at Akash, he got nothing for his demands. Your lucky the circuit above is available to view.

      Like or Dislike: Thumb up 1 Thumb down 0

    15. its toooooo nice… very smalll … can u mail the complete components required , ckt ,detailed explanation of this ckt.

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    16. can u please send me the following details
      apparatus required
      procedure to perform this

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    17. I am making the minor project of “Mobile Bug” Plz send me all the information an layout diagram of mobile bug ,,,
      plz send me all documantation at my email address””tom.iitdelhi.jerry@gmail.com””
      plz plz plz its urgent for me…..
      send me soonn….

      Like or Dislike: Thumb up 0 Thumb down 0

    18. Mr Picky says: on May 25, 2010 at 3:52 am

      LOL This is NOT “do-my-homework-for-me.com”

      I think there is a batch of ignorant lazy and to put it bluntly completely incompetent “engineers” coasting through school.

      They can’t even compose proper sentences, nor do they seem to be able to spell.

      Are these losers really in college?! Did any of them bother to read the article before they begged for their homework to be done for them?

      It is *simple* enough to understand.

      Great design, there is also the possibility to use the 4000 series CMOS AND or NAND gates. The other 2 gates can be used to compare the outputs and make a PWM signal to drive a MOSFET for a teeny vibrator. Would be great for silent operation or for deaf people.

      Like or Dislike: Thumb up 1 Thumb down 0

      • SlideruleSam E.E. '73 says: on October 4, 2012 at 3:24 am

        Yep, academia isn’t what it used to be. Entitlement instead of accomplishment.
        -SlideruleSam class of ’73-

        Like or Dislike: Thumb up 1 Thumb down 0

    19. gud day can you plz send me the complete diagram of that detector?? i want also to create that kind of detector so pls.thnk you thnk u

      Like or Dislike: Thumb up 0 Thumb down 0

    20. Hari Krishnan says: on September 20, 2010 at 1:48 pm

      hi,
      this is absolutly interesting.I’m really surprised to see this kind of a simple circuit for a metal detector.impressive very impressive.And i think this will become more helpful and attractive if you provide the correct details of the components and equipments required and the procedure for making this device…

      Like or Dislike: Thumb up 0 Thumb down 0

    21. shafeeq irumbuzhi says: on November 5, 2010 at 8:08 am

      good circuit

      Like or Dislike: Thumb up 0 Thumb down 0

    22. just watched the video looks very impressive i sure it works fine.never seen one made out of wood before.i like the funny song
      keep up the good work

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    23. please send the information about metal detector

      Like or Dislike: Thumb up 0 Thumb down 0

    24. lilmas master says: on March 17, 2011 at 2:11 pm

      انا طالب و لدي مشروع في الكلية عن جهاز كشف المعادن و اطلب المساعدة …. شكرا
      I am a student and I have a project in college for a metal detector and ask for help …. Thank you

      Like or Dislike: Thumb up 0 Thumb down 0

    25. helo
      aim need circuit detector metall
      tanks

      Like or Dislike: Thumb up 0 Thumb down 0

    26. good day sir, i have no idea about electronics or something to do with detectors. i just want to have a simple metal or gold detector for my personal use because i know how expensive metal detectors cost in the market today and i just can’t afford to buy one. i am just an ordinary man trying to find one of the long time gossip of hidden yamashita treasure in mindanao by simply digging in an area where it is being shown and detected by other people with their own gadget and even sometimes pointed by the so called medium which unfortunately is unreliable as i experienced. this is the real reason why i want to have this simple kind of metal/gold detector perhaps to start anew and hope to find one thru’ this…thank you very much and looking forward to see a brighter future tommorow…GOD BLESS US ALL

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    27. BY THE WAY , I WILL ASK MY DAUGHTER (computer engineering graduate) TO PREPARE THIS THING FOR ME…OR I WILL TRY A FRIEND WHO IS KNOWLEDGEABLE IN THIS FIELD TO ASSEMBLE THE GADGET FOR ME…thank you to anybody out there who can help me make this project posible and realistic…thank you

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      • This metal detector is a “low quality” one, is not accurate and its sensitivity is very low and is not suitable for treasure hunting.

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    28. ok sir, so can you suggest a more reliable and accurate one …and most especially affordable for me …thanks

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    29. New developed Mini Underwater metalprobe MD2012

      Under water 20-30 feet
      flashlight bright distance:
      5 meter / 6 yard
      Nylon Holster ( under water )
      Auto sensitivity adjustment
      Easy battery installation
      9V battery charger
      Sensitivity 1.5 inch
      testing USD 25cent
      Communicates with
      buzzer alarm
      LED light ( green for power,
      red for warning )
      Vibration ( switchover ON, OFF,
      a sound of light or mode of vibration )
      Top LED flashlight brightness
      distance 3 meters
      Telescopic handle 1-5 meters,
      can help you to search in Narrow hole
      Net Weight: 0.25 lbs / 0.45 lbs
      with belt holster
      Color: Black

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    30. Nigreats tech says: on September 25, 2011 at 10:06 am

      Sir, i want to appreciate your effort in the field of engineering.but sir i need a wireless transmitter and reciever circuit email me sir.pls sir how can i get more acquinted to you

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    31. how to boost the minimum range of this?

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    32. dear friend i am loooking for a metal detector if u have a simple detector as u said i would like to buy from u
      pls let me know if u r interested

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    33. R.VENKATESH says: on December 11, 2011 at 6:32 am

      I WANT METAL DETECTOR DOCUMENTARY FOR PROJECT.IT FROM VEGA KIT 557.

      Like or Dislike: Thumb up 0 Thumb down 0

    34. plz send me the details of this project..

      Like or Dislike: Thumb up 0 Thumb down 0

    35. Nate Youngblood says: on March 15, 2012 at 10:47 pm

      1. This is a one-way website, it’s for comments. How the website works should be obvious to anyone with even one year of university.

      2. If you can’t spell out “please” or “good” but prefer to use the EZScript abbreviations, you’re insulting other readers with your laziness.

      3. Among the students, there are Indian and Arabic names. I have worked with Indians and Arabs, in the States and in Europe, who believe in integrity and self-reliance. What happened to that?

      4. It’s an easy circuit, 3 components and a battery case. I have never seen simpler.

      5. If there is a person who needs such a device — maybe you have land mines in your village — this device is not sophisticated enough to help you. There is a “Metal detector faq” at the top that explains this.

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    36. RAMBABU,GAVARA says: on March 23, 2012 at 4:15 pm

      kits pricelist wanted

      Like or Dislike: Thumb up 0 Thumb down 0

    37. please send me detail circite digram ofgold metal detector with guide line fo aprox one ft defth capacity .I will be thank full to you .

      Like or Dislike: Thumb up 0 Thumb down 0

    38. Dont work at all

      Like or Dislike: Thumb up 0 Thumb down 0

    39. muskoka_survey_tech says: on October 22, 2012 at 7:14 pm

      Mr. Marion,

      Hello, I am survey technician with some training in computer technology. I want to build this project as a protoype with my sons. Also, wanted to thank you for posting it.

      Could you please verify the following:
      - that 470p is 470 picofarads?
      - is the project in the video about this detector because they seem to have alot more parts in their circuit than shown in the diagram
      - is this detector particularily for ferrous metals?
      - would you be interested me keeping you posted with with what we come up with? (I noted your email from above)

      I’m sure I could build other more elaborate and more expensive ones, but I think its good to start small and work my way up. I liked the video with the kids, looks like they had lots of fun!

      Looking forward to your replies,
      Sincerely,
      mst

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      • Jim Keith Jim Keith says: on October 23, 2012 at 1:20 am
          member

        470 picofarads, and perhaps it could be tweaked with a trimmer capacitor to make the frequency what you want. If your receiver has a BFO, it will be a great help.

        Ferrous materials tend to reduce frequency while non-ferrous tend to increase frequency. By setting the BFO tone at perhaps 400hZ, you can experiment with different materials to see if the tone increases or decreases frequency.

        Ground unused inputs of the 40106 as there are 4 more sections. Ungrounded CMOS inputs can cause sections to oscillate at several mHZ.

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      • Jim Keith Jim Keith says: on October 23, 2012 at 4:38 am
          member

        Watched the video clip. Wish they had something like that when I was a kid. I complain about how poor an attention span children have today, while forgetting what it was like for me as a kid. I now remember that I was in the Radio Club when in Jr. High and I was the only one that had an interest in the subject. Everyone else was goofing off.

        I got a glimpse of the schematic capture on the screen. It is indeed more complex as it has a multivibrator that is probably used as a local oscillator. The other stages probably were the search oscillator, mixer and headphone amp. That would make a good project for electrcircuits.com.

        They also put a good deal of effort into the search coil.

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    40. i m trying it but its not working ,,,,,,,,,,,plzzzz help n send me more details

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    41. seif helal says: on February 15, 2013 at 3:38 pm
        member

      how can i make it work to detect metals under ground
      range about 1m

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    42. samyak jain says: on March 14, 2013 at 3:50 pm
        member

      plz let me aware of use of hcf40106 ic in metal detection

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    43. hey
      I made this circuit with 2 capacitors and different Ic and the maximum distance that the frequency changes is about 15 cm .
      I wanna improve the maximum distance, so my question is can I do it by this circuit or should I change my circuit entirely…
      I tried different capacitors , does it works or not?
      If I give the ic more voltage, does the current of coil increase or not?…
      can you help me…

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    44. dear sir/madame, I found your aticle quiet interesting in its simplisity,i,m looking for something with a bit more sensitivity IE 600 mm range and am not worried about the complexity of the circuit and I wondered if you could recomend a web site where I might look for said circuit as I,m very new to computers and websites as regards to some of the comments/demands you appear to have attracted you have my simpathies in england we have a saying (some people dont know their arse from their elbow)they seam prevalent in your comments section if these folks are students then god help their education system and their countrys economic prosperity thanks again for an interesting read kevin

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