Metal simple and powerful detector

Metal simple and powerful detector

My daughter got into her head to want to use a metal detector to search for ancient artifacts, where I live there are many areas to explore, the possibility of discovery are very low but, with a little luck you can find exhibits ranging from Etruscan times up to World War II. Not wanting to spend on a desire that could last less than a month before, find myself with a metal detector in the house that takes dust I decided to build one I. I appreciate this hobby, because it relaxes and leaves the mind free from everyday problems. Currently, the commercial metal detectors are equipped with microprocessors, This facilitates the processing of information, making them faster and more accurate identification and localization of metals.

But there are several detectors unprocessed who hit among those who want to realize their metal detector, including the Surfmaster PI and this

all of PI technology (Pulse Induced). But even these detectors are considered by many difficult to achieve, This is why I decided to design a version metal easiest detector, but with PI technology.

Although many engineers do not agree, a PI detector can discriminate if well designed, different metals, It depends on the sampling frequency.

Metal Detector Amilcar PI

My metal detector with false modesty that I called Amilcar Pi is easy to build it is already pre-adjusted for maximum efficiency and does not contain components difficult to find, and what not least is also very low cost.

The metal detector is composed of two main units, a transmitter that uses the generator of narrow pulses to be 150us, retrieved from the literature on the network is the most efficient solution and to lower consumption. These pulses amplified by a mosfet IRF740 piloting an emitter coil. The same coil also acts as a receiver and its main component is the LM324, a quadruple operational amplifier.

The starting point of this handset is inspired by a metal detector originally developed in Russia. In my there is a reworking of the same ideas with European components and, while I was there optimize the oscillator part to save mA always useful for battery-powered devices. The result was a very similar to Surfmaster PI detector in its operating principle, but much simpler and “quasi” the same efficiency.

The electronic circuit works so: It starts with a square wave oscillator which rotates on an oscillating operational at a frequency of about 130Hz with on-off ratio very unbalanced while 7,3mS Ton = Toff = 0,15mS.

The output is inverted by Q2 which serves to drive the mosfet, the scelda of R6 and R7 is designed to compensate for the fact that the operational amplifier output never reaches the supply voltage, They are typically 1.5V “eaten” by the operational, the divider serves precisely to ensure that when the output is at one of the transistor Vbe is below the conduction threshold to zero while when it is able to take it into saturation. The resistors R8 and R9 ensure that the mosfet has rising edges and very rapid descent to avoid unnecessary heat loss and give the maximum power to the transmitter coil. R11 together with D3 and D4 act with C4 ago detector for the extra voltage induced when stopping driving the mosfet. It appears obvious that esa will be much higher as much as a metallic element will be found in the magnetic circuit of the coil. R12, R13 and R14 securing the comparator threshold levels for signal detection so as not to have anything in headphones if not in the presence of a metal object. R15, r16, The potentiometer R17 and C3 serve to filter out high frequencies and simultaneously regulate the volume of the headphones. C7, R18 and the last transistor amplifies the signal picked up at an optimum level for headphones.

The consumption at idle settles on 20mA, these expedients guarantee an acceptable duration of 9V battery, But nothing prohibits to use a lithium battery pack 2S or 3S for a full day of uninterrupted research.

The metal detector coil

The construction of the metal detector coil is simple, the coil is composed of 25 turns of wire from 0,5 mm with a diameter of 19 cm.Con this setting the sensitivity to a coin 25 mm is 20 centimeters. Other diameters may be tested for an optimal result, the table below by some indications regarding the number depending on the diameter coils to always have an inductance of approximately 400uH

coil Diameter Number of turns inductance
100 mm 42 402uH
120mm 36 405uH
150 mm 31 394uH
175 mm 28 387uH
190 mm 25 401uH
200 mm 26 406uH
250 mm 22 380uH
300 mm 20 390uH
400 mm 17 396uH
500 mm 15 400uH

The base dual electronics face is 44mm x 58mm but it is not critical and you can achieve it however you like

I by the time I left everything in the hands of my daughter, at least until it will not be fed up of the new “toy” and shall put on a mobile gathering dust.

Amilcare Greetings

59 replies
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  1. Angelo
    Angelo says:

    First of all, a greeting to all. Excuse me but I'm not familiar with forums and the like.
    I am Angelo last arrived. An old man who, in order not to be stupid, delights in building electronic toys for and with his grandchildren.
    Say. Amilcare, without compliments, you are really good! I came across your metal detector project by chance, me and’ liked it very much.
    I decided to make it for my nephew Helghin, I live abroad and I e’ difficult to find material, anyway , if possible, could you provide i
    PCB drawings ? I would be very grateful to you.
    Thank you.

    • Picmicro675
      Picmicro675 says:

      Welcome Angelo. I am also an AIRE. I see that the article is of wide interest.

      To make the printout, as we spend time spending the day, just lay out the circuit in an electronic design program. A valid one could be Kicad ( Eagle, or do it online with and others like Altium, LabCenter Proteus.
      Then once you have the Gerbers, you can have the printout done at a modest expense (PCB for the Anglo-philosophers) from the dear Chinese, or also, having some time to develop it home made.
      For the components, just look for them on international distributors like RS-online, Element14, Mouser e Digikey, except local ones. Except that you are in the ASEAN area that offers a good relationship with China and therefore ordering at and sometimes it takes a couple of weeks.

      • Angelo
        Angelo says:

        Salve ” Picmicro”,
        The topic and’ really followed, at least here in Albania,
        thanks for the tips, I found them useful, I live in Albania, worked well,
        but lately since e’ took over ” Ali Baba” arrive on 25% of orders with empty packages. A delusion. Lately I order in a shop in Padua, A friend brings them to me who comes and goes on his own business.
        A warm greeting.

      • Angelo
        Angelo says:

        Thank you very much , out of courtesy , solersia and patience, Thanks again.
        I managed to open the file. Now let's see what (( io )) saro’ able i do.
        A warm greeting.

  2. Daniele Guidi
    Daniele Guidi says:

    My name is Daniele and I'm from Bologna, I wanted to ask you kindly if it is possible by changing the amplifier, improve the power of this metal detector. Thank you and wish you and your family a good day.

    • Amilcare
      Amilcare says:

      This metal detector has limited room for improvement.
      As you can see for yourself the number of components is reduced to “minimum wage”.
      To get more power you should increase the current flowing in the coil ma, unfortunately, the option would result in reduced battery life to unsustainable levels.
      For greater sensitivity, another detection system should be used. You need to switch to circuits with two tuned coils, one sender and one receiver, the presence of any metal between the two coils affects the signal picked up by the receiving coil both in terms of amplitude and frequency.
      By detecting this variation it is possible to discriminate the size of the metal or its depth.

    • Amilcare
      Amilcare says:

      The transistor can be replaced with any NPN equivalent with at least 20V Vce and a current of at least 100mA.
      The transistor can be replaced with any NPN equivalent with at least 20V Vce and a current of at least 100mA
      The transistor can be replaced with any NPN equivalent with at least 20V Vce and a current of at least 100mA. The transistor can be replaced with any NPN equivalent with at least 20V Vce and a current of at least 100mA, The transistor can be replaced with any NPN equivalent with at least 20V Vce and a current of at least 100mA.

  3. tech
    tech says:

    Ciao, using the formula for the inductance of a solenoid, with your data: 25 coils with wire diameter 0.5mm and coil diameter 19 cm assuming that the coils are superimposed one all’ the other gives me an inductance of 0.00178 H and not 400 microH (400*10^-6 H). What formula did you use?

  4. walter
    walter says:

    good morning Amilcare, I'm making the metal detector, I have two questions:
    1) i developed the PCB using 3 single opamps to simplify connections but I don't know which opamps to use. I have TL071s, can be fine?
    2) since the pcb was in a board 5 x 7 cm I would also like to use it as a wire finder placed under plaster and therefore in addition to the normal reel I will also try to wind a reel with a smaller diameter: 5 O 6 cm maximum You think it might be a good idea?
    Thank you

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