Special: How to make a metal detector 3

Metal detector case

In this third and last post of the special to learn how to make a metal detector, I will show you how to make a metal detector. the box is the most complicated part of the invention. and where the most important components of the whole assembly will go, we could say that is the brain of the metal detector.

3- The Box

3.1- Materials

Materials for making a metal detector

  • TuperWare nice (mine was chosen by my girlfriend ¬_¬) and spacious, so that inside it fit all the elements no problems.
  • Two-position switch.
  • 9v battery and corresponding connector.
  • Jack female connector and ones cool headphones (the ones they give away on the AVE are worthless).
  • 2.5-inch diameter, 8-ohm impedance speaker.
  • Printed circuit board already assembled, for this you will need a sketch of the tracks (see picture) and know how to make a printed circuit board, very well explained in this other post. Be very careful with the emirror effectyou should be left with howtodo-everything legible when you have the finished plaque.

Printed circuit board metal detectorHere is also the list of the components of the board that you can order in our own shop with the total guarantee of ComoHacer.eu:

Metal detector plate

  • 2 electrolytic capacitors of 220uF and 16v, keep in mind that these must be well placed, that is to say, positive with positive and negative with negative (in the image you can see perfectly that the negative is down). (1 in the image)
  • 5 polyester capacitors of 0.01uF. (2 in the picture)
  • 5 polyester capacitors of 0.1uF. (3 in the picture)
  • 6 resistors of 10,000 ohms and 1/4 watt at 5% tolerance. (4 in the picture)
  • 1 resistor of 1,000 ohms and 1/4 watt at 5% tolerance. (5 in the picture)
  • 1 resistor of 2.2 Mega ohms and 1/4 watt at 5% tolerance. (6 in the picture)
  • 2 resistors of 39,000 ohms and 1/4 watt at 5% tolerance. (7 in the picture)
  • 6 BC183B or BC184C transistors, although the ones we sell in our shop, the BC547CZL1G, are also equivalent. (8 in the picture)


  • Hollow plastic thread (18mm internal diameter) and metal nut for that thread (these two things are the ones that I had the hardest time findingbut if you go to a swimming pool pump replacement shop with these characteristics and this photo, you will probably get something similar). (1. in the picture)

Metal detector coil and thread

  • Plastic or wooden stick 12mm in diameter and 50mm long (this is where we will wind the small coil). (2. in the picture)
  • 5 metres of 0.5 millimetre coil.
  • 4 x 10A plug-in sockets, you're not going to get 10 amps through there, that's just the right size socket. more comfortable to work with.

3.2- Assembly

  • To begin with, let's get the most cumbersome part out of the way, which is the board itself. Here is the circuit diagram in case you want to put it into a program like this one to reduce it and customize it to your liking.

Metal detector circuit

  • We make the plate with the help of this other post and when we have it ready, we will we give a tin bath to all the tracks to increase durability and better fight against future corrosion, we soldered the components mentioned above, yes, at first it may seem difficult to identify the components, but if you are going to doing in order and discarding components will be very easy for you. Remember that the resistors are the components that are soldered first, then the capacitors and finally the transistors, this order goes from higher to lower heat endurance. When we have the board ready, we put it to one side to later mount it inside the box. In the connections of the coils, the audio and the power supply, we will put some connection terminals.
  • Now we are going to prepare the small coil on the 50mm long stick, if we don't get confused, it is not very difficult, first we take the stick and on it we make 120 turns with the coil, making it look as follows uniform and bearing in mind to leave, at the beginning and at the end, a bit of thread so that it can be spliced into the plate, and before we do anything else, we impregnate everything that results with a thin layer of silicone to protect our small coil, not too much, because then we will have to put it as it is into the hollow plastic thread, now make sure you centre it well and when you have it, fix it with silicone so that it does not move, and then, finally, place the metal nut that only serves for adjust the detector to your likingRemember to fix it with insulating tape so that it does not fall out of place. (of course the detector is graduated when it is up and running).
1- Case 2- Plastic thread 3- Metal nut 4- Coil wound and protected with silicone 5- Wooden stick
  • Now we will assemble everything in the box, we will we will make the complete connection We will also include the headphone jack, the on/off button, the loudspeaker and the battery connector.

Mounting the metal detector

Explanation of the wiring of the box, shown in the picture above:

1. Here it is connected the large coil that we had already made, don't worry because it has no polarity, you can connect it as you see fit.

1.1 Address to the large coil or dish.

2. In this other point goes the small coilThe same as with the coil, connect it as you wish, it has no polarity.

2.1 Small coil.

3. On this terminal go the audioThe polarity of the speaker is the same, first towards the jack and then towards the speaker. Here you have to be careful with the polarity of the speaker, anyway, if you make a mistake I don't think it will be a problem as we are not mounting a Dolby Surround.

3.1 Jack connector to plug in our headphones and deactivate the loudspeaker.

3.2 SpeakerThe headphone jack works when there is no headphone plugged into the jack.

4. On this other terminal, it goes the foodAs long as you get the polarity right, you don't have to worry about it.

4.1 Two-position switchis placed between the circuit and the 9v battery, cutting off and opening the power supply.

4.2 9v battery connector (behind the box in the picture), I recommend having it handy, although the metal detector wastes almost nothing, it is good for not having to be opening and closing the box and thus avoid breaking any cable or component by accident.

From here we would have finished our beautiful and perfect metal detectorAnd now it is your turn. Oh, and if you have any questions, suggestions or typos, just post them in the forum!

Buy - Materials to make the metal detector

More information - How to make a metal detector I, How to make a metal detector II

124 thoughts on “Especial: Cómo hacer un detector de metales 3”

  1. hola quisiera que si me pueden pasar los equema del pdf que subio alberto ya ise la placa solo me falta armarlo pero me falta el pdf

  2. Good afternoon, although the post is old (21/11/08), has anyone described or practised how to boost this circuit?
    Loco I really congratulate you on your work!!!!!
    motivates me and now that I'm out of work even more!!!! XD

  3. hola alberto, otra ves yo, ya hice la placa y monte los elementos pero no me da resultado no se me da resultado no se que sucede, segui todos los pasos que explicas pero nada, habra algun herror en el diseño

    1. Alberto Navarro

      Good morning Jose, I did this project myself and it worked well, the design is fine.

      What did give a lot of problems was the connections of the coils and the pinning, you have to be very neat and careful with all the assembly and especially with these two points that I mention.


      1. hola Alberto navarro me pregunto el diametro de la bobina y las vueltas cuanto son, otra cosa el tiempo de uso con la bateria de 9v cuanto es. gracias.

    2. Hello, I can attest that the design works, I have made two of them, one of them at the first time worked and however the second I did the same but it does not work, the plate gets very hot so I have to start again but it works.
      Don't be discouraged, it will work for sure

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