Making a dd coil for a metal detector. Making a DD sensor for an IB metal detector. Radio engineering, electronics and do-it-yourself circuits. Production of individual parts

When I was just starting to dig the old days, I had a standard, full-time search coil from my old Minelab x terra 34 - 9 inches, mono. The finds came across by themselves, sometimes even very good ones, but after a while I began to feel that the mono coil was still rather weak for searching for coins in the fields, this is where we search most often with my comrades. And for the next search season, I bought an additional coil for quickly knocking out large areas, DD with a frequency of 7.5 kHz, coil size 10.5″. For those who don't know, this is a stock coil that comes with the cooler x terra 505 and 705 models.

What is the difference between dd and mono coil? Firstly, the volume of the tested ground in DD is larger, because it hits the ground in the same way, without narrowing the scanned beam. It turns out, something like a blade. The mono coil, on the other hand, does not hit so deeply, and even its beam narrows downwards. It turns out that at a depth of at least 10 cm, the diameter of the beam will be not 9 ″, but 2 times less. That is why it is very difficult to find anything at a depth of more than 20 cm with a mono coil. at this depth, the beam narrows to 3-5 cm in diameter. But DD hits evenly, its beam is cylindrical. Accordingly, the volume of the earth is larger and the depth is also greater.

Secondly, double coils go better on mineralized soil, better cope with mineralization, do not bug like mono.

On the other hand, mono perfectly center the target, with such a coil you will not dig large holes, it is enough to dig the target from 4 sides, it will not run away from the edges of the hole, as in cases with a DD coil. So for searching in garbage areas, a mono coil, standard and inexpensive, is better suited. Depth is not its main trump card, the main thing is the accuracy of the readings, so when searching for a beach, it fits one hundred percent.

However, there are also small DD coils, their size is very small, 6″ or slightly larger. They are also great for the beach, especially if the beach is sea, there will be strong mineralization, and DD copes with this perfectly. Well, the small size will allow you to clearly and accurately knock out the territory, there will be finds and you will dig less garbage.

For searching in large areas - fields, for example, a double coil will allow you to comb the area much faster, identify places where coins come across, which means it will be effective. if there is a lot of garbage on the field, then you can put a mono coil, however, the speed of surveying the site will drop. Set mono when you have already found a place of accumulation of coins, there you can already thoroughly finish off the place with a mono coil. Although DD will also cope, especially if the coins come across at a depth. The general conclusions are that mono is for debris and clear centering of targets, and DD is for most other cases. By the way, the Nel Tornado coil received the most positive feedback, it has a signal amplifier and can be installed on budget metal detectors, the depth increase will be very noticeable.

Making a DD sensor for an IB metal detector

This article describes the process of making a self-made "sniper" type DD type sensor for an IB metal detector. It is named sniper because of its small size (diameter is 20 centimeters) and acute sensitivity. It is well suited for beach gold prospecting.

Coils are wound on a mandrel, which is a small carnation driven into a plank. The shape of the mandrel can be either in the form of the letter D or round. In the latter case, the coils are shaped manually.

For the transmitting coil (Tx, in the photo - on the left), a wire with a diameter of 0.45-0.6 mm is used. In its absence, it is permissible to use a thinner one, however, this may worsen the sensor parameters. The diameter of the wire for the receiving coil (Rx, in the photo - on the right) should be around 0.2mm. The number of turns for coils depends on the design of a particular metal detector, but the receiving coil is always multi-turn.

Before removing from the mandrel, the turns must be pulled together with a thread at an interval of 1-1.5 cm. It is better to do this twice.

The next step is to impregnate the coils. This step is mandatory for this sensor design. Impregnation will stiffen the coils and eliminate the smallest possible movements of the coils during operation. Epoxy resin and non-solvent varnishes are suitable for impregnation, so as not to damage the wire insulation.

Drying under a hot air gun is much faster. But after that, they should still be left, squeezed between two parallel planes, for final drying, at least for the night.

The impregnated and dried coils must be covered with a layer of insulation. You can use electrical tape here. In this case, the FUM tape was used.

In order for the coils not to react to electric fields and not give false positives, they must be shielded. The easiest way to do this is to use aluminum foil. The most affordable is food, but it is too thick. The forums recommend using thin foil from capacitors, but nowhere is it specified from which ones. The foil of electrolytic capacitors is too thick. In capacitors of the MBM type, there is no foil at all, but there is only a layer of translucent metallization. When unwinding an old capacitor, this thinnest layer further deteriorates its conductive properties. It is unlikely that it will be a good screen.

After a series of analyzes of capacitors, we managed to find the one we were looking for, which is ideal for shielding metal detector coils: this is MBGO. Perhaps there are others similar. The foil in them is very thin and easily torn, so you need to work carefully.

When unfolding such a capacitor, be sure to delaminate the tape to the end. Otherwise, you will get not a foil, but a sandwich of two foil dielectrics.

The coils are wrapped in foil, each turn should have a slight overlap on the previous one. A gap must be made between the beginning and end of the winding to avoid a short-circuited turn, which will negate all the quality factors. However, it is still desirable to overlap the end to the beginning, but through a dielectric. So the coil will be 100% shielded.

A wire without insulation should be wound over the foil. It is highly desirable that it be tinned. This will provide good electrical conductivity for many years. The photo uses just a twisted pair wire that has not been tinned.

Whoever says anything must be shielded both coils, not just the receiver. Otherwise, there will be false positives from wet grass.

The final stage of preparing the coils is wrapping with electrical tape. Its obligation has not yet been established.

The sensor body for the DD is most easily made from Styrofoam or Styrofoam. By itself, polystyrene foam is very durable and is quite suitable for the case. Additionally, it can be reinforced from the inside and outside. Styrofoam must be reinforced, as it is much less durable.

Grooves for coils can be made very easily if you use a cutter as a cutter. After the second pass, the surface of the grooves is clean, but rough enough for good adhesion of the epoxy. The depth of the grooves is chosen so that the coils are completely immersed in them and a couple of millimeters for epoxy remain on top.

In the inner surface of one of the coils, it is necessary to mill a hole for a pressure seal and cable desoldering. The germovood can be immediately fixed with epoxy. The photo shows that the edges of the place for desoldering are smeared with epoxy - this is a mistake. It is not necessary to do so. It is enough just to moisten the pressure seal nut with epoxy (the very bottom of this recess).

Expect to continue!

The scheme of the Kyiv developer Ciklona, ​​known in some circles, was taken as a basis.

Device name Groza4gt. The figure below shows a diagram of the electronic unit.

I must say right away that I am friends with a soldering iron, but not to such an extent that I can solder smd parts, so I bought the electronic unit of the device ready. However, whoever feels strong in himself can try to assemble it on his own, the above circuit is 100% efficient. I will tell you how to make a coil for this device. Coil type - DD.

The above diagram shows a ring-type coil. It is quite difficult to manufacture, so for starters it is better to assemble a simpler type DD coil.

We will need the following things:

Enamelled wire with a diameter of 0.3-0.4 mm

Enamelled wire with a diameter of 0.18-0.2 mm

Epoxy adhesive

Foil (as thin as possible)

Audio video cable

Housing for future reel

Oscilloscope (or at least a good multimeter)

Sea of ​​patience

I’ll dwell separately on the coil body. Again, I ordered a ready-made one on the Internet (it’s easy to google), but it’s quite possible to make it yourself. For example, cut off the bottom of a bucket or a flower pot stand or a plastic plate. We need a case with a diameter of 21-23 cm and a height of 1.5-2.5 cm.

The coil itself contains two windings - receiving and transmitting.

We need to make them.

Begin.

We make a form for winding.

We take a board. We draw a large Latin letter D on it with a pencil. The height of this letter is 190 mm, the width is 110 mm. We smooth the upper sharp corners so that they are more rounded. We drew ... Now, around the perimeter of this D, we drive in a series of nails. We bite off their hats. We put vinyl tubes or one or two turns of electrical tape on the nails.

So the form for winding the coil is ready. On these nails we first wind a transmitting coil consisting of 80 turns of 0.4mm wire. After winding, loosely tie the resulting coil with a thread. We impregnate with epoxy glue and put it in a plastic bag. We put it all on a flat surface and press it on top with a piece of glass. We make sure that our coil does not lose its shape. I remind you that the shape should be in the form of the Latin letter D. In a day, the coil is ready. We wrap the frozen coil with a layer of electrical tape. Now it needs to be shielded. We use foil for shielding. The foil is needed as thin as possible. I used foil from old capacitors. By the way, you can take foil from cigarette packs (the one that is paper-based). We cut it into strips 1 cm wide and about half a meter in length.

We wrap the coil in foil in a spiral. You need to wrap it with a gap of 2-3 mm in one place so that a short-circuited coil does not turn out. After that, we wind the tinned wire on top of the foil with a step of 2-3 cm and on top of this we wrap the whole thing with a layer of electrical tape. In general, it should turn out as in the photo.

The transmitting coil is ready. The receiving coil is made in the same way only with a 0.2mm wire 180-200 turns. We repeat the same procedure for impregnating with glue and shielding.

So we have two shielded coils ready. Each coil has three leads.

Actually the circuit of the coil.

Now about resonance. It is necessary to select for each coil a capacitor of such a value that the coil, together with this capacitor, forms an oscillatory circuit with a resonance at a frequency of 8.192 kilohertz. If you do not know how to look for resonance, then it is better not to take the coil at all. Capacitors must be metal-film thermostable. Suitable Soviet type K71-7. In extreme cases, you can use Chinese ones (similar to green pads). In a very extreme case, you can (but not need) K73-17. Let me remind you that for the receiving coil, the conder is in parallel resonance, and for the transmitting coil, in series.

We take our coils, put them in a box, solder the selected capacitors.

Now the coil needs to be balanced. The meaning of balancing is to find such a position of the receiving coil relative to the transmitting coil at which a signal of the smallest possible amplitude was induced in the receiving coil. To do this, we put the transmitting winding in the coil body, on top of it the receiving winding with an overlap of about 1.5-2 cm. We turn on the transmitting winding to the device, and the receiving winding to the millivoltmeter. This is where the balance point will be. Normally, the reception should be no more than 50 mV. After that, we fix the coils in the case with superglue so as not to lose balance.

After that, we connect both windings to the device with a cable. We check the device.

On a properly tuned device, the reaction to non-ferrous metal should be high tone, to black low. It is also important to correctly set the ground balance (hereinafter BG).

BG is checked with a piece of ferrite. In the extreme position of the BG regulator, the reaction to the ferrite should be a high tone, in the other extreme position it should be low. In the middle of the range of the regulator, there should be no reaction to ferrite. This is a properly configured BG. If it doesn’t work out as it should, we try to slightly change (+ - several Nanofarads) the capacitance of the resonant conder on the receiving winding or swap the ends of the receiving winding. If this does not help, we try to pick up the capacitor c15.

The sensitivity with such a coil should be 25-30 cm for a coin the size of a Soviet penny.

If the setup is finished, fill the whole thing with epoxy glue.

To make the weight of the coil after pouring smaller, you can put it into the body

small pieces of foam.

After solidification, we have an almost finished coil. Let's check the balance again. If it’s gone a little, you can correct it with a small metal object glued somewhere on the coil body. The place of gluing is searched experimentally. That's all. That's what can be found with a similar device.

Let's start with the manufacture of a device with which we will wind the coil. We need a piece of board measuring at least 18 by 18 centimeters, nails and cambric. The nails should be of such a diameter that the cambrics fit freely enough on them.

On the board we draw a circle with a diameter of 16 centimeters and drive in at least 16 nails in a circle, evenly distributing them. Nails should stick out of the board by at least two centimeters. We bite off hats from the nails, put cambrics on the nails. The length of the cambric should be equal to or slightly longer than the length of the protruding nail. The device is ready.

As you understand, the diameter of our coil is 16 cm. We will wind it with a copper wire with a diameter of about 0.3 mm. We wind 80 turns of wire on our device, then we tighten the resulting coil in 12 places with thick threads and remove it from the device. If the coil is impregnated with epoxy resin, then the frequency stability of the search generator will increase and the coil will be reliably protected from moisture.

The length of the coil leads should be about 4 cm. When winding, the turns should not be too tight, but they should not hang out either. We tightly wrap the coil with one layer of electrical tape, but so that the turns do not stretch. To do this, we first wrap the coil in eight places with small pieces of electrical tape.

Now I need to make a screen for the coil, for this I use foil strips from electrolytic capacitors. The foil must be washed with water from the electrolyte and dried. We wrap the coil with foil, leaving a gap in the area of ​​\u200b\u200bthe coil leads. The screen should not hang on the coil. We fix the end of the screen with electrical tape.

We take a piece of copper wire, about 0.5 mm in diameter, 125 cm long. We remove the varnish coating with sandpaper and service it along the entire length. Next, with this wire we tightly wrap the coil around the screen, in increments of about 1 cm, after leaving a lead 12 cm long. Between the beginning and end of the winding, it is necessary to leave a gap in the area of ​​\u200b\u200bthe coil leads.

Ordinary people, to whom I also belong, divide metal detector coils into 2 types - Mono and DD. Metal detector manufacturers cut thinner...

Why does a DD coil have this designation? Do you know the difference between Mono and Concentric coils? And if you do not have a pulse metal detector, then what you call a mono coil is more correctly considered concentric. We look at the difference between search coils, and how this affects practical search.

Mini educational program... A metal detector coil most often consists of 2 components - a transmitting loop (Transmit Coil, TX) and a receiving loop (Receive Coil, RX). The first generates an electromagnetic field, the second monitors changes in this field (when a metal object gets under the coil, the field is deformed, these distortions give the metal detector a reason to tell you “dig!”).

If the transmitting loop is larger, then the generated field will also be larger. Hence the dependence of the size of the coil and the depth of detection. A small nuance, high ground mineralization can interfere with the field, and this is part of the search environment.

Concentric Coil

A concentric coil is what we most commonly refer to as a Mono coil (eg on the Garrett ACE 250). But just a mono coil is a kind of Concentric.

A feature of the concentric coil is that the transmitting and receiving loops are spaced as far apart as possible. This allows you to create a symmetrical field (hence the accuracy of the pipoint), a slightly better separation of nearby finds with one wire (from the conical shape of the field).

Concentric coils are designed to cover the full range of existing finds. Logical positioning - universal coils. Subject to the influence of high mineralization of the soil, with an increase, the coil loses in depth.

Mono coil

The classical understanding of the Mono coil means that it is used on a pulsed metal detector (most modern detectors are not pulsed). Mono coil, this is a kind of Concentric (we remember the terms, we will put pressure on the field with the brain).

The peculiarity of a mono coil is that the receiving and transmitting loops are located side by side. It has the same properties as the concentric, including the influence of the soil.

Imaging Coils

Also a kind of concentric coil. By the way, some metal detector sellers claim that this is a DD coil. We all know ourselves, and politely correct))

The peculiarity of the coil is that it has an additional receiving loop. This allows the metal detector to more accurately determine the intended find. For example, in assessing the size of the find, before digging it out.

Garrett claims that only they have this type of coils (the GTI series of detectors), and no other metal detector in the world can boast of this.

Coils DD

Do you know why DD is called DD? Because, the transmitting and receiving loops are in the shape of the Latin letter "D", and are mirrored.

The features of the DD coil are significant. Designed for non-ferrous targets, good sensitivity to small finds. Unlike Concentric coils with a cone-shaped field, DD coils have a “flat bucket” field (the same visibility at any depth, but pinpoint accuracy suffers). Also, DD coils are less affected by high mineralization, and in such an environment they do not lose detection depth.

In the form of coils

I will add how metal detector coils differ in shape. There are ellipsoid and round. Coil Ellipse better "separates" targets that are close to each other (in theory, in practice this is imperceptible). Ellipsoidal coils have a higher accuracy of the pinpoint mode (in practice, it can be a stretch to say that it is), plus a little less weight (doubtful).

Round coil has more depth than an ellipse. It is difficult to check this in practice - you need to try the same coil of a different shape, try it on the same model of a metal detector. But if we compare different manufacturers, it always turned out that the round one on the coin really adds 1-2 centimeters.

In his own, he indicated the type that the manufacturer claims. If the type is not specified, then it could not find an explicit confirmation.