It's almost like a treasure hunt. Some are stopped by the fact that they live far from mountains or rivers in order to search for nuggets by washing sand. Others do not understand radio components to know how to extract gold from them. And still others prefer to look for precious metal with a metal detector, but do not have the means to buy it. Fortunately, the device is quite simple, and even without being a radio amateur, you can make it yourself.
Operating principle
What is a metal detector? This is a device that, with the help of certain radiations, finds metal located underground, without direct contact with it. The response data that comes in helps identify the find and informs about it with an audible or visual signal.
The principle of operation of the metal detector
The electromagnetic field emitted by the device comes into contact with metals, in this case with gold, which provokes the occurrence of eddy currents on their surface. By measuring the electrical conductivity, metals are identified and this data is transmitted by a signal.
Metal detectors can have different wave parameters, return signal processing techniques, additional functions and much more. Therefore, before you start making a device, you need to decide what exactly you want to get as an output.
The standard frequency for metal detectors is 6-20 kHz, but for gold it should be slightly higher, 14-20 kHz or more. This is because gold often occurs as tiny nuggets, so higher sensitivity is needed. If there is such an opportunity, then it is good to have a device with a multi-frequency adjustable search, then it will be possible to increase the number of objects that it recognizes.
Among all the schemes of metal detectors on the Internet, experts advise choosing devices with balanced induction, which have two coils in the head and a powerful electronic circuit. Of great interest are also circuits that have the principle of operation of the receiver-transmitter, acting on high frequencies, about 20 kHz, which makes it possible to distinguish non-ferrous metals from ferrous ones.
Common parameters
Various technical methods can be applied to the construction of a metal detector. Much depends on the conditions in which it will be operated. Therefore, the idea of what requirements the device must meet must be defined as clearly as possible. The following device parameters are distinguished:
- sensitivity - a characteristic that determines how small objects the detector can detect;
- selectivity - the ability to identify metals and react to specific ones;
- resistance to interference - the ability not to respond to extraneous radio signals from radio stations, cars, lightning strikes and others;
- power consumption - how much the device consumes and how much the built-in battery or batteries last;
- penetrating power - the depth at which the device can recognize metals;
- device dimensions;
- search area size - the area that the device covers without changing its location.
Resolution is the main parameter, in turn, it is also a composite one. There are one or two signals at the output of the device, and there are more properties that determine the object and its location. For example, if you lower the generator frequency, you can achieve an increase in the search area and penetration, but lose in sensitivity, as well as mobility due to an increase in the size of the coil.
Scheme of a simple metal detector The design feature of the metal detector is that all of the above parameters in combination or individually depend on the frequency of the coil. Thus, this characteristic is decisive in the design of the device. By frequency, metal detectors are divided into the following:
- ultra-low-frequency: frequency up to several hundred hertz, low mobility, high power consumption, complex in design and signal processing;
- low-frequency: hundreds, thousands of Hz, low sensitivity, high noise immunity, simple design, permeability depends on power - from 1 to 4 m, mobile;
- increased frequency: tens of kHz, the design is simple, the permeability is up to 1.5 m, the noise immunity is poor, the discrimination is so-so, the sensitivity is good;
- high-frequency: radio frequencies, typical "for gold", discrimination is excellent, the permeability is small, up to 80 cm, low consumption, other parameters are poor.
Instrument design
A device that does not require absolutely no knowledge in radio engineering can be assembled with your own hands, having: a calculator, a radio receiver, a box with a plastic or cardboard hinged lid, double-sided tape. The calculator should be as cheap as possible to serve as the basis of radio interference, and the receiver should not have noise immunity.
Do-it-yourself metal detector, instructions:
- We unfold the box, forming a book out of it.
- We fix the calculator and the receiver in the box, the last one in the lid.
- We turn on the receiver and look for a free section at the top of the AM band.
- We turn on the calculator: the receiver should make a sound, set it to maximum volume.
- If there is no tone, adjust until it appears.
- We fold the lid so that the tone disappears. In this position, the magnetic vector of the primary impulses will be perpendicular to the axis of the magnetic antenna rod.
- We fix the cover.
Thus, it is quite simple to assemble a primitive device, but in order to get more data, you already need to have some knowledge and skills in radio electronics. On the Internet you can find a suitable one from a variety of schemes.
Not everyone can afford to buy a metal detector. And to search for iron, it is not at all necessary to purchase an expensive device. Enough to assemble it yourself. And he will find it too.
By the way, I will say that I saw a report on TV, as a man who assembled a metal detector and searched for scrap metal with it, found a box with cartridges from the Civil War era in the forest.
I myself have been trying to assemble such a device for a long time and it even worked! But it will not work to search for coins with it, since it reacts mainly to large metal objects.
And so, to assemble a simple metal detector, we need:
~ two transistors KT315 or similar;
~ two capacitors 1000 pF;
~ two capacitors 10000 pF;
~ two resistors 100 kOhm.
In addition, the following will come in handy: a 3.7-5 volt battery, headphones, wire in enamel insulation with a diameter of 0.5-0.7 mm.
The assembly scheme is the simplest!
Coils can be wound on a regular pan. After ten turns, a loop is made and the winding of the remaining twenty turns continues.
The case is made of any material, preferably sealed. The bar can be piled from pipes. The coils are placed on the same plane at a distance of 10 cm.
If, when the device is turned on, a squeak appears in the headphones, then it means that the device needs to be adjusted - to change the distance between the coils. Or tune with ferrite.
Thus, you can earn by searching for scrap metal for a good branded device. And a good deed will be done - the earth will be cleansed. Well, the metal will be reused.
The photos in this post are mine and were taken in 2014. And the first picture with the scheme is taken from open sources.
How to make a simple metal detector for searching on the beach
In this article I will show you how to assemble a simple metal detector to search for coins and jewelry on the beach. It consists of one microcircuit - the NE555N timer, a coil and several other radio components.
Expect to spend up to 300 rubles on the construction of this metal detector!
Required Materials
To assemble a metal detector you will need:
- timer chip NE555N, in a DIP package;
- resistor 47 kOhm;
- two capacitors 2.2 uF, 16 V;
- piece of contact breadboard;
- 9 volt battery, switch, battery block;
- electromechanical sound emitter;
- 100 meters of copper wire with a diameter of 0.2 mm;
- some thick cardboard and glue.
Instead of an electromechanical sounder, you can use a 10 uF capacitor and any speaker with an impedance of 8 ohms, connected in series.
Metal detector scheme
The idea of a metal detector is taken from the book " 499 circuits on the NE555 timer". I just added a switch between the battery and the chip, and I also use an electromechanical buzzer from an old electronic alarm clock instead of a speaker.
search coil
The most difficult part of a metal detector is its coil. I calculated that a 90mm diameter coil should have about 260 turns of 0.2mm lacquered copper wire. At the same time, its inductance will just be about 10 millihenries.
I wound the coil carefully, coil to coil. To prevent the wires from unraveling, I wrapped the winding with white electrical tape on top.
If you want to make a larger diameter coil in order to increase the target detection range, then there are several on the network online calculators with which you can calculate it.
Circuit board
I placed all the electronic components on a piece of breadboard. The connections were made with the most common wire that was at hand. The soldering of the board itself took no more than 15 minutes.
The size of the board turned out to be approximately equal to the size of a matchbox.
Frame
For simplicity, I decided to make the handle of the metal detector out of cardboard. A circuit board, a switch and a battery are installed in the handle.
All this was cut out of thick cardboard and glued with PVA glue. After the glue had dried, I made holes in the cardboard for the board and wires.
Then, I glued the searchcoil to the handle with hot glue. The last step I, also using hot glue, glued the board and the battery inside the handle.
Conclusion
The metal detector works as follows: while there are no metal objects near the coil, the sound emitter beeps with the same frequency; when a metal object is presented, the tone of the sound changes towards a higher one.
The detection range of a large coin in the air, according to my measurements, was 5 - 7 centimeters!
Simple metal detector kid FM-2 improved
I present to your attention a diagram of a more improved metal detector Malysh FM-2. The metal detector kid fm2 is not so difficult to assemble with your own hands, despite its significant changes. This is perhaps the simplest selective metal detector that even a novice radio amateur can assemble.
You have probably heard, and perhaps collected, such metal detectors as the "Kid" and "Kid FM-2". But progress does not stand still and therefore we have a scheme for a more improved metal detector Malysh FM-2. IN new version added LED indication of metals, added power-on notification function, increased notification sound, the device became much more stable in operation.
Scheme of the improved metal detector Kid FM-2
Specifications and features:
- Supply voltage - 9 Volts
- The depth of detection of metals is about 15 cm.
- Selection of metals - black, non-ferrous
- LED indication of metals - black, color
- Power on indicator
So, this printed circuit board of the Kid FM-2 metal detector is designed to use DIP components, which would be convenient for everyone, since many novice radio amateurs have not yet encountered SMD components.
Capacitors C5-22nF and C1-100nF must be film
Voltage regulator AMS1117 -3.3v
This is how the finished board of the “Kid FM-2” metal detector looks like
View from the paths
After assembling the board, we proceed to the manufacture of the coil.
The standard coil contains 150 turns, wire diameter 0.3, and wound on a mandrel 150 mm. But I decided to slightly reduce the diameter to 10-11 cm in order for the metal detector to see small objects better, the detection depth decreases but the sensitivity increases. I did not have a 0.3 wire, and therefore wound 0.4 on a 10 cm rim, 130 turns.
So, after the coil is wound, it is necessary to tighten it very tightly with tape.
Now it is necessary to shield the coil so that the metal detector does not react to interference and there are no false positives. We take food foil and tightly wrap the coil. Please note that the ends of the foil should not touch each other!
Then we take the wire, clean the end and wind it to one edge of the coil screen, then tighten it and wrap it tightly with tape again.
We connect the coil to the board. The wire from the screen must be soldered to the minus of the board.
Now it remains to flash the microcontroller and that's it, you can use it)
If you do everything right, then the device should work without problems when you first turn it on. Carefully check the ratings of the parts and do not forget that the capacitors C2-22nF and C6-100nF must be film, NOT ceramic!
When turned on, the device should make a characteristic sound similar to “peak-fut”, which means that the device has turned on and is working correctly.
IMPORTANT! “According to the scheme, there are 8 resistances, and in the photo there are 9” - the 9th resistor (100 Ohm) I myself put it additionally on the second LED, although you can not put it! Diode 1N4007 can also be omitted, as I did!
The printed circuit board, firmware, as well as a list of parts that can be bought very cheaply on AliExpress with free shipping, is below the video!
Video of the metal detector kid FM-2 v2
Good do-it-yourself metal detector
The case was several years ago. I wanted to do something with my hands, and pass the evenings, bringing the treasure-hunting season closer. It was decided to assemble a metal detector. For assembly, I chose the “Pirate” metal detector scheme. Since it is not complicated, but the device itself is quite interesting. The assembly was started with a search for parts. I even had to go to the workshop for some resistors. When everything was found, it was necessary to prepare a printed circuit board, namely, to etch it using the LUT method. Then the matter was small: to solder all the details. Well, check the finished board. It didn't turn on the first time. The K157UD2 chip turned out to be faulty. By changing it, the scheme worked! 
Now you can do the body. In its capacity, the body was taken from Koschey 5I, a new front panel was made. It's about the coil. For the coil, a frame was cut with a jigsaw and a groove was machined along the side edge, where the coil winding was wound, a cable with a connector was soldered. The bar was made of plastic pipes and fittings. The armrest is cut from a sewer pipe. It all turned out quite culturally. The device turned out to be light, but not rigid enough. 
The end result is a quality instrument. Its only disadvantage is the lack of discrimination of metals. Therefore, it can be said that it is not suitable for searching for coins. After all, nails and coins ring the same way. 
But with its help, you can successfully dig scrap metal and take it to collection points, thereby earning money! There is a video with the test of this device. It was taken by me in the spring of 2015.
Among amateur radio designs, developments that help detect metal objects hidden in the ground are of particular interest. Especially if the latter are small in size, lie at a considerable depth and are, moreover, non-ferromagnets.
Good-quality electrical circuits of such devices, called metal detectors by analogy with well-known military developments, and descriptions of fully functional designs have been published in various technical
Editions, but they are often designed for trained, experienced do-it-yourselfers who have a good material base, scarce parts.
But the design we propose can be completely repeated, made even by a beginner. Moreover, the necessary parts (including a 1 MHz quartz resonator) will be quite affordable to purchase. Well, as for the sensitivity of the assembled metal detector... It can be judged at least by the fact that with the help of the proposed device it is easy to find, for example, a copper coin with a diameter of 20 mm and a thickness of 1.5 mm at a depth of 0.9 m.
Operating principle
It is based on comparing two frequencies. One of them is standard, and the other is changing. Moreover, its deviations depend on the appearance of metal objects in the field of a highly sensitive search coil. In modern metal detectors, to which the design under consideration can be quite reasonably attributed, the reference generator operates at a frequency that differs by an order of magnitude from that which occurs in the field of the search coil. In our case, the reference generator (see circuit diagram) is implemented on two logic elements ZI-NOT integrated DD2. Its frequency is stabilized and is determined by a ZQ1 quartz resonator (1 MHz). The generator with a variable frequency is made on the first two elements of the IC DD1. The oscillatory circuit here is formed by the search coil L1, capacitors C2 and C3, as well as the varicap VD1. And for tuning to a frequency of 100 kHz, the potentiometer R2 is used, which sets the required voltage to the varicap VD1.
Fig.1. principled circuit diagram highly sensitive homemade metal detector.
Used as buffer amplifiers logical elements DD1.3 and DD2.3, working on the mixer DD1.4. The indicator is a high-resistance telephone capsule BF1. And the capacitor C10 is used as a shunt for the high-frequency component coming from the mixer.
The printed circuit board configuration is shown in the corresponding illustration. And the layout of the radio elements on the side opposite to the printed conductors is given here in a different color.
Fig.2. The printed circuit board of a homemade metal detector, indicating the location of the elements.
The metal detector is powered by a 9 V DC source. And since high stabilization is not required here, a Krona battery is used. Capacitors C8 and C9 successfully work as a filter.
The search coil requires special precision and attention in manufacturing. It is wound on a vinyl tube with an outer diameter of 15 mm and an inner diameter of 10 mm, bent in the shape of a circle 0 200 mm. The coil contains 100 turns of PEV-0.27 wire. When the winding is done, it is wrapped with aluminum foil to create an electrostatic shield (reducing the effect of capacitance between the coil and ground). It is important to prevent electrical contact between the winding wire and the sharp edges of the foil. In particular, “twisting obliquely” will help here. And to protect the aluminum coating itself from mechanical damage the coil is additionally wrapped with an insulating bandage tape.
The diameter of the coil may be different. But the smaller it is, the higher the sensitivity of the entire device, but the search area for hidden metal objects narrows. With an increase in the diameter of the coil, the effect is reversed.
Work with a metal detector as follows. Having placed the search coil in close proximity to the earth's surface, tune the generator with potentiometer R2. And so that the sound is not heard in the telephone capsule. When the coil moves above the surface of the earth (almost close to the latter), the cherished place is found - by the appearance of sound in the telephone capsule.
When using the device discussed above to find objects hidden in the ground of archaeological and national cultural value, prior permission is required from the relevant authorities.
Attention!!! The information contained on this page was added from unverified sources, may be out of date and contain errors. Therefore, it is provided for informational purposes only.
N. Kochetov, based on the materials of "Mlad Constructor"
A metal detector is used when searching for objects with certain electromagnetic characteristics, namely metals. IN professional activity This device is used by searchers, archaeologists, geologists and professional treasure hunters. In addition, a metal detecting device is often used in construction, for example, to detect fittings, wires and profiles in walls.
Professional equipment has a very significant drawback - very high cost, which varies depending on the detection depth, interface type, and metal detection function.
The need for a metal detector also arises among ordinary people. Often these are those who decided to try themselves as a treasure hunter. Unlike professionals who have equipment or are provided by an organization, novice hobbyists do not always want to purchase an expensive device. This is due to the fact that such a purchase will not be used for professional use and is unlikely to realize itself.
For an amateur who is just starting to work with these devices, a self-assembled metal detector may be suitable. Homemade devices are relatively easy to manufacture, there are many on the Internet. detailed instructions. Anyone can assemble a metal detector with their own hands if they have the desire and the components required in the assembly; and their assembly is within the power of even those who are poorly versed in radio wiring. Home-made devices can have both relatively weak characteristics and not be inferior to branded expensive goods. Before assembling the device, you need to know its device and varieties.
In order to understand what kind of metal detector needs to be assembled, it is necessary to determine the list of work to be carried out, as well as which metals will be the target of the search. Outwardly similar devices for prospecting for gold and carrying out construction work differ in design and technical specifications. There are the following Common parameters search devices:
Search discrimination can occur in three ways:
- Spatial, which indicates the location of the found object in the zone of the electromagnetic field, as well as its location depth.
- Geometric, showing the size and shape of the found object.
- Qualitative, which determines what properties the found material has.
Operating frequency range
Metal detectors operate in a certain frequency range:
- Ultra-low frequency, up to several hundred Hz. Powerful metal detectors that require high voltage, impressive dimensions, and computer signal decoding make these devices unsuitable for amateur use.
- Low-frequency, up to several kHz. Enough simple circuits and design, good noise immunity and insensitive to the ground. Possess penetration depending on the supplied voltage, up to 5 meters. They react most sharply to ferrous metals and reinforced concrete structures.
- Increased frequency, up to tens of kHz. They have more complex circuits, but are less demanding on coils. Relative noise immunity and detection depth up to one and a half meters. They work very poorly in wet and mineral soils.
- Radio frequency, used to search for non-ferrous metals, such as gold. The detection depth is less than a meter in dry soils, very critical to the design and quality of the coils used.
Classification by type of search
There are many search methods, but many of them are applicable only in professional activities, and are not feasible in homemade devices. More applicable at home include:
- Without receiver (parametric).
- On the beat.
- phase accumulation.
- Receiving-transmitting.
Parametric metal detector
These devices do not have a receiving coil and receiver, and the detection of an object occurs due to its influence on the generator coil, a change in its parameters, such as the frequency and amplitude of the generated oscillations, is fixed by different possible ways. Quite easy to assemble and have a relatively high noise immunity. They are often used as magnetic detectors due to their low sensitivity.
Transceiver
The device consists of a transmitting and receiving coils, an EM transmitter, and can also be equipped with a discriminator that will detect only certain metals.
The coil creates an electromagnetic field; if there are materials with an excellent electromagnetic field in its zone, the receiver picks them up and beeps about the detection. If an object is detected that does not have electrical properties, but has ferromagnetic characteristics, then it will distort the electromagnetic field due to shielding.
These devices achieve the best performance in their operating frequency range, but their independent production requires a high-quality coil system, which must be ideally located relative to each other.
A transceiver metal detector with a single coil is called inductive. Its creation is simpler due to the fact that there is no need to select coils, but it is required to separate the secondary weak signal relative to the emitted primary.
Phase sensitive device
These metal detectors are either pulsed with a single coil or devices with two coils, each of which is acted upon by a separate generator.
In the case of a pulsed phase-sensitive metal detector, the emitted pulses are delayed when they collide with the target metal, and during the increasing phase shift, the discriminator fires and gives a signal. The closer the instrument is to the object, the more frequent the signals become. The popular home-made Pirate metal detector with metal discrimination works on this principle.
The principle of operation of the device with two coils is based on the fact that the electromagnetic fields of the two coils are synchronized and work in time; and when the field is distorted, desynchronization occurs, and the discriminator begins to emit signals. This type of device is easier to manufacture than a single coil, but the depth of possible detection is reduced.
Based on the principle of harmonics
IN this instrument Structurally, there are two coils: working and support. The reference oscillatory coil is small, protected from extraneous interference, or stabilized by a resonator. The frequency of the working search coil depends on the presence of the desired objects in the radiation zone.
Before starting the search, they are tuned to match the frequencies and, as a result, a monotonous sound. A change in tonality means that metal objects enter the zone of an electromagnetic field, and the size and depth of the object are determined from the level of change.
metal detector coils
The main requirement for the quality of home-made devices is competent manufacture of the coil and its reliable shielding.
When creating a device, the device circuit is adjusted to the coil until optimal values are obtained. With an incorrectly selected coil, the metal detector, if it works, will have very poor performance. In this regard, when choosing an option for manufacturing, you need to carefully look at the description of the coil. If it is not complete enough, it is better to make another device.
The size of the coil is also important. Wide ones ring the ground deeper, but if large objects are detected, their signal will clog potentially necessary small objects. Also, to increase the depth of detection, you need to have a wider coil.
It is generally accepted to use coils with a diameter of up to 90 mm when searching for profiles and fittings, up to 150 mm for small things, and diameters up to 600 mm for searching for large iron.
It will be ideal if the metal detector is designed to work with coils of different sizes.
Noise immunity
Coils are good at catching various types of pickups, and There are 2 common ways to improve noise immunity:
baskets
These coils are presented in flat and volume versions, they are stable, less sensitive to pickups, and have high discrimination. For a beginner, it is easier to wind a flat coil.
As its mandrel can serve computer disks, plates and saucers, and you can calculate the winding yourself. The volumetric option is wound without calculation using computer programs impossible.
A simple do-it-yourself metal detector
This version of a homemade metal detector consists of a signal decoder, a signaling device and a coil. To assemble it you will need:
- Chip PIC12F675 or its analogues and a programmer for firmware.
- Resonator at 20 MHz.
- Voltage stabilizer AMS1117.
- Capacitors 15 pF and 100 nF ceramic, electrolytic 10 uF and film 100 nF.
- Resistors 470 Ohm, 10 kOhm.
- Sound emitter.
Soldering is carried out by a hinged or mounting method, a voltage of 9-12 V is required to power the circuit. The stabilizer controls the output 3.3 V.
The coil is wound on a mandrel 10 cm with a wire section of 0.3 mm. It is required to tightly wind 90 turns, and wrap the resulting structure tightly with adhesive tape and place it in the Faraday shield.
It turns out a fairly powerful metal detector for deep search, which can be set to discrimination: when ferrous and non-ferrous metals are detected, a sound of different frequencies will be emitted.
Professional metal detectors are often quite expensive and not affordable for amateurs. There are schemes of metal detectors on the Internet, some of them can be assembled with your own hands, without special radio installation skills and professional equipment. If desired, you can even assemble an underwater metal detector that will work equally both on land and in water.
In order for a self-assembled device to ideally fulfill all possible requirements, it is necessary to understand the design of the metal detector, determine the type of search work that will be carried out with the device after its assembly. This will help you choose exactly the version of the metal detector that a novice treasure hunter needs.
It was developed on the basis of the already known device "Terminator Pro". Its main advantage is high-quality discrimination, as well as low current consumption. Also, the assembly of the device will not be expensive, and it is able to work on any type of soil.
Here brief characteristics devices
According to the principle of operation, the metal detector is also pulse-balanced.
The operating frequency is 8-15 kHz.
As for the discrimination mode, two-tone voice acting is used here. When iron is detected, the device gives a low signal, and if a non-ferrous metal is found, the tone will be high.
The device is powered by a source of 9-12V.
There is also the possibility of adjusting the sensitivity and there is a manual detuning from the ground.
Well, now about the main thing, about the depth of detection of a metal detector. The device is able to detect coins with a diameter of 25 mm at a distance of 35 cm through the air. The golden ring can be caught at a distance of 30 cm. The device detects a helmet at a distance of about 1 meter. The maximum detection depth is 150 cm. As for consumption, without sound it is about 35 mA.
Assembly materials and tools:
- minidrill (the author has a self-made motor);
- wire for winding the coil;
- four core shielded cable;
- soldering iron with solder;
- materials for the manufacture of the case;
- printed circuit board;
- all the necessary radio components and their ratings can be seen in the photo of the circuit.
Metal detector manufacturing process:
Step one. Board manufacturing
The board is made by etching. Then you can drill holes, their diameter is 0.8 mm. For these purposes, the author uses a small motor with a drill installed.
Step two. Board Assembly
The assembly must begin with soldering the jumpers. After that, you can install panels for microcircuits and other solder other elements. It is very important to have a tester for quality assembly that can measure the capacitance of capacitors. Since the device uses two identical amplification channels, the amplification for them should be as close as possible to the same value, that is, be the same. Both channels of the same stage must have the same readings when measured by the tester.
What the already assembled circuit looks like can be seen in the photo. The author did not install a node that determines the degree of battery discharge.
After assembly, the board must be checked by a tester. You need to connect power to it and check all the strategically important inputs and outputs. Everywhere food should be exactly the same as in the diagram.
Step three. Assembling the coil
The DD sensor is assembled according to the same principle as for all similar balancers. The transmitting coil is denoted by the letters TX, and the receiving coil is RX. In total, you need to make 30 turns with a wire folded in half. The wire used is enameled, with a diameter of 0.4 mm. Both the receiving and transmitting coils are formed by double wires, resulting in four wires at the output. Next, the tester needs to determine the arms of the windings and connect the beginning of one arm to the end of the other, as a result, the average output of the coil is formed.
To fix the coil after winding, it is necessary to wrap it well with threads and then soak it with varnish. After the varnish dries, the coils are wrapped with electrical tape.
Subsequently, a foil screen is made from above, a gap of about 1 mm must be made between the beginning and end in order to avoid a short-circuited coil.
The middle output of the TX must be connected to the ground of the board, otherwise the generator will not start. As for the middle RX output, it is needed for frequency tuning. After tuning the resonance, it must be isolated and the receiving coil turns into a normal one, that is, without an output. As for the receiving coil, it is connected instead of the transmitting one and tuned 100-150 Hz lower than the transmitting one. Each coil must be tuned separately; when tuning, there should not be any metal objects near the coil.
To bring the balance, the coils are shifted, as you can see in the photo. The balance should be within 20-30 mV, but not more than 100 mV.
The operating frequencies of the device are in the range from 7 kHz to 20 kHz. The lower the frequency, the deeper the device will take, but at a low frequency, discrimination becomes worse. Conversely, the higher the frequency, the better discrimination, but the depth of detection is less. The golden mean can be considered a frequency of 10-14 kHz.
To connect the coil, a four-wire shielded wire is used. the screen is connected to the body, two wires go to the transmitting coil and two to the receiving one.
