Do-it-yourself underwater metal detector shuf 1 2. Making a metal detector for gold with your own hands: diagrams and step-by-step instructions

With the onset of spring, more and more often you can see people with metal detectors on the banks of rivers. Most of them are engaged in “gold mining” purely out of curiosity and passion. But a certain percentage actually earn a lot of money from searching for rare things. The secret to the success of such research is not only in experience, information and intuition, but also in the quality of the equipment with which they are equipped. A professional instrument is expensive, and if you have a basic knowledge of radio mechanics, you have probably thought more than once about how to make a metal detector with your own hands. The editors of the site will come to your aid and tell you today how to assemble the device yourself using diagrams.

Read in the article:

Metal detector and its structure

This model costs more than 32,000 rubles, and, of course, non-professionals will not be able to afford such a device. Therefore, we suggest studying the design of a metal detector in order to assemble a variation of such a device yourself. So, the simplest metal detector consists of the following elements.

The operating principle of such metal detectors is based on the transmission and reception of electromagnetic waves. The main elements of a device of this type are two coils: one is transmitting, and the second is receiving.

The metal detector works like this: the magnetic field lines of the primary field (A) of red color pass through the metal object (B) and create a secondary field (green lines) in it. This secondary field is picked up by the receiver and the detector sends an audible signal to the operator. Based on the operating principle of the emitters electronic devices this type can be divided into:

1. Simple, working on the “receive-transmit” principle.
2. Induction.
3. Pulse.
4. Generating.

The cheapest devices belong to the first type.

An induction metal detector has one coil that sends and receives a signal simultaneously. But devices with pulse induction differ in that they generate a transmitter current, which turns on for a while and then turns off abruptly. The coil field generates pulsed eddy currents in the object, which are detected by analyzing the attenuation of the pulse induced in the receiver coil. This cycle repeats continuously, perhaps hundreds of thousands of times per second.

How a metal detector works depending on its purpose and technical device

The operating principle of a metal detector varies depending on the type of device. Let's consider the main ones:

• Dynamic type devices. The simplest type of device that continuously scans the field. Main feature When working with such a device, you must be in motion all the time, otherwise the signal will disappear. Such devices are easy to use, however, they are poorly sensitive.
• Pulse type devices. They have great sensitivity. Often such a device comes with several additional coils for tuning different types soils and metals. Requires certain skills to set up. Among the devices of this class we can distinguish electronic devices operating at low frequencies - no higher than 3 kHz.

• Electronic devices, on the one hand, do not give a reaction (or give a weak one) to unwanted signals: wet sand, small pieces of metal, shot, for example, and, on the other hand, they provide good sensitivity when searching for hidden water pipes and central heating routes, as well as coins and other metal objects.
• Depth detectors designed to search for objects located at impressive depths. They can detect metal objects at a depth of up to 6 meters, while other models “pierce” only up to 3. For example, the Jeohunter 3D depth detector is capable of searching and detecting voids and metals, while showing objects found in the ground in 3- measured form.

Depth detectors operate on two coils, one is parallel to the ground surface, the other is perpendicular.

• Stationary detectors- these are frames established at particularly important protected sites. They detect any metal objects in people's bags and pockets that pass through the circuit.

Which metal detectors are suitable for making yourself at home?

The simplest devices that you can assemble yourself include devices that operate on the principle of reception and transmission. There are schemes that even a novice radio amateur can do; for this you just need to select a certain set of parts.

There are many video instructions on the Internet with detailed explanations of how to make a simple metal detector with your own hands. Here are the most popular ones:

1. Metal detector "Pirate".
2. Metal detector - butterfly.
3. Emitter without microcircuits (IC).
4. Series of metal detectors "Terminator".

However, despite the fact that some entertainers are trying to offer systems for assembling a metal detector from a phone, such designs will not pass the battle test. It’s easier to buy a children’s metal detector toy, it will be more useful.

And now more about how to make a simple metal detector with your own hands using the example of the “Pirate” design.

Homemade metal detector “Pirate”: diagram and detailed description of the assembly

Homemade products based on the “Pirate” series metal detector are among the most popular among radio amateurs. Thanks to the good performance of the device, it can “detect” an object at a depth of 200 mm (for small items) and 1500 mm (large items).

Parts for assembling a metal detector

The Pirate metal detector is a pulse type device. To make the device you will need to purchase:

1. Materials for making the body, rod (you can use a plastic pipe), holder, and so on.
2. Wires and electrical tape.
3. Headphones (suitable for the player).
4. Transistors – 3 pieces: BC557, IRF740, BC547.
5. Microcircuits: K157UD2 and NE
6. Ceramic capacitor - 1 nF.
7. 2 film capacitors - 100 nF.
8. Electrolytic capacitors: 10 μF (16 V) – 2 pieces, 2200 μF (16 V) – 1 piece, 1 μF (16 V) – 2 pieces, 220 μF (16 V) – 1 piece.
9. Resistors – 7 pieces per 1; 1.6; 47; 62; 100; 120; 470 kOhm and 6 pieces for 10, 100, 150, 220, 470, 390 Ohm, 2 pieces for 2 Ohm.
10. 2 diodes 1N148.

DIY metal detector circuits

The classic circuit of the metal detector of the “Pirate” series is built using the NE555 microcircuit. The operation of the device depends on a comparator, one output of which is connected to the IC pulse generator, the second to the coil, and the output to the speaker. If metal objects are detected, the signal from the coil is sent to the comparator, and then to the speaker, which notifies the operator of the presence of the desired objects.

The board can be placed in a simple junction box, which can be purchased at an electrical store. If such a tool is not enough for you, you can try to make a more advanced device; a diagram for making a gold-oriented metal detector will help you.

How to assemble a metal detector without using microcircuits

This device uses Soviet-style transistors KT-361 and KT-315 to generate signals (you can use similar radio components).

How to assemble a metal detector circuit board with your own hands

The pulse generator is assembled on the NE555 chip. By selecting C1 and 2 and R2 and 3, the frequency is adjusted. The pulses obtained as a result of scanning are transmitted to transistor T1, and it transmits the signal to transistor T2. The audio frequency is amplified using the BC547 transistor to the collector, and headphones are connected.

To place radio components, a printed circuit is used, which can be easily made independently. To do this, we use a piece of sheet getinax covered with copper electrical foil. We transfer the connecting parts onto it, mark the fastening points, and drill holes. We cover the tracks with a protective varnish, and after drying, we lower the future board into ferric chloride for etching. This is necessary to remove unprotected areas of copper foil.

How to make a metal detector coil with your own hands

For the base you will need a ring with a diameter of about 200 mm (ordinary wooden hoops can be used as the base), on which 0.5 mm wire is wound. To increase the depth of metal detection, the coil frame should be in the range of 260−270 mm, and the number of turns should be 21−22 vol. If you don't have anything suitable on hand, you can wind a reel on a wooden base.

Copper wire spool on wooden base

Illustration	Description of action
	For winding, prepare a board with guides. The distance between them is equal to the diameter of the base on which you will attach the reel.
	Wind the wire around the perimeter of the fastenings in 20-30 turns. Secure the winding with electrical tape in several places.
	Remove the winding from the base and give it a rounded shape; if necessary, additionally fasten the winding in several more places.
	Connect the circuit to the device and test its operation.

Twisted pair coil in 5 minutes

We will need: 1 twisted pair 5 cat 24 AVG (2.5 mm), knife, soldering iron, solder and multitester.

Illustration	Description of action
	Twist the wire into two skeins. Leave 10 cm on each side.
	Strip the winding and free the wires for connection.
	We connect the wires according to the diagram.
	For better fastening, solder them with a soldering iron.
	Test the coil in the same manner as the copper wire device. The winding terminals must be soldered to a stranded wire with a diameter in the range of 0.5−0.7 mm.

Brief instructions for setting up a DIY metal detector “Pirate”

Once the main elements of the metal detector are ready, we proceed to assembly. We attach all the components to the metal detector rod: the body with the coil, the receiving and transmitting unit and the handle. If you did everything correctly, then additional manipulations with the device will not be required, since it initially has maximum sensitivity. More fine tuning performed using variable resistor R13. Normal operation of the detector should be ensured with the regulator in the middle position. If you have an oscilloscope, then use it to measure the frequency at the gate of transistor T2, which should be 120−150 Hz, and the pulse duration should be 130−150 μs.

Is it possible to make an underwater metal detector with your own hands?

The principle of assembling an underwater metal detector is no different from a conventional one, with the only difference being that you will have to work hard to create an impenetrable shell using sealant, as well as to place special light indicators that can report a find from under water. An example of how this will work is in the video:

Do-it-yourself metal detector “Terminator 3”: detailed diagram and video instructions for assembly

The Terminator 3 metal detector has occupied an honorable place among homemade metal detectors for many years. The two-tone device operates on the principle of induction balance.

Its main features are: low power consumption, metal discrimination, non-ferrous metals mode, gold only mode and very good search depth characteristics, compared to semi-professional branded metal detectors. We offer you the most detailed description assembly of a similar device from folk craftsman Viktor Goncharov.

How to make a metal detector with your own hands with metal discrimination

Metal discrimination is the ability of the device to distinguish between the detected material and classify it. Discrimination is based on different electrical conductivities of metals. The most simple ways metal type definitions were implemented in older and entry-level devices and had two modes - “all metals” and “non-ferrous”. The discrimination function allows the operator to respond to a phase shift of a certain magnitude, compared to a configured (reference) level. In this case, the device cannot distinguish between non-ferrous metals.

Learn how to make a homemade professional metal detector using improvised materials in this video:

Features of deep metal detectors

Metal detectors of this type can detect objects at great depths. A good metal detector, made by yourself, looks to a depth of 6 meters. However, in this case the size of the find must be substantial. These detectors work best for detecting old shells or large enough debris.

There are two types of deep metal detectors: frame and transceiver on a rod. The first type of device is capable of covering a large area of ​​land for scanning, however, in this case, the efficiency and focus of the search is reduced. The second version of the detector is a point detector; it works directed inward over a small diameter. You need to work with it slowly and carefully. If your goal is to build such a metal detector, the following video can tell you how to do it.

If you have experience in assembling such a device and using it, tell others about it!

Instrumental search is simply enormously popular. Adults and children, amateurs and professionals are looking for it. They are looking for treasures, coins, lost things and buried scrap metal. And the main search tool is metal detector.

There are a great variety of different metal detectors to suit every taste and color. But for many people, buying a ready-made branded metal detector is simply financially expensive. And some people want to assemble a metal detector with their own hands, and some even build their own small business on their assembly.

Homemade metal detectors

In this section of our website about homemade metal detectors, I will be collected: best metal detector circuits, their descriptions, programs and other data for manufacturing DIY metal detector. There are no metal detector circuits from the USSR or circuits with two transistors here. Since such metal detectors are only suitable for visually demonstrating the principles of metal detection, but are not at all suitable for real use.

All metal detectors in this section will be quite technologically advanced. They will have good search characteristics. And a well-assembled homemade metal detector is not much inferior to its factory-made counterparts. Mainly presented here various schemes pulse metal detectors And metal detector circuits with metal discrimination.

But to make these metal detectors, you will need not only desire, but also certain skills and abilities. We tried to break down the diagrams of the given metal detectors by level of complexity.

In addition to the basic data required to assemble a metal detector, there will also be information about the required minimum level of knowledge and equipment for making a metal detector yourself.

To assemble a metal detector with your own hands, you will definitely need:

This list will include necessary tools, materials and equipment for self-assembly of all metal detectors without exception. For many schemes you will also need various additional equipment and materials, here are just the basics for all schemes.

1. Soldering iron, solder, tin and other soldering supplies.
2. Screwdrivers, pliers, wire cutters and other tools.
3. Materials and skills for making a printed circuit board.
4. Minimum experience and knowledge in electronics and electrical engineering as well.
5. And also straight hands will be very useful when assembling a metal detector with your own hands.

Here you can find diagrams for self-assembly of the following models of metal detectors:

	Operating principle	I.B.
	Metal discrimination	There is
	Maximum search depth
		There is
	Operating frequency	4 - 17 kHz
	Difficulty level	Average

	Operating principle	I.B.
	Metal discrimination	There is
	Maximum search depth	1-1.5 meters (Depends on the size of the coil)
	Programmable microcontrollers	There is
	Operating frequency	4 - 16 kHz
	Difficulty level	Average

	Operating principle	I.B.
	Metal discrimination	There is
	Maximum search depth	1 - 2 meters (Depends on the size of the coil)
	Programmable microcontrollers	There is
	Operating frequency	4.5 - 19.5 kHz
	Difficulty level	High

A metal detector or metal detector is designed to detect objects that differ in their electrical and/or magnetic properties from the environment in which they are located. Simply put, it allows you to find metal in the ground. But not only metal, and not only in the ground. Metal detectors are used by inspection services, criminologists, military personnel, geologists, builders to search for profiles under cladding, fittings, to verify plans and diagrams of underground communications, and people of many other specialties.

Do-it-yourself metal detectors are most often made by amateurs: treasure hunters, local historians, members of military historical associations. This article is primarily intended for them, beginners; The devices described in it allow you to find a coin the size of a Soviet nickel at a depth of 20-30 cm or a piece of iron the size of a sewer manhole approximately 1-1.5 m below the surface. However, this homemade device can also be useful on the farm during repairs or at construction sites. Finally, having discovered a hundredweight or two of abandoned pipes or metal structures in the ground and selling the find for scrap metal, you can earn a decent amount. And there are definitely more such treasures in Russian land than pirate chests with doubloons or boyar-robber pods with efimkas.

Note: If you are not knowledgeable in electrical engineering and radio electronics, do not be intimidated by the diagrams, formulas and special terminology in the text. The essence is stated simply, and at the end there will be a description of the device, which can be made in 5 minutes on a table, without knowing how to solder or twist the wires. But it will allow you to “feel” the peculiarities of metal searching, and if interest arises, knowledge and skills will come.

A little more attention compared to the others will be paid to the “Pirate” metal detector, see fig. This device is simple enough for beginners to repeat, but its quality indicators are not inferior to many branded models costing up to $300-400. And most importantly, it showed excellent repeatability, i.e. full functionality when manufactured according to descriptions and specifications. The circuit design and operating principle of the “Pirate” are quite modern; There are enough manuals on how to set it up and how to use it.

Operating principle

The metal detector operates on the principle of electromagnetic induction. IN general scheme The metal detector consists of a transmitter of electromagnetic waves, a transmitting coil, a receiving coil, a receiver, a circuit for isolating a useful signal (discriminator) and an indication device. Separate functional units are often combined in circuitry and design, for example, the receiver and transmitter can operate on the same coil, the receiving part immediately releases the useful signal, etc.

The coil creates an electromagnetic field (EMF) of a certain structure in the medium. If there is an electrically conductive object in its area of ​​action, pos. And in the figure, eddy currents or Foucault currents are induced in it, which create its own EMF. As a result, the structure of the coil field is distorted, pos. B. If the object is not electrically conductive, but has ferromagnetic properties, then it distorts the original field due to shielding. In both cases, the receiver detects the difference between the EMF and the original one and converts it into an acoustic and/or optical signal.

Note: in principle, for a metal detector it is not necessary that the object be electrically conductive; the soil is not. The main thing is that their electrical and/or magnetic properties are different.

Detector or scanner?

In commercial sources, expensive highly sensitive metal detectors, e.g. Terra-N are often called geoscanners. This is not true. Geoscanners operate on the principle of measuring the electrical conductivity of soil in different directions at different depths; this procedure is called lateral logging. Using logging data, the computer builds a picture on the display of everything in the ground, including geological layers of different properties.

Varieties

General Settings

The operating principle of a metal detector can be implemented technically in different ways according to the purpose of the device. Metal detectors for beach gold prospecting and construction and repair prospecting may be similar in appearance, but differ significantly in design and technical data. To make a metal detector correctly, you need to clearly understand what requirements it must satisfy for this type of work. Based on this, The following parameters of search metal detectors can be distinguished:

1. Penetration, or penetrating ability, is the maximum depth to which an EMF coil extends in the ground. The device will not detect anything deeper, regardless of the size and properties of the object.
2. The size and dimensions of the search zone is an imaginary area in the ground in which the object will be detected.
3. Sensitivity is the ability to detect more or less small objects.
4. Selectivity is the ability to respond more strongly to desirable findings. The sweet dream of beach miners is a detector that beeps only for precious metals.
5. Noise immunity is the ability not to respond to EMF from extraneous sources: radio stations, lightning discharges, power lines, electric vehicles and other sources of interference.
6. Mobility and efficiency are determined by energy consumption (how many batteries will last), the weight and dimensions of the device and the size of the search zone (how much can be “probed” in 1 pass).
7. Discrimination, or resolution, gives the operator or control microcontroller the opportunity to judge the nature of the found object by the device’s response.

Discrimination, in turn, is a composite parameter, because At the output of the metal detector there is 1, maximum 2 signals, and there are more quantities that determine the properties and location of the find. However, taking into account the change in the reaction of the device when approaching an object, 3 components are distinguished:

• Spatial – indicates the location of the object in the search area and the depth of its occurrence.
• Geometric – makes it possible to judge the shape and size of an object.
• Qualitative – allows you to make assumptions about the properties of the object’s material.

Operating frequency

All parameters of a metal detector are connected in a complex way and many relationships are mutually exclusive. So, for example, lowering the frequency of the generator makes it possible to achieve greater penetration and search area, but at the cost of increasing energy consumption, and worsens sensitivity and mobility due to an increase in the size of the coil. In general, each parameter and their complexes are somehow tied to the frequency of the generator. That's why The initial classification of metal detectors is based on the operating frequency range:

1. Ultra-low frequency (ELF) - up to the first hundred Hz. Absolutely not amateur devices: power consumption of tens of W, without computer processing it is impossible to judge anything from the signal, transportation requires vehicles.
2. Low frequency (LF) - from hundreds of Hz to several kHz. They are simple in circuit design and design, noise-resistant, but not very sensitive, discrimination is poor. Penetration - up to 4-5 m with power consumption from 10 W (so-called deep metal detectors) or up to 1-1.5 m when powered by batteries. They react most acutely to ferromagnetic materials (ferrous metal) or large masses of diamagnetic materials (concrete and stone building structures), which is why they are sometimes called magnetic detectors. They are little sensitive to soil properties.
3. High frequency (IF) – up to several tens of kHz. LF is more complex, but the requirements for the coil are low. Penetration - up to 1-1.5 m, noise immunity at C, good sensitivity, satisfactory discrimination. Can be universal when used in pulse mode, see below. On watered or mineralized soils (with fragments or particles of rock that shield EMF), they work poorly or do not sense anything at all.
4. High, or radio frequencies (HF or RF) - typical metal detectors “for gold”: excellent discrimination to a depth of 50-80 cm in dry non-conductive and non-magnetic soils (beach sand, etc.) Energy consumption - as before. n. The rest is on the verge of failure. The effectiveness of the device largely depends on the design and quality of the coil(s).

Note: mobility of metal detectors according to paragraphs. 2-4 good: from one set of AA salt cells (“batteries”) you can work for up to 12 hours without overworking the operator.

Pulse metal detectors stand apart. In them, the primary current enters the coil in pulses. By setting the pulse repetition rate within the LF range, and their duration, which determines the spectral composition of the signal corresponding to the IF-HF ranges, you can obtain a metal detector that combines the positive properties of LF, IF and HF or is tunable.

Search method

There are at least 10 methods of searching for objects using EMFs. But such as, say, the method of direct digitization of the response signal with computer processing is for professional use.

A homemade metal detector is constructed in the following ways:

• Parametric.
• Transceiver.
• With phase accumulation.
• On the beats.

Without receiver

Parametric metal detectors in some way fall outside the definition of the operating principle: they have neither a receiver nor a receiving coil. For detection, the direct influence of the object on the parameters of the generator coil - inductance and quality factor - is used, and the structure of the EMF does not matter. Changing the parameters of the coil leads to a change in the frequency and amplitude of the generated oscillations, which is recorded in different ways: by measuring the frequency and amplitude, by changing the current consumption of the generator, by measuring the voltage in the PLL loop (a phase-locked loop system that “pulls” it to a given value), etc.

Parametric metal detectors are simple, cheap and noise-resistant, but using them requires certain skills, because... the frequency “floats” under the influence of external conditions. Their sensitivity is weak; Most of all they are used as magnetic detectors.

With receiver and transmitter

The device of the transceiver metal detector is shown in Fig. at the beginning, to an explanation of the principle of operation; The principle of operation is also described there. Such devices make it possible to achieve best efficiency in their frequency range, but are complex in circuit design, require a particularly high-quality coil system. Transceiver metal detectors with one coil are called induction detectors. Their repeatability is better, because the problem of the correct arrangement of the coils relative to each other disappears, but the circuit design is more complicated - you need to isolate a weak secondary signal against the background of a strong primary one.

Note: In pulsed transceiver metal detectors, the problem of isolation can also be eliminated. This is explained by the fact that the so-called “catch” is “caught” as a secondary signal. the “tail” of the pulse re-emitted by the object. Due to dispersion during re-emission, the primary pulse spreads out, and part of the secondary pulse ends up in the gap between the primary ones, from where it is easy to isolate.

Until it clicks

Metal detectors with phase accumulation, or phase-sensitive, are either single-coil pulsed or with 2 generators, each operating on its own coil. In the first case, the fact that pulses not only spread out during re-emission, but are also delayed. The phase shift increases over time; when it reaches a certain value, the discriminator is triggered and a click is heard in the headphones. As you approach the object, the clicks become more frequent and merge into a sound of increasingly higher pitch. It is on this principle that “Pirate” is built.

In the second case, the search technique is the same, but 2 strictly symmetrical electrically and geometrically oscillators operate, each with its own coil. In this case, due to the interaction of their EMFs, mutual synchronization occurs: the generators work in time. When the general EMF is distorted, synchronization disruptions begin, heard as the same clicks, and then a tone. Double-coil metal detectors with synchronization failure are simpler than pulse detectors, but less sensitive: their penetration is 1.5-2 times less. Discrimination in both cases is close to excellent.

Phase-sensitive metal detectors are the favorite tools of resort prospectors. Search aces adjust their instruments so that exactly above the object the sound disappears again: the frequency of clicks goes into the ultrasonic region. In this way, on a shell beach, it is possible to find gold earrings the size of a fingernail at a depth of up to 40 cm. However, on soil with small inhomogeneities, watered and mineralized, metal detectors with phase accumulation are inferior to others, except parametric ones.

By the squeak

Beats of 2 electrical signals - a signal with a frequency equal to the sum or difference of the fundamental frequencies of the original signals or their multiples - harmonics. So, for example, if the inputs special device– mixer – apply signals with frequencies of 1 MHz and 1,000,500 Hz or 1.0005 MHz, and connect headphones or a speaker to the mixer output, then we will hear a pure tone of 500 Hz. And if the 2nd signal is 200-100 Hz or 200.1 kHz, the same thing will happen, because 200 100 x 5 = 1,000,500; we “caught” the 5th harmonic.

In a metal detector, there are 2 generators operating on beats: a reference and a working one. The coil of the reference oscillating circuit is small, protected from extraneous influences, or its frequency is stabilized by a quartz resonator (simply quartz). The circuit coil of the working (search) generator is a search generator, and its frequency depends on the presence of objects in the search area. Before searching, the working generator is set to zero beats, i.e. until the frequencies match. As a rule, a complete zero sound is not achieved, but is adjusted to a very low tone or wheezing, this is more convenient to search for. By changing the tone of the beats one judges the presence, size, properties and location of the object.

Note: Most often, the frequency of the search generator is taken several times lower than the reference one and operates on harmonics. This allows, firstly, to avoid the harmful mutual influence of generators in this case; secondly, adjust the device more accurately, and thirdly, search at the optimal frequency in this case.

Harmonic metal detectors are generally more complex than pulse detectors, but they work on any type of soil. Properly manufactured and tuned, they are not inferior to impulse ones. This can be judged at least by the fact that gold miners and beachgoers will not agree on what is better: an impulse or a beating one?

Reel and stuff

The most common misconception of novice radio amateurs is the absolutization of circuit design. Like, if the scheme is “cool”, then everything will be top-notch. Regarding metal detectors, this is doubly true, because... their operational advantages greatly depend on the design and quality of manufacture of the search coil. As one resort prospector put it: “Findability of the detector should be in the pocket, not the legs.”

When developing a device, its circuit and coil parameters are adjusted to each other until the optimum is obtained. Even if a certain circuit with a “foreign” coil works, it will not reach the declared parameters. Therefore, when choosing a prototype to replicate, look first of all at the description of the coil. If it is incomplete or inaccurate, it is better to build another device.

About coil sizes

A large (wide) coil emits EMF more effectively and will “illuminate” the soil more deeply. Its search area is wider, which allows it to reduce “being found with its feet.” However, if there is a large unnecessary object in the search area, its signal will “clog” the weak one from the small thing you are looking for. Therefore, it is advisable to take or make a metal detector designed to work with coils of different sizes.

Note: typical coil diameters are 20-90 mm for searching for fittings and profiles, 130-150 mm for “beach gold” and 200-600 mm “for large iron”.

monoloop

The traditional type of metal detector coil is called. thin coil or Mono Loop (single loop): a ring of many turns of enameled copper wire with a width and thickness 15-20 times less than the average diameter of the ring. The advantages of a monoloop coil are a weak dependence of the parameters on the type of soil, a narrowing search zone, which allows, by moving the detector, to more accurately determine the depth and location of the find, and design simplicity. Disadvantages - low quality factor, which is why the setting “floats” during the search process, susceptibility to interference and vague response to the object: working with a monoloop requires considerable experience in using this particular instance of the device. It is recommended that beginners make homemade metal detectors with a monoloop in order to get a workable design without any problems and gain search experience with it.

Inductance

When choosing a circuit, in order to ensure the reliability of the author’s promises, and even more so when independently designing or modifying it, you need to know the inductance of the coil and be able to calculate it. Even if you are making a metal detector from a purchased kit, you still need to check the inductance by measurements or calculations, so as not to rack your brains later: why, everything seems to be working properly, and not beeping.

Calculators for calculating the inductance of coils are available on the Internet, but computer program cannot foresee all cases of practice. Therefore, in Fig. an old, decades-tested nomogram for calculating multilayer coils is given; thin coil - special case multilayer.

To calculate the search monoloop, the nomogram is used as follows:

• We take the inductance value L from the description of the device and the dimensions of the loop D, l and t from the same place or according to our choice; typical values: L = 10 mH, D = 20 cm, l = t = 1 cm.
• Using the nomogram we determine the number of turns w.
• We set the laying coefficient k = 0.5, using the dimensions l (height of the coil) and t (its width) we determine the cross-sectional area of ​​the loop and find the area of ​​​​pure copper in it as S = klt.
• Dividing S by w, we obtain the cross-section of the winding wire, and from it the diameter of the wire d.
• If it turns out d = (0.5...0.8) mm, everything is OK. Otherwise, we increase l and t when d>0.8 mm or decrease when d<0,5 мм.

Noise immunity

The monoloop “catches” interference well, because is designed exactly the same as a loop antenna. You can increase its noise immunity, firstly, by placing the winding in the so-called. Faraday shield: a metal tube, braid or foil winding with a break so that a short-circuited turn does not form, which will “eat up” all the EMF coils, see fig. right. If on the original diagram there is a dotted line near the designation of the search coil (see diagrams below), this means that the coil of this device must be placed in the Faraday shield.

Also, the screen must be connected to the common wire of the circuit. There is a catch here for beginners: the grounding conductor must be connected to the screen strictly symmetrically to the cut (see the same figure) and brought to the circuit also symmetrically relative to the signal wires, otherwise noise will still “crawl” into the coil.

The screen also absorbs some of the search EMF, which reduces the sensitivity of the device. This effect is especially noticeable in pulse metal detectors; their coils cannot be shielded at all. In this case, increasing noise immunity can be achieved by balancing the winding. The point is that for a remote EMF source, the coil is a point object, and the emf. interference in its halves will suppress each other. A symmetrical coil may also be needed in the circuit if the generator is push-pull or inductive three-point.

However, in this case it is impossible to symmetry the coil using the bifilar method familiar to radio amateurs (see figure): when conductive and/or ferromagnetic objects are in the field of the bifilar coil, its symmetry is broken. That is, the noise immunity of the metal detector will disappear just when it is most needed. Therefore, you need to balance the monoloop coil by cross-winding, see the same fig. Its symmetry is not broken under any circumstances, but winding a thin coil with a large number of turns in a crosswise manner is hellish work, and then it is better to make a basket coil.

Basket

Basket reels have all the advantages of monoloops to an even greater extent. In addition, basket coils are more stable, their quality factor is higher, and the fact that the coil is flat is a double plus: sensitivity and discrimination will increase. Basket coils are less susceptible to interference: harmful emf. in crossing wires they cancel each other out. The only negative is that basket coils require a precisely made, rigid and durable mandrel: the total tension force of many turns reaches large values.

Basket coils are structurally flat and three-dimensional, but electrically a three-dimensional “basket” is equivalent to a flat one, i.e. creates the same EMF. The volumetric basket coil is even less sensitive to interference and, which is important for pulse metal detectors, the pulse dispersion in it is minimal, i.e. It's easier to catch the variance caused by the object. The advantages of the original “Pirate” metal detector are largely due to the fact that its “native” coil is a voluminous basket (see figure), but its winding is complex and time-consuming.

It is better for a beginner to wind a flat basket on his own, see fig. below. For metal detectors “for gold” or, say, for the “butterfly” metal detector described below and a simple 2-coil transceiver, a good mount would be unusable computer disks. Their metallization will not harm: it is very thin and nickel. An indispensable condition: an odd, and no other, number of slots. A nomogram for calculating a flat basket is not required; the calculation is carried out as follows:

• They are set with a diameter D2 equal to the outer diameter of the mandrel minus 2-3 mm, and take D1 = 0.5D2, this is the optimal ratio for search coils.
• According to formula (2) in Fig. calculate the number of turns.
• From the difference D2 – D1, taking into account the flat laying coefficient of 0.85, the diameter of the wire in insulation is calculated.

How not to and how to wind baskets

Some amateurs take it upon themselves to wind large baskets using the method shown in Fig. below: make a mandrel from insulated nails (pos. 1) or self-tapping screws, wind them according to the diagram, pos. 2 (in this case, pos. 3, for a number of turns that is a multiple of 8; every 8 turns the “pattern” is repeated), then foam, pos. 4, the mandrel is pulled out and the excess foam is cut off. But it soon turns out that the stretched coils cut the foam and all the work went to waste. That is, in order to wind it reliably, you need to glue pieces of durable plastic into the holes of the base, and only then wind it. And remember: independent calculation of a volumetric basket coil without the appropriate computer programs is impossible; The technique for a flat basket is not applicable in this case.

DD coils

DD in this case does not mean long-range, but a double or differential detector; in the original – DD (Double Detector). This is a coil of 2 identical halves (arms), folded with some intersection. With an accurate electrical and geometric balance of the DD arms, the search EMF is contracted into the intersection zone, on the right in Fig. on the left is a monoloop coil and its field. The slightest heterogeneity of space in the search area causes an imbalance, and a sharp strong signal appears. An DD coil allows an inexperienced seeker to detect a small, deep, highly conductive object when a rusty can lies next to it and above it.

DD coils are clearly oriented “to gold”; All metal detectors marked GOLD are equipped with them. However, on shallow, heterogeneous and/or conductive soils, they either fail altogether or often give false signals. The sensitivity of the DD coil is very high, but the discrimination is close to zero: the signal is either marginal or there is none at all. Therefore, metal detectors with DD coils are preferred by searchers who are only interested in “pocket-fitting”.

Note: More details about DD coils can be found further in the description of the corresponding metal detector. The DD shoulders are wound either in bulk, like a monoloop, on a special mandrel, see below, or with baskets.

How to attach the reel

Ready-made frames and mandrels for search coils are sold in a wide range, but sellers are not shy about mark-ups. Therefore, many hobbyists make the base of the coil from plywood, on the left in the figure:

Multiple designs

Parametric

The simplest metal detector for searching for fittings, wiring, profiles and communications in walls and ceilings can be assembled according to Fig. The ancient transistor MP40 can be replaced without any problems with the KT361 or its analogues; To use pnp transistors, you need to change the polarity of the battery.

This metal detector is a parametric type magnetic detector operating on LF. The sound tone in the headphones can be changed by selecting the capacitance C1. Under the influence of the object, the tone decreases, unlike all other types, so initially you need to achieve a “mosquito squeak”, and not wheezing or grumbling. The device distinguishes live wiring from “empty” wiring; a 50 Hz hum is superimposed on the tone.

The circuit is a pulse generator with inductive feedback and frequency stabilization by an LC circuit. A loop coil is an output transformer from an old transistor receiver or a low-power “bazaar-Chinese” low-voltage power one. A transformer from an unusable Polish antenna power source is very suitable; in its own case, by cutting off the mains plug, you can assemble the entire device, then it is better to power it from a 3 V lithium coin cell battery. Winding II in Fig. – primary or network; I – secondary or step-down by 12 V. That’s right, the generator operates with transistor saturation, which ensures negligible power consumption and a wide range of pulses, making the search easier.

To turn a transformer into a sensor, its magnetic circuit must be opened: remove the frame with windings, remove the straight jumpers of the core - the yoke - and fold the W-shaped plates to one side, as on the right in the figure, then put the windings back on. If the parts are in working order, the device starts working immediately; if not, you need to swap the ends of any of the windings.

A more complex parametric scheme is shown in Fig. right. L with capacitors C4, C5 and C6 is tuned to 5, 12.5 and 50 kHz, and the quartz passes the 10th, 4th harmonics and fundamental tone to the amplitude meter, respectively. The circuit is more for the amateur to solder on the table: there is a lot of fuss with the settings, but there is no “flair”, as they say. Provided as an example only.

Transceiver

Much more sensitive is a transceiver metal detector with an DD coil, which can be made at home without much difficulty, see Fig. On the left is the transmitter; on the right is the receiver. The properties of different types of DD are also described there.

This metal detector is LF; search frequency is about 2 kHz. Detection depth: Soviet nickel - 9 cm, tin can - 25 cm, sewer hatch - 0.6 m. The parameters are “three”, but you can master the technique of working with DD before moving on to more complex structures.

The coils contain 80 turns of PE wire 0.6-0.8 mm, wound in bulk on a mandrel 12 mm thick, the drawing of which is shown in Fig. left. In general, the device is not critical to the parameters of the coils; they would be exactly the same and located strictly symmetrically. Overall, a good and cheap simulator for those who want to master any search technique, incl. "for gold." Although the sensitivity of this metal detector is low, the discrimination is very good despite the use of DD.

To set up the device, first turn on headphones instead of the L1 transmitter and check by the tone that the generator is working. Then L1 of the receiver is short-circuited and by selecting R1 and R3, a voltage equal to approximately half the supply voltage is set on the collectors VT1 and VT2, respectively. Next, R5 sets the collector current VT3 within 5..8 mA, opens L1 of the receiver and that’s it, you can search.

Cumulative phase

The designs in this section show all the advantages of the phase accumulation method. The first metal detector, primarily for construction purposes, will cost very little, because... its most labor-intensive parts are made... from cardboard, see fig.:

The device does not require adjustment; integrated timer 555 is an analogue of the domestic IC (integrated circuit) K1006VI1. All signal transformations occur in it; The search method is pulsed. The only condition is that the speaker needs a piezoelectric (crystalline) one; a regular speaker or headphones will overload the IC and it will soon fail.

Coil inductance is about 10 mH; operating frequency – within 100-200 kHz. With a mandrel thickness of 4 mm (1 layer of cardboard), a coil with a diameter of 90 mm contains 250 turns of 0.25 PE wire, and a 70 mm coil contains 290 turns.

Metal detector “Butterfly”, see fig. on the right, in terms of its parameters it is already close to professional instruments: the Soviet nickel is found at a depth of 15-22 cm, depending on the soil; sewer hatch - at a depth of up to 1 m. Effective in case of synchronization failures; diagram, board and type of installation - in Fig. below. Please note that there are 2 separate coils with a diameter of 120-150 mm, not DD! They must not intersect! Both speakers are piezoelectric, as before. case. Capacitors - heat-stable, mica or high-frequency ceramic.

The properties of the “Butterfly” will improve, and it will be easier to configure it if, firstly, you wind the coils with flat baskets; inductance is determined by the given operating frequency (up to 200 kHz) and the capacitances of the loop capacitors (10,000 pF each in the diagram). Wire diameter is from 0.1 to 1 mm, the larger the better. The tap in each coil is made from a third of the turns, counting from the cold (lower in the diagram) end. Secondly, if individual transistors are replaced with a 2-transistor assembly for K159NT1 amplifier circuits or its analogues; A pair of transistors grown on the same crystal has exactly the same parameters, which is important for circuits with synchronization failure.

To set up the Butterfly, you need to accurately adjust the inductance of the coils. The author of the design recommends moving the turns apart or moving them or adjusting the coils with ferrite, but from the point of view of electromagnetic and geometric symmetry, it would be better to connect 100-150 pF trimming capacitors in parallel with 10,000 pF capacitors and twist them in different directions when tuning.

The actual setup is not difficult: the newly assembled device beeps. We alternately bring an aluminum saucepan or a beer can to the coils. To one - the squeak becomes higher and louder; to the other - lower and quieter or completely silent. Here we add a little capacity to the trimmer, and in the opposite shoulder we remove it. In 3-4 cycles you can achieve complete silence in the speakers - the device is ready for searching.

More about "Pirate"

Let's return to the famous "Pirate"; It is a pulse transceiver with phase accumulation. The diagram (see figure) is very transparent and can be considered a classic for this case.

The transmitter consists of a master oscillator (MG) on the same 555 timer and a powerful switch on T1 and T2. On the left is the ZG version without an IC; in it you will have to set the pulse repetition rate on the oscilloscope to 120-150 Hz R1 and the pulse duration to 130-150 μs R2. Coil L is common. A limiter on diodes D1 and D2 for a current of 0.5 A saves the receiver amplifier QP1 from overload. The discriminator is assembled on QP2; together they make up the dual operational amplifier K157UD2. Actually, the “tails” of re-emitted pulses accumulate in container C5; when the “reservoir is full,” a pulse jumps at the output of QP2, which is amplified by T3 and gives a click in the dynamics. Resistor R13 regulates the filling speed of the “reservoir” and, consequently, the sensitivity of the device. You can learn more about “Pirate” from the video:

Video: “Pirate” metal detector

and about the features of its configuration - from the following video:

Video: setting the threshold of the “Pirate” metal detector

On the beats

Those who want to experience all the delights of the beating search process with replaceable coils can assemble a metal detector according to the diagram in Fig. Its peculiarity, firstly, is its efficiency: the entire circuit is assembled on CMOS logic and, in the absence of an object, consumes very little current. Secondly, the device operates on harmonics. The reference oscillator on DD2.1-DD2.3 is stabilized by ZQ1 quartz at 1 MHz, and the search oscillator on DD1.1-DD1.3 operates at a frequency of about 200 kHz. When setting up the device before searching, the desired harmonic is “caught” with a varicap VD1. Mixing of the working and reference signals occurs in DD1.4. Third, this metal detector is suitable for working with replaceable coils.

It is better to replace the IC 176 series with the same 561 series, the current consumption will decrease and the sensitivity of the device will increase. You can’t just replace old Soviet high-impedance headphones TON-1 (preferably TON-2) with low-impedance ones from the player: they will overload the DD1.4. You need to either install an amplifier like the “pirate” one (C7, R16, R17, T3 and a speaker on the “Pirate” circuit), or use a piezo speaker.

This metal detector does not require any adjustments after assembly. The coils are monoloops. Their data on a 10 mm thick mandrel:

• Diameter 25 mm – 150 turns PEV-1 0.1 mm.
• Diameter 75 mm – 80 turns PEV-1 0.2 mm.
• Diameter 200 mm – 50 turns PEV-1 0.3 mm.

It couldn't be simpler

Now let’s fulfill the promise we made at the beginning: we’ll tell you how to make a metal detector that searches without knowing anything about radio engineering. A metal detector “as simple as shelling pears” is assembled from a radio, a calculator, a cardboard or plastic box with a hinged lid and pieces of double-sided tape.

The metal detector “from the radio” is pulsed, but to detect objects it is not dispersion or delay with phase accumulation that is used, but the rotation of the magnetic vector of the EMF during re-emission. On the forums they write different things about this device, from “super” to “sucks”, “wiring” and words that are not customary to use in writing. So, in order for it to be, if not “super,” but at least a fully functional device, its components—the receiver and the calculator—must meet certain requirements.

Calculator you need the most tattered and cheapest, “alternative”. They make these in offshore basements. They have no idea about the standards for electromagnetic compatibility of household appliances, and if they heard about something like that, they wanted to choke it from the bottom of their hearts and from above. Therefore, the products there are quite powerful sources of pulsed radio interference; they are provided by the calculator's clock generator. In this case, its strobe pulses on the air are used to probe space.

Receiver We also need a cheap one, from similar manufacturers, without any means of increasing noise immunity. It must have an AM band and, which is absolutely necessary, a magnetic antenna. Since receivers that receive short waves (HF, SW) with a magnetic antenna are rarely sold and are expensive, you will have to limit yourself to medium waves (SW, MW), but this will make setup easier.

1. We unfold the box with the lid into a book.
2. We paste strips of adhesive tape onto the back sides of the calculator and the radio and secure both devices in the box, see fig. right. Receiver - preferably in a cover so that there is access to the controls.
3. We turn on the receiver and look for an area at maximum volume at the top of the AM band(s) that is free from radio stations and as clean as possible from ethereal noise. For CB this will be around 200 m or 1500 kHz (1.5 MHz).
4. We turn on the calculator: the receiver should hum, wheeze, growl; in general, give the tone. We don't turn down the volume!
5. If there is no tone, carefully and smoothly adjust until it appears; We caught some of the harmonics of the calculator's strobe generator.
6. We slowly fold the “book” until the tone weakens, becomes more musical, or disappears altogether. Most likely this will happen when the lid is turned about 90 degrees. Thus, we have found a position in which the magnetic vector of the primary pulses is oriented perpendicular to the axis of the ferrite rod of the magnetic antenna and it does not receive them.
7. We fix the lid in the found position with a foam insert and an elastic band or supports.

Note: depending on the design of the receiver, the opposite option is possible - to tune to the harmonic, the receiver is placed on the turned on calculator, and then, by unfolding the “book,” the tone softens or disappears. In this case, the receiver will catch pulses reflected from the object.

What's next? If there is an electrically conductive or ferromagnetic object near the opening of the “book,” it will begin to re-emit probing pulses, but their magnetic vector will rotate. The magnetic antenna will “sense” them, and the receiver will again give a tone. That is, we have already found something.

Something weird at last

There are reports of another metal detector “for complete dummies” with a calculator, only instead of a radio you allegedly need 2 computer disks, a CD and a DVD. Also - piezo headphones (precisely piezo, according to the authors) and a Krona battery. Frankly speaking, this creation looks like a technomyth, like the ever-memorable mercury antenna. But - what the hell is not joking. Here's a video for you:

try it if you wish, maybe you’ll find something there, both in the subject matter and in the scientific and technical sense. Good luck!

As an application

There are hundreds, if not thousands, of metal detector designs and designs. Therefore, in the appendix to the material we also provide a list of models, in addition to those mentioned in the test, which, as they say, are in circulation in the Russian Federation, are not overly expensive and are available for repetition or self-assembly:

• Clone.
8 ratings, average: 4,88 out of 5)

It is known that in the seas and lakes - especially in the coastal zone, where there are many vacationers, you can find a lot of gold and silver jewelry. But to search in water, the metal detector coil must be sealed, and the circuit must have its own characteristics - underwater specialization, so to speak. The Underwater P.I homemade underwater metal detector is intended for these purposes, the assembly and configuration of which does not present any particular difficulties. The test parameters turned out to be the following: 5 kopecks of the USSR is about 23-25 ​​cm, large objects are about a meter, maybe a little more (also depends on the position of the DELAY regulator). I checked the device at home.

At the moment I have almost completed the structure for the Surfmaster P.I. (the armrest remains). I soldered on the signet surf rev1.2 (from АpBerg), it can be used. Pay in bark. file is correct, the circuit works immediately after assembly - only the zero at the output of the NE5534 chip needs to be adjusted. What I liked about the metal detector was its sensitivity to small objects (pellets, a small gold earring of complex shape, a pin), the ability to use the DELAY knob to cut off small metal debris made of ferrous metal (nails or long-shaped objects made of black metal give a double peak-peak).

Disadvantages - the inability to ignore various plugs and large iron objects. I wound the coil for the Underwater P.I underwater detector on a three-liter jar. It contains 25-30 turns of 0.5 mm wire. A sketch of the coil is shown below.

In the absence of an IRF9640 field-effect transistor, I installed an IRF9630. Regarding this replacement (and the coil), I selected a reference resistance - installed a variable and tried it by range, since I don’t have an oscilloscope. It turned out to be 600 ohms. When I make the next copy of the submariner, I will try to find the right components and complete the setup more carefully. I installed a button on the pinpointer (it should be Push-off), but I didn’t have to install it. The device is dynamic, so it quite accurately determines the center of the target. The board is interesting, long, and fits well into a silicone glue tube.

Many people make equipment with their own hands - this way it costs less than if it were bought in a store. Is it possible to assemble an underwater metal detector with your own hands? Every beginner and professional search engine has this opportunity. It should immediately be noted that the assembly process will require experience in assembling electronic circuits and knowledge in the field of electronics. Without all this, attempts to assemble a full-fledged underwater metal detector with your own hands will be unsuccessful.

What is needed to assemble a metal detector? First you need to find a suitable scheme. It should provide the possibility of underwater search in salt and fresh water, and to the maximum possible depth. Many schemes allow you to find a five-kopeck coin of the USSR in the ground at a depth of 20-25 cm. The depth of immersion depends on your ability to create sealed enclosures. In total we need to do the following things:
- Find a suitable scheme;
- Purchase parts;
- Draw up a diagram of the layout of elements on a printed circuit board;
- Create a printed circuit board and place all the circuit elements on it.

Pay attention to the quality of soldering - it must be high so that the metal detector can operate without failures. You can fill the board with epoxy resin to provide protection from water, but this can make it difficult to replace parts if the metal detector breaks down.

When creating an underwater metal detector with your own hands, you will need to create a search coil. On the Internet you will find many options for coils, and you can ensure their tightness using any plastic material, for example, by covering the coil in the same epoxy resin and waiting for it to dry completely. The result is a sealed search coil that can be used to search at a wide range of depths.

At the last stage you need to come up with a body. It must be sealed and not allow water to pass through even at great depths. If the circuit you choose has any controls, you need to ensure that they are sealed and can operate in water. We also ensure the tightness of the battery compartment and connectors for connecting the search coil and headphones.

When assembling an underwater metal detector with your own hands, you may encounter various difficulties:
- The circuit works successfully in air, but begins to act weird under water;
- Setting up the circuit requires the use of an expensive oscilloscope;
- The resulting metal detector is not sensitive;
- There is no place to get waterproof items or underwater headphones.

All these problems can be avoided if you purchase a ready-made underwater metal detector. Factory-assembled devices are distinguished by stable operation in the most difficult conditions and high sensitivity, and underwater headphones are already supplied with them. Ready-made metal detectors from leading brands allow you to find even the smallest metal particles in the ground, and some models can withstand immersion to depths of up to 60 meters. They easily tolerate prolonged exposure to water, notable for their tightness. Well, more advanced search coils will provide a decent search depth. If you have experience in assembling electronic circuits and are well versed in electronics, try assembling an underwater metal detector with your own hands - homemade devices, well configured and adjusted, often give brilliant results. Well, their most important advantage is their affordable cost, which compares favorably with the cost of factory-assembled metal detectors.