Many people unreasonably believe that homemade metal detectors are inferior in many respects to branded samples produced at the factory.

But in fact, structures that are correctly assembled with your own hands sometimes turn out to be not only better, but also cheaper than “factory” competitors.

Worth knowing: Most treasure hunters and local historians, in order to save money, try to choose the cheapest options. As a result, they either assemble metal detectors themselves or purchase homemade custom devices.

Beginners, as well as people who do not understand electronics, are at first intimidated by the abundance of not only special terminology, but also various formulas and circuits. However, if you delve a little deeper, everything immediately becomes clear, even with the knowledge gained in school physics lessons.

Therefore, it is worth, first of all, to understand the principle of operation of a metal detector, what it is and how you can assemble it yourself at home.

How does it work

The operating principle of this device is to use an electromagnetic field. It is created by the transmitter coil and after a collision with an object that conducts current (and this is most metals), eddy currents are created that introduce distortion into the EPM of the coil.

In cases where the object is not electrically conductive, but has its own magnetic field, the interference it creates will also be captured due to shielding.

After this, changes in the electromagnetic field are sent directly to the control unit, which emits a special sound signal to notify that a person has been found, and in more expensive models displays data on the display.

It is worth examining how such devices are created following the example of a “Pirate” type metal detector.

Metal detector "Pirate"

Making a printed circuit board with your own hands

First you need to create a printed circuit board, where all the nodes of the metal detector will be located in the future. The best method is laser-iron technology or simply LUT.

To do this, it will be necessary to perform the manufacturing steps in the following sequence:

1. First, using only a laser printer, you need to print the corresponding diagram created through the Sprint-Layout program. It is best to use light weight photo paper for this.
2. We prepare the PCB workpiece, first sand it, and then clean it with a solution. It should have dimensions 84x31.
3. Now on top of the blank we place photo paper with the diagram on the front side on which it was printed. Cover with an A4 sheet and begin ironing with a hot iron in order to transfer the marking scheme to the textolite.
4. After fixing the circuit from the toner, we place it all in water, where we carefully remove the paper with our fingers.
5. Next, if there are smeared areas, we correct them using a regular needle.
6. Now the board needs to be placed in a solution of copper sulfate for several hours (ferric chloride can also be used).
7. The toner can be removed without any problems with any solvent, such as acetone.
8. We drill holes for later placement of structural elements (the drill must be very thin).
9. The last stage is to lay out the board tracks. To do this, a special solution “LTI-120” is smeared on the surface, which needs to be spread over the solder of the soldering iron.

Installing elements on the board

This stage of creating a metal detector consists of installing all the elements on the created board:

1. The main microcircuit is the domestic KR1006VI1 or its foreign analogue NE555. Please note that before installation, a jumper must be soldered underneath it.
2. Next, a two-channel amplifier K157UD2 is installed. You can buy it or take it from Soviet tape recorders.
3. After this, 2 SMD capacitors are mounted, as well as one resistor of the MLT C2-23 type.
4. Now you need to solder two transistors. One should be NPN structure, and the other PNP. It is advisable to use BC557 and BC547. However, analogues will also work. It is recommended to use IRF-740 or other options with similar characteristics as a field-effect transistor.
5. The capacitors are installed last. They should be taken with a minimum TKE indicator, which will increase the thermal stability of the entire structure.

Note: The hardest thing will be to get the K157UD2 amplifier out of this circuit. The reason is that it is already an old chip. That is why you can try to find similar modern options with similar parameters.

The creation of a homemade coil is made on a frame with a diameter of 20 cm. The total number of turns should be approximately 25 pieces. This indicator is based on the fact that PEV wire is used, which has a diameter of 0.5 mm.

However, there is a certain peculiarity. The total number of turns can be changed up or down. To find the most optimal option, you need to take a coin and check in which case there will be the longest distance to “catch” it.

Other elements

A signal speaker can be used taken from a portable radio. It is important that it has a resistance of 8 ohms (Chinese options can be used).

To carry out the adjustment, you will need two potentiometer models of different power: the first is 10 kOhm, and the second is 100 kOhm. To minimize the influence of interference (it will be difficult to eliminate it completely), it is recommended to use a shielded wire that will connect the circuit and the coil. The metal detector's power source must be at least 12 V.

When the entire structure has been tested for functionality, it is necessary to make a frame for the future metal detector. However, here we can only give some recommendations, because everyone will create it from the items at hand:

• to make the bar more convenient, it is worth purchasing 5 meters of ordinary PVC pipe (which are used in plumbing), as well as several jumpers. It is worth installing a special palm rest at its upper end to make it more comfortable to hold. For the board, you can find any box of the appropriate size that needs to be mounted on the rod;
• To power the system, you can use a battery from a regular screwdriver. Its advantages are low weight and high capacity;
• When creating the body and structure, keep in mind that there should not be any unnecessary metal elements in them. The reason is that they significantly distort the resulting electromagnetic field of the future device.

Checking the metal detector

First of all, you need to adjust the sensitivity using potentiometers. The threshold will be a uniform, but not very frequent, crackling.

So, he will have to “find” a five-ruble coin from a distance of approximately 30 cm, but if the coin is the size of a Soviet ruble, then from about 40 cm. He will “see” large and voluminous metal from a distance of more than a meter.

Such a device will not be able to search for small objects at significant depths. In addition, he will not be able to distinguish between the size and type of metal found. That is why, while searching for coins, you may come across ordinary nails.

This model of homemade metal detector is suitable for people who are just starting to learn the basics of treasure hunting or do not have the necessary funds to purchase an expensive device.

Their this video You will learn how to make a homemade metal detector:

Now, perhaps, there is no person who does not know what a metal detector or metal detector is. But let us remind you once again that this is a device that allows you to determine the hidden location of metals. The metal detector is very popular among amateur archaeologists and treasure hunters. The device is quite expensive, and some models are even sky-high, which is why most radio amateurs prefer to assemble it themselves. In today's article we will look at how to make a metal detector with your own hands, the principle of operation of the device, popular circuits, as well as assembly and configuration features.

Read in the article

How does a metal detector work?

A metal detector, or metal detector, is an electronic device consisting of a primary sensor (coil with winding) and a secondary unit. Metal detection devices are divided into several types:

1. "reception and transmission";
2. induction;
3. pulse;
4. generator

Devices in the mid-price category are mainly of the “receive-transmit” type. 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 first coil transmits electromagnetic waves that freely pass through a neutral medium and which, when colliding with metal objects, are reflected and transmitted to the receiving device. After the reflected signal hits the second coil, the operator is informed by a buzzer that the target has been found.

An induction-type metal detector operates on the same principle as transmit-receive devices. The main difference between them is the number of coils with winding. An induction metal detector has one coil that sends and receives a signal simultaneously. Pulse devices are insensitive to the concentration of salts in the soil and include in their design a coil, the electromagnetic field of which creates eddy currents on the metal surface that are captured by the detector. This principle of operation reduces the possibility of discrimination, which can complicate the search.

Generator-type metal detectors come in different types, but they are all built on the basis of an LC generator. They have a low level of sensitivity and are generally designed to find only one type of metal. Metal detectors can also be divided into three categories:

1. common use;
2. middle class;
3. professional equipment.

Functional and technical parameters of metal detectors

Before choosing and buying a good metal detector, you should clearly decide in what environment the search work will be carried out. It is also necessary to take into account the expected size of the objects being sought and the depth of their location. Let's look at the main characteristics that you need to pay special attention to when purchasing a detector:

• operating principle;
• operating frequency of the device;
• sensitivity;
• ground balancing;
• target designation;
• discriminator;
• additional functions.

The operating principle and operating frequency of the detector are the main characteristics that determine the capabilities of the device and show which category it can be classified into (simple ground, middle class or professional). Sensitivity determines the depth of objects with which the device can operate. As a rule, this figure ranges from 100−150 mm to 600−1500 mm. However, there are depth models designed to search for objects at a depth of 5 meters. The discriminator makes it possible to configure the device to search for a specific type of metal. This prevents the operator from being distracted by metallized debris.

What types of metal detectors can you make yourself?

You can purchase a detector at a specialized store or make a metal detector with your own hands at home. There are schemes that even a novice radio amateur can do. Devices that you can assemble yourself include:

• "butterfly";
• device without microcircuits (IC);
• model "Pirate";
• "Terminator 3" etc.

There is information on the Internet that you can supposedly assemble a metal detector from your phone with your own hands. Remember two words - this is fiction. There are some applications that allow you to include a tablet or smartphone in the detector circuit, but it is impossible to make a full-fledged device for searching for metals and recognizing them.

How to assemble a “Pirate” metal detector with your own hands: detailed instructions

Models of the “Pirate” series cost about $100–300. This cost is due to the device’s ability to detect objects at a depth of 200 mm (for small items) and 1500 mm (large items). Let's look at the features of assembling and setting up a device for detecting metals, as well as its components.

Materials needed to assemble a powerful metal detector with your own hands

To make a metal detector you will need the following materials and components:

• IC KR 1006VI1 or NE 555 (foreign equivalent) to create a transmitting unit;
• transistor IRF 740;
• IC K 157UD2 and transistor BC 547 for assembling the receiving unit;
• NPN type transistors;
• PEV 0.5 wire to create a coil;
• materials for the manufacture of the body, rod, etc.;
• a plate covered with copper sheet for making a printed circuit board;
• wires;
• insulating tape;
• side cutters;
• soldering iron;
• scalpel;
• Screwdriver Set;
• pliers;
• various types of fasteners.

Assembling a metal detector with your own hands: diagrams

Currently, there are many circuits for the “Pirate” metal detector, since some radio amateurs have begun to modernize them to suit their needs. All options will not be considered, only the most proven and most popular.

NE555 detector circuit

The classic circuit of a metal detector of the “Pirate” series, built on the NE555 IC timer. 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.

DIY metal detector assembly without microcircuits

Unlike the previous circuit, this device uses Soviet-style transistors KT-361 and KT-315 to generate signals (you can use similar radio components).

DIY printed circuit board

The parts have been purchased, the diagram is available, and now you need to assemble it all. To place radio components, a printed circuit is used, which can be easily made independently. To do this, you will need a piece of sheet getinax covered with copper electrical foil. Transfer the selected diagram to the workpiece, mark the tracks connecting the parts, and drill holes in the places where they are attached and soldered. Cover the tracks with protective varnish, and after drying, lower the future board into ferric chloride for etching (removing unprotected areas of copper foil).

After the board is ready, you can install and solder the radio components. The next step is to check the circuit using measuring instruments.

Metal detector coil - how to make it yourself

Due to the fact that the Pirate metal detector is a pulse-type device, accuracy when assembling the coil is not important. For the base you will need a ring with a diameter of about 200 mm, onto which you need to wind 25 turns of 0.5 mm PEV wire. 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. Next, the mandrel with the wire must be well wrapped with insulating tape.

Place the finished coil in a housing made of dielectric material. To do this, you can use suitable-sized cases from faulty “throw away” household appliances. By the way, this will protect the coil from mechanical damage while working with the detector. The winding terminals must be soldered to a stranded wire with a diameter in the range of 0.5-0.7 mm. It is best to use twisted pair cable.

Checking and setting up the metal detector

We attach all the components of the device to the metal detector rod: the body with the coil, the receiving and transmitting unit and the handle. If the control circuit is assembled correctly, then adjustment of the device will not be required, since it initially has maximum sensitivity. Fine tuning is 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.

The video shows how to set up a metal detector.

How to make an underwater metal detector with your own hands

Sometimes search work has to be moved from land to water. What to do in this case, because the electronics will fail? There are, of course, special devices for working underwater, but you can make a deep metal detector with your own hands. To do this, you can take the most ordinary homemade detector and place all the components in hermetically sealed housings. In addition, it is worth slightly modifying the device and installing light indicators instead of an audible alarm.

How to make a Terminator 3 metal detector with your own hands: detailed instructions

The Terminator 3 model has long been popular among radio amateurs, and over the many years of its existence the device has received many improvements. We offer step-by-step instructions on how to make a metal detector yourself at home. The device has low power consumption, can be configured to search for certain types of metal, and has good depth characteristics.

Tools

Before making a homemade metal detector, you need to prepare the following tools:

• soldering iron or soldering station;
• solder, tin, rosin;
• pliers, round nose pliers, side cutters;
• Screwdriver Set;
• hacksaw for metal;
• oscillography and other instrumentation.

Diagram, selection of parts and circuit board

To manufacture the control unit, it is necessary to make a circuit board on which all the necessary radio components will be placed. The circuit presented below must be transferred to a getinax plate coated with copper foil and a circuit board must be made in the same way as described above in the article for the Pirate metal detector. The size of the circuit should be within 104x66 mm, and the board blank should be 10 mm larger on each side.

We will describe in detail how to prepare a printed circuit board for a metal detector in step-by-step instructions:

Illustration	Process description
	We take a textolite plate coated with copper foil. We degrease chemically or mechanically (sand).
	We apply the diagram to the plate, cover the tracks with a protective varnish and subject the workpiece to etching (described above, as for the “Pirate” metal detector). Using a thin drill, drill holes for radio components and fastenings to the body.
	We place the radio components in accordance with the diagram and carry out the wiring.
	This is what the finished Terminator 3 metal detector board will look like.

Metal detector coil

This is, in fact, the most sensitive part of the device. She is responsible for scanning the space underground. Let's look at the steps to create a simple coil for a metal detector:

Illustration	Process description
	On a piece of plywood we draw two circles corresponding to the diameters of the coils - internal and external. We drive nails around the perimeter of the circle. The diameter of the outer winding TX should be within 200mm. The coil is made from two folded wires. We wind 30 turns on the nails.
	We tie the winding around the circumference with threads. We take out the nails, cover the resulting coil with varnish, and after it dries, wrap it with electrical tape and foil. In exactly the same way we make the internal winding RX, which is half the size of TX and contains 48 turns of wire.
	We place the coils in the housing and wire the wires that will be connected to the control unit.
	This is what the finished metal detector frame will look like.

Homemade metal detector: detailed description of assembly diagram and setup

We discussed in detail the stages of assembling the board and the main elements of the metal detector earlier, now we are faced with the very last and most important steps: assembling the case and setting up the device.

Illustration	Process description
	We take a suitable box or make the case ourselves. We drill holes for trimming resistors and a connector. We mount the finished board and regulators in the case.
	We close the case, connect the metal detector frame and attach everything to a plastic pipe with a handle. The metal detector is assembled and ready for use.

This video will help you set up your metal detector.

Features of a DIY metal detector with a metal discrimination circuit

Metal detectors with a simple circuit allow you to detect hidden objects, but in order to find out which ones you will have to work with a shovel. Instead of a gold coin or a military helmet, you can find just a piece of pipe and spend a lot of time on it. To make the task easier for search engines, detectors began to be equipped with discriminators that make it possible to distinguish the type of metal and allow various types of debris to pass through. The simplest methods for determining the types of metals were implemented in old instruments 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.

Professional metal detectors use discriminators with range selection. The microprocessor systems used in such devices make it possible to program the device to respond only to certain groups of metals. Discrimination is useful in littered areas, but reduces detection depth by 10−20%.

Assembly features of a deep metal detector

A deep-type metal detector is a special device capable of detecting objects hidden at a great distance from the surface of the earth. It is at considerable depth that the most interesting and valuable objects can be found. Some models can detect metals at a distance of 4 to 6 m underground.

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. Thus, the search speeds up, but has a negative impact on performance. The second version of the detector works in a small area, but better determines the center of the target. With such a device it is good to search in grass, forest or reeds. Therefore, when choosing the type of metal detector, you need to determine the conditions under which scanning will be carried out.

If you have experience assembling a metal detector yourself, tell others about it! If you have questions for the author of the article, ask him in the comments.

The smell of travel, the aroma of adventure, or the prosaic ridding of your summer cottage from various metal debris may suggest the idea of ​​purchasing a special device. Professional metal detectors, reviews of which are known to everyone, are quite expensive. But they meet all the requirements of real professional diggers. You need to choose. Reviews will help you understand this difficult matter. Or you can make this device yourself.

Where are metal detectors used?

In addition to searching for real treasures and surveying private land plots for soil purification, metal detectors are used in various areas:

• to locate cables and pipelines;
• to assist in archaeological excavations;
• in civil engineering and forensics;
• in the sapper troops.

Sports treasure hunting

One type of active hobby - sports treasure hunting - is becoming increasingly popular among enterprising and enthusiastic people. What's interesting about this case?

• The element of the unknown is always exciting. How to make a metal detector at home? What lies beneath the surface of the earth? Until you get it and try it, you won’t know.
• Whose device will “look” deeper under the ground? Who can better determine the quality of a metal trinket that has lain in obscurity for many years?
• And if this piece of hardware also has value, that’s the extent of the joy of the inventor, who independently figured out how to make a metal detector at home from improvised materials.
• At rallies and competitions, of course, coins are buried specifically to determine the capabilities of homemade and factory detectors.

What is the operating principle of metal detectors based on?

Any metal detectors operate based on the principles of “Foucault currents” known from the school curriculum. We will not go into details of the experiments. When the search coil and a metal object come closer, a change in frequency occurs in the generator, which the device reports. If a squeak is heard in the headphones, it means that there is something metal lying underground.

Modern inventors work on two problems:

• increasing search depth;
• improvement of identification parameters of devices;
• reduction of energy costs;
• convenient operating characteristics.

What do you need to stock up on to make a detector?

How to make a metal detector at home? It’s worth getting a little acquainted with electronics and reading physics for the 7th grade of high school. Experience with some tools and available materials will be useful. It is necessary to study and test a number of electrical circuits in order to choose the one that will really work. Materials you will need for work:

• small generator (from an old tape recorder);
• film capacitors and resistors;
• vinyl or wooden ring for the search coil;
• plastic, bamboo or wooden cane holder;
• aluminium foil;
• wires for coil winding;
• piezoelectric emitter;
• metal box - screen;
• headphones for receiving sound signals from the device;
• two identical transformer coils;
• 2 Krona batteries;
• perseverance and patience.

Assembly sequence of a search metal detector

A search coil is made from a plywood circle with a diameter of 15 cm: the wire is wound in turns (15-20) onto a template. The stripped ends are soldered to the connecting cable. A layer of thread is wound around the perimeter of the coil over the wire for fastening.

All parts of the circuit are soldered onto PCB in the following order: capacitors, resistor system, quartz filter, signal amplifier, transistor, diodes, search generator. A soldered board is inserted into the prepared case, connected to the search coil and mounted on a holder stick.

The signal from the search coil reflected by a metal object increases the frequency of the generator. When amplified, it is converted by an amplitude detector into a constant pulse, which produces sound.

How to dig up asphalt and go off the beaten path?

Not all those who are wondering how to make a metal detector at home think about the fact that the earth is an electrical conductor. However, this very fact can greatly influence search performance. "AKA" metal detectors, in which the creators mathematically calculated and minimized the influence of the Earth's electromagnetic field, process the entire wave flow. In addition, the signal reflected from the object is sent to the monitor of the device. The device shows a certain image by which you can determine what kind of piece of iron lies under the soil layer:

• or is it a pile of coins;
• maybe it's an ancient nail;
• mine or fragment;
• helmet or ;
• single metal object.

A smart detector reports the depth of an object. Patented technology for averaged visualization of search objects allows you to decide whether to dig in a given location. The device has a convenient design and is easy to prepare for use.

The most enthusiastic inventors love to do everything themselves. Some even complicate the process for themselves and figure out how to make a simple metal detector at home. And it doesn’t matter that he can only find an old button at a depth of 5-6 cm from the surface. But how much pride the creator gets from the process itself!

Have all the treasures been dug up yet?

And maps with legendary treasures captivate not only treasure-hungry seekers. Historians, researchers and archaeologists have been searching for years for what Napoleon took from Moscow. And what about the wealth looted by Stenka Razin? Where are they lying, who are they waiting for? Have pirate treasures already been found on the Caribbean islands?

From some sources it is known that the Ataman’s prey is quietly waiting for the lucky ones on one of the islands of the Caspian Sea. And the gold taken out by Napoleon, it turns out, was recaptured and hidden by the Cossacks. And they drove the French to Paris. But only one returned, and even then he could not recognize the area. While he was waiting for winter, he fell ill and died. Since those times, a sheet of paper with a plan has remained in one of the archives, on which the designations of all the chests and ten barrels of gold are marked.

Russia is not Europe, and there were no banks in the old days. Where they could, they hid wealth there from spiteful critics and robbers. So, even if the find isn’t such a big one, but a smaller one, it’s still nice. How to make a metal detector at home? If you really want it, you just need to try.

As a favorite character said in one famous film, we will search!

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, the metal detector circuit consists of an electromagnetic vibration transmitter, a transmitting coil, a receiving coil, a receiver, a useful signal extraction circuit (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

Common parameters

The operating principle of a metal detector can be implemented technically in different ways, depending on 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 metal search 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 built 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 allow achieving the best efficiency in their frequency range, but are complex in circuit design and 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 highlight the weak secondary signal against the background of the 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 signals with frequencies of 1 MHz and 1,000,500 Hz or 1.0005 MHz are applied to the inputs of a special device - a mixer, and headphones or a speaker are connected to the output of the mixer, 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 a computer program cannot provide for all practical cases. Therefore, in Fig. an old, decades-tested nomogram for calculating multilayer coils is given; a thin coil is a special case of a multilayer coil.

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. on 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 volumetric, but electrically a volumetric “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 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 tone of the sound 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 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 searching 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. on 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 to be piezoelectric (crystalline), 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 PE 0.25 wire, and a 70 mm coil contains 290 turns.

Metal detector “Butterfly”, see fig. on the right, in 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 precisely 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 setup itself 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 QP1 receiver amplifier 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 (SV, 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. on 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.
10 ratings, average: 4,90 out of 5)

This is what keeps a person from purchasing metal detectors, which cost a lot of money, but do not guarantee that anything will be found or not.

On the other hand, if you got such a device practically for nothing, then you wouldn’t have to walk through the forests in search of mythical treasures. Even on a personal plot, it is possible to dig up several meters of pipe or abandoned cable, which, when delivered to a collection point, can bring money. But, as you know, they are never superfluous.

In this case, you need to figure out whether it is possible to make a metal detector from a radio or disks with your own hands without the use of microcircuits, how complicated this process is and whether it requires any specific knowledge, whether the circuits of simple metal detectors are complex, what is required for this, and what is the algorithm for such work.

What is a metal detector

Such a device, homemade or made in a factory, is designed to search for any metal under a layer of soil, regardless of whether it is pieces of iron, copper or something even more valuable. Such devices are used not only by gold miners, but also by various archaeological groups, patriotic communities (in search of remains and objects left in the ground after the Second World War) and even sappers when demining territories.

The shapes, as well as the circuits of metal detectors, are different. This could be a disk mounted on a handle, or it could be some kind of microphone. The essence of this device does not change from this - when any metal object is detected at a shallow depth, it emits a certain sound using a buzzer built into it, signaling the discovery.

Such devices operate on the basis of the physical law according to which electromagnetic induction operates. Its components are a transmitter, which, upon receiving a signal, sends it to a warning device (audio or visual), the signal receiver itself and a buzzer or screen. Electromagnetic waves are sent to the surface and reflected. If the transmitted signal returns unchanged, nothing happens in the circuit, but provided that any metal enters the signal transmission area, the returned wave turns out to be distorted and this is recorded by the transmitter, which gives an audio or visual alert.

Operating frequencies

A metal detector combines complex parameters that are sometimes mutually exclusive. For example, if you lower the frequency generated by the generator, you can achieve a greater search depth, but this will increase energy consumption, and also reduce sensitivity, as well as mobility due to the increase in the coil. But basically all the parameters, one way or another, are tied to the frequency of the generator, and therefore such devices are classified precisely according to the parameter of operating frequency ranges.

VLF

The circuit of a simple metal detector that operates in the range from approximately 100 to 500-600 Hertz is called ultra-low frequency. Such devices are amateur, with a power of no more than a hundred watts. Such devices are weak and it is almost impossible to recognize the signal without the use of computer processing.

LF

The next class of metal detectors is low-frequency. A little more powerful than the previous ones, the circuit is simple, they are resistant to interference, but the sensitivity is still quite low. With an energy consumption of more than 10 Watts, the possible search depth will be about 5 meters. Their inconvenience is also that, in addition to metal, they also react to large fragments of stone or concrete. The best signal is detected on ferrous metals, and therefore such a metal detector is also called a magnetic detector. They have low sensitivity to soil properties.

IF

Another classification is metal detectors of higher frequencies - several tens of kilohertz. They have less good noise immunity compared to LF. Convenient when performed using the pulse mode, which will be discussed a little later. The disadvantage of such devices is that with increased mineralization or in swampy areas, they completely stop receiving the changed signal, as a result of which they do not “see” metals.

HF

The most powerful metal detector, suitable for searching for precious metals, but at shallow depths. Not bad for finding gold items lost by vacationers in the sand on the beaches. The depth of penetration of the signal into the ground is no more than 80–90 cm. The results of the work depend on the power of the transmitter coil; they work with the result only on dry non-magnetic soil, which includes sand.

Pulsers

Such metal detectors are the best equipment in the line. They stand separately from other similar devices. The fact is that current flows to the coil in a pulsed mode. It is possible to set the pulse frequency in low ranges, and the duration, which determines the area of ​​the spectral composition, in high or high frequencies. Thus, you get a metal detector that combines the best qualities of all categories of detectors, or a device that can be reconfigured, depending on the required parameters.

How to make a metal detector with your own hands?

Based on the fact that the cost of such detectors is very high, it makes sense to look into the possibility of making a simple metal detector with your own hands at home. Homemade products require practically no costs, except, of course, a small amount of time.

Since the design of the metal detector is quite simple, to operate it you will need two disks (CD and DVD), headphones, a regular calculator, a 9-volt battery (“crown”), electrical tape and glue, and you assemble it practically on your knees.

So, detailed instructions for assembling a metal detector with your own hands.

To assemble a metal detector from disks, you need to adhere to the following algorithm of actions:

• The headphone plug is not required, so it is cut off and the wires are stripped to a length of about 1 cm.
• Each stripped wire is divided into two equal parts, one of which will go to the mirror part of the disk, and the second to the power element.
• Provided that the mirror surface of the disks is on both sides, one of the parts of the wire is attached to it separately using glue. If the discs are single-sided, then everything is simpler. The contact side is the writing side.
• The wires on the CDs and DVDs themselves are secured with electrical tape.
• When the calculator is turned on, it is secured with the same electrical tape between the disks, and the battery is secured to the surface of the DVD.

At this point the work is completed and the metal detector using improvised means is ready. As you can see, the process is completely uncomplicated and inexpensive, both financially and in time.

Of course, if you make a metal detector whose circuits are so simple, then its characteristics will not be comparable to professional devices, but you can find elementary structures in the ground with its help.

If you need a more powerful device than a simple metal detector, it can be made from an old radio.

Metal detector from radio

Using this method, you can make a detector that will be more powerful than a simple metal detector. To do this, you will need an empty CD case, a calculator, an AM radio, double-sided tape and electrical tape.

On the inside of the disc box, a radio is glued to double-sided tape, and on the other side - a calculator in the turned on state. The receiver sets the highest frequency in the AM range, or the one closest to it, at which there are no extraneous sounds other than noise.

You can attach any mop stick to the resulting structure. After this, all that remains is to configure the detector. To do this, you need to move the doors of the box apart or move until a sharp sound appears. After moving the doors apart, the same, barely noticeable sound is heard and the box is fixed in this position. After the work has been done, when approaching the metal, the same sound will be heard, but in a sharper sound range.

Of course, you cannot assemble a good metal detector with your own hands, but an acceptable one is quite possible.

Needed or not

Of course, if a person is not engaged in professional excavations, there is no point in purchasing such a device - it is simply throwing away a considerable amount of money. But for home use, you can assemble a simple metal detector. Of course, it won’t help you find treasures buried in the bowels of the earth, but a simple metal detector with your own hands or from a radio is quite capable of determining the location of a metal frame behind a gypsum board wall or the location of hidden wiring in the concrete floors of houses, which is already important. Well, making a metal detector at home without the use of microcircuits using a phone (the description of the work is identical to assembling a metal detector with your own hands from disks or a radio, but a phone is used instead of a calculator) is not difficult.