How to make a homemade metal detector at home. Metal detector circuit: how to make a simple and effective metal detector with your own hands

As a child, did you want to have a device that could find metal objects and even treasure? Most children want to have such a unit. Fortunately, it exists. This is a conventional metal detector that allows you to detect various metals under a layer of soil and in other places. The principle is that it finds a material that differs in its magnetic or electrical properties from the environment. It is noteworthy that you can find not only metal objects and not only in the ground.

The metal detector is used by geologists, inspection services, the military, criminologists and builders. This is a very useful thing in the household. Is it possible to make a metal detector with your own hands? Yes, and this article will help you with that.

How a metal detector works and what it consists of

In order to make such a device at home with your own hands, you need to understand the principle of its operation. How is it able to detect metal and signal it? It's all about electromagnetic induction. Metal detectors have their own scheme, consisting of:

1. Transmitter of oscillations of electromagnetic waves.
2. receiver.
3. A special signal-transmitting coil.
4. Coil that receives the signal.
5. Display devices.
6. Discriminator (scheme for extracting a useful signal).

Some working nodes can be combined schematically and constructively. For example, both the receiver and the transmitter will be able to operate on the same coil. The receiver part will immediately emit a positive signal, and so on.

Now more about the principle of operation of the metal detector. Thanks to the coil, an EMF (electromagnetic field) of a certain structure begins to be created in the medium. In the case when an object conducting electricity is within the range of this field, Foucault or eddy currents appear in it. They create their own EMF of the object. Now the original structure of the coil begins to distort. And when an object in the ground does not conduct electricity, but has ferromagnetic properties, the structure of the coil is also distorted due to shielding. Both in the first and in the second case, the metal detector captures the electromagnetic field from the object and converts it into a signal (acoustic or optical). You hear a specific sound and can see the signal on the screen.

Note! In general, for the operation of a metal detector, it is not necessary that the body conducts current, the ground does not. It is important that the magnetic and electrical properties of the bodies differ.

This is how the metal detector system works. The principle is simple and effective. Now, let's take a closer look at how to make a metal detector with your own hands. The first thing you need is to prepare all the tools and materials.

Metal Detector Components

So, if you want to make a device, then you can’t do without special devices. It's all the same electronic device, which must be assembled from different components. What will be required? The set is as follows:

You can see other components in the diagram below.

Also, you will need a plastic box to mount electronic circuit. And also prepare a plastic pipe to create a rod with a coil attached to it. Now you can get to work.

We assemble a metal detector with our own hands: creating a printed circuit board

The most difficult stage of work is electronics. Everything here is subtle and complex. Therefore, it is rational to start with the creation of a working printed circuit board. There are only a few options for different boards. It all depends on the radio elements used to create. There is a board operating on the NE555 chip and on transistors. Below you can see what these boards look like.

We assemble a metal detector with our own hands: installing electronic elements on the board

Further work will also not be easy. All electronic elements of the metal detector will have to be soldered and installed as shown in the diagram. In the photo you can see the capacitors. They are film-like and have high thermal stability. Due to them, the work of the metal detector will be much more stable. This indicator is very useful, especially in the autumn period of using the device. After all, then it is quite cool outside.

It remains to solder. We will not describe the process itself, since the soldering technology should be known to everyone. To clearly understand how to perform all the work on the electronic part of the metal detector, we suggest that you additionally familiarize yourself with this video:

We assemble a metal detector with our own hands: food

In order for the device to receive current, you need to provide a 9-12 V power source. It is worth noting that the metal detector consumes electricity quite voraciously. This is not surprising, since the device is quite powerful. If you think that one "Krona" (battery) will be enough, then it is not. It won't work for long. You will need two or even three batteries connected in parallel. Alternatively, use one powerful battery. It will be cheaper, as it can be discharged and charged for a long time.

We assemble a metal detector with our own hands: a coil

Since we are making a pulsed metal detector, accuracy and precise assembly of the coil is not required. The normal diameter of the coil will be 19-20 cm. To do this, you will have to wind 25 turns. When you have made the coil, wrap it well on top with electrical tape. To increase the depth of detection by the coil of objects, wind the diameter on the shipment about 26-27 cm. In this case, you need to reduce the number of turns to 21-23. In this case, a wire Ø 0.5 mm is used.

When you have wound the coil, it will need to be mounted on the hard case of the metal detector. It is important that there is no metal on the body. Think and look for any case that will fit in size. The body will perform a protective function. The coil will be protected from hitting the ground during the search.

To make a tap from the coil, solder two wires Ø 0.5-0.75 mm to it. It is recommended to use 2 wires twisted together.

We assemble a metal detector with our own hands: setting up the device

When assembling a metal detector according to the scheme, you do not need to configure it. It already has maximum sensitivity. To fine tune the metal detector, adjust the variable resistor R13 by twisting it a little. Do this until you hear rare clicks. In the event that this is achieved at the extreme position of the resistor, change the rating of the device R12. Such a variable resistor should set the metal detector to optimal performance in the middle position.

There is a special oscilloscope with which you can measure the gate frequency of the resistor T2. The pulse length should be 130-150 µs, and the optimal operating frequency is 120-150 Hz.

To start the search process with a metal detector, you need to turn it on and wait about 20 seconds. Then he stabilizes. Now twist resistor R13 to adjust it. That's it, you can start your search with a simple metal detector.

Summing up

Such detailed instructions will help you learn how you can make a metal detector with your own hands. It is simple but fully capable of finding metal objects. More complex models of metal detectors require more effort and time.

A device that allows you to search for metal objects located in a neutral environment, for example, the ground, due to their conductivity is called a metal detector (metal detector). This device allows you to find metal objects in various environments, including in the human body.

Largely due to the development of microelectronics, metal detectors, which are produced by many enterprises around the world, have high reliability and small overall weight characteristics.

Not so long ago, such devices could most often be seen with sappers, but now they are used by rescuers, treasure hunters, public utilities workers when searching for pipes, cables, etc. Moreover, many "treasure hunters" use metal detectors that they assemble with their own hands .

The design and principle of operation of the device

Metal detectors on the market operate on different principles. Many believe that they use the principle of pulsed echo or radar. Their difference from locators lies in the fact that the transmitted and received signals operate constantly and simultaneously, in addition, they operate at the same frequencies.

Devices operating on the principle of "reception-transmission" register the signal reflected (re-radiated) from a metal object. This signal appears due to the impact on a metal object of an alternating magnetic field, which is generated by the metal detector coils. That is, the design of devices of this type provides for the presence of two coils, the first is transmitting, the second is receiving.

Devices of this class have the following advantages:

• simplicity of design;
• great ability to detect metallic materials.

At the same time, metal detectors of this class have certain disadvantages:

• metal detectors can be sensitive to the composition of the soil in which they search for metal objects.
• technological difficulties in the production of the product.

In other words, devices of this type must be configured by hand before operation.

Other devices are sometimes referred to as a beat detector. This name comes from the distant past, more precisely from the time when superheterodyne receivers were widely used. Beating is a phenomenon that becomes noticeable when two signals with close frequencies and equal amplitudes are summed. The beating consists in pulsing the amplitude of the summed signal.

The pulse frequency of the signal is equal to the difference in the frequencies of the summed signals. By passing such a signal through a rectifier, it is also called a detector, the so-called difference frequency is isolated.

Such a scheme was used for a long time, but today, it is not used. They were replaced by synchronous detectors, but the term remained in use.

The beat metal detector works using the following principle - it registers the frequency difference from two generator coils. One frequency is stable, the second contains an inductor.

The device is set up by hand so that the generated frequencies match or at least are close. As soon as metal enters the coverage area, the set parameters change and the frequency changes. Frequency difference can be registered different ways ranging from headphones to digital methods.

Devices of this class are characterized by a simple sensor design, low sensitivity to the mineral composition of the soil.

But besides this, during their operation it is necessary to take into account the fact that they have high energy consumption.

Typical design

The structure of the metal detector includes the following components:

1. The coil is a box-type design, it houses the receiver and transmitter of the signal. Most often, the coil has an elliptical shape and polymers are used for its manufacture. A wire is connected to it, connecting it to the control unit. This wire transmits the signal from the receiver to the control unit. The transmitter generates a signal when metal is detected, which is transmitted to the receiver. The coil is installed on the lower rod.
2. The metal part on which the coil is fixed and its angle of inclination is adjusted is called the lower rod. Thanks to this solution, a more thorough examination of the surface occurs. There are models in which the lower part can adjust the height of the metal detector and provides a telescopic connection with the rod, which is called the middle one.
3. The middle shaft is the node located between the lower and upper shafts. Fixing devices are fixed on it, allowing you to adjust the size of the device. on the market you can find models that consist of two rods.
4. The top bar usually has curved look. It resembles the letter S. This form is considered optimal for fixing it on the hand. An armrest, a control unit and a handle are installed on it. The armrest and handle are made of polymeric materials.
5. The metal detector control unit is required to process the data received from the coil. After the signal is converted, it is sent to headphones or other means of indication. In addition, the control unit is designed to adjust the operating mode of the device. The wire from the coil is connected using a quick-release device.

All devices included in the metal detector are waterproof.

This is the relative simplicity of the design and allows you to make metal detectors with your own hands.

Varieties of metal detectors

The market offers a wide range of metal detectors used in many areas. Below is a list that shows some of the varieties of these devices:

Most modern metal detectors can find metal objects at a depth of up to 2.5 m, special deep products can detect a product at a depth of up to 6 meters.

Operating frequency

The second parameter is the frequency of operation. The whole point is that low frequencies allow the metal detector to see to a fairly large depth, but they are not able to see fine details. High frequencies allow you to notice small objects, but do not allow viewing the ground to a great depth.

The simplest (budget) models operate at one frequency, models that are classified as average price levels use 2 or more frequencies in operation. There are models that use 28 frequencies when searching.

Modern metal detectors are equipped with such a function as metal discrimination. It allows you to distinguish the type of material located at depth. In this case, when ferrous metal is detected, one sound will sound in the searcher's headphones, and another when non-ferrous metal is detected.

Such devices are referred to as pulse-balanced. They use frequencies from 8 to 15 kHz in their work. Batteries of 9 - 12 V are used as a source.

Devices of this class are able to detect a gold object at a depth of several tens of centimeters, and ferrous metal products at a depth of about 1 meter or more.

But, of course, these parameters depend on the device model.

How to assemble a homemade metal detector with your own hands

There are many models of devices on the market for searching for metal in the ground, walls, etc. Despite its external complexity, making a metal detector with your own hands is not so difficult and almost anyone can do it. As noted above, any metal detector consists of the following key components - a coil, a decoder and a power supply signaling device.

To assemble such a metal detector with your own hands, you need the following set of elements:

• controller;
• resonator;
• capacitors of various types, including film ones;
• resistors;
• sound emitter;
• Voltage regulator.

The simplest do-it-yourself metal detector

The metal detector circuit is not complicated, and you can find it either in the vastness of the global network, or in specialized literature. Above is a list of radio elements that are useful for assembling a metal detector with your own hands at home. A simple metal detector can be assembled with your own hands using a soldering iron or another available method. The main thing at the same time, the parts should not touch the body of the device. To ensure work assembled metal detector use power supplies of 9 - 12 volts.

To wind the coil, a wire with a cross-sectional diameter of 0.3 mm is used, of course, this will depend on the selected circuit. By the way, the wound coil must be protected from the effects of extraneous radiation. To do this, it is screened with your own hands using ordinary food foil.

To flash the controller, use special programs which can also be found on the Internet.

Metal detector without chips

If a novice "treasure hunter" has no desire to get involved with microcircuits, there are schemes without them.

There are more simple circuits based on the use of traditional transistors. Such a device can find metal at a depth of several tens of centimeters.

Deep metal detectors are used to search for metals at great depths. But it is worth noting that they are not cheap and therefore it is quite possible to assemble it with your own hands. But before you start making it, you need to understand how a typical circuit works.

The scheme of a deep metal detector is not the simplest and there are several options for its execution. Before assembling it, it is necessary to prepare the following set of parts and elements:

• capacitors of various types - film, ceramic, etc .;
• resistors of different ratings;
• semiconductors - transistors and diodes.

Nominal parameters, quantity depend on the selected circuit diagram device. To assemble the above elements, you will need a soldering iron, a set of tools (screwdriver, pliers, wire cutters, etc.), material for making the board.

The process of assembling a deep metal detector is approximately as follows. First, a control unit is assembled, the basis of which is a printed circuit board. It is made from textolite. Then the assembly scheme is transferred directly to the surface of the finished board. After the drawing has been transferred, the board must be etched. To do this, use a solution that includes hydrogen peroxide, salt, electrolyte.

After the board is etched, holes must be made in it to install the circuit components. After the board has been tinned. The most important step is coming. Do-it-yourself installation and soldering of parts on a prepared board.

To wind the coil with your own hands, use a wire of the PEV brand with a diameter of 0.5 mm. The number of turns and the diameter of the coil depend on the chosen scheme of the deep metal detector.

A little about smartphones

There is an opinion that it is quite possible to make a metal detector from a smartphone. This is not true! Yes, there are applications that install under the Android OS.

But in fact, after installing such an application, he will really be able to find metal objects, but only pre-magnetized ones. He will not be able to search and, moreover, discriminate against metals.

Metal detectors or metal detectors are a diverse family of measuring instruments whose operation is based on differences in the electromagnetic radiation of objects.

Using a metal detector

Professional highly sensitive metal detectors are used in the daily work of various checkpoints, they are used to conduct search and inquiry activities of police and rescue services.

A huge army of amateur treasure hunters around the world practice long and leisurely trips with metal detectors. Sometimes such entertainment brings income and even fame.

In our time, the industry of detector (recognizing) devices for all occasions has already been established, differing not only in the principles of operation, but also in a wide range of prices and technical characteristics.

Simple magnetic detectors

The principle of operation of the simplest metal detector is based on electromagnetic induction - the device contains an electromagnetic coil, which, due to vibrations and distortions of its field, detects nearby electrically conductive and iron-magnetic materials, while creating an audible or visual signal.

The first experience of assembling a metal detector at home can be the beginning of a serious hobby: new design solutions and even inventions in this field of applied radio electronics are not excluded even at an amateur level.

The diagram shows the structure of the simplest low-frequency magnetic detector.

Hundreds of different developments are used in the production of metal detectors. In order to implement one of them on your own, you will need to make printed circuit board with your own hands, purchase the necessary coils, transistors, resistors, capacitors, etc., and assemble the device.

Metal detector from improvised means

Another option is to assemble a metal detector from improvised means, more suitable for humanitarians and novice techies with a passion for finding treasures and lost artifacts.

During the operation of such homemade device electromagnetic waves emitted by the calculator are caught on the AM band of the receiver.

The indicator of the presence of an object in this device is the rotation of the electromagnetic field during re-emission, which changes the parameters sound signal. A photo of such a do-it-yourself metal detector can be found on the Internet and at the end of our material.

To use such a prefabricated option, you need not detailed diagram or assembly instructions, and compliance with certain requirements for the two main constituent parts a home-made detector, namely, a properly working calculator and a radio receiver.

Both devices must be from the category of the cheapest, the receiver must have an AM band and a magnetic antenna, and the calculator must emit impulse radio interference during operation.

To work on the model, you will also need a suitable plastic box with an opening lid, like a book, which will become the body of the finder.

For these purposes, an old CD box is ideal. You will need double-sided tape to attach the parts.

Assembling a metal detector

• Fixing devices inside the case: a strip of adhesive tape is attached to the back side of the devices, then the calculator is placed at the base of the box, the receiver is on the inside of the cover.
• Receiver setup: you need to turn on the receiver at maximum sound and select the upper position of the AM band, free from broadcasting radio stations and interference.
• Tuning the calculator: when the calculator is turned on, the receiver should react with a sharp noise with a hum or wheeze, if this is not the case, you need to adjust the range.
• Fixing the position: we begin to smoothly close the box until the sound disappears or becomes more uniform and fix the box doors in this position using a foam cube, rubber bands, etc.
• The metal detector is ready. If there is a product with electromagnetic radiation nearby, the receiver will beep.

By combining the elements of other radio devices in the simplest detector, it will be possible to observe the principle of operation of metal detectors in action and enjoy your first search expedition.

Note!

Such a detector, assembled at home, can be tested on the search for coins or metal construction debris lying in the surface layer of the earth in almost any area, on any open ground.

DIY metal detector photo

Note!

Note!

If you need to find objects whose properties differ from those that are usually present in the soil, use a metal detector (metal detector). The principle of operation of such devices is based on determining the differences in the magnetic field of the solenoid, which is located in the area of ​​the anomalous object.

If desired, it is easy to purchase an inexpensive metal analyzer. Anyone who can hold a soldering iron and a screwdriver will be able to make a metal detector with their own hands.

Why do you need a metal detector?

Many believe that such tools are needed only to search for metals (coins, weapons, household items at the battlefields), explosives where mines could be installed. In fact, the range of use of such funds is much wider. They are used when screening passengers at airports, geologists are looking for ore deposits, doctors determine the presence of steel or alloys in the human body. When laying highways inside settlements, the location of pipelines with water, gas or sewage is specified.

The metal detector is in demand among amateurs who want to search outside their own home:

• treasure hunters can be seen in places where old buildings are being demolished. There are possible items and cash set aside for a rainy day. Almost every week there are reports about the finds of certain treasures, in which there are coins and jewelry;
• search engines on the sites of past battles are looking for weapons, shells and cartridges, helmets, household items. The device helps to find random burials of combatants. According to awards and other sources, the names of the dead are determined. They are looking for relatives to inform them about the burial place of their father, grandfather, and more often great-grandfather;
• representatives of the armed forces are searching for mine-explosive objects that pose a danger to civilians. Over the past few months, more than 120 tons of dangerous substances, shells and mines have been recovered from Syrian territory. Terrible bookmarks did not work, they did not take the lives of children, women and the rest of the population who want to live a peaceful life.

Young people and middle-aged people may have the idea to search for any objects. Some are interested in the possibility of creating a metal detector that can be used not only on land, but also under water. In the coastal zone, especially near the beaches, coins, lost crosses and rings are often found.

"Metallists" (people who sell scrap metal to large quantities) are busy searching for forgotten pipes, metal structures and large deposits of unwanted metal. By renting out such items, they earn a living.

Attention! Do not despair for those who practically do not encounter electrical engineering or radio electronics. Here, options for manufacturing the simplest metal detectors will be outlined, which you can do yourself with your own hands, without resorting to the use of complex equipment. If there are certain difficulties with soldering, then the wiring can be twisted together, getting a good result.

Principle of operation

The principle of operation of the metal detector is based on the study of changes in electromagnetic induction. The design of the device includes:

• synthesizer of electromagnetic oscillations;
• oscillation amplifier;
• coil for transmitting changes in the magnetic field (metal discrimination);
• a coil for receiving information about the state of the magnetic field in the radiation zone;
• receiver with signal amplifier;
• devices for accounting for a discriminating signal or devices for indicating.

Quite often, the functions of some elements are combined in the same device:

• reception and transmission are made by one amplifier;
• the same coil is given an alternating electromagnetic field in the study area, and then receives a signal about the presence or absence of distortion.

When the magnetic field changes, the coil perceives the changed signal.
It is recorded by readings on the scale of the device or by the sound in the microphone.

A general idea of ​​how the device works can be summarized in the following sequence:

1. The coil creates an alternating magnetic field in the search area (see pos. A).
2. When an object that has any distinctive properties compared to the surroundings enters the area under study, eddy currents arise inside the coil field (they are also called Foucault currents).
3. The resulting currents create a different electromagnetic field (EMF).
4. As a result, the field itself changes in its characteristics (see pos. B).
5. All changes are registered by devices (optical or sound indicators). The signal changing operator can determine the presence of an object with ferromagnetic properties. Metals that conduct electricity are also determined.

For a metal detector, the main thing is the presence of certain differences in the current conductivity of the surrounding soil from the object present in the thickness of the earth. The device determines the difference between electrical and magnetic properties.

A few words about geoscanners

Geoscanners are special devices capable of drawing a three-dimensional picture of the state of the soil over a large area and depth. These are quite expensive devices that are used to obtain information about the presence of water sources, laid main pipelines at a considerable depth. The received information is displayed on the screen of a computer or laptop.

Such studies are carried out by special field laboratories. It is customary to call them side cartoning.

What are metal detectors?

Common parameters

The basic principle of operation, in which the magnitude of electromagnetic induction in a certain part of space is analyzed, is implemented by various technical designs. A device for searching for beach gold, including other precious materials (silver, platinum), as well as devices for searching for pipelines hidden in the depths, may look the same outwardly. But upon closer examination of the design, cardinal differences in the schemes and technical capabilities.

Starting to create your own metal detector, you need to quite clearly define the requirements that will be imposed on the device. Experts identify a number of characteristic parameters for search engines:

1. Depth of signal penetration into the soil (penetrating power). This characteristic depends on the properties inherent in the receiving coil.
2. The search area by the size of the trace of an active coil emitting an electromagnetic field.
3. The sensitivity level characterizes the ability to detect objects small in size and mass (coins, cartridge cases, bullets, crosses, small jewelry).
4. Electoral scores. For some categories of search engines, a special reaction to precious (gold or silver items) or non-ferrous metals is important. They even create special filters that let in information about the presence of objects made of similar materials in the depths.
5. Noise immunity determines the ability not to perceive the influence of power lines located near repeaters or television stations. There are other sources of interference that can degrade the performance of the search device. As practice shows, it is near the sources of electromagnetic oscillations that the most interesting objects that seekers are interested in are more often lost.
6. Small size and the ability to use small-sized energy sources for work (device mobility) are quite important characteristic. With a heavy and bulky metal detector, a person gets tired pretty quickly, labor productivity will be low. With a light and small-sized metal detector, you can overcome small obstacles while moving over rough terrain.
7. Discrimination - this parameter characterizes the ability to separate the main parameters of a find located at a certain depth by the type of the received signal. The search efficiency is increased.

Among specialists, it is customary to correlate device discrimination in terms of indicators of information displays and sound accompaniment. She must be able to determine the properties of the found object. It is customary to distinguish the components:

1. The spatial characteristic determines the features of the location of the object in the zone prospecting work. Shows the possible depth of the location.
2. Geometric characteristics give an idea of ​​the mass and possible dimensions of the find.
3. Qualitative determines the properties of the material from which the found item is made. For gold, one type of signal is desirable, and for iron-containing products, another.

Operating frequency

The presence of an alternating magnetic field created by the search device itself determines the features of the work. For example, as the frequency decreases, the depth of penetration of magnetic waves into the depth of the soil increases. You can achieve a larger width of the device. However, it is not possible to significantly reduce the frequency value. The metal detector will require a lot of energy to maintain performance. This will lead to the need to use a more massive battery. It is generally accepted that the main parameters of a metal detector depend on the operating frequency. Therefore, the classification by operating frequency is presented as:

1. Super low frequency (VLF) operate up to 100 ... 150 Hz. Such devices are classified as professional devices. It has not yet been possible to put into practice a mobile metal detector. Power consumption is measured in tens of watts (W). Similar search tools are located on vehicles. The signal is analyzed by computers.
2. Low-frequency (LF) operate in the range of 150 ... 2000 Hz. These devices are distinguished by a simple design scheme, even a novice master will be able to assemble. The design is pretty simple. It differs by a rather large penetration depth of an electromagnetic pulse (up to 4 ... 5 m). However, such devices are less sensitive. There is practically no discrimination in terms of size and composition of the material. Such metal detectors respond well to ferrous metals, which contain iron in various types of compounds. But when finding large concrete or stone structures, the search engine will also find them. Such devices are classified under the name of magneto-detectors. Such devices distinguish the properties of soils and objects in them worse.
3. Increased frequency (IF) devices use an operating range of 1700 ... 75000 Hz. The design of such metal detectors is much more complicated. Their signal penetrates to a depth of 1.0 ... 1.5 m. Relatively good noise immunity. Sensitivity is rated quite high. Discrimination is also quite high. The disadvantages of such search devices are manifested in the presence of heterogeneous rock in the soil. Unstable indicators are possible with a high standing of groundwater. Such metal detectors are used to work in a pulsed mode, which will have to come a little later.
4. High frequency (HF), sometimes professionals call such devices operating at radio frequencies (RF). In these devices, discrimination for heavy precious metals works perfectly. The search depth can reach 0.5 ... 0.8 m. They are usually not able to enlighten deeper. These metal detectors are quite demanding on the quality of the coil. Any negligence will lead to a sharp deterioration in the performance of the device.

For devices according to points 2 ... 4, low power consumption is noted. A set of AA batteries (finger type) can work continuously up to 12 hours.

feature pulse metal detectors is to work not in the constant supply of a signal of a given frequency. Periodic impulses are applied. You can set the frequency of the send and the duration of the impact. By creating such a device, you can get a device in which positive characteristics will be obtained from LF, IF and HF devices. However, such schemes require special assembly and adjustment. For novice search engines and masters, such devices can be difficult to implement. Therefore, you need to start a home-made design with simple devices.

Search Method

In practice, there are about a dozen methods for searching for objects located deep in the ground using an electromagnetic field. Unfortunately, some of them are quite complex. The proposed methods can be implemented by large enterprises, where it is possible to purchase expensive components.

For real use, devices with relatively inexpensive components and circuits are used. Even a novice master can implement them:

• parametric search method, carried out by comparing the parameters before and after;
• the transceiver is based on the use of the reflected signal, which was previously sent by the transmitting device;
• with phase accumulation, they are usually equipped with two coils;
• on beats. This method is implemented on two signals.

Without receiver (parametric devices)

The parametric method does not require a receiver. Even the pickup coil itself is missing. When searching, the inductance, which is perceived by the generating coil itself, changes. When an object with certain properties that change the inductance in the zone of influence of the electromagnetic field is found, frequency modulation occurs in the oscillations of the devices. Change:

• oscillation frequency, this change can be heard in the speaker or headphones;
• the amplitude increases, which leads to a higher volume at the audio signal detector device.

Such metal detectors are cheap. They have good noise immunity. However, the user will have to practice to be able to use such a device. Weak sensitivity limits the possibilities of use.

With receiver and transmitter

Devices that implement the principle of receiving and transmitting a signal allow you to get much better performance. With a certain complexity in manufacturing (coils must be created strictly following the description and design features).

It is customary to define devices according to the following indicators:

• metal detectors with one coil are commonly called induction. The disadvantage is the difficulty in determining the secondary signal;
• metal detectors with two coils are more difficult to set up. Here it is important to ensure the complete identity of both solenoids. But the secondary signal is defined much better than a single coil circuit can offer.

If a pulsed transceiver is implemented, then discrimination properties are more easily manifested. Based on the type of secondary signal at the beginning or end of the phase, it is easier to guess the type of metal found.

Until click (with phase accumulation)

The method is implemented in devices with phase accumulation. Structurally, it happens:

• single-coil with pulsed signaling;
• two-coil, equipped with two signal generators (each is powered by its own coil).

In the first variant, there is some delay between the emitted and perceived pulses. The operator hears a click. It corresponds to the difference between the applied pulse and the received one. When an object of interest appears in the search area, the click frequency increases. If the mass of the found object is quite large, and it is located quite close, then the clicks merge into the noise of a certain sound frequency.

Attention! Metal detectors under the general name "Pirate" are built on a similar scheme.

In the presence of a two-coil device, there is no need to create a pulsed device. Generators each work on their own solenoid. If EMF distortion occurs, then clicks also occur. Can be customized to additional receipt sounding a particular tone.

On the beaches and in places where the stay is observed a large number tourists, resort miners most often use such metal detectors. They are even made protected from fresh and sea water. Then it is possible to search for small objects in the water.

Practice shows that such devices are able to feel small earrings, having a mass of only 0.3 g at a depth of up to 40 cm.

Unfortunately, such devices do not work well in places where the soil structure is heterogeneous. Here they begin to react even to branches.

By squeak (on the beat)

The presence of two signals supplied with different frequencies makes it possible to hear not the supplied frequencies themselves, but their difference.

1. One is given a frequency 1 MHz = 1,000,000 Hz.
2. On the second frequency 1.0005 MHz = 1,000,500 Hz.
3. The user will hear a signal equal to the difference between the second and first value of the supplied frequencies - 1,000,500 - 1,000,000 = 500 Hz.

On the different types devices select their frequencies, which are used in further work.

The control system has the ability to adjust one of the frequencies, which allows you to hear sounds (beats) of different frequencies. It is even possible to reduce this difference to zero, if the equality of the supplied oscillations is ensured.

Before searching, the differences are reduced to the threshold of audibility. For some people, it is 20-25 Hz. When the metal detector is in the zone of influence of a metal object, the difference between the frequencies of the signals changes. The operator hears a different tone.

To recognize the properties of the found object, you can change the setting on the second generator. Then other sounds will be heard from interaction with the found object. Based on a number of preliminary trainings, the operator can accurately determine what is located in the thickness of the soil, what is the mass and size of the find.

It is recommended to tune to the sound "la" of the first octave, which corresponds to a frequency of 432 Hz. This tone sounds on radio stations at the moment of a short break. Practice shows that devices tuned to such a sound capture even fairly small objects, the mass of which is a few tenths of a gram.

Many "gold diggers" on the beaches use similar devices. They work more reliably in heterogeneous soils.

Influence of the coil on the performance of the installation

Among the craftsmen who make coils for their devices, there are different opinions on how this part of the metal detector should be made. Beginners often do not think about the design. They can purchase a branded product, expecting to receive only dividends from their investment. Unfortunately, even the most "cool" coil can show low performance. There must be a correspondence between the solenoid and the rest of the circuit of the device.

When developing the design of a metal detector, they try to adjust the parameters of each element to each other. Sometimes you have to select some parameters empirically. The spread in the characteristics of radio components can be very significant. We need not only rough, but also fine tuning.

What size coil do you need?

The larger the coil, the larger the area covered by its signal. There are some craftsmen who make solenoids with a diameter of 1500 mm or more. They claim that such a device allows you to cover a wide area. But you have to wear such a tool on your shoulders. If you need to move in the forest or in the plantations, such a device will not allow you to penetrate between the bushes and trees. It’s easier to run a coil placed on the bar several times with your hand.

• Ø 20…100 mm used to search for reinforcement and profiles buried in the ground;
• Ø 130…150 mm used by gold miners on beaches and in crowded places;
• Ø 200…600 mm coils are made by metalworkers who search for scrap metal in large quantities.

Monoloop as a coil

Designs are widespread, in which a monoloop is taken as a basis. For manufacturing, a long wire is used. The thickness of the winding should be 15-20 times less than the diameter of the loop used.

Users note the advantages of such a device:

• the operation of a metal detector equipped with such a receiving device is practically independent of the properties of the soil;
• the mass of such a device is relatively low, so it can be moved for a long time around the territory;
• having found metal in the depth, you can change the settings of the transmitting device to recognize the value of the find.

There are also disadvantages:

• you have to constantly make adjustments to the device settings;
• any radio equipment interferes with the work. Therefore, on the beaches, hunters for "gold" are often affected by working devices;
• for effective use it is necessary to train with different items from different materials in order to learn to recognize the desired item and start mining it.

These shortcomings do not reduce the value of such a solenoid. Novice users can take the monoloop as the basis of their first design. Make it easy. In the hands will be quite solid metal detector.

Step-by-step production of the simplest coil

In practice, many different manufacturing options are used. One of them will be one that uses modern materials: plastic pipes. They initially prevent moisture from entering the solenoid wires.

	You need to have the following materials: enameled wire with a diameter of 0.5 mm. Its length is calculated from the need to wind 25 turns on a circle Ø150 mm. 3.14 150 25 = 11775 mm. Taking into account the exit of the ends, 12 m can be taken; plastic tube with an inner diameter of 12.5 mm, its length must be at least 3.15 150 = 471 mm; tee from polypropylene pipes Ø 20 mm; fragments of a polypropylene pipe Ø 20 mm (2 pieces, 15 mm long); shielded TV wire 120 cm long.
	Before starting work, you should check how convenient it is to make a circle from a plastic tube. If there is a rigid workpiece, then during the manufacture it will be necessary to warm it up with hot water or with a hair dryer. The trial ring is folded, the type of the resulting circle is evaluated.
	A Ø6 mm hole must be drilled in the tee. Through it, wires will be inserted into the future coil. It is desirable to clean the edges from burrs.
	Additional inserts from a polypropylene pipe are carefully processed. They need to be soldered into a tee. In this case, plastic must be inserted into each fragment.
	You will have to select the length of the plastic tube to get a circle of exactly the specified diameter. If you do not adjust the dimensions, then there may not be enough wire. Trial inputs are made into fragments.
	It is checked how tightly the tubes can be inserted into each other. After the final fitting, you can warm up the joints and solder them together.
	A slight mobility when connecting will allow you to adjust the size of the future product. You have to check the resulting diameter.
	It's time to push the wire inside the plastic tube. This is the most labor intensive process.
	When the wire is in place, you can evaluate how well the work was done. You may need to tighten some screws. It is desirable that the styling looks better.
	The ends of the wire should be soldered to the shielded cable.
	The coil is ready. You should think about how to fix it on the bar.

If such a process seems complicated, then you can approach the issue of making a coil differently.

	On a sheet of oriented strand board (OSB), you need to draw the contours of the future coil.
	A circle of the required diameter is cut with a jigsaw.
	The wire is wound along the outer contour of the resulting circle.
	A rod is welded from polypropylene pipes. It is easy to attach to the coil itself.
	As a result, the metal detector acquires a marketable appearance.
	After insulating the coil, it is desirable to paint it with alkyd enamel. The layers of paint prevent moisture from entering the OSB.

How to calculate the inductance of a coil?

When designing a metal detector, it may be necessary to calculate the value of the inductance. For an accurate calculation, there is a special technique, where the main parameters are taken into account. But to quickly determine the desired value, it is easier to use a nomogram.

Nomogram for quick determination of coil inductance

• inductance L = 10 mH;
• average ring diameter D = 20 cm;
• height and thickness of the ring, l = t = 1 cm.

Using the nomogram, determine the number of turns w, which should be wound in the manufacture of the coil. The stacking density is set to k = 0.5. According to the accepted dimensions, the cross-sectional area is determined S=klt, here l is the height of the coil layers; t is the width of the layers.

By dividing the S value by the w value, the diameter d (of the winding wire) is obtained. Upon receipt of d = 0.5 ... 0.8 mm, the calculation stops. If it turned out more, then adjust the thickness and width of the ring.

Coil noise immunity

The similarity with the loop antenna determines the high activity of the coil. She is susceptible to interference from outside. To eliminate possible external influence the manufactured coil is placed inside a metal braid. They create a special screen invented by Faraday.

The presence of such a screen prevents the entry of external electromagnetic impulses.

Beginners should carefully study the design. The position of the ground contact must be strictly along the axis of symmetry. Otherwise, the search coil itself may malfunction. The end from the shield wire is connected to general scheme devices. If the symmetry requirements are neglected, then the characteristics of the solenoid will deteriorate, and the interference will finally suppress the desired signals.

The presence of the screen somewhat reduces the magnitude of the electromagnetic field. The sensitivity is somewhat reduced. It is necessary to increase the supply voltage supplied to the winding.

A shielded wire connects the coil itself to the device circuit. Then the effect of interference is minimized. The metal detector works more reliably.

The figure below shows the winding methods: a - bifilar; b - cross.

From the practice of using coils in search devices, it has been established that the usual bifilar winding is inefficient. When ferromagnets are in the thickness of the soil, the signal begins to fade. If cross winding is used, then when the object is located strictly in the center of the coil, the signal is amplified.

Therefore, some radio amateurs do not undertake to wind many turns in a cross way. They prefer to build a basket type coil. It is easier to manufacture.

Coil-basket

The disadvantages of do-it-yourselfers include the need for precise manufacture of such a device. You need a fairly strong frame. When the wires are pulled when winding, deformation is possible.

When creating a basket, the manufacturer has options:

• get a three-dimensional design;
• make a flat basket coil.

The fairly well-known metal detector "Pirate" uses a three-dimensional basket. It is easier for beginners to make a flat product. They got the name "butterfly".

Basket coil design

The calculation is carried out according to the formulas:

1. First you need to set the value of the diameter D₂. It is taken equal to the diameter of the existing mandrel minus 2 ... 4 mm.
2. The D₁ value is defined as D₁ = 0.5 D₂.
3. Calculate the number of turns according to the formula:

where L is the inductance of the coil, calculated by the formula

k - correction factor determined from the table.

Table: definition of the correction factor

D₂+D₁	k
1,2	3,31
1,5	2,98
1,8	2,72
2,0	2,58
3,0	2,07
5,0	1,57
8,0	2,23
10,0	1,03

Knowing the difference D₂ - D₁, calculate the diameter of the wire. The packing density is believed to be 0.85.

Monoloop and double loop

The designation DD indicates the use of a double loop (Double Detector). The presence of two windings can significantly increase the susceptibility of the coil. It does not analyze the new emerging signal itself. These circuits analyze the distortions that occur when metal enters the zone of action of the solenoids.

They are preliminarily balanced so that the same impulses exist in different arms. Place similar loops in parallel.

When ferrous metal hits, low sounds are generated. And if non-ferrous metal or gold is present, the operator will hear the signal change to higher frequency sounds.

All metal detectors marked with GOLD symbols use the Double Detector. It is more interesting to work with them. But it should be remembered that in loose soils such coils can squeak even from a cluster of ants.

How to fix the coil yourself?

If desired, a special frame for your coil can be ordered online. Prices vary quite widely. Therefore, many use plywood as a base.

Frame manufacturing options: a - from plywood; b - from CDs

1. It seems to many that the easiest way is to use ordinary plywood. It's easy to cut. It has sufficient strength.
   In practice, it turns out that plywood is able to absorb moisture. As a result, the performance of the device may be extremely low.
2. Best results are obtained when using CDs. Between them leave a gap of about 5 ... 7 mm. You can glue pieces of foam. Then, along the generatrix, they are wrapped with adhesive tape or insulating tape. It turns out a reliable and durable three-dimensional construction.
3. When using cellular polycarbonate with a thickness of 6 or 8 mm, a light and fairly durable frame is obtained. It is only necessary to close the cells so that moisture does not get into them. Normal will do scotch. Professionals use silicone sealant, it will reliably fill the holes at the entrance to the honeycomb. It is proved that such a frame is the most successful. It does not induce additional interference.

Several designs of metal detectors

Parametric metal detector

To search for ferrous metal and pipelines in the ground. Finding electrical wiring in the walls uses simple and reliable circuits. They are based on the MP40 transistor, the price of which today is several rubles (cheaper than taking a tram). Can be replaced with more powerful model KT361 (keep in mind that it has reverse polarity, when connecting the power, you should change the way the battery is turned on).

The simplest metal detector

This device operates at low frequency. The selection of the sound frequency is carried out by changing the capacitance of the capacitor C₁. When metal is found, the tone decreases markedly. Therefore, when initial setup they try to make a squeak like a mosquito.

When metal is in the working area of ​​the device, the operator will hear a low bass sound. Its frequency corresponds to 50 Hz. It is this current that flows in household and industrial wiring.

Pulse parametric device

Scheme of a device for searching for metals with a simple quartz filter

This design is implemented on the basis of an old transistor receiver operating on medium waves. It is used only because there is a ferrite antenna inside. It is she who sets the desired frequency of oscillation.

The whole device is powered by two AA batteries. The power consumption is quite low.

The circuit is quite simple, it is not difficult to solder it. Parts are inexpensive. A set of components will cost (domestic parts) within 200 rubles.

Many are scared off by such a design because it requires a long and thorough debugging. We have to select resistors and capacitors. Previously, such radio devices used parts with a wide range of indicators. Since then, no one has eliminated the spread.

Transceiver metal detectors

Scheme of the transceiver device

If you want to create an effective device for searching for non-ferrous and precious metals, they are guided by the use of metal detectors equipped with a transmitter and receiver.

DD coils work here, which are powered at a frequency of 2000-2500 Hz. Such devices can detect non-ferrous metal alloys at a depth of 9-11 cm. Ferrous metals weighing up to 100 g are diagnosed at a depth of about 20 cm. Large objects made of cast iron or steel can be detected at a depth of up to 60-70 cm.

Sometimes such devices are placed in hermetic shells, deep metal detectors are obtained to work underwater. Underwater metal detector expands the search for valuable items

When creating such metal detectors, the coils are wound according to special patterns.

Step-by-step technology for manufacturing and testing a metal detector

	A wire Ø 0.65 mm is being prepared. It will need a little more than 14 m. 30 turns will be laid on a diameter of 150 mm.
	A plastic bucket lid is used as a sample for drawing a circle of the desired diameter. It has the correct diameter.
	The board is a circle. It will serve as the basis for the next steps.
	To wind the wire, you need to drive in nails. Used hardware with a length of 30 mm. To obtain a high-quality circle, it is desirable to score at least 16 of them. It is possible and more.
	You can start winding the wire. One end is fixed.
	When winding, you need to try to lay the turns more tightly.
	The resulting coil should be isolated. First, wrap it with masking tape.
	Having made the first coil, the second one is made in a similar way.
	The transceiver is manufactured according to the proposed scheme.
	To receive a sound signal, you need an earpiece from your phone.

	The entire circuit of the device is assembled on one board.
	A suitable metal box is selected in which the board will be located.
	Inside there is a place not only for the board. This is where the battery is placed. Professionals try to use small-sized batteries. They can be charged. Having two or three batteries with you, you can not worry that the device will be de-energized.
	The coils are placed on a sheet cut from cellular polycarbonate.
	The bar is made of polypropylene pipes.
	For ease of use, the handle has a half ring. It is easier to manage when searching for metal objects.
	Scattering various objects, you can diagnose the health of the metal detector. Assess the detection distance for each type of metal. The device is being set up.
	You can start looking for metals in nature. You should go without haste. The coils move around, trying to cover the maximum width.
	Having found an object in the ground, you can begin to dig it out. While in places where there were fights, you should follow the rules for the safe removal of objects.
	Even small coins can be found in the depths.

Finding Simple Solutions

If there is a desire to try yourself in a new business, but the desire to create circuits has not yet come, then you can make the simplest metal detector without microcircuits and soldering.

The simplest metal detector

You will need:

1. The cheapest radio. It should be in the mid-wave range. It is usually labeled AM. In such receivers, a ferrite magnetic antenna was installed.
2. Calculator released at the end of the 20th century. They can be bought at the collapse of the old ladies.
3. A small book or just its cover. Cardboard would be preferable. She will have a certain strength.

Now you have to fiddle around a bit. Such a device is arranged very simply:

1. Cover opens.
2. On each side you need to stick double-sided tape.
3. On one side is a calculator.
4. A radio receiver is glued on the other side. It is necessary to ensure that when closed they exactly match.
5. The receiver is turned on at the highest volume. You need to find a band in which there are no radio stations. It is desirable that there are no ethereal noises.
6. The calculator turns on. When the second device is turned on, a signal will be induced in the receiver. It should respond to the inclusion of the second device. A roar or some other noise will be heard. If there is no noise, you will have to look for the range where you can hear the inclusion of the calculator.
7. You need to fold the cover until the tone becomes quieter. He may disappear altogether. This is usually observed when the devices are located at an angle of 90 ⁰.
8. Now you need to fix this position. Use rubber bands or other auxiliary material.

Now you can start searching. When bringing such a device to metal objects, noise will appear. Depending on the type of metal, different noise will be synthesized. After experimenting with iron objects, you can listen to what the reaction of non-ferrous metals and gold will be.

It remains to fix the cover on the rod and start searching for treasures.

More metal detector ideas

Very unusual designs are offered by users from the Internet. You can try them too.

Even the most serious and respectable citizens, at the word "treasure" experience a slight excitement. We literally walk through treasures, of which there are immeasurably many in our land.

But how do you look under the soil layer to know exactly where to dig?

Professional treasure hunters use expensive equipment, the purchase of which can pay off after one successful find. Archaeologists, builders, geologists, members of search societies - use the equipment provided by the organization in which they work.

But what about novice treasure hunters on a limited budget? You can make a metal detector at home with your own hands.

To understand the subject, consider the design and principle of operation of the device

Popular metal detectors work using the properties of electromagnetic induction. Main components:

• transmitter - generator of electromagnetic oscillations
• transmitting coil, receiving coil (in some models, the coils are combined for compactness)
• electromagnetic wave receiver
• decoder that separates the useful signal from the general background
• signaling device (indicator).

The generator, with the help of a transmitting coil, creates an electromagnetic field (EMF) around it with specified characteristics. The receiver scans the environment and compares the field performance with the reference. If there are no changes, nothing happens in the scheme.

• When a conductor (any metal) enters the zone of action of the field, the base EMF induces Foucault currents in it. These eddy currents create their own electromagnetic field of the object. The receiver determines the distortion of the base EMF and gives a signal to the indicator (sound or visual notification).
• If the object under test is not metallic, but has ferromagnetic properties, it shields the underlying EMF, also causing distortion.

Important! There is an erroneous opinion that the soil in which searches are made should not be electrically conductive.

This is not true. The main thing is that the electromagnetic or ferromagnetic properties of the medium and search objects should be different from each other.

That is, against the background of certain characteristics of the EMF formed by the search environment, the field of individual objects will stand out.

Varieties of metal detectors

Understanding the features of different circuits will help not only choose a ready-made detector. If you decide to assemble a metal detector for coins with your own hands, you do not need to put a detector for water pipes or fittings in concrete into it.

You should initially know what the device is for, since universal metal detectors have high cost, both when buying, and when self-assembling. In addition, the narrow-profile device is more compact and lightweight.

main parameters

1. Search depth. Determines the penetrating power for standard soils: below this band, the coil will not respond to artifacts.
2. Coverage area: the wider it is, the less time it will take to "comb". True selectivity and sensitivity is reduced.
3. Selectivity: selection of the required object from a set of objects. For example, when searching for gold jewelry on the beach, your device will not respond to steel hair clips or coins.
4. Sensitivity: the higher it is, the more likely it is to find small objects. True, in this case, the coil reacts to various debris, such as nails or hairpins.
5. Noise immunity. The detector's sensor is affected by many extraneous factors: thunderstorms, power lines, Cell phones etc. It is necessary to filter them out.
6. Autonomy: this is both energy consumption and battery charge reserve.
7. Discrimination is the ability to distinguish artifacts by type. Let's take a closer look at this option.