The simplest and most effective metal detector. How to make a metal detector from improvised materials

Today, there are many different ideas on the Internet that allow you to make a metal detector with your own hands at home. Some of them require certain skills in working with electrical appliances, soldering and understanding of simple electrical circuits, while some do not require any knowledge in these areas to create. However, there are many non-working, fake methods floating around the Internet, captivating with their simplicity and accessibility. It is very easy for an inexperienced person to fall for the bait of deceivers - to spend time and effort on making a device that is obviously not working and lose all interest in it. But don’t be discouraged, then readers of “” will be provided with an interesting and really working scheme for creating a homemade metal detector!

Idea No. 1 – Discs in action!

Surely you have already seen or heard that you can make the simplest metal detector yourself using a CD and DVD disc, as shown in the photo. The scheme is quite simple and does not require any professional tools or skills.

This instruction is the most popular due to the availability of the necessary components and the simplicity of its assembly; all you need to do is connect a couple of wires and the crown together and the device is ready. At the same time, the characteristics of this device are attributed to be quite good - it finds a coin at a distance of 25-30 cm, which is quite enough for searching for coins and treasures. However, unfortunately, this instruction is fake.

The fact is that the metal detector itself is a rather complex device; its operation is based on several physical phenomena at once. Therefore, a calculator and a pair of disks cannot even remotely replicate its operating principle, no matter what the creators of such instructions claim, who sometimes write that they even find treasures with the help of such homemade products.

It is very easy to understand that you are being deceived even without knowledge of the laws of physics. The wires from the headphones that need to be attached to the disk do not actually contact it in any way, since the copper is under a layer of varnish insulation, which must be removed by firing and labor-intensive cleaning of carbon deposits; of course, none of the authors of the instructions does this in their devices . Consequently, the headphones are simply not connected to any circuit, and there can be no talk of any work, much less metal detecting.

A real metal detector operates on the basis of an induction balance; its design must have at least one coil of copper wire. When a metal object enters the field of the coil, its characteristics or the received signal, depending on the design, change. These changes are recorded and amplified by the circuit, and also displayed in a form understandable to humans, usually by means of sound signals.

Video instructions for assembling a metal detector from disks

Idea No. 2 – Metal detector according to the “Pirate” scheme

This is a scheme that has been tested by many DIYers and allows you to achieve good results. It contains two microcircuits, so you will have to make a small printed circuit board or assemble the device on a breadboard. But don’t be alarmed, anyone can make this option if they put in the necessary effort. Below is an electronic circuit diagram of the device and a printed circuit board for it.

The coil is made of enameled copper wire with a diameter of 0.5 mm. Winding should be done on a frame with a diameter of 200-260 mm, the number of turns from 21 to 25. For reliability, it is better to install the coil in a protective plastic casing, which can then be attached to a handle made of PVC pipes.

After assembling the metal detector, it must be checked. The procedure for use is as follows: turn on the device away from metal objects for about 30 seconds so that its operation is more stable, then rotate the variable resistor knob for coarse and fine adjustment, you need to achieve rare clicks. When metal enters the action area, you will hear a characteristic sound.

Below is a detailed video assembly instruction, which clearly shows all the stages of creating a homemade metal detector.

Many people mistakenly believe that if they make a metal detector with their own hands, it will be of much worse quality than a factory one. However, a homemade device can be not only better, but also much cheaper than models produced at the factory. Most people who like to look for various treasures are looking for cheap options to save money. Typically, they end up assembling the metal detector themselves.

Operating principles of a metal detector

Beginners at the first stages may be intimidated by various schemes and formulas when assembling them on their own. But if you look for available information on the Internet, you can easily understand all the nuances. Therefore, in order to ultimately get a good device with discrimination, it is necessary to carefully study the various diagrams, instructions and operating principles of the metal detector.

The operating principle of such a device is to use an electromagnetic field. It is created by the transmitter coil after detecting an object that conducts current (mostly all metals). The process is accompanied by characteristic sounds due to the creation of eddy currents and distortion of the EPM coil.

If the found object does not conduct current, but the metal detector still detects it, then this means that it has its own electromagnetic field.

When an object is detected, cheaper devices create a special sound after transmitting information to the control unit. But in expensive factory models, information can also be displayed on the screen.

In order to assemble the device efficiently, you must first study the detailed instructions; Making a metal detector with your own hands is not so easy. Although with the right approach it is quite possible even without special training. Moreover, it is possible to make an underwater vehicle that can search for gold and other precious metals. Although it is unlikely that it will be possible to make a deep metal detector, such devices are manufactured in factories.

The metal detector consists of:

Preparing the PCB

First you need to prepare a printed circuit board, where all the parts and components of the metal detector will subsequently be located. Basically, the method of laser-iron technology (abbr. LUT) is used for this.

At this stage To produce a board, you must follow these steps:

Installing all elements

After the PCB board is ready, it is necessary to solder the circuit elements onto it. They can be taken from old and unnecessary tape recorders, televisions, and radios. But in principle, if the list of necessary parts is ready, then you can buy everything on the radio market. They cost pennies.

The installation process is as follows:

1. First you need to install the main chip. You can use the foreign NE555 or the Soviet KR1006VI1, both will do. But problems may arise with domestic ones, since they are no longer manufactured. There should be no problems with a foreign analogue. Before installing the main part, a jumper is soldered underneath it.
2. After this, K157UD2 is installed - a two-channel amplifier. It can be found in an old tape recorder.
3. Next, capacitors and resistors are mounted.
4. At the next stage, you need to solder two transistors like BC557 or analogues.

Metal detector coil assembly

In order to make a high-quality metal detector with your own hands at home, you need to approach the assembly of the coil with great responsibility.

You can make a homemade coil from a frame with a diameter of 20 centimeters. To create such a frame, you need to take PEV wire 0.5 millimeters in diameter. 25 skeins will be enough. But in any case, the number of turns of wire can either increase or decrease. In order to understand how many of them actually need to be made, for quality work you need to use a coin. The maximum catching distance should be checked.

The speaker that produces the signal can be removed from the portable radio. An important factor is its resistance. It should not be less than 8 ohms. Alternatively, you can use cheap Chinese speakers.

Installation of additional elements

To configure the device, two potentiometer models of different power are required. One for 100 kOhm, and the second only for 10 kOhm. During operation of the metal detector, interference can often occur. To avoid this result, shielded wire is used to connect the coil and the circuit. But you need to understand that it will not be possible to completely get rid of interference. A minimum 12 V battery is used as the power source for the device.

The stability of the electrical circuit can be increased by additionally using a voltage stabilizer type L7812.

After all the electronic elements are ready, you should begin assembling the frame for the metal detector. But here it is necessary to give only general recommendations, since everyone will assemble it from improvised means.

For beginners we can advise:

• Purchase 5 meters of PVC pipe (which is used in plumbing) to create a rod, as well as a jumper. A special hand rest is installed on top of the pipe. It allows you to feel more comfortable when working. To place the board you need to find any box of appropriate size.
• The device can be powered from a regular battery from a screwdriver. The advantages of using such a battery in its small capacity.
• When creating the body of the structure, you need to take into account that there should be no unnecessary metal elements. They can negatively affect the electromagnetic field of the metal detector.

How to check functionality

A metal detector on a chip can be tested in different ways. First, sensitivity is adjusted using potentiometers. The boundary indicator will be a uniform, very strong crackling. For example, he must find a 5-ruble coin from a distance of 30 centimeters, and a Soviet ruble from 40 centimeters. Large pieces of metal should be detected from a meter or more away.

But on the other hand, he will not be able to find small objects at great depths. Moreover, he will not distinguish between the size of the detected metal and its type. Because of this, when working on such equipment, nails or pieces of unnecessary metal will be a common find.

Many who are interested in the question of how to make a homemade metal detector turn out to be novice treasure hunters who do not have the necessary funds to purchase a factory-made device.

Simple homemade designs

Today there are many ways you can make a metal detector at home, using almost only improvised means. To implement some methods, you need to have special knowledge in the field of electrical engineering, while other options can be used without any knowledge.

Metal detector made from computer disks

There is a lot of information on the Internet on how to make a metal detector from computer CDs or DVDs. The circuit is not complicated, and even a schoolchild can make such a device. To do this, you do not need to have experience with electrical engineering or special tools. Theoretically, you can also make a DIY metal detector from a phone (cell or landline) yourself.

The main material used is:

In order to To assemble a working metal detector from these parts, you need to:

• Cut off the plug from the headphones and remove the insulation by 5-10 millimeters.
• Each stripped wire must be divided into two parts. As a result, four parts should be formed.
• A disk must be attached to each wire using glue. If the disc is single-sided, then it needs to be glued to the writing side.
• Additionally, the wires must be secured with electrical tape.
• The remaining separations from the wires must be attached to the plus and minus of the battery.
• Carefully insulate the wires.
• The included calculator should be installed to the CD using electrical tape.
• Place a DVD on top and connect them with tape.
• Attach the battery to the top of the DVD disc with electrical tape.
• Testing phase.

Additionally, you can make a handle for convenient operation of the metal detector. Basically, such metal detectors are used to search for insignificant and small objects, for example, to search for a metal profile in a wall. This device is not suitable for searching for various coins and precious metals, but it is just right for home needs.

Radio receiver as a basis

In practice, they use a good and cheap way to create a metal detector from a radio receiver. This option is no worse than the previous one, but, on the contrary, has increased power.

To create such a metal detector you need:

• a box from an ordinary computer disk;
• radio receiver operating on AM frequency;
• calculator;
• scotch.

These materials should be used as follows:

As you can see from the situation, making a more or less powerful search engine will not be difficult, and will take no more than 5 minutes. This option is for novice users, since it can be done without microcircuits, drawings and the necessary experience in electrical engineering. You can also attach a handle to it for convenient use. The device is ideal for detecting old wiring or metal profiles.

This is one of the most prudent ways to create a metal detector yourself. The decision is up to everyone. On the one hand, there is an opportunity to save up to 5,000 rubles, but on the other hand, homemade devices do not always work as they should.

A small number of people believe that factory-made devices for detecting metal objects are significantly superior to home-made devices, but this is a mistaken opinion. If you properly make a metal detector with your own hands and configure it, it can surpass branded metal detectors. Which, in turn, will save a considerable amount of money. But in order to build a homemade product, you should know the principle of operation and design.

Operating principle

The device detects metal underground using an electromagnetic field created by a transmitter coil. It begins to interact with the object (almost all metals are conductive), resulting in the formation of an eddy current that vibrates the radio waves of the metal detector coil. Shielding on a computer will pick up interference even from metals that do not conduct electricity, but only if they have electromagnetic properties.

When the equipment begins to pick up interference, it the data is immediately sent to the control unit. This part of the detector produces an audible signal indicating that a find has been found. The sound may be strong or weak. A strong signal indicates that the object is shallow, and a weak signal, on the contrary. There may be a coin at a distance of 50 cm, its signal will be weak. And with the same level of sound alert, large objects in the form of a helmet, weapons, and so on can lie at a depth of 100 cm. This factor must be taken into account.

Some expensive factory models display the received data on a monitor; they are very difficult to build at home. The Pirate detector is the easiest to assemble. Therefore, using his example, you can analyze the process of assembling a homemade device.

If you still can’t make a metal detector at home, then you can go to the store and buy a branded device or order a homemade one from craftsmen who assemble at home. You can find craftsmen through friends or the Internet.

Attention! Beginners who take on assembling a metal detector with their own hands for the first time often get confused by the electronics. As a result, they give up this activity because formulas, diagrams and special terminologies scare them. To build a homemade device, it is enough to understand the essence of the system by plunging into school physics lessons.

Printed circuit board

One of the most important parts of the device is the board. In the future, all detector components will be attached to it. The most optimal method for creating a board is LUT (laser ironing technology). Manufacturing involves compliance with all stages, the implementation of which must occur in strict order.

A detailed description of assembling a circuit on a homemade metal detector or how to make a board from scratch:

Luding the board tracks is the last step. The entire surface is treated with LTI-120 solution.

Soldering elements

The manufactured board must be inspected. You need to make sure that all the track lines are clearly visible and the holes are in their places. After that, all the necessary elements are soldered onto the made metal detector board:

The most difficult thing is to find the K157UD2 amplifier. Because it hasn't been produced for a long time. Therefore, it is preferable to look for modern analogues that match the characteristics of the Soviet version.

Creating a Reel

To make a coil, you need a frame with a cross-section of 20 cm. An average of 25 turns are wound on it, but the total number can be changed up or down. Craftsmen advise adjusting the amount of wire winding by testing the device on a coin. It may turn out to be either 23 or 26 wikis. This is the only way to determine the farthest detection distance of a small object. It is advisable to use PEV wire half a centimeter thick.

After the master has decided on the amount of wire, it should be wound tightly around the frame. Insulated tape is applied to all homemade coils. There is no need to make a thick protective coating; one layer is enough so that the turns are not visible. The work with the homemade coil can be considered complete.

Additional equipment

In addition to the board and coil, you will have to supplement the metal detector with other necessary accessories that will significantly improve its performance. Experienced experts recommend equipping the device with the following devices:

1. Signal speaker. It can be removed from an ordinary radio. An important condition: it must have a resistance of 8 ohms. To save money, it is better to purchase a portable version made in China.
2. 2 potentiometers, their power should be different. One model is 10 kOhm and the other is 100 kOhm. It is almost impossible to eliminate interference, so you will have to minimize it as much as possible. For these purposes, a shielded wire connecting the coil and the circuit will serve. The metal detector must operate from a power supply of 12 V no less.
3. The L7812 voltage stabilizer increases the stability of the electrical microcircuit. It is mounted at the entrance.
4. Detector frame. It is mounted from any materials available at hand. However, for convenience, it is better to use a 5 m long PVC pipe. They are often used for laying pipeline lines. You will also need to buy several jumpers. A semicircular hand rest is installed on the top. Then you need to find a sealed plastic box in which the board will fit. After this, it is mounted above the middle of the rod.
5. A battery from a screwdriver is suitable to power the system. The advantage is that the battery is lightweight and has a long service life.

Important! The entire skeleton and other parts of the metal detector should not be metal. Their presence can distort the electromagnetic field. It is better to give preference to plastic.

Setup and testing

First of all, on the detector with potentiometers sensitivity is adjusted. You need to achieve uniform crackling. It is advisable to set it up on a small object. A DIY metal detector made at home should detect it at a distance of 30 cm. It will show a Soviet ruble at a depth of 45 cm. Larger objects are detected from a distance of 100 cm.

At very great depths, the device will not be able to find coins and similar small pieces of iron. Experienced treasure hunters are, of course, capable by sound, approximately understand the parameters of the detected object, but it is impossible to distinguish the type. In this case, a beginner will very often stumble upon nails and other unnecessary pieces of iron.

Making a metal detector with your own hands is not too difficult. Homemade models are great for training for novice treasure hunters. You can get a lot of experience and even an important find from them. In addition, you do not have to spend money on purchasing the device. And after honing your skills, you can buy a professional detector with a monitor that will even look for coins at great depths.

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

If you wish, it is easy to purchase an inexpensive metal analyzer. Anyone capable of holding a soldering iron and a screwdriver can make a metal detector with their own hands.

Why do you need a metal detector?

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

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

• Treasure hunters can be seen in places where old buildings are being demolished. There may be items and money put aside for a rainy day. Almost every week there are reports of the discovery of certain treasures containing coins and jewelry;
• Search engines at the sites of past battles are looking for weapons, shells and cartridges, helmets, and household items. The device helps to find random burials of battle participants. The names of the dead are determined based on awards and other sources. 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 mines and 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 Syria. The terrible bombs did not work; they did not take the lives of children, women and the rest of the population who wanted to live a peaceful life.

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

“Metal workers” (people who sell scrap metal in large quantities) are busy searching for forgotten pipes, metal structures and large deposits of unnecessary metal. They make a living by renting out such items.

Attention! Those who have practically no experience with electrical engineering or radio electronics should not despair. Here we will outline options for manufacturing the simplest metal detectors, which you can make yourself with your own hands, without resorting to the use of complex equipment. If there are certain difficulties with soldering, then the wires can be twisted together, getting a good result.

Principle of operation

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

• synthesizer of electromagnetic oscillations;
• vibration 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 recording the discriminating signal or indicating devices.

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

• reception and transmission are carried out by one amplifier;
• the same coil emits an alternating electromagnetic field into the study area, and then receives a signal about the presence or absence of distortion.

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

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

1. The coil creates an alternating magnetic field in the search area (see position A).
2. When an object that has any distinctive properties compared to its surroundings enters the study area, eddy currents arise inside the field of the coil (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 position B).
5. All changes are recorded by instruments (optical or sound indicators). By changing the signals, the operator can determine the presence of an object with ferromagnetic properties. Metals that conduct electric current are also determined.

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

A few words about geoscanners

Geoscanners are special devices that can draw 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 and main pipelines laid at considerable depths. 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 cardboard.

What types of metal detectors are there?

Common parameters

The basic principle of operation, in which the magnitude of electromagnetic induction in a certain part of space is analyzed, is implemented in different 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 in appearance. But upon careful examination of the design, fundamental differences in circuits and technical capabilities will be visible.

When starting to create your own metal detector, you need to clearly define the requirements that will be placed on the device. Experts identify a number of characteristic parameters for search devices:

1. The depth of signal penetration into the soil (penetration ability). This characteristic depends on the properties inherent in the receiving coil.
2. Search area based on the size of the trace of an active coil emitting an electromagnetic field.
3. The level of sensitivity characterizes the ability to detect objects that are small in size and weight (coins, shell casings, bullets, crosses, small jewelry).
4. Electoral indicators. For some categories of search engines, a special reaction to precious (gold or silver products) or non-ferrous metals is important. They even create special filters that transmit 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, nearby repeaters or television stations. There may be other sources of interference that can degrade the performance of the search device. As practice shows, it is near sources of electromagnetic oscillations that the loss of the most interesting objects in which searchers are interested most often occurs.
6. Small size and the ability to use small-sized energy sources for operation (device mobility) are quite important characteristics. With a heavy and bulky metal detector, a person gets tired quite quickly, and labor productivity will be low. With a lightweight 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 based on the type of signal received. Search efficiency increases.

Among specialists, device discrimination is usually correlated by indicators of information boards and sound. 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 location of the object in the search area. Shows the possible depth of placement.
2. Geometric characteristics give an idea of ​​the mass and possible size of the find.
3. Qualitative determines the properties of the material from which the found object 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 operating features. 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 working width of the device. However, it is impossible to significantly reduce the frequency value. A metal detector will require a lot of energy to remain operational. This will lead to the need to use a larger 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. Ultra-low frequency (ELF) operate up to 100…150 Hz. Such devices are classified as professional devices. It has not yet been possible to implement a mobile metal detector in practice. Energy consumption is measured in tens of watts (W). Similar search tools are located on vehicles. The signal is analyzed using computers.
2. Low frequency (LF) operate in the range of 150…2000 Hz. These devices have a simple design that even a novice master can assemble. The design is quite simple. It is distinguished by a rather large penetration depth of the electromagnetic pulse (up to 4...5 m). However, such devices have low sensitivity. There is virtually no discrimination based on size and material composition. Such metal detectors respond well to ferrous metals that contain iron in various types of compounds. But if large concrete or stone structures are found, the search engine will find them too. Such devices are classified under the name magnetodetectors. Such devices are worse at distinguishing the properties of soils and objects contained in them.
3. High frequency (IF) devices use an operating range of 1700…75000 Hz. The design of such metal detectors is much more complex. 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 appear in the presence of heterogeneous rock in the soil. Unstable indicators are possible if groundwater levels are high. Such metal detectors are used to operate in pulse mode, which will have to be achieved a little later.
4. High frequency (HF), sometimes professionals call such devices operating at radio frequencies (RF). In these devices, discrimination against heavy precious metals works perfectly. The search depth can reach 0.5...0.8 m. They are usually not able to illuminate 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 energy consumption is noted. A set of AA batteries (finger-type) can operate continuously for up to 12 hours.

A special feature of pulse metal detectors is that they do not constantly supply a signal of a given frequency. Periodic pulses are sent. You can set the frequency of the send and the duration of the impact. By creating such a device, it is possible to obtain a device in which positive characteristics will be obtained from LF, IF and HF devices. However, such circuits require special assembly and adjustment. For novice searchers and craftsmen, such devices can be difficult to implement. Therefore, you need to start a homemade 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. Large enterprises, where it is possible to purchase expensive components, can implement the proposed methods.

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;
• transceiver is based on the use of a reflected signal that was previously sent by the transmitting device;
• phase accumulation is usually equipped with two coils;
• on the beats. This method is implemented on two signals.

Without receiver (parametric devices)

The parametric method does not require a receiver. Even the take-up coil itself is missing. When searching, the inductance changes, which is perceived by the generating coil itself. When an object with certain properties that change the inductance is located in the area affected by the electromagnetic field, frequency modulation occurs in the oscillations of the devices. Changes:

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

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

With receiver and transmitter

Devices that implement the principle of signal reception and transmission allow one to obtain significantly better performance. With a certain complexity in manufacturing (coils must be created strictly following the description and design features).

It is customary to identify devices by the following indicators:

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

If a pulse transceiver device is implemented, then the discriminatory 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.

Before click (with phase accumulation)

The method is implemented in devices with phase accumulation. Structurally, the execution is:

• single-coil with pulse signal supply;
• dual-coil, equipped with two signal generators (each supplied with power to its own coil).

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

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

If you have a two-coil device, there is no need to create a pulse device. The generators each operate on their own solenoid. If EMF distortion occurs, then clicks also occur. You can configure it to additionally produce the sound of a certain tone.

On beaches and in places where there are a large number of tourists, resort prospectors 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 capable of sensing small earrings weighing 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 (by beat)

The presence of two signals supplied at different frequencies allows you to hear not the supplied frequencies themselves, but their difference.

1. One is supplied with frequency 1 MHz = 1,000,000 Hz.
2. To 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.

For different types of devices, they select their own frequencies, which they use 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. You can even reduce this difference to zero if you ensure equality of the supplied oscillations.

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 sounding 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. Through a series of preliminary training, the operator can quite accurately determine what is located in the soil, what is the mass and size of the find.

It is recommended to tune to the “A” sound of the first octave, which corresponds to a frequency of 432 Hz. This tone is heard on radio stations during a short break. Practice shows that devices tuned to such sound pick up even quite small objects, the mass of which is a few tenths of a gram.

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

The 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 don't think about the design. They can purchase a branded product and then expect to receive only dividends from their investment. Unfortunately, even the coolest reel can show poor performance. There must be a correspondence between the solenoid and the rest of the device circuit.

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 experimentally. The spread in the characteristics of radio components can be quite significant. Not only rough but also fine tuning is needed.

What sizes does the reel need?

The larger the coil, the larger the area its signal covers. 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 carry such an instrument on your shoulders. If you need to move in the forest or in plantings, such a device will not allow you to penetrate between bushes and trees. It’s easier to move your hand several times with a coil placed on the rod.

• 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 The coils are made by metal workers who search for scrap metal in large quantities.

Monoloop as a coil

Designs in which a monoloop is taken as a basis are common. A long wire is used for production. The winding thickness 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 across the territory;
• Having discovered metal in the depths, 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 devices interfere with operation. Therefore, gold hunters on beaches are often exposed to operating devices;
• To use it effectively, you need to train with different objects from different materials in order to learn to recognize the desired item and begin to mine it.

These disadvantages do not reduce the value of such a solenoid. Beginner users can use the monoloop as the basis for their first design. It's not difficult to make. You will have a very good metal detector in your hands.

Step-by-step production of a simple coil

In practice, many different manufacturing options are used. One of them will be one that uses modern materials: plastic pipes. They initially help 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, you can take 12 m; plastic tube with an internal 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 polypropylene pipe Ø 20 mm (2 pieces, 15 mm long); shielded television 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 hard workpiece, then during production you will need to warm it up with hot water or using a hairdryer. A test ring is rolled up and the shape of the resulting circle is assessed.
	You need to drill a Ø6 mm hole in the tee. Through it the wires will be inserted into the future coil. It is advisable to clean the edges from burrs.
	Additional polypropylene pipe inserts 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 obtain a circle of exactly the specified diameter. If you do not adjust the dimensions, there may not be enough wire. Test entries into fragments are made.
	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.
	Slight mobility during connection 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.
	Once the wire is in place, you can evaluate how well the job was done. You may need to tighten some of the coils. It is desirable that the styling looks better.
	The ends of the wire should be soldered to a shielded cable.
	The reel is ready. You should think about how to secure it to 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 out 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 it to the reel itself.
	As a result, the metal detector acquires a marketable appearance.
	After insulating the coil, it is advisable to paint it with alkyd enamel. A layer of paint prevents moisture from penetrating the OSB.

How to calculate the inductance of a coil?

When developing a metal detector design, it may be necessary to calculate the inductance value. 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 quickly determining the inductance of coils

• 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 that should be wound when making the coil. The packing density is set to k = 0.5. The cross-sectional area is determined based on the accepted dimensions S = klt, Here l– height of the coil layers; t– width of layers.

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

Coil noise immunity

The similarity with a loop antenna determines the high activity of the coil. She is susceptible to interference from outside. To eliminate possible external influences, 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 arrival of external electromagnetic pulses.

Beginners should carefully study the design. The position of the grounding contact must be strictly along the axis of symmetry. Otherwise, the search coil itself may malfunction. The end from the shielding wire is connected to the general circuit of the device. If you neglect the requirements of symmetry, the characteristics of the solenoid will deteriorate, and interference will completely suppress the desired signals.

The presence of a screen somewhat reduces the magnitude of the electromagnetic field. Sensitivity decreases slightly. 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 influence of interference is minimized as much as possible. The metal detector works more reliably.

The figure below shows 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 ineffective. When ferromagnets are present in 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 crosswise manner. They prefer to create a basket type reel. It is easier to make.

Reel-basket

The disadvantages of DIYers include the need for precise manufacturing of such a device. You need a fairly strong mandrel. When tensioning the wires when winding, deformation is possible.

When creating a basket, the manufacturer has options:

• obtain a three-dimensional structure;
• make a flat basket reel.

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

Basket reel design

The calculation is carried out using 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 value of D₁ is defined as D₁ = 0.5·D₂.
3. Calculate the number of turns using the formula:

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

k – correction factor determined from the table.

Table: determination of 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, the diameter of the wire is calculated. The packing density is believed to be 0.85.

Mono-loop 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 area of ​​action of the solenoids.

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

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

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

How to secure the reel yourself?

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

Options for making the frame: a – from plywood; b – from CDs

1. Many people think that it is easiest to use regular plywood. It is easy to saw. It has sufficient strength.
   In practice, it turns out that plywood can absorb moisture. As a result, the performance of the device may be extremely low.
2. The best results are obtained when using CDs. A gap of about 5...7 mm is left between them. You can glue pieces of foam plastic. Then they wrap it along the generatrix with adhesive tape or insulating tape. The result is a reliable and durable three-dimensional structure.
3. When using cellular polycarbonate with a thickness of 6 or 8 mm, a lightweight and fairly durable frame is obtained. You just need to close the honeycombs to prevent moisture from getting into them. Regular tape will do. Professionals use silicone sealant; it will reliably fill the holes at the entrance to the honeycomb. It has been proven that such a frame is the most successful. It does not cause additional interference.

Several designs of metal detectors

Parametric Metal Detection Instrument

For searching ferrous metal and pipelines in the ground. Finding electrical wiring in 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). It is possible to replace it with a more powerful model KT361 (note that it has reverse polarity; when connecting the power, you should change the method of turning on the battery).

The simplest metal detector

This device operates at low frequency. The sound frequency is selected by changing the capacitance of the capacitor C₁. When metal is found, the tone noticeably decreases. Therefore, during the initial setup, they try to set a squeak similar to a mosquito.

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

Pulse parametric device

Diagram of a device for detecting 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 it has a ferrite antenna inside. It is she who sets the desired oscillation frequency.

The entire device is powered by two AA batteries. Energy consumption is quite low.

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

Many people are put off by this design because it requires lengthy and careful debugging. You 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, you should focus on using metal detectors equipped with a transmitter and receiver.

Here, DD coils work, to which power is supplied at a frequency of 2000-2500 Hz. Such devices can detect alloys of non-ferrous metals 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 60-70 cm.

Sometimes such devices are placed in hermetically sealed shells, making deep metal detectors for working underwater. Underwater metal detector expands the range of searches 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 prepared. It will require a little more than 14 m. 30 turns will be laid on a diameter of 150 mm.
	The lid from a plastic bucket is used as a sample for drawing a circle of the required diameter. It has the required diameter.
	A circle is formed on the board. It will serve as the basis for subsequent actions.
	To wind the wire you need to drive in nails. Hardware 30 mm long is used. To obtain a high-quality circle, it is advisable to hammer in at least 16 pieces. More is possible.
	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 insulated. First, it is wrapped with masking tape.
	Having made the first coil, the second one is made in a similar way.
	The transceiver device is manufactured according to the proposed scheme.
	To receive a sound signal you need an earphone 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.
	There is space inside not only for the board. The battery is placed here. Professionals try to use small-sized batteries. They can be recharged. Having two or three batteries with you, you don’t have to worry that the device will be de-energized.
	The coils are placed on a sheet cut from cellular polycarbonate.
	The rod is made of polypropylene pipes.
	For ease of use, the handle has a half ring. It is easier to control when searching for metal objects.
	By scattering various objects, you can diagnose the functionality of the metal detector. Estimate the detection distances for each type of metal. The device is being configured.
	You can start searching for metals in nature. You should walk slowly. The coils move from side to side, trying to cover the maximum width.
	Having found an object in the ground, you can start digging it out. When in places where there have been battles, you should follow the rules for safely removing objects.
	Even small coins can be found in the depths.

Finding simple solutions

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

The simplest metal detector

You will need:

1. The cheapest radio receiver. It should have a mid-wave range. It is usually labeled AM. A ferrite magnetic antenna was installed in such receivers.
2. A calculator released at the end of the 20th century. You can buy them at bargain shops from old ladies.
3. A small book or just its cover. Cardboard would be preferable. It will have a certain strength.

Now you have to tinker a little. The structure of such a device is extremely simple:

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

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

All that remains is to attach the cover to the rod and start searching for treasures.

More ideas for creating a metal detector

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

Many radio amateurs dream of making a metal detector with their own hands. It can be used to detect metal objects in the ground at different depths. On the Internet you can find many photos of metal detector circuits that are simple to use. Any beginning radio amateur can make them.

Easy assembly

For example, let's take the circuit of a simple metal detector. It is of the pulse type, but due to the simplicity of its design it is not able to distinguish between types of metals. Therefore, it will not be possible to operate such a device in areas where objects made of non-ferrous metal are found.

How to assemble the device

To assemble a simple metal detector circuit with your own hands, you will need the following tools and parts:

• Presence of KR1006VI1 microcircuit and IRF740 transistor;
• Presence of K157UD2 microcircuit and VS547 transistor;
• Copper conductor 0.5mm (PEV);
• NPN transistor;
• Housing, and various materials for it;
• Solder, flux, soldering iron.

Other details are shown in the diagram. In order for the assembled circuit to be securely fastened, a plastic case should be prepared for it.

The bar can be made using a small diameter plastic tube. A metal detecting coil will be installed in its lower part.

Beginning of work

The circuit diagram of a metal detector using transistors is a common option for many models. Assembly begins with the manufacture of a printed circuit board. Next, all radio elements are mounted on it exactly as shown in the diagram.

To ensure stable operation of the device, film capacitors are used in the circuit. This will allow you to use it in cold weather without any problems.

Power type for device

The device can operate on a voltage of 9-12 V. Due to its sufficient power, energy is intensively consumed. It is recommended to install up to 3 batteries and connect them in a parallel circuit. You can use a small battery that has a charger. Thanks to its capacity, the metal detector will work longer.

Coil installation

There are different types and schemes for the manufacture of metal detectors, but in the pulsed version, inaccuracies are allowed in the installation of the coil. When making a mandrel, the winding should be up to 25 turns, and the diameter of the ring should be 1900-200mm.

All turns of the coil must be insulated with electrical tape. Reducing the number of turns to 22, and the mandrel diameter of 270 mm will allow you to detect objects at a deeper location. The wire cross-section on the coil is 0.5 mm.

When the winding is ready, it is attached to a durable housing with sufficient rigidity, on which there should be no metal parts. Otherwise, they are able to shield the magnetic field, and the operation of the metal detector will be disrupted. The body can be made of wood or plastic, but so that it can withstand various impacts that can damage the coil.

The leads on it should be soldered to a conductor of several cores. The best option is a two-core wire.

The installation of a non-ferrous metal detector circuit is a little more complicated, and high precision must be observed in the manufacture of the coil. The number of turns reaches 100pcs, and a vinyl tube is used as the core. Foil is wound on top of the winding, which forms an electrostatic screen.

Device setup

If the installation of the circuit is done exactly, then the metal detector will not need additional settings. Its sensitivity indicators will be maximum, but fine adjustment is possible through variable resistance R13. It must be performed until rare clicks begin in the headphones.

If the adjustment fails, then the resistances must be replaced with R12. When the resistor adjustment is in the middle, this will be considered normal.

An oscilloscope is suitable for checking the device. The frequency of transistor T2 is measured on it, and the pulse should last up to 150 ms. The optimal operating frequency is up to 150 Hz.

How to use the device

You should not rush and start working immediately after turning on the metal detector. It should stabilize, so you need to wait up to 20 seconds. After adjusting the resistor appropriately, you can start looking for metal.

Note!

Photo of the metal detector circuit

Note!

Note!

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