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Homemade powerful do-it-yourself metal detector with a selector. Onward, in search of treasure! How to make a powerful metal detector at home with your own hands. Creation of generator coils

This article will focus on one of the simple metal detectors, the assembly of which can be done with affordable Soviet radio components. These include transistors marked KT and MP, as well as resistors and capacitors from popular radio equipment. Most of the necessary parts can be easily found in old radio devices.

The scheme consists of five nodes, the structure of which can be viewed in Figure 1:

  1. A master frequency oscillator used to create a reference frequency.
  2. Search frequency generator. Its frequency will change when metal is found.
  3. Low-frequency amplifier to increase the signal difference of the generators.
  4. The node that plays the sound.
  5. Source of power.

This device resembles a metal detector on two transistors, but it has an added sound amplifier, and, despite its simplicity, it has good metal detection performance. It is perfect for mass search and collection of ferrous metal. If you find radio components and a little time, then you can easily assemble a metal detector using this informative article as an example.

Assembly of circuit elements

The assembly of the circuit can be carried out on a one-sided foil textolite. Guided by Figure 2, which shows a transistor metal detector circuit, we count the number of connections and create the corresponding number of contact pads with a sharp object. After tinning, the board is ready for assembly of parts (Fig. 3). For a better assembly, you can think over and draw a homemade printed circuit board.

Below is a list of required parts and instructions for some of them:

  1. 14 resistors with a power of 0.125 W. Denominations:
    1. R1, R5 - 100 kOhm;
    2. R2, R6, R11 - 10 kOhm;
    3. R3, R7 - 1 kOhm;
    4. R4, R8 - 5.1 kOhm;
    5. R9 - 6.2 kOhm;
    6. R10, R13 - 220 kOhm;
    7. R12 - 3.9 kOhm;
    8. R14 - 3 kOhm.
  2. 14 capacitors, preferably heat resistant:
    1. Electrolytic for 6 V: C10, C14 - 47 microfarads; C12, C13 - 22 uF;
    2. Variable capacitors C7 - up to 10 pF / from 150 pF;
    3. Trimmer capacitor C8 - 6 / 25 pF;
    4. C1, C11 - 47 nF;
    5. C2, C6 - 4.7 nF;
    6. C3 - 100 pF;
    7. C4 - 47 pF;
    8. C5, C9 - 2.2 nF.
  3. Five transistors:
    1. 3.1 VT1, VT2 - KT315. As analogues, you can use KT3102, KT312 or KT316;
    2. 3.2 VT3, VT4, VT5 - MP35. You can replace it with MP from 36 to 38;
    3. 3.3 VT6 - MP39. MP from 40 to 42 will also do;
  4. 2 diodes D9Zh, or others - D18, D2, GD 507.
  5. 4.5 V battery in the form of three AA batteries. You can use a 9 V krona battery, but in this case it is necessary to change the electrolytic capacitors to a voltage higher than 9 V.
  6. Speaker impedance from 5 to 100 ohms. Suitable speakers from children's toys, intercom handsets, radios or a headset.
  7. Contact connector for the battery (Fig. 4).
  8. Microswitch or toggle switch to turn off.

Metal detectors cannot work without coils that play a major role in the device. In the next paragraph of the article, we will describe in detail their role in the work and the manufacturing process.

Creation of generator coils

The primary coil L1 is exemplary and, together with the capacitor C3, serves to create the master frequency of the generator. The secondary coil L2 works in the same way, but it is made without a core. This allows metal objects to act on it and change the frequency of the generator, which leads to a frequency difference for the signal.

The following describes how to make homemade coils without much difficulty.

For the frame of the L1 coil, a metal rod with a diameter of 8 mm and a length of 3 cm is needed. An antenna with a radio can be used. Whatman paper must be wound on the rod. We do this in order to be able to adjust the frequency by moving the rod relative to the coil, so it is important that the paper fits very tightly to prevent spontaneous movement. After the final adjustment of the metal detector in the last paragraph, you can fix the rod with glue. A sample coil is shown in Figure 5.

We wind the L1 coil with a PEV wire with a diameter of 0.2 - 0.3 mm. We wind 110 turns on whatman paper strictly in one row, trying to avoid gaps or gaps between the turns. On the 16th turn, we make a tap without breaking the wires. After winding, the wire can be varnished, but the movement of the metal rod inside must be maintained. We make the wire connection according to the diagram.

The second coil L2 is made in the form of a rectangular frame measuring 12 x 22 cm. The frame can be made of plastic, plexiglass, plywood and other non-conductive material. We make a tray or collect only a supporting rectangle in which it will be possible to lay the winding in bulk. Finished samples can be seen in Figure 6.

The wire, as in the first case, we choose the PEV brands, but with a diameter of 0.4 - 0.6 mm. We wind 45 turns, making a conclusion on the 10th turn. After complete manufacturing and adjustment of the metal detector, it will be possible to fix and insulate the winding with varnish. The connection to the circuit is carried out with a shielded cable with at least two cores. Such cables are used in high-quality audio equipment and in trunk communication lines, they can also be purchased at an electronics store.

Production of a metal detector design

First of all, you need to decide what material to make the bar. It is better to give preference to a dielectric material in order to eliminate problems in the operation of the metal detector. There are many options: PVC pipe, telescopic fishing rod, wooden pole. When choosing, it is worth considering indicators such as weight, flexibility, ability to disassemble, convenience.

If you plan to spend a lot of time looking for metal, the light weight and comfortable armrest with handle will save you a lot of effort. But do not forget that lightweight material can bend. In the case of a PVC pipe, this can be compensated by sand poured inside or additional supporting structures. With a collapsible bar there will be no problems with transportation. To implement this idea, you can visit a plumbing store and assemble an excellent metal detector with your own hands on various adapters (Fig. 7).

After you have decided on the choice of the rod, you need to fix the coil on it. Everything is simple - no metal. Use plastic fasteners, pre-fixed ears on the coil frame, adapters, or just reliable glue.

The scheme is placed in a plastic box. For the speaker, you can make small holes for good audibility. The board, speaker, primary coil and battery box can be fixed with glue. We place the box a meter from the search coil and fasten it in a convenient way - using plastic fasteners or glue.

At this point, you have assembled a simple transistor metal detector that needs to be fine-tuned and checked.

Device setup

Setting up the metal detector is to create the same frequency in both generators. When such a result is achieved, the lowest, barely audible tone will be emitted from the speaker.

To begin with, we remove all metal objects from the range of the metal detector. We take into account concrete walls and floors, as they may contain metal reinforcement. Set all variable capacitors to the middle position. By changing the position of the rod in the coil L1, we achieve the desired tone or its absence. With further operation of the device, we use capacitor C7 to adjust. After tuning, we bring a metal object to various distances from the search coil and make sure that the metal detector is working.

If the metal detector does not work, we check the blocks and details of the circuit. We start the test with transistors, and then we check the diodes. To check the sound amplifier, it is enough to fold the resistor R9 from the generators and connect it to the sound output of any device that reproduces sound (Fig. 8).

If the parts and the amplifier are in working condition, then we set up transistor generators. To do this, we try to change the values ​​​​of the capacitor C4 and the resistor R2 for the master oscillator, and the resistor R6 for the search oscillator. You can try to start the second generator with a tuning capacitor C8.

Device search is just huge popularity. Looking for adults and children, and amateurs and professionals. They are looking for treasures, coins, lost things and buried scrap metal. And the main search tool is metal detector.

There is a great variety of different metal detectors for every “taste and color”. But for many people, buying a ready-made branded metal detector is simply financially expensive. And someone wants to assemble a metal detector with their own hands, and someone even builds their own small business on assembling them.

Homemade metal detectors

In this section of our site about homemade metal detectors, will be collected: best metal detector circuits, their descriptions, programs and other data for manufacturing DIY metal detector. There are no metal detector circuits from the USSR and circuits on two transistors here. Since such metal detectors are only suitable for a visual demonstration of the principles of metal detection, they are not at all suitable for real use.

All metal detectors in this section will be quite technologically advanced. They will have good search characteristics. And a well-assembled home-made metal detector will be a little inferior to factory counterparts. Basically, there are different schemes. pulse metal detectors and metal detector circuits with metal discrimination.

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

In addition to the basic data required for assembling a metal detector, there will also be information on the required minimum level of knowledge and equipment for self-manufacturing of a metal detector.

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

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

  1. Soldering iron, solder, tin and other soldering accessories.
  2. Screwdrivers, pliers, wire cutters and other tools.
  3. Materials and skills for the manufacture of printed circuit boards.
  4. Minimum experience and knowledge in electronics and electrical engineering as well.
  5. As well as straight arms - they will be very useful when assembling a metal detector with your own hands.

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

Principle of operation IB
Metal Discrimination there is
Maximum search depth
there is
Operating frequency 4 - 17 kHz
Difficulty level Average

Principle of operation IB
Metal Discrimination there is
Maximum search depth 1-1.5 meters (Depends on coil size)
Programmable microcontrollers there is
Operating frequency 4 - 16 kHz
Difficulty level Average

Principle of operation IB
Metal Discrimination there is
Maximum search depth 1 - 2 meters (Depends on the size of the coil)
Programmable microcontrollers there is
Operating frequency 4.5 - 19.5 kHz
Difficulty level Tall

The article presents a diagram of a simple but powerful 1.5 volt metal detector, very easy to repeat. The generators are assembled according to a circuit that has a number of useful properties, one of which is the stability of the output voltage (both DC and AC) when the supply voltage changes. The coil L1 is included in the oscillatory circuit of the search generator on the transistor VT1. It operates at a frequency of about 100 kHz, which is optimal for this type of metal detector. Its frequency can be changed within small limits by a variable capacitor C2. The second generator (on transistor VT2) is exemplary and operates at a frequency of about 300 kHz.
The generator signals through resistors R2, R4 are fed to a balanced mixer, where the frequency difference (beats) of the third harmonic of the search generator signal and the first harmonic of the exemplary one is separated. This was done to increase sensitivity - when the frequency of the search generator at a frequency of 10 Hertz changes, the beat frequency changes by 30 Hertz, which is more noticeable by ear.
The signal from the output of the mixer through the capacitor C8 is fed to the input of the ultrasonic frequency converter and, after amplification, to the headphones BF1, BF2. Capacitor C7 suppresses signals with oscillator frequencies.
When the search generator coil approaches a metal object, the generation frequency changes, so the signal tone in the headphones will also change. By the nature of the change in tone, one can judge the material from which this object is made.
Most of the parts are mounted on a printed circuit board made of one-sided foil fiberglass.

You can use transistors of the KT312, KT315, KT3102 series with any letter indices. In a balanced mixer, only germanium transistors of the GT309, GT313, GT322, GT346 series or earlier ones - P416, P422, P423 with any letter indices can be used. In UZMCH, the transistor must be with the highest possible current transfer coefficient, for example, KT3102BM - KT3102EM, KT342BM, KT342VM - the volume of the sound signal depends on this. Power switch - any small-sized. Headphones are suitable with a resistance of 8 to 32 ohms, they are connected in series. To connect them, you can install a socket on the body of the metal detector. The device is powered by a galvanic cell or an AA or AAA battery, the maximum current consumption is about 12 mA.
To wind the L2 coil, a frame was used from the IF circuit (455 kHz) of a foreign-made receiver. It consists of a ferrite "dumbbell" (on which 66 turns of PEV-2 wire with a diameter of 0.06 ... 0.1 mm are wound) and a ferrite cup covering it, by moving which the coil inductance is regulated. The frame is enclosed in a metal screen.

The sensitivity of the device to metal objects of different sizes depends on the size of the search coil itself. To search for large objects (a sheet of metal measuring 80x80 cm, a sewer manhole cover), a coil with a diameter of about 30 cm is more suitable. With it, the maximum detection depth of such objects is reached up to 60 cm.
For searching small objects, a coil with a diameter of about 120 mm is better suited. Such a coil contains 56 turns of PEL wire with a diameter of 0.2 ... 0.5 mm.
A coil of even larger diameter (for example, 300 mm) is more technologically manufactured from a multi-core shielded twisted-pair cable, which is used for laying computer local area networks. The cable must contain four such "pairs", and the coil must contain four turns of such a cable. First, two outer turns are wound and fastened in four places with insulating tape. Then two inner ones are wound and everything is also wrapped with insulating tape, preferably on a cloth basis. The ends of the cable are cut in such a way that there is an "overlap" of 5 mm ... 10 mm, and the outer insulation is removed from them by 15 mm, and the ends of the wires are stripped by 5 mm and tinned.
All radio components of the device are domestic and have foreign counterparts:
L1 - coil
R1 - 1 kOhm
R2 - 10 kOhm
R3 - 1 kOhm
R4 - 10 kOhm
R5 - 1 kOhm
R6 - 1 kOhm
R7 - 100 kOhm
C1-2200
C2 - 10...240
C3-4700
C4 - 0.047uF
C5-2200
C6-4700
C7 - 0.047uF
C8 - 2.2 uF x 16 volts
VT1 - KT315B
VT2 - KT315B
VT3 - GT322B
VT4 - GT322B

Devices capable of detecting metal objects in weakly conductive environments are called metal detectors, or metal detectors. They can be used to search for ferrous and non-ferrous metals. A homemade metal detector for coins is able to detect small things at a distance of 10 to 50 cm, and larger metals from 0.5 to 3 m.

The use of metal detectors has been known since ancient times, and a large increase in their production occurred at the end of the 60s. Thanks to the progress and many schemes, any novice radio amateur can make a metal detector with his own hands without resorting to extensive knowledge in electronics. The main advantage of homemade metal detectors is low costs.

Let's assemble the simplest metal detector operating on two frequency generators - a beat metal detector. At the same frequency, the generators are synchronized, but when one of the metal coils enters the field, the frequency changes in one of the generators. As a result, the circuit reproduces in dynamics the sound of the frequency difference of the two generators.

Tools and materials for the device

To make a homemade metal detector, you need to divide the process into three stages - creating a structure, implementing a circuit, and assembling into a single whole. We will describe an approximate list of tools and materials that may be needed for these purposes. Further on the article will be explained in more detail: from what you can assemble a metal detector for gold, and what kind of material is better to use. Let's start with preparing a tool for beginner diggers. For work you will need:

  1. Nippers for working with wires and parts;
  2. Knife;
  3. Saw for plastic. In extreme cases, you can use a knife or a regular saw;
  4. soldering iron;
  5. Screwdriver Set.

Necessary materials:

  1. Insulating tape;
  2. Soldering kit. You can just use rosin and solder;
  3. Glue;
  4. Details and circuit board;
  5. Wire for coil;
  6. A piece of plastic and a plastic pipe;
  7. Fasteners.

Part preparation

Detailed instructions on selecting and searching for parts are described here.

First you need to decide on the material and fastening of the components of the metal detector and find the necessary components.

As a barbell, you can use a crutch with an armrest, a fishing rod, a pipe made of cross-linked polyethylene or polyvinyl chloride (Fig. 2).

The coils and circuitry will be placed at the bottom on a stand attached to the rod. So it is important to consider the rigidity of the rod and its material. It is better to give preference to dielectrics, i.e. non-conductive electric current - plastic, wood and more. It is necessary to make a handle so that it is comfortable to hold the manufactured metal detector. In the case of a crutch, it is not needed, but in another case, you can attach both a bicycle handlebar and another home-made structure.

The stand for the circuit and coils can be made from ordinary plastic. It is easy to trim and is light weight. You will need one bottom sheet, as you need access to the coils to adjust the device. To reduce the vibration of the circuit with coils, it is advisable to choose a plastic that is stronger.

After preparing the rod and stand, you need to connect them. You can use fasteners, but do not forget that for the circuit to work properly, you should not bring metal products closer than 30 cm. Therefore, we use good glue, for example, liquid nails. You can use other materials - it all depends on your abilities in plumbing and carpentry.

The wire for the coils must be insulated. Suitable enameled copper wire with a diameter of 0.5 - 0.7 mm brand PEV or PEL. The length of the wire is about 100 meters. Oil varnish is suitable for fixing parts.

Installation of parts can be carried out by a hinged method on textolite or on cardboard. For beginner radio amateurs in specialized stores, you can buy processed textolite from the factory or material with holes for parts. You can also make a board yourself from a single raw textolite. To do this, you need to mark the placement of the contacts of the radio components on the diagram, then separate the textolite sections with a knife and tin the pads and tracks (Fig. 3). We cut off the excess part of the textolite with a saw for plastic.

To assemble a working metal detector, radio components can be found at home in old radio equipment, but it is advisable to purchase it in a store. Identical parts must be completely identical and preferably from the same batch. Table 1 contains a list of necessary parts and comments, the implementation of which will lead you to the assembly of a high-quality metal detector.

After finding all the necessary parts, you can easily assemble a metal detector at home.

Device Assembly

Having considered the list of necessary materials and parts, we will answer in detail how to assemble a metal detector from them with your own hands.

To wind the coils, we use any round object with a diameter of 20 - 25 cm. The number of turns is 30. We bring out one end of the wire and wind 10 turns, after which, without breaking, we bring out the second end. We continue winding another 20 turns and bring out the third end. We make wire leads with a margin of 10 to 20 cm. Remove the resulting winding from the object and wrap it tightly with electrical tape, leaving three wire leads (Fig. 5).

The second coil is performed in a similar way. For the greatest success, we perform the coils as much as possible in the same way, with a mirror reflection.

Let's start assembling the radio components. We expose the parts on the board and carry out soldering according to the diagram in Figure 4. When using cardboard or material with holes, we connect the parts with insulated wires with any cross section. When using prepared textolite, we perform soldering to finished tracks. The scheme can be placed in a wooden or plastic box.

We solder the leads of the coils, according to the diagram. We solder and output two wires with a battery connector.

We prepare a stand for the circuit and coils. We select the dimensions taking into account the fact that the distance between the coils must be at least 10 cm, since the circuit and the attached rod must fit between them, respectively.

To properly fix the coils, temporarily throw the headphones to the circuit and insert the battery. With small movements of the coils, we achieve silence in the headphones with single clicks or the highest, barely audible sound. We try to bring metal to one of the coils, if we hear significant changes, this indicates that the metal detector is working. We fix the coils and the board in this position. If possible, it is better to glue them immediately, and then cover them with oil varnish.

For headphones, we make two holes in the bar - from below and from above. With the help of wire cutters, electrical tape and a soldering iron, we increase the headphone wire to the required length - from the circuit to the area of ​​\u200b\u200bthe person's ears. Growth must be taken into account. We stretch the wire inside the rod and solder it to the circuit.

We cut off the excess of the stand and attach the barbell to it in a way convenient for you.

Adjustment

The most accurate setting is the absence of clicks in the headphones, and the presence of a barely audible high-frequency squeak.

There are three ways to adjust:

  1. We bring the metal alternately to the coils. On the coil where the noise stopped, we bring the last turn inside the coil ring.
  2. You can use small pieces of aluminum. We bring them to the coils and achieve silence or single clicks. We fix with glue.
  3. We fix the tube on the coil and push the ferrite rod through it. Having achieved the desired result, we fix the rod in this position. Watch the video below, which demonstrates how to make a homemade regulator for tuning in this way.

With good hearing and experience, you can use the manufactured metal detector as a simple metal detector with discrimination, that is, with recognition of metal types.

Modernization

If you figured out how to make the simplest metal detector with your own hands, you can start a small upgrade without chips in Figure 9. The list of parts is compiled in Table 2.

The new circuit adds an RC circuit consisting of a resistor and a capacitor. It will allow you to achieve increased sensitivity.

Added variable resistors to regulate the circuit without touching the coils. This will seal the sensitive unit of the metal detector in a strong shockproof box.

Instead of headphones, you can use a speaker with a capacitor to slightly increase the volume.

In this scheme, the coils are placed one on one, as shown in Figure 10. Before fixing the coils, we adjust them by moving them.

When turned on, we set the variable resistors to the same position and rotate to achieve fine tuning. After that, it remains only to take a metal detector and go in search of nuggets or metals. It has been tested in practice - if you search on any Russian beach, you can find gold and silver.

A deep metal detector is similar in design to a conventional one, with the exception of some technical details. Its difference is also an increased sensitivity to metal objects, which makes it possible to detect them at a greater depth compared to a simple metal detector. In addition, there is a selective search function, that is, the ability to find objects of a certain size without reacting to inappropriate parameters.

Diagram of a deep metal detector

It is quite simple, despite the apparent complexity. The metal detector consists of two parts - receiving and transmitting. The main device is a high frequency transmitter generator. Two loop antennas, one of which serves as a signal transmitter, the second as a receiver. They must be located strictly at an angle of 90 degrees to each other to prevent the signal from the generator from being picked up by the receiving antenna. When a metal object is found, the magnetic field generated by the generator is distorted and subsequently picked up by the receiving antenna. In this case, the mass of a metal object is used as a radiation source, sending the energy produced to the receiving antenna.

Metal detector receiver circuit

The transmitter includes a thyristor with a power of 0.25 to 1 W, a sound generator with a frequency of 200 Hz. When a metal object is found, the operator hears a sound with a frequency of 200 Hz, the strength of which depends on the size of the found object and the distance to it.

A detector receiver whose oscillation circuit responds to a frequency of 120 kHz and consists of two diodes. Absolutely any low-frequency generator that can be found in an old radio can serve as an amplifier. Enough transistor amplifier in the amount of 5-6 pieces. A transistor is also used as a current amplifier for a pointer device, which allows you to measure the level of the received signal. That is, the device has two types of indicators - visual and acoustic. The frequency of operation is set in such a way as not to interfere with the operation of the signal receiver.

Transmitter circuit

Required parts and tools for assembly

To assemble such a metal detector, you must first prepare a set of necessary parts and tools.

In the case of a pulse metal detector, an approximate parts list will look like this:

  1. Electrolytic capacitors with a voltage of at least 16 V of the following capacities: 2 capacitors with a capacity of 10 uF, one with a capacity of 2200 uF, 2 pcs - 1 uF.
  2. Ceramic capacitors: 1 piece with a capacity of 1 nF.
  3. Film capacitors of the lowest voltage value, for example, 63 V - 2 pcs of 100 nF each.
  4. Resistors of 0, 125 W: 1 k - one, 1.6 k - one, 47 k - one, 62k - two, 100 k - one, 120 k - one, 470 k - one, 2 ohms - one, 100 ohms - one, 470 ohm - one, 150 ohm - one,
  5. Resistors of 0.25 W: 10 ohms - one.
  6. 0.5 W resistors: 390 ohms - one
  7. Resistors 1 W: 220 ohms - one.
  8. Variable resistors: 10 k - one, 100 k - one,
  9. Transistors: BC 557 - one, BC 547 - one, IRF 740 - one,
  10. Diodes: 1N4148 - two, 1N4007 - one.
  11. Chips: K157 UD2, NE555.
  12. panels for each.

Metal detector parts

From tools when performing work you will need:

  • Soldering iron, tin, special solder, other soldering accessories.
  • A set of screwdrivers, wire cutters, pliers and other metalwork tools.
  • Materials for the production of printed circuit boards.

Stages of assembling a metal detector

The process of assembling a deep metal detector with your own hands includes the following steps:

At the first stage, it is necessary to assemble the electronic part, namely the control unit.

The step by step process looks like this:

  • Cutting textolite of the required size.
  • Preparation of a printed circuit board drawing and its transfer directly to the board.
  • Preparation of pickling solution. It consists of table salt, electrolyte and hydrogen peroxide.
  • Etching the board and drilling process holes.
  • Tinning the board with a soldering iron.
  • Next comes the most important stage in the assembly of the control unit. This is the selection, search and soldering of parts directly to the board.
  • Winding the test coil. There are several options for winding it. The easiest option is to use a 0.5 PEV wire and wind it 25 turns on a suitable frame with a diameter of about 19-20 cm.

The best option would be to solder everything directly, and after the setup is completed, select the necessary connectors and adapters. It is better not to twist, it has a negative effect on the sensitivity of the device.

The second good option would be to make such a ring from a twisted pair wire. It will take about 2.5 - 2.7 m of wire.

To achieve maximum sensitivity, do the following:

  1. Wind 25 turns of wire.
  2. Carry out a test by cutting off small pieces of wire and observing the increase in sensitivity.
  3. It is necessary to do this until the sensitivity begins to decrease.
  4. Count the number of turns, wind the final version of the coil by adding 1-2 turns. Thus, the maximum sensitivity value is reached.

Upon completion of the main work, the control unit, coil and other parts are fixed in place on the rod. The metal detector can be turned on and checked.

Possible assembly problems

  • The assembled device does not react to metal objects. The cause may be a breakdown of the diodes, or the transistor. Defective parts need to be replaced.
  • Excessive heating of the transistor. You should install a resistor of lower resistance, reducing it until the heating stops.

The assembly of this type of metal detector is not too difficult, with strict observance of all the rules and instructions.