Homemade metal detectors: simple and more complex - for gold, ferrous metal, for construction. How to make a simple metal detector with your own hands - step-by-step instructions The simplest metal detector using circuit beats

A metal detector is an electronic device for searching and distinguishing metals, metal objects that can be hidden at different depths under a layer of sand, earth, in the walls of rooms and various structures.

Schematic diagrams of metal detectors made on transistors, microcircuits and microcontrollers are given. A factory-made metal detector is a fairly expensive device, so making a homemade metal detector yourself can save quite a bit of money.

The circuits of modern metal detectors can be built according to different operating principles; we list the most popular of them:

• Beat method (measuring changes in reference frequency);
• Induction balance at low frequencies;
• Induction balance on spaced coils;
• Pulse method.

Many novice radio amateurs and treasure hunters are wondering: how to make a metal detector yourself? It is advisable to start your acquaintance with assembling a simple metal detector circuit; this will allow you to understand the operation of such a device and gain first skills in searching for treasures and products made of multi-colored metals.

The metal detector is designed to detect a metal object (well cover, pipe section, hidden wiring). The metal detector consists of a parallel voltage stabilizer (transistors V1 V2) at a high frequency generator (about 100 kHz) on transistor V4, an RF vibration detector (V5) and...

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The metal detector allows you to detect any metal object at a distance of up to 20 cm. The detection range depends only on the area of ​​the metal object. For those for whom this distance is not enough, for example treasure hunters, we can recommend increasing the size of the frame. This should also increase the detection depth. The schematic diagram of the metal detector is shown in the figure. The circuit is assembled using transistors operating in...

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Circuit diagram of a homemade beat metal detector, which is built on five microcircuits. Finds a 0.25mm coin at a depth of 5cm, a pistol at a depth of 10cm, and a metal helmet at 20cm. The schematic diagram of a beat metal detector is shown below. The circuit consists of the following components: a crystal oscillator, a measuring oscillator, a synchronous detector, a Schmidt trigger, an indication device...

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The circuit shown in the figure is a classic metal detector. The operation of the circuit is based on the principle of superheterodyne frequency conversion, which is usually used in a superheterodyne receiver. Schematic diagram of a metal detector with an integrated ULF; it uses two radio frequency generators, the frequencies of which are 5.5 MHz. The first radio frequency generator is assembled on a T1 transistor type BF494, frequency...

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This metal detector, despite the small number of parts and ease of manufacture, is quite sensitive. It can detect large metal objects, such as a heating battery, at a distance of up to 60 cm, while small ones, for example, a coin with a diameter of 25 mm, can be detected at a distance of 15 cm. The operating principle of the device is based on a change in frequency in the measuring generator under the influence of nearby metals and. ..

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A simple compact metal detector is needed to detect various metal objects (for example, pipes, wiring, nails, fittings) in walls under a layer of plaster. This device is completely autonomous, powered by a 9-volt Krona battery, consuming 4-5 mA from it. The metal detector has sufficient sensitivity to detect: pipes at a distance of 10-15 cm; wiring and nails at a distance of 5-10...

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Scheme of a small-sized, highly economical metal detector with good repeatability and high performance characteristics, using widely available and inexpensive parts. An analysis of most common circuits has shown that they are all powered from a source with a voltage of at least 9 V (that is, “Krona”), and this is both expensive and uneconomical. So, assembled on the K561LE5 chip...

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The metal detector circuit does not have any special features, it is simple and can be repeated even by novice radio amateurs. As is often written in books and magazines, with proper installation and working parts, it starts working immediately. The printed circuit board of the device is shown in the figure, it is made for SMD components, all parts are installed from the foil side, and no drilling is required. Manufacturing a search coil requires high...

After reading a little on amateur radio forums production of metal detectors, found that most people collecting metal detectors, in my opinion, are unfairly written off beat metal detectors- so called BFO metal detectors. Allegedly, this is the technology of the last century and “children’s toys.” — Yes, this is a simple and unprofessional device that requires certain skills and experience in handling. It does not have a clear metal selectivity and requires adjustment during operation. However, it is also possible to perform a successful search under certain circumstances. As an option - beach search- perfect option for a metal detector on beats.

Place to search with a metal detector.

You need to go with a metal detector where people lose something. I'm lucky to have a place like this. Not far from my house there is an abandoned river sand quarry, where people constantly relax in the summer, drinking and swimming in the river. It’s clear that they are constantly losing something. In my opinion, the best place for searching with a metal detectorBFO I can't think of it. Lost items are instantly buried at a shallow depth in dry sand and it is almost impossible to find them manually. Some kind of mysticism. I remember when I was a child I dropped my apartment keys in the sand there. Here I am standing, the keys fell here, but no matter how much I dug up that area, it was all to no avail. They literally fell through the ground. Just an enchanted place. At the same time, on this “golden” beach, I constantly found other people’s keys, lighters, coins, jewelry and phones in the sand. And on my last trip with a metal detector, I found a woman’s thin gold ring. It was almost at the surface, slightly sprinkled with sand. Perhaps it was just luck. Actually, it was for this beach that I made my metal detector.

Advantages of a beat metal detector.

Why exactly BFO? - First of all, this is the most simple metal detector option. Secondly, it has at least some signal dynamics depending on the properties of the object. Not really pulse metal detector- “beeping” for everything the same. I in no way want to belittle advantages of a pulse metal detector. This is also a wonderful device, but it is not suitable for a beach littered with corks and foil. Many will say that a beating metal detector does not distinguish the properties of an object, howls and buzzes at everything the same. However, it is not. After practicing on the beach for a couple of days, I became quite good at identifying foil as a sharp and profound change in frequency. Beer bottle caps cause a strictly defined frequency change that needs to be remembered. But the coins emit a weak, “point” signal - a subtle change in frequency. All this comes with experience, patience and good hearing. Beat metal detector- it’s still "auditory" metal detector. The analyzer and signal processor here is a person. For this reason, you must search on headphones, and not on the speaker. Moreover, the best option is large headphones, not earplugs.

Metal detector design.

Structurally I decided to make a metal detector foldable and compact. So that it fits into a regular bag, so as not to attract the attention of “normal” people. Otherwise, when you get to the search site, you look like an “alien” or a scrap metal collector. For this purpose, I bought the smallest (two-meter five-legged) telescopic rod in the store. Left three knees. The result was a fairly compact folding base, on which I assembled my metal detector.

The entire electronic unit was assembled in the 60x40 plastic wiring box I already loved. The end cap, the power compartment partition and the power compartment cover were also made from its plastic. The parts were glued together with superglue and mounted on M3 bolts. Fastening metal detector electronic unit to the rod is made in the form of a metal bracket, which is inserted into place of the fishing reel with fishing line and secured with the standard nut of the rod. The result is an excellent lightweight and durable design. On the outside of the unit there is a power button, a coil connection socket (a five-pin socket from a “grandfather’s” tape recorder), a frequency regulator and a headphone jack.

Metal detector circuit board was made on site by laying out the paths with a waterproof marker. For this reason, unfortunately, I cannot provide a seal. Surface mounting - no holes - "lazy" - my favorite. It is also important, after assembling the board, to cover it with any varnish to protect it from moisture and debris. In field conditions this is very important. For example, I lost one day because some debris got inside under the microcircuit. The metal detector just stopped working. And I had to return home, disassemble it, blow it out and open the board with varnish.

Diagram of a beat metal detector.

The circuit itself (see below) was redesigned and optimized by me from two metal detector circuits. This is "" - Radio magazine, 1987, No. 01, pp. 4, 49 and " High sensitivity metal detector" - Radio magazine, 1994, No. 10, page 26.

The result is a simple and functional circuit that provides stable low-frequency resulting beats - what is needed to determine by ear the slightest changes in frequency.

The stability and sensitivity of the metal detector are ensured by the following circuit solutions:

The reference and measuring generators are separated- made in separate microcircuit packages - DD1 and DD2. At first glance, this is wasteful - only one logical element of the microcircuit package is used out of four. That is, yes, the reference generator is assembled on only one logical element of the microcircuit. The remaining three logical elements of the microcircuit are not used at all. The measuring generator is built in exactly the same way. It would seem that it makes no sense not to use the free logical elements of the microcircuit package. However, this is precisely what makes a lot of sense. And it consists in the fact that if, for example, you assemble two generators in one microcircuit package, they will synchronize each other at close frequencies. It will not be possible to obtain the slightest changes in the resulting frequency. In practice, this will look like a sharp change in frequency only when a massive metal object is close to the measuring coil. In other words, sensitivity sharply decreases. Metal detector does not react to small objects. The resulting frequency seems to “stick” to zero—up to a certain point, there are no beats at all. They also say - “ dumb metal detector", "dull sensitivity". By the way " Metal detector on a chip" - Radio magazine, 1987, No. 01, pp. 4, 49 is built on just one microcircuit at all. This effect of frequency synchronization is very noticeable there. It is completely impossible for him to search for coins and small objects.

Also, both generators must be shielded with separate small screens made of tin. This increases by an order of magnitude stability and sensitivity of the metal detector as a whole. It is enough to simply solder small partitions made of tin at minus between the generator chips to ensure that the parameters of the metal detector are improved. The better the screen, the better the sensitivity (the influence of the generators on each other is weakened and plus protection from external influences on the frequency).

Electronic tuning.

Comparator on DD3.2 – DD3.4.

This circuit element converts the sinusoidal signal from the output of the DD3.1 mixer into rectangular pulses of double frequency.

Firstly, rectangular pulses are clearly audible at hertz frequencies as clear clicks. While a sinusoidal signal of hertz frequencies is already difficult to distinguish by ear.

Secondly, doubling the frequency allows the adjustment to come closer to zero beats. As a result, by adjusting you can achieve a “clicking” sound in the headphones, the change in frequency of which can already be detected when you bring a small coin to the coil at a distance of 30 cm.

Generator power stabilizer.

Naturally, in this circuit, the supply voltage noticeably affects the frequency of generators DD1.1 and DD2.1 metal detector. Moreover, each of the generators is affected differently. As a result, with the battery draining a little The beat frequency of the metal detector also “floats”. To prevent this, a five-volt stabilizer DA1 was introduced into the circuit to power generators DD1.1 and DD2.1. As a result, the frequency stopped “floating”. However, it should be said that on the other hand, due to the five-volt power supply of the generators, several The sensitivity of the metal detector has decreased generally. Therefore, this option should be considered optional and, if desired, generators DD1.1 and DD2.1 can be powered from the crown without a DA1 stabilizer. You just have to adjust the frequency manually more often using a regulator.

Metal detector coil design.

(See diagram below).

Since this not a pulse metal detector, butBFO, then the search coil (L2) is not afraid of metal objects in its design. We don't need a plastic bolt. That is, we can safely use a metal (but only open!) frame and a regular metal bolt for the hinge to make it. Subsequently, when setting up the circuit, all the influences of the metal in the structure will be brought to zero by the tuning core of the L1 coil. The L2 coil itself contains 32 turns of PEV or PEL wire with a diameter of 0.2 - 0.3 mm. The diameter of the coil should be about 200 mm. It is convenient to wind on a small plastic conical bucket. The resulting turns are completely wrapped with electrical tape and tied with thread. Next, this entire structure is wrapped in foil (cooking foil for baking). Tinned wire is wound on top of the foil in several turns around the entire perimeter of the coil. This wire will be the output of the foil screen of the coil. Once again everything is wrapped together with electrical tape. The coil itself is ready.

The frame on which the reel will be located and with which it will be attached to the fishing rod is made of springy steel (not soft) wire 3-4 mm. It actually consists of three parts (see figure) - two twisted wire loops of the hinge, which will be connected by a bolt to each other and a wire ring threaded into the tube from the dropper (the ring should not be a closed turn).

This entire structure, together with the finished wire spool, is also tied together with threads and electrical tape.

The joint itself with the reel is attached to the rod by tying it with nylon threads and gluing it with epoxy resin.

It is advisable not to wet the coil during the search process, and especially not to use it for underwater searching. It is not airtight. Moisture that gets inside can destroy it over time.

Coil L1 (see diagram) is wound on a frame from a small-sized radio receiver with a metal screen and a tuning core. The coil contains 65 turns of PEV wire with a diameter of 0.06mm

Me and Diode. © site.

The proposed metal detector is designed for “close-range” search for objects. It is assembled according to the simplest scheme. The device is compact and easy to manufacture. Detection depth is:
coin 025mm......5 cm;
gun........................10 cm;
helmet................................20 cm.

Structural scheme

The block diagram is shown in Fig. 8. It consists of several functional blocks. The quartz oscillator is a source of rectangular pulses with a stable frequency. An oscillatory circuit is connected to the measuring generator, which includes a sensor - an inductor. The output signals of both generators are fed to the inputs of a synchronous detector, which generates a difference frequency signal at its output. This signal has an approximately sawtooth shape. For convenience of further processing, the signal from the synchronous detector is converted using a Schmidt trigger into a rectangular signal. The indication device is designed to generate a difference frequency sound signal using a piezo emitter and to visually display the value of this frequency using an LED indicator.

Rice. 8. Block diagram of a beat metal detector

Schematic diagram

QUARTZ GENERATOR

The quartz oscillator has a circuit similar to that of a metal detector generator on the “transmit-receive” principle, but implemented on inverters D1.1-D1.3. The frequency of the generator is stabilized by a quartz or piezoceramic resonator Q with a resonant frequency of 215 Hz ~ "32 kHz (“clock quartz”). Circuit R1C2 prevents excitation of the generator at higher harmonics. The OOS circuit is closed through resistor R2, and the POS circuit is closed through the resonator Q.

The generator is simple, has low current consumption from the power source, operates reliably at a supply voltage of 3..15 V, and does not contain tuning elements or overly high-resistance resistors. The output frequency of the generator is about 32 kHz. An additional counting trigger D2.1 is needed to generate a signal with a duty cycle exactly equal to 2, which is required for the subsequent synchronous detector circuit.

Rice. 9. Schematic diagram of a beat metal detector

MEASURING GENERATOR

The generator itself is implemented on a differential stage using transistors VT1, VT2. The PIC circuit is implemented galvanically, which simplifies the circuit. The load of the differential cascade is the oscillatory circuit L1C1. The generation frequency depends on the resonant frequency of the oscillatory circuit and, to some extent, on the operating current of the differential stage. This current is set by resistors R3 and R3." Adjustment of the frequency of the measuring generator when setting up the device is carried out roughly by selecting capacitance C1 and smoothly by adjusting the potentiometer R3."

To convert the low-voltage output signal of the differential stage to standard logic levels of digital CMOS chips, a common-emitter stage on transistor VT3 is used. A shaper with a Schmidt trigger at the input of element D3.1 provides steep pulse edges for the normal operation of the subsequent counting trigger.

An additional counting trigger D2.2 is needed to generate a signal with a duty cycle exactly equal to 2, which is required for the subsequent synchronous detector circuit.

SYNCHRONOUS DETECTOR

The detector consists of a multiplier implemented on the D4.1 "Exclusive OR" element and an integrating circuit R6C4. Its output signal is close in shape to a sawtooth, and the frequency of this signal is equal to the difference between the frequencies of the quartz oscillator and the measuring oscillator.

SCHMIDT TRIGGER

The Schmidt trigger is implemented on element D3.2 and generates rectangular pulses from the sawtooth voltage of the synchronous detector.

INDICATION DEVICE

It is simply a powerful buffer inverter, implemented on the three remaining inverters D1.4-D1.6, connected in parallel to increase the load capacity. The load of the display device is an LED and a piezo emitter. Types of parts and design

Instead of K561 series microcircuits, it is possible to use K1561 series microcircuits. You can try to use some K176 series microcircuits. The inputs of unused elements of digital microcircuits cannot be left unconnected! They should be connected either to a common bus or to a power bus.

Transistors VT1, VT2 are elements of an integrated transistor assembly of type K159NT1 with any letter. They can be replaced with discrete transistors with primary conductivity of types KT315, KT312, etc. Transistor VT3 - type KT361 with any letter or a similar type with p-p-p conductivity.

There are no special requirements for the resistors used in the metal detector circuit. They just need to have a solid design and be easy to install. The rated power dissipation should be 0.125...0.25 W. Compensation potentiometer R3" is preferably a multi-turn type SP5-44 or with a vernier adjustment type SP5-35. You can get by with conventional potentiometers of any type. In this case, it is advisable to use two in series. One is for coarse adjustment, with a nominal value of 1 kOhm. The other is for fine adjustments, nominal 100 Ohm.

Inductor L1 has an internal winding diameter of 160 mm and contains 100 turns of wire. Type of wire - PEL, PEV, PELSHO, etc. Wire diameter 0.2...0.5 mm. See below for coil design.

Capacitor SZ is electrolytic. Recommended types - K50-29, K50-35, K53-1, K53-4 and other small ones. The remaining capacitors, with the exception of the capacitor of the oscillatory circuit of the measuring generator coil, are ceramic type K10-7, etc. Circuit capacitor C1 is special. High demands are placed on it in terms of accuracy and thermal stability. The capacitor consists of several (5...10 pcs.) individual capacitors connected in parallel. Rough tuning of the circuit to the frequency of the quartz oscillator is carried out by selecting the number of capacitors and their rating. Recommended type of capacitors K10-43. Their thermal stability group is MPO (i.e. approximately zero TKE). It is possible to use precision capacitors of other types, for example K71-7. Ultimately, you can try to use thermally stable mica capacitors with silver plates such as KSO or polystyrene capacitors.

LED VD1 type AL336 or similar with high efficiency. Any other visible LED will also work.

Quartz resonator Q - any small-sized watch quartz (similar ones are also used in portable electronic games).

Piezo emitter Y1 - can be type ZP1-ZP18. Good results are obtained when using piezo emitters from imported phones (they go to waste in huge quantities when making phones with caller ID). The design of the device can be quite arbitrary. When developing it, it is advisable to take into account the recommendations set out in the sections on sensors and housing design.

The printed circuit board of the electronic part of the metal detector can be manufactured using any of the traditional methods; it is also convenient to use ready-made prototype printed circuit boards for DIP chip housings (pitch 2.5 mm). Setting up the device

1. Check the correct installation according to the schematic diagram. Make sure there are no short circuits between adjacent conductors of the printed circuit board, adjacent legs of microcircuits, etc.

2. Connect the battery or 9V power source, strictly observing the polarity. Turn on the device and measure the current consumption. It should be about 10 mA. A sharp deviation from the specified value indicates incorrect installation or malfunction of the microcircuits.

3. Make sure that there is a pure square wave with a frequency of about 32 kHz at the output of the quartz oscillator and at the output of element D3.1.

4. Make sure that there are signals with frequencies of about 16 kHz at the outputs of triggers D2.1 and D2.2.

5. Make sure that there is a sawtooth difference frequency voltage at the input of element D3.2, and rectangular pulses at its output.

6. Make sure that the display device is working - visually and audibly. Possible modifications

The design of the device is extremely simple and therefore we can only talk about further improvements. These include:

1. Adding an optional LED logarithmic frequency indicator.

2. Using a transformer sensor in a measuring generator.

Let's take a closer look at these modifications.

LOGARITHMIC FREQUENCY INDICATOR

The logarithmic frequency indicator is an advanced LED indicator. Its scale consists of eight separate LEDs. When the measured frequency reaches a certain threshold, the corresponding LED on the scale lights up, the other seven do not light up. The peculiarity of the indicator is that the frequency response thresholds for neighboring LEDs differ from each other by a factor of two. In other words, the indicator scale has a logarithmic graduation, which is very convenient for a device such as a beat metal detector. The schematic diagram of a logarithmic frequency indicator is shown in Fig. 10.

Despite the fact that the circuit of this indicator was developed by the author independently, it does not claim to be original, since a patent search showed that similar circuits are known. Nevertheless, both the indicator circuit itself and its implementation on a domestic element base are, in the author’s opinion, of some interest.

Fig. 10. Schematic diagram of a logarithmic indicator

The logarithmic indicator works as follows. The input of the indicator receives a signal from the output of the Schmidt trigger of the beat metal detector circuit (see Fig. 9). This signal is the input for binary counters D5.1-D5.2 (the numbering continues according to the scheme in Fig. 9). These counters are periodically reset to zero by a high-level signal from the auxiliary oscillator on the Schmidt trigger D3.3 with a frequency of about 10 Hz. At the rising edge of the auxiliary generator signal, the state of the counters is also recorded in parallel four-bit registers D6 and D7. Thus, at the outputs of registers D6 and D7 there is a digital code for the frequency of the beat signal. It is possible to convert this code into a logarithmic scale quite simply (and this is the “highlight” of this scheme) if the lighting of the corresponding scale LED is set in correspondence with the appearance of a one in a certain bit of the frequency code with all zeros in the higher bits of the code.

Obviously, this task must be performed by a combinational circuit. The simplest implementation of such a circuit consists of periodically repeating links of OR elements. The practical circuit uses NOR elements D8, D9 together with powerful buffer inverters D10, D11. At the output of the circuit, a logical signal for controlling the scale LEDs is obtained in the form of a “wave of units”. From the point of view of saving battery power, of course, it is more advisable to make the scale not in the form of a glowing column of LEDs (up to 8 pieces at a time), but in the form of a moving point from one glowing LED. To do this, the LEDs of the indicator line are connected between the outputs of the combinational circuit.

For very low frequencies, a flashing LED indication is still more suitable. In the proposed scheme, it is combined with the beginning of the LED scale and goes out as soon as its next segment lights up. By selecting elements R8, C5, you can change the frequency value of the auxiliary generator, thus changing the frequency scale limit. Types of parts and design

The types of microcircuits used are given in table. 4.

Table 4. Types of chips used

Instead of K561 series microcircuits, it is possible to use K1561 series microcircuits. You can try to use some K176 series microcircuits. The wiring of power circuits and numbering of pins for microcircuits D8-D11 are not shown for simplicity.

LEDs VD2-VD9 type AL336 or similar with high efficiency. Their current-setting resistors R9-R17 have the same rating of 1.0...5.1 kOhm. The lower the resistance of these resistors, the brighter the LEDs will glow. However, the load capacity of the K561LN2 microcircuits may not be enough.

In this case, it is recommended to use parallel-connected output inverters in the indicator circuit. The most convenient way to organize this parallel connection is by simply soldering additional chip packages of the same type (up to 4 pcs.) on top of each of the K561LN2 chips installed in the circuit.

FURTHER IMPROVEMENTS WITH FREQUENCY INDICATOR

The logarithmic frequency indicator proposed above is essentially a kind of digital frequency meter. A promising direction for improving beat-based metal detectors involves using the principle of an electronic frequency meter to record small frequency deviations. Section is devoted to this topic. 2.3.

TRANSFORMER SENSOR

The way to eliminate the listed shortcomings is simple and obvious - you need to use a coil consisting of a minimum number of turns - one turn! Naturally, such a solution does not work “head-on”, since the insignificant inductance of one turn would require gigantic capacitances of the capacitors of the oscillating circuits, signal generators with a huge output current and special tricks to ensure high quality factor. And here it’s time to remember the existence of a device designed to match impedances, to convert high-voltage alternating signals with low current into low-voltage signals with high current, and vice versa about a transformer.

The transformer sensor allows you to implement a folding design of a compact beat metal detector. Its sketch is shown in Fig. 11. The sensor transformer is made on a toroidal magnetic core installed directly on the metal detector board, housed in a plastic case. The step-down winding of the transformer and the coil of the sensor are structurally a single unit in the form of a rectangular frame made of insulated single-core copper wire with a cross-section of 6 mm², closed by soldering. This frame has the ability to rotate.

When folded, the frame is located around the perimeter of the device body and does not take up extra space. In working position it rotates 180°. To ensure that the frame is fixed in position, sealing sleeves made of rubber or other similar material are used. It is also possible to use any other suitable mechanical frame fasteners.

Rice. 11. Design of a beating metal detector with a folding sensor frame

The cross-section of the conductor from which the transformer sensor coil is made must be no less than the total cross-section of all the turns that make up a conventional metal detector sensor coil. This is necessary not only to give the structure the necessary strength and rigidity, but also to ensure that the quality factor of the oscillatory circuit with such a transformer analogue of the inductor is not too low (by the way, when using such a turn as a radiating coil, the current in it can reach tens ampere!). For the same reason, proper selection of the wire cross-section of the step-down winding of the transformer is necessary. It may have a smaller cross-section than the cross-section of the coil conductor, but its ohmic resistance should not be greater than the ohmic resistance of the coil.

To reduce losses due to ohmic resistance, it is necessary to very carefully connect the turn to the step-down winding of the transformer. The recommended connection method is soldering (for a copper coil) and inert gas welding (for an aluminum coil).

The following requirements apply to the transformer. First, it must operate with low losses at the required frequency. In practice, this means that its magnetic core must be made of low-frequency ferrite. Secondly, its windings should not make a noticeable contribution to the sensor impedance. In practice, this means that the inductance of the step-down winding should be noticeably greater than the inductance of the turn. For toroidal ferrite magnetic cores with magnetic permeability c = 2000 and a diameter of more than 30 mm, this is true even for one turn of the step-down winding. Thirdly, the transformation ratio must be such that the inductance of the step-up winding when the sensor coil is connected to the step-down winding is approximately the same as that of a conventional coil of a typical sensor.

Unfortunately, the advantages of a transformer sensor significantly outweigh its disadvantages only for beat metal detectors. For more sensitive devices, such a sensor is not applicable due to its rather high sensitivity to mechanical deformations, which leads to false signals that appear during movement. That is why the transformer sensor is discussed only in the section devoted to the beat metal detector.

A device that allows you to search for metal objects located in a neutral environment, such as soil, 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 thanks to the development of microelectronics, metal detectors, which are produced by many enterprises around the world, are highly reliable and have small overall and weight characteristics.

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

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 pulse echo or radar. Their difference from locators lies in the fact that the transmitted and received signals act constantly and simultaneously; in addition, they operate at the same frequencies.

Devices operating on the “receive-transmit” principle record the signal reflected (re-emitted) from a metal object. This signal appears due to the exposure of a metal object to an alternating magnetic field 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 potential for detecting 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 with your own hands before work.

Other devices are sometimes called beat metal detectors. This name comes from the distant past, more precisely from the times when superheterodyne receivers were widely used. Beating is a phenomenon that becomes noticeable when two signals with similar frequencies and equal amplitudes are summed. The beat consists of pulsating the amplitude of the summed signal.

The signal pulsation frequency 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, and the so-called difference frequency is isolated.

This scheme has been used for a long time, but nowadays it is not used. They were replaced by synchronous detectors, but the term remained in use.

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

The device is configured with your own hands so that the generated frequencies match or at least are close. As soon as metal enters the action zone, the set parameters change and the frequency changes. The frequency difference can be recorded in a variety of ways, from headphones to digital methods.

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

But besides this, when using them, it is necessary to take into account the fact that they have high energy consumption.

Typical design

The metal detector includes the following components:

1. The coil is a box-type structure that houses the signal receiver and transmitter. 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 reel 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 to the rod, which is called the middle one.
3. The middle rod is the unit located between the lower and upper rods. Devices are attached to it that allow you to adjust the size of the device. On the market you can find models that consist of two rods.
4. The top rod usually has a curved appearance. It resembles the letter S. This shape is considered optimal for attaching it to the hand. An armrest, a control unit and a handle are installed on it. The armrest and handle are made of polymer materials.
5. The metal detector control unit is necessary to process the data received from the coil. After the signal is converted, it is sent to headphones or other display devices. In addition, the control unit is designed to regulate 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.

It is this relative simplicity of design that allows you to make metal detectors with your own hands.

Types of metal detectors

There is a wide range of metal detectors on the market, 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 operating frequency. The thing is that low frequencies allow the metal detector to see to a fairly large depth, but they are not able to see small details. High frequencies allow you to notice small objects, but do not allow you to view the ground to great depths.

The simplest (budget) models operate at one frequency; models that fall into the middle price range use 2 or more frequencies. There are models that use 28 frequencies when searching.

Modern metal detectors are equipped with a function such 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 search engine’s headphones, and when non-ferrous metal is detected, another sound will sound.

Such devices are classified 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 capable of detecting 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 detecting metal in the ground, walls, etc. Despite its external complexity, making a metal detector with your own hands is not that 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.

Do-it-yourself simple metal detector

The metal detector circuit is not complicated, and you can find it either on the vast world wide web 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. You can assemble a simple metal detector with your own hands using a soldering iron or other available method. The main thing is that the parts should not touch the body of the device. To ensure the operation of the assembled metal detector, power supplies of 9 - 12 volts are used.

To wind the coil, use a wire with a cross-sectional diameter within 0.3 mm; of course, this will depend on the chosen circuit. By the way, the wound coil must be protected from exposure to extraneous radiation. To do this, shield it with your own hands using ordinary food foil.

To flash the controller firmware, special programs are used, 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 circuits without them.

There are simpler 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 yourself. But before you start making it, you need to understand how a typical circuit works.

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

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

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

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

After the board is etched, it is necessary to make holes in it to install the circuit components. After tinning the board. The most important stage is coming. Do-it-yourself installation and soldering of parts onto a prepared board.

To wind the coil with your own hands, use PEV brand wire with a diameter of 0.5 mm. The number of turns and the diameter of the coil depend on the selected circuit 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 wrong! Yes, there are applications that install under Android OS.

But in fact, after installing such an application, he will actually be able to find metal objects, but only pre-magnetized ones. It will not be able to search for, much less discriminate against, metals.

To make a metal detector for synchronization failures, a metal-plastic water pipe is used. The rod can be detachable, pipes with a diameter of 16 and 20 fit tightly into each other. We assemble the parts using any non-conductive glue and packing tape. Capacitors with good temperature stability, mica - this is important. Coat the coils and circuit with oil varnish.
The battery from a mobile phone lasts for 20-30 hours of continuous operation.

In beat-based circuits, synchronization of generators is undesirable. The frequencies of the generators are shifted in advance, which leads to a decrease in sensitivity. We propose to use instability on the verge of synchronization failure. The closer to the point of failure, the higher the sensitivity.
A simple scheme senses a coin from 15 cm.

Let's take the simplest scheme. The circuit is not critical to power supply, number of turns and part ratings. There is only one condition: the left and right parts must be the same.

The symmetrically assembled circuit works immediately.
But it's interesting to watch. We feed the pipe.

Signals from the generators are supplied to the X and Y plates.

Frequency and phase are the same.

Capture on harmonics.

Shift 90 degrees.

These are the breakdowns. There's a clicking sound in the headphones.

Shift 180 degrees.

Generators are not synchronized.

Before the breakdown we measure the phase.
If you place the coils next to each other, the soil does not affect. The generators move simultaneously and in one direction. When moving sideways, an object falls under the coils, alternately increasing the difference in sound.

Before the breakdown, super noises.