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Many people unreasonably believe that homemade metal detectors are inferior in many respects to factory-made branded samples.

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

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

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

Therefore, it is worth, first of all, to disassemble the principle of operation of a metal detector, what it is and how it can be assembled independently at home.

How does it work

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

In cases where the object is not electrically conductive, but has its own magnetic field, the interference created by it will also be caught by shielding.

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

It is worth analyzing how such devices are created following the example of a Pirate-type metal detector.

Metal detector "Pirate"

We make a printed circuit board with our own hands

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

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

First, using only a laser printer, it is necessary to print the appropriate diagram created through the Sprint-Layout program. It is best to use light weight photo paper for this.
We prepare the workpiece from textolite, first we sand it, after which we clean it with a solution. It should have dimensions of 84x31.
Now on top of the blank we put photo paper with the diagram on the front side on which it was printed. We cover it with an A4 sheet and begin to iron it with a hot iron in order to transfer the marking scheme to the textolite.
After fixing the circuit from the toner, we place it all in water, where we carefully remove the paper with our fingers.
Further, if there are smeared areas, we correct them with a regular needle.
Now the board needs to be put into the solution for several hours blue vitriol(you can also ferric chloride).
The toner can be removed without any problem with any solvent, such as acetone.
Drilling holes for later placement structural elements(the drill should be very thin).
The last stage is to lude the tracks of the board. To do this, a special solution "LTI-120" is smeared on the surface, which needs to be smeared with soldering iron solder.

Installing elements on the board

This stage creating a metal detector consists in mounting all the elements on the created board:

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

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

The creation of a homemade coil is carried out on a frame with a diameter of 20 cm. The total number of turns should be approximately 25 pcs. This indicator assumes that a PEV wire is used, which has a diameter of 0.5 mm.

However, there is a certain feature. The total number of turns can be changed up or down. To find the best option, you need to take a coin to check in which case there will be the largest distance of its “catching”.

Other elements

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

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

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

to make the bar more convenient, it is worth buying 5 meters of an ordinary PVC pipe (which are used in plumbing), as well as several jumpers. At its upper end, it is worth installing a special palm rest to make it more comfortable to hold. For the board, you can find any box of the appropriate size that needs to be fixed on the rod;
to power the system, you can use a battery from a conventional screwdriver. Its advantages are light weight and large capacity;
when creating the body and structure, please note that they should not contain any extra metal elements. The reason is that they significantly distort the resulting electromagnetic field of the future device.

Checking a metal detector

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

So, he will have to “find” a five-ruble coin from a distance of approximately 30 cm, but if the coin has dimensions like the Soviet ruble, then already somewhere from 40 cm. He will “see” large and bulky metal from a distance of more than a meter.

Such a device will not be able to search for small objects at a considerable depth. In addition, he will not be able to distinguish the size and type of metal found. That is why, while searching for coins, it will be possible to stumble upon ordinary nails.

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

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

A metal detector or metal detector is designed to detect objects that differ in their electrical and / or magnetic properties from the environment in which they are located. Simply put, it allows you to find metal in the ground. But not only metal, and not only in the ground. Metal detectors are used by inspection services, criminologists, the military, geologists, builders to search for profiles under the skin, fittings, reconciliation of underground utility plans, and people of many other specialties.

Do-it-yourself metal detectors are most often made by amateurs: treasure hunters, local historians, members of military historical associations. They, beginners, are primarily intended for this article; the devices described in it allow you to find a coin with a Soviet penny at a depth of up to 20-30 cm or a piece of iron with manhole about 1-1.5 m below the surface. However, this home-made device can also be useful on the farm during repairs or at a construction site. Finally, having found a centner or two of an abandoned pipe or metal structures in the ground and handing over the find for scrap, you can get a decent amount. And there are definitely more such treasures in the Russian land than pirate chests with doubloons or boyar-robber egg-pods with efimki.

Note: if you are not well versed in electrical engineering with radio electronics, do not be afraid of diagrams, formulas and special terminology in the text. The very essence is stated simply, and at the end there will be a description of the device, which can be made in 5 minutes on the table, not knowing how to not only solder, but twist the wires. But it will allow you to "feel" the features of the search for metals, and if interest arises, knowledge and skills will come.

A little more attention compared to the rest will be given to the Pirate metal detector, see fig. This device is quite simple for beginners to repeat, but in terms of its quality indicators it is not inferior to many branded models priced up to $300-400. And most importantly, it showed excellent repeatability, i.e. full performance when manufactured according to descriptions and specifications. Circuitry and the principle of operation of the "Pirate" are quite modern; There are plenty of guides on how to set it up and how to use it.

Operating principle

The metal detector operates on the principle electromagnetic induction. In general, the metal detector circuit consists of an electromagnetic oscillation transmitter, a transmitting coil, a receiving coil, a receiver, a useful signal extraction circuit (discriminator) and an indication device. Separate functional units are often combined in circuitry and design, for example, the receiver and transmitter can work on one coil, the receiving part immediately highlights the useful signal, etc.

The coil creates an electromagnetic field (EMF) of a certain structure in the medium. If an electrically conductive object is in the area of \u200b\u200bits action, pos. And in the figure, eddy currents or Foucault currents are induced in it, which create its own EMF. As a result, the structure of the coil field is distorted, pos. B. If the object is not electrically conductive, but has ferromagnetic properties, then it distorts the original field due to shielding. In both cases, the receiver captures the difference between the EMF and the original one and converts it into an acoustic and/or optical signal.

Note: in principle, for a metal detector it is not necessary that the object be electrically conductive, the ground is not. The main thing is that their electrical and / or magnetic properties are different.

Detector or scanner?

In commercial sources, expensive highly sensitive metal detectors, e.g. Terra-N are often called geoscanners. This is not true. Geoscanners operate on the principle of measuring the electrical conductivity of the soil in different directions at different depths, this procedure is called lateral logging. According to the logging data, the computer builds on the display a picture of everything in the earth, including geological layers of various properties.

Varieties

Common parameters

The principle of operation of a metal detector can be implemented in technically different ways, according to the purpose of the device. Metal detectors for beach gold digging and construction and repair searches may look similar in appearance, but differ significantly in design and technical data. To properly make a metal detector, you need to clearly understand what requirements it must meet for this type of work. Based on this, the following parameters of search metal detectors can be distinguished:

Penetration, or penetrating power - the maximum depth to which the EMF of the coil extends in the ground. Deeper, the device will not detect anything at any size and properties of the object.
The size and dimensions of the search area is an imaginary area in the ground in which the object will be found.
Sensitivity is the ability to detect more or less small objects.
Selectivity is the ability to respond more strongly to desirable findings. The sweet dream of beach miners is a detector that only beeps for precious metals.
Noise immunity - the ability not to respond to EMF of extraneous sources: radio stations, lightning discharges, power lines, electric vehicles and other sources of interference.
Mobility and efficiency are determined by power consumption (how many batteries are enough), the device’s weight and dimensions, and the size of the search area (how much you can “probe” in 1 pass).
Discrimination, or resolution - gives the operator or control microcontroller the ability to judge the nature of the object found by the reaction of the device.

Discrimination, in turn, is a composite parameter, since there are 1, maximum 2 signals at the output of the metal detector, and there are more values that determine the properties and location of the find. However, taking into account the change in the reaction of the device while approaching the object, 3 components are distinguished in it:

Spatial - indicates the location of the object in the search area and the depth of its occurrence.
Geometric - makes it possible to judge the shape and size of an object.
Qualitative - allows you to make assumptions about the properties of the material of the object.

Operating frequency

All parameters of the metal detector are connected in a complex way and many relationships are mutually exclusive. For example, lowering the oscillator frequency makes it possible to achieve greater penetration and search area, but at the cost of increased power consumption, and worsens sensitivity and mobility due to an increase in coil size. In general, each parameter and their complexes are somehow tied to the frequency of the generator. That's why The initial classification of metal detectors is based on the operating frequency range:

Super-low-frequency (VLF) - up to the first hundreds of Hz. Absolutely non-amateur devices: power consumption from tens of watts, without computer processing, it is impossible to judge anything from a signal, vehicles are needed to move.
Low-frequency (LF) - from hundreds of Hz to several kHz. Simple circuitry and design, noise-resistant, but not very sensitive, bad discrimination. Penetration - up to 4-5 m with power consumption from 10 W (the so-called deep metal detectors) or up to 1-1.5 m when powered by batteries. They react most sharply to ferromagnetic materials (ferrous metal) or large masses of diamagnetic materials (concrete and stone building structures), therefore they are sometimes called magnetic detectors. They are not very sensitive to the properties of the soil.
Increased frequency (IF) - up to several tens of kHz. More difficult than bass, but the requirements for the coil are low. Penetration - up to 1-1.5 m, C grade noise immunity, good sensitivity, satisfactory discrimination. Can be universal when used in pulsed mode, see below. On flooded or mineralized soils (with fragments or particles of rock that shield EMF), they work poorly or do not smell anything at all.
High, or radio frequency (HF or RF) - typical metal detectors "for gold": excellent discrimination to a depth of 50-80 cm in dry non-conductive and non-magnetic soils (beach sand, etc.) Power consumption - as before. n. The rest is on the verge of "failure". The efficiency of the device largely depends on the design and quality of the coil(s).

Note: mobility of metal detectors according to paragraphs. 2-4 is good: from one set of salt cells ("batteries") AA and without overworking the operator, you can work up to 12 hours.

Pulse metal detectors stand apart. Their primary current flows into the coil in pulses. By setting the pulse repetition rate within the LF, and their duration, which determines the spectral composition of the signal corresponding to the IF-HF ranges, you can get a metal detector that combines the positive properties of LF, IF and HF or is tunable.

Search method

There are at least 10 EMF search methods. But such as, say, the method of direct digitization of the response signal with computer processing is the lot of professional use.

A home-made metal detector is schematically built most of all in the following ways:

Parametric.
Receiving-transmitting.
With phase accumulation.
On the beat.

Without receiver

Parametric metal detectors in some way fall outside the definition of the principle of operation: they have neither a receiver nor a receiving coil. For detection, the direct influence of the object on the parameters of the generator coil is used - inductance and quality factor, and the structure of the EMF does not matter. Changing the parameters of the coil leads to a change in the frequency and amplitude of the generated oscillations, which is fixed in various ways: by measuring the frequency and amplitude, by changing the current consumption of the generator, by measuring the voltage in the PLL loop (phase locked loop, "pulling" it to a given value), etc.

Parametric metal detectors are simple, cheap and noise-resistant, but their use requires certain skills, because. the frequency "floats" under the influence of external conditions. Their sensitivity is weak; most of all are used as magnetic detectors.

With receiver and transmitter

The device of the transceiver metal detector is shown in fig. at the beginning, to an explanation of the principle of operation; the principle of operation is also described there. Such devices allow to achieve the best efficiency in their frequency range, but are complex in circuitry, require a particularly high-quality coil system. Transceiver metal detectors with a single coil are called induction. Their repeatability is better, because the problem of the correct arrangement of the coils relative to each other disappears, but the circuitry is more complicated - you need to highlight a weak secondary signal against the background of a strong primary.

Note: in pulsed transceiver metal detectors, the emission problem can also be eliminated. This is explained by the fact that as a secondary signal they “catch” the so-called. "tail" of the pulse re-radiated by the object. The primary pulse spreads due to dispersion during reemission, and a part of the secondary pulse is in the gap between the primary ones, from where it can be easily distinguished.

Click to Click

Metal detectors with phase accumulation, or phase-sensitive, are either single-coil pulsed, or with 2 generators, each working on its own coil. In the first case, the fact is used that during re-emission pulses not only spread out, but are also delayed. In time, the phase shift increases; when it reaches a certain value, the discriminator is triggered and a click is heard in the headphones. As you get closer to the object, the clicks become more frequent and merge into a higher pitched sound. It is on this principle that Pirate is built.

In the second case, the search technique is the same, but 2 strictly symmetrical electrically and geometrically generators work, each on its own coil. At the same time, due to the interaction of their EMF, mutual synchronization occurs: the generators work in time. When the overall EMF is distorted, synchronization breaks begin, audible as the same clicks, and then a tone. Two-coil metal detectors with a synchronization breakdown are simpler than impulse ones, but less sensitive: their penetration is 1.5-2 times less. Discrimination in both cases is close to excellent.

Phase-sensitive metal detectors are the favorite tools of resort miners. Aces of the search adjust their devices so that exactly above the object the sound disappears again: the frequency of the clicks goes into the ultrasonic region. In this way, on a shell beach, it is possible to find gold earrings the size of a fingernail at a depth of up to 40 cm. However, on soil with small inhomogeneities, watered and mineralized, metal detectors with phase accumulation are inferior to others, except for parametric ones.

By squeak

Beats of 2 electrical signals - a signal with a frequency equal to the sum or difference of the main frequencies of the original signals or multiples of them - harmonics. So, for example, if signals with frequencies of 1 MHz and 1,000,500 Hz or 1.0005 MHz are applied to the inputs of a special device - a mixer, and headphones or a speaker are connected to the mixer output, then we will hear a pure tone of 500 Hz. And if the 2nd signal is 200 100 Hz or 200.1 kHz, the same thing will happen, because 200 100 x 5 = 1,000,500; we "caught" the 5th harmonic.

There are 2 generators in the beat detector: reference and working. The reference oscillatory circuit coil is small, protected from extraneous influences, or its frequency is stabilized by a quartz resonator (simply, quartz). The contour coil of the working (search) generator is a search coil, and its frequency depends on the presence of objects in the search area. Before searching, the working generator is tuned to zero beats, i.e. until the frequencies match. As a rule, they don’t achieve a complete zero sound, but tune it to a very low tone or wheezing, so it’s more convenient to search. By changing the tone of the beats, the presence, size, properties and location of the object are judged.

Note: most often, the frequency of the search generator is taken several times lower than the reference one and works on harmonics. This allows, firstly, to avoid harmful this case mutual influence of generators; secondly, to tune the device more precisely, and thirdly, to search at the optimal frequency in this case.

In general, metal detectors based on harmonics are more complicated than impulse ones, but they work on any ground. Properly made and tuned, they are not inferior to impulse ones. This can be judged at least by the fact that beach gold diggers do not agree in any way on what is better: impulse or beat?

Coil and more

The most common misconception of novice radio amateurs is the absolutization of circuitry. Like, if the scheme is "cool", then everything will be tip-top. With regard to metal detectors, this is doubly untrue, because. their operational advantages strongly depend on the design and workmanship of the search coil. As a resort prospector put it: "The findability of a detector should pull the pocket, not the legs."

When developing a device, its circuit and coil parameters are adjusted to each other until an optimum is obtained. A certain scheme with a “foreign” coil, if it works, will not reach the declared parameters. Therefore, when choosing a prototype for repetition, see first of all the description of the coil. If it is incomplete or inaccurate, it is better to build another device.

About coil dimensions

A large (wide) coil radiates EMF more efficiently and “enlightens” the ground deeper. Its search area is wider, which allows you to reduce the "finding by feet". However, if there is a large unwanted object in the search area, its signal will be "hammered" by a weak one from the desired trifle. Therefore, it is advisable to take or make a metal detector designed to work with coils of different sizes.

Note: typical coil diameters are 20-90 mm for finding rebar and profiles, 130-150 mm "for beach gold" and 200-600 mm "for big iron".

Monoloop

The traditional type of metal detector coil is the so-called. thin coil or Mono Loop (single loop): a ring of many turns of enameled copper wire with a width and thickness of 15-20 times less than the average diameter of the ring. The advantages of a monoloop coil are the weak dependence of parameters on the type of soil, the search area narrowing downwards, which allows, by moving the detector, to more accurately determine the depth and location of the find, and structural simplicity. Disadvantages - low quality factor, which is why the tuning “floats” during the search, susceptibility to interference and a vague reaction to the object: working with a monoloop requires considerable experience in using this particular instance of the device. Homemade metal detectors beginners are advised to do it with a monoloop in order to get a workable design without any problems and gain search experience with it.

Inductance

When choosing a circuit, in order to verify the authenticity of the author's promises, and even more so when designing or refining it yourself, you need to know the inductance of the coil and be able to calculate it. Even if you are making a metal detector from a purchased kit, you still need to check the inductance by measurements or by calculation, so as not to rack your brains later: why, everything seems to be in order, and not beeping.

Calculators for calculating the inductance of coils are available on the Internet, but a computer program cannot foresee all cases of practice. Therefore, in fig. given an old, decades-tested nomogram for calculating multilayer coils; a thin coil is a special case of a multilayer coil.

To calculate the search monoloop, the nomogram is used as follows:

We take the value of the inductance L from the description of the device and the dimensions of the loop D, l and t from there or at our choice; typical values: L = 10 mH, D = 20 cm, l = t = 1 cm.
According to the nomogram, we determine the number of turns w.
We set the laying coefficient k = 0.5, by the dimensions l (coil height) and t (its width) we determine the cross-sectional area of \u200b\u200bthe loop and find the area of pure copper in it as S = klt.
Dividing S by w, we get the cross section of the winding wire, and along it - the diameter of the wire d.
If it turned out d = (0.5 ... 0.8) mm, everything is OK. Otherwise, we increase l and t at d>0.8 mm or decrease at d<0,5 мм.

Noise immunity

The monoloop "catches" interference well, because arranged in exactly the same way as a loop antenna. You can increase its noise immunity, firstly, by placing the winding in the so-called. Faraday shield: a metal tube, braid or foil winding with a break so that a short-circuited coil does not form, which will “eat” all the EMI of the coil, see fig. on right. If there is a dotted line near the designation of the search coil on the original diagram (see the diagrams below), this means that the coil of this device must be placed in the Faraday shield.

Also, the screen must be connected to the common wire of the circuit. There is a catch for beginners here: the grounding conductor must be connected to the screen strictly symmetrically to the section (see the same figure) and connected to the circuit also symmetrically with respect to the signal wires, otherwise the interference will still “penetrate” into the coil.

The screen also absorbs some of the search EMF, which reduces the sensitivity of the device. This effect is especially noticeable in pulsed metal detectors; their coils cannot be shielded at all. In this case, an increase in noise immunity can be achieved by balancing the winding. The bottom line is that for a remote source of EMF, the coil is a point object, and emf. interference in its halves will overwhelm each other. A symmetrical coil may also be needed in circuitry if the generator is a push-pull or inductive three-point.

However, in this case it is impossible to symmetricalize the coil with the usual bifilar method (see Fig.): when conducting and / or ferromagnetic objects are in the field of the bifilar coil, its symmetry is violated. That is, the noise immunity of the metal detector will disappear just when it is most needed. Therefore, the monoloop coil must be symmetrical by cross winding, see the same fig. Its symmetry is not broken under any circumstances, but winding a thin coil with a large number of turns in a cross way is hellish work, and then it is better to make a basket coil.

Basket

Basket coils have all the advantages of mono-loops to an even greater extent. In addition, basket coils are more stable, their quality factor is higher, and the fact that the coil is flat is a double plus: sensitivity and discrimination will increase. Basket coils are less susceptible to interference: harmful emfs. in crossing wires they cancel each other out. The only negative is that basket coils need a precisely made rigid and durable mandrel: the total tension force of many turns reaches large values.

Basket coils are structurally flat and voluminous, but electrically voluminous "basket" is equivalent to flat, i.e. creates the same EMF. The volumetric basket coil is even less sensitive to interference and, which is important for pulsed metal detectors, the pulse dispersion in it is minimal, i.e. easier to catch the variance caused by the object. The advantages of the original "Pirate" metal detector are largely due to the fact that its "native" coil is a voluminous basket (see Fig.), but its winding is complex and time-consuming.

It is better for a beginner to wind a flat basket on his own, see fig. below. For metal detectors "for gold" or, say, for the "butterfly" metal detector described below and a simple transceiver 2-coil, unusable computer disks will be a good mandrel. Their plating will not hurt: it is very thin and nickel. An indispensable condition: an odd, and nothing else, the number of slots. A nomogram is not required for calculating a flat basket; calculation is carried out in this way:

They are set with a diameter D2 equal to the outer diameter of the mandrel minus 2-3 mm, and take D1 = 0.5D2, this is the optimal ratio for search coils.
According to formula (2) in fig. calculate the number of turns.
From the difference D2 - D1, taking into account the flat laying factor of 0.85, the diameter of the wire in insulation is calculated.

How not to and how to wind baskets

Some amateurs take it upon themselves to wind bulky baskets in the manner shown in fig. below: make a mandrel from insulated nails (pos. 1) or self-tapping screws, wind according to the scheme, pos. 2 (in this case, pos. 3, for the number of turns, a multiple of 8; every 8 turns the “pattern” is repeated), then foam, pos. 4, the mandrel is pulled out, and the excess foam is cut off. But it soon turns out that the stretched coils cut the foam and all the work went soft. That is, in order to wind securely, you need to glue pieces of durable plastic into the holes of the base, and only then wind it. And remember: an independent calculation of a volumetric basket coil without appropriate computer programs is impossible; the flat basket technique is not applicable in this case.

DD coils

DD in this case does not mean long-range, but a double or differential detector; in the original - DD (Double Detector). This is a coil of 2 identical halves (shoulders), folded with some intersection. With an accurate electrical and geometric balance of the DD arms, the search EMF is pulled into the intersection zone, on the right in Fig. on the left - a monoloop coil and its field. The slightest inhomogeneity of space in the search area causes an imbalance, and a sharp strong signal appears. The DD-coil allows an inexperienced searcher to detect a shallow, deep, well-conducting object when a rusty can lies next to it and above.

Coils DD are clearly oriented "on gold"; all metal detectors with the GOLD marking are equipped with them. However, on finely heterogeneous and / or conductive soils, they either fail completely, or often give false signals. The sensitivity of the DD coil is very high, but the discrimination is close to zero: the signal is either marginal or not at all. Therefore, metal detectors with DD coils are preferred by seekers who are only interested in "being in the pocket."

Note: more details about DD coils can be found later in the description of the corresponding metal detector. They wind their shoulders DD or in bulk, like a monoloop, on a special mandrel, see below, or with baskets.

How to attach a coil

Ready-made frames and mandrels for search coils are sold in a wide range, but sellers are not shy about cheating. Therefore, many amateurs make the base of the plywood coil, on the left in the figure:

Multiple designs

Parametric

The simplest metal detector for searching for fittings, wiring, profiles and communications in walls and ceilings can be assembled according to fig. The ancient transistor MP40 changes without any change to KT361 or its analogues; to use pnp transistors, you need to reverse the polarity of the battery.

This metal detector is a parametric type magnetic detector operating at low frequencies. The tone of the sound in the headphones can be changed by selecting the capacitance C1. Under the influence of the object, the tone drops, unlike all other types, so initially you need to achieve a “mosquito squeak”, and not wheezing or grumbling. The device distinguishes wiring under current from “empty”, a hum of 50 Hz is superimposed on the tone.

The circuit is a pulse generator with inductive feedback and frequency stabilization by an LC circuit. Loop coil - an output transformer from an old transistor receiver or a low-power "Bazaar-Chinese" low-voltage power transformer. A transformer from an unusable power source of a Polish antenna is very well suited, in its own case, by cutting off the mains plug, you can assemble the entire device, then it is better to power it from a 3 V lithium tablet battery. Winding II in fig. – primary or network; I - secondary or step-down at 12 V. That's right, the generator works with transistor saturation, which provides negligible power consumption and a wide range of pulses, making it easier to find.

To turn the transformer into a sensor, its magnetic circuit must be opened: remove the frame with the windings, remove the straight jumpers of the core - the yoke - and fold the W-shaped plates in one direction, as on the right in the figure, then put the windings back on. With serviceable parts, the device starts working immediately; if not, you need to swap the ends of any of the windings.

The parametric scheme is more complicated - in fig. on right. L with capacitors C4, C5 and C6 is tuned to 5, 12.5 and 50 kHz, and quartz passes the 10th, 4th harmonics and fundamental tone to the amplitude meter, respectively. The scheme is more for an amateur to get drunk on the table: there is a lot of fuss with the setting, but there is no "flair", as they say. Provided as an example only.

transceiver

Much more sensitive is a transceiver metal detector with a DD coil, which can be easily made at home, see fig. Left - transmitter; on the right is the receiver. It also describes the properties of different types of DD.

This metal detector is LF; search frequency is about 2 kHz. Depth of detection: Soviet penny - 9 cm, canning tin - 25 cm, sewer hatch - 0.6 m. The parameters are “triple”, but you can master the technique of working with DD before moving on to more complex structures.

The coils contain 80 turns of 0.6-0.8 mm PE wire, wound in bulk on a mandrel 12 mm thick, the drawing of which is shown in fig. left. In general, the device is not critical to the parameters of the coils, they would be exactly the same and arranged strictly symmetrically. In general, a good and cheap simulator for those who want to master any search technique, incl. "for gold". Although the sensitivity of this metal detector is not high, but the discrimination is very good despite the use of DD.

To set up the device, first, instead of the L1 transmitter, turn on the headphones and make sure that the generator is working by the tone. Then L1 of the receiver is short-circuited and, by selecting R1 and R3, a voltage is set on the collectors VT1 and VT2, respectively, equal to about half the supply voltage. Next, R5 set the collector current VT3 within 5..8 mA, open L1 of the receiver and that's it, you can search.

With phase accumulation

The designs in this section show all the advantages of the phase accumulation method. The first metal detector mainly for construction purposes will be very inexpensive, because. its most labor-intensive parts are made ... of cardboard, see fig.:

The device does not require adjustment; integrated timer 555 - an analogue of the domestic IC (integrated circuit) K1006VI1. All signal transformations take place in it; search method - impulse. The only condition is that the speaker needs a piezoelectric (crystalline), a regular speaker or headphones will overload the IC and it will soon fail.

Coil inductance - about 10 mH; operating frequency - within 100-200 kHz. With a mandrel thickness of 4 mm (1 layer of cardboard), a coil with a diameter of 90 mm contains 250 turns of PE 0.25 wire, and a 70 mm coil contains 290 turns.

Metal detector "Butterfly", see fig. on the right, in terms of its parameters it is already close to professional devices: the Soviet penny is found at a depth of 15-22 cm, depending on the soil; sewer manhole - at a depth of up to 1 m. Acts on disruption of synchronization; diagram, board and type of installation - in fig. below. Please note, there are 2 separate coils with a diameter of 120-150 mm, not DD! They must not overlap! Both speakers are piezoelectric, as in the previous. case. Capacitors - thermostable, mica or high-frequency ceramic.

The properties of the "Butterfly" will improve, and it will be easier to set it up if, firstly, wind the coils with flat baskets; the inductance is determined by the given operating frequency (up to 200 kHz) and the capacitances of the loop capacitors (10,000 pF each in the diagram). Wire diameter - from 0.1 to 1 mm, the larger the better. The tap in each coil is made from a third of the turns, counting from the cold (lower according to the diagram) end. Secondly, if individual transistors are replaced with a 2-transistor assembly for K159NT1 dif-amplifier circuits or its analogues; a pair of transistors grown on a single chip has exactly the same parameters, which is important for circuits with a synchronization failure.

To establish the "Butterfly" you need to accurately adjust the inductance of the coils. The author of the design recommends moving apart and shifting the turns or adjusting the coils with ferrite, but from the point of view of electromagnetic and geometric symmetry, it would be better to connect trimmer capacitors of 100-150 pF in parallel with 10,000 pF capacitances and twist them when tuning in different directions.

The actual adjustment is not difficult: the newly assembled device beeps. We alternately bring an aluminum saucepan or a beer can to the coils. To one - the squeak becomes higher and louder; to the other - lower and quieter or completely silent. Here we add a little capacity of the trimmer, and remove it in the opposite shoulder. For 3-4 cycles, you can achieve complete silence in the speakers - the device is ready to search.

More about Pirate

Let's return to the famous "Pirate"; it is a pulse transceiver with phase accumulation. The scheme (see fig.) is very transparent and can be considered a classic for this case.

The transmitter consists of a master oscillator (MG) on the same 555th timer and a powerful key on T1 and T2. On the left - a variant of the ZG without an IC; it will have to set the pulse repetition rate of 120-150 Hz R1 and the pulse duration of 130-150 μs R2 on the oscilloscope. Coil L - common. The limiter on diodes D1 and D2 for a current of 0.5 A saves the QP1 receiver amplifier from overload. The discriminator is assembled on QP2; together they make up the dual operational amplifier K157UD2. Actually, the "tails" of the reradiated pulses are accumulated in the capacitance C5; when the “reservoir is full”, a pulse jumps at the output of QP2, which is amplified by T3 and gives a click in the dynamics. Resistor R13 regulates the filling rate of the "reservoir" and, consequently, the sensitivity of the device. More about "Pirate" can be found in the video:

Video: Pirate metal detector

and about the features of its settings - from the following video:

Video: setting the threshold of the Pirate metal detector

On the beat

Those who wish to experience all the delights of the process of searching on beats with replaceable coils can assemble a metal detector according to the scheme in fig. Its peculiarity, firstly, is efficiency: the entire circuit is assembled on CMOS logic and, in the absence of an object, consumes very little current. Secondly, the device works on harmonics. The reference oscillator on DD2.1-DD2.3 is stabilized by ZQ1 quartz at 1 MHz, and the search oscillator on DD1.1-DD1.3 operates at a frequency of about 200 kHz. When setting up the device before searching, the desired harmonic is “caught” by the VD1 varicap. The mixing of the working and reference signals occurs in DD1.4. Thirdly, this metal detector is suitable for work with replaceable coils.

It is better to replace the ICs of the 176th series with the same 561st ones, the current consumption will decrease, and the sensitivity of the device will increase. It is simply impossible to replace the old Soviet high-resistance headphones TON-1 (preferably TON-2) with low-resistance ones from the player: they will overload DD1.4. You need to either put an amplifier like a "pirate" one (C7, R16, R17, T3 and a speaker on the "Pirate" circuit), or use a piezo speaker.

This metal detector does not require settings after assembly. Coils are monoloops. Their data on a mandrel 10 mm thick:

Diameter 25 mm - 150 turns of PEV-1 0.1 mm.
Diameter 75 mm - 80 turns of PEV-1 0.2 mm.
Diameter 200 mm - 50 turns of PEV-1 0.3 mm.

It doesn't get easier

Now let's fulfill the promise given at the beginning: we will tell you how to make, without knowing anything about radio engineering, the metal detector that you are looking for. The metal detector is “easier than simple” assembled from a radio, a calculator, a cardboard or plastic box with a hinged lid, and pieces of double-sided tape.

The metal detector "from the radio" is pulsed, however, to detect objects, it is not dispersion and not delay with phase accumulation that are used, but the rotation of the EMF magnetic vector during re-emission. On the forums, they write different things about this device, from “super” to “sucks”, “wiring” and words that are not customary to use in writing. So, in order to get, if not “super”, but at least a fully functional device, its components - the receiver and the calculator - must meet certain requirements.

Calculator we need the tiniest and cheapest, "alternative". They make them in offshore cellars. They have no idea about the standards for electromagnetic compatibility of household appliances, and if they heard about something like that, then they wanted to spit from the bottom of their hearts. Therefore, local products are quite powerful sources of impulse radio interference; they are given by the clock generator of the calculator. In this case, its strobe pulses on the air are used to probe the space.

Receiver you also need a cheap one, from similar manufacturers, without any means of increasing noise immunity. It must have an AM band and, absolutely necessary, a magnetic antenna. Since receivers with short wave (HF, SW) reception on a magnetic antenna are rarely sold and are expensive, you will have to limit yourself to medium waves (MW, MW), but this will make tuning easier.

We unfold the box with a lid into a book.
We stick strips of adhesive tape on the back sides of the calculator and the radio and fix both devices in the box, see fig. on right. The receiver - preferably in the lid, so that there is access to the controls.
We turn on the receiver, we are looking for a section free from radio stations and as clean as possible from radio noise by setting it to maximum volume at the top of the AM band (bands). For MW this will be around 200 m or 1500 kHz (1.5 MHz).
We turn on the calculator: the receiver should buzz, wheeze, growl; in general, give a tone. We do not remove the volume!
If there is no tone, carefully and smoothly adjust until it appears; we caught some of the harmonics of the calculator's strobe generator.
We slowly fold the “book” until the tone weakens, becomes more musical, or disappears altogether. Most likely this will happen when the lid is rotated about 90 degrees. Thus, we have found a position in which the magnetic vector of primary impulses is oriented perpendicular to the axis of the ferrite rod of the magnetic antenna and it does not receive them.
We fix the cover in the found position with a foam insert and an elastic band or supports.

Note: depending on the design of the receiver, the reverse option is possible - to tune in to the harmonica, the receiver is placed on the included calculator, and then, laying out the “book”, the tone is softened or disappears. In this case, the receiver will catch the pulses reflected from the object.

And what's next? If there is an electrically conductive or ferromagnetic object near the opening of the "book", it will re-emit probing pulses, but their magnetic vector will turn. The magnetic antenna will “smell” them, the receiver will again give a tone. That is, we have already found something.

Something strange in the end

There are reports of another metal detector "for complete dummies" with a calculator, but instead of a radio, supposedly 2 computer disks, a CD and a DVD, are needed. Also - piezo headphones (precisely piezo, according to the authors) and a Krona battery. Frankly speaking, this creation looks like a techno-myth, like a memorable mercury antenna. But - what the hell is not joking. Here's a video for you:

try it, if you wish, maybe something will be found there, both in the subject and in the scientific and technical sense. Good luck!

as an application

There are hundreds, if not thousands, of schemes and designs of metal detectors. Therefore, in the appendix to the material, we also give a list of models, in addition to those mentioned in the test, which, as they say, are in circulation in the Russian Federation, are not overly expensive and are available for repetition or self-assembly:

Clone.

4,88

Do-it-yourself metal detector - as the name implies, such devices are made independently and are designed to search for metal objects, they are used for a rather narrow purpose. However, the methods of their implementation are quite diverse and constitute a whole direction in radio electronics.

Metal detector N. Martynyuk

The metal detector according to the scheme of N. Martynyuk (Fig. 1) is made on the basis of a miniature radio transmitter, the radiation of which is modulated by an audio signal [RL 8 / 97-30]. Modulator - a low-frequency generator is made according to the well-known scheme of a symmetrical multivibrator.

The signal from the collector of one of the multivibrator transistors is fed to the base of the high-frequency generator transistor (VT3). The operating frequency of the generator is located in the frequency range of the VHF-FM broadcasting range (64 ... 108 MHz). A piece of television cable in the form of a coil with a diameter of 15 ... .25 cm was used as an inductor of the oscillatory circuit.

Rice. 1. Schematic diagram of the metal detector N. Martynyuk.

If a metal object is brought near the inductor of the oscillatory circuit, the generation frequency will noticeably change. The closer the object is brought to the coil, the greater the frequency drift will be. To register a change in frequency, a conventional FM radio tuned to the frequency of the RF generator is used.

The receiver's auto-tuning system should be disabled. In the absence of a metal object, a loud beep is heard from the receiver's speaker.

If a piece of metal is brought to the inductor, the generation frequency will change, and the signal volume will decrease. The disadvantage of the device is its reaction not only to metal, but also to any other conductive objects.

Metal detector based on a low-frequency LC generator

On fig. 2 - 4 shows a metal detector circuit with a different principle of operation, based on the use of a low-frequency LC generator and a bridge indicator of frequency change. The search coil of the metal detector is made in accordance with fig. 2, 3 (with correction of the number of turns).

Rice. 2. Search coil of a metal detector.

Rice. 3. Search coil metal detector.

The output signal from the generator goes to the bridge measuring circuit. A high-resistance telephone capsule TON-1 or TON-2 was used as a zero-indicator of the bridge, which can be replaced by a pointer or other external measuring device for alternating current. The generator operates at a frequency f1, for example 800 Hz.

The bridge is balanced to zero before starting work by adjusting the capacitor C* of the oscillatory circuit of the search coil. The frequency f2=f1 at which the bridge will be balanced can be determined from the expression:

Initially, there is no sound in the telephone capsule. When a metal object is introduced into the field of the search coil L1, the generation frequency f1 will change, the bridge will be unbalanced, and a sound signal will be heard in the telephone capsule.

Rice. 4. Scheme of a metal detector with an operating principle based on the use of a low-frequency LC generator.

Bridge circuit metal detector

The bridge circuit of a metal detector using a search coil that changes its inductance when metal objects approach is shown in fig. 5. An audio frequency signal is supplied to the bridge from a low-frequency generator. With the potentiometer R1, the bridge is balanced for the absence of an audio signal in the telephone capsule.

Rice. 5. Bridge circuit of the metal detector.

To increase the sensitivity of the circuit and increase the amplitude of the unbalance signal of the bridge, a low-frequency amplifier can be connected to its diagonal. The inductance of the coil L2 should be comparable to the inductance of the search coil L1.

Metal detector based on a receiver with a MW range

A metal detector operating in conjunction with a broadcasting superheterodyne radio receiver of the medium wave range can be assembled according to the scheme shown in fig. 6 [R 10/69-48]. The design shown in Fig. 1 can be used as a search coil. 2.

Rice. 6. A metal detector that works in conjunction with a superheterodyne radio receiver in the MW range.

The device is a conventional high frequency oscillator operating at 465 kHz (the intermediate frequency of any AM broadcast receiver). The circuits presented in Chapter 12 can be used as a generator.

In the initial state, the frequency of the RF generator, mixing in a nearby radio receiver with the intermediate frequency of the signal received by the receiver, leads to the formation of a difference frequency signal in the audio range. When the generation frequency changes (if there is metal in the field of action of the search coil), the tone of the sound signal changes in proportion to the amount (volume) of the metal object, its removal, and the nature of the metal (some metals increase the generation frequency, others, on the contrary, lower it).

Simple metal detector on two transistors

Rice. 7. Scheme of a simple metal detector on silicon and field-effect transistors.

A diagram of a simple metal detector is shown in fig. 7. The device uses a low-frequency LC generator, the frequency of which depends on the inductance of the search coil L1. In the presence of a metal object, the generation frequency changes, which can be heard using the BF1 telephone capsule. The sensitivity of such a scheme is low, because it is quite difficult to determine small changes in frequency by ear.

Metal detector for small amounts of magnetic material

A metal detector for small amounts of magnetic material can be made according to the scheme in fig. 8. A universal head from a tape recorder is used as a sensor for such a device. To amplify weak signals taken from the sensor, it is necessary to use a highly sensitive low-frequency amplifier, the output signal of which is fed to the telephone capsule.

Rice. 8. Scheme of a metal detector for small amounts of magnetic material.

Metal indicator circuit

Another method for indicating the presence of metal is used in the device according to the scheme in Fig. 9. The device contains a high-frequency generator with a search inductor and operates at a frequency f1. A simple high-frequency millivoltmeter was used to indicate the signal magnitude.

Rice. 9. Schematic diagram of the metal indicator.

It is made on a diode VD1, a transistor VT1, a capacitor C1 and a milliammeter (microammeter) PA1. A quartz resonator is connected between the generator output and the input of the high-frequency millivoltmeter. If the generation frequency f1 and the frequency of the quartz resonator f2 are the same, the instrument needle will be at zero. As soon as the generation frequency changes as a result of the introduction of a metal object into the field of the search coil, the arrow of the device will deviate.

The operating frequencies of such metal detectors are usually in the range of 0.1 ... 2 MHz. For the initial setting of the generation frequency of this and other devices of similar purpose, a variable capacitor or trimmer capacitor is used, connected in parallel with the search inductor.

Typical metal detector with two generators

On fig. 10 shows a typical diagram of the most common metal detector. Its operating principle is based on the frequency beats of the reference and search generators.

Rice. 10. Scheme of a metal detector with two generators.

Rice. 11. Schematic diagram of a block generator for a metal detector.

A node of the same type, common to both generators, is shown in fig. 11. The generator is made according to the well-known "capacitive three-point" scheme. On fig. 10 shows a complete diagram of the device. As a search coil L1, the design shown in fig. 2 and 3.

The initial frequencies of the generators must be the same. The output signals from the generators through the capacitors C2, C3 (Fig. 10) are fed to the mixer, which selects the difference frequency. The selected audio signal through the amplifying stage on the transistor VT1 is fed to the telephone capsule BF1.

Metal detector based on the principle of generation frequency disruption

The metal detector can also work on the principle of generation frequency disruption. A diagram of such a device is shown in Fig. 12. Under certain conditions (the frequency of the quartz resonator is equal to the resonant frequency of the oscillatory LC circuit with the search coil), the current in the emitter circuit of the transistor VT1 is minimal.

If the resonant frequency of the LC circuit changes noticeably, then the generation will fail, and the readings of the device will increase significantly. It is recommended to connect a capacitor with a capacity of 1 ... 100 nF in parallel with the measuring device.

Rice. 12. Scheme of a metal detector that works on the principle of disruption of the generation frequency.

Metal detectors for searching for small objects

Metal detectors designed to search for small metal objects in everyday life can be assembled according to those shown in fig. 13 - 15 schemes.

Such metal detectors also work on the principle of generation disruption: the generator, which includes a search inductor, operates in a “critical” mode.

The mode of operation of the generator is set by tuned elements (potentiometers) so that the slightest change in the conditions of its operation, for example, a change in the inductance of the search coil, will lead to a breakdown of the oscillations. To indicate the presence / absence of generation, LED indicators of the level (presence) of alternating voltage were used.

Inductors L1 and L2 in the circuit in fig. 13 contain, respectively, 50 and 80 turns of wire with a diameter of 0.7 ... 0.75 mm. The coils are wound on a 600NN ferrite core with a diameter of 10 mm and a length of 100 ... 140 mm. The operating frequency of the generator is about 150 kHz.

Rice. 13. Scheme of a simple metal detector on three transistors.

Rice. 14. Scheme of a simple metal detector on four transistors with light indication.

Inductors L1 and L2 of another circuit (Fig. 14), made in accordance with the German patent (No. 2027408, 1974), have 120 and 45 turns, respectively, with a wire diameter of 0.3 mm [P 7 / 80-61 ]. A ferrite core 400НН or 600НН with a diameter of 8 mm and a length of 120 mm was used.

Household metal finder

The household metal detector (BIM) (Fig. 15), previously produced by the Radiopribor plant (Moscow), allows you to detect small metal objects at a distance of up to 45 mm. The winding data of its inductors are unknown, however, when repeating the circuit, one can be guided by the data given for devices of a similar purpose (Fig. 13 and 14).

Rice. 15. Scheme of a household metal detector.

Literature: Shustov M.A. Practical Circuitry (Book 1), 2003

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

Read in the article

How a metal detector works

A metal detector, or metal detector, is an electronic device consisting of a primary sensor (a coil with a winding) and a secondary assembly. Instruments for detecting metals are divided into several types:

"transmission and reception";
induction;
impulse;
generator.

Metal detector device

Devices of the middle price category are mainly of the "receiving and transmitting" type. The principle of operation of such metal detectors is based on the transmission and reception of electromagnetic waves. The main elements of a device of this type are two coils: one is a transmitter, and the second is a receiver. The first coil transmits electromagnetic waves that freely pass through a neutral medium and which, when colliding with metal objects, are reflected and transmitted to the receiving device. After the reflected signal hits the second coil, the operator is informed by a buzzer about finding the target.

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

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

common use;
middle class;
professional equipment.

Functional and technical parameters of metal detectors

Before choosing and buying a good metal detector, you should clearly define the environment in which the search will be carried out. It is also necessary to take into account the estimated dimensions of the objects being sought and the depth of their occurrence. Consider the main characteristics that you need to pay special attention to when buying a detector:

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

The principle of operation and the operating frequency of the detector are the main characteristics that determine the capabilities of the device and show which category it can be attributed to (simple soil, middle class or professional). Sensitivity determines the depth of objects with which the device can work. As a rule, this figure is in the range from 100-150 mm to 600-1500 mm. However, there are depth models designed to search for objects at a depth of 5 meters. The discriminator allows you to configure the device to search for a specific type of metal. This allows the operator not to be distracted by metallized debris.

What types of metal detectors can be made with your own hands

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

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

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

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

Models of the "Pirate" series cost about $ 100-300. This cost is due to the ability of the device to detect objects at a depth of 200 mm (for small items) and 1500 mm (large items). Consider the features of assembling and setting up a device for searching for metals, as well as its components.

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

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

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

Do-it-yourself metal detector assembly: diagrams

Currently, there are a lot of Pirate metal detector circuits, since some radio amateurs began to upgrade them to fit their needs. All options will not be considered, only the most proven and most popular.

Detector circuit on the NE555 chip

The classic scheme of the metal detector of the "Pirate" series, built on the IC timer NE555. The operation of the device depends on the comparator, one output of which is connected to the IC pulse generator, the second to the coil, and the output to the speaker. In case of detection of metal objects, the signal from the coil goes to the comparator, and then to the speaker, which notifies the operator about the presence of the objects being searched for.

Do-it-yourself assembly of a metal detector without microcircuits

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

DIY printed circuit board

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

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

Coil for a metal detector - how to do it yourself

Due to the fact that the Pirate metal detector is a pulse type device, the accuracy when assembling the coil is unimportant. For the base, you need a ring with a diameter of about 200 mm, on which you need to wind 25 turns of 0.5 mm PEV wire. To increase the depth of metal detection, the coil frame should be in the range of 260–270 mm, and the number of turns should be 21–22 rpm. Next, the mandrel with the wire must be well wrapped with insulating tape.

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

Checking and setting up a metal detector

We fix all the components of the device on the metal detector rod: the body with the coil, the receiving-transmitting unit and the handle. If the control circuit is assembled correctly, then the device will not need to be configured, since it initially has maximum sensitivity. Finer tuning is performed using a variable resistor R13. Normal operation of the detector should be ensured with the middle position of the regulator. If there is an oscilloscope, then with its help at the gate of the transistor T2 it is necessary to measure the frequency, which should be 120–150 Hz, and the pulse duration should be 130–150 μs.

The video shows the setup of the metal detector.

How to make an underwater metal detector with your own hands

Sometimes search operations have to be transferred from land to water. What to do in this case, because the electronics will fail? There are, of course, special devices for working underwater, but you can make a deep metal detector with your own hands. To do this, you can take the most common home-made detector and place all the nodes in hermetically sealed cases. In addition, it is worth modifying the device a little and installing indicator lights instead of an audible alarm.

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

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

Instruments

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

soldering iron or soldering station;
solder, tin, rosin;
pliers, round pliers, side cutters;
screwdriwer set;
hacksaw for metal;
oscillography and other instrumentation.

Diagram, parts selection and circuit board

To manufacture the control unit, it is necessary to make a circuit board on which all the necessary radio components will be placed. The circuit below must be transferred to a copper foil-coated getinax plate and a circuit board made in the same way as described above in the article for the Pirate metal detector. The circuit size should be within 104x66mm and the board blank should be 10mm larger on each side.

List of required radio components

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

Illustration	Process description
	We take a textolite plate coated with copper foil. Degrease chemically or mechanically (sand).
	We put the circuit on the plate, cover the tracks with a protective varnish and subject the workpiece to etching (described above, as for the Pirate metal detector). Use a thin drill to drill holes for radio components and fasteners to the case.
	We place the radio components in accordance with the diagram and carry out the wiring.
	This is how the finished board of the Terminator 3 metal detector will look like.

metal detector coil

This is actually the most sensitive part of the device. She is responsible for scanning the space underground. Consider the steps for creating a simple coil for a metal detector:

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

Homemade metal detector: a detailed description of the assembly scheme and settings

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

We take a suitable box or make the case ourselves. We drill holes for tuning resistors and a connector. We mount the finished board and regulators in the case.

We close the case, connect the metal detector frame and fasten everything to a plastic pipe with a handle. The metal detector is assembled and ready to go.

The proposed video will help with setting up the metal detector.

Features of a self-assembled metal detector with a metal discrimination circuit

Metal detectors with a simple circuit can detect hidden objects, but in order to find out which ones, you have to work with a shovel. Instead of a gold coin or a military helmet, you can find just a piece of pipe and spend a lot of time on it. To make it easier for search engines, detectors began to be equipped with discriminators that allow you to distinguish between the type of metal and skip various debris. The simplest ways to determine the types of metals were implemented in old devices and entry-level devices and had two modes - “all metals” and “non-ferrous”. The Discrimination feature allows the operator to respond to a phase shift of a certain amount compared to a set (reference) level. In this case, the device cannot distinguish between non-ferrous metals.

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

Features of assembling a deep metal detector

The deep type of metal detector is a special device capable of detecting objects hidden at a great distance from the surface of the earth. It is at a considerable depth that you can find the most interesting and valuable items. Some models are able to detect metals at a distance of 4 to 6 m underground.

There are two types of deep metal detectors: frame and transceiver on the rod. The first type of device is capable of covering a large area of land for scanning. So, the search is accelerated, but it negatively affects the performance. The second version of the detector works on a small area, but it determines the center of the target better. With such a device, it is good to search in the grass, forest or reeds. Therefore, when choosing the type of metal detector, you need to determine in what conditions the scanning will be carried out.