Do-it-yourself non-ferrous metal detector detailed instructions. The simplest do-it-yourself metal detector

Metal detector scheme

Today I want to bring to your attention metal detector diagram, and everything about him, what you see in the photo. After all, it is sometimes so difficult to find an answer to a question in a search engine - Scheme of a good metal detector

In other words, the metal detector has a name Tesoro Eldorado

The metal detector can work in the mode of both searching for all metals and in background discrimination.

Technical characteristics of the metal detector.

The principle of operation is inductively balanced
-Working frequency, kHz 8-10kHz
-Dynamic operation mode
-Mode accurate detection(Pin-Point) is in static
- Power, V 12
- There is a sensitivity level control
- There is a threshold tone control
- Detuning from the ground is (manual)

Depth of detection in the air with a sensor DD-250mm In the ground, the device sees targets almost the same as in the air.
- coins 25mm - about 30cm
- gold ring - 25cm
- helmet 100-120cm
-max depth 150cm
-Consumption current:
- Mute approximately 30mA

And the most important and intriguing is the scheme of the device itself

The image can be easily enlarged by clicking on it.

To assemble a metal detector, you need the following parts:

So that you do not have to spend a long time setting up the device, do the assembly and soldering carefully, the board should not contain any clamps.

For tinning boards, it is best to use rosin in alcohol, after tinning the tracks, do not forget to wipe the tracks with alcohol

Parts side fee

We start the assembly from soldering jumpers, then resistors, further panels for microcircuits and everything else. Another little tip, now regarding the manufacture of the device board. It is highly desirable to have a tester that can measure the capacitance of capacitors. The point is that the device there are two identical amplification channels, therefore, the amplification through them should be as identical as possible, and for this it is desirable to select those details that are repeated on each amplification stage so that they have the most identical parameters measured by the tester (that is, what indications in a particular stage on one channel - the same readings on the same stage and in another channel)

Making a coil for a metal detector

Today I would like to talk about the manufacture of a sensor in a finished case, so the photo is more than words.
We take the case and fix it in right place pressurized wire and install the cable, call the cable and mark the ends.
Next we wind the coils. The DD-sensor is made according to the same principle as for all balancers, so I will focus only on the required parameters.
TX - transmitting coil 100 turns 0.27 RX - receiving coil 106 turns 0.27 enameled winding wire.

Coils after winding are tightly wound with threads, impregnated with varnish.

After drying, tightly wrap with electrical tape around the entire circumference. It is shielded from above with foil, between the end and the beginning of the foil there must be a gap of 1 cm uncovered by it, in order to avoid a short-circuited coil.

The coil can also be shielded with graphite, for this we mix graphite with nitro varnish 1: 1 and cover it with an even layer on top of a 0.4 tinned copper wire wound on a coil (without gaps), we connect the wire to the cable screen.

We wet it into the case, connect and approximately bring the coils into balance, there should be a double beep on the ferrite, a single beep on the coin, if on the contrary, we swap the conclusions of the receiving winding. Each of the coils is tuned in frequency separately, there should not be any metal objects nearby!!! The coils are tuned with a prefix for measuring resonance. We connect the prefix to the Eldorado board in parallel with the transmitting coil and measure the frequency, then with the RX coil and the selected capacitor we achieve a frequency 600 Hz higher than that in TX.

After selecting the resonance, we assemble the coil together and check whether the device sees the entire VDI scale from aluminum foil to copper, if the device does not see the entire scale, then we select the capacitance of the resonant capacitor in the RX circuit in increments of 0.5-1nf in one direction or another, so the moment when the device will see foil and copper at the minimum of discrimination, and when the discrimination is wound up, the entire scale will be cut out in turn.

We finally bring the coils to zero, fixing everything with hot glue. Next, to facilitate the coil, we glue the voids with pieces of foam, the foam sits on hot glue, otherwise it will pop up after filling the coil.

Pour the first layer of epoxy without adding 2-3mm to the top

We fill in the second layer of resin with color. As a color, aniline dye is well suited for dyeing fabrics, the powder is different colors and costs a penny. The dye must first be mixed with the hardener, then the hardener must be added to the resin, the dye will not dissolve immediately in the resin.

Correct assembly of the board, start by checking the correct power supply to all nodes.

Take the circuit and the tester, turn on the power on the board, and referring to the circuit, go through the tester at all points of the nodes where power should be supplied.
With the discrim knob position at a minimum, the device should see all non-ferrous metals

, when winding the discrim should be cut out

all metals in order to copper should not be cut if the deviceit works this way, it means it is set up correctly. The discrim scale must be selected in such a way that it fits completely into the full turn of the discrimination knob, this is done by selecting c10. When the capacitance decreases, the scale stretches and vice versa.

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, 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 make it possible to find a coin with a Soviet penny at a depth of up to 20-30 cm or a piece of iron with a sewer 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 of electromagnetic induction. AT general scheme The metal detector consists of a transmitter of electromagnetic oscillations, a transmitting coil, a receiving coil, a receiver, a useful signal separation 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 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:

1. 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.
2. The size and dimensions of the search area is an imaginary area in the ground in which the object will be found.
3. Sensitivity is the ability to detect more or less small objects.
4. 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.
5. 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.
6. 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).
7. 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. So, 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:

1. 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.
2. 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.
3. 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.
4. 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.

stand apart pulse metal detectors. 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 set value) and 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 make it possible to best efficiency in their frequency range, but complex 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 output of the mixer, 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. Coil oscillatory circuit the reference 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. complete zero as a rule, they don’t achieve sound, but tune it to a very low tone or wheezing, 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 the mutual influence of generators, which is harmful in this case; 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 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. fine coil or Mono Loop (single loop): a ring of many turns of enamelled copper wire 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 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. AT otherwise 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.

1. We unfold the box with a lid into a book.
2. 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.
3. 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).
4. We turn on the calculator: the receiver should buzz, wheeze, growl; in general, give a tone. We do not remove the volume!
5. If there is no tone, carefully and smoothly adjust until it appears; we caught some of the harmonics of the calculator's strobe generator.
6. 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.
7. 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.
13 ratings, average: 4,92 out of 5)

The number of treasure hunters is steadily growing. And although everything has been dug up for a long time, there are such enthusiasts who want to try their luck and go on another search for gold, antiques or coins. This is not strange, because the procedure itself has a peculiar atmosphere and gives each participant a lot of unforgettable emotions. It is enough to charge the batteries, drive away from the city, make the first couple of strokes of the coil and wait for the sound signal about the find. Here it is, the secret of a good mood for every treasure hunter.

Currently, there is a large selection of instruments for detecting metals. On sale it is easy to find models costing less than a hundred dollars. But besides this, there are also expensive products that sell for over $1,000. Does it make sense to buy such an expensive device for a beginner? Of course not. The more expensive the device, the more difficult it is to set up. Naturally, a novice digger will not be able to figure out all the possibilities of such an invention without having the appropriate experience and minimal skills. Or maybe try to make a simple metal detector with your own hands? After all, this is a completely doable procedure and it is within the power of everyone.

How to make a metal detector with your own hands

Before you make a simple metal detector at home, you should deal with the principle of its work.

A metal detector (metal detector, metal scanner, etc.) is a special device for quickly identifying metal objects underground. Several varieties of such inventions are available on the market, which differ in characteristics and capabilities. To a greater extent, the key differences lie in the depth of detection and ease of use. Naturally, the deeper the device “sees”, the more expensive it will cost.

The principle of operation is based on the use of the law of magnetic attraction of objects. The device generates a magnetic field and sends it to a specific area underground. If there is any object with metallic properties, a signal is displayed from it and returns back, notifying the treasure hunter about the find.

To build a high-frequency instrument, you need to assemble quality command block. It is used as a laptop or radio receiver, on which the maximum frequency is AM. First make sure that the wave is “clean” and that there are no radio stations on it.

The next step involves creating a search head, which is easy to make from a thin plywood sheet. We cut out two circles with a diameter of 15 and 10 centimeters and tightly fix them together.

Then you need to cut sticks out of wood to arrange the rings parallel to each other. It is necessary to wrap the plate with enameled copper wire, making 10-15 turns. After that, the fake can be attached directly to the block itself. We run the highest frequency. If the procedure is successful, you will hear a soft tone. For clearer playback, it is better to use an external speaker or headphones. It is very easy to install a metal detector according to such instructions. In addition, training videos and diagrams can be downloaded on the Web to complete the action.

Do-it-yourself metal detector: scheme

Finding circuits for a simple metal detector with discrimination support is very simple. To make a device need to stock up:

To make a coil with a diameter of 90 millimeters, you need to wrap circles of cardboard with copper wire, making 250 turns. If we are talking about a coil with a diameter of 70 mm, then here you have to make from 290 turns. As a result, it will be possible to obtain 10 mH.

After you assemble the circuit, you need to make sure that it works. After that, you can start manufacturing a printed circuit board, where all the other elements of the metal detector will be installed.

The next step involves preparing the pen. It can be made from cardboard by cutting out three identical blanks in the form of a boomerang. It is necessary to cut holes in the handle for the batteries, after which three separate ones can often be fixed together with glue. You should also cut out a place for the on and off button. After attaching the circuit, battery and switch, you can complete the coil.

Do-it-yourself metal detector from DVDs

You can make a simple metal detector with your own hands using two CDs and DVDs. The instruction is particularly simple and does not require the use of additional circuits or complex instructions. All you need to make is:

Calculator. It doesn't matter what type of device you get. You can take the most simple and cheap model;

1. Headphones;
2. Accumulator "Krona";
3. Glue and a roll of electrical tape;

Sequencing when creating a metal detector from DVDs:

• Take the headphones and cut off the plug.
• Then you need to strip 10 centimeters of insulating wire and divide by two to get two pairs of wires;
• After that, you should attach one wire from a pair on the disk. If you are using a single-sided disc, you need to fix it on the writing side;
• We fix the wires with electrical tape, and connect the rest of the “bare” part to the battery, to the plus and minus contacts.
• The next step is to carefully insulate the bare cable;
• We tightly attach a previously included and charged calculator to the surface of the CD;
• Then you need to place a DVD on it, and at the final stage wrap the structure with electrical tape;
• At the final stage, it is necessary to fix the Krona battery on the surface of the disk;

That's all, the scheme of the simplest, but very effective metal detector is ready. It remains to test it in real conditions and make sure that everything works without failures. Of course, it will not be possible to search for coins at a depth of half a meter with such a device, but nevertheless, it is quite suitable for home use.

Do-it-yourself metal detector "Pirate"

Among homemade metal detectors, the most popular is variant called "Pirate". Pirate is a pulsed metal detector, which is built on a simple and affordable circuit. The design uses several small elements and a small coil. If you equip the device with a coil with a diameter of 280 mm, then it will be able to "see" coins at a depth of up to 20 centimeters. The device will also find large metal objects at a depth of one and a half meters.

The name "Pirate" (PIRAT) comes from the developers of the scheme - PI - indicates the principle of operation, and RAT - is an abbreviation for "Radio Cattle" - the site of the developers.

Homemade device "Pirate" is not able to discriminate against metals. But to search for large objects will fit quite well. Such a device is especially appreciated among beginner metal seekers. Everything is determined by ease of use and good search results. You can find circuits and buy components for creating a "Pirate" in any market or in a parts store for radios and other radio equipment. For the manufacture of such a device, it is not necessary to have a high level of training.

In the end, we can say with confidence that it is quite possible to assemble a metal detector with your own hands at home. To do this, you should study the detailed instructions and deal with the manufacturing scheme. It is important to understand that homemade devices are not suitable for more serious searches, such as coins or small antiques. This is due to the small range. In any case, making a metal detector with your own hands will allow you to create a very good device that will fit for acquiring the initial skills of a real treasure hunter.

Probably, what this electronic device is intended for, it is not necessary to tell. Everything is clear to everyone. These devices are used by sappers, at airports, in special services, in various institutions, one way or another related to security. But that's not all.

Metal detector in the 90s

These devices in the 90s of the twentieth century helped people not to die of hunger. At that difficult time, one could often see young people and not only those who walked the streets with metal detectors. The device was used to search for metals and alloys. In particular, in cities near which large industries were located, it was possible to dig out real wealth with it.

Basically, these guys made metal detectors with their own hands and looked for waste from metallurgical plants or native metals that remained in the bowels of the earth. The latter were used in the construction of tracks. After all, many asphalt, and even dirt, roads were covered with slag, and often in its composition one could find metal and an alloy of iron and manganese - ferromanganese. In the late 90s, it has already risen in price enough. In one day of such work on city and country roads, one could earn as much as a worker at a factory earned in a week. Since many people were out of work, this activity became especially popular. After all, this alloy is one of the components for creating steels of various grades at the same metallurgical industries.

Metal detectors today

To date, the topic of searching with the help of electronic devices has not been developed so massively. However, these devices are still popular among certain groups of people. They roam the places of former glory of the valiant Soviet soldiers, trying to dig up something valuable from the objects of history. For example, you can find coins from the times of the Patriotic War, German of course. And some people manage to dig up really valuable things. You just need to know where to look.

What can really be found?

If you don’t pick up the device yourself and walk along the roads of the city or through memorable and historical places, you will hardly believe how many interesting objects the earth holds. And for this it is worth building a metal detector with your own hands.

coins

You can often dig them out. In the times of Ancient Rus', coins of the Arab East were used for trade. Then they used coins of Byzantine and Tatar production. Silver bullion is now found in the form of money.

Today in the Crimea (namely, where you can find well-preserved objects) you can see people with these devices.

Crosses, icons, serpentines

The cross in Ancient Rus' was worn by every self-respecting Christian. All crosses were different from each other, depending on the type and its purpose. Often you can find the so-called vests.

Buckles, buttons, various household items

This group of items is very numerous. Most of them have been used since the Bronze Age and are still in use today. Often the objects were made of bronze, copper or iron.

Echoes of war

This is the most popular group of items that are targeted for search. They are especially popular with collectors. Enthusiasts are searching, getting, restoring. Something ends up in museums, something settles on the hands.

How to make a metal detector with your own hands

In the era of the popularity of ferromanganese and high prices for it, grubby youth did not shy away from digging in the ground to earn some money. More often they purchased devices to search for their prey in numerous markets or from various specialists who, by chance, were fired from radio factories or TV repair shops. One way or another, these professionals assembled the metal detector with their own hands from radio components remaining in stores using various schemes and technologies. The guys often argued about who had the better and more technologically advanced device. After all, then it was actually a working tool, and not a device for a hobby, as at the present time.

Do-it-yourself metal detectors were also made by those who knew at least a little about electronics. But these guys weren't interested in digging up a metallurgical ingredient from the ground. But it looks like we've gotten off topic.

Principle of operation

Before proceeding to the assembly of various circuits, you need to look at the principle of operation of these devices.

The operation of a metal detector is based on the principles of magnetic attraction. The device through one coil creates a magnetic field. The second receives feedback signals. Then, in case of a find, it sends a return signal through an audible signaling device. You can even make a special non-ferrous metal detector with your own hands.

The larger the coil, the more sensitive the instrument will be. Although in modern devices, and especially in industrial models, the coil is small. But there are amplifiers on microcircuits.

Types

The ultra-low frequency seeker is the simplest device. Every student knows how to make a metal detector with their own hands using an ultra-low-frequency scheme. But this does not mean that such a searcher is inefficient. Just the opposite. With proper tuning, you can achieve good results.

The pulse seeker is a deeper apparatus. With it, you can easily find jewelry, coins and other small things at great depths. Such schemes are popular among professional treasure hunters.

A device that works on beats makes it possible to detect absolutely any metal or mineral object in the bowels of the earth at a depth of up to a meter. It is designed for certain types of alloys. This is a cheap device to build.

The radio detector is able to find metals at a depth of up to a meter. Make it simple. This is a suitable device for beginners, but is not popular among diggers.

Primitive metal detector on a single transistor

If you still have a long-wave radio receiver in working condition at home, then even if you are poorly versed in electronics, you can assemble a metal detector attachment for this receiver.

To make a metal detector with your own hands, the circuit is drawn without much difficulty. The circuit diagram is the most common LC oscillator, designed for frequencies in the region of 140 kHz. The coil for the device, which is used as an oscillatory circuit, must contain 16 turns of the simplest insulated wire up to 0.5 mm in diameter. The coils must be laid on plywood of suitable dimensions. The resulting contour is fixed to the base with glue. This is how a do-it-yourself coil for a metal detector is usually made.

Required Parts

Resistors and capacitors for this device can be used absolutely any. As a transistor, a low-power high-frequency one with reverse conduction will suffice. This may be the popular and easily accessible KT315. Or KT3102 with any letter index.

To assemble this simple metal detector with your own hands, the circuit is assembled either by surface mounting or on a pre-prepared board made of getinax or textolite.

Setting up a simple metal detector

After the part is ready, you need to place it next to our coil. The device should have a comfortable handle. The radio receiver must be mounted on the handle of the finder, and then tuned to a frequency in the region of 140 kHz. You will hear a squeak or creak. If you bring the coil closer to a metal object, the sound in the headphones will change its tone.

Despite the fact that these are the simplest metal detectors in terms of design and scheme, it is elementary easy to make them with your own hands, the sensitivity of such devices makes it possible to work at depths up to 200 mm.

High frequency finder

This assembly scheme is a little more complicated than the previous one. But also much more efficient. Its difference is that there are two coils.

The first is the outer contour. This coil creates a direct magnetic field. The second is the receiving circuit. This detail is designed to receive, process, amplify the signals that come from the ground.

We make a deep metal detector with our own hands

First you need to assemble the so-called command block. To create it, an old computer, the same old laptop or radio is suitable. Then you need to find the highest frequency in the AM band. You need to make sure that there is no radio station on the frequency.

search head

To assemble the search head, you need to cut two circles from thin plywood. One of them should have a diameter of about 15 cm, the second should be made a little smaller. This is done so that the rings can be inserted into each other. Then we need to cut out small pieces of wood so that our head rings are parallel.

After that, 10-15 turns of enameled wire with a cross section of 0.25 mm should be removed from the plates from the outer circle. You also need to fix the resulting design. To make it work, you need to connect the head from below, and the detector - from above.

It's time to turn on our frequency. In this case, a faint tonal sound will be heard. It's better to use headphones.

Metal detector "Pirate"

Assembling the device is quite easy. The device circuit does not contain programmable microcircuits, it is easy to make and configure this metal detector with your own hands. Detailed instructions will help. Also, this scheme does not contain expensive or scarce parts. "Pirate" in its parameters can surpass foreign, quite expensive industrial analogues.

Options

For power, you need from 9 to 12 V. The current that the device consumes is up to 40 mA. Sensitivity will be up to 150 cm, subject to large metal objects.

How is the element base for a metal detector made?

The "Pirate" type scheme consists of two nodes. This is a transmission circuit, which consists of a pulse generator on KR1006VI1 and a key from an IRF740 transistor. The receiver is made on the basis of the K157UD2 chip and the VS547 transistor.

The coil should be 190 mm in diameter. The number of turns on the PEV wire is 0.5 - 25. The transistor in the circuit can be pulled out of an ordinary economy light bulb or any mobile charger. A properly assembled metal detector "Pirate" with your own hands practically does not need to be adjusted.

"Terminator"

The device has good features. For example, the device will detect a coin with a face value of 5 Russian rubles from 25 cm. The searcher will recognize a German military helmet from 80 cm. These values ​​​​are given under the condition of a coil with a diameter of 240 mm. "Terminator" can recognize metals even at the maximum depth of work.

It is worth saying that beginners are unlikely to be able to assemble the Terminator metal detector with their own hands. The device requires careful adjustment. Even experienced craftsmen sometimes make mistakes when assembling this circuit. The main thing here is not to rush.

In order to assemble the Terminator, you will need a multimeter, as well as an oscilloscope and an LC meter. They are not available to everyone. However, you can try to create a special hardware-software complex based on an ordinary home personal computer.

Description

The terminator is a single-tone device that operates on pulsed beats. The finder is great for finding coins. Also, if you make small improvements, you can search for gold on the beaches, while completely ignoring any other metals. "Terminator" is also suitable for searching for any other objects from any alloys.

In conclusion

So, we found out how to make a Pirate metal detector with our own hands, we also examined the Terminator. As you can see, by devoting the minimum amount of free time and effort to the assembly, you can get a rather interesting, and most importantly, a workable tool with which you can find ancient objects, and possibly expensive coins.

In terms of its popularity, metal detecting is comparable to fishing or hunting, not yielding to them in excitement with a certain degree of commercialism. An increase in the technical culture of the population and a wide range of electrical parts market contribute to an increase in the number of people who want to make their own metal detector with their own hands in order to try themselves as a treasure hunter. On fig. Below is a metal detecting enthusiast using a homemade metal detector to detect metal items on the seashore.

The principle of operation of the metal detector

A metal detector (hereinafter referred to as MI), also called a metal detector, is an electronic device that generates a directed electromagnetic field (primary signal) and detects its changes when the field contacts metal objects. During the propagation of electromagnetic waves in an inhomogeneous physical medium, they interact with metals, creating eddy currents on their surface that generate their own electromagnetic fields. The MI receiving equipment captures these fields (secondary signal) and informs the searcher about the discovered find by sound or visual means.

How a metal detector works

The technical implementation of the operating principle of MI is based on the use of two basic functional elements of a modular type:

• search coils for generating a primary electromagnetic field of a directional nature and receiving re-reflected secondary radio signals;
• control units for processing information from the search coils and issuing the processing result to the operator.

Depending on the purpose of the MI, the search coils operate in the following frequency ranges:

• low-frequency range within 2.5-6.6 kHz - to detect gold, silver, copper and their alloys at a depth of up to 4 meters;
• in the mid-frequency range - to search for metals of any type;
• in the high-frequency range - for the search for aluminum, nickel and the detection of small targets at shallow depths.

The parameters of the magnetic field induced on the surface of a metal target are changed as follows:

• signal amplitude decreases with distance from the transmitter;
• the phase of the induced field is determined by the electrical conductivity of the metal.

The MI equipment calculates the distance to the target from the difference in amplitude, and the type of metal is determined from the phase shift.

On fig. Below is a schematic diagram of the analysis of MI information.

Metal detector - detector or scanner

At their core, MIs are detector devices (from Latin detector - detector), indicating a change in the parameters of the primary directional radio signal. The quality of metal detection directly depends on the level of complexity of the metal detector equipment that processes the secondary signal. At the initial stage of the appearance of the operator's MI, the squeak in the headphones, which occurs when a metal target is detected, was quite satisfied. The development of the element base for microelectronics has significantly expanded the possibilities of manual metal detection. Professional hand-held metal detectors are capable of solving the following tasks:

• identification of the “find” by the type of metal;
• determination of the depth of its location;
• assessment of the size and configuration of the detected object.

Using the latest software developments, leading manufacturers have launched sales of medical devices with the ability to build an image of a detected target. For example, the German company OKM has developed a deep 3D scanner (from the English scan - to consider) model EXP 6000, which displays the configuration of a metal object on the screen.

On fig. The MI Model EXP 6000 monitor is shown below with the target displayed on the screen.

Varieties of MI by purpose

In accordance with the intended purpose, MI is divided into the following types:

1. Ground models designed for underground surveys in the upper layers of the soil. Devices of this category are most common among metal searchers and treasure hunters who are able to assemble a metal detector with their own hands at home. The simplest homemade product has low accuracy and does not always distinguish between metals of different types. Professional instruments can detect small gold grains, ignoring other metals.
2. Depth models designed to detect targets at a depth of up to 6 meters. However, they can "see" only large objects with an area of ​​​​over 400 square meters. see. Downhole instruments are in demand by engineering services as line finders, by geologists as specialized ground penetrating radars for searching for native gold, etc.
3. Underwater metal detectors operating underwater. They are subject to increased requirements for the tightness of the search system. The operating conditions of an underwater MP in sea and fresh water differ significantly. Underwater detectors use only sound indication.

Note! Underwater MI can be used on the surface in the mode of a conventional ground metal detector. Search engines only need to adjust the length of the rod and the position of the stop to make it more convenient to use the device.

1. Special metal detectors:

• security devices for detecting metal products in luggage, in clothes or on a person's body during inspection;
• industrial metal detectors as part of conveyor lines, signaling the presence of metals in products;
• army devices, collectively called mine detectors;
• detectors tuned exclusively to gold items.

On fig. Below is a hand-held security metal detector.

Motivation for choosing the design of a homemade metal detector

Long before assembling a metal detector at home, the craftsman needs to compare the numerous factors that affect the operation of the MP, and choose the best design option that fully meets his needs. When making a metal detector with your own hands, the following technical and operational indicators are taken into account:

• general parameters of the search device that determine its functionality;
• operating frequencies in the range of which it is supposed to work;
• a search method that determines the circuit design of the device with setting the method for fixing the change in the MI response when it approaches a metal object.

General MI parameters

For homemade search equipment, the following parameters are distinguished:

1. The penetrating power, which characterizes the maximum depth of penetration of the electromagnetic field, deeper than which the device is no longer able to detect a metal object.
2. Sensitivity indicating the ability to detect small objects.
3. Resolution, more commonly referred to as MI discrimination, providing information about specific properties of an object. A metal detector requires the full implementation of the three components of discrimination:

• geometric - to judge the size and configuration of the found target;
• spatial - for information about the depth of the target and its location in the search area;
• by quality - for assumptions about the type of material of the object and its likely characteristics.

1. The size of the search area within which it is possible to detect metal.
2. Selectivity - an increased reaction to finds of a given type (gold, non-ferrous metals, military artifacts, etc.).
3. Noise immunity - no response to electromagnetic fields of extraneous sources.
4. Power consumption, which determines how long the mobile power supply of the device will last for active work.

On fig. below, in an ironic form, the process of metal detection (metal search) using a home-made MI is shown:

• pos. "A" - no metal targets;
• pos. "B" - metal objects of a certain value were found (for the sake of which the metal search was started).

The search area of ​​the metal detector is highlighted in red.

Operating frequencies of homemade MI

The metal detector circuit and its assembly tie all the parameters of a homemade metal detector to the frequency range in which the operator intends to work. The practice of amateur metal detecting has shown the limited effectiveness of low-frequency (vlf) and high-frequency (hf) metal detectors, which require computer signal processing, consume a lot of energy and do not work well on mineralized wet soils. Most search engines interested in how to make a metal detector multifunctional in detecting and recognizing non-ferrous metal, ferrous metal, with minimal susceptibility to soil features, are guided by low-frequency and mid-frequency ranges ranging from 30 kHz to 3 MHz. Operation in this frequency range allows the use of a simple metal detector to detect targets of any type of metal.

Search method

There are more than a dozen methods for finding metal objects using a directed electromagnetic field, including state-of-the-art digital processing of a secondary signal on a computer with professional use of MI. When assembling home-made metal detectors for metal detecting at an amateur level, craftsmen are guided by methods that make it possible to simplify the circuit design of the detector as much as possible and reduce the cost of its configuration. The most popular in the manufacture of homemade products are the following metal detection methods:

• parametric method, for the implementation of which the receiver is not needed;
• receiving-transmitting method - using a transmitter and receiver;
• phase accumulation method - “until it clicks”;
• method on beats - “on a squeak”.

Parametric method

Parametric type metal detectors are equipped with only one coil, which is both transmitting and receiving. When a metal target is detected, the parameters of the generating coil change: inductance, frequency and amplitude of the generated oscillations, which is fixed by the MI equipment. The main problem when operating a detector without a receiver is the selection of a relatively weak induced signal against the background of a powerful primary electromagnetic field.

Receiving-transmitting method

In the design of models operating according to the "reception-transmission" method, two coils are provided:

• transmitting - for generating an electromagnetic field;
• reception room - for registration of the signal re-emitted from the metal target.

Important! When assembling the receiving-transmitting MI coils must be positioned in such a way as to minimize the inductive coupling between them. If the axes of both coils are mutually perpendicular, the transmitter signal will not go directly to the receiving device and will not be heard.

Metal detectors with phase accumulation (until click)

In the operation of phase-sensitive devices, the process of delaying pulses during re-radiation is used, which leads to an increase in the phase shift. When a specific value is reached, the discriminator is triggered, a click is heard in the headphones. When approaching a metal object, clicks become more and more frequent, merging into a sound of a certain tonality. With an appropriate sound setting directly above the object, a synchronization breakdown occurs, the sound disappears due to the transition of the click movement frequency to the ultrasonic range.

Beat metal detectors (squeak method)

If you make a metal detector on beats, then in a home-made design it is necessary to use two generators of an electromagnetic field:

• a reference oscillator whose frequency is stabilized and is a reference frequency parameter;
• a working (search) generator, the frequency of which depends on the presence of metal in the search zone.

Prior to the start of search operations, the search generator is tuned to zero beats (frequency coincidence). When setting up, they achieve a low sound tone (squeak) so that it is convenient to search. By changing the tone, the properties of the detected object and its location are judged.

On fig. Below is a homemade MI made from scrap materials.

Homemade MI schemes

Factory-made metal detector equipment is represented on the market by quite expensive professional-level electronic systems, so enthusiasts are constantly exchanging information on how to make a home-made metal detector at home with minimal financial costs. Step-by-step instructions for assembling and debugging the device allow you to create a fully functional metal detector from available radio components. Metal detectors, including a do-it-yourself mine detector, the circuit of which is identical to those for standard MI, are made on transistors and microcircuits. The package of schemes for homemade products also includes:

• capacitors of various types: ceramic, film, electrolytic;
• resistors;
• resonators;
• controllers.

Additional Information. Quite often, circuits of amateur equipment for metal detecting use the NE 555 microcircuit, which is a universal timer that generates single and repetitive pulses of stable temporal characteristics.

A worthy competitor to a metal detector on microcircuits is a metal detector on transistors, in which signals are generated using KT-361 and KT-315 transistors or similar radio components manufactured since Soviet times.

Do-it-yourself manufacturing of MI components

When designing a home-made metal detector, craftsmen are guided by the creation of a small-sized, structurally balanced, relatively light product. Mobile design and thoughtful ergonomics should minimize operator fatigue during many hours of continuous search work, and high-quality assembly of a home-made design will ensure good repeatability of results and high performance.

MI of handicraft production consists of the following components:

• control unit;
• frames with a search coil;
• holding rod, on which the search coil and control unit are mounted.

Control block

To assemble the control unit, it is necessary to select a box-type plastic case. The case should compactly accommodate:

• printed circuit board with electronic stuffing, assembled in accordance with the scheme;
• batteries;
• devices for sound and visual notification of the find.

The main element of the control unit is the printed circuit board.

Do-it-yourself printed circuit board MI

The printed circuit board is used for compact placement of radio components that are part of the MI circuit. The following is a generalized description of the stages of self-manufacturing of a printed circuit board with a detailed description of the operations performed:

1. The scheme of the metal detector is selected. In accordance with the scheme, a sketch of the board is drawn on paper or printed on a printer.
2. A piece of sheet textolite is cut out to fit the dimensions of the board.
3. In any available way, the drawing is transferred to the textolite blank.
4. On the surface of the workpiece, markings are made for the attachment points of radio components. Holes with a diameter of 1.0-1.5 mm are drilled.
5. Tracks are drawn with a permanent marker or brush with varnish in accordance with the paper template.
6. The board is etched with ferric chloride or copper sulfate.
7. After etching, the board is wiped and cleaned with sandpaper.
8. A tin tinning operation is being carried out.

On fig. Below is the PCB of the metal detector after tinning.

Frame with coil

The search frame of a metal detector is a flat rigid body with a search coil attached to it, designed to perform the following tasks:

• rigid fixation of the search coil relative to the holding rod;
• ensuring the constancy of the geometric dimensions of the emitting and receiving loops of the search coil;
• protection of the wires of the coils from damage when the operator moves over rough terrain.

The body of the MI frame of round or rectangular shape is made of plastic tubes without the use of metal elements. Among craftsmen, ½ inch (15 mm) PVC tubes are popular. Small frames are made non-separable in the form of a ring or square. When manufacturing a large rectangular body, it is appropriate to use fittings so as not to deform the tubes at bends. The size and shape of the housing must correspond to the dimensions and configuration of the coil, taking into account the peculiarities of the placement of the transmitting and receiving circuits in it.

The most important search element of the MP, which determines its operational characteristics, is the search coil.

Coils MI

The functional properties of the MI are determined by the quality of the search coil manufacturing. The parameters of the coil and the overall design of the metal detector need to be adjusted to each other until an optimal result is achieved. The performance of the coil is influenced by various factors, of which the following are decisive:

• coil dimensions;
• design of the coil ring;
• the value of the inductance of the coil;
• degree of noise immunity;
• method of winding the wire of the basket coil;
• coil attachment method.

Coil dimensions

Practice has shown that the efficiency of the coil directly depends on its size. Large coils are able to penetrate the ground deeper and cover a wider search area than their smaller diameter counterparts. The following gradation of search coil sizes has been adopted:

• a diameter of 20-90 mm is optimal for searching for ferrous metal (rebar, profiles);
• a diameter of 130-150 mm is convenient for searching for the so-called "beach gold";
• diameter 200-600 mm is focused on overall metal objects.

Coil design

The classic design of the search coil is a monoloop (single loop), made in the form of a single flat ring of coils of copper wire. The width and thickness of the ring are selected 15-20 times less than the average diameter of the ring. Monoloop MIs are recommended for beginners to gain initial search experience.

A more "advanced" design, compared to a monoloop, is a DD coil, which is a double detector (hence the name - from the English. Double Detector). Structurally, the DD-coil is made of two semicircles folded with intersection. DD coils are highly sensitive, but on inhomogeneous soils they can give a false signal.

Coil inductance

When assembling an MI at home, it is very important to ensure that the parameters of a self-made search coil match those parameters that are incorporated in the selected detector circuit. The size of the inductance is affected by the geometric dimensions of the coil, the cross section of the wire, the number of turns, the stacking density and other factors. In networks, you can find various methods for calculating inductance, simple formulas and nomograms with explanations of how to use them. Failure to follow these recommendations may lead to the fact that the assembled circuit will not work.

Coil noise immunity

Since the monoloop is similar to a loop antenna, it is susceptible to numerous interferences. To expand the noise-immune capabilities of the device, simple devices of the type are used:

• Faraday screen, which is a steel tube with a braid or foil winding;
• symmetrical windings of bifilar or cross type.

Basket coils

On fig. one of the modifications of the MI basket coil is shown below.

With all its advantages, the basket coil is endowed with two significant drawbacks:

• the complexity and laboriousness of performing high-quality reliable winding;
• methods for calculating flat and volumetric baskets differ significantly and require the use of appropriate computer programs.

Important! When handicraft winding of the coil-basket, the mandrel must be rigid and strong, since the total tension force of all turns is large enough to deform or break the mandrel.

So that the wires stretched during winding do not cut through the frame of the coil, it is recommended to first glue pieces of durable plastic into the slot of the frame and only after that start winding.

coil mount

Fastening the coil wire is quite often done on home-made frames made of plywood, plastic and other improvised materials, even on computer disks. Plywood has many disadvantages, including:

Polycarbonate-based plastics do not have these drawbacks. Moreover, two glued polymer discs form a hermetically sealed enclosure that expands the possibilities of using the MI.

Homemade rod-holder

The holding rod is the supporting element of the metal detector - the search coil and the control unit are fixed on it. The main requirement for the rod is the strength of the material of manufacture, since a constant weight load from the operator acts on the holder during prospecting. Damage to the supporting structure can occur in rough terrain, in forest plantations, in a mountainous area. Breakage of the rod can lead to a forced cessation of prospecting.

Note! There are no specific requirements for the metal detector rod, each MI user has the right to adjust the size and shape of the holder to suit their height and weight.

In self-manufacturing of a metal detector for the housing of the holding rod, crutches for the elbow (Canadians) are often used as the initial semi-finished product, the design of which already provides for the height adjustment of the stand and the arm rest. Telescopic rods and ordinary metal-plastic water pipes are also popular among craftsmen, from which full-fledged MP holders are obtained.

Homemade underwater metal detector

The process of manufacturing, assembling and setting up a metal detector designed for underwater metal detection is identical to the work on creating a conventional MI. However, it is necessary to point out two significant differences that accompany the manufacture of an underwater MP:

• all equipment must be placed in a sealed enclosure that does not allow parts to come into contact with moisture;
• to report from under the water about the found find, it is advisable to use special light indicators.

Do-it-yourself underwater MI manufacturing steps:

1. The choice of scheme for operation in river and sea water.
2. PCB manufacturing.
3. Connecting the power supply.
4. Placement of the finished board with a power source in a sealed container. Masters recommend using a sealant tube as a body. LED indicator lights are displayed on the outer surface of the tube. Each joint is additionally sealed with silicone sealant.
5. Making a rod from a thin-walled stainless pipe or a regular plastic water pipe. Quite often, a fishing rod body is used.

Important! The bar should not be too light so as not to float, but also very heavy so as not to sink to the bottom.

1. Fixing the assembled block with a printed circuit board on the rod.
2. Search coil winding. The coil body is a standard polypropylene pipe. The wound wire is filled with sealant.
3. Soldering coil leads to stranded wire.
4. Visual assessment of the tightness of the product. Any gaps and joints that “do not inspire confidence” for tightness are filled / smeared with sealant.
5. Water tightness test.

Features of deep MP

Deep MI uses RF technology, which is effective in the high-frequency range. The transmitting and receiving coils are mutually perpendicular, they can operate at several frequencies simultaneously. Deep instruments are insensitive to small targets, their objects are large objects located on the ground with differences in ground levels.

If we turn to the numerous forums of metal detecting enthusiasts, which are full of Internet pages, then the high level of manufacturing and adjustment of home-made structures, which are described there, attracts attention. Do-it-yourself metal detectors are not inferior to factory-made search equipment, although they are many times cheaper. On fig. below is a home-made "deep hole", the frame of which is made of durable polymer tubes.

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