Iron drawing. Metallic bond: mechanism of formation and examples. Required materials for the drawing

Aroused great interest among radio amateurs. And this is not surprising, because in terms of technical characteristics that metal detector was not inferior to many industrial devices of the average price level, and in its ease of assembly and configuration it surpassed them.

Over the course of several months, the metal detector circuit was repeated many times by many radio amateurs, even not very experienced ones, and almost always left the most positive reviews about it on the forum. In some cases, of course, problems arose with the setup, which raised many questions and long discussions at the conference, so it was decided to systematize all the information on this metal detector and post it here, along with the updated diagram.

The fundamental one is in the archive as a file sPlan. As can be seen from the diagram, the input stage on the LM358 has undergone some changes, it has become possible to change the signal phase with a button, added led indicator response from a target in the ground, which allows you to visually determine iron - non-ferrous metal and one transistor is added to the ULF. Now you can safely install an ordinary small-sized 8-ohm speaker there. It is recommended to use it for sound emission, since headphones will interfere with making your way through the bushes, and the ZP-shka is too quiet for searching on the banks of noisy rivers and seas.

Everyone makes a metal detector body out of whatever they have at hand. The main thing is that it is strong enough, waterproof and preferably made of metal. Additional shielding will not be superfluous at all, because the metal detector contains very sensitive op-amps. At the back there are two tulips for connecting search coils with high-quality shielded wire.

The metal detector is powered by 12V, but it is quite acceptable to reduce it to 8. When choosing a power source, keep in mind that you will have to walk with it outdoors all day, so the battery should last 10 hours. In the author’s version, naturally with slightly worse sensitivity, the device worked even from two old lithium-ion batteries from a mobile phone. The current consumption of the metal detector is about 50 mA, so in some cases you can install a 9-volt power supply, but such power will be enough for 2 hours of operation, no more.

To charge the batteries, a socket is provided, to which power is supplied from the charger or, in the simplest case, from the power supply through a resistor. Be sure to install a volume control, because sometimes you will have to search in an atmosphere of secrecy (behind enemy lines), guided only by the LEDs. On the other side of the front panel there is a Trash control - threshold. It is used to set the moment when the metal detector stops beeping on its own, and the sound appears only when there is metal within sight search coil.

A lot has been written about making a metal detector coil; I’ll just add some recent information. We start by making a template for winding.

Any suitable material (fibreboard, plywood, plexiglass, plastic, etc.) is made from 5 mm plywood. We process the edges of the finished template and cover it with tape so that the template does not stick to the reel. We clamp the finished template with the axle in a vice and wind 80 turns of wire onto it, impregnating every 20 turns with tsaponlac. You can impregnate with epoxy at your own peril and risk; on many forums they write that batches of resin with different electrical conductivity come across, which affects the parameters of the coil not in better side. After drying, we disassemble the template, remove the spool and “tighten” its “waist” with foam tape. I consider the use of electrical tape inappropriate since electrical tape has a sticky side and can displace the coils - tsaponlak is not epoxy.

Next, we shield it with foil (I use lavsan foil taken from an RG-6U antenna cable, a piece 2 meters long is enough for 2 coils), then we wrap it with tinned wire, and on top with electrical tape or fum tape. As a result, we obtain coils that are absolutely identical in parameters, geometry and quality factor, which is important for a balanced metal detector, since balanced coils are very critical to the geometry of the coils. Then we tune the coils to resonance and begin to reduce to “0”. It should be remembered that for this model, reduction to absolute “0” is undesirable - discrimination will disappear, so an imbalance of 0.2-0.6 millivolts is enough, even though the detection depth will decrease by a couple of centimeters. Having brought the coils together, we fix them together with cyanoacrylate and threads, and dry them. Now we begin to manufacture the sensor housing.

The most optimal and cheapest, in my opinion, is a sensor made of ceiling tiles. We make a template, cut the blanks and glue the body. I don’t recommend making the cheeks of the reel seat from plexiglass - it’s very fragile, it’s better to use fiberglass, or even better - plastic inserts that railway workers put under the rail on the sleeper (just don’t let the train derail). The result is quite decent, lightweight and cheap to manufacture metal detector search sensors.

As supporting tubes, you can use a telescopic painting rod, cut to the desired size. A sliding handle from a Chinese mop or a Chinese three-legged landing net for fishing will also work.

A lot has also been said about setting up contours. Let's give the floor to the forum guests: I turned on the search coil for transmission as a series oscillatory circuit, and for reception as a parallel oscillatory circuit. I set up the transmitting coil first, connected the assembled sensor structure to the metal detector, an oscilloscope parallel to the coil, and selected capacitors based on the maximum amplitude. After this, I connected the oscilloscope to the receiving coil and selected the capacitors for RX based on the maximum amplitude. Setting the circuits to resonance takes several minutes if you have an oscilloscope. Further reduction to zero. It’s easier to solder a switch (sensitive voltmeter) to the output of the 1st stage and overlap the coils by about 1cm and move them apart. And the arrow will show the zero point. It can be quite accurate and not easy to catch right away. But it is there. If it still doesn’t work, try turning one of the coils over.

The metal detector circuit can and should be checked first without coils. To do this, let’s mentally break it down into blocks, which we set up and launch separately:

Bipolar voltage former on U6A - makes from 12V + -6V.
Quartz frequency generator on 561LA7 - creates 32768Hz.
Frequency divider on 561TM2 - divides 32768Hz by 4, we get 8192Hz at pins 1,2,12,13.
Speaker tone generator on U6B - generates a squeak on pin 4.
Controlled sound amplifier on Q5, Q6, Q7 - amplifies the sound of the U6B generator if there is a response signal from U2B.
Target response signal amplifiers U1B, U2A, U2B - the low response voltage is accelerated to several volts, which allows the LED to be illuminated and the amplifier to be turned on.

Of course, not all possible questions are covered here, so please check. Additional information on setting up a metal detector on the forum. And I just have to thank Elektrodych separately for a good description of the coil design, and slavake for drawing new scheme, and all other forum participants - for their interest in the metal detector.

Discuss the article METAL DETECTOR DIAGRAM

Modern home furniture should satisfy not only the aesthetic taste of the owner, but also be comfortable and reliable. Today, metal beds can often be seen in the interiors of fashionable bedrooms.

Simple design

Metal furniture is not only durable, it also brings a special flavor of avant-garde and modernism to the atmosphere of the room.

Scheme metal bed

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Self-production

Try making a metal bed with your own hands. Thanks to this, you will purchase a stylish bed for the bedroom, significantly reducing the cost of your household budget for the purchase of furniture.

Diagram of the design and individual components of the bed.

Simple is characterized by special mechanical strength and ease of assembly. There are no bent elements in it, which complicate the assembly process of furniture models with ornate decorative elements. To produce the described bed, common and publicly available materials are taken, supplied by the modern metal market for the manufacture of metal furniture. Almost all sales points will help you cut metal parts of the required size, corresponding to the customer’s drawings.

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Consumables

We will construct the bed frame from profile pipeØ 20x20 mm, and the frame will be made from steel channel with outgoing dimensions 65x32 mm. You will also need a metal corner 40x40 mm and a sheet of steel 2 mm thick for preparing plugs and bearings. The list and dimensions of the required parts are given in the table.

Table “Do-it-yourself bed”

The dimensions of the bed structure have a direct relationship with standard sizes mattresses with a width of 80-200 cm and a length of 190-200 cm. For a long time, everyone has fallen in love with mattresses 20 cm high with independent spring blocks. In such mattress products, in places of the highest load there are reinforced longitudinal zones, which create an orthopedic effect and extend the service life of the mattress.

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Assembly tools

Velcro sandpaper structure.

• welding machine;
• angle grinder (grinder);
• drill with metal drill Ø 9 mm;
• roulette;
• square;
• square file;
• metal brush;
• sandpaper;
• paint brushes;
• primer for metal surfaces;
• paintwork.

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Manufacturing of the structure

Home production of a metal bed begins with the manufacture of its backs: profile pipes of the appropriate diameter are cut according to the dimensions from the table and laid out on a flat surface. It is advisable to carefully fix all parts in the desired position. Subsequent welding work is carried out with constant check construction diagonals and right angles.

The next stage includes the production of tenon mounting brackets: 4 side and 2 central parts. These structural elements are made from the remaining channel scraps and using an angle grinder, popularly nicknamed the “grinder”. The bracket tenon should have a slight bevel of 5º relative to the vertical plane. The manufactured fasteners are welded to the headboards at a distance of 35 cm from the floor.

Installation diagram of metal bed brackets.

These elements - the brackets - will subsequently be subject to the greatest load, so they are welded to the headboards with a continuous seam.

Frames for mattresses are made of metal corners and channels. Steel corners - the end parts of the frame - are connected to long channel blanks - drawers. For high-quality joining and reliable welding of the frame and the transverse part, small sections are cut off at the ends of the angle along its horizontal flange.

To insert the bracket tenons in the frames, you need to drill matching holes. For correct marking Where the holes are located, the bed backs are installed in a vertical position, and welded frames are placed on them. The locations of the tenons are marked along the bottom flange of the steel channel. The holes are drilled using a drill with a Ø 9 mm drill bit. The shape of the drilled holes is adjusted to the shape of the tenon using a square file.

Scheme of joining frames for mattresses.

When the main part is assembled, it’s time to make a grid for the mattress. Steel strips of the appropriate size - 2 longitudinal and 6 transverse elements - are alternately welded to the bed frame.

Now all that remains is to weld the footrests (thrust bearings) and the top plugs to the bed posts: circles Ø 22 mm, cut from steel, are carefully welded in the appropriate places.

Metal stoves are very popular due to their low cost, and are widely used for heating country houses, bathhouses, utility rooms, and garages.

For example, on the website of the Teplodar company https://www.teplodar.ru/catalog/otopitelnie-pechi-kaminy/ there are 6 stoves for heating houses and cottages at a price of 6,760 rubles.

But you can do it yourself, it’s not that difficult. Of course, they have advantages compared to brick kilns, but they also have disadvantages.

Design Features

The simplest design of a metal stove is the so-called potbelly stove. Its design is quite simple: a metal box with legs, a door, and a pipe for removing combustion products. The main disadvantage of this stove is its high fuel consumption and low heat output. Another big disadvantage is the risk of fire.

The Russian name for this type of stove is based on the association with the caricature of the bourgeois, depicted as a man with a fat belly.

https://ru.wikipedia.org/wiki/%D0%91%D1%83%D1%80%D0%B6%D1%83%D0%B9%D0%BA%D0%B0

Modern metal stoves are much safer than stoves. Their production is carried out from sheet steel, up to 4–5 mm thick. The design includes a special chamber for laying stones. A water tank with a capacity of up to 70 liters is provided as a heat storage tank. To heat the stove evenly, as well as to reduce its fire hazard, it is recommended to line the stove with heat-resistant bricks.

Advantages

• Metal is quite durable, but it is also a more malleable material that allows you to give it any shape. Able to withstand large temperature changes and severe loads during product operation.
• It is worth noting the high efficiency of the metal stove, reaching 95%.
• The thermal conductivity of the metal is high; accordingly, the furnace warms up quite quickly and the room heats up.
• The strength of metal only increases with decreasing thickness, unlike ceramics.
• The weight of a stove is an order of magnitude, and sometimes more, lower than a stone or brick one, which in turn makes it possible to avoid constructing a bulky monolithic foundation.
• The low cost of heat produced (for metal stoves is 10–20 times lower than for brick stoves) is another plus in the treasury of advantages of this type of stove.
• An important factor is the transportability of such a stove and ease of installation on site; you only need to install a chimney.
• When no longer needed, it can be easily stored until the next heating season.

Flaws

• Probably the most basic drawback is that the stove does not “breathe.” Whereas a brick stove, when cooled, absorbs moisture, thereby maintaining optimal humidity. A slight “breathing” of the stove will appear after brick lining, but mobility will disappear and the dimensions will increase.
• Due to the low heat capacity of the metal, heat transfer after fuel combustion usually does not exceed 2–3 hours.
• The big disadvantage of a metal stove is its lifespan. At operating temperatures, the metal actively reacts with moisture contained in the air, and as a result, accelerates corrosion. The service life of a metal furnace usually does not exceed twenty years. But this is fully compensated by the easy and inexpensive replacement of the stove and cheap fuel.

Kinds

At the moment, the market offers two types of metal stoves for the home, made from cast iron and steel. In terms of heat transfer, a cast iron stove is between brick and steel. The option of making a cast iron stove with your own hands disappears immediately, since you need to organize the process of cast iron, which suburban area basically impossible. This requires special equipment. But you can build a stove made of sheet metal with your own hands, and in some cases, practically without spending money.

Operating principle and design

Let's look at the general operating diagrams of furnaces. The main diagrams used in the figures:

Chamber system

In the furnace of the chamber system, combustion products are bypassed into gas chamber and there they burn out. The air flow is formed naturally. In chamber furnaces intended for household use, the firebox and afterburning chamber are located in one module - the crucible. For complete afterburning of gases, the chamber must have vaulted walls. A good example of a chamber system is the Russian stove. With a certain improvement chamber furnaces quite effective.

Channel system

The duct system organizes the forced movement of gases from the fire source, through channels inside the stove, to the chimney. Combustion products, burning out and passing through the channels, cool down, giving off heat to the stove. The efficiency of such a furnace is about 60%, and in order for the gases to begin to burn out, it is necessary to first bring the furnace to an operating temperature of 400 degrees.

Bell system

In this system, the gases are under the dome of the bell and, when burned, go down the walls of the furnace, giving off the remaining heat. In this system, to start combustion of gases, it is necessary to warm up a small area of ​​the hood dome. The efficiency in furnaces of this type can reach 70% or higher.

Schemes of metal furnaces and improvements

It is well known that metal heats up quickly, but also cools down quickly, its low heat capacity makes it an unimportant heat storage device, but if you take into account some of the properties of the material, classical schemes can be applied to metal furnaces and get the most out of them, since heat losses for heating are minimized. Let's consider two schemes.

Chamber (A)

A typical representative is the “potbelly stove”. Its prototypes, indoor stoves, were used in the 19th century and were extremely voracious in terms of fuel. During the times of devastation and upheaval after the revolution, the “potbelly stove” was improved and christened by its current name.

The following improvements have been made:

1. To adjust the heat transfer power, a grate and a blower with a door were inserted into the furnace.
2. The chimney diameter is 9–10 millimeters per 0.23 kilocalories of thermal energy.
3. Low chimney height, up to 3 meters from the plane of the grate.
4. The beginning of the chimney up to 1–1.5 m is made vertically and covered with heat-insulating non-combustible material.
5. Next, the chimney continued with a horizontal section - a hog - no less than 2.5 m long; it was inserted into the window and another vertical segment of 1–1.5 meters was added to provide draft.

Duct (B)

The potbelly stove can be easily adapted to a duct scheme. Of course, the only thing in common with a brick stove will be appearance. The channels will be of little use due to the high thermal conductivity of the metal; all that remains of the original system is a horizontal section separating the afterburning chamber and the firebox. Extra air for afterburning gases comes from holes on the hob or through a separate adjustable air duct. The chimney outlet is horizontal.

Results of improvements:

1. Thanks to the afterburning of gases in a localized place, the efficiency increased to 70–80%
2. The released thermal energy increased by 2–3 times.
3. The stove is undemanding in terms of draft force and chimney characteristics; it behaves like a simple potbelly stove: the draft has increased, the combustion and the rarefaction of the environment in the gas afterburner have increased. More secondary air enters and the gases burn completely.
4. Since the main power is produced in the afterburner, the furnace can operate in two modes: flame and long combustion.
5. Good heat transfer from the firebox through a fairly thin partition is achieved in the afterburner desired temperature to ignite unburned gases, so the stove enters operating mode almost instantly.
6. A separate air supply to the firebox and afterburner allows the stove to be configured for almost any solid fuel.
7. The heat transfer power of the furnace can be easily adjusted by the level of the blower air supply. In a classic potbelly stove, air power control is severely limited.
8. Thanks to the afterburner, the temperature under the hob is kept within 250–300 degrees, which is quite comfortable for cooking.
9. The high release of thermal energy from the stove allows you to heat the room evenly and quickly.
10. At the entrance to chimney You can also install a heat exchange circuit for hot water supply.
11. When using high-quality firewood or coal, you will have to clean the chimney every 5 years.

Drawing and calculation of parameters

What size the stove will have and what it will look like should be decided by everyone for themselves. People with engineering thinking and practical skills can make their own adjustments to the simplest design to improve and simplify the system.

Sketch and drawing of a potbelly stove:

Materials and tools

• Drawing and sketch of the future structure with dimensions.
• Sheet metal, 4–5 mm thick.
• Steel corners.
• Steel tubes with a diameter of 15–20 mm or fittings with a diameter of 10–12 mm for the grate.
• Metal pipe with a diameter of 180 mm.
• Arc welding, electrodes 3.
• An angle grinder (grinder) with a cutting wheel, a hammer, a tape measure, a pencil or a marker.

How to make a metal stove with your own hands: step-by-step steps

1. The furnace body will be assembled from rectangular steel sheets, butt welding them. Take a grinder and cut five rectangles according to the dimensions given in the drawing. WITH front part We'll figure it out later, since there will be a door for the firebox and a vent.
2. First you need to weld the sides to the bottom. First, we place one side panel to the bottom, using a square to control the right angle between the planes, and tack the joint at several points by welding. We make the second sidewall by analogy with the first. We check the right angles, the width of the bottom corresponds to the distance between the side walls at the top where it will be hob. After making sure that everything is correct, we weld the joints completely.
3. We weld back wall to the side panels and bottom. We mark the side walls from the inside for smoke circulation of the firebox and ash pan according to the drawing into three zones. Between the firebox and the ash pan there will be a grate on which the fuel is directly placed. To attach it to the inner surface of the sidewalls at a height of 10–15 cm from the bottom, corners are welded along the entire length of the panels. The corners should be welded with the shelf down.
4. We proceed to the manufacture of the grate. Materials required: scraps water pipes with a diameter of 15–20 mm and a length equal to or greater (the excess is cut off) to the internal width of the oven. Instead of pipes, fittings with a diameter of 10–12 mm are perfect. Reinforcement or two steel rods with a diameter of 15–20 mm or strips of thick (4–5 mm) steel along the length of the stove.
5. We place the fittings (tubes) on the rods in increments of 3–5 cm and weld them securely.
6. The grate must be removable, so it is not welded to the corners. The need to remove the grate arises when cleaning and repairing a potbelly stove or replacing the grate itself.
7. Next, we weld two rods (pieces of reinforcement) at the top of the stove to install the reflector. It shares the firebox with the afterburner and the chimney and is removable. More details in the picture:
8. The length of the reflector should be 10/11 the length of the potbelly stove to create a gap for the smoke to escape. It is advisable to make it from thicker metal, since it will heat up much more than other structural elements.
9. Let's get started finishing work. We weld a hole in the lid required sizes and sections for the chimney, it can also be done on an already assembled structure. We weld the lid to the stove body. Then you need to cut two jumpers. One is narrow and the other is wide (the exact dimensions depend on the specific dimensions of the oven). The narrow one is welded at the level of the grate to separate the firebox doors and ash pan, and the wide one is welded at the top to the sides and lid.
10. It is best to make the door for the firebox almost the entire width of the stove, both for the convenience of loading firewood and for easy removal of the mirror and grate. For the ash pan you can make it narrower. We make curtains from tubes and rods.
11. Door handles can be made from either metal plates, and from scraps of pipes. Alternatively, you can use the same universal fittings. We fasten the finished handles by welding. I think there shouldn’t be any difficulties with making door latches.
12. After finishing the assembly, you should think about the stove supports. The legs can be made from pipe sections of the desired height. The supports can also be made adjustable in height; for these purposes, a nut is welded to the end of the tube ( inner diameter nuts and tubes must match each other) and the bolt is screwed in.
13. Let's start making the chimney. A pipe with a diameter of 15–20 cm is suitable for its manufacture. We take the end of the pipe outside the room through a hole in the wall or roof. The angles in the pipe should be 45 degrees, that is, there should be a complete absence of horizontal segments along the entire path. We make a rotary damper at the bottom of the chimney. It can be made from a piece of sheet steel; the diameter of the cut valve should be slightly smaller than the diameter of the pipe. We drill a hole in the pipe for the damper adjustment handle; a steel rod is suitable for this purpose. We weld a sleeve from a pipe section of 15–20 cm to the hole in the lid; its diameter should be slightly smaller than the diameter of the chimney pipe in order to make the process of installing or dismantling the chimney as easy as possible. All that remains is to install the stove and test it.

Photo gallery: stove manufacturing process

The damper is in the closed position The damper is in the half-open position Checking the operation of the damper Assembled chimney Chimney installed on the stove

Lining

Metal stoves are often lined with bricks on the outside and inside. But there are two reasons why you shouldn’t do this:

1. Brick has rather low thermal conductivity and high heat capacity. The heat generated by burning fuel in the firebox simply flies out into the chimney along with the smoke. without having time to warm up the metal walls of the potbelly stove.
2. The stove surface is deprived of air access, thereby significantly accelerating the burnout of the walls and the risk of getting into the room carbon monoxide dangerous to human health and life.

Selection and preparation of installation site

For this type of stoves, there is no need to build a monolithic foundation due to their low weight. To select an installation location, you should be guided by such parameters as distance from doors and windows (for less heat loss) and the convenience of removing the chimney from the room. Garages and utility rooms usually have a concrete floor, so no underlayment is required. In rooms with wooden floors, a sheet of asbestos or tin should be laid over the installation site and secured around the perimeter with self-tapping screws. To avoid heat loss, foil thermal insulation can be glued to the walls near the installation site.

Decoration

To decorate a potbelly stove, you can use chamotte plates or decorative metal plates, or you can simply paint the stove with special heat-resistant paints to your taste, after cleaning the surfaces with sandpaper.

Exploitation

Some requirements for safe operation, if followed, you will protect yourself and your loved ones:

• The stove must be placed on a fireproof base.
• All flammable objects and liquids must be kept at a safe distance of 80–100 cm from the stove.
• You should not completely fill the firebox with wood at one time.
• Always make sure that the firebox door is closed when using the stove.
• Regularly inspect the chimney for leaky places to avoid smoke entering the room.
• Do not leave the oven running unattended for long periods of time.
• Do not try to touch the oven body while it is operating to avoid burns.

Cleaning and Maintenance

With intensive use of the stove, soot and dirt are deposited in the chimney channel, and gradually accumulating, narrowing the lumen of the channel, which entails a decrease in draft and overall efficiency of the structure. It is enough to check the chimney once a year for contamination and, if necessary, clean it of soot. There are several ways to clean a chimney:

• Mechanical, with a brush or brush.
• Chemical, by combustion potato peelings in the firebox, while the released starch softens the soot and it comes out.

For better efficiency, you can combine these two methods. The best way to remove carbon deposits from the walls of the firebox is with a metal brush. The mirror and grate are easily removed for replacement or minor repairs.

Video: how to make a potbelly stove yourself

Making a metal stove yourself is not as difficult as it might initially seem. Of course, this design is not the only option in its own way, but already proven and reliable.

Any fence becomes unusable over time or needs maintenance, and maybe even major renovation. But, as practice shows, correctly established from quality material fencing will serve its owners much longer than those on which the owner decided to save.

For example, the service life of some metal fences can reach 60 years, however, with proper care. Here are the simple ones, but durable designs and the speech will begin.

Fencing base

Not a single fence can do without supporting elements, and the more stable they are installed, the more reliable the structure will be. Even a front garden fence will look more respectable if it is equipped with support posts, and the service life of such a fence is much longer.

Metal fences are often installed on supports made of the same material. Massive, monumental fences for a private house are installed on strip or columnar foundations, while less heavy structures for a summer house or front garden around a house can be built without a foundation.

The pillars are secured in several ways:

1. For driven supports, shallow holes are dug or drilled. Their diameter should be slightly larger than the diameter of the supports themselves. Then the supports are inserted into the holes and driven in. It is better to do this procedure together, so that one person holds the support in strict vertical position. After filling the void, the holes are filled with crushed stone or covered with earth and thoroughly compacted.
2. The combined installation is carried out by drilling holes with a diameter twice the diameter of the pillars to half the immersion depth. The support is inserted into the hole, driven to the required depth, and secured with spacers. The voids of the hole are filled with concrete in several stages, each of which is accompanied by compaction.
3. Backfilling differs in that the bottom of the hole for support is filled construction waste(small stones or broken bricks), crushed stone. After installing the post, the hole is filled to the top with crushed stone, carefully compacted, and poured on top concrete mixture.
4. Full concreting is carried out by digging holes for pillars to the required depth, installing and reinforcing supports, and pouring concrete mixture. To make the support more stable, the bottom of the pit is slightly widened towards the bottom, covered with 10 cm of sand or crushed stone, a support is installed, reinforced and filled with concrete.

The depth of the holes for supporting elements depends on many factors, such as the complexity of the soil, the occurrence of groundwater, uneven terrain, and the severity of the fence spans, but the optimal range is considered to be from 80 cm to 1.5 m.

Simple metal fences of light weight do not require volumetric supports; for them it is enough to purchase pipes with a diameter of 80 * 80 mm. Better to buy metal pipes, manufactured in production according to GOST requirements, thus their service life can be extended. These products are made of high-quality metal and treated with anti-corrosion agents.

The height of the pipe is calculated depending on the height of the fence plus the buried part. Most often, pipes with a length of 3 - 3.5 m are used.

Cheap and high quality

A building material such as chain-link mesh is one of the simplest for fencing areas of any shape, length and height. It has found its application for fencing a dacha and the site of a private house, in the form of a fence for a front garden and for fencing industrial areas. This is one of those metal materials that is easy to deform, in a good way.

For example, for a figured front garden, a material that is easier to install cannot be found. Well, if you need to fence an area of ​​your house or cottage, then a properly installed high-quality chain-link mesh will last for decades. And the most attractive thing is that for installing fencing from metal mesh No special skills are needed. It is enough to prepare drawings and calculate the amount of material.

And if we talk about service life, then a structure created using a sectional method will be more reliable. To do this, you will need to separately manufacture the required number of sections, and then mount them on pre-installed poles.

If you want to get a more aesthetically pleasing fence for a private home or cottage, you can purchase ready-made sections with posts, manufactured in production according to GOST. Manufacturing products are predominantly coated with protective agents, which can significantly increase their service life.

Simple welded construction

More expensive designs include metal fences made of welded mesh. Due to the fact that when producing sections of such structures in production, the material is galvanized and coated polymer composition. For production, high-quality metal rods are used that comply with GOST, which ensures a long service life for the fences.

To install such structures, you do not need welding equipment; you can get by with a screwdriver and self-tapping screws.

A metal fence in the form of a welded mesh is installed in several stages:

• the area around the house or in front of the dacha is marked;
• Marking posts are installed along the edges;
• the rope is pulled at the expected height of the fence;
• 2.5 m is measured from the outermost pillar, and so it is repeated required amount once;
• in the marked places, supporting elements are installed using any of the above methods;
• if finished products manufactured in accordance with GOST are used to fence a dacha or house, then a diagram with the sequence of installation of sections is attached to the structure;
• everything else is assembled like a construction set, adhering to the drawing.

The manufacturer provides connecting brackets with holes. They are secured with a screwdriver to the supports, and sections of welded mesh are already attached to them. More details about the installation of a simple design can be found in the video.

Popular corrugated sheets

It is considered no less easy to install metal fence from corrugated sheets. Its installation principle is practically no different from the two previous designs. To facilitate installation, the distance between the supporting elements should be equal to the width of the profiled sheet.

If the pillars are supposed to be left open, then the distance from the end of the pillar is calculated, and if the supports need to be covered with a sheet, then the distance should be measured from the middle of the support.

For fencing in the country or for the front garden, cheaper models of corrugated sheets are often used, for example, only galvanized sheets. If it is necessary to fence the area of ​​a private house, then it is better to use higher quality products that meet the requirements of GOST. Such metal material has a longer service life and does not require annual maintenance.

In order not to make a mistake in calculating the material, and to purchase exactly as much as required, it is necessary to prepare drawings in advance, which will indicate all the dimensions of the fence elements.

Garden fence

Not every owner is ready to pay a tidy sum for metal fences in the garden, manufactured by the manufacturer in accordance with GOST. In order to save money, many try to build fencing structures from cheaper materials.

If you have a welding machine at hand, then a simple fence made of reinforcement or profile pipe will fit perfectly into the design garden plot, private house or cottage, it is important to prepare drawings. And its unattractive appearance can be decorated climbing plants or paint. Many craftsmen even fence off their front garden with such a simple design.

We will assume that the pillars are already installed, all that remains is to fill the spans. To do this, you need to determine the width of the spans and the height of the fence. It is better, of course, to draw up a diagram in order to correctly calculate the material.

The transverse joists are immediately welded to the pillars. The lower crossbar should be 20 cm from the ground, and the upper crossbar should be at the same distance from the top of the support. Next, the places where the vertical elements are welded are marked, according to the design drawing.

Such fences made from metal rods for a summer house or from reinforcement for a front garden are installed locally. Pipe cutting is carried out in stages, for each span separately. This method allows the welding equipment, which was heated during welding of parts of the first span, to cool down. While the material is being cut for the next filling, the device has time to cool down, and the work is carried out almost continuously.

For the front garden, as a rule, used material is used. It is not necessary to purchase rods or fittings of an expensive series, manufactured in accordance with GOST and make drawings. Even a rusty rod can be thoroughly cleaned and used to fence small areas. And the shape and configuration of the fence depends on the imagination of the manufacturer.

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 personnel, geologists, builders to search for profiles under cladding, fittings, to verify plans and diagrams of underground communications, 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. This article is primarily intended for them, beginners; The devices described in it allow you to find a coin the size of a Soviet nickel at a depth of 20-30 cm or a piece of iron with sewer hatch approximately 1-1.5 m below the surface. However, this homemade device can also be useful on the farm during repairs or at construction sites. Finally, having discovered a hundredweight or two of abandoned pipes or metal structures in the ground and selling the find for scrap metal, you can earn a decent amount. And there are definitely more such treasures in Russian land than pirate chests with doubloons or boyar-robber pods with efimkas.

Note: If you are not knowledgeable in electrical engineering and radio electronics, do not be intimidated by the diagrams, formulas and special terminology in the text. The essence is stated simply, and at the end there will be a description of the device, which can be made in 5 minutes on a table, without knowing how to solder or twist the wires. But it will allow you to “feel” the peculiarities of metal searching, and if interest arises, knowledge and skills will come.

A little more attention compared to the others will be paid to the “Pirate” metal detector, see fig. This device is simple enough for beginners to repeat, but its quality indicators are not inferior to many branded models costing up to $300-400. And most importantly, it showed excellent repeatability, i.e. full functionality when manufactured according to descriptions and specifications. The circuit design and operating principle of the “Pirate” are quite modern; There are enough manuals on how to set it up and how to use it.

Operating principle

The metal detector operates on the principle of electromagnetic induction. IN general scheme The metal detector consists of a transmitter of electromagnetic waves, a transmitting coil, a receiving coil, a receiver, a circuit for isolating a useful signal (discriminator) and an indication device. Separate functional units are often combined in circuitry and design, for example, the receiver and transmitter can operate on the same coil, the receiving part immediately releases the useful signal, etc.

The coil creates an electromagnetic field (EMF) of a certain structure in the medium. If there is an electrically conductive object in its area of ​​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 detects 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 soil 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 soil electrical conductivity in different directions in different depths, this procedure is called lateral logging. Using logging data, the computer builds a picture on the display of everything in the ground, including geological layers of different properties.

Varieties

Common parameters

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

1. Penetration, or penetrating ability - maximum depth, which is affected by the EMF of the coil in the ground. The device will not detect anything deeper, regardless of the size and properties of the object.
2. The size and dimensions of the search zone is an imaginary area in the ground in which the object will be detected.
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 beeps only for precious metals.
5. Noise immunity is the ability not to respond to EMF from extraneous sources: radio stations, lightning discharges, power lines, electric vehicles and other sources of interference.
6. Mobility and efficiency are determined by energy consumption (how many batteries will last), the weight and dimensions of the device and the size of the search zone (how much can be “probed” in 1 pass).
7. Discrimination, or resolution, gives the operator or control microcontroller the opportunity to judge the nature of the found object by the device’s response.

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

• 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 object’s material.

Operating frequency

1. Ultra-low frequency (ELF) - up to the first hundred Hz. Absolutely not amateur devices: power consumption of tens of W, without computer processing it is impossible to judge anything from the signal, transportation requires vehicles.
2. Low frequency (LF) - from hundreds of Hz to several kHz. They are simple in circuit design and design, noise-resistant, but not very sensitive, discrimination is poor. Penetration - up to 4-5 m with power consumption from 10 W (so-called deep metal detectors) or up to 1-1.5 m when powered by batteries. They react most acutely to ferromagnetic materials (ferrous metal) or large masses of diamagnetic materials (concrete and stone building construction), which is why they are sometimes called magnetodetectors. They are little sensitive to soil properties.
3. High frequency (IF) – up to several tens of kHz. LF is more complex, but the requirements for the coil are low. Penetration - up to 1-1.5 m, noise immunity at C, good sensitivity, satisfactory discrimination. Can be universal when used in pulse mode, see below. On watered or mineralized soils (with fragments or particles of rock that shield EMF), they work poorly or do not sense anything at all.
4. High, or radio frequencies (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.) Energy consumption - as before. n. The rest is on the verge of failure. The effectiveness of the device largely depends on the design and quality of the coil(s).

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

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

Search method

There are at least 10 methods of searching for objects using EMFs. But such as, say, the method of direct digitization of the response signal with computer processing is for professional use.

A homemade metal detector is built in the following ways:

• Parametric.
• Transceiver.
• With phase accumulation.
• On the beats.

Without receiver

Parametric metal detectors in some way fall outside the definition of the operating principle: they have neither a receiver nor a receiving coil. For detection, the direct influence of the object on the parameters of the generator coil - inductance and quality factor - is used, 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 recorded in different ways: by measuring the frequency and amplitude, by changing the current consumption of the generator, by measuring the voltage in the PLL loop (a phase-locked loop system that “pulls” it to a given value), etc.

Parametric metal detectors are simple, cheap and noise-resistant, but using them requires certain skills, because... frequency “floats” under the influence external conditions. Their sensitivity is weak; Most of all they 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 achieving the best efficiency in their frequency range, but are complex in circuit design and require a particularly high-quality coil system. Transceiver metal detectors with one coil are called induction detectors. Their repeatability is better, because the problem of the correct arrangement of the coils relative to each other disappears, but the circuit design is more complicated - you need to highlight the weak secondary signal against the background of the strong primary one.

Note: In pulsed transceiver metal detectors, the problem of isolation can also be eliminated. This is explained by the fact that the so-called “catch” is “caught” as a secondary signal. the “tail” of the pulse re-emitted by the object. Due to dispersion during re-emission, the primary pulse spreads out, and part of the secondary pulse ends up in the gap between the primary ones, from where it is easy to isolate.

Until it clicks

Metal detectors with phase accumulation, or phase-sensitive, are either single-coil pulsed or with 2 generators, each operating on its own coil. In the first case, the fact that pulses not only spread out during re-emission, but are also delayed. The phase shift increases over time; when it reaches a certain value, the discriminator is triggered and a click is heard in the headphones. As you approach the object, the clicks become more frequent and merge into a sound of increasingly higher pitch. 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 oscillators operate, each with its own coil. In this case, due to the interaction of their EMFs, mutual synchronization occurs: the generators work in time. When the general EMF is distorted, synchronization disruptions begin, heard as the same clicks, and then a tone. Double-coil metal detectors with synchronization failure are simpler than pulse detectors, 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 prospectors. Search aces adjust their instruments so that exactly above the object the sound disappears again: the frequency of 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 parametric ones.

By the squeak

Beats of 2 electrical signals - a signal with a frequency equal to the sum or difference of the fundamental frequencies of the original signals or their multiples - 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.

In a metal detector, there are 2 generators operating on beats: a reference and a working one. The coil of the reference oscillating circuit is small, protected from extraneous influences, or its frequency is stabilized by a quartz resonator (simply quartz). The circuit coil of the working (search) generator is a search generator, and its frequency depends on the presence of objects in the search area. Before searching, the working generator is set to zero beats, i.e. until the frequencies match. As a rule, a complete zero sound is not achieved, but is adjusted to a very low tone or wheezing, this is more convenient to search for. By changing the tone of the beats one judges the presence, size, properties and location of an object.

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

Harmonic metal detectors are generally more complex than pulse detectors, but they work on any type of soil. Properly manufactured and tuned, they are not inferior to impulse ones. This can be judged at least by the fact that gold miners and beachgoers will not agree on what is better: an impulse or a beating one?

Reel and stuff

The most common misconception of novice radio amateurs is the absolutization of circuit design. Like, if the scheme is “cool”, then everything will be top-notch. Regarding metal detectors, this is doubly true, because... their operational advantages greatly depend on the design and quality of manufacture of the search coil. As one resort prospector put it: “Findability of the detector should be in the pocket, not the legs.”

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

About coil sizes

A large (wide) coil emits EMF more effectively and will “illuminate” the soil more deeply. Its search area is wider, which allows it to reduce “being found with its feet.” However, if there is a large unnecessary object in the search area, its signal will “clog” the weak one from the small thing you are looking for. 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 searching for fittings and profiles, 130-150 mm for “beach gold” and 200-600 mm “for large iron”.

monoloop

The traditional type of metal detector coil is called. thin coil or Mono Loop (single loop): a ring of many turns of enameled copper wire with a width and thickness 15-20 times less than the average diameter of the ring. The advantages of a monoloop coil are a weak dependence of the parameters on the type of soil, a narrowing search zone, which allows, by moving the detector, to more accurately determine the depth and location of the find, and design simplicity. Disadvantages - low quality factor, which is why the setting “floats” during the search process, susceptibility to interference and vague response to the object: working with a monoloop requires considerable experience in using this particular instance of the device. Homemade metal detectors Beginners are recommended 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 ensure the reliability of the author’s promises, and even more so when independently designing or modifying it, 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 calculations, so as not to rack your brains later: why, everything seems to be working properly, and not beeping.

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

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

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

Noise immunity

The monoloop “catches” interference well, because is designed exactly the same 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 turn does not form, which will “eat up” all the EMF coils, see fig. on right. If on the original diagram there is a dotted line near the designation of the search coil (see 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 here for beginners: the grounding conductor must be connected to the screen strictly symmetrically to the cut (see the same figure) and brought to the circuit also symmetrically relative to the signal wires, otherwise noise will still “crawl” 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 pulse metal detectors; their coils cannot be shielded at all. In this case, increasing noise immunity can be achieved by balancing the winding. The point is that for a remote EMF source, the coil is a point object, and the emf. interference in its halves will suppress each other. A symmetrical coil may also be needed in the circuit if the generator is push-pull or inductive three-point.

However, in this case it is impossible to symmetry the coil using the bifilar method familiar to radio amateurs (see figure): when conductive and/or ferromagnetic objects are in the field of the bifilar coil, its symmetry is broken. That is, the noise immunity of the metal detector will disappear just when it is most needed. Therefore, you need to balance the monoloop coil 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 crosswise manner is hellish work, and then it is better to make a basket coil.

Basket

Basket reels have all the advantages of monoloops 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 emf. in crossing wires they cancel each other out. The only negative is that basket coils require a precisely made, rigid and durable mandrel: the total tension force of many turns reaches large values.

Basket coils are structurally flat and three-dimensional, but electrically a three-dimensional “basket” is equivalent to a flat one, i.e. creates the same EMF. The volumetric basket coil is even less sensitive to interference and, which is important for pulse metal detectors, the pulse dispersion in it is minimal, i.e. It's 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 figure), 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 2-coil transceiver, a good mount would be unusable computer disks. Their metallization will not harm: it is very thin and nickel. An indispensable condition: an odd, and no other, number of slots. A nomogram for calculating a flat basket is not required; the calculation is carried out as follows:

• 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 coefficient 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 large baskets using the method shown in Fig. below: make a mandrel from insulated nails (pos. 1) or self-tapping screws, wind them according to the diagram, pos. 2 (in this case, pos. 3, for a number of turns that is 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 to waste. That is, in order to wind it reliably, you need to glue pieces of durable plastic into the holes of the base, and only then wind it. And remember: independent calculation of a volumetric basket coil without appropriate computer programs is impossible; The technique for a flat basket 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 (arms), folded with some intersection. With an accurate electrical and geometric balance of the DD arms, the search EMF is contracted into the intersection zone, on the right in Fig. on the left is a monoloop coil and its field. The slightest heterogeneity of space in the search area causes an imbalance, and a sharp strong signal appears. An DD coil allows an inexperienced seeker to detect a small, deep, highly conductive object when a rusty can lies next to it and above it.

DD coils are clearly oriented “to gold”; All metal detectors marked GOLD are equipped with them. However, on shallow, heterogeneous and/or conductive soils, they either fail altogether 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 there is none at all. Therefore, metal detectors with DD coils are preferred by searchers who are only interested in “pocket-fitting”.

Note: More details about DD coils can be found further in the description of the corresponding metal detector. The DD shoulders are wound either in bulk, like a monoloop, on a special mandrel, see below, or with baskets.

How to attach the reel

Ready-made frames and mandrels for search coils are sold in a wide range, but sellers are not shy about mark-ups. Therefore, many hobbyists make the base of the coil from plywood, 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 can be replaced without any problems with the KT361 or its analogues; To use pnp transistors, you need to change the polarity of the battery.

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

The circuit is a pulse generator with inductive feedback and frequency stabilization by an LC circuit. A loop coil is an output transformer from an old transistor receiver or a low-power “bazaar-Chinese” low-voltage power one. A transformer from an unusable Polish antenna power source is very suitable; in its 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 coin cell battery. Winding II in Fig. – primary or network; I – secondary or step-down by 12 V. That’s right, the generator operates with transistor saturation, which ensures negligible power consumption and a wide range of pulses, making searching easier.

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

A more complex parametric scheme is shown in Fig. on right. L with capacitors C4, C5 and C6 is tuned to 5, 12.5 and 50 kHz, and the quartz passes the 10th, 4th harmonics and fundamental tone to the amplitude meter, respectively. The circuit is more for the amateur to solder on the table: there is a lot of fuss with the settings, but there is no “flair”, as they say. Provided as an example only.

Transceiver

Much more sensitive is a transceiver metal detector with an DD coil, which can be made at home without much difficulty, see Fig. On the left is the transmitter; on the right is the receiver. The properties of different types of DD are also described there.

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

The coils contain 80 turns of PE wire 0.6-0.8 mm, 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 located strictly symmetrically. Overall, 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 low, the discrimination is very good despite the use of DD.

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

Cumulative phase

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

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

Coil inductance is 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 0.25 PE wire, and a 70 mm coil contains 290 turns.

Metal detector “Butterfly”, see fig. on the right, in its parameters it is already close to professional instruments: the Soviet nickel is found at a depth of 15-22 cm, depending on the soil; sewer hatch - at a depth of up to 1 m. Effective in case of synchronization failures; diagram, board and type of installation - in Fig. below. Please note that there are 2 separate coils with a diameter of 120-150 mm, not DD! They must not intersect! Both speakers are piezoelectric, as before. case. Capacitors - heat-stable, mica or high-frequency ceramic.

The properties of the “Butterfly” will improve, and it will be easier to configure it if, firstly, you wind the coils with flat baskets; 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 is 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 in the diagram) end. Secondly, if individual transistors are replaced with a 2-transistor assembly for K159NT1 amplifier circuits or its analogues; A pair of transistors grown on the same crystal has exactly the same parameters, which is important for circuits with synchronization failure.

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

The actual setup 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 to the trimmer, and in the opposite shoulder we remove it. In 3-4 cycles you can achieve complete silence in the speakers - the device is ready for searching.

More about "Pirate"

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

The transmitter consists of a master oscillator (MG) on the same 555 timer and a powerful switch on T1 and T2. On the left is the ZG version without an IC; in it you will have to set the pulse repetition rate on the oscilloscope to 120-150 Hz R1 and the pulse duration to 130-150 μs R2. Coil L is common. A 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 re-emitted pulses accumulate in container 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 speed of the “reservoir” and, consequently, the sensitivity of the device. You can learn more about “Pirate” from the video:

Video: “Pirate” metal detector

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

Video: setting the threshold of the “Pirate” metal detector

On the beats

Those who want to experience all the delights of the beating search process with replaceable coils can assemble a metal detector according to the diagram in Fig. Its peculiarity, firstly, is its efficiency: the entire circuit is assembled on CMOS logic and, in the absence of an object, consumes very little current. Secondly, the device operates 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” with a varicap VD1. Mixing of the working and reference signals occurs in DD1.4. Third, this metal detector is suitable for working with replaceable coils.

It is better to replace the IC 176 series with the same 561 series, the current consumption will decrease and the sensitivity of the device will increase. You can’t just replace old Soviet high-impedance headphones TON-1 (preferably TON-2) with low-impedance ones from the player: they will overload the DD1.4. You need to either install an amplifier like the “pirate” one (C7, R16, R17, T3 and a speaker on the “Pirate” circuit), or use a piezo speaker.

This metal detector does not require any adjustments after assembly. The coils are monoloops. Their data on a 10 mm thick mandrel:

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

It couldn't be simpler

Now let's fulfill the promise we made at the beginning: we'll tell you how to make a metal detector that searches without knowing anything about radio engineering. A metal detector “as simple as shelling pears” is 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, but to detect objects it is not dispersion or delay with phase accumulation that is used, but the rotation of the magnetic vector of the EMF 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 for it to be, if not “super,” but at least a fully functional device, its components—the receiver and the calculator—must meet certain requirements.

Calculator you need the most tattered and cheapest, “alternative”. They make these in offshore basements. They have no idea about the standards for electromagnetic compatibility of household appliances, and if they heard about something like that, they wanted to choke it from the bottom of their hearts and from above. Therefore, the products there are quite powerful sources of pulsed radio interference; they are provided by the calculator's clock generator. In this case, its strobe pulses on the air are used to probe space.

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

1. We unfold the box with the lid into a book.
2. We paste strips of adhesive tape onto the back sides of the calculator and the radio and secure both devices in the box, see fig. on right. Receiver - preferably in a cover so that there is access to the controls.
3. We turn on the receiver and look for an area at maximum volume at the top of the AM band(s) that is free from radio stations and as clean as possible from ethereal noise. For CB this will be around 200 m or 1500 kHz (1.5 MHz).
4. We turn on the calculator: the receiver should hum, wheeze, growl; in general, give the tone. We don't turn down 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 turned about 90 degrees. Thus, we have found a position in which the magnetic vector of the primary pulses is oriented perpendicular to the axis of the ferrite rod of the magnetic antenna and it does not receive them.
7. We fix the lid in the found position with a foam insert and an elastic band or supports.

Note: depending on the design of the receiver, the opposite option is possible - to tune to the harmonic, the receiver is placed on the turned on calculator, and then, by unfolding the “book,” the tone softens or disappears. In this case, the receiver will catch pulses reflected from the object.

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

Something weird at last

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

try it if you wish, maybe you’ll find something there, both in the subject matter and in the scientific and technical sense. Good luck!

As an application

There are hundreds, if not thousands, of metal detector designs and designs. Therefore, in the appendix to the material we also provide 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.
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