Not everyone can afford to buy a metal detector. And to search for iron, it is not at all necessary to purchase an expensive device. It is enough to assemble it yourself. And he will find it too.

By the way, I will say that I saw a report on TV about how a man who had assembled a metal detector and was looking for scrap metal with it found a box of ammunition from the Civil War in the forest.

I myself have been trying to assemble such a device for a long time and it even worked! But you won’t be able to search for coins with it, since it reacts mainly to large metal objects.

And so, to assemble a simple metal detector we need:

~ two KT315 transistors or similar;
~ two 1000 pf capacitors;
~ two capacitors 10000 pf;
~ two 100 kOhm resistors.

In addition, the following will be useful: a 3.7-5 volt battery, headphones, enamel-insulated wire with a diameter of 0.5-0.7 mm.

The assembly diagram is simple!

The coils can be wound on a regular pan. After ten turns, a loop is made and the winding of the remaining twenty turns continues.

The body is made of any material, preferably sealed. The bar can be made from pipes. The coils are placed on the same plane at a distance of 10 cm.

If, when you turn on the device, a squeak appears in the headphones, then it means that you need to adjust the device - change the distance between the coils. Or customize with ferrite.

Thus, you can make money by searching for scrap metal for a good branded device. And a good deed will be done - the earth will be cleansed. Well, the metal will be reused.

The photos in the article are mine, taken back in 2014. And the first picture with the diagram is taken from open sources.

How to make a simple metal detector for searching on the beach

In this article I will tell you how to build a simple metal detector for searching for coins and jewelry on the beach. It consists of one chip - the NE555N timer, a coil and several other radio components.

Expect to spend up to 300 rubles to build this metal detector!

Required materials

To assemble the metal detector you will need:

• NE555N timer chip, in DIP package;
• resistor 47 kOhm;
• two capacitors 2.2 µF, 16 V;
• piece of contact breadboard;
• 9 volt battery, switch, battery socket;
• electromechanical sound emitter;
• 100 meters of copper wire with a diameter of 0.2 millimeters;
• some thick cardboard and glue.

Instead of an electromechanical sound emitter, you can use a 10 µF capacitor and any speaker with an 8 Ohm impedance, connected in series.

Metal detector circuit

The idea of ​​a metal detector was taken from the book " 499 circuits on NE555 timer" I just added a switch between the battery and the chip, and I also use an electromechanical sound emitter from an old electronic alarm clock instead of a speaker.

Search coil

The most difficult part of a metal detector is its coil. I calculated that a 90mm diameter coil would have approximately 260 turns of 0.2mm diameter varnished copper wire. In this case, its inductance will be approximately 10 millihenry.

I wound the coil carefully, turn to turn. To prevent the wires from unraveling, I wrapped the winding with white electrical tape on top.

If you want to make a larger diameter coil to increase the target detection range, then there are several online calculators on the Internet with which you can calculate it.

Circuit board

I placed all the electronic components on a piece of breadboard. The connections were made using the most ordinary wire that was at hand. Soldering the board itself took no more than 15 minutes.

The size of the board turned out to be approximately equal to the size of a matchbox.

Frame

To simplify things, I decided to make the handle of the metal detector out of cardboard. The handle contains a circuit board, a switch and a battery.

All this was cut out of thick cardboard and glued together with PVA glue. After the glue had dried, I made holes in the cardboard for the board and wires.

Next, I glued the search coil to the handle with hot glue. The last step, also using hot glue, I glued the board and battery inside the handle.

Conclusion

The metal detector works as follows: as long as there are no metal objects near the coil, the sound emitter beeps at the same frequency; when a metal object is brought up, the tone of the sound changes towards a higher one.

The detection range of a large coin through the air, according to my measurements, was 5 – 7 centimeters!

Simple metal detector baby FM-2 improved

I present to your attention a diagram of a more improved metal detector Malysh FM-2. The baby fm2 metal detector is not so difficult to assemble with your own hands, despite its significant changes. This is perhaps the simplest selective metal detector that even a novice radio amateur can assemble.

You have probably heard of, and perhaps collected, such metal detectors as “Malysh” and “Malysh FM-2”. But progress does not stand still and therefore we have a diagram of a more improved metal detector Malysh FM-2. The new version adds LED indication of metals, a power-on notification function is added, the notification sound is enhanced, and the device has become much more stable in operation.

Diagram of the improved metal detector Malysh FM-2

Specifications and features:

• Supply voltage - 9 Volts
• Metal detection depth is about 15 cm.
• Selection of metals - black, non-ferrous
• LED indication of metals - black, color
• Power-on indicator

So, this printed circuit board of the Malysh FM-2 metal detector is designed to use DIP components, which would be convenient for everyone, since many novice radio amateurs have not yet encountered SMD components.

Capacitors C5-22nF and C1-100nF must be film

Voltage stabilizer AMS1117 -3.3v

This is what the finished board of the “Malysh FM-2” metal detector looks like:

View from the paths

After assembling the board, we proceed to making the coil.

A standard coil contains 150 turns, wire diameter 0.3, and wound on a frame of 150 mm. But I decided to slightly reduce the diameter to 10-11 cm so that the metal detector could better see small objects; the detection depth decreases but the sensitivity increases. I didn’t have 0.3 wire, so I wound 0.4 on a 10 cm frame, 130 turns.

So, after the coil is wound, it is necessary to tighten it very tightly with tape.

Now it is imperative to shield the coil so that the metal detector does not react to interference and there are no false alarms. Take food foil and wrap the coil tightly. Please note that the ends of the foil should not touch each other!

Then we take the wire, strip the end and wrap the coil to one edge of the screen, then tighten it and wrap it tightly with tape again.

We connect the coil to the board. The wire from the screen needs to be soldered to the minus of the board.

Now all that remains is to flash the microcontroller and that’s it, you can use it)

If you do everything correctly, the device should work without problems the first time you turn it on. Carefully check the ratings of the parts and do not forget that the capacitors C2-22nF and C6-100nF must be film, NOT ceramic!

When turned on, the device should make a characteristic sound similar to a “peep-fang”, this means that the device has turned on and is working correctly.

IMPORTANT! “According to the diagram there are 8 resistances, but in the photo there are 9” - the 9th resistor (100 Ohm) I myself installed additionally on the second LED, although it doesn’t have to be installed! The 1N4007 diode can also be omitted, as I did!

The printed circuit board, firmware, as well as a list of parts that can be bought very cheaply on AliExpress with free shipping are located below the video!

Video of the metal detector baby FM-2 v2

Good DIY metal detector

This happened several years ago. I wanted to keep my hands busy and while away the evenings as the treasure hunting season approached. It was decided to assemble a metal detector. For assembly I chose the “Pirate” metal detector circuit. Since it is not complicated, but the device itself is quite interesting. The assembly began with the search for parts. I even had to go to the workshop to get some resistors. When everything was found, it was necessary to prepare the printed circuit board, namely, etch it using the LUT method. Then it was just a matter of small things: soldering all the parts. Well, check the finished board. The first time it didn't turn on. The K157UD2 chip turned out to be faulty. After changing it, the scheme worked!
Now you can work on the body. The body from Koschey 5I was taken as its quality, and a new front panel was made. It's up to the coil. For the coil, a frame was cut out with a jigsaw and a groove was machined along the side edge, where the coil winding was wound, and a cable with a connector was soldered. The rod was made of plastic pipes and fittings. The armrest is cut from a sewer pipe. It all turned out quite culturally. The device turned out to be light, but not rigid enough.
The result was a working, high-quality device. Its only drawback is the lack of metal discrimination. Therefore, it can be said that it is not suitable for searching for coins. After all, both nails and coins ring the same way.
But with its help, you can successfully dig scrap metal and hand it over to collection points, thereby earning money! There is a video with a test of this device. It was filmed by me in the spring of 2015.

If it is necessary to find objects whose properties differ from those usually present in the soil, use a metal detector (metal detector). The principle of operation of such devices is based on determining differences in the magnetic field of the solenoid, which appears in the area where the anomalous object is located.

If you wish, it is not difficult to purchase an inexpensive metal analyzer. Anyone capable of holding a soldering iron and a screwdriver can make a metal detector with their own hands.

Why do you need a metal detector?

Many people believe that such tools are only needed to search for metals (coins, weapons, household items at battle sites), and explosives where mines could be installed. In fact, the range of use of such tools is much wider. They are used when screening passengers at airports, geologists look for ore deposits, doctors determine the presence of steel or alloys in the human body. When laying highways inside populated areas, the location of pipelines with water, gas or sewage is specified.

The metal detector is in demand among amateurs who want to conduct searches outside their own home:

• Treasure hunters can be seen in places where old buildings are being demolished. There may be items and money put aside for a rainy day. Almost every week there are reports of the discovery of certain treasures containing coins and jewelry;
• Search engines at the sites of past battles are looking for weapons, shells and cartridges, helmets, and household items. The device helps to find random burials of battle participants. The names of the dead are determined based on awards and other sources. They are looking for relatives to inform them about the burial place of their father, grandfather, and more often, great-grandfather;
• Representatives of the armed forces are searching for mines and explosive objects that pose a danger to civilians. Over the past few months, more than 120 tons of dangerous substances, shells and mines have been recovered from Syria. The terrible bombs did not work; they did not take the lives of children, women and the rest of the population who wanted to live a peaceful life.

Young people and middle-aged people may have an idea to search for some objects. Some are interested in the possibility of creating a metal detector that can be used not only on land, but also underwater. In the coastal area, especially near beaches, coins, lost crosses and rings are often found.

“Metal workers” (people who sell scrap metal in large quantities) are busy searching for forgotten pipes, metal structures and large deposits of unnecessary metal. They make a living by renting out such items.

Attention! Those who have practically no experience with electrical engineering or radio electronics should not despair. Here we will outline options for manufacturing the simplest metal detectors, which you can make yourself with your own hands, without resorting to the use of complex equipment. If there are certain difficulties with soldering, then the wires can be twisted together, getting a good result.

Principle of operation

The operating principle of the metal detector is based on the study of changes in electromagnetic induction. The design of the device includes:

• synthesizer of electromagnetic oscillations;
• vibration amplifier;
• coil for transmitting changes in the magnetic field (metal discrimination);
• a coil for receiving information about the state of the magnetic field in the radiation zone;
• receiver with signal amplifier;
• devices for recording the discriminating signal or indicating devices.

Quite often, the functions of some elements are combined in the same device:

• reception and transmission are carried out by one amplifier;
• the same coil emits an alternating electromagnetic field into the study area, and then receives a signal about the presence or absence of distortion.

When the magnetic field changes, the coil perceives a changed signal.
It is recorded by readings on the instrument scale or by the sound in the microphone

A general idea of ​​how the device works can be presented in the following sequence:

1. The coil creates an alternating magnetic field in the search area (see position A).
2. When an object that has any distinctive properties compared to its surroundings enters the study area, eddy currents arise inside the field of the coil (they are also called Foucault currents).
3. The resulting currents create a different electromagnetic field (EMF).
4. As a result, the field itself changes in its characteristics (see position B).
5. All changes are recorded by instruments (optical or sound indicators). By changing the signals, the operator can determine the presence of an object with ferromagnetic properties. Metals that conduct electric current are also determined.

For a metal detector, the main thing is the presence of certain differences in the conductivity of the surrounding soil from the object existing in the earth's thickness. The device determines the difference between electrical and magnetic properties.

A few words about geoscanners

Geoscanners are special devices that can draw a three-dimensional picture of the state of the soil over a large area and depth. These are quite expensive devices that are used to obtain information about the presence of water sources and main pipelines laid at considerable depths. The received information is displayed on the screen of a computer or laptop.

Such studies are carried out by special field laboratories. It is customary to call them side cardboard.

What types of metal detectors are there?

Common parameters

The basic principle of operation, in which the magnitude of electromagnetic induction in a certain part of space is analyzed, is implemented in different technical designs. A device for searching for beach gold, including other precious materials (silver, platinum), as well as devices for searching for pipelines hidden in the depths, may look the same in appearance. But upon careful examination of the design, fundamental differences in circuits and technical capabilities will be visible.

When starting to create your own metal detector, you need to clearly define the requirements that will be placed on the device. Experts identify a number of characteristic parameters for search devices:

1. The depth of signal penetration into the soil (penetration ability). This characteristic depends on the properties inherent in the receiving coil.
2. Search area based on the size of the trace of an active coil emitting an electromagnetic field.
3. The level of sensitivity characterizes the ability to detect objects that are small in size and weight (coins, shell casings, bullets, crosses, small jewelry).
4. Electoral indicators. For some categories of search engines, a special reaction to precious (gold or silver products) or non-ferrous metals is important. They even create special filters that transmit information about the presence of objects made of similar materials in the depths.
5. Noise immunity determines the ability not to perceive the influence of power lines, nearby repeaters or television stations. There may be other sources of interference that can degrade the performance of the search device. As practice shows, it is near sources of electromagnetic oscillations that the loss of the most interesting objects in which searchers are interested most often occurs.
6. Small size and the ability to use small-sized energy sources for operation (device mobility) are quite important characteristics. With a heavy and bulky metal detector, a person gets tired quite quickly, and labor productivity will be low. With a lightweight and small-sized metal detector, you can overcome small obstacles while moving over rough terrain.
7. Discrimination - this parameter characterizes the ability to separate the main parameters of a find located at a certain depth based on the type of signal received. Search efficiency increases.

Among specialists, device discrimination is usually correlated by indicators of information boards and sound. She must be able to determine the properties of the found object. It is customary to distinguish the components:

1. The spatial characteristic determines the location of the object in the search area. Shows the possible depth of placement.
2. Geometric characteristics give an idea of ​​the mass and possible size of the find.
3. Qualitative determines the properties of the material from which the found object is made. For gold, one type of signal is desirable, and for iron-containing products, another.

Operating frequency

The presence of an alternating magnetic field created by the search device itself determines the operating features. For example, as the frequency decreases, the depth of penetration of magnetic waves into the depth of the soil increases. You can achieve a larger working width of the device. However, it is impossible to significantly reduce the frequency value. A metal detector will require a lot of energy to remain operational. This will lead to the need to use a larger battery. It is generally accepted that the main parameters of a metal detector depend on the operating frequency. Therefore, the classification by operating frequency is presented as:

1. Ultra-low frequency (ELF) operate up to 100…150 Hz. Such devices are classified as professional devices. It has not yet been possible to implement a mobile metal detector in practice. Energy consumption is measured in tens of watts (W). Similar search tools are located on vehicles. The signal is analyzed using computers.
2. Low frequency (LF) operate in the range of 150…2000 Hz. These devices have a simple design that even a novice master can assemble. The design is quite simple. It is distinguished by a rather large penetration depth of the electromagnetic pulse (up to 4...5 m). However, such devices have low sensitivity. There is virtually no discrimination based on size and material composition. Such metal detectors respond well to ferrous metals that contain iron in various types of compounds. But if large concrete or stone structures are found, the search engine will find them too. Such devices are classified under the name magnetodetectors. Such devices are worse at distinguishing the properties of soils and objects contained in them.
3. High frequency (IF) devices use an operating range of 1700…75000 Hz. The design of such metal detectors is much more complex. Their signal penetrates to a depth of 1.0...1.5 m. Relatively good noise immunity. Sensitivity is rated quite high. Discrimination is also quite high. The disadvantages of such search devices appear in the presence of heterogeneous rock in the soil. Unstable indicators are possible if groundwater levels are high. Such metal detectors are used to operate in pulse mode, which will have to be achieved a little later.
4. High frequency (HF), sometimes professionals call such devices operating at radio frequencies (RF). In these devices, discrimination against heavy precious metals works perfectly. The search depth can reach 0.5...0.8 m. They are usually not able to illuminate deeper. These metal detectors are quite demanding on the quality of the coil. Any negligence will lead to a sharp deterioration in the performance of the device.

For devices according to points 2...4, low energy consumption is noted. A set of AA batteries (finger-type) can operate continuously for up to 12 hours.

A special feature of pulse metal detectors is that they do not constantly supply a signal of a given frequency. Periodic pulses are sent. You can set the frequency of the send and the duration of the impact. By creating such a device, it is possible to obtain a device in which positive characteristics will be obtained from LF, IF and HF devices. However, such circuits require special assembly and adjustment. For novice searchers and craftsmen, such devices can be difficult to implement. Therefore, you need to start a homemade design with simple devices.

Search method

In practice, there are about a dozen methods for searching for objects located deep in the ground using an electromagnetic field. Unfortunately, some of them are quite complex. Large enterprises, where it is possible to purchase expensive components, can implement the proposed methods.

For real use, devices with relatively inexpensive components and circuits are used. Even a novice master can implement them:

• parametric search method, carried out by comparing the parameters before and after;
• transceiver is based on the use of a reflected signal that was previously sent by the transmitting device;
• phase accumulation is usually equipped with two coils;
• on the beats. This method is implemented on two signals.

Without receiver (parametric devices)

The parametric method does not require a receiver. Even the take-up coil itself is missing. When searching, the inductance changes, which is perceived by the generating coil itself. When an object with certain properties that change the inductance is located in the area affected by the electromagnetic field, frequency modulation occurs in the oscillations of the devices. Changes:

• vibration frequency, this change can be heard in the speaker or headphones;
• the amplitude increases, which leads to a higher volume at the sound signal detector device.

Such metal detectors are inexpensive. They have good noise immunity. However, the user will have to practice to be able to use such a device. Poor sensitivity limits the possibilities of use.

With receiver and transmitter

Devices that implement the principle of signal reception and transmission allow one to obtain significantly better performance. With a certain complexity in manufacturing (coils must be created strictly following the description and design features).

It is customary to identify devices by the following indicators:

• metal detectors with one coil are usually called induction. The disadvantage is the difficulty of determining the secondary signal;
• Metal detectors with two coils are more difficult to set up. Here it is important to ensure complete identity of both solenoids. But the secondary signal is detected much better than a single-coil circuit can offer.

If a pulse transceiver device is implemented, then the discriminatory properties are more easily manifested. Based on the type of secondary signal at the beginning or end of the phase, it is easier to guess the type of metal found.

Before click (with phase accumulation)

The method is implemented in devices with phase accumulation. Structurally, the execution is:

• single-coil with pulse signal supply;
• dual-coil, equipped with two signal generators (each supplied with power to its own coil).

In the first option, there is some delay between the emitted and perceived pulses. The operator hears a click. It corresponds to the difference between the given impulse and the received one. When an object of interest appears in the search area, the frequency of clicks increases. If the mass of the found object is quite large and it is located quite close, then the clicks merge into noise of a certain sound frequency.

Attention! Metal detectors under the general name “Pirate” are built on a similar scheme.

If you have a two-coil device, there is no need to create a pulse device. The generators each operate on their own solenoid. If EMF distortion occurs, then clicks also occur. You can configure it to additionally produce the sound of a certain tone.

On beaches and in places where there are a large number of tourists, resort prospectors most often use such metal detectors. They are even made protected from fresh and sea water. Then it is possible to search for small objects in the water.

Practice shows that such devices are capable of sensing small earrings weighing only 0.3 g at a depth of up to 40 cm.

Unfortunately, such devices do not work well in places where the soil structure is heterogeneous. Here they begin to react even to branches.

By squeak (by beat)

The presence of two signals supplied at different frequencies allows you to hear not the supplied frequencies themselves, but their difference.

1. One is supplied with frequency 1 MHz = 1,000,000 Hz.
2. To the second frequency 1.0005 MHz = 1,000,500 Hz.
3. The user will hear a signal equal to the difference between the second and first value of the supplied frequencies - 1,000,500 – 1,000,000 = 500 Hz.

For different types of devices, they select their own frequencies, which they use in further work.

The control system has the ability to adjust one of the frequencies, which allows you to hear sounds (beats) of different frequencies. You can even reduce this difference to zero if you ensure equality of the supplied oscillations.

Before searching, the differences are reduced to the threshold of audibility. For some people it is 20-25 Hz. When the metal detector is in the zone of influence of a metal object, the difference between the frequencies of the signals changes. The operator hears a different sounding tone.

To recognize the properties of the found object, you can change the setting on the second generator. Then other sounds will be heard from interaction with the found object. Through a series of preliminary training, the operator can quite accurately determine what is located in the soil, what is the mass and size of the find.

It is recommended to tune to the “A” sound of the first octave, which corresponds to a frequency of 432 Hz. This tone is heard on radio stations during a short break. Practice shows that devices tuned to such sound pick up even quite small objects, the mass of which is a few tenths of a gram.

Many gold miners on the beaches use similar devices. They work more reliably in heterogeneous soils.

The influence of the coil on the performance of the installation

Among the craftsmen who make coils for their devices, there are different opinions on how this part of the metal detector should be made. Beginners often don't think about the design. They can purchase a branded product and then expect to receive only dividends from their investment. Unfortunately, even the coolest reel can show poor performance. There must be a correspondence between the solenoid and the rest of the device circuit.

When developing the design of a metal detector, they try to adjust the parameters of each element to each other. Sometimes you have to select some parameters experimentally. The spread in the characteristics of radio components can be quite significant. Not only rough but also fine tuning is needed.

What sizes does the reel need?

The larger the coil, the larger the area its signal covers. There are some craftsmen who make solenoids with a diameter of 1500 mm or more. They claim that such a device allows you to cover a wide area. But you have to carry such an instrument on your shoulders. If you need to move in the forest or in plantings, such a device will not allow you to penetrate between bushes and trees. It’s easier to move your hand several times with a coil placed on the rod.

• Ø 20…100 mm used to search for reinforcement and profiles buried in the ground;
• Ø 130…150 mm used by gold miners on beaches and in crowded places;
• Ø 200…600 mm The coils are made by metal workers who search for scrap metal in large quantities.

Monoloop as a coil

Designs in which a monoloop is taken as a basis are common. A long wire is used for production. The winding thickness should be 15-20 times less than the diameter of the loop used.

Users note the advantages of such a device:

• the operation of a metal detector equipped with such a receiving device is practically independent of the properties of the soil;
• the mass of such a device is relatively low, so it can be moved for a long time across the territory;
• Having discovered metal in the depths, you can change the settings of the transmitting device to recognize the value of the find.

There are also disadvantages:

• you have to constantly make adjustments to the device settings;
• Any radio devices interfere with operation. Therefore, gold hunters on beaches are often exposed to operating devices;
• To use it effectively, you need to train with different objects from different materials in order to learn to recognize the desired item and begin to mine it.

These disadvantages do not reduce the value of such a solenoid. Beginner users can use the monoloop as the basis for their first design. It's not difficult to make. You will have a very good metal detector in your hands.

Step-by-step production of a simple coil

In practice, many different manufacturing options are used. One of them will be one that uses modern materials: plastic pipes. They initially help prevent moisture from entering the solenoid wires.

	You need to have the following materials: enameled wire with a diameter of 0.5 mm. Its length is calculated from the need to wind 25 turns on a circle Ø150 mm. 3.14·150·25 = 11775 mm. Taking into account the exit of the ends, you can take 12 m; plastic tube with an internal diameter of 12.5 mm, its length must be at least 3.15 150 = 471 mm; tee from polypropylene pipes Ø 20 mm; fragments of polypropylene pipe Ø 20 mm (2 pieces, 15 mm long); shielded television wire 120 cm long.
	Before starting work, you should check how convenient it is to make a circle from a plastic tube. If there is a hard workpiece, then during production you will need to warm it up with hot water or using a hairdryer. A test ring is rolled up and the shape of the resulting circle is assessed.
	You need to drill a Ø6 mm hole in the tee. Through it the wires will be inserted into the future coil. It is advisable to clean the edges from burrs.
	Additional polypropylene pipe inserts are carefully processed. They need to be soldered into a tee. In this case, plastic must be inserted into each fragment.
	You will have to select the length of the plastic tube to obtain a circle of exactly the specified diameter. If you do not adjust the dimensions, there may not be enough wire. Test entries into fragments are made.
	It is checked how tightly the tubes can be inserted into each other. After the final fitting, you can warm up the joints and solder them together.
	Slight mobility during connection will allow you to adjust the size of the future product. You have to check the resulting diameter.
	It's time to push the wire inside the plastic tube. This is the most labor-intensive process.
	Once the wire is in place, you can evaluate how well the job was done. You may need to tighten some of the coils. It is desirable that the styling looks better.
	The ends of the wire should be soldered to a shielded cable.
	The reel is ready. You should think about how to secure it to the bar.

If such a process seems complicated, then you can approach the issue of making a coil differently.

	On a sheet of oriented strand board (OSB) you need to draw the contours of the future coil.
	A circle of the required diameter is cut out with a jigsaw.
	The wire is wound along the outer contour of the resulting circle.
	A rod is welded from polypropylene pipes. It is easy to attach it to the reel itself.
	As a result, the metal detector acquires a marketable appearance.
	After insulating the coil, it is advisable to paint it with alkyd enamel. A layer of paint prevents moisture from penetrating the OSB.

How to calculate the inductance of a coil?

When developing a metal detector design, it may be necessary to calculate the inductance value. For an accurate calculation, there is a special technique where the main parameters are taken into account. But to quickly determine the desired value, it is easier to use a nomogram.

Nomogram for quickly determining the inductance of coils

• inductance L = 10 mH;
• average ring diameter D = 20 cm;
• height and thickness of the ring, l = t = 1 cm.

Using the nomogram, determine the number of turns w that should be wound when making the coil. The packing density is set to k = 0.5. The cross-sectional area is determined based on the accepted dimensions S = klt, Here l– height of the coil layers; t– width of layers.

By dividing the S value by the w value, the diameter d (of the winding wire) is obtained. When d = 0.5...0.8 mm is obtained, the calculation stops. If it turns out more, then adjust the thickness and width of the ring.

Coil noise immunity

The similarity with a loop antenna determines the high activity of the coil. She is susceptible to interference from outside. To eliminate possible external influences, the manufactured coil is placed inside a metal braid. They create a special screen invented by Faraday.

The presence of such a screen prevents the arrival of external electromagnetic pulses.

Beginners should carefully study the design. The position of the grounding contact must be strictly along the axis of symmetry. Otherwise, the search coil itself may malfunction. The end from the shielding wire is connected to the general circuit of the device. If you neglect the requirements of symmetry, the characteristics of the solenoid will deteriorate, and interference will completely suppress the desired signals.

The presence of a screen somewhat reduces the magnitude of the electromagnetic field. Sensitivity decreases slightly. It is necessary to increase the supply voltage supplied to the winding.

A shielded wire connects the coil itself to the device circuit. Then the influence of interference is minimized as much as possible. The metal detector works more reliably.

The figure below shows winding methods: a – bifilar; b – cross.

From the practice of using coils in search devices, it has been established that the usual bifilar winding is ineffective. When ferromagnets are present in the soil, the signal begins to fade. If cross winding is used, then when the object is located strictly in the center of the coil, the signal is amplified.

Therefore, some radio amateurs do not undertake to wind many turns in a crosswise manner. They prefer to create a basket type reel. It is easier to manufacture.

Reel-basket

The disadvantages of DIYers include the need for precise manufacturing of such a device. You need a fairly strong mandrel. When tensioning the wires when winding, deformation is possible.

When creating a basket, the manufacturer has options:

• obtain a three-dimensional structure;
• make a flat basket reel.

The fairly well-known Pirate metal detector uses a volumetric basket. It is easier for beginners to make a flat product. They got the name "butterfly".

Basket reel design

The calculation is carried out using the formulas:

1. First you need to set the value of the diameter D₂. It is taken equal to the diameter of the existing mandrel minus 2...4 mm.
2. The value of D₁ is defined as D₁ = 0.5·D₂.
3. Calculate the number of turns using the formula:

where L is the inductance of the coil, calculated by the formula

k – correction factor determined from the table.

Table: determination of correction factor

D₂+D₁	k
1,2	3,31
1,5	2,98
1,8	2,72
2,0	2,58
3,0	2,07
5,0	1,57
8,0	2,23
10,0	1,03

Knowing the difference D₂ – D₁, the diameter of the wire is calculated. The packing density is believed to be 0.85.

Mono-loop and double-loop

The designation DD indicates the use of a double loop (Double Detector). The presence of two windings can significantly increase the susceptibility of the coil. It does not analyze the new emerging signal itself. These circuits analyze the distortions that occur when metal enters the area of ​​action of the solenoids.

They are first balanced so that the same impulses exist in different arms. Place similar loops in parallel.

When contacted with ferrous metal, low sounds are generated. And if non-ferrous metal or gold is present, the operator will hear a change in the signal to sounds of a higher frequency.

All metal detectors marked with GOLD symbols use Double Detector. It's more interesting to work with them. But it should be remembered that in loose soils such coils can squeak even from a concentration of ants.

How to secure the reel yourself?

If desired, a special frame for your reel can be ordered online. Prices vary quite widely. Therefore, many people use plywood as a base.

Options for making the frame: a – from plywood; b – from CDs

1. Many people think that it is easiest to use regular plywood. It is easy to saw. It has sufficient strength.
   In practice, it turns out that plywood can absorb moisture. As a result, the performance of the device may be extremely low.
2. The best results are obtained when using CDs. A gap of about 5...7 mm is left between them. You can glue pieces of foam plastic. Then they wrap it along the generatrix with adhesive tape or insulating tape. The result is a reliable and durable three-dimensional structure.
3. When using cellular polycarbonate with a thickness of 6 or 8 mm, a lightweight and fairly durable frame is obtained. You just need to close the honeycombs to prevent moisture from getting into them. Regular tape will do. Professionals use silicone sealant; it will reliably fill the holes at the entrance to the honeycomb. It has been proven that such a frame is the most successful. It does not cause additional interference.

Several designs of metal detectors

Parametric Metal Detection Instrument

For searching ferrous metal and pipelines in the ground. Finding electrical wiring in walls uses simple and reliable circuits. They are based on the MP40 transistor, the price of which today is several rubles (cheaper than taking a tram). It is possible to replace it with a more powerful model KT361 (note that it has reverse polarity; when connecting the power, you should change the method of turning on the battery).

The simplest metal detector

This device operates at low frequency. The sound frequency is selected by changing the capacitance of the capacitor C₁. When metal is found, the tone noticeably decreases. Therefore, during the initial setup, they try to set a squeak similar to a mosquito.

When there is metal in the operating area of ​​the device, the operator will hear a low, bass sound. Its frequency corresponds to 50 Hz. This is the current that flows in household and industrial electrical wiring.

Pulse parametric device

Diagram of a device for detecting metals with a simple quartz filter

This design is implemented on the basis of an old transistor receiver operating on medium waves. It is used only because it has a ferrite antenna inside. It is she who sets the desired oscillation frequency.

The entire device is powered by two AA batteries. Energy consumption is quite low.

The circuit is quite simple, soldering it is not difficult. The parts are inexpensive. A set of components will cost (domestic parts) about 200 rubles.

Many people are put off by this design because it requires lengthy and careful debugging. You have to select resistors and capacitors. Previously, such radio devices used parts with a wide range of indicators. Since then, no one has eliminated the spread.

Transceiver metal detectors

Scheme of the transceiver device

If you want to create an effective device for searching for non-ferrous and precious metals, you should focus on using metal detectors equipped with a transmitter and receiver.

Here, DD coils work, to which power is supplied at a frequency of 2000-2500 Hz. Such devices can detect alloys of non-ferrous metals at a depth of 9-11 cm. Ferrous metals weighing up to 100 g are diagnosed at a depth of about 20 cm. Large objects made of cast iron or steel can be detected at a depth of 60-70 cm.

Sometimes such devices are placed in hermetically sealed shells, making deep metal detectors for working underwater. Underwater metal detector expands the range of searches for valuable items

When creating such metal detectors, the coils are wound according to special patterns

Step-by-step technology for manufacturing and testing a metal detector

	A wire Ø 0.65 mm is prepared. It will require a little more than 14 m. 30 turns will be laid on a diameter of 150 mm.
	The lid from a plastic bucket is used as a sample for drawing a circle of the required diameter. It has the required diameter.
	A circle is formed on the board. It will serve as the basis for subsequent actions.
	To wind the wire you need to drive in nails. Hardware 30 mm long is used. To obtain a high-quality circle, it is advisable to hammer in at least 16 pieces. More is possible.
	You can start winding the wire. One end is fixed.
	When winding, you need to try to lay the turns more tightly.
	The resulting coil should be insulated. First, it is wrapped with masking tape.
	Having made the first coil, the second one is made in a similar way.
	The transceiver device is manufactured according to the proposed scheme.
	To receive a sound signal you need an earphone from your phone.

	The entire circuit of the device is assembled on one board.
	A suitable metal box is selected in which the board will be located.
	There is space inside not only for the board. The battery is placed here. Professionals try to use small-sized batteries. They can be recharged. Having two or three batteries with you, you don’t have to worry that the device will be de-energized.
	The coils are placed on a sheet cut from cellular polycarbonate.
	The rod is made of polypropylene pipes.
	For ease of use, the handle has a half ring. It is easier to control when searching for metal objects.
	By scattering various objects, you can diagnose the functionality of the metal detector. Estimate the detection distances for each type of metal. The device is being configured.
	You can start searching for metals in nature. You should walk slowly. The coils move from side to side, trying to cover the maximum width.
	Having found an object in the ground, you can start digging it out. When in places where there have been battles, you should follow the rules for safely removing objects.
	Even small coins can be found in the depths.

Finding simple solutions

If you want to try yourself in a new business, but have not yet come to the desire to create circuits, then you can make the simplest metal detector without microcircuits and soldering.

The simplest metal detector

You will need:

1. The cheapest radio receiver. It should have a mid-wave range. It is usually labeled AM. A ferrite magnetic antenna was installed in such receivers.
2. A calculator released at the end of the 20th century. You can buy them at bargain shops from old ladies.
3. A small book or just its cover. Cardboard would be preferable. It will have a certain strength.

Now you have to tinker a little. The structure of such a device is extremely simple:

1. The cover is revealed.
2. You need to stick double-sided tape on each side.
3. A calculator is glued to one side.
4. A radio receiver is glued to the other side. You need to make sure that when closed they match exactly.
5. The receiver is turned on at the highest volume. You need to find a range in which there are no radio stations. It is desirable that there be no ethereal noise.
6. The calculator turns on. When you turn on the second device, a signal will be induced in the receiver. It should respond to the second device being turned on. You will hear a roar or some other noise. If there is no noise, you will have to look for a range where you can hear the calculator turning on.
7. You need to fold the cover until the tone becomes quieter. It may disappear completely. This is usually observed when the devices are located at an angle of 90 ⁰.
8. Now you need to fix this position. Use elastic bands or other auxiliary material.

Now you can start searching. When you bring such a device near metal objects, noise will appear. Depending on the type of metal, different noise will be synthesized. After experiments with iron objects, you can listen to what reaction non-ferrous metals and gold will have.

All that remains is to attach the cover to the rod and start searching for treasures.

More ideas for creating a metal detector

Very unusual designs are offered by users from the Internet. You can try them too.

Hello readers! Today I want to talk about how to assemble a metal detector with your own hands. When you really want to buy something, but there is no money for it, you have to postpone the purchase until later or take out a loan. Credit is expensive. And the thought arises in my head: “If only I could find a treasure.” Which one then ? That's right, a metal detector. This article will tell you how this device works and what parts are needed to assemble it.

The design of metal detectors consists of the following main elements:

1. The coil receives and transmits an electromagnetic signal, scanning the surface with the desired metal.
2. The control unit processes the signal received from the coil, notifies the user with a graphic or sound signal, and also allows you to manually configure the operating modes of the detector.
3. The lower rod fixes the reel and adjusts its angle.
4. The middle rod is an intermediate link between the lower and upper rods and allows you to adjust the height of the metal detector.
5. Upper rod. The control unit is located here, as well as a comfortable handle with an armrest so that the user’s hands do not get tired from holding the metal detector for a long time.

The metal detector emits an electromagnetic field through a coil. When metal or any other conductive material is in this field, the field is distorted and weakened. The control unit detects this and sends a signal.

More electrically conductive non-ferrous metals distort the field emitted by the detector more than ferrous metals.

Therefore, sensitive electronic circuits allow you to create devices with metal discrimination that can distinguish non-ferrous metal from ferrous metal.

Types of metal detectors

Metal detectors are divided into:

• induction;
• pulse;
• phase sensitive;
• parametric.

What types can you make at home with your own hands?

Parametric and phase-sensitive detectors are well suited for homemade products. They are easy to make, and the parts for them cost mere pennies. To assemble it yourself, it is enough to have basic knowledge of radio engineering.

Metal detectors with phase accumulation are much more sensitive than parametric ones. They have good discrimination and can find even small jewelry, making them a favorite tool for beach gold diggers. On dry sand it is possible to find earrings and rings at a depth of up to 38 cm.

Main settings

Search method

Induction metal detectors (MD) consist of a transceiver inductor.

When the emitted signal hits a metal object, it is reflected back and recorded by the receiver. These devices are quite simple to make with your own hands, but their sensitivity greatly depends on the type of soil and the quality of the coil.

Pulsed MDs excite eddy currents in the search zone and measure the secondary damped electromagnetic field. The sensitivity of these devices is higher and does not depend on the type of soil. However, they consume a lot of electricity, which does not allow them to work in autonomous mode for a long time.

Phase-sensitive MDs can be:

1. Impulse. The receiver and transmitter here are one and the same element. It records the phase shift of the signal reflected from the metal. The increase in phase shift causes clicks in the headphones: the closer the MD is to the metal, the more frequent they become, eventually merging into a single sound. The work of the popular metal detector “Pirate” is based on this method.
2. Double-circuit. Consist of 2 symmetrical generators and 2 detectors. A metal object disrupts the synchronization of the generators, and the same clicks occur, merging into a continuous tone.
   

   Double-circuit ones are easier to make with your own hands than pulse ones.

3. Parametric MDs have neither a receive nor a transmit coil, making them simple, cheap, and popular for DIY assembly. An LC generator creates an electromagnetic field at audio frequency. Any metal near the metal detector changes the parameters of the coil detector, which affects the frequency and amplitude of the generated signals. The diagram of such devices is easy to find. However, their sensitivity is low and does not allow complex searches. Parametric MDs are divided into:
4. Frequency MD. They emit multi-frequency signals. When approaching metals, the device detects a change in frequency.
5. Metal detectors that record changes in the quality factor of the circuit. When the distance between the device and the metal decreases, the device records this.

Detection depth

The detection depth depends on the coil diameter, electronic circuit and operating frequency. The larger the diameter of the wire coil, the more powerful the emitted electromagnetic field and the lower its frequency, the deeper the detection zone of a DIY metal detector.

However, as the search depth increases, the sensitivity of the metal detector to small objects deteriorates, and its selective capabilities also decrease. Energy consumption and weight of the device increase, which makes it difficult to hold the metal detector in your hands for a long time.

Operating frequency

Based on the frequency of operation, MDs are divided into:

1. High frequency. They operate at frequencies of several hundred kHz. They are used in devices designed to search for gold, as they have excellent discrimination. But they sharply lose sensitivity on wet and magnetic soils, as well as at a depth of more than 40 cm.
2. Mid-frequency. Operating frequency up to several tens of kHz. The requirements for the quality of the coil are lower, good sensitivity. Detection depth is up to 1.5 meters, provided that the soil is dry and low-mineralized.
3. Low frequency. They operate at frequencies from hundreds of Hz to several kHz. These are deep metal detectors that detect objects up to 5 meters underground. They are easy to make with your own hands. Disadvantages: low sensitivity and high power consumption. Suitable as magnetic detectors, as well as for searching for large objects made of ferrous metal (fittings, wiring).
4. Ultra-low frequency. They are not suitable for amateur searches, as they have high power consumption and large dimensions, and special programs are required for signal processing. Operating frequency up to several hundred Hz. These metal detectors cannot be held by hand, so they are mounted on a car.

Step-by-step instructions for assembling a simple homemade metal detector with your own hands

Required tools and materials

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

1. Tools: wire cutters, knife, small saw, screwdriver, soldering iron.
2. Materials: wire, solder, flux, glue, electrical tape, radio components, wooden or plastic stick.

Dielectrics (polymers, wood, glue) must be used as a rod, as well as elements for its fastening, so that they do not interfere with the operation of the metal detector.

Preparing parts

You need to prepare a board on which the electrical circuit will be mounted. Even cardboard can be used as a board. The location of future parts is marked on it by hand and holes are made.

Radio components are bought in a store or soldered from old equipment. However, you need to make sure that the details are the same. This will make it easier to coordinate the operation of the two detectors.

Metal detector circuits for manufacturing

Sensitive metal detector based on a dual-circuit oscillator circuit

Manufacturing stages:

1. Transistors, resistors and capacitors are placed on the board and soldered according to the diagram below.
2. Solder two wires from the battery compartment, as well as two piezoelectric speakers.
3. Wind the wire onto a round frame with a diameter of about 22 cm. After 10 turns, make a wire tap 20 cm long. The wire at the tap site is not torn, but folded in half by hand. Make another 20 turns. The result should be three leads 20 cm long: the beginning of the wire, the end and the outlet after the 10th turn.
4. Remove the coil from the frame, holding the coils with your hands, and secure tightly with electrical tape.
5. Wind a second coil, which should mirror the first. Remove it from the frame and secure it with electrical tape.
6. Solder the leads of the coil detectors according to the diagram.
7. Assembling the stand. The coils are placed at a distance of approximately 15 cm from each other, and a board is attached between them.
8. Adjust the detectors before mounting. Turn on the metal detector and, moving the coils with your hands, achieve maximum silence. They bring metal to one of them. If the sound changes noticeably, it means the metal detector is working.
9. The elements are fixed with glue and covered with oil varnish.
10. Attach the handle to the stand.

On a transformer with W-shaped plates

This is a simple parametric metal detector with inductive feedback. Allows you to detect hidden wiring, reinforcement in walls and ceilings, as well as large metals in the soil. A low-power transformer is used from any radio receiver. To turn a transformer into a detector with your own hands, you need to open its magnetic circuit: remove the frame, straight jumpers and windings.

There are two schemes for converting a transformer. The first one uses old windings, the second one rewinds them.

In the first case, the W-shaped plates need to be folded together and windings put on them. Winding in diagram II is network, winding I is step-down by 12 V. Capacitor C1 adjusts the tone of the sound. Instead of the MP40 transistor, you can use KT361.

In the second case, windings of 1000 turns (in Scheme I) and 200 turns (in Scheme II) are wound on W-shaped plates. For winding I, PEL-0.1 wire is used. After 500 turns, a tap is made. Winding II is wound with PEL-0.2 wire.

The transformer is sealed and placed on the bottom rod of the metal detector. When approaching metal, the tone of the signal in the headphones will change.

On transistors

Also a simple circuit consisting of transistors K315B or K3102, capacitors, resistors, an earphone and a battery.

The first transistor creates a master oscillator, the second - a search oscillator. If you bring metal close to the coil, sound appears in the headphones. A detailed diagram is given below.

On the K561LE5 chip

The circuit consists of a microcircuit, headphones, resistors and capacitors. Coil L1 is connected to the master oscillator, and L2 is connected to the search oscillator of the microcircuit. A metal object affects the frequency of the search generator, changing the sound in the headphones. It is adjusted by MD capacitor C6. It eliminates unnecessary noise. The device supply voltage is 9 V.

How to assemble with your own hands without using microcircuits

This is the easiest option to assemble. So to speak, for dummies. You don't even need to solder anything. The metal detector is built from a calculator, a radio and a cardboard or CD box. The receiver and calculator should be taken as simple as possible, without protection from electromagnetic interference.

The principle of operation is based on the fact that the calculator creates radio interference in the AM range, and the receiver picks it up. Making a metal detector with your own hands consists of the following stages:

1. Set the radio to the highest AM range, but at the same time free from stations. Only interference should be heard.
2. Glue the receiver with double-sided tape on the back side to one flap of the CD box. Glue the calculator to the other sash.
3. Turn on the calculator. When the shutter is fully open, the receiver should enhance its sound.
4. Fold the box smoothly. When the angle between the receiver and the calculator is approximately 90°, the radio will go silent.
5. Fix the box in this position.

When metal enters the MD's coverage area, the field vector will rotate and the receiver will again intensify its sound. Depending on the design of the receiver, it may turn out that at an angle of 90°, the sound, on the contrary, is enhanced. In this case, the angle between the doors of the box is gradually increased, achieving a weakening of the tone.

PCB assembly

There are several options for wiring boards yourself. The figures below show circuit diagrams for wiring boards for metal detectors on a double-circuit oscillator, on a transformer, transistors and on a K561LE5 microcircuit.

Do-it-yourself electronics must be placed in a plastic case to avoid interference.

How to make a reel

An enameled copper wire with a diameter of 0.4–0.6 mm and a frame of the required size are used. The diameter of the frame depends on the purpose of using the metal detector:

• up to 9 cm – suitable for searching for reinforcement and profiles;
• 14-18 cm – for searching for small jewelry;
• 22-50 cm – for searching for large and deep-lying objects.

Also, for proper operation of the metal detector, you need to monitor the inductance of the coil. Inductance can be measured with a special device or calculated on the Internet using a calculator.

You can buy a frame for the reel in a store or make it yourself. Plywood or durable plastic are suitable for this. It is best to use plastic (polycarbonate, computer disk, bucket), as it has the least effect on the electromagnetic field and does not absorb moisture.

Location of parts on the board for a chip in a DIP package

If a chip in a DIP package is used, then the parts are placed as in the figure below.

Location of parts on the board for a chip in an SM package

Below is a diagram of the arrangement of parts when using a microcircuit in an SM package.

Brief instructions for setting up the device

The general rule when adjusting a metal detector with your own hands is to achieve the lowest sound in the “idle” mode, so that squeaks or clicks appear only when a metal object is detected. This can be achieved by changing the inductance of the coils, the capacitance of the capacitor or the resistance of the resistor.

Modernization

To make the metal detector better at finding small jewelry, you need to increase its operating frequency.

The sensitivity of the device also increases when an additional RC circuit is added to the circuit.

Installing variable resistors allows you to configure the device yourself without touching the coils.

The use of speakers with capacitors makes the sound produced louder. It is also useful to create a secure mounting for the coils and control unit. Protection from shocks and shocks will reduce interference, and settings will be less likely to be lost.

Conclusion

Now you know how to make a metal detector with your own hands. I will be glad if this article helps you find the treasure. Subscribe to new articles and share useful information on social networks.