A metal detector is electronic device for searching and distinguishing metals, metal objects that can be hidden at different depths under a layer of sand, earth, in the walls of rooms and various structures.
Schematic diagrams of metal detectors made on transistors, microcircuits and microcontrollers are given. A factory-made metal detector is a fairly expensive device, so making a homemade metal detector yourself can save quite a bit of money.
The circuits of modern metal detectors can be built according to different principles works, we list the most popular of them:
- Beat method (measuring changes in reference frequency);
- Induction balance at low frequencies;
- Induction balance on spaced coils;
- Pulse method.
Many novice radio amateurs and treasure hunters are wondering: how to make a metal detector yourself? It is advisable to start your acquaintance with assembling a simple metal detector circuit; this will allow you to understand the operation of such a device and gain first skills in searching for treasures and products made of multi-colored metals.
Now there is a fairly large selection of multimeters, at very different prices. Now the radio amateur can not be limited to the modest set of functions of the “legendary” M-838. For slightly more expensive, you can purchase a more modern device that is also capable of measuring the frequency of alternating current...
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The metal detector is designed to detect a metal object (well cover, pipe section, hidden wiring). The metal detector consists of a parallel voltage stabilizer (transistors V1 V2) at a high frequency generator (about 100 kHz) on transistor V4, an RF vibration detector (V5) and...
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The metal detector allows you to detect any metal object at a distance of up to 20 cm. The detection range depends only on the area of the metal object. For those for whom this distance is not enough, for example treasure hunters, we can recommend increasing the size of the frame. This should also increase the detection depth. Schematic diagram metal detector is shown in the figure. The circuit is assembled using transistors operating in...
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Circuit diagram of a homemade beat metal detector, which is built on five microcircuits. Finds a 0.25mm coin at a depth of 5cm, a pistol at a depth of 10cm, and a metal helmet at 20cm. The schematic diagram of a beat metal detector is shown below. The circuit consists of the following components: a crystal oscillator, a measuring oscillator, a synchronous detector, a Schmidt trigger, an indication device...
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The circuit shown in the figure is a classic metal detector. The operation of the circuit is based on the principle of superheterodyne frequency conversion, which is usually used in a superheterodyne receiver. Schematic diagram of a metal detector with an integrated ULF; it uses two radio frequency generators, the frequencies of which are 5.5 MHz. The first radio frequency generator is assembled on a T1 transistor type BF494, frequency...
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This metal detector, despite the small number of parts and ease of manufacture, is quite sensitive. It can detect large metal objects, such as a heating battery, at a distance of up to 60 cm, while small ones, for example, a coin with a diameter of 25 mm, can be detected at a distance of 15 cm. The operating principle of the device is based on a change in frequency in the measuring generator under the influence of nearby metals and. ..
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A simple compact metal detector is needed to detect various metal objects (for example, pipes, wiring, nails, fittings) in walls under a layer of plaster. This device is completely autonomous, powered by a 9-volt Krona battery, consuming 4-5 mA from it. The metal detector has sufficient sensitivity to detect: pipes at a distance of 10-15 cm; wiring and nails at a distance of 5-10...
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Scheme of a small-sized, highly economical metal detector with good repeatability and high performance characteristics, using widely available and inexpensive parts. An analysis of most common circuits has shown that they are all powered from a source with a voltage of at least 9 V (that is, “Krona”), and this is both expensive and uneconomical. So, assembled on the K561LE5 chip...
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This is almost akin to searching for treasures. Some are stopped by the fact that they live far from mountains or rivers in order to look for nuggets by washing sand. Others do not understand radio components to know how to extract gold from them. Still others prefer to look for precious metal using a metal detector, but do not have the funds to buy it. Fortunately, the device is quite simple, and even without being a radio amateur, you can make it yourself.
Operating principle
What is a metal detector? This is a device that, using certain radiation, finds metal located underground, without direct contact with it. The response data that comes back helps to identify the find and informs about it using an audio or visual signal.
The principle of operation of the metal detector
The electromagnetic field that the device emits is in contact with metals, in in this case with gold, which provokes the appearance of eddy currents on their surface. By measuring electrical conductivity, metals are identified and data about this is transmitted by a signal.
Metal detectors can have different wave parameters, return signal processing techniques, additional functions and much more. Therefore, before you start making a device, you need to decide what exactly you want to get as a result.
The standard frequency for metal detectors is 6–20 kHz, but for gold it should be slightly higher, 14–20 kHz or more. This is because gold often occurs in tiny nuggets, so higher sensitivity is needed. If there is such a possibility, then it is good to have a device with a multi-frequency customizable search, then it will be possible to increase the number of objects that it recognizes.
Among all the metal detector circuits on the Internet, experts advise choosing devices with balanced induction, which have two coils in the head and a powerful electronic circuit. Also of great interest are circuits that have a receiver-transmitter operating principle, operating on high frequencies, about 20 kHz, which allows you to distinguish non-ferrous metals from ferrous ones.
Common parameters
Various technical methods can be used to design a metal detector. Much depends on the conditions in which it will be used. Therefore, the idea of what requirements the device must meet must be defined as clearly as possible. The following device parameters are distinguished:
- sensitivity - a characteristic that determines how small objects the detector can detect;
- selectivity - the ability to identify metals and react to specific ones;
- resistance to interference - the ability not to respond to extraneous radio signals from radio stations, cars, lightning strikes and others;
- energy consumption - how much the device consumes and how long the built-in battery or batteries last;
- penetrating power - the depth at which the device can recognize metals;
- dimensions of the device;
- search area size - the area covered by the device without changing its location.
Resolution is the main parameter, in turn, it is also a composite one. There are one or two signals at the output of the device, and there are more properties that determine the object and its location. For example, if you lower the frequency of the generator, you can achieve an increase in the search and penetration area, but lose in sensitivity, as well as mobility due to the increase in the size of the coil.
Diagram of a simple metal detector The peculiarity of the design of the metal detector is that all of the above parameters, in combination or individually, depend specifically on the frequency of the coil. Thus, this characteristic is decisive when designing the device. By frequency, metal detectors are divided into the following:
- ultra-low frequency: frequency up to several hundred hertz, low mobility, high power consumption, complex in design and signal processing;
- low-frequency: hundreds, thousands of Hz, low sensitivity, high noise immunity, simple design, permeability depends on power - from 1 to 4 m, mobile;
- high frequency: tens of kHz, simple design, permeability up to 1.5 m, poor noise immunity, so-so discrimination, good sensitivity;
- high-frequency: radio frequencies, typical “gold”, excellent discrimination, small permeability, up to 80 cm, low consumption, other parameters are poor.
Device design
The device, which does not require absolutely any knowledge in radio engineering, can be assembled with your own hands, having: a calculator, a radio receiver, a box with a hinged lid made of plastic or cardboard, and double-sided tape. The calculator must be as cheap as possible to serve as a basis for radio interference, and the receiver must not be immune to interference.
DIY metal detector, instructions:
- We unfold the box, forming it into a book.
- We fix the calculator and receiver in the box, the latter in the lid.
- Turn on the receiver and look for a free area at the top of the AM band.
- Turn on the calculator: the receiver should make a sound, set it to maximum volume.
- If there is no tone, we adjust until it appears.
- Fold the lid so that the tone disappears. In this position, the magnetic vector of the primary pulses will be perpendicular to the axis of the magnetic antenna rod.
- We fix the cover.
Thus, it is quite simple to assemble a primitive device, but in order to obtain more data, you already need to have some knowledge and skills in radio electronics. On the Internet you can find a suitable one from many schemes.
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. IN new version LED indication of metals has been added, a power-on notification function has been added, the notification sound has been strengthened, 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!
Printed circuit board, firmware, as well as a list of parts that can be bought very cheaply on AliExpress with free shipping, is 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.
Many people unreasonably believe that homemade metal detectors are inferior in many respects to branded samples produced at the factory.
But in fact, structures that are correctly assembled with your own hands sometimes turn out to be not only better, but also cheaper than “factory” competitors.
Worth knowing: most treasure hunters and local historians to save money cash, try to choose the cheapest options. As a result, they either assemble metal detectors themselves or purchase homemade custom devices.
Beginners, as well as people who do not understand electronics, are at first intimidated by the abundance of not only special terminology, but also various formulas and circuits. However, if you delve a little deeper, everything immediately becomes clear, even with the knowledge gained in school physics lessons.
Therefore, it is worth, first of all, to understand the principle of operation of a metal detector, what it is and how you can assemble it yourself at home.
How does it work
Operating principle of this device consists of using an electromagnetic field. It is created by the transmitter coil and after a collision with an object that conducts current (which is most metals), eddy currents are created that introduce distortion into the EPM of the coil.
In cases where the object is not electrically conductive, but has its own magnetic field, the interference it creates will also be caught due to shielding.
After this, changes in the electromagnetic field are sent directly to the control unit, which emits a special signal to notify that a person has been found. sound signal, and in more expensive models displays data on the display.
It is worth examining how such devices are created following the example of a “Pirate” type metal detector.
Metal detector "Pirate"
Making a printed circuit board with your own hands
First you need to create a printed circuit board, where all the nodes of the metal detector will be located in the future. The best method is laser-iron technology or simply LUT.
To do this, it will be necessary to perform the manufacturing steps in the following sequence:
- In the beginning it is necessary, using exclusively laser printer, print the corresponding diagram created through the Sprint-Layout program. It is best to use light weight photo paper for this.
- We prepare the PCB workpiece, first sand it, and then clean it with a solution. It should have dimensions 84x31.
- Now on top of the blank we place photo paper with the diagram on the front side on which it was printed. Cover with an A4 sheet and begin ironing with a hot iron in order to transfer the marking scheme to the textolite.
- After fixing the circuit from the toner, we place it all in water, where we carefully remove the paper with our fingers.
- Next, if there are smeared areas, we correct them using a regular needle.
- Now the board needs to be placed in a solution of copper sulfate for several hours (ferric chloride can also be used).
- The toner can be removed without any problems with any solvent, such as acetone.
- We drill holes for later placement of structural elements (the drill must be very thin).
- The last stage is to lay out the board tracks. To do this, a special solution “LTI-120” is smeared on the surface, which needs to be spread over the solder of the soldering iron.
Installing elements on the board
This stage of creating a metal detector consists of installing all the elements on the created board:
- The main microcircuit is the domestic KR1006VI1 or its foreign analogue NE555. Please note that before installation, a jumper must be soldered underneath it.
- Next, a two-channel amplifier K157UD2 is installed. You can buy it or take it from Soviet tape recorders.
- After this, 2 SMD capacitors are mounted, as well as one resistor of the MLT C2-23 type.
- Now you need to solder two transistors. One must be NPN structure, and the other PNP. It is advisable to use BC557 and BC547. However, analogues will also work. As field effect transistor It is recommended to take IRF-740 or other options with similar characteristics.
- The capacitors are installed last. They should be taken with a minimum TKE indicator, which will increase the thermal stability of the entire structure.
Note: The hardest thing will be to get the K157UD2 amplifier out of this circuit. The reason is that it is already an old chip. That is why you can try to find similar modern options with similar parameters.
A homemade coil is created on a frame with a diameter of 20 cm. The total number of turns should be approximately 25 pieces. This indicator is based on the fact that PEV wire is used, which has a diameter of 0.5 mm.
However, there is a certain peculiarity. The total number of turns can be changed up or down. To find the most best option, you need to take a coin and check in which case there will be the greatest distance to “catch” it.
Other elements
A signal speaker can be used taken from a portable radio. It is important that it has a resistance of 8 ohms (Chinese options can be used).
To carry out the adjustment, you will need two potentiometer models of different power: the first is 10 kOhm, and the second is 100 kOhm. To minimize the influence of interference (it will be difficult to eliminate it completely), it is recommended to use a shielded wire that will connect the circuit and the coil. The metal detector's power source must be at least 12 V.
When the entire structure has been tested for functionality, it is necessary to make a frame for the future metal detector. However, here we can only give some recommendations, because everyone will create it from the items at hand:
- to make the bar more convenient, it is worth purchasing 5 meters of ordinary PVC pipe (which are used in plumbing), as well as several jumpers. It is worth installing a special palm rest at its upper end to make it more comfortable to hold. For the board, you can find any box of the appropriate size that needs to be mounted on the rod;
- To power the system, you can use a battery from a regular screwdriver. Its advantages are low weight and high capacity;
- When creating the body and structure, keep in mind that there should not be any unnecessary metal elements in them. The reason is that they significantly distort the resulting electromagnetic field of the future device.
Checking the metal detector
First of all, you need to adjust the sensitivity using potentiometers. The threshold will be a uniform, but not very frequent, crackling.
So, he will have to “find” a five-ruble coin from a distance of approximately 30 cm, but if the coin is the size of a Soviet ruble, then from about 40 cm. He will “see” large and voluminous metal from a distance of more than a meter.
Such a device will not be able to search for small objects at significant depths. In addition, he will not be able to distinguish between the size and type of metal found. That is why, while searching for coins, you may come across ordinary nails.
This model of homemade metal detector is suitable for people who are just starting to learn the basics of treasure hunting or do not have the necessary funds to purchase an expensive device.
Their this video You will learn how to make a homemade metal detector:
Among amateur radio designs, developments that help detect metal objects hidden in the ground are of particular interest. Especially if the latter are small in size, lie at a considerable depth and are also non-ferromagnetic.
Quite a few good electrical diagrams of such devices, called metal detectors by analogy with well-known military developments, and descriptions of fully functional designs have been published in various technical
Publications, but they are often designed for trained, experienced home-made workers who have a good material base and scarce parts.
But even a beginner can easily repeat and make the design we propose. Moreover, it will be quite possible to purchase the necessary parts (including a 1 MHz quartz resonator). Well, the sensitivity of the assembled metal detector... It can be judged at least by the fact that with the help of the proposed device it is easy to find, for example, a copper coin with a diameter of 20 mm and a thickness of 1.5 mm at a depth of 0.9 m.
Operating principle
It is based on a comparison of two frequencies. One of them is reference, and the other is variable. Moreover, its deviations depend on the appearance of metal objects in the field of the highly sensitive search coil. In modern metal detectors, to which the design under consideration can quite rightly be included, the reference generator operates at a frequency that is an order of magnitude different from that which appears in the field of the search coil. In our case, the reference generator (see the circuit diagram) is implemented on two logic elements ZI-NOT integrated DD2. Its frequency is stabilized and determined by a quartz resonator ZQ1 (1 MHz). The generator with varying frequency is made on the first two elements of the IC DD1. The oscillatory circuit here is formed by the search coil L1, capacitors C2 and SZ, as well as a varicap VD1. And to adjust to a frequency of 100 kHz, use potentiometer R2, which sets the required voltage to the varicap VD1.
Fig.1. Fundamental electrical diagram highly sensitive homemade metal detector.
Logic elements DD1.3 and DD2.3, operating on mixer DD1.4, are used as signal buffer amplifiers. The indicator is a high-impedance BF1 telephone capsule. And capacitor C10 is used as a shunt for the high-frequency component coming from the mixer.
The configuration of the printed circuit board is shown in the corresponding illustration. And the layout of radio elements on the side opposite the printed conductors is shown here in a different color.
Fig.2. Printed circuit board of a homemade metal detector, indicating the locations of the elements.
The metal detector is powered by a source direct current voltage 9 V. And since high stabilization is not necessary here, a Krona type battery is used. Capacitors C8 and C9 work successfully as a filter.
The search coil requires special precision and attention during manufacture. It is wound on a vinyl tube with an outer diameter of 15 mm and an inner diameter of 10 mm, bent in the shape of a circle 0 200 mm. The coil contains 100 turns of PEV-0.27 wire. Once the winding is complete, it is wrapped in aluminum foil to create an electrostatic shield (reduce the effect of capacitance between the coil and ground). It is important to prevent electrical contact between the winding wire and the sharp edges of the foil. In particular, “wrapping obliquely” will help here. And to protect the aluminum coating itself from mechanical damage, the coil is additionally wrapped with insulating bandage tape.
The diameter of the coil may be different. But the smaller it is, the higher the sensitivity of the entire device becomes, but the search area for hidden metal objects narrows. When the diameter of the coil increases, the opposite effect is observed.
Work with a metal detector as follows. Having placed the search coil in close proximity to the surface of the earth, adjust the generator with potentiometer R2. And in such a way that the sound in the telephone capsule cannot be heard. When the coil moves above the surface of the earth (almost close to the latter), the treasured place is found - by the appearance of sound in the telephone capsule.
When using the device discussed above to find objects hidden in the ground that are of archaeological and national cultural value, prior permission is required from the relevant authorities.
Attention!!! The information contained on this page has been added from unverified sources and may be out of date and contain errors. Therefore, it is provided for informational purposes only.
N. Kochetov, based on materials from “Mlad Constructor”