Scheme of deep metal detectors to make at home. How to make a simple metal detector with your own hands - step-by-step instructions
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 comes into contact with metals, in this case 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 at high frequencies, about 20 kHz, which makes it possible to distinguish non-ferrous metals from ferrous ones.
Common parameters
Various technical methods can be used to construct 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.
With the onset of spring, more and more often you can see people with metal detectors on the banks of rivers. Most of them are engaged in “gold mining” purely out of curiosity and passion. But a certain percentage actually earn a lot of money from searching for rare things. The secret to the success of such research is not only in experience, information and intuition, but also in the quality of the equipment with which they are equipped. A professional instrument is expensive, and if you have a basic knowledge of radio mechanics, you have probably thought more than once about how to make a metal detector with your own hands. The editors of the site will come to your aid and tell you today how to assemble the device yourself using diagrams.
Read in the article:
Metal detector and its structure
This model costs more than 32,000 rubles, and, of course, non-professionals will not be able to afford such a device. Therefore, we suggest studying the design of a metal detector in order to assemble a variation of such a device yourself. So, the simplest metal detector consists of the following elements.
The operating principle of such metal detectors is based on the transmission and reception of electromagnetic waves. The main elements of a device of this type are two coils: one is transmitting, and the second is receiving.
The metal detector works like this: the magnetic field lines of the primary field (A) of red color pass through the metal object (B) and create a secondary field (green lines) in it. This secondary field is picked up by the receiver and the detector sends an audible signal to the operator. Based on the principle of operation of emitters, electronic devices of this type can be divided into:
- Simple, working on the “receive-transmit” principle.
- Induction.
- Pulse.
- Generating.
The cheapest devices belong to the first type.
An induction metal detector has one coil that sends and receives a signal simultaneously. But devices with pulse induction differ in that they generate a transmitter current, which turns on for a while and then turns off abruptly. The coil field generates pulsed eddy currents in the object, which are detected by analyzing the attenuation of the pulse induced in the receiver coil. This cycle repeats continuously, perhaps hundreds of thousands of times per second.
How does a metal detector work depending on its purpose and technical device?
The operating principle of a metal detector varies depending on the type of device. Let's consider the main ones:
- Dynamic type devices. The simplest type of device that continuously scans the field. The main feature of working with such a device is that you must be in motion all the time, otherwise the signal will disappear. Such devices are easy to use, however, they are poorly sensitive.
- Pulse type devices. They have great sensitivity. Often, such a device comes with several additional coils for adjustment to different types of soils and metals. Requires certain skills to set up. Among the devices of this class we can distinguish electronic devices operating at low frequencies - no higher than 3 kHz.
- Electronic devices, on the one hand, do not give a reaction (or give a weak one) to unwanted signals: wet sand, small pieces of metal, shot, for example, and, on the other hand, they provide good sensitivity when searching for hidden water pipes and central heating routes, as well as coins and other metal objects.
- Depth detectors designed to search for objects located at impressive depths. They can detect metal objects at a depth of up to 6 meters, while other models “pierce” only up to 3. For example, the Jeohunter 3D depth detector is capable of searching and detecting voids and metals, while showing objects found in the ground in 3- measured form.
Depth detectors operate on two coils, one is parallel to the ground surface, the other is perpendicular.
- Stationary detectors- these are frames established at particularly important protected sites. They detect any metal objects in people's bags and pockets that pass through the circuit.
Which metal detectors are suitable for making yourself at home?
The simplest devices that you can assemble yourself include devices that operate on the principle of reception and transmission. There are schemes that even a novice radio amateur can do; for this you just need to select a certain set of parts.
There are many video instructions on the Internet with detailed explanations of how to make a simple metal detector with your own hands. Here are the most popular ones:
- Metal detector "Pirate".
- Metal detector - butterfly.
- Emitter without microcircuits (IC).
- Series of metal detectors "Terminator".
However, despite the fact that some entertainers are trying to offer systems for assembling a metal detector from a phone, such designs will not pass the battle test. It’s easier to buy a children’s metal detector toy, it will be more useful.
And now more about how to make a simple metal detector with your own hands using the example of the “Pirate” design.
Homemade metal detector “Pirate”: diagram and detailed description of the assembly
Homemade products based on the “Pirate” series metal detector are among the most popular among radio amateurs. Thanks to the good performance of the device, it can “detect” an object at a depth of 200 mm (for small items) and 1500 mm (large items).
Parts for assembling a metal detector
The Pirate metal detector is a pulse type device. To make the device you will need to purchase:
- Materials for making the body, rod (you can use a plastic pipe), holder, and so on.
- Wires and electrical tape.
- Headphones (suitable for the player).
- Transistors – 3 pieces: BC557, IRF740, BC547.
- Microcircuits: K157UD2 and NE
- Ceramic capacitor - 1 nF.
- 2 film capacitors - 100 nF.
- Electrolytic capacitors: 10 μF (16 V) – 2 pieces, 2200 μF (16 V) – 1 piece, 1 μF (16 V) – 2 pieces, 220 μF (16 V) – 1 piece.
- Resistors – 7 pieces per 1; 1.6; 47; 62; 100; 120; 470 kOhm and 6 pieces for 10, 100, 150, 220, 470, 390 Ohm, 2 pieces for 2 Ohm.
- 2 diodes 1N148.
DIY metal detector circuits
The classic circuit of the “Pirate” series metal detector is built using the NE555 microcircuit. The operation of the device depends on a comparator, one output of which is connected to the IC pulse generator, the second to the coil, and the output to the speaker. If metal objects are detected, the signal from the coil is sent to the comparator, and then to the speaker, which notifies the operator of the presence of the desired objects.
The board can be placed in a simple junction box, which can be purchased at an electrical store. If such a tool is not enough for you, you can try to make a more advanced device; a diagram for making a gold-oriented metal detector will help you.
How to assemble a metal detector without using microcircuits
This device uses Soviet-style transistors KT-361 and KT-315 to generate signals (you can use similar radio components).
How to assemble a metal detector circuit board with your own hands
The pulse generator is assembled on the NE555 chip. By selecting C1 and 2 and R2 and 3, the frequency is adjusted. The pulses obtained as a result of scanning are transmitted to transistor T1, and it transmits the signal to transistor T2. The audio frequency is amplified using the BC547 transistor to the collector, and headphones are connected.
To place radio components, a printed circuit is used, which can be easily made independently. To do this, we use a piece of sheet getinax covered with copper electrical foil. We transfer the connecting parts onto it, mark the fastening points, and drill holes. We cover the tracks with a protective varnish, and after drying, we lower the future board into ferric chloride for etching. This is necessary to remove unprotected areas of copper foil.
How to make a metal detector coil with your own hands
For the base you will need a ring with a diameter of about 200 mm (ordinary wooden hoops can be used as the base), on which 0.5 mm wire is wound. To increase the depth of metal detection, the coil frame should be in the range of 260−270 mm, and the number of turns should be 21−22 vol. If you don't have anything suitable on hand, you can wind a reel on a wooden base.
Copper wire spool on wooden base
| Illustration | Description of action |
 | For winding, prepare a board with guides. The distance between them is equal to the diameter of the base on which you will attach the reel. |
 | Wind the wire around the perimeter of the fastenings in 20-30 turns. Secure the winding with electrical tape in several places. |
 | Remove the winding from the base and give it a rounded shape; if necessary, additionally fasten the winding in several more places. |
 | Connect the circuit to the device and test its operation. |
Twisted pair coil in 5 minutes
We will need: 1 twisted pair 5 cat 24 AVG (2.5 mm), knife, soldering iron, solder and multitester.
| Illustration | Description of action |
 | Twist the wire into two skeins. Leave 10 cm on each side. |
 | Strip the winding and free the wires for connection. |
 | We connect the wires according to the diagram. |
 | For better fastening, solder them with a soldering iron. |
 | Test the coil in the same manner as the copper wire device. The winding terminals must be soldered to a stranded wire with a diameter in the range of 0.5-0.7 mm. |
Brief instructions for setting up a DIY metal detector “Pirate”
Once the main elements of the metal detector are ready, we proceed to assembly. We attach all the components to the metal detector rod: the body with the coil, the receiving and transmitting unit and the handle. If you did everything correctly, then additional manipulations with the device will not be required, since it initially has maximum sensitivity. Fine tuning is performed using variable resistor R13. Normal operation of the detector should be ensured with the regulator in the middle position. If you have an oscilloscope, then use it to measure the frequency at the gate of transistor T2, which should be 120−150 Hz, and the pulse duration should be 130−150 μs.
Is it possible to make an underwater metal detector with your own hands?
The principle of assembling an underwater metal detector is no different from a conventional one, with the only difference being that you will have to work hard to create an impenetrable shell using sealant, as well as to place special light indicators that can report a find from under water. An example of how this will work is in the video:
Do-it-yourself metal detector “Terminator 3”: detailed diagram and video instructions for assembly
The Terminator 3 metal detector has occupied an honorable place among homemade metal detectors for many years. The two-tone device operates on the principle of induction balance.
Its main features are: low power consumption, metal discrimination, non-ferrous metals mode, gold only mode and very good search depth characteristics, compared to semi-professional branded metal detectors. We offer you the most detailed description of the assembly of such a device from folk craftsman Viktor Goncharov.
How to make a metal detector with your own hands with metal discrimination
Metal discrimination is the ability of the device to distinguish between the detected material and classify it. Discrimination is based on different electrical conductivities of metals. The simplest methods for determining the types of metals were implemented in old instruments and entry-level devices and had two modes - “all metals” and “non-ferrous”. The discrimination function allows the operator to respond to a phase shift of a certain magnitude, compared to a configured (reference) level. In this case, the device cannot distinguish between non-ferrous metals.
Learn how to make a homemade professional metal detector using improvised materials in this video:
Features of deep metal detectors
Metal detectors of this type can detect objects at great depths. A good metal detector, made by yourself, looks to a depth of 6 meters. However, in this case the size of the find must be substantial. These detectors work best for detecting old shells or large enough debris.
There are two types of deep metal detectors: frame and transceiver on a rod. The first type of device is capable of covering a large area of land for scanning, however, in this case, the efficiency and focus of the search is reduced. The second version of the detector is a point detector; it works directed inward over a small diameter. You need to work with it slowly and carefully. If your goal is to build such a metal detector, the following video can tell you how to do it.
If you have experience in assembling such a device and using it, tell others about it!
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 in 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.
Source
Metal detectors are used to detect invisible objects that, in their electromagnetic properties, differ from the environment in which they are located. Metal detectors are used by amateur archaeologists, geologists, and treasure hunters. These devices are also used by sappers to detect shells, builders to search for metal parts of structures (fittings, pipes...).
Most metal detectors look very similar, but in fact they differ greatly in their properties, and depending on the purpose of use. Here are some photos of commonly used metal detectors. And also a diagram of a simple metal detector.
How do metal detectors work?
The device of the metal detector is quite simple. And you can assemble it with your own hands at home. To do this, you do not need to have deep knowledge of electrical engineering. We have prepared step-by-step instructions for you that will help you assemble an amateur metal detector from available materials.
But first, let's find out what types of metal detectors exist, what properties different models have, and how to choose the right model for you. In order to choose the appropriate type of metal detector, you need to decide what technical characteristics you need.
Here are a few characteristics by which the quality of the device is judged:
Penetrating ability of the detector. To what depth does the electromagnetic field of the detector coil penetrate? This determines how deeply the device will “see” metal in the ground or other environment.
Search area covered. Typically, metal detectors examine the soil in stripes. This parameter determines the width of such stripes.
Device sensitivity. This determines whether your metal detector will detect small metal objects (for example, coins).
Detector fragmentation. This function is responsible for the detector's ability to respond only to the desired objects (for example, non-ferrous metals).
Finder immunity to interference. In addition to its own electromagnetic field, the device can enter the electromagnetic fields of other devices. (mobile devices, power lines, radio stations...). The best metal detectors are those that do not respond to fields from other sources.
Energy intensity. How many hours of searching should one battery or battery charge last?
Frequency classification
In addition, metal detectors are classified by operating frequency. Exist:
Metal detectors operating at ultra-low frequencies. Such devices are used only by professionals. They have good technical parameters, but their operation requires tens of watts of energy. Usually installed on special vehicles with high-capacity batteries and equipment that allows you to determine the size, shape and structure of detected objects.
Metal detectors operating in the low frequency range (from 300 Hz to several thousand Hz). Easy to make. Resistant to interference, but have low susceptibility. They are also called deep detectors (“they see” metal at a depth of up to five meters).
Metal detectors with a higher operating frequency range. (up to several tens of KHz). They are more difficult to assemble than low-frequency ones. Their penetrating ability is up to one and a half meters. Detects small objects well. They are rarely used due to their low technical characteristics.
How to assemble a metal detector with your own hands at home
7 simple steps:
- In order to assemble a metal detector, we will need a Chinese radio receiver (must have a magnetic antenna, AM range), a cheap calculator, a box and double-sided tape.
- We unfold the box so that it has the shape of a book (the main part on one side, the lid on the other)
- We glue the radio and calculator to the book with double-sided tape. (the radio is attached to the lid, and the calculator is attached to the base of the box).
- We turn on the receiver and find a frequency segment that is not used by radio stations (about 1.5 MHz).
- Let's start working with the calculator. At the same time, the radio receiver begins to make loud noise.
- We begin to slowly bring the box lid closer to the main part. We need to find a position where the noise disappears.
- We fix the book in this position. Ready! You have made the simplest amateur metal. detector.
Metal detectors with metal discrimination
Among all metal detectors, devices with a discrimination function are considered especially effective. What does it mean?
The metal detector not only shows the presence of an object with a characteristic field in the ground, but also displays on the screen the approximate shape, size and material of the detected object.
Of course, with such a device, work is much more efficient (there is no need to dig the soil with each detector signal) and requires less time. But such metal detectors consume energy very quickly. Plus they are several times more expensive. For an amateur treasure hunter, a cheaper analogue is also suitable.
We hope that our article was useful to you, helped you understand the main types of metal detecting devices, and perhaps even suggested how to make your own amateur metal detector!
Photos of do-it-yourself metal detectors
In terms of its popularity, metal detecting is comparable to fishing or hunting, not inferior to them in excitement with a certain amount of commercialism. The increase in the technical culture of the population and the wide range of the market for electrical parts are contributing to the growth in the number of people who want to make their own metal detector with their own hands in order to try themselves as a treasure hunter. In Fig. Below is a metal detecting enthusiast using a homemade metal detector to detect metal items on the seashore.
The principle of operation of the metal detector
A metal detector (hereinafter referred to as MI), also called a metal detector, is an electronic device that generates a directed electromagnetic field (primary signal) and detects its changes when the field comes into contact with metal objects. During the propagation of electromagnetic waves in an inhomogeneous physical environment, they interact with metals, creating eddy currents on their surfaces that generate their own electromagnetic fields. The MI receiving equipment records these fields (secondary signal) and informs the searcher about the detected find by audio or visual means.
How does a metal detector work?
The technical implementation of the operating principle of the MI is based on the use of two basic functional elements of a modular type:
- search coils for generating a primary electromagnetic field of a directional nature and receiving re-reflected secondary radio signals;
- control units for processing information from search coils and providing the operator with the processing result.
Depending on the purpose of the MI, search coils operate in the following frequency ranges:
- low-frequency range within the range of 2.5-6.6 kHz - to detect gold, silver, copper and their alloys at a depth of up to 4 meters;
- in the mid-frequency range - for searching for metals of any type;
- in the high-frequency range - for searching aluminum, nickel and detecting small targets at shallow depths.
The parameters of the magnetic field induced on the surface of the metal target change as follows:
- the signal amplitude decreases with distance from the transmitter;
- the phase of the induced field is determined by the electrical conductivity of the metal.
Based on the difference in amplitude, the MI equipment calculates the distance to the target; based on the phase shift, the type of metal is determined.
In Fig. Below is a schematic diagram of the analysis of MI information.
Metal detector – detector or scanner
At their core, MIs are detector devices (from the Latin detector - detector), indicating changes in the parameters of the primary directional radio signal. The quality of metal detection directly depends on the level of complexity of the metal detector equipment that processes the secondary signal. At the initial stage of the emergence of MI, the operator was quite satisfied with the squeaking sound in the headphones that occurred when a metal target was detected. The development of the element base for microelectronics has significantly expanded the capabilities of manual metal detection. Professional hand-held metal detectors are capable of solving the following tasks:
- identification of the “find” by type of metal;
- determining the depth of its location;
- assessment of the size and configuration of the detected object.
Using the latest software developments, leading manufacturers have launched sales of MI with the ability to image a detected target. For example, the German company OKM has developed an in-depth 3D scanner (from the English scan - to examine) model EXP 6000, which displays the configuration of a metal object on the screen.
In Fig. Below is an EXP 6000 MI monitor with a target image displayed on the screen.
Types of MI by purpose
In accordance with their intended purpose, MI is divided into the following types:
- Soil models designed for underground surveys in the upper layers of soil. Devices in this category are the most common among metal detectors and treasure hunters who can assemble a metal detector with their own hands at home. The simplest homemade product has low accuracy and does not always distinguish between different types of metals. Professional instruments can detect small grains of gold, ignoring other metals.
- Depth models designed to detect targets at a depth of up to 6 meters. However, they can only “see” large objects with an area of over 400 square meters. see. Deep devices are in demand by engineering services as route finders, by geologists as specialized georadars for searching for native gold, etc.
- Underwater metal detecting devices operating underwater. They are subject to increased requirements for the tightness of the search system. The operating conditions of underwater MI in sea and fresh water differ significantly. Underwater detectors use only sound indication.
Note! Underwater MI can be used on the surface in the mode of a conventional ground metal detector. Searchers only need to adjust the length of the rod and the position of the stop to make it more convenient to use the device.
- Special metal detectors:
- security devices for detecting metal products in luggage, clothing or on a person’s body during inspection;
- industrial metal detectors as part of conveyor lines, signaling the presence of metals in products;
- military devices, collectively called mine detectors;
- detectors tuned exclusively to gold objects.
In Fig. Below is a hand-held security metal detector.
Motivation for choosing the design of a homemade metal detector
Long before assembling a metal detector at home, the craftsman needs to compare numerous factors that influence the operation of the detector and choose the optimal design option that fully meets his needs. When making a metal detector with your own hands, the following technical and operational indicators are taken into account:
- general parameters of the search device that determine its functionality;
- operating frequencies in the range of which it is intended to operate;
- a search method that determines the circuit design of the device, specifying a method for recording changes in the reaction of the MI when it approaches a metal object.
General parameters of MI
For homemade search equipment, the following parameters are distinguished:
- Penetrating ability, which characterizes the maximum depth of penetration of the electromagnetic field, deeper than which the device is no longer able to detect a metal object.
- Sensitivity, indicating the ability to detect small objects.
- Resolution, more often called MI discrimination, providing information about specific properties of an object. A metal detector requires full implementation of three components of discrimination:
- geometric – for judging the size and configuration of the found target;
- spatial – for information about the depth of the target and its location in the search area;
- by quality - for assumptions about the type of material of the object and its probable characteristics.
- The size of the search area within which metal can be detected.
- Selectivity - an increased reaction to finds of a given type (gold, non-ferrous metals, military artifacts, etc.).
- Noise immunity – lack of response to electromagnetic fields from foreign sources.
- Energy consumption, which determines how long the device’s mobile power source will last for active operation.
In Fig. Below, in an ironic form, the process of metal detection (metal detecting) using a homemade MI is shown:
- pos. “A” – absence of metal targets;
- pos. “B” – metal objects of a certain value were discovered (for which the metal detecting was started).
The metal detector search area is highlighted in red.
Operating frequencies of homemade MI
The metal detector circuit and its assembly tie all the parameters of a homemade metal detector to the frequency range in which the operator expects to work. The practice of amateur metal detecting has shown the limited effectiveness of low-frequency (vlf) and high-frequency (hf) metal detectors, which require computer signal processing, consume a lot of energy and do not work well on mineralized wet soils. Most search engines interested in how to make a metal detector multifunctional in identifying and recognizing non-ferrous metals, ferrous metals, with minimal sensitivity to soil characteristics, focus on the low-frequency and mid-frequency ranges ranging from 30 kHz to 3 MHz. Operating in this frequency range allows the use of a simple metal detector to detect targets of any type of metal.
Search method
There are more than a dozen methods for finding metal objects using a directed electromagnetic field, including ultra-modern digital processing of the secondary signal on a computer when using MI professionally. When assembling homemade metal detectors for metal detecting at the amateur level, craftsmen focus on techniques that make it possible to simplify the circuit design of the detector as much as possible and reduce the cost of its configuration. The most popular methods for making homemade products are the following metal detection methods:
- parametric method, for the implementation of which a receiver is not needed;
- transceiver method - using a transmitter and receiver;
- method with phase accumulation - “until a click”;
- the beating method - “by squeaking”.
Parametric method
Parametric type metal detectors are equipped with only one coil, which is both transmitting and receiving. When a metal target is detected, the parameters of the generating coil change: inductance, frequency and amplitude of the generated oscillations, which is recorded by the MI equipment. The main problem when operating a detector without a receiver is the isolation of a relatively weak induced signal against the background of a powerful primary electromagnetic field.
Transceiver method
The design of models operating using the “receive-transmit” method has two coils:
- transmitting – for generating an electromagnetic field;
- receiving - for recording the signal re-emitted from a metal target.
Important! When assembling the transceiver MI, the coils must be positioned in such a way as to minimize the inductive coupling between them. If the axes of both coils are mutually perpendicular, the transmitter signal will not go directly to the receiving device and will not be listened to.
Metal detectors with phase accumulation (until a click)
The operation of phase-sensitive devices uses the process of delaying pulses during re-emission, which leads to an increase in the phase shift. When a specific value is reached, the discriminator is triggered and a click is heard in the headphones. As you approach a metal object, the clicks become more frequent, merging into a sound of a certain tonality. When the sound is adjusted appropriately, synchronization is disrupted directly above the object, and the sound disappears due to the transition of the click frequency to the ultrasonic range.
Metal detectors using beats (the “squeak” method)
If you make a metal detector using beats, then in your homemade design you need to use two electromagnetic field generators:
- a reference oscillator, the frequency of which is stabilized and is the reference frequency parameter;
- a working (search) generator, the frequency of which depends on the presence of metal in the search area.
Before the start of search work, the search generator is tuned to zero beats (frequency matching). When setting up, they achieve a low sound tone (squeak) so that it is convenient to search. By changing the tone, the properties of the detected object and its location are judged.
In Fig. Below is a homemade MI made from scrap materials.
Schemes of homemade MI
Factory-made metal detecting equipment is presented on the market with quite expensive professional-level electronic systems, so enthusiasts constantly exchange information on how to make a homemade metal detector at home with minimal financial costs. Step-by-step instructions for assembling and debugging the device allow you to create a fully functional metal detector from available radio components. Metal detectors, including a do-it-yourself mine detector, the circuit of which is identical to those developed for standard MIs, are made using transistors and microcircuits. The kit for DIY circuits also includes:
- capacitors of various types: ceramic, film, electrolytic;
- resistors;
- resonators;
- controllers.
Additional Information. Quite often, circuits of amateur metal detecting equipment use the NE 555 microcircuit, which is a universal timer that generates single and repeating pulses with stable timing characteristics.
A worthy competitor to a metal detector on microcircuits is a metal detector on transistors, in which signals are generated using transistors KT-361 and KT-315 or similar radio components produced since Soviet times.
Do-it-yourself manufacturing of MI components
When designing a homemade metal detector, craftsmen focus on creating a small-sized, structurally balanced, relatively lightweight product. The mobile design and thoughtful ergonomics should minimize operator fatigue during hours of continuous search work, and high-quality assembly of the home-made structure will ensure good repeatability of results and high performance characteristics.
Homemade MI consists of the following components:
- control unit;
- frames with search coil;
- a holding rod on which the search coil and control unit are mounted.
Control block
To assemble the control unit, you need to select a box-type plastic case. The housing should compactly accommodate:
- printed circuit board with electronic filling, assembled in accordance with the circuit diagram;
- batteries;
- devices for sound and visual notification of a find.
The main element of the control unit is the printed circuit board.
Making your own MI printed circuit board
A printed circuit board is used for compact placement of radio components included in the MI circuit. Below is a generalized description of the stages of self-manufacturing a printed circuit board with a detailed description of the operations performed:
- The metal detector circuit is selected. In accordance with the diagram, a sketch of the board is drawn on paper by hand or printed on a printer.
- A piece of sheet PCB is cut to fit the dimensions of the board.
- Using any available method, the design is transferred to a textolite blank.
- The mounting locations for radio components are marked on the surface of the workpiece. Holes with a diameter of 1.0-1.5 mm are drilled.
- Using a permanent marker or a brush with varnish, traces are drawn in accordance with the paper template.
- The board is etched with ferric chloride or copper sulfate.
- After etching, the board is wiped and cleaned with sandpaper.
- Tinning operation is carried out.
In Fig. Below is a printed circuit board of the metal detector after tinning.
Frame with reel
The search frame of a metal detector is a flat, rigid body with a search coil mounted on it, designed to perform the following tasks:
- rigid fixation of the search coil relative to the holder rod;
- ensuring the constancy of the geometric dimensions of the emitting and receiving loops of the search coil;
- protecting coil wires from damage when the operator moves over rough terrain.
The body of the MI frame, round or rectangular in shape, is made of plastic tubes without the use of metal elements. PVC pipes with a nominal diameter of ½ inch (15 mm) are popular among craftsmen. Small frames are made non-separable in the form of a ring or square. When making a large rectangular body, it is appropriate to use fittings so as not to deform the tubes at bends. The size and shape of the housing must correspond to the size and configuration of the coil, taking into account the placement of the transmitting and receiving circuits in it.
The most important search element of the MI, which determines its operational characteristics, is the search coil.
MI coils
The functional properties of the MI are determined by the quality of manufacture of the search coil. The coil parameters and the general circuit of the metal detector need to be mutually adjusted until the optimal result is achieved. The performance of the coil is influenced by various factors, of which the following are decisive:
- coil dimensions;
- design of the coil ring;
- coil inductance value;
- degree of noise immunity;
- method of winding the wire of a basket coil;
- way to secure the coil.
Coil dimensions
Practice has shown that the efficiency of a coil directly depends on its size. Larger coils are able to penetrate deeper into the ground and cover a wider search area than their smaller diameter counterparts. The following gradation of search coil sizes is accepted:
- a diameter of 20-90 mm is optimal for searching for ferrous metal (fittings, profiles);
- diameter 130-150 mm is convenient for searching for so-called “beach gold”;
- diameter 200-600 mm is aimed at large metal objects.
Coil design
The classic design of a search coil is a monoloop (single loop), made in the form of a single flat ring of turns of copper wire. The width and thickness of the ring are selected 15-20 times less than the average diameter of the ring. Monoboop MIs are recommended for beginners to gain initial searching experience.
A more “advanced” design, compared to a monoloop, is the DD coil, which is a double detector (hence the name - from the English Double Detector). Structurally, the DD coil is made of two semicircles folded with an intersection. DD coils are highly sensitive, but on heterogeneous soils they can give a false signal.
Coil inductance
When assembling a MI at home, it is very important to ensure that the parameters of a self-made search coil match the parameters that are included in the selected detector circuit. The inductance value is influenced by the geometric dimensions of the coil, wire cross-section, number of turns, packing density and other factors. In networks you can find various methods for calculating inductance, simple formulas and nomograms with explanations of how to use them. Failure to follow these recommendations may result in the assembled circuit not working.
Coil noise immunity
Since the monoloop is designed similarly to a loop antenna, it is susceptible to a lot of interference. To expand the noise immunity capabilities of the device, simple devices such as:
- Faraday shield, which is a steel tube with braiding or foil winding;
- symmetrical windings of bifilar or cross type.
Basket reels
In Fig. Below is one of the modifications of the MI basket coil.
For all its advantages, the basket reel is endowed with two significant disadvantages:
- complexity and labor intensity of performing high-quality reliable winding;
- Calculation methods for flat and volumetric baskets differ significantly and require the use of appropriate computer programs.
Important! When making handicraft winding of a basket coil, the mandrel must be rigid and strong, since the total tension force of all the turns is large enough to deform or break the mandrel.
To prevent the wires stretched during winding from cutting through the coil frame, it is recommended to first glue pieces of durable plastic into the slots of the frame and only then begin winding.
Reel mount
Fastening the coil wire is quite often done on homemade frames made of plywood, plastic and other improvised materials, even on computer disks. Plywood has many disadvantages, including:
Polycarbonate-based plastics do not have these disadvantages. Moreover, two glued polymer disks form a sealed housing, expanding the possibilities of using the MI.
Homemade rod holder
The holder rod is the supporting element of the metal detector - the search coil and control unit are attached to it. The main requirement for the rod is the strength of the manufacturing material, since the holder is subject to constant weight load from the operator during search operations. Damage to the supporting structure can occur in rough terrain, forest plantations, and mountainous areas. Breakage of the rod may lead to forced cessation of search operations.
Note! There are no specific requirements for the metal detector rod; each MI user has the right to adjust the size and shape of the holder to his height and weight.
When independently manufacturing a metal detector for the housing of a rod-holder, elbow crutches (canadians) are often used as an initial semi-finished product, the design of which already provides for height adjustment of the stand and an armrest support. Also popular among craftsmen are telescopic fishing rods and ordinary metal-plastic water pipes, which are used to make full-fledged MI holders.
Homemade underwater metal detector
The process of manufacturing, assembling and setting up a metal detector designed for underwater metal detection is identical to the work on creating a conventional MI. However, it is necessary to point out two significant differences that accompany the manufacture of underwater MI:
- all equipment must be placed in a sealed housing that does not allow parts to come into contact with moisture;
- To report a discovery from under the water, it is advisable to use special light indicators.
Stages of making an underwater MI with your own hands:
- Selecting a circuit for working in river and sea water.
- Manufacturing of printed circuit board.
- Connecting the power supply.
- Placing the finished board with a power supply in a sealed container. Craftsmen recommend using a sealant tube as a housing. LED indicator lights are displayed on the outer surface of the tube. Each joint is additionally sealed with silicone sealant.
- Making a rod from a thin-walled stainless pipe or an ordinary plastic water pipe. The body of a fishing rod is used quite often.
Important! The bar should not be too light so as not to float, but also very heavy so as not to sink to the bottom.
- Fastening the assembled block with the printed circuit board to the rod.
- Winding the search coil. The reel body is a standard polypropylene pipe. The wound wire is filled with sealant.
- Soldering the coil leads to a stranded wire.
- Visual assessment of product tightness. Any cracks and joints that “do not inspire confidence” in terms of tightness are filled/covered with sealant.
- Checking for leaks in water.
Features of deep MI
Deep MI uses RF technology, which is effective in the high-frequency range. The transmitting and receiving coils are mutually perpendicular and can operate at several frequencies simultaneously. Deep devices are insensitive to small targets; their objects are large objects located in areas with differences in ground levels.
If you turn to the numerous forums of metal detecting enthusiasts that fill the Internet, you will notice the high level of manufacturing and adjustment of home-made structures that are described there. Self-made metal detectors are not inferior to factory-made search equipment, although they are many times cheaper. In Fig. Below is a homemade “deep sink”, the frame of which is made of durable polymer tubes.
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