It's almost like a treasure hunt. Some are stopped by the fact that they live far from mountains or rivers in order to search for nuggets by washing sand. Others do not understand radio components to know how to extract gold from them. And still others prefer to look for precious metal with a metal detector, but do not have the means 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, with the help of certain radiations, finds metal located underground, without direct contact with it. The response data that comes in helps identify the find and informs about it with an audible or visual signal.
The principle of operation of the metal detector
The electromagnetic field emitted by the device comes into contact with metals, in this case with gold, which provokes the occurrence of eddy currents on their surface. By measuring the electrical conductivity, metals are identified and this data 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 an output.
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 as tiny nuggets, so higher sensitivity is needed. If there is such an opportunity, then it is good to have a device with a multi-frequency adjustable search, then it will be possible to increase the number of objects that it recognizes.
Among all the schemes of metal detectors on the Internet, experts advise choosing devices with balanced induction, which have two coils in the head and a powerful electronic circuit. Of great interest are also circuits that have the principle of operation of a receiver-transmitter 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 applied to the construction of a metal detector. Much depends on the conditions in which it will be operated. 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;
- power consumption - how much the device consumes and how much the built-in battery or batteries last;
- penetrating power - the depth at which the device can recognize metals;
- device dimensions;
- search area size - the area that the device covers 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 generator frequency, you can achieve an increase in the search area and penetration, but lose in sensitivity, as well as mobility due to an increase in the size of the coil.
Scheme of a simple metal detector The design feature of the metal detector is that all of the above parameters in combination or individually depend on the frequency of the coil. Thus, this characteristic is decisive in the design of 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;
- increased frequency: tens of kHz, the design is simple, the permeability is up to 1.5 m, the noise immunity is poor, the discrimination is so-so, the sensitivity is good;
- high-frequency: radio frequencies, typical "for gold", discrimination is excellent, the permeability is small, up to 80 cm, low consumption, other parameters are poor.
Instrument design
A device that does not require absolutely no knowledge in radio engineering can be assembled with your own hands, having: a calculator, a radio receiver, a box with a plastic or cardboard hinged lid, and double-sided tape. The calculator should be as cheap as possible to serve as the basis of radio interference, and the receiver should not have noise immunity.
Do-it-yourself metal detector, instructions:
- We unfold the box, forming a book out of it.
- We fix the calculator and the receiver in the box, the last one in the lid.
- We turn on the receiver and look for a free section at the top of the AM band.
- We turn on the calculator: the receiver should make a sound, set it to maximum volume.
- If there is no tone, adjust until it appears.
- We fold the lid so that the tone disappears. In this position, the magnetic vector of the primary impulses 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 get more data, you already need to have some knowledge and skills in radio electronics. On the Internet you can find a suitable one from a variety of schemes.
A device that allows you to search for metal objects located in a neutral environment, for example, the ground, due to their conductivity is called a metal detector (metal detector). This device allows you to find metal objects in various environments, including in the human body.
Largely due to the development of microelectronics, metal detectors, which are produced by many enterprises around the world, have high reliability and small overall weight characteristics.
Not so long ago, such devices could most often be seen with sappers, but now they are used by rescuers, treasure hunters, public utilities workers when searching for pipes, cables, etc. Moreover, many "treasure hunters" use metal detectors that they assemble with their own hands .
The design and principle of operation of the device
Metal detectors on the market operate on different principles. Many believe that they use the principle of pulsed echo or radar. Their difference from locators lies in the fact that the transmitted and received signals operate constantly and simultaneously, in addition, they operate at the same frequencies.
Devices operating on the principle of "reception-transmission" register the signal reflected (re-radiated) from a metal object. This signal appears due to the impact on the metal object of the variable magnetic field, which is generated by the metal detector coils. That is, the design of devices of this type provides for the presence of two coils, the first is transmitting, the second is receiving.
Devices of this class have the following advantages:
- simplicity of design;
- great ability to detect metallic materials.
At the same time, metal detectors of this class have certain disadvantages:
- metal detectors can be sensitive to the composition of the soil in which they search for metal objects.
- technological difficulties in the production of the product.
In other words, devices of this type must be configured by hand before operation.
Other devices are sometimes referred to as a beat detector. This name comes from the distant past, more precisely from the time when superheterodyne receivers were widely used. Beating is a phenomenon that becomes noticeable when two signals with close frequencies and equal amplitudes are summed. The beating consists in pulsing the amplitude of the summed signal.
The pulse frequency of the signal is equal to the difference in the frequencies of the summed signals. By passing such a signal through a rectifier, it is also called a detector, the so-called difference frequency is isolated.
Such a scheme was used for a long time, but today, it is not used. They were replaced by synchronous detectors, but the term remained in use.
The beat metal detector works using the following principle - it registers the frequency difference from two generator coils. One frequency is stable, the second contains an inductor.
The device is set up by hand so that the generated frequencies match or at least are close. As soon as metal enters the coverage area, the set parameters change and the frequency changes. Frequency difference can be registered different ways ranging from headphones to digital methods.
Devices of this class are characterized by a simple sensor design, low sensitivity to the mineral composition of the soil.
But besides this, during their operation it is necessary to take into account the fact that they have high energy consumption.
Typical design
The structure of the metal detector includes the following components:
- The coil is a box-type design, it houses the receiver and transmitter of the signal. Most often, the coil has an elliptical shape and polymers are used for its manufacture. A wire is connected to it, connecting it to the control unit. This wire transmits the signal from the receiver to the control unit. The transmitter generates a signal when metal is detected, which is transmitted to the receiver. The coil is installed on the lower rod.
- The metal part on which the coil is fixed and its angle of inclination is adjusted is called the lower rod. Thanks to this solution, a more thorough examination of the surface occurs. There are models in which the lower part can adjust the height of the metal detector and provides a telescopic connection with the rod, which is called the middle one.
- The middle shaft is the node located between the lower and upper shafts. Fixtures are fixed on it, allowing you to adjust the size of the device. on the market you can find models that consist of two rods.
- The top bar is usually curved. It resembles the letter S. This form is considered optimal for fixing it on the hand. An armrest, a control unit and a handle are installed on it. The armrest and handle are made of polymeric materials.
- The metal detector control unit is required to process the data received from the coil. After the signal is converted, it is sent to headphones or other means of indication. In addition, the control unit is designed to adjust the operating mode of the device. The wire from the coil is connected using a quick-release device.
All devices included in the metal detector are waterproof.
This is the relative simplicity of the design and allows you to make metal detectors with your own hands.
Varieties of metal detectors
The market offers a wide range of metal detectors used in many areas. Below is a list that shows some of the varieties of these devices:
Most modern metal detectors can find metal objects at a depth of up to 2.5 m, special deep products can detect a product at a depth of up to 6 meters.
Operating frequency
The second parameter is the frequency of operation. The whole point is that low frequencies allow the metal detector to see to a fairly large depth, but they are not able to see fine details. High frequencies allow you to notice small objects, but do not allow viewing the ground to a great depth.
The simplest (budget) models operate at one frequency, models that are classified as average price levels use 2 or more frequencies in operation. There are models that use 28 frequencies when searching.
Modern metal detectors are equipped with such a function as metal discrimination. It allows you to distinguish the type of material located at depth. At the same time, when ferrous metal is detected, one sound will sound in the searcher's headphones, and another when non-ferrous metal is detected.
Such devices are referred to as pulse-balanced. They use frequencies from 8 to 15 kHz in their work. Batteries of 9 - 12 V are used as a source.
Devices of this class are able to detect a gold object at a depth of several tens of centimeters, and ferrous metal products at a depth of about 1 meter or more.
But, of course, these parameters depend on the device model.
How to assemble a homemade metal detector with your own hands
There are many models of devices on the market for searching for metal in the ground, walls, etc. Despite its external complexity, making a metal detector with your own hands is not so difficult and almost anyone can do it. As noted above, any metal detector consists of the following key components - a coil, a decoder and a power supply signaling device.
To assemble such a metal detector with your own hands, you need the following set of elements:
- controller;
- resonator;
- capacitors of various types, including film ones;
- resistors;
- sound emitter;
- Voltage regulator.
The simplest do-it-yourself metal detector
The metal detector circuit is not complicated, and you can find it either in the vastness of the global network, or in specialized literature. Above is a list of radio elements that are useful for assembling a metal detector with your own hands at home. A simple metal detector can be assembled by hand using a soldering iron or other accessible way. The main thing at the same time, the parts should not touch the body of the device. To ensure the operation of the assembled metal detector, power supplies of 9-12 volts are used.
To wind the coil, a wire with a cross-sectional diameter of 0.3 mm is used, of course, this will depend on the selected circuit. By the way, the wound coil must be protected from the effects of extraneous radiation. To do this, it is screened with your own hands using ordinary food foil.
To flash the controller, use special programs which can also be found on the Internet.
Metal detector without chips
If a novice "treasure hunter" has no desire to get involved with microcircuits, there are schemes without them.
There are more simple circuits based on the use of traditional transistors. Such a device can find metal at a depth of several tens of centimeters.
Deep metal detectors are used to search for metals at great depths. But it is worth noting that they are not cheap and therefore it is quite possible to assemble it with your own hands. But before you start making it, you need to understand how a typical circuit works.
Scheme deep metal detector not the easiest and there are several options for its implementation. Before assembling it, it is necessary to prepare the following set of parts and elements:
- capacitors of various types - film, ceramic, etc .;
- resistors of different ratings;
- semiconductors - transistors and diodes.
Nominal parameters, quantity depend on the selected circuit diagram of the device. To assemble the above elements, you will need a soldering iron, a set of tools (screwdriver, pliers, wire cutters, etc.), material for making the board.
The process of assembling a deep metal detector is approximately as follows. First, a control unit is assembled, the basis of which is a printed circuit board. It is made from textolite. Then the assembly scheme is transferred directly to the surface of the finished board. After the drawing has been transferred, the board must be etched. To do this, use a solution that includes hydrogen peroxide, salt, electrolyte.
After the board is etched, holes must be made in it to install the circuit components. After the board has been tinned. The most important step is coming. Do-it-yourself installation and soldering of parts on a prepared board.
To wind the coil with your own hands, use a wire of the PEV brand with a diameter of 0.5 mm. The number of turns and the diameter of the coil depend on the chosen scheme of the deep metal detector.
A little about smartphones
There is an opinion that it is quite possible to make a metal detector from a smartphone. This is not true! Yes, there are applications that install under the Android OS.
But in fact, after installing such an application, he will really be able to find metal objects, but only pre-magnetized ones. He will not be able to search and, moreover, discriminate against metals.
I present to you the scheme and design a simple DIY metal detector
Fig.1. Schematic diagram of a metal detector
The circuit is based on two NE555 chips. There is a transmitting (Tx) and receiving (Rx) coils here, so the circuit can be divided into two parts. The left side is a generator rectangular pulses. The timing components R1, R2, C1 are selected so that the output frequency is about 700 Hz. This is the frequency of the audible range. The pulses are transmitted through a current-limiting resistor R3.
Both coils are located in space in such a way that they together form a certain overlap zone and the system is in induction balance. At the same time, there is zero voltage in the receiving coil and the right side of the circuit does not react in any way. If a metal object appears nearby, then an imbalance occurs and an audible signal appears.
The signal from the receiving coil is amplified by the transistor VT1 and fed to the input of the second microcircuit. As bipolar transistor VT1 used KT3102EM, it can be replaced by any similar one with a high gain. With the help of four resistors R5 - R8, a voltage divider is formed. Variable resistors are used to adjust the metal detector. R6 is a trimmer and is adjusted after the mutual placement of the coils. And R7 and R8 are used for coarse and fine tuning, they should be installed on the body of the device (provide easy access to them).
The sound signal is created thanks to the BA1 piezo emitter, which can be taken from an unnecessary multimeter. But when testing the circuit, I liked the sound of a piezo emitter with a built-in generator. Despite the fact that a pulse signal is generated at the output of DD2, it will not only signal well, but will also allow you to catch the slightest sound changes when a metal object is detected.
Creating coils
To wind the metal detector coils, you will need an enameled winding wire with a diameter of 0.3 mm or more. In my case, the maximum allowable diameter of 0.7 mm was used.
The optimal diameter of the coil winding is approximately 15-16 cm. You should pick up some kind of round object (for example, a bucket) to wind the coil around it. But you can use the tool. To do this, on a clean wooden surface, you need to hammer nails in a pre-drawn circle.
The inner diameter in my case is 15.5 cm. I wound 25 full turns. The number of turns can and even needs to be done more than mine, for example, about 50 turns. The winding wire itself can be taken from unnecessary electric motors or power transformers.
When the coil is wound, carefully remove it from the device and wrap it with paper tape. As a result, it is necessary to make two absolutely identical coils. Next, scrape off the varnish with a knife and, after cleaning, these ends need to be tinned.
The windings tend to bend and lose the correct geometry, so the coils must be completely wrapped, for example, with paper tape. After that, they need to be flattened a little where they overlap each other. Often they are made to look like the letter "D" as shown in the figure below.
It is convenient to use a sandwich panel as a base for search coils, which is used for slopes of plastic windows.
The board will be some distance away from the searchcoils and it is not recommended to use regular wires. To connect the coils to the board, I used a shielded wire, if I'm not mistaken from a microphone.
Shielded wire for connecting the coils to the board.
The central wire must be soldered to the beginning of the coil, and the other to the power minus as shown above.
For both coils, of course, the wires will be separate so that there is no interference.
Location and setting of coils
The setup of the system begins before the coils are glued to the base.
We set the tuning resistor R6 to approximately 90 kOhm, and set the adjusting resistors R7 and R8 to the middle position. Now you need to move the coils. The device will emit sound in two positions. With wide and narrow overlap. I suggest locking the coils at their narrow overlap as shown in the picture below (position 2). According to my observations, in position 2, the sensitivity is better and more accurate positioning occurs.
After that, you need to properly glue to the base. I did this with hot glue. But if you wish, you can make recesses for the coils in the base and fill them with epoxy.
After the glue has hardened, you need to adjust the settings again. We do not touch R7 and R8 yet, they are set to the middle position and the resistor R6 needs to achieve such a position at which the sound emitter crackles a little and, so to speak, is in the borderline position between silence and beeping (on the verge of breakdown). In the future, when using a metal detector, you only need to adjust the position of R7 and R8. This is due to the fact that the device is not perfect, the coils are not shielded, and the settings will deteriorate if the battery voltage is lost.
Refinement option
Optionally, you can make additional refinement of the coils - shielding from external electromagnetic fields ("Faraday shield"). This is done after the initial covering of the windings, which was described earlier (with paper tape or electrical tape). Then you need to take long strips of aluminum foil and wrap the coils. This is not done completely, but a gap of about 1-2 cm is left at the point where the wires exit. The foil connects with end coils and connects to the minus power supply. After that, the coil is covered with electrical tape.
I did not do this, because I was afraid of loss of sensitivity.
Metal detector design
After soldering the components, it is desirable to remove the remaining flux and rosin from the surface of the board, because. they can adversely affect the operation of the circuit.
I decided to place the board in a metal box, and so that there was no short circuit with soldered joints, the bottom of the case was covered with electrical tape. Later I will most likely pick up a plastic case.
Always pay attention to the rigidity of the cable fastening, as It will be a shame if something gets soldered during use.
The circuit will be powered by a "crown" battery. The circuit has low power consumption, but still it is better to put an alkaline battery, it will ensure the operation of the device for several "cops".
The handle was made of a metal-plastic water pipe, and closer to the base it was continued with plastic tubes so that the coils would not react to the metal-plastic handle itself. The design is pretty light. The shielded wires were laid with electrical tape. I installed the box with the metal detector board higher so that the adjusting resistor was at hand.
Advice
Each time before using the metal detector, you should use a variable resistor to achieve a quick crackle of the emitter. The faster the crackle, the greater the sensitivity.
First find
Experiment: I buried a coin with a diameter of 2.5 cm in the ground at a depth of 25 cm. When scanning, the coils were at a distance of 5 cm from the ground. At the same time, the metal detector emitted a distinct signal. I suppose that large metal objects will "ring out" deeper.
In any case, it takes me some time to get used to the metal detector and, after some searching, to sum up the final results of its abilities.
This article has a video that shows the process of creating a metal detector and its test.
List of radio elements
| Designation | Type of | Denomination | Quantity | Note | Score | My notepad |
|---|---|---|---|---|---|---|
| DD1, DD2 | Programmable timer and oscillator | NE555 | 2 | To notepad | ||
| VT1 | bipolar transistor | KT3102EM | 1 | To notepad | ||
| R1 | Resistor | 1 kOhm | 1 | To notepad | ||
| R2 | Resistor | 100 kOhm | 1 | To notepad | ||
| R3 | Resistor | 470 - 680 Ohm | 1 | To notepad | ||
| R4 | Resistor | 2 - 2.2 MΩ | 1 | To notepad | ||
| R5 | Resistor | 10 kOhm | 1 | To notepad | ||
| R6 | Trimmer resistor | 100 kOhm | 1 | To notepad | ||
| R7 | Variable resistor | 100 - 500 kOhm | 1 | coarse tuning |
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. Enough to assemble it yourself. And he will find it too.
By the way, I will say that I saw a report on TV, as a man who assembled a metal detector and searched for scrap metal with it, found a box with cartridges from the times of 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 it will not work 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 transistors KT315 or similar;
~ two capacitors 1000 pF;
~ two capacitors 10000 pF;
~ two resistors 100 kOhm.
In addition, the following will come in handy: a 3.7-5 volt battery, headphones, wire in enamel insulation with a diameter of 0.5-0.7 mm.
The assembly scheme is the simplest!
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 case is made of any material, preferably sealed. The bar can be piled from pipes. The coils are placed on the same plane at a distance of 10 cm.
If, when the device is turned on, a squeak appears in the headphones, then it means that the device needs to be adjusted - to change the distance between the coils. Or tune with ferrite.
Thus, you can earn 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 this post are mine and were taken in 2014. And the first picture with the scheme is taken from open sources.
How to make a simple metal detector for searching on the beach
In this article I will show you how to assemble a simple metal detector to search for coins and jewelry on the beach. It consists of one microcircuit - the NE555N timer, a coil and several other radio components.
Expect to spend up to 300 rubles on the construction of this metal detector!
Required Materials
To assemble a metal detector you will need:
- timer chip NE555N, in a DIP package;
- resistor 47 kOhm;
- two capacitors 2.2 uF, 16 V;
- a piece of contact breadboard;
- 9 volt battery, switch, battery block;
- electromechanical sound emitter;
- 100 meters of copper wire with a diameter of 0.2 mm;
- some thick cardboard and glue.
Instead of an electromechanical sounder, you can use a 10 uF capacitor and any speaker with an impedance of 8 ohms, connected in series.
Metal detector scheme
The idea of a metal detector is taken from the book " 499 circuits on the NE555 timer". I just added a switch between the battery and the chip, and I also use an electromechanical buzzer 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 should have about 260 turns of 0.2mm lacquered copper wire. At the same time, its inductance will just be about 10 millihenries.
I wound the coil carefully, coil to coil. 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 in order to increase the target detection range, then there are several on the network online calculators with which you can calculate it.
Circuit board
I posted everything electronic components on a piece of breadboard. The connections were made with the most common wire that was at hand. The soldering of 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
For simplicity, I decided to make the handle of the metal detector out of cardboard. A circuit board, a switch and a battery are installed in the handle.
All this was cut out of thick cardboard and glued with PVA glue. After the glue had dried, I made holes in the cardboard for the board and wires.
Then, I glued the searchcoil to the handle with hot glue. The last step I, also using hot glue, glued the board and the battery inside the handle.
Conclusion
The metal detector works as follows: while there are no metal objects near the coil, the sound emitter beeps with the same frequency; when a metal object is presented, 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 kid FM-2 improved
I present to your attention a diagram of a more improved metal detector Malysh FM-2. The metal detector kid fm2 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, and perhaps collected, such metal detectors as the "Kid" and "Kid FM-2". But progress does not stand still and therefore we have a scheme for a more improved metal detector Malysh FM-2. AT new version added LED indication of metals, added power-on notification function, increased notification sound, the device became much more stable in operation.
Scheme of the improved metal detector Kid FM-2
Specifications and features:
- Supply voltage - 9 Volts
- The depth of detection of metals is about 15 cm.
- Selection of metals - black, non-ferrous
- LED indication of metals - black, color
- Power on indicator
So, this circuit board of the Kid 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 regulator AMS1117 -3.3v
This is how the finished board of the “Kid FM-2” metal detector looks like
View from the paths
After assembling the board, we proceed to the manufacture of the coil.
The standard coil contains 150 turns, wire diameter 0.3, and wound on a mandrel 150 mm. But I decided to slightly reduce the diameter to 10-11 cm in order for the metal detector to see small objects better, the detection depth decreases but the sensitivity increases. I did not have a 0.3 wire, and therefore wound 0.4 on a 10 cm rim, 130 turns.
So, after the coil is wound, it is necessary to tighten it very tightly with tape.
Now it is necessary to shield the coil so that the metal detector does not react to interference and there are no false positives. We take food foil and tightly wrap the coil. Please note that the ends of the foil should not touch each other!
Then we take the wire, clean the end and wind it to one edge of the coil screen, then tighten it and wrap it tightly with tape again.
We connect the coil to the board. The wire from the screen must be soldered to the minus of the board.
Now it remains to flash the microcontroller and that's it, you can use it)
If you do everything correctly, then the device should work without problems when you first 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 “peak-fut”, which means that the device has turned on and is working correctly.
IMPORTANT! “According to the scheme, there are 8 resistances, and in the photo there are 9” - the 9th resistor (100 Ohm) I myself put it additionally on the second LED, although you can not put it! Diode 1N4007 can also be omitted, as I did!
Circuit board, firmware, as well as a list of parts that can be bought very cheaply on AliExpress from free shipping, located below the video!
Video of the metal detector kid FM-2 v2
Good do-it-yourself metal detector
The case was several years ago. I wanted to do something with my hands, and pass the evenings, bringing the treasure-hunting season closer. It was decided to assemble a metal detector. For assembly, I chose the “Pirate” metal detector scheme. Since it is not complicated, but the device itself is quite interesting. The assembly was started with a search for parts. I even had to go to the workshop for some resistors. When everything was found, it was necessary to prepare a printed circuit board, namely, to etch it using the LUT method. Then the matter was small: to solder all the details. Well, check the finished board. It didn't turn on the first time. The K157UD2 chip turned out to be faulty. By changing it, the scheme worked! 
Now you can do the body. In its capacity, the body was taken from Koschey 5I, a new front panel was made. It's about the coil. For the coil, a frame was cut with a jigsaw and a groove was machined along the side edge, where the coil winding was wound, a cable with a connector was soldered. The bar 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 end result is a quality device. Its only disadvantage is the lack of discrimination of metals. Therefore, it can be said that it is not suitable for searching for coins. After all, nails and coins ring the same way. 
But with its help, you can successfully dig scrap metal and take it to collection points, thereby earning money! There is a video with the test of this device. It was taken by me in the spring of 2015.
Many radio amateurs dream of making a metal detector with their own hands. With it, you can detect metal objects in the ground at different depths. On the Internet, you can find many photo metal detector circuits that are easy to use. Any novice radio amateur can make them.
Easy Assembly
For example, let's take a simple metal detector circuit. It belongs to the impulse type, but due to the simplicity of the design, it is not able to distinguish between varieties of metals. Therefore, it will not be possible to work with such a device in areas where non-ferrous metal objects are found.
How to assemble the device
To assemble a simple metal detector circuit with your own hands, you will need the following tools and parts:
- The presence of the KR1006VI1 chip, and the IRF740 transistor;
- The presence of a K157UD2 chip and a VS547 transistor;
- Copper conductor 0.5mm (PEV);
- NPN transistor;
- Case, and various materials for it;
- Solder, flux, soldering iron.
Other details are shown in the diagram. In order for the assembled circuit to be securely fixed, a plastic case should be prepared for it.
The bar can be made using a plastic tube of small diameter. A metal search coil will be installed in its lower part.
Beginning of work
The device circuit of a metal detector on transistors is a common option for many models. The assembly begins with the manufacture of the printed circuit board. Further, all radio elements are mounted on it exactly as shown in the diagram.
To ensure stable operation of the device, film capacitors are used in the circuit. This will allow you to use it without problems in cold weather.
Power type for the device
The device can operate from a voltage of 9-12 V. Due to its sufficient power, energy is intensively consumed. It is recommended to install up to 3 batteries and connect them in parallel circuit. You can use a small battery that has Charger. Due to its capacity, the metal detector will work longer.
Coil mounting
Available different types and schemes for the manufacture of metal detectors, but in the pulsed version, inaccuracies are allowed in the installation of the coil. In the manufacture of the mandrel, winding up to 25 turns should be made, and the diameter of the ring is 1900-200mm.
All turns of the coil must be insulated with electrical tape. Reducing the number of turns to 22, and a mandrel diameter of 270mm will allow you to detect objects at a deeper location. The cross section of the wire on the coil is 0.5 mm.
When the winding is ready, it is attached to a strong case with sufficient rigidity, on which there should be no metal parts. Otherwise, they are able to shield the magnetic field, and the operation of the metal detector will be disrupted. The body can be made of wood or plastic, but so that it can withstand various impacts that can damage the coil.
The findings on it should be soldered to a conductor of several cores. The best option considered to be a two-wire cable.
Mounting the circuit of a non-ferrous metal detector is a little more complicated, and high accuracy must be observed in the manufacture of the coil. The number of turns reaches 100 pieces, and a vinyl tube is used as a core. A foil is wound on top of the winding, which forms an electrostatic screen.
Instrument setup
If the installation of the circuit is done exactly, then the metal detector will not need additional setting. Its sensitivity indicators will be maximum, but fine adjustment is possible through the variable resistance R13. It must be performed until rare clicks begin in the headphones.
If the setting fails, then the resistance must be replaced with R12. When the resistor adjustment is in the middle, this will be considered normal.
An oscilloscope is suitable for checking the device. It measures the frequency of the transistor T2, and the pulse should last up to 150 msec. The optimum operating frequency is up to 150 Hz.
How to use the device
Do not rush and start working immediately after turning on the metal detector. It should stabilize, so you need to wait up to 20 seconds. After adjusting the resistor accordingly, you can start looking for metal.
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Photo of the metal detector circuit
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