A simple and powerful Soviet-era metal detector. Homemade metal detectors, or how to make a metal detector with your own hands. To understand the subject, consider the design and principle of operation of the device
Probably, what this electronic device is intended for, it is not necessary to tell. Everything is clear to everyone. These devices are used by sappers, at airports, in special services, in various institutions, one way or another related to security. But that is not all.
Metal detector in the 90s
These devices in the 90s of the twentieth century helped people not to die of hunger. At that difficult time, one could often see young people and not only those who walked the streets with metal detectors. The device was used to search for metals and alloys. In particular, in cities near which large industries were located, it was possible to dig out real wealth with it.
Basically, these guys made metal detectors with their own hands and looked for waste from metallurgical plants or native metals that remained in the bowels of the earth. The latter were used in the construction of tracks. After all, many asphalt, and even dirt, roads were covered with slag, and often in its composition one could find metal and an alloy of iron and manganese - ferromanganese. In the late 90s, it has already risen in price enough. In one day of such work on city and country roads, one could earn as much as a worker at a factory earned in a week. Since many people were out of work, this activity became especially popular. After all, this alloy is one of the components for creating steels of various grades at the same metallurgical industries.
Metal detectors today
To date, the topic of searching with the help of electronic devices has not been developed so massively. However, these devices are still popular among certain groups of people. They roam the places of former glory of the valiant Soviet soldiers, trying to dig up something valuable from the objects of history. For example, you can find coins from the times of the Patriotic War, German of course. And some people manage to dig up really valuable things. You just need to know where to look.
What can really be found?
If you yourself do not take the device in your hands and walk along the roads of the city or through memorable and historical places, you will hardly believe how many interesting objects the earth holds. And for this it is worth building a metal detector with your own hands.
coins
You can often dig them out. In the times of Ancient Russia, coins of the Arab East were used for trade. Then they used coins of Byzantine and Tatar production. Silver bullion is now found in the form of money.
Today in the Crimea (namely, where you can find well-preserved objects) you can see people with these devices.
Crosses, icons, serpentines
The cross in Ancient Russia was worn by every self-respecting Christian. All crosses were different from each other, depending on the type and its purpose. Often you can find the so-called vests.
Buckles, buttons, various household items
This group of items is very numerous. Most of them have been used since the Bronze Age and are still in use today. Often the objects were made of bronze, copper or iron.
Echoes of War
This is the most popular group of items that are targeted for search. They are especially popular with collectors. Enthusiasts are searching, getting, restoring. Something ends up in museums, something settles on the hands.
How to make a metal detector with your own hands
In the era of the popularity of ferromanganese and high prices for it, grubby youth did not shy away from digging in the ground to earn some money. More often they purchased devices to search for their prey in numerous markets or from various specialists who, by chance, were fired from radio factories or TV repair shops. One way or another, these professionals assembled the metal detector with their own hands from radio components remaining in stores using various schemes and technologies. The guys often argued about who had the better and more technologically advanced device. After all, then it was actually a working tool, and not a device for a hobby, as at the present time.
Do-it-yourself metal detectors were also made by those who knew at least a little about electronics. But these guys weren't interested in digging up a metallurgical ingredient from the ground. But it looks like we've gotten off topic.
Principle of operation
Before proceeding to the assembly of various circuits, you need to look at the principle of operation of these devices.
The operation of a metal detector is based on the principles of magnetic attraction. The device through one coil creates a magnetic field. The second receives feedback signals. Then, in case of a find, it sends a return signal through an audible signaling device. You can even make a special non-ferrous metal detector with your own hands.
The larger the coil, the more sensitive the instrument will be. Although in modern devices, and especially in industrial models, the coil is small. But there are amplifiers on microcircuits.
Types
The ultra-low frequency seeker is the simplest device. Every student knows how to make a metal detector with their own hands using an ultra-low-frequency circuit. But this does not mean that such a searcher is inefficient. Just the opposite. With proper tuning, you can achieve good results.
The pulse seeker is a deeper apparatus. With it, you can easily find jewelry, coins and other small things at great depths. Such schemes are popular among professional treasure hunters.
A device that works on beats makes it possible to detect absolutely any metal or mineral object in the bowels of the earth at a depth of up to a meter. It is designed for certain types of alloys. This is a cheap device to build.
The radio detector is able to find metals at a depth of up to a meter. Make it simple. This is a suitable device for beginners, but is not popular among diggers.
Primitive metal detector on a single transistor
If you still have a long-wave radio receiver in working condition at home, then even if you are poorly versed in electronics, you can assemble a metal detector attachment for this receiver.
To make a metal detector with your own hands, the circuit is drawn without much difficulty. The circuit diagram is the most common LC oscillator, designed for frequencies in the region of 140 kHz. The coil for the device, which is used as an oscillatory circuit, must contain 16 turns of the simplest insulated wire up to 0.5 mm in diameter. The coils must be laid on plywood of suitable dimensions. The resulting contour is fixed to the base with glue. This is how a do-it-yourself coil for a metal detector is usually made.
Required Parts
Resistors and capacitors for this device can be used absolutely any. As a transistor, a low-power high-frequency one with reverse conduction will suffice. This may be the popular and easily accessible KT315. Or KT3102 with any letter index.
To assemble this simple metal detector with your own hands, the circuit is assembled either by surface mounting or on a pre-prepared board made of getinax or textolite.
Setting up a simple metal detector
After the part is ready, you need to place it next to our coil. The device should have a comfortable handle. The radio receiver must be mounted on the handle of the finder, and then tuned to a frequency in the region of 140 kHz. You will hear a squeak or creak. If you bring the coil closer to a metal object, the sound in the headphones will change its tone.
Despite the fact that these are the simplest metal detectors in terms of design and scheme, it is elementary easy to make them with your own hands, the sensitivity of such devices makes it possible to work at depths of up to 200 mm.
High frequency finder
This assembly scheme is a little more complicated than the previous one. But also much more efficient. Its difference is that there are two coils.
The first is the outer contour. This coil creates a direct magnetic field. The second is the receiving circuit. This detail is designed to receive, process, amplify the signals that come from the ground.
We make a deep metal detector with our own hands
First you need to assemble the so-called command block. To create it, an old computer, the same old laptop or radio is suitable. Then you need to find the highest frequency in the AM band. You need to make sure that there is no radio station on the frequency.
search head
To assemble the search head, you need to cut two circles from thin plywood. One of them should have a diameter of about 15 cm, the second should be made a little smaller. This is done so that the rings can be inserted into each other. Then we need to cut out small pieces of wood so that our head rings are parallel.
After that, 10-15 turns of enameled wire with a cross section of 0.25 mm should be removed from the plates from the outer circle. You also need to fix the resulting design. To make it work, you need to connect the head from below, and the detector - from above.
It's time to turn on our frequency. In this case, a faint tonal sound will be heard. It's better to use headphones.
Metal detector "Pirate"
Assembling the device is quite easy. The device circuit does not contain programmable microcircuits, it is easy to make and configure this metal detector with your own hands. Detailed instructions will help. Also, this scheme does not contain expensive or scarce parts. "Pirate" in its parameters can surpass foreign, quite expensive industrial analogues.
Options
For power, you need from 9 to 12 V. The current that the device consumes is up to 40 mA. Sensitivity will be up to 150 cm, subject to large metal objects.
How is the element base for a metal detector made?
The "Pirate" type scheme consists of two nodes. This is a transmission circuit, which consists of a pulse generator on KR1006VI1 and a key from an IRF740 transistor. The receiver is made on the basis of the K157UD2 chip and the VS547 transistor.
The coil should be 190 mm in diameter. The number of turns on the PEV wire is 0.5 - 25. The transistor in the circuit can be pulled out of an ordinary economy light bulb or any mobile charger. A properly assembled metal detector "Pirate" with your own hands practically does not need to be adjusted.
"Terminator"
The device has good features. For example, the device will detect a coin with a denomination of 5 Russian rubles from 25 cm. The searcher will recognize a German military helmet from 80 cm. These values \u200b\u200bare given on the condition of a coil with a diameter of 240 mm. "Terminator" can recognize metals even at the maximum depth of work.
It is worth saying that beginners are unlikely to be able to assemble the Terminator metal detector with their own hands. The device requires careful adjustment. Even experienced craftsmen sometimes make mistakes when assembling this circuit. The main thing here is not to rush.
In order to assemble the Terminator, you will need a multimeter, as well as an oscilloscope and an LC meter. They are not available to everyone. However, you can try to create a special hardware-software complex based on an ordinary home personal computer.
Description
The terminator is a single-tone device that operates on pulsed beats. The finder is great for finding coins. Also, if you make small improvements, you can search for gold on the beaches, while completely ignoring any other metals. "Terminator" is also suitable for searching for any other objects from any alloys.
In conclusion
So, we found out how to make a Pirate metal detector with our own hands, we also examined the Terminator. As you can see, by devoting the minimum amount of free time and effort to the assembly, you can get a rather interesting, and most importantly, a workable tool with which you can find ancient objects, and possibly expensive coins.
Device search is just huge popularity. Looking for adults and children, and amateurs and professionals. They are looking for treasures, coins, lost things and buried scrap metal. And the main search tool is metal detector.
There is a great variety of different metal detectors for every “taste and color”. But for many people, buying a ready-made branded metal detector is simply financially expensive. And someone wants to assemble a metal detector with their own hands, and someone even builds their own small business on assembling them.
Homemade metal detectors
In this section of our website about homemade metal detectors, will be collected: best metal detector circuits, their descriptions, programs and other data for manufacturing DIY metal detector. There are no metal detector circuits from the USSR and circuits on two transistors here. Since such metal detectors are only suitable for a visual demonstration of the principles of metal detection, they are not at all suitable for real use.
All metal detectors in this section will be quite technologically advanced. They will have good search characteristics. And a well-assembled home-made metal detector will be a little inferior to factory counterparts. Basically, there are different schemes. pulse metal detectors and metal detector circuits with metal discrimination.
But for the manufacture of these metal detectors, you will need not only desire, but also certain skills and abilities. We tried to break down the schemes of the given metal detectors according to the level of complexity.
In addition to the basic data required for assembling a metal detector, there will also be information on the required minimum level of knowledge and equipment for self-manufacturing of a metal detector.
To assemble a metal detector with your own hands, you will definitely need:
This list will provide the necessary tools, materials and equipment for self-assembly of all metal detectors without exception. For many circuits, you will also need various additional equipment and materials, here are just the basic ones for all circuits.
- Soldering iron, solder, tin and other soldering accessories.
- Screwdrivers, pliers, wire cutters and other tools.
- Materials and skills for the manufacture of printed circuit boards.
- Minimum experience and knowledge in electronics and electrical engineering as well.
- As well as straight arms - they will be very useful when assembling a metal detector with your own hands.
Here you can find schemes for self-assembly of the following models of metal detectors:
 |
Principle of operation | IB |
| Metal Discrimination | there is | |
| Maximum search depth | ||
| there is | ||
| Operating frequency | 4 - 17 kHz | |
| Difficulty level | Average | |
 |
Principle of operation | IB |
| Metal Discrimination | there is | |
| Maximum search depth | 1-1.5 meters (Depends on coil size) | |
| Programmable microcontrollers | there is | |
| Operating frequency | 4 - 16 kHz | |
| Difficulty level | Average | |
 |
Principle of operation | IB |
| Metal Discrimination | there is | |
| Maximum search depth | 1 - 2 meters (Depends on the size of the coil) | |
| Programmable microcontrollers | there is | |
| Operating frequency | 4.5 - 19.5 kHz | |
| Difficulty level | Tall | |
You can buy for about 100-300 dollars. The price of metal detectors is strongly interconnected with their detection depth, not every metal detector can "see" coins at a depth of 15 cm. In addition, the presence of a metal type recognizer and interface type also greatly affects the cost of a metal detector, fashionable metal detectors are sometimes equipped with a display for convenient operation .
This article will consider an example of assembling a powerful metal detector called Pirat with your own hands. The device is able to catch coins underground at a depth of 20 cm. As for large objects, it is quite possible to work at a depth of 150 cm.
Video of working with a metal detector:
This metal detector received such a name due to the fact that it is a pulse, this is the designation of its first two letters (PI-impulse). Well, RA-T is consonant with the word radioskot - this is the name of the developers' site, where the homemade product was posted. According to the author, the Pirate is going to be very simple and fast, even basic skills in working with electronics are enough for this.
The disadvantage of such a device is that it does not have a discriminator, that is, it cannot recognize non-ferrous metals. So working with him on areas contaminated with various kinds of metals will not work.
Assembly materials and tools:
- microcircuit KR1006VI1 (or its foreign analogue NE555) - a transmitting node is built on it;
- transistor IRF740;
- K157UD2 microcircuit and VS547 transistor (the receiving unit is assembled on them);
- wire PEV 0.5 (for winding the coil);
- NPN type transistors;
- materials for creating the body and so on;
- electrical tape;
- soldering iron, wires, other tools.
The remaining radio components can be seen in the diagram.
You also need to find a suitable plastic box for mounting the electronic circuit. You will also need a plastic pipe to create a rod on which the coil is attached.
Metal detector assembly process:
Step one. We create a printed circuit board
The most difficult part of the device is, of course, the electronics, so it is advisable to start with it. First of all, you need to make a printed circuit board. In total there are several options for boards, depending on the radio elements used. There is a board for NE555, and there is a transistor board. All the necessary files for creating the board are in the article. You can also find other board options on the Internet.
Step two. We install electronic elements on the board
Now the board needs to be soldered, all electronic elements are installed exactly as in the diagram. In the picture on the left you can see the capacitors. These capacitors are film type and have high thermal stability. Thanks to this, the metal detector will work more stably. This is especially true if you use a metal detector in the fall, when it is already quite cold outside.
Step three. Power supply for metal detector
To power the device, you need a source from 9 to 12 V. It is important to note that the device is rather voracious in terms of energy consumption, and this is logical, because it is powerful. One krone battery is not enough for a long time, it is recommended to use 2-3 batteries at once, which are connected in parallel. You can also use one powerful battery (best rechargeable).
Step four. Assembling a coil for a metal detector
Due to the fact that this is a pulse metal detector, the accuracy of the coil assembly is not so important here. The optimal diameter is a mandrel of 1900-200 mm, in total you need to wind 25 turns. After the coil is wound, it must be carefully wrapped on top with electrical tape for insulation. To increase the detection depth of the coil, you need to wind it on a mandrel with a diameter of about 260-270 mm, and reduce the number of turns to 21-22. The wire is used with a diameter of 0.5 mm.
After the coil is wound, it must be installed on a rigid body, there should be no metal on it. Here you need to think a little and look for any case that is suitable in size. It is needed in order to protect the coil from shock while working with the device.
The leads from the coil are soldered to a stranded wire with a diameter of about 0.5-0.75 mm. It is best if these are two wires twisted together.
Step five. Setting up a metal detector
When assembling exactly according to the scheme, it is not necessary to adjust the metal detector, it already has maximum sensitivity. To fine-tune the metal detector, you need to turn the variable resistor R13, you need to achieve rare clicks in the speaker. If this is achieved only in the extreme positions of the resistor, then it is necessary to change the value of the resistor R12. The variable resistor should adjust the device for normal operation in the middle positions.
No one needs to explain what a metal detector is. This device is expensive, and some models are very decent.
However, you can make a metal detector with your own hands at home. Moreover, you can not only save thousands of rubles on its acquisition, but also enrich yourself by finding a treasure. Let's talk about the device itself and try to figure out what's in it and how.
Step-by-step instructions for assembling a simple metal detector
In this detailed instruction, we will show how you can assemble the simplest metal detector from improvised means with your own hands. We will need: an ordinary plastic CD box, a portable AM or AM / FM radio receiver, a calculator, a VELCRO-type contact tape (Velcro). So let's get started!
Step 1. Disassemble CD box case. Carefully disassemble the case of the plastic CD case by removing the insert that holds the disc in place.
STEP 1. Removing the plastic insert from the sidyboxStep 2 Cut off 2 Velcro strips. Measure the area at the center of the back of your radio. Then cut out 2 pieces of Velcro the same size.
STEP 2.1. We measure approximately in the middle of the area on the back of the radio (highlighted in red) 
STEP 2.2. Cut out 2 Velcro of the appropriate size, measured in step 2.1 Step 3 Fasten the radio. Attach one sticky side of Velcro to the back of the radio and a second to one of the inside sides of the CD case. Then attach the radio to the body of the plastic CD box with Velcro to Velcro.
Step 4 Clip the calculator. Repeat steps 2 and 3 with the calculator, but apply Velcro to the other side of the CD case. Then attach the calculator to that side of the box using the standard Velcro to Velcro method.
Step 5 Setting the radio band. Turn on the radio and make sure it is tuned to the AM band. Now tune it to the end of the AM band, but not to the radio station itself. Turn up the volume. You should hear only one interference.
Clue:
If there is a radio station that is at the very end of the AM band, then try to get as close to it as possible. In this case, you should hear only one interference!
Step 6 Roll up the CD box. Turn on the calculator. Start rolling the side of the calculator box towards the radio until you hear a loud beep. This beep signals to us that the radio has picked up an electromagnetic wave from the calculator's electrical circuit.
STEP 6. We turn the sides of the CD box towards each other until a characteristic loud signal is heard Step 7 Bring the assembled device to a metal object. Open the plastic box again so that the sound we heard in step 6 is barely audible. Then start moving the box with your radio and calculator close to the metal object and you will hear the loud sound again. This indicates the correct operation of our simplest metal detector.
Instructions for assembling a sensitive metal detector based on a two-circuit oscillator circuit
Operating principle:
In this project, we will build a metal detector based on a double oscillator circuit. One oscillator is fixed and the other varies depending on the proximity of metallic objects. The beat frequency between these two oscillator frequencies is in the audio range. As the detector passes over a metal object, you will hear this beat frequency change. Different types of metals will cause a positive or negative shift, raising or lowering the audio frequency.
We will need materials and electrical components:
| Copper multilayer PCB, single-sided 114.3 mm x 155.6 mm | 1 PC. |
| Resistor 0.125W | 1 PC. |
| Capacitor, 0.1μF | 5 pieces. |
| Capacitor, 0.01μF | 5 pieces. |
| Capacitor, electrolytic 220μF | 2 pcs. |
| PEL winding wire (26 AWG or 0.4 mm in diameter) | 1 unit |
| Audio jack, 1/8', mono, panel mount, optional | 1 PC. |
| Headphones, 1/8' plug, mono or stereo | 1 PC. |
| Battery, 9 V | 1 PC. |
| 9V battery binding connector | 1 PC. |
| Potentiometer, 5 kOhm, audio taper, optional | 1 PC. |
| Switch, single pole switching | 1 PC. |
| Transistor, NPN, 2N3904 | 6 pcs. |
| Sensor wire (22 AWG or 0.3250 mm2) | 1 unit |
| Wired speaker 4′ | 1 PC. |
| Speaker, small 8 ohm | 1 PC. |
| Locknut, brass, 1/2′ | 1 PC. |
| Threaded PVC pipe connector (1/2' hole) | 1 PC. |
| 1/4′ wooden dowel | 1 PC. |
| 3/4′ wooden dowel | 1 PC. |
| 1/2′ wooden dowel | 1 PC. |
| Epoxy resin | 1 PC. |
| 1/4' plywood | 1 PC. |
| Wood glue | 1 PC. |
We need tools:
So let's get started!
Step 1: Make a PCB. To do this, download the board design. Then print it out and etch it onto the copper board using the toner-to-board transfer method. With the toner transfer method, you print a mirror image of the board design with a conventional laser printer, and then transfer the design onto the copper cladding with an iron. During the etching stage, the toner acts as a mask, keeping the copper tracks, while like the rest copper dissolves in chemical bath.
Step 2: Will fill the board with transistors and electrolytic capacitors . Start by soldering 6 NPN transistors. Pay attention to the orientation of the collector, emitter and base legs of the transistors. The base leg (B) is almost always in the middle. Next add two 220μF electrolytic capacitors.
Step 2.2. Add 2 electrolytic capacitors Step 3: Fill the board with polyester capacitors and resistors. Now we need to add 5 0.1μF polyester capacitors in the places shown below. Next, add 5 0.01μF capacitors. These capacitors are not polarized and can be soldered onto the board with the pins pointing in any direction. Next, add 6 resistors of 10 kΩ (brown, black, orange, gold).
Step 3.2. Add 5 0.01μF Capacitors 
Step 3.3. Add 6 resistors 10 kOhm Step 4: We continue to fill the electrical board with elements. Now we need to add one 2.2 mΩ resistor (red, red, green, gold) and two 39 kΩ resistors (orange, white, orange, gold). And then solder the last 1 kΩ resistor (brown, black, red, gold). Next, add pairs of wires for power (red/black), audio output (green/green), reference coil (black/black), and detector coil (yellow/yellow).
Step 4.1. Add 3 resistors (one for 2 mΩ and two for 39 kΩ) 
Step 4.2. Add 1 1 kΩ resistor (far right) 
Step 4.3. Adding wires Step 5: We wind the coils on the coil. The next step is to wind the turns on 2 coils, which are part of the LC generator circuit. The first is the reference coil. I used wire 0.4mm in diameter for this. Cut off a piece of dowel (about 13 mm in diameter and 50 mm in length).
Drill three holes in the dowel to pass the wires through: one lengthwise through the middle of the dowel, and two perpendicularly at each end.
Slowly and carefully wind as many turns of wire as you can around the dowel in one layer. Leave 3-4 mm of bare wood at each end. Resist the temptation to "twist" the wire - this is the most intuitive way to wind, but it's not the right way. You must rotate the dowel and pull the wire along with you. Thus, he winds the wire around himself.
Pull each end of the wire through the perpendicular holes in the dowel, and then one of them through the slotted hole. Secure the wire with tape once you're done. Finally, use sandpaper to remove the coating on the two open ends of the spool.
Step 6: We make a receiving (search) coil. It is necessary to cut the spool holder from 6-7mm plywood. Using the same wire 0.4 mm in diameter, wind 10 turns around the groove. My reel has a diameter of 152mm. Using a 6-7 mm wooden peg, attach the handle to the holder. Do not use a metal bolt (or something similar) for this - otherwise the metal detector will constantly detect treasure for you. Again, using sandpaper, remove the coating on the ends of the wire.
Step 6.1. Cut out the spool holder 
Step 6.2 We wind 10 turns around the groove with a wire 0.4 mm in diameter 
Step 7: Setting up the reference coil. Now we need to tune the frequency of the reference coil in our circuit to 100 kHz. For this I used an oscilloscope. You can also use a multimeter with a frequency counter for these purposes. Start by connecting the coil to the circuit. Next, turn on the power. Connect the probe from an oscilloscope or multimeter to both ends of the coil and measure its frequency. It must be less than 100 kHz. You can, if necessary, shorten the coil - this will reduce its inductance and increase the frequency. Then new and new dimensions. Once I got below 100kHz, my coil was 31mm long.
Metal detector on a transformer with Ш-shaped plates
The simplest metal detector circuit. We will need: a transformer with W-shaped plates, a 4.5 V battery, a resistor, a transistor, a capacitor, headphones. Leave only the W-shaped plates in the transformer. Wind 1000 turns of the first winding, and after the first 500 turns make a tap with PEL-0.1 wire. Wind the second winding 200 turns with PEL-0.2 wire.
Attach the transformer to the end of the rod. Seal it from water ingress. Turn on and close to the ground. Since the magnetic circuit is not closed, when approaching the metal, the parameters of our circuit will change, and the tone of the signal will change in the headphones.
A simple scheme on common elements. You need transistors of the K315B or K3102 series, resistors, capacitors, headphones, a battery. The ratings are shown in the diagram.
Video: How to make a metal detector (metal detector) with your own hands
A master oscillator with a frequency of 100 Hz is assembled on the first transistor, and a search oscillator with the same frequency is assembled on the second. As a search coil, I took an old plastic ladle with a diameter of 250 mm, cut it off and wound a copper wire with a cross section of 0.4 mm2 with 50 turns. I placed the assembled circuit in a small box, sealed it and fixed everything on the bar with adhesive tape.
Scheme with two generators of the same frequency. There is no signal in standby mode. If a metal object appears in the field of the coil, then the frequency of one of the generators changes and sound appears in the headphones. The device is quite versatile and has good sensitivity.
A simple scheme on simple elements. You need a microcircuit, capacitors, resistors, headphones, power supply. It is advisable to first assemble the L2 coil, as shown in the photo:
A master oscillator with an L1 coil is assembled on one element of the microcircuit, and the L2 coil is used in the search oscillator circuit. When metal objects enter the sensitivity zone, the frequency of the search circuit changes and the sound in the headphones changes. With the knob of the capacitor C6, you can rebuild unnecessary noise. A 9V battery is used as a battery.
In conclusion, I can say that every person who is familiar with the basics of electrical engineering and has enough patience to complete the work that has been started can assemble the device.
Principle of operation
So, a metal detector is an electronic device, where there is a primary sensor and a secondary device. The role of the primary sensor is performed, as a rule, by a coil with a wound wire. The work of the metal detector is based on the principle of changing the electromagnetic field of the sensor with any metal object.
The electromagnetic field created by the metal detector sensor causes eddy currents in such objects. These currents cause their own electromagnetic field, which changes the field created by our device. The secondary device of the metal detector registers these signals and signals us about the discovery of a metal object.
The simplest metal detectors change the sound of the signaling device when a desired object is detected. More modern and expensive samples are equipped with a microprocessor and a liquid crystal display. The most advanced firms equip their models with two sensors, which allows you to search more efficiently.
Metal detectors can be divided into several categories:
- public devices;
- middle class devices;
- devices for professionals.
The first category includes the cheapest models with a minimum set of functions, but their price is very attractive. The most popular brands in Russia: IMPERIAL - 500A, FISHER 1212-X, CLASSIC I SL. Devices of this segment use the “receiver-transmitter” scheme, operating at an ultra-low frequency and require constant movement of the search sensor.
The second category, these are more expensive units, have several interchangeable sensors and several control knobs. They can work in different modes. The most common models: FISHER 1225-X, FISHER 1235-X, GOLDEN SABER II, CLASSIC III SL.
Photo: general view of a typical metal detector All other devices should be classified as professional. They are equipped with a microprocessor, can work in dynamic and static modes. Allow to determine the composition of the metal (object) and the depth of its occurrence. Settings can be automatic, or you can adjust them manually.
To assemble a homemade metal detector, you need to prepare several items in advance: a sensor (a coil with a wound wire), a holding rod, an electronic control unit. The sensitivity of our device depends on its quality and size. The bar-holder is selected according to the height of the person so that it is convenient to work. All structural elements are fixed on it.
I propose for repetition personally assembled recently and successfully earned a simple metal detector. This metal detector works on the transmit-receive principle. A multivibrator was used as a transmitter, and an audio frequency amplifier was used as a receiver. The circuit diagram was published in Radio magazine.
MD receiver circuit - second option
Metal detector parameters
Operating frequency - about 2 kHz;
- detection depth of a coin with a diameter of 25 mm - 9 cm;
- an iron seaming lid from a can - 25 cm;
- aluminum sheet with dimensions 200x300 mm - 45 cm;
- sewer hatch - 60 cm.
The search coils connected to it must be exactly the same in size and winding data. They must be positioned so that in the absence of foreign metal objects there is practically no connection between them, examples of coils are shown in the figure.
If the transmitter and receiver coils are positioned in this way, then the transmitter signal in the receiver will not be heard. When a metal object appears near this balanced system, the so-called eddy currents arise in it under the influence of the alternating magnetic field of the transmitting coil and, as a result, its own magnetic field, which induces an alternating EMF in the receiving coil.
The signal received by the receiver is converted by phones into sound. The circuit of the metal detector is really very simple, but despite this, it works quite well, and the sensitivity is not bad. The multivibrator of the transmitting unit can also be assembled on other transistors of a similar structure.
The metal detector coils are 200x100 mm in size and contain about 80 turns of 0.6-0.8mm wire. To check the operation of the transmitter, instead of the L1 coil, connect headphones and make sure that sound is heard in them when the power is turned on. Then, having connected the coil in place, the current consumed by the transmitter is controlled - 5 ... 8 mA.
The receiver is tuned with the input closed. By selecting the resistor R1 in the first stage and R3 in the second, a voltage is set on the collectors of the transistors, respectively, equal to about half the supply voltage. Then, by selecting the resistor R5, it is ensured that the collector current of the transistor VT3 becomes equal to 5 ... 8 mA. After that, having opened the input, connect the L1 receiver coil to it and, receiving the transmitter signal at a distance of about 1 m, make sure that the device is working.
