home » Construction » A simple metal detector at home. Do-it-yourself metal detector: detailed instructions for assembling at home Choosing a do-it-yourself metal detector

A simple metal detector at home. Do-it-yourself metal detector: detailed instructions for assembling at home Choosing a do-it-yourself metal detector

Have you decided to figure out how to create a metal detector and try to make your own experimental device to get acquainted with the principle of operation and to test your own strength, but you don’t know where to start? Let's figure it out together, because recreating simple electronic circuits, including metal detectors, with your own hands is not so difficult.

Metal detector allows you to find objects that have certain electrical and electromagnetic properties that distinguish them from their environment. Such objects include, for example, various metals in the ground. Metal detectors are used by inspection services, the military, geologists, builders and specialists in a number of other professions to find metal in the soil and more.

Nowadays, a metal detector is often used by ordinary people to search for scrap metal from ferrous metallurgy and find non-ferrous metals that make up various coins, jewelry and military paraphernalia: shell casings, tokens and much more. Also, a metal detector can help in searching for items lost due to negligence that are vital or have material or moral value (parts of mechanisms, keys, rings, jewelry, etc.).

The sensitivity of this device depends on the diameter of the search coil. The larger its diameter (from 30 cm), the less sensitivity to small objects, but increases in sensitivity to large, deep ones. Conversely, the smaller its diameter, the better the reaction to smaller objects. Industrial designs provide detailed instructions on the sensitivity and use of the various coils.

Metal detector signal for large and small coins

In a homemade device, the dependence of its sensitivity on the diameter of the coil is also preserved. But you need to remember that a homemade device will be far from professional equipment in its qualities due to various nuances of the physical processes occurring. In one phrase, the operating principle of a metal detector can be described as follows: the coil sends electromagnetic waves and simultaneously reacts to inductively induced currents in the metal, which generate their own magnetic field under the influence of the coil winding.

In reality, the physical processes are much more complex, and the search for treasures with professional equipment (with selectivity and separation) is not as simple as it might seem, and the abundance of debris in the soil can completely discourage digging when a high-quality device beeps every time. Therefore, the device given below cannot guarantee lucky finds of unimaginable treasures, but it will help you understand from your own experience the very principle of interaction between metal and the search coil of a metal detector.

Creating a device of this type does not present any great difficulties; you just need to be able to understand circuits and use a soldering iron. In this case, a simple circuit will be described using mainly a 555 chip (universal timer).

To familiarize yourself with the operation of such a timer, it is recommended to read the corresponding sheet with the parameters of this microcircuit (datasheet).

Required materials and tools:

555 chip (universal timer);
2 capacitors of 2.2 µF;
resistor=47 kOhm;
batteries = 9 V, wires for connections, cable for battery, switch;
circuit board;
copper wire=100 m (d=0.2 mm);
buzzer for sound signals (it can be replaced with a speaker with resistance = 8 ohms and capacitor = 10 μF);
wood glue and electrical tape;
cardboard;
pliers with which you can make a hole, tweezers;
solder in the form of a wire and a soldering iron;
ruler, sharp knife, compass, pencil;
glue used for hot gluing;
wires and breadboard.

Materials for making a simple metal detector

Metal detector circuit

You may come across various homemade metal detectors. They are freely available, you just need to enter “metal detector circuits” in the search bar. This one was taken in the same way from the Internet, but a buzzer was added instead of a speaker and a switch (for the battery).

Making a coil

For ease of calculation, you can use an online air coil calculator. Using it, you can calculate that for a coil with a diameter of 9 cm, 250 turns (turns) of varnished copper wire d = 0.2 mm are needed. The inductance of this coil will be approximately 10 MGn.

The smaller its d (diameter), the more revolutions will be needed (for a coil with a diameter of 7 cm, 290 revolutions are required).

Metal detector screen

Buying a ready-made one is not difficult. If you still decide to assemble it yourself, then before soldering the two ends of the wire you need to clean them using sandpaper. You must try to make all connections very carefully in order to exclude the influence of poor-quality installation on a homemade device, which will already respond to a lot of interference.

Assembled metal detector screen

Coil testing and PCB creation

In order not to spoil the working board, it is better to test this circuit on a breadboard.

Checking functionality on a breadboard

The next step is to make the circuit board. If you don’t know how, then it’s better to find a description on the Internet with video lessons.

Circuit board assembled

Testing

Basis for construction

The base for your simple metal detector can be made of any materials convenient for you (wood, plastic, etc.). In this case, cardboard served as the basis. It is easier to use.

First you need to make a sketch of the handle (3 parts), you can even do it without calculations. This handle will have to fit the battery, circuit board, switch and coil.

Metal detector handle made of cardboard

Cut out holes for the switch and battery. Glue the cardboard parts together using wood glue and leave to dry overnight (approximately 12 hours).

Cutting holes for batteries and wires

glue these parts together

After the glue has dried, you need to make a hole in the handle next to the switch so that the wires can pass through it freely. Finally, glue the spool to the cardboard handle using hot glue.

We place the battery and other parts on the handle

Assembly of parts and conclusion

When all the parts have been completed individually, all that remains is to assemble them. First you need to glue the switch to the handle using hot glue, insert the battery and then glue the circuit board.

Now it's time to connect all the components to each other and test the device you created. It will not be easy for a beginner to understand this manual, but if this is not your first time making a metal detector, you will quickly figure it out.

Assembled metal detector

This assembled metal detector is quite powerful for finding small objects at close distances and preferably indoors, in order to avoid problems. But it should be remembered that this homemade product will be very inferior in sensitivity, detection quality, separation and selectivity, resistance to interference to industrial equipment, and it is worth repeating it rather for the sake of sporting interest and familiarization with the principle of operation of a metal detector.

What happened eventually:

Metal detector circuit

Today I would like to present to your attention a diagram of a metal detector, and everything related to it, what you see in the photograph. After all, it is sometimes so difficult to find the answer to a question in a search engine - Diagram of a good metal detector

In other words, the metal detector has a name Tesoro Eldorado

The metal detector can operate in both the search mode for all metals and background discrimination.

Technical characteristics of the metal detector.

Operating principle: induction balanced
-Operating frequency, kHz 8-10kHz
-Dynamic operating mode
-Precise detection mode (Pin-Point) is available in static mode
-Power supply, V 12
-There is a sensitivity level regulator
-There is a threshold tone control
-Ground adjustment is available (manual)

Detection depth in the air with a DD-250mm sensor In the ground, the device sees targets almost the same as in the air.
-coins 25mm - about 30cm
-gold ring - 25cm
-helmet 100-120cm
-maximum depth 150cm
-Consumption current:
-No sound approximately 30 mA

And the most important and intriguing thing is the diagram of the device itself

The picture is easily enlarged when you click on it

To assemble the metal detector you need the following parts:

So that you don’t have to spend a long time setting up the device, do the assembly and soldering carefully; the board should not contain any clamps.

For tinning boards, it is best to use rosin in alcohol; after tinning the tracks, do not forget to wipe the tracks with alcohol

Parts side board

We begin assembly soldering jumpers, then resistors, further sockets for microcircuits And all the rest. One more small recommendation, now regarding the manufacture of the device board. It is very desirable to have a tester that can measure the capacitance of capacitors. The fact is that the device These are two identical amplification channels, therefore the amplification through them should be as identical as possible, and for this it is advisable to select those parts that are repeated on each amplification stage so that they have the most identical parameters as measured by the tester (that is, what are the readings in a particular stage on one channel - the same readings on the same stage and in another channel)

Making a coil for a metal detector

Today I would like to talk about the manufacture of a sensor in a finished housing, so the photo is more than words.
We take the housing, attach the sealed wire in the right place and install the cable, ring the cable and mark the ends.
Next we wind the coils. The DD sensor is manufactured according to the same principle as for all balancers, so I will focus only on the required parameters.
TX – transmitting coil 100 turns 0.27 RX – receiving coil 106 turns 0.27 enameled winding wire.

After winding, the coils are tightly wrapped with thread and impregnated with varnish.

After drying, wrap tightly with electrical tape around the entire circumference. The top is shielded with foil; between the end and the beginning of the foil there should be a gap of 1 cm not covered by it, in order to avoid a short-circuited turn.

It is possible to shield the coil with graphite; to do this, mix graphite with nitro varnish 1:1 and cover the top with a uniform layer of tinned copper 0.4 wire wound on the coil (without gaps), connect the wire to the cable shield.

We put it into the case, connect it and roughly bring the coils into balance, there should be a double beep for the ferrite, a single beep for the coin, if it’s the other way around, then we swap the terminals of the receiving winding. Each of the coils is adjusted in frequency separately; there should be no metal objects nearby!!! The coils are tuned with an attachment for measuring resonance. We connect the attachment to the Eldorado board in parallel with the transmitting coil and measure the frequency, then with the RX coil and a selected capacitor we achieve a frequency 600 Hz higher than that obtained in TX.

After selecting the resonance, we assemble the coil together and check whether the device sees the entire VDI scale from aluminum foil to copper; if the device does not see the entire scale, then we select the capacitance of the resonant capacitor in the RX circuit in steps of 0.5-1 nf in one direction or another, and in addition the moment when the device will see foil and copper at a minimum of discrimination, and when the discrimination is turned up, the entire scale will be cut out in turn.

We finally reduce the coils to zero, fixing everything with hot glue. Next, to lighten the coil, we glue the voids with pieces of polystyrene foam, the foam sits on the hot glue, otherwise it will float up after filling the coil.

Pour the first layer of epoxy, without adding to the top 2-3mm

Fill in the second layer of resin with color. An aniline dye is a good choice for dyeing fabric; the powder comes in different colors and costs a penny. The dye must first be mixed with the hardener, then the hardener must be added to the resin; the dye will not dissolve in the resin immediately.

To assemble the board correctly, start by checking the correct power supply to all components.

Take the circuit and the tester, turn on the power on the board, and, checking the circuit, go through the tester at all points on the nodes where power should be supplied.
When the discrimination knob is set to minimum, the device should see all non-ferrous metals

, when screwing the discrim, they should be cut out

all metals in order up to copper should not be cut out if the deviceit works this way, which means it is configured correctly. The discrimination scale needs to be selected so that it fits completely into a full turn of the discrimination knob, this is done by selecting c10. When the capacity decreases, the scale stretches and vice versa.

Many people unreasonably believe that homemade metal detectors are inferior in many respects to branded samples produced at the factory.

But in fact, structures that are correctly assembled with your own hands sometimes turn out to be not only better, but also cheaper than “factory” competitors.

Worth knowing: Most treasure hunters and local historians, in order to save money, try to choose the cheapest options. As a result, they either assemble metal detectors themselves or purchase homemade custom devices.

Beginners, as well as people who do not understand electronics, are at first intimidated by the abundance of not only special terminology, but also various formulas and circuits. However, if you delve a little deeper, everything immediately becomes clear, even with the knowledge gained in school physics lessons.

Therefore, it is worth, first of all, to understand the principle of operation of a metal detector, what it is and how you can assemble it yourself at home.

How does it work

The operating principle of this device is to use an electromagnetic field. It is created by the transmitter coil and after a collision with an object that conducts current (which is most metals), eddy currents are created that introduce distortion into the EPM of the coil.

In cases where the object is not electrically conductive, but has its own magnetic field, the interference it creates will also be captured due to shielding.

After this, changes in the electromagnetic field are sent directly to the control unit, which emits a special sound signal to notify that a person has been found, and in more expensive models displays data on the display.

It is worth examining how such devices are created following the example of a “Pirate” type metal detector.

Metal detector "Pirate"

Making a printed circuit board with your own hands

First you need to create a printed circuit board, where all the nodes of the metal detector will be located in the future. The best method is laser-iron technology or simply LUT.

To do this, it will be necessary to perform the manufacturing steps in the following sequence:

First, using only a laser printer, you need to print the corresponding diagram created through the Sprint-Layout program. It is best to use light weight photo paper for this.
We prepare the PCB workpiece, first sand it, and then clean it with a solution. It should have dimensions 84x31.
Now on top of the blank we place photo paper with the diagram on the front side on which it was printed. Cover with an A4 sheet and begin ironing with a hot iron in order to transfer the marking scheme to the textolite.
After fixing the circuit from the toner, we place it all in water, where we carefully remove the paper with our fingers.
Next, if there are smeared areas, we correct them using a regular needle.
Now the board needs to be placed in a solution of copper sulfate for several hours (ferric chloride can also be used).
The toner can be removed without any problems with any solvent, such as acetone.
We drill holes for later placement of structural elements (the drill must be very thin).
The last stage is to lay out the board tracks. To do this, a special solution “LTI-120” is smeared on the surface, which needs to be spread over the solder of the soldering iron.

Installing elements on the board

This stage of creating a metal detector consists of installing all the elements on the created board:

The main microcircuit is the domestic KR1006VI1 or its foreign analogue NE555. Please note that before installation, a jumper must be soldered underneath it.
Next, a two-channel amplifier K157UD2 is installed. You can buy it or take it from Soviet tape recorders.
After this, 2 SMD capacitors are mounted, as well as one resistor of the MLT C2-23 type.
Now you need to solder two transistors. One must be NPN structure, and the other PNP. It is advisable to use BC557 and BC547. However, analogues will also work. It is recommended to use IRF-740 or other options with similar characteristics as a field-effect transistor.
The capacitors are installed last. They should be taken with a minimum TKE indicator, which will increase the thermal stability of the entire structure.

Note: The hardest thing will be to get the K157UD2 amplifier out of this circuit. The reason is that it is already an old chip. That is why you can try to find similar modern options with similar parameters.

A homemade coil is created on a frame with a diameter of 20 cm. The total number of turns should be approximately 25 pieces. This indicator is based on the fact that PEV wire is used, which has a diameter of 0.5 mm.

However, there is a certain peculiarity. The total number of turns can be changed up or down. To find the most optimal option, you need to take a coin and check in which case there will be the longest distance to “catch” it.

Other elements

A signal speaker can be used taken from a portable radio. It is important that it has a resistance of 8 ohms (Chinese options can be used).

To carry out the adjustment, you will need two potentiometer models of different power: the first is 10 kOhm, and the second is 100 kOhm. To minimize the influence of interference (it will be difficult to eliminate it completely), it is recommended to use a shielded wire that will connect the circuit and the coil. The metal detector's power source must be at least 12 V.

When the entire structure has been tested for functionality, it is necessary to make a frame for the future metal detector. However, here we can only give some recommendations, because everyone will create it from the items at hand:

to make the bar more convenient, it is worth purchasing 5 meters of ordinary PVC pipe (which are used in plumbing), as well as several jumpers. It is worth installing a special palm rest at its upper end to make it more comfortable to hold. For the board, you can find any box of the appropriate size that needs to be mounted on the rod;
To power the system, you can use a battery from a regular screwdriver. Its advantages are low weight and high capacity;
When creating the body and structure, keep in mind that there should not be any unnecessary metal elements in them. The reason is that they significantly distort the resulting electromagnetic field of the future device.

Checking the metal detector

First of all, you need to adjust the sensitivity using potentiometers. The threshold will be a uniform, but not very frequent, crackling.

So, he will have to “find” a five-ruble coin from a distance of approximately 30 cm, but if the coin is the size of a Soviet ruble, then from about 40 cm. He will “see” large and voluminous metal from a distance of more than a meter.

Such a device will not be able to search for small objects at significant depths. In addition, he will not be able to distinguish between the size and type of metal found. That is why, while searching for coins, you may come across ordinary nails.

This model of homemade metal detector is suitable for people who are just starting to learn the basics of treasure hunting or do not have the necessary funds to purchase an expensive device.

Their this video You will learn how to make a homemade metal detector:

There is no need to explain to anyone what a metal detector is. This device is expensive, and some models cost quite a lot.

However, you can make a metal detector with your own hands at home. Moreover, you can not only save thousands of rubles on its purchase, 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 a simple metal detector with your own hands from available materials. We will need: a regular plastic CD box, a portable AM or AM/FM radio, a calculator, VELCRO type contact tape (Velcro). So let's get started!

Step 1. Disassemble the CD box body. Carefully disassemble the plastic CD case body, removing the insert that holds the disc in place.

STEP 1. Removing the plastic insert from the sidebox

Step 2. Cut 2 strips of Velcro. Measure out the area at the center back of your radio. Then cut 2 pieces of Velcro the same size.

STEP 2.1. Measure approximately in the middle the area on the back of the radio (highlighted in red)

STEP 2.2. Cut out 2 Velcro strips of the appropriate size measured in step 2.1

Step 3. Secure the radio. Use the sticky side to attach one piece of Velcro to the back of the radio and another to one of the inside sides of the CD case. Then attach the radio to the body of the plastic CD case using Velcro to Velcro.

Step 4. Secure the calculator. Repeat steps 2 and 3 with the calculator, but apply the Velcro to the other side of the CD case. Then secure the calculator to this 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 AM end of the band, but not to the radio station itself. Turn up the volume. You should only hear static.

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 only hear interference!

Step 6. Roll up the CD box. Turn on the calculator. Start folding the side of the calculator box toward the radio until you hear a loud beep. This beep tells us that the radio has picked up an electromagnetic wave from the calculator's circuitry.

STEP 6. Fold 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 flaps of the plastic box again until 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 a loud sound again. This indicates the correct operation of our simplest metal detector.

Instructions for assembling a sensitive metal detector based on a dual-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 metal objects. The beat frequency between these two oscillator frequencies is in the audio range. When the detector passes over a metal object, you will hear a change in this beat frequency. 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 114.3mm x 155.6mm	1 PC.
Resistor 0.125 W	1 PC.
Capacitor, 0.1μF	5 pieces.
Capacitor, 0.01μF	5 pieces.
Capacitor, electrolytic 220μF	2 pcs.
PEL type 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.
Connector for binding 9V battery	1 PC.
Potentiometer, 5 kOhm, audio taper, optional	1 PC.
Switch, single pole	1 PC.
Transistor, NPN, 2N3904	6 pcs.
Wire for connecting the sensor (22 AWG or cross-section - 0.3250 mm 2)	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′ wood dowel	1 PC.
1/2′ wooden dowel	1 PC.
Epoxy resin	1 PC.
1/4′ plywood	1 PC.
Wood glue	1 PC.

We will 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 using a regular laser printer, and then transfer the design onto the copper cladding using an iron. During the etching stage, the toner acts as a mask, preserving the copper traces while like the rest copper dissolves in chemical bath.

Step 2: Fills 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 we add two 220μF electrolytic capacitors.

Step 2.2. Add 2 electrolytic capacitors

Step 3: Fill the board with polyester capacitors and resistors. Now you need to add 5 polyester capacitors with a capacity of 0.1μF in the places shown below. Next, add 5 capacitors with a capacity of 0.01μF. These capacitors are not polarized and can be soldered onto the board with legs in any direction. Next, add 6 10 kOhm resistors (brown, black, orange, gold).

Step 3.2. Add 5 capacitors with a capacity of 0.01μF

Step 3.3. Add 6 10 kOhm resistors

Step 4: We continue to fill the electrical board with elements. Now you need to add one 2.2 mOhm resistor (red, red, green, gold) and two 39 kOhm resistors (orange, white, orange, gold). And then solder in the last 1 kOhm 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 2 mOhm and two 39 kOhm)

Step 4.2. Add 1 1 kOhm resistor (far right)

Step 4.3. Adding wires

Step 5: We wind the turns onto the reel. The next step is to wind turns on 2 coils, which are part of the LC generator circuit. The first is the reference coil. I used 0.4mm diameter wire for this. Cut a piece of dowel (about 13mm in diameter and 50mm in length).

Drill three holes in the dowel to allow the wires to pass through: one lengthwise through the middle of the dowel, and two perpendicularly at each end.

Slowly and carefully wrap as many turns of wire as you can around the dowel in one layer. Leave 3-4mm of bare wood at each end. Resist the temptation to "twist" the wire - this is the most intuitive way to wind, but this is the wrong way. You must rotate the dowel and pull the wire behind you. This way he will wrap the wire around himself.

Pull each end of the wire through the perpendicular holes in the dowel, and then one of them through the longitudinal hole. Secure the wire with tape once you're done. Finally, use sandpaper to remove the coating on the two open ends of the coil.

Step 6: We make a receiving (search) coil. It is necessary to cut the spool holder from 6-7 mm plywood. Using the same 0.4mm diameter wire, wind 10 turns around the slot. My reel has a diameter of 152 mm. Using a 6-7 mm wooden peg, attach the handle to the holder. Do not use a metal bolt (or anything 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 adjust 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 meter for these purposes. Start by connecting the coil into 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 should 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 the frequency under 100kHz, my coil was 31mm long.

Metal detector on a transformer with W-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 against water. Turn it on and bring it 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 in the headphones will change.

A simple circuit based on common elements. You need transistors of the K315B or K3102 series, resistors, capacitors, headphones, and a battery. The values are shown in the diagram.

Video: How to properly make a metal detector with your own hands

The first transistor contains a master oscillator with a frequency of 100 Hz, and the second transistor contains a search oscillator with the same frequency. As a search coil, I took an old plastic bucket with a diameter of 250 mm, cut it off and wound a copper wire with a cross-section of 0.4 mm2 in the amount of 50 turns. I placed the assembled circuit in a small box, sealed it and secured everything to the rod with tape.

Circuit 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, 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 circuit based on simple elements. You need a microcircuit, capacitors, resistors, headphones, and a power source. It is advisable to first assemble coil L2, as shown in the photo:

A master oscillator with coil L1 is assembled on one element of the microcircuit, and coil L2 is used in the search generator circuit. When metal objects enter the sensitivity zone, the frequency of the search circuit changes and the sound in the headphones changes. Using the handle of capacitor C6 you can tune out excess noise. A 9V battery is used as a battery.

In conclusion, I can say that anyone who is familiar with the basics of electrical engineering and has enough patience to complete the job can assemble the device.

Principle of operation

So, a metal detector is an electronic device that has a primary sensor and a secondary device. The role of the primary sensor is usually performed by a coil with a wound wire. The operation of the metal detector is based on the principle of changing the electromagnetic field of the sensor by 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 notifies us that a metal object has been found.

The simplest metal detectors change the sound of the alarm when the desired object is detected. More modern and expensive samples are equipped with a microprocessor and a liquid crystal display. The most advanced companies equip their models with two sensors, which allows them to search more efficiently.

Metal detectors can be divided into several categories:

public devices;
mid-range devices;
devices for professionals.

The first category includes the cheapest models with a minimal set of functions, but their price is very attractive. The most popular brands in Russia: IMPERIAL - 500A, FISHER 1212-X, CLASSIC I SL. Devices in this segment use a “receiver-transmitter” circuit operating at ultra-low frequencies and require constant movement of the search sensor.

The second category, these are more expensive units, have several replaceable 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 and can operate in dynamic and static modes. Allows you to determine the composition of the metal (object) and the depth of its occurrence. The 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 holder rod, an electronic control unit. The sensitivity of our device depends on its quality and size. The holder bar is selected according to the person’s height so that it is convenient to work. All structural elements are fixed to it.

If you have lost a ring, a key, a screwdriver... and you know the approximate location of the loss, then do not despair! You can assemble a metal detector with your own hands or ask a radio amateur you know to assemble simple DIY metal detector. Below is a diagram of an easy-to-make and time-tested metal detector, which (with certain skills) can be made in one day. The simplicity of the described metal detector is that it is assembled on just one very common chip K561LA7 (CD4011BE). Setup is also simple and does not require expensive measuring instruments. To configure the generators, an oscilloscope or frequency meter is sufficient. If everything is done without errors and from serviceable elements, then these devices will not be needed.

Sensitivity of this metal detector:

metal jar lid “sees” up to 20 cm, cell phone up to 15 cm, Krona battery up to 10 cm, 5 ruble coin up to 8 cm.

At this distance the tone of the oscillator in the headphones barely changes; at a closer distance the tone increases. The larger the metal area, the greater the detection distance. Distinguishes between diamagnetic materials and ferromagnetic materials.

For making a metal detector we will need:

Chip K561LA7 (or K561LE5, analogue of CD4011);
Transistor - low-power low-frequency, for example - KT315, KT312, KT3102, analogues: BC546, BC945, 2SC639, 2SC1815, etc.);
Diode - any low-power one, for example - kd522B, kd105, kd106, analogues: in4148, in4001, etc.;
Variable resistor - 3 pcs (1 kOhm, 5 kOhm, 20 kOhm with a switch or a separate switch);
Fixed resistor - 5 pcs (22 Ohm, 4.7 kOhm, 1.0 kOhm, 10 kOhm, 470 kOhm);
Ceramic, or even better, mica capacitors - 5 pcs: 1000 pF -3 pcs, 22 nF -2 pcs, 300 pf);
Electrolytic capacitor (100.0 uF x 16V) - 1 piece;
Wire PEL, PEV, PETV, etc., with a diameter of 0.4-0.7 mm;
Low impedance headphones (from the player);
Battery 9V.

Metal detector circuit

Appearance of the metal detector board

In the case of an old pocket radio (you can use the case from a soap dish, a shoe-cleaning sponge, or in the housing from the electrical junction box.

Attention! To eliminate interference and the influence of human hands when touching the regulators, the housings of variable resistors must be connected to the minus of the board.

If the metal detector circuit is properly soldered, the elements are in good working order and have the correct values, and the search coil is properly made, the device operates without problems. If, when you turn on the headphones for the first time, you do not hear a squeak or change in frequency when adjusting the “FREQUENCY” control, then you need to select a resistor (10 kOhm) , standing in series with the regulatorand/or a capacitor in this generator (300 pF). Thus, we make the frequencies of the reference and search generators the same.

When the generator is excited, whistling, hissing, and distortion appear, solder a 1000 pF capacitor (1H0 aka 102) to the pin. 6 chips per case.

Using an oscilloscope or frequency meter, look at the signal frequencies at pins 5 and 6 of the K561LA7. Achieve their equality using the above-described adjustment method. The operating frequency of the generators itself can vary from 80 to 200 kHz.

A protective diode (any low-power one) is needed to prevent damage to the microcircuit when the battery is turned on by mistake (which often happens:).

Making a metal detector coil

The coils are wound on a mandrel with a diameter of 15-25 cm (for example, a bucket or on a shuttle made of thick wire or plywood - the smaller the diameter, the less sensitivity, but the greater the selectivity of small metals). Choose for what purpose you need it.

A wire is used in varnish insulation PEL, PEV, PETV..., with a diameter of 0.4 - 0.7 mm (well suited for old color TVs with a kinescope demagnetization loop or deflection system) and contains about 100 turns (you can wind from 80 to 120 turns ). Wrap the wire tightly with electrical tape.

Then we wrap the coil over the electrical tape with a strip of foil, leaving 2-3 cm of the unwrapped area. You can take foil from some types of cables or, as a last resort, cut foil from a chocolate bar into strips 2 cm wide :)

We wrap everything tightly with electrical tape again.

Photo of the finished coil. All that remains is to wrap the top with electrical tape.

We attach the resulting finished coil to a dielectric (for example, non-foil PCB or getinax). Next we attach it to the holder.

We connect the coil with the circuit with a double shielded wire (screen to body). The wire can be taken from old cords for dubbing from tape recorder to tape recorder or a low-frequency (audio-video) cord for connecting a TV to a DVD, etc.

Correct operation of the metal detector: When you turn on the “frequency” control in the headphones, we set a low-frequency hum; when approaching metal, the frequency changes.

The second option is to stop the buzzing in your ears by setting the beats to zero, i.e. combine two frequencies. Then there will be silence in the headphones, but as soon as we bring the coil to the metal, the frequency of the search generator changes and a squeak appears in the headphones. The closer to the metal, the higher the frequency in the headphones. But the sensitivity with this method is not great. The device will react only when the generators are strongly detuned, for example, when brought close to a jar lid.