Homemade metal detector for precious metals. How to make a metal detector with your own hands - cost-effective and proven schemes. What sizes does the reel need?

Hello readers! Today I want to talk about how to assemble a metal detector with your own hands. When you really want to buy something, but there is no money for it, you have to postpone the purchase until later or take out a loan. Credit is expensive. And the thought arises in my head: “If only I could find a treasure.” Which one then ? That's right, a metal detector. This article will tell you how this device works and what parts are needed to assemble it.

The design of metal detectors consists of the following main elements:

1. The coil receives and transmits an electromagnetic signal, scanning the surface with the desired metal.
2. The control unit processes the signal received from the coil, notifies the user with a graphic or sound signal, and also allows you to manually configure the operating modes of the detector.
3. The lower rod fixes the reel and adjusts its angle.
4. The middle rod is an intermediate link between the lower and upper rods and allows you to adjust the height of the metal detector.
5. Upper rod. The control unit is located here, as well as a comfortable handle with an armrest so that the user’s hands do not get tired from holding the metal detector for a long time.

The metal detector emits an electromagnetic field through a coil. When metal or any other conductive material is in this field, the field is distorted and weakened. The control unit detects this and sends a signal.

More electrically conductive non-ferrous metals distort the field emitted by the detector more strongly than ferrous metals.

Therefore, sensitive electronic circuits allow you to create devices with your own hands that discriminate between metals, which can distinguish non-ferrous metal from ferrous metal.

Types of metal detectors

Metal detectors are divided into:

• induction;
• pulse;
• phase sensitive;
• parametric.

What types can you make at home with your own hands?

Parametric and phase-sensitive detectors are well suited for homemade products. They are easy to make, and the parts for them cost mere pennies. To assemble it yourself, it is enough to have basic knowledge of radio engineering.

Metal detectors with phase accumulation are much more sensitive than parametric ones. They have good discrimination and can find even small jewelry, making them a favorite tool for beach gold diggers. On dry sand it is possible to find earrings and rings at a depth of up to 38 cm.

Main settings

Search method

Induction metal detectors (MD) consist of a transceiver inductor.

When the emitted signal hits a metal object, it is reflected back and recorded by the receiver. These devices are quite simple to make with your own hands, but their sensitivity greatly depends on the type of soil and the quality of the coil.

Pulsed MDs excite eddy currents in the search zone and measure the secondary damped electromagnetic field. The sensitivity of these devices is higher and does not depend on the type of soil. However, they consume a lot of electricity, which does not allow them to work in autonomous mode for a long time.

Phase-sensitive MDs can be:

1. Impulse. The receiver and transmitter here are one and the same element. It records the phase shift of the signal reflected from the metal. An increase in phase shift causes clicks in the headphones: the closer the MD is to the metal, the more frequent they become, eventually merging into a single sound. The work of the popular metal detector “Pirate” is based on this method.
2. Double-circuit. Consist of 2 symmetrical generators and 2 detectors. A metal object disrupts the synchronization of the generators, and the same clicks occur, merging into a continuous tone.
   

   Double-circuit ones are easier to make with your own hands than pulse ones.

3. Parametric MDs have neither a receive nor a transmit coil, making them simple, cheap, and popular for DIY assembly. An LC generator creates an electromagnetic field at audio frequency. Any metal near the metal detector changes the parameters of the coil detector, which affects the frequency and amplitude of the generated signals. The diagram of such devices is easy to find. However, their sensitivity is low and does not allow complex searches. Parametric MDs are divided into:
4. Frequency MD. They emit multi-frequency signals. When approaching metals, the device detects a change in frequency.
5. Metal detectors that record changes in the quality factor of the circuit. When the distance between the device and the metal decreases, the device records this.

Detection depth

The detection depth depends on the coil diameter, electronic circuit and operating frequency. The larger the diameter of the wire coil, the more powerful the emitted electromagnetic field and the lower its frequency, the deeper the detection zone of a DIY metal detector.

However, as the search depth increases, the sensitivity of the metal detector to small objects deteriorates, and its selective capabilities also decrease. Energy consumption and weight of the device increase, which makes it difficult to hold the metal detector in your hands for a long time.

Operating frequency

Based on the frequency of operation, MDs are divided into:

1. High frequency. They operate at frequencies of several hundred kHz. They are used in devices designed to search for gold, as they have excellent discrimination. But they sharply lose sensitivity on wet and magnetic soils, as well as at a depth of more than 40 cm.
2. Mid-frequency. Operating frequency up to several tens of kHz. The requirements for the quality of the coil are lower, good sensitivity. Detection depth is up to 1.5 meters, provided that the soil is dry and low-mineralized.
3. Low frequency. They operate at frequencies from hundreds of Hz to several kHz. These are deep metal detectors that detect objects up to 5 meters underground. They are easy to make with your own hands. Disadvantages: low sensitivity and high power consumption. Suitable as magnetic detectors, as well as for searching for large objects made of ferrous metal (fittings, wiring).
4. Ultra-low frequency. They are not suitable for amateur searches, as they have high power consumption and large dimensions, and special programs are required for signal processing. Operating frequency up to several hundred Hz. These metal detectors cannot be held by hand, so they are mounted on a car.

Step-by-step instructions for assembling a simple homemade metal detector with your own hands

Required tools and materials

To assemble a metal detector with your own hands you will need:

1. Tools: wire cutters, knife, small saw, screwdriver, soldering iron.
2. Materials: wire, solder, flux, glue, electrical tape, radio components, wooden or plastic stick.

Dielectrics (polymers, wood, glue) must be used as a rod, as well as elements for its fastening, so that they do not interfere with the operation of the metal detector.

Preparing parts

You need to prepare a board on which the electrical circuit will be mounted. Even cardboard can be used as a board. The location of future parts is marked on it by hand and holes are made.

Radio components are bought in a store or soldered from old equipment. However, you need to make sure that the details are the same. This will make it easier to coordinate the operation of the two detectors.

Metal detector circuits for manufacturing

Sensitive metal detector based on a dual-circuit oscillator circuit

Manufacturing stages:

1. Transistors, resistors and capacitors are placed on the board and soldered according to the diagram below.
2. Solder two wires from the battery compartment, as well as two piezoelectric speakers.
3. Wind the wire onto a round frame with a diameter of about 22 cm. After 10 turns, make a wire tap 20 cm long. The wire at the tap site is not torn, but folded in half by hand. Make another 20 turns. The result should be three leads 20 cm long: the beginning of the wire, the end and the outlet after the 10th turn.
4. Remove the coil from the frame, holding the coils with your hands, and secure tightly with electrical tape.
5. Wind a second coil, which should mirror the first. Remove it from the frame and secure it with electrical tape.
6. Solder the leads of the coil detectors according to the diagram.
7. Assembling the stand. The coils are placed at a distance of approximately 15 cm from each other, and a board is attached between them.
8. Adjust the detectors before mounting. Turn on the metal detector and, moving the coils with your hands, achieve maximum silence. They bring metal to one of them. If the sound changes noticeably, it means the metal detector is working.
9. The elements are fixed with glue and covered with oil varnish.
10. Attach the handle to the stand.

On a transformer with W-shaped plates

This is a simple parametric metal detector with inductive feedback. Allows you to detect hidden wiring, reinforcement in walls and ceilings, as well as large metals in the soil. A low-power transformer is used from any radio receiver. To turn a transformer into a detector with your own hands, you need to open its magnetic circuit: remove the frame, straight jumpers and windings.

There are two schemes for converting a transformer. The first one uses old windings, the second one rewinds them.

In the first case, the W-shaped plates need to be folded together and windings put on them. Winding in diagram II is network, winding I is step-down by 12 V. Capacitor C1 adjusts the tone of the sound. Instead of the MP40 transistor, you can use KT361.

In the second case, windings of 1000 turns (in Scheme I) and 200 turns (in Scheme II) are wound on W-shaped plates. For winding I, PEL-0.1 wire is used. After 500 turns, a tap is made. Winding II is wound with PEL-0.2 wire.

The transformer is sealed and placed on the bottom rod of the metal detector. When approaching metal, the tone of the signal in the headphones will change.

On transistors

Also a simple circuit consisting of transistors K315B or K3102, capacitors, resistors, an earphone and a battery.

The first transistor creates a master oscillator, the second - a search oscillator. If you bring metal close to the coil, sound appears in the headphones. A detailed diagram is given below.

On the K561LE5 chip

The circuit consists of a microcircuit, headphones, resistors and capacitors. Coil L1 is connected to the master oscillator, and L2 is connected to the search oscillator of the microcircuit. A metal object affects the frequency of the search generator, changing the sound in the headphones. It is adjusted by MD capacitor C6. It eliminates unnecessary noise. The device supply voltage is 9 V.

How to assemble with your own hands without using microcircuits

This is the easiest option to assemble. So to speak, for dummies. You don't even need to solder anything. The metal detector is built from a calculator, a radio and a cardboard or CD box. The receiver and calculator should be taken as simple as possible, without protection from electromagnetic interference.

The principle of operation is based on the fact that the calculator creates radio interference in the AM range, and the receiver picks it up. Making a metal detector with your own hands consists of the following stages:

1. Set the radio to the highest AM range, but at the same time free from stations. Only interference should be heard.
2. Glue the receiver with double-sided tape on the back side to one flap of the CD box. Glue the calculator to the other sash.
3. Turn on the calculator. When the shutter is fully open, the receiver should enhance its sound.
4. Fold the box smoothly. When the angle between the receiver and the calculator is approximately 90°, the radio will go silent.
5. Fix the box in this position.

When metal enters the MD's coverage area, the field vector will rotate and the receiver will again intensify its sound. Depending on the design of the receiver, it may turn out that at an angle of 90°, the sound, on the contrary, is enhanced. In this case, the angle between the doors of the box is gradually increased, achieving a weakening of the tone.

PCB assembly

There are several options for wiring boards yourself. The figures below show circuit diagrams for wiring boards for metal detectors on a double-circuit oscillator, on a transformer, transistors and on a K561LE5 microcircuit.

Do-it-yourself electronics must be placed in a plastic case to avoid interference.

How to make a reel

An enameled copper wire with a diameter of 0.4–0.6 mm and a frame of the required size are used. The diameter of the frame depends on the purpose of using the metal detector:

• up to 9 cm – suitable for searching for reinforcement and profiles;
• 14-18 cm – for searching for small jewelry;
• 22-50 cm – for searching for large and deep-lying objects.

Also, for proper operation of the metal detector, you need to monitor the inductance of the coil. Inductance can be measured with a special device or calculated on the Internet using a calculator.

You can buy a frame for the reel in a store or make it yourself. Plywood or durable plastic are suitable for this. It is best to use plastic (polycarbonate, computer disk, bucket), as it has the least effect on the electromagnetic field and does not absorb moisture.

Location of parts on the board for a chip in a DIP package

If a chip in a DIP package is used, then the parts are placed as in the figure below.

Location of parts on the board for a chip in an SM package

Below is a diagram of the arrangement of parts when using a microcircuit in an SM package.

Brief instructions for setting up the device

The general rule when adjusting a metal detector with your own hands is to achieve the lowest sound in the “idle” mode, so that squeaks or clicks appear only when a metal object is detected. This can be achieved by changing the inductance of the coils, the capacitance of the capacitor or the resistance of the resistor.

Modernization

To make the metal detector better at finding small jewelry, you need to increase its operating frequency.

The sensitivity of the device also increases when an additional RC circuit is added to the circuit.

Installing variable resistors allows you to configure the device yourself without touching the coils.

The use of speakers with capacitors makes the sound produced louder. It is also useful to create a secure mounting for the coils and control unit. Protection from shocks and shocks will reduce interference, and settings will be less likely to be lost.

Conclusion

Now you know how to make a metal detector with your own hands. I will be glad if this article helps you find the treasure. Subscribe to new articles and share useful information on social networks.

I offer for repetition a simple metal detector that I personally assembled recently and successfully operated. This metal detector operates on the transmit-receive principle. A multivibrator is used as a transmitter, and an audio amplifier is used as a receiver. The schematic 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;
- iron sealing lid from a jar - 25 cm;
- aluminum sheet measuring 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 this way, the transmitter signal will not be heard in the receiver. When a metal object appears in the vicinity of this balanced system, under the influence of the alternating magnetic field of the transmitting coil, so-called eddy currents arise in it 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 metal detector circuit is really very simple, but despite this, it works quite well, and the sensitivity is not bad. The multivibrator of the transmitting unit can be assembled using other transistors of a similar structure.

Metal detector coils have a size of 200x100 mm and contain about 80 turns of 0.6-0.8 mm wire. To check the operation of the transmitter, connect headphones instead of the L1 coil and make sure that sound is heard in them when the power is turned on. Then, having connected the coil in place, they control the current consumed by the transmitter - 5...8 mA.

The receiver is configured with the input closed. By selecting resistor R1 in the first stage and R3 in the second, a voltage equal to approximately half the supply voltage is set on the collectors of the transistors, respectively. Then, by selecting resistor R5, they ensure that the collector current of transistor VT3 becomes equal to 5...8 mA. After this, opening the input, connect the receiver coil L1 to it and, receiving the transmitter signal at a distance of about 1 m, make sure that the device is working.

I can say without a doubt that this is the simplest metal detector I have ever seen. It is based on just one TDA0161 chip. You won't need to program anything - just assemble it and that's it. Another huge difference is that it does not make any sounds during operation, unlike a metal detector based on the NE555 chip, which initially beeps unpleasantly and you have to guess the metal found by its tone.

In this circuit, the buzzer starts beeping only when it detects metal. The TDA0161 chip is a specialized industrial version for induction sensors. And metal detectors for production are mainly built on it, giving a signal when metal approaches the induction sensor.
You can purchase such a microcircuit at -
It is not expensive and is quite accessible to everyone.

Here is a diagram of a simple metal detector

Metal detector characteristics

• Microcircuit power supply voltage: from 3.5 to 15V
• Generator frequency: 8-10 kHz
• Current consumption: 8-12 mA in alarm mode. In search state approximately 1 mA.
• Operating temperature: -55 to +100 degrees Celsius

The metal detector is not only very economical, but also very unpretentious.
An old cell phone battery works well for power supply.
Coil: 140-150 turns. The diameter of the coil is 5-6 cm. Can be converted to a coil of larger diameter.

The sensitivity will depend directly on the size of the search coil.
In the scheme I use both light and sound signaling. You can choose one if you want. Buzzer with internal generator.
Thanks to this simple design, you can make a pocket metal detector or a large metal detector, depending on what you need more.

After assembly, the metal detector works immediately and does not require any adjustments, except for setting the response threshold with a variable resistor. Well, this is standard procedure for a metal detector.
So, friends, collect the things you need and, as they say, they will come in handy around the house. For example, to search for electrical wiring in a wall, even nails in a log...

Finding artifacts underground is a fairly popular activity. For some, this is a profession, others are simply interested in archaeology. There are numerous groups of treasure hunters: both romantics and pragmatic treasure hunters. All these people are united by one passion: searching for metal objects hidden at various depths.

Just because you have an accurate map showing where the treasure is buried, or plans for fighting during the war, this does not guarantee success. You can shovel tons of soil, and the desired item will calmly lie a couple of meters from the active search site.

To search for gold and less valuable metals, you will need a metal detector that you can make yourself.

Important information: The use of such devices is not prohibited by law. However, there are penalties for the consequences of such a search regarding excavations, as well as the recovery of discovered objects.

We won’t go into details; that’s the topic of another article. Simply put: if you find a gold ring on the beach, or a handful of Soviet coins in the forest, there will be no problems associated with the use of electronic search tools.

But for recovered bronze spoons that are 100 years old or older, you can get a real sentence or a large fine.

Nevertheless, devices for searching for metal objects in the depths of the earth are freely sold, and those who want to save money can make a metal detector with their own hands at home.

How the device works

Unlike ground detectors, which work using waves of different frequencies or ultrasound, a metal detector (either factory-made or home-made) works with inductance.

The coil emits an electromagnetic field, which is then analyzed by the receiver. If any object that conducts electric current or has ferromagnetic properties is in the coverage area, the field format is distorted. More precisely, under the influence of the active field of the coil, the object forms its own. This event is recorded by the receiver, and an alert is generated: the instrument needle moves, a tone sounds, and indicator lights light up.

Knowing the operating method, you can calculate the electrical circuit and create a powerful metal detector with your own hands. The complexity of the design depends only on the availability of the element base and your desire. Let's look at several popular options for assembling a homemade metal detector:

The so-called "butterfly"

This nickname was received due to the characteristic shape of the platform on which the inductors are located.

The arrangement of the elements is related to the operating principle. The circuit is made in the form of two generators operating at the same frequency. When identical coils are connected to them, an induction balance is created. As soon as a foreign object with electrical conductivity gets into the electromagnetic field, the balance of the field is destroyed.

Generators are implemented on NE555 chips. The illustration shows a typical diagram of such a device.

The coil for the metal detector (there are two of them, in the diagram: L1 and L2) is made with your own hands from wire with a cross section of 0.5–0.7 mm². The ideal option is a transformer winding copper core in varnish insulation (removed from any unnecessary transformer). The characteristics do not have to be maintained with pinpoint precision, under one condition: the coils must be identical.

Approximate parameters: diameter 190 mm, each coil has exactly 30 turns. The assembled product must be monolithic. To do this, the turns are grabbed with a mounting thread and filled with transformer varnish. If this is not done, vibration of the turns will throw the circuit off balance.

Electrical diagram

There are two manufacturing options:

• given the small number of elements, you can assemble it on a breadboard by connecting the legs of the parts using conductors;
• For accuracy and reliability, it is better to etch the board according to the proposed drawing.

Any “snot-based” soldering can fail in the field, and you will be offended for wasting your time.

Just like a transistor metal detector, the NE555 device needs fine tuning before use. The diagram shows three variable resistors:

• R1 is designed to adjust the frequency of the generator and achieve that same balance;
• R2 coarsely adjusts sensitivity;
• Using resistor R3, you can set the sensitivity with an accuracy of 1 cm.

Information: This scheme cannot discriminate against metals. The seeker only makes it clear that the object exists. And by the tone of the signal (based on your experience) you can determine the approximate volume and depth of the deposit.

The power supply is quite universal: 9–12 volts. You can select a battery from an uninterruptible power supply, or assemble a power supply from AAA batteries. A good option is 18650 batteries (they are also used for vaping).

Butterfly setting

The principle of operation is described above, so let’s just look at the technology. We set all resistors to the middle position, and ensure that the synchronization of the generators is disrupted. To do this, we fold the coils in a figure eight and move them relative to each other until the squeaking turns into crackling. This is a synchronization failure.

We fix the rings and rotate the resistor R1 until a steady crackling sound appears at even intervals.

By bringing metal objects to the place where the coils overlap (this is the search point), achieve a steady squeak. The sensitivity is adjusted by resistor R2.

All that remains is adjustment with resistor R3, which is used rather to correct the voltage drop in the power source.

Mechanical part

A do-it-yourself metal detector rod is made from a lightweight plastic pipe or wood. The use of aluminum is undesirable as it will interfere with operation. The circuit and controls can be hidden in a sealed housing (for example, a junction box for wiring).

The butterfly finder is ready to go.

Pirate

Another popular pulse model for beginner treasure hunters is the “Pirate” metal detector. It is also easy to make with your own hands, detailed instructions in two versions:

It is advisable to bring the power supply closer to 12 volts, since the quality of operation depends on the voltage. Printed circuit boards have already been tested, both options are shown in the illustration.

The coil (in this case one) is made from the same 0.5 mm transformer wire. The optimal diameter is 20 mm, the number of turns is 25. Since we are making the “Pirate” metal detector with our own hands, the external design fades into the background. Any materials that you were ready to throw away will do.

It is better to make the handle detachable for ease of transportation. We remember that the use of metals is unacceptable.

Sensitivity is adjusted by two variable resistors in real time while searching. No fine tuning of the generator is required.

And if you manage to properly seal the case, you can start searching for “treasures” in the beach surf, and even at the bottom of the reservoir.

It is more difficult to make an underwater metal detector with your own hands, but it will give you an undeniable advantage over your competitors.

Improved performance

You can make a deep metal detector with your own hands from a ready-made “Pirate” without additional costs. There are two ways to do this:

1. Increasing the diameter of the inductor. This significantly increases downward permeability, but reduces sensitivity to small objects.
2. Reducing the number of coil turns while simultaneously adjusting the circuit. To do this, you will have to sacrifice one coil for experiments. We remove (and cut off) turn after turn until we see that the sensitivity begins to decrease. We remember the number of turns at maximum parameters, and make a new coil for this circuit. Then we change the resistor R7 to a variable one, with similar power parameters. After conducting several experiments with sensitivity, we fix the resistance and change the variable to a constant resistor.

The Pirate metal detector can be assembled using the popular Arduino controller.

It is more convenient to use such a device, but there will still be no metal discrimination.

Having figured out how to make a metal detector with your own hands for amateur tasks, we will briefly examine several serious models.

DIY metal detector Clone PI W

In essence, this is a cheaper version of the professional finder Clone PI-AVR, only instead of an LCD display, a line of LEDs is used. This is not as convenient, but still allows you to control the depth of artifacts.

The best option for the price is the CD4066 chip and ATmega8 microcontroller.

Of course, there is also a printed circuit board layout for this solution, only the control buttons are placed on a separate panel.

Programming ATmega8 is a topic for a separate article; if you have worked with such controllers, no difficulties will arise.

The powerful Clone PI W metal detector, made by yourself, allows you to find metal no more than a meter deep, although without discrimination.

Seeker "Chance"

A similar circuit on the ATmega8 controller is called “Chance”. The principle of operation is similar, only the possibility of screening out (partial discrimination) of ferrous metals has become possible.

A printed circuit board design has also been worked out, which can be successfully replaced with a classic “breadboard” for Arduino

DIY Terminator 3

If you need a homemade metal detector with metal discrimination, pay attention to this model. The scheme is quite complicated, but your efforts pay off with the coins you find, which may turn out to be gold.

The peculiarity of the “Terminator” is the separation of the receiving and transmitting coils. A 200 mm ring is made to emit the signal. 30 turns of wire are laid for it, then it is cut, as a result we get 2 half-coils with a total capacity of 60 turns (see diagram).

The receiving coil is located inside, 48 turns with a diameter of 100 mm.

The adjustment is made using an oscilloscope; after achieving optimal amplitude results, the windings are fixed in the housing by pouring epoxy resin.

Then an experimental hands-on adjustment of the discrimination switch is performed. For this, real objects made of various metals are used, and their type is marked on the mode switch (after verification).

Radio amateurs are working on an improved version of Terminator 4, but there is no practical copy yet.

Simple metal detectors from ready-made electrical appliances

Bottom line

Regardless of the complexity of the design, making a homemade metal detector will require a lot of time and effort from you. Therefore, out of curiosity, such devices are not made. But for professional use, this is an excellent alternative to factory copies.

Video on the topic

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 you 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′ wood 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 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 winding 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.