Scheme of a metal detector for non-ferrous metals. Powerful do-it-yourself Pirat metal detector. And as negative traits, they distinguish

A deep metal detector is similar in design to a conventional one, with the exception of some technical details. It also differs in increased sensitivity to metal objects, which makes it possible to detect them at a greater depth compared to a simple metal detector. In addition, there is a selective search function, that is, the ability to find objects of a certain size without reacting to inappropriate parameters.

Diagram of a deep metal detector

It is quite simple, despite the apparent complexity. The metal detector consists of two parts - receiving and transmitting. The main device is a high frequency transmitter generator. Two loop antennas, one of which serves as a signal transmitter, the second as a receiver. They must be located strictly at an angle of 90 degrees to each other to prevent the signal from the generator from being picked up by the receiving antenna. When a metal object is found, the magnetic field generated by the generator is distorted and subsequently picked up by the receiving antenna. In this case, the mass of a metal object is used as a radiation source, sending the energy produced to the receiving antenna.

Metal detector receiver circuit

The transmitter includes a thyristor with a power of 0.25 to 1 W, a sound generator with a frequency of 200 Hz. When a metal object is found, the operator hears a sound with a frequency of 200 Hz, the strength of which depends on the size of the found object and the distance to it.

A detector receiver whose oscillation circuit responds to a frequency of 120 kHz and consists of two diodes. Absolutely any low-frequency generator that can be found in an old radio can serve as an amplifier. Enough transistor amplifier in the amount of 5-6 pieces. A transistor is also used as a current amplifier for a pointer device, which allows you to measure the level of the received signal. That is, the device has two types of indicators - visual and acoustic. The frequency of operation is set in such a way as not to interfere with the operation of the signal receiver.

Transmitter circuit

Required parts and tools for assembly

To assemble such a metal detector, you must first prepare a set of necessary parts and tools.

In the case of a pulse metal detector, an approximate parts list will look like this:

1. Electrolytic capacitors with a voltage of at least 16 V of the following capacities: 2 capacitors with a capacity of 10 uF, one with a capacity of 2200 uF, 2 pcs - 1 uF.
2. Ceramic capacitors: 1 piece with a capacity of 1 nF.
3. Film capacitors of the lowest voltage value, for example, 63 V - 2 pcs of 100 nF each.
4. Resistors of 0, 125 W: 1 k - one, 1.6 k - one, 47 k - one, 62k - two, 100 k - one, 120 k - one, 470 k - one, 2 ohms - one, 100 ohms - one, 470 ohm - one, 150 ohm - one,
5. Resistors of 0.25 W: 10 ohms - one.
6. 0.5 W resistors: 390 ohms - one
7. Resistors 1 W: 220 ohms - one.
8. Variable resistors: 10 k - one, 100 k - one,
9. Transistors: BC 557 - one, BC 547 - one, IRF 740 - one,
10. Diodes: 1N4148 - two, 1N4007 - one.
11. Chips: K157 UD2, NE555.
12. panels for each.

Metal detector parts

From tools when performing work you will need:

• Soldering iron, tin, special solder, other soldering accessories.
• A set of screwdrivers, wire cutters, pliers and other metalwork tools.
• Materials for the production of printed circuit boards.

Stages of assembling a metal detector

The process of assembling a deep metal detector with your own hands includes the following steps:

At the first stage, it is necessary to assemble the electronic part, namely the control unit.

The step by step process looks like this:

• Cutting textolite of the required size.
• Preparation of a printed circuit board drawing and its transfer directly to the board.
• Preparation of pickling solution. It consists of table salt, electrolyte and hydrogen peroxide.
• Etching the board and drilling process holes.
• Tinning the board with a soldering iron.
• Next comes the most important stage in the assembly of the control unit. This is the selection, search and soldering of parts directly to the board.
• Winding the test coil. There are several options for winding it. The easiest option is to use a 0.5 PEV wire and wind it 25 turns on a suitable frame with a diameter of about 19-20 cm.

The best option would be to solder everything directly, and after the setup is completed, select the necessary connectors and adapters. It is better not to twist, it has a negative effect on the sensitivity of the device.

The second good option would be to make such a ring from a twisted pair wire. It will take about 2.5 - 2.7 m of wire.

To achieve maximum sensitivity, do the following:

1. Wind 25 turns of wire.
2. Carry out a test by cutting off small pieces of wire and observing the increase in sensitivity.
3. It is necessary to do this until the sensitivity begins to decrease.
4. Count the number of turns, wind the final version of the coil by adding 1-2 turns. Thus, the maximum sensitivity value is reached.

Upon completion of the main work, the control unit, coil and other parts are fixed in place on the rod. The metal detector can be turned on and checked.

Possible assembly problems

• The assembled device does not react to metal objects. The cause may be a breakdown of the diodes, or the transistor. Defective parts need to be replaced.
• Excessive heating of the transistor. You should install a resistor of lower resistance, reducing it until the heating stops.

The assembly of this type of metal detector is not too difficult, with strict observance of all the rules and instructions.

Metal detectors are used to detect invisible objects that, in their electromagnetic properties, differ from the environment in which they are located. Metal detectors are used by: amateur archaeologists, geologists, treasure hunters. Also, sappers use these devices to detect shells, builders, to search for metal parts of structures (reinforcement, pipes ...).

Most metal detectors look very similar, but in fact they differ greatly in their properties, and depending on the purpose of use. Here are some photos of commonly used metal detectors. As well as a diagram of a simple metal detector.

How are metal detectors arranged?

The device of the metal detector is quite simple. And you can assemble it yourself at home. For this, you do not need to have deep knowledge in electrical engineering. We have prepared for you step-by-step instructions that will help you assemble an amateur metal detector from improvised means.

But first, let's find out what types of metal detectors exist, what properties different models have, and how to choose the right model for you. In order to choose a suitable type of metal detector for yourself, you need to decide: what technical characteristics you need.

Here are a few characteristics by which the quality of the device is judged:

penetrating power of the detector. How deep does the electromagnetic field of the detector coil penetrate? This determines how deeply the device will "see" the metal in the ground or other environment.

Covered search area. Usually metal detectors examine the ground in strips. This parameter determines the width of such stripes.

The susceptibility of the device. Whether your metal detector will detect small metal objects (such as coins) depends on this.

Fragmentation of the detector. This feature is responsible for the detector's ability to respond only to the items it is looking for (eg non-ferrous metals).

Seeker resistance to interference. In addition to its own electromagnetic field, the device can get into the electromagnetic fields of other devices. (mobile devices, power lines, radio stations…). The best metal detectors are those that do not respond to the fields of other sources.

Energy intensity. How many hours of searching should be enough for one charge of batteries or accumulator.

Frequency classification

In addition, metal detectors are classified according to their operating frequency. Exist:

Metal detectors operating at ultra-low frequencies. Such devices are used only by professionals. They have good technical parameters, but their operation requires tens of watts of energy. They are usually installed on special vehicles with high-capacity batteries and equipment that allows you to determine the size, shape and structure of the detected objects.

Metal detectors operating in the low frequency range (from 300 Hz to several thousand Hz). Easily manufactured. Resistant to interference, but have low susceptibility. They are also called deep detectors (“they see” metal at a depth of up to five meters).

Metal detectors with increased operating frequency range. (up to several tens of kHz). They are more difficult to assemble than low-frequency ones. Their penetrating ability is up to one and a half meters. Good for detecting small objects. They are rarely used due to their low technical specifications.

How to assemble a metal detector with your own hands at home

7 easy steps:

• In order to assemble a metal detector, we need a Chinese radio (must have a magnetic antenna, AM band), a cheap calculator, a box and double-sided tape.
• We unfold the box so that it has the shape of a book (on the one hand the main part, on the other the lid)
• We glue the radio device and the calculator to the book on double-sided tape. (the radio is attached to the lid, and the calculator to the base of the box).
• We turn on the receiver and find the frequency segment that is not used by radio stations (about 1.5 MHz).
• Let's start with the calculator. At the same time, the radio begins to make a lot of noise.
• We begin to slowly bring the lid of the box closer to the main part. We need to find the position when the noise disappears.
• We fix the book in this position. Ready! You have made the simplest amateur metal. detector.

Metal detectors with metal discrimination

Among all metal detectors, devices with a discrimination function are considered especially effective. What does it mean?

The metal detector not only shows the presence of an object with a characteristic field in the ground, but also displays on the screen the approximate shape, size and material of the detected object.

Of course, with such a device, work is much more efficient (no need to dig the ground with each detector signal) and requires less time. But such metal detectors consume energy very quickly. Plus they are several times more expensive. For an amateur treasure hunt, a cheaper analogue is also suitable.

We hope that our article was useful for you, helped you understand the main types of metal detectors, and perhaps even suggested how to make your own amateur metal detector!

DIY metal detector photo

With the onset of spring, more and more often on the banks of the rivers you can meet people with metal detectors. Most of them are engaged in "gold mining" purely out of curiosity and excitement. But a certain percentage really earns a lot of money looking for rare gizmos. The secret of the success of such research is not only in experience, information and intuition, but also in the quality of the equipment with which they are equipped. A professional tool is expensive, and if you know the basics of radio mechanics, then you have probably thought more than once about how to make a metal detector with your own hands. The editors of the site will come to your aid and tell you today how to assemble the device yourself using diagrams.

Read in the article:

Metal detector and its device

Such a model costs more than 32,000 rubles, and, of course, such a device will not be affordable for non-professionals. Therefore, we suggest studying the device of a metal detector in order to assemble a variation of such a device yourself. So, the simplest metal detector consists of the following elements.

The principle of operation of such metal detectors is based on the transmission and reception of electromagnetic waves. The main elements of a device of this type are two coils: one is a transmitter, and the second is a receiver.

The metal detector works like this: the magnetic lines of force of the primary field (A) of red color pass through the metal object (B) and create a secondary field in it (green lines). This secondary field is picked up by the receiver and the detector sends a sound signal to the operator. According to the principle of operation of emitters, electronic devices of this type can be divided into:

1. Simple, working on the principle of "reception-transmission".
2. Induction.
3. Pulse.
4. Generator.

The cheapest devices are of the first type.

An induction metal detector has one coil that sends and receives a signal at the same time. But devices with pulse induction differ in that they generate a transmitter current that turns on for a while and then turns off abruptly. The coil field generates pulsed eddy currents in the object, which are detected by analyzing the attenuation of the pulse induced in the receiver coil. This cycle repeats continuously, maybe hundreds of thousands of times per second.

How a metal detector works depending on the purpose and technical device

The principle of operation of a metal detector varies depending on the type of device. Let's consider the main ones:

• Dynamic Type Devices. The simplest type of device that scans the field all the time. The main feature of working with such a device is that it is necessary to be in motion all the time, otherwise the signal will disappear. Such devices are easy to use, however, they are weakly sensitive.
• Devices of impulse type. They have great sensitivity. Often, such a device comes with several additional coils for tuning to different types of soils and metals. Requires certain skills to set up. Among the devices of this class, one can single out electronic devices operating at a low frequency - not higher than 3 kHz.

• Electronic devices, on the one hand, do not give a reaction (or give a weak one) to unwanted signals: wet sand, small pieces of metal, shot, for example, and, on the other hand, provide good sensitivity when searching for hidden water pipes and central heating routes, as well as coins and other metal objects.
• Depth detectors imprisoned for the search for objects located at an impressive depth. They can detect metal objects at a depth of up to 6 meters, while other models “penetrate” only up to 3. For example, the Jeohunter 3D depth detector is capable of searching and detecting voids and metals, while showing objects found in the ground in 3- measured form.

Deep detectors work on two coils, one is parallel to the ground surface, the other is perpendicular.

• Stationary detectors- this is a framework established at especially important protected objects. They calculate any metal objects in the bags and pockets of people passing through the loop.

Which of the metal detectors are suitable for DIY at home

The simplest devices that you can assemble yourself include devices that work on the principle of receiving and transmitting. There are schemes that even a novice radio amateur can do, for this you just need to pick up a certain set of parts.

There are many video instructions on the Internet with a detailed explanation of how to make a simple metal detector with your own hands. Here are the most popular ones:

1. Metal detector "Pirate".
2. Metal detector - butterfly.
3. Emitter without microcircuits (IC).
4. A series of metal detectors "Terminator".

However, despite the fact that some entertainers are trying to offer systems for assembling a metal detector from a phone, such designs will not pass the “battle” test. It’s easier to buy a children’s toy metal detector, it will be more sense.

And now more about how to make a simple metal detector with your own hands using the Pirate design as an example.

Homemade metal detector "Pirate": a diagram and a detailed description of the assembly

Homemade products based on the metal detector of the Pirate series are one of the most popular among radio amateurs. Due to the good working qualities of the device, it can “detect” an object at a depth of 200 mm (for small items) and 1500 mm (large items).

Parts for assembling a metal detector

Metal detector "Pirate" is a device of impulse type. To make the device, you will need to purchase:

1. Materials for the manufacture of the body, rod (you can use a plastic pipe), holder and so on.
2. Wires and electrical tape.
3. Headphones (suitable from the player).
4. Transistors - 3 pieces: BC557, IRF740, BC547.
5. Chips: K157UD2 and NE
6. Ceramic capacitor - 1 nF.
7. 2 film capacitors - 100 nF.
8. Electrolytic capacitors: 10 microfarad (16 V) - 2 pieces, 2200 microfarad (16 V) - 1 piece, 1 microfarad (16 V) - 2 pieces, 220 microfarad (16 V) - 1 piece.
9. Resistors - 7 pieces per 1; 1.6; 47; 62; one hundred; 120; 470 kOhm and 6 pieces for 10, 100, 150, 220, 470, 390 Ohm, 2 pieces for 2 Ohm.
10. 2 diodes 1N148.

Do-it-yourself metal detector schemes

The classic circuit of the metal detector of the "Pirate" series is built on the NE555 chip. The operation of the device depends on the comparator, one output of which is connected to the IC pulse generator, the second to the coil, and the output to the speaker. In case of detection of metal objects, the signal from the coil goes to the comparator, and then to the speaker, which notifies the operator about the presence of the objects being searched for.

The board can be placed in a simple junction box, which you can buy at an electrician's store. If such a tool is not enough for you, you can try to make a device of a more perfect plan, a scheme for making a metal detector with a reference to gold will help you.

How to assemble a metal detector without using chips

This device uses Soviet-style transistors KT-361 and KT-315 to generate signals (you can use similar radio components).

How to assemble a metal detector circuit board with your own hands

The pulse generator is assembled on the NE555 chip. Through the selection of C1 and 2 and R2 and 3, the frequency is adjusted. The pulses obtained as a result of scanning are transmitted to transistor T1, and it transmits a signal to transistor T2. Amplification of the audio frequency occurs on the transistor BC547 to the collector, and headphones are connected.

To place radio components, a printed circuit is used, which can be easily made independently. To do this, we use a piece of sheet getinax covered with copper electrical foil. We transfer the connecting parts to it, mark the attachment points, drill holes. We cover the tracks with a protective varnish, and after drying, we lower the future board into ferric chloride for etching. This is necessary to remove unprotected sections of copper foil.

How to make a coil for a metal detector with your own hands

For the base, you need a ring with a diameter of about 200 mm (ordinary wooden hoops can be used as the base), on which 0.5 mm wire is wound. To increase the depth of metal detection, the coil frame should be in the range of 260–270 mm, and the number of turns should be 21–22 rpm. If you do not have anything suitable on hand, you can wind the coil on a wooden base.

Coil of copper wire on a wooden base

Illustration	Action Description
	For winding, prepare a board with guides. The distance between them is equal to the diameter of the base on which you will mount the coil.
	Wind the wire around the perimeter of the fasteners in 20-30 turns. Fasten the winding with electrical tape in several places.
	Remove the winding from the base and give it a rounded shape, if necessary, additionally fasten the winding in a few more places.
	Connect the circuit to the device and test its operation.

Twisted pair coil in 5 minutes

We will need: 1 twisted pair 5 cat 24 AVG (2.5 mm), a knife, a soldering iron, solder and a multitester.

Illustration	Action Description
	Fold the wire into two skeins with a pigtail. Leave 10 cm on each side.
	Strip the winding and free the wires for connection.
	We connect the wires according to the diagram.
	For better fixing, solder them with a soldering iron.
	Test the coil in the same order as the copper wire device. The winding leads must be soldered to a stranded wire with a diameter in the range of 0.5–0.7 mm.

Brief instructions for setting up a do-it-yourself Pirate metal detector

After the main elements of the metal detector are ready, we proceed to assembly. We fix all the nodes on the metal detector rod: a body with a coil, a receiving-transmitting unit and a handle. If you did everything correctly, then additional manipulations with the device will not be required, since it initially has maximum sensitivity. Finer tuning is performed using a variable resistor R13. Normal operation of the detector should be ensured with the middle position of the regulator. If there is an oscilloscope, then with its help at the gate of the transistor T2 it is necessary to measure the frequency, which should be 120–150 Hz, and the pulse duration should be 130–150 μs.

Is it possible to make an underwater metal detector with your own hands

The principle of assembling an underwater metal detector is no different from the usual one, with the only difference being that you have to work on creating an impenetrable shell using a sealant, as well as placing special light indicators that can report a find from underwater. An example of how it will work in the video:

Do-it-yourself metal detector "Terminator 3": detailed diagram and video assembly instructions

For many years, the Terminator 3 metal detector has taken pride of place in the ranks of homemade metal detectors. The two-tone device works on the principle of induction balance.

Its main features are: low power consumption, metal discrimination, non-ferrous metal mode, gold only mode and very good search depth performance compared to semi-professional branded metal detectors. We offer you the most detailed description of the assembly of such a device from the craftsman Viktor Goncharov.

How to make a do-it-yourself metal detector with metal discrimination

Metal discrimination is the ability of the device to distinguish between the detected material and to classify it. Discrimination is based on the different electrical conductivity of metals. The simplest ways to determine the types of metals were implemented in old devices and entry-level devices and had two modes - “all metals” and “non-ferrous”. The Discrimination feature allows the operator to respond to a phase shift of a certain amount compared to a set (reference) level. In this case, the device cannot distinguish between non-ferrous metals.

How to make a homemade professional metal detector from improvised means in this video:

Features of deep metal detectors

Metal detectors of this type can detect objects at great depths. A good do-it-yourself metal detector looks to a depth of 6 meters. However, in this case, the size of the find should be solid. Such detectors work best for detecting old shells or debris of a sufficiently large size.

There are two types of deep metal detectors: frame and transceiver on the rod. The first type of device is capable of covering a large area of ​​land for scanning, however, in this case, the efficiency and focus of the search is reduced. The second variant of the detector is a point one, it works directed deep into a small diameter. It must be handled slowly and carefully. If you set a goal - to build such a metal detector, the following video may tell you how to do it.

If you have experience in assembling such a device and its application, tell others about it!

It was developed on the basis of the already known device "Terminator Pro". Its main advantage is high-quality discrimination, as well as low current consumption. Also, the assembly of the device will not be expensive, and it is able to work on any type of soil.

Here are the brief specifications of the device
According to the principle of operation, the metal detector is also pulse-balanced.
The operating frequency is 8-15 kHz.

As for the discrimination mode, two-tone voice acting is used here. When iron is detected, the device gives a low signal, and if a non-ferrous metal is found, the tone will be high.

The device is powered by a source of 9-12V.

There is also the possibility of adjusting the sensitivity and there is a manual detuning from the ground.

Well, now about the main thing, about the depth of detection of a metal detector. The device is able to detect coins with a diameter of 25 mm at a distance of 35 cm through the air. The golden ring can be caught at a distance of 30 cm. The device detects a helmet at a distance of about 1 meter. The maximum detection depth is 150 cm. As for consumption, without sound it is about 35 mA.

Assembly materials and tools:
- minidrill (the author has a self-made motor);
- wire for winding the coil;
- four core shielded cable;
- soldering iron with solder;
- materials for the manufacture of the case;
- printed circuit board;
- all the necessary radio components and their ratings can be seen in the photo of the circuit.

Metal detector manufacturing process:

Step one. Board manufacturing
The board is made by etching. Then you can drill holes, their diameter is 0.8 mm. For these purposes, the author uses a small motor with a drill installed.

Step two. Board Assembly
The assembly must begin with soldering the jumpers. After that, you can install panels for microcircuits and other solder other elements. It is very important to have a tester for quality assembly that can measure the capacitance of capacitors. Since the device uses two identical amplification channels, the amplification for them should be as close as possible to the same value, that is, be the same. Both channels of the same stage must have the same readings when measured by the tester.

What the already assembled circuit looks like can be seen in the photo. The author did not install a node that determines the degree of battery discharge.

After assembly, the board must be checked by a tester. You need to connect power to it and check all the strategically important inputs and outputs. Everywhere food should be exactly the same as in the diagram.

Step three. Assembling the coil
The DD sensor is assembled according to the same principle as for all similar balancers. The transmitting coil is denoted by the letters TX, and the receiving coil is RX. In total, you need to make 30 turns with a wire folded in half. The wire used is enameled, with a diameter of 0.4 mm. Both the receiving and transmitting coils are formed by double wires, resulting in four wires at the output. Next, the tester needs to determine the arms of the windings and connect the beginning of one arm to the end of the other, as a result, the average output of the coil is formed.

To fix the coil after winding, it is necessary to wrap it well with threads and then soak it with varnish. After the varnish dries, the coils are wrapped with electrical tape.

Subsequently, a foil screen is made from above, a gap of about 1 mm must be made between the beginning and end in order to avoid a short-circuited coil.

The middle output of the TX must be connected to the ground of the board, otherwise the generator will not start. As for the middle RX output, it is needed for frequency tuning. After tuning the resonance, it must be isolated and the receiving coil turns into a normal one, that is, without an output. As for the receiving coil, it is connected instead of the transmitting one and tuned 100-150 Hz lower than the transmitting one. Each coil must be tuned separately; when tuning, there should not be any metal objects near the coil.

To bring the balance, the coils are shifted, as you can see in the photo. The balance should be within 20-30 mV, but not more than 100 mV.

The operating frequencies of the device are in the range from 7 kHz to 20 kHz. The lower the frequency, the deeper the device will take, but at a low frequency, discrimination becomes worse. Conversely, the higher the frequency, the better the discrimination, but the lower the depth of detection. The golden mean can be considered a frequency of 10-14 kHz.

To connect the coil, a four-wire shielded wire is used. the screen is connected to the body, two wires go to the transmitting coil and two to the receiving one.

This article will focus on one of the simple metal detectors, the assembly of which can be done with affordable Soviet radio components. These include transistors marked KT and MP, as well as resistors and capacitors from popular radio equipment. Most of the necessary parts can be easily found in old radio devices.

The scheme consists of five nodes, the structure of which can be viewed in Figure 1:

1. A master frequency oscillator used to create a reference frequency.
2. Search frequency generator. Its frequency will change when metal is found.
3. Low-frequency amplifier to increase the signal difference of the generators.
4. The node that plays the sound.
5. Source of power.

This device resembles a metal detector on two transistors, but it has an added sound amplifier, and, despite its simplicity, it has good metal detection performance. It is perfect for mass search and collection of ferrous metal. If you find radio components and a little time, then you can easily assemble a metal detector using this informative article as an example.

Assembly of circuit elements

The assembly of the circuit can be carried out on a one-sided foil textolite. Guided by Figure 2, which shows a transistor metal detector circuit, we count the number of connections and create the corresponding number of contact pads with a sharp object. After tinning, the board is ready for assembly of parts (Fig. 3). For a better assembly, you can think over and draw a homemade printed circuit board.

Below is a list of required parts and instructions for some of them:

1. 14 resistors with a power of 0.125 W. Denominations:
   1. R1, R5 - 100 kOhm;
   2. R2, R6, R11 - 10 kOhm;
   3. R3, R7 - 1 kOhm;
   4. R4, R8 - 5.1 kOhm;
   5. R9 - 6.2 kOhm;
   6. R10, R13 - 220 kOhm;
   7. R12 - 3.9 kOhm;
   8. R14 - 3 kOhm.
2. 14 capacitors, preferably heat resistant:
   1. Electrolytic for 6 V: C10, C14 - 47 microfarads; C12, C13 - 22 uF;
   2. Variable capacitors C7 - up to 10 pF / from 150 pF;
   3. Trimmer capacitor C8 - 6 / 25 pF;
   4. C1, C11 - 47 nF;
   5. C2, C6 - 4.7 nF;
   6. C3 - 100 pF;
   7. C4 - 47 pF;
   8. C5, C9 - 2.2 nF.
3. Five transistors:
   1. 3.1 VT1, VT2 - KT315. As analogues, you can use KT3102, KT312 or KT316;
   2. 3.2 VT3, VT4, VT5 - MP35. You can replace it with MP from 36 to 38;
   3. 3.3 VT6 - MP39. MP from 40 to 42 will also do;
4. 2 diodes D9Zh, or others - D18, D2, GD 507.
5. 4.5 V battery in the form of three AA batteries. You can use a 9 V krona battery, but in this case it is necessary to change the electrolytic capacitors to a voltage higher than 9 V.
6. Speaker impedance from 5 to 100 ohms. Suitable speakers from children's toys, intercom handsets, radios or a headset.
7. Contact connector for the battery (Fig. 4).
8. Microswitch or toggle switch to turn off.

Metal detectors cannot work without coils that play a major role in the device. In the next paragraph of the article, we will describe in detail their role in the work and the manufacturing process.

Creation of generator coils

The primary coil L1 is exemplary and, together with the capacitor C3, serves to create the master frequency of the generator. The secondary coil L2 works in the same way, but it is made without a core. This allows metal objects to act on it and change the frequency of the generator, which leads to a frequency difference for the signal.

The following describes how to make homemade coils without much difficulty.

For the frame of the L1 coil, a metal rod with a diameter of 8 mm and a length of 3 cm is needed. An antenna with a radio can be used. Whatman paper must be wound on the rod. We do this in order to be able to adjust the frequency by moving the rod relative to the coil, so it is important that the paper fits very tightly to prevent spontaneous movement. After the final adjustment of the metal detector in the last paragraph, you can fix the rod with glue. A sample coil is shown in Figure 5.

We wind the L1 coil with a PEV wire with a diameter of 0.2 - 0.3 mm. We wind 110 turns on whatman paper strictly in one row, trying to avoid gaps or gaps between the turns. On the 16th turn, we make a tap without breaking the wires. After winding, the wire can be varnished, but the movement of the metal rod inside must be maintained. We make the wire connection according to the diagram.

The second coil L2 is made in the form of a rectangular frame measuring 12 x 22 cm. The frame can be made of plastic, plexiglass, plywood and other non-conductive material. We make a tray or collect only a supporting rectangle in which it will be possible to lay the winding in bulk. Finished samples can be seen in Figure 6.

The wire, as in the first case, we choose the PEV brands, but with a diameter of 0.4 - 0.6 mm. We wind 45 turns, making a conclusion on the 10th turn. After complete manufacturing and adjustment of the metal detector, it will be possible to fix and insulate the winding with varnish. The connection to the circuit is carried out with a shielded cable with at least two cores. Such cables are used in high-quality audio equipment and in trunk communication lines, they can also be purchased at an electronics store.

Production of a metal detector design

First of all, you need to decide what material to make the bar. It is better to give preference to a dielectric material in order to eliminate problems in the operation of the metal detector. There are many options: PVC pipe, telescopic fishing rod, wooden pole. When choosing, it is worth considering indicators such as weight, flexibility, ability to disassemble, convenience.

If you plan to spend a lot of time looking for metal, the light weight and comfortable armrest with handle will save you a lot of effort. But do not forget that lightweight material can bend. In the case of a PVC pipe, this can be compensated by sand poured inside or additional supporting structures. With a collapsible bar there will be no problems with transportation. To implement this idea, you can visit a plumbing store and assemble an excellent metal detector with your own hands on various adapters (Fig. 7).

After you have decided on the choice of the rod, you need to fix the coil on it. Everything is simple - no metal. Use plastic fasteners, pre-fixed ears on the coil frame, adapters, or just reliable glue.

The scheme is placed in a plastic box. For the speaker, you can make small holes for good audibility. The board, speaker, primary coil and battery box can be fixed with glue. We place the box a meter from the search coil and fasten it in a convenient way - using plastic fasteners or glue.

At this point, you have assembled a simple transistor metal detector that needs to be fine-tuned and checked.

Device setup

Setting up the metal detector is to create the same frequency in both generators. When such a result is achieved, the lowest, barely audible tone will be emitted from the speaker.

To begin with, we remove all metal objects from the range of the metal detector. We take into account concrete walls and floors, as they may contain metal reinforcement. Set all variable capacitors to the middle position. By changing the position of the rod in the coil L1, we achieve the desired tone or its absence. With further operation of the device, we use capacitor C7 to adjust. After tuning, we bring a metal object to various distances from the search coil and make sure that the metal detector is working.

If the metal detector does not work, we check the blocks and details of the circuit. We start the test with transistors, and then we check the diodes. To check the sound amplifier, it is enough to fold the resistor R9 from the generators and connect it to the sound output of any device that reproduces sound (Fig. 8).

If the parts and the amplifier are in working condition, then we set up transistor generators. To do this, we try to change the values ​​​​of the capacitor C4 and the resistor R2 for the master oscillator, and the resistor R6 for the search oscillator. You can try to start the second generator with a tuning capacitor C8.