Schemes of capacitive metal detectors. A simple metal detector at home. Metal detector bridge circuit

Devices capable of detecting metal objects in weakly conductive environments are called metal detectors, or metal detectors. They can be used to search for ferrous and non-ferrous metals. A homemade metal detector for coins is capable of detecting small items at a distance of 10 to 50 cm, and larger metals from 0.5 to 3 m.

The use of metal detectors has been known since ancient times, and a large increase in their production occurred at the end of the 60s. Thanks to progress and a variety of schemes, any novice radio amateur can make a metal detector with his own hands, without resorting to extensive knowledge in electronics. The main advantage of homemade metal detectors is low costs.

Let's collect simple metal detector, operating on two frequency generators - a metal detector on beats. At the same frequency, the generators are synchronized, but when one of the metal coils enters the field, the frequency in one of the generators changes. As a result, the circuit reproduces the sound of the difference in frequencies of two generators in the dynamics.

Tools and materials for the device

To make a homemade metal detector, you need to divide the process into three stages - creating a design, implementing a circuit, and assembling it into a single whole. We will describe an approximate list of tools and materials that may be needed for these purposes. Further on in the article, we will explain in more detail: what a metal detector for gold can be assembled from, and what kind of material is best to use. Let's start by preparing a tool for beginning diggers. To work you will need:

1. Cutters for working with wires and parts;
2. Knife;
3. Saw for plastic. In extreme cases, you can use a knife or a regular saw;
4. Soldering iron;
5. Screwdriver set.

Required materials:

1. Insulating tape;
2. Soldering kit. You can just use rosin and solder;
3. Glue;
4. Parts and board for the circuit;
5. Wire for coil;
6. A piece of plastic and a plastic pipe;
7. Fasteners.

Preparing parts

Described here detailed instructions about choosing and searching for parts.

First, you need to decide on the material and fastening of the components of the metal detector and find the necessary components.

As a barbell, you can use a crutch with an armrest, a fishing rod, or a pipe made of cross-linked polyethylene or polyvinyl chloride (Fig. 2).

The coils and circuitry will be placed underneath on a stand attached to the rod. So it is important to consider the stiffness of the bar and its material. It is better to give preference to dielectrics, i.e. non-conductive electric current– plastic, wood and more. It is necessary to make a handle to make it comfortable to hold the metal detector being manufactured. In the case of a crutch, it is not needed, but in another case, you can attach either a bicycle handlebar or another homemade structure.

The stand for the circuit and coils can be made from ordinary plastic. It is easy to trim and weighs little. You will need one bottom sheet, since access to the coils is required to adjust the device. To reduce the vibration of the circuit with coils, it is advisable to choose stronger plastic.

After preparing the rod and stand, you need to connect them. You can use fasteners, but do not forget that for the circuit to work properly, you should not bring metal products closer than 30 cm. Therefore, we use good glue, for example, liquid nails. You can use other materials - it all depends on your abilities in plumbing and carpentry.

The wire for the coils must be insulated. Suitable enameled copper wire with a diameter of 0.5 - 0.7 mm grade PEV or PEL. The wire length is about 100 meters. An oil-based varnish is suitable for fixing parts.

The parts can be mounted using a hinged method on PCB or cardboard. For beginning radio amateurs, in specialized stores you can buy processed textolite from the factory or material with holes for parts. You can also make a board yourself from solid unprocessed PCB. To do this, you need to mark the location of the contacts of the radio components on the diagram, then separate the sections of the textolite with a knife and tin the pads and tracks (Fig. 3). We cut off the excess part of the PCB with a plastic saw.

To assemble a working metal detector, radio components can be found at home in old radio equipment, but it is advisable to purchase them in a store. Identical parts must be completely identical and preferably from the same batch. Table 1 provides a list of necessary parts and comments, the implementation of which will lead you to assembling a high-quality metal detector.

After finding all the necessary parts, you can easily assemble the metal detector at home.

Assembling the device

Having considered the list necessary materials and parts, we will answer in detail how to assemble a metal detector from them with your own hands.

To wind the coils, we use any round object with a diameter of 20 - 25 cm. The number of turns is 30. We bring out one end of the wire and wind 10 turns, after which, without breaking, we bring out the second end. We continue winding another 20 turns and bring out the third end. We make the wire leads with a margin of 10 to 20 cm. Remove the resulting winding from the object and wrap it tightly with electrical tape, leaving three wire leads (Fig. 5).

We perform the second coil in a similar way. For the greatest success, we make the coils as identically as possible, with a mirror image.

Let's start assembling the radio components. We arrange the parts on the board and carry out soldering according to the diagram in Figure 4. When using cardboard or material with holes, we connect the parts with insulated wires of any cross-section. When using prepared PCB, we perform soldering to the finished tracks. The circuit can be placed in a wooden or plastic box.

Solder the coil leads according to the diagram. We solder and bring out two wires with a connector for the battery.

We prepare a stand for the circuit and coils. We select the dimensions taking into account that the distance between the coils must be at least 10 cm, since the circuit and the attached rod must fit between them.

To properly secure the coils, temporarily attach the headphones to the circuit and insert the battery. By slightly moving the coils, we achieve silence in the headphones with single clicks or the highest possible, barely audible sound. We try to bring metal to one of the coils, if we hear significant changes, this indicates the functionality of the metal detector. We fix the coils and the board in this position. If possible, it is better to glue them immediately and then cover them with oil varnish.

For headphones, we make two holes in the rod - bottom and top. Using wire cutters, electrical tape and a soldering iron, we extend the headphone wire to the required length - from the circuit to the human ear area. You need to take growth into account right away. We stretch the wire inside the rod and solder it to the circuit.

We cut off the excess stand and attach the bar to it in a way convenient for you.

Adjustment

The most accurate setting is the absence of clicks in the headphones, and the presence of a barely audible high-frequency squeak.

Adjustment is carried out in three ways:

1. We bring the metal one by one to the coils. On the coil where the noise has stopped, we bring the last turn inside the coil ring.
2. You can use small pieces of aluminum. We bring them to the coils and achieve silence or single clicks. Secure with glue.
3. We attach a tube to the coil and insert a ferrite rod through it. Having achieved the desired result, we fix the rod in this position. Watch the video below, which demonstrates how to make a homemade regulator for tuning using this method.

With good hearing and experience, you can use the manufactured metal detector as a simple metal detector with discrimination, that is, with recognition of types of metal.

Modernization

If you have figured out how to make the simplest metal detector with your own hands, you can proceed with a small modernization without microcircuits in Figure 9. The list of parts is collected in Table 2.

IN new scheme an RC circuit has been added, consisting of a resistor and a capacitor. It will allow you to achieve increased sensitivity.

Variable resistors have been added to adjust the circuit without touching the coils. This will seal the sensitive unit of the metal detector in a durable box that protects it from shock.

Instead of headphones, you can use a speaker with a capacitor to increase the volume slightly.

In this scheme, the coils are placed one on top of the other, as shown in Figure 10. Before fixing the coils, we adjust them by moving them.

When turned on, we set the variable resistors to the same position and by rotating we achieve precise adjustment. After that, all that remains is to take a metal detector and go in search of nuggets or metals. Tested in practice - if you search on any Russian beach, you can find gold and silver.

This metal detector is capable of detecting: large metal objects (iron bucket, manhole cover, water pipe) at a depth of up to one meter, as well as small objects (coins or screws) at a depth of 15-20 cm.

The device is built on the basis of the most common parts that are available in the supplies of any radio amateur. The metal detector is made according to the well-known and widely used principle in such devices of beating between the frequencies of two high-frequency generators. The frequency of one of them (reference) is constant, and the frequency of the second (search) changes under the influence of external metal objects that change the inductance of its coil when it enters its action zone.

Schematic diagram

The schematic diagram of the metal detector is shown in Fig. 1. The reference oscillator is made on transistor VT1. Its oscillation frequency is determined by the parameters of the L1C3 circuit and is about 1 MHz.

The search generator is made on transistor VT2; it also produces a signal of approximately the same frequency. The difference is that the reference oscillator circuit uses a small coil with a ferrite core.

Fig 1. Schematic diagram of a simple homemade metal detector.

Therefore, external metal objects have practically no significant effect on its inductance.

The coil of the search generator circuit is wound on a larger frame in the form of a frame. It has no core. As a result, its inductance changes greatly as it approaches a metal object, which in this case begins to act as a moving core.

Signals from both generators are sent to a diode mixer using diode VD1. As a result, the product of subtraction of generator frequencies is obtained on capacitor C12.

The closer the values ​​of these frequencies, the lower the audio tone on this capacitor, and the more different the frequencies of the generators are, the higher the sound tone in speaker B1, to which the signal is received (the product of the diode mixer).

The signal enters through a low-frequency amplifier using transistors VTZ-VT6.

Using a variable capacitor C7, the search generator can be configured in such a way that, in the absence of metal objects nearby, the sound tone in the speaker is the lowest.

Then, as coil L2 approaches the metal, the frequency of the generator at VT2 begins to change. The frequency difference between the generators increases, and therefore the tone in the dynamics will rise. When the metal is precisely located, the sound will turn into a piercing squeak.

Details and design

Coil L1 should be wound on a ferrite rod with a diameter of 8 mm, for example, from a magnetic antenna of a radio receiver. The length of the rod is reduced to 30 mm.

First, you need to put a frame on the rod - a sleeve glued together from whatman paper, which moves along it with some friction.

Coil L1 should contain 110 turns of PEV wire with a diameter of 0.2-0.3 mm. The tap must be made from the 16th turn counting from the VT1 collector.

Coil L2 is a search coil. It must be wound on a frame, which is a frame measuring 120 x 220 mm, made of plexiglass, plastic or wood.

Winding should be done with PEV wire with a diameter of 0.4 x 0.6 mm. The coil should contain 45 turns with a tap from the 10th, counting from the VT2 collector.

The coil must be connected to the main unit with a three-core shielded wire. The coil should be located at a distance of about 1 meter from the main unit (attached to an aluminum tube or wooden strip).

The device itself (the main unit containing a generator on VT1 and an ultrasonic sounder with a speaker and a battery) can be mounted in a housing from a radio receiver. From the same receiver it is advisable to use:

• speaker;
• variable capacitor;
• coil rod L1.

The design may be different, it all depends on capabilities and desires.

Capacitor C7 can have a minimum capacitance of no more than 10 pF, and a maximum of no less than 150 pF.

Transistors KT315 can be replaced with KT3102 or KT312, KT316. Transistors MP35 can be replaced with MP35-MP38, and transistor MP39 with MP39-MP42.

Diodes D9 - with any letter, or D2, D18, GD507. Speaker - any resistance from 4 ohms to 100 ohms, for example, a speaker from a radio receiver or headphones. The battery is 9 V, you can use a “Krona” or a suitable battery.

Attention:Power supply from a 220 V network source is not advisable, because this creates a background AC and the sensitivity of the device as a whole decreases.

Settings

The setting consists of adjusting coil L1 in such a way that when the rotor of capacitor C7 is in the middle position and in the absence of external metal objects, the sound of the lowest tone is heard in the speaker.

In the future, during operation, adjustment before starting the search will be performed by capacitor C7.

If there are no oscillations from the generator at VT1, you need to select the value of C4 and/or adjust the operating mode of the cascade by selecting the value of R2. If the generator at VT2 is not excited, you need to adjust C8 and adjust the operating mode of the transistor by selecting the value of R6.

The device is highly sensitive, and working with it requires certain skills. So you need to practice.

When working, it is important to take into account that when approaching ferrous metals (iron, steel, cast iron), the frequency of the generator on VT2 decreases, and when approaching non-ferrous metals, it increases.

With the onset of spring, more and more often you can see people with metal detectors on the banks of rivers. Most of them are engaged in “gold mining” purely out of curiosity and passion. But a certain percentage actually earn a lot of money from searching for rare things. The secret to 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 instrument is expensive, and if you have a basic knowledge of radio mechanics, 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 structure

This model costs more than 32,000 rubles, and, of course, non-professionals will not be able to afford such a device. Therefore, we suggest studying the design 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 operating principle 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 transmitting, and the second is receiving.

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

1. Simple, working on the “receive-transmit” principle.
2. Induction.
3. Pulse.
4. Generating.

The cheapest devices belong to the first type.

An induction metal detector has one coil that sends and receives a signal simultaneously. But devices with pulse induction differ in that they generate a transmitter current, which 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 its purpose and technical device

The operating principle 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 continuously scans the field. The main feature of working with such a device is that you must be in motion all the time, otherwise the signal will disappear. Such devices are easy to use, however, they are poorly sensitive.
• Devices pulse type. They have great sensitivity. Often, such a device comes with several additional coils for adjustment to different types of soils and metals. Requires certain skills to set up. Among the devices of this class we can distinguish electronic devices operating at low frequencies - no 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 lines, as well as coins and other metal objects.
• Depth detectors designed to search for objects located at impressive depths. They can detect metal objects at a depth of up to 6 meters, while other models “pierce” 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.

Depth detectors operate on two coils, one is parallel to the ground surface, the other is perpendicular.

• Stationary detectors- these are frames established at particularly important protected sites. They detect any metal objects in people's bags and pockets that pass through the circuit.

Which metal detectors are suitable for making yourself at home?

The simplest devices that you can assemble yourself include devices that operate on the principle of reception and transmission. There are schemes that even a novice radio amateur can do; for this you just need to select a certain set of parts.

There are many video instructions on the Internet with detailed explanations 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. 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 metal detector toy, it will be more useful.

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

Homemade metal detector “Pirate”: diagram and detailed description of the assembly

Homemade products based on the “Pirate” series metal detector are among the most popular among radio amateurs. Thanks to the good performance 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

The Pirate metal detector is a pulse type device. To make the device you will need to purchase:

1. Materials for making the body, rods (can be used plastic pipe), holder and so on.
2. Wires and electrical tape.
3. Headphones (suitable for the player).
4. Transistors – 3 pieces: BC557, IRF740, BC547.
5. Microcircuits: K157UD2 and NE
6. Ceramic capacitor - 1 nF.
7. 2 film capacitors - 100 nF.
8. Electrolytic capacitors: 10 μF (16 V) – 2 pieces, 2200 μF (16 V) – 1 piece, 1 μF (16 V) – 2 pieces, 220 μF (16 V) – 1 piece.
9. Resistors – 7 pieces per 1; 1.6; 47; 62; 100; 120; 470 kOhm and 6 pieces for 10, 100, 150, 220, 470, 390 Ohm, 2 pieces for 2 Ohm.
10. 2 diodes 1N148.

DIY metal detector circuits

The classic circuit of the metal detector of the “Pirate” series is built using the NE555 microcircuit. The operation of the device depends on a comparator, one output of which is connected to the IC pulse generator, the second to the coil, and the output to the speaker. If metal objects are detected, the signal from the coil is sent to the comparator, and then to the speaker, which notifies the operator of the presence of the desired objects.

The board can be placed in a simple distribution box, which can be purchased at an electrical store. If such a tool is not enough for you, you can try to make a more advanced device; a diagram for making a gold-oriented metal detector will help you.

How to assemble a metal detector without using microcircuits

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. By selecting 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 the signal to transistor T2. The audio frequency is amplified using the BC547 transistor 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 onto it, mark the fastening points, and 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 areas of copper foil.

How to make a metal detector coil with your own hands

For the base you will 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 vol. If you don't have anything suitable on hand, you can wind a reel on a wooden base.

Copper wire spool on wooden base

Illustration	Description of action
	For winding, prepare a board with guides. The distance between them is equal to the diameter of the base on which you will attach the reel.
	Wind the wire around the perimeter of the fastenings in 20-30 turns. Secure 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 several 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), knife, soldering iron, solder and multitester.

Illustration	Description of action
	Twist the wire into two skeins. 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 fastening, solder them with a soldering iron.
	Test the coil in the same manner as the copper wire device. The winding terminals 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 DIY metal detector “Pirate”

Once the main elements of the metal detector are ready, we proceed to assembly. We attach all the components to the metal detector rod: the body with the coil, the receiving and transmitting unit and the handle. If you did everything correctly, then additional manipulations with the device will not be required, since it initially has maximum sensitivity. Fine tuning is performed using variable resistor R13. Normal operation of the detector should be ensured with the regulator in the middle position. If you have an oscilloscope, then use it to measure the frequency at the gate of transistor T2, 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 a conventional one, with the only difference being that you will have to work hard to create an impenetrable shell using sealant, as well as to place special light indicators that can report a find from under water. An example of how this will work is in the video:

Do-it-yourself metal detector “Terminator 3”: detailed diagram and video instructions for assembly

The Terminator 3 metal detector has occupied an honorable place among homemade metal detectors for many years. The two-tone device operates 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 characteristics search depth, compared to semi-professional branded metal detectors. We offer you the most detailed description assembly of a similar device from folk craftsman Victor Goncharov.

How to make a metal detector with your own hands with metal discrimination

Metal discrimination is the ability of the device to distinguish between the detected material and classify it. Discrimination is based on different electrical conductivities of metals. The most simple ways metal type definitions were implemented in older and entry-level devices and had two modes - “all metals” and “non-ferrous”. The discrimination function allows the operator to respond to a phase shift of a certain magnitude, compared to a configured (reference) level. In this case, the device cannot distinguish between non-ferrous metals.

Learn how to make a homemade professional metal detector using improvised materials in this video:

Features of deep metal detectors

Metal detectors of this type can detect objects at great depths. A good metal detector, made by yourself, looks to a depth of 6 meters. However, in this case the size of the find must be substantial. These detectors work best for detecting old shells or large enough debris.

There are two types of deep metal detectors: frame and transceiver on a 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 version of the detector is a point detector; it works directed inward over a small diameter. You need to work with it slowly and carefully. If your goal is to build such a metal detector, the following video can tell you how to do it.

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