Coil winding for a metal detector drawings. Do-it-yourself metal detector manufacturing schemes

The main advantage that pulse devices for searching non-ferrous metal objects have is that it is quite simple to build a coil for a metal detector from a twisted pair. Equipped with a fairly simple coil, these devices have excellent detection rates. This article will describe detailed instructions for creating twisted pair coils for metal detector Pirat, thanks to which you can independently make this design. Thanks to this, you will not need to purchase it on the radio market for a rather impressive amount. In the process of work, you will need standard elements that every electronics engineer probably has. Coils, which are created by the following simple methods, can be used with almost all impulse devices that are very popular today.

Twisted Pair Pulse Metal Detector Coil

From a twisted pair of wires, it is possible to build a wonderful sensor, which is an indispensable component for a pulsed device. Such a coil will have a search depth of more than one and a half meters. This design has good sensitivity to various small-sized products, which include gold jewelry, small change, and so on. In order to make such a coil, you need to first prepare a twisted pair wire, which can be purchased without any problems wherever radio devices are sold. The wire is made of four twisted pairs without a shield, it is very important that it be copper, not bimetallic

In order to make such a coil, you need to follow these instructions:
· Make a piece of wire, the length of which is 2.7 meters.
· Mark exactly half of the line. After that, you should also measure 41 cm from each end.
· According to the marks made, you need to make a ring from this wire and fix it using ordinary tape or adhesive tape.
· The ends of the future coil should be slightly bent inward.

· This is followed by a thorough stripping of the insulation of the wires, after which you need to solder these wires in this order:

· After the above procedure, it is necessary to isolate the adhesions using special thermotubes or adhesive tape.

· In order to draw the conclusion of the manufactured coil, you need to take a wire 2 * 0.75 mm, which is in rubber insulation and has a length of 1.2 meters, and then solder it to the other ends of the future coil. After that, it is also necessary to insulate the wires.
· You should decide on the most suitable coil housing. You may well purchase a factory product. An ordinary plate made of plastic is also suitable.

· The coil must be inserted into the housing and the elements must be fixed using hot melt adhesive. Spikes and wires will also need to be fixed.
· The next step is to glue the body. In the event that you did not use a finished case, but a plastic plate, then to make it more rigid, you need to fill it with epoxy. First, you still need to conduct a trial test of functionality, because after you glue everything together, you will not be able to make amendments.
· In order to fix the coil to the rod, you can use the factory bracket or come up with an analogue yourself, it all depends on your choice.
· After soldering the connector to the second end of the wire, the coil will be completely ready for use.

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:

Simple, working on the principle of "reception-transmission".
Induction.
Pulse.
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:

Metal detector "Pirate".
Metal detector - butterfly.
Emitter without microcircuits (IC).
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:

Materials for the manufacture of the body, rod (you can use a plastic pipe), holder and so on.
Wires and electrical tape.
Headphones (suitable from the player).
Transistors - 3 pieces: BC557, IRF740, BC547.
Chips: K157UD2 and NE
Ceramic capacitor - 1 nF.
2 film capacitors - 100 nF.
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.
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.
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 KT-361 and KT-315 transistors to generate signals (similar radio components can be used).

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 scheme.
	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 function 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!

Metal detectors are used to search for metal in the soil at a certain depth. This device can be assembled independently at home, having at least minimal experience in this matter, or following the clear instructions of the instructions. The main thing is the desire and the availability of the necessary tools.

Do-it-yourself detailed instructions for the terminator 3 metal detector

This type of design is designed to search for coins. Its assembly process is quite simple. However, experience in assembling such a tool is still necessary. The Terminator is able to detect an item even if the target of capture is minimal.

First you need to prepare the necessary equipment, namely:

multimeter that measures speed.
LC meter.
Oscilloscope.

Next, you need to find a diagram with a breakdown into nodes. Now you can make a printed circuit board, into which jumpers, resistors, panels for microcircuits and other parts should be soldered in order. The next step is to flush the board with alcohol.. Be sure to check for defects. Whether the board is in working order can be checked as follows:

Turn on the power.
Unscrew the sensitivity control until no sound is heard in the speaker.
Touch the sensor connector with your fingers.
When turned on, the LED should flash and then turn off.

If all actions have taken place, then everything is done correctly. Now you can make a coil. It is necessary to prepare a winding enamel wire with a diameter of 0.4 mm, which must be folded in half. A circle is drawn on a sheet of plywood, having a diameter of 200 mm and 100 mm. Now you need to drive nails in a circle, the distance between them should be 1 cm.

Next, you can proceed to winding the turns. At 200 mm, you should make them 30, and at 100 - 48. Then the first coil must be impregnated with varnish, when it dries, you can wrap it with thread. The thread can be removed, and by soldering the middle, you get a whole winding of 60 turns. After the coil must be wrapped with electrical tape quite tightly. And a foil of 1 cm is superimposed on top, this will be a screen, another electrical tape is wound on top of it. The ends should come out.

On the second coil, it is also necessary to solder the middle. In order to start the generator, you need to connect the first coil to the board. The second coil should be wrapped with a wire of 20 turns, then we connect it to the board. Now you need to connect the oscilloscope minus to minus to the board, and the plus is connected to the coil. Be sure to look at what frequency will be when turned on and remember it or fix it on paper.

Now the coils must be put in a special form, then to fill them with resin. Next, the oscilloscope is connected to the board, with a negative pole, the amplitude should reach zero. Coils in the form are filled with resin to about half the depth. When everything is ready, the metal discrimination scale is adjusted.

List of parts for metal detector terminator 3

As parts for the trio metal detector you will need:

If you have these details, you can assemble the terminator pro metal detector on your own.

Scheme of a metal detector with metal discrimination

A do-it-yourself metal detector with metal discrimination can be made using the scheme for the Chance impulse device. The process of making a coil is quite simple.

The diagram itself can be found on the Internet. But still, experience in assembling such devices will be useful. Assembling the metal detector should begin with the board.

After the board is made, it is necessary to flash the microcontroller. And at the end of the work, we connect the metal detection device to the power supply.

Homemade equipment can be made without complex microcircuits, but using a simple transistor generator. The metal detector will be without discrimination. He will detect objects in the ground 20 centimeters deep, and in dry sand - 30 centimeters. In this device, the transmitting and receiving coils work simultaneously.

Coil for metal detector terminator 3

To begin with, you should take the winding enamel, having a diameter of 0.4 mm. Fold it so that there are two ends and two beginnings. Next, it is worth winding from two coils at a time.

Now we need to make a transmitting and receiving coil, for this, two circles of 200 mm and 100 mm are drawn on a plywood sheet. Carnations are driven in according to these circles, the distance between them should be 1 cm. 30 turns are wound on a large mandrel with enamel wire. Then you should apply varnish to the coil and wrap it with a thread, then remove it from the winding and solder the middle. So you get one middle wire and two extreme wires.

The resulting coil should be wrapped with electrical tape and put on top of a piece of foil, and foil again on top. The ends of the windings must come out.

Now it's time to move on to the receiving coil. 48 turns are already wound here. To start the generator, you need to connect the transmitting coil to the board. The middle wire is connected to negative. And the receiving coil does not use the middle terminal. For the transmitting coil, a compensating coil is needed, on which 20 turns are wound.

We connect the oscilloscope to the board as follows: the probe with a minus to the minus of the board, and the positive probe to the coil. Be sure to measure the frequency of the coils and record it.

After connecting the coils according to the scheme, they must be placed in a special container and filled with resin. Now the oscilloscope is set to divide time (10 ms and 1 volt per cell). Now you should reduce the amplitude to zero. We wind the turns until the volt value reaches zero. We make a compensating loop at the coil, which will be outside.

Half of the mold should be spilled with resin. When everything hardens, you need to connect the oscilloscope and bend the loop inward. Then twist it until the amplitude value becomes minimal. After the loop must be glued, the balance checked, and now you can fill the second half of the container with resin. The coil is ready to go.

Before proceeding with the repair, you should prepare the following tools:

Stationery knife;
Incandescent lamp;
Container for glue, preferably flat;
Special or epoxy resin;
Medium and fine emery;
Small spatula.

First of all, you need to dry the coil with an incandescent lamp. And with the help of a clerical knife, expand the cracks on it. Squeeze the glue onto a flat surface and mix with a spatula. Apply this substance to the coil. In places of cracks, you can apply more resin. Now it's worth waiting until it all hardens thoroughly. And then process with emery, using medium first, and then fine. This procedure will help smooth out all the bumps. In such a fairly simple way, you can reanimate the oldest coil from a metal search device.

Circuit board for device terminator 3

A printed circuit board for this type of equipment can be made and configured independently. The circuit board for the terminator 3 is on the Internet. After it is found, you can begin to manufacture a printed circuit board. After that, jumpers, smd resistors and panels for microcircuits are soldered into it. Capacitors in the board must have high thermal stability.

DIY metal detector sensor

Before starting work, it is necessary to prepare a device that will accurately measure capacitance and inductance. Now you should take the body for the coil and make textolite inserts into the ears. Pieces of fabric are used for sealing. The upper surface of the ears should be sanded. The fabric must be impregnated with epoxy resin. When everything is dry, everything should be sanded and a pressure seal should be inserted, thus making the grounding. Next, you need to apply a special varnish Dragon.

Now windings are made, which are tied with threads. All windings are placed in a coil and capacitors are glued. Everything can be connected and configured. A body is required for pouring. Required: there should be no metal nearby. After pouring, the epoxy should be sanded and dried thoroughly. The sensor is suitable for terminator 3 and terminator 4 metal detectors, which are the most popular models of devices.

Metal detector terminator 3: reviews

Many consider this model of the device popular. The positive qualities are:

Finding non-ferrous metal objects.
No false positives.

And as negative features, they distinguish:

Rusty iron detects rather poorly.
You can lose some of the finds.

The search depth of the device is higher than that of other similar models. Basically it is 30 centimeters on the example of a coin.

Sokha 3 metal detector: diagram and description

The metal detector has an operating frequency of 5 to 17 kHz. Its power supply is 12 volts. The ground balance is manual.

The circuit of this device is not quite simple, since it contains two microcontrollers. The diagram can be found on the Internet. The device itself has good characteristics. However, due to the lack of detailed assembly information, difficulties may arise in the manufacture of the apparatus.

In the manufacture of a metal detector, you can make sure that the coil is the main element of this design. As a rule, this part consists of a copper wire. With the help of special pulses emitted by the coil, metal objects can be identified in soil of various densities.

The metal detector coil is a fairly simple element, so it will not be difficult to wind it yourself. As a basis for work, you can take the metal detector "Kid FM2". The coil of this device must be wound quite accurately. Experienced people will be able to do this work on their own. For a beginner, it is better to use specialized software. To do this, you need to download the Coil32 program file located at the end of the article.

The inductance of a metal detector coil is measured in units of microhenries. According to the detector circuit, this value should be 2290 mkH. There is also an instruction for selecting the thickness of the wire, depending on the diameter of the element.

In the event that only a wire with a certain cross section is available, and the size of the coil is needed more (or less), then a special program comes to the rescue. When starting Coil32, a window should appear, which is shown in the following figure:

In the window of the running program, you need to press the "PLUGINS" button, in the menu that opens, select the "Multi loop" parameter. In this subsection, the coils necessary for operation should be displayed. If everything is done in sequence, then a window should appear on the computer screen:

This window details which wire diameter is appropriate for a particular frame. Here you can also find the values of the "Inductance" parameter.

Before starting work, you need to set the necessary parameters in the cells:

inductance - 2290 mkH;
wire thickness - 0.4 mm;
coil frame - 111 mm.

After entering these parameters in the program window, you will need to click the appropriate button for calculations. The required information will appear on the right, and will look like the following figure:

Self-calculation of parameters for winding a metal detector coil using the appropriate software will seem quite easy. The program itself will determine for each diameter and inductance values the optimally suitable wire section. The Coil32 program is available for download in an archive file.

Attached files: ARCHIVE

Handy fringe cutter for transformers. Soldering iron heating regulator with power indicator A simple scheme for controlling radio and electrical appliances through Com-ports Scheme of a homemade water leakage sensor

A metal detector or a metal detector is designed to detect objects that differ in their electrical and / or magnetic properties from the environment in which they are located. Simply put, it allows you to find metal in the ground. But not only metal, and not only in the ground. Metal detectors are used by inspection services, criminologists, the military, geologists, builders to search for profiles under the skin, fittings, reconciliation of underground utility plans, and people of many other specialties.

Do-it-yourself metal detectors are most often made by amateurs: treasure hunters, local historians, members of military historical associations. They, beginners, are primarily intended for this article; the devices described in it make it possible to find a coin with a Soviet penny at a depth of up to 20-30 cm or a piece of iron with a sewer manhole about 1-1.5 m below the surface. However, this home-made device can also be useful on the farm during repairs or at a construction site. Finally, having found a centner or two of an abandoned pipe or metal structures in the ground and handing over the find for scrap, you can get a decent amount. And there are definitely more such treasures in the Russian land than pirate chests with doubloons or boyar-robber egg-pods with efimki.

Note: if you are not well versed in electrical engineering with radio electronics, do not be afraid of diagrams, formulas and special terminology in the text. The very essence is stated simply, and at the end there will be a description of the device, which can be made in 5 minutes on the table, not knowing how to not only solder, but twist the wires. But it will allow you to "feel" the features of the search for metals, and if interest arises, knowledge and skills will come.

A little more attention compared to the rest will be given to the Pirate metal detector, see fig. This device is quite simple for beginners to repeat, but in terms of its quality indicators it is not inferior to many branded models priced up to $300-400. And most importantly, it showed excellent repeatability, i.e. full performance when manufactured according to descriptions and specifications. Circuitry and the principle of operation of the "Pirate" are quite modern; There are plenty of guides on how to set it up and how to use it.

Operating principle

The metal detector operates on the principle of electromagnetic induction. In general, the metal detector circuit consists of an electromagnetic oscillation transmitter, a transmitting coil, a receiving coil, a receiver, a useful signal extraction circuit (discriminator) and an indication device. Separate functional units are often combined in circuitry and design, for example, the receiver and transmitter can work on one coil, the receiving part immediately highlights the useful signal, etc.

The coil creates an electromagnetic field (EMF) of a certain structure in the medium. If an electrically conductive object is in the area of \u200b\u200bits action, pos. And in the figure, eddy currents or Foucault currents are induced in it, which create its own EMF. As a result, the structure of the coil field is distorted, pos. B. If the object is not electrically conductive, but has ferromagnetic properties, then it distorts the original field due to shielding. In both cases, the receiver captures the difference between the EMF and the original one and converts it into an acoustic and/or optical signal.

Note: in principle, for a metal detector it is not necessary that the object be electrically conductive, the ground is not. The main thing is that their electrical and / or magnetic properties are different.

Detector or scanner?

In commercial sources, expensive highly sensitive metal detectors, e.g. Terra-N are often called geoscanners. This is not true. Geoscanners operate on the principle of measuring the electrical conductivity of the soil in different directions at different depths, this procedure is called lateral logging. According to the logging data, the computer builds on the display a picture of everything in the earth, including geological layers of various properties.

Varieties

Common parameters

The principle of operation of a metal detector can be implemented in technically different ways, according to the purpose of the device. Metal detectors for beach gold mining and construction and repair searches may look similar in appearance, but differ significantly in design and technical data. To properly make a metal detector, you need to clearly understand what requirements it must meet for this type of work. Based on this, the following parameters of search metal detectors can be distinguished:

Penetration, or penetrating power - the maximum depth to which the EMF of the coil extends in the ground. Deeper, the device will not detect anything at any size and properties of the object.
The size and dimensions of the search area is an imaginary area in the ground in which the object will be found.
Sensitivity is the ability to detect more or less small objects.
Selectivity is the ability to respond more strongly to desirable findings. The sweet dream of beach miners is a detector that only beeps for precious metals.
Noise immunity - the ability not to respond to EMF of extraneous sources: radio stations, lightning discharges, power lines, electric vehicles and other sources of interference.
Mobility and efficiency are determined by power consumption (how many batteries are enough), the device's weight and dimensions, and the size of the search area (how much you can "probe" in 1 pass).
Discrimination, or resolution - gives the operator or control microcontroller the ability to judge the nature of the object found by the reaction of the device.

Discrimination, in turn, is a composite parameter, since there are 1, maximum 2 signals at the output of the metal detector, and there are more values that determine the properties and location of the find. However, taking into account the change in the reaction of the device while approaching the object, 3 components are distinguished in it:

Spatial - indicates the location of the object in the search area and the depth of its occurrence.
Geometric - makes it possible to judge the shape and size of an object.
Qualitative - allows you to make assumptions about the properties of the material of the object.

Operating frequency

All parameters of the metal detector are connected in a complex way and many relationships are mutually exclusive. For example, lowering the oscillator frequency makes it possible to achieve greater penetration and search area, but at the cost of increased power consumption, and worsens sensitivity and mobility due to an increase in coil size. In general, each parameter and their complexes are somehow tied to the frequency of the generator. That's why The initial classification of metal detectors is based on the operating frequency range:

Super-low-frequency (VLF) - up to the first hundreds of Hz. Absolutely non-amateur devices: power consumption from tens of watts, without computer processing, it is impossible to judge anything from a signal, vehicles are needed to move.
Low-frequency (LF) - from hundreds of Hz to several kHz. Simple circuitry and design, noise-resistant, but not very sensitive, bad discrimination. Penetration - up to 4-5 m with power consumption from 10 W (the so-called deep metal detectors) or up to 1-1.5 m when powered by batteries. They react most sharply to ferromagnetic materials (ferrous metal) or large masses of diamagnetic materials (concrete and stone building structures), therefore they are sometimes called magnetic detectors. They are not very sensitive to the properties of the soil.
Increased frequency (IF) - up to several tens of kHz. More difficult than bass, but the requirements for the coil are low. Penetration - up to 1-1.5 m, C grade noise immunity, good sensitivity, satisfactory discrimination. Can be universal when used in pulsed mode, see below. On flooded or mineralized soils (with fragments or particles of rock that shield EMF), they work poorly or do not smell anything at all.
High, or radio frequency (HF or RF) - typical metal detectors "for gold": excellent discrimination to a depth of 50-80 cm in dry non-conductive and non-magnetic soils (beach sand, etc.) Power consumption - as before. n. The rest is on the verge of "failure". The efficiency of the device largely depends on the design and quality of the coil(s).

Note: mobility of metal detectors according to paragraphs. 2-4 is good: from one set of salt cells ("batteries") AA and without overworking the operator, you can work up to 12 hours.

Pulse metal detectors stand apart. Their primary current flows into the coil in pulses. By setting the pulse repetition rate within the LF, and their duration, which determines the spectral composition of the signal corresponding to the IF-HF ranges, you can get a metal detector that combines the positive properties of LF, IF and HF or is tunable.

Search Method

There are at least 10 EMF search methods. But such as, say, the method of direct digitization of the response signal with computer processing is the lot of professional use.

A home-made metal detector is schematically built most of all in the following ways:

Parametric.
Receiving-transmitting.
With phase accumulation.
On the beat.

Without receiver

Parametric metal detectors in some way fall outside the definition of the principle of operation: they have neither a receiver nor a receiving coil. For detection, the direct influence of the object on the parameters of the generator coil is used - inductance and quality factor, and the structure of the EMF does not matter. Changing the parameters of the coil leads to a change in the frequency and amplitude of the generated oscillations, which is fixed in various ways: by measuring the frequency and amplitude, by changing the current consumption of the generator, by measuring the voltage in the PLL loop (phase locked loop, "pulling" it to a given value), etc.

Parametric metal detectors are simple, cheap and noise-resistant, but their use requires certain skills, because. the frequency "floats" under the influence of external conditions. Their sensitivity is weak; most of all are used as magnetic detectors.

With receiver and transmitter

The device of the transceiver metal detector is shown in fig. at the beginning, to an explanation of the principle of operation; the principle of operation is also described there. Such devices allow to achieve the best efficiency in their frequency range, but are complex in circuitry, require a particularly high-quality coil system. Transceiver metal detectors with a single coil are called induction. Their repeatability is better, because the problem of the correct arrangement of the coils relative to each other disappears, but the circuitry is more complicated - you need to highlight a weak secondary signal against the background of a strong primary.

Note: in pulsed transceiver metal detectors, the emission problem can also be eliminated. This is explained by the fact that as a secondary signal they “catch” the so-called. "tail" of the pulse re-radiated by the object. The primary pulse spreads due to dispersion during reemission, and a part of the secondary pulse is in the gap between the primary ones, from where it can be easily distinguished.

Click to Click

Metal detectors with phase accumulation, or phase-sensitive, are either single-coil pulsed, or with 2 generators, each working on its own coil. In the first case, the fact is used that during re-emission pulses not only spread out, but are also delayed. In time, the phase shift increases; when it reaches a certain value, the discriminator is triggered and a click is heard in the headphones. As you get closer to the object, the clicks become more frequent and merge into a higher pitched sound. It is on this principle that Pirate is built.

In the second case, the search technique is the same, but 2 strictly symmetrical electrically and geometrically generators work, each on its own coil. At the same time, due to the interaction of their EMF, mutual synchronization occurs: the generators work in time. When the overall EMF is distorted, synchronization breaks begin, audible as the same clicks, and then a tone. Two-coil metal detectors with a synchronization breakdown are simpler than impulse ones, but less sensitive: their penetration is 1.5-2 times less. Discrimination in both cases is close to excellent.

Phase-sensitive metal detectors are the favorite tools of resort miners. Aces of the search adjust their devices so that exactly above the object the sound disappears again: the frequency of the clicks goes into the ultrasonic region. In this way, on a shell beach, it is possible to find gold earrings the size of a fingernail at a depth of up to 40 cm. However, on soil with small inhomogeneities, watered and mineralized, metal detectors with phase accumulation are inferior to others, except for parametric ones.

By squeak

Beats of 2 electrical signals - a signal with a frequency equal to the sum or difference of the main frequencies of the original signals or multiples of them - harmonics. So, for example, if signals with frequencies of 1 MHz and 1,000,500 Hz or 1.0005 MHz are applied to the inputs of a special device - a mixer, and headphones or a speaker are connected to the output of the mixer, then we will hear a pure tone of 500 Hz. And if the 2nd signal is 200 100 Hz or 200.1 kHz, the same thing will happen, because 200 100 x 5 = 1,000,500; we "caught" the 5th harmonic.

There are 2 generators in the beat detector: reference and working. The reference oscillatory circuit coil is small, protected from extraneous influences, or its frequency is stabilized by a quartz resonator (simply, quartz). The contour coil of the working (search) generator is a search coil, and its frequency depends on the presence of objects in the search area. Before searching, the working generator is tuned to zero beats, i.e. until the frequencies match. As a rule, they don’t achieve a complete zero sound, but tune it to a very low tone or wheezing, so it’s more convenient to search. By changing the tone of the beats, the presence, size, properties and location of the object are judged.

Note: most often, the frequency of the search generator is taken several times lower than the reference one and works on harmonics. This allows, firstly, to avoid the mutual influence of generators, which is harmful in this case; secondly, to tune the device more precisely, and thirdly, to search at the optimal frequency in this case.

In general, metal detectors based on harmonics are more complicated than impulse ones, but they work on any ground. Properly made and tuned, they are not inferior to impulse ones. This can be judged at least by the fact that beach gold diggers do not agree in any way on what is better: impulse or beat?

Coil and more

The most common misconception of novice radio amateurs is the absolutization of circuitry. Like, if the scheme is "cool", then everything will be tip-top. With regard to metal detectors, this is doubly untrue, because. their operational advantages strongly depend on the design and workmanship of the search coil. As a resort prospector put it: "The findability of a detector should pull the pocket, not the legs."

When developing a device, its circuit and coil parameters are adjusted to each other until an optimum is obtained. A certain scheme with a “foreign” coil, if it works, will not reach the declared parameters. Therefore, when choosing a prototype for repetition, see first of all the description of the coil. If it is incomplete or inaccurate, it is better to build another device.

About coil dimensions

A large (wide) coil radiates EMF more efficiently and “enlightens” the ground deeper. Its search area is wider, which allows you to reduce the "finding by feet". However, if there is a large unwanted object in the search area, its signal will be "hammered" by a weak one from the desired trifle. Therefore, it is advisable to take or make a metal detector designed to work with coils of different sizes.

Note: typical coil diameters are 20-90 mm for finding rebar and profiles, 130-150 mm "for beach gold" and 200-600 mm "for big iron".

Monoloop

The traditional type of metal detector coil is the so-called. thin coil or Mono Loop (single loop): a ring of many turns of enameled copper wire with a width and thickness of 15-20 times less than the average diameter of the ring. The advantages of a monoloop coil are the weak dependence of parameters on the type of soil, the search area narrowing downwards, which allows, by moving the detector, to more accurately determine the depth and location of the find, and structural simplicity. Disadvantages - low quality factor, which is why the tuning “floats” during the search, susceptibility to interference and a vague reaction to the object: working with a monoloop requires considerable experience in using this particular instance of the device. It is recommended for beginners to make homemade metal detectors with a monoloop in order to get a workable design without any problems and gain search experience with it.

Inductance

When choosing a circuit, in order to verify the authenticity of the author's promises, and even more so when designing or refining it yourself, you need to know the inductance of the coil and be able to calculate it. Even if you are making a metal detector from a purchased kit, you still need to check the inductance by measurements or by calculation, so as not to rack your brains later: why, everything seems to be in order, and not beeping.

Calculators for calculating the inductance of coils are available on the Internet, but a computer program cannot foresee all cases of practice. Therefore, in fig. given an old, decades-tested nomogram for calculating multilayer coils; a thin coil is a special case of a multilayer coil.

To calculate the search monoloop, the nomogram is used as follows:

We take the value of the inductance L from the description of the device and the dimensions of the loop D, l and t from there or at our choice; typical values: L = 10 mH, D = 20 cm, l = t = 1 cm.
According to the nomogram, we determine the number of turns w.
We set the laying coefficient k = 0.5, by the dimensions l (coil height) and t (its width) we determine the cross-sectional area of \u200b\u200bthe loop and find the area of pure copper in it as S = klt.
Dividing S by w, we get the cross section of the winding wire, and along it - the diameter of the wire d.
If it turned out d = (0.5 ... 0.8) mm, everything is OK. Otherwise, we increase l and t at d>0.8 mm or decrease at d<0,5 мм.

Noise immunity

The monoloop "catches" interference well, because arranged in exactly the same way as a loop antenna. You can increase its noise immunity, firstly, by placing the winding in the so-called. Faraday shield: a metal tube, braid or foil winding with a gap so that a short-circuited coil does not form, which will “eat” all the EMI of the coil, see fig. on right. If there is a dotted line near the designation of the search coil on the original diagram (see the diagrams below), this means that the coil of this device must be placed in the Faraday shield.

Also, the screen must be connected to the common wire of the circuit. There is a catch for beginners here: the grounding conductor must be connected to the screen strictly symmetrically to the section (see the same figure) and connected to the circuit also symmetrically with respect to the signal wires, otherwise the interference will still “penetrate” into the coil.

The screen also absorbs some of the search EMF, which reduces the sensitivity of the device. This effect is especially noticeable in pulsed metal detectors; their coils cannot be shielded at all. In this case, an increase in noise immunity can be achieved by balancing the winding. The bottom line is that for a remote source of EMF, the coil is a point object, and emf. interference in its halves will overwhelm each other. A symmetrical coil may also be needed in circuitry if the generator is a push-pull or inductive three-point.

However, in this case it is impossible to symmetricalize the coil with the usual bifilar method (see Fig.): when conducting and / or ferromagnetic objects are in the field of the bifilar coil, its symmetry is violated. That is, the noise immunity of the metal detector will disappear just when it is most needed. Therefore, the monoloop coil must be symmetrical by cross winding, see the same fig. Its symmetry is not broken under any circumstances, but winding a thin coil with a large number of turns in a cross way is hellish work, and then it is better to make a basket coil.

Basket

Basket coils have all the advantages of mono-loops to an even greater extent. In addition, basket coils are more stable, their quality factor is higher, and the fact that the coil is flat is a double plus: sensitivity and discrimination will increase. Basket coils are less susceptible to interference: harmful emfs. in crossing wires they cancel each other out. The only negative is that basket coils need a precisely made rigid and durable mandrel: the total tension force of many turns reaches large values.

Basket coils are structurally flat and voluminous, but electrically voluminous "basket" is equivalent to flat, i.e. creates the same EMF. The volumetric basket coil is even less sensitive to interference and, which is important for pulsed metal detectors, the pulse dispersion in it is minimal, i.e. easier to catch the variance caused by the object. The advantages of the original "Pirate" metal detector are largely due to the fact that its "native" coil is a voluminous basket (see Fig.), but its winding is complex and time-consuming.

It is better for a beginner to wind a flat basket on his own, see fig. below. For metal detectors "for gold" or, say, for the "butterfly" metal detector described below and a simple transceiver 2-coil, unusable computer disks will be a good mandrel. Their plating will not hurt: it is very thin and nickel. An indispensable condition: an odd, and nothing else, the number of slots. A nomogram is not required for calculating a flat basket; calculation is carried out in this way:

They are set with a diameter D2 equal to the outer diameter of the mandrel minus 2-3 mm, and take D1 = 0.5D2, this is the optimal ratio for search coils.
According to formula (2) in fig. calculate the number of turns.
From the difference D2 - D1, taking into account the flat laying factor of 0.85, the diameter of the wire in insulation is calculated.

How not to and how to wind baskets

Some amateurs take it upon themselves to wind bulky baskets in the manner shown in fig. below: make a mandrel from insulated nails (pos. 1) or self-tapping screws, wind according to the scheme, pos. 2 (in this case, pos. 3, for the number of turns, a multiple of 8; every 8 turns the “pattern” is repeated), then foam, pos. 4, the mandrel is pulled out, and the excess foam is cut off. But it soon turns out that the stretched coils cut the foam and all the work went soft. That is, in order to wind securely, you need to glue pieces of durable plastic into the holes of the base, and only then wind it. And remember: an independent calculation of a volumetric basket coil without appropriate computer programs is impossible; the flat basket technique is not applicable in this case.

DD coils

DD in this case does not mean long-range, but a double or differential detector; in the original - DD (Double Detector). This is a coil of 2 identical halves (shoulders), folded with some intersection. With an accurate electrical and geometric balance of the DD arms, the search EMF is pulled into the intersection zone, on the right in Fig. on the left - a monoloop coil and its field. The slightest inhomogeneity of space in the search area causes an imbalance, and a sharp strong signal appears. The DD-coil allows an inexperienced searcher to detect a shallow, deep, well-conducting object when a rusty can lies next to it and above.

Coils DD are clearly oriented "on gold"; all metal detectors with the GOLD marking are equipped with them. However, on finely heterogeneous and / or conductive soils, they either fail completely, or often give false signals. The sensitivity of the DD coil is very high, but the discrimination is close to zero: the signal is either marginal or not at all. Therefore, metal detectors with DD coils are preferred by seekers who are only interested in "being in the pocket."

Note: more details about DD coils can be found later in the description of the corresponding metal detector. They wind their shoulders DD or in bulk, like a monoloop, on a special mandrel, see below, or with baskets.

How to attach a coil

Ready-made frames and mandrels for search coils are sold in a wide range, but sellers are not shy about cheating. Therefore, many amateurs make the base of the plywood coil, on the left in the figure:

Multiple designs

Parametric

The simplest metal detector for searching for fittings, wiring, profiles and communications in walls and ceilings can be assembled according to fig. The ancient transistor MP40 changes without any change to KT361 or its analogues; to use pnp transistors, you need to reverse the polarity of the battery.

This metal detector is a parametric type magnetic detector operating at low frequencies. The tone of the sound in the headphones can be changed by selecting the capacitance C1. Under the influence of the object, the tone drops, unlike all other types, so initially you need to achieve a “mosquito squeak”, and not wheezing or grumbling. The device distinguishes wiring under current from “empty”, a hum of 50 Hz is superimposed on the tone.

The circuit is a pulse generator with inductive feedback and frequency stabilization by an LC circuit. Loop coil - an output transformer from an old transistor receiver or a low-power "Bazaar-Chinese" low-voltage power transformer. A transformer from an unusable power source of a Polish antenna is very well suited, in its own case, by cutting off the mains plug, you can assemble the entire device, then it is better to power it from a 3 V lithium tablet battery. Winding II in fig. – primary or network; I - secondary or step-down at 12 V. That's right, the generator works with transistor saturation, which provides negligible power consumption and a wide range of pulses, making it easier to find.

To turn the transformer into a sensor, its magnetic circuit must be opened: remove the frame with the windings, remove the straight jumpers of the core - the yoke - and fold the W-shaped plates in one direction, as on the right in the figure, then put the windings back on. With serviceable parts, the device starts working immediately; if not, you need to swap the ends of any of the windings.

The parametric scheme is more complicated - in fig. on right. L with capacitors C4, C5 and C6 is tuned to 5, 12.5 and 50 kHz, and quartz passes the 10th, 4th harmonics and fundamental tone to the amplitude meter, respectively. The scheme is more for an amateur to get drunk on the table: there is a lot of fuss with the setting, but there is no "flair", as they say. Provided as an example only.

transceiver

Much more sensitive is a transceiver metal detector with a DD coil, which can be easily made at home, see fig. Left - transmitter; on the right is the receiver. It also describes the properties of different types of DD.

This metal detector is LF; search frequency is about 2 kHz. Depth of detection: Soviet penny - 9 cm, canning tin - 25 cm, sewer hatch - 0.6 m. The parameters are "triple", but you can master the technique of working with DD before moving on to more complex structures.

The coils contain 80 turns of 0.6-0.8 mm PE wire, wound in bulk on a mandrel 12 mm thick, the drawing of which is shown in fig. left. In general, the device is not critical to the parameters of the coils, they would be exactly the same and arranged strictly symmetrically. In general, a good and cheap simulator for those who want to master any search technique, incl. "for gold". Although the sensitivity of this metal detector is not high, but the discrimination is very good despite the use of DD.

To set up the device, first, instead of the L1 transmitter, turn on the headphones and make sure that the generator is working by the tone. Then L1 of the receiver is short-circuited and, by selecting R1 and R3, a voltage is set on the collectors VT1 and VT2, respectively, equal to about half the supply voltage. Next, R5 set the collector current VT3 within 5..8 mA, open L1 of the receiver and that's it, you can search.

With phase accumulation

The designs in this section show all the advantages of the phase accumulation method. The first metal detector mainly for construction purposes will be very inexpensive, because. its most labor-intensive parts are made ... of cardboard, see fig.:

The device does not require adjustment; integrated timer 555 - an analogue of the domestic IC (integrated circuit) K1006VI1. All signal transformations take place in it; search method - impulse. The only condition is that the speaker needs a piezoelectric (crystalline), a regular speaker or headphones will overload the IC and it will soon fail.

Coil inductance - about 10 mH; operating frequency - within 100-200 kHz. With a mandrel thickness of 4 mm (1 layer of cardboard), a coil with a diameter of 90 mm contains 250 turns of PE 0.25 wire, and a 70 mm coil contains 290 turns.

Metal detector "Butterfly", see fig. on the right, in terms of its parameters it is already close to professional devices: the Soviet penny is found at a depth of 15-22 cm, depending on the soil; sewer manhole - at a depth of up to 1 m. Acts on disruption of synchronization; diagram, board and type of installation - in fig. below. Please note, there are 2 separate coils with a diameter of 120-150 mm, not DD! They must not overlap! Both speakers are piezoelectric, as in the previous. case. Capacitors - thermostable, mica or high-frequency ceramic.

The properties of the "Butterfly" will improve, and it will be easier to set it up if, firstly, wind the coils with flat baskets; the inductance is determined by the given operating frequency (up to 200 kHz) and the capacitances of the loop capacitors (10,000 pF each in the diagram). Wire diameter - from 0.1 to 1 mm, the larger the better. The tap in each coil is made from a third of the turns, counting from the cold (lower according to the diagram) end. Secondly, if individual transistors are replaced with a 2-transistor assembly for K159NT1 dif-amplifier circuits or its analogues; a pair of transistors grown on a single chip has exactly the same parameters, which is important for circuits with a synchronization failure.

To establish the "Butterfly" you need to accurately adjust the inductance of the coils. The author of the design recommends moving apart and shifting the turns or adjusting the coils with ferrite, but from the point of view of electromagnetic and geometric symmetry, it would be better to connect trimmer capacitors of 100-150 pF in parallel with 10,000 pF capacitances and twist them when tuning in different directions.

The actual adjustment is not difficult: the newly assembled device beeps. We alternately bring an aluminum saucepan or a beer can to the coils. To one - the squeak becomes higher and louder; to the other - lower and quieter or completely silent. Here we add a little capacity of the trimmer, and remove it in the opposite shoulder. For 3-4 cycles, you can achieve complete silence in the speakers - the device is ready to search.

More about Pirate

Let's return to the famous "Pirate"; it is a pulse transceiver with phase accumulation. The scheme (see fig.) is very transparent and can be considered a classic for this case.

The transmitter consists of a master oscillator (MG) on the same 555th timer and a powerful key on T1 and T2. On the left - a variant of the ZG without an IC; it will have to set the pulse repetition rate of 120-150 Hz R1 and the pulse duration of 130-150 μs R2 on the oscilloscope. Coil L - common. The limiter on diodes D1 and D2 for a current of 0.5 A saves the QP1 receiver amplifier from overload. The discriminator is assembled on QP2; together they make up the dual operational amplifier K157UD2. Actually, the "tails" of the reradiated pulses are accumulated in the capacitance C5; when the “reservoir is full”, a pulse jumps at the output of QP2, which is amplified by T3 and gives a click in the dynamics. Resistor R13 regulates the filling rate of the "reservoir" and, consequently, the sensitivity of the device. More about "Pirate" can be found in the video:

Video: Pirate metal detector

and about the features of its settings - from the following video:

Video: setting the threshold of the Pirate metal detector

On the beat

Those who wish to experience all the delights of the process of searching on beats with replaceable coils can assemble a metal detector according to the scheme in fig. Its peculiarity, firstly, is efficiency: the entire circuit is assembled on CMOS logic and, in the absence of an object, consumes very little current. Secondly, the device works on harmonics. The reference oscillator on DD2.1-DD2.3 is stabilized by ZQ1 quartz at 1 MHz, and the search oscillator on DD1.1-DD1.3 operates at a frequency of about 200 kHz. When setting up the device before searching, the desired harmonic is “caught” by the VD1 varicap. The mixing of the working and reference signals occurs in DD1.4. Thirdly, this metal detector is suitable for work with replaceable coils.

It is better to replace the ICs of the 176th series with the same 561st ones, the current consumption will decrease, and the sensitivity of the device will increase. It is simply impossible to replace the old Soviet high-resistance headphones TON-1 (preferably TON-2) with low-resistance ones from the player: they will overload DD1.4. You need to either put an amplifier like a "pirate" one (C7, R16, R17, T3 and a speaker on the "Pirate" circuit), or use a piezo speaker.

This metal detector does not require settings after assembly. Coils are monoloops. Their data on a mandrel 10 mm thick:

Diameter 25 mm - 150 turns of PEV-1 0.1 mm.
Diameter 75 mm - 80 turns of PEV-1 0.2 mm.
Diameter 200 mm - 50 turns of PEV-1 0.3 mm.

It doesn't get easier

Now let's fulfill the promise given at the beginning: we will tell you how to make, without knowing anything about radio engineering, the metal detector that you are looking for. The metal detector is “easier than simple” assembled from a radio receiver, a calculator, a cardboard or plastic box with a hinged lid, and pieces of double-sided tape.

The metal detector "from the radio" is pulsed, however, to detect objects, it is not dispersion and not delay with phase accumulation that are used, but the rotation of the EMF magnetic vector during re-emission. On the forums, they write different things about this device, from “super” to “sucks”, “wiring” and words that are not customary to use in writing. So, in order to get, if not “super”, but at least a fully functional device, its components - the receiver and the calculator - must meet certain requirements.

Calculator we need the tiniest and cheapest, "alternative". They make them in offshore cellars. They have no idea about the standards for electromagnetic compatibility of household appliances, and if they heard about something like that, then they wanted to spit from the bottom of their hearts. Therefore, local products are quite powerful sources of impulse radio interference; they are given by the clock generator of the calculator. In this case, its strobe pulses on the air are used to probe the space.

Receiver you also need a cheap one, from similar manufacturers, without any means of increasing noise immunity. It must have an AM band and, absolutely necessary, a magnetic antenna. Since receivers with short wave (HF, SW) reception on a magnetic antenna are rarely sold and are expensive, you will have to limit yourself to medium waves (MW, MW), but this will make tuning easier.

We unfold the box with a lid into a book.
We stick strips of adhesive tape on the back sides of the calculator and the radio and fix both devices in the box, see fig. on right. The receiver - preferably in the lid, so that there is access to the controls.
We turn on the receiver, we are looking for a section free from radio stations and as clean as possible from radio noise by setting it to maximum volume at the top of the AM band (bands). For MW this will be around 200 m or 1500 kHz (1.5 MHz).
We turn on the calculator: the receiver should buzz, wheeze, growl; in general, give a tone. We do not remove the volume!
If there is no tone, carefully and smoothly adjust until it appears; we caught some of the harmonics of the calculator's strobe generator.
We slowly fold the “book” until the tone weakens, becomes more musical, or disappears altogether. Most likely this will happen when the lid is rotated about 90 degrees. Thus, we have found a position in which the magnetic vector of primary impulses is oriented perpendicular to the axis of the ferrite rod of the magnetic antenna and it does not receive them.
We fix the cover in the found position with a foam insert and an elastic band or supports.

Note: depending on the design of the receiver, the reverse option is possible - to tune in to the harmonica, the receiver is placed on the included calculator, and then, laying out the “book”, the tone is softened or disappears. In this case, the receiver will catch the pulses reflected from the object.

And what's next? If there is an electrically conductive or ferromagnetic object near the opening of the "book", it will re-emit probing pulses, but their magnetic vector will turn. The magnetic antenna will “smell” them, the receiver will again give a tone. That is, we have already found something.

Something strange in the end

There are reports of another metal detector "for complete dummies" with a calculator, but instead of a radio, supposedly 2 computer disks, a CD and a DVD, are needed. Also - piezo headphones (precisely piezo, according to the authors) and a Krona battery. Frankly speaking, this creation looks like a techno-myth, like a memorable mercury antenna. But - what the hell is not joking. Here's a video for you:

try it, if you wish, maybe something will be found there, both in the subject and in the scientific and technical sense. Good luck!

as an application

There are hundreds, if not thousands, of schemes and designs of metal detectors. Therefore, in the appendix to the material, we also give a list of models, in addition to those mentioned in the test, which, as they say, are in circulation in the Russian Federation, are not overly expensive and are available for repetition or self-assembly:

Clone.

4,90

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