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Do-it-yourself metal detector - the best ideas. Homemade metal detectors: simple and more complicated - for gold, ferrous metal, for construction Simple DIY metal detector with discrimination

Even the most serious and respectable citizens, at the word "treasure" experience a slight excitement. We literally walk through treasures, of which there are immeasurably many in our land.

But how do you look under the soil layer to know exactly where to dig?

Professional treasure hunters use expensive equipment, the purchase of which can pay off after one successful find. Archaeologists, builders, geologists, members of search societies - use the equipment provided by the organization in which they work.

But what about novice treasure hunters on a limited budget? You can make a metal detector at home with your own hands.

To understand the subject, consider the design and principle of operation of the device

Popular metal detectors work using the properties of electromagnetic induction. Main components:

transmitter - generator of electromagnetic oscillations
transmitting coil, receiving coil (in some models, the coils are combined for compactness)
electromagnetic wave receiver
decoder that separates the useful signal from the general background
signaling device (indicator).

The generator, with the help of a transmitting coil, creates an electromagnetic field (EMF) around it with specified characteristics. The receiver scans the environment and compares the field performance with the reference. If there are no changes, nothing happens in the scheme.

When a conductor (any metal) enters the zone of action of the field, the base EMF induces Foucault currents in it. These eddy currents create their own electromagnetic field of the object. The receiver determines the distortion of the base EMF and gives a signal to the indicator (sound or visual notification).
If the object under test is not metallic, but has ferromagnetic properties, it shields the underlying EMF, also causing distortion.

Important! There is an erroneous opinion that the soil in which searches are made should not be electrically conductive.

This is wrong. The main thing is that the electromagnetic or ferromagnetic properties of the medium and search objects should be different from each other.

That is, against the background of certain characteristics of the EMF formed by the search environment, the field of individual objects will stand out.

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

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

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

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

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

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

Metal detector manufacturing process:

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

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

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

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

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

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

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

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

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

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

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

Well, in conclusion, it remains only to configure the device. With the discriminator knob set to minimum, the instrument should see all non-ferrous metals. Further, when winding the discriminator, all metals should be cut out in order to copper, but copper should not be cut out. If the device works exactly as described, then it is assembled correctly.

See other metal detector schemes.

Updated 11/01/2018

Metal detector discrimination ( metal detector discrimination - English) is a function that allows you to distinguish (recognize) detected objects by type of metal and classify them in a very specific way.

How does a metal detector distinguish between metals? It is known that different metals have different electrical conductivity. The electronic unit ("brain") of the metal detector analyzes the phase shift between the signal from the transmitting and receiving coils. The phase shift varies with the conductivity of the metal. Each type of metal has its own characteristic phase shift that is unique to that metal.

This makes it easy to distinguish ferrous metal from non-ferrous, as well as non-ferrous metals among themselves (aluminum, silver, copper, bronze, lead). The discrimination function is best implemented in metal detectors based on the VLF (VLF/TR) principle...

Pulse metal detectors ( Pulse induction metal detectors – English) are not capable of the same degree of discrimination as VLF detectors. Many attempts have been made to create pulse metal detectors that can distinguish between iron, silver and copper, however, all these attempts have had very limited success. This is due to the physics of the pulsed signal.

Therefore, the use of pulsed metal detectors in search areas with a high concentration of metal debris is extremely difficult.

Simple and professional metal detector discrimination function

The simplest discrimination function (discriminator) of a metal detector is implemented in outdated models and simple entry-level devices. Selecting one of two modes, “all metals” or “non-ferrous metals”, allows the metal detector to respond to a phase shift of a certain amount (a certain electrical conductivity of the target metal), which is compared with the configured (set) discrimination level.

But at the same time, the metal detector does not distinguish between non-ferrous metals, and with a high level of discrimination, it will practically not react to some coins and most of the jewelry.

Professional grade metal detectors use a range discriminator ( notch discriminator- English). Function notch is best implemented in microprocessor systems and allows you to program the detector so that it reacts to certain groups of metals (range of electrical conductivity) and excludes reaction to other metals.

However, it should be noted that absolutely accurate discrimination of a metal detector is impossible. This is due to the fact that different metals have similar conductivity values (for example, gold and aluminum).

That is, when searching, for example, on the beach, the device will give the operator a reaction signal to aluminum foil similar to a signal to a gold jewelry.

The numerical value of the conductivity of the metal of the detected object is displayed on the indicator VDI(visual indicator of discrimination). This makes it possible to identify the object and make a decision on excavation.

Metal discrimination comes in handy in very littered search areas. If the scanned ground does not contain a lot of metal debris, then it is better not to use this function, since this mode reduces the detection depth by 10 - 20%. All metal mode provides the highest sensitivity and the most complete use of the metal detector.

related tags: metal detector discrimination, metal discrimination, metal detector discrimination function, notch function, visual discrimination indicator, all metal mode, metal detector discriminator, what does a metal detector with discrimination mean, the principle of metal discrimination, how a metal detector distinguishes metals

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

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

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

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

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

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

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

Metal detector manufacturing process:

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

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

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

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

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

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

The Chance impulse metal detector proposed for repetition was developed by the famous designer Andrey Fedorov and received recognition from radio amateurs both in our country and abroad. This metal detector is a kind of continuation of the Klon series of devices and embodies the most advanced developments in the field of building these metal detectors. In addition to metal selection, the device has a discrimination function: by turning on the built-in masks, you can achieve detuning from ferrous metals when searching.

Indication of instrument readings is carried out with the help of an LCD indicator (VDI scale, Amplitude scale (size, location of the object), indication of battery voltage (battery charge level)) and sound signals of different tones. The heart of the metal detector is the Atmega8-16PI microcontroller already known to us in conjunction with an external ADC. The use of an external ADC is due to the expansion of the set of device functions - the introduction of such a set of functions without an external ADC is physically impossible due to the small internal resource of the microcontroller.

I will give some characteristics of the device. Sensitivity for coins 5kop USSR up to 25cm. Selection for metals under ideal conditions: the "blacker" metal - the lower its conductivity, and the closer to the left edge of the VDI scale the readings will be; the more "colorful" the metal - the greater its conductivity, respectively, the readings on the scale will be closer to the right edge (the readings on the scale depend on the choice of the instrument's firmware and may change). Discrimination function: turning on one of the four masks in turn, you can tell the device not to react to "ferrous" metals to the required extent (up to the complete elimination of the influence of ferrous metal). Barrier function: at 16 levels helps to build up from the influence of the "earth" and other external factors.

To repeat Chance, first of all, you need to visit the page of the author fandy.vov.ru, where there are diagrams, firmware, configuration bits for microcontroller firmware, a description of the operation of the buttons and other useful information. The main, rare and most expensive parts of the device are the ADC chip and the LCD indicator. The analogue of the ADC chip (MCP3201) is the ADS7816 chip, for which the author wrote a corrected firmware (0.8.4). The next important part of the metal detector is the LCD indicator. With all the variety and current abundance of such components, the most suitable, in my opinion, are reliable and fairly cheap indicators from Winstar, which are superior in terms of price / quality to indicators of the domestic manufacturer MELT. When buying an indicator, you should choose based on the following guidelines: character-synthesizing indicator, 2 lines of 16 characters, Cyrillic support (the ability to use the indicator in any other development), the presence of an integrated HD44780 controller. You can view and download datasheets and pinouts on the Winstar website. The archive also contains a list of parts.

The OP37 operational amplifier can be replaced with a cheaper and more common analogue NE5534P. The ICL7660S DC / DC converter can, although not desirable, be replaced with a similar one without the letter S (with the letter S for 12 volts, without it for 10 volts, it will work, but with an overload). The microcontroller is our old friend Atmega8-16PI (Atmega8-16PU, Atmega8A-PU). The controller is programmed using the simplest programmer, which was used when programming the microcontroller for the Clone device. Here, the device parameters and a step-by-step description of the programming process for this controller. The most important thing here is not to forget about the configuration bits! Archive with for the microcontroller.

The planar coil of the metal detector is made on a dielectric frame 4 mm thick and wound with a wire with a diameter of 0.65 - 0.8 mm. The coil template is shown in the figure below. The rod of the device is made according to the technology described in the article. You can assemble a metal detector on the author's printed circuit board or use a much easier to repeat (for beginners) board from DesAlex - see the picture on the forum. I myself redid 5 pieces of such coils - I changed the number of turns, the thickness of the frame from 2 to 6 mm. The best result was obtained on a 4mm frame, the number of turns is the same as that of the author, the inductance is 389uH. Experiments with winding / unwinding did not affect the final result (noted by many who repeated this device), that is, a spread of + -10% does not affect anything. Although each result will be different from the other (wire diameter, wire quality, presence of impurities, winding quality, coil waterproofing (varnish, epoxy, paint)), the quality and length of the supply cable - everything affects the quality factor of the search element.

A properly assembled device does not need adjustment and is fully functional! In conclusion, I would like to thank the author of the metal detector (AndyF) for the excellent pulsed metal detector with discrimination, as well as DesAlex "and for the reliable printed circuit board, without which the device would not have received such mass popularity among radio amateurs and outdoor enthusiasts, which is the search for historical relics! The material was provided by Elektrodych .

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