Ib simple powerful sensitive metal detector with your own hands. A simple yet sensitive metal detector! The principle of operation of a metal detector and much more for beginners

This metal detector is an improved version of a metal detector based on comparing the frequencies of two generators, one of which is a reference, and the second is a search one - it changes the frequency of its oscillations when approaching metal objects. The device can "distinguish" non-ferrous and ferrous metals.

circuit diagram

The reference generator is assembled on the element DD1.1, and the search generator is assembled on the elements DD2.1 and DD2.2. The oscillation frequency of the reference oscillator, determined by the data of its loop coil L1 and capacitors C1 and C2, and at the indicated ratings is 100 kHz (Fig. 1).

The frequency of the search oscillator, the oscillatory circuit of which is formed by the remote coil L2 and capacitors C3-C5, is close to the frequency of the reference oscillator. It is smoothly changed by a variable capacitor C3 within one or two kilohertz.

Element DD1.2 performs the function of a cascade that serves to isolate between generators by alternating voltage. Microcircuits DD1 and DD2 of the metal detector are powered by a DC source GB1 through decoupling filters R6C8 and R7C9.

Element DD3.1 - generator signal mixer. At its output, oscillations are formed with the total and difference frequencies of the generators and their harmonics. The low-pass filter (LF) R3C6 is designed to isolate the difference signals, i.e., the audio frequency.

Such a circuit design of a metal detector makes it possible to obtain generator beats with a frequency of several hertz.

To ensure listening to signals of such low frequencies on headphones, a sinusoidal, or rather, a triangular signal, was converted into short pulses with a double repetition rate. This is achieved using a voltage comparator assembled on the elements DD3.2 - DD3.4.

Rice. 1. Schematic diagram of a high-sensitivity metal detector based on three K561LE5 microcircuits.

In one period of the beat frequency, the comparator switches twice from one logical state to another. The rectangular pulses it generates are differentiated by the C7R8 circuit.

Therefore, telephones connected to connector X2 receive short voltage pulses and the volume of the sound signal depends little on its frequency.

In phones, which can be both high-resistance and low-resistance, “clicks” are heard. Their volume is regulated by a variable resistor R8 (it is combined with the power switch SA1).

All parts, except for connectors and the loop coil of the search generator, must be placed on a printed circuit board made of double-sided foil material (Fig. 2).

Mounting is one-sided - from the side of the printed conductors. The foil of the other side, which is connected to the common power wire along the edges of the board, acts as a screen.

Details and design of the metal detector

It is better to place the circuit board and the power source (Korund battery) in a metal case of suitable dimensions, for example, soldered from foil textolite plates.

If a plastic box serves as the case, then along the edges of the board, as well as in the places indicated in Fig. 1 with dashed lines, it is necessary to solder vertically strips of copper foil 7-10 mm wide.

Chips K561LE5 can be replaced with K176LE5, K176LA7, K561LA7. Capacitor SZ - KP-180 or another, with a maximum capacitance of 180-240 pF. Capacitors C8-C10 - oxide K50-6 or series K52, K53, the rest - KM, KLS.

Fig 2. Printed circuit board for a high sensitivity metal detector based on K561LE5 microcircuits.

Resistor R8 - SDR-Sv, the rest - BC, MLT. Connectors X1 and X2 - any small-sized. To increase thermal stability, capacitors C1, C2, C4 and C5 must be used with TKE no worse than MI500.

Coil L1, containing 300 turns of wire PEV-2 0.08, must be wound on the frame of the IF circuit of the Alpinist-407 radio receiver.

The remote coil L2 of the search generator (Fig. 3) is recommended to be performed in the following sequence:

1. wind 30 turns of PEV-2 wire 0.6 mm on a mandrel with a diameter of 240-250 mm;
2. fasten the resulting tourniquet in 10-12 places with a thin, strong thread;
3. heating the coil over the flame of a gas stove to a temperature of 50-60 ° C, impregnate with epoxy resin;
4. after curing the resin, wrap the coil with varnished cloth or (in extreme cases) with insulating tape;
5. shield the finished coil by wrapping it with thin copper foil in such a way that a small, 5-10 mm long, open section of the coil screen is formed in the front part (you can, of course, use aluminum foil);
6. connect the finished remote coil and its screen (via connector X1) to the metal detector structure with a two-wire shielded wire.

Rice. 3. Remote coil of the search generator of the metal detector.

Setting up the device

Setting up a metal detector should begin with setting up the reference oscillator and checking the performance of the voltage comparator. To do this, set the rotor of the capacitor C3 to the position of medium capacity and use the trimmer of the coil L1 to change the frequency of the reference oscillator until a sound signal appears in the phone.

Then, with the same trimmer, you should achieve “zero beats” - “clicks” in the phone, following at a frequency of several hertz. Sometimes this cannot be achieved. The reason for this may be a malfunction in the comparator.

In this case, it is necessary to check the operability of the rest of the device - connect a high-resistance telephone (for example, TON-2) to the output of the DD3.1 element and achieve a sound signal with the same L1 coil trimmer.

Otherwise, you will have to look for an error in the installation of generators or faulty parts.

Setting up the comparator consists in selecting the resistor R9 shown in fig. 1 with dashed lines. Its resistance can be in the range of 300 kOhm ... 1 MΩ.

If at the output of the comparator (pins 10, 11 of the DD3 chip) the voltage is high, then this resistor is connected between pins 5 and 6 of the DD3.2 element and the common wire.

After adjusting the reference oscillator, the coil trimmer L1 must be fixed in the frame with a drop of glue. For the convenience of working with a metal detector, it is best to equip its remote coil with a wooden or plastic handle. You can, in addition, make several remote coils of different diameters.

Continuous operation at maximum depth settings can help retrieve deep targets. Otherwise, adjusting the depth is impractical. It is best to test the increase in detection depth in a specially prepared place in the field or on your own land.

Here 9 tips how to achieve maximum depth performance of a metal detector coil.

1. Sensitivity

Adjusting the sensitivity is the most popular way to increase depth. Usually, as the sensitivity increases, so does the depth. But keep in mind that there is a side effect, too high sensitivity can reduce the likelihood of identifying a target, as well as drive you crazy with constant erratic sounds.

2. Ground balance

Every modern metal detector usually has a ground balance function. Correctly identifying it and installing it is a direct way to increase depth. After all, a lot depends on the mineralization of the soil, including the depth at which you will detect targets.

3. Sweep the coil as close to the ground as possible

Simple calculation: if you can bring the coil closer to the ground by 1.5 cm, then the detection depth will increase by the same 1.5 cm. Sometimes this is enough to catch a weak signal from a coin. Sometimes the grass makes it difficult to move the coil closer to the ground. In this case, take a larger and heavier coil, it is easier for it to crush the vegetation. However, take care of its additional protection.

4. Reduce discrimination

Very deep targets are often detected incorrectly by a metal detector. But you will never detect these many false positives if the level of discrimination is too high, for example, as with the Coin programs. Reducing discrimination to a minimum can lead to success. Maybe you will dig up an ancient artifact, not just another nail.

5. Interference elimination

There is a lot of interference in civilized places, as well as near power lines and buried cables. Working electrical appliances also emit a lot of noise. Usually in such cases, reduce the sensitivity, and this reduces the depth. Therefore, it is better to try to work away from interference. Also turn off your cell phone and remove all metal objects from your pockets. Do not wear shoes with metal elements. Do not stack the cables from the reel onto the reel itself.

6. Special settings and devices

Study the instructions for your metal detector inside and out. Your device may have some unique features that can help you hear and see deep targets better. Some detectors are specially designed to amplify deep, but weak signals, for example, recently there has been some revival among domestic search engines about the deep firmware of the AKA Signum MFT metal detector. Or the use of deep nozzles also gives a good result. XP released one recently for the Deus.

7. Large coil

Larger searchcoils provide greater detection depth and clearer readings from targets. Carefully! A large reel can carry a lot of weight. Therefore, it would be good to purchase a special unloading for the metal detector, which makes it easier to carry the device. Recall that a large coil cannot be effective on areas heavily littered with iron and on highly mineralized soils.

8. Experiment with speed

For example, moving fast with the Fisher F75 has a better chance of detecting deep targets than moving slowly. Again, refer to the user manual and tirelessly test - what speed of movement for your metal detector gives a deeper penetrating signal.

9. Wear headphones

If you use a conventional metal detector speaker, then you can quite naturally not distinguish signals from deep targets. With headphones, you are distracted from external noise and pick up fast, weak signals. If for some reason you don't want to use headphones, then try a series of air tests and memorize the sounds for the most distant purposes. Sometimes tiny, imperceptible changes in the audio tone do not show up on the detector's display.

Based on two interconnected oscillators. One oscillator in such a circuit will be fixed, and the other will be dependent on it and its frequency will change depending on whether there are metal objects nearby or not. Due to the fact that the frequency of the beats of the oscillators is less than 100 kHz, these beats can be heard in headphones or speakers. Accordingly, if there is a metal object under the coil, the sound will change.

All types of metals change the frequency in different ways, they can raise or lower it.

Materials and tools for homemade:
- one-sided copper multilayer printed circuit board with dimensions of 114.3 mm x 155.6 mm;
- five capacitors 0.1μF;
- five capacitors 0.01μF;
- two electrolytic capacitors 220μF;
- wire type PEL with a diameter of 0.4 mm;
- jack for headphones and earphones;
- 9V battery;
- connector for battery installation;
- switch;
- six NPN type transistors, 2N3904;
- wire type 22 AWG or cross-section - 0.3250 mm 2 for connecting the sensor;
- wired speaker;
- small speaker 8 ohm;
- threaded PVC pipe with a diameter of 1/2;
- wooden dowel size 1/4;
- wooden dowel 3/4';
- wooden dowel 1/2';
- epoxy;
- plywood 1/4';
- wood glue.

From tools:
- 3/4″ drill for cutting holes;
- drill with drills;
- electric iron;
- hacksaw;
- laser printer;
- oscilloscope or multimeter with frequency counter;
- sandpaper and more.

Metal detector manufacturing process:

Step one. Making a printed circuit board

First of all, you will need to download the board design:

Next, the board needs to be printed and etched onto the copper board. The author used a laser printer for such purposes, where the toner is then transferred to the board using an iron. As a result, the etched toner works like a mask, protecting the metal tracks.

Well, at the end of this step, you need to solder six 10 kOhm resistors. Such a resistor is color-coded - brown, black, orange, gold.

Transmitting
There are two coils in the metal detector, you need to start the assembly with a reference coil. For these purposes, you need a wire with a thickness of 0.4 mm. For the base, you will need a piece of dowel about 13 mm in diameter and 50 mm in length. Three holes will need to be made in the dowel, one in full length, and the other two along the edges across. The wire will pass through these holes.

Each wire will need to be pulled through the perpendicular hole, and then one of the ends through the inner longitudinal one. When the coil is fully wound, the winding must be fixed with electrical tape.

It is also important not to forget that the wire is varnished and this coating must be removed before further assembly. It can be burned or sanded off.

Reception
For the search coil, plywood 6-7 mm thick will be needed, the base, the body for the future coil, is made from such plywood. Having made the base, you need to wind 10 turns of wire with a cross section of 0.4 mm into the groove. The author has a coil diameter of 152 mm.

The handle to the holder must be fastened with wood or other non-metal materials, otherwise the metal detector will always show the presence of metal.

The scheme of this metal detector is simple, from the active elements there is one microcircuit, a transistor and several diodes. Despite the simplicity of the scheme, the metal detector is able to respond to the approach of a copper coin (2.5 cm in diameter) to the coil at a distance of about 10 cm, and large objects made of non-ferrous metals, at a distance of more than 1 meter!

Due to the small number of parts, the device has very low power consumption (about 5 mA from a 9V Krona battery), ease of setup and no problems with any pickups.

Schematic diagram of a simple metal detector

Its sensitive element is the oscillatory circuit of the generator, assembled according to the classical scheme on the transistor VT1. At the same time, with the help of resistor R1, on which the depth of feedback depends, the generator is set to a special mode, very sensitive to the quality factor of the oscillatory circuit. The latter, in turn, depends on the environment in which the circuit is located.

The depth of excitation of the generator determines the constant voltage at point "A".

Since this voltage does not depend on frequency, but only on the depth of excitation of the generator, this, unfortunately, does not make it possible to differentiate the metals being detected by their magnetic properties, but due to this, high requirements are not imposed on the coil in terms of rigidity and other parameters to achieve the required sensitivity.

The constant voltage taken from point “A” is fed through a shielded wire (of any brand) to a two-stage amplifier assembled on two op-amps that are part of the DA1 chip.

It is advisable to connect capacitor C4 not to a common wire, but exactly as shown in the diagram - to the power plus to exclude positive feedback.

Diodes VD1 and VD2 are silicon, with low reverse current. They are necessary to quickly restore amplifier modes when large metal objects are detected.

An audio frequency generator is assembled on the op-amp DA1.3, the excitation of which occurs when the potential difference at the inverting and non-inverting inputs decreases.

With the help of diodes VD3 and VD4, the voltage at the inputs is limited, and the effect of frequency control is achieved. This is a very useful property, because with some skill, changing the frequency helps not only to determine the location of the object, but also to estimate its size. Diodes VD3 and VD4 must have a minimum voltage drop in direct connection (for example, you can use KD419).

An inverter is assembled on the DA1.4 element, which serves to increase the volume of the piezo emitter.

Generator setup

The generator is set up as follows. Instead of a fixed resistor R1, a variable resistor with a resistance of 10 kOhm is installed, and its slider is brought to the position corresponding to the maximum resistance.

With a decrease in its resistance, the voltage at point "A" will also decrease, as shown in Fig. left. At some point, it will stop decreasing and start increasing. It is necessary to fix the moment when the voltage at point "A" becomes minimal, measure the resistance of the variable resistor corresponding to it and be sure to replace it with a constant one with the same resistance.

The generator is located on a separate small board in close proximity to the coil. All parts of the generator must be precision.

The transistor can be almost any p-n-p structure, even germanium with low gain.

It would be desirable to select capacitor C1 with a capacitance in the range of 5–20 nF (502–203) according to the maximum sensitivity of the circuit. Sometimes a good result happens when C1 is connected not to winding II, which is the base, but to a common wire. Capacitors C1 and C2 are preferably film capacitors with a small TKE.

The circuit coil has a diameter of 14–16 cm, 260 turns of wire with a diameter of 0.2–0.5 mm are wound on it in varnish insulation with a tap from the one hundred and sixtieth turn. If the coil is assembled in good faith, then the sensitivity of the device will be noticeably higher (up to 15–20 cm for a coin).

A coil frame made of three circles of corrugated cardboard turns out to be very simple and rather rigid. The middle circle should be slightly smaller in diameter than the outer ones. In addition to rigidity, corrugated cardboard has good thermal insulation properties, which can be used to increase the stability of the device.

So, if the generator is assembled on chip elements (smd), it can be easily placed between layers of cardboard, which will drastically reduce the impact of temperature drops and changes on it. It is not necessary to shield or insulate the rest of the device.

The device must be powered by a stabilized source. One version of the stabilizer is shown in Fig. higher. As a stabilizer, you can use an imported L7808 microcircuit with 8 V stabilization or a domestic equivalent.

PCB variant on the side of the tracks.

P O P U L I R N O E:

A set of radio components and a printed circuit board for self-assembly of the PIRATE pulse metal detector

Metal detector PIRATE- one of the popular simple pulse metal detectors with good sensitivity. Even a novice radio amateur can assemble it.

If everything is soldered correctly, the coil is made without errors, the parts are all serviceable, then the circuit starts working immediately. Of the basic settings, only one variable resistor.

SMALL RADIATION DANGER WITH LIGHT INDICATION.

The device responds to changes in ionizing radiation in the surrounding person

space by increasing or decreasing the number of light flashes per unit of time, for example, per minute. It is sensitive to the cosmic radiation background, warns a person about changes in the radiation situation in a given area and can be used, for example, as an indicator of the level of concentration of radioactive elements contained in materials. It can be useful for geologists, commanders of civil defense headquarters, maintenance personnel in radiological institutions, in the performance of work related to non-destructive quality control of materials using ionizing radiation sources in conditions of high noise, when sound alarms are ineffective. It is also useful for those who are engaged in the study and protection of nature.

The principle of operation of the air conditioner

Split system (air conditioning) is now in almost every home. Let's see - how does a split system (air conditioner) work?

The metal detector is a relatively simple device, the electronic circuit of which provides good sensitivity and stability.

A distinctive feature of such a device is its low operating frequency. The inductors of the metal detector operate at a frequency of 3 kHz. This provides:

• on the one hand, a weak response to unwanted signals (for example, signals that occur in the presence of wet sand, small pieces of metal, etc.);
• on the other hand, good sensitivity when searching for hidden water pipes and central heating lines, coins and other metal objects.

The metal detector generator excites oscillations in the transmitting coil at a frequency of about 3 kHz, creating an alternating magnetic field in it. The receiving coil is located perpendicular to the transmitting coil in such a way that the magnetic lines of force passing through it will create a small EMF. At the output of the receiving coil, the signal is either absent or very small.

A metal object, falling into the field of the coil, changes the value of the inductance. In this case, an electrical signal appears at the output, which is then amplified, rectified and filtered.

Thus, at the output of the system there is a constant voltage signal, the value of which increases slightly as the coil approaches a metal object.

This signal is fed to one of the inputs of the comparison circuit, where it is compared with the reference voltage applied to its second input. The reference voltage level is adjusted in such a way that even a small increase in the signal voltage leads to a change in the state at the output of the comparison circuit.

This in turn actuates the electronic switch. As a result of this process, an audio signal is sent to the output amplifying stages, notifying the operator of the presence of a metal object.

The circuit diagram of the metal detector is shown in fig. 3.38.

The transmitter, consisting of a transistor VT1 and associated elements, excites oscillations in the coil L1. The signals arriving at the L2 coil are then amplified by the D1 chip and rectified by the D2 chip, which is included in the amplitude detector circuit.

The signal from the detector goes to capacitor C9 and is smoothed out by a low-pass filter, which consists of resistors R14, R15 and capacitors C10 and C11.

Then the signal is fed to the input of the comparison circuit D3, where it is compared with the reference voltage set by the variable resistors RP3 and RP4. Variable resistor RP4 is used for quick and coarse adjustment, and RP3 provides fine adjustment of the reference voltage.

Rice. 3.38. Schematic diagram of a metal detector with a low operating frequency.

The generator, assembled on a transistor with one VT2 junction, operates in continuous mode. However, the signal generated by it enters the base of the VT4 transistor only when the VTZ transistor closes. After all, being in the open state, this transistor shunts the output of the generator.

When a signal is received at the input of the D3 microcircuit, the voltage at its output decreases, the VTZ transistor closes, and the signal from the VT2 transistor through the VT4 transistor and the RP5 volume control enters the output stage and loudspeaker.

The circuit uses two power supplies, which eliminates the possibility of any feedback from the circuit's output to its sensitive input.

The main circuit is powered by an 18 V battery, which is lowered to a stable voltage of 12 V using the D4 chip. At the same time, a decrease in battery voltage during circuit operation does not change the device settings.

The output stages are powered by a separate 9V power supply. The power requirements are quite low, so three batteries can be used to power the unit. The output stage battery does not require a special switch, since the output stage draws practically no current in the absence of a signal.

First of all, 64 cuts must be made in the strips and three mounting holes must be drilled.

Then on the back of the board you need to install:

• 20 jumpers;
• pins for external connections;
• two pins for capacitor C5.

Then you can install capacitors C16, SL7 and chip D4. These elements form a 12 V power supply.

This stage is checked by temporarily connecting a battery with a voltage of 18 V. In this case, the voltage across the capacitor C16 should be 12 ± 0.5 V.

After that, you can proceed to the installation of the elements of the output stage: - resistors R23-R26;

• capacitors C14 and C15;
• transistors VT4-VT6.

The body of the transistor VT6 is connected to its collector, so the contact of the body with neighboring elements and jumpers is unacceptable.

Since the output stage draws no current in the absence of a signal, it is enough to check it by temporarily connecting a loudspeaker, a variable resistor RP5 and a 9 V battery.

Then you need to install resistors R20-R22 and transistor VT2, which form a sound signal generator.

Rice. 3.39. Printed circuit board and layout of elements.

When two power sources are connected, the sound background is heard in the speaker, which changes with the position of the volume control knob.

After that, it is necessary to mount resistors R16-R19, capacitor C12, VTZ transistor and D3 chip on the board.

The operation of the comparison circuit is checked as follows. Variable resistors RP3 and RP4 must be connected to the measuring input D3. This input is formed using two 10 kΩ resistors, one of which is connected to the positive +12 V supply rail, and the other to the zero rail.

Connect the second terminals of the resistors to pin 2 of the D3 chip. The jumper from this pin serves as a temporary connection point.

With coarse tuning (both batteries are on), which is carried out by a variable resistor RP4, in a certain position, the sound signal is interrupted, while fine tuning with a variable resistor RP3 should be a smooth change in the signal near this position.

When these conditions are met, you can proceed to install resistors R6-R15, capacitors C6-C11, diode VD3 and microcircuits D1 and D2.

Turning on the power source, you first need to check for a signal at the output of the D1 chip (pin 6). It should not exceed half the value of the power supply (approximately 6V).

The voltage across capacitor C9 should not differ from the output voltage of this chip, although interference from the AC mains may cause a slight increase in this voltage.

Touching the input of the microcircuit (the base of the capacitor C6) with your finger causes an increase in voltage due to an increase in the noise level.

If the tuning knobs are in a position in which there is no sound signal, touching the capacitor Cb with your finger leads to the appearance and disappearance of the sound signal.

This concludes the preliminary check of the performance of the cascades.

The final check and adjustment of the metal detector are carried out after the manufacture of the inductors. After a preliminary check of the cascades of the circuit, the rest of the elements can be installed on the board, with the exception of the capacitor C5.

Variable resistor RP2 temporarily set to the middle position. Attach the board to the L-shaped aluminum chassis through plastic washers (to eliminate the possibility of a short circuit) using three screws.

The chassis is fixed in the control console body with two bolts that hold two clamps that are designed to fasten the console body to the search bar.

The side of the chassis secures the power supplies to the chassis.

When assembling the remote control, make sure that the switch leads on the reverse side of the variable resistor RP5 do not touch the board elements.

After drilling a rectangular hole, glue the speaker. The stem and connecting parts that form the finder head holder can be made from plastic tubes with a diameter of 19 mm.

The finder head itself is a plate with a diameter of 25 cm, made of durable plastic. The interior must be carefully sanded to ensure good adhesion to the epoxy.

Manufacturing of the transmission coil. The main characteristics of a metal detector largely depend on the coils used, so their manufacture requires special attention.

Coils having the same shape and dimensions should be wound on a D-shaped loop, which is created from pins fixed on a suitable piece of the board. Each coil shall consist of 180 turns of 0.27 mm enameled copper wire, tapped from the 90th turn.

Rice, 3.40. Metal detector coils: a - method of winding coils; 6—scheme of assembly of finished coils.

Before removing the coils from the pins, they must be tied in several places, as shown in fig. 3.40 a.

Then each coil must be wrapped with a strong thread so that the turns fit snugly together. This completes the production of the transmitting coil.

Receiving coil manufacturing. The receiving coil must be equipped with a screen. The shielding of the coil is provided as follows. First, it must be wrapped with wire, and then wrapped with a layer of aluminum foil, which again needs to be wrapped with wire.

This double winding guarantees good contact with the aluminum foil. There should be a small gap or gap in the wire windings and in the foil, as shown in fig. 3.40, 6, which prevents the formation of a closed loop around the circumference of the coil.

Coils made in this way must be fixed with clamps at the edges of a plastic plate and connected to the control unit using a four-core shielded cable.

Connect the two central taps and the screen of the receiving coil to the neutral bus through shielding wires.

If you turn on the metal detector and the radio located near the coil, you can hear a high-pitched whistle (at the frequency of the metal detector), due to the pickup of the audio signal in the radio. This indicates the health of the metal detector generator.

In this case, it does not matter what band the radio is tuned to, so any cassette recorder can be used instead to check it.

The place of the working position of the coils is determined:

• or by the output signal of the metal detector, which should be minimal;
• or according to the readings of a search device (voltmeter) connected directly to capacitor C9.

The second option for fitting coils is much simpler.

The voltage across the capacitor should be approximately 6 volts. After that, the outer parts of the coils can be glued with epoxy, and the inner parts, passing through the center, must be left loose, allowing for final adjustment.

The final adjustment consists of placing the loose parts of the coils in such a position that non-ferrous objects such as coins cause a rapid increase in the output signal, and other objects cause a slight decrease in it.

If the desired result is not achieved, it is necessary to swap the ends of one of the coils.

It should be remembered that the final adjustment or adjustment of the coils should be carried out in the absence of metal objects.

After installing and firmly fixing the coils, you need to cover them with a layer of epoxy, then put fiberglass on them and seal all this with epoxy.

After manufacturing the search head, the following actions should be carried out:

• embed capacitor C5 in the circuit;
• set the variable resistor RP1 to the middle position;
• adjust the variable resistor RP2 to the minimum output signal.

At the same time, on one side of the middle position, the variable resistor RP1 provides recognition of steel objects, and on the other side - objects made of non-ferrous metal.

With each change in the nominal value of the resistance of the variable resistor RP1, it is necessary to re-configure the device.

In practice, the metal detector is a light, well-balanced, sensitive device. During the first few minutes after turning on the device, there may be a zero level imbalance, but after a while it disappears or becomes insignificant.