The circuit of a sensitive metal detector on powerful transistors. Simple transistor metal detector

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

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

Schematic diagram

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

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

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

Therefore, external metal objects practically do not have a significant effect on its inductance.

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

The signals from both generators are fed to the diode mixer on the VD1 diode. As a result, the product of the subtraction of the frequencies of the generators is obtained on the capacitor C12.

The closer the values \u200b\u200bof these frequencies, the lower the sound tone on this capacitor, and the more the frequencies of the generators differ, the higher the sound tone in the B1 speaker, which receives the signal (the product of the diode mixer).

The signal comes through a low-frequency amplifier on transistors ѴТЗ-Т6.

With the variable capacitor C7, the search generator can be adjusted so that, in the absence of metal objects nearby, the sound in the speaker is the lowest.

Then, when the L2 coil approaches the metal, the frequency of the generator at ѴT2 begins to change. The frequency difference between the generators increases, and therefore the tone in the dynamics will rise. When the metal is located accurately, the sound will turn into a high-pitched squeak.

Details and construction

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

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

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

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

The winding should be carried out with a PEV wire with a diameter of 0.4 x 0.6 mm. The coil should contain 45 turns tapped from the 10th, counting from the VT2 collector.

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

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

• speaker;
• variable capacitor;
• spool pin L1.

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

Capacitor C7 can be with a minimum capacity of no more than 10 pF, and a maximum of at least 150 pF.

KT315 transistors can be replaced with KT3102 or KT312, KT316. The MP35 transistors can be replaced with the MP35-MP38, and the MP39 transistor for the MP39-MP42.

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

Attention:Power supply from a 220 V mains source is not desirable, because this causes an alternating current background and the sensitivity of the device as a whole decreases.

Customization

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

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

In the absence of oscillations from the generator on VT1, it is necessary to select the C4 rating and / or adjust the cascade operating mode by selecting the R2 rating. If the generator on VT2 is not excited, you need to adjust C8 and adjust the operating mode of the transistor by selecting the value of R6.

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

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

With the onset of spring, more and more people with metal detectors can be found on the banks of rivers. Most of them are engaged in "gold mining" purely out of curiosity and excitement. But a certain percentage do make a lot of money looking for rare things. The secret to the success of such research is not only in experience, information and intuition, but also in the quality of the equipment with which they are equipped. A professional tool is expensive, and if you have the basics of knowledge in radio mechanics, you probably have 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 independently assemble the device 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 propose to study 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 transmitting and the other is receiving.

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

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

The cheapest devices are of the first type.

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

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

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

• Dynamic type devices... The simplest type of device that scans the field continuously. 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.
• Pulse type devices.They have great sensitivity. Often there are several additional coils for such a device for tuning for different types of soil and metals. Requires certain skills to set up. Among the devices of this class, one can distinguish 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) to unwanted signals: wet sand, small pieces of metal, shot, for example, and, on the other hand, provide good sensitivity when searching for hidden water pipes and central heating lines, as well as coins and other metal objects.
• Depth detectors sharpened for the search for objects located at an impressive depth. They can detect metal objects at a depth of 6 meters, while other models "pierce" only up to 3. For example, the Jeohunter 3D depth detector is capable of searching and detecting voids and metals, while showing objects detected in the ground in 3- dimensional form.

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

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

Which metal detectors are suitable for making with your own hands at home

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

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

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

However, in spite of the fact that some entertainers try to offer systems for assembling a metal detector from a phone, such designs will not pass the "battle" test. It is easier to buy a metal detector toy for children, there will be more sense.

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

Homemade metal detector "Pirate": diagram and detailed assembly description

Homemade products based on the Pirate series metal detector are among 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 pulse-type device. To manufacture the device, you will need to purchase:

1. Materials for making the body, the rod (you can use a plastic pipe), the holder, and so on.
2. Wire and electrical tape.
3. Headphones (suitable from the player).
4. Transistors - 3 pieces: ВС557, IRF740, ВС547.
5. Microcircuits: K157UD2 and NE
6. Ceramic capacitor - 1 nF.
7. 2 film capacitors - 100 nF.
8. Electrolyte capacitors: 10 μF (16 V) - 2 pieces, 2200 μF (16 V) - 1 piece, 1 μF (16 V) - 2 pieces, 220 μF (16 V) - 1 piece.
9. Resistors - 7 pieces per 1; 1.6; 47; 62; 100; 120; 470 kΩ and 6 pieces for 10, 100, 150, 220, 470, 390 ohms, 2 pieces for 2 ohms.
10. 2 diodes 1N148.

DIY metal detector circuits

The classical scheme of the Pirate series metal detector is based on the NE555 microcircuit. The operation of the device depends on a comparator, one output of which is connected to the IC pulse generator, the second to the coil, and the output to the speaker. If metal objects are detected, the signal from the coil goes to the comparator, and then to the speaker, which notifies the operator about the presence of the desired objects.

The board can be housed in a simple junction box, which can be purchased from an electrical store. If such a tool is not enough for you, you can try to make a device of a more perfect plan, to help you with a diagram for making a metal detector with a reference to gold.

How to assemble a metal detector without using microcircuits

In this device, Soviet-style transistors KT-361 and KT-315 are used to generate signals (you can use similar radio components).

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

The pulse generator is assembled on the NE555 microcircuit. 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 the transistor T1, and it transmits the signal to the transistor T2. Amplification of the audio frequency occurs on the BC547 transistor to the collector, and headphones are connected.

To accommodate radio components, a printed circuit is used, which can be easily made by yourself. For 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 in ferric chloride for etching. This is necessary to remove unprotected areas 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 a wire of 0.5 mm is wound. To increase the depth of metal detection, the coil frame should be within 260-270 mm, and the number of turns should be 21-22 vol. If you don't have anything suitable on hand, you can wind the spool on a wooden base.

Copper wire coil on wooden base

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

Twisted pair coil in 5 minutes

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

Illustration	Action Description
	Roll the wire into two coils with a pigtail. Leave 10 cm on each side.
	Strip the winding and free the wires for connection.
	We connect the veins according to the diagram.
	For better attachment, solder them with a soldering iron.
	Test the coil in the same manner as for 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 DIY metal detector "Pirate"

After the main elements of the metal detectors are ready, we proceed to the assembly. We attach all the assemblies to the metal detector rod: the body with the coil, the receiving-transmitting unit and the handle. If you did everything correctly, then additional manipulations with the device will not be required, since it initially has maximum sensitivity. More fine tuning is done by means of a variable resistor R13. Normal operation of the detector should be ensured with the middle position of the regulator. If you have an oscilloscope, then with its help, at the gate of the transistor T2, you need to measure the frequency, which should be 120-150 Hz, and the pulse duration - 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 that you have to work hard on creating an impenetrable shell using a sealant, as well as on placing special light indicators that can report a find from under the water. An example of how this will work in the video:

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

The Terminator 3 metal detector has occupied an honorable place in the ranks of home-made metal detectors for many years. 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 characteristics, 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 metal detector with your own hands with metal discrimination

Discrimination against metals is the ability of an instrument to distinguish between detected material and to classify it. Discrimination is based on the different electrical conductivity of metals. The simplest methods of determining the types of metals were implemented in old devices and devices of the entry level and had two modes - "all metals" and "non-ferrous". The discrimination function allows the operator to respond to a specific amount of phase shift compared to a set (reference) level. At the same time, 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, hand-made metal detector looks at a depth of 6 meters. However, in this case, the size of the find must be solid. These detectors work best for detecting old projectiles or large enough debris.

There are two types of deep metal detectors: frame and boom-mounted transceiver. The first type of device is capable of covering a large area of \u200b\u200bland for scanning, however, in this case, the effectiveness and focus of the search is reduced. The second version of the detector is a point detector, it works directed inward at a small diameter. You must work with it slowly and carefully. If your goal is to build such a metal detector, the following video may show you how to do it.

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

Simple metal detector circuit

Diagram of the second version of the metal detector

A diagram of a very simple metal detector "Metelik" was sent. Consists of two generators on kt315. Another high frequency transistor can be used. The operating frequency is no more than 0.5 MHz (apparently 150-200 kHz). When at rest, the generators produce the same frequency. The difference of which gives modulation. It is quite difficult to achieve - synchronous operation of the generators, therefore deviation (most likely) will be present constantly - low-frequency squeak. But as soon as the antenna frame is brought to the metal object, the frequency of one of the generators will change (the frequency decreases). This difference between the two oscillators will be modulated into the speaker. The closer to metal, the more the tone of the sound changes. By the sound, you can determine about a metal object in the range of the metal detector. The circuit is powered by battery, enough up to 20-30 hours of work. Usual low impedance headphones are used.

Antenna frame 15 cm in diameter, winding 30 + 10 turns. The number of turns can be more, but the frames must be the same. The circuit is assembled and installed by "surface mounting". It is glued to a piece of lightweight and durable plastic or cardboard, but it must be treated with a waterproof varnish.

Assembly of parts

Parts are spaced as close as possible from each other. It is desirable that the parts of the generators are the same.

Photo of a metal worker.

The structure is attached to a plastic pipe, or you can use a wooden stick. It will probably be necessary to configure the generators. Without an oscilloscope, this adjustment is difficult. The main thing is that the difference between the generators in a quiet state is as small as possible.

I can say without a doubt that this is the simplest metal detector I've ever seen. It is based on only one TDA0161 microcircuit. You don't need to program anything - just build and that's it. Also, its huge difference is that it does not emit any sounds during operation, unlike the metal detector on the NE555 microcircuit, which initially squeaks unpleasantly and you need to guess about the found metal by its tonality.

In this circuit, the buzzer only starts beeping when it detects metal. The TDA0161 microcircuit is a specialized industrial version for inductive sensors. And on it, metal detectors are mainly built for production, which give a signal when a metal approaches an induction sensor.
You can buy such a microcircuit at -
It is not expensive and is quite affordable for everyone.

Here is a diagram of a simple metal detector

Metal detector characteristics

• Microcircuit supply voltage: from 3.5 to 15V
• Generator frequency: 8-10 kHz
• Current consumption: 8-12 mA in alarm mode. In the search state, approximately 1 mA.
• Working temperature: -55 to +100 degrees Celsius

The metal detector is not only very economical, but also very unpretentious.
A battery from an old cell phone works well for power.
Coil: 140-150 turns. The diameter of the coil is 5-6 cm. Can be converted to a coil with a larger diameter.

The sensitivity will depend directly on the size of the search coil.
In the circuit, I use both light and sound alarms. You can choose one if you like. Buzzer with internal generator.
Thanks to this simple scheme, you can make a pocket metal detector or a large metal detector, whichever is more necessary for you.

After assembly, the metal detector works immediately and does not need any settings, except for setting the response threshold with a variable resistor. Well this is standard procedure for a metal detector.
So friends, collect the thing you need and, as they say, fit in the household. For example, to search for electrical wiring in the wall, even nails in a log ...

A simple metal detector with transistors.

Hello everyone who wants to assemble a metal detector.

When carrying out repair and construction work, especially in old houses, a device is needed with which it is possible to detect various metal objects under a layer of wallpaper or in the thickness of walls or ceilings. To search for water pipes embedded in walls, wires chaotically laid under a thick layer of wallpaper or in the thickness of plaster, as well as "treasures" and hiding places hidden under wallpaper or boards, a simple device is suitable that works on the principle of comparing two frequencies by the beat method.

In my opinion, this is the simplest and most proven scheme on the Internet. It does not contain any controversial elements. Basically, this book is dedicated to novice radio amateurs. Well, if all your brains have not yet dried up, then you can proceed.

The principle of operation of a metal detector boils down to the fact that when a metal object approaches the inductor coil of the generator - the main unit of the device - the frequency of the generator changes. The closer the object and the larger it is, the stronger its influence on the frequency of the generator - (in our case, the transistor).

Schematic diagram

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Resistor marking for 100kΩ - brown, the black, yellow.

Capacitor

Stores a charge of energy

Transistor

Switches voltage.

Its pinout:

This is how the diagram, assembled on cardboard, looks like:

How to wind the coil: We take a 3 liter can and 100 meters of copper wire with a diameter of 0.3-0.5 mm. We wound 20 turns, solder the beginning of the winding to the capacitors and make a recess to which we then solder the wire from the emitter of the transistor. We finish the remaining 10 turns and solder to the bottom of the circuit, as it were, to another coil.

As you already understood there are 2 coils, everything should be symmetrical, because the metal detector will not work correctly.

It is imperative to soak the coils with building varnish and wrap them with threads.

Each coil makes a different sound: when it hits its El. The magnetic field of the metal one amplifies the squeak, while in the other, on the contrary, the sound disappears.

It is advisable to fill the transistors with wax.

It operates at approximately 1 MHz.

Depth: coin-10cm, pipe-15cm, hatch-20cm. Also looking for some non-ferrous metals.

Photo of the assembled device.

The circuit was assembled by me and it just might not work.

Good luck!!!