In this article we will talk about one of the simple metal detectors, the assembly of which can be carried out using available Soviet radio components. These include transistors marked CT and MP, as well as resistors and capacitors from popular radio equipment. Most of the necessary parts can be found without problems in old radio devices.
The circuit consists of five nodes, the structure of which can be viewed in Figure 1:
- Master frequency oscillator, used to create a reference frequency.
- Search frequency generator. Its frequency will change when metal is found.
- Low-frequency amplifier to increase the signal difference of the generators.
- A node that produces sound.
- Power supply.
This device resembles a metal detector with two transistors, but it has an added sound amplifier, and, despite its simplicity, it has good metal detection performance. It is perfect for mass search and collection of ferrous metal. If you find radio components and a little time, you can easily assemble a metal detector using the example of this educational article.
Assembling circuit elements
The circuit can be assembled on a one-sided foil-coated PCB. Guided by Figure 2, which shows the circuit of a metal detector using transistors, we count the number of connections and create the corresponding number of contact pads with a sharp object. After tinning, the board is ready for assembly of parts (Fig. 3). For better assembly, you can think over and draw a homemade printed circuit board.
Below is a list of required parts and instructions for some of them:
- 14 resistors with a power of 0.125 W. Denominations:
- R1, R5 – 100 kOhm;
- R2, R6, R11 – 10 kOhm;
- R3, R7 – 1 kOhm;
- R4, R8 – 5.1 kOhm;
- R9 – 6.2 kOhm;
- R10, R13 – 220 kOhm;
- R12 – 3.9 kOhm;
- R14 – 3 kOhm.
- 14 capacitors, preferably heat-resistant:
- Electrolytic at 6 V: C10, C14 – 47 µF; C12, C13 – 22 µF;
- Variable capacitors C7 – up to 10 pF / from 150 pF;
- Trimmer capacitor C8 – 6/25 pF;
- C1, C11 – 47 nF;
- C2, C6 – 4.7 nF;
- C3 – 100 pF;
- C4 – 47 pF;
- C5, C9 – 2.2 nF.
- Five transistors:
- 3.1 VT1, VT2 – KT315. As analogues you can use KT3102, KT312 or KT316;
- 3.2 VT3, VT4, VT5 – MP35. Can be replaced with MP from 36 to 38;
- 3.3 VT6 – MP39. MP from 40 to 42 are also suitable;
- 2 diodes D9Zh, or others - D18, D2, GD 507.
- Power supply 4.5 V in the form of three AA batteries. You can use a 9V Krona battery, but in this case it is necessary to change the electrolytic capacitors to a voltage higher than 9V.
- Speaker with resistance from 5 to 100 Ohms. Speakers from children's toys, intercom handsets, radios or a headphone are suitable.
- Contact connector for battery (Fig. 4).
- Microswitch or toggle switch to turn off.
Metal detectors cannot operate without coils, which play a major role in the device. In the next paragraph of the article we will describe in detail their role in the work and the manufacturing process.
Creating Generator Coils
The primary coil L1 is exemplary and, together with capacitor C3, serves to create the reference frequency of the generator. The secondary coil L2 works in the same way, but it is made without a core. This allows metal objects to act on it and change the frequency of the generator, which leads to a difference in frequencies for the signal.
Below is how to make homemade coils without much difficulty.
For the frame of the L1 coil, you need a metal rod with a diameter of 8 mm and a length of 3 cm. You can use an antenna with a radio. Whatman paper must be wound around the rod. We do this to be able to adjust the frequency by moving the rod relative to the coil, so it is important that the Whatman paper fits very tightly to prevent spontaneous movement. After the final setup of the metal detector in the last step, you can fix the rod with glue. A sample coil is shown in Figure 5.
We wind the L1 coil with PEV wire with a diameter of 0.2 - 0.3 mm. We wind 110 turns on whatman paper strictly in one row, trying to avoid gaps or gaps between turns. At the 16th turn we make a tap without breaking the wire. After winding, you can varnish the wire, but you must ensure that the metal rod inside can move freely. We connect the wire according to the diagram.
The second coil L2 is made in the form of a rectangular frame measuring 12 x 22 cm. The frame can be made of plastic, plexiglass, plywood and other non-conducting material. We make a tray or assemble only a supporting rectangle into which the winding can be laid in bulk. Finished samples can be seen in Figure 6.
The wire, as in the first case, we choose PEV brand, but with a diameter of 0.4 - 0.6 mm. We wind 45 turns, making a conclusion on the 10th turn. After the metal detector is fully manufactured and configured, it will be possible to fix and insulate the winding with varnish. The connection to the circuit is made with a shielded cable with at least two cores. Such cables are used in high-quality audio equipment and in trunk communication lines, and they can also be purchased at an electronics store.
Making a metal detector design
First of all, you need to decide what material the bar will be made of. It is better to give preference to dielectric material to eliminate problems with the operation of the metal detector. There are many options: PVC pipe, telescopic fishing rod, wooden pole. When choosing, it is worth considering such indicators as weight, flexibility, disassembly ability, and convenience.
If you plan to spend a lot of time searching for metal, the light weight and comfortable armrest with handle will save you a lot of effort. But do not forget that lightweight material can bend. In the case of a PVC pipe, this can be compensated for by sand poured inside or additional supporting structures. With a collapsible rod there will be no problems with transportation. To implement this idea, you can visit a plumbing store and assemble an excellent metal detector with your own hands using various adapters (Fig. 7).
Once you have decided on the choice of rod, you need to attach the reel to it. Everything is simple here - no metal. Use plastic fasteners, pre-attached ears on the reel frame, adapters, or simply reliable glue.
We place the circuit in a plastic box. You can make small holes for the speaker for good audibility. The board, speaker, primary coil and battery box can be secured with glue. We place the box a meter from the search coil and fasten it in a convenient way - using plastic fasteners or glue.
At this point, you have assembled a simple transistor metal detector that needs fine tuning and testing.
Device setup
Setting up a metal detector involves creating the same frequency in both generators. When this result is achieved, the lowest, barely audible tone will be emitted from the speaker.
First, remove all metal objects from the range of the metal detector. We take into account concrete walls and floors, since they may contain metal reinforcement. We set all variable capacitors to the middle position. By changing the position of the rod in coil L1, we achieve the desired tone or lack thereof. During further operation of the device, we use capacitor C7 for adjustment. After setting up, we bring a metal object to different distances from the search coil and make sure that the metal detector is working.
If the metal detector does not work, we check the blocks and circuit parts. We start the test with transistors, and then check the diodes. To check the sound amplifier, just remove the resistor R9 from the generators and connect it to the sound output of any device that reproduces sound (Fig. 8).
If the parts and the amplifier are in working order, then we set up the transistor generators. To do this, we try to change the values of capacitor C4 and resistor R2 for the master oscillator, and resistor R6 for the search oscillator. You can try starting the second generator with tuning capacitor C8.
Even the most serious and respectable citizens feel a slight excitement when they hear the word “treasure”. We literally walk through treasures, of which there are immeasurably many in our land.
But how can you look under the soil layer to know exactly where to dig?
Professional treasure hunters use expensive equipment, the purchase of which can pay for itself after one successful find. Archaeologists, builders, geologists, members of exploration societies use equipment provided by the organization in which they work.
But what about novice treasure hunters on a budget? You can make a metal detector at home with your own hands.
To understand the subject, consider the design and operating principle of the device
Popular metal detectors operate 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, using a transmitting coil, creates an electromagnetic field (EMF) around it with specified characteristics. The receiver scans the environment and compares the field indicators with the reference ones. If there are no changes, nothing happens in the circuit.
- When any conductor (any metal) enters the field of action, the basic EMF induces Foucault currents in it. These eddy currents create the object's own electromagnetic field. The receiver detects the distortion of the basic EMF and gives a signal to the indicator (audio or visual alert).
- If the object being examined is not metallic, but has ferromagnetic properties, it will shield the underlying EMF, also causing distortion.
Important! There is a misconception that the soil in which searches are carried out should not be electrically conductive.
This is wrong. The main thing is that the electromagnetic or ferromagnetic properties of the environment and the search objects are different from each other.
That is, against the background of certain characteristics of the EMF generated by the search environment, the field of individual objects will stand out.
Types of metal detectors
Understanding the features of different circuits will not only help you choose a ready-made detector. If you decide to build a metal detector for coins with your own hands, you do not need to install a detector for water pipes or fittings in concrete.
You should initially know what the device is for, since universal metal detectors are expensive, both when purchased and when assembled yourself. In addition, a narrow-profile device is more compact and lightweight.
Basic parameters
- Search depth. Determines the penetrating power for standard primers: below this band the coil will not respond to artifacts.
- Coverage area: the wider it is, the less time it will take to “comb through”. True, selectivity and sensitivity are reduced.
- Selectivity: selecting the required object from a variety of objects. For example, when searching for gold jewelry on the beach, your device will not respond to steel hairpins or coins.
- Sensitivity: the higher it is, the more likely it is to find small objects. True, the coil reacts to various debris, such as nails or hairpins.
- Noise immunity. The detector sensor is affected by many extraneous factors: thunderstorms, power lines, mobile phones, etc. It is necessary to filter them out.
- Autonomy: this means both energy consumption and battery charge reserve.
- Discrimination is the ability to distinguish artifacts by type. Let's look at this parameter in more detail.
Today we will talk about how to make a highly sensitive metal detector with your own hands at home from scrap materials. We will also consider assembly methods, visual photos, circuit boards, diagrams and drawings of homemade metal detectors and metal detectors with different operating principles
The operation of a metal detector is based on the principle of magnetic attraction. Thanks to this, a magnetic field is created by the device through the search coil, and then the MF is directed into the ground. The second coil of the metal detector receives return signals and reports the find using a tone signaling device. The moment the coil is passed over the ground and a metal object is detected near the magnetic field, the tone will change in pitch. This change in the field means that you are near the search object.
It is necessary to take into account the fact that the larger the coil, the more sensitive the metal detector becomes, although in modern devices it is often necessary to install small search heads, but equipped with powerful circuits. But how can you make it yourself and for free?
There are four types of metal detectors:
1. Ultra Low Frequency (ELF) finder: The simplest of the home remedies, it is not difficult to make. Has the ability to track various metals (with special settings). The most widely used type.
2. Pulse metal detector (ID): a deep device, capable of detecting objects located very deep. Popular among professional gold hunters because it is primarily tuned to non-ferrous metals.
3. Beat detector: can detect any metal or mineral in the range of its pulse (to a depth of up to 1 meter), if you make it yourself, you can distinguish only metals of a certain group. This is the cheapest and simplest type of device.
4. Radio Detector: Can detect metals hidden up to 1 meter in the ground. It is made very quickly, within a few minutes, this is the best option for demonstrating the principle of operation of the device or for presenting it at children's art fairs. He's not that popular.
Regardless of the type of metal detector you plan to make yourself, most detectors have a similar design assembly. What and how can you make the most primitive metal detector?
1. Control box: consists of a board, microspeaker, battery pack and microprocessor.
2. Holder: connects the command block and the coil. Often reaches the size of a human being.
3. Magnetization coil: this is the part that senses the metal, as well as the source of the MF. Also known as a "search head", "loop" or "antenna", consists of disks.
4. Stabilizer (optional): needed to control the position of the detector.
Making a high frequency metal detector
A high-frequency metal detector differs from other models in that it uses two coils at once:
· transfer coil: the outer circuit of the coil that contains the wires. Electricity is transmitted through these cables, which creates a magnetic field.
· receiving reel: a reel with a coil of wire. This part receives, processes and amplifies the frequencies coming from the metal in the ground, and, therefore, signals the discovery of treasure.
Step-by-step instructions, photos and diagrams for beginners on how to make a high-frequency metal detector:
1. You need to assemble a command block. It can be made from a computer, laptop or radio.
2. Find the highest AM frequency on the radio. Check that the receiver is not tuned to a radio station.
3. Now we assemble the search head. To do this, cut out two circles from an ordinary thin plywood sheet. One is about 15 centimeters in diameter, the other is slightly smaller – 10-13. This is necessary so that one ring can fit into another. Now you need to cut out small wooden sticks to position the rings parallel to each other. .
4. From these plates we take 10-15 turns of enameled copper wire with a cross-section of 0.25 mm from the outer circle. Now you need to attach the structure to the block.
5. Pole connection. Mount the head on the bottom end, radio detector on the top.
6. Now you need to turn on the radio frequency, you should hear a faint tonal sound. You may need to do a little work with the radio settings. If necessary, you can attach headphones to the kit for better audibility.
Assembling a pulse detector
You need to assemble the control unit. Hack a regular transistor type radio to find usable parts. We will need:
· 9 volt battery;
· Amplification transistor 250+;
· A small 8 ohm speaker will do.
Assembling the search coil
You need to cut 3 rings from 3mm plywood, the diameter of one is 15 cm and the diameter of two is 16 cm. Use wood glue to make a sandwich, with a 15cm circle in the center.
Along the edge, equip the plywood with 10 turns of wire, as in the method above.
Setting up a radio station. Make sure the tone is sounding and the radio is out of range.
Turn on the block. You may need to tilt it. Also, before making a metal detector with your own hands, you need to check the board settings; perhaps it will not detect metals due to the board settings.
Attach the search head to the shaft. Test your metal detector on a plug or other metal parts. Important: before you make a powerful metal detector with your own hands, you need to select a higher-frequency receiver, in which case we advise you to buy a special unit for the detector in a radio store or take the Terminator metal detector as a starting point.
In principle, everything is quite simple, you just need to find everything you need and make a metal detector at home yourself. Here's another way:
1. To make a metal detector at home, you will first need to find an empty box from a regular CD.
2. Now you need to find the radio and glue its back wall to the first flap of the disc box. For this purpose, you can use double-sided tape or special adhesive tape.
4. Now that such a device is almost ready, it’s time to start setting it up. Turn on the radio and make sure that the device is working, and that it is operating on the AM band. At the same time, it is also necessary to ensure that no other radio stations operate on this frequency. Now you should make the sound bigger and make sure that you don’t hear anything else except noise from the receiver.
5. Now we check the functionality of the created metal detector. We begin to close the box. At a certain moment you will hear a strong sound. This means that the radio was able to pick up the electromagnetic waves that were emitted by the calculator.
6. When you open the box slightly, this noise will disappear. Now it is enough to open the box slightly so that the noise is not strong, but audible. In this position, present the box to any metal object. After this, you can hear this loud noise again. A loud sound indicates that the metal detector model is working. In this case, you can use it to look not only for metal things lost in the house, but also to go to the forest or to another place in order to find something interesting, and maybe even precious. But it’s still better to use such a device at home.
Even the simplest DIY metal detector needs an inductive coil. It is a ring with a diameter from 6-8 cm to 14-16 cm, depending on the size of the metal objects to be looked for. To make a homemade coil, take a blank of a suitable diameter, onto which an enameled copper wire with a cross-section of 0.4-0.5 mm is wound. The number of turns can be calculated using a well-known formula that takes into account the diameter of the coil. After winding, the coil is carefully removed from the workpiece and secured with insulating tape. It will protect it from mechanical damage and atmospheric moisture. After this, a foil screen is wound over the coil with a gap of approximately 10-15 mm in length.
The resulting screen should not be a short-circuited loop. A tinned copper wire must be wound over the screen in 1 cm increments, which is connected to the braid of the coaxial cable leading to the electronic unit. The coil is connected to the circuit with a two-wire coaxial cable.
It is recommended to make several coils with different internal diameters, which will allow them to be connected for each specific case. In conclusion, all that remains is to design the metal detector structurally: place the electronic unit in a sealed case, protected from moisture and dust, and install the inductive coil on the end of a non-metallic pole of the required length. A small speaker or headphones can be used as a source of sound signal generated by an electronic circuit if the device is to be used in noisy places. The device is powered from an autonomous current source - a battery or accumulator.
A deep homemade metal detector differs from a surface one in its higher sensitivity, which allows you to find metal objects at depths of up to several meters. In addition, such devices provide selectivity, allowing small objects to be ignored. In technological terms, such a device is no different from the one described above. As a rule, the inductive coil for a deep metal detector is made of a larger diameter (up to 300 mm) and has better protection from external interference. Setting up such a device may require the use of electronic measuring equipment. This will allow you to achieve the required level of sensitivity of the device.
Any metal detectors operate based on the principles of “Foucault currents” known from the school curriculum. We will not go into details of the experiments. When the search coil and a metal object come closer together, a change in frequency occurs in the generator, which the device reports with an audio signal. If you hear a squeaking sound in your headphones, it means there is something metal lying underground. Modern inventors are working on two tasks: increasing search depth; improvement of identification parameters of devices; reduction of energy costs; convenient operating characteristics.
How to make a metal detector at home? It’s worth getting a little acquainted with electronics and reading physics for the 7th grade of high school. Experience with some tools and available materials will be useful. It is necessary to study and test a number of electrical circuits in order to choose the one that will really work
Materials you will need for work:
small generator (from an old tape recorder); quartz resonator; film capacitors and resistors; vinyl or wooden ring for the search coil; plastic, bamboo or wooden cane holder; aluminum foil; wires for coil winding; piezoelectric emitter; metal box – screen; headphones for receiving sound signals from the device; two identical transformer coils; 2 Krona batteries; perseverance and patience.
Sequence of assembling a search metal detector A search coil is made from a plywood circle with a diameter of 15 cm: the wire is wound in turns (15-20) onto a template. The stripped ends are soldered to the connecting cable. A layer of thread is wound around the perimeter of the coil over the wire for fastening. All parts of the circuit are soldered on a PCB board in the following order: capacitors, resistor system, quartz filter, signal amplifier, transistor, diodes, search generator. A soldered board is inserted into the prepared case, connected to the search coil and mounted on a holder stick. The signal from the search coil reflected by a metal object increases the frequency of the generator. Amplified by a quartz filter, it is converted by an amplitude detector into a constant pulse that produces sound.
The principle of operation of a metal detector comes 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.
Now let’s look at the design of a simple metal detector assembled using two transistors. Metal detector circuit The generator is made on transistor VT1 according to the circuit of three-point capacitors. Generation is formed due to positive feedback between the emitter and base circuits of the transistor. The frequency of the generator depends on the capacitance of capacitors C1-C3 and the inductance of coil L1. As the coil approaches a metal object, its inductance changes - it increases if the metal is ferromagnetic, for example iron, and decreases if the metal is non-ferrous - copper, brass.
But how can you monitor the change in frequency? For this purpose, a receiver assembled on a second transistor is used. This is also a generator, assembled, like the first one, according to a three-point capacitive circuit. Its frequency depends on the capacitance of capacitors C4-C6 and the inductance of coil L2 and is not much different from the frequency of the first generator. The required frequency difference is selected using a coil trimmer. In addition, the cascade on transistor VT2 also combines the function of a detector that isolates low-frequency oscillations of high-frequency oscillations arriving at the base of the transistor. The detector load is BF1 headphones; capacitor C1 bypasses the load for high frequency oscillations.
The oscillatory circuit of the receiver is inductively coupled to the generator circuit, therefore, currents flow at the frequency of both generators, as well as a current of the difference frequency, in other words, the beat frequency, in the collector circuit of transistor VT2. If, for example, the frequency of the main generator is 460 kHz, and the frequency of the receiver generator is 459 kHz, then the difference will be 1 kHz, i.e. 1000 Hz. This signal is heard in phones. But as soon as you bring the L1 search coil closer to the metal, the sound frequency in the phones will change; depending on the type of metal, it will either decrease or become higher.
Instead of those indicated in the diagram, P401, P402 and other high-frequency transistors are suitable. Headphones are high-impedance TON-1 or TON-2, but their capsules must be connected in parallel so that the total resistance is 800...1200 Ohms. The sound volume in this case will be slightly higher. Resistors - MLT-0.25, capacitors - KLS-1 or BM-2.
Coil L1 is a rectangular frame with dimensions of 175x230 mm, consisting of 32 turns of PEV-2 0.35 wire (PELSHO 0.37 wire is suitable).
L2 coil design. In two paper cylindrical frames 6 there are pieces of a rod with a diameter of 7 mm made of 400NN or 600NN ferrite: one (1) 20...22mm long, permanently fixed, the other (2) 35...40mm (movable - for adjusting the coil). The frames are wrapped with paper tape 3, on top of which a coil L2 (5) - 55 turns of PELSHO wire (possibly PEV-1 or PEV-2) with a diameter of 0.2 mm is wound. The coil terminals are secured with rubber rings 4.
Power sources - battery 3336, switch SA1 - toggle switch, connector X1 - two-socket block.
Transistors, capacitors and resistors are mounted on a board made of insulating material. The board is connected to coils, a battery, a switch and connector, and an insulated stranded wire. The board and other parts are placed in a glued plywood case with dimensions of 40x200x350 mm. Coil L1 is attached to the bottom of the case, and coil L2 is placed inside the coil at a distance of 5...7 mm from its turns. A board is attached next to this coil. The connector and switch are attached from the outside to the side wall of the case. A wooden handle about a meter long is attached to the top of the case (preferably with glue).
Setting up a metal detector begins with measuring the operating modes of the transistors. Having turned on the power, measure the voltage at the emitter of the first transistor (relative to the common wire - the power plus) - it should be 2.1V. More precisely, this voltage can be selected using resistor R2. Then measure the voltage at the emitter of the second transistor - it should be 1 V (set more precisely by selecting resistor R4). After this, by slowly moving the tuning core of the L2 coil, a loud, clear, low-frequency sound appears in the headphones.
By bringing a tin can closer to the search coil, the beginning of a change in the sound tone is recorded. As a rule, this occurs at a distance of 30...40 cm. By more accurately adjusting the frequency of the second generator, the highest sensitivity of the device is achieved.
Frequency generators of 160 kHz and 161 kHz, respectively, are assembled on elements IC1.1 and IC1.2. Where C1, L1 is the oscillatory circuit of the first generator, C4, L2 is the oscillatory circuit of the second generator. The inductance of the second generator L2 is a search coil. A mixer is assembled on element IC1.3, at the output of which we obtain a frequency difference between the generators equal to 1000 Hz. When a metal object appears near the search coil, its inductance changes and changes the frequency of the generator, which in turn changes the frequency at the mixer output. Variable resistor R5 is a volume control. Element IC1.4 is used as a buffer amplifier stage, cutting off unnecessary frequencies and amplifying the signal. A push-pull amplifier is assembled using elements VT1, VT2, VT3, designed to work with headphones with a resistance of 32-200 Ohms.
The IC1 chip is of the CD4030 type. It can be replaced with any other chip OR CMOS technology. VT1, VT3-BC547, VT2-BC557. All electrolytic capacitors are rated at 16V. Resistors with a power of 0.125W. Supply voltage - 6V.
Coil L1 - inductance 100 mH.
Search coil L2 - 140 turns of wire with a diameter of 0.8 mm, coil diameter - 150 mm.
Tuning comes down to tuning the generators to frequencies of about 160 kHz with a difference of 1 kHz.
When a metal object enters the working area of the coil, the inductive coupling between the coils changes. In this case, a signal appears at the terminals of coil L2, limited in amplitude (if the object is large) by diodes VD1 and VD2, which is subsequently amplified by the action of the operational amplifier DA1.1.
At the output of the filter, which is built on this operational amplifier, a constant voltage appears, increasing as the coils approach the metal target. Next, the voltage goes to the inverting input in the comparator DA2.1. It compares this voltage with the reference voltage supplied to its second input.
When the comparator is triggered, its output voltage decreases, this leads to the closure of transistor VT3, and the sound generator made on the basis of the DA2.2 microcircuit is activated. From the sound generator the signal goes to the amplifier, and from there to the main telephone from the hearing aid. You can adjust the volume using variable resistor R38.
To wind the coil, a circle with a diameter of 14 cm is used. For each coil, 200 turns of copper wire with insulation are supposed to be made. The wire should have a diameter of 0.27 mm and should be removed from the middle of the coil. Before removing the finished spool from the frame, you need to bandage it, and after removing it, wind the thread around it so that the turns fit more tightly to each other. The removed coil is configured as in Figure 2 and secured with threads to a plastic plate. There should be a transmitting coil at the bottom, and a receiving coil at the top.
The take-up coil must have an aluminum screen with a hole designed to prevent short-circuited turns. It is necessary to connect the coil leads to the device using a shielded cable. The vertical turns of the coils should be separated by distances of 25 mm. The last step is to secure the coils with glue or sealant.
Not so often, but losses still happen in our lives. For example, we went into the forest to pick mushrooms and berries and dropped the keys. It will not be so easy to find them in the grass under the leaves. Don’t despair: a homemade metal detector, which we will make with our own hands, will help us. So I decided to collect my first metal detector. Nowadays, few people decide to make a metal detector. Homemade devices were popular twenty to twenty-five years ago, when there was simply nowhere to buy them.
Modern metal detectors from manufacturers such as Garrett, Fisher and many others have high sensitivity, metal discrimination, and some even have a hodograph. They are able to adjust the ground balance and tune out electrical interference. Thanks to this, the detection depth of a modern coin metal detector reaches 40 cm.
I chose a scheme that was not very complicated, so that it could be repeated at home. The principle of operation is based on the difference in the beat of two frequencies that we will pick up by ear. The device is assembled on two microcircuits, contains a minimum of parts, and at the same time has quartz frequency stabilization, thanks to which the device operates stably.
Metal detector circuit on microcircuits
The scheme is very simple. It can be easily repeated at home. It is built on two 176 series microcircuits. The reference oscillator is made on La9 and stabilized by quartz at 1 MHz. Unfortunately, I didn’t have this, I had to set it to 1.6 MHz.
The tunable generator is assembled on the K176la7 microcircuit. To achieve zero beats, varicap D1 will help, the capacity of which varies depending on the position of the variable resistor R2 slider. The basis of the oscillatory circuit is the search coil L1, when it approaches a metal object, the inductance changes, as a result of which the frequency of the tunable generator changes, which is what we hear in headphones.
I use regular headphones from a player, the emitters of which are connected in series to reduce the load on the output stage of the microcircuit:
If the volume turns out to be too much, you can introduce a volume regulator into the circuit:
Details of a homemade metal detector:
- Microcircuits; K176LA7, K176LA9
- Quartz resonator; 1 MHz
- Varicap; D901E
- Resistors; 150k-3pcs., 30k-1pc.
- Variable resistance resistor; 10k-1pcs.
- Electrolytic capacitor; 50 microfarads/15 volts
- Capacitors; 0.047-2pcs., 100-4pcs., 0.022, 4700, 390
Most of the parts are located on the printed circuit board:
I placed the entire device in an ordinary soap dish, shielding it from interference with aluminum foil, which I connected to a common wire:
Since there is no place on the printed circuit board for quartz, it is located separately. For convenience, I removed the headphone jack and frequency control from the end of the soap dish:
The entire metal detector unit was placed on a piece of ski pole using two clamps:
The most important part remains: making the search coil.
Metal detector coil
The sensitivity of the device and resistance to false alarms, the so-called fontons, will depend on the quality of the coil's manufacturing. I would like to immediately note that the depth of detection of an object directly depends on the size of the coil. So, the larger the diameter, the deeper the device will be able to detect the target, but the size of this target should also be larger, for example, a sewer manhole (the metal detector simply will not see a small object with a large coil). Conversely, a small-diameter coil can detect a small object, but not very deep (for example, a small coin or ring).
Therefore, I first wound a medium-sized reel, so to speak, a universal one. Looking ahead, I want to say that the metal detector was designed for all occasions, that is, the coils should be of different diameters and they can be changed. To quickly change the coil, I installed a connector on the rod that I pulled out of an old tube TV:
I attached the mating part of the connector to the coil:
As a frame for the future reel, I used a plastic bucket that I bought at a hardware store. The diameter of the bucket should be approximately 200 mm. Part of the handle and bottom should be cut off from the bucket so that a plastic rim remains, onto which 50 turns of PELSHO wire with a diameter of 0.27 millimeters should be wound. The connector should be attached to the part of the remaining handle. We insulate the resulting coil using electrical tape in one layer. Then we need to shield this coil from interference. To do this, we need aluminum foil in the form of a strip, which we will wrap on top so that the ends of the resulting screen do not close and the distance between them is approximately 20 millimeters. The resulting screen should be connected to a common wire. I also wrapped it with electrical tape on top. Of course, you can soak it all with epoxy glue, but I left it that way.
After testing a large coil, I realized that I needed to make a small one, the so-called sniper, to make it easier to detect small objects.
The finished coils look like this:
Setting up a finished metal detector
Before you start setting up your metal detector, you need to make sure that there are no metal objects near the search coil. The setup consists of selecting the capacitance of capacitor C2 in order to obtain the maximum level of beats that we hear in headphones, since there are many harmonics in the signal (we need to highlight the strongest one). In this case, the slider of the variable resistor R2 should be as close to the middle as possible:
I made the rod from two parts, the tubes were selected in such a way that they fit into each other very tightly, so I didn’t have to come up with a special fastening for these tubes. An armrest and handle were also made to make it easier to wire above the ground. As practice has shown, this is very convenient: the hand does not get tired at all. When disassembled, the metal detector turned out to be very compact and literally fits into a bag:
The appearance of the finished device looks like this:
In conclusion, I would like to say that this metal detector is not suitable for people who are going to work in the old way. Since it doesn't discriminate against metals, you'll have to dig for everything. You will most likely be very disappointed. But for those who like to collect scrap metal, this device will be of help. And just as entertainment for children.
I can say without a doubt that this is the simplest metal detector I have ever seen. It is based on just one TDA0161 chip. You won't need to program anything - just assemble it and that's it. Another huge difference is that it does not make any sounds during operation, unlike a metal detector based on the NE555 chip, which initially beeps unpleasantly and you have to guess the metal found by its tone.
In this circuit, the buzzer starts beeping only when it detects metal. The TDA0161 chip is a specialized industrial version for induction sensors. And metal detectors for production are mainly built on it, giving a signal when metal approaches the induction sensor.
You can purchase such a microcircuit at -
It is not expensive and is quite accessible to everyone.
Here is a diagram of a simple metal detector
Metal detector characteristics
- Microcircuit power supply voltage: from 3.5 to 15V
- Generator frequency: 8-10 kHz
- Current consumption: 8-12 mA in alarm mode. In search state approximately 1 mA.
- Operating temperature: -55 to +100 degrees Celsius
An old cell phone battery works well for power supply.
Coil: 140-150 turns. The diameter of the coil is 5-6 cm. Can be converted to a coil of larger diameter.
The sensitivity will depend directly on the size of the search coil.
In the scheme I use both light and sound signaling. You can choose one if you want. Buzzer with internal generator.
Thanks to this simple design, you can make a pocket metal detector or a large metal detector, depending on what you need more.
After assembly, the metal detector works immediately and does not require any adjustments, except for setting the response threshold with a variable resistor. Well, this is standard procedure for a metal detector.
So, friends, collect the things you need and, as they say, they will come in handy around the house. For example, to search for electrical wiring in a wall, even nails in a log...