The design of a deep metal detector is similar to a regular one, with the exception of some technical details. It also differs in its increased sensitivity to metal objects, which makes it possible to detect them at greater depths compared to a simple metal detector. In addition, there is a selective search function, that is, the ability to find objects of a certain size without reacting to those that do not fit the parameters.
It is quite simple, despite its apparent complexity. The metal detector consists of two parts – receiving and transmitting. The main device is a high frequency transmitter generator. Two loop antennas, one of which serves as a signal transmitter, the second as a receiver. They must be located strictly at an angle of 90 degrees to each other to prevent the receiving antenna from picking up the generator signals. When a metal object is found, the magnetic field created by the generator is distorted and subsequently picked up by the receiving antenna. In this case, the mass of a metal object is used as a source of radiation, sending the energy produced to the receiving antenna.
Metal detector receiver circuit
The transmitting device includes a thyristor with a power of 0.25 to 1 W and a sound generator with a frequency of 200 Hz. When a metal object is found, the operator hears a sound with a frequency of 200 Hz, the strength of which depends on the size of the object found and the distance to it.
A detector receiver whose oscillation circuit responds to a frequency of 120 kHz, and consists of two diodes. The amplifier can be absolutely any low-frequency generator that can be found in an old radio. An amplifier with transistors in the amount of 5-6 pieces is enough. A transistor is also used as a current amplifier for a pointer instrument, allowing the level of the received signal to be measured. That is, the device contains two types of indicators - visual and acoustic. The operating frequency is adjusted so as not to interfere with the operation of the signal receiver.
Transmitter circuit
To assemble such a metal detector, you must first prepare a set of necessary parts and tools.
In the case of a pulse metal detector, approximate parts list will look like this:
Metal detector parts
From tools When performing work you will need:
The process of assembling a deep metal detector with your own hands includes the following steps:
At the first stage, it is necessary to assemble the electronic part, namely the control unit.
The step-by-step process looks like this:
The best option would be to solder everything directly, and after the setup is complete, select the necessary connectors and adapters. It is better not to twist, as this has a negative effect on the sensitivity of the device.
The second good option would be to make such a ring from twisted pair wire. You will need about 2.5 - 2.7 m of wire.
To achieve maximum sensitivity, do the following:
Upon completion of the main work, the control unit, coil and other parts are fixed in place on the rod. The metal detector can be turned on and checked.
Assembly of this type of metal detectors is not too difficult, provided all rules and instructions are strictly followed.
BEST METAL DETECTOR
Why was Volksturm named the best metal detector? The main thing is that the scheme is really simple and really working. Of the many metal detector circuits that I have personally made, this is the one where everything is simple, thorough and reliable! Moreover, despite its simplicity, the metal detector has a good discrimination scheme - determining whether iron or non-ferrous metal is in the ground. Assembling the metal detector consists of error-free soldering of the board and setting the coils to resonance and to zero at the output of the input stage on the LF353. There is nothing super complicated here, all you need is desire and brains. Let's look at the constructive metal detector design and a new improved Volksturm diagram with description.
Since questions arise during the assembly process, in order to save you time and not force you to flip through hundreds of forum pages, here are the answers to the 10 most popular questions. The article is in the process of being written, so some points will be added later.
1. The operating principle and target detection of this metal detector?
2. How to check if the metal detector board is working?
3. Which resonance should I choose?
4. Which capacitors are better?
5. How to adjust resonance?
6. How to reset the coils to zero?
7. Which wire is better for coils?
8. What parts can be replaced and with what?
9. What determines the depth of target search?
10. Volksturm metal detector power supply?
How the Volksturm metal detector works
I will try to briefly describe the principle of operation: transmission, reception and induction balance. In the search sensor of the metal detector, 2 coils are installed - transmitting and receiving. The presence of metal changes the inductive coupling between them (including the phase), which affects the received signal, which is then processed by the display unit. Between the first and second microcircuits there is a switch controlled by pulses of a generator phase-shifted relative to the transmitting channel (i.e. when the transmitter is working, the receiver is turned off and vice versa, if the receiver is turned on, the transmitter is resting, and the receiver calmly catches the reflected signal in this pause). So, you turned on the metal detector and it beeps. Great, if it beeps, it means many nodes are working. Let's figure out why exactly it beeps. The generator on the u6B constantly generates a tone signal. Next, it goes to an amplifier with two transistors, but the amplifier will not open (it will not let a tone pass) until the voltage at the output u2B (7th pin) allows it to do so. This voltage is set by changing the mode using this same thrash resistor. They need to set the voltage so that the amplifier almost opens and passes the signal from the generator. And the input couple of millivolts from the metal detector coil, having passed through the amplification stages, will exceed this threshold and it will finally open and the speaker will beep. Now let's trace the passage of the signal, or rather the response signal. At the first stage (1-у1а) there will be a couple of millivolts, up to 50. At the second stage (7-у1B) this deviation will increase, at the third (1-у2А) there will already be a couple of volts. But there is no response everywhere at the outputs.
How to check if the metal detector board is working
In general, the amplifier and switch (CD 4066) are checked with a finger at the RX input contact at maximum sensor resistance and maximum background on the speaker. If there is a change in the background when you press your finger for a second, then the key and opamps work, then we connect the RX coils with the circuit capacitor in parallel, the capacitor on the TX coil in series, put one coil on top of the other and begin to reduce to 0 according to the minimum reading of the alternating current on the first leg of the amplifier U1A. Next, we take something large and iron and check whether there is a reaction to metal in the dynamics or not. Let's check the voltage at y2B (7th pin), it should change with a thrash regulator + a couple of volts. If not, the problem is in this op-amp stage. To start checking the board, turn off the coils and turn on the power.
1. There should be a sound when the sense regulator is set to maximum resistance, touch the RX with your finger - if there is a reaction, all op-amps work, if not, check with your finger starting from u2 and change (inspect the wiring) of the non-working op-amp.
2. The operation of the generator is checked by the frequency meter program. Solder the headphone plug to pin 12 of the CD4013 (561TM2), carefully removing p23 (so as not to burn the sound card). Use In-lane on the sound card. We look at the generation frequency and its stability at 8192 Hz. If it is strongly shifted, then it is necessary to unsolder the capacitor c9, if even after it is not clearly identified and/or there are many frequency bursts nearby, we replace the quartz.
3. Checked the amplifiers and generator. If everything is in order, but still does not work, change the key (CD 4066).
Which coil resonance to choose?
When connecting the coil into series resonance, the current in the coil and the overall consumption of the circuit increases. The target detection distance increases, but this is only on the table. On real ground, the ground will be felt the more strongly, the greater the pump current in the coil. It is better to turn on parallel resonance, and increase the sense of input stages. And the batteries will last much longer. Despite the fact that sequential resonance is used in all branded expensive metal detectors, in Sturm it is parallel that is needed. In imported, expensive devices, there is a good detuning circuitry from the ground, so in these devices it is possible to allow sequential.
Which capacitors are best installed in the circuit? metal detector
The type of capacitor connected to the coil has nothing to do with it, but if you experimentally changed two and saw that with one of them the resonance is better, then simply one of the supposedly 0.1 μF actually has 0.098 μF, and the other 0.11. This is the difference between them in terms of resonance. I used Soviet K73-17 and green imported pillows.
How to adjust coil resonance metal detector
The coil, as the best option, is made from plaster floats, glued with epoxy resin from the ends to the size you need. Moreover, its central part contains a piece of the handle of this very grater, which is processed down to one wide ear. On the bar, on the contrary, there is a fork with two mounting ears. This solution allows us to solve the problem of coil deformation when tightening the plastic bolt. The grooves for the windings are made with a regular burner, then zero is set and filled. From the cold end of the TX, leave 50 cm of wire, which should not be filled initially, but make a small coil from it (3 cm in diameter) and place it inside the RX, moving and deforming it within small limits, you can achieve an exact zero, but do this It’s better outside, placing the coil near the ground (as when searching) with GEB turned off, if any, then finally fill it with resin. Then the detuning from the ground works more or less tolerably (with the exception of highly mineralized soil). Such a reel turns out to be light, durable, little subject to thermal deformation, and when processed and painted it is very attractive. And one more observation: if the metal detector is assembled with ground detuning (GEB) and with the resistor slider located centrally, set zero with a very small washer, the GEB adjustment range is + - 80-100 mV. If you set zero with a large object - a coin of 10-50 kopecks. the adjustment range increases to +- 500-600 mV. Do not chase the voltage when setting up the resonance - with a 12V supply, I have about 40V with a series resonance. To make discrimination appear, we connect the capacitors in the coils in parallel (series connection is only necessary at the stage of selecting capacitors for resonance) - for ferrous metals there will be a drawn-out sound, for non-ferrous metals - a short one.
Or even simpler. We connect the coils one by one to the transmitting TX output. We tune one into resonance, and after tuning it, the other. Step by step: Connected, poked a multimeter in parallel with the coil with a multimeter at the alternating volts limit, also soldered a 0.07-0.08 uF capacitor parallel to the coil, look at the readings. Let's say 4 V - very weak, not in resonance with the frequency. We poked a second small capacitor in parallel with the first capacitor - 0.01 microfarads (0.07+0.01=0.08). Let's look - the voltmeter has already shown 7 V. Great, let's increase the capacitance further, connect it to 0.02 µF - look at the voltmeter, and there is 20 V. Great, let's move on - we'll add a couple thousand more peak capacitance. Yeah. It has already started to fall, let's roll back. And so achieve maximum voltmeter readings on the metal detector coil. Then do the same with the other (receiving) coil. Adjust to maximum and connect back to the receiving socket.
How to zero metal detector coils
To adjust the zero, we connect the tester to the first leg of the LF353 and gradually begin to compress and stretch the coil. After filling with epoxy, the zero will definitely run away. Therefore, it is necessary not to fill the entire coil, but to leave places for adjustment, and after drying, bring it to zero and fill it completely. Take a piece of twine and tie half of the spool with one turn to the middle (to the central part, the junction of the two spools), insert a piece of stick into the loop of the twine and then twist it (pull the twine) - the spool will shrink, catching the zero, soak the twine in glue, after almost complete drying adjust the zero again by turning the stick a little more and fill the twine completely. Or simpler: The transmitting one is fixed in plastic, and the receiving one is placed 1 cm over the first one, like wedding rings. There will be an 8 kHz squeak at the first pin of U1A - you can monitor it with an AC voltmeter, but it’s better to just use high-impedance headphones. So, the receiving coil of the metal detector must be moved or shifted from the transmitting coil until the squeak at the output of the op-amp subsides to a minimum (or the voltmeter readings drop to several millivolts). That's it, the coil is closed, we fix it.
Which wire is better for search coils?
The wire for winding the coils does not matter. Anything from 0.3 to 0.8 will do; you still have to slightly select the capacitance to tune the circuits to resonance and at a frequency of 8.192 kHz. Of course, a thinner wire is quite suitable, it’s just that the thicker it is, the better the quality factor and, as a result, the instinct. But if you wind it 1 mm, it will be quite heavy to carry. On a sheet of paper, draw a rectangle 15 by 23 cm. From the upper and lower left corners, set aside 2.5 cm and connect them with a line. We do the same with the upper right and lower corners, but set aside 3 cm each. We put a dot in the middle of the lower part and a point on the left and right at a distance of 1 cm. We take plywood, apply this sketch and drive nails into all the points indicated. We take a PEV 0.3 wire and wind 80 turns of wire. But honestly, it doesn’t matter how many turns. Anyway, we will set the frequency of 8 kHz to resonance with a capacitor. As much as they reeled in, that's how much they reeled in. I wound 80 turns and a capacitor of 0.1 microfarads, if you wind it, say 50, you will have to put a capacitance of about 0.13 microfarads. Next, without removing it from the template, we wrap the coil with a thick thread - like how wire harnesses are wrapped. Afterwards we coat the coil with varnish. When dry, remove the spool from the template. Then the coil is wrapped with insulation - fum tape or electrical tape. Next - winding the receiving coil with foil, you can take a tape from electrolytic capacitors. The TX coil does not need to be shielded. Remember to leave a 10mm GAP in the screen, down the middle of the reel. Next comes winding the foil with tinned wire. This wire, together with the initial contact of the coil, will be our ground. And finally, wrap the coil with electrical tape. The inductance of the coils is about 3.5mH. The capacitance turns out to be about 0.1 microfarads. As for filling the coil with epoxy, I didn’t fill it at all. I just wrapped it tightly with electrical tape. And nothing, I spent two seasons with this metal detector without changing the settings. Pay attention to the moisture insulation of the circuit and search coils, because you will have to mow on wet grass. Everything must be sealed - otherwise moisture will get in and the setting will float. Sensitivity will worsen.
What parts can be replaced and with what?
Transistors:
BC546 - 3 pcs or KT315.
BC556 - 1 piece or KT361
Operators:
LF353 - 1 piece or exchange for the more common TL072.
LM358N - 2pcs
Digital chips:
CD4011 - 1 piece
CD4066 - 1 piece
CD4013 - 1 piece
Resistors are constant, power 0.125-0.25 W:
5.6K - 1 piece
430K - 1 piece
22K - 3pcs
10K - 1 piece
390K - 1 piece
1K - 2pcs
1.5K - 1 piece
100K - 8pcs
220K - 1 piece
130K - 2 pieces
56K - 1 piece
8.2K - 1 piece
Variable resistors:
100K - 1 piece
330K - 1 piece
Non-polar capacitors:
1nF - 1 piece
22nF - 3pcs (22000pF = 22nF = 0.022uF)
220nF - 1 piece
1uF - 2pcs
47nF - 1 piece
10nF - 1 piece
Electrolytic capacitors:
220uF at 16V - 2 pcs
The speaker is miniature.
Quartz resonator at 32768 Hz.
Two ultra-bright LEDs of different colors.
If you cannot get imported microcircuits, here are domestic analogues: CD 4066 - K561KT3, CD4013 - 561TM2, CD4011 - 561LA7, LM358N - KR1040UD1. The LF353 microcircuit has no direct analogue, but feel free to install LM358N or better TL072, TL062. It is not at all necessary to install an operational amplifier - LF353, I simply increased the gain to U1A by replacing the resistor in the negative feedback circuit of 390 kOhm with 1 mOhm - the sensitivity increased significantly by 50 percent, although after this replacement the zero went away, I had to glue it to the coil in a certain place tape a piece of aluminum plate. Soviet three kopecks can be sensed through the air at a distance of 25 centimeters, and this is with a 6-volt power supply, the current consumption without indication is 10 mA. And don’t forget about the sockets - the convenience and ease of setup will increase significantly. Transistors KT814, Kt815 - in the transmitting part of the metal detector, KT315 in the ULF. It is advisable to select transistors 816 and 817 with the same gain. Replaceable with any corresponding structure and power. The metal detector generator has a special clock quartz at a frequency of 32768 Hz. This is the standard for absolutely all quartz resonators found in any electronic and electromechanical watches. Including wrist and cheap Chinese wall/table ones. Archives with a printed circuit board for the variant and for (variant with manual detuning from the ground).
What determines the depth of target search?
The larger the diameter of the metal detector coil, the deeper the instinct. In general, the depth of target detection by a given coil depends primarily on the size of the target itself. But as the diameter of the coil increases, there is a decrease in the accuracy of object detection and sometimes even the loss of small targets. For objects the size of a coin, this effect is observed when the coil size increases above 40 cm. Overall: a large search coil has a greater detection depth and greater capture, but detects the target less accurately than a small one. The large coil is ideal for searching for deep and large targets such as treasure and large objects.
According to their shape, coils are divided into round and elliptical (rectangular). An elliptical metal detector coil has better selectivity compared to a round one, because the width of its magnetic field is smaller and fewer foreign objects fall into its field of action. But the round one has a greater detection depth and better sensitivity to the target. Especially on weakly mineralized soils. The round coil is most often used when searching with a metal detector.
Coils with a diameter of less than 15 cm are called small, coils with a diameter of 15-30 cm are called medium, and coils over 30 cm are called large. A large coil generates a larger electromagnetic field, so it has a greater detection depth than a small one. Large coils generate a large electromagnetic field and, accordingly, have greater detection depth and search coverage. Such coils are used to view large areas, but when using them, a problem may arise in heavily littered areas because several targets may be caught in the field of action of large coils at once and the metal detector will react to a larger target.
The electromagnetic field of a small search coil is also small, so with such a coil it is best to search in areas heavily littered with all sorts of small metal objects. The small coil is ideal for detecting small objects, but has a small coverage area and a relatively shallow detection depth.
For universal searching, medium coils are well suited. This search coil size combines sufficient search depth and sensitivity to targets of different sizes. I made each coil with a diameter of approximately 16 cm and placed both of these coils in a round stand from under an old 15" monitor. In this version, the search depth of this metal detector will be as follows: aluminum plate 50x70 mm - 60 cm, nut M5-5 cm, coin - 30 cm, bucket - about a meter. These values were obtained in the air, in the ground it will be 30% less.
Metal detector power supply
Separately, the metal detector circuit draws 15-20 mA, with the coil connected + 30-40 mA, totaling up to 60 mA. Of course, depending on the type of speaker and LEDs used, this value may vary. The simplest case is that the power was taken from 3 (or even two) lithium-ion batteries connected in series from a 3.7V mobile phone and when charging discharged batteries, when we connect any 12-13V power supply, the charging current starts from 0.8A and drops to 50mA per an hour and then you don’t need to add anything at all, although a limiting resistor certainly wouldn’t hurt. In general, the simplest option is a 9V crown. But keep in mind that the metal detector will eat it in 2 hours. But for customization, this power option is just right. Under any circumstances, the crown will not produce a large current that could burn something on the board.
Homemade metal detector
And now a description of the process of assembling a metal detector from one of the visitors. Since the only instrument I have is a multimeter, I downloaded O.L. Zapisnykh’s virtual laboratory from the Internet. I assembled an adapter, a simple generator and ran the oscilloscope at idle. It seems to show some kind of picture. Then I started looking for radio components. Since signets are mostly laid out in the “lay” format, I downloaded “Sprint-Layout50”. I found out what laser-iron technology is for manufacturing printed circuit boards and how to etch them. Etched the board. By this time, all the microcircuits had been found. Whatever I couldn’t find in my shed, I had to buy. I started soldering jumpers, resistors, microcircuit sockets, and quartz from a Chinese alarm clock onto the board. Periodically checking the resistance on the power buses to ensure there are no snot. I decided to start by assembling the digital part of the device, as it would be the easiest. That is, a generator, a divider and a commutator. Collected. I installed a generator chip (K561LA7) and a divider (K561TM2). Used ear chips, torn out from some circuit boards found in a shed. I applied 12V power while monitoring the current consumption using an ammeter, and the 561TM2 became warm. Replaced 561TM2, applied power - zero emotions. I measure the voltage on the generator legs - 12V on legs 1 and 2. I am changing 561LA7. I turn it on - at the output of the divider, on the 13th leg there is generation (I observe it on a virtual oscilloscope)! The picture is really not that great, but in the absence of a normal oscilloscope it will do. But there is nothing on legs 1, 2 and 12. This means the generator is working, you need to change TM2. I installed a third divider chip - there is beauty on all outputs! I came to the conclusion that you need to desolder the microcircuits as carefully as possible! This completes the first step of construction.
Now we set up the metal detector board. The "SENS" sensitivity regulator did not work, I had to throw out the capacitor C3 after that the sensitivity adjustment worked as it should. I didn’t like the sound that appeared in the extreme left position of the “THRESH” regulator - threshold, I got rid of it by replacing resistor R9 with a chain of series-connected 5.6 kOhm resistor + 47.0 μF capacitor (negative terminal of the capacitor on the transistor side). While there is no LF353 microcircuit, I installed the LM358 instead; with it, Soviet three kopecks can be sensed in the air at a distance of 15 centimeters.
I turned on the search coil for transmission as a series oscillatory circuit, and for reception as a parallel oscillatory circuit. I set up the transmitting coil first, connected the assembled sensor structure to the metal detector, an oscilloscope parallel to the coil, and selected capacitors based on the maximum amplitude. After this, I connected the oscilloscope to the receiving coil and selected the capacitors for RX based on the maximum amplitude. Setting the circuits to resonance takes several minutes if you have an oscilloscope. My TX and RX windings each contain 100 turns of wire with a diameter of 0.4. We start mixing on the table, without the body. Just to have two hoops with wires. And to make sure of the functionality and possibility of mixing in general, we will separate the coils from each other by half a meter. Then it will be zero for sure. Then, having overlapped the coils by about 1 cm (like wedding rings), move and push apart. The zero point can be quite accurate and it is not easy to catch it right away. But it is there.
When I raised the gain in the RX path of the MD, it began to work unstably at maximum sensitivity, this was manifested in the fact that after passing over the target and detecting it, a signal was issued, but it continued even after there was no target in front of the search coil, this manifested itself in the form of intermittent and fluctuating sound signals. Using an oscilloscope, the reason for this was discovered: when the speaker is operating and the supply voltage drops slightly, “zero” goes away and the MD circuit goes into a self-oscillating mode, which can only be exited by coarsening the sound signal threshold. This didn’t suit me, so I installed a KR142EN5A + super bright white LED for power supply to raise the voltage at the output of the integrated stabilizer; I didn’t have a stabilizer for a higher voltage. This LED can even be used to illuminate the search coil. I connected the speaker to the stabilizer, after that the MD immediately became very obedient, everything started working as it should. I think the Volksturm is truly the best homemade metal detector!
Recently, this modification scheme was proposed, which would turn the Volksturm S into the Volksturm SS + GEB. Now the device will have a good discriminator as well as metal selectivity and ground detuning; the device is soldered on a separate board and connected instead of capacitors C5 and C4. The revision scheme is also in the archive. Special thanks for the information on assembling and setting up the metal detector to everyone who took part in the discussion and modernization of the circuit; Elektrodych, fez, xxx, slavake, ew2bw, redkii and other fellow radio amateurs especially helped in preparing the material.
With the onset of spring, more and more often you can see people with metal detectors on the banks of rivers. Most of them are engaged in “gold mining” purely out of curiosity and passion. But a certain percentage actually earn a lot of money from searching 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 instrument is expensive, and if you have a basic knowledge of radio mechanics, you have probably thought more than once about how to make a metal detector with your own hands. The editors of the site will come to your aid and tell you today how to assemble the device yourself using diagrams.
Read in the article:
This model costs more than 32,000 rubles, and, of course, non-professionals will not be able to afford such a device. Therefore, we suggest studying the design 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 operating principle 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 second is receiving.
The metal detector works like this: the magnetic field lines of the primary field (A) of red color pass through the 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 audible signal to the operator. Based on the principle of operation of emitters, electronic devices of this type can be divided into:
The cheapest devices belong to the first type.
An induction metal detector has one coil that sends and receives a signal simultaneously. But devices with pulse 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, perhaps hundreds of thousands of times per second.
The operating principle of a metal detector varies depending on the type of device. Let's consider the main ones:
Depth detectors operate on two coils, one is parallel to the ground surface, the other is perpendicular.
The simplest devices that you can assemble yourself include devices that operate on the principle of reception and transmission. There are schemes that even a novice radio amateur can do; for this you just need to select a certain set of parts.
There are many video instructions on the Internet with detailed explanations of how to make a simple metal detector with your own hands. Here are the most popular ones:
However, despite the fact that some entertainers are trying to offer systems for assembling a metal detector from a phone, such designs will not pass the battle test. It’s easier to buy a children’s metal detector toy, it will be more useful.
And now more about how to make a simple metal detector with your own hands using the example of the “Pirate” design.
Homemade products based on the “Pirate” series metal detector are among the most popular among radio amateurs. Thanks to the good performance of the device, it can “detect” an object at a depth of 200 mm (for small items) and 1500 mm (large items).
The Pirate metal detector is a pulse type device. To make the device you will need to purchase:
The classic circuit of the “Pirate” series metal detector is built using 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 is sent to the comparator, and then to the speaker, which notifies the operator of the presence of the desired objects.
The board can be placed in a simple junction box, which can be purchased at an electrical store. If such a tool is not enough for you, you can try to make a more advanced device; a diagram for making a gold-oriented metal detector will help you.
This device uses Soviet-style transistors KT-361 and KT-315 to generate signals (you can use similar radio components).
The pulse generator is assembled on the NE555 chip. By selecting C1 and 2 and R2 and 3, the frequency is adjusted. The pulses obtained as a result of scanning are transmitted to transistor T1, and it transmits the signal to transistor T2. The audio frequency is amplified using the BC547 transistor to the collector, and headphones are connected.
To place radio components, a printed circuit is used, which can be easily made independently. To do this, we use a piece of sheet getinax covered with copper electrical foil. We transfer the connecting parts onto it, mark the fastening points, and drill holes. We cover the tracks with a protective varnish, and after drying, we lower the future board into ferric chloride for etching. This is necessary to remove unprotected areas of copper foil.
For the base you will need a ring with a diameter of about 200 mm (ordinary wooden hoops can be used as the base), on which 0.5 mm wire is wound. To increase the depth of metal detection, the coil frame should be in the range of 260−270 mm, and the number of turns should be 21−22 vol. If you don't have anything suitable on hand, you can wind a reel on a wooden base.
| Illustration | Description of action |
 | For winding, prepare a board with guides. The distance between them is equal to the diameter of the base on which you will attach the reel. |
 | Wind the wire around the perimeter of the fastenings in 20-30 turns. Secure the winding with electrical tape in several places. |
 | Remove the winding from the base and give it a rounded shape; if necessary, additionally fasten the winding in several more places. |
 | Connect the circuit to the device and test its operation. |
We will need: 1 twisted pair 5 cat 24 AVG (2.5 mm), knife, soldering iron, solder and multitester.
| Illustration | Description of action |
 | Twist the wire into two skeins. Leave 10 cm on each side. |
 | Strip the winding and free the wires for connection. |
 | We connect the wires according to the diagram. |
 | For better fastening, solder them with a soldering iron. |
 | Test the coil in the same manner as the copper wire device. The winding terminals must be soldered to a stranded wire with a diameter in the range of 0.5-0.7 mm. |
Once the main elements of the metal detector are ready, we proceed to assembly. We attach all the components to the metal detector rod: the body with the coil, the receiving and 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. Fine tuning is performed using variable resistor R13. Normal operation of the detector should be ensured with the regulator in the middle position. If you have an oscilloscope, then use it to measure the frequency at the gate of transistor T2, which should be 120−150 Hz, and the pulse duration should be 130−150 μs.
The principle of assembling an underwater metal detector is no different from a conventional one, with the only difference being that you will have to work hard to create an impenetrable shell using sealant, as well as to place special light indicators that can report a find from under water. An example of how this will work is in the video:
The Terminator 3 metal detector has occupied an honorable place among homemade metal detectors for many years. The two-tone device operates on the principle of induction balance.
Its main features are: low power consumption, metal discrimination, non-ferrous metals 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 folk craftsman Viktor Goncharov.
Metal discrimination is the ability of the device to distinguish between the detected material and classify it. Discrimination is based on different electrical conductivities of metals. The simplest methods for determining the types of metals were implemented in old instruments and entry-level devices and had two modes - “all metals” and “non-ferrous”. The discrimination function allows the operator to respond to a phase shift of a certain magnitude, compared to a configured (reference) level. In this case, the device cannot distinguish between non-ferrous metals.
Learn how to make a homemade professional metal detector using improvised materials in this video:
Metal detectors of this type can detect objects at great depths. A good metal detector, made by yourself, looks to a depth of 6 meters. However, in this case the size of the find must be substantial. These detectors work best for detecting old shells or large enough debris.
There are two types of deep metal detectors: frame and transceiver on a rod. The first type of device is capable of covering a large area of land for scanning, however, in this case, the efficiency and focus of the search is reduced. The second version of the detector is a point detector; it works directed inward over a small diameter. You need to work with it slowly and carefully. If your goal is to build such a metal detector, the following video can tell you how to do it.
If you have experience in assembling such a device and using it, tell others about it!
Due to its electric or magnetic waves, a metal detector, or as it is also called a metal detector, is able to distinguish and respond to metal objects hidden in another environment. This device is an indispensable assistant for inspection services, environmentalists, builders, “gold miners” and many other specialties. The average price of a metal detector in the Russian Federation varies from 15-60 thousand rubles. This article is intended for those who do not want to overpay, want to understand the device themselves, and make a metal detector with their own hands.
The operating principle of a metal detector is complex only in words. Its essence lies in the formation of magnetic fields using electrical voltage, when these same waves encounter metal objects on their way, the device emits a signal, notifying about the find. For beginners who have not yet encountered such “inventions,” this seems quite difficult, but if you carefully follow the instructions, in reality everything will be much easier. And with a little understanding, you can easily create a device for finding an ancient coin at a depth of 30 cm underground.
In order to create a magnetic field, it is necessary for the current to pass through the riot ( bundle, winding) copper wire with nylon insulation. It is wound on a plastic spool several times. Then wrap with polyester, durable packing tape. This is necessary so that the wire cannot unwind back. If inside the reel ( special reel) place pure iron, the magnetic field will increase significantly, this method is usually used for security metal detectors.
The operation of the system depends entirely on the electronic circuit; this is the brain of the device. The remaining piece of copper wire is soldered to the printed circuit board, the other output of the board is connected by electrical wiring to sensors: LEDs, vibrators, speakers. In the event of a collision of magnetic waves with metal, an electrical signal will flow from the coil to the indicators through the board. This is perhaps the most difficult part of creating a device with your own hands. Then the device is calibrated, adjusted, and placed in a plastic protective case.
Based on their properties, metal detectors are divided into 3 main groups: deep, underwater, and ground. From the name it is immediately clear what their features are. Although they often create hybrids, for example, in ground ones - a waterproof reel with a housing. Naturally, these will cost an order of magnitude higher. To make a metal detector yourself, you need to clearly understand for what purposes it will be used; based on this, there are general parameters of the device:
On average, the search depth of a metal detector ranges from 1 to 100 centimeters. Different models have different accuracy and depth of action. Basically, the visibility range depends on the size of the coil, the larger it is, the deeper you can look. And the very first mistake of most beginners is, without knowing why, without knowing why, they choose a metal detector with the greatest depth of investigation. On average, ancient coins are buried 30-35 centimeters, and lost precious jewelry is even closer to the surface. In addition, the greater the depth, the more errors and errors. You can dig 10 holes 1 meter deep, and in the same time you can find something really valuable almost on the surface, without bothering at all.
Like any device, a metal detector has an interconnection of its components. Using the device at full power, you increase the energy consumption of the battery. If we consider the metal detector as a whole, we can conclude that all its component dimensions and functionality depend on the frequency of the generator. This is perhaps the most important evaluation criterion by which they are classified:
There are a large number of diagrams, videos, forums, and tips on assembling a metal detector on the Internet. And among the many reviews, there are many negative ones about the device of its own production. Many write that it didn’t work out for them, it doesn’t work, that it’s better to buy than to spend a lot of time... It’s very simple to answer such comments: if you set a goal and approach the issue seriously, then production with your own hands will turn out to be much better than factory metal detectors. If you want to do something well, do it yourself.
For a person who at least at school level knows and is interested in physics and electronics, such a task will not be difficult. And the matter will remain only with the selection of quality materials. But beginners should not retreat, step by step, following the instructions, adding a little persistence, everything will certainly work out.
The most difficult stage in detector assembly is the manufacture of the printed circuit board. Since this is the brain of the entire structure, and without it the device simply will not work. Let's start with the simplest manufacturing technology - Laser ironing.
More details about this method can be found in our article:
At this stage, it is necessary to equip the board with all the necessary radio components. Don’t be afraid of complex names or unknown combinations of numbers and letters. All details are signed. You just need to find the right ones, buy them, and install them in your place.
Here is an example of a fairly simple but effective scheme - PIRATE
So, let's begin:
As already written earlier, when making a homemade coil, you need to wind approximately 25-30 turns of PEV wire if its diameter is 0.5 millimeters. But it is best, when testing the device in action, to select and change the number of turns to achieve the desired result.
To recognize the device's discovery, you can use any speaker with a resistance of zero ohms. As a power supply, you can use a battery or simple batteries with a total voltage of more than 13 volts. For greater stability and electrical balance of the circuit, a stabilizer is mounted at the output. For a pirate circuit, the ideal voltage type would be L7812.
Once we are convinced that the metal detector is working, we turn on our imagination and create a frame that will be primarily convenient for the operator. There are some practical tips for creating a case:
Butterfly scheme
Koschey scheme
Quasar scheme
Chance Scheme
Anyone can assemble such a device, even those who are completely far from electronics, you just need to solder all the parts as in the diagram. The metal detector consists of two microcircuits. They do not require any firmware or programming.
Power supply is 12 volts, you can use AA batteries, but it’s better to use a 12V battery (small)
The coil is wound on a 190mm mandrel and contains 25 turns of PEV 0.5 wire
Characteristics:
- Current consumption 30-40 mA
- Reacts to all metals, no discrimination
- Sensitivity 25 mm coin - 20 cm
- Large metal objects - 150 cm
- All parts are inexpensive and easily accessible.
List of required parts:
1) Soldering iron
2) Textolite
3) Wires
4) Drill 1mm
Here is a list of required parts
The circuit uses 2 microcircuits (NE555 and K157UD2). They are quite common. K157UD2 - can be picked out from old equipment, which I did with success
For K157UD2 it is better to install an adapter socket.
We wind the coil on anything of a suitable diameter and wrap it tightly with electrical tape so that the turns are tightly next to each other.
Now we connect everything and test the circuit to see if it works.
After applying power, you need to wait 15-20 seconds until the circuit warms up. We place the coil away from any metal, it is best to hang it in the air. Then we begin to twist the 100K variable resistor until clicks appear. As soon as the clicks appear, turn it in the opposite direction; as soon as the clicks disappear, that’s enough. After this, we also adjust the 10K resistor.
Regarding the K157UD2 microcircuit. In addition to the one I picked out, I asked one more from a neighbor and bought two at the radio market. I inserted the purchased microcircuits, turned on the device, but it refused to work. I racked my brains for a long time until I simply installed another microcircuit (the one I removed). And everything started working right away. So this is why you need an adapter socket, so that you can select a live microcircuit and not have to worry about desoldering and soldering.
Purchased chips
