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 field performance with reference values. 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 help not only to 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.
Main settings
- 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, Cell 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.
Do-it-yourself metal detector - as the name suggests, such devices are made independently and are designed to search for metal objects and are used for a fairly narrow purpose. However, the methods for their implementation are quite diverse and constitute a whole direction in radio electronics.
Metal detector N. Martynyuk
The metal detector according to N. Martynyuk’s scheme (Fig. 1) is made on the basis of a miniature radio transmitter, the radiation of which is modulated by an audio signal [Рл 8/97-30]. The modulator is a low-frequency generator made according to the well-known symmetrical multivibrator circuit.
The signal from the collector of one of the multivibrator transistors is fed to the base of the high-frequency generator transistor (VT3). The operating frequency of the generator is located in the frequency range of the VHF-FM broadcast range (64... 108 MHz). A piece of television cable in the form of a coil with a diameter of 15...25 cm was used as the inductor of the oscillating circuit.
Rice. 1. Schematic diagram of N. Martynyuk’s metal detector.
If a metal object is brought closer to the inductor of the oscillating circuit, the generation frequency will noticeably change. The closer the object is brought to the coil, the greater the frequency shift will be. To record frequency changes, a conventional FM radio receiver is used, tuned to the frequency of the HF generator.
The receiver's automatic frequency control system should be disabled. If there is no metal object present, a loud beep is heard from the receiver's speaker.
If you bring a piece of metal to the inductor, the generation frequency will change and the volume of the signal will decrease. The disadvantage of the device is its reaction not only to metal, but also to any other conductive objects.
Metal detector based on a low-frequency LC generator
In Fig. 2 - 4 shows a circuit of a metal detector with a different operating principle, based on the use of a low-frequency LC oscillator and a bridge frequency change indicator. The search coil of the metal detector is made in accordance with Fig. 2, 3 (with correction of the number of turns).
Rice. 2. Metal detector search coil.
Rice. 3. Metal detector search coil.
The output signal from the generator is fed to a bridge measuring circuit. A high-resistance telephone capsule TON-1 or TON-2 is used as a bridge null indicator, which can be replaced with a pointer or other external alternating current measuring device. The generator operates at frequency f1, for example, 800 Hz.
Before starting work, the bridge is balanced to zero by adjusting the capacitor C* of the oscillating circuit of the search coil. The frequency f2=f1 at which the bridge will be balanced can be determined from the expression:
Initially, there is no sound in the telephone capsule. When a metal object is introduced into the field of the search coil L1, the generation frequency f1 will change, the bridge will become unbalanced, and a sound signal will be heard in the telephone capsule.
Rice. 4. Diagram of a metal detector with an operating principle based on the use of a low-frequency LC generator.
Metal detector bridge circuit
The bridge circuit of a metal detector using a search coil that changes its inductance when metal objects approach is shown in Fig. 5. An audio frequency signal from a low-frequency generator is supplied to the bridge. Using potentiometer R1, the bridge is balanced for the absence of an audio signal in the telephone capsule.
Rice. 5. Bridge circuit of a metal detector.
To increase the sensitivity of the circuit and increase the amplitude of the bridge unbalance signal, a low-frequency amplifier can be connected to its diagonal. The inductance of the L2 coil should be comparable to the inductance of the L1 search coil.
Metal detector based on a receiver with the CB range
A metal detector operating in conjunction with a mid-wave superheterodyne radio broadcast receiver can be assembled according to the circuit shown in Fig. 6 [R 10/69-48]. The design shown in Fig. 1 can be used as a search coil. 2.
Rice. 6. A metal detector operating in conjunction with a superheterodyne radio receiver in the CB range.
The device is a conventional high-frequency generator operating at 465 kHz (the intermediate frequency of any AM broadcast receiver). The circuits presented in Chapter 12 can be used as a generator.
In the initial state, the frequency of the HF generator, mixing in a nearby radio receiver with the intermediate frequency of the signal received by the receiver, leads to the formation of a difference frequency signal in the audio range. When the generation frequency changes (if there is metal in the field of action of the search coil), the tone of the sound signal changes in proportion to the amount (volume) of the metal object, its distance, and the nature of the metal (some metals increase the generation frequency, others, on the contrary, lower it).
A simple metal detector with two transistors
Rice. 7. Scheme of a simple metal detector using silicon and field-effect transistors.
The diagram of a simple metal detector is shown in Fig. 7. The device uses a low-frequency LC generator, the frequency of which depends on the inductance of the search coil L1. In the presence of a metal object, the generation frequency changes, which can be heard using the BF1 telephone capsule. The sensitivity of such a scheme is low, because It is quite difficult to detect small changes in frequency by ear.
Metal detector for small quantities of magnetic material
A metal detector for small quantities of magnetic material can be made according to the diagram in Fig. 8. A universal head from a tape recorder is used as a sensor for such a device. To amplify weak signals taken from the sensor, it is necessary to use a highly sensitive low-frequency amplifier, the output signal of which is fed to the telephone capsule.
Rice. 8. Diagram of a metal detector for small quantities of magnetic material.
Metal indicator circuit
A different method of indicating the presence of metal is used in the device according to the diagram in Fig. 9. The device contains a high-frequency generator with a search coil and operates at frequency f1. To indicate the signal magnitude, a simple high-frequency millivoltmeter is used.
Rice. 9. Schematic diagram of a metal indicator.
It is made on diode VD1, transistor VT1, capacitor C1 and milliammeter (microammeter) PA1. A quartz resonator is connected between the output of the generator and the input of the high-frequency millivoltmeter. If the generation frequency f1 and the frequency of the quartz resonator f2 coincide, the needle of the device will be at zero. As soon as the generation frequency changes as a result of introducing a metal object into the field of the search coil, the needle of the device will deviate.
The operating frequencies of such metal detectors are usually in the range of 0.1...2 MHz. To initially set the generation frequency of this and other devices of similar purpose, a variable capacitor or a tuning capacitor connected in parallel with the search coil is used.
Typical metal detector with two generators
In Fig. Figure 10 shows a typical diagram of the most common metal detector. Its operating principle is based on the frequency beats of the reference and search oscillators.
Rice. 10. Diagram of a metal detector with two generators.
Rice. 11. Schematic diagram of the generator block for a metal detector.
A similar node, common to both generators, is shown in Fig. 11. The generator is made according to the well-known “three-point capacitive” circuit. In Fig. Figure 10 shows a complete diagram of the device. The design shown in Fig. 1 is used as search coil L1. 2 and 3.
The initial frequencies of the generators must be the same. The output signals from the generators through capacitors C2, SZ (Fig. 10) are fed to a mixer that selects the difference frequency. The selected audio signal is fed through the amplifier stage on transistor VT1 to the telephone capsule BF1.
Metal detector based on the principle of generation frequency interruption
The metal detector can also operate on the principle of disrupting the generation frequency. The diagram of such a device is shown in Fig. 12. If certain conditions are met (the frequency of the quartz resonator is equal to the resonant frequency of the oscillatory LC circuit with the search coil), the current in the emitter circuit of transistor VT1 is minimal.
If the resonant frequency of the LC circuit changes noticeably, the generation will fail, and the readings of the device will increase significantly. Parallel measuring device It is recommended to connect a capacitor with a capacity of 1 ... 100 nF.
Rice. 12. Circuit diagram of a metal detector that works on the principle of disrupting the generation frequency.
Metal detectors for searching for small objects
Metal detectors, designed to search for small metal objects in everyday life, can be assembled according to those shown in Fig. 13 - 15 schemes.
Such metal detectors also operate on the principle of generation failure: the generator, which includes a search coil, operates in a “critical” mode.
The operating mode of the generator is set by adjusted elements (potentiometers) so that the slightest change in its operating conditions, for example, a change in the inductance of the search coil, will lead to disruption of the oscillations. To indicate the presence/absence of generation, LED indicators of the level (presence) of alternating voltage are used.
Inductors L1 and L2 in the circuit in Fig. 13 contain, respectively, 50 and 80 turns of wire with a diameter of 0.7...0.75 mm. The coils are wound on a 600NN ferrite core with a diameter of 10 mm and a length of 100... 140 mm. The operating frequency of the generator is about 150 kHz.
Rice. 13. Circuit of a simple metal detector with three transistors.
Rice. 14. Scheme of a simple metal detector using four transistors with light indication.
Inductors L1 and L2 of another circuit (Fig. 14), made in accordance with the German patent (No. 2027408, 1974), have 120 and 45 turns, respectively, with a wire diameter of 0.3 mm [P 7/80-61 ]. A 400NN or 600NN ferrite core with a diameter of 8 mm and a length of 120 mm was used.
Household metal detector
A household metal detector (HIM) (Fig. 15), previously produced by the Radiopribor plant (Moscow), allows you to detect small metal objects at a distance of up to 45 mm. The winding data of its inductors are unknown, however, when repeating the circuit, you can rely on the data given for devices of similar purposes (Fig. 13 and 14).
Rice. 15. Scheme of a household metal detector.
Literature: Shustov M.A. Practical circuit design (Book 1), 2003
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:
Metal detector and its structure
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:
- Simple, working on the “receive-transmit” principle.
- Induction.
- Pulse.
- Generating.
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.
How does a metal detector work depending on its purpose and technical device?
The operating principle of a metal detector varies depending on the type of device. Let's consider the main ones:
- Dynamic type devices. The simplest type of device that continuously scans the field. The main feature of working with such a device is that you must be in motion all the time, otherwise the signal will disappear. Such devices are easy to use, however, they are poorly sensitive.
- Pulse type devices. They have great sensitivity. Often, such a device comes with several additional coils for adjustment to different types of soils and metals. Requires certain skills to set up. Among the devices of this class we can distinguish electronic devices operating at low frequencies - no higher than 3 kHz.
- Electronic devices, on the one hand, do not give a reaction (or give a weak one) to unwanted signals: wet sand, small pieces of metal, shot, for example, and, on the other hand, they provide good sensitivity when searching for hidden water pipes and central heating routes, as well as coins and other metal objects.
- Depth detectors designed to search for objects located at impressive depths. They can detect metal objects at a depth of up to 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 found in the ground in 3- measured form.
Depth detectors operate on two coils, one is parallel to the ground surface, the other is perpendicular.
- Stationary detectors- these are frames established at particularly important protected sites. They detect any metal objects in people's bags and pockets that pass through the circuit.
Which metal detectors are suitable for making yourself at home?
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:
- Metal detector "Pirate".
- Metal detector - butterfly.
- Emitter without microcircuits (IC).
- Series of metal detectors "Terminator".
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 metal detector “Pirate”: diagram and detailed description of the assembly
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).
Parts for assembling a metal detector
The Pirate metal detector is a pulse type device. To make the device you will need to purchase:
- Materials for making the body, rods (can be used plastic pipe), holder and so on.
- Wires and electrical tape.
- Headphones (suitable for the player).
- Transistors – 3 pieces: BC557, IRF740, BC547.
- Microcircuits: K157UD2 and NE
- Ceramic capacitor - 1 nF.
- 2 film capacitors - 100 nF.
- Electrolytic 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.
- Resistors – 7 pieces per 1; 1.6; 47; 62; 100; 120; 470 kOhm and 6 pieces for 10, 100, 150, 220, 470, 390 Ohm, 2 pieces for 2 Ohm.
- 2 diodes 1N148.
DIY metal detector circuits
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.
How to assemble a metal detector without using microcircuits
This device uses Soviet-style transistors KT-361 and KT-315 to generate signals (you can use similar radio components).
How to assemble a metal detector circuit board with your own hands
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.
How to make a metal detector coil with your own hands
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.
Copper wire spool on 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. |
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 | 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. |
Brief instructions for setting up a DIY metal detector “Pirate”
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.
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 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:
Do-it-yourself metal detector “Terminator 3”: detailed diagram and video instructions for assembly
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 metal mode, gold only mode and very good characteristics search depth, compared to semi-professional branded metal detectors. We offer you the most detailed description assembly of a similar device from folk craftsman Viktor Goncharov.
How to make a metal detector with your own hands with metal discrimination
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 most simple ways definitions of metal types were implemented in older instruments and devices entry level 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:
Features of deep metal detectors
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!
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), prudently removing p23 (so that sound card do not burn). 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. How is the most simplest option- crown at 9V. 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.
Among amateur radio designs, developments that help detect metal objects hidden in the ground are of particular interest. Especially if the latter are small in size, lie at a considerable depth and are also non-ferromagnetic.
Quite a few good electrical diagrams of such devices, called metal detectors by analogy with well-known military developments, and descriptions of fully functional designs have been published in various technical
Publications, but they are often designed for trained, experienced home-made workers who have a good material base and scarce parts.
But even a beginner can easily repeat and make the design we propose. Moreover, it will be quite possible to purchase the necessary parts (including a 1 MHz quartz resonator). Well, the sensitivity of the assembled metal detector... It can be judged at least by the fact that with the help of the proposed device it is easy to find, for example, copper coin with a diameter of 20 mm and a thickness of 1.5 mm at a depth of 0.9 m.
Operating principle
It is based on a comparison of two frequencies. One of them is reference, and the other is variable. Moreover, its deviations depend on the appearance of metal objects in the field of the highly sensitive search coil. In modern metal detectors, to which the design under consideration can quite reasonably be attributed, the reference generator operates at a frequency at whole order different from that which appears in the field of the search coil. In our case, the reference generator (see the circuit diagram) is implemented on two logic elements ZI-NOT integrated DD2. Its frequency is stabilized and determined by a quartz resonator ZQ1 (1 MHz). The generator with varying frequency is made on the first two elements of the IC DD1. The oscillatory circuit here is formed by the search coil L1, capacitors C2 and SZ, as well as a varicap VD1. And to adjust to a frequency of 100 kHz, use potentiometer R2, which sets the required voltage to the varicap VD1.
Fig.1. Schematic diagram of a highly sensitive homemade metal detector.
Logic elements DD1.3 and DD2.3, operating on mixer DD1.4, are used as signal buffer amplifiers. The indicator is a high-impedance BF1 telephone capsule. And capacitor C10 is used as a shunt for the high-frequency component coming from the mixer.
The configuration of the printed circuit board is shown in the corresponding illustration. And the layout of radio elements on the side opposite the printed conductors is shown here in a different color.
Fig.2. Printed circuit board of a homemade metal detector, indicating the locations of the elements.
The metal detector is powered by a 9 V DC source. And since high stabilization is not necessary here, a Krona type battery is used. Capacitors C8 and C9 work successfully as a filter.
The search coil requires special precision and attention during manufacture. It is wound on a vinyl tube with an outer diameter of 15 mm and an inner diameter of 10 mm, bent in the shape of a circle 0 200 mm. The coil contains 100 turns of PEV-0.27 wire. Once the winding is complete, it is wrapped in aluminum foil to create an electrostatic shield (reduce the effect of capacitance between the coil and ground). It is important to prevent electrical contact between the winding wire and the sharp edges of the foil. In particular, “wrapping obliquely” will help here. And to protect the aluminum coating itself from mechanical damage, the coil is additionally wrapped with insulating bandage tape.
The diameter of the coil may be different. But the smaller it is, the higher the sensitivity of the entire device becomes, but the search area for hidden metal objects narrows. When the diameter of the coil increases, the opposite effect is observed.
Work with a metal detector as follows. Having placed the search coil in close proximity to the surface of the earth, adjust the generator with potentiometer R2. And in such a way that the sound in the telephone capsule cannot be heard. When the coil moves above the surface of the earth (almost close to the latter), the treasured place is found - by the appearance of sound in the telephone capsule.
When using the device discussed above to find objects hidden in the ground that are of archaeological and national cultural value, prior permission is required from the relevant authorities.
Attention!!! The information contained on this page has been added from unverified sources and may be out of date and contain errors. Therefore, it is provided for informational purposes only.
N. Kochetov, based on materials from “Mlad Constructor”
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