There is a clone-pi metal detector circuit on the Internet, but this requires connecting a display, and you also need to get it from somewhere else. In this article we will look at the circuit diagram of a metal detector DIY clone-pi with LED indication. The main advantage of "Clone PI V" is: its reduced power consumption to 120 mA at maximum volume and when the entire LED scale is fully activated.
Device diagram:
Printed circuit board and firmware from DexAlex - download
When flashing the controller, the configuration bits must be set as follows:
Metal detector assemblyCloneP.I.W do it yourself
Assembling a metal detector should begin by choosing a printed circuit board option. Since they have slight differences in the components used. We recommend choosing the version from DexAlex, his version of breeding this and other metal detectors has proven itself to be excellent.
Then we purchase the parts. Attention should be paid to the following components: It is better to use ceramic capacitors, or even better, film capacitors, this will have a positive effect on the stability of operation. The construction resistor must be of good quality and multi-turn; cheap single-turn stand-offs are not suitable here! TL431 and the resistors in its harness also deserve special attention and must be of 100% quality.
We etch and assemble the printed circuit board, flash the microcontroller and launch the metal detector. To power the Clone PI V metal detector, you can use 8 AA batteries or a 12 battery. "Crown" will not work! Also, when you turn on the metal detector for the first time and configure it, you must use new batteries or a fully charged battery. For the power supply circuit, it is recommended to use a protective diode against “polarity reversal” and a fuse; this will help protect your metal detector from your own negligence, especially at the stages of its assembly and testing!
If your metal detector does not work right away, then in troubleshooting, a voltage map can help you - download.
Making a coil for the Clone PI W metal detector
A standard coil for the Klon PI V metal detector can be made by winding it on a mandrel with a diameter of 19-20 cm, 25 turns, with a wire of 0.7-0.8 mm in diameter. You can increase the diameter of the coil, this will have a positive effect on the detection depth, but then the number of turns should be reduced. When the coil diameter is greater than 28-30 cm, sensitivity to small objects will begin to decrease, this should also be taken into account.
Instructions for operating the Clone PI W metal detector
Control of the metal detector Clone PI V, is carried out using 6 buttons. The buttons have the following purposes:
- S1“Barrier-“/”Guard interval-“
- S2"Barrier+"/"Guard interval+"
- S3“Volume-“/”Up min-“
- S4"Volume+"/"Up min+"
- S5 Function not assigned yet
- S6"Zero" (0)
- S5+S6“Settings mode”/”Exit settings mode”
A sign that you are in the settings mode (i.e., where you can set the guard interval and the minimum permissible supply voltage) is the lighting of the last LED (VD13).
The guard interval is indicated very approximately; the number of LEDs lit on the left must be multiplied by 8. After turning off the power of the metal detector, the value is not saved!
The minimum permissible voltage is indicated in 0.5 volt increments, from 7.5 to 11 volts. The default value is 8 volts. The value is saved. If the supply voltage drops below the set value, the device continues to operate, but emits a double low sound every 15 seconds.
Setting up the Clone PI W metal detector
The Clone PI W metal detector does not require complex settings. The whole setup comes down to this: We turn on the metal detector away from metal objects and wait until the entire LED scale passes. Then we bring a reference metal object (for example a coin) and check the sensitivity of the metal detector. Then we tighten the trimming resistor, reboot the metal detector and check the sensitivity again. We repeat the manipulation until we achieve a better result!
After you have completed the adjustment, in the metal detector you can also use the control buttons to adjust the volume and sensitivity of the metal detector. The higher the Barrier (Adjustment range 0 – 10), the lower the sensitivity. We lower the threshold until false alarms appear when the metal detector coil is raised in the air. For a normally assembled and configured metal detector, the normal threshold is 3-5.
You should also remember that there should not be any metal objects in the coil area when turning on and rebooting the metal detector, otherwise the metal detector will lose some of its sensitivity!
This completes the setup of the metal detector, and you can start searching!
Clone PI This is a pulse metal detector, without determining the type of metals. Clone PI can work with coils of various sizes.
When using a ring coil with a diameter of 20 cm, the Clone metal detector has a search depth for coins of up to 25 cm and large metals of up to 1 meter.
The Clone is based on the circuit of the Tracker PI-2 metal detector, with some changes made to it.
The Clone PI metal detector has the following differences from the original (Tracker PI-2 Metal Detector):
- Place of the AVR microcontroller, PIC controller is used.
- For indication, the metal detector uses an LCD screen, without LED support.
- The device has built-in automatic adjustment: fast and slow.
- All controls of the metal detector are push-button (without variable resistors).
Circuit diagram of the Clone PI metal detector:
Attention: the latest firmware versions for metal detectors were released for the microcontroller PIC18F252
!!!
PI clone Pulse metal detector, of average complexity, for a beginner it will be difficult to manufacture. But a person with little experience in making metal detectors or other electronics will be able to handle it.
The Clone metal detector circuit contains several expensive elements: an LCD screen, an MCP3201 ADC and a microcontroller. Before starting to manufacture a metal detector, be sure to purchase an ADC, since purchasing it may be difficult!
Also, the metal detector circuit contains a programmable microcontroller, so to make it you will need a programmer that supports programming microcontrollers - PIC18F252 and how to use it
On the screen, the Clone Pi metal detector displays the following information:
- Response level ("fast" and "slow" sliders).
- Supply voltage.
- Threshold (the inverse value of sensitivity).
- Volume.
- A sign that auto-tuning is active (the response exceeds the threshold in any direction).
- A sign of slow auto-adjustment (response deviation in the positive direction) coincides with the sound alarm.
- Indicator that the display backlight is on.
The Clone metal detector showed itself in operation quite good, and some “homemade” people even started selling them. With high-quality assembly, the Clone practically does not differ in search characteristics from Tracker PI and other pulse metal detectors.
But from my own experience I will say that everything is not so rosy, and two metal detectors assembled in the same way may differ greatly in operation (True, they were assembled with the first versions of the firmware, and perhaps in newer versions, this problem was eliminated).
DIY metal detector assembly Clone PI
The assembly of the Clone PI metal detector, as mentioned above, should begin with the search and purchase of parts for the manufacture of a printed circuit board. After purchasing them, you can proceed to the direct process of manufacturing and assembly.
First of all, you need to etch the printed circuit board, the printed circuit board drawing is shown below (Double-sided board), and this archive contains the board drawing, markings for drilling holes, as well as the diagram and arrangement of elements on the board.
In the archive you can download a version of the Clone PI-M board. Here some improvements have already been made to the basic circuit, and errors have been corrected: a ULF has been added, a key has been added for backlighting the LCD, and a circuit wired on a single-sided board
- ClonePI-M
After manufacturing the printed circuit board, all radio components must be soldered into it. It is better to install microcircuits on sockets. We also connect control buttons, a screen, a speaker, and connectors for the coil and power supply of the metal detector to the board. After soldering is completed, the board must be washed with alcohol and dried thoroughly.
Then we carefully inspect the board in order to identify any “mis-soldering” and “stickiness”. If everything is OK, then you can start programming the microcontroller.
Microcontroller firmware ( PIC18F252 ) version 1.8.1(Last) - CPI_PRG_181_18
Other firmware versions and program source code for the Clone PI metal detector can be downloaded
After programming, we install the microcontroller on the board, and you can already see the first fruits of your labor. It is better to supply power to the metal detector through a fuse (2-5A); in case of a short circuit or a soldering error, it can save your board! If the metal detector turns on, shows everything on the screen, makes sound and responds to control buttons, then you can proceed to making a search coil. If something doesn’t work, then we return to the stage of visual inspection, checking the board according to the diagram and identifying errors and assembly defects!
Manufacturing a search coil for the Clone PI metal detector
A simple search coil for the Clone PI metal detector can be made from winding enamel wire with a diameter of 0.6 - 0.8 mm, wound on a mandrel (diameter 25-27 cm) - 25 turns. And as a mandrel you can use a saucepan or a suitable round object with an arc.
Then the turns of the coil are tightly wrapped with electrical tape or tape. And to the ends of the coil we solder a twisted stranded wire with a cross-section of 0.75 mm and a length of 1 - 1.3 meters. For ease of use, protecting the coil from shock and giving it an aesthetic appearance, you can put it in a case like this (It can be easily bought online, and I often use it to make coils for metal detectors).
We solder the connector to the end of the coil and connect it to the metal detector. We turn it on and check for the presence of a metal reaction. If there is a reaction and you have good sensitivity. Then you can adjust the metal detector and begin the final assembly of the metal detector into the Housing. The photo below shows an example of the location of the metal detector elements inside the housing.
We recommend that you use a larger case than in the photo above. This will allow you to freely arrange all the elements and conveniently secure the board there.
After assembling the metal detector and coil into the housing, all you have to do is make a rod for it and start your search!
The Clone PI metal detector project was continued in the form Clone PI AVR with more affordable components and simplified circuitry, and Clone Pi W– LED version of the metal detector.
When creating this material, information from the developer’s website was used - fandy.hut2.ru/ClonePI.htm
Discussions, theoretical and practical issues on the manufacture and operation of the Clone PI metal detector can be found on this forum md4u.ru/
Pulse metal detectors, among homemade ones, are known for the highest metal detection depths. They are also better able to work in salt water and highly mineralized soil than others. All pulse generators are similar in principle of operation and have common pros and cons. The clone metal detector that we will assemble has the following advantages:
- The sensor is made of a single coil, both transmitting and receiving. This greatly simplifies assembly and eliminates time-consuming setup. The size of the coil can be selected independently depending on the intended purpose of the metal detector.
- A simplified diagram in comparison with high-quality homemade metal detectors.
- Simple push-button adjustment.
- Slightly reduced power consumption compared to pulse metal detectors with screen display.
The disadvantages include:
- No discrimination.
- The need to flash the microcircuit firmware. However, this cannot be called a big problem, since the article will provide detailed instructions for this process.
Assembling a metal detector clone pi w begins with electrical components: circuit, sensor, their connection and firmware of the microcircuit. The final stage is the manufacture or purchase of housing parts and configuration of the device.
Circuit assembly
All necessary parts, their analogues and comments are indicated in the table in Figure 2.
We purchase strictly new parts! This will free you from problems in the performance of the circuit.
The Clone pi w metal detector circuit is assembled on two circuit boards. One is the main one, and the second is a control and indication board with buttons and LEDs. Both printed circuit boards for the Sprint Layout program can be downloaded from the link. For future fastening of the main board, you can leave a supply of PCB or use hot glue. For the second board, the mounting connectors are already provided on the mounting board. The connection of the two circuits is made using signed pins B1 – B4 and VD4 – VD13 and is implemented with a multi-core cable, for example, from old hard drives or disk drives.
Soldering of radio components is carried out in accordance with the diagram and circuit boards in Figures 3 and 4. 
The main requirements for assembly are accuracy, care and the absence of accidental connections between tracks and parts. After manufacturing the printed circuit board, it is necessary to thoroughly rinse it from flux.
Chip firmware
The clone metal detector works according to a specially written program that needs to be written into the ATmega8 chip. You can download firmware version 1.2.2m from the link.
Let's look at a few simple ways to write firmware:
Method 1. We take the microcircuit, downloaded firmware, and go to the nearest electronics repair shop or to a friend who understands this. We ask you to perform the firmware update for free or for a low fee.
If the firmware is installed in the PonyProg program, we show the wizard Figure 5, which shows the settings of the configuration bits.
When flashing other programs, pay attention to the SPIEN item. If there is no checkmark when reading the information, then set all other configuration bits to the opposite state! This is very important, because if an error occurs, returning the processor to its original state is much more difficult than the firmware process.
For example, you can look at the settings of the Uniprof program (Fig. 6), when reading in which the SPIEN parameter was unchecked.
Method 2. Let's build the simplest programmer, called the "Gromov programmer", and do the firmware ourselves.
The circuit is connected to the COM port of the computer. If you don’t have one, you can, again, contact someone you know who has an older computer or purchase a board with a COM connector. All parts, contacts of the processor and programmer are labeled on the corresponding diagrams.
When assembling, please note that a separate power supply for the processor with a constant voltage of 5 V is required. You can take it from a USB cable by connecting it to the computer.
Don’t forget to connect the minus of the programmer and the minus of the power supply.
After assembling the programmer, we flash the clone pi w metal detector step by step:
- Insert the processor;
- Connect the programmer to the COM port;
- Launch the Uniprof program;
- We supply 5 V power to the processor;
- We make sure that the program has seen the processor;
- We read the configuration bits and configure them as described above;
- Open the firmware with the program and click “write”.
At this point, the firmware of the microcircuit is considered complete.
Making a sensor (coil)
The sensor consists of a sealed coil, a rod mount and a wire.
As described above, the coil for pulse metal detectors is very simple. We find a wire with any insulation with a diameter of 0.4 - 0.5 mm. And, according to the table in Figure 8, we select the number of turns and the diameter of the coil. The optimal diameter of the coil is 20 - 26 cm. You can also build a square deep coil, but it will not give a significant increase.
There are many ways to make windings, for example, basket type or in one plane, but they do not provide great improvements, so we choose any simple type. We make a bulk winding on some round object of suitable diameter, after which we tightly fasten the coil with electrical tape and bring out the two ends of the wire. We do not shield the coil!
The body is made from any available materials, from plywood to plastic, but it is better to purchase a mandrel with ears for the rod in the store, this will give quality and an acceptable appearance to the sensor. No metal should be used in the sensor.
It is advisable to use a wire for connecting the sensor and the unit with good insulation and a pair of cores with a cross-section of about 0.7 mm². Shielding is also not needed. We connect the coil terminals and the wire by soldering and securely insulate them. At the end of the wire we attach a connector.
After making the coil, we arrange it in a mandrel and seal it with special means - epoxy glue, polyurethane foam or other dielectric compounds.
The manufactured sensor can be installed on any clone pulse metal detector.
Figure 9 shows the various coil options for this metal detector.
Assembly of body elements
To make a body for a metal detector with your own hands, you will need a little metalwork, suitable tools and materials, as well as the desire to make something beautiful.
For the control unit you will need a box made of plastic or wood. We select the dimensions in such a way that it would fit two boards and, in the case of using batteries, a contact box. The contact box can also be taken out separately and secured next to the control unit housing. The main board can be secured with hot glue or silicone. For the control and display board, we cut out or drill suitable holes for the LEDs and buttons. After all the holes for the buttons and LEDs match, we fix the board like the main one. We make holes on the box for the switch and the connector for the coil, and secure them. We try to make the box airtight to prevent moisture from entering, for example when it rains.
The bar is made of PVC pipe. Having thought through the design, we purchase the necessary pipes and adapters in the store, taking into account the fact that the rod should be collapsible, dielectric and comfortable - the presence of a handle, an armrest and a place for a battery, if it is used (Fig. 11).
You can use a gas stove to bend the pipe. To adjust the length, we use the difference in pipe diameters and screw-on rings. If desired, the barbell can be made from other items - a crutch, a fishing rod. The main condition is the absence of metal parts. A well-assembled rod is suitable not only for the clone pi w metal detector, but also for other types of metal detectors.
After manufacturing the rod, we attach the control unit to it and attach the sensor using plastic fasteners or other means. Labeling the buttons.
Configuration and performance check
After assembling the metal detector, turn it on. Self-diagnosis should occur with voice acting and LED flashing. To avoid a decrease in sensitivity, the device must be turned on away from metals.
The adjustment is made away from the ground, metal and other objects, for example, in the air. Don't forget to remove anything that may contain conductive material. Use the S1 button to set the minimum barrier. By rotating resistor R7 we achieve a loud continuous signal. Then we return its position little by little until the metal detector goes silent.
In the future, when using the metal detector, we perform ground balancing using the S1 and S2 buttons. The S3 and S4 buttons decrease and increase the volume respectively. The S5 button is designed to configure some functions, but in this diagram it is removed. Button S6 – reset. We use it after detuning from the ground, as well as when the device freezes and glitches.
When the battery is low, the metal detector will emit two short sounds every few seconds.
Unlike the Clone Pi Avr metal detector, which is assembled with a display, LEDs act as a visual indication. The number of lights indicates the depth and power of the signal, as well as the level of sound and ground balance during setup.
Clone Pi-V is a simplified and cheaper version of the pulse metal detector (MD) Clone PI-AVR (which has a two-line LCD screen). Here is a description on the website of Andrei Fedorov - the author of all clones: http://fandy.hut2.ru/ClonePI_W.htm
The design of the Klon metal detector (or, as it is also called, Elephant) was so successful that word of mouth spread far beyond the borders of our country and the device deservedly gained international fame. I came across videos on YouTube posted by radio amateurs in Greece, England, Germany and other European countries.
The main advantage of this device is that, despite its excellent characteristics, its circuit is so simple that even a beginner can assemble it. A correctly assembled circuit begins to work immediately; the setup consists of adjusting one single trimming resistor. You can even do without an oscilloscope!
The only difficulty for beginners is the need to flash the microcontroller firmware. But don’t worry: to flash this 28-legged scolopendra, any computer with a COM port and a simple circuit with just a few elements will do (more on this later).
But after overcoming all the difficulties, you will have a device capable of detecting a hundred hundred square meters of nail at the depth of a bayonet (with a 20-centimeter coil). Soviet 5 kopecks in our heavy soil - at a depth of 25 cm, my 3 gram hoop in the air - 22 cm (flat) and - 10 cm (edge). I’m generally silent about the large one - the heating radiator is 170 cm in air.
But Clone also has disadvantages - lack of discrimination of metals, i.e. he sees absolutely everything. And this is extra effort when excavating, because you will have to dig everything in a row (there may be a coin, or there may be a bottle cap). He also has a low sensitivity to gold.
Balance bars with discriminability are well suited for searching for gold (nuggets and jewelry). But to make such a metal detector, you need experience and an understanding of the principle of operation of the device, otherwise nothing may work out. Of the available and good balancers, I recommend looking towards Terminators. They are not inferior to many foreign brands, and in some respects they even surpass them. For experienced radio amateurs, I would recommend a Quasar metal detector with an elongated DD coil (the so-called “narrow eggs”) to search for gold.
In a word, if you need a device for searching for ferrous metal, then Clone is your choice. You won't find anything simpler or more effective. For comparison, the vaunted Sturm is approximately 1.5 times inferior in detection depth. The good old Asya 250 also remains far behind when searching for ferrous metals.
So, do you already want such a device and are ready to start assembling? Then let's go!
Circuit diagrams (3 options)
There are three of the best and repeatedly tested schemes, which differ only in the key chips:
- circuit with ADG444 (aka KR590KN5);
- circuit with KR590KN2 (it differs from the first one only in the printed circuit board);
- circuit with CD4066 (4016).
These circuits are 100% working, so no claims regarding their inoperability will be accepted. If something doesn’t work for you, then it’s your own fault.
Which scheme is better?
KH5 is difficult to find, and there are many defects among them (there are even cases described when sunlight falling on the microcircuit caused self-excitation). If you come across a KN-ka after the 91st year of production or in a brown case, do not take it under any circumstances - they are almost all defective.
KH5 has a complete analogue - ADG444, but these microcircuits are not very common, and are also quite expensive (300-400 rubles).
Devices assembled on KN2 operate a little more stable. But now it is almost impossible to get it.
Personally, my choice is a circuit using a 4066 key chip (third option). This microcircuit costs a penny (10...25 rubles), is sold everywhere, and at the same time works without glitches.
But let's go in order.
Scheme with ADG444 (KR590KN5)
Purpose of elements
Resistor R1 is designed to dampen reverse pulses (IRP) in the sensor that arise due to the phenomenon of self-induction. If it is not there (for example, if there is a break or too much resistance), the IOC will heat up the powerful field device (more precisely, the diode built into it), electrolyte C1, and can even break through the diode protection VD1, VD2 at the input of the analog part.
R3 also helps reduce the quality factor of the sensor when the signal amplitude is large (then this resistor is connected in parallel with R1 through diodes). By the way, the sense of the metal detector to some extent depends on the resistances R1 and R3, but not so much as to bother with their selection.
If resistor R2 breaks, the field operator can absorb interference from the air and open spontaneously. In this case, huge currents will flow through the sensor, which will lead to burnout of resistor R12. By the way, the resistance of R12 can be anything within 1...27 Ohms (small resistance is for more “deep” options).
Capacitor C3 in conjunction with R14 is part of the integrator, which allows you to suppress random noise at the sensor input that occurs due to industrial interference. I usually set C3 = 0.047...0.068 µF. The resistance of R14 can be from 1.8 to 2.7 MOhm, the difference will not be noticeable.
If the device is well-debugged and no false alarms occur, then by increasing the rating of R15 and decreasing C5, you can increase the device’s sense of smell to the maximum.
If the power is supplied from a battery, then C1 can be left at 2200 uF. If it comes from weak batteries, then it is better to significantly increase its capacity. For example, up to 6800 µF. It is this electrolyte that serves as the energy source for the formation of powerful short current pulses through the coil.
Components used and their estimated price (August 2017):
| Designation | Name | A comment | Price | Qty |
|---|---|---|---|---|
| Microcircuits | ||||
| U1 | ATmega8 | ATmega8А-16PU and ATmega8А-PU are interchangeable, the firmware and configuration bits are completely the same. | 110 rub. | 1 |
| U2 | 78L05 | 10 rub | 1 | |
| U3 | TL074 | Sometimes it’s worth playing with the TL074 opamp - try from a different batch (different year of manufacture). Sometimes one is normal, while the other has almost zero gain. If you choose this microcircuit properly, you can win a couple more centimeters of sensitivity. Can be replaced with 2 pcs TL072. |
25 rub. | 1 |
| U4 | KR590KN5 (ADG444) | As it turned out, the stability of the device and the search range are affected not only by the selection of the TL074 op-amp, but also by the KN5 switch microcircuits - the best result is for microcircuits manufactured before 1993, and excellent results are for microcircuits in planar metal-ceramic packages (1984). They can be tapped directly onto the board without changing the seal. The bourgeois version of AGD444 does not cause any complaints. By changing the printed circuit board accordingly, the KH5 (444) chip can be replaced with a 590KH2 or CD4066CN (more on this below). |
206 RUR | 1 |
| U5 | TL431 | Analogous to K1156ER5. | 15 rub. | 1 |
| Transistors | ||||
| VT1 | IRF740/TO | Analogs: KP776A, IRF630, IRF640, IRF840, BUZ73, 04N60, 5N60. Any n-channel field device will do, with a drain-source voltage of at least 200 volts, 2 amperes, and a gate capacitance of no more than 1200 pF. | 35 rub. | 1 |
| VT2 | BSN304A | Instead of BSN304A, you can use the more affordable BS170. It can also be replaced with a transistor C945, 2N7000 or KP501A. | 6 rub | 1 |
| Diodes | ||||
| VD1, VD2, VD14-VD17 | 1N4148 | You can have ours: KD521, KD522. | 1 rub | 6 |
| VD4-VD13 | Instead of domestic diodes, it is better to install super-bright ones (ours are not visible in the sun at all, and for bright ones, a protective sun visor would not hurt). | 15 rub. | 10 | |
| Capacitors | ||||
| C1 | 2200uF 16V | We definitely set this capacitor at 4700 microfarads (or even better, 6800, 10000) - and the stability of the device increases and will help if the voltage on the battery drops (if it’s old or not charged). In addition, the charge per pulse of the device increases. | 63 RUR | 1 |
| C3 | 0.1uF | It’s better to set it to 0.047uF (if its capacity is increased, sensitivity decreases, and if it is decreased, stability decreases). So there's a golden mean. Ideally, this capacitor (like C5) should be film. But don’t get too carried away, our KM types or imported ones (almost any, except mica of course) - Mylar, palladium, etc. will do. You can even put in dark green Chinese pads from old broken equipment. | 10 rub | 1 |
| C4, C10, C11, C14 | 0.1uF | 5 rub | 4 | |
| C5 | 2200pF | It is possible at 1500pF, the main thing is that it is thermally stable (like C3). Personally, I set both 1500 pF and 2200 pF - I didn’t notice much of a difference. | 10 rub | 1 |
| C6 | 220uF 16V | 15 rub. | 1 | |
| C7 | 470uF 6.3V | 12 rub. | 1 | |
| C9, C12 | 0.01uF | 1 rub | 2 | |
| C13 | 1000uF 16V | 13 rub. | 1 | |
| Resistors | ||||
| R1, R3 | 390 Ohm, 0.5W | minimum 0.25 W | 3 rubles | 2 |
| R2, R12 | 20 ohm | 3 rubles | 2 | |
| R4, R9, R11, R16, R19, R21 | 10 kOhm | 3 rubles | 5 | |
| R6, R8, R13 | 1 kOhm | 3 rubles | 3 | |
| R7 | 1 kOhm | If you have a high-quality multi-turn resistor with a resistance of 470 to 1000 Ohms, then you can install it. If this is not the case, then it is better to do without a multi-turner at all - an ordinary imported trimmer will suffice. The fact is that now purchasing a high-quality multi-turn resistor is a big problem. High precision is not needed here; a high-quality trimmer is enough. | 30 rub | 1 |
| R14 | 2.4 MOhm | from 2 to 2.7 megs | 3 rubles | 1 |
| R15 | 56 kOhm | or 68 kOhm (any one) | 3 rubles | 1 |
| R17, R23 | 3 kOhm | 3 rubles | 2 | |
| R18 | 100 Ohm | 3 rubles | 1 | |
| R20, R22 | 12 kOhm | 3 rubles | 2 | |
| R24 | 100 kOhm | 3 rubles | 1 | |
| R25 | 47 Ohm | 3 rubles | 1 | |
| R26-R35 | 510 Ohm | Instead of all these resistors, it is better to put one common one at 470 Ohms (see the description of the printed circuit boards below) | 3 rubles | 10 |
| R36 | 5.1 kOhm | 3 rubles | 1 | |
| Miscellaneous | ||||
| HA1 | The speaker was pulled out of an old landline phone, there is a plastic speaker, it screams awesome. I tried tweeters from a computer (those little black barrels) and 50-ohm speakers. There is nothing louder than a 50-ohm speaker from an intercom handset (and the sound is more pleasant). You can install a piezoceramic emitter (PP), but then you need to solder a 1 kOhm resistor in parallel to it. |
60 rub | 1 | |
| Cribs | If you put microcircuits on blocks, then take not the usual cheap ones with flat sockets, but high-quality ones with collet connectors. After the circuit has started, I recommend removing all the pads and soldering the microcircuits into the board. | 15 rub. | ||
To protect against polarity reversal, you can place a Schottky diode 5819 between the batteries and the circuit. At a current of up to 100mA, the maximum drop across it is about 0.3V, at 1A - about 0.6V. If you feel sorry for losing these fractions of volts, you can use a reverse polarity protection circuit on a field-effect transistor with a low contact resistance (on the order of milliohms): 
I made a version using a p-channel transistor IRLML5203. It has a drain current of 3A and a gate-source voltage of 20 Volts. Fits perfectly.
Any microcircuit can be replaced with the same microcircuit, only with planar pins. The pinout is the same, but you will have to bend your legs a little. To form the planar body legs, use a crib with the collets pulled out.
Printed circuit board
Below is the most stable version of the Clone PI-W board on the 561KH5 chip (ADG444).
This PCB has undergone a lot of experimentation.
It all started with the fact that on some tested boards a glitch was noticed such as howling at the minimum barrier and maximum flair. This made it difficult to set maximum sensitivity. The glitch decreased if you put your hand against the board or grasp the wire.
The reason for this phenomenon is the incorrectly connected ground of the MK and the bus connecting a number of LEDs and key chips. On the bus near the keys there is constantly a sinusoidal noise from the operation of the generator, and not at a bad level, and working LEDs add even more dirt to this bus. Moreover, the more they light up or blink, the greater the level of interference and, accordingly, the more false ones.
To eliminate this unpleasant effect, a whole bunch of experiments were carried out and, as a result, a printed circuit board with spaced lands was developed. So take it and solder, everything is for you. With a standard reel, you'll get maximum flair and fewer glitches.
(in program format)
Mandatory requirement: supply power strictly to the places provided for this - to the spots near the air conditioners. Otherwise, numerous glitches are possible. Perfectionists can cut off all ADG444 ground pins from the board and run them with a separate wire to the battery. Then the result will be even better (compare with KH2).
Instead of putting one resistor on each LED (in accordance with the circuit diagram), it is easier to put 1 resistor per color group. For example, you have 3 colors: red, green and blue, which means you supply plus directly from the MK, and minus for each group through its own resistor. This board generally has one resistor for all 10 LEDs.
Finished board: 
Printed circuit board for SMD components:
(download this board at)
Scheme with KR590KN2
If you have KH2, then you have a chance to collect the best version of the Clone. Only the board must be routed according to the mind: no ground of the KN-ki (except for the field operator’s key) should be connected to the ground of the mega, the line of LEDs should also be run on a separate bus.
The big plus of KN-2 is that it does not have a +5 Volt power supply. Due to power decoupling, the clarity and stability of the entire circuit increases. If you make such a board (with the correct routing of the tracks), you will get a super device. It will seem that this is not a Clone at all.
The circuit diagram is no different from the previous one, but since the pinout of the 590KN2 microcircuit does not coincide with the 561KN5, then, accordingly, the printed circuit board is slightly different: 
(with *lay-file and description)
The device assembled on this board is characterized by increased operating stability. People experimented with the KR590KN2 - it would seem a banal switch and nothing more, but when replacing this microchip, the MD showed different results in terms of stability, and most interestingly, in terms of detection depth. The best results were shown by microcircuits produced in 1993 and metal-ceramic ones with planar leads (produced in 1984). But, again, it’s very difficult to get this chip now.
Circuit with CD4066
This is the most budget-friendly and easily accessible device option.
In order for the 4066 microcircuit to fully replace KH5, additional wiring will be required in the form of several capacitors, resistors and 4 2N5551 transistors. This is what it looks like: 
The complete circuit of the Pi-V Clone on the 4066 chip looks like this: 
Accordingly, in this case you also need your own printed circuit board: 
(in lay format for the Sprint Layout program)
Complete board assembled with control panel: 
Noticed that one button is missing? The button to enter the settings (aka “service settings”) was removed on purpose, because The device was manufactured for sale to people who did not need unnecessary complications.
Personally, I prefer the version of the signet, where all the buttons are in place and the LEDs are placed separately: 
()
This board has dimensions of 90x70mm and is designed both for a separate LED socket (in this case, you need to connect each LED to the microcircuit through a 510 Ohm resistor), and for LEDs located on a panel with buttons (and then simply connect the ground of the main board to the ground of the socket through resistor 510 Ohm).
Transistors 2N5551 can be replaced with S9014, KT503 or KT3102.
All the above printed circuit boards are already mirrored, you just need to print them.
After desoldering, the scarf MUST be washed of flux. Don’t even try to assemble it on a circuit board; it either won’t work or will be terribly glitchy.
Microcontroller firmware
To upload the firmware to ATMEG you will need a programmer. The two most primitive circuits, developed specifically for ATmega8, are given in. You can choose any of them.
PonyProg
If you decide to flash using the PonyProg program, then the fuses need to be set as in the picture: 
When using another program, you may need to place these checkboxes inversely (that is, where there is a checkmark in the picture, on the contrary, it should not be checked). If, after reading the bits in your program, the checkbox next to “SPIEN” is not checked, then all other bits should be set directly opposite the screenshot. The SPIEN bit itself CANNOT be changed under any circumstances.
Gromov programmer
After connecting the programmer (read how to do this in the same article), the first thing we do is check whether the fuse bits are read. If everything is ok, set the bits as follows: 
We carefully check and record everything. At this point, programming the microcontroller can be considered complete.
Which firmware is better?
All currently existing firmware versions were tested. In my opinion (and many diggers will agree with me), firmware 1.2.2m turned out to be the most successful. It absorbed all the best from 1.2.1 and 1.2.4 and in the end it turned out to be just a fairy tale! It’s impossible to think of anything better, in my opinion.
As for me, it is more stable, it gives very few false alarms (you can go for a long time without hearing a single beep). I also really like the overload alarm - a loud low-frequency sound that sounds after the last 10th LED lights up. The signal allows you to very accurately localize the target. This sound seems to say that the target is here, right under the coil! The reset in firmware 1.2.2m was made silent, which is also a definite plus in my opinion.
I think that with this version the depth sensors will work stably.
Trial run (SMOKE test)
Since manufacturing the housing, sensor and rod is the most labor-intensive, it is most advisable to check the functionality of the metal detector board immediately after flashing the controller.
There is no need to connect the coil. You just need to solder the socket with LEDs and buttons and don’t forget about the tweeter.
After power is applied, the Clone initiates some self-diagnosis, which manifests itself in the alternate lighting of the LEDs and the generation of sounds of different tones. If everything is assembled and stitched correctly, it should be something like this:
Reaction of the operating circuit to pressing the reset button:
In some firmware (for example, 1.2.2), there is no sound when resetting the Clone.
If the box is silent, look for errors in the circuit, faulty parts, or check the operation of the Atmega. Typical reasons for inoperability are given at the end of the article.
Purpose of the buttons
The purpose of the buttons does not depend on the firmware version.
- Barrier buttons: S1 - minus, S2 - plus. The barrier raises the threshold at which the signal from the analog part of the device is perceived as the presence of a target. Thus, by increasing the barrier, we raise the threshold for the metal detector to respond to metal, thereby reducing sensitivity. In other words, the higher we set the barrier (more LEDs), the lower the sensitivity to metal and the fewer false positives. The set barrier value is remembered even after the power is turned off. The value of the barrier does not affect the value guard interval (GI). The guard interval is set automatically every time the power is turned on (the microcontroller calculates the protection interval depending on the circuit settings, coil parameters and the environment). The GI value can be changed manually in the settings mode using the barrier adjustment buttons, but this is meaningless and in practice no one ever does this. After the power is turned off, the RF value is not saved.
- Volume: S3 - minus, S4 - plus (maximum level - 7). In the settings mode, these buttons set the minimum permissible supply voltage (from 7.5 to 11V, step - 0.5, default is 8 Volts). If the voltage drops below the set level, the device will continue to operate, but a characteristic low-frequency signal will sound every 15 seconds.
- Button S5 - enter settings mode(not in all firmware versions). If you are not making a metal detector for yourself, then it is better not to install this button at all. So as not to tempt you again.
- Button S6 - reset. Used when the device is self-excited or freezes - in which case, press reset and continue the search. Pressing the reset button just clears the microcontroller's registers, stacks, flags and other internals of the processor (I'm not very good at this), allowing it to continue normal operation. The reset button does not in any way affect the guard interval calculated when the device was turned on, the set barrier and the volume level.
Sensor (coil)
A huge advantage of this metal detector is the ease of manufacturing the sensor. In the simplest case, it consists of 27 turns of wire with a diameter of 0.6-0.8 mm, wound in bulk on a mandrel with a diameter of 21 cm.
The “basket” coil from KASCHEY Ø22cm is very suitable for this MD.
The “sniper” coil allows you to very accurately localize the target: diameter 18.5 cm, 23 turns of 0.5 mm wire.
To find out the number of turns for coils of a different diameter, you can use the following table: 
There are ready-made forms for coils on sale, in which you can place sensors with a diameter of 19 or 26 cm. You cannot place two coils in one form at the same time, so wind the one that is 26 cm. This is approximately 21-23 turns of 0.7...0.8 mm wire. The total resistance should be from 0.7 to 2 ohms. 
For deep search, you can build a frame with sides 70x70cm or even meter by meter (16 turns of wire is enough). But based on experience, I can say that with such a sensor you basically won’t gain anything. It also catches small things (relatively speaking), but carrying it is VERY inconvenient. It will only be suitable for working on an open field, and then you will need to raise it above the ground by 70 centimeters - and with such distances you will miss a lot of interesting things. Although for those who are going to catch tanks, it will do. 
If you want a larger one, make a sensor Ø30-35 cm, 20 turns. With such a coil, having gained a little experience, it will be possible to look for small things and large ones, changing the sensor-ground distance. And forget about the depth frames, it’s a bummer.
An elliptical coil for an impulse generator is nothing more than a show-off. There is a lot of fuss during manufacturing, and the expansion of the target capture area is not that large (5-7 cm). But if you already have a suitable frame, then ok.
By the way, a good frame for winding can be made, for example, from a spool from a semi-automatic welding machine. Trim off all excess, remove the partitions and you will get a very durable case with a diameter of 24.5 cm. 
Anyone who wants to experiment can wind a planar reel (like Chance’s). The sensitivity turns out to be terrible: the sewer hatch is 170 cm. But the truth does not react weakly to the ground, you have to coarse the sensitivity. So the end result won't be much different from a ring-shaped sensor. 
Out of curiosity, I tried a coil like the one in the picture above - it works great. Frame thickness ~4 mm. It is easier to wind it than a truly planar one: 
A basket-type coil is also suitable (http://www.metdet.ru/Sensor_K1.htm): 
With it, the sensitivity is a little higher (by a couple of centimeters), but it also picks up more interference.
You can use a reel like the one in the photo below, but believe me, this “beard” is not worth such effort. The ring winds much easier, and the performance is almost the same. 
In short, there are many suitable options for making sensors, but nothing is simpler than a regular ring. And the difference in detection depth is either insignificant or is offset by false positives from the ground.
There is also an interesting option - the usual “double ring” (or double-circuit coil). Two coils are wound - 15 turns on a mandrel of about 12 cm and 12 turns on a mandrel of about 23 cm. One is located inside the other, connected in series and connected to the device. The idea is that a small coil will catch small targets, and a large coil will catch large targets at a good depth. 
My advice to you: first, wind the sensor on a 21 cm frame, with a wire of 0.65 mm, seal it all properly with bauxite and you will have an excellent coil, suitable for the requirements of even the most spoiled digger. 
Glue the resulting coil between sheets of plywood and you’re done: 
And only then, when you gain experience, make an oval basket sensor and use it to add 1-2 cm of depth.
If you have problems with the winding wire, use aluminum wire (1mm diameter). Only the ends of the coil must be properly soldered to the copper terminals. Twists are not allowed. Either do not use acid flux or rinse it off very carefully.
Impregnation/filling
Before pouring into the mold, you need to make a small frame to tie together the coil itself, the ears, and the cable entry. Then the whole thing is wrapped in fiberglass or just a medical bandage and filled in. I fill it with epoxy. It is very advisable to choose the shape in such a way that there is not a lot of resin leaking out, otherwise when the sensor hits a tree/stone, it may burst or crack. I use about 150-200 grams of resin per spool.
Filling molds are made from anything - bucket lids, Teflon-coated pancake pans, Frisbee plates, some even mill molds from thick plexiglass. Some are simply wrapped in fiberglass and impregnated with resin. One of my friends cuts out a form from plasterboard, and after hardening, throws the entire structure into water. After a couple of hours, the entire drywall turns into pumpkin mush and falls off. What remains is a clean coil.
By the way, polyurethane foam is excellent for sealing all sorts of cracks and joints. You just need to know one trick: release a little foam into the water, mix it directly in the water, and as soon as it settles (quenches), you take the resulting mass and use it for your own purposes. The material turns out to be superb: moderately hard, non-porous, easy to sand and cut. In general, you can sculpt anything. Dries instantly - 20-30 minutes. 
To make the epoxy opaque, it can be mixed with flour. Reinforcing the resin with microspheres also gives an amazing result - the sensor with them is light, durable and less affected by temperature. Microspheres are small granules, they come in glass and plastic. They are so small that they look like powder: 
Reel cannot be screened- This is a pulse device, not a balanced or beat-based one. There is a completely different operating principle here.
From personal experience: for me, a sensor in the form of a solid pancake is better than one with a jumper in the middle. Grass constantly gets into these slots and gets in the way. And the solid pancake calmly slides along it, not catching anything. But the pancake is slightly heavier, so consider what is more important to you - convenience or light weight.
The wire from the block to the coil is ordinary, unshielded, with good insulation and a cross-section of about 0.75 square (you can, for example, cut it from a neighbor’s floor lamp or vacuum cleaner). Wires from high-quality audio systems, in transparent insulation, are well suited. 
The cable for the pulse generator, the shorter the better, 3-4 turns are enough for a fully extended rod.
Regarding the attachment of the reel to the bar - make it as powerful as possible! From my experience in repairing MDs, I can responsibly state that broken “ears” on the sensor are the most common breakdown that is dealt with. They break everything and everyone (company and non-company). Making their way through the kusheri, they step on the sensor and say hello to the family. The factory rod, as a rule, can withstand it, but the ears do not. A classic of the genre - one ear is completely missing, the other is 50% broken.
Thick fiberglass or impact-resistant polystyrene with a thickness of at least 3-4 mm is well suited for the ears. You can cut them out of a toilet lid (they can be very thick).
By the way, I don’t recommend making the barbell in the form of just a straight stick, as in the photo above - it’s not very convenient and fatigue will not keep you waiting long. It’s better to immediately do the proven S-shaped forearm hold: 
An armrest is a must-have element (unless, of course, you want to rest under the bushes with aching pain in your arm in a couple of hours). The ideal armrest is metal. The plastic one will break sooner or later, hundreds of treasure hunters have already been convinced of this. 
A few words about the design of the block itself
Do not take a case that is too tall; a height of 36-50 mm is quite enough. And it will look more beautiful. It is better to take the case without ventilation slots so that it is sealed. Otherwise, after a couple of cops, there will be anything inside: dirt, water, grass, dust, flies, ants, spiders, mice and various beetles. And all these living creatures will constantly crowd and get in the way there (checked personally by a cop).
In a box measuring 150x88x47, in addition to the board, a cassette for 8 fingers fits. The D150Ak box (91x147x36) fits perfectly. 
It is best to make small holes for the speaker (or piezo emitter) from below, so that sudden rain does not penetrate inside through these holes and flood the membrane.
For my latest Clone, I adapted an aluminum case measuring 120x97x40 mm. Three 18650 lithium batteries (from old laptop batteries, bought for 100 rubles per piece), the metal detector board itself, on which I also placed three simple chargers on a TIP41 transistor (taken) fit in there without any problems. 
Thus, everything turned out compactly, in one single case and no extra wires. Sticked the reel in and went digging!
Nutrition
Batteries or AA size batteries in the amount of 8 pcs are suitable for power supply. People using this device with such batteries wrote that they last for 5-7 hours of operation. A set of 8 AA is enough for 10 hours of active search.
In one of the devices I used 4 Li-Ion batteries from old cell phones, they were still lying around idle.
I know that some were even powered by an 18-volt battery from a screwdriver. And it worked. The main thing here is to make sure that all capacitors are rated at least 25V.
The main requirement is that the power source must deliver 160-180 mA without drawdown (this is the maximum consumption of the device when the LEDs are on and there is a metal object nearby). So any kind of Crohn's or D-0.125 tablets will not work!!!
The device will not work with a weak power supply. For reference, the pulse amplitude in the coil reaches 200 Volts, and the current is 20 Amperes. So it's serious.
The ideal option is 3 or 4 18650 batteries and something like this box for them: 
If you plan to use some kind of heavier battery (for example, a lead or gel battery from an uninterruptible power supply), then it would be advisable to consider placing it under the armrest. This will contribute to better balancing of the entire structure. 
Setting up MD Clone PI-W
Setting up a working device involves balancing a bridge consisting of a sensor and resistors R1, R3, R6, R9 and R7, R8, R11. This is done by selecting the resistance of the trimmer R7.
There are two settings options - by ear or using an oscilloscope.
Tuning by ear
For each position of the trimming resistor found, press the reset button and check the sensitivity. A good result in the air can be considered 22-25 cm per Soviet five kopecks. You need to check not “by eye”, but using a wooden strip with marks marked on it.
If the specified sensitivity is achieved, the setup of the metal detector can be considered complete.
Due to the high sensitivity of the analog part of the device, I strongly recommend making the final adjustment somewhere in nature, away from power lines and industrial interference. For example, go to a field, find a lonely tree there, hang the reel on a branch and then you can turn R7.
We never touch this tuning resistor again, and generally forget about its existence. If it is necessary to harden the sensitivity (for example, to “detach from the ground”), we do this using the barrier buttons.
Setting up with an oscilloscope
The point is to use R7 to achieve a flat horizontal section of the oscillogram between the pulses on the pin. 1 op-amp chip TL074: 
At this stage, it sometimes turns out that the resistance of resistor R7 is not enough to fully balance the Clone. Then you also have to select resistor R8.
The adjustment must be accompanied by control of the sensitivity of the device! The fact is that a flat section of the oscillogram is achieved in a fairly wide range of resistances R7, so we observe the behavior of the device: turn it on/off, bring in coins, look for the most suitable position of the trimmer.
We set the minimum supply voltage
By default, the minimum supply voltage at which the device turns on the low battery alarm is set to 8 Volts. If you need something else (for example, to avoid damaging the batteries), then this value can be set manually through the service menu.
We enter the settings by pressing the S5 button. A sign that you are in settings mode is the lighting of the last LED (VD13). Use the volume buttons to set the required voltage value. The minimum permissible voltage is indicated by LEDs from the first to the tenth in half-volt increments - from 7.5 to 11V.
If during operation of the device the supply voltage decreases below the specified value, the metal detector continues to operate, but once every few seconds it produces a double low sound. This is a signal that it’s time to get the second set of batteries.
The supply voltage sensor for the controller is the divider R22, R23.
Guard interval
Any impulse signal has such a concept as a protective interval (GI). This is the time interval between the moment the pulse is generated until the moment the reflected signal begins to be received. 
In this MD, the value of the guard interval is selected automatically when the device is turned on (this is when the LEDs begin to go out one by one). It can also be set manually through the menu. After the power is turned off, the value is not remembered. Therefore, it is very important that when turning on the device there are no metal objects near the sensor. In practice, this is achieved by simply raising the coil in the air above your head.
If you turn on a metal detector near, for example, a shovel, the device will set the HI value for the given operating conditions and will not notice targets at close range, the reflection from which will be less than from this shovel. The approximate value of the guard interval can be determined by how many LEDs go out simultaneously at the end of the test after switching on - the more, the greater the SI.
Although, if you are only interested in the largest targets, the device can be turned on directly on the ground. Large mines, shells, factories and steamships will still ring.
Now regarding the button to enter setup mode. It's no secret that some people remove it altogether.
I agree, this button is almost never used, and few people understand why it is needed at all. Therefore, if you are making a device for someone who does not really understand the principle of operation of pulse generators, then it is better to remove the button out of harm’s way.
Personally, I sometimes set the protective interval to plus, thereby cutting the sensitivity to small things. It would seem, why is this necessary when there is a barrier? It turns out everything is not so simple. The barrier really helps with ground balance. But the increase in the protective interval manifests itself somewhat differently. This can only be felt when searching, although during room tests it may seem that this function is unnecessary or even harmful - after all, it reduces the sensitivity of the device.
I'll try to explain based on my own experience. In short, every metal object lying in the ground spreads a gallo (aura) from the mineralized soil, so even a small nail can sound like a borscht pan. And the protective interval function helps to tune out (although in some cases not completely) from such rotten small things and focus on finding larger objects. In practice, proper use of the protective interval allows you to dig less idle. Something like this...
What to do if nothing works
Most likely, this will not happen to you, but even if it does, don’t panic! It's OK.
First of all, check the current consumption - it should be in the range of 60-80 mA. If you bring a large metal object to the coil, the current should increase to 150-170 mA. If the currents are too high, we immediately turn everything off and look for a short circuit on the board, look at which elements are very hot, and find out the reason.
If everything is fine with the currents, make sure that the controller is flashed correctly. A controller that has not been flashed will blink the first LED, as if hinting that it is empty.
When turned on, a correctly programmed controller, regardless of the functionality of the analog part of the circuit, should turn on the LED illumination and beep in every possible way. If the LEDs do not light up, check the power supply to the MK and whether the LEDs are installed correctly.
If there is no sound, the pinout of field-effect transistor VT2 may be reversed. Please note that BSN304 and BSN304A have different pin assignments!
If everything is in order, bring the magnet close to the coil - you should feel it itching and vibrating. Not much, of course, but noticeable. If there is a buzzing sound, then the controller, key chip and powerful field-effect transistor IRF740 are working. Already good.
If the magnet does not buzz, touch the field switch - it should not get very hot. If it gets hot, there may be either a short circuit in the coil, or it is constantly open (there is a suspicion of a key chip or controller).
If R12 constantly burns out - either there is a short circuit somewhere, or C1 was plugged in incorrectly, or the controller itself is faulty, or they forgot to insert a key chip (444, KN or 4066) into the socket - one of its elements acts as a field driver.
I repeat that the device can be turned on without a sensor - first one LED will light up, then the entire scale of 10 pieces will light up at once, and then they will all go out at once and there will be silence. At least on firmware 1.2.2 everything happens exactly like this. On firmware 1.0.1, LEDs without a sensor will go out one at a time. And if this is not the case for you, then the microcontroller is not working: check the power circuits and firmware. When checking the firmware, pay special attention to the configuration or fuse bits (count them and check them with the picture I gave above).
If, when you turn on the device, there is sound and light illumination, the coil causes the magnet to “buzz,” but there is no reaction to the metal and adjusting the R7 trimmer does not lead to anything, carefully check that your board matches the circuit diagram. Somewhere they hung up a snot while soldering, forgot to draw a path, etc. Pay special attention to the resistor values in the TL074 harness - name them directly on the board.
There may be no reaction to metal if, when turned on, the coil was near a large metal object (battery, chair frame, contents of desk drawers, etc.)
Make sure that the flux has not flowed into the socket and has not broken the contact (if you use sockets, take those with gold-plated collet clamps - such a problem is eliminated in principle). If the error cannot be found, sequentially replace first the key chip, then the TL074 op-amp.
The working device, with a sensor connected and no metal nearby, should have the following voltages at the terminals of the TL074 op-amp:
- Pins 5, 10 - voltage equal to Uref 4.5 - 4.9 V. These voltages come directly from the TL431 stabilizer. If there is a strong deviation, check the divider R19, R20.
- On a balanced op-amp, the same voltage (with a difference of hundredths of a volt) should be at pins 1, 2, 3, 5, 7 and 14. With serviceable parts, but an unbalanced op-amp, the voltages may differ slightly - by 0.2...0.5 Volts (they will fall into place when balancing with a trimmer). If torsion of resistor R7 does not lead to a change in the voltage at pin 7 of the op-amp, the trimmer must be replaced.
- The voltage at pins 12 and 13 should be the same and slightly less than the power supply voltage (by about 0.6-0.7V). If this is not the case, check the trimmer and the entire input circuit.
- Pin voltage 8 and 9 should be approximately equal to half the voltage of the power source and depends on the quality of the op-amp and the correctness of the wiring. The more meticulousness you put into selecting parts, the closer the voltage will be to half the supply. As a rule, it is equal to 4.5...7V. The closer to the pin. 8 voltage to half the voltage of the power supply, the better the copy of the op-amp you came across.
- Pin voltage 6 op-amps - approximately 3...5 volts. It is difficult to measure with a digital device; it is advisable to have a dial voltmeter.
Here is a diagram of the voltages taken from the working device at a supply voltage of 10.7V (the batteries are already slightly weak): 
The most common beginner mistakes:
- stuck the microcircuits in at the wrong end;
- when flashing the firmware, they messed with the MK configuration bits and put it to sleep forever;
- Short circuit in the search coil (low sensitivity, high current consumption);
- they twisted the trimmer's head;
- there is no contact (poor contact) in the cable connector. Solution: temporarily (or better yet permanently) solder the sensor directly. Or use a high-quality connector with reliable gold-plated contacts;
- the board is dirty, the flux has not been washed, acid flux was used during soldering (the latter is generally unacceptable under any circumstances);
- poor-quality soldering, false soldering, snot on the board.
Reasons for all sorts of glitches:
Check everything. Check the board ten times, call or replace questionable elements. The circuit is quite simple and the fault is 100% right before your eyes. If you show a little attention and patience, you will find it.
If the device works, but has low sensitivity, and the adjustment does not help, then you may have come across a “dumb” TL074 microcircuit. Try replacing it. In my practice, different microcircuits from the same batch gave significantly different sensitivity (almost twice!).
The gain of the first stage of the op-amp is 7 and is set by resistor R11. The gain of the second stage is about 10, set by resistor R15. By changing R15, you can slightly raise or, conversely, coarse the sensitivity of the device. I know craftsmen who even replace R15 with a variable resistor and place it on the front panel (like adjusting sensitivity!).
Recently, reports of marriage among TL074 have become more frequent. If you can't find the problem, this may be the problem.
If you suspect a defective TL074 chip, try taking it from old equipment, or buy it in another store from a different batch, or use analogues: TL064, TL084, TLC274, LF347, MCP604, MC34004P, TA75074P, ECG859. You can also pre-wire the signet for two dual op-amps (for example, TL072 or TL082).
Or, as an option, you can try adding 074 in SMD version to the board (no defects have been noticed among them yet). 
Impressions from the device
I love this metal detector! I gave some to the diggers here, and they went wide-eyed: they rang the rifle cell with a branded “Fisher”, it showed nothing, and my Clone lit the third diode. We dug for about 20 minutes, the soil was heavy, there were stones on top. As a result, we lifted three three-inch cartridges from a depth of at least 40 cm!
And once, one of my friends wanted to wander around with a metal detector outside our village and an hour later he returned with a gold-plated button. He says that he dug it right on the side of the road at a depth of one bayonet. He said that the device screamed like crazy.
Judging by numerous reviews, a well-tuned Clone has approximately twice as much sensitivity for large fish as an ICQ 250 with its original coil. True, ICQ has discriminability, you can find more flower beds (if this flower bed is still left in the ground), it’s good to tinker with it on the beach in the sand. And so, the ACE-250 is an entry-level device, a children's toy, one might say. As the owner of ICQ in the past, I can add that if it had satisfied me in everything, I would not have taken the soldering iron out of the closet.
By the way, I recently tested my Elephant on the Black Sea. There were no problems, it works great in sea water. The main thing is that I’m walking along the beach with a clone, and my comrade with a minilab costs a grand, and the result is the same for everyone. In general, this device was originally conceived by the author as an option for underwater search.
A slight increase in sensitivity was noticed with coils starting from 30 cm. But with them it becomes more difficult to localize the target. In other words, when digging a small object, you can miss a hole - you dig and dig, but it’s still not there, and the Clone keeps ringing and ringing. You dig and imagine a super-treasure at great depths, but in the end it turns out that a beer cork rang at a depth of 15 cm a little to the side.
By the way, Clone Pi-W works in static mode. This allows you to more accurately localize the target. Only the latest firmware 1.2.5 implements a dynamic search mode. In my opinion, static is much more convenient.
When searching in heavily littered areas, it is enough to raise the coil above the ground (20 centimeters). And all the big stuff is yours. And not just the big ones.
The Clone has also been seen choking other metal detectors with his interference. So we have to run further away.
conclusions
Among homemade impulse generators, Clone has no equal yet. Walking for ferrous metal or through war is the very fire! For searching for coins and the like, it will also do, you just have to dig a little more. Look, for example, at what we managed to dig up: 
Apparently, this is the Libavo-Romny railway plaque from 1874.
Well, below are my very first finds by Clone (I saved them as a souvenir): 
In general, if you need a balancer with a discriminator, I recommend trying to assemble and configure a digital Quasar or an analog Terminator. Although, for example, the same “Anker” will be much longer-range, and “Spectrum” will be more informative... It’s up to you to decide!
I suggest everyone who wants to build an excellent pulse microprocessor metal detector Clone PI-W.
Distinctive features and advantages:
- simple diagram;
— ten-digit visual display, loud and adjustable sound;
— high sensitivity — up to 30 cm per coin (diameter 2.5 cm);
— there is no dependence of sensitivity on the degree of battery discharge;
— modern quasi-touch controls (buttons, not knobs).
Flaws:
- higher consumption (100-160 mA);
— there are rare parts (replacements have been selected for them);
- sensitive to interference and interference.
You can connect any coil with an inductance of 300-400 μH to it.
For example, I used a sensor ring with a diameter of 21 cm and 27 turns of 0.63 wire (you can use a pan for winding). You can use a 1.5m by 1.5m depth coil to search for large objects over long distances. Basket coils give a gain of 2-3 cm for small objects (Diagram for manufacturing http://www.metdet.ru/Sensor_K1.htm). Planar ones, like the basket, are more sensitive than a simple ring. The diagram is below. 
The device is powered by 12V. Current consumption (average) is about 120 mA, so a small battery is desirable rather than salt batteries. When the supply voltage drops to 8V, the device begins to produce a characteristic double signal every 15 seconds. It continues to work, up to about 6.5V. In this case, only the sound volume decreases, the sensitivity to metal in the range from approximately 8 to 16 V remains at the same level (thanks to the source of exemplary voltage on the TL431).
This device has virtually no settings. We take the sensor away from metal and other objects (just lift it up) and turn it on. A scale of ten LEDs lights up, then goes out, with a corresponding sound - this device adapts to the sensor and the surrounding environment, taking it for the “no metal” position. If at this moment there is any metal object near the sensor coil, the device will naturally adjust incorrectly, accepting any objects from the slipped one or less as “but there is no metal.” After this, a characteristic sound signal sounds, notifying that the device is configured. We bring it to the metal and check - the closer the metal, the further to the right the “light” on the scale moves and the higher the sound becomes. By tightening the resistor, we adjust it to maximum sensitivity (after each adjustment, be sure to move it away from the metal and press the “reset” button - the “lights” will beautifully, with sound, run towards the center of the scale). That's it, the device is configured. No fiddling around with a soldering iron, selecting elements, balancing the sensor, taking measurements with a device, an oscilloscope... We continue playing with the buttons. Two buttons regulate the sound (“more” and “less”, maximum seven), another two regulate the “barrier” - this is the inverse value of sensitivity - and not to be confused with adjusting the sense of smell! By pressing “more” or “less” (maximum - 10, minimum - 0), we set a barrier at which the device’s instinct will be maximum with satisfactory stability. However, if the barrier has to be greatly coarsened - up to the 7th and higher LEDs, then this is no longer good. You need to move away from industrial noise (forest, field) and also adjust the trimmer. A well-tuned device does not give false alarms with 3-4 LEDs.
If you also installed the sixth button - “service”, then in the device you can still adjust the voltage at which the low battery alarm is triggered (by default - 8V, while the device continues to work until the batteries are completely depleted, only every 15 seconds it gives a characteristic double sound signal) and adjust the guard interval - well, this is necessary for experimental sensors.
Now tell me, would any normal person, after playing with buttons on a modern microprocessor MD, get a sense of up to 30 cm on a coin and the pleasure of having assembled such a cool thing himself, return to “on the beats” with a sense of the ground, constant adjustment of the 19th century air control gear, fraying headphone wires, constant ringing in the ears... 
Details:
microcircuits
ADG444 or KR590KN5
TL074
ATmega8
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transistors
IRF740
78L05
KP501A or BSN304A or 2N7000 When replacing, look at the pinout!
TL431
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diodes
1N4148—6pcs
1N5819
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capacitors
2200.0 x 16V
1000.0 x 16V
220.0 x 16V
470.0 x 6.3V
2200
0.1—5pcs
0,01
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resistors
2M
100K
56K
12K—2pcs
10K—5pcs
5K1
1K—3pcs
3K—2pcs
510—10pcs
390—2pcs
100
20—2pcs
47
1k change
—————————-
Notes! It is better to set the trimming resistor not to 1k, but to 330-510 ohms or multi-turn - the adjustment will be smoother, it can be of any power, but it must be of guaranteed quality. It is impossible to use Soviet cheap “tin” ones, where the terminals are simply pressed against the conductive layer. There is also no need to shield the device, since this will not help, and on the contrary, it will do harm. A simple stranded wire should be used to connect the circuit and the sensor.
DesAlex comments from the forum of the site http://cxem.net were used to write this article
Firmware, seal, description can be downloaded
