How to convert a metal detector to a coil. Powerful DIY metal detector Pirat

1080 878 Search with a Garrett ACE 250 metal detector http://site/wp-content/uploads/2013/11/cda775a0bad3-1259x1024.jpg 01.11.2013 23.03.2018

I decided to wind the reel “on gold”. According to my estimates, it should be a small DD coil operating at double the frequency. If the native coil on the ACE 250 gives approximately 6.5 kHz, then I will try to develop 11-12 kHz on a “homemade” one.

Let's try to see at what frequency the ACE 250 is currently operating:

I did this. I wound a test probe coil. This is said loudly, because winding took... 10 seconds. Here it is:

There are only 5 turns in the test coil (I took one core from the so-called “twisted pair”). The picture also shows a connecting cable (“twisted pair” 2 m long) and a connector (“jack” in green electrical tape) - it is needed to connect the test coil to the computer sound card. The connector/jack/plug contains two limiting diodes KD103, connected back-to-back, they are designed to protect the microphone input of the sound card from interference and overvoltage (based on the results of the first application, it turned out that diodes do not need to be installed, see below).

Next, I needed to temporarily turn my computer into a virtual laboratory. I went to this site and picked up an oscilloscope and a frequency meter - they are listed first on the site, I’ll show you what they look like below.

I turned on the ACE 250 with its original 6.5x9″ coil and placed the coil on a test coil-probe, which, in turn, connected to the computer’s sound card at the microphone input (i.e., I pulled out the audio cable coming from the webcam and plugged in my own). On the screen of the virtual oscilloscope, I saw that the probe, despite its simplicity, picks up the signal emitted by ACEY. You can calculate in milliseconds exactly what frequency is generated by the ASI coil, but it’s better install virtual frequency meter and look at it.

The virtual frequency meter showed a frequency of 6700 Hz.

conclusions: the test coil-probe is working, the virtual instruments also coped with their task. Judging by the shape of the signal on the oscilloscope, the probe has sufficient sensitivity, in addition, we can conclude that protective diodes (KD103) are not needed: no signal overload is observed on the oscillogram, although the probe was located close to the emitting coil. The probe shown works either from the microphone input of the sound card or from the linear one (I have it integrated into the motherboard).

We have the devices. (I recently noticed that the virtual frequency meter shown could not work with WINDOWS7 (x64), so I advise you to use the virtual spectrum analyzer Simple Audio Spectrum Analyzer to measure frequency specan22 from this site, the program also works under WINDOWS-10). Now you can move on to the practical part, namely: wind a small coil (one half of the future DD coil) and connect it to the generator part of the ASI circuit, reaching a resonance of 12 kHz.
I wound this coil from twisted pair wires.


There are 9 turns of this cable, devoid of an outer sheath, i.e. 9 x 8 = 72 turns, respectively, soldered end-to-end. I connect the coil output through a 1.1 Ohm safety resistor to contacts 1.4 of the connector (bought for 5 UAH). In order to prevent the ASI input from being excited, I temporarily solder a 10 Ohm resistor to pins 2.3 (to which the Rx coil will be connected). Here is the diagram:

I plug in the connector and turn on the ACE 250 - it beeps twice and turns on as usual, without noticing the change. The oscilloscope showed the presence of generation of the “newly appeared” Tx coil (the signal was recorded with a test coil-probe):

And the frequency meter showed the expected frequency:

The sound card was a little capricious - it didn’t want to recognize the test probe coil as a microphone, so I had to trick it by soldering a 10 kOhm resistor and a 0.47 µF capacitor to the coil, see pictures:

I made the receiving coil with 11 x 8 = 88 turns (I found a “twisted pair” of a slightly thinner diameter, so the coils seem the same, although the Rx has 22% more turns).

Now we have both halves of the DD coil, let’s check the possibility of “combining” the coils.

I connected the Tx coil to the ACE 250 (see the previous message for the diagram for starting the Tx coil from the ACE 250 generator), and connected a multimeter to the output of the Rx coil in the alternating voltage measurement mode. By moving one coil relative to the other, you can easily get three zeros after the decimal point in alternating voltage on the receiving coil, i.e. “Mixing” the coils is done without problems. I outlined the relative position on the underlying piece of paper in order to roughly transfer the configuration to the future “bed”.

The coils turned out to be “plump” - when they are round, they have a diameter of exactly 10 cm from edge to edge, they can easily be turned into oval ones:

For the sake of beauty, I introduced a multimeter into the frame, but mixing with it does not work. However, if you remove the measuring device by 30 centimeters, then by mutual movement of the coils you can easily achieve “zeros” on the display (i.e., an imbalance of less than 0.001 V).
Of course, I will make the DD coil using oval coils: the sensitivity will be lower than on round coils, but judging even from these pictures, the area of ​​“transmission” of the ground with oval coils is 50 percent larger.
The main estimates have been made, installation will begin soon.

Don’t think that I’m using waste cheap materials, in fact, it’s the other way around - these are the best materials. The coils are made of wire in thick polyethylene insulation with a twist, which helps to reduce the interturn capacitance and, ultimately, gives a high quality factor Q, which means a well-pronounced inductive effect and a large circulating current in the generator coil Tx, high quality factor is also useful for the receiving coil Rx . The coils are “loose”, i.e. there is no mechanical tension in the wire - this gives increased thermal stability. (When heated, the polyethylene will “move”, where outward, where inward, and the total area of ​​the coil will remain unchanged, which means L = const, R will change when heated, you can’t get away from the formulas, but it will change less than with simple coils, since initially there is no mechanical tension). There are other positive effects (for example, the absence of aging of the wire insulation due to magnetostriction - it is because of this that the varnish on conventional winding wires wears out). The coils are wound without any tricks, in one minute, on an ordinary coffee can. It is also important that in the assembled structure, in addition to the wire, there will be no radio components (and remember entire boards with radio components and trimming resistors (!) in coils from “brands”). Even higher parameters can be obtained by using a twisted pair cable for computer networks, in which each core is made of stranded wire - but I did not find this on sale, and this one was just on hand.
Very modest expenses had to be incurred for the manufacture of the connecting cable (connector - 5 UAH, 4 pieces of stranded oxygen-free copper wire in fluoroplastic insulation and a silver-plated copper screen - 4 x 2 m. x 1 UAH = 8 UAH. The fifth wire is intended for connecting the static shielding of the coil with the “ground” of the ASI block - also in fluoroplastic insulation, multi-core MGTF - 2 m x 1 UAH = 2 UAH. Heat-shrinkable tubes were only meter long - another 4 UAH). As a result, the cable together with the connector cost 19 UAH.

The cable turns out to be the best of all possible (without exaggeration): each coil will be connected to the ACE 250 unit with two shielded cables, the signal will not be transmitted through the screens, the “ground” connecting the “ground” of the ACE 250 unit with the static screen of the DD-coil goes through a separate wire from pin 5 of the connector (see diagram). All wires of the connecting cable are MGTF. (The radio amateur will immediately notice that the “ground” is separated by a “spider” - thus, all interference coming from the environment in different phases and amplitudes will be mutually subtracted at point 5 of the connector).
(For reference: all spacecraft cable routing is done only MGTF wire).

So the dug graphite came in handy))). It weighs about 20 kilograms, apparently from an electrolysis bath, there are 3 holes on top for connecting the cable.

Both coils and the "bed" are shown here. The bed / slipway / substrate is fiberglass, 3 mm thick, mounting the coils on it means that there will be no work on the bottom of the future DD-coil - in fact: put the Rx, Tx coils on the bed, bring them together, fix them with epoxy with fiberglass and EVERYTHING .

In the morning I went to the garden, sawed off a piece of graphite from my “super stash” and took further steps along the coil.

I took a 10 mm drill, drilled a hole and a little dispersed it in a graphite cube, and collected the resulting powder. I wrapped the Rx spool with cotton thread to improve adhesion with PVA glue. I mixed glue with graphite powder in a ratio of 50 to 50 and coated the Rx coil with this mixture. He put the oiled coil on the place designated for it on the “bed” and left it to dry. I won’t coat the Tx coil with antistatic at all.

The Rx coil, coated yesterday with “antistatic”, has dried out. I checked the resistance of the graphite screen:

I cut the screen (you can see the red stripe from the insulating tape) and started working on the connecting cable.
After I made the connecting cable (stretched 4 shielded wires and one simple wire into a heat-shrinkable tube) and soldered everything (both coils and the shield wire, see diagram above), then connecting the connector to the ACE 250 and making sure that everything works (the frequency dropped to 11 kHz), reduced the coils to an imbalance of 1 mV and tested a DD coil with a golden earring on the table in comparison with the original coil from the ACE 250.
Bottom line. For a buttoned gold earring it became 17 cm, but it was 13, for an unbuttoned one: it became 7 cm, but it was 5. The longitudinal size of the “asa” coil, 6.5x9″, is 22.5 cm, and mine, size 5x5.8″, is only 12 cm.
It is interesting that the scale of discrimination has shifted significantly in the area of ​​ferrous metals (expanded), and starting from the USSR nickel, it has remained the same and in its place, 5 kopecks. USSR and 50 kop. Ukrainian. - they respond with “bellton”, but the nickel is Ukrainian. from stainless steel it moved one cell to the right (scale cell 2). Pinpoint works. I also noticed that for 25 kopecks in Ukrainian, 50 kopecks in Ukrainian and a nickel of the USSR, the sensitivity, in comparison with the native reel, fell, but for gold it increased, i.e. the gold “stuck out” against the background of the walker, as intended.

If you click on the left frame - this is the first step in filling the coil with epoxy with fiberglass - you can see the “ground” drain from the screen. It is a bare copper wire, 10 cm long, fused in places with a soldering iron into a graphite screen.

In the meantime, I repaired the original “Asin” coil, there were nicks, and with the remaining black putty (epoxy with SAMSUNG laser printer powder) I glued a couple of fiberglass patches to the sensor. My baby is moving towards the finish line, I’ll soon take him out for a walk and breathe some sea air, although I didn’t get it right with the epoxy - it dries slowly. Please note that the Rx and Tx coils were not actually impregnated with epoxy before the wires - this is as intended - this also saves weight, but the main thing is maintaining the highest electrical quality factor Q. We get an armored body made of epoxy resin with fiberglass, but the coils themselves are dry, The epoxy didn't reach them.

Below is a comparison of the main parameters of a new homemade “gold reel” and a small native coil from ASI (I show two screenshot specan22 programs).

The reel was more or less successful, after checking the new reel made on a nearby beach (it showed 10 cm on the primer in the sand, which made me very happy), I immediately wanted to go to the beach and have a real run with it.


The first vacationers appeared on the city beach of Kerch, so I chose a quiet corner outside it. This place was examined a couple of days earlier with two coils (6.5x9″ and NEL Tornado), however, my homemade baby suddenly began to pull out USSR pennies and Ukrainian nickels. It was clear with Ukrainian stainless steel nickels - previously, if you turned off the first square of the discrimination scale, the device saw them, but did not voice them, because it considered them ferrous metal, and the new coil operating at a frequency of 11 kHz “stretched” the left side of the metal scale (like at Ace 350 Euro) and began to squeak “color” on the stainless steel. But the USSR kopecks really became an indicator of the quality of my reel, because some jumped out from a depth of 15 cm and were clearly missed by me earlier when I was using my original and “Tornado” reels. Despite its small size, the reel showed quite a large coverage, similar to the usual one from the native Asevskaya 6.5x9″ reel (along the center line the coverage was 18 cm for a 10 kopeck coin lying on the sand surface), so I did not have to compact steps when searching.

Then I came across an openwork silver chain. I'm not sure that I could find it with the original Acev coil (I'll have to check).


Found a silver chain somewhere here.
I liked the sharp sound and sharp reaction to the target, probably characteristic of this type of coil.
The clouds began to thicken, a cold breeze blew, and in order to avoid getting caught in the downpour, I drove home.

Modest discoveries made during testing. The gold medallion was raised two days earlier using my native ASE reel, I’m showing it because I also tested my “gold reel” on it.

The frequency response of the coil is shown in comparison with other coils (practical screenshots specan22 programs of some reels for ASI in comparison with this new-made “gold reel”).

I started the article in December 2013, but I carried out the final test of the reel’s reaction to small gold only at the beginning of June 2014, together with a friend.

And you can see this coil in comparison with the factory coils for the ACE 250.

And the work of the reel on the beach in 2017 is shown.

— — — — — — — — — — — —

In March 2015, I received questions. I in no way think that there are stupid questions, but I think that there are stupid answers.

Let's start with the first question.

1. Connecting the headphone jack to which contacts, or does it matter?

Answer: doesn't matter. Solder the “jack”, plug it into the input of the computer’s sound card and the probe will begin to receive frequencies emitted by the coils of metal detectors, and the computer, turned into an analyzer, will “figure it out” and show the frequency. a slightly different diagram of the probe and details of the work in the program are given specan22.

2. How are the wires on the coils soldered? 8 in one or in colors with each other? How did you get 2 exits?

Answer:

This is the future Tx radiating coil (the second Rx coil will be made according to the same principle).

In the main text (see above) I write: “There are 9 turns of this cable, devoid of an outer sheath, i.e. 9 x 8 = 72 turns, respectively, soldered end-to-end.

Let's describe it in more detail.

First, I wound 9 turns of cable on a coffee can (the diameter is approximately the same as a liter glass jar), then I removed the coil, grabbed it in four places with white electrical tape and began to unsolder it. Those. Before I started working on turning it into a single coil of 72 turns, I had 8 separate coils of 9 turns each (or 8 “beginnings” and 8 “ends” lying opposite each other - I separated them with a conventional red line), which I had to connect it into one coil.

Let's now look at this particular picture of the coil, although it is not very good for demonstration.

We take the first “start” vein we come across - for me it’s a green vein (it dives into the coil in the upper half of all “starts” and is indicated by a red arrow), now we find this green vein among the “ends” at the bottom of the coil (i.e. our green vein made 9 turns and finally emerged among the “ends” - I also marked it with a red arrow) and we solder this “end” to the “beginning” of any other vein (if you click on the frame and look closely, you can see that the end of the green vein is soldered with the beginning of some next vein and an insulating tube with an asterisk is put on the splice). Then we find the end of the second vein and connect it to the beginning of a third vein. We will have to do such operations, on record, 7 times, i.e. make 7 splices of cable cores until there is only one “end” left, which has nowhere to solder - in the picture it is a white core with a green streak.

As a result, we get a single coil of 72 turns, the “beginning” of which is a green vein and the “end” is a white vein with a green vein.

I recently saw this picture and took it to my website - this is how you need to join the ends together to get a single coil, it is clear that there are different colors for the beginning and end of the coil.

3. There are 2 outputs from the coil. Which one should I solder on the connector? Or does it matter?

Answer: Each coil has 2 outputs, in order to test the future Tx coil for frequency generation and measure it, the coil needs to be connected to pins 1, 4 of the connector, and the connector must be plugged into the AC. The completed coil will have 4 outputs, the wiring to the connector is shown in the text. For a long time it won’t matter how exactly the ends are soldered - you’ll have already completed the coil, you’ll go to the beach to test it (and do the final mixing operation, as I recommend to the most inquisitive designers) and only then will you need to cross the ends on the connector and test the pinpointer in operation with "colored" targets. In the literature, such a finishing operation is called “phasing” the coils. I don’t need any equipment; opponents cannot do without a separate generator, oscilloscope and other instruments. A correctly phased sensor does not move the pin away from the object, but clearly shows that the target lies at the intersection of the windings.

4. Does the resistor remain on the TX coil after checking on the computer and assembly on the substrate?

Answer: No, I installed this 1.1 Ohm resistor only to estimate the frequency and not accidentally burn out the ACE 250. There are no resistors, capacitors or anything at all on the working coil, just the coils themselves.

5. How to properly check the resistance on a graphite screen? And why cut the graphite screen?

Answer:

The picture shows that I simply pressed the probes to the graphite screen at opposite points of the coil, the device showed a resistance between the probes of slightly more than 1 kOhm - this is quite normal resistance. The screen will work perfectly with a resistance of 10 kOhm. It is designed so that colossal static charges of tens of thousands of volts flow down to the “ground” of the MD, so the resistance of the shielding coating of the Rx coil is not of fundamental importance.

The annular cut is needed to prevent the formation of a closed loop (turn) in the form of a graphite screen. Despite the rather large resistance of the screen, it seems to me that such a cut needs to be made. Different authors think differently. I was getting the most out of this coil at every step, so I made a cut in the screen so that the screen would never be a shorted TURN on this coil.

6. Is it worth covering the TX coil with a graphite screen?

Answer: I left the Tx transmitting coil without a screen. I believe that the screen will at least slightly reduce the signal that will be “pumped” into the ground. Further tests showed a neutral reaction to static electricity - i.e. It is really enough to shield only the Rx receive coil.

7. What are the dimensions of the reel mounting lugs? What were they made of and what were they glued to? What is the cross on the backing and how was it calculated?

Answer: It seemed to me that the lugs should have been attached directly to the bed/substrate and not mechanically connected to the coils. I prepared the seats at the ends of the bed and first glued these 2 ears with some kind of glue, and then reinforced them with epoxy and fiberglass in the process of forming the entire coil. The ears are cut from a sheet of textolite, 0.5 cm thick. The distance between them is not standard for the ACE 250. The ears are clearly visible if you click on the corresponding frames above. The lower rod elbow assembly is made from a garden hose "T" splitter and cut to fit frictionally between the tabs. The cross on the backing means almost nothing, it was just clearly visible through the paper sheet on which I did the initial mixing of the coils and outlined their relative positions.

8. Regarding the cable: did you shrink the heat shrink with a hairdryer? What and how did you attach the cable itself to the reel? Well, the main question: HOW was the cable soldered? They just connected the 4 outputs from the coils and soldered them to the connector, and what did they attach the 5th cable to on the finished coil?

Answers: I heated the heat shrink tube over a regular electric kitchen stove.

The cable simply sank into layers of epoxy with fiberglass and was fixed on the reel.

My cable wiring is better than any factory or homemade reel. Now I will gradually explain why, although I will not describe the physics.

First, I will characterize the wire itself, which formed the basis of the connecting cable: I used 4 identical pieces of shielded MGTF wire and one piece of unshielded MGTF wire, all of them have a length of 1.5 m. This is the best existing multi-core wire (in my 24 it is very thin copper wires with a diameter of 0.08 mm, and its insulation can withstand the temperature of a soldering iron, since it is made of fluoroplastic; its shielding braid (sometimes I just write “screen”) is silver-plated copper, in short, it is an excellent “military” wire).

And secondly, let's turn to the wiring of the connecting cable, which is shown in the blue frame. It can be seen that all the shielded wires are prepared in the same way, as shown in the red frame, namely, the left end has no shield lead (only the wire itself), and the right end has a shield lead, and all such shield leads of the four wires are collected at one point, indicated by a circle. For complete clarity of perception, I’ll add that the cylinder in the red frame is the wire screen, and the signal wire itself runs inside the cylinder, as is usually indicated on most circuits in the world and, of course, the wire is isolated from the shielding braid (screen), the insulator is fluoroplastic film .

All that remains is to deal with the fifth wire, which does not have a screen (but has insulation). Its left end is shown as such a “chicken foot” - in this place the wire has contact with the graphite coating of the Rx coil - the wire there is bare and glued (more precisely, fused with a soldering iron tip) at several points to the graphite screen. No matter how tempting it may be to run this contact through any of the shields of the four wires (and many factory coils sin with this to save copper), I do this with a separate wire (and also of the highest quality).

What do we get as a result of unsoldering the connecting cable? - all ends of all coils are run along shielded wires, each with its own wire, all shielding braids of wires and the wire coming from the shielding shell of the Rx receiving coil are soldered at one point (and then connected through the 5th pin of the connector to the main “ground” on the MD board) .

The resulting homemade cable is wrapped with electrical tape along its entire length and then pulled through a heat-shrinkable tube.

Theoretically, the parameters of the connecting cable can still be improved if you use not just shielded wires, but each of them is additionally insulated along its entire length (my wires had a bare braided shield).

9. Could you tell us in more detail about mixing the coils? Interested in how to connect the tester if the plug and coils are soldered to the cable?

Answer: You need to measure (and reduce to zero) the AC voltage at the output of the Rx receiving coil and it is advisable to do this in the field. But first you need to test everything on the table in order to make a drawing of the relative position of the coils, and make a bed/substrate based on the drawing.
The pins of connector 1, 4 now go to the ASI block and the Tx coil starts generating from it. The induction voltage is induced in the receiving coil Rx and when tuning/mixing the coils should be reduced to a minimum (to all zeros on the tester). In practice, do this: do not touch pins 1, 4, and completely unsolder the Rx coil pins from the pins 2, 3 of the connector and connect the tester to these wires (solder the probes) in the AC voltage measurement mode. After obtaining “zero” voltage at the output of the Rx coil, sketch the relative position of the coils and cut out the bed/substrate based on the drawing. Then glue the Rx coil to it (it should already be in the graphite screen, and the screen is connected by wire to pin 5 of the connector), now you can go to the beach to set the “zero” as accurately as possible, taking into account the influence of the ground. (In the ACE 250 there is no ground detuning, it is set only once “to the average” at the factory, so by making a coil with pre-compensated ground influence, you will significantly improve the MD parameters set by the factory. “Ground roar”, by the way, is tens of times higher than the useful signal ).
In the field, you need to first find the abs. a place that is clear of metal debris (your original coil will help you here), then place a new coil on the sand and carry out the “mixing” as at home, on the table, i.e. connect the coil according to the method described above, “reduce” to four zeros on the device, and after “reconciling the coils,” fix their position on the substrate with glue. The tester should be kept away from the coil. To fix the final position of the coils, you should use non-plastic glue (it can “float” when using the coil in the heat), but preferably the “droplet” type, which is sold in small tubes. Upon arrival home, you can already apply the first layer of epoxy with fiberglass.

The lower leg of the rod was made from suitable polyethylene tubing. This friction elbow fits onto an aluminum rod and does not have any other fastening elements. The ends of the knee are reinforced with epoxy and fiberglass.

And one last thing. If I started making this coil now, I would give a much larger allowance for the “bed”. What’s wrong with the fact that it would be the one that would encounter all sorts of obstacles in the way of the coil’s movement? - then with the coil (the protruding edge of the bed/substrate) you could literally dig the sand.

All pictures are clickable.

Clone PI-W and, now, it came to making a mono search coil. And since I am currently experiencing some financial difficulties, I was faced with a difficult task - to make a reel myself from the cheapest materials possible.

Looking ahead, I’ll say right away that I coped with the task. As a result, I got this sensor:

By the way, the resulting ring coil is perfect not only for Clone, but also for almost any other impulse generator (Koschei, Tracker, Pirate).

I will tell you in great detail, since the devil is often in the details. Moreover, there are a dime a dozen short stories about making reels on the internet (like, take this, then cut it off, wrap it, glue it and you’re done!) But you start doing it yourself and it turns out that the most important things were mentioned in passing, and some things were completely forgotten to say ... And it turns out that everything is more complicated than it seemed at the very beginning.

This won't happen here. Ready? Go!

Idea

The easiest design for me to make on my own seemed to be this: take a disk made of sheet material ~4-6 mm thick. The diameter of this disk is determined by the diameter of the future winding (in my case it should be 21 cm).

Then we glue two disks of slightly larger diameter to this pancake on both sides to make a bobbin for winding wire. Those. such a coil greatly increased in diameter, but flattened in height.

For clarity, I’ll try to depict this in a drawing:

I hope the main idea is clear. Just three disks glued together over the entire area.

Material selection

I planned to use plexiglass as the material. It is perfectly processed and glued with dichloroethane. But, unfortunately, I couldn’t find it for free.

All sorts of collective farm materials such as plywood, cardboard, bucket lids, etc. I immediately discarded them as unsuitable. I wanted something strong, durable and preferably waterproof.

And then my gaze turned to fiberglass...

It's no secret that fiberglass (or glass mat, fiberglass) can be used to make whatever your heart desires. Even motor boats and car bumpers. The fabric is impregnated with epoxy resin, given the desired shape and left until completely cured. The result is a durable, water-resistant, easy-to-handle material. And this is exactly what we need.

So, we need to make three pancakes and ears for attaching the barbell.

Manufacturing of individual parts

Pancakes No. 1 and No. 2

Calculations showed that to obtain a sheet 5.5 mm thick, you need to take 18 layers of fiberglass. To reduce epoxy consumption, it is better to pre-cut the fiberglass into circles of the required diameter.

For a disk with a diameter of 21 cm, 100 ml of epoxy resin was just enough.

Each layer must be thoroughly coated, and then the entire stack must be placed under the press. The greater the pressure, the better - the excess resin will be squeezed out, the mass of the final product will become a little less, and the strength will be a little greater. I loaded about a hundred kilograms on top and left it until the morning. The next day I ended up with this pancake:

This is the most massive part of the future coil. He weighs - be healthy!

Then I’ll tell you how using this spare part it will be possible to significantly reduce the weight of the finished sensor.

A disk with a diameter of 23 cm and a thickness of 1.5 mm was made in exactly the same way. Its weight is 89 g.

Pancake #3

There was no need to glue the third disk. I had at my disposal a sheet of fiberglass of suitable size and thickness. It was a printed circuit board from some ancient device:

Unfortunately, the board had metallized holes, so I had to spend some time drilling them.

I decided that this would be the top disk, so I made a hole in it for the cable entry.

Ears for barbell

There was just enough leftover textolite for the ears to attach the sensor housing to the rod. I cut out two pieces for each ear (to make it durable!)

You should immediately drill holes in your ears for the plastic bolt, as it will be very inconvenient to do this later.

By the way, this is a mounting bolt for the toilet seat.

So, all the components of our coil are ready. All that remains is to glue it all together into one big sandwich. And don't forget to run the cable inside.

Assembly into one piece

First, the upper disk made of holey fiberglass was glued to the middle pancake made of 18 layers of fiberglass. This took literally a few milliliters of epoxy - this was enough to coat both surfaces to be glued over the entire area.

Ear mounting

I cut the grooves using a jigsaw. Naturally, I overdid it a little in one place:

To make the ears fit well, I made a small bevel on the edges of the cuts:

Now we had to decide which option is better? Ears can be placed in different ways...

Industrially produced reels are often made according to the right-hand version, but I prefer the left-handed one. In general, I often make leftist decisions...

In theory, the right method is better balanced, because The rod mount is closer to the center of gravity. But it is far from a fact that after lightening the coil, its center of gravity will not shift in one direction or another.

The left mounting method looks more visually pleasing (IMHO), and in this case the total length of the metal detector when folded will be a couple of centimeters shorter. For someone who plans to carry the device in a backpack, this may be important.

In general, I made my choice and started gluing. He generously smeared it with bauxite, securely fixed it in the desired position and left it to harden:

After hardening, I sanded off everything sticking out from the back side with sandpaper:

Cable entry

Then, using a round file, I prepared grooves for the conductors, inserted the connecting cable through the hole and glued it tightly:

To prevent strong kinks, the cable at the entry point needed to be somehow reinforced. For these purposes, I used this little rubber thing that I got from God knows where:

In short, I cut some fiberglass:

and mixed it thoroughly with bauxite with the addition of ballpoint pen paste. The result was a viscous substance similar to wet hair. With this composition you can cover any cracks without problems:

Pieces of fiberglass give the putty the necessary viscosity, and after hardening, provide increased strength to the adhesive joint.

So that the mixture is properly compacted, and the resin saturates the turns of the wire, I wrap it all with electrical tape tightly:

The electrical tape must be green or, at worst, blue.

After everything froze thoroughly, I wondered how strong the structure turned out to be. It turned out that the reel could easily support my weight (about 80 kg).

In fact, we don’t need such a heavy-duty reel; its weight is much more important. Too much mass of the sensor will definitely cause shoulder pain, especially if you plan to conduct a long search.

Facilitating

To reduce the weight of the coil, it was decided to cut out some sections of the structure:

This manipulation allowed me to lose 168 grams of excess weight. At the same time, the strength of the sensor has practically not decreased, as can be seen in this video:

Now, with hindsight, I understand how the coil could have been made a little lighter. To do this, it was necessary to make large holes in the middle pancake in advance (before gluing everything together). Something like this:

The voids inside the structure would have almost no effect on the strength, but would reduce the total mass by another 20-30 grams. Now, of course, it’s too late to rush around, but I’ll keep it in mind for the future.

Another way to simplify the design of the sensor is to reduce the width of the outer ring (where the wire turns are laid) by 6-7 millimeters. Of course, this can be done now, but there is no such need yet.

Finish painting

I found an excellent paint for fiberglass and fiberglass products - epoxy resin with the addition of a dye of the desired color. Since the entire structure of my sensor is made on the basis of bauxite, the resin-based paint will have excellent adhesion and will fit like original.

I used alkyd enamel PF-115 as a black dye, adding it until the required hiding power was obtained.

As practice has shown, a layer of such paint holds very firmly, and looks as if the product was dipped in liquid plastic:

In this case, the color can be any depending on the enamel used.

The final weight of the search coil together with the cable after painting is 407 g

The cable separately weighs ~80 grams.

Examination

After our homemade metal detector coil was completely ready, we had to check it for internal breaks. The easiest way to check is to use a tester to measure the winding resistance, which normally should be very low (maximum 2.5 Ohms).

In my case, the resistance of the coil together with two meters of connecting cable turned out to be around 0.9 Ohm.

Unfortunately, this simple method will not be able to detect an interturn short circuit, so you have to rely on your accuracy when winding. A short circuit, if there is one, will immediately manifest itself after starting the circuit - the metal detector will consume increased current and have extremely low sensitivity.

Conclusion

So, I think that the task was completed successfully: I managed to make a very durable, waterproof and not too heavy reel from the most waste materials. List of expenses:

• Fiberglass sheet 27 x 25 cm - free;
• Sheet of fiberglass, 2 x 0.7 m - free;
• Epoxy resin, 200 g - 120 rubles;
• Enamel PF-115, black, 0.4 kg - 72 RUR;
• Winding wire PETV-2 0.71 mm, 100 g - 250 rub;
• Connecting cable PVS 2x1.5 (2 meters) - 46 rubles;
• Cable entry is free.

Now I am faced with the task of making exactly the same rogue barbell. But that's already it.

In this article I will show you how to wind a metal detector coil yourself. For example, let's take this metal detector. The coil in it must wind with a certain precision, but how can a simple person who does not understand anything about this do this? To help us, the greatest minds have created an interesting program (Coil32) for those who do not have the program, download it at the end of the article.

And so, on the diagram of the metal detector it is written that the coil should have an inductance of 2290mkH (microhenry). It even says which wire and what diameter to use. But what if I want a larger or smaller diameter coil or the wire is of the wrong thickness??

Then we turn on our program (Coil32)

In the open program, click (PLUGINS) then (Multi loop) this is where the coils we need will be.

The following window will pop up:

Now everything is simple, everything is signed in the windows, what is the diameter of the wire, on which frame to wind it and, most importantly, the window with the inductance. We insert our parameters into the windows: we need an inductance of 2290 mkH, the wire I had was 0.4, and I want to wind the coil on a mandrel of 11 cm (111 mm). Once all the values ​​are set, click the calculate button and the information we need will appear in the window on the right

So now you can independently calculate and wind for yourself a coil of any diameter that suits you best.

A metal detector is used to search for objects with certain electromagnetic characteristics, namely metals. In professional activities, this device is used by inspection services, archaeologists, geologists and professional treasure hunters. In addition, a metal detecting device is often used in construction, for example, to detect reinforcement, wiring and profiles in walls.

Professional equipment has a very significant drawback - very high cost, which varies depending on the detection depth, interface type and metal recognition function.

The need for a metal detector also arises among ordinary people. Often these are those who decided to try themselves as a treasure hunter. Unlike professionals, who are provided with equipment or provided by an organization, novice amateurs do not always want to purchase an expensive device. This is due to the fact that such a purchase will not be used for professional use and is unlikely to sell itself.

For an amateur who is just starting to work with these devices, a self-assembled metal detector may be suitable. Homemade devices are relatively easy to make; there are many detailed instructions on the Internet. Anyone can assemble a metal detector with their own hands if they have the desire and the required components for assembly; and their assembly can be done even by those who have little knowledge of radio installation. Homemade devices can have both relatively weak characteristics and not be inferior to expensive branded products. Before assembling the device, you need to know its structure and types.

In order to understand what kind of metal detector you need to assemble, you need to decide on the list of work to be carried out, as well as which metals will be the target of the search. Externally similar devices for gold prospecting and construction work differ in design and technical characteristics. The following general search device parameters exist:

Search discrimination can occur in three ways:

• Spatial, which indicates the location of the found object in the electromagnetic field zone, as well as its depth.
• Geometric, showing the size and shape of the found object.
• Qualitative, determining what properties the found material has.

Operating frequency range

Metal detectors operate in a certain frequency range:

• Ultra-low frequency, up to several hundred Hz. Powerful metal detectors that require high voltage, impressive dimensions, and computer signal decoding make these devices unsuitable for amateur use.
• Low frequency, up to several kHz. Quite simple circuits and design, good noise immunity and insensitive to the ground. They have penetration, depending on the supplied voltage, up to 5 meters. They react most acutely to ferrous metals and reinforced concrete structures.
• High frequency, up to tens of kHz. They have more complex circuits, but are less demanding on coils. Relative noise immunity and detection depth of up to one and a half meters. They work very poorly in wet and mineral soils.
• Radio frequency, used to search for non-ferrous metals, such as gold. The detection depth is less than a meter in dry soils, which is very critical to the design and quality of the coils used.

Classification by search type

There are many search methods, but many of them are applicable only in professional activities and are not feasible in home-made devices. More applicable at home include:

• Without receiver (parametric).
• On the beats.
• Accumulation phase.
• Transceiver.

Parametric metal detector

These devices do not have a receiving coil or receiver, and detection of an object occurs due to its influence on the generator coil; changes in its parameters, such as the frequency and amplitude of the generated oscillations, are recorded in various possible ways. They are quite easy to assemble and have relatively high noise immunity. They are often used as magnetic detectors due to their low sensitivity.

Transceiver device

The device consists of transmitting and receiving coils, an EM vibration transmitter, and can also be equipped with a discriminator that will detect only certain metals.

The coil creates an electromagnetic field; If there are materials in its zone that have an excellent electromagnetic field, the receiver picks them up and gives an audible signal about detection. If an object is detected that does not have electrically conductive properties, but has ferromagnetic characteristics, then it will distort the electromagnetic field due to shielding.

These devices achieve the best performance in their operating frequency range, but their independent production requires a high-quality system of coils, which must be ideally positioned relative to each other.

A transmit-receive metal detector with one coil is called inductive. Its creation is simpler due to the fact that there is no need to select coils, but it is necessary to separate the secondary weak signal relative to the emitted primary one.

Phase sensitive device

These metal detectors are presented as pulse detectors with one coil or devices with two coils, each of which is influenced by a separate generator.

In the case of a pulsed phase-sensitive metal detector, the emitted pulses when colliding with the desired metal are delayed, and during an increasing phase shift, the discriminator is triggered and sends a signal. The closer the device is to the object, the more frequent the signals become. The popular homemade metal detector “Pirate” with metal discrimination works on this principle.

The principle of operation of a device with two coils is based on the fact that the electromagnetic fields of the two coils are synchronized and work in time; and when the field is distorted, desynchronization occurs and the discriminator begins to emit signals. This type of device is easier to manufacture than a single coil device, but the depth of possible detection is reduced.

Based on the harmonic principle

This device contains two coils: working and supporting. The reference oscillating coil is small, protected from extraneous interference, or stabilized by a resonator. The frequency of the working search coil depends on the presence of the desired objects in the radiation zone.

Before starting the search, they are tuned to match the frequencies and, as a result, a single-tone sound. A change in tone means that metal objects enter the electromagnetic field zone, and the size and depth of the object are determined from the level of change.

Metal detector coils

The main requirement for the quality of homemade devices is competent manufacturing of the coil and its reliable shielding.

When creating a device, the device circuit is adjusted to the coil until optimal values ​​are obtained. If the metal detector works with an incorrectly selected coil, it will have very poor performance. In this regard, when choosing an option for manufacturing, you need to carefully look at the description of the coil. If it is not complete enough, it is better to make another device.

The size of the coil is also important. Wide ones penetrate the ground deeper, but if large objects are detected, their signal will block potentially necessary small objects. Also, to increase detection depth, you need to have a wider coil.

It is common to use coils with a diameter of up to 90 mm when searching for profiles and fittings, up to 150 mm for small items, and diameters up to 600 mm for searching large-sized iron.

It would be ideal if the metal detector is designed to work with coils of different sizes.

Noise immunity

The coils catch various types of pickups well, and There are 2 common ways to increase noise immunity:

Baskets

These coils are available in flat and volumetric versions; they are stable, less sensitive to interference, and have high discrimination. For a beginner, it is easier to wind a flat reel.

Computer disks, plates and saucers can serve as its mandrel, and you can calculate the winding yourself. It is impossible to wind a volumetric version without calculations using computer programs.

Simple DIY metal detector

This version of a homemade metal detector consists of a signal decoder, a signaling device and a coil. To assemble it you will need:

• PIC12F675 chip or its analogs and programmer for firmware.
• Resonator at 20 MHz.
• Voltage stabilizer AMS1117.
• 15 pF and 100 nF ceramic capacitors, 10 µF electrolytic and 100 nF film capacitors.
• Resistors 470 Ohm, 10 kOhm.
• Sound emitter.

Soldering is carried out using a hinged or mounting method; a voltage of 9-12 V is required to power the circuit. The stabilizer controls the output 3.3 V.

The coil is wound on a 10 cm mandrel with a wire with a cross section of 0.3 mm. It is required to tightly wind 90 turns, and wrap the resulting structure tightly with tape and place it in a Faraday shield.

The result is a fairly powerful metal detector for deep searching, which can be set to discriminate: when detecting ferrous and non-ferrous metals, a sound of different frequencies will be emitted.

Professional metal detectors are often quite expensive and beyond the reach of amateurs. There are diagrams of metal detectors on the Internet; some of them can be assembled with your own hands, without special radio installation skills or professional equipment. If desired, you can even assemble an underwater metal detector that will work equally both on land and in water.

In order for a self-assembled device to ideally meet all possible requirements, it is necessary to understand the design of the metal detector and decide on the type of search work that will be carried out with the device after its assembly. This will help you choose exactly the version of the metal detector that a novice treasure hunter needs.

When making a metal detector, you can make sure that the main element of this design is the coil. Typically, this part consists of copper wire. With the help of special pulses emanating from the coil, metal objects can be identified in soil of varying densities.

The metal detector coil is a fairly simple element, so winding it yourself will not be difficult. As a basis for work, you can take the “Malysh FM2” metal detector. The coil of this device must be wound quite accurately. Experienced people will be able to do this kind of work themselves. For a beginner, it is better to use specialized software. To do this, you need to download the Coil32 program file located at the end of the article.

The inductance of a metal detector coil is measured in microhenry units. According to the detector circuit, this value should be 2290 mkH. There are also instructions for selecting the thickness of the wire depending on the diameter of the element.

If only a wire with a certain cross-section is available, but a larger (or smaller) coil size is needed, then a special program comes to the rescue. When you launch Coil32, a window should appear as shown in the following figure:

In the window of the running program, you need to press the “PLUGINS” button, in the menu that opens, select the “Multi loop” option. This subsection should display the coils required for operation. If everything is done sequentially, a window should appear on the computer screen:

This window details what wire diameter is suitable for a particular frame. Here you can also find the values ​​of the Inductance parameter.

Before starting work, you need to set the necessary parameters in the cells:

• inductance – 2290 mkH;
• wire thickness – 0.4 mm;
• reel frame – 111 mm.

After entering these parameters in the program window, you will need to click the corresponding button for calculations. The necessary information will appear on the right and will look like the following figure:

Independently calculating the parameters for winding a metal detector coil using the appropriate software will seem quite easy. The program itself will determine the optimal wire cross-section for each diameter and inductance values. The Coil32 program is available for download in an archive file.

Attached files: ARCHIVE

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