How can i make a metal detector

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	Re: How can i make a metal detector « Reply #20 on: November 02, 2009, 07:28:49 pm »

Hi Xavier,
I'm glad you found your fault, I thought it would be something simple as the circuit had been working previously.

Best regards Mike.

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	Re: How can i make a metal detector « Reply #21 on: November 03, 2009, 05:23:47 am »

Hi Mike

Thanks .Yes it was a simple fault but I just could not put my hand on it .I am busy molding the casing so Ill be posting some pics soon .I think by tomorrow I should have some thing to show. Got to go

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	Re: How can i make a metal detector « Reply #22 on: November 04, 2009, 09:16:24 pm »

	Quote:	Posted by xavier
Hi Goldigger We were struck by lightning on the power line and have been with out power for about 18H00 reason why I have not responded to your post till now. You have an interesting project and will require about 190m of wire per coil if you use 20 turns what will the gage of the wire be? And what kind of support are you planning to make also what distance will you require between the two coils? Ok last question for now are you going to encapsulate these coils? Sorry for all the questions but what the hek I?m curious :)Thanks for all the info it's been very help full Best regards Xavier PS I will get some fiber and resin to make the casing for the detector tomorrow will post some pics soon. Ho yes I'm from Belgium but I live in South Africa and parts can be a bit of a problem

OK? Had to reread my post, ha!

The coils will be adjacent, at right angles, that is, the edge of one would be AT the plain of the other. Otherwise, I would have two coils in the same plane, with one, smaller, for noise cancelling... only one main coil makes it lighter and less cumbersome, but it has to turn at least 180 degrees.

NO encapsulation (open,) and I figure to use multi-strand speaker wire, as a Litz-like wire, the winding will either be planar, or cylindrical - around the perimeter, which is easier to calculate. the wire has to be spaced at least 1/4 inch or 6.5mm, minimum. I would like 1cm/turn but 20 turns is 20 cm while 6.5mm is only 13cm. The windings would be on notched dowels (a sawn slot for each wire.) I have been collecting PDFs that have various ideas for feeding the resulting sigs to a receiver, but I think a series capacitor (tuned to desired resonance,) would work best, into coax as a series tuned circuit has very low impedance, making for less loss in the coax. Ideally I would have UV proof insulation and a Faraday shield.... but....

20 turns, 5 inches long, 10 feet diameter = 2440.67 uHy, aprox and 40t X 10 inch = 9000.0uHy..... 20 t on each side and have a 20t tap, it would cover a wide range of frequency with 2440 and 9000 uHy! If I used 15.36 kHz (30.72 kHz crystal,) I should be able to blow all the TVs for 2 miles, as that is the NTSC horizontal scan frequency, here. Grin

By spacing the windings, both distributed capacitance and proximity losses are reduced. There are amazing things to hear, on VLF, and I want to experiment with the VMSK. Because, IF I can make it work at 200 to 400 km, I will have a way to *ET call home,* from out in the bush! Kiss

Hey! Look at all the high power car sound systems there are, out there, most of which work to 150 kHz! Common, around here, are 200 watt units, that should work over 400 km. You want to turn off your VLF detector, though, it might blow up, in close proximity to 200 watts of VLF computer signal. Shocked

By using both channels, push-pull, and running 100 watts per channel, it should be 200 watts without running peak power (only 50% per channel.)

One of my fav stores has 200 ft rolls (of double wire) speaker wire... or I can use some old surplus phone wire, but it is only single strand steel with a copper skin. (Bad stuff.) All I need is 2 rolls of the speaker wire and split it. That gives me 243.8 m. Shocked

I will probably start a topic about distributed capacitance, in building your own detector coils, but not tonight... ! Grin

goldigger

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	Re: How can i make a metal detector « Reply #23 on: November 05, 2009, 03:00:00 am »

Hi Goldigger

Sounds like a very interesting project there is only one thing that dose bother me if you have it cylindrical you will end up with a wind tunnel well lets say it will be like a kite even if you have spacing of X mm you still have to consider the diameter of the wire x 20 T that will result in the area that will be resistant to the wind not to mention the snow and ice you guys have out there in your parts of the woods (we only have wind to concider)will result in Kg on that wire and it's not the kind of thing that you will be able to put in the kitchen at night after use Grin

come to think of it you could have it on wheels then wheel it in and out of your garage but then you will require height won't you I seem to remember having seen some thing like that but it was like a spider?s web and a other that was like a box that was in the day?s when CB radio was big in SA .Tell me how did you work out the amount of uH your coil would be? (What is the formula used )I am working on what I call 3D detection for VLF using a series of coil?s and analyzing the resulting sig from each coil then using that information to paint a picture, get the idea but I must first complete this project or I?ll never complete any thing I just cant help my self from doing some research.

Best regards
Xavier

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	Re: How can i make a metal detector « Reply #24 on: November 05, 2009, 09:20:34 pm »

	Quote:	Posted by xavier
Hi Goldigger Sounds like a very interesting project there is only one thing that dose bother me if you have it cylindrical you will end up with a wind tunnel well lets say it will be like a kite even if you have spacing of X mm you still have to consider the diameter of the wire x 20 T that will result in the area that will be resistant to the wind not to mention the snow and ice you guys have out there in your parts of the woods (we only have wind to concider)will result in Kg on that wire and it's not the kind of thing that you will be able to put in the kitchen at night after use come to think of it you could have it on wheels then wheel it in and out of your garage but then you will require height won't you I seem to remember having seen some thing like that but it was like a spider?s web and a other that was like a box that was in the day?s when CB radio was big in SA .Tell me how did you work out the amount of uH your coil would be? (What is the formula used )I am working on what I call 3D detection for VLF using a series of coil?s and analyzing the resulting sig from each coil then using that information to paint a picture, get the idea but I must first complete this project or I?ll never complete any thing I just cant help my self from doing some research. Best regards Xavier

Yes, unfortunately, it would be something like a big (box) kite, but IF I can set it up, to raise and lower, half the problem may be solved. I hope! I need a small gin-pole, for emergency lowering, when we get wind warnings... sometimes we can get up to 120km Chinook winds (adiabatic winds - flowing from Pacific lows to Arctic highs.)

The inductance formula is the same as for small coils:

(Turns squared) X (radius squared) / (9 X Radius) + 10 X Length

This one only works in inches

So if (to make it even) it is 12 inches (all in inches not cm!)long, 24 turns, radius of 60 inches:

R squared = 3600

9R = 540

L X 10 = 120

T = 24 turns

3600 X 576 / 540 + 120

Inductance = 3141.8181 uHys

It would be easier if I could print superscript but you should be able to decipher the above mish-mash!

When you have a planar coil, you have to average the OD and the ID to find average radius, otherwise the formula is the same. Planar coils may have a broader null point b(90 degrees to the plane.)

During CB days, I had a 216.5 foot long-wire Vee antenna (11.97 X half-wave, about 12bB gain?) that was like a beam antenna, except it did not rotate, I also used TV twin lead (300 ohm) with a balun, to feed it. When it snowed, it was OK, but when the snow melted it screwed the match, because of the twin lead. So I expect much the same to happen, with big coils. Cold, frozen, snow is a good insulator, but semi-melt it and you have weird effects. The twin lead has far less loss than co-ax.

I never talked to S.Africa, but did talk to Austria once, Hawaii twice, often heard New Zealand and Vladivostok! All on single-sideband. It was fun! Daytime skip was N/S so I heard a lot of Spanish! Cambio! Cambio!

My long wire was oriented so I could mainly talk to Alaska and southern Manitoba and Saskatchewan, in Canada.... it worked super, for that.

I never tried a one wire loop, but that should have worked, OK, as well. Generally loops work best at low frequencies and that is why detectors use them, of course.

Let me know if you want to see a schematic for generating VMSK and for receiving same.

goldigger

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	Re: How can i make a metal detector « Reply #25 on: November 06, 2009, 10:50:00 am »

Hi goldigger

Thanks for the formulae I?m sure that I will come right with it. I was wondering if you could not place your antenna in your roof mined you, you will not have very much height but for the winter months it could work I was told that the thin air and the position of the stars and planets had quite an effect on the transmission and that it was the reason why some times you could talk to people in very far places. As for the schematics I would be very interested as it could make a great future project .I am almost finished with my metal detector and very eager to take it out for a test on the beach which is 400m down my alley and just waiting to be explored by me as there are no detectorist in my sector come to think of it there aren?t many around in SA DAM Shocked

that?s nice when you think a bout it Grin

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	Re: How can i make a metal detector « Reply #26 on: November 09, 2009, 06:42:33 pm »

	Quote:	Posted by xavier
Hi goldigger Thanks for the formulae I?m sure that I will come right with it. I was wondering if you could not place your antenna in your roof mined you, you will not have very much height but for the winter months it could work I was told that the thin air and the position of the stars and planets had quite an effect on the transmission and that it was the reason why some times you could talk to people in very far places. As for the schematics I would be very interested as it could make a great future project .I am almost finished with my metal detector and very eager to take it out for a test on the beach which is 400m down my alley and just waiting to be explored by me as there are no detectorist in my sector come to think of it there aren?t many around in SA DAM that?s nice when you think a bout it Best regards Xavier

ROOF?? Heavens, no! The noise (wind) would be terrible! Actually, I do not think height is a concern... I figured 10 feet would be manageable, and I think I will make a small set, first, to see what kind of problems may occur. Besides, on the roof would block satellite dishes!! Shocked

When I was a kid, I asked about the reasons for (Rayleigh sp?) fading and why reception was better, during daytime and why distance increased, at night. I got some answers from my expert uncle... but found real answers later in life! Like the E and F ionosphere layers. It is much more pronounced at VLF frequencies and the ionosphere has very little effect. It is more like ducting. Kiss

I will dig up my schematics and write an explanation, to go with it, then I can send it to you by a PM, rather than post it. Even though there may be others who might be interested, it is badly off topic. This VMSK, which I think is a poor name, can be used at any frequency... for instance, my drawings use 3.5795 mHz, because that is the NTSC TV colour burst crystal and I have a dozen of them, but I could as easily used 32.768 kHz, a RTC crystal.

So, you have the detector field wide open to you... sounds great. You never know what you will find, in that case! Coins to nuggets!

How is your Afrikaans?

goldigger

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	Re: How can i make a metal detector « Reply #27 on: November 10, 2009, 05:23:39 am »

Hi Goldigger

My Afrikaans is great I speak it on a daily basis with the neighbors got to keep the lingo up to date Grin

but how do you know about Afrikaans? (not a common language)got my VLF metal detector completed and am now doing some test?s but I?m not happy with it yet I think that I must re-design the coil the electronics seem fine to me but it is still on Vero board I must still make a proper PCB for it and to get all the thing?s that I need to make it is the big problem for me even thought it?s been a while since I have made one something like twenty years ago Shocked

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Xavier

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	Re: How can i make a metal detector « Reply #28 on: November 10, 2009, 11:48:46 pm »

	Quote:	Posted by xavier
Hi Goldigger My Afrikaans is great I speak it on a daily basis with the neighbors got to keep the lingo up to date but how do you know about Afrikaans? (not a common language)got my VLF metal detector completed and am now doing some test?s but I?m not happy with it yet I think that I must re-design the coil the electronics seem fine to me but it is still on Vero board I must still make a proper PCB for it and to get all the thing?s that I need to make it is the big problem for me even thought it?s been a while since I have made one something like twenty years ago Best regards Xavier

Afrikaans is anders kant bo English-Hollands! More or less. I read a lot, and have read a lot of Wilbur Smith books on S.A.... they usually give a good picture of the setting of each story, plus a lot of folklore. (I could not finish the last book, though.) I have a bunch of Dutch ancestors (Niew Amsterdam.) Even my surname, which my father,s family thought was French, turns out to possibly be New Amsterdam in origin. Shocking! It explains a lot, in the family tree, also why my great grandma married my great grandpa, whom she divorced, later. They must have both been Dutch Reformed Church members. I have Voorhees, Hollenbecks, van Shykes, and more, in the tree.

I got interested in Afrikaans and saw a *teach yourself* book, in Read,s books, so bought it along with a book on Hindi! There are tons of words in common, between Celtic/English and Hindi! They never came from the British Raj, either. I can not make a lot of sense of the Afrikaans book, I need to hear it and speak it. I have a long-time friend, here, who emigrated from Holland, about 1948. For years I have been telling him he only THINKS he is speaking English.... it is really half Dutch. He found this out when he started emailing relatives in what he thought was Dutch!! I like languages, I figure I can understand 16 dialects of English and even know some Pitsin, from the S.Pacific. Grin

We have quite a large number of SA doctors, here, names like Botha, Vorster, etc. My current doc is Vorster.

Your picture of your locator puts me in mind of a Jeep, I do NOT know why. Yellow? Maybe. Shocked

I will, probably, get into making stuff, later, this winter.... I want a 2 box and a BFO (good, old-fashioned BFO.) I have a bunch of ICs, SE612 (or was it SA??) that have doubly balanced mixers AND an on board oscillator, should be super for BFO. I have already drawn up some ideas, though mostly VLF or Ham receivers, it is only a short throw of the stone from receiver to detector. These ICs are small 8 pin DIPs.

A thought: My experience has shown me a circuit with minimum capacitance, is most sensitive to capacitive changes, also a circuit with minimum inductance has more sensitivity to inductive changes.... so what I am saying if your detector works, but not great, try a turn less, and add capacitance to bring it back to frequency, etc. If you can experiment, you can carry on until no more turns can come off and have it work. Of course, if it is PI, the theory is different. I would like to build an experimental PI with an LM386, as the coil driver.

goldigger

Can you get perf-board, there? It is a pretty good alternative to PC board and you can follow the bread board design, closer.

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	Re: How can i make a metal detector « Reply #29 on: November 11, 2009, 03:35:05 am »

Hi Goldigger

There is a post by Cornelius he has posted a BFO with discriminator I think that it should make a good project did you see it? ::)The thing with BFO is the stability they just seem so unstable I have build two of them and had no fun with them at all. Angry

Ground penetration was about 10cm on large coins you could get 15cm now with this VLF on the bench test that I did I could detect a 3gr gold ring at 22cm a large coin(5 Swiss Frank)at 28cm now the funny thing is that the coin is far larger than the ring and yet the distance dose not change very much however the window frame?s are of aluminium and I detect them at 110cm and my solder sucker (aluminium) 40cm I wanted to shield the coils but by doing so it did not work at more than 5cm for the large coin. The coil is encapsulated so I will make a new one the thing is that I use old copper wire that I got out of a TV set from the deflector coils I think that?s what they are called. As far as I am concerned the electronics are OK it? just a transmitter and a receiver the rest is up to the coils (that?s the hard part) how ever I may be totally wrong about that. The way that I see it you could use any transmitter with any frequency from 1Khz to 30Khz as long as your receiver is tuned to the same frequency. I would like to try experimenting with LF from 30Khz and see what I get but I think that the problem is like you mentioned with the capacitance and induction I don?t have all the necessary measuring equipment and to top it all the coils are jumbled wound so two coils are never the same and I should use an LC meter to see how many uH?s I got on the coil and go from there any how that?s not the end of the word I may have to make a few coils to get it right that?s all. I have been thinking of making flat coils it should be much better and much easier to remove a turn or two but the wire is very thin 0.3mm that?s the problem .With thick wire making flat coils is much easier as the coils have less tendency of over lapping one another so now you are going to say use thicker wire yes but the coils will be bigger and heavier. As far as parts are concerned we can get mostly everything in SA but I live in a remote area with the closest big town 80km from me and often they have to bring the parts in from Johannesburg and that 1200km from me get my problem? By the way here is Q for you if I have a frequency of 8Khz I will have a wave length of 37.478m now 8.000Khz has a wave length 37.48m if I use a wire 37.48m long and make a coil out of it what will the result be if I use it on my 8Khz receiver????See that?s how I did the coil for the metal detector and it could be that I did it all wrong it did make sense to me at the time but now I am having doubts about it. Idea

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Xavier

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