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Simple metal detector(for a noob that doesn't know anything about electronics)?

Hello. I would like to start by saying that i don't have a clue how electronics work. I don't know how to connect parts, i don't know what ohm value to search etc.. Now, i realyl wanted all y life a metal detector, but im a mechanics, so why dont I build my own? 

BECAUSE I DON'T KNOW HOW! thats why..

Some say i need to use some kind of thng called beat frequency oscillator, and I found one on ebay but I don't know if i can use it in a metal detector.. Can you tell me so?

http://www.ebay.com/itm/455-kHz-BFO-Kit-Great-for-QRP-/261497948756?pt=LH_DefaultDomain_0&hash=item3ce27e0a54

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Big magnet on a stick :-)

You can make one out of a calculator and a radio. No electronics skills required

https://www.instructables.com/id/HomeMade-Metal-Det...

but if you are looking for one that waorks well and for more "professional" use, just buy one. You can get some cheap ones for less than 50€

framistan3 years ago

If you go to radioshack , get one of those 200 in one kits... or any one of those such as the 160 in one... or the 300 in one .... whatever. They are also on ebay for about 30 bucks and up. That's how I got started in electronics back in 1965. My father got me a 50 in one electronics project kit. They also should have the metal detector circuit you want to build... mine did. here is a picture of the primitive 50 in one kit that I used.

RS_50n1_i.jpg
dsirotic (author)  framistan3 years ago

Sorry and no offense but i have no interest in learning electronics. I just need a tutorial on how to build one, and an exact parts list i can find on ebay.. I don't really like electricity and electronics..

Hey, nice one Fram!

Just for reminding me of it, I am going to up some pictures of my old N-in-1 project kit, including a picture of the page of the manual for project 30, the metal detector project. I had to blow the dust of it first.

In my case, N=160. The inside cover of the manual says it is copyrighted 1982, and that sounds about right. I think it was sometime in the 1980s when I first started playing with this toy, and probably sometime in the 1990s when I stopped playing with it.

The circuit described in this picture is just an oscillator. I think the other oscillator and mixer-detector were provided by a local radio station and an AM radio respectively.

I'm trying to remember: I think I actually built this project, but I couldn't get it to work very well.

radioshack-160-in-1-project-kit.jpgradioshack-160-in-1--project-30-metal-detector.jpg

I have searched online, just now, for a simple, clear, explaination of how the so-called BFO (beat frequency oscillator) metal works,

http://electronics.howstuffworks.com/gadgets/other...

but I have not found anything as simple or clear I as would like.

So I have attached a circuit diagram I copied out of a book, the reference, ie. which book, what page, is in a little box pasted into the image, near the bottom edge. The book, a sort of recipe-book of circuits, called this circuit, "micropower metal detector", and I might use the same words to refer to it also. The picture is here:

https://www.instructables.com/files/orig/FHO/9A5Z/G...

Also I have attached a hand-drawn block diagram of the same circuit, for the purpose of explaining how this thing actually works. Here:

https://www.instructables.com/files/orig/FLP/MABD/H...

Two of the blocks are oscillators. In fact they're almost exactly the same oscillator, and they run at almost the same frequency. The frequency of each is determined by its resonant whatchacallit, L*C, and the formula for this is: f=((2*pi)^-1)*((L*C)^-0.5) Substituting in the actual values for L and C, gives:

C=100e-12;L=10e-3;f=((2*pi)^-1)*((L*C)^-0.5)
f = 1.5915e+05 ~= 160 000
so f is approximately 160 000 Hz, or 160 KHz.

What makes these oscillators different is one has its inductor (L2) in the form of a big wide circular coil (i.e a circle about 15 cm in diammeter). For a big wide coil like this, the value of its inductance actually changes when metal objects are brought into the space near the coil. The change in the inductance of L2 causes a change in the frequency f2 of the oscillator it is a part of. In my block diagram, I have called this oscillator a "perturbable" oscillator, since its frequency is perturbed, changed, by the presence of nearby metal objects.

In contrast, the inductor L1, in the other oscillator, is in a very small space. The magnetic fields surrounding L1 are likewise also confined to that very small space. The intent is to make things so the inductance of L1 is not easily influenced by its surroundings, and it is intended that the frequency of this oscillator be constant. In the block diagram I call this a "stable" oscillator, and I imagine its frequency f1 is constant.

The next block is a mixer. The purpose of the mixer is to "mix" frequencies f1 and f2 together, so as to produce sum (f1+f2) and difference (f1-f2) frequencies. It turns out that for, the "micropower metal detector" in the attached circuit diagram, the mixer is simply a XOR gate, and that works somehow, for reasons that I am not totally prepared to explain.

As it turns out, the difference frequency, f1-f2, is the only frequency I want to keep. That difference frequency, as a tone, as a sound, is the output from this metal detector, and what it indicates is how different the frequencies of these two oscillators are from each other.

This difference frequency, f1-f2 is a relatively low frequency, probably somewhere between 0 and 10 KHz, compared to f1 and f2, both near 160 KHz, and f1+f2, near 320 KHz. So the last block is a low-pass filter, it passes all frequencies less than 10 KHz (and mutes all frequencies greater than 10 KHz).

By the way, I have not built this circuit, this "micropower metal detector", in the circuit in the attached picture. So I can't confirm if it actually works, or if there might be any weird pitfalls or difficulties in building it.

But it looks kinda simple, to me, I mean just from looking at the diagram and the parts list.

Of course, there are other recipes out there.
I found these instructables:
https://www.instructables.com/id/Home-Made-BFO-meta...

https://www.instructables.com/id/bfo-metal-detector...
which look to be based on the same circuit. Both appear to contain the exact same image for the circuit diagram.

Also I found a bunch of metal detector circuits here.
http://www.talkingelectronics.com/projects/200TrCc...

I dunno. At this point I guess the decision is up to you, and what you consider to be "simple", as DIY metal detector recipes go. Or keep searching.

Or... buying a metal detector would be pretty simple too, provided you can find someone selling one for not too much money. That's not DIY, rather it's SEDIFY(somebody else does it for you), but, you know, sometimes that's what it takes to get things done. I don't know what the metal-detector-market looks like in your part of the world. In my home country, the Former United States, the go-to store for cheap tools is this place called "Harbor Freight Tools", and yes, they have metal detectors, ...erm here:
http://www.harborfreight.com/metal-detector-97245....
http://www.harborfreight.com/6-function-metal-dete...

That oscillator doesn't have a inductor coil you could modifie to turn it into a metal detector.

Ebay does have kits you can buy or you can just use a compass.

Joe

That oscillator doesn't have a inductor coil you could modifie to turn it into a metal detector.

Ebay does have kits you can buy or you can just use a compass.

Joe