Introducing myself and looking for help on making a coil for the first time

[azigta]

Hi, I'm new here but I've always wanted a metal detector. I never had one, and I never built one. I'm 21 years old and I have experience soldering stuff and making projects such as guitar pedal effects and repairing bad capacitors on motherboards, power supplys etc. So I have a little bit of experience soldering. I was planning to make the Geotech Barracuda PI since I found that I had 32 of the required 46 elements (67 units out of 91) and that made the project cheaper. Also I found a pdf with step by step instructions that I think it's going to make the building process interesting.

The thing is that I don't want to start buying the pcb and the components because I have no idea how to make a working coil for this project. I looked for copper wire in ebay (I'm not sure if I can post a link to ebay) But there's copper wire from 0.4mm to 5mm in lengths of 20 to 50 meters for a reasonable price but that's as far as I can go. I've seen a coil calculator but I don't know how to use it, I'm missing a measurement that I'm not being able to find in the ebay article. Maybe I should buy it in other place.

Can anyone help me? I'm a total noob in this copper winding things. Maybe a noob friendly tutorial or something like that? I can't find anything like that xD Thanks

[azigta]

I have ordered the parts already xD I want to make a metal detector so badly. just spent 20€ but I'm missing 8 elements that I will try to buy in the next days. If not in my city's electronics store (a bit expensive) Will do it in aliexpress or ebay or whatever. Silverdog didn't have all the parts that I needed.

[tutanxamon32]

good morning Guys 8 '00 azigta 0,4 -0,5 is the most common searsh coil wire , not less.

[azigta]

Hey thanks for the reply. In the baracuda building tutorial it says the following thing in step 4 (transmit tx circuit):

"The coil inductance should be between 300uH and 500uH. You can utilise the Coil Calculator (atthe top of the Coil forum) to determine the correct number of turns for the diameter you intend to
use. The damping resistor (R1) may need to be adjusted to suit your particular coil."

So if I buy that 0.4mm coil how do I use the calculator to know how many turns do I have to wind? And having done that, how do I calculate R1? In fact, R1 is noted as a 330ohm 2w resistor, but it also says:
"A 330R damping resistor is shown in the schematic, but the actual value required will
depend directly on the coil used."

Maybe now I have 2 problems, 1st problem is the coil, second problem is that resistor. Maybe the resistor thing I should open another thread on the geotech barracuda sub-forum...

I found this info written by Quiaozhi:

"Try this damping resistor adjustment tool:10k pot in series with a 200R resistor, and a 2k resistor in parallel with both the pot and resistor.
This will give you an adjustment range from 181R to 1672R.
Attach your oscilloscope to the output of the preamp, and adjust the pot until you achieve critical damping.
Disconnect the adjustment tool and measure the final resistance. R
eplace with a fixed resistor that has the closest value."

I find it very useful but I don't have an oscilloscope. Is it possible to do this without the oscilloscope? (I hope so D: ) and those 200r and 2k resistors could be 1/4w?

Also, I can't find the following components: 2N5484, 2N5485. They seem to be obsolete. Is there other transistor I could in place in the place of those two?

[Qiaozhi]

Hi, I'm new here but I've always wanted a metal detector. I never had one, and I never built one. I'm 21 years old and I have experience soldering stuff and making projects such as guitar pedal effects and repairing bad capacitors on motherboards, power supplys etc. So I have a little bit of experience soldering. I was planning to make the Geotech Barracuda PI since I found that I had 32 of the required 46 elements (67 units out of 91) and that made the project cheaper. Also I found a pdf with step by step instructions that I think it's going to make the building process interesting.

The thing is that I don't want to start buying the pcb and the components because I have no idea how to make a working coil for this project. I looked for copper wire in ebay (I'm not sure if I can post a link to ebay) But there's copper wire from 0.4mm to 5mm in lengths of 20 to 50 meters for a reasonable price but that's as far as I can go. I've seen a coil calculator but I don't know how to use it, I'm missing a measurement that I'm not being able to find in the ebay article. Maybe I should buy it in other place.

Can anyone help me? I'm a total noob in this copper winding things. Maybe a noob friendly tutorial or something like that? I can't find anything like that xD Thanks

Since you don't have an oscilloscope, simply wind 20 turns of enamelled copper wire (from 0.4mm to 0.7mm thickness) on a 254mm (10") diameter former, and use a 470 ohm damping resistor. That should get you a working coil. If you want to tweak the damping resistor, or reduce the sampling delay, then you really need a scope to do that.

The Baracuda is designed for finding coins on the beach, so there's no need to be pedantic about winding a fast coil. The preamp isn't fast enough to cope with low conductivity items anyway, and the sample timing circuitry is a limiting factor.

It would also be useful to get a copy of -> Inside the METAL DETECTOR - Second Edition - Published 2015

[azigta]

Thanks! I was very worried about this thing. About the 470ohm resistor, does it have to be 2 watts ? Also, apart from coins in the beach could I find things like rings too? Just on the beach? I live near a mountain that not so long ago was a big war scenario (spanish civil war 1936-1939) and my mother told me that even today you can still find bullet caps in some areas of the mountain, and I was thinking to use this metal detector for that purpose too. Would it work? Althouh my idea was to look for things in the beach, it would be fun to use it on the mountain too and maybe find old coins and stuff like that. Thanks again

edit: Some odd question: I have an analog brand new amperimeter that goes from 0 to 20amps AC. Could I use it in the project? Maybe connect it to the audio output with a switch and use either the audio, the meter or both things? I'm afraid the scale is to big for this purpose but I think it would give the project a good look, maybe adding some component I could make it work? No idea. Sorry for the odd question, I just had to ask since I bought this thing long ago for a project I never finished and it's new and it looks good xD I also have a smaller 0-15v analog meter that I will put as an indicator for the battery. I will be posting the progress on the baracuda sub forum xD

[Qiaozhi]

Thanks! I was very worried about this thing. About the 470ohm resistor, does it have to be 2 watts ? Also, apart from coins in the beach could I find things like rings too? Just on the beach? I live near a mountain that not so long ago was a big war scenario (spanish civil war 1936-1939) and my mother told me that even today you can still find bullet caps in some areas of the mountain, and I was thinking to use this metal detector for that purpose too. Would it work? Althouh my idea was to look for things in the beach, it would be fun to use it on the mountain too and maybe find old coins and stuff like that. Thanks again

Rings are even easier to find than coins due to their shape which enhances the flow of eddy currents. Of course you will be able to use the Baracuda inland as well as on the beach, but remember that there is no iron discrimination. But maybe on the mountain you will be ok.

[Qiaozhi]

Also, I can't find the following components: 2N5484, 2N5485. They seem to be obsolete. Is there other transistor I could in place in the place of those two?

There are plenty available here -> http://uk.farnell.com/fairchild-semi...el3%3A2N5484E3

[azigta]

Great, I was looking in mouser electronics and there it says "obsolete" Maybe in spain they are not selling it. I will buy it from internet if I can't find them on my local electronics store.
Glad to hear that I will also be able to find rings and use it on the mountain. Thanks

[azigta]

Hey,I recieved the copper wire today (finally). I gave it 20 turns on a 10" diameter form like Qiaozhi told me. Now, I've seen people wrap the coil in tin foil. I have this kind of tape that's sticky tin foil, should I use it? Also, I've read that you don't have to cover all the coil with it, that you have to leave a gap non covered by tin foil. How long does this gap have to be? Also, I was thinking about leaving that gap in the place where the 2 wires of the coil come out. Is that ok? I've read lots of things but I don't know if this thing is for this kind of coil (mono coil) , Thanks.

Also, the coil folded in a 8 shape by itself due to the tension so I adjusted the tension more or less to make it look flat, although it folds upwards a little bit on one side of the circle. But I think that If I put tin foil tape and then I put this thing (I will try to put 2 layers of it) I should be able to mantain it flat. When I finish testing the coil and see that it works, I'm going to cover it in a form with silicone. I will post images, I'm sure everybody here has seen something like that but I've never done it and I will be kind of proud of myself if everything goes right... xD It's the first time I build something this big ^^

[azigta]

Anyone here? I need some help to continue with the project. Thanks

[Carl-NC]

Yes, but you'll need to ask questions to get help.

[homefire]

Someone is always around . LOL

[azigta]

Yes, but you'll need to ask questions to get help.

I did ask questions 2 days ago, if you read in the post number 10. I'm sorry if I sounded rude in post 11, I didn't mean to

[azigta]

Someone is always around . LOL

Glad to hear that, I'm new here and I don't know how much activity does this forum have, thanks