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New Prototype Detector - My First Analog Attempt


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I love this post! good for you! is this something you are building a 1 off for you or are you thinking about going in business? I have used many metal detectors over the years and for most detecting I prefer a digital metal detector but when it comes to relic hunting in farm fields I prefer analog. In my opinion, after using many metal detectors analog works through the iron better time and time again. A new digital detector will come out and I think it will be the answer, "this one will finally be the one to beat out my old analog metal detectors" but so far it hasn't happened.

I would love to have a simple 2 tone analog metal detector, 1 tone for iron another for everything else with a volume control for the iron tone (which could be set up on a pot to determine your own break point) with about 3 different size coils starting with about a 5 inch and going up.

Can't wait to see what becomes of this.

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Thanks Mike,

For now I'm only making one, and until I get the coil wound and do some real world testing I'm not sure if it's worth seriously pursuing.  I'm a builder/designer, I've worked with magnetic's instruments in the past that gave me the foundation for what I'm doing here.  I know the old revision will discriminate well, but I've made some updates to the new revision that are meant to improve the design, hope it works.

About the two tone option for ferrous and non ferrous material, I have my design set up to do something similar to that, when I get further down the road I'll be able to elaborate on this feature.

A quick question:  When I see guys using their machines, they have to be swinging in order to get a signal, is this the case with most VLF detectors?  Can you guys give me a quick rundown on some of the machines and how they detect?

I ask this because I've set up my machine in a configuration where you don't have to swing to get a signal, it's in constant search mode, kind of like the machines that have the pinpoint mode.

-S

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"A question:  When I see guys using their machines, they have to be swinging in order to get a signal, is this the case with most VLF detectors?  Can you guys give me a quick rundown on some of the machines and how they detect?"

Nearly all commercially available VLF machines are 'motion mode' in operation, except when in 'pinpoint mode'. A few have a 'permanent pinpoint mode' as a feature, such as the Fisher F75. One manufacturer that still makes a range of true non-motion machines is C-Scope in the United Kingdom, the CS1220XD is the flagship of the models:

https://www.csmetaldetectors.com/shop/category/non-motion-metal-detectors

 

 

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....so, when we last left our hero's....we were giving a rundown of some mechanical hardware which I proceeded to put in boxes on my kitchen table.....and not touch since then....

But , I did do some parts soldering on the new board today......only to find out that I'm not as good as I used to be when it comes to putting down LLC packages, (sigh), it was the heart of the power supply.  So I decided to put that aside for now and moved on to populating the oscillator, it's a pierce crystal oscillator running at 120KHz, it's then divided down to 60KHz, this is going to be my operating frequency.  I also use the divider to give me a good 50 50 duty cycle.  It gave me some trouble before I got it running. but it's looking good now.

I'm using an older NI Virtual Bench on my laptop for the bench testing/troubleshooting.

Sorry for the dark photo, I may replace it later.

Oscillator.jpg.f797bbed6bec105089f4ba83c6aa4ca5.jpg

I experimented with manually placing solderpaste on the board to place the LLC package and only proceeded to make a mess.  It's the only one on the board, so I'll just have to wrestle it down.

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Ever consider using a stock coil from someone and adapting it to your machine? Coil housings are usually vacuum formed. I had thought it would be possible to 3d print one though for a 1 off.

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Hi Kac,

There is a little "something" happening in my custom coil that I can't replicate with an off the shelf one, I may experiment with some in the future, but for now I need to use my wiring configuration for my system to work properly.

-S

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There is a possibility with off the shelf coils for newer machines that they may use parts inside that make them proprietary to specific machines. Not sure if the older Tesoro compatible coils have that, probably unlikely.

Shouldn't be that tough to have a 3d printed coil other than size.

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  • 3 weeks later...

I'm curious about your choice of 60kHz for the operating freq. This is pretty high, and it would typically be chosen for one of two reasons:

* Hunting very small gold nuggets ( or other targets that would be classed as 'low on the ID scale' , including some ancient coins )

* Hunting in extremely iron/nail-infested locations, where the high frequency tends to make the iron less 'visible' , and the chance of finding non-ferrous items increases.

An example of the first case would be the Fisher GoldBug2, a dedicated nugget-hunter operating at 72 kHz. The second case is a niche which few modern machines fill. Classic examples include the Compass Yukon, running at 100 kHz. It's possible the HF coils used on the XP Deus could fill either of these two categories.

60kHz also makes experimenting with commercial coils all but impossible, as most are operated at 5 - 20 kHz.

As you haven't described your coil construction, I can't offer much advice, though such a high frequency would likely benefit from the use of Litz wire ( or at least many paralleled strands of finer gauge wire ) for the TX in particular; skin effects can hinder performance.

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9 hours ago, PimentoUK said:

I'm curious about your choice of 60kHz for the operating freq. This is pretty high, and it would typically be chosen for one of two reasons:

* Hunting very small gold nuggets ( or other targets that would be classed as 'low on the ID scale' , including some ancient coins )

* Hunting in extremely iron/nail-infested locations, where the high frequency tends to make the iron less 'visible' , and the chance of finding non-ferrous items increases.

An example of the first case would be the Fisher GoldBug2, a dedicated nugget-hunter operating at 72 kHz. The second case is a niche which few modern machines fill. Classic examples include the Compass Yukon, running at 100 kHz. It's possible the HF coils used on the XP Deus could fill either of these two categories.

60kHz also makes experimenting with commercial coils all but impossible, as most are operated at 5 - 20 kHz.

As you haven't described your coil construction, I can't offer much advice, though such a high frequency would likely benefit from the use of Litz wire ( or at least many paralleled strands of finer gauge wire ) for the TX in particular; skin effects can hinder performance.

Litz wire is a good choice, I'll try some experiments with it in the future, for now I'm winding them with regular magnet wire - do you have a good source for Litz wire?

About the 60KHz, I came to that frequency through testing, I tested my system with multiple frequencies and found that gold worked best right at 60KHz , and that iron, silver, nickle, etc., worked well with either low or high frequencies - and if the detector can't see gold, well, it really has to find gold :cool:.

 

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Unfortunately, Litz wire is hard to come by, especially in small quantities. And there's usually not much choice, either, which is difficult when you're attempting to juggle resistance and inductance values.
One UK supplier of all types of wire is wires co uk :
https://www.wires.co.uk/cgi-bin/sh000001.pl?WD=litz&PN=litzwire.html#aLZ00710090_2d100

 

They also stock multi-stranded ecw, which could be useful as an improvised alternative to Litz.
Most commercial Litz uses typically 0.035mm to 0.05mm strands, which is probably overkill for 60kHz, and 0.07mm - 0.10mm would be adequate if you're going to homebrew some. The cotton wrap ( serving ) is also not needed for detectors' low voltage use. So the simplest method is to wind multiple ecw strands together, eg. 9 strands of 0.1mm in place of one 0.3mm wire.
I'm looking into making a coil for my Equinox, and that needs a Litz-like TX winding, and the prospect of making a 300 x 0.05mm bundle is one of the challenges. I'm needing about 14 metres, so obviously don't really want to purchase 100 Dollar reels of the stuff. So I'm thinking about winding jigs etc.

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