New Prototype Detector - My First Analog Attempt

[PimentoUK]

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.

[Sun-Boy]

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 .

 

[PimentoUK]

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.

[Sun-Boy]

Hi Folks,

Well...life, work, and health happened and I had to put the detector on hold, but I'm getting back to it.  I got new boards and components on order, as well as a few mechanical parts.

I'm sticking to the all analog design for now, but have a recently retired embedded programmer friend whose interested in helping out, my programming skills are basic at best.

I'll update the thread as I progress through the design.

-S

[Erik Oostra]

On 1/30/2021 at 1:47 PM, Sun-Boy said:

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 .

I really like your thread and detector, it'll be interesting to see how it performs in the wild..

As mentioned above 60kHz is great for tiny shallow gold, you even show this in your photo where your detector picks up a thin gold chain with a little cross.. But this is in your workshop, on a beach this sort of chain can be very hard to find, even with beach detectors like the Equinox (40kHz) or Deus 2 (45kHz)..

On my beaches these detectors are hard to run on high single frequencies and I normally run them in multi frequency programs.. To find small gold jewellery I've also used my mate's Gold Monster (single frequency - 45kHz) which just tolerates dry salty sand but freaks out on the wet stuff, it also can't handle black sand.. I've had more luck in these situations with my Gold Bug Pro (single frequency - 19kHz).. 

Have you considered lowering the frequency on your detector so it can be used in the wild? I think that you'll have more luck running at a lower frequency, say 15kHz which in my mind is at the higher end of the 'general purpose' frequencies and will still hit on small gold jewellery.. A lower frequency is also better if you want to get any real depth out of your detector, this will also increase your finds (good and bad) in the wild.. 

I guess it'll come down to how the beast behaves in a workshop versus the wild.. 

It's a very interesting project and I'll be keeping an eye on your thread for updates.. Thanks for showing us the fruits of your labour..   

 

[Sun-Boy]

Hi Erik,

Thanks for the input, reducing the frequency to 15kHz won't be a problem, running dual frequency is also an option, the original system I worked on eons ago was running at 3kHz.  This revision is pretty well set unless I cut up the pcb, which I don't want to do right now.  I'm a builder designer and my actual in the wild detecting is limited to near nothing.  This design is based on a system I worked on many years ago, its going to be fun seeing how it performs.

I'm in South Texas, so I'm going to see if I can get some locals in San Antonio to test it out and give feedback.

[Sun-Boy]

Well, looks like I'm being 'encouraged' to take early retirement, so as of mid May I'm going to have plenty of time to get back to my detector.  I left this hanging for a long time, but I think the fun is fixing to start.  It's given me plenty of time to think about the architecture, think I'm going with a new amplifier input, we'll see how it works.

[GB_Amateur]

16 hours ago, Sun-Boy said:

It's given me plenty of time to think about the architecture, think I'm going with a new amplifier input, we'll see how it works.

If you're not familiar with this recently released book, IMO you should give serious thought into acquiring it.  I look forward to your future updates on the detector's progress.

[Fugio]

Very interesting detector. I hope you get it finished up. I think it's great you can do this and I love seeing new/different detectors, especially analog. I look forward to hearing how it performs. Good luck!