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Eclectic VLF
Posted by: Mike D.
Date: May 19, 2018 12:43AM
I am still drawing schematics of old transmit/receive VLF detectors that I am purchasing and am finding great similarity in them.

The goal is to acquire an understanding of the key sections of the signal flow and pick the best functional designs to incorporate into a micro nugget gold detector.

I may be striving for a circuit that I cannot develop without extensive electronic engineering background, but I have not smoked any Op Amps yet, and I suspect that Texas Instruments, Analog Devices, and many others have come up with some nice new chips with enhanced engineering specifications.

I must emphasize that this activity is purely for the understanding and achievement of a single detector for personal use to find very small native gold.
Without limitless funds to purchase and dissect newer (and still expensive!) used gold detectors I pose some questions here:

What are the best 'modern' op amps to employ and which for what sections of the circuit, or are oldies/goodies still prized?

For frequencies above 50KHz to 100KHz, where should I start, what window best avoids radio interferences?

Should I crystal lock the transmit oscillator and forcefully drive the transmit coil or should it be part of a resonant (Colpitts like) oscillator?

On good gold detectors of renown (Thank You David Johnson and All Others) are the coils the critical starting point?

In the medical laboratory world the terms sensitivity and specificity are used to statistically target bio-markers of disease.
Which one / or both would apply best to a good gold detector without a DSP (digital signal processor) to describe the action of discretely flagging a small target in a sea of 'ground' noise?

Sorry I don't know much about the actual detection phase of the circuits (an inverse or reversal of superheterodyned radio signals?).
Not visualizing how a good detector captures that little signal for snagging a quarter grain piece of wire gold in a heavily mineralized soil.
Makes me think of viewing the signal expansion option on my old Techtronics oscilloscopes.

If you capture an analog data stream of a single manual sweep of the detector head over the ground, pump it through an analog to digital converter and store it in a syndrome memory type loop maybe the little goldie bleeps could be filtered out from the back "ground" signals by masking them with a synced overlay of the averaged ground signal. OK, just guessing, probably already done years ago with 'ground' tracking feedback circuits.

If I were to start with a simple (maybe the wrong word) manual ground balance circuit, what would be the best low powered-on resistance CMOS switch available today to use or should I apply a FET, NMOS, BIMOS, ect to pick-off the receive signal?
I am guessing that better techniques are being employed now via code/compiled software. If so which language is best for application to this type of signal processing? Whats simple without purchasing an expensive development system.
If coding should I employ fuzzy logic format neural net or a straight recursive feed back type iterations process?

Right now just trying to get some analog hardware to bark for gold bits.
Like my friend's (Musk Mobile) Tesla car, something gets lost in the driving-detecting experience when it is filtered through eleven high powered graphics processors.

For core hardware should I just slam all ideas through a SPICE program (circuit development and test program) and keep all those noisy little antennas on the breadboard at bay?

Again this is about understanding more than show n tell of what I found on the weekend; though that would be a nice 'proof of theory' validation.
I think we all would like to pay for gas to and from 'the diggens' or just buy a new truck with the finds.

OK, toooo many questions I know; these are just starters.

Many of you have great wisdom in this field of endeavor and recreation.

I most appreciate any ideas. I am just starting, year one.


Edited 1 time(s). Last edit at 05/19/2018 01:02AM by Mike D..

Inside the metal detector
Posted by: kt315
Date: May 19, 2018 06:47AM
sorry Mike that i reminder. good book to start reading. Carl Moreland and George O. those guys you see in Geotech1.
i asked Eric to write a book too... he refused... he is living 3 lifes.

Re: Inside the metal detector
Posted by: Mike D.
Date: May 19, 2018 08:04PM
Thank You Kt315.

Great Idea!
I have heard that book is a great gold level reference for metal detecting.
I will have to add a copy to my library.

As I mentioned in my rambling blab above, I am trying to get a mental picture of how different sections of the transmit/receive VLF detector work.
I like to play with ideas sometimes, but do not have a plug and play "Lego" type prototyping system for analog circuits.
Ideally I would find a way to quickly test ideas without hours of breadboarding.
That is why I thought of possibility running circuits in the SPICE circuit analysis software.

Mike D.

Re: Eclectic VLF
Posted by: Carl-NC
Date: May 22, 2018 07:28PM
Mike, Findmall is good for high-level tech stuff, but not detailed design info. The Geotech forums are full of folks who build this stuff. It's clear from your questions you have a looonnngggg way to go; first step is to build a simple TR circuit, see if you can detect a coffee can. Go from there. You have, by the way, chosen the most difficult detector to design, even a seasoned detector designer can struggle to make a really good gold detector.

Re: Eclectic VLF
Posted by: Mike D.
Date: May 23, 2018 04:29PM
Hi Carl-NC,

Thanks for the wisdom perspective.
Yes, Shoot for the Stars, expect to hit a mud hole, and hope for something in between.

Back in the day, I used to troubleshoot digital systems to the component level.
However, never worked on the analog computers that the company serviced.
Now, I have friends that want me to troubleshoot /repair their Fanuc and Motoman robots.
Yikes! Big multiaxis servo systems can throw you - literally across the room!

Electronics has gotten tiny, super fast, diverse, and mysterious - as in software driven black box logic.

So many incredible realms of endeavor to investigate.

At one time was going to grow diamonds in the garage, (epitaxial carbon vapor deposition from focused cold plasma).
Resolved that I needed a nice clean room facility and better vacuum systems, and just plan more physical room for that.
Never mind that the neighbors might think that I was cooking street drugs with a high frequency - high voltage ion deposition chamber and tanks of purified specialty gases. Not a good fit for the suspicious residential suburbs.

Playing with this stuff will be safer and I'm hoping educational also.
Gee, Look at the first few Space X reentry landings.
Will be fun to see what evolves.
Probably will turn into a robot or drown project.
Oooops, again to much rambling.

Thanks again, be safe, and have a great summer.

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