Inside the Metal Detector, 3rd Edition

[Carl-NC]

A year ago I pronounced a New Year's resolution to get ITMD-3 completed by the end of 2022. It ain't gonna happen, and there is enough left to do that it won't be early 2023, either. As I polish the completed chapters and begin writing the unwritten chapters I try to think of ways to better explain things and it occurs to me that maybe I should just ask the folks who bought the previous editions. So this thread is for everyone to offer feedback & suggestions on ITMD.

ITMD-3 is a major re-write and is expanded considerably. The list of chapters below will let you know at least what the general contents will look like:

PART 1: TECHNOLOGY

1. History
2. Basic Types of Metal Detectors
3. Magnetics & Induction
4. Target Responses
5. Complex Responses
   
   PART 2: COILS
   
6. Coil Types
7. Coil Performance
8. Building Coils
   
   PART 3: PROXIMITY DESIGNS
   
9. Energy Theft
10. BFO
11. Off-Resonance
12. PLL
    
    PART 4: IB DESIGNS
    
13. TR
14. TR-Disc
15. VLF-GB
16. Motion Discrimination
17. Target Analysis
    
    PART 5: PI DESIGNS
    
18. PI Concepts
19. Basic PI
20. Improved PI
21. Ground Balanced PI
22. Bipolar PI
    
    PART 6: ADVANCED TOPICS
    
23. Multifrequency
24. Advanced PI
25. Half-Sine
26. Oddball Circuits

Although a few of the chapters might look familiar I have tried to re-write, clarify, and expand on the material in ITMD-2. Also, ITMD-3 continues to offer "teaching circuits" in most of the chapters but I believe in all cases I did not re-use any of the old circuits so ITMD-2 will still have value as a supplement to ITMD-3. Another major difference from previous editions is that only the schematics for projects are presented. BOMs, PCBs, build instructions, and any source code are not in the book, they will be supported in the Geotech forums separately. The reason for this is because the book is already over 500 pages and there just isn't room, plus putting this stuff on the forums makes it easier to issue updates. I wanted to include a CD-ROM for this kind of stuff but Amazon self-publish doesn't support this.

Currently 12 chapters are considered "finished" and the chapters that are below 50% done are 11, 17, and all of Part 6. So it's coming along nicely, if slowly. It's a spare-time project, after all. I expect it to go over 600 pages, and that's after I increased it from a 6x9" format to a 7x10" format. No idea on price yet. I also plan to try a hardback version. Sorry, there will be no electronic version; sadly ITMD-2 was widely pirated, done with that.

Please join in and help me make this better than I can do alone.

Thanks!

[bbsailor]

Carl,

This is a good outline. Since I do not know the details you have already written, I will offer some points that I believe will be helpful to metal detector builders.

1. Coil diameter, alternate shapes, recommended inductance, and optimum depth of detection for a common variety of targets.
2. Defining coil seen capacitance to reveal how this has a great influence on the damping resistor value and the potential for a coil to sample at very low delays. Define all sources and ways to minimize. Define why a low delay in necessary for targets with a low TC.
3. How the concept of a lock-in amplifier improves the RX signal to noise ratio and becomes the technical basis for integrating many RX signals to improve coil sensitivity for smaller targets.
4. The consequence of making low delay detectors has on coil style, inductance, wire gauge, and coil construction techniques.
5. Coil shielding techniques and the consequences in different search locations and range of targets sought.
6. Explain how a one size coil works well for general metal detecting but requires size and design changes to adapt to specialized target detection. Example: coins, jewelry, gold nuggets and other common sought objects. Also include common search locations such as: lawns, beaches, salt water, fresh water, rock filled rivers, and mineralized soil.
7. Add a glossary of technical terms.


I hope other geotech1 members jump in and share their insights, ideas, and desired content.

Joseph J. Rogowski

[ivconic]

It depends on what your intention is? That from issue to issue you finally create a huge "bible" that will cover everything... or
that you have a series of books that will deal with the problem at different levels.
ITMD1 has completely done its job.
I didn't have a chance to see ITMD2 (not even the pirated version).
And the ITMD3 that you are announcing seems to me to be trying to deal with all the topics again, but this time more extensively. In detail.
I think that is unnecessary.
Up to Chapter 4 should be abolished.
And chapters 4, 5 and 6 are books unto themselves.
I think you should divide that big job into several independent jobs.
I will give you an illustrative example. I am personally interested; the whole process of how the Fisher 1265 came to be (for example).
And why every stage in it was done the way it was done. What would be the alternatives to those solutions. Pros and cons for each of the solutions in those assemblies, etc.
When I say "Fisher 1265", I also mean "Minelab Musketeer", "Cscope 1220B"..."White's 6000 DiPro"..
You know what I mean.
An explanation of each possible component and stage in such designs. Why is it done that way, why is it not different, etc. What are the alternatives to some solutions. Advantages, disadvantages.
Frontends, filters, sumers, synchro-demodulators, audio solutions, etc.
PI detectors are something I'm less interested in. Well, I probably wouldn't pay too much attention to that part of the book.
Making a coil? 30 years ago I would have been very interested. I'm not interested in that today.
Can you dig it?
You cannot satisfy all tastes and requirements.
So don't cram it all into one book. Because someone will always be deprived. Better to divide it into several books, by topic. But each of them should explore the given topic to the end.
The hands-on projects in such a single book... are mostly simple and nonsensical.
Waste of space and pages.
It is much better to devote that space to some legendary project that has come to life and has proven itself in practice.
Ok, I might be wrong, but that's my opinion.

[kt315]

i offer to add detailed chart about ESFI shielding must and his physics. i notices it is very hard problem to understand even for advanced in electronics people.
i answer on this matter again and again, for every new member, from zero point understanding.
thinking western school level and school level in another countries is very low on physics. seems probably general degradation of the school.

[MartinB]

Hi Carl,
I would like to see a detailed explanation of signal sampling. Not just pictures of oscope traces, but practical examples using real components. How to sample early, late and at the right time.

[Carl-NC]

1. Coil diameter, alternate shapes, recommended inductance, and optimum depth of detection for a common variety of targets.

This is covered in Ch7. Inductance trade-offs depend on the detector topology so that is covered in various other chapters.

2. Defining coil seen capacitance to reveal how this has a great influence on the damping resistor value and the potential for a coil to sample at very low delays. Define all sources and ways to minimize. Define why a low delay in necessary for targets with a low TC.

Yup, all covered.

3. How the concept of a lock-in amplifier improves the RX signal to noise ratio and becomes the technical basis for integrating many RX signals to improve coil sensitivity for smaller targets.

I don't cover lock-in amps but do talk about SNR improvement using integration.

4. The consequence of making low delay detectors has on coil style, inductance, wire gauge, and coil construction techniques.

ITMD-3 doesn't dig too deep into high performance, but it does cover general methods for improvements. Part of this is keeping the book to a reasonable size and a reasonable completion time. Several chapters got punted to ITMD-4.

5. Coil shielding techniques and the consequences in different search locations and range of targets sought.

I'm not sure what you mean by this. Maybe

6. Explain how a one size coil works well for general metal detecting but requires size and design changes to adapt to specialized target detection. Example: coins, jewelry, gold nuggets and other common sought objects. Also include common search locations such as: lawns, beaches, salt water, fresh water, rock filled rivers, and mineralized soil.

Ch7 covers this to some extent, but I don't talk about locations or techniques.

7. Add a glossary of technical terms.

Not yet, but maybe before it's finished.

Thanks!

[Carl-NC]

It depends on what your intention is? That from issue to issue you finally create a huge "bible" that will cover everything... or
that you have a series of books that will deal with the problem at different levels.
ITMD1 has completely done its job.
I didn't have a chance to see ITMD2 (not even the pirated version).
And the ITMD3 that you are announcing seems to me to be trying to deal with all the topics again, but this time more extensively. In detail.
I think that is unnecessary.
Up to Chapter 4 should be abolished.
And chapters 4, 5 and 6 are books unto themselves.
I think you should divide that big job into several independent jobs.

ITMD-3 will be what it is. Yes, it's a big book and will cover a lot of topics, and I have even removed some chapters because I want to get this finished sooner. Now that I see how big it will be I may re-think any future editions and maybe split them up. But I'm not sure of a good way to do this.

I will give you an illustrative example. I am personally interested; the whole process of how the Fisher 1265 came to be (for example).
And why every stage in it was done the way it was done. What would be the alternatives to those solutions. Pros and cons for each of the solutions in those assemblies, etc.
When I say "Fisher 1265", I also mean "Minelab Musketeer", "Cscope 1220B"..."White's 6000 DiPro"..
You know what I mean.
An explanation of each possible component and stage in such designs. Why is it done that way, why is it not different, etc. What are the alternatives to some solutions. Advantages, disadvantages.
Frontends, filters, sumers, synchro-demodulators, audio solutions, etc.

I'm sure a separate book could be written on each of these. Sorry, I don't have time.

PI detectors are something I'm less interested in. Well, I probably wouldn't pay too much attention to that part of the book.

Making a coil? 30 years ago I would have been very interested. I'm not interested in that today.
Can you dig it?
You cannot satisfy all tastes and requirements.

Yes, that is true of all technical books. ITMD needs to cover intro material for the newbie but also dives in to some pretty advanced stuff. It's kinda like a book on opamps, where it needs to show the basic inverting topology but eventually gets to meatier and more interesting circuits.

So don't cram it all into one book. Because someone will always be deprived. Better to divide it into several books, by topic. But each of them should explore the given topic to the end.

The hands-on projects in such a single book... are mostly simple and nonsensical.
Waste of space and pages.
It is much better to devote that space to some legendary project that has come to life and has proven itself in practice.
Ok, I might be wrong, but that's my opinion.

There is a trade-off in project complexity. Simpler circuits are good for teaching concepts, which is what ITMD is mostly about. But it can leave the reader wanting more. At the end of each chapter I have added an EXPLORE section where more advanced topics are presented, though not in as much detail as the main material.

When I decided to remove all the project support material (BOM, PCB, code, etc) from the book I thought it might be a good idea to create an ITMD "supplement" book that was purely project-oriented. Maybe that's what ITMD-4 will be, a main technical book and a supplemental project book. Or maybe someone else would like to write the supplement. But really advanced projects, even a single one like a VLF-Disc or multifrequency design, can easily take up a whole book by itself. Look at the 2 books George published. But I'll give it some thought.

Thanks!

[Carl-NC]

i offer to add detailed chart about ESFI shielding must and his physics. i notices it is very hard problem to understand even for advanced in electronics people.
i answer on this matter again and again, for every new member, from zero point understanding.
thinking western school level and school level in another countries is very low on physics. seems probably general degradation of the school.

Sorry, I don't know what you mean by EFSI shielding.

[Carl-NC]

Hi Carl,
I would like to see a detailed explanation of signal sampling. Not just pictures of oscope traces, but practical examples using real components. How to sample early, late and at the right time.

Do you mean VLF, PI, or both? I've added a lot of graphical examples for TR & VLF sampling. Also more info on PI, including ground balance.

[kt315]

Sorry, I don't know what you mean by EFSI shielding.

electro static field influence was been meant.

[dbanner]

Perhaps a paragraph or two on the future of these devices and the technology.
Where's it going to be say by mid century? Is there any promise of some radical breakthrough( using ai to help better identify targets) or are we stuck with the equations we have.



Are our humanoid robots going to be swinging away at the beach while we relax in the shade.
End the book with something optimistic and fun.

A reference to relevant patents at the end of each chapter so the reader might further explore the topic.
Or maybe have a list of patents relevant to the field somewhere in the book. Or at least a reference to where such a list could be found.

And something about the legal aspects of metal detecting in various jurisdiction.( Just some general advice)

[kt315]

Perhaps paragraphs
1. dual preamp in PI, inverted type and uninverted. 5us FIRST DELAY
2. preamp inserted in VLF coil.
3. 1mH coil in PI

[Carl-NC]

I'm still writing Ch8 so I will be sure to include a section on shielding.
ITMD1/2 have an appendix listing a bunch of patents. I'm updating that list now.
Legal aspects are only covered in discussing patents legalities. There are lots of books on general detecting that cover detecting laws. I've kept ITMD focused on designing & building detectors, not using them.
I'm not sure what I can say about the future of detector design but Ch26 is a catch-all for misc "other stuff" so I'll try to include a page on possibilities.
The single vs dual preamp needs to be added somewhere, probably in one of the Explore sections.
Preamp-in-the-coil will be mentioned in Ch8, along with induced ground effect from putting static metal in the coil.
I think somewhere I talk about PI coil inductance trade-offs.

Thanks to all, this is helpful!

[bbsailor]

Carl,

The concept of a lock-in amplifier dates back to around the 1940s when weak signals were trying to be extracted from noise. Since noise is random, the concept of a lock-in amplifier was to do many repeat samples always at the same place in many multiple signals but exactly in the same place which tends to improve the signal to noise ratio. With a PI detector and always sampling the wave form in the same place and integrating these signals, creates the same signal to noise benefits as integrating as many samples as possible derived from:
1. Coil size
2. TX frequency
3. Sweep speed

The benefits from integrating many samples for a better signal to noise ratio originated many years ago but seemed to easily be adapted to PI detectors. See this web link for some background history. https://en.wikipedia.org/wiki/Lock-in_amplifier

Joseph J. Rogowski

[MartinB]

Do you mean VLF, PI, or both? I've added a lot of graphical examples for TR & VLF sampling. Also more info on PI, including ground balance.

PI definitely, VLF would also be useful. More info on PI including ground balance sounds good.