Inside the Metal Detector, 3rd Edition

[bernte_one]

my great wish is a simple analog pi with powerfull output, based on 24V
maye you can set a memorial for Eric Foster in you book

[ivconic]

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

Exactly!
I "dream" about such a book. It doesn't matter which of the mentioned models... and a dozen more could be on the list.
But I think you missed the point of my suggestion.
I did not suggest that you literally take and explain the Fisher 1265 model.
Rather, you should give such a similar concept in your book and explain it in detail.
A project that would have the same "weight" as 1265. Or any other one from the list.
...
I have a "problem in my head"... when I think about the series of detectors that have been created in the
last... say 10-15 years. They are all on the same "mold".
Copying and using something that someone has already done long ago.
There is no "magic". I don't think beginners can learn much from such examples.
Unless they join a long line of such "copyists".
But if we go back 30, 40 and even 50 years back.
Let's take one or several top models of the time, which btw are completely analog;
let's break them down into simple parts, and go through the analysis to slowly clarify each of those parts...
I think a lot more can be learned that way.
You mentioned "Opamp book" somewhere.
Exactly!
For me, those few "Opamp books" are my favorite reading and revisiting regularly.
I always find something new and super interesting in them.
"Opamp book" is an eternal "bible" to which I always gladly return and always learn something new.
The book I would like to see should look like an "opamp book". But adapted to the theme of metal detectors.
I don't know how clear my suggestion is here.
Take, say, the 50 best frontends and explain them all, differences, similarities, flaws, virtues, etc.
And so with each subsequent standard stage in one such detector.
I myself got a similar desire a couple of times, to go through my entire archive and choose ten-ish of the most
interesting solutions, put them in the same article and try to compare them in the described way.
The problem is that my technical knowledge is lacking and my vocabulary is poor.
I don't think I would explain those things in the best way.
I thought I'd put together my own metal detector "bible" that way.
To collect and arrange in one place all those parts of the schemes that I have liked over the decades.
And which I had the opportunity to try on real machines and in real conditions.
But... firstly, I'm not at that level to do it properly, secondly, it's a lot of work and requires a lot
of commitment and I'm not in such conditions.

[Carl-NC]

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

The chapter list in post #1 does not include the Appendices. Appendix D is called "PI Math" where I cover all the math behind the TX and RX signals in excruciating detail. Including synchronous demod averaging. I don't mention lock-in amplifiers in particular because practically no one will know what they are and I can explain everything without that reference. Maybe I'll throw in a footnote and mention that they operate in the same manner, then curious people can look up lock-in amps if they want.

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

Ch21 is an all-new chapter on designing a ground balanced PI. That, and other chapters, cover various sampling trade-offs.

my great wish is a simple analog pi with powerfull output, based on 24V
maye you can set a memorial for Eric Foster in you book

The only chapter I have not even started is Ch24: Advanced PI. It will cover Minelab MPS and DVT schemes, as well as other PI variants. Explaining how DVT works includes explaining the trade-offs in TX supply voltage. I probably will not offer a specific project schematic for a high-voltage design but everything needed to do that is covered in the book.

Exactly!
I "dream" about such a book. It doesn't matter which of the mentioned models... and a dozen more could be on the list.
But I think you missed the point of my suggestion.
I did not suggest that you literally take and explain the Fisher 1265 model.
Rather, you should give such a similar concept in your book and explain it in detail.
A project that would have the same "weight" as 1265. Or any other one from the list.

Throughout the book I offer alternative way to do things and try to explain the trade-offs. For example, the "Explore" sections of Ch 14, 15, & 16 cover a bunch of alternative demodulator designs that have been used over the years. I also present a variety of TX designs, and cover various preamp topologies. But all this is distributed throughout the book, not done in a step-by-step systematic manner. In short, I think I have a lot of the info you are interested in, but maybe not presented the way you would like.

There are a couple of problems with dissecting an all-analog design and explaining all the trade-offs in how it was done. First, a lot of designs had oddities due either to the designer's preference for doing things a certain way (whether or not it was the best) or because of limitations in the chips available at the time. For example, at one time Dave Johnson like to use the LM13700 opamp in his designs. No one does it that way anymore so is it worth diving into that? Another example is the White's XL-Pro; it is a massive conglomeration of opamps, comparators, and logic chips because those were the chips available at the time. No one today would ever design an equivalent detector in that manner. And that brings up the other problem: modern designs have moved most of the circuitry to DSP.

So my approach with ITMD is to explain the fundamentals initially using all-analog circuits, but those circuits usually represent about the simplest way to get the job done. Alternative methods are tossed about in the Explore sections but usually without the detailed presentation of the main approach. I expect that the book will generate a lot of discussion on the forums and I will likely use that to improve on the book.

[Skippy]

I think the Chapter 1 'History' section should be pretty brief in printed form, and refer to an online resource, where plenty of photos, patent references etc could be accommodated.
I see 'Target Response' gets its own chapter. Does 'Ground response' deserve a seperate chapter, considering how important it is to obtaining depth/good ID. And the differences between dirt / wet salt beach, the way VLF / PI see dirt differently etc.

Would you contemplate sending out individual chapters / sub-sections to trusted individuals for proof-reading / appraisal ? ( I don't know if this is possible, presumably some conversion to pdf or whatever would be required ? )

[ivconic]

...Throughout the book I offer alternative way to do things and try to explain the trade-offs. For example, the "Explore" sections of Ch 14, 15, & 16 cover a bunch of alternative demodulator designs that have been used over the years. I also present a variety of TX designs, and cover various preamp topologies. But all this is distributed throughout the book, not done in a step-by-step systematic manner. In short, I think I have a lot of the info you are interested in, but maybe not presented the way you would like.There are a couple of problems with dissecting an all-analog design and explaining all the trade-offs in how it was done. First, a lot of designs had oddities due either to the designer's preference for doing things a certain way (whether or not it was the best) or because of limitations in the chips available at the time. For example, at one time Dave Johnson like to use the LM13700 opamp in his designs. No one does it that way anymore so is it worth diving into that? Another example is the White's XL-Pro; it is a massive conglomeration of opamps, comparators, and logic chips because those were the chips available at the time. No one today would ever design an equivalent detector in that manner. And that brings up the other problem: modern designs have moved most of the circuitry to DSP. So my approach with ITMD is to explain the fundamentals initially using all-analog circuits, but those circuits usually represent about the simplest way to get the job done. Alternative methods are tossed about in the Explore sections but usually without the detailed presentation of the main approach. I expect that the book will generate a lot of discussion on the forums and I will likely use that to improve on the book...

Very accurate and beautifully worded. I agree, of course.
And indeed; the question is whether what suits me to see; does it suit others?
Because I'm "nostalgic", old school, I understand analog solutions more easily.
And when the assembly is divided into many subassemblies; it's easier for me to follow the idea.
But today are modern times.
"Some new kids" are coming and it will be much easier for them to present things in a modern way.
So it's a rhetorical question; what is more correct, how to direct the writing of such a book.
For most of those who are "from yesterday", my vision will not suit them, they will be too bored.
And for most of us "oldies" reminiscing about the "good old days" will be a better approach.
Ok, you've said enough that the book is already becoming very interesting to me.

[MartinB]

[FONT=comic sans ms]
I'm sure a separate book could be written on each of these. Sorry, I don't have time.

You must have at least forty years in front of you unless you get hit by that beer truck or try to drink it dry.

[Carl-NC]

I think the Chapter 1 'History' section should be pretty brief in printed form, and refer to an online resource, where plenty of photos, patent references etc could be accommodated.
I see 'Target Response' gets its own chapter. Does 'Ground response' deserve a seperate chapter, considering how important it is to obtaining depth/good ID. And the differences between dirt / wet salt beach, the way VLF / PI see dirt differently etc.

I treat ground (mineral or salt) as a target, so it's covered in Ch4. In fact, Ch4 is divided into 2 sections: Magnetic Responses (ground and ferrous), and Eddy Responses (non-ferrous and salt). Ch5 adds complexities like mixed responses such as flat steel. Also covers non-sinusoidal systems time-domain responses.

Would you contemplate sending out individual chapters / sub-sections to trusted individuals for proof-reading / appraisal ? ( I don't know if this is possible, presumably some conversion to pdf or whatever would be required ? )

Yes, I am thinking about that. I want to do it in sections though, where I send the entire PART 4 (IB) to someone interested in that technology, and the entire PART 5 (PI) to someone, etc. Chapters build on previous chapters so it's hard to review isolated chapters. Right now no complete section is ready to go.

[Carl-NC]

Because I'm "nostalgic", old school, I understand analog solutions more easily.
And when the assembly is divided into many subassemblies; it's easier for me to follow the idea.

We are not much different. All of the projects are analog with the exception of micros used for timing pulses (both VLF & PI). The circuits are built up from subcircuits that are individually presented and discussed. So maybe you will like it after all!

[Carl-NC]

[FONT=comic sans ms]You must have at least forty years in front of you unless you get hit by that beer truck or try to drink it dry.

If I tell my partner I'm writing another book, then she'll kill me.

[ivconic]

We are not much different. All of the projects are analog with the exception of micros used for timing pulses (both VLF & PI). The circuits are built up from subcircuits that are individually presented and discussed. So maybe you will like it after all!

What's not to like!
ITMD1 paved the way and laid good foundations.
Everything that is further developed in that direction; it can only get better.
What are your predictions; when will the first copies be off the press and ready for distribution?

[Carl-NC]

What are your predictions; when will the first copies be off the press and ready for distribution?

I have no idea. I think I can now say with certainty it will publish in 2023, but not the first half. I will set Sept 1 as a goal.

[6666]

Carl is Sept 1 still the goal. ?

[Carl-NC]

Still a chance, but slim. Still hoping before December.

[6666]

Still a chance, but slim. Still hoping before December.

cool thanks

[green]

Still a chance, but slim. Still hoping before December.

Still hoping before December?