IGSL

[Davor]

There is another "stealth IGSL" modification on the way: LF351 is not required at all. There is an identical circuit with ample driving force, U1b LM833 (or NE5532, same thing). Modification means just rewiring a potentiometer P2 (of the FE block) so that CCW and CW terminals go parallel to the respective terminals of a P1 potentiometer, and a wiper terminal goes to its usual place on PCB. LF351 can then be safely extracted, and a few milliamps are saved. And everything works perfectly well

I populated most of my 2 IGSL boards, and now I have to decide what modifications will be applied prior to reviving them. I decided to go with "ikebana" solution for correcting LM339 mistake in FE channel.

Mosquitoes are murder at night, and seawater is so good by days.

[Davor]

Just found something... capacitors C7 and C9 might need some beefing up for a musketeer version. While playing with lower impedance frontend, I encountered a little SNAFU: If I do it right and make it true differential, coil loading becomes more pronounced and Rx response becomes phase shifted more than the expected ~12° so GEB comes to question. Hence, I need some more phase span.
Whoever encountered a problem of GEB that does not behave can increase C7 and C9 to 220pF, and thus widen GEB tuning range by double in the right direction.

[Davor]

So whoever wishes to play with discrimination/GEB switchers, I'm attaching a LTspice circuit that is somewhat changed version of a circuit by porkluvr from a post #1150 of this topic. I replaced comparators with switches so that it converges while I'm still young (it is darn fast this way). I also replaced Rx frontend values with equivalent differential impedance of 6k8 - it is comprised of the most common values I could combine, and a differential impedance error is negligible.

And I changed a 100p to 220p as indicated in a previous post.

Enjoy

[ivconic]

Davor i am really having good faith in your capabilities to improve IGSL.

But:

"...I populated most of my 2 IGSL boards..."

This directly indicates that you are still not having finished and operational IGSL?
Other words; you haven't it, at least, yet, switched on, to see it's behavior?
Other words; you don't have at least 1 second experience with "live" IGSL?
Right?
Than how can you say something like:

"...LF351 is not required at all..." and "...LM339 mistake in FE channel..." !???

And at the same time you are claiming something like:
"...And everything works perfectly well..." !?!?!?!?

So? Let's summarize all this:
actually; you are not having finished and ready detector and you actually NEVER ever saw it in "live" action - YET you are claiming it has terrible mistakes and lacks and
your virtual and imaginary mods "are working perfectly well" !!?!?!?



Sorry, but i am completely confused!

[Davor]

Yes, it is one way of looking at it

On the other hand, there are some things in electronics, as well as in any other creative process, that are more obvious to a complete lamer than the author himself. A procedure is called "proofreading" and I am never ashamed to ask someone outside of a project to take a peek and clear some obvious mistakes. Those are the most difficult to spot.

Of all MD projects I picked IGSL, not to make fun of the author's work, but to own a good DIY detector and learn a lot in a process. I do think IGSL is a very mature project worth building, and tinkering with.

For example, LF351 rotates a phase in exactly the same fashion as the second LM833 opamp does, but the business part of the process is happening at the potentiometer wiper. Placing two potentiometers in parallel, and supplying their wipers signals to separate comparators works exactly the same as if you use additional LF351. No difference at all. OK, there are a few milliamps less power, but that's even better.

I am confident that my IGSL will beep by the end of the week, if no delays come its way, and I hope to have a video of its operation.

You are right about my unsubstantiated claims. It is kind of wrong to count one's chickens before they are hatched, but trouble is that making changes afterwards is more painful than making them while populating a board, so I tend to analyse circuits as I go and make changes where I find appropriate. This IGSL project of mine is my study of VLF MDs in general and please don't be offended by my comments. At the end it will be just fine, and I just hope we all benefit from it.

Peace?

[Qiaozhi]

On the other hand, there are some things in electronics, as well as in any other creative process, that are more obvious to a complete lamer than the author himself. A procedure is called "proofreading" and I am never ashamed to ask someone outside of a project to take a peek and clear some obvious mistakes. Those are the most difficult to spot.

I think what Ivconic is trying to say is:
If you have 2 IGSL boards, then it would make more sense to build one using the original scheme, and then use the second one for your improvements. As it stands, you have nothing to compare with the original.

[ivconic]

I think what Ivconic is trying to say is:
If you have 2 IGSL boards, then it would make more sense to build one using the original scheme, and then use the second one for your improvements. As it stands, you have nothing to compare with the original.

Yes, something like that!
Even if he had only one pcb; would be smarter to finish it with original components, try it, test it, analyze... and than having some live experiences with it : to modify it.
That's how he would have references.
Otherwise; he is risking to fall in to numerous "traps" as such design can have.
I am talking from personal experience. Also i remember, from the past, lot of similar situations related to TGSL.
To avoid trivial issues; it is better to make it as it is than later to change it.

[ivconic]

"...On the other hand, there are some things in electronics, as well as in any other creative process, that are more obvious to a complete lamer than the author himself. A procedure is called "proofreading" and I am never ashamed to ask someone outside of a project to take a peek and clear some obvious mistakes. Those are the most difficult to spot...."

Yes you are right, i agree. I was "victim" (being blind to see some obvious mistakes, many times so far) of my own work.
If there were no good people from this forum; i would never finish some of my works. That's for sure.

"..Of all MD projects I picked IGSL, not to make fun of the author's work, but to own a good DIY detector and learn a lot in a process. I do think IGSL is a very mature project worth building, and tinkering with...."

As i said before: i am very glad that somebody is interested in my efforts. IGSL is not finished project. Need much more to be done.
Reading your observations on other threads; i see that you are well educated and conversant fellow.
Reason more to feel honored with your good will to continue work on this unfinished idea.
I only want to prevent you from wasting time and making wrong conclusions that you may get playing only with simulators.

"..For example, LF351 rotates a phase in exactly the same fashion as the second LM833 opamp does, but the business part of the process is happening at the potentiometer wiper. Placing two potentiometers in parallel, and supplying their wipers signals to separate comparators works exactly the same as if you use additional LF351. No difference at all. OK, there are a few milliamps less power, but that's even better...."

Ok, that's negotiable. I involved second GEB because i couldn't make it right with only one.
Hopefully you are right on this, nobody will be more happy than me!
Yet involving second GEB i finally got pretty clear situation there. Both blocks can be separately adjusted.
Even more; Fe block can be used further to "listen" even soil change itself, not only presence of iron in soil (even better if one day nonmotion is added).
Beneficial in meteorite hunting and nugget hunting.

"..I am confident that my IGSL will beep by the end of the week, if no delays come its way, and I hope to have a video of its operation...."

Looking forward!

"...You are right about my unsubstantiated claims. It is kind of wrong to count one's chickens before they are hatched, but trouble is that making changes afterwards is more painful than making them while populating a board, so I tend to analyse circuits as I go and make changes where I find appropriate. This IGSL project of mine is my study of VLF MDs in general and please don't be offended by my comments. At the end it will be just fine, and I just hope we all benefit from it..."

It is good that you are having 2 boards. One you can do as "original" and on another you can apply changes in parallel.
C'mon! No offends at all! My bad English maybe looks like i am angry or offended but i can assure you it is not the case.
I just want to clear up all the steps you are taking, one by one.
Because i am waiting further ideas and following each move and suggestion.
If i don't ask now; later i may loose connection with progress.
There are few huge threads on Geotech which i followed only occasionally and got completely lost in numerous pages and posts.
Now when i need some info ; i have troubles to find exact post.
Just look TGSL thread! It is scary even to think on searching some old info there!
Ok, we are clear now, i hope.
Keep on going.
Wish you success!
Cheers!

[simonbaker]

I am still populating my IGSL and due to some family obligations I'll have to stop for the weekend

Anyway, I think I found the main source of chatter and odd and shortened responses. It is the combination of LPF and compression that in effect shift phases between GEB and Disc channels. Otherwise they are in phase or in counterphase, but these shifts make things more interesting. I'd say signal is overfilterred, and I may come up to some bullet proofgain stage that behaves.

Keep tuned...

Can you describe more fully in detail what you mean?

-SB

[Davor]

...Ok, that's negotiable. I involved second GEB because i couldn't make it right with only one.
Hopefully you are right on this, nobody will be more happy than me!
Yet involving second GEB i finally got pretty clear situation there. Both blocks can be separately adjusted.
Even more; Fe block can be used further to "listen" even soil change itself, not only presence of iron in soil (even better if one day nonmotion is added).
Beneficial in meteorite hunting and nugget hunting.

Now that you are mentioning a second GEB... I didn't foresee these soil features that you mention, but they make sense. I'll surely try experimenting on these once my rig is ready.
Anyway, LF351 - or not, all features remain the same as before.

[ivconic]

Now that you are mentioning a second GEB... I didn't foresee these soil features that you mention, but they make sense. I'll surely try experimenting on these once my rig is ready.
Anyway, LF351 - or not, all features remain the same as before.

Yes, NFe GEB will provide you good immunity on soil conditions when detecting nonferrous metals and signal will be indicated with high pitched audio.
While at the same time a bit lose Fe GEB will allow low pitched audio to indicate sudden soil changes, presence of iron and ferittes etc..etc...
This is not possible with only one GEB channel.
With one GEB channel you will "choke" both blocks.
However; it is not mistake to omit one GEB and adjust GB to both blocks the same, in case you are not interested in other signals i mentioned.
Either way is ok.

[Davor]

Can you describe more fully in detail what you mean?

-SB

This will require a short "ab ovo" explanation, but here you go. In these VLF Rx-es coil signal is sampled by two phase shifted LO-s and a resulting signal is amplified by respective gain block. These resulting signals are either in phase or in counterphase, and represent target response envelope. Phase as defined by LO-s will decide whether this signal is positive or negative at some moment, and that results in target discrimination. In case of IGSL and TGSL both gain blocks must supply positive signal to the comparators gates (AND function), and they turn high impedance and a GEB signal is passed to a tone producing circuitry.

So, to have a positive confirmation of a target in a specified span of angles (discrimination) both disc and GEB channels must be positive. That is the one quadrant detection: positive I and positive Q.

In all other instances there should be no firing of tone.

But... there are also noise, interferences, and phase troubles.

For noise you have a threshold control, in IGSL this is called "Disc sens". So you set it to the lowest possible setting that will not annoy you.

Interferences are a bit different because their result may rotate in phase at speed that passes through gain block filters, and their power may be quite high, e.g. two metal detectors operating nearby. I'm afraid that only a coil arrangement that cancels far field can help here for real. Or you crank up the "Disc sens".

And now - the feature content: phase troubles. Both TGSL and IGSL, and I guess many Tesoro detectors have a very specific gain block configuration with one diode in each stage. There is nothing wrong with it when you deal with low signals, but there is a phase shift with stronger signals. This shift comes from the fact that net. impedance in gain stage feedback lowers when diode conducts, and more so with stronger signals. If both disc and GEB channels are supplied with equally strong signals there would be no problem because both shifts would be ~ the same and nothing spectacular would happen. Trouble is that it is seldom the case, and being a motion compensated detector as it is, even for situations with GEB and disc being in counterphase at samplers - there are spikes at phase overlap later on.

TGSL's gain block diodes create a phase shift with rising signal, but tackle its problems by making a positive response shrink to a shorter pulse, and on top of it apply the severe "anti chatter filter" to make it even shorter. Doing so they hurt low signal detection, and also detection of signals that produce big differences in amplitude in GEB against disc. That is the main reason it got so much of my attention.

How to fix it? I think the easy way to fix the unruly gain stages phases is to remove all compression function from the first stage, and remove all LPF function from the other. In other words, a diode is removed in the first stage and placed antiparallel to the diode in second stage, and remove a capacitor in feedback of the second stage - so that you have a place for diode. This removes phase and pulse shortening problems, and some spikes appear only when first stage's output hits the rails.

I won't put the whole LTspice shebang here again because the mother of this solution is already placed in post #1289 - here is only a printscreen picture of the setup:

[ivconic]

Davor you are killing the depth like that.
Ok, i'll stop annoying, wait to finish your detector and you'll see.
Cheers!

[Davor]

Yes. The ultimate test.

I concluded that matching GEB and Disc phases stand for squeezing maximum juice from the lemon, and it just can't hurt depth. Total gain is the same, if not even better this way. We'll see.

Anyway, I hear only laments about black sands, but nothing about red clays and karst, Mediteranean white (non volcanic) beaches and stuff. What can I expect? OK, not golden nuggets, but what else?

[ivconic]

Yes. The ultimate test.

I concluded that matching GEB and Disc phases stand for squeezing maximum juice from the lemon, and it just can't hurt depth. Total gain is the same, if not even better this way. We'll see.

Anyway, I hear only laments about black sands, but nothing about red clays and karst, Mediteranean white (non volcanic) beaches and stuff. What can I expect? OK, not golden nuggets, but what else?

I checked your suggestions last night. Have one TGSL for such matters. Before mods it could detect coin at 32cm and after i applied mods it drops to barely 20cm.
I removed diodes from first LM358 (347 at IGSL) and removed 22nF from LM308's (also 347 at IGSL) and put another reversed diode instead there.
Audio response turned to be more sharp but detection drops significantly.
.....
Ancient Roman sites. I guess there are plenty of those, especially in North of your country.