TESORO GOLDEN SABRE

[simonbaker]

I probably have 30+ hours of field use on Ivconic's version with fantastic results. I only have a few hours on this version and my only concern is stability. I actually replaced the 1M Ohm resistors with the original 470K Ohm resistors used on earlier versions, just because I can't keep it quiet on occasion. Doubling the gain on this stage is a two edged sword. I'm not saying that someone else may not have good results with this version and replacing the 1M Ohm resistors is easy. I think that I may have better results far away from electrical noise.

Also, question for Eduardo: Is the 100uF cap circled below a substitute for all the 100nF decoupling caps on Ivconic's version? (Note.. Decoupling caps are not pictured on any of the schematics but are evident on Ivconic's TGSL PCB version). There is a reason for using 100nF decoupling caps, especially for the LM308s. Typically, smaller ceramics do a better job of filtering noise over the electrolytics, at least that is what I have read. I'm just looking for justification on leaving off the 100nF caps.

As far as the audio section, this is the way to go to drive an speaker!

Silverdog, I'm working on documentation at the moment. I need to get more than just a "read only" version of Adobe!!

I use NitroPDF which is not bad and was cheap (with a rebate at Frys) and can be had with a 14 day free trial. I know there are others too. Adobe is usually expensive!

-SB

[eduardo1979]

Tgsl Edu

Hello. All 100nF capacitors have been replaced by one, which is to 100uF. I have tried to simplify this circuit and give more profit by replacing the 470K and 1M resistors and capacitors of 10uF,and 22uF capacitors. The good part of my project is the audio and power supply is put into the top plate and the negative speaker connects directly to the mass of the source of alimentacion.Si to someone more interested in the version of Ivconic the same can be done with it, all you have to change the values of the above components. Honestly I like how my version and I've never had problems with some vital signs false. Greetings. Eduardo.

[Qiaozhi]

Silverdog, I'm working on documentation at the moment. I need to get more than just a "read only" version of Adobe!!

If you download OpenOffice, you can create PDF files from "File > Export as PDF...".

http://download.openoffice.org/

[dfbowers]

Now all the previous boards have gone, I have just taken delivery of some new ones, based on the TGSL-EDU design by Eduardo, and very sexy they are too, black with immersion gold (well it is Golden Sabre)

Hopefully these are 100% correct.
It would be nice to have a matching schematic and "idiots" guide, I will start a new thread TGSL-EDU, and post details of these boards, if anyone can help populate the thread with useful info , scope pics, coil help etc.. it would be a great help to members

regards

Silverdog

I probably have 30+ hours of field use on Ivconic's version with fantastic results. I only have a few hours on this version and my only concern is stability. I actually replaced the 1M Ohm resistors with the original 470K Ohm resistors used on earlier versions, just because I can't keep it quiet on occasion. Doubling the gain on this stage is a two edged sword. I'm not saying that someone else may not have good results with this version and replacing the 1M Ohm resistors is easy. I think that I may have better results far away from electrical noise.

Also, question for Eduardo: Is the 100uF cap circled below a substitute for all the 100nF decoupling caps on Ivconic's version? (Note.. Decoupling caps are not pictured on any of the schematics but are evident on Ivconic's TGSL PCB version). There is a reason for using 100nF decoupling caps, especially for the LM308s. Typically, smaller ceramics do a better job of filtering noise over the electrolytics, at least that is what I have read. I'm just looking for justification on leaving off the 100nF caps.

As far as the audio section, this is the way to go to drive an speaker!

Silverdog, I'm working on documentation at the moment. I need to get more than just a "read only" version of Adobe!!

[simonbaker]

I agree that it is very confusing, and the correct position for the overlap is best determined by experiment. There is also a difference between the way a concentric and a DD coil reacts to metal targets. The description that you quoted in your post is an old one, and it refers to the concentric coil. With the GEB control set to mid-position, simply adjust the coil overlap such that the GEB sample pulse is over the zero-crossing point on the RX signal (as measured at the pre-amp output). You will find there are two possible positions that work, but one of them will give better results.

I keep returning to the point that the null phase may have a "non-magnetic" component that is irrelevant to ground-balancing. In other words, the null signal is:

A*sin(phi1) + B*sin(phi2)

If the "B" component is non-magnetic, then ferrite is only modulating the "A" component, and it will be misleading to use the entire null signal phase as a basis for positioning coils for best GB pot setting.

Here is a practical test. Null your coils. Now put a big honking piece of ferrite in the overlap of the coils and look at the RX signal. The signal should be much larger than the simple null signal. If the phase of the big signal is shifted from the original null signal, then I suspect that your original null signal is misleading -- it is not the signal that will be amplitude-modulated by ferrite/ground material because it has a non-magnetic component.

So to see your "real" null signal, the one that ferrite will modulate, put a piece of ferrite in the overlap to create a big, dominent null signal. I'll bet that this large signal will have two main phases, one on each side of the null point, as you shift your coils around, and there will only be a very small region where the phase takes on intermediate values. Following Qiaohzi's overlap advice, I would choose the side with more overlap, and a fairly small null value, and really not fuss too much about intermediate phase values because they are non-important for ground balancing.

I guess I'm really saying you can't choose the null phase for ground balancing (by shifting the coils) other than one of the two main phases with the TGSL. And by serendipity, both work fairly well.

There may be other considerations regarding which main null phase to choose which we haven't been referring to here, so always more discussion possible.

-SB

[bernte_one]

sexy one

it looks nice bling bling would be my first non pi

[silverdog]

TGSl New Boards

Now all the previous boards have gone, I have just taken delivery of some new ones, based on the TGSL-EDU design by Eduardo, and very sexy they are too, black with immersion gold (well it is Golden Sabre)

Hopefully these are 100% correct.
It would be nice to have a matching schematic and "idiots" guide, I will start a new thread TGSL-EDU, and post details of these boards, if anyone can help populate the thread with useful info , scope pics, coil help etc.. it would be a great help to members

regards

Silverdog

[Qiaozhi]

Hello!

Sorry that I digged up this old post, but I got a question:
In Gifford patent, mineral/starting signal you ar talking about is leading TX so isnt that mean its +90deg instead of -90deg?
And for TGS , rx phase should be lagging TX about 20deg(-20deg)? Im asking this because I can get TGSL working with eather + and - (20 till 30)deg null shift (disc is same good, as well as GB and sensivity with both)
And I read as well (Qiaozhi said that too)that all targets should shift to the left and for ferros targets A should decrease and for non-f A should increase. And GB sample (square wave 0V part) should be at zero cross of RX signal(where sine goes from neg to pos) and DISC at positive peak of RX. I can make this happen if RX null shift relative to TX is -20deg.
But why i dont see difference? Why one is better than other? Im testing only on bench....
Which phase should I choose?Positive or negative?

Gifford patent: http://www.geotech1.com/pages/metdet.../US4486713.pdf

I agree that it is very confusing, and the correct position for the overlap is best determined by experiment. There is also a difference between the way a concentric and a DD coil reacts to metal targets. The description that you quoted in your post is an old one, and it refers to the concentric coil. With the GEB control set to mid-position, simply adjust the coil overlap such that the GEB sample pulse is over the zero-crossing point on the RX signal (as measured at the pre-amp output). You will find there are two possible positions that work, but one of them will give better results.

[habitbraker]

Hi Max,

I don't think this is quite correct.
The Gifford patent can be a bit confusing, especially when you start building your own detectors, and the results don't appear to match.
I think the main problem is that the Gifford patent shows the phase-shifts associated with an under-nulled coil, whereas the Tesoro coils are over-nulled. (See my previous reply to zzy.) This means that all the phase-shifts are to the right, and the metal sampling point is on the negative-going zero-crossing, not the positive-going, as for the Tesoro. You should also note that the MINERAL signal is actually the RX signal in it's ground balanced position (i.e. no metal present) and this has been assumed to have a starting phase-shift (relative to the TX) of -90 degrees. For the Tesoro coils, this phase-shift is something like +30 degrees.

Hello!

Sorry that I digged up this old post, but I got a question:
In Gifford patent, mineral/starting signal you ar talking about is leading TX so isnt that mean its +90deg instead of -90deg?
And for TGS , rx phase should be lagging TX about 20deg(-20deg)? Im asking this because I can get TGSL working with eather + and - (20 till 30)deg null shift (disc is same good, as well as GB and sensivity with both)
And I read as well (Qiaozhi said that too)that all targets should shift to the left and for ferros targets A should decrease and for non-f A should increase. And GB sample (square wave 0V part) should be at zero cross of RX signal(where sine goes from neg to pos) and DISC at positive peak of RX. I can make this happen if RX null shift relative to TX is -20deg.
But why i dont see difference? Why one is better than other? Im testing only on bench....
Which phase should I choose?Positive or negative?

Gifford patent: http://www.geotech1.com/pages/metdet.../US4486713.pdf

[simonbaker]

Hi Don ,

That was my exact same idea when I started my ' TGS for Dummies '.
I've started with much enthusiasm to gather all information and would add photo's as in the 'TGScompare' document and / or with videoclips as the ones I've posted on Youtube.

Unfortunately my pcb would not co-operate is much as I would ( perhaps this is an other way to say that I just don't understand it ), especially the phase shift between Tx and Rx.
So how to write , photograph etc without a working pcb, thats why it will take some more time , the enthusiasm however is still there.

I've ran into the same problems as Habitbraker posted : Phase shift >> 20 degrees ...
I guess I've been staring myself blind on this issue and it's time to move on.

kind regards ,

Dennis the Mennis

Hi DtM! You'll get there because you have the right approach!

On the general topic:

Even though I've said my piece about the null phase, let's review what we mean.

1. When someone says 20 degrees, what signal is being measured? Rx coil leads, or output of LF353? Is the Rx coil connected to the PCB or disconnected (I assume connected).

2. What is the null signal phase referenced to? (The Tx signal I presume).

3. What does 20 deg mean, leading, or lagging? How do we measure lead or lag?

Diagrams would be useful to make sure we're meaning the same thing here.


-SB

[simonbaker]

Problem solved! I was sprayed pcb standers too so that they touched PCBs GND plane on the sides(where screws are). In other words I was grounded PCB to case with more than one "wire". I guess ground loops occured.
Took off that spray from few places and it took care of case touching problem

Good work. Just curious, what was the azimuth and right ascension of Venus at the time...?

[Dennis the Mennis]

Thanks Qiaozhi..

I'm wondering if that is just to get the phasing for DISC an GB to work correctly, and if there is some mathamatical explanation that's easy to understand.

I'm in the middle of writing a TGSL "101" manual, sort of like the "TGS(L) for Dummies" idea.
I would like to get that detail correct as that question comes up frequently.

When I complete it, maybe add it to the "TGSL compete details".. It may curb a lot of the repetitive questions from new builders that don't read or cannot find a lot of the important points buried in the huge thread! But.. reading all the threads give great insight on how things are arrived at!!

Of course, one of the best ways to learn something is to write about it..

Hi Don ,

That was my exact same idea when I started my ' TGS for Dummies '.
I've started with much enthusiasm to gather all information and would add photo's as in the 'TGScompare' document and / or with videoclips as the ones I've posted on Youtube.

Unfortunately my pcb would not co-operate is much as I would ( perhaps this is an other way to say that I just don't understand it ), especially the phase shift between Tx and Rx.
So how to write , photograph etc without a working pcb, thats why it will take some more time , the enthusiasm however is still there.

I've ran into the same problems as Habitbraker posted : Phase shift >> 20 degrees ...
I guess I've been staring myself blind on this issue and it's time to move on.

kind regards ,

Dennis the Mennis

[habitbraker]

Problem solved! I was sprayed pcb standers too so that they touched PCBs GND plane on the sides(where screws are). In other words I was grounded PCB to case with more than one "wire". I guess ground loops occured.
Took off that spray from few places and it took care of case touching problem

[habitbraker]

Hmm... Try this. Unmount it and see if that fixes your problem. Or, ground the case of the pot with an extra wire right to ground.. I will bet that your problem goes away!

I think that adding a small bit of capacitance to the pot with your hand is just enough to cause a small phase shift in the GB circuit.

tried unmounting GB pot - no difference. Tried lift all panel out - no difference. And back panel is sensitive too though...
Its almoast like its detecting metal - when I dinamically move metal very close those panels, It beeps. I think I failed a litte bit with that spraying
Its hapening in all metal mode only. Disc mode is perfect quiet.
In spite of this little problem its working perfect. Although my shielded coil makes large min null (about 1.3VPP) and my null phase is far from 20deg(around 70deg), I can totally reject 20cm ferrite in close to middle GB pot, with close to max sensivity can detect silver and coins at 30cm while discriminating iron and al foil.
Next is coil enclosure and potting.

[Qiaozhi]

... in which case, you are stuck with choosing one or the other by choosing one side of the null point or the other.

The "normal" decision is to choose the side that provides the largest overlap between the coils. This will increase the size of the sensitive area.