IGSL

[der_fisherman]

Yes, you would need to look at schematic and see which channel is connected to high tone, and which to low tone. It would be nice to label the low tone disc1 and high tone disc2 for example on the PCB/schematic.

However you can easily determine this experimentally before you mount the pots in the enclosure. Other than the tones, the two channels are identical I believe so you can set them up (disc pot positions) any way you want by experimenting.

I would probably just mark 10 positions and experiment with targets to see where they discriminate.

Then I would probably set up my IGSL in one of many creative modes:

1. One channel detects iron, the other channel detects everything.

2. One channel detects the bottom 2/3 metals (iron, foil, nickel, pull-tab), the other channel detects
the top 2/3 channels (nickel, pull-tab, copper, silver). This gives:

a. low-tone = iron, foil
b. both tones = nickel, pull-tab
c. high tone = copper, silver

3. Both channels overlap on a single metal such as gold/foil

a. low = iron
b. both = foil/gold
c. high = nickel, pull-tab, copper, silver



Regards,

-SB

Great post Simon, I (I am sure I am not alone!) am starting to understand IGSL better, many thanks.

Andy

[simonbaker]

Great post Simon, I (I am sure I am not alone!) am starting to understand IGSL better, many thanks.

Andy

My typo error:

2. One channel detects the bottom 2/3 metals (iron, foil, nickel, pull-tab), the other channel detects
the top 2/3 channels (nickel, pull-tab, copper, silver). This gives:

should be:

2. One channel detects the bottom 2/3 metals (iron, foil, nickel, pull-tab), the other channel detects
the top 2/3 metals (nickel, pull-tab, copper, silver). This gives:


-SB

[golfnut]

tones

sounds like an 80's tennis game - 30 love

Seriously though if you stamped a blank ally disk, a gold coin, iron, all the same size... etc would they all sound the same?

Is the phase response different for the metals? An acid test would be same physical size/thickness targets - but different metals.

If these continue to look good - and I think they will I be dusting the soldering iron off and have a go.

The coil and sheilding stuff is the only bit I am scared of, the basic electronics is clear enough.

It does take loads of dedication to get this much info into one place - so thanks to the relevant people - you know who you are.

steve

[simonbaker]

Yes, you would need to look at schematic and see which channel is connected to high tone, and which to low tone. It would be nice to label the low tone disc1 and high tone disc2 for example on the PCB/schematic.

However you can easily determine this experimentally before you mount the pots in the enclosure. Other than the tones, the two channels are identical I believe so you can set them up (disc pot positions) any way you want by experimenting.

I would probably just mark 10 positions and experiment with targets to see where they discriminate.

Then I would probably set up my IGSL in one of many creative modes:

1. One channel detects iron, the other channel detects everything.

2. One channel detects the bottom 2/3 metals (iron, foil, nickel, pull-tab), the other channel detects
the top 2/3 channels (nickel, pull-tab, copper, silver). This gives:

a. low-tone = iron, foil
b. both tones = nickel, pull-tab
c. high tone = copper, silver

3. Both channels overlap on a single metal such as gold/foil

a. low = iron
b. both = foil/gold
c. high = nickel, pull-tab, copper, silver



Regards,

-SB

Well, I was a little sloppy in my thinking so I need to correct myself for the umpteenth time.

Other than the tones, the two channels are identical I believe so you can set them up (disc pot positions) any way you want by experimenting.

Not so fast glib gums... there is another important difference between the two channels (besides tone), which a kit builder would want to know about when assigning pots to the front panel of his/her control box.

One disc channel rejects metals below a certain phase (pot setting), the other channel rejects metals above a certain phase (pot setting). (If I'm saying this wrong just shoot me.)

This is the property that allows the creative modes described.

I would have to stare at the circuit for a while to hazard a guess as to which tone is assigned to which of those channels. I would guess that probably the low tone is assigned to the channel that rejects metals above a certain phase (the unconventional channel), and the high tone is assigned to the channel that rejects metals below a certain phase (conventional channel).

I hope I did not add too much to the informational entropy of this topic with these comments.

Regards,

-SB

Someday Qiaozhi might as well make my posts 24 hour editable so I can clean up the moose droppings I habitually leave and realize in the middle of the night...

[der_fisherman]

Search coil construction

sounds like an 80's tennis game - 30 love
Seriously though if you stamped a blank ally disk, a gold coin, iron, all the same size... etc would they all sound the same?
Is the phase response different for the metals? An acid test would be same physical size/thickness targets - but different metals.
If these continue to look good - and I think they will I be dusting the soldering iron off and have a go.
The coil and shielding stuff is the only bit I am scared of, the basic electronics is clear enough.
It does take loads of dedication to get this much info into one place - so thanks to the relevant people - you know who you are.
steve

Hi Golfnut (love the name by the way! But have you only one? "Golfnuts" might be even better!!),

if you follow the advice given in Don Bower's great TGSL 101.pdf, part I with regard to building a former for the coil production first, you really won't have any problems in producing the Tx & Rx coils, including Faraday shield and insulation. (Even I did it!!)

I took a simple electronic counter (2 x on ebay for about $8 including post), see that attachment, added some short wires and a micro-switch to it and it counts exactly how many coil turns are made. Still allows the button to work as well if ever needed.....I was happy to buy 2 just in case I screwed the first one up!!

Now by the time you get those coils done, we (not me though!) should have decided here as to whether a "deep null" or a "4-15mVolt" null is best.....I feel that the "4-15mVolt" is "Winning" at this moment because Ivconic recommends it, but come back and read these pages before setting the coils forever in epoxy!!!

If you happen to have a wood router in the garage, and you can handle it, I can show you some pictures of the plywood search coil head that I have made, but not yet Epoxyed up!! Light but strong and really easy to produce and make it and make it look good. A few simple rules to make the coil slots as small as possible to reduce the amount of Epoxy (heavy stuff) needed. Any cutting errors can also be corrected with flexible car body filler!

I have made search coils in this way before and they are still 100% in order!! It seems to work quite well....

Nuff said!!

Regards

Andy

[Qiaozhi]

Someday Qiaozhi might as well make my posts 24 hour editable so I can clean up the moose droppings I habitually leave and realize in the middle of the night...

There is already a 60 minute limit on editing a post. Which means you have a maximum of 60 minutes to discover any gaffs before they become permanent.

It's always better to think twice and write once.

[Qiaozhi]

Now by the time you get those coils done, we (not me though!) should have decided here as to whether a "deep null" or a "4-15mVolt" null is best.....I feel that the "4-15mVolt" is "Winning" at this moment because Ivconic recommends it, but come back and read these pages before setting the coils forever in epoxy!!!

This has already been discussed many many times, ad infinitum.
The deep null will not produce the best results for two fairly obvious reasons:

1. The initial phase-shift between the TX and RX coils must be correct for the discrimination circuitry to work properly, otherwise it will be out of range of the sample pulse timing. With a deep null, the initial phase-shift is completely wrong. You can clearly see this in the graphs posted earlier in this thread, and a simple experiment involving an oscilloscope will demonstrate this fact. You can even see it in a SPICE simulation.
2. With a deep null, the residual amplitude is very small (close to zero), which again means the discrimination circuitry is unable to do its job. Commercial Tesoro coils I have measured usually have a residual voltage of approximately 15mV. The discrimination circuits need to sample the RX waveform at the in-phase and quadrature positions. If the RX signal is buried in noise, the detector will fail to function correctly. However, this second point is somewhat academic, in the case of the TGSL (or IGSL), as point one has already been violated.

As I said several times before - the simplest method of balancing the coils is to use a small ferrite slug. Set the GEB pot to its center position, with DISC off. Move the coils closer together until you reach the null, then continue overlapping the coils until ferrite is rejected. After that, follow Ivconic's suggestions for testing with both ferrous and non-ferrous targets before fixing the coils in position.

[der_fisherman]

This has already been discussed many many times, ad infinitum.
The deep null will not produce the best results for two fairly obvious reasons:

1. The initial phase-shift between the TX and RX coils must be correct for the discrimination circuitry to work properly, otherwise it will be out of range of the sample pulse timing. With a deep null, the initial phase-shift is completely wrong. You can clearly see this in the graphs posted earlier in this thread, and a simple experiment involving an oscilloscope will demonstrate this fact. You can even see it in a SPICE simulation.
2. With a deep null, the residual amplitude is very small (close to zero), which again means the discrimination circuitry is unable to do its job. Commercial Tesoro coils I have measured usually have a residual voltage of approximately 15mV. The discrimination circuits need to sample the RX waveform at the in-phase and quadrature positions. If the RX signal is buried in noise, the detector will fail to function correctly. However, this second point is somewhat academic, in the case of the TGSL (or IGSL), as point one has already been violated.

As I said several times before - the simplest method of balancing the coils is to use a small ferrite slug. Set the GEB pot to its center position, with DISC off. Move the coils closer together until you reach the null, then continue overlapping the coils until ferrite is rejected. After that, follow Ivconic's suggestions for testing with both ferrous and non-ferrous targets before fixing the coils in position.

Thanks

[petravka]

IGSL 27cm coils

[golfnut]

question-s

Hi Silverdog.

I know you do kits for the IB detectors.

I also realise that as these projects continually evolve / modify / enhance - project names, revisions, pcbs, placement, acronyms change too.

If I wanted the latest 'x'gsl - what would I ask you for?
What would turn up?


The pcbs are
TGSL - older beast - well proven
TGSL - EDU - Eduardos version?
IGSL - Initial one, or only one?
IGSL - Musketeer - Recent with mods to cct for a dedicated coil from a vendors unit?

Im a bit like andy (not as bad tho) - as stuff is being sold, Ive got a bit of a customer view to it - not full on hobbyist.

Steve

[silverdog]

Hi Golfnut

The latest is IGSL, the 2 versions are for a Tesoro Coil or a Minelab Musketeer Coil
You can buy a coil, or attempt to make your own (if buying the Tesoro must be a 5 pin)

TGSL-EDU is simpler and still very good
IGSL is more advanced, more control, 2 tones for target ID, but more complicated to setup

regards

Silverdog

[golfnut]

order

Hi Silverdog.

If I ordered one of the IGSL kits today, would you include an up to date schematic and placement.

Plus a link to the exact coil to make. That others have done to go with my kit..

Im not being fussy beleive me , I am a dyslexic - and the thought of reading 4700 posts whould put me out.



Steve

[Qiaozhi]

Hi Silverdog.

If I ordered one of the IGSL kits today, would you include an up to date schematic and placement.

Plus a link to the exact coil to make. That others have done to go with my kit..

Im not being fussy beleive me , I am a dyslexic - and the thought of reading 4700 posts whould put me out.



Steve

If you are a beginner at building your own metal detector, I would strongly suggest that you start with the TGSL. All the details you need can be found here ->
http://www.geotech1.com/forums/showthread.php?t=15710
Buy a kit from Silverdog, and you're halfway there. If you can acquire an original Tesoro coil (5-pin), then get one. This will make your job a lot easier. After that you can experiment with your own coils, and eventually work your way up to an IGSL from there.

[simonbaker]

This has already been discussed many many times, ad infinitum.
The deep null will not produce the best results for two fairly obvious reasons:

1. The initial phase-shift between the TX and RX coils must be correct for the discrimination circuitry to work properly, otherwise it will be out of range of the sample pulse timing. With a deep null, the initial phase-shift is completely wrong. You can clearly see this in the graphs posted earlier in this thread, and a simple experiment involving an oscilloscope will demonstrate this fact. You can even see it in a SPICE simulation.
2. With a deep null, the residual amplitude is very small (close to zero), which again means the discrimination circuitry is unable to do its job. Commercial Tesoro coils I have measured usually have a residual voltage of approximately 15mV. The discrimination circuits need to sample the RX waveform at the in-phase and quadrature positions. If the RX signal is buried in noise, the detector will fail to function correctly. However, this second point is somewhat academic, in the case of the TGSL (or IGSL), as point one has already been violated.

Respectfully I have not finished considering this subject, and may have some more thoughts about it that do not concur exactly with those statements. I know it seems beaten to death and that Qiaozhi and I spent a lot of time on it, but some new angles have come to mind that I need to look into before signing off on the "conventional wisdom". However, I agree with the nulling method described.

Regards,

-SB

[silverdog]

Hi Silverdog.

If I ordered one of the IGSL kits today, would you include an up to date schematic and placement.

Plus a link to the exact coil to make. That others have done to go with my kit..

Im not being fussy beleive me , I am a dyslexic - and the thought of reading 4700 posts whould put me out.



Steve

Hi Golfnut

There is no placement as such - use the silkscreen on the pcb

I have added the relevant documents to the library box on the right hand side of my shop (silverdog.co.uk)

regards

Silverdog