IGSL

[der_fisherman]

Hi Gentlemen (any Ladies also here?),

I have a question about the setting up of the two coils for a VLF metal detector, that although I have made several VLF search coils in my life, I never gave any thought to this:-

1) Let us assume that I have say glued the left hand coil to the head, except for the part that may need to get adjusted to get a good null of course.
2) Now I lay the second coil on top, overlapping the first coil, but without glueing it for the moment. test.
3) I get a null, I think a "good" one so to say.
4) Does swapping the connections to the second coil make any difference, better or worse. Does it "change anything?
5) Is swapping the connections as above, electrically the same as "flipping the second coil over, end for end"?
6) Does it make any difference as to the direction the coil connections have? Phase?

Can anyone throw any light on this (particularly asking DFBowers!), or is it all just a waste of thought time and makes no difference whatsoever......

I have not see anything mentioned by anyone, not even Don in his great .pdf article on TGSL coil building which is more like a Bible than just a book for me!!!

I may be wracking my brain for nothing! But it would be great to know.

I cannot personally see that it matters, but what do I know????

Thanks to all in advance,

Andy

PS If I haven't made it clear enough as to my question, let me know and I will make a few diagrams.....

[ivconic]

Hi Gentlemen (any Ladies also here?),

I have a question about the setting up of the two coils for a VLF metal detector, that although I have made several VLF search coils in my life, I never gave any thought to this:-

1) Let us assume that I have say glued the left hand coil to the head, except for the part that may need to get adjusted to get a good null of course.
2) Now I lay the second coil on top, overlapping the first coil, but without glueing it for the moment. test.
3) I get a null, I think a "good" one so to say.
4) Does swapping the connections to the second coil make any difference, better or worse. Does it "change anything?
5) Is swapping the connections as above, electrically the same as "flipping the second coil over, end for end"?
6) Does it make any difference as to the direction the coil connections have? Phase?

Can anyone throw any light on this (particularly asking DFBowers!), or is it all just a waste of thought time and makes no difference whatsoever......

I have not see anything mentioned by anyone, not even Don in his great .pdf article on TGSL coil building which is more like a Bible than just a book for me!!!

I may be wracking my brain for nothing! But it would be great to know.

I cannot personally see that it matters, but what do I know????

Thanks to all in advance,

Andy

PS If I haven't made it clear enough as to my question, let me know and I will make a few diagrams.....

1) Correct. That's how i usually do.
2) Correct.
3) Correct. Good "null" is usually meaning minimal induced voltage at RX coil. Minimal residual voltage. At TGS/TGSL and now IGSL this is usually 5-15mV.
4) Of course! Shifting phase completely.
5) Seems so. But sometimes "electrically" can not replace "physically". So you better pay attention on coil windings orientation, "start" and "end" of windings... etc...etc..
6) Coils are usually gathered with same orientation of their windings. Clockwise or anticlockwise, both. It is irrelevant where on coil exactly you will "pull out" connections.
But you must respect orientation of windings at both coils.
So you better mark somehow both coils - to know later how to gather and overlap them.
"Start" and "End" of windings at both coils is important to know; which is where.
"Mother" of all answers lays in own personal experiments and experience!
Everything is much better understandable if done by your own hand and seen by your own eye.
Make detector, make coils, connect them together... put some voltage in there... and ... EXPERIMENT!

[der_fisherman]

Many thanks for that. I will experiment when I have built my machine.
regards
Andy

[ivconic]

Some hints more:
Today i finished IGSL (for Musketeer coils) on last pcb version posted already on this topic.
Haven't LF351 for U12 so put TL071 instead... Not happy with it!
IGSL is working. Air depths with TS1000 coil are just great! 1 e coin at 34cm loud and clear.
But U12 TL071 is kind affecting phase and i can not adjust GEB (at Iron block) with it to completely reject ferrite rod i usually use for such matters.
The other GEB, part of LM833 is doing that job just fine. At Disc block GEB is easy adjusted to reject ferrite rod completely (if needed, but in real conditions we actually don't need that).
So... TL071 will simply not do.
Must wait few days to obtain LF351 and than will replace TL071.
Also noticed one more thing (not important at TGSL coils version) - when inverting part of RX input is additionally tied to pcb GND; somehow i have feeling that overall behavior is a bit better. That's the case with TS1000 Minelab coil. Can't tell about other coils..
Everything else is functioning just fine, from the very first switch ON.
Oscillator is very nice and powerful. Now it can be adjusted to rise amplitude over 20vPP !!!
But also it will not start to oscillate if trimmer P5 (220) is by accident set at higher resistance at the moment of powering ON the detector. So do not be confused , just lower trimmer to middle value for first stating of the detector. Later connect scope at TX and fine readjust amplitude. Today i left it at 16Vpp and it is working all good.
Tomorrow will continue with experiments..

[ivconic]

Aha! One more thing!
I also made another check!
I removed U92 (7809), C2 (220uF) and D17(01) from pcb. Made two connections as on picture bellow and made oscillator to be supplied from the main 7808.
No difference!? Everything is working just nice! So... actually no need for my previous "over philosophy" with additional voltage regulator, cap and diode.
So those can be freely omitted!
Shame on me!

[dfbowers]

Aha! One more thing!
I also made another check!
I removed U92 (7809), C2 (220uF) and D17(01) from pcb. Made two connections as on picture bellow and made oscillator to be supplied from the main 7808.
No difference!? Everything is working just nice! So... actually no need for my previous "over philosophy" with additional voltage regulator, cap and diode.
So those can be freely omitted!
Shame on me!

Yes, I observed the same thing. Powering the oscillator from the main 7808 seems to work just fine.. At least for the "Minelab" oscillator I added to my TGSL.

[ivconic]

Yes, I observed the same thing. Powering the oscillator from the main 7808 seems to work just fine.. At least for the "Minelab" oscillator I added to my TGSL.

Yes that's the fact. Seems i wanted to be "smarter" than i am; adding those there....
The fact is that i wanted to see if additional 1V supply will make any difference, but it didn't. "Useful" range of amplitude seems to be from 11 to 16Vpp at this particular design, and this can be achieved from main 7808.

[der_fisherman]

Good moves Ivconic, but don't blame yourself in any way for trying that, if it had made a good difference we would also be happy!! Experimentation is part of the deal here, we all are simply happy that there is someone prepared to do this for us, thanks.

By the way, did you happen to measure current consumption with and without the extra regulator? I am sure you saved a few miilliamps by reducing the component count.....it would be fun to know just how much. It will certainly extend battery life somewhat.

By the way, may I be so nosy as to inquire as to how such testing is made? (please anyone here with ideas answer!) Do you have a "test" area in your garden, or do you (like me) rely on air testing for all comparison.

I have often given some thought to this, but I have simply not thought up another method (other than air testing) that would be in any way accurate enough. We could (with your help of course) start a whole new blog on ways of testing/comparing various metal detectors with each other....(there is maybe a blog for this already, I haven't looked. Apologies to all if true...)

But I do feel that it would be great if we could get a) a way of testing at least in our "own backyard" with friends and b) a way to test and compare online.......

The idea of mine may be crap, say so if you think that, its best to be open and honest.....or it may be simply impossible to accurately carry out...input please!

Regards

Andy

[ivconic]

I have several "materials", collected during years, in my workshop, which i use always when checking behavior of some metal detector.
Ferrite rod, few hotrocks, piece of old Roman ceramic, some metal alloys (piece of bronze, piece of brass, various irons etc..etc..)
In the center of my workshop i put huge plastic table (non magnetic, non conductive) where usually i test coils.
Table is 80cm high... far enough from floor and iron armature.
Also in my backyard i have few buried items on previously cleaned and prepared places.
I am kind in advance comparing to many other colleagues because of the fact that i am living far away from city noise and power lines, deep in mountain, forest.
No artificial noise sources, no TX beams, no much interferences. Pretty "clean" place, you may say.
....
Your idea is not stupid...but also not new.
In the past we already talked much here (on Geotech) about testing methods and conditions.
Generally, we can establish some uniform method for testing...and i think we already done that.
But it is trivial to obey some "must" method when testing outdoor on soils - simply because soils are different and conditions can vary much from here to there.
Soil tests can be irrelevant, same as air tests, just because of the "factor of versatility".
Geographical position can cause all "micro" factors to vary that much and than tests can produce so much different results!
That's why we can accept those tests as only approximative - but certainly not as 100% accurate.

[ivconic]

At TGSL power consumption can be in range 25 to 60mA.
At IGSL i didn't measured it yet!?
I will do that.

[silverdog]

IGSL Boards

Back from my summer holiday and IGSL boards are here

As previously stated they are a pair of boards with a snap off groove between
One board for each coil type

They are in my shop now

Kits will be added in a few days

thanks again to Ivconic

Silverdog

[der_fisherman]

Back from my summer holiday and IGSL boards are here

As previously stated they are a pair of boards with a snap off groove between
One board for each coil type

They are in my shop now

Kits will be added in a few days

thanks again to Ivconic

Silverdog

Brilliant.

I will wait for a kit.

Will it include any "off-Board" parts like switches and pots, or do I need to order all "off-Board" parts separately from you? (2nd kit?)

Thanks for your news, time and trouble. It saves us all time and trouble finding the different parts and I am sure that your parts will fit and are of good quality.

I hope you get sold out repeatedly......

regards

Andy

[SVEN1]

Silverdog, I would like 2 or 3 boards of each, sent you a PM.
Just picked up a Musketeer coil

[bernte_one]

i was a step before ordering last night
but i will wait for a kit (two board plate and components for at least build one of them completly)
it would take too long if i collect all single parts at local shops and web
but when the kit is in stock i take it sure and some extra pcb then you have to go to postal office only once

good job andy

[ivconic]

Back from my summer holiday and IGSL boards are here

As previously stated they are a pair of boards with a snap off groove between
One board for each coil type

They are in my shop now

Kits will be added in a few days

thanks again to Ivconic

Silverdog

Splendid pcb's ! Very nice!