IDX-PRO+VDI

[ivconic]

I am trying to fine tune the homemade DD coils, and I am finding something strange! In the TGSL, the TX coil you would come up with about 14.6 KHZ. For RX coil you would come up with about 16.2 KHZ 14.6 divided by 16.2 = .9 ratio.

If you input data into a LCR calculator for IDX with DD coil you get 6.5 KHZ for TX coil. Ok, but when you input data for RX coil you get 14.6 KHZ! a ratio of .445! Should'nt the receive coil be 7.22 KHZ?

TX coil .587 MH, 1MF.
RX coil 35.6 MH .0033 MF

Tesoro's "resonance ratio" is not the rule for White's coils. Don't be confused about that.

[Wiltran]

Tesoro's "resonance ratio" is not the rule for White's coils. Don't be confused about that.

Ok then, In order to get proper phase angle for discrimination etc. how would you calculate RX coil specs, if you already knew Whites TX coil specs and freq?

[ivconic]

Ok then, In order to get proper phase angle for discrimination etc. how would you calculate RX coil specs, if you already knew Whites TX coil specs and freq?

I wouldn't calculate nothing, because we already do know coil specs.
Few descent White's coils are already explained here on forum in the past.
Also there is complete rip off of White's coil done by Russian colleagues.
But, once in the past i didn't knew that. So i was pushed to make something on my own.
First coil i made for CL3 was complete wild guess - but worked fantastic!
I used coil former exactly the same as for Fisher's Quicksilver 27cm coil.
Concentric - not DD.
I made 31 turns for TX (can't exactly be sure about gauge, but think it was 0.5mm or so..),
11 turns for feedback (same wire) and 250 turns for elliptical RX, wire was 0.22mm.
Main "trick" was the tuning with proper capacitors (that's the point of whole story).
White's design, such as CL3 or IDX (call it anyway you want) is pretty tolerant on coil specs BUT ONLY if coil is tuned properly with capacitances.
White's CL3 specs says it can operate in range 6.35kHz to 6.95kHz, if i remembered it good.
Originally there is 1uF+ ~80nF parallel to 0.54mH TX coil, and 33nF parallel to 36mH RX coil, so calculation is easy than?

[eduardo1979]

Coils IDX

I am trying to fine tune the homemade DD coils, and I am finding something strange! In the TGSL, the TX coil you would come up with about 14.6 KHZ. For RX coil you would come up with about 16.2 KHZ 14.6 divided by 16.2 = .9 ratio.

If you input data into a LCR calculator for IDX with DD coil you get 6.5 KHZ for TX coil. Ok, but when you input data for RX coil you get 14.6 KHZ! a ratio of .445! Should'nt the receive coil be 7.22 KHZ?

TX coil .587 MH, 1MF.
RX coil 35.6 MH .0033 MF

TX coil 0,587MH-1MF
RX coil 35,6MH-33nF,(0,033)MF

[holyuser]

It can be hacked, but i will not do that for public, because "author" is already member here.
It is up to him to decide about that message.

Very noble of you!
Well, anyway, do not be angry with me, my friend!
Friends have to say to each other the truth, not only when it is warm and sweet as "a piece of cake", is not it?
Congratulations on your good work!
As previously promised, I will change the welcome message, but it will happen in the next revision of VDI, now test.

[ivconic]

Good decision.

[Wiltran]

IDX DD COIL

TX coil 0,587MH-1MF
RX coil 35,6MH-33nF,(0,033)MF

Ok now I see it clear, Eduardo previously posted RX coil capacitor at 0033 MF (3.3 NF) which would result in a resonant freq of 14. KHZ. If you put .033 ( 33NF) into calculator, it gives you 4643 HZ! This points out a previous mistake, but it seems on this design the receive coil resonates at a freq. of a .7 ratio, the TGSL resonates at a .9 ratio! This differential must result in different phase angles for discrimination. Thanks to all for help!

TX coil 6.5 KHZ
RX coil 4.6 KHZ.

[der_fisherman]

Fascinating design and posts. My personal thanks to all concerned.
Regards
Andy

[Wiltran]

IDX VDI

I don't understand why there aren't more posts on this subject, I find it fascinating. Is anyone else building this project? I built this thing and it works! It seems to have some drawbacks. One is the VDI doesnt work at the same depths as the analogue. any comments?

[ivconic]

I don't understand why there aren't more posts on this subject, I find it fascinating. Is anyone else building this project? I built this thing and it works! It seems to have some drawbacks. One is the VDI doesnt work at the same depths as the analogue. any comments?

Same case with all "VDI"s i have seen so far: White's, Minelab's etc...etc.
Certain level of signal is needed for VDI, while analogues can react on slightest hum sometimes.
Working with White's Spectrum; i had my best and deepest finds without VDI information, but just relying on Treshold changes!
Funny but true....(and educative)!
Same case with IGSL and VDI, it is giving me VDI info only up to some depths, approximative would be some 70% of depths.

[Qiaozhi]

Same case with IGSL and VDI, it is giving me VDI info only up to some depths, approximative would be some 70% of depths.

Does it maintain the same accuracy throughout the 70% range? Or does the VDI reading change for different depths?

[ivconic]

Does it maintain the same accuracy throughout the 70% range? Or does the VDI reading change for different depths?

Yes good question.
It is changing numbers, but in range, so not a problem.
For example: if coin was detected, numbers will change in "coin range", let's say from 40 to 65.
If proper VDI number is 49 for given coin (alloy) and max air depth for such coin is 30cm, than up to 22-24cm displayed number will be in range 45-50, but from 24cm number will change in a bit wider range, let's say 42 to 60.
At end (edge) of detection number sometimes can disappear or turn pretty wrong.
But i wouldn't make big fuss about this, because i met the very same case at White's Spectrum, XLT, DFX and later at Minelab Explorer II, XS and SE.
Recently i saw this at Deuce too.
It is simple to understand and also to compare with simple analogue detectors behavior.
You can't calculate accurate VDI number if signal is poor.
That's why i adopted nice habit from long time ago; to use treshold changes and experience to decide whether to dig the target or not.
(that's why i do favorize older non motions still, and all those habits i adopted long time ago, working with Cscope 1220B)

[der_fisherman]

VDI Battery life - Possible problems

I get the impression here that VDI is really good and useful for objects at up to say maybe 70% of the depth that a metal detector can achieve without VDI. Up to this point, it gives a good indication of the type of target, possibly with changes and improvements to the µcode, it may eventually be better and deeper....

So my thoughts was that as VDI appears to be fairly insignificant for many, all wanting to add one to their detector, why not add it as something that is only active WHEN you want to see the information it can display, for instance with a button that only activates VDI when pressed, for example.

It could even be set up to indicate say only for 10 seconds, though I have to admit that I am unaware of how long VDI needs to power up and stabilize, so my suggestion may not be practical for other reasons!

Maybe it could even be slightly redesigned to use really low power components to further reduce power usage also.....sleep mode for the processor for example until a target is located or similar.......there are ways and means.....

Can someone with actual VDI experience "chime in" with the facts to see if such an idea is truly practical or not? Or even with better ones?

Just some thoughts to provoke some ideas from this great forum.....

Regards

Andy

[ivconic]

All the LCD based metal detectors i have seen so far are suffering from a bit higher power consumption.
Especially if back light is used.
That's the fact we have do deal with it.
Russian colleagues tried to overcome that by use of low power LCD's like the one from Nokia 3310 phones.
It is cute solution and only drawback can be the size of such LCD - it is to small.
In case IGSL+VDI problem is not in VDI but in IGSL, which is having a bit higher power consumption, some 60-70mA.
Ordinary "smart" LCD's , based on Hitachi chips are easy available to each one of us, but those are also not low power.
So, main goal here is to find a way to lower consumption as less as possible.
So... at the end, all we can do is to design detector which will be ultra low power....
Speaking of VDI... nothing more seriously we should resent to it, because it is only processing the outer signal.
Better signal from outer world - better results.
Worse signal - worse results.
It is up to detector and not up to VDI.

[holyuser]

Power consumption of the VDI is about 3.2 milliamps (without backlight, of course), which is not so much.
Approximately half of this consumption is LCD, I use type AC-162BYILY-H.
It minimizes power I used MCP1703 regulator instead of 78L05. Also MCP607 could be used instead MCP602.