IGSL

[o.mag]

Yes, smart use of uPc implies full digital control over synchronous demodulators, at first place!
Gating, timing and filtering; that's the real task for uPc.
That's what is relevant and that's what we may name as "smart uPc implementation".

hi ivconic
The choice of the PIC is not final (16F873 for exemple). The different options in the settings and specify their help to choose it.

olivier

[Davor]

FKK=Freikörperkultur ; nudism, naked people roaming around on the beaches

So it is a coil with nothing on

[ivconic]

Why don't you make a FKK coil with a center tap on Rx coil
Just for the fun of it.

I am lost in all those acronyms!
Remind me what FKK stands for!
Yes i made center tapped coils in the past.
No problem.
I made few for my Eldorado's.
But those were shielded later!
Right now i am having old Fisher 1260 which seems is having center tapped coil too.

[Davor]

Why don't you make a FKK coil with a center tap on Rx coil
Just for the fun of it.

[ivconic]

Ok, your solution will be quite good on some soils, no doubts in that.
But there are soils and soils.
I am pessimistic because i am user rather than designer.
I had cases when i made "perfect" detector for my local soils, which later turned BS on other soils!
I can recognize circuit behavior only by watching how it performs for few minutes, of course if testing is done enough good.
Your skim testing on your video is quite enough for me to "see" and "hear" what i need to see and hear and later to make conclusion.
Seems your circuit is alright. Well optimized.
I wouldn't touch it no more if i was you. I would shield the coil now!
Rest... yes i am following your work and i do intend to implement your modifications.
But right now i don't have proper coil for my IGSL (recently sold it! )
So most probably i will have to make one or obtain one soon.
Cheers!

[Davor]

You may call me bone-headed if you want, but I'm seeing a streak of light at the end of a tunnel, and I'm sure you'll like what I've got when it is finished

I'll pursue the FKK coil way because I see that in spite of a few obstacles on the way, there are rewards worth the effort. Yes, you can do it the way everyone does, and there are reasons good enough for such classic solution, however, there are other solutions ready and waiting.

I'm quite happy with my IGSL as is now, and I see that you recognised the optimisations to the discrimination gain blocks and comparator stages. Normally I'd stop here, but that extra noise just won't let me. Anyway, I'll make it as a pre-pre and you are free to try it and keep it if you like, or revert to your original solution if you don't. It will not cost you much

[ivconic]

hi ivconic
I spring this old post asked for your opinion:
The UPC should simply replace the part setting and thus manage 4066 control and generate audio frequencies

olivier

Yes, smart use of uPc implies full digital control over synchronous demodulators, at first place!
Gating, timing and filtering; that's the real task for uPc.
That's what is relevant and that's what we may name as "smart uPc implementation".

[o.mag]

uPC_GSL

In addition;
now.... i am plain amateur with very limited capabilities, so analogue approach is all i can do.
Would be nice to see IGSL idea transfered into "digital" area (two simple detectors in one, controlled by uPC).
Main goals would be accuracy, small sizes, smt and very low consumption (which is now the main issue at present IGSL; some 65-70mA) ....
and possible more benefits than i can name right now.
..
Referring the power drain; i was thinking to ask here about LP versions of some IC's.
LM339, LM883, LF347..and others.. are those having LP versions?
Can we calculate power savings if use LP versions?
I bet we can... but i would rather let somebody more conversant than me to do that...

hi ivconic
I spring this old post asked for your opinion:
The UPC should simply replace the part setting and thus manage 4066 control and generate audio frequencies

olivier

[ivconic]

BTW forget "microphone" preamplifier solutions for now. You are on wrong track there.
Wasting time.
Microphone preamps are designed for quite different task.
If you want to follow some analogy than better pay attention on how is done at tape recorders. Even that may be analogy which may mislead you too.
Soil is pretty tough and unpredictable media due it's variety.
That's what involves much more things to be considered than you can anticipate right now.
Ain't no simulator that can simulate all what's going on in soil conditions which may vary from square meter to square meter.
Looking at your videos i see that you made well optimized circuitry.
Only what lefts to be done is proper shielded coil.
Cheers!

[ivconic]

Before I get to answering previous posts, here are two more videos. Live action. I did all my stunts myself
http://youtu.be/Kqbee8gYWM8 This one is about discrimination of small things in a string. Perhaps a bit too close, but you'll get the idea anyway. This time I shifted discrimination to exclude kuna tokens from Fe tone and there is only a high pitched tone on kunas. Lipa (small tokens) that are iron cored sound just as they should: iron. Al foil is on double tone.
http://youtu.be/FZRSgCuzyWI is a small hunt in a back yard. Full of "ancient" trash. Tried to clean it, but in vain.

For example this video:

http://www.youtube.com/watch?v=FZRSgCuzyWI&feature=youtu.be

is showing me that you are almost there, a nick to what i would call success.
You are pretty hard headed about coil shielding and that's what stopping you to make descent detector.
You circuit acts pretty optimized and that's what i like to see.
It is obvious to me when watching the video.
But can't you finally make same but shielded coil and give it a try?
Ok i see you hate Al foil. It is not perfect solution, of course.
But give it a try, just for comparision between unshielded and shielded.
I am sure that your setup will work perfect with shielded coil. Trust me.
Don't be hard headed.
Cheers!

[ivconic]

Hi all,

My IGSL is over and here's a video of a test in the grass.

http://youtu.be/mjy5ZpFoZ2U


There was an error on my front! normally this is "accept NF" and "reject Ferrous" ....

The two sensitivities is almost at max (ca chatters)
The coil was "nulling" to a value of AC 4mV on RX and filled in with epoxy.
Discrimination ferrous and nonferrous seems correct (seen on the oscilloscope and compared with images in the folder of Don B.)

GB are the potentiometer on the front and 50% are what looks good for potential adjustments.


The igsl works well until 20/25 cm

I always used to make the transition from coil and my tests of the target high enough so the sounds are limits

I would like a little more power / heights ... but I'm really excited to try that in the fields. The discimination of aluminum works.

If you have any advice or tests for enhanced depth, I'm interested.

I would like to increase volume of HP .. I can replace the two 330R by 220R on the BD140 ?

I just watched the video.
Not exactly good.
I think your problem is in coil:

"DETECTEUR IGSL avec bobine TGSL
-Bobine 6.55mH RX et 6.12 mH TX
-nulling à 4mVolt AC sur RX"

6mH and 6.5mH will do. Even better if you make 5.6mH and 6.3mH.
4mV - 15mV on RX coil leads (not after first opamp) is alright.

[Davor]

stability.

try wrapping a wire around the GEB and Disc pot wires and grounding it at one end.

In earlier posts, the gain of one of the amps following the det/mix were a little too high and could take off. Try less gain there with a resistor change.

S

I've noticed that, but the other way around - I had a DISC. wire floating instead of being connected to its place and it picked ... something and my disc channel was working for no apparent reason. I couldn't adjust disc. though. Obviously that 100k could be lowered for stability.
But my quest is for the better frontend at the moment. I think I already did what I could with the rest of the IGSL without going to the third dimension ... much. The ikebana pin swap mod is the most drastic one, and the rest of them are using the existing PCB real estate. So even the existing rigs can be easily fixed that way.

Now this is a bit different.

You noticed perhaps some chattering at the edge of sensitivity, most probably related to some external source or some instability. Well, that's because of the very edge of the frontend noise level is peeking through. Bear with me for a short calculation.

We have system gain as follows: 47 preamp, 1/2 mixer, 100 first gain stage, 20 second stage. Total gain is 47000. Disc sens. potentiometer minimum is set at 3mV on the comparators inputs, hence, the lowest possible signal expected there is 3mV in peaks, or about 2mVrms. When this signal is divided with 47000 we get 42nV.
Assuming we have a noise bandwidth limited to 16Hz, a square root of it is 4, so 42nV/4 makes ~10nV/sqrt(Hz) of input noise.
Well, simulation says that IGSL frontend has ~14nV/sqrt(Hz) noise. No wonder you hit the chatter once in a while. It would happen even more often, but having Disc. and GEB channels that have to coincide, and being orthogonal, it gives some extra decibels noise immunity.

I don't know about you, but in my book 14nV/sqrt(Hz) is not something to brag about. It can be waaaaaay better than that.

Now that I got it to work well, and discriminate very well, I want more depth. From what I see now I can get additional 40% depth just by fixing the frontend.

[Jerry]

I
Anyway, I just wonder if there is any interest here about such an add on, and if there are some wishes to try to meet. My kinda goal is to make it non-resonant, and balanced, with or without a center tap signal ground connection, with some additional high pass filtering to avoid piking up hum from the mains etc. Such frontend would also promote unshielded coils usage.

So, how about that?

I am always interested in ways to make improvements. That is the reason my current project is modular, stage by stage type of construction. I can rebuild, change or substitute any stage. Great for experimenting, sort of a physical version of Spice

Anyways, I have already tried many of your ideas and am willing to try more. Right now I am taking advantage of some very nice weather to actually use my detectors for a change so have not been posting much.

Keep it up.

Jerry

[simonbaker]

I'm about to investigate a better frontend for VLFs in general, but with high hopes to improve my IGSL. My guess is that it will be some kind of add-on that will be able to accommodate some wider range of Rx coils and run near the theoretical noise limit. There are a few implementations that are on my mind, some of which are using discrete BJTs to reach low noise at low cost.
Anyway, I just wonder if there is any interest here about such an add on, and if there are some wishes to try to meet. My kinda goal is to make it non-resonant, and balanced, with or without a center tap signal ground connection, with some additional high pass filtering to avoid piking up hum from the mains etc. Such frontend would also promote unshielded coils usage.

So, how about that?

Always interested in new ideas and circuits to try, especially if don't add too much complexity. We know there are newer MD designs that have more complexity.

-SB

[golfnut]

The main difference of IGSL, IDX etc to modern commercial dets - is they only detect and use half of the incoming signal.
Half of the Rx signal is discarded.


A good jump forward towards an average current machine is to demodulate both halves of the incoming signal - which doubles the Rx signal power for little or no extra noise.

The verator 3 on here has such a scheme or the Whites Patent 4783630 - sheet5
S