Ground balance add on board for Mini pulse .

[6666]

Digger I get invalid link, on both links.

[Digger429]

Having been away from the forums for a few months, I come back to some questions being asked. Hopefully I can clarify here.

The on/off switch for the GB is indeed a two pole switch that just switches to ground. That is, the grey and white wires going to the FETs in this picture here...

...are switched to ground.

The two potentiometers (blue circle and pink circle) that geoscash1 asked about in post 6 no longer exist. Neither does the potentiometer at top left, which is now fixed timing by a resistor.

Here is a diagram of the timings I've setup, so I can run the machine at about 1000 pulses per second:


After two trips into the goldfields of Victoria, I've decided its about as good as its going to get. Anything from here on would be a complete redesign from the ground up. It is now able to completely cancel out the ground, but it comes at a great cost of reduced sensitivity and the "hole" where gold samples can completely vanish from detection. In practise I found myself having to turn the ground balance amount down to as low as possible without the ground interference becoming too annoying. Aside from the on/off switch, thats the only GB control - the potentiometer "GB sample width" that can provide 8 - 245 uS of sample.

What other questions were there?

[Teleno]

EF sample turns every PI Rx into an auto-zero amplifier.

That's right. Auto-zeroing the amplifier is simpler than a differential integrator and less tolerance sensitive.

[Davor]

EF sample turns every PI Rx into an auto-zero amplifier.

[godigit1]

Thank you all for the answers, It appears I still have allot of reading to do.
Im really just barley starting to get grasp on how things work on a pi.
Im a carpenter by trade but have a distant backgroung in Pwbs.
This started out as a simple working GB solution started by Digger427. But when I started digging through the forum It got much more interesting.
So Let me Say Im sorry for my lack of true electrical experiance.
Ive built a HH surf Pi Cuda And 4 MPPs but have just been going through the motions tell now. I want to say thank you to all of you on the forum for helping to open my eyes lateley.
That doesnt mean I wont still ask stupid questions though so please bear with me and let me know when Im wrong. No one gets any better without constructive criticism.
That being said .

Teleno,
Ive been trying to wrap my head around your current feedback op amp design. Could you expand on it a little for me?
Im not positive how it works but Am I correct in saying this is a one sample amp and ef is cancled by the auto 0 function of the tl082.
So could then a second sample for GB be added right at C input or is the 0 function actual GB?
If so then the Mpp stock Sample pulse generator could be capable of providing all the samples I need without a second sample generator?

Like I said I have allot of reading to do so if this has been discussed in a thread I havent found yet please let me know.

Thanks again

[Davor]

Hi godigit1, a few answers...

>were you ever able to implement it on to your Mpp build?
No. I made a GB circuit and tested it, but many other things came with higher priority. Heck, even MPP is still unfinished.

>Ive been side tracked a little
A story of my life, but I'm not complaining. Life is good

>Is there a example of a simplified absolute balance circut on the forum that you can point me too?
Pick any. Practically all solutions work with 2 opamps, and it can be piggybacked to MPP. The other solution would be using a through zero VCO, which is even more complex, so absolute value that is.

[green]

https://www.geotech1.com/forums/showthread.php?24251-My-take-on-the-HH2[/URL]

I do use a microprocessor to generate all timing pulses and user adjustments. This allows easy to change methods without messing with all those hardware timing chips, multiple channels, etc.
I do not understand why everyone keeps using these timing chips that are a mess to make changes.

Why I used timing chips. ITMD suggested building coils and detector circuits might be difficult. Since I didn't know how to code micro's and knew nothing about PI's I decided to stay with timing chips and try to learn two just things. I can see it would be a lot less wiring.

[waltr]

I was thinking about another channel and implementing it somewhere down the line. Is there a example of a simplified absolute balance circut on the forum that you can point me too?
Thanks again!

There has been much discussion of various GEB methods.

I used the Three Sample method on my HH2 and it works very well without any mods to the analog differenctial integrator.
Read about his method (with links to original discussions) in my thread here:
https://www.geotech1.com/forums/show...ake-on-the-HH2

I do use a microprocessor to generate all timing pulses and user adjustments. This allows easy to change methods without messing with all those hardware timing chips, multiple channels, etc.
I do not understand why everyone keeps using these timing chips that are a mess to make changes.

[Teleno]

I would like to get the timing as close to Carls example in post#68 of the Ground balance Thread where Davor introduces his GB solution.

Post#

Too many pulses. Within 1 period the EFis actually equivalent to amplifier offset. Cancel the offset when SW4 is high and you don't need any iffy differential integrators that require tight tolerances. A simple integrator is then good enough. You also don't need to separately cancel EF for the ground balance.

[godigit1]

Hi Davore.
Thank you for checking in on this thread.
On your Gb Board you designed it with the MPP in mind if I remember correclty.
were you ever able to implement it on to your Mpp build?
Ive looked around and cant find anything on the forum. I was wondering if it worked out ok for you?

I now have the Mpp sample generator and add on completly adjustable so I can play with any timing schem I want.
Where I left off it was working OK
I have to revisite the project Ive been side tracked a little and needed to learn a little before moving on I think Im almost there.

I was thinking about another channel and implementing it somewhere down the line. Is there a example of a simplified absolute balance circut on the forum that you can point me too?
Thanks again!

[Davor]

Hi guys, long time...

Just a quick note. All GB schemes, including mine, work by means of splitting the tau range into two, one positive, one negative, and a zero in between them. Because of dual polarity, the simple detectors that have only a positive signal detection will not see the negative values. Detectors that come with GB all have an absolute value circuit prior to sound generation, but all of them have a zero. Fighting a zero is possible if there are two signal paths, so zero in one path will not affect the other channel. It all makes things more complicated, and detection near a zero loses sensitivity.
In case you are after small gold, a simple scheme without absolute value will be good, since all detection happens on the positive side of a signal.

[godigit1]

Ive got it all hooked up and it works but I know the timings are not right .
Also was wrong about triggering off tp5 Im still trying to learn all this.
Ive tried moving samples around a bit and so far I cant get it totally correct.

Here is a drawing of where I have the timings at now!



The top row is where I started out with diggers component values.
Bottom row is where things are now.

I changed the R11 resistor to 2.2k and made the Gb sample abjustable down to 10us with a range to 74us.
Added a 10 k pot in place of R10 but, this gives me some adjustment to second sampe spacing but I need to be able to move it more.
Im using a MPP beach as the Gb board everything works but im not able to get any adjustment from pl 6. Ive added the 1 k resistor as suggested and kept the pot and for c8 I have a 5pf cap.
Unpluging this cap makes no difference with any of the timings.

Performance actually seems just slightly better with the GB turned on but with the GB turned off the MPP samples are being broadcast to the GB board. Doesnt effect performance but a half amplitude timing matched signal is feeding back to the GB board. Someway to isolate them would be good or maybe a switch there as well.
I still need to get some hot ground to test with as well so I dont have any results for if its actually working or not .
My guess by the timings is its not.



I would like to get the timing as close to Carls example in post#68 of the Ground balance Thread where Davor introduces his GB solution.

Post#
Im still trying to learn just how things work so if someone could help me with a couple questions It would be greatly appreciated.

What components should I adjust to specifically move sample spacing both for target and EF independatly?

And not so related but related On Davors GB circut,
Does this gb module completly replace the sample timing on the minipulse or just piggy back on?

And on connection of his GB circut is VDD reference to -5?

I have all the components to build his balance module as well and it looks really good so since Im in learning mode, might as well try that as well.

Thanks

[6666]

You lost me 6666, What 4011 ??? ... the mpp doesn't have a 4011 nor does the GB circuit from digger429 that is being used here.

My questions still stand as far as a couple of digger429's connections on his schematic, cant tell if they are just resistors to -5v or if they are supposed to be trimmers, also the pot after/around the 22k resistor, I think that 22k can be eliminated and a 50k panel pot used in that position but I could be wrong.

I want to work digger429's circuit into the mmp full schematic that way I can just have a board made with all components on it instead of using an addon board. I love my mpp but it is terrible in hot ground so am hoping this may help it out a bit even if losing some depth/sensitivity. I have the circuit drawn up but want to make sure of a few of his connections before doing a board for it.

I thought you were using Davors ground balance circuit, dont know why I thought this.

I

[godigit1]

Hi Geoscash
I think I may have figured out at least one of our problems.
I finally have a working sample generator.
I had a extra MPP beach board I had bought when I ordered my kit so I figured that was the perfect proto platform for working out this circut.
With the Mpp Beach board adding another integrator may be easier if needed.

So first thing.
On Diggers drawing at C and D outputs he draws a connection to -5 via pots. These were deleted acording to his post so both thos circuts dont need to be pulled to -5.

Next thing is he has it triggered from tp 7.
I tried tp 7 but the timings are way out .
Best place to trigger Is at tp5 as far as I can tell.

Triggering at tp 5 with my MPP 1st sample delay set to 10 us and second delat at 114us with a sample duration of 52 us.
On the GB board my first sample delay is at 16us and second sample is at 128us. Sample widths are adjustable from 58 us to 234us
The other benefit to using tp5 is that the sample delay is adjustable in unison with the sample delay pot.

I still have to dial in the timings to get the 3 us delay, right now its at 6 and the sample withs are a little fat.

Can anyone tell me what the pulse duration should be of the ground balance samples? On diggers drawing it shows a -5 ?
Im not sure if thats a error of we want a 5us pulse.

Thanks for all the help on this project guys.

[green]

http://www.geotech1.com/forums/attac...2&d=1545232767

An example of times I needed to balance ground with my PI when changing first delay time. Your times could be different but gives ballpark ratios. Greater the first delay, less the ratio(ground sample/target sample). Ground decays faster than 1/T with my detector making the ratio higher than it would if decay was 1/T. Reducing second delay to 3usec should reduce the ratio a small amount.