Ground balance add on board for Mini pulse .

[geoscash1]

Hi Geoscash,
It definatly sounds a bit off from mine but ive not done any Krnaz mods to it yet also my bench Mpp is stock.
Sound like the target hole is pretty big as most the coins dissapear and the nugget has a almost normal gain as the it aproaches the coil. Thats positive..
Diggers Schematic is the Mpp Schem with just a few value changes . I think my board is going to act the same way when I get it up and running.
So first thought is Digger was running 10 to 150 us on the sample and your at 7us I wonder if this may be enuf to throw things off a little. Im not sure totally how it works but if his set up with the fixe dresistor and the 5.6pf cap was for 10us min and a 3 us delay for ground balance, And your running at 7us does that mean the GB offset is 6us now?? Digger if I remember right did say tuning was much harder.

I think Im going to throw in a pot there seems like we may have to tweak it for each individual Mpp maybe.

Those are good questions and I did think about that when I used his mod values.

The way I understood his setup, with the 1k/5.6pf for 3us is it would take the GB sample 3us after the main sample was done. So I was under the impression even with my delay set to 7us the GB sample would still be taken following that.

I hadnt thought much more about it since he mentioned it would parallel the primary board functions.

Now after I had built it, I remembered my main tx pulse is set to 42us so the second GB sample would need different values to line up with that portion or the 2nd GB sample would be well beyond the next pulse. So I used a 1k with the 10N but that is still probably to far out.

Im horrible with the calculating the math/figures so Im more than likely using the wrong resistor value for the second GB sample. For the width, using a 50k pot should still be close since it replaced the series 22k. I have tried a few different pots there and am using a 10k now and it seems the adjustment is better.

But, its still not quite right and like you said, there is a big hole. But I did notice I can make it go negative meaning the detection sound goes silent as the target gets closer or passed by the coil. The good part, the nuggets I have to test with are all still detected no matter where I set the ground balance pot.

The other issue so far is I am unable to turn the GB off. If I disco the 0v and/or the -5 the main board (my mpp) no longer detects anything and goes to a steady slow ticking.

I tried disconnecting the 0v and the wire going to tp7 as well and it does the same thing so I can only assume since the add on j113's being soldered on and still connected with the C/D wires it must cause a total timing issue. So we would need to figure that out.
Im still playing around with it and will keep adjusting values to see what I can come up.

[godigit1]

Hi Geoscash,
It definatly sounds a bit off from mine but ive not done any Krnaz mods to it yet also my bench Mpp is stock.
Sound like the target hole is pretty big as most the coins dissapear and the nugget has a almost normal gain as the it aproaches the coil. Thats positive..
Diggers Schematic is the Mpp Schem with just a few value changes . I think my board is going to act the same way when I get it up and running.
So first thought is Digger was running 10 to 150 us on the sample and your at 7us I wonder if this may be enuf to throw things off a little. Im not sure totally how it works but if his set up with the fixe dresistor and the 5.6pf cap was for 10us min and a 3 us delay for ground balance, And your running at 7us does that mean the GB offset is 6us now?? Digger if I remember right did say tuning was much harder.

I think Im going to throw in a pot there seems like we may have to tweak it for each individual Mpp maybe.

[Tibuck19]

Hi Tibuck,

Yep, here you go. It definitely changed how the vco acts during detection. Im using an 8x10 3dss 7 strand teflon wired coil with my delay set to min 7us, full sat and sensitivity set to 75%. The threshold is a little erratic but its because of the double tube flo light 3ft above me.

Anyway, the ground balance is direct wired to the mpp with no on/off. I havent added a switch yet since im just bench testing.

This vid is just to show how it changed the audio. I guess its not really minelab sounding but does have that warbly sound when target is directly under the coil.

https://youtu.be/eOFy_AXH4tY

My mmp always had that Audio when anything things is detected less the 5 inches away from the coil, it started having that sound when I change R7 and R8 to trimpots, and tweaked the values, Going by memory, R7 is set at 2K or 2.5K and R8 at 19K if I remember right, Pretty much what the MMP beach Rev E, has going on now. What I like about the Minelab is the humming sound it does while its searching , The tick tick tick of the MMP drives me nuts! Funny thing to say but, I feel the chattering in my teeth when im detecting with the head phones on. Your a lucky Guy your in California, you will be able to go outside and test the GB! If you see French Canadian couple, Say hi, it might be my sister and brother in-law, their there on their sailboat for the winter.

[geoscash1]

Do you have the means to post a initial video while its on the bench , And sounding like a minelab as bonus! is it not lol

Hi Tibuck,

Yep, here you go. It definitely changed how the vco acts during detection. Im using an 8x10 3dss 7 strand teflon wired coil with my delay set to min 7us, full sat and sensitivity set to 75%. The threshold is a little erratic but its because of the double tube flo light 3ft above me.

Anyway, the ground balance is direct wired to the mpp with no on/off. I havent added a switch yet since im just bench testing.

This vid is just to show how it changed the audio. I guess its not really minelab sounding but does have that warbly sound when target is directly under the coil.

https://youtu.be/eOFy_AXH4tY

[Tibuck19]

hey godigit, nah, I just did the final mod that digger did. removed the 1M trimmer and left a 1k/5.6n for the 3us on the first sample and used a 50k pot for the panel for the 10us to 150us adjust. I got it all hooked up and it is working as we speak. Although, using a board that is on the bench and a coil hanging from the ceiling isn't going to be good for testing. I will check the measurements today sometime to double check that it is at the estimated 3us/190us and check the pot adjust for its range as well.

It definitely changed how my bench mpp operates and it seems very touchy to adjust with the krinaz mods I have done to it. At full open on the 50k pot it seems to give it a similar sound to a minelab, it wobbles somewhat and seems to have a higher tone as the object being detected gets closer then it disappears. At full closed it definitely loses depth in detection and almost acts like an SAT pot but super fast. Detection lost is variable depending on the target used but it seems a fair compromise if it handles hot ground. My air detection depth with a US nickel without the ground balance plugged in was at 10 inches. With the ground balance plugged in that drops to right around 5/6 inches so roughly half lost.

I think really the only way to test it is to box it up and take it out to the field for a true ground test which unfortunately I wont be able to do right now. It would be easier to modify one of my other mpp's that is already done then to box this one up...lol

I'll keep messing with it though.. Anxious to see how your board comes out too. I assume you have left it with the original digger drawing with the trimmers on board???

[ATTACH]44862[/ATTACH]

Do you have the means to post a initial video while its on the bench , And sounding like a minelab as bonus! is it not lol

[godigit1]

Right on glad to hear your up and running. It will be interesting to see if it can handle that green basalt thats around your area. A Vlf wont touch it And I ve never had my Tdi out that way over that bad a ground yet to see if it can even handle it.

I put a place for the pots on the board but it can be pinned and put in the panel as well or replacd with a fixed resistor. This time I didnt make a schematic and convert it to the PCB I Just built it on the in the PCB program and copied the mini pulse trace for trace.


I just tried to go to office depot to have transparencies made but they could not scale it right for me My printer has been acting up but I panelized it to 12 pcs and I think I have a couple I can double up and single image a couple boards.
Its Raining like hell here so were not working , Ill try to get them done today I hope.



Looking forward to your results whene you can get a chance to get out ,
Be Well.

[geoscash1]

Looks good Geoscash.
Good luck with the hook up. Are you going with the trimmers on the control box?
Ive picked up some more double sidedid material and will make some boards soon.
Hope it all goes perfect.

hey godigit, nah, I just did the final mod that digger did. removed the 1M trimmer and left a 1k/5.6n for the 3us on the first sample and used a 50k pot for the panel for the 10us to 150us adjust. I got it all hooked up and it is working as we speak. Although, using a board that is on the bench and a coil hanging from the ceiling isn't going to be good for testing. I will check the measurements today sometime to double check that it is at the estimated 3us/190us and check the pot adjust for its range as well.

It definitely changed how my bench mpp operates and it seems very touchy to adjust with the krinaz mods I have done to it. At full open on the 50k pot it seems to give it a similar sound to a minelab, it wobbles somewhat and seems to have a higher tone as the object being detected gets closer then it disappears. At full closed it definitely loses depth in detection and almost acts like an SAT pot but super fast. Detection lost is variable depending on the target used but it seems a fair compromise if it handles hot ground. My air detection depth with a US nickel without the ground balance plugged in was at 10 inches. With the ground balance plugged in that drops to right around 5/6 inches so roughly half lost.

I think really the only way to test it is to box it up and take it out to the field for a true ground test which unfortunately I wont be able to do right now. It would be easier to modify one of my other mpp's that is already done then to box this one up...lol

I'll keep messing with it though.. Anxious to see how your board comes out too. I assume you have left it with the original digger drawing with the trimmers on board???

[godigit1]

Looks good Geoscash.
Good luck with the hook up. Are you going with the trimmers on the control box?
Ive picked up some more double sidedid material and will make some boards soon.
Hope it all goes perfect.

[geoscash1]

Do you have a 3d printer ? I was looking at the bottom board, It gave me an idea for a easy bending tool, for your wires that would give them straight lines and perfect 22, 45 and 90 degree bends. Not that I'm saying there is anything wrong with yours, I just gave me a idea that's all.

No, I don't have a 3d printer but have been looking at a few of the smaller units and will more than likely get one one of these days.

[Tibuck19]

Well, was finally able to finish up getting this handwired up.

Will try to get it wired to my mpp and see if/how it works.

Do you have a 3d printer ? I was looking at the bottom board, It gave me an idea for a easy bending tool, for your wires that would give them straight lines and perfect 22, 45 and 90 degree bends. Not that I'm saying there is anything wrong with yours, I just gave me a idea that's all.

[geoscash1]

Well, was finally able to finish up getting this handwired up.

Will try to get it wired to my mpp and see if/how it works.

[geoscash1]

You guys been busy....lol.. all the while I was fixing my mistake on it too... So, I added the 2 caps that were missing, double, triple and quadruple checked it this time.. all connections are based on Digger429's hack and using the minipulse plus rev D as the base.

Check it over using diggers draw and the revd mini pulse schematic.. No guarantee it works, just wanted to help try to get this project working.

[godigit1]

I did another board last night . Once again its a little funky looking but all the connections are there (I think).
Ive added a couple extra pads to -5 at C and D outputs. Just in case we need a pot there I cant tell really from the Digger 429 Scematic.
Ive also added the Reject pot but it can just be bypassed by a jumper if wanted.
It has a top layer circut layer but I just did that to mark a couple traces that need hardwired.
Everything is labled to rev d components

If it works I will redo the board as double sided and make it smaller.

WOW. I had to erase the attached ZIP It somehow downloaded all my desktop files even my pictures into the file
Sorry Ill Try Again Later.

[waltr]

No ... I never said that.

There have been lots of discussions on how to add ground balance to some of the Geotech detector projects, but no-one (until now) has decided to test out some of the ideas. Actually that's not quite true, as some members have implemented solutions for their own designs, but there is no complete open-source project that's been published. The idea of a ground-balanced MPP was always on the list of future projects, but time is the limiting factor.

In Post #5 of this thread I linked to my project which has GEB. The method I used could be added to any of the simple PI detectors. All that is needed to do is add/change the sample timing and does not change the integrator/sampling circuit.

[Tibuck19]

I thought ground balancing the mini pulse wasn't possible because of the integrator used, think I was wrong.

Being wrong is my thing lol Part of the leaning curve.