SD2100 SD2000 Auto Ground Balancing Modification

[mario]

Hi Mario,

Looking good have you had a chance to have a look at my code glitch yet as I plan a testing trip away in about 6 weeks.

Regards, Ian.

I apologize about that glitch. I will fwd a fix to every member that got one of my boards.

I made the software update to include fine tuning AFTER doing the necessary board changes to support ground balancing so that last software update obviously would not work on those boards.

I will get you a fix as soon as possible.

The program included with the package posted in the other thread should not be affected since it was written with the board revision in mind.

[IBGold]

Hi Mario,

Looking good have you had a chance to have a look at my code glitch yet as I plan a testing trip away in about 6 weeks.

Regards, Ian.

[mario]

Looking good guys!

I have the hardware finalized, so expect a schema in the next few weeks. Hardware differences between the SD models gave me some issues, but the mod should work with the SD2000s just fine in spite of my targeting a SD2100. Most of these old detectors have different IC configurations, but the differences should not give us any issues.

I even found use of the old pots, which will now be used to calibrate the detectors for ground balancing to work properly. Ground balancing will be adjustable to the user's preference, while being automatic; meaning, ground balancing may be configured positive or negative.

I still have some software issues to resolve, but I see no difficulties over coming them. Having said that, I have everything working in pieces, but I still have to unite everything as a whole. It may take me a few more months considering my limited time to bring everything together.

I'll keep you updated.

[mario]

Hi guys,

I got around interfacing with the LTC1859 encoder. It's quiet impressive, a very stable chip, and much easier to program than the Digital Analog stuff: Indeed, I ended up using a publicly available generic spi library, with very few modifications!

I have yet to write anything other than several test routines, but I'm getting all 16bits. Before starting the auto gb code, I figured I would release the X9118 library (for the two digital potentiometers).

I recently visited Intersil's site, and it seems like they lowered the price of this pot to a more competitive amount ( http://www.intersil.com/products/dev...o.asp?pn=X9118). This chip is now less than $5 USD.

At 10bits, this pot means serious business, so much more sensitive than the older 8bit pot.

Make sure to go over the Readme file if you decide to use the library.

[Mechanic]

G'day Mario,

Nice looking ADC very versatile. Should suit the application. In a much more practical package too.

When you get up to programming make sure you have a sufficient delay between adjusting the pot and re-sampling because when the pot is adjusted a response will be seen at the output of the channel that is being adjusted.

Cheers Mick

[mario]

Ye ok Mick would be good to leave the switch in situ as you could make comparisons ..
Powerful chip to by the way and interesting times ahead albeit a lot of hard work for Mario.
So Mario this would be an upgrade and replace your existing mod .. hope you all had a great xmas..
cheers

Hi Geoff,

I'll end up doing a separate board, but for a different project, and not related to our SD2XXX detectors. I need a full featured development board and haven't found one with the features I would like.

However, that wont happen for another few months, after completing this project. I would like to start on a pin pointer project Steffan had been helping me designing. I have procrastenated for too long and will likely design my board around it.

Anyway, getting back to our current work, I will likely use the LTC1859 I found at Linear's website. It has everything we need and will fit in the little smd->dip board ( I found on eBay) nicely.

[gef12]

Ye ok Mick would be good to leave the switch in situ as you could make comparisons ..
Powerful chip to by the way and interesting times ahead albeit a lot of hard work for Mario.
So Mario this would be an upgrade and replace your existing mod .. hope you all had a great xmas..
cheers

[mario]

G'day Mario,

This sucker may be just what the doctor ordered http://www.analog.com/static/importe...ets/AD7609.pdf

Will handle +-16v on the inputs! No scaling required....

Cheers Mick

Wow Mick, those are serious specs!!
+-16V differential inputs
18bit with oversampling
8 simultaneous channels
internal oscillator (!)

We have enough resources to handle both gb channels in addition to automating emi handling if we wanted to.

At 64 pin QFP package, this chip makes me want to draw a second board instead of using a soic-dip solution (like the one for the two X9118 I found on ebay). However, if we go this route, we might as well replace our little 28 pin Mega with something faster like an ARM CORTEX 3 with full speed USB (and boot loader) to better compliment our setup. That way, we may also integrate the two X9118 RDACS and even use a more affordable DSS solution instead of the pricey AD9851.

Before considering this overhaul, we have to can find something with a lower pin count. All we need is the differential inputs , two channel inputs, and at least 16 bits IMHO. Otherwise, it might be another year before completing this project (lol)...

Last DSS project was done in almost 7-9 months...I know I slacked off for most of the time, but hey, between it, the gf, my job, and house/car repairs, I kept my sanity....lol

Merry Christmas guys,

I know we'll figure something out.

[Mechanic]

G'day Mario,

This sucker may be just what the doctor ordered http://www.analog.com/static/importe...ets/AD7609.pdf

Will handle +-16v on the inputs! No scaling required....

Cheers Mick

[Mechanic]

Hi Guys,

The thing is the micro needs to know when the coil is lowered to the ground. Currently it would be impossible for the micro to sense this, because if you were just sampling the existing channels the pitch/ voltage direction would change if we went past the gb spot. So we would need to sample the output of the bandpass filter(final signal processing stage) as little as 10 times a second to know if the ground signal is getting stronger or weaker as well as sampling both ch1 and ch2 to identify which way the gb needs to be adjusted and how close the actual gb is. There would need to be some provision for the adc to sample voltages from -5v to +5v, so there may need to be a voltage divider that keeps all of the voltages within the rails of the adc. Also it needs to be sensitive down to 5mv change on the -5 to +5 side of things.

There would be no need to remove the functionality of the channel selector switch, this is after the stage where we would need to sample and I like it as it can help give you an idea on what to expect to jump from the ground!

Cheers Mick

[gef12]

So what you are saying Mic (I think) is that they have included a summing amp of sorts for both the channels .. It would be good to have the both channels .. No doubt Mario there will be a bit of work in doing this GB mod

[mario]

Mario,
...sorry to be a spoil sport and make it harder.

Or would it be easier to leave the manual ground balance as it is as a fixed manually adjustable G/B and just add an Auto G/B mode so you could use both if that is possible I can see advantages there Just to be difficult Hi.

Best Regards, Ian.

No, not at all. Like I mention earlier, I would like to do it right, so I don't mind undertaking this new challenge. I've been wanting to do multimedia processing with my uCs, so this will be a nice problem to tackle.

I needed clarification on the issue because I wasn't entirely sure how the later models handle both channels. After reading several posts, some people appear to miss the selection switch for ground balancing. I'm now going to assume those same people are misinformed with how Minelab handles the timings. Like Mick mentions earlier, Minelab doesn't eliminate any of the channels. It just implements them differently.

Also, I plan on following your suggestion and making manual ground balancing optional. I'm currently finding the range narrowing feature (seen on the video) very useful in my working unit.

However, the manual ground balancing option will be 100% digital, through the LCD/uC/RDACS, so those two 100k pots and selection switch will have to go.

I'll keep you updated and thanks for all the feedback

[IBGold]

Mario,

What the 2000 does is process both channels target response then picks the strongest and passes this on to the audio that is why the two tone response either High Low or Low High which ever is the strongest channel sorry to be a spoil sport and make it harder.

Or would it be easier to leave the manual ground balance as it is as a fixed manually adjustable G/B and just add an Auto G/B mode so you could use both if that is possible I can see advantages there Just to be difficult Hi.

Best Regards, Ian.

[mario]

Thank you for the input guys.

I don't want to half *** this, so your suggestions will definitely make a difference.

However, it looks like we're pushing the limits of our little Atmega. The addition of a 2nd channel for manual ground balancing will bring the total close to 21k of data space, leaving us with 11k for auto gb. I've never done any hard core signal processing, so I'm not sure what to expect.

Remember, our original intention was to use this processor for driving the DSS sub board. I chose the Atmega328 because it had a decent feature set and is fairly flexible. Had I anticipated more hard processing work, like the one we will be doing, I would have chosen something with at least 40 MIPS. Still, from what I've been readying, we definitely have something to work with, so our implementation should be fairly ok.

Also, I still don't want to post schematics because I have not experimented with the additional hardware required for processing. To date, I've only worked on the manual ground balancing part. And manual gb is not something that our detectors currently need since it's a stock feature.

All in all, I'm happy with how work is taking shape, and it's been a great learning experience, which I hope to continue even after we've completed work on this project.

I'll keep you updated.

[Jiminy]

Hi Mario and all. I also would opt for both. This will be a great addition to a good machine. Definitely a needed upgrade.!!!!!!!