WELCOME!!

[Sean_Goddard]

Hi All, and WELCOME!

Moving on from the hugely successful Surfmaster PI created by Whites Electronics, I have tried to address a number of what I consider to be design issues with this machine. The list is this (not exhaustive);

1) More depth

2) Smoother threshold

3) Less "noise" - spits pops and squeaks

4) Overall more solid performance (for example as better voltage drops, then so does the drive to the main FET and thus the performance drops off exponentially)

5) Increased versatility and sensitivity to thin section gold.

I know there are many other PI's out theere, the Hammerhead being probably one of the best designs, but they ALL have high front end gain, the SM II does the opposite, and instead makes up the gain AFTER the demodulation (sampling) has been done. Dealing with "DC" is easier than a dynamic signal. Also, I have included a snubber to stop the FET going into avalanche and thus generating a heap of noise.

Other things to try are taking the ground sample just BEFORE the main pulse, rather than the usual 120-150us after the pulse.

I will post the initial circuit which people can play with and modify, but I would like to keep this an EASY project to follow, therefor there will be sub secionts here, designed for bugs/gripes/fixes etc. There will be ONE set of files in the main area at ALL times, and these will be the LATEST releasee so that anyone who wants to build a SM PI II wont have to spend the time hunting around trying to find what works (sadly like so many other projects and good designs on here) so PLEASE respect that and ONLY post to the "modifications" section or post with something on the ilk in the title that way we can keep track of and delte the older version to keep the place tidy.

Thanks all and HAVE FUN..

[WM6]

You are very Welcome Sean_Goddard with this famous William (Bill) Lahr PI design (sold to Whites), modification. (small intro mod - sorry).

[ivconic]

Hi All, and WELCOME!

Moving on from the hugely successful Surfmaster PI created by Whites Electronics, I have tried to address a number of what I consider to be design issues with this machine. The list is this (not exhaustive);

1) More depth

2) Smoother threshold

3) Less "noise" - spits pops and squeaks

4) Overall more solid performance (for example as better voltage drops, then so does the drive to the main FET and thus the performance drops off exponentially)

5) Increased versatility and sensitivity to thin section gold.

I know there are many other PI's out theere, the Hammerhead being probably one of the best designs, but they ALL have high front end gain, the SM II does the opposite, and instead makes up the gain AFTER the demodulation (sampling) has been done. Dealing with "DC" is easier than a dynamic signal. Also, I have included a snubber to stop the FET going into avalanche and thus generating a heap of noise.

Other things to try are taking the ground sample just BEFORE the main pulse, rather than the usual 120-150us after the pulse.

I will post the initial circuit which people can play with and modify, but I would like to keep this an EASY project to follow, therefor there will be sub secionts here, designed for bugs/gripes/fixes etc. There will be ONE set of files in the main area at ALL times, and these will be the LATEST releasee so that anyone who wants to build a SM PI II wont have to spend the time hunting around trying to find what works (sadly like so many other projects and good designs on here) so PLEASE respect that and ONLY post to the "modifications" section or post with something on the ilk in the title that way we can keep track of and delte the older version to keep the place tidy.

Thanks all and HAVE FUN..

You have all my attention Sean.
Looking forward.

[6666]

Looking forward to your fun project

[localbug]

Please add wireless charging circuit into the design.

[Old cart]

Thanks for doing this Sean. Is it planned to have this culminate in a PCB ( maybe even a group buy)?

[Sean_Goddard]

Hi again all.

Local bug, GREAT idea though it will be in the form of an add-on later in the project.

Old cart, Yes, I'm hoping if it there is a good enough performance increase that Silverdog will take it on. I have designed the project with a specific case in mind so apologies for that in advance but I think you will like it. Here > http://www.hammondmfg.com/pdf/1598B.pdf it is. There is enough space for the wireless charging coil, some other neat add ons like wireless headphones etc. Sadly the case is NOT waterproof, but if you were careful with some sealer, you could make it splash proof so not the end of the world.

Now, I include the following;

1 PDF of the updated schematic

2) Diptrace (you will need the NON PROFIT standard version) but you can download the free 30 day trial of the TOP version then use the next one down so you get 60 days over all .

3) the New Gerbers for the 4 layer PCB.

If you want cheap PCB's go here > http://dirtypcbs.com/ $84 for a 10cm X 10cm 4 layer board? No for $84 you get TEN of them that's a 4 layer board for $8.40. That's just NUTS!

I also apologise for the partial use of SMD but I had no choice with some of the ultra low noise devices.

I haven't run an analysis on the PCB so don't hang me if it's not optimised yet, this is a first off and is bound to have bugs and the filters are no where near ideal but that is something we are going to work out I hope.

I'm doing this because I have been away from here for over two years now as there was nothing to keep me here, but I'm hoping to learn and enhance my design skills after all there are people on here who are miles ahead of me in so many areas, so here's my shot at what I hope will be a simple yet powerful design. If you want to build and sell then go ahead, this is an OPEN SOURCE project and all I ask is a few beers or a bottle of whiskey (Irish of course) if you sell any you build (assuming the darn thing works at al that is ).

Anyway here are the files.

[ivconic]

Oh... i see what are you aiming...
Fancy non-obtainable components... 4 layer board...
Good luck!
Cheers!

[Davor]

Nice. There are a few goodies lying about. You may even connect a voltmeter at TP102 (after a LPF at, say 10Hz) to act as a crude ferrous discrimination.
I'm not sure NE5534 will be happy with 110 ohm loading. Even if you increase it 5 fold it will still be fine regarding input noise, even with a better op amp.
There is also a simple but faster MOSFET driving circuit.

[Sean_Goddard]

Oh... i see what are you aiming...
Fancy non-obtainable components... 4 layer board...
Good luck!
Cheers!

Which parts are unobtainable? I can source all in that design from Mouser or Avnet.

What is wrong with a 4 layer board for $8.40?

[Sean_Goddard]

Nice. There are a few goodies lying about. You may even connect a voltmeter at TP102 (after a LPF at, say 10Hz) to act as a crude ferrous discrimination.
I'm not sure NE5534 will be happy with 110 ohm loading. Even if you increase it 5 fold it will still be fine regarding input noise, even with a better op amp.
There is also a simple but faster MOSFET driving circuit.[ATTACH]34413[/ATTACH]

Yup, the original input amp was made from pure unobtainium ($50 a pop) so I dropped in a 5534. I know the original worked because it's in an existing design (not yet released but working none the less). I agree, maybe making it 100R and R106 1K might be a better idea. THe plan was to keep the Gaussian noise as low as possible.

Re the updated driver. Feel free to add it to the design. I take your point and bow to your experience in this area, but this driver is OK for the application, doesnt need to be any faster (yet). Lets see how it performs once the bugs have been driven out.

[WM6]

What is wrong with a 4 layer board for $8.40?

Nothing if it is factory populated, tested and sold as end solution board.

We amateurs usually threaten all our boards as prototype boards with expected
soldering and desoldering some parts due wrong parts used, wrong placed,
wrong orientation, destroyed by static etc. So our board should be serviceable.
It is hard to perform desoldering work on 4-layers board and not to destroy it.

If possible, I prefer to work with single or two layers boards.

[Old cart]

I am pretty new to these boards but one of these issues I see is as soon as someone kindly releases a design we attack it. Some of this has do with all the languages spoken here and to some extent cultural differences. As long as the original designer/ modifier is OK with suggestions and criticism that is fine but some get offended and go away.

In this case Sean has said he seeks feedback but I want him to know his design and efforts are appreciated.
I do like simplicity and clarity of the design and the fact that is is closely based on a proven design. I also like the non switching power supply and the extensive use of bypass caps. Sean you must be an RF designer.

That having been said i do have one question for Sean.
I noticed that all the amps after the 5534 are fast current feedback op amps.
Can you share with us your thoughts in using those as opposed to say slower precision op amps that won't accumulate DC errors. It would seem that using more bandwidth than is necessary will increase noise levels.

Also so how do we Create the subsection MODIFICATIONS where all these comments should be posted?

[Qiaozhi]

Also so how do we Create the subsection MODIFICATIONS where all these comments should be posted?

I created this project section after a special request from Sean. Other sub-sections will be created as and when Sean feels they are required.

[Old cart]

Thanks, that should help.