WELCOME!!

[soverey]

Thank you for publishing this project , I have succesfully build the surf pi from silverdog, and l'm interested to buy a pcb ,when they become available.

[Qiaozhi]

It's already seen on these forums. Not my intention to start debate here; but everyday more and more topics and threads here are polluted with "references" and appeals made by one moderator here, reminding and asking people to order and buy "this and that " from one and the same source, quite coincidently directly related to his own and personal wallet. How about that? The one is not able to start own MD industry; instead, the one is misusing public forum to spread own small niche business protected and secured by the fact he is moderator and nobody can't do nothing against

Just to put the record straight, and to stop any misunderstandings ...

The PCBs and kits that Silverdog sells are supplied as a service to the Geotech community, and to support several of the most popular projects. I personally receive no money whatsoever from this enterprise, and Silverdog himself makes only a minimal profit, considering the effort required to put these kits together. The Minipulse Plus (MPP) project was completely funded out of my own pocket, and I have made absolutely no money from it. I purchased the original Minipulse via eBay (in a non-working state) and returned it to full working condition, prior to completing the back-engineering exercise. After that I decided to improve the design and make it available to Geotech members, since there were a number of advantages over the existing Surf-PI and Baracuda projects. Even though this took many hours of my own time, I did this without any regard to personal gain.

Also, I would like to remind everyone that Carl pays for this site out of his own pocket, and you will note that there is no funding from advertisers. Nor is there any annual fee to join, unlike many other metal detector forums.

And, with regard to the book "Inside the METAL DETECTOR", this took both Carl and I many many months of experimentation, writing, and re-writing, to produce the final result. If anyone thinks that writing such a book is a quick route to riches, then think again. ITMD came from a desire by both of us to create something that was missing from the market. That is, a book on metal detector technology. If such a book had already existed, then we both would have bought a copy. Since it didn't exist, we decided to create it. If we had to survive from the small profit made on this book, we would have starved to death by now.

Finally, I would like to remind Ivconic that I (again, out of my own pocket) sent him a FREE copy of ITMD, when we released Edition 1, as a personal thank you for the contribution he had made to the forum. Obviously there is no pleasing some people.

[ivconic]

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?

WM6 already explained. Nothing much to add except maybe to emphasize the difference between conditions in UK, EU and other countries, respecting the availability of some newer material on market.
Some of those components are not possible to obtain in local shops. Ordering them from abroad will seriously affect overall costs, than we can't talk any more about hobby and diy project here.
Eventually it will end up with reduced number of participants, therefore the feedback too will be reduced. It can not be called "diy" project any more. It's just a modern kind of trading and making small niche business.
It's already seen on these forums. Not my intention to start debate here; but everyday more and more topics and threads here are polluted with "references" and appeals made by one moderator here, reminding and asking people to order and buy "this and that " from one and the same source, quite coincidently directly related to his own and personal wallet. How about that? The one is not able to start own MD industry; instead, the one is misusing public forum to spread own small niche business protected and secured by the fact he is moderator and nobody can't do nothing against.
I expected this to remain strictly diy&hobby place for us; the plain and honest enthusiasts. The way it was in recent past. Sorry if i lost my compass. My mistake!
Whatever... your effort is still respected from my side, i salute it. But at the same time i deeply regret because i can't participate.
Cheers!

[Old cart]

Thanks, that should help.

[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]

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?

[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.

[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.

[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?

[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.