WELCOME!!

[Monolith]

One of the thoughts that I have had for some time is to use higher voltage supplies for op amps to increase the dynamic range. For example if you used +/-10 volts then the 1st preamp would not saturate if it had a gain of 10 and used the traditional diode protected inputs. Without saturation the amplifier would recover quickly. We could do this with a charge pump like the LTC3260. This device has integrated low drop out linear regulars for low noise and operates at high frequencies for efficiency. The frequency is adjusted by a single resistor. I think we could then tap into the device clock, divide the frequency by 100 and use it to drive the transmitter and audio for a fully synchronized system. The adjustable frequency could be used to reduce the effects of external noise and still remain synchronized.

Any thoughts on whether this will work?

The attached Sepic converter generates a variable positive and negative output. I think it runs at 100kHz, need to check.

Schematic and PCB layout attached

[Old cart]

Altra, one more question. Using a charge pump as described how much P-P noise should we expect on the supply lines? Have you ever measured you GS 5 for example?

[Altra]

As for the GS5, it is synchronized and only changes states during the tx on and off. So during sampling it is quiet. The only problem
with a voltage doubler design is that you need a enough voltage on the drive side to keep the regulator from dropping out. For a
+5 output you want at least -8v feeding the doubler.

[Old cart]

I have that in my workshop ;-)

OK I've asked to have su sections for the different modules created then we can move the convos for each to the relevant section.

I like the debate on the Power supply, I was going to use a TLE with X1 1A Op Amp as the splitter. As per Old Carts advice, I was going to drop that 10R in the line.

When we ge the threads set up can all those who have proposed a solution post in this main part with a brief of what they have done? I'll need to keep this top level tidy.

Thanks ALL.

Sean can you move all the conversations to the relavent section? Then make a reference in the original thread to refer to the specific sections for details. I am very ignorant as to how these forums are managed.

[Altra]

Without the dc to dc converter doesn't this then constrain you max coil voltage of about 1/2 battery voltage? Also the rail splitter has to absorb the big current pulses from the coil.

Exactly..

[Old cart]

Gold Scan 5 PS.pdf

The attached Sepic converter generates a variable positive and negative output. I think it runs at 100kHz, need to check.

Schematic and PCB layout attached

That looks good but pretty complicated. After conversing with Altra, I am thinking that maybe a low noise synchronized charge pump is a better solution. The main reason we went this way in the first place is to hold down noise. If we can provide a simple means to do so for the (low power) analog section and then allow the battery to drive the high power section directly from the battery we should be OK. Something like this snippet of the GS5 power supply and front end. Note it includes a simple constant current driver for the coil. Something Carl has said is a good idea.

[Qiaozhi]

Having read all the posts here related to this project, (IMHO) I think you need to decide whether this is really intended as an evolution of the original Surfmaster PI (as this thread is actually entitled "Surfmaster II") or more of a revolution (something completely different). Otherwise, I can already see that this project is starting to suffer from the "getting ready to get ready" syndrome.

Everyone obviously has their own ideas, and so far there are numerous suggestions for the power supply section, some disagreements about whether to use common (or garden) components or something more exotic, and even whether the PCB should be anything from single-sided to 4-layer. Personally, I would suggest that you have an overall objective (set by Sean) with clearly defined goals, to keep the project on the straight and narrow. The problem with committee-run projects, is that they become a compromise (usually driven by whoever shouts the loudest), with a "camel" as the result.

https://en.wiktionary.org/wiki/a_cam...by_a_committee

Just my two pennyworth.

[Old cart]

Spot on!

George, I agree completely. Interesting process, this. We do need direction for sure. If you start out in your car with no idea of your destination you will never get there. We did originally have a destination and even a map to get there. The map may have had a few wrong turns but we would have eventually gotten there. Now we tore up the map and have two or three destination.

I think the original idea was to just improve the original. I consider your suggestion as a positive one and would definitely like to see the project move forward to a completion.

That having been said the supply can not be completely designed until the power requirements are better known. So all we are doing now is just tossing ideas around. It is somewhat like Edson inventing the light bulb in that we have now found many ways that won't work, and that is good thing!

[Qiaozhi]

I think the original idea was to just improve the original. I consider your suggestion as a positive one and would definitely like to see the project move forward to a completion.

Yes - my comment was meant to be positive. I just thought I'd give you all a nudge, and prompt you to get back on the road.

Here's an idea for consideration; you can take it or leave it as you please:

1) Identify the major downsides to the original Surf-PI.
2) Agree on an alternative solution for each problem identified. (Needs to be time-limited.)
3) Knock up a prototype, either from scratch or by modifying an existing Surf-PI.
4) Tweak things until you're happy. (Also time-limited.)
5) Create final schematic and layout.
6) Get some PCBs made.

Most people interested in the project would (I expect) buy a couple of boards. One to test the initial design, and the second to modify further.

You probably don't need to go to the extreme of creating a PERT chart, as long as each step is not open-ended. Above all ... keep it simple - the project I mean, not necessarily the design.

Again, just my two-pennyworth.

[Old cart]

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- increased by more gain, earlier sampling, faster coil, optimized damping.

2) Smoother threshold-lower supply noise, less low frequency gain stage noise, optocoupler audio stage

3) Less "noise" - spits pops and squeaks- same as above

4) Overall more solid performance (for example as battery voltage drops, then so does the drive to the main FET and thus the performance drops off exponentially)-larger capacity battery, regulated coil drive voltage/ current.

5) Increased versatility and sensitivity to thin section gold- SAT on/of/ variable speed, earlier sampling, faster coil. Most importantly optimized damping to allow the earlier sampling.

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.

Ok I will bite and put my comments on what might help for Sean's initial project goals. See comments above in the goals section.
i don't think it is possible to edit others posts so everyone can just comment on this comment. In this way the last reply with comments will contain the design goals with proposed solutions. If anyone has a better way to do this speak now...

[Old cart]

Ok I will bite and put my comments on what might help for Sean's initial project goals. See comments above in the goals section.
i don't think it is possible to edit others posts so everyone can just comment on this comment. In this way the last reply with comments will contain the design goals with proposed solutions. If anyone has a better way to do this speak now...

NO comments?????

[Sean_Goddard]

OK Just a quick update, watch this put a smile then a frown on Ivconics face (lol).

I've gone for low noise OP series op amps with 0.9nV/RootHz noise levels and a 75MHz response, they are available in DIP and I'm now aiming at a double sided PTH board (smiles).

The Op amps are $6.35 per pop and I hope they are available in Bulgaria (frowns).

See, told you (look carefully at your monitor, you can see him cursing me again) ROFLMAO - Sorry Brother ;-)

I really have tried. Mind you looking at the Amplifier thread, this might end up being a totally discrete design, I mean that's not such a bad thing right?

Old Cart, ALL comments are welcome, or I'd be sitting at home doing this by myself. I've been on this forum for eons now and it's time I gave something back.

I like that idea, it's difficult to implement and I have amin rights for this thread so PLEASE don't be offended if a post get's deleted of edited and intergated with someone elses. I want to TRY tokeep this main thread clean and concise.

[Sean_Goddard]

ABANDONED due to lack of interest. If someone else wants to take this on feel free. I no longer (after 40 years) have an interest in metal detectors or electronics.

[WM6]

I no longer (after 40 years) have an interest in metal detectors or electronics.

Me too.

Probably it is time, for us "golden age" boys, to switch to medicine electronic:

http://ww.scientificamerican.com/art...ights-disease/

[Qiaozhi]

Me too.

Probably it is time, for us "golden age" boys, to switch to medicine electronic:

http://ww.scientificamerican.com/art...ights-disease/

The link is incorrect. You have ww. instead of www. ->
http://www.scientificamerican.com/ar...ights-disease/