Surf Pi Professional Pcb's back in stock - NEW Prices

[bklein]

How may a DD coil be incorporated with the Surf PI circuit? I have a couple Minelab DD coils I want to compare without messing with the Minelab detector.

[TH Jim]

My coil will allow me to sample down to 12uS, using a 5k1 and a 10K pot for delay adjustment. 12uS provides good sensitivity to gold and all other small iitems.

[Waikiki_Sweep]

Are you using a twisted pair all the way from the coil to the control box ?

Yes. It works for me but I am not sure is it bad or good design because all brand name PI detectors using coaxial cables. You can experimenting with it but I can't recommend it for everybody because without electrostatic shield this twisted pair may add some noises for example when ocean wave covers the detector.

[6666]

I am using twisted pair of stranded wires to keep coaxial shield away from coil.

Are you using a twisted pair all the way from the coil to the control box ?

[Waikiki_Sweep]

Fix your Surf PI delay timing

For some reason I can pick all types of metals, including Silver. But not 14k gold, only 10k gold and I think that I can pick 10k gold because is not that pure. Why? should I work on my coil to do it better? I got a signal on a medallion and when I bring it home the first thing I did is to pass it near to a magnet and it stick it to the magnet and ... I try different setups using some 14k gold chains and nothing.

I have no problems to detect gold with my PI. Any gold. 10k, 14k, 24k. And more. Most of gold rings I am detecting from distance 1.5 times far then distance I detect coins.
First of all I am using short delays. 20 micro seconds or less. Check your R25 and delay pot P3 (hear input 8 of U4C - MC14093). If you have it 15k + 100k it is just wrong.

Every 1 kilo Ohm in R25 + P3 chain is practically equal to 1 micro second of delay.

So if you using 15k + 100k in max range it will give you more than 115 micro seconds that is far away from gold ring decay time and good to detect coca can .
You will never set precise delay with such range.

Check original Surf PI Pro schematics below. It has 5.1k + 10k pot on the place instead of 15k + 100k pot for version we all building till now.
I am using 7.5k + 22k pot to be able adjust delay in range I need but only because I search in salt water. For dry sand 5.1k + 20k pot will be OK.

Also I think that coil design is important too. If you using single AWG 24 wire, not stranded, it will decay as long as your gold ring.
If you have connected coaxial cable straight to the coil than shield
in your coaxial cable will keep eddy currents even longer than gold ring decays. I am using twisted pair of stranded wires to keep coaxial shield away from coil.

Regarding chains. It picks chains with very short delays. And as delay shorter distance of detection of chain increasing.
With longer delays it can't be detected at all. Consider chain as a very small gold rings that decays very very fast.

[satdaveuk]

Funny this subject coming up again at this time its because im building the mini pulse 3 with a few refinements for being able to adapt and advance its capabilities , and perfecting to detect gold at long range in the real world is what this project is all about, as alot of PI projects here fall short of that.
Its interesting because with the IB format the better detection of gold everything thing else follows through simple as that.
Gold is a alloy so needs to be treated different with PI due to the very nature of it design.

[TH Jim]

Hi Goldstar,

The reason you are not getting very good results using chains is that chains are very difficult to detect. Each link behaves like an individual target, with each magnetic field orientated in a slightly different plane, so many fields will cancel each other out. The net result is a very small target.

As an example, i have tested my PI with a 20 gram, 22k chain and it can barely be detected at a distance of 2 inches. Compare that to a 22k mans finger ring of only 7 grams that is easily detected at a distance of 12 inches.

As long as you sample somewhere between 12 and 20 micro seconds you will be ok to detect gold rings

Cheers, Jim.

[der_fisherman]

For some reason I can pick all types of metals, including Silver. But not 14k gold, only 10k gold and I think that I can pick 10k gold because is not that pure. Why? should I work on my coil to do it better? I got a signal on a medallion and when I bring it home the first thing I did is to pass it near to a magnet and it stick it to the magnet and ... I try differents setups using some 14k gold chains and nothing.

I read on here time and again that some PI detectors have problems with Gold as due to the fact that it has a very low resistance, the induced target signal is basically shorted out very quickly. You need to sample sooner than you are doing.

Conversely, if you sample fast enough to detect gold, other more resistive (slower) metals will be missed.....which is why some PI MDs have an adjustment for that.....

I did recently suggest that having a programmable PIC to do the job, it could be quickly switching back & forth, so catching all metals....

This is all hearsay as i do not have a PI detector myself....

Best of luck

andy

[goldstar]

For some reason I can pick all types of metals, including Silver. But not 14k gold, only 10k gold and I think that I can pick 10k gold because is not that pure. Why? should I work on my coil to do it better? I got a signal on a medallion and when I bring it home the first thing I did is to pass it near to a magnet and it stick it to the magnet and ... I try differents setups using some 14k gold chains and nothing.

[6666]

Thanks for the explanation about making the coil, thats very clever ,
I was originally thinking along the lines of you having a single dummy winding to start it
Cheers

[Waikiki_Sweep]

How did you physically hold the wire while you wound the coil so you could get the zig zag pattern ?

To make such coil you need that tool for winding spiral coils (two plates with spacer between) but you have to make spacer a little bit thicker.
Let say 1.7 of wire diameter. Sure you will not have ideal zigzag but something very close to it.

[6666]

How did you physically hold the wire while you wound the coil so you could get the zig zag pattern ?

[Waikiki_Sweep]

Coil for Surf PI

.

Should I wind my coil in a flat possition like the one on the picture or it doesn't matter?

In my beliefs it is the best shape for PI coil to search in water.

[goldstar]

.

Should I wind my coil in a flat possition like the one on the picture or it doesn't matter?

[Waikiki_Sweep]

Discrimination of ferrous targets in PI detector.

OK. Here some useful info.

Quote:

"SSP-2010. This is an unique system, combining PI detector and magnetometer, allowing the discrimination of the unwanted ferrous objects no matter their size and ageing in the ground."

"Detech Ltd is the first company in the world, applying search coil with built in magnetic sensors in the middle sector. This allows perfect discrimination of the ferrous objects by the PI detectors."

http://www.detech-metaldetectors.com/about-us.html

So I have found easy to build magnetometer on 555 timer.

To build one you have to find magnetic security strip

http://www.ebay.com/sch/i.html?_nkw=Sensormatic+Ultra+Strip

in one of your books, drugs or electronic goods. Remove Metglas strip
from it and use it as a core for your magnetometer coil.
(there is 2-3 strips inside the tag but only one is Metglas, others are magnets)

I did not tried it yet but it looks very promising.

http://www.youtube.com/watch?v=dP84iJlQCDI

Enjoy!!!