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

[itsazoo2013]

How do I go about ordering a Surf PI kit from your webpage?

[bklein]

OK, that's right I remember now testing I think some USB3 cables and they were detectable by the coil.
In regards to the series diodes, I just came across this article: http://www.eecs.berkeley.edu/Pubs/Te...-2012-265.html
I may be off-base but perhaps some of the design techniques apply.

[Waikiki_Sweep]

Foil acts like a target, just like small gold ring.

You can find coaxial cable with cooper wires mesh instead of foil, also center conductor is better if it is stranded or you will detect solid wire in it.

In many cables also you will see a Mylar screen that looks like an aluminum foil but in real it is a plastic with very thin aluminum layer made with vacuum emission.
That is practically undetectable or making very low signal so probably you can use it. (Try to detect piece of cable with your detector to be sure)

Also hook it on LC meter and check capacitance. Lower is better. Thin cable tends to have more capacitance and it will make your coil slow decaying.

I tried "Belkin Synapse Gold Plated Video RCA Coax Cable" for monocoils but it has a Mylar shield over cooper stranded wires shield. Central conductor is stranded as I need. It works fairly good.

For DD coils I am using "Belkin Synapse Silver Series S-Video" because of two insulated stranded coaxial cables inside with separated not connected together shields, stranded cores and even no Mylar.
It fits specification perfectly!!! If you cut Minelab Excalibur or Fisher CZ or most other VLF detector cables you will see the same picture.
Just one drawback. It full of woven instead or plastic cords. May suck water. But two years of use on salt water beach shows OK!

Also that Belkin cables are very robust and will survive a lot of bending and other mechanical damage when you will use if in field.

But most of other S-video cables on eBay are scam: 4 wires in one shield (too bad!) or shields touching each other (bad!).

You can find many good cables once you know what to searching for.

[bklein]

Why no foil in coax? Most hf coax has foil. What do you use then?

[Waikiki_Sweep]

Connect oscilloscope to preamp output pin (6) of NE5534. Debugging of SurfPI unfortunately scattered over many threads. This one you are reading now may helps too.

[multieagle]

Where do you place the oscilloscope probes to measure coil decays? Is there somewhere a thread on calibrating the Surf PI 1.2 ? Tks.

[Waikiki_Sweep]

Use oscilloscope to see how long your coil decays. You may see it somewhere between 10-40 uS before decay settles down depending on coil interwire capacitance, dumping resistor, cable, shield and MOSFET capacitances. If you want to detect smaller targets sure small coil will help but also shorter and better coaxial cable (stranded shield and central conductor), spacer between coil and shield, fast diode in series with MOSFET to block its Coss capacitance, Teflon insulated stranded wires to stop coil wires acting like a targets. And NO FOIL in shield or coax. Impulse width has influence on decay time as well as inductance of the coil. So you can use lower inductance coil with shorter TX impulses and higher frequency to detect small staff deeper.
Once you can see that your coil decays faster you have to move sampling frame close to TX impulse and detect that smallest targets.
For 5-15 uS delays you also will see much more ground problems and falsing on salt water / salt water beaches.

Also some special construction of coil may help to make it faster:
- flat spiral coil, reducing interwire capacitance (but not a coil-shield capacitance);
- basket coil reducing interwire capacitance;
- separated TX and RX coils helps to work only with RX decay which is much softer;
- balanced TX and RX coils reducing TX influence on RX almost to nothing so you will see only targets and ground decay not a coil decay.

[golfnut]

" I wound it in approx. 28cm dia. coil, and found around 17-18 turns finds my gold wedding ring at around 30cm, or a 20 cent Aussie coin at around 28cm. I can only detect a small gold earring at around 1.5cm. Is this normal?"

Seems about right.

I found a smaller coil gives a more crisp/positive response to smaller items try one ~dia 7-8" S

[silverdog]

The Shop is open for 2014

A big thank you for all who purchased a kit in 2013 and supported the supply of pcbs/kits to this great forum

Good Luck to everyone in 2014 , I hope you find something really nice while hunting

Silverdog

[itsazoo2013]

Wondering if you have any more Surf PI kits available and all the details.
Thanks

[Tarsier79]

Gday

I have just finished assembling my first metal detector, the Surf 1.2. I spent half a day trying to discover why I could not detect anything, only to find by trial and error playing with the pots and coil windings, i stumbled across something that responded to a large bottle opener.

For my coil, I am using a multi strand wire that has each wire individually laquered, approx .6mm dia. I wound it in approx. 28cm dia. coil, and found around 17-18 turns finds my gold wedding ring at around 30cm, or a 20 cent Aussie coin at around 28cm. I can only detect a small gold earring at around 1.5cm. Is this normal?
At the moment my "coil" is loosely held together with about 10 pieces of tape, and there is an additional length strewn around the floor, as I intend to wind it tightly before cutting the excess, as I have to tin the end before I can connect to my surf. I also have just connected it with a 1.2m piece of speaker wire, which I am thinking to replace with some medium duty AV coax. In its current state, my coil measures 235 uH. When I add more coils to make it up to 300, it just won't read.

Also, when I wind this coil more tightly, will it respond similarly or better, or has my experimenting been leading me down the garden path?

I have been trying to read up on this forum, but there is a massive amount of information here, and I haven't even scratched the surface.

Cheers

[satdaveuk]

Well, I finally got my SURF PI to the testing stage. I initially screwed it up pretty badly, and was about to throw it in the trash. Fortunately for me, chemelec took me under wing and offered to fix it for the cost of return postage. Did not know what to expect, but Gary turned out to be a 100% good guy! He managed to repair my board and replace some parts - even prepared the wiring for me. Without his help I would not have completed this project . . . not by a long shot! Gary remarked that it would have helped if the board was not so dark as to make it hard to follow the trace. Initially I could not get any sound. Gary suggested bypassing the speaker output and running the speaker/headphones directly from the volume control. That did the trick.

Now, on to the adjustments. Inside on my work table, I'm getting a rather loud scream, which the volume does not fully compensate. So am heading outside to attempt some adjustments. Even inside with the noise, it is detecting metal of varying sizes.

If you have not stumbled across Gary's site: http://chemelec.com/ If I had met, or perused his site first, would probably have dealt with him here in Canada.

THANKS AGAIN GARY!

Hi
Joined Garrys site long before becoming a member on here, his electric fencer2 works well , supplied a few of my MD permissions with them long back and there still working well.
Garry will be pleased for your thank you , its a pity that those who he has helped in the past didn't all follow suit, a big thank you costs nothing and yet its worth its wight in gold.
Regards

[multieagle]

Well, I finally got my SURF PI to the testing stage. I initially screwed it up pretty badly, and was about to throw it in the trash. Fortunately for me, chemelec took me under wing and offered to fix it for the cost of return postage. Did not know what to expect, but Gary turned out to be a 100% good guy! He managed to repair my board and replace some parts - even prepared the wiring for me. Without his help I would not have completed this project . . . not by a long shot! Gary remarked that it would have helped if the board was not so dark as to make it hard to follow the trace. Initially I could not get any sound. Gary suggested bypassing the speaker output and running the speaker/headphones directly from the volume control. That did the trick.

Now, on to the adjustments. Inside on my work table, I'm getting a rather loud scream, which the volume does not fully compensate. So am heading outside to attempt some adjustments. Even inside with the noise, it is detecting metal of varying sizes.

If you have not stumbled across Gary's site: http://chemelec.com/ If I had met, or perused his site first, would probably have dealt with him here in Canada.

THANKS AGAIN GARY!

[metal mania]

http://www.silverdog.co.uk/shop/inde...&product_id=76

Thanks so much

[Qiaozhi]

Cool kit how much GBP please thanks

http://www.silverdog.co.uk/shop/index.php?route=product/product&path=36&product_id=76