Surf PI 1.2

[Wasp]

Here's some info I have found in various places;

I wound a teflon mono coil then reused the wire to make a basket (same length ~ 65 feet for 300 uh).

[ATTACH]30945[/ATTACH]

Thanks for the info.

Quick update, I made one of those coils. 205 mm OD, 195 mm ID, 30 turns, 0.5 mm enameled copper wire, 1.9 ohm. I believe the pdf says 317 uH, which sounds appropriate.

Here is a pic: http://i.imgur.com/J7zPsl1.jpg

I'll be testing it tomorrow

Cheers,
Wasp

[mschmahl]

Nice coil wasp. How did you made your winding patern? And what is the material?

[Wasp]

Hello again,

Just tested the latest basket coil, after tuning it i can get a faint signal on the very thin gold ring and copper block at about 20 cm with the threshold a bit high. Can easily pick it up at 15 cm even with the threshold in the minimum. I also tested a soda can (a steel one) with a clear signal over 40 cm.

I think for a smaller diameter coil, it's a pretty good result and very close to Nezocas results. Hopefully with a shielded cable (from coil to board) i can get an even more stable signal and/or better result.

I already have a nice crutch (light, nice rubber handle and plastic arm support) that i intend to convert into a stem/shaft by replacing the extendable aluminium tube with a nylon one. I still have to think how i'll make the coil base/cover and hinge.

I was thinking about having only the coil on the stem and everything else on a waist bag, but i might get into trouble being wired with the antenna cable while digging and it's extended lenght affecting performance. Has anyone tried this? Is an extended RG6 cable going to affect performance (added resistance)?

I can also go back to only having the battery pack in my waist bag, with only the battery cable and headphones leaving the stem. I might put them both in a single cable. I don't like the idea of the extra weight of the battery in the stem.

Nice coil wasp. How did you made your winding patern? And what is the material?

Thank you!

I followed the instructions that Silver Dollar gave me in his last post (Coil howto.pdf). It was pretty simple, i printed the pattern linked in the pdf file, cut it and glued it to a paint bucket lid (it's plastic, feels like PP). Cut the plastic until i had the ring, made the notches with a dremel and a thin cutting disc, removed the glued paper pattern and started coiling like in the instructions.

Have some pics:
Plastic ring http://i.imgur.com/k6Nz1SN.jpg
The other side had the pattern glued: http://i.imgur.com/nTUxeFd.jpg
After cutting the notches: http://i.imgur.com/XysUCZC.jpg
Pattern removed and coiled: http://i.imgur.com/J7zPsl1.jpg

Cheers,
Wasp

[mschmahl]

Nice pictures. I got my last pattern from a friend. He milled it with cnc milling cutter.
But your idea is much cheaper and easier to handle.
I have done my coil in a donutstyle coilshell, so putting all on a stem is no problem. For the lower stem you can use a pice of fishing rod and fill the lowest part with epoxyd or similar.

[baum7154]

Hello again,

I've followed Tepco's post and tried a PVC insulated cable coil. I wanted to do a 30 turn coil but i quickly ran out of cable and only made it to 25 turns.

Here is the second coil i've made: http://i.imgur.com/eIrzsbQ.jpg

And here are it's specs: 0.9 ohm, 25 turns, ID 125 mm, OD 205 mm, double 0.25 mm copper (wired in parallel).

Damping resistor gets warm and i can now use the full trimmer range of the delay with the best results close to the full clockwise regulation.

I'm using a thin gold ring as my smallest detection target and a 150 grams copper block as my biggest detection target (i'm assuming anything in between in size/volume can also be detected). It can detect them both at around 15 cm max which i think is an improvement from the first coil.



Thank you for your reply.

It looks very interesting but a search for "basket coil" in the forum brings only indirect threads and it's hard to find a thread dedicated to the subject.

Do you know where i can go and read on the subject? I need some guide lines. How do i calculate it's inductance? Do i make an aproximation on it's diameter? Has anyone made a successful basket coil for this project? If so, what kind of specs should i go for?

Cheers,
Wasp

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Take a look in the COILS FORUM for the CHANCE PI COIL thread. I have built many of these coils and have detailed construction techniques to optimize speed and performance of this type of coil.

Good luck!

Dan

[davy74]

Re basket coil for Surf PI project

Hi Wasp
'A Wealth of information on here', I've decided to join as I'm building the Surf PI & this forum is highly recommended.
I Like this coil, a very tidy job, one question, did u have to shield it with alu foil? - faraday shield?
I want to make this basket coil, I'm an electrical engineer with use of workshop etc -but I doubt I could improve on what you've come up with there so any info on your method is most welcome.
David.

[davy74]

Finally almost finished my first ever build - the Surf PI 1.2 silverdog kit.

Finished building my Surf PI 1.2 using silverdog kit as the core.
Coil is a gutted Garret crossfire DD shell I had lying around - used 25 turns of braided (litz?) wire from a computer monitor - have left unsheilded for the time being until I figure out if needed...using the stem etc from my GTAX550 (which it is modded so control box slides on or off)Dont currently know inductance of coil - LCR meter in the post as is an oscilloscope (can't wait to get these)...I have put the delay pot on side of box along with some testpoints which will allow me to tweak & learn (I hope) once I have scope...I've got plenty more to learn.......I have posted a few photos & a video showing build overview (youtube link) I'll also post another video with air tests - the detection distance is at least as good as or exceeds that of the GTAX 550 by 1 - 2" on most items. It also seems to ignore small balls of foil. Any feedback on increasing detection range? currently 9 - 10 " on a victorian penny....is this ballpark for the kit I've used? See additional video for air tests in next post below.

[video=youtube;3-bz7M5XzZY]

[davy74]

Surf PI 1.2 build - Finally almost finished my first ever build - This is 2nd of two posts & is showing only the air tests on an oval mono coil with 26 turns of braided (litz?) wire taken from a computer monitor....seems to perform OK for a first attempt... See video & photos in last post above which show build overview using the Surf PI 1.2 silverdog kit & additional outsourced parts.

See video & photos in last post above which show build overview - internal wiring etc...etc...this is an additional video showing only air tests....with mainly old pre-decimal UK coinage - some rings & a small solid gold pendant....Dont yet know coil inductance...waiting on an LCR meter & a scope.......then will post more info...I've purchased a copy of 'Inside the Metal detector' & I've got the bug for building these so once I finish this build, I will likely do the barracuda then the minipulse ........

[kosacid]

i have just built mine using a 0.9mm 30 turns 6" coil magnet wire, im getting 6" on a small gold ring i might try a few of the coils thing is my garret 150 only gets 4" on the same ring
is it worth covering the coil in foil tape to shield it ?
http://i943.photobucket.com/albums/a...161005_003.jpg

[davy74]

i have just built mine using a 0.9mm 30 turns 6" coil magnet wire, im getting 6" on a small gold ring i might try a few of the coils thing is my garret 150 only gets 4" on the same ring
is it worth covering the coil in foil tape to shield it ?
http://i943.photobucket.com/albums/a...161005_003.jpg

Kosacid;
From what I've experienced so far - your air test (depth) might start to max-out around a distance = the diameter of the coil used, which in your case is 6", A range of 2" more than your Garrett sounds about right, my surf is running a 10x6" oval... my max depth was 10 -11 " on a thick gold ring & all my test pieces averaged out getting detected about 2" greater than with my Garrett GTAX550 running a similar sized coil. Do you know the inductance of your coil? I'm still undecided about whether or not to shield mine.
Davy.

[kosacid]

i used the coil calculator but its around 280 according to the calc, i replayed on another post about shielding it didn't work it damped the coil right down i used aluminum foil tape, so now its unshielded and its fine, i have already found lots of stuff with it
but ill tell you there is a slight flaw with surf build and it took me ages to work it out, and it will cure most of the problems and prob wont need the shield, its going to sound silly but remove the buzzer and use headphones only, the dam buzzer puts out pulses what the detector picks up and loops and there was me thinking it was interference,but it is good that its that sensitive, now i have it maxed out i just get a gentle hum now no stray pulses, sick of finding nail heads and hair pins lol, next build is going to be the barracuda
let me know if it fixes yours to

[Qiaozhi]

i used the coil calculator but its around 280 according to the calc, i replayed on another post about shielding it didn't work it damped the coil right down i used aluminum foil tape, so now its unshielded and its fine, i have already found lots of stuff with it
but ill tell you there is a slight flaw with surf build and it took me ages to work it out, and it will cure most of the problems and prob wont need the shield, its going to sound silly but remove the buzzer and use headphones only, the dam buzzer puts out pulses what the detector picks up and loops and there was me thinking it was interference,but it is good that its that sensitive, now i have it maxed out i just get a gentle hum now no stray pulses, sick of finding nail heads and hair pins lol, next build is going to be the barracuda
let me know if it fixes yours to

The Geotech Baracuda Build Document also mentions a potential problem with the piezo buzzer. It was discovered that, for some inexplicable reason, small (polarity sensitive) piezo speakers will function with a 12V supply even if connected the wrong way round. However, once the battery voltage drops to around 11V, they stop working. If this happens, then check you have the piezo connected correctly.

[kosacid]

thing is you shield the box then put a source of interference in a box with sensitive circuits, a bit like sticking a microphone into a amplifier
now i get just a hum and no chatter what a difference removing the buzzer

[kosacid]

had a good mess around with coils and best so far is this 6" 28 turns of 0.4mm here is the build

http://i943.photobucket.com/albums/a...161027_008.jpg

next stage warping you can see i have a bit tape marking last wind

http://i943.photobucket.com/albums/a...161027_009.jpg

giving it a test before adding the shield

https://www.youtube.com/watch?v=vVZm_109n18

next adding the shield using the same wire wind it round the coil and solider it to the wire you marked with tape thats your ground, the surf pi has a direct ground so no need for a 3rd wire to ground you can test with a meter what one is ground

http://i943.photobucket.com/albums/a...161028_002.jpg

as you can see from the test gold was a problem after adding the shield and returning the delay i got 10" on the big gold ring and over 6+ on the small one, the marks on the stick are 6 10 and 12