My Surf PI 1.2 search coil housing.

[kenny444]

Hello to you all, having worked my way through building the PI detector and having built a coil or two for testing purposes I was left with a coil housing dilema so here is my present solution. It is a cake decorating turntable, it came with some form of bearing ring inside which was discarded, there is plenty of room inside for an 8" coil and it just pops open when gently splayed. I got some number plate fastenings and some 90 degree shelf brackets. The finished result is here. inside and out I hope this is found to be useful.

May there always be gold at the end of your rainbow.

[6666]

What did the cake decorating turntable look like before you modified it ?.

[kenny444]

Hello it is just 2 flat disc's, joined in the middle, all I have done is take out the bearing ring, it is a plastic/flexible material, it should be unbreakable in normal use. it is about 1.5cm thick and 25cm wide. Bought via "E by gum Bay"

[SmugWimp]

Kenny,

I couldn't help but notice you're using enamel coated magnet wire for your coil. So am I. 24AWG Solid Copper Magnet wire (with green enamel).

I was thinking of dumping the wire and trying something else. But if yours works ok and reasonable depths, then I'll know "I" have a problem that needs to be worked out, rather than the wire I've chosen.

For the life of me, I can't seem to get more than 4" of 'detection' out of my coils. I've done two, and I don't mind doing more, but I'm curious if there was anything 'special' about your coil, or any tricks to the alignment. I've set my 'offset' to zero, but with respect to the delay, I don't have a scope available to do any 'fine tuning', and so arbitrarily spinning it this way or that way will only yield about 4" of air max (and it seems that fully ccw is the 'most' sensitive). This seems to be large or medium metal objects only. Gold Ring (my Wedding Band) or Steel Pliers (which I was working with) don't detect 'reliably' over 4".

2 of my 3 coil attempts I've used copper tape to create a faraday shield. But with it or without it, there doesn't seem to be a difference.

How is yours working out for you?

Cheers!

-- Smug

[kenny444]

Hello Smugwimp, My knowledge of coil building is just mine and what I have read on the forum. I have based my coils on low inductance and kept them to a reasonable size, because of an unsure housing plan. I have wound 4 coils all with .5mm enamelled copper one was scrapped because of my poor technique on coil number one. I have 16 turns, 24 turns both about 200mm and a 24 turn coil which is about 240mm. The size was decided on by the cake icing turntable that I bought to house the final coil. I have only done indoor air tests and the interference I have is not good, I did a single outside test to check the interference went away and left it at that. I have as yet have not completed the build fully as I am undecided as to what the best feed cable will be. Screening has proved a complete mystery to me as each time I screened the coils they stopped working and only continued after removed the screening. As far as I know a large coil makes a bigger field and should provide more depth (I am NOT an expert and could be completely wrong) What is the coil resistance? is your coil an ohm or two? what is the calculated or measured inductance? (I am waiting for an LCR meter as I write) I assume you are using a Surf PI 1.2? Is your feed cable high capacitance? can you replace it with a tested pair? have you tried twin screened audio cable. It may (this is me talking now and could be rubbish) be that a small capacitor inline with the feed cable may improve the signal (or stop it completely), as capacitors in serise reduce the overall value, it is the opposite of resistors in parallel. I hope this gives you something to point you in the general direction of success. Regards.

[SmugWimp]

Hi Kenny,

I am building for a Surf PI v1.2

My housing is 6.5 in/165 mm. My housing is semi-commercial, bought off ebay.

My first coil came in at 373uh when finished (about 30 turns). It was coil, plastic spiral wrap, and faraday shield.

My second coil came in at 272uh when finished (about 25 turns). Another coil, plastic spiral wrap, and faraday shield.

Then I started getting frustrated, lol! Neither of these would detect much further than 4 inches.

I wrapped a quickie 20 turn coil that came in at 177uh, with no shield or plastic. Same results.

all of them can be and were 'offset' to 0v.

At the moment, there is no 'feed line', I'm still just connecting the loop wires to the board.

Although there is probably interference in my home office, I've taken it outside and away from any interference, with no noticible improvement in performance.

Coil resistance measurement is a bit of a challenge; my meters lowest setting is 10x, so I can 'guess' that my resistance is below 1 ohm, but nothing more accurate can be assessed.

I'll give putting some capacitors in the mix and see what happens. My 'goal' is for 10+ inches of 'valid' detection. In my area, I'm in the water, and most of my finds have been no less than 6" in the sand (unless it's a pop-top).

What distances are you achieving with your coil?

Cheers!

-- Smug

[kenny444]

Hello Smug, firstly well done on the work you have put in. my first board gets about 8 inches in free air, that is for a pond coin and for a gold ring. How long is the connection between the coil and the PCB? is it too close and therefore the coil is detecting the PCB? I did read about various chip/IC problems and swapping them out to cure problems, I did proved the circuit was working on the active components by replacing them all. I am actually building two more so I can see any differences or improvements. I have an odd pulsing when the search head is moved which is constant with all coils, so if the problem is the same with different coils them then it must be on board or local interference. Hence my 3 board build, I suppose that if I had not spent on all these bits it would have been a good way to buying a good used detector. Silverdog did do a list of voltages that you could check, but I cannot find it at the moment, perhaps a forum search "Surf pi 1.2 voltages" "or Surf PI 1.2 depth" may help? I will have to hunt. I think the bottom line is a board error or a component fault. I cannot suggest much else, Check voltages, check all IC legs are in the sockets and not tucked under the IC, (I wonder have you got the resistor mix up problem? was it R18 R22 {may not be right}) dry joint. If you have not got the full voltage swing +5 & -5 that may be your problem. Hope this gives you hope. K.

[kenny444]

Hello Smug, this is on the forum: http://www.geotech1.com/forums/showt...rf+PI+voltages gives mods and voltage in the right areas. K

[SmugWimp]

I'll take a look at the voltages, thanks!

I'm fairly certain it's probably just me, lol! I've dug out my oscilloscope, but can't find my probes. I'm borrowing one from a friend, and will start a thorough investigation. If I can see the signals, that ought to help out a bit.

I also bought an additional kit, so I do have 'spare' parts if I need them. I also bought a TGSL kit, hopefully the coil on it won't be much more difficult, it'll need to be a DD. And much bigger.

Cheers!

-- Smug

[kenny444]

Hello, well first the good news I have built No2 and No3, bad news, both have different faults and presently do not function. So I brought me head away from the work area and and contemplate a plan of action. Further good news is that I think I know what is causing the pulsing on No1 are you ready for a major operator error, the wireless router is on, here so there is RF all over and it is also in the garden, What a plonker Rodney :-( Hope you can sort yourself out as I need a break from it for the time being. K.

[multieagle]

Hello, well first the good news I have built No2 and No3, bad news, both have different faults and presently do not function. So I brought me head away from the work area and and contemplate a plan of action. Further good news is that I think I know what is causing the pulsing on No1 are you ready for a major operator error, the wireless router is on, here so there is RF all over and it is also in the garden, What a plonker Rodney :-( Hope you can sort yourself out as I need a break from it for the time being. K.

Crap, never thought about that. I'm only 15 feet from my router! Does that really effect coil performance?

[dfbowers]

I have about 1/2 dozen each, 7" and 10" shells with or without covers ready to mail if anyone is interested. It would make a nice finish to all those Surf PIs. They are great in the surf when epoxy filled! See link below for details.
Don

https://sites.google.com/site/dbcoilshells/

[kenny444]

I really am unsure about the interference levels from the router, the laptops, the router next door etc. but something is driving my builds crazy. Anyway I was back on the case this afternoon and I seem to have sorted No3 with some chip changing, what I have now is build No2 not doing anything at switch on but beeps at switch off?

[SmugWimp]

I spent a while last night cozying up to my copy of 'fast coils'. Reading that a couple of times turned the light on for a few things... some things I'm still going to have to work out.

But I 'think' I'm actually doing ok, for not having modified my PCB. What I 'think' I need to do is find the resonant frequency of my coil, and adjust the damping resistor accordingly. Somehow, lol!

It 'seems' that my getting 5-6" out of my coil is about right for a 6.5" inch coil, given that I haven't 'tuned the coil' for it. Hopefully if I can squeeze a couple of more inches of sensitivity out of it, I might end up ok.

Odd thing, and I'm not sure if it's right or wrong, but I got my scope running yesterday, and with one probe on the output of the MOSFET and one probe on 'TP2' and things 'look' ok so far... but regardless of turning the 'delay' trim pot, it didn't seem to affect the width of the signal...

coil on scope; probes at Mosfet and TP2:

https://dl.dropboxusercontent.com/u/...scopecoil1.jpg

board, with probes:

https://dl.dropboxusercontent.com/u/...ugPI/board.jpg

my coil:

https://dl.dropboxusercontent.com/u/...mugPI/coil.jpg

coil, in housing, next to board, mounted in case:

https://dl.dropboxusercontent.com/u/.../photo%201.JPG

'operator' side of case (a repurposed chinese style waterproof lunchbox):

https://dl.dropboxusercontent.com/u/.../photo%202.JPG

Cheers!

-- Smug

[kenny444]

Hello Smug, Happy that you are happy. So if you replace R6 390 with a small pot and a 100R in series (so as not to short the coil) and adjust for depth, do you think that will do it? Also where did you get the coil case? (or is it a coil cover upside down?) Well done.