Surf PI - Looked at decay curve when dunking coil in saltwater ... was not as dramatic as I thought

[Goaty]

[QUOTE=Polymer;237408]

I'd love to, but don't know which details to start with. Give me some pointers please.

I'm also working on a snorkelling detector using a Pickini and plan to use a pvc plumbing pipe housing similar to what you have, from what I could see in the photo.
Some more detailed photos and info on seals and switches/controls would be helpful.
Have you tested your setup underwater yet?

[6666]

if you are only snorkelling a very simple water proof housing can be made from simple PVC pipe, once you are in the water the controls do not need altering
so just set any adjustment , put the end cap on and off you go, no need for special parts, there is a video somewhere that shows the simple setup.

[Polymer]

[QUOTE=Goaty;237418]

I'm also working on a snorkelling detector using a Pickini and plan to use a pvc plumbing pipe housing similar to what you have, from what I could see in the photo.
Some more detailed photos and info on seals and switches/controls would be helpful.
Have you tested your setup underwater yet?

Here's a link to a thread on this http://www.geotech1.com/forums/showt...METER-QUESTION

I'm travelling in a couple of days, so have packed everything away ... will take photos when I'm back.

My setup may be overkill, I do hope to obsolete the delay pot by putting in a fixed resistor.
Signal display is an LED, vibro motor will come later when threshhold jitter is solved.
On/Off is with reed switch & mosfet.
Pipe and stem are sealed separately from each other inside, so if one part leaks it stays there.
Coil wire is inside pipe, twisted & set in a removable foam sausage.
I used a lot of MEK to glue most together. The compartment separators are transparent PVC Plugs I made out of thick PVC foils.

I have only tested it to the top part where the cables came out for measuring. That turned out to be waterproof so far.

I wanted a snorkelling detector with an adjustable angle for the coil. That turned out to be more work intensive than a fixed one.

I am going to simplify my next version once I have experience with this one.

Hope this helps, cheerio

[Polymer]

if you are only snorkelling a very simple water proof housing can be made from simple PVC pipe, once you are in the water the controls do not need altering
so just set any adjustment , put the end cap on and off you go, no need for special parts, there is a video somewhere that shows the simple setup.

I love that simple setup principle. I did do something like this with the NuPI pinpointer and found that on the beach there is always sand or salt spray getting in somewhere when doing adjustments. So I would love to keep it sealed and preferably not open it at the beach.
Would love to find that video though!

[6666]

it appears the video has been deleted but still working on it.

[Goaty]

Here's a link to a thread on this http://www.geotech1.com/forums/showt...METER-QUESTION

I'm travelling in a couple of days, so have packed everything away ... will take photos when I'm back.

My setup may be overkill, I do hope to obsolete the delay pot by putting in a fixed resistor.
Signal display is an LED, vibro motor will come later when threshhold jitter is solved.
On/Off is with reed switch & mosfet.
Pipe and stem are sealed separately from each other inside, so if one part leaks it stays there.
Coil wire is inside pipe, twisted & set in a removable foam sausage.
I used a lot of MEK to glue most together. The compartment separators are transparent PVC Plugs I made out of thick PVC foils.

I have only tested it to the top part where the cables came out for measuring. That turned out to be waterproof so far.

I wanted a snorkelling detector with an adjustable angle for the coil. That turned out to be more work intensive than a fixed one.

I am going to simplify my next version once I have experience with this one.

Hope this helps, cheerio

Thanks for the link - some really useful info!

It seems I was thinking along similar lines to your setup but have not started with that aspect until I see how well the Pickini works - still waiting for a few components to arrive on the slow boat from China.

I have already made a Surf PI wading version which works very well on the beach but we tend to get too much shore-break here to use it comfortably - hence the snorkelling model project.

Just a thought on the paraffin idea - I wonder if it would be practicable to fill the housing with liquid parafin oil rather than wax. Not sure how it would affect the components, especially the pots and the batteries would probably need isolating in a separate compartment but it would alleviate the pressure problem due to temperature changes and also make it easier to work on the board if needed.

Also, beeswax may be a better alternative to paraffin if you are planning to go that way - it tends to be more flexible when solid but I'm not sure about it's electrical properties.

Regarding the coil housing, I am considering building one out of pvc pipe to the required shape and then splitting it longitudinally to lay the coil in. I am hoping it would then be possible to glue it back together using plumbing solvent glue and keeping it water-tight

[Polymer]

Thanks for the link - some really useful info!

It seems I was thinking along similar lines to your setup but have not started with that aspect until I see how well the Pickini works - still waiting for a few components to arrive on the slow boat from China.

I have already made a Surf PI wading version which works very well on the beach but we tend to get too much shore-break here to use it comfortably - hence the snorkelling model project.

Just a thought on the paraffin idea - I wonder if it would be practicable to fill the housing with liquid parafin oil rather than wax. Not sure how it would affect the components, especially the pots and the batteries would probably need isolating in a separate compartment but it would alleviate the pressure problem due to temperature changes and also make it easier to work on the board if needed.

Also, beeswax may be a better alternative to paraffin if you are planning to go that way - it tends to be more flexible when solid but I'm not sure about it's electrical properties.

Regarding the coil housing, I am considering building one out of pvc pipe to the required shape and then splitting it longitudinally to lay the coil in. I am hoping it would then be possible to glue it back together using plumbing solvent glue and keeping it water-tight

Did you shield your coil on the surf PI? I haven't and have yet to test while real life snorkelling.

You might want to re-think sourcing components from China ... it could be or become a quality problem.

Your thoughts on liquid paraffin have also crossed my mind, so I'm taking this opportunity to finally look this up ... search ... search ... search
It looks like that stuff is quite benign at a quick glance.
I couldn't explicitly find liquid paraffin though, so not too sure, will have to dig deeper.
I might look up glycerine as well, just popped up in my mind.

It's interesting that beeswax is more flexible than paraffin ... didn't know that.
The dielectric values in charts for Beeswax range from 2.4-2.8
and 2-3 for paraffin. So not much difference from my perspective, unless aiming for super fast coils.

Ah, the coil housing. That was a pain, threading the wire through, spacing it, solving the problems on the fly ... leaving it ... trying something else again.
I like the idea splitting the coil pipe. I assume this is different to cutting, where you lose material?

The thought of losing material when cutting the pipe (making a smaller diameter later), probably not getting it really straight and not knowing if the small cross section of pipe being glued would mechanically be sound or hold up to detectorists usage, kept me from trying this.

If you go down the splitting/glueing path I would be interested to know how it goes.

[6666]

If you go down the splitting/glueing path I would be interested to know how it goes.

Very difficult if you dont get the cutting straight.

[Goaty]

@polymer

"Did you shield your coil on the surf PI?"
I used a 3dss coil with a homebrew epoxy fibreglass housing.

"You might want to re-think sourcing components from China ... it could be or become a quality problem."
More a convenience thing - I live in the country and there are no retail electronics shops close by. Australia Post rates make buying a few components un-economical. I was recently considering a cheap Chinese hot air rework station 'till I read the online reviews on some of them re electrical safety!

"I might look up glycerine as well, just popped up in my mind."
My guess is that it would not be suitable as it is miscible with water.

"I like the idea splitting the coil pipe. I assume this is different to cutting, where you lose material?"
I planned to use a "Renovator" oscillatory tool with a semi-circular blade which is quite thin so the material removed should be minimal. Straightness of the cuts should not matter too much as I would mark the housing first so the piece removed went back in the same place. My description of where I planned to cut was probably not very clear - I meant horizontal cuts around the inner and outer circumferences so the top (or bottom) could be lifted off.If gaps in the join were a problem when glueing I'm sure they could be filled with more solvent cement thickened with scraps of pvc pipe. With the housing opened up this way it should even be possible to shield the inside with graphite paint (probably not necessary for an under-water coil) and embed the windings in expanded foam.
I started experimenting with bending pvc pipe into a circle. Achieved a rough circle approx 250mm diam by filling the pipe with compacted sand and then softening it with a heat gun in a fabricated 'tunnel'. Was quite successful, so now my next step will be to re-soften it in an oven and wrap it around a mandrel (old saucepan) to get a uniform shape. The pre-bending was necessary as the straight length would not fit in the oven. Still, it's all a work in progress and whether I press ahead depends on how well the Pickini works.

[Davor]

Did you shield your coil on the surf PI? I haven't and have yet to test while real life snorkelling.

I don't think it would make any difference under water, only a complication. Because you'll have a coil on a short distance from a Surf, it makes no sense making any interconnections - just wind a number of flexible insulated wire turns and terminate the wire ends in your Surf. You'll have to make the coil rigid, but if you take care wires of a coil are intact, the very coil may as well be soaked in water - It would make no difference.
I'll make sure my Surf goes under water in the summer. I had other things to do, but now I'll be available for more detectors stuff.

[Polymer]

I don't think it would make any difference under water, only a complication. Because you'll have a coil on a short distance from a Surf, it makes no sense making any interconnections - just wind a number of flexible insulated wire turns and terminate the wire ends in your Surf. You'll have to make the coil rigid, but if you take care wires of a coil are intact, the very coil may as well be soaked in water - It would make no difference.
I'll make sure my Surf goes under water in the summer. I had other things to do, but now I'll be available for more detectors stuff.

Hello Davor,

Wouldn't putting the coil windings directly in water change the winding capacitance considerably,
because of greatly increased dielectric value between windings, making a slower coil?

I will measure this myself one of these days, because answers on internet vary wildly ...

[Goaty]

If you go down the splitting/glueing path I would be interested to know how it goes.

Well, I have finished my snorkelling housing for the Pickini and given it a couple of tests in the water and all seems good.
I re-designed the original housing as some initial tests revealed that the 0-ring seals were not effective and went for a two-piece threaded one with the electronics in the front section and the batteries at the back. This seams to seal with no leaks and makes for easy access to the batteries and electronics.
Because the Pickini is self calibrating I have only needed switches for on/off and pinpoint through the case. I used modified rubber boots over the toggle switches and have used a high brightness white LED for indicating. I have left the sensitivity pot floating on leads inside the case so I can adjust it if necessary.
The split pvc tubing coil housing seems to be effective and , being quite thin, swings easily under water.
I have made the handle and armrest adjustable and removable courtesy of a wing nut clamp and a stainless hose clamp - looks a bit 'agricultural' but seems to work OK.
The whole thing was spray painted with black acrylic lacquer to tidy it up and cover all of the pvc solvent cement on the joins.

Here is the pvc coil housing with the shielded coil epoxied into the bottom half -




And here is the finished detector-



I have since moved the arm rest forward to reduce flexing on the seal when swinging the detector under water.

All in all, am pretty happy with the way it turned out.
So far, I have managed to find a USB memory stick (very corroded!) and a 5c coin in the local saltwater lake and can't wait for a calm day swell-wise to try it in the sea.
Down the track I hope to try adding a piezo as the LED indicator takes a bit of getting used to.

[Polymer]

I don't think it would make any difference under water, only a complication. Because you'll have a coil on a short distance from a Surf, it makes no sense making any interconnections - just wind a number of flexible insulated wire turns and terminate the wire ends in your Surf. You'll have to make the coil rigid, but if you take care wires of a coil are intact, the very coil may as well be soaked in water - It would make no difference.
I'll make sure my Surf goes under water in the summer. I had other things to do, but now I'll be available for more detectors stuff.

It looks like you are right. At least this is so with the measurements I made with a relatively slow & open coil (just a bundle of windings)
immersed in air, sweet water and salt water.
The much higher dielectric value of water between coil windings does not change the settle time as much as I imagined.
Actually in this case it's neglegible as far as I can see. Here the three scope pictures:

[kg5cm]

Instead of coating the PC board in wax try a conformal coating. All the boards we used in seismic work in the Louisiana swamps were coated with it. It can be pried off a component if you need to replace a part, then paint over the new part and PC board, both sides, in the repaired area.

[Polymer]

Well, I have finished my snorkelling housing for the Pickini and given it a couple of tests in the water and all seems good.
I re-designed the original housing as some initial tests revealed that the 0-ring seals were not effective and went for a two-piece threaded one with the electronics in the front section and the batteries at the back. This seams to seal with no leaks and makes for easy access to the batteries and electronics.
Because the Pickini is self calibrating I have only needed switches for on/off and pinpoint through the case. I used modified rubber boots over the toggle switches and have used a high brightness white LED for indicating. I have left the sensitivity pot floating on leads inside the case so I can adjust it if necessary.
The split pvc tubing coil housing seems to be effective and , being quite thin, swings easily under water.
I have made the handle and armrest adjustable and removable courtesy of a wing nut clamp and a stainless hose clamp - looks a bit 'agricultural' but seems to work OK.
The whole thing was spray painted with black acrylic lacquer to tidy it up and cover all of the pvc solvent cement on the joins.

Here is the pvc coil housing with the shielded coil epoxied into the bottom half -

[ATTACH]42202[/ATTACH]


And here is the finished detector-

[ATTACH]42203[/ATTACH]

I have since moved the arm rest forward to reduce flexing on the seal when swinging the detector under water.

All in all, am pretty happy with the way it turned out.
So far, I have managed to find a USB memory stick (very corroded!) and a 5c coin in the local saltwater lake and can't wait for a calm day swell-wise to try it in the sea.
Down the track I hope to try adding a piezo as the LED indicator takes a bit of getting used to.

Gee, time flies. Thanks for your lengthy and great description!

I am gobsmacked at how you got the coil housing together again ... extra cheers for that!
That surely beats threading the windings thru the pipe I guess.

Where did you place the indicating LED?
I am asking, because I have the LED in the wrong spot as I now know, at least for me.
Have been snorkelling with my PI too. Thought I could watch the coil directly and see the LED
sorta on the edge of my vision. That does not work well for me.

I will try and describe:
Underwater everything was moving and me with it, even when there isn't any appreciable swell.
Trying to "lock in" the beep position on the ground optically whilst refocussing eyes from LED
in housing around 50cm away with goggles on, made me all sorta dizzy.

Maybe it's just me, or a human thing - optical perception quirkies.

I have found junk, coins, junk jewellery etc ... but searching like that was not much joy.

Second thing that bugged me was my device is not foldable for transport. Coil is foldable,
but the general length of the outfit is not practical for me.

I will mainly be working on those two things now.

How did your search by the sea go?

Happy Hunting