Operate a microprocessor at 10 Meter depth of water

[tytower]

I'm looking for ideas and suggestions about what to use to operate an Arduino at depth in water
Does anyone have any experience in this and if so what did you use ?

I want to be able to get at it to reprogram it from time to time and I need to get a couple of shields onto it probably also

 

[Diver300]

Well you need to keep the water out. You need a waterproof case. It must be pressure proof or you have to fill it with oil.

What wires or signals do you need to get in and out of the box?

 

[tytower]

Nothing in or out .
If I fill it with oil will that not short the electrical connections and battery?

 

[Diver300]

Nothing in or out .
If I fill it with oil will that not short the electrical connections and battery?

Oil does not conduct electricity. Many transformers, some switchgear and some diving computers are full of oil.

(gearbox oil may conduct, but that is the iron filings in it, not the oil itself)

 

[Reloadron]

What I believe you are after is not a water proof enclosure but a water tight enclosure. Figure it this way. On the surface the atmospheric pressure is about 100 kPa (14.7 PSI) at a depth of 10 meters the pressure doubles to about 200 kPa (29.4 PSI).

My lousy everyday watch is "water proof" which really means "splash proof" as in at a depth of 10 meters it would leak like a sieve. It gets to be a play on words. This is where you need to be careful. There are specifications on real products that spell out to what depth they are water tight.

Hammond Manufacturing is an example of an enclosure maker that manufactures enclosures to various depth specifications. Again, look for enclosures that use gasket materials.

If this project is going down sans a tether or umbilical cord then no big deal but if you want to maintain communication with the box then you need to look at through the bulkhead connectors designed to be water tight. Water proof and Splash Proof are just generic terms.

Personally I would not go the oil filled route but if you do then mineral oil that is 99% pure is what you want.

Before I forget, look for a hackable underwater camera enclosure for a quick and dirty solution.

Ron

 

[Boncuk]

Using silicone oil you'll have an excellent isolator.

A friend of mine built a high voltage capacitor using silicone oil which works perfect as dielectric.

You might check for silicone oil at a foam mattress manufacturer. They use silicone oil to cut the foam, which gets sticky when cut by hot blades.

The oil takes care of good separation of foam and simultaneously cools the blade of the band saw. It's being sprayed at high pressure (24bar +) onto the blade only with little effect on the quality of the mattress.

It's water clear and doesn't look as ugly as engine oil in a transparent acrylic glass enclosure.

Since silicone oil is not compressible you might use it for any desired water depth.

Boncuk

 

[KJ6EAD]

It also helps to keep the enclosure as small as possible.

 

[tytower]

Good stuff -thanks all

 

[tytower]

Oil does not conduct electricity. Many transformers, some switchgear and some diving computers are full of oil.
(gearbox oil may conduct, but that is the iron filings in it, not the oil itself)

I hope you are right . I am about to put my precious Arduino , pressure sensor and Lipo Battery into the oil.
Are you sure you are right?

 

[ericgibbs]

I hope you are right . I am about to put my precious Arduino , pressure sensor and Lipo Battery into the oil.
Are you sure you are right?

If you decide on oil, use ONLY transformer MINERAL oil, not regular hydro carbon oil.

and do not immerse any type of connector into the oil.

I would go with Ron's suggestion in post #5, a water proof box.

 

[tytower]

Oh well that was close Thanks Eric
By connector I hope you mean the plastic is broken down so no plastic connectors right?
It will of course have battery connectors ,solder connections ,arduino connections exposed to the oil.
I like the oil idea because I will have three different plastic pressure sensors immersed in it and pressure difference should be more noticeable and detectable rather than a sealed box with air. Or so I thought?

 

[ericgibbs]

Oh well that was close Thanks Eric
By connector I hope you mean the plastic is broken down so no plastic connectors right?
It will of course have battery connectors ,solder connections ,arduino connections exposed to the oil.
I like the oil idea because I will have three different plastic pressure sensors immersed in it and pressure difference should be more noticeable and detectable rather than a sealed box with air. Or so I thought?

hi,
Ref the connectors, its mainly to avoid an insulating oil film on the two contacting surfaces, else you will get an open circuit contact.

Are you trying measure water pressure/depth with these sensors?.

As you may know 10mtrs is ~1Bar which is equal to one atmosphere, so at 10mtrs depth you will have approx 14.7lb per sqr inch pressure on the box.

If you want to measure the exact water depth using a pressure sensor you must have a vented cable to the surface, else barometric pressure can change your apparent depth by as much as +/1mtr.
You can get 4 core cable with a central small bore plastic air pipe for this type of work.

 

[JimB]

Eric, you are usually spot on with everything you say, however, you seem to be having a bit of an off day on this one.

If you decide on oil, use ONLY transformer MINERAL oil, not regular hydro carbon oil.

Mineral oil is a hydro-carbon, it came out of the ground as crude oil before it was refined into petrol, diesel, lubricants etc.

and do not immerse any type of connector into the oil.

Why?
Electrical connectors intended for use subsea have their contacts inside a pressure compensated oil chamber.
Have a look here:

Page 5 explains how they work.
(No I am not proposing that these connectors are used for the application in this thread!)

As to the wider context of this thread, I am not sure what to OP is trying to do, something with pressure transducers and a microprocessor inside a waterproof box at 10m depth?

JimB

 

[ericgibbs]

hi Jim,
I guess I should have said not regular Engine Oil.!, as you know transformer oil is considered a mineral oil

With reference to the OP's contacts, I imaged the OP using for example PIC sockets, Molex etc, not the professional types we used on submerged devices.

I have seen a number of failed attempts at using mineral oil with regular connectors, the connector seem to be OK at first but after a few immersions at pressure an oil film film appears between the contact faces of the connectors.

I would still advise the OP not to use oil, but a sealed enclosure suitable for that immersion depth.
Especially as he wants to access the PCB/PIC for reprogramming.

E.

 

[JimB]

I have seen a number of failed attempts at using mineral oil with regular connectors, the connector seem to be OK at first but after a few immersions at pressure an oil film film appears between the contact faces of the connectors.

That surprises me. I would have expected that the contact force would have been sufficient to break through the oil film on the contact surfaces.
Unless of course the contacts were particularly weak, or the oil had some agressive additive which was reacting chemically with the contact surface.

I guess I should have said not regular Engine Oil.!, as you know transformer oil is considered a mineral oil

Yes, lubricating oil for internal combustion engines is a different thing altogether.
Most of the "new" oils are synthetic, which means that they are made from scratch with chemistry rather than processing something which came out of the ground.

The ideal thing would be a "transformer oil" if you can get hold of the stuff in small quantities.

JimB

 

[tytower]

Thanks
I once used that Lanolin grease on my car battery terminals . I always grease them to prevent corrosion, especially the negative connector on negative earth cars. With Lanolin grease the car would not turn over . With normal grease no trouble . I went to copper included marine grease anyway after that.