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'[EE]: Scuba diving computers'
2001\10\04@111151 by D Lloyd

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Hi,

Has anyone been involved with diving computers? Presumably, it wouldn't be
too difficult to construct a simple "dive profile data logger" recording
pressure against time but a more interesting exercise would be to involve
functions for calculating nitrogen buildup in the body. Obviously, this
wouldnt be used in anger but anyone had experience with such
functions/devices?

Regards,
Dan

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2001\10\04@111608 by Bond, Peter

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> Has anyone been involved with diving computers? Presumably,
> it wouldn't be
> too difficult to construct a simple "dive profile data
> logger" recording
> pressure against time but a more interesting exercise would
> be to involve
> functions for calculating nitrogen buildup in the body.
> Obviously, this
> wouldnt be used in anger but anyone had experience with such
> functions/devices?

Using them, breaking and bending them, basic understanding of the theory
behind decompression and a brief foray into seeing whether the midrange PICs
were suitable.  IIRC, my clunky dive computer uses a 68HC11.

What do you want to know?

Peter
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2001\10\04@115152 by Walter Banks

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I know of two companies that have developed them. Both developments
including testing were several man years. Both used a small processor
similar to some of the PIC mid range parts about 8 K bytes of code
optimized for low power consumption.

One was basically a status type data logger the other computed
decompression times based on the dive profile.


Walter Banks


D Lloyd wrote:
{Quote hidden}

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2001\10\04@122129 by Scott Beatty

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Dan

       I have been using one for about 11 years.  There are quite a few
that are commercially avaliable like the Brigde II and the Alladin.  Are you
just interested in the theory behind them or are you intending on building
one and diving with it?  I had a couple of ideas for a dive computer that
could automate portions of technical or complex dives but found that the
liability of producing and selling such a computer was to grate for an
individual inventor.

Scott

> {Original Message removed}

2001\10\04@124000 by Wayne Bjorken
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Dan;
I'm working on such a device now. Can I help?

Regards;

Wayne
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From: "D Lloyd" <spam_OUTdan.lloydTakeThisOuTspamGB.ABB.COM>
To: <.....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU>
Sent: Saturday, March 31, 2001 9:11 PM
Subject: [EE]: Scuba diving computers


{Quote hidden}

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2001\10\04@153852 by Steven Bakaletz

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Presumably, it wouldn't be
> too difficult to construct a simple "dive profile data logger" recording
> pressure against time but a more interesting exercise would be to involve
> functions for calculating nitrogen buildup in the body. Obviously, this
> wouldnt be used in anger but anyone had experience with such
> functions/devices?
>
> Regards,
> Dan


There's an articile in June 2001 Circuit Cellar Magazine
(www.circuitcellar.com/pastissues/Index-frame.htm
that might help you out.

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2001\10\04@183123 by steve

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>         I have been using one for about 11 years.  There are quite a
>         few
> that are commercially avaliable like the Brigde II and the Alladin.
> Are you just interested in the theory behind them or are you intending
> on building one and diving with it?  I had a couple of ideas for a
> dive computer that could automate portions of technical or complex
> dives but found that the liability of producing and selling such a
> computer was to grate for an individual inventor.

I intend to make one for my own use. Like you, I came to
conclusion that it isn't worth trying to do it commercially. Not just
the liability issues, but there are too many on the market already
and there isn't much between them.

I use an Atmos Pro and there are some things that I find really
annoying. For example, the biggest number on the display after a
single dive day is the time from when you turned the thing on to
when you jumped in the water. Who cares ?

Something that I consider to be dangerous is the behaviour in a
violation situation. It turns off for 24 hours. It seems to me that if
that situation arises, I want the doc at the chamber to see exactly
what I did to get there.

I'll gladly take an increase in size to enable having a backlight that
stays on. Trying not to blind your buddy on the way up on a night
dive is bad enough without having to find another hand to keep
pressing that damn button. Oh - the ascent rate indicators are a
waste of time.

I'm too tight to buy the downloader for the Aeris (and no-one will
lend me one to put on the scope) but I figure I can build something
for about the same amount. That way I get logging, redundancy
and something that tells me what I want to know.

There are a few things I would like to add. I would like it to be
buddy and tables aware. I might be using Nitrox and a computer
but my buddy might be on air and tables.  Since we would both be
doing the same profile, it can give me an idea of their status.

It is one of those nice things where once you have the basis of a
system - display, micro, pressure sensor and few buttons in a
waterproof housing, the rest becomes just a matter of growing the
software. (eg. gas changes, etc).

On a slightly different tangent - Does anyone know of a suitable
earpiece or small headset for use underwater ? Dangling on a rope
under a boat is the ideal place for a MP3 player.
That would have to be a marketable gimmick for a dive computer -
a built in MP3 player, preloaded with the theme from Jaws. :-)


Steve.


======================================================
Steve Baldwin                Electronic Product Design
TLA Microsystems Ltd         Microcontroller Specialists
PO Box 15-680, New Lynn      http://www.tla.co.nz
Auckland, New Zealand        ph  +64 9 820-2221
email: stevebspamKILLspamtla.co.nz      fax +64 9 820-1929
======================================================

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2001\10\04@231248 by Kris Wilk

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At 08:11 PM 3/31/2001, you wrote:
>Hi,
>
>Has anyone been involved with diving computers? Presumably, it wouldn't be
>too difficult to construct a simple "dive profile data logger" recording
>pressure against time but a more interesting exercise would be to involve
>functions for calculating nitrogen buildup in the body. Obviously, this
>wouldnt be used in anger but anyone had experience with such
>functions/devices?
>
>Regards,
>Dan

Yes.

See our SENSUS product (http://www.reefnet.on.ca) for an example of a simple
diver's "black box" type data logger. It's not PIC-based, but it could just
as easily have been. We used the TI MSP430F1121 for its extensive clock
configurability and (very) low current draw. Highly recommended.

There is nothing extraordinarily difficult about making a full-blown dive
computer. I think the hardest part is usually the mechanics of
waterproofing while maintaining good size/look/usability. The housed
circuit can be nothing more than a micro, a pressure (and perhaps
temperature) sensor, and an LCD. There are a variety of algorithms out
there, but they all typically boil down to models of various tissue
compartments with assorted 'tweaks'. Look up the name Buhlmann for starters.

A lot of what the big manufacturers talk up as groundbreaking new features
are nothing more than adjustments of 'correction parameters' and conservatism.

Now not to sound alarming, but if you're going to make a dive computer for
yourself, the biggest piece of advice I can give you is: KNOW WHAT YOU'RE
DOING. That is, don't copy an algorithm from someone else. Don't transcribe
from a book. LEARN THE PHYSICS and UNDERSTAND FOR YOURSELF every inner
working of code YOU write. You're literally playing with your life.

And if you're considering this as a possibly commercial venture, don't
bother. There are too many nice dive computers out there already. Not to
mention the liability issue (can you say $$$ insurance?). We decided to go
the data logger route because it's a remaining open niche in the scuba
gadget market, and there's no liability since it's not used for
life-support. Much more relaxing :).

Have fun,

Kris Wilk
ReefNet Inc.
http://www.reefnet.on.ca

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2001\10\05@044308 by Bond, Peter

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> I use an Atmos Pro and there are some things that I find really
> annoying. For example, the biggest number on the display after a
> single dive day is the time from when you turned the thing on to
> when you jumped in the water. Who cares ?

No fly time?

> Something that I consider to be dangerous is the behaviour in a
> violation situation. It turns off for 24 hours. It seems to me that if
> that situation arises, I want the doc at the chamber to see exactly
> what I did to get there.

Downloads from the computer are not generally locked out.  Over here, the
major chambers try to have an interface for every computer going.

A lot of divers (as with every other walk of life) are idiots.  Anything
that can be done to prevent them racking up DCS hits is usually a good
thing...

> I'll gladly take an increase in size to enable having a backlight that
> stays on. Trying not to blind your buddy on the way up on a night
> dive is bad enough without having to find another hand to keep
> pressing that damn button. Oh - the ascent rate indicators are a
> waste of time.

Battery life on the computer...

Ascent rate indicators - I don't want an absolute value, I just want to know
if I'm starting to go up too fast.  Too slow an ascent racks up additional
deco penalties.

> There are a few things I would like to add. I would like it to be
> buddy and tables aware. I might be using Nitrox and a computer
> but my buddy might be on air and tables.  Since we would both be
> doing the same profile, it can give me an idea of their status.

Gas switching?  My computer doesn't support it, so if I do deco on a richer
mix, I track CNS & OTUs manually.  Not ideal, but the recreational dive
market hasn't caught up on that one yet.

> It is one of those nice things where once you have the basis of a
> system - display, micro, pressure sensor and few buttons in a
> waterproof housing, the rest becomes just a matter of growing the
> software. (eg. gas changes, etc).

So it'll need to be easy to dismantle...  Which means more difficult to
build so that it doesn't leak.

> On a slightly different tangent - Does anyone know of a suitable
> earpiece or small headset for use underwater ? Dangling on a rope
> under a boat is the ideal place for a MP3 player.

I've seen "waterproof" speakers for sale - but never saw any tech data on
them, so don't know *how* w/proof they'd be.

> That would have to be a marketable gimmick for a dive computer -
> a built in MP3 player, preloaded with the theme from Jaws. :-)

A diver recall signal with a difference...

Peter
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2001\10\05@081244 by D Lloyd

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Hi,

"And if you're considering this as a possibly commercial venture, don't
bother. There are too many nice dive computers out there already. Not to
mention the liability issue (can you say $$$ insurance?). We decided to go
the data logger route because it's a remaining open niche in the scuba
gadget market, and there's no liability since it's not used for
life-support. Much more relaxing :)."

Too right about the commercial venture - I know far too little about the
physicalities to go ahead with such a thing. It was more for my own
non-safety critical purposes. I had thought about it, on the first pass, as
being an exercise for calculating nitrogen absorbtion then calculating
remaining dive time (based on no deco stops being required).

At a first pass, I imagined the data logger could simply involve a depth
measurement every 10 seconds. Piggy-backed onto this would be the
absorbtion calculation functionality involving (and I haven't read too much
into this as yet):
Absorbtion of nitrogen is a function of depth (due to partial pressures),
breathing mixture, specific physical factors concerning the diver involved
and rate of work. As the data logger would not be measuring air consumption
and would not know the specific physical characteristics of the "host",
these two factors could be discounted/normalised to a 'bog standard
person'/consumption rate. Hence, a simplified absorbtion model purely based
upon the max depth encountered in a given 10 second period being used in a
standard absorbtion function. These could be summed to give total
absorbtion and related to remaining dive time. (Clearly, this is all to a
first approximation of thinking).

I'm quite sure it is nowhere near that simple so I'll probably just stick
to the data logger for the time being ;-)

Regards,
Dan

To: .....PICLISTKILLspamspam.....MITVMA.MIT.EDU
cc:
From: Kris Wilk <EraseMEwilkspam_OUTspamTakeThisOuTREEFNET.ON.CA>
Subject: Re: [EE]: Scuba diving computers



At 08:11 PM 3/31/2001, you wrote:
{Quote hidden}

Yes.

See our SENSUS product (http://www.reefnet.on.ca) for an example of a simple
diver's "black box" type data logger. It's not PIC-based, but it could just
as easily have been. We used the TI MSP430F1121 for its extensive clock
configurability and (very) low current draw. Highly recommended.

There is nothing extraordinarily difficult about making a full-blown dive
computer. I think the hardest part is usually the mechanics of
waterproofing while maintaining good size/look/usability. The housed
circuit can be nothing more than a micro, a pressure (and perhaps
temperature) sensor, and an LCD. There are a variety of algorithms out
there, but they all typically boil down to models of various tissue
compartments with assorted 'tweaks'. Look up the name Buhlmann for
starters.

A lot of what the big manufacturers talk up as groundbreaking new features
are nothing more than adjustments of 'correction parameters' and
conservatism.

Now not to sound alarming, but if you're going to make a dive computer for
yourself, the biggest piece of advice I can give you is: KNOW WHAT YOU'RE
DOING. That is, don't copy an algorithm from someone else. Don't transcribe
from a book. LEARN THE PHYSICS and UNDERSTAND FOR YOURSELF every inner
working of code YOU write. You're literally playing with your life.

And if you're considering this as a possibly commercial venture, don't
bother. There are too many nice dive computers out there already. Not to
mention the liability issue (can you say $$$ insurance?). We decided to go
the data logger route because it's a remaining open niche in the scuba
gadget market, and there's no liability since it's not used for
life-support. Much more relaxing :).

Have fun,

Kris Wilk
ReefNet Inc.
http://www.reefnet.on.ca

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2001\10\05@221421 by steve

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> > the time from when you turned the thing on to
> > when you jumped in the water. Who cares ?
> No fly time?

It's supposed to be the surface interval but since it is before the
first dive and they couldn't possibly put no information there, they
decided to put something with no meaning instead.
It's a symptom of a diver telling a marketroid who creates a spec
and passes it to a developer.

> Downloads from the computer are not generally locked out.  Over here,
> the major chambers try to have an interface for every computer going.

I'll take your word on that. Hopefully I'll never need to find out.

> A lot of divers (as with every other walk of life) are idiots.
> Anything that can be done to prevent them racking up DCS hits is
> usually a good thing...

No argument with that.

> >  a backlight that stays on.
> Battery life on the computer...

I would sacrifice battery life (or preferably bigger batteries) for the
ability to see what it says.

> Ascent rate indicators - I don't want an absolute value, I just want
> to know if I'm starting to go up too fast.

Exactly - Mine shows one dot for half the prescribed rate, one for
spot on and the next is for twice as fast. Just a dot or two in
betweeen would be very helpful. There's also a delay that appears
to be about a second so it tells you that you were going too fast
(but you are probably going faster now).
It also doesn't lock out the last foot or so. I discovered this
standing in a pool one day. I picked up my guages and all the
ascent indicators were flashing as if my lungs should have been
bursting out of my ears. I hadn't even got my hair wet.

> > buddy and tables aware.
> Gas switching?

Gas switching is a bit out of my league at the moment (other than
EANx to pony/buddy - but then the dive is over anyway). I was
thinking more along the lines of your idiot statement. If I know that
my buddy is pushing their tables, I can end the dive without a
drama. Much the same way as signalling that you are cold to
someone that is obviously narc'd out of their tree.

>  just a matter of growing the software.
> So it'll need to be easy to dismantle...  Which means more difficult
> to build so that it doesn't leak.

Not really an issue. It's a one-of and to the untrained eye it will look
very much like my old dive-light. :-)

> > preloaded with the theme from Jaws. :-)
> A diver recall signal with a difference...

ROFL !
I hadn't thought of that. That's almost too tempting. :-)

Steve.


======================================================
Steve Baldwin                Electronic Product Design
TLA Microsystems Ltd         Microcontroller Specialists
PO Box 15-680, New Lynn      http://www.tla.co.nz
Auckland, New Zealand        ph  +64 9 820-2221
email: stevebspamspam_OUTtla.co.nz      fax +64 9 820-1929
======================================================

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2001\10\08@092923 by Bond, Peter

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> It's supposed to be the surface interval but since it is before the
> first dive and they couldn't possibly put no information there, they
> decided to put something with no meaning instead.

Ah, I see.  Mine tells me I'm desaturated, 0% CNS, 0 OTU and the max time &
depth on the last dive.

> It's a symptom of a diver telling a marketroid who creates a spec
> and passes it to a developer.

Cor, I can't imagine that happening <G>
A non-diving developer at that, I presume?

> I'll take your word on that. Hopefully I'll never need to find out.

Ditto.  Touch wood.

> I would sacrifice battery life (or preferably bigger
> batteries) for the
> ability to see what it says.

Yeah, but for commercial comps, the sealing is usually such a swine that the
fewer times the thing is opened, the better.  Not *that* many have user
replaceable batteries.

> Exactly - Mine shows one dot for half the prescribed rate, one for
> spot on and the next is for twice as fast. Just a dot or two in
> betweeen would be very helpful. There's also a delay that appears
> to be about a second so it tells you that you were going too fast
> (but you are probably going faster now).

Mine warns "slow" if I'm bordering on dangerous, I'm told it will still
display the profile on request if it gets bent.  But it won't let you dive
for 24hrs if you do.

I'm usually following my slowest bubbles anyway, so I don't hear it complain
too often.

As a matter of interest, what comp is yours?

> It also doesn't lock out the last foot or so. I discovered this
> standing in a pool one day. I picked up my guages and all the
> ascent indicators were flashing as if my lungs should have been
> bursting out of my ears. I hadn't even got my hair wet.

dP/dt.  Yes, last foot or so really should be locked out.  I don't want the
computer ordering me to the chamber because I surfaced in heavy swell!

> Gas switching is a bit out of my league at the moment (other than
> EANx to pony/buddy - but then the dive is over anyway). I was
> thinking more along the lines of your idiot statement. If I know that
> my buddy is pushing their tables, I can end the dive without a
> drama. Much the same way as signalling that you are cold to
> someone that is obviously narc'd out of their tree.

My pony may be up to 50% nitrox for deco - depending on many things
(including what I want as bailout).  So I'd want user intervention on the
gas switch - not just "gas switch occurs at 6m" or similar.  This is still
recreational diving, not tech.

If your buddy is pushing their tables, then the dive plan should have shown
it up (yeah, I know - "should" again).  Trying to communicate coherently
with a narced buddy is always fun...

> Not really an issue. It's a one-of and to the untrained eye
> it will look
> very much like my old dive-light. :-)

Bearing an amazing similarity to some of my home-made strobes, then?

> > > preloaded with the theme from Jaws. :-)
> > A diver recall signal with a difference...
>
> ROFL !
> I hadn't thought of that. That's almost too tempting. :-)

I've heard about it being done as a test of an UW sound system - it
supposedly got the majority of the divers back to the boat quite quickly...

Peter
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