Thanks Kris, and sorry I missed your previous posting. I have never had more
of an opportunity to look at anyone else's product other than having had a
few different models in my hand for a quick look. That' a sure clue that
more research is needed on my part. The  experience you have shared is much
appreciated. The Intersema sensor seems to be much more like what I was
hoping to find. I will let you know how it works out.

Chris

-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Kris Wilk
Sent: Monday, February 04, 2002 5:48 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [OT]: Measuring Depth of Submarine using Differential
Pressure


At 03:04 AM 2/4/2002, you wrote:
>Just one more thought on this for me today...
>
>I have seen commercial dive computers that have no port, tube or balloons
>visible, and yet they are amazingly accurate in sensing depth. I have
>searched and phoned sensor makers, foguring that someone must have a
>chip-scale sensing element, but have found nothing of the sort. Has anyone
>ever seen what I'm talking about? Know a way to sense pressure or depth
>without porting water or bagging air? This thread has me thinking of
>re-inventing my own rather small wheel...

I know of no commercial dive computer that does not have an open port to a
sensor element. The port may be (very) small, and is almost always
covered/protected so that it doesn't get fouled with debris. It is usually
filled with a silicone gel over which a thin rubber 'sheet' is laid to
prevent the sticky silicone from gathering junk. Many dive computers are
completely filled with oil so that the designers needn't even consider the
effect of pressure on the case.

Also, I replied just a day or two ago to someone looking for a sensor for
barometric pressure. My reply may be of interest to you too, so I've pasted
it below.

The 0-14 bar sensor has a stainless steel cap which is (relatively) simple
to seal with an o-ring. If you're like me and prefer not to deal with
analog design if it can be reasonably avoided, this is a great solution. A
complete digital pressure + temperature sensor module in < 0.5
cm^3...pretty damn good if you ask me.

Kris Wilk
ReefNet Inc.
www.reefnet.on.ca

PREVIOUS POST******************

An absolutely BEAUTIFUL sensor module is made by Intersema
(www.intersema.com). They have a 0-15 psi surface mount package that's
completely temperature compensated, has a digital interface (i.e. talk to
it directly from your uC), and is also a temperature sensor. Literally
plug-and-play. And it's *VERY* power efficient...designed for building into
wristwatches and other portable devices.

They also make an identical module with 0-14 bar range, which is what we
have been using in our marine data logging equipment to measure depth.

What's really amazing is that they're not expensive (probably $20 in
singles, and about 11 bucks in 1000s). If you've seen the new Swiss Army
knife with the built-in altimeter, that's one place this module has been
used...

I have no ties to Intersema other than being a very happy customer of
theirs.

******************

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