Dive Computer Ramblings

[Martin Gysel]

Am 10.09.2014 18:21, schrieb Robert C. Helling:
> 
> On 10 Sep 2014, at 15:42, Martin Gysel <me at bearsh.org> wrote:
> 
> Martin,
> 
>> the company I work for has that experience (electronics, watertight
>> and pressure related stuff) but I personally doubt there's much
>> demand for such a device in the diving community. most people I can
>> think of care for the tank pressure during the dive not
>> afterwards. but we would be happy to develop such a device if
>> someone is willing to pay for it :) of course, as Davide mentioned,
>> kickstarter would be an option... need to think about it.
> 
> with that type of professional experience, could you tell me if my
> price tag of 120$ for the pressure sensor (up to 300bar, better
> 350bar, 7/16 UNF connector) could be significantly lowered (and I am
> not talking about buying 1000 at once) by using something different
> (I would think that it could be really slow, like one datapoint per
> 10s would be good enough and an accuracy in the percent range would
> be sufficient as well).

your price tag seems to be realistic, but the most expensive part is the
pressure sensor which already can make one third of the cost. then you
need some small electronic to compensate and condition the sensor signal
plus a uC, a 'big' flash, a battery and connectors. it doesn't really
matter how fast but how fast you do the measurement...

> What about the case? Cut it out from a block of Delrin (POM)? That
> should have a price insignificant compared to the rest. Would I have
> to fill it to make is resist the pressure or would a box of air be
> ok?

it depends, if you want to be able to access the electronic i.e. replace
the battery then it's probalby easier to use a box but then you need to
care about the o-rings etc. easier is to use a rechargeable battery and
seal everything with resin or silicone.

unfortunately this all is not very cheap and speaking about a sensor
with a BOM of $100-120 would probably end in a end user price between
$200 and $300 or even more as you also need to do the development and
assembling and also the distribution. and all this for a quite low
number of units :(

/martin