Which protocol to implement on a home brewed diving computer ?

Martin Gysel me at bearsh.org
Thu Mar 19 07:01:52 PDT 2015


Am 19.03.2015 um 14:14 schrieb Anton Lundin:
> On 17 March, 2015 - Thomas Schrein (mailinglists) wrote:
> 
>> Robert,
>>
>> Am 16.03.2015 um 17:35 schrieb Robert Helling:
>>> Thomas,
>>>
>>>> On 16.03.2015, at 14:29, Thomas Schrein (mailinglists)
>>>> <tsx508 at schrein.de <mailto:tsx508 at schrein.de>> wrote:
>>>>
>>>> The housing of oDiCo is made from plexiglas version 0.1 and filled with
>>>> silicon oel. The next housing 0.2 will be milled from POM and the
>>>> electronic will be an industry factored PCB. Awating to have it in the
>>>> lake in June ...
>>>
>>> once you are in the habit of making housings, you might be interested in a
>>> project idea that came up here a while ago: We all love to have cylinder
>>> pressure graphs in our logs. But for the dive computer to records those
>>> you either need a hose that tends to be in your way or a radio
>>> transmission which is hard to make reliable. The idea was, during the dive
>>> to stick with an analogue gauge (as the history is mainly important in the
>>> log only) but attach a little data recorder with pressure sensor directly
>>> to the first stage to be read out later together with the dive computer.
>>>
>>> I did not really pursue this idea much further since all the pressure
>>> sensors I could find that fit the specs (up to 400bar with at most a few
>>> bar resolution an simple readout) almost costed as much as the pressure
>>> radio transmitters (120-150 Euro/pcs) and, more importantly, my total lack
>>> of experience in building watertight housings.
>>>
>>> You might be at least the solution to part two of the problem. What do you
>>> think?
>>
>> Nice idea, never thought about such a logger.
>>
>> Let me first give you an overview about our approach:
>> We have an 400bar industry sensor in test. We will connect it to our
>> hardware version 0.1 in the next weeks and go diving.
>> We made an adapter to connect it to the high pressure hole on the regulator
>> and connect it with an M12-Sensor wire to the existing odico housing.
>> http://www.skin-diver.org/skd/export/sites/default/sdiv/bastelecke/odico/odico-entwicklung-2014/IMG_2159.JPG_1997443631.jpg
>> It works on the land, but we are not sure if its really watertight, that we
>> will see in the dive.
>> http://www.skin-diver.org/skd/export/sites/default/sdiv/bastelecke/odico/odico-entwicklung-2014/IMG_2179.JPG_1997443631.jpg
>>
>> One option (may be you better say vision ;-) in our project is to use the
>> odico electronics to control a rebreather using CANBUS (the controller has
>> it build in already) and therefore the high pressure sensor would act as an
>> CANBUS node with its own buildin controller, in particular a STMF1x, less
>> then 5€ each.  The electronics could be sealed with casting resin.
>> For our rebreather approach we accept the existence of wires, so we don't
>> need to care about energy and communication. The pressure sensors cost about
>> 80€, plus the adapter for the high pressure, plus the wiring, but that costs
>> are not a big deal to run a rebreather.
>> My fellow, Marco, also doesn't care to much building even an self made
>> pressure sensor with build in electronics . He has a degree as mechanical
>> engineer and he's really gifted for job!
>> So we don't care too much to get it water tight.
>>
>> From my point of view a logger could be designed like this:
>> - located at the high pressure hole of the first stage
>> - length about 5 - 10 cm, cylindrical
>> - collecting data for pressure + time
>> - as an option: collection depth+temp
>> - energy by an AAA or 1/2 AA lithium 3v cell than could be replaced once a
>> year
>> - communication via radio (bluetooth, ...)
>> - shop price < 200 €
>>
>> Again, I never thought that would be worth to think about it. I will discuss
>> with Marco!
>> If you like we can discuss more.
>>
> 
> I would be interested in such a device, even if they would be built as
> one off jobs.
> 
> 
> Only thing i would argue is really important is to make sure they fail
> in a sane manner, and doesn't leak or dump my gas.

It seems there's at least some interest in such a device but to get a
retail price below 200 € one needs to produce/sell more then a couple...
I also doubt a kickstarter project will help here :(

Maybe the only option would be to design such a device in the public...
I have some contacts to a pressure sensor company and a university,
maybe that's a nice student project...


> Now this one is seriously OT but a idea i hand a couple of mates had as
> a idea, a depth/time logger with a accelerometer/gyro and try to use that
> as a mapping device to try to figure out how your movements under water
> actually where.
> 
> I talked with another mate who's in the defense industry and they have
> such devices on there (semi)autonomous rovs, but they combine the
> accelerometer/gyro with sonar and doppler radar against its surroundings
> for more input to their odometry models.
> 
> 
> That would be really cool =)

Personally I doubt you get the needed accuracy by only using the
accelerometer and gyro... but you could also couple it with some buoys
which sends a ultrasonic beacon on which you can triangulate (like gps)

/martin


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