Which protocol to implement on a home brewed diving computer ?

Tue Mar 17 03:33:27 PDT 2015

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.

Best
Tom

> Best
> Robert
>
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> Robert C. Helling     Elite Master Course Theoretical and Mathematical 
> Physics
>                       Scientific Coordinator
>                       Ludwig Maximilians Universitaet Muenchen, Dept. 
> Physik
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