HighPressureLogger ... Re: Which protocol to implement on a home brewed diving computer ?

[Anton Lundin]

On 17 March, 2015 - Thomas Schrein (mailinglists) wrote:

> 
> 
> Betreff: 	HighPressureLogger ... Re: Which protocol to implement on a home
> brewed diving computer ?
> Datum: 	Tue, 17 Mar 2015 15:58:09 +0100
> Von: 	Thomas Schrein (mailinglists) <tsx508 at schrein.de>
> An: 	Robert Helling <helling at atdotde.de>
> 
> 
> 
> Am 17.03.2015 um 11:48 schrieb Robert Helling:
> >Hi,
> >
> >>On 17.03.2015, at 11:33, Thomas Schrein (mailinglists)
> >><tsx508 at schrein.de <mailto:tsx508 at schrein.de>> wrote:
> >>
> >>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 €
> >
> >80 Euros for the sensor sound like a good price. May I ask which sensor
> >this is?
> http://www.automation24.de/prozesssensoren/elektronischer-drucksensor-automation24-pc6706-i10-374-0.htm
> 
> >When I did my research I found that you can buy sensors that already have
> >the correct fitting to go into the HP port of a first stage (UNF 7/16”).
> Where can I get it ?
> >For prototyping the logger I would have started with something like
> >http://www.exp-tech.de/sparkfun-logomatic-v2-serial-sd-dataloger-fat32
> >That has everything including battery recharging logic (and is a USB mass
> >storage device).
> Looks good for prototyping. I would take a SD device only if I wanted to use
> the SD card for the data transfer to the PC. They burn about 100mA, lot more
> than the processor itself. I wourld prefer SPI FLASH.
> 
> As said, we will connect that sensor to our already existing housing (odico)
> and will go diving, the logging function is only a subset of the odico
> functions. So its hard to me to plan for logger an extra prototype/proof of
> concept.
> 
> Our next steps would be more focussed in
> 1. integrate the highpressure piezo sensor into a selfmade housing
> 2. build a prototype with an EAGLE designed PCB that fits in a size < 10cm
> 
> What about communication? USB / radio ?
> Energy ? Rechargeable or change of the cell ?
> 

I'm kinda in the area of the fewer o-rings the better. Less failure
points. That is a upside with radio/bt.

I'm also kinda against using rechargeable cells, because of their
failure patterns in a lot of cases. One really nice path that both HW
and Shearwater took with the OSTC3/Petrel is that they just take any
AA-sized cell, and use a internal voltage regulator, so you can run them
of a regular alkaline battery or a SAFT LS14500 if you would like more
battery time.


For the form factor, i would love something that fits on my right post
of my doubles.

Some nice references about dir-rigged doubles can be found at Peters
site:
http://dir-diver.com/en/equipment/reg_config_doubles.html

As you see in those pictures, theres quite a bit of room below the right
regulator, or "between" the doubles. Then you can safely store the data
logger nicely tucked away in a protected spot.

Maybe with a 15cm cable/hp hose between the port and the "brick",
depending on the size of the brick.


The problem comes when you try to use the second hp-port on a stage
bottle. That one is in a really exposed position:
http://dir-diver.com/en/equipment/reg_config_stages.html

I don't really know how to do something sane there...


//Anton


-- 
Anton Lundin	+46702-161604