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

[Martin Gysel]

Am 25.03.2015 um 14:18 schrieb 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.

+1

> 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.

I would rather take rechargeable cells at they allow a smaller form
factor. it's much easier to seal everything than have a water resistant
housing...

> 
> 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.

I wouldn't use a hp hose to connect the sensor with the 1st stage as it
increase the risk of failure. I think it's better to connect the sensor
to the hp port directly but place the rest of the electronic away from
it. so you can have a very tiny sensor and only one hp connection and
one O-ring. the 'logger' and battery can be place away at a place where
size is nit critical.
I also find it very annoying that most or even all wireless pressure
sensors are very bulky. it also lead to people carrying the tank holding
the wireless sensor :(

> 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...

/martin