deco code rewrite

[Jan Schubert]

On 12/08/12 22:09, Jef Driesen wrote:
> On 07-12-12 19:44, Jan Schubert wrote:
>> On 12/07/12 17:51, Dirk Hohndel wrote:
>>> Jef Driesen <jefdriesen at telenet.be> writes:
>>>>>>> - Battery voltages (nice to have)
>>>>>> I've always wondered why anyone would need this? I mean as long as
>>>>>> you have
>>>>>> enough, everything is fine, and if you don't then probably no dive
>>>>>> will be recorded.
>>>>> It's nice to download your dives and get the nice warning that your
>>>>> battery is low in the dive log program. Believe it or not, that's
>>>>> something that I intended to implement for Uemis (especially for the
>>>>> tank sensor battery) as it's so easy to do and so helpful to have.
>>>> Of course it's important to know the battery status. However I see
>>>> this
>>>> as something that's important while operating the device, and not
>>>> something that goes into your logbook. I mean it's very important that
>>>> the device shows you the battery status, so you can decide whether to
>>>> charge it or not. But what's the added value of having this info for
>>>> each dive? My point is that I consider the battery status more a
>>>> property of the device.
>>>>
>>>> Showing some kind of low battery warning during (or after) the
>>>> download
>>>> is something different then what Jan meant with adding support for
>>>> battery voltages. I think (and correct me if I'm wrong), that Jan
>>>> referred to supporting the battery status in the header or even the
>>>> full
>>>> battery profile in the samples (the predator has this).
>>> I think what would be nice is to have a way for libdivecomputer to
>>> report to the application "at the end of the dive the dive computer
>>> reported that its batteries / the tank sensor batteries are low and
>>> need
>>> to be charged or replaced". So this wouldn't be sample information
>>> (good
>>> for Shearwater to support that) but simply dive level header
>>> information.
>>
>> Didn't get Jef's mail so answering to this one.
>>
>> In general: For CCR divers it is quite important to rely on good
>> batteries as someones life may rely on this!
>>
>> Jef is right, the Shearwater logs the battery voltage during a dive and
>> the newest Shearwater Desktop software also shows a new nice graph for
>> this (see attachment, sry for the high res) where before it just showed
>> the voltage at the begin and the end of a dive (see header in
>> attachment).
>>
>>  From my point of view I also like to see any information which is
>> reportet by the dive computer. Seeing Battery Voltage afterwards is not
>> that important but as you can see in this example it fluctuated quite
>> much in this dive where it has been very stable before all the others
>> dives. In fact this battergot replaced right after as I also got a
>> warning in my computer itself.
>>
>> In the Shearwater itself I can check current voltages (any time, also
>> while diving), no way to see how it behaved during a dive afterwards, so
>> having this is quite nice and allows one some prediction about the
>> oncoming lifetime of his batteries.
>
> I'm absolutely no battery expert, but I think battery voltage
> fluctuations are perfectly normal depending on the load, temperature,
> etc. So I'm not sure that you can judge whether batteries are good or
> bad based on the voltage profile during the dive.
>
> Also a battery voltage discharge curve is certainly not linear, so
> judging when a battery is close to empty isn't that easy I think. I
> guess the device (and indirectly its manufacturer) is in a much better
> position to make such a decision.
>
> For example the voltage alone can already depend on the type of
> battery: alkaline (1.5V), NiMh (1.2V), Lithium (many possible
> voltages). There are also devices that accept multiple types of
> batteries (Petrel, Frog), so the voltage range isn't even fixed.
>
> So these things may be more complex then they look.

Yes, Jef you are absolutely right and thats exactly the reason why CCR
divers like to check the voltage throughout a dive :-). For the dive log
it would be a nice to have, to see this afterwards but nothing really
important.

To become more off topic: Discussions about batteries are quite common
for CCR sensitive people. The Shearwater (Predator) uses a 3,6V Lithium
battery and there are some specific recommendations which brands and
models to use and which not. The profile I posted shows extrem
fluctuations where all the profiles before showed very little or no
fluctuation at all. Seems that this behaviour is typical for the
specific kind of battery at the end of life and/or a strong indicator
for using a bad battery. Both is quite important to know and seeing the
battery drain afterwards in nice graph makes it quite easy to judge over
your oncoming relationship with your battery.

Sorry for digging into even more background information, but maybe for
someone this is interesting :-)

Thx,
Jan