log book memory

[kurt.sys]

Hey, I'm considering buying this computer and during my last search on the 'properties' of the dive computer, I found out that there is 32kB of memory for the dive log. At first sight, this seems enough, but I've been calculating some stuff and I might be wrong... So, first of all, my first question: how many dives do you guys store more or less with which settings?

Here's the extreme: imagine you want to log everything every second (except gas#6 and gas change, nobody changes gasses every second :p ) - which is fairly useless, but anyway, let's do the exercise:
depth: 2 bytes
profileflag: 1 byte
eventbyte: 1 byte
temperature: 1 byte
deco/NDL: 2 bytes
which means already 7 bytes/second, 420 bytes/minute, 25200 bytes/hour. This is not included tank pressure, ppO2 sensor, and some 'not yet used'-bytes. So, this means only 1 dive of about 1 hour storage in this extreme situation (plus a small header of 46 bytes/dive). If you dive for 1h20m, there's not enough storage.
Let's do only storage of the depth each second: 2 bytes/second, i.e. 7200 bytes for a 1 hour dive, or storage for about 4 dives.
Second question: am I missing something, or am I right that storage is rather limited and that sampling rate shoudn't be set to e.g. 1 second if you go on a holiday diving (and you want to download your profiles when you're back home)...? - Again, I woudn't set the sampling rate to 1 second anyway, I'm just trying to find out how many dives I would be able to store, and started with this exercise. It's just to know what 'the best' sampling rate would be for me (trade-off between 'I like to know a lot' and the number of dives I'd like to store ).

[heinrichsweikamp]

Hello Kurt,

Thanks for your post!

Your calculations are correct, when saving every available information every second the profile memory is very limited indeed.

a) With the default settings, depending on the events we have about 30...35Bytes/minute+Header (About 14...16hours in total).
b) When there is no PC available during a longer trip, you should set the sampling rate to 20 or 30sec.
c) It's useless to sample the temperature more often then twice/minute because the measurement is quite slow
d) Sampling rates of one seconds were intentionally added for Freedivers...
e) As some already noticed from the code, we're currently using only 50% of the 24LC515 EEPROM. The other 50% can be added to the profile memory quite easy but until today we are not sure if we should better use this for something else

With kind regards,
Matthias

[kurt.sys]

Hey,

Well, it all makes sense to me now: I was wondering why the 1 second was in the 'recommended range' (which seems to be for free diving, logically). Well, thanks a lot. I suppose I might have to take some kind of small laptop on diving holidays :p.

thanks,
Kurt

[Hiasl]

Wie gro? ist denn nun (V1.24) der Logbuchspeicher? Wioe sollte die Sample-Rate eingestellt sein, damit mind. 15 Tauchg?nge mit je 1h Dauer in den Speicher passen? (Ich m?chte kein Notebook in den Urlaub mitschleppen )

Gr??e
der Hiasl

[heinrichsweikamp]

Hallo,

Mit den Standard-Einstellungen passen etwa 30 1-St?ndige TG mit Profil in den Speicher.

Viele Gr?sse,
Matthias

[wrobell]

i have some thoughts about logbook memory. i was
on a week trip and had 21 dives - 1025 minutes,
which is about 17h.

i ended up with 19 dives recorded in ostc (i have
all of them as i dumped logbook memory once after
a few dives).

anyway, i am wondering if it is possible to gain
2-3h more without changing standard settings.

1. when ndl is maximum (deco time 160, depth 0), then maybe
it is worth _not_ saving deco information? there were
559 samples having max ndl (almost 55% of time). assuming
2 bytes for deco info, we could save 2 * 559 / 30 ~ 37 minutes
(assuming 30 bytes of data per minute).

2. ostc header contains dive time information. but ostc
logbook stores samples beyond the dive time (i.e.
dive time was 40min, then ostc stores more samples
for dive times 40:10, 40:20, 40:30). in my case, there are
500 samples beyond dive time. each such sample is at least
3 bytes, which gives 1500 bytes ~ 50 minutes.

above savings could give 8% or 1h 27min more, which is about 2 dives
(perfect for my last trip ).

3. looking at temperature graphs of my dives and considering the latency
of temperature sensor, i would suggest to change default temperature
divisor value from 6 (every minute) to 15 (every 2.5min). this would
give another 50 minutes.

i hope my above calculations are correct.

does anyone have more ideas?