On Wed, Sep 10, 2014 at 12:27 AM, Robert Helling <hell...@atdotde.de> wrote: > > So let’s combine that information: It seems to me what you want is not an > air integrated computer but in fact a data logger that is in a small box > that sits on the first stage of your regulator like the transmitters do.
So I don't think that's _crazy_, but you'll find that it has several problems. For example, high-pressure ports on the first stage are very limited. Many first stages have just one, in fact. Yes, two is pretty common, but I don't think I've ever seen three. So to connect something to a HP port, it needs to add a fair amount of value. And for the logging to be useful, it needs to be correlated with the actual dive. And that means that the data logger needs to not have just a real-time clock, but something else to synchronize with the dive computer. I'm pretty anal about my clocks, and I keep them fairly closely synchronized (probably more so than most), but some dive computer timekeeping is less than wonderful. I notice that my dive computers drift apart between dive trips, quite a bit. And realistically, the only thing to synchronize with is having a depth pressure log too. So now your electronics need to have a real-time clock, a USB interface to read the data off and set the clock with, a cylinder pressure sensor, and depth. The battery to power it all, and the CPU/memory to do the logging. You're pretty close to having a dive computer there. Sure, you're missing the display and the actual deco calculations. And the lack of display turns out to be a big thing: if you cannot read the cylinder pressure data from the logger during the dive, that really limits you. Remember the HP port scarcity. If it doesn't have a display, you now absolutely *have* to have two HP ports. Yeah, I'm sure we all have that on our primary first stage, but still.. And even with two HP ports, it means that you've effectively limited it to just a single port, so now your SPG has no backup, and so you don't even really have much of a choice - you'll almost certainly have to use an analog SPG. Yeah, they break too (I've certainly have that happen - people throw those things around), but my real point is that you're limiting yourself. You're basically saying "I'll never use a dive computer with air integration", because I will only use the logger. And with a display, you'll have a harder time verifying that it's all working when you're on the boat. Yeah, maybe you can have just a low-power LED light that turns on when it senses cylinder pressure and everthing is ok. If it's truly low-power, it's going to be really hard to see in the tropics during the day. I know, because I've had that problem: the newer versions of the Suunto wireless pressure transmitters have exactly that, and they are completely impossible to see. So a dive computer with air integration is actually *so* much better. The integration with the dive computer really solves all these problems. Thanks to the display, you can see when the logger isn't working. Thanks to the integration, there's no question about synchronizing the cylinder pressure with the actual dive. Thanks to the display, the thing now acts as a backup SPG (or, more likely, your _primary_ SPG, with an analog backup that you never have to look at). Or, you might be willing (like I am) to just have two different of these somewhat unreliable wireless dive computer interfaces - I've had the wireless fail a lot of times, but I've not so far ever had two independent and different wireless connections fail at the same dive. And if that ever were to happen, I'd be ok with it - aborting the dive is in the end the right thing to do if you really have equipment issues, I just want to make sure it's really really rare. So I like the logger idea as a concept, but realistically speaking, I just like the concept of air integrated computers much more. The display really turns the logger into so much more. And the air-integrated computer is, I think, a much larger market. You can sell air integration to "normal divers", and in fact that is currently the main market, because so many serious divers scoff at it (for all the wrong reasons, imho). The existing scuba market is pretty clear about that market existing and being sustainable. In contrast, a very specialized logger? It doesn't have the same kind of wide market appeal. Good wireless air integration also allows one dive computer to see multiple wireless transmitters. Yes, it's rare. And yes, the transmitters tend to be expensive enough that maybe you don't want to put them on your deco bottles. But I'd like to have the *option*. But again, with a wireless transmitter, that's possible and more reasonable with a dive computer than with a display-less logger. So the dive computer with a wireless cylinder pressure sensor is just a more flexible and complete solution (that also allows for other usage scenarios, like seeing your buddy's air, or seeing students' air data etc etc). I'm not saying the multi-transmitter case is all that common, but I've had cases where I would have liked it. Linus _______________________________________________ subsurface mailing list subsurface@hohndel.org http://lists.hohndel.org/cgi-bin/mailman/listinfo/subsurface