Perdix AI alternatives?

[tridacna]

I already have a grey one. A new transmitter costs $350, while a used one can be found for <$200 - but only in grey, so a new yellow will in fact cost extra.

,,,and with a dot of yellow צבע problem solved!

 

[dmaziuk]

So a 5 sec interval is standard. It is not a random interval.

So the fun part in that case is that three grey transmitters turned on at proper intervals have in fact less chance of collision than green, gray, and yellow.

 

[Mike1967]

So the fun part in that case is that three grey transmitters turned on at proper intervals have in fact less chance of collision than green, gray, and yellow.

This ^^

 

[broncobowsher]

But with mixed transmitters if you get a collision of signals, you get one. 5 seconds (or so) later they clear. With matched transmitters if you get a collision of signals they will keep colliding until one of the clocks drifts off enough.

Going through my checklist doesn't includes adding a timer to turning the first valve on and timing the second to be far enough off. I would be the one who opened the second valve at 15 seconds delay instead of 12½ seconds.

 

[dmaziuk]

But with mixed transmitters if you get a collision of signals, you get one. 5 seconds (or so) later they clear. With matched transmitters if you get a collision of signals they will keep colliding until one of the clocks drifts off enough.

Going through my checklist doesn't includes adding a timer to turning the first valve on and timing the second to be far enough off. I would be the one who opened the second valve at 15 seconds delay instead of 12½ seconds.

But with mixed transmitters you're guaranteed to get collisions. If you're lucky: not when you're checking your gas.

 

[stuartv]

I just finished a TDI AN+DP+sidemount course, and in the process, I learned (among other things) that my Aeris Elite T3 is completely inadequate for tech diving, even in gauge mode. The primary issue is that it shows elapsed dive time in hour:minute format only, and when the instructor had me running the deco schedule, I needed to see seconds in order to know when to give the appropriate signals (the rental Suunto Zoop was fine for that). It should still be okay as a backup depth/timing device, and I need a redundant computer anyway, so I'm considering options now.
My criteria are:

• Air integration with 2+ MH8A transmitters. I want to be able to dive sidemount and see my remaining pressure on both wrists.
• Hour:Minute:Second time display.
• Integrated compass would be a plus.
• Reasonable cost. I'm planning to crossover into CCR next year, and when I do, I'm pretty sure I will want a NERD 2 with it. It's kind of hard to justify the cost a Perdix AI and a NERD. If there was a way to run a NERD with OC sidemount, I'd just get one and be done with it, but seeing as how its OC mount is to a regulator hose, that won't work for me.

I looked at Oceanic VTX and OCi; both are available for ~$500 with transmitter, but both appear to have the same problem of showing dive runtime in minutes rather than minutes:seconds. Looking at the user manual for Aqualung i750TC, I also see only minutes. Are there any other options, or should I just bite the bullet and get a used Perdix AI, then run it as a backup when I dive CCR?

I personally would not even consider running a T3 or an OCi as a backup on a tech dive, other than in gauge mode. The algorithm is not intended for tech use (neither algorithm that they support).

I don't see any reason whatsoever to pay attention to seconds on a deco stop. If you're that worried about it, make sure you leave the bottom 1 minute before your planned max time. Personally, none of my tech training (3 different instructors, so far) have ever said anything about paying attention to seconds.

If you're not going to pay attention to seconds, then your T3 is okay as a backup (in gauge mode).

Given all that, it seems like going ahead and getting a NERD2 with a Fischer cable is a reasonable option. You'd just know that when you get a CCR, you need to factor into your purchase criteria that your chosen unit can support a Fischer cable connection.

Fischer cable connections are not popular in some quarters. The problem with the only other option is that it is proprietary. There are 2 or 3 CCRs that share the same protocol for a DiveCAN monitor, so you could (in theory) interchange a DiveCAN NERD for one of those units with one of the other units. But, there are a lot of other units where it won't work, even though they both be "DiveCAN". The NERD monitor for rEvo even goes so far as to have a "DiveCAN" connector, but it's not actually DiveCAN at all - it is an analog connection that just happens to use the same wet-mateable connector.

In contrast, a Fischer connector is universal. The connector is higher maintenance than a DiveCAN-style connector. But, that doesn't mean it's a problem. It's just something to do a little more maintenance on than if you had the other kind of connector. And, because it's a universal connector, a NERD2 w/Fischer is less expensive than any of the proprietary NERDs.

If you go ahead with getting a wrist unit, I will say that I dived a Perdix AI and a Teric together for a while and I liked the Teric so much better that I sold the Perdix AI and bought a second Teric. It's down to personal preference, but a Teric IS a perfectly good tech computer. It does everything the Perdix does, plus more.

On my CCR, I have a Predator controller, and a NERD2 (with AI to monitor my CCR cylinders) with Fischer cable to 3 O2 sensors as a monitor. And for more serious tech dives on it, I will use my Teric as a standalone backup to the 2 hardwired computers. To ME, a Shearwater controller with a NERD2 monitor is an ideal config for a CCR. With the Teric as tertiary, even if my controller took a **** AND I had to bail off the loop completely for some reason, I still have a computer that is working and that I can see (since I wouldn't be able to see the NERD easily if I had to completely bail off the loop). That said, if the controller dies, that by itself is not very likely to cause me to have to bail off the loop. So, it's not too likely that I would have to bail off the loop AND not be able to see my controller. So, a Teric is really kind of suspenders and belt, with my specific config. But I digress...

As others, I have also used 2 grey transmitters in sidemount and never had a conflict. Obviously, that does not mean that one cannot happen. But, as the frequency is every 5 seconds, my thinking is that if you have your tanks turned on for at least a minute or so before you splash, and you don't see any issues with the tank pressures displayed on your computer, then you're probably good. And if you DO see an issue before you splash, turn off one tank, purge the reg, maybe wait 2 minutes (maybe? From what Shearwater says, maybe the transmitter doesn't turn off for 2 minutes after pressure goes to zero), then turn the tank back on. Pretty darn unlikely to have a conflict twice in a row.

Lastly, if you're going CCR, I would not spend any more money than you can possibly avoid on stuff that is only for OC. Once you go CCR, why would you continue doing any tech dives on OC? On the other hand, you'll probably still do some OC rec diving, at least occasionally, and a Teric (or Perdix) is a really nice computer for that. So, buying a Shearwater now that will only (mostly) get used for OC diving after you CCR is not a bad thing at all. Just not money that you would NEED to spend. Ever since I drank the CCool-Aid, I've been telling everyone, if you plan to go CCR ever, then forget all your "in the meantime" plans and do what you have to do to get on CCR ASAP. Furthering your OC diving is just wasting valuable time.

You may want to contact Shearwater and their latest version is V72. I know when I am diving on OC Tec mode deco clear shows minutes and seconds. I do not know if this works on closed circuit.

It only does that after you complete your safety stop or final deco stop. It does not display like that when it is showing you the time remaining on a mandatory deco stop. As noted, the only indication of seconds is a thin bar that jumps up every 15 seconds, I think.

 

[stuartv]

But with mixed transmitters you're guaranteed to get collisions.

Not if you don't turn them on on the same 0.20 or 0.25 second interval.

If you turn on your grey one, and then turn on your green one at 4.90 seconds, they will never collide. Unless one clock drifts enough - which would be true for having 2 of the same color as well.

 

[dmaziuk]

Not if you don't turn them on on the same 0.20 or 0.25 second interval.

If you turn on your grey one, and then turn on your green one at 4.90 seconds, they will never collide

... but if you're off by 0.1 second ...

 

[tursiops]

Forget it Stuart, dmaziuk has sunk his anal teeth (is there such a thing?) into this, and he is determined to have the last, useless word.

 

[dmaziuk]

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