Pondering simplicity: analog o2 monitoring?

[heyydude]

Guess the old days aren't what they use to be. I'm a tad young myself for nostalgia but I do like the process of reinventing the wheel as a way of learning how life rolls.

Without some decent sampling I'll withhold option on the aggregated failure rates analog vs digital. You are most likely are right I'd imagine.

I will own the second possible suggestion. A nice clean lcd ppo2 monitor is beyond my tinkering abilities at this point, especially if I would expect it to be less failure prone. My camera housing designs and flashlight encounters have proved this over the years.


In way of update... Thanks for the various inputs. Without horribly good reasons not to I'm going for it for kicks and giggles, since arguably ppo2 monitoring on an o2 breather isn't critical anyway it shouldn't hurt to drag them along.

Placed the order for four 45mm 200mv 10Ω voltmeters this evening. Now the fun part.

I'd appreciate heads up on some signs of failure to watch for as well from the mk15, topaz crowd if some of you stumble across this thread. ...for that matter I am in the market for a mcc as much as I enjoy bench time

Well, thanks for tolerating my whim, I'll update on the build as it develops, keeping in this thread to avoid clutter.

So, the cool thing about these milliamp gauges is like you said, they don't need batteries.

The uncool thing about them is that they:

a) Require a Switch to change from sensor to sensor. That switch then must have a Sealed Shaft, and then a Panel Seal which can handle up to 100m of pressure. The Sealed Shaft isn't so hard (Grayhill still makes them) but they changed the Panel Seal from the old style 150 psi model to a new version (frustratingly with the EXACT same part number) which can only handle 15 psi. You then need a way to transit those three different signals to your Meter, which, in the case of the Mark 15, included a custom PCB with a second right-angle PCB attached in tandem.

b) Require potentiometers to calibrate each cell individually. That means that whatever water tight seal you may have has to be opened, and you must then tweak each pot to calibrate each sensor.

c) The meter puts a tiny load on the cells, which can affect (albeit small) each sensor signal to the Primary Electronics (which I'm assuming you'd do digitally, because Analog Controllers is a whole 'nuther can o' beeswax - and trust me, I built these buggers myself, so I know whereof I speak).

d) The meters are unobtanium - they can be custom ordered from Jewell (or the company that took them over) but I'd hate to see what they cost today, or how many quantities you'd have to buy. To give you an idea just how bad these companies DON'T want to build this stuff anymore - I got a quote from Amphenol for the "Bendix" connectors used in the Mark 15 (which are the same as the Mark 16, except the 16's are rated non-mag and screened). They quoted me $2,500 EACH! And a minimum quantity of 100! That is what we call a "screw you" price where I come from...

So, you have a great increase in components, failure points, complexity, and multiple leak points just to go "old school"...

Best thing to do is to find an old Mark 15 Secondary and use that in your home-build.

But hey, this is a very cool hobby anyway, so have at it! If you need any advice or pictures of the older stuff, let me know.

Kevin.

[Captain Starfish]

Oh, since I somewhat have you stopped buy... can I at least expect a binary failure when the electromechanical gauge goes wonky on me? Eg. Will the wheels fall off my wagon or just wobble till get a headache?

I have a fuel gauge in my car which sometimes works, sometimes stops at 3/4 full even when I've filled the tank, and sometimes sits dead. Dunno if it's the gauge or something further back, possibly the sender is jamming for some reason. But I wouldn't put any faith in it failing in any kind of go/no go fashion, they could do anything.

[Sparedone]

So, the cool thing about these milliamp gauges is like you said, they don't need batteries.

-snipping off the goodies to ponder-

But hey, this is a very cool hobby anyway, so have at it! If you need any advice or pictures of the older stuff, let me know.

Kevin.

Thank you for taking the time to share. I'm must admit I'm slightly awed and even more convinced the rebreather community is a great bunch with your reply.

I'll see what I can do to build around those limitations and maybe even end up with a somewhat wonky occasionally accurate and unreasonably expensive guage that looks worse, less durable and is harder to read compared to what you were engineering 20 years ago. But I just may learn something about ohms law along the way.

I'll do some more legwork and be back with some more questions. I've got a quote that seems reasonable for a small batch of the 1.5" guages in 10KΩ, 200mv, current 20uA flavor (thanks to the inadvertent help of mr. Raymaekers... though I doubt it will make EN14143 in this revision either.) And 4 samples with the custom coils headed my way by the end of the month.


Thanks for the offer of advice. I'll try to spend my three wishes wisely. Just hoping a Mark 15 Secondary isn't going for, let's say, 2,500$, when I finally come to my senses.

Cheers,
Cameron

[Sparedone]

I have a fuel gauge in my car which sometimes works, sometimes stops at 3/4 full even when I've filled the tank, and sometimes sits dead. Dunno if it's the gauge or something further back, possibly the sender is jamming for some reason. But I wouldn't put any faith in it failing in any kind of go/no go fashion, they could do anything.

With this in mind perhaps my most accurate reading should be obtained by leaving a lead disconnected or a dab of epoxy on the needle once I finalize the build and have my fun... a stopped clock is right twice daily.

And thanks, I'll keep my wits about me and also try to read up on common failures.

[heyydude]

Thank you for taking the time to share. I'm must admit I'm slightly awed and even more convinced the rebreather community is a great bunch with your reply.

I'll see what I can do to build around those limitations and maybe even end up with a somewhat wonky occasionally accurate and unreasonably expensive guage that looks worse, less durable and is harder to read compared to what you were engineering 20 years ago. But I just may learn something about ohms law along the way.

I'll do some more legwork and be back with some more questions. I've got a quote that seems reasonable for a small batch of the 1.5" guages in 10KΩ, 200mv, current 20uA flavor (thanks to the inadvertent help of mr. Raymaekers... though I doubt it will make EN14143 in this revision either.) And 4 samples with the custom coils headed my way by the end of the month.


Thanks for the offer of advice. I'll try to spend my three wishes wisely. Just hoping a Mark 15 Secondary isn't going for, let's say, 2,500$, when I finally come to my senses.

Cheers,
Cameron

Cameron,

Just don't go diving with it until you've thoroughly tested it. The bottom of the sea is lined with dudes who were "trying something out"...

Kevin.

[wedivebc]

I assume from your posts here you have some steam punk fetish or something.
Please don't take me wrong I love homebrew stuff and applaud your efforts for bare bones simple but the thing that brought rebreathers into the forefront of diving was the availability of reliable (ish) low(er) cost electronic PO2 monitoring devices.
There are tons of reliable devices to monitor PO2 albeit the cells are the weakest link in that chain.
If you insist on adding mechanical/analog PO2 monitoring I can assure you the cells will no longer be the weak link and your costs will far surpass any electronic equipment on the market today.
check out Mark Munro at ppo2.com he makes some nice DIY circuit boards and panel meter kits.

[wedivebc]

Cameron,

Just don't go diving with it until you've thoroughly tested it. The bottom of the sea is lined with dudes who were "trying something out"...

Kevin.

what he said!

[Sparedone]

I assume from your posts here you have some steam punk fetish or something.
Please don't take me wrong I love homebrew stuff and applaud your efforts for bare bones simple but the thing that brought rebreathers into the forefront of diving was the availability of reliable (ish) low(er) cost electronic PO2 monitoring devices.
There are tons of reliable devices to monitor PO2 albeit the cells are the weakest link in that chain.
If you insist on adding mechanical/analog PO2 monitoring I can assure you the cells will no longer be the weak link and your costs will far surpass any electronic equipment on the market today.
check out Mark Munro at ppo2.com he makes some nice DIY circuit boards and panel meter kits.

Fair enough. I remain convinced I may be very well the weakest link in anything I design so mechanically I'd rather not add extra unreliability.

Since I have some parts on the way and the gauges in the works I'll see the project through but for an actual diving build I'll at least stay digital for my primaries keeping this as an entirely independent backup system... did someone say buying more cells with the added value of reduced reliability?

As a film producer doubling as a repair technician my whole world is digital and everything electronic fails at the worst moment so I'm on a misguided kick to reduce complexity....

However, after hearing you out, analog gauges do sound too finicky to be worth the gained 'simplicity'.

And rest assured with my tinkering my odds of getting wet aren't very good for the rest of the summer.... Messing around with a bg 174 as well. Perhaps a little dirt diving with a buddy to knock the mouthpiece loose or convince him to put me on a leash again.

I'll get another set of led volt meters, pots and resistors on their way for a halfway respectable simple ppo2 monitoring system. Ppo2.com is a great resource. Good recommendation, thank you. Nearly pulled the trigger on one of his kits a couple years back but stayed OC a couple more seasons.

The learning is good fun at least on the homebuild route, feeling safe enough behind a screen or on the bench. I hear diving is overrated anyway, I'm just here for the girls.

Well, I'll go back to trying to discover fire now and maybe research flint.

Thanks again for thoughtful replies.

Regards,
Cameron

[heyydude]

Fair enough. I remain convinced I may be very well the weakest link in anything I design so mechanically I'd rather not add extra unreliability.

Since I have some parts on the way and the gauges in the works I'll see the project through but for an actual diving build I'll at least stay digital for my primaries keeping this as an entirely independent backup system... did someone say buying more cells with the added value of reduced reliability?

As a film producer doubling as a repair technician my whole world is digital and everything electronic fails at the worst moment so I'm on a misguided kick to reduce complexity....

However, after hearing you out, analog gauges do sound too finicky to be worth the gained 'simplicity'.

And rest assured with my tinkering my odds of getting wet aren't very good for the rest of the summer.... Messing around with a bg 174 as well. Perhaps a little dirt diving with a buddy to knock the mouthpiece loose or convince him to put me on a leash again.

I'll get another set of led volt meters, pots and resistors on their way for a halfway respectable simple ppo2 monitoring system. Ppo2.com is a great resource. Good recommendation, thank you. Nearly pulled the trigger on one of his kits a couple years back but stayed OC a couple more seasons.

The learning is good fun at least on the homebuild route, feeling safe enough behind a screen or on the bench. I hear diving is overrated anyway, I'm just here for the girls.

Well, I'll go back to trying to discover fire now and maybe research flint.

Thanks again for thoughtful replies.

Regards,
Cameron

Film Producer becoming Rebreather Mechanic... Did I just respawn someplace?

The key is to have fun, Cameron. The journey of discovery has it's own rewards. Just take a piece of advice from someone who's been-there, done-that - don't quit your day job... Quickest way to wind up with a Million Dollars in the Scuba Business is to start with Two Million Dollars...

Later,

Kevin.

[Sparedone]

While I appreciate this millionaire fast road you speak of I prefer the slow route. With this in mind I have a special offer of accepting 4 million dollars which will allow a Nigerian prince to match your investment and I will guarantee 1 million dollars returned to you.

And if you indeed respawned I seem to be missing my equipment loadout, something you can rectify along with your investment in my million dollar business strategy.


In other news, here's the guage.
ITERNAL RESISTANCE TESTING.jpg