Oxygen Sensor

[Tansis]

Hello all,
my younger brother has roped me in for a project to build his own CCR , he's the scuba fan , as for me I'm the electronics boffin of the family.( Personally I think it's part of a fiendish plot to have me freezing my ass off up at stony cove to get qualified so I can be his dive buddy.)

Now I've looked around the web and as far as I can tell every commercial and homebrew rig uses an oxygen sensor that is built into the hardware. From an electronics point of view it's not that difficult to make my own but they are expensive and can be a significant drain on a battery power supply, as this is of critical importance to safe operation I wondered if there was a alternative method that used less power and a cheaper sensor.

Suffice to say I found one. Hospitals use a simple clip on device that attaches to a finger or earlobe that can measure oxygen concentration actually in the blood stream by using nothing more than a couple of light emitting diodes. (This is perhaps a gross over simplification I admit )

My question is , has this approach been considered and rejected for whatever reason or is it an avenue worth exploring?

[NotDeadYet]

I'd imagine the moisture in the loop would play havoc with an optical system. Everything is worth exploring but O2 sensors are already designed, tested and available straight off the shelf for not a lot of money. Remember, these are something your bro's life will depend on, how good is your handiwork when doing something never done before Unless of course you have a fat insurance policy...

[nigelH]

Originally Posted by Tansis

My question is , has this approach been considered and rejected for whatever reason or is it an avenue worth exploring?

That's not measuring oxygen but the saturation of red blood cells (they go blue when they are not carrying oxygen).
I fear you need a lot more research before you try this. Even the normal galvanic cells fail (I had one go with 38 minutes of stops pending) so you want more than one. The electronics is not trivial and keeping the water out ain't that easy either. If your brother is trying to do this on the cheap make sure you are a beneficiary in his will.

[narked at 90]

the monitors you are talking about would be useles to you as they monitor blood oxogen which is fine but it's far to late to find out your blood o2 is to low and you now need to inject more o2 but you dont have the energy before you pass out! you need to know your o2 before you breather it,
another problem with the medical clip on is that it would need bear skin to shine though to take a reading,this could be a big problem in colder water, and when you are cold you blood will move to your inturnal bit and pieces so there would be no blood to get a reading from.
although sensers are expensive they are the cheepest way to monitoe o2,
they have no drain on your ciruit as they are batterys of a type so all you need is power to drive your voltmeter display
are you thinking of using LED or LCD?
remember that you have to increse the gain on the display and incorperate a refferance voltage for the display for calibrating
it's all very simple as im shoure you know but please be very awere this is for life surport and getting this wrong may very well kill your brother
i've just tested my new displays today inwater at stoney to 30m which went great!
kind regards john routley

Originally Posted by Tansis

Hello all,
my younger brother has roped me in for a project to build his own CCR , he's the scuba fan , as for me I'm the electronics boffin of the family.( Personally I think it's part of a fiendish plot to have me freezing my ass off up at stony cove to get qualified so I can be his dive buddy.)

Now I've looked around the web and as far as I can tell every commercial and homebrew rig uses an oxygen sensor that is built into the hardware. From an electronics point of view it's not that difficult to make my own but they are expensive and can be a significant drain on a battery power supply, as this is of critical importance to safe operation I wondered if there was a alternative method that used less power and a cheaper sensor.

Suffice to say I found one. Hospitals use a simple clip on device that attaches to a finger or earlobe that can measure oxygen concentration actually in the blood stream by using nothing more than a couple of light emitting diodes. (This is perhaps a gross over simplification I admit )

My question is , has this approach been considered and rejected for whatever reason or is it an avenue worth exploring?

[Sutty]

I use these sort of sensors all the time at work, Thay measure the saturation of haemoglobin with oxygen. I can't imagine they would be any use for diving as:
1. They don't work well on cold tissues.
2. We dive at high PO2 (compared with surface air) and if healthy will be 100% saturated all the time - won't give you any info about inert gas.