Homemade PO2 meter

**Dave Sutton** · 1st April 2007, 15:12

Quote: (Originally Posted by marekm)

This is what I was aiming at with the analogue LED based PO2 meter. And also the fact that it removes the 'black box' component out of the PO2 meter, since I know what each transistor does, rather than have a unknown IC on a DPM.

As for the mechanical analogue mV gauges, I did not realize they were so fragile, I simply assumed they were not used because they were retro and uncool. In terms of how fragile they are, does anyone know if they are more or less delicate than a HID bulb?

An LED based meter would ROCK, especially if the LED's were small enough to be carried as a HUD...(sort of like the mini-Primary that is being built for the Mark-15 now....) Remote the transistors to a pod in the rig and have the LED's in a small potted display at the end of a cord.

The HID light bulb comparison is probably a good one. They are likely about the same in durability, as I've busted an equal number of both over the years......

(several of each)

Dave

Tom Rose · 1st April 2007, 15:45

Quote: (Originally Posted by Dave Sutton)

An LED based meter would ROCK, especially if the LED's were small enough to be carried as a HUD...(sort of like the mini-Primary that is being built for the Mark-15 now....) Remote the transistors to a pod in the rig and have the LED's in a small potted display at the end of a cord.

A few years ago when I showed how to program a led display using a basic stamp 1. It was a learning exercise with a number of divers emailing with their views as the project moved along. When it was working a number of divers built them and corresponded with me after the post had potted them. They potted the leds in everything from tick tack boxes to small test tubes. Somewhere I have a collection of pictures of their final solutions.

Here is the link to that article.

LEDHUD REPORT 1

I also took another route....I used a fiber optic cable from the top of the scrubber where the red green led was to my mask. In my final version I also used a single red-green led. Instead of powering the leds with the port on, I used the port off command and powered the led from the common lead.

Not real rocket science but it allowed the system to be completely waterproof.

Maybe I should update the pages.........

Tom

Joseph Grech · 1st April 2007, 17:24

Tom, you bet you should update. Even you Dave. You are both my tinkering heroes.

Joseph

DepthCharge · 1st April 2007, 20:48

Tom,
Just took a quick look at your code. How are you calibrating the sensors? Or are you not calibrating at all?

Tom Rose · 2nd April 2007, 00:51

Quote: (Originally Posted by DepthCharge)

Tom,
Just took a quick look at your code. How are you calibrating the sensors? Or are you not calibrating at all?

I stopped publishing at that point.

The cell needed a 10,000 ohm resistance as an impedance match.

Calibration was actually simple....I used a pot as a voltage divider and resistance for the cell. I set the output of the voltage divider at 9 mv for a ppo of .2 I show this approach in my dual display system. Just adjust the pot to calibrate the system.

At this point William Smithers and I started a private dialog concerning a PIC that I found with several internal a/d ports that would not require an op amp. Smithers figured out how to make it twice as sensitive...really scooping me.....He was quite a clever guy and a lot of fun to work with. It would not serve his needs in the hammerhead because it did not have enough programing space...but we were able to make the pic work for a simple display system...with plenty of sensitivity removing the need for op amps and a/d converters. He died before we finished it.

Thus the display system consisted of oxygen sensors with pots, the PIC and the LEDs.

I simply lost heart and interest at his untimely death.

Tom

Mike · 2nd April 2007, 01:41

Quote: (Originally Posted by Dave Sutton)

The HID light bulb comparison is probably a good one. They are likely about the same in durability, as I've busted an equal number of both over the years......

(several of each)

Dave

Dave's probably pretty much right on this one - the secondaries need to be looked after but they are not completely fragile.
Some of the guys have had other bits of the Prism break, but the secondaries seem to be holding up OK.

Clip both of them up, and they should last just fine. I've dropped both my secondary and my HID on to boat decks, and they both still work. I don't expect that this will always be true if I keep doing it though

Mike

marekm · 2nd April 2007, 04:39

Hi Mike,

Was the HID bulb in a Greenforce light head that is particularly resistant to being dropped? As that is an idea I was considering, using the same shock dampening technology that Greenforce uses to put around the analogue PO2 gauge, hence resolving the fragility issue.

-Marek

Woz · 2nd April 2007, 11:04

The thing that makes an HID bulb fragile is the striker wire- Greenforce and Salvo use Brightstar bulbs which have a different striking method than the Welch Allyn bulbs (which are the fragile ones).

undrh2o · 2nd April 2007, 20:37

Quote: (Originally Posted by Tom Rose)

I stopped publishing at that point.

The cell needed a 10,000 ohm resistance as an impedance match.

Calibration was actually simple....I used a pot as a voltage divider and resistance for the cell. I set the output of the voltage divider at 9 mv for a ppo of .2 I show this approach in my dual display system. Just adjust the pot to calibrate the system.

At this point William Smithers and I started a private dialog concerning a PIC that I found with several internal a/d ports that would not require an op amp. Smithers figured out how to make it twice as sensitive...really scooping me.....He was quite a clever guy and a lot of fun to work with. It would not serve his needs in the hammerhead because it did not have enough programing space...but we were able to make the pic work for a simple display system...with plenty of sensitivity removing the need for op amps and a/d converters. He died before we finished it.

Thus the display system consisted of oxygen sensors with pots, the PIC and the LEDs.

I simply lost heart and interest at his untimely death.

Tom

Tom,
Was that the PICAXE you where playing with? I've been working with the PICaxe 18x which has built in ADCs but I haven't got very far yet - I'm planning on initially using DPMs for my first display.

Sorry about Will I've seen a lot of references to him and his work (TP2000 was great) but I got interested in rebreathers after his passing.

Chris

P.S. I'm going to use the "O2 sensor simulators" from your site to test out my code when my PICaxe project is complete

Tom Rose · 2nd April 2007, 22:46

Quote: (Originally Posted by undrh2o)

Tom,
Was that the PICAXE you where playing with? I've been working with the PICaxe 18x which has built in ADCs

I was not aware of that product....

I just looked at the 18x....it is a killer product....at that price.

It is so simple, I could put something together...program.... pcb and all in a day.

The code is simple...enough like a stamp to be a no brainer. Size is perfect. It could run on a small battery power supply.

Did you import them or is there a dealer in the US?

Please advise so I can get and use some of them.....

Note that 10 bits is a resolution of 5 millivolts. If a o2 cell puts out 9 millivolts at 1 bar, it will put out about

With no op amp.....

9x3 at a ppo of .6.....giving a 3 at the ADC
9x4 at a ppo of .8.....giving a 7 at the ADC
9x5 at a ppo of 1 .....giving a 9 at the ADC
9x6 at a ppo of 1.2...giving a 10 at the ADC
9x7 at a ppo of 1.4...giving a 11 at the ADC

So less than 7 is low
7 to 10 is just fine
and greater than 10 is to high

The board could be only 2 inches long and a 6/10s inch wide.

Add a 8 pin op amp and the resolution is even better with an additional cost of about 50 cents and 1/2 inch longer PC board.

A display for less than 15 bucks. Plus the housing.

This is going to cost me a day in the near future.
Tom

1st April 2007, 15:12	#31 (permalink)
Dave Sutton Diveshop of Horrors Current Rebreather/s: Sport Kiss MK 15.X rEvo Other CCR Azimuth Home Build Other Rebreather/s: Evolution Megalodon rEvo Other CCR Azimuth Home Build Join Date: Jun 2006 Location: Narragansett, Rhode Island and Hackettstown, New Jersey Posts: 2,907	Re: Homemade PO2 meter Quote: (Originally Posted by marekm) This is what I was aiming at with the analogue LED based PO2 meter. And also the fact that it removes the 'black box' component out of the PO2 meter, since I know what each transistor does, rather than have a unknown IC on a DPM. As for the mechanical analogue mV gauges, I did not realize they were so fragile, I simply assumed they were not used because they were retro and uncool. In terms of how fragile they are, does anyone know if they are more or less delicate than a HID bulb? An LED based meter would ROCK, especially if the LED's were small enough to be carried as a HUD...(sort of like the mini-Primary that is being built for the Mark-15 now....) Remote the transistors to a pod in the rig and have the LED's in a small potted display at the end of a cord. The HID light bulb comparison is probably a good one. They are likely about the same in durability, as I've busted an equal number of both over the years...... (several of each) Dave __________________ "Silent Diving with No Bubbles and No Politics".... www.nobubblediving.com
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1st April 2007, 15:45	#32 (permalink)
Tom Rose Still Learning Current Rebreather/s: Other CCR Home Build Other Rebreather/s: Prism Topaz Other CCR Home Build Join Date: Oct 2005 Location: USA,North Carolina Posts: 331	Re: Homemade PO2 meter Quote: (Originally Posted by Dave Sutton) An LED based meter would ROCK, especially if the LED's were small enough to be carried as a HUD...(sort of like the mini-Primary that is being built for the Mark-15 now....) Remote the transistors to a pod in the rig and have the LED's in a small potted display at the end of a cord. A few years ago when I showed how to program a led display using a basic stamp 1. It was a learning exercise with a number of divers emailing with their views as the project moved along. When it was working a number of divers built them and corresponded with me after the post had potted them. They potted the leds in everything from tick tack boxes to small test tubes. Somewhere I have a collection of pictures of their final solutions. Here is the link to that article. LEDHUD REPORT 1 I also took another route....I used a fiber optic cable from the top of the scrubber where the red green led was to my mask. In my final version I also used a single red-green led. Instead of powering the leds with the port on, I used the port off command and powered the led from the common lead. Not real rocket science but it allowed the system to be completely waterproof. Maybe I should update the pages......... Tom __________________ The 50-50-90 rule: Anytime I have a 50-50 chance of getting something right, there's a 90% probability I'll get it wrong the first time. www.atlimp.com
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1st April 2007, 17:24	#33 (permalink)
Joseph Grech Joseph Grech Current Rebreather/s: Azimuth Other Rebreather/s: Azimuth Join Date: Mar 2005 Location: Malta Posts: 104	Re: Homemade PO2 meter Tom, you bet you should update. Even you Dave. You are both my tinkering heroes. Joseph
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1st April 2007, 20:48	#34 (permalink)
DepthCharge New Member Current Rebreather/s: Inspiration Classic Home Build Other Rebreather/s: Home Build Join Date: Mar 2005 Location: upstate NY Posts: 234	Re: Homemade PO2 meter Tom, Just took a quick look at your code. How are you calibrating the sensors? Or are you not calibrating at all? __________________ Later, John It's better to beg forgiveness than ask permission
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2nd April 2007, 00:51	#35 (permalink)
Tom Rose Still Learning Current Rebreather/s: Other CCR Home Build Other Rebreather/s: Prism Topaz Other CCR Home Build Join Date: Oct 2005 Location: USA,North Carolina Posts: 331	Re: Homemade PO2 meter Quote: (Originally Posted by DepthCharge) Tom, Just took a quick look at your code. How are you calibrating the sensors? Or are you not calibrating at all? I stopped publishing at that point. The cell needed a 10,000 ohm resistance as an impedance match. Calibration was actually simple....I used a pot as a voltage divider and resistance for the cell. I set the output of the voltage divider at 9 mv for a ppo of .2 I show this approach in my dual display system. Just adjust the pot to calibrate the system. At this point William Smithers and I started a private dialog concerning a PIC that I found with several internal a/d ports that would not require an op amp. Smithers figured out how to make it twice as sensitive...really scooping me.....He was quite a clever guy and a lot of fun to work with. It would not serve his needs in the hammerhead because it did not have enough programing space...but we were able to make the pic work for a simple display system...with plenty of sensitivity removing the need for op amps and a/d converters. He died before we finished it. Thus the display system consisted of oxygen sensors with pots, the PIC and the LEDs. I simply lost heart and interest at his untimely death. Tom __________________ The 50-50-90 rule: Anytime I have a 50-50 chance of getting something right, there's a 90% probability I'll get it wrong the first time. www.atlimp.com
(Offline)

2nd April 2007, 01:41	#36 (permalink)
Mike Prism 'prentice Current Rebreather/s: Prism Topaz Other Rebreather/s: Inspiration Classic Evolution Join Date: Feb 2005 Location: Melbourne Posts: 332	Re: Homemade PO2 meter Quote: (Originally Posted by Dave Sutton) The HID light bulb comparison is probably a good one. They are likely about the same in durability, as I've busted an equal number of both over the years...... (several of each) Dave Dave's probably pretty much right on this one - the secondaries need to be looked after but they are not completely fragile. Some of the guys have had other bits of the Prism break, but the secondaries seem to be holding up OK. Clip both of them up, and they should last just fine. I've dropped both my secondary and my HID on to boat decks, and they both still work. I don't expect that this will always be true if I keep doing it though Mike __________________ Open ....... Closed Mind ........ Loop
(Offline)

2nd April 2007, 04:39	#37 (permalink)
marekm Banned Current Rebreather/s: Not Bought Yet Other Rebreather/s: Not Bought Yet Join Date: Oct 2006 Location: Brisbane, Australia Posts: 196	Re: Homemade PO2 meter Hi Mike, Was the HID bulb in a Greenforce light head that is particularly resistant to being dropped? As that is an idea I was considering, using the same shock dampening technology that Greenforce uses to put around the analogue PO2 gauge, hence resolving the fragility issue. -Marek
(Offline)

2nd April 2007, 11:04	#38 (permalink)
Woz Custom Title Allowed! Current Rebreather/s: Home Build Other Rebreather/s: Home Build Join Date: Jun 2005 Location: Nottingham Posts: 186	Re: Homemade PO2 meter The thing that makes an HID bulb fragile is the striker wire- Greenforce and Salvo use Brightstar bulbs which have a different striking method than the Welch Allyn bulbs (which are the fragile ones). __________________ Still punting shiny diving tatt to gullible divers www.kitfondle.co.uk
(Offline)

2nd April 2007, 20:37	#39 (permalink)
undrh2o Chris Miller Current Rebreather/s: Other CCR Dolphin Home Build Other Rebreather/s: Inspiration Classic Other CCR Dolphin Home Build Join Date: Apr 2006 Location: Ottawa, Canada Posts: 206	Re: Homemade PO2 meter Quote: (Originally Posted by Tom Rose) I stopped publishing at that point. The cell needed a 10,000 ohm resistance as an impedance match. Calibration was actually simple....I used a pot as a voltage divider and resistance for the cell. I set the output of the voltage divider at 9 mv for a ppo of .2 I show this approach in my dual display system. Just adjust the pot to calibrate the system. At this point William Smithers and I started a private dialog concerning a PIC that I found with several internal a/d ports that would not require an op amp. Smithers figured out how to make it twice as sensitive...really scooping me.....He was quite a clever guy and a lot of fun to work with. It would not serve his needs in the hammerhead because it did not have enough programing space...but we were able to make the pic work for a simple display system...with plenty of sensitivity removing the need for op amps and a/d converters. He died before we finished it. Thus the display system consisted of oxygen sensors with pots, the PIC and the LEDs. I simply lost heart and interest at his untimely death. Tom Tom, Was that the PICAXE you where playing with? I've been working with the PICaxe 18x which has built in ADCs but I haven't got very far yet - I'm planning on initially using DPMs for my first display. Sorry about Will I've seen a lot of references to him and his work (TP2000 was great) but I got interested in rebreathers after his passing. Chris P.S. I'm going to use the "O2 sensor simulators" from your site to test out my code when my PICaxe project is complete
(Offline)

2nd April 2007, 22:46	#40 (permalink)
Tom Rose Still Learning Current Rebreather/s: Other CCR Home Build Other Rebreather/s: Prism Topaz Other CCR Home Build Join Date: Oct 2005 Location: USA,North Carolina Posts: 331	Re: Homemade PO2 meter Quote: (Originally Posted by undrh2o) Tom, Was that the PICAXE you where playing with? I've been working with the PICaxe 18x which has built in ADCs I was not aware of that product.... I just looked at the 18x....it is a killer product....at that price. It is so simple, I could put something together...program.... pcb and all in a day. The code is simple...enough like a stamp to be a no brainer. Size is perfect. It could run on a small battery power supply. Did you import them or is there a dealer in the US? Please advise so I can get and use some of them..... Note that 10 bits is a resolution of 5 millivolts. If a o2 cell puts out 9 millivolts at 1 bar, it will put out about With no op amp..... 9x3 at a ppo of .6.....giving a 3 at the ADC 9x4 at a ppo of .8.....giving a 7 at the ADC 9x5 at a ppo of 1 .....giving a 9 at the ADC 9x6 at a ppo of 1.2...giving a 10 at the ADC 9x7 at a ppo of 1.4...giving a 11 at the ADC So less than 7 is low 7 to 10 is just fine and greater than 10 is to high The board could be only 2 inches long and a 6/10s inch wide. Add a 8 pin op amp and the resolution is even better with an additional cost of about 50 cents and 1/2 inch longer PC board. A display for less than 15 bucks. Plus the housing. This is going to cost me a day in the near future. Tom __________________ The 50-50-90 rule: Anytime I have a 50-50 chance of getting something right, there's a 90% probability I'll get it wrong the first time. www.atlimp.com
(Offline)

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