PPO2 monitor

[divetheworld]

How many of you have home built, and how many buy ready made units?

I am looking into making some swanky kit.

First drafts use a backlit display with single O2 cells. The cell readings will be displayed with a real time filter, with 8 samples per second with the average of 4 concecutive samples on the display.

There would be four buttons on the front cover
button 1 : Toggles backlighting on and off.
button 2: Displays highest encountered reading since power-up.
button 3 : Displays lowest encountered reading since power-up.
button 4: Enters the setup menu (four digit password required).

Calibration is menu driven, not using pots.
- The display shows SETLEVEL1, followed by +00000
- Apply the first known PPO2 to the sensor (air).
- Use the Up and Down Arrows to change the polarity and digit values (use the Menu button to progress to
the next digit.) so the resulting reading corresponds with 0.21
- Press Enter to accept the reading.
- The display shows SETLEVEL2, followed by +10000
- Apply the second PPO2 to the sensor (pure O2).
- Use the Up and Down Arrows to change the polarity and digit values (use the Menu button to progress to
the next digit.) so the resulting reading corresponds with 1.0
- Press Enter to accept the reading.
- The module is now calibrated.
You would now save this calibration in the flash memory in one of four locations.

Alternatively you could do this from your PC via infra-red.

Next to this will be a red 10mm square indicator for alarms. The alarm upper and lower setpoint will be user programmable in flash memory. The alarm would be a static or flashing indicator with or without a buzzer sounding (user selectable)

The only problem I have is the calibration is saved in volatile memory, so user configurations would have to be loaded from store before each use.
There are four user configurable configurations which are held in the devices memory.

So you would need to turn on, and load the configuration before each dive. Configurations would only be saved periodically or when you change an O2 cell.

Is this unacceptable for you as users? If it is, then I will have to find a way of maintaining memory without undue power drains.

So far the estimated cost would be £200 including the cells.

[NotDeadYet]

I don't mean to sound discouraging, but why would I need all of that? This sounds like a product aimed at the KISS diver or someone building a KISS style rebreather, in which case it is the simplicity that appeals. My monitoring system costs £20 per display if you go for the fancy backlit ones.

A few ideas, why the sampling system? A reading that has any real variation will probably have a dodgy sensor or wiring and I'd like to see the variation. A simple analogue system just reads the volateg continuously and displays it (with gain adjustment) and you see anything that goes wrong. It's often a good indicator of problems with connectiosn and wiring.

I'm not a fan of electronic calibration either after that guy in Oz switched his Insp into calibrate mode at 60m. You'd need a depth/wet switch that would prevent this. Mechanical systems don't need calibration that often unless the cells haven't been used in a while and the output has dropped. Usually, on mine anyway, you switch it on and it reads 0.21 (or thereabouts). Calibrating the pot takes a second. The pots I use are environmentally sealed so a little condensate shouldn't matter and the boards are potted in clear silicone.

I think most KISS/KISS-style RB divers went that way because they felt the best monitoring/control system was between their ears and didn't want warnings/buzzers, etc.

£200 plus the housing would be far too expensive for me. To be honest, the electronics are the easiest part. If you are looking to develop a useful product then I'd look at housings, that is the difficult thing.