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Thread: Op Amp choice

  1. #31
    RBW Member risototh is an unknown quantity at this point risototh's Avatar
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    Re: Op Amp choice

    I was today in my office and the oxymeter was still alive. Nothing strange on that, except, that it showed 72% of oxygen in the air. There were around 13 mV out of the cell. As you can see on the image below, it was calibrated on around 4 mV (maybe less as there was constant decrease in the time)... The cell is out of date and out of order, of course. But i'm surprised with the voltage! And it is quasi imune to oxygen change. Do you know something about this type of oxygen cell failure? (Yes, i checked the output with voltmeter),

  2. #32
    RBW Member Igor P is just really nice Igor P is just really nice Igor P is just really nice Igor P is just really nice Igor P is just really nice Igor P is just really nice Igor P is just really nice Igor P is just really nice Igor P is just really nice Igor P is just really nice Igor P is just really nice Igor P's Avatar
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    Re: Op Amp choice

    Never saw something similar...

    Sent from my PAP4500DUO using Tapatalk 2

  3. #33
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    Re: Op Amp choice

    I had an AP12 cell fail reading over 200mV in air, two days after i opened the packet. Replaced under warranty but I have no idea how it did that: didn't even realise the chemistry would let it go that high!

  4. #34
    RBW Member risototh is an unknown quantity at this point risototh's Avatar
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    Re: Op Amp choice

    It is old APD12...

    Quote Originally Posted by Captain Starfish  View Original Post
    I had an AP12 cell fail reading over 200mV in air, two days after i opened the packet. Replaced under warranty but I have no idea how it did that: didn't even realise the chemistry would let it go that high!

  5. #35
    One Breath From Death testuser is an unknown quantity at this point testuser's Avatar
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    Re: Op Amp choice

    I know it'a a little late, but here's an alternative idea to try. AVR microcontrollers are 10-bits across the 0-AREF range, which is usually either teh supply rail(Vcc) or the internal 1.1V bandgap. I believe you can also supply your own voltage reference externally. putting a 200mV reference (e.g. a voltage divider from some precise LDO) would get you all 10 bits across that tiny range, and might produce a simpler design overall.

    just a thought,
    -James

  6. #36
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    Re: Op Amp choice

    nevermind, further down the datasheet i see that the minimum ARef voltage is 1V, so you'd only really get 1mV resolution ever. bummer.

  7. #37
    RBW Member Snusmumrik will become famous soon enough Snusmumrik will become famous soon enough Snusmumrik will become famous soon enough Snusmumrik's Avatar
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    Re: Op Amp choice

    Quote Originally Posted by Captain Starfish  View Original Post
    I had an AP12 cell fail reading over 200mV in air, two days after i opened the packet. Replaced under warranty but I have no idea how it did that: didn't even realise the chemistry would let it go that high!
    That's not the chemistry, but defective resistive voltage divider on the PCB attached to the cell.

  8. #38
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    Re: Op Amp choice

    Quote Originally Posted by Snusmumrik  View Original Post
    That's not the chemistry, but defective resistive voltage divider on the PCB attached to the cell.
    Thanks, kinda figured later on that it would be something like that. Meh, they replaced it.

    Turtle Dude - got yours finished yet?

  9. #39
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    Re: Op Amp choice

    Ha ha, just been reading your new project Captain - nice.
    Funny you asked about mine, I took my housing diving the other day and it flooded (was empty so no bigie), I was more concerned with my 2.2 bar ppo2 at 70m at the time didn't even notice my torch implode either lol.
    Hoping to make up a new lid this week and test again soon.
    Baz

  10. #40
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    Re: Op Amp choice

    Yeah, not looking forward to "debugging" that part of mine :-/

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