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Thread: Electronics/O2 injection

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    Electronics/O2 injection

    If this is being designed as something that people can out together themselves. I'd sugest that the unit is designed as a mCCR:- that way the electronics can be simple to construct, and if someone doesn't want to construct their own electronics they can fit any of the comercialy available 3 cell monitoring solutions.

    Simon A

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    RBW Member tumbler is an unknown quantity at this point tumbler's Avatar
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    Re: Electronics/O2 injection

    Quote Originally Posted by Scuba_Vixen  View Original Post
    Running a low VRef just introduces additional issues. Better to run a 12 bit ADC (4096 steps) and a 4.096V VRef which yields 1mv per step which lets you monitor each cell's mv output, and with a gain stage, you can calibrate such that whatever is the cell's output on 100% O2 the ADC counts 1000 for 1000mv and everything reads directly. Obviously, Air would yield 209 mv.

    In my system (just using it as an example because I know it well) ... The digital controlled potentiometers can vary the gain between 15 and 30. That allows the system to calibrate with cell outputs in air of ~7.5mv to ~13.5mv.

    I use an 8 channel ADC. 3 channels read the cells directly in mv, 3 others read the gained input so it displays in PO2, 1 channel reads the depth module's output and displays in feet, and the 8th channel is a spare.

    If you do calibration in software and read the cells directly, you'll need 14 or 16 bit adc capability.


    Darlene
    OK, I'm slowly coming to terms with the fact that I will most likely need to depend on a 16bit ADC in order to get the resolution I need and account for a calibration routine. Any ideas about a nice chip to use for this?

    Thanks for all your info! It's really nice to talk to someone who has actually built one of these darn things before :)

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    RBW Member Oldefors is on a distinguished road Oldefors is on a distinguished road Oldefors's Avatar
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    Apoc O2-OEM with HW PO2

    IDA-71, mCCR

    Re: Electronics/O2 injection

    Quote Originally Posted by tumbler  View Original Post
    Any ideas about a nice chip to use for this?
    How about the O2 OEM module for the OSTC? It uses a serial communication protocol, and with three LEDs it can also be used stand-alone as a HUD.

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    Re: Electronics/O2 injection

    Quote Originally Posted by tumbler  View Original Post
    OK, I'm slowly coming to terms with the fact that I will most likely need to depend on a 16bit ADC in order to get the resolution I need and account for a calibration routine. Any ideas about a nice chip to use for this?

    Thanks for all your info! It's really nice to talk to someone who has actually built one of these darn things before :)
    One thing to keep in mind as you increase the resolution of the adc (# of bits), is that board layout becomes increasingly an issue if you want to maintain the gains of higher resolution. Noise is your enemy, and when you get to where you're working in micro-volt levels, noise is everywhere and makes accurate measurement difficult. Trying to set up a 16 bit system on a breadboard just doesn't work too well.

    If you try a 12 or 13 bit first, and get some experience writing the programming and learning to use them, you may find you don't need much more for DIY level systems.

    Look at the MCP3208 and MCP3304

    Darlene

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    Re: Electronics/O2 injection

    Quote Originally Posted by Oldefors  View Original Post
    How about the O2 OEM module for the OSTC? It uses a serial communication protocol, and with three LEDs it can also be used stand-alone as a HUD.
    OSTC seems to go along the lines intended for this project and seems to be one possible way of moving, I am wondering if all parts of this unit are obtainable i.e. schematic drawings and the such so as anyone could reproduce it in its entirety, I will inquire further. Has anyone that have purchased one of these units, recieved all info needed to go and build this in its current form? I know that the programming is user changeable but is the design also changeable?

    Cheers,
    Hunter
    Last edited by 19Hunter68; 19th August 2009 at 17:29.

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    Re: Electronics/O2 injection

    Ok, have the schematic for the electronics, the monitor. This is based on the:
    Microchip PIC18F4685 Processor, which is an 8-bit solution, however, has been incorporated seemingly successfully. The O2 board is not quite available in schematic drawing form:
    Attached Files
    Last edited by 19Hunter68; 19th August 2009 at 17:50.

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    Re: Electronics/O2 injection

    Quote Originally Posted by 19Hunter68  View Original Post
    Ok, have the schematic for the electronics, the monitor. This is based on the:
    Microchip PIC18F4685 Processor, which is an 8-bit solution, however, has been incorporated seemingly successfully. The O2 board is not quite available in schematic drawing form:
    Sorry the PIC18F4685 does seem to be 10-bit, I also mistated using "monitor" which this is actually the "computer".
    Last edited by 19Hunter68; 20th August 2009 at 01:56.

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    Re: Electronics/O2 injection

    Quote Originally Posted by Simon A  View Original Post
    If this is being designed as something that people can out together themselves. I'd sugest that the unit is designed as a mCCR:- that way the electronics can be simple to construct, and if someone doesn't want to construct their own electronics they can fit any of the comercialy available 3 cell monitoring solutions.

    Simon A
    I would vote for an extremely durable, impossible to break, triple PPO2 monitor system and a smaller wired separately back-up unit. No controller electronics

  9. #9
    Darlene Starr - DIY Diva Scuba_Vixen has a brilliant future Scuba_Vixen has a brilliant future Scuba_Vixen has a brilliant future Scuba_Vixen has a brilliant future Scuba_Vixen has a brilliant future Scuba_Vixen has a brilliant future Scuba_Vixen has a brilliant future Scuba_Vixen has a brilliant future Scuba_Vixen has a brilliant future Scuba_Vixen has a brilliant future Scuba_Vixen has a brilliant future Scuba_Vixen's Avatar
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    Re: Electronics/O2 injection

    Quote Originally Posted by 19Hunter68  View Original Post
    Ok, have the schematic for the electronics, the monitor. This is based on the:
    Microchip PIC18F4685 Processor, which is an 8-bit solution, however, has been incorporated seemingly successfully. The O2 board is not quite available in schematic drawing form:

    That's really more of a flow/layout drawing than a schematic. The data sheet for the PIC is almost 500 pages, I had a brief look-see. I'd like to see pin numbers on the drawing, correlating that with the data sheet's information would be good information as to what registers were being used for what functions.

    The 4685 has a built in uart (that's the comm driver) connected directly to the Fischer without any opto, That's a potential issue, unless it's there, but not on the drawing.

    With the cells being digitized externally, and the data transmitted to the PIC, the 10 bit internal adc probably isn't used for anything. The Sensor 1 in the drawing is an Intersema part number for a digitally interfaced depth sensor.

    All in all, it's probably more information that other manufacturers would divulge.


    Darlene

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    RBW Member tumbler is an unknown quantity at this point tumbler's Avatar
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    Re: Electronics/O2 injection

    It's trivial to set the pins on the Arduino to take serial input, so I'm going to get a couple of ADCs ordered and experiment a little. Even though some of the other boards out there have higher resolution ADCs, I'm still inclined towards the Arduino because of it's openness and because standard C algorithms can be used. Tomorrow I'll place an order for both the MCP3208 and the MCP3304. If anyone else has had good experience with another ADC, let me know and I'll order one up.

    I have to admit though, that I'm very partial to doing calibration in software. Not that I have anything against potentiometers, but doing it through menus on the LCD just seems so nice and elegant! Makes me wonder how bouncy magnetic read switches are...

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