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Thread: Let's Build a PO2 Monitor / Setpoint Controller For a Homebuild mCCR

  1. #1
    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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    Let's Build a PO2 Monitor / Setpoint Controller For a Homebuild mCCR

    Recently there have been some threads about building a setpoint controller, and I've had some PMs on the subject as well.

    I thought if there was interest, I'd take some of the tweaks I put in the latest PO2 monitoring electronics I recently made for my baby Dolphin, and incorporate them into a controller that could work with a variety of homebuild / modded units.

    My idea was to do it in this thread, writing up each stage as I go along and posting pics.

    While there are a lot of microcontrollers to choose from, this project will be based on the BS2p40 version of Parallax's Basic Stamp for several reasons;

    There's tons of free support, information, and documentation for it.

    The programming is about as easy as it gets, and since I'll post the program, it'll be that much easier to see what's going on

    The programming interface is free to download from Parallax and easy to learn so you can customize the code where it needs tweaks to work best with your unit.

    I'm not as proprietary about relatively simple code I write for stamps as I am about some other things.

    The biggest downside to Basic Stamps is their lack of floating point math support, but that doesn't have to be a deal breaker. .... Remember that every decimal point effectively wastes a character space on a display and calibration done with digital pots allows the secondary display to function, even if the program somehow locks up.


    A little bit about the overall design;

    It's design is to be used in addition to a manual PO2 control system

    It will monitor and base O2 control on 3 cells averaged

    It's the divers responsibility to operate in manual mode whenever the master computer (the one between his / her ears) isn't willing to trust all 3 cells

    If there's a KISS principle for eCCR, that's it.

    The primary display will be a 4 line by 20 character per line, LCD display.

    There will be three buttons to navigate the menus and handle calibration.

    The last calibration data is retained in eeprom, so that in the event of a reboot, just paging thru the calibration pages reloads the last cal data.

    The secondary display will be comprised of LCD or LED (your choice) digital voltmeter modules like you typically see in Mark Munroe style PO2 meters, just in a different input range.

    The design will support a 9 led HUD, where you have "LO - OK - HI" leds for each cell

    The battery pack and main electronics boards will be housed as a group, with all the remote modules plugging into it. Each remote module has it's own dedicated voltage regulator chip on the power distribution board, so that any module that fails/floods/cut cord can't crash the other modules or main system.


    Well folks, that's the overview. Let me know what you think, and ask about what more you'd like to know.


    I'm off to work on the circuit board design.


    Darlene
    Last edited by Scuba_Vixen; 19th June 2010 at 19:47.

  2. #2
    RBW Member Chris Kennedy is a glorious beacon of light Chris Kennedy is a glorious beacon of light Chris Kennedy is a glorious beacon of light Chris Kennedy is a glorious beacon of light Chris Kennedy is a glorious beacon of light Chris Kennedy is a glorious beacon of light Chris Kennedy is a glorious beacon of light Chris Kennedy is a glorious beacon of light Chris Kennedy is a glorious beacon of light Chris Kennedy is a glorious beacon of light Chris Kennedy is a glorious beacon of light Chris Kennedy's Avatar
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    Re: Let's Build a PO2 Monitor / Setpoint Controller For a Homebuild mCCR

    Thanks Darlene,I am sure that there quite a few hombuilders like myself who will appreciate your generous imparting of knowledge and will enjoy !! .
    Regards
    Chris

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    Thumbs up Re: Let's Build a PO2 Monitor / Setpoint Controller For a Homebuild mCCR

    Same here - really looking forward to seeing how you tackle the project. Very interested in your ideas to protect areas from faults in other parts.

  4. #4
    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: Let's Build a PO2 Monitor / Setpoint Controller For a Homebuild mCCR

    I've spent today revamping the Processor Board and the Power Distribution board from a previous project so that it should work well with what I have planned for this project.

    The processor board has the microcontroller and most of the input and output connections on it, as well as the main connect back to the PD board and the connects to the op amp/ADC board. The only I/O on the amp/ADC board should be the cells in and the secondary display out connections.

    I'm anticipating getting all the amp/ADC functions on a single board, but we'll find out down the road a bit if it works out that way.

    The PD board has all the voltage regulators, the reed switch, and the High Side Driver chip for the O2 solenoid control.

    As with any prototype or early revision, I tried to leave some options open, (like for a vibe alarm and depth module) and some alternate wiring options for ground runs & the interconnections between the boards. When you don't have a multi-layer board with ground plane, grounding can be a problem in that when you activate a backlight for example, the display changes by a few tenths of a percent.

    Tomorow, I'll make the power and processor boards, and start to protoboard the amp/ADC board.


    Darlene

  5. #5
    RBW Member moribund is a glorious beacon of light moribund is a glorious beacon of light moribund is a glorious beacon of light moribund is a glorious beacon of light moribund is a glorious beacon of light moribund is a glorious beacon of light moribund is a glorious beacon of light moribund is a glorious beacon of light moribund is a glorious beacon of light moribund is a glorious beacon of light moribund is a glorious beacon of light moribund's Avatar
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    Re: Let's Build a PO2 Monitor / Setpoint Controller For a Homebuild mCCR

    What cells are you designing for?

    Great project, BTW.

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    Re: Let's Build a PO2 Monitor / Setpoint Controller For a Homebuild mCCR

    Awesome project Darlene...

  7. #7
    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: Let's Build a PO2 Monitor / Setpoint Controller For a Homebuild mCCR

    Quote Originally Posted by moribund  View Original Post
    What cells are you designing for?

    Great project, BTW.

    It's going to be relatively universal; The nominal 10mV in air cells are by far the most common, but accomodating HO cells is really easy because of the board layout.

    I was really wanting to keep it to a 2 board (+PD board) project, but I've become partial to having my millivolt reading to tenths of a mV, which requires a precision X 10 op amp stage, which the layout I'm adapting to this project did not have.

    If I add another small board to handle the cell input circuitry, then I can have both the X 10 op amp stage and an active buffer (X 1) stage for each cell. That offers active isolation if you want to run something else off the cells. It also offers an easy way to select whether you want this device to have a 10k input resistance, or a much higher one with little jumper blocks.

    In the original design, the main op amp circuitry uses two 150k resistors in series (need 300k but using 2 resistors aids in board layout) in the feedback loops and has a gain range of 15 to 30 which allows calibration with cells between 7 and 13mV in air.

    By replacing one of the 150k resistors in each pair with a jumper, the gain would be half, and suitable to using HO cells. ... Worst case scenario with HO cells that are a full 25mV in air, you'd change the 150k to 120k.

    If you contemplate maybe using HO cells, you could use 120k and 180k in series and then just jump out the 180k with the HO cells.

    I have plenty of 150k resistors on hand, but since I have to order some supplies from Digikey anyway, I'll get some 120k and 180k and use that combination in the project build.

  8. #8
    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: Let's Build a PO2 Monitor / Setpoint Controller For a Homebuild mCCR

    Project Update:

    The weather has been crap all weekend, so I spent the day working on board design and I made the PD board, the Processor board, and a Cell Input board.

    I'm hoping the CI board will fit in the canister once all the parts are on it. It should just make it, but I've been over optimistic before.

    If all I had on the CI board was the cell input circuitry, it would be significantly smaller and be an easy fit, but I shoehorned on the circuitry for the instrument amp and interface that goes with an analog depth sensor. The microcontroller is too maxed to use a digital depth module, and it will be nice to have that infrastructure in place later in the build perhaps.

    Worst case scenario, I'll have to redesign the CI board with only the CI circuitry, and remotely place the instrument amp for the depth sensor in the sensor module housing.

    Anyway, I just got called into work, so here's a pic of the boards ready to drill and trim to size.


    Darlene
    Attached Images

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    RBW Member david_1 is an unknown quantity at this point david_1's Avatar
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    Re: Let's Build a PO2 Monitor / Setpoint Controller For a Homebuild mCCR

    Darlene

    I sent you pm ?

    David

  10. #10
    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: Let's Build a PO2 Monitor / Setpoint Controller For a Homebuild mCCR

    Quote Originally Posted by david_1  View Original Post
    Darlene

    I sent you pm ?

    David

    Getting to it now

    Darlene

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