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

  1. #41
    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

    Quote Originally Posted by Scuba_Vixen  View Original Post
    Weekend Update....

    I really do need a life or an intervention or something .......

    Fourth of July weekend and I'm writing code and making circuit boards.

    Darlene
    ...and the problem with this is?


  2. #42
    Just add ice & water plazma is a name known to all plazma is a name known to all plazma is a name known to all plazma is a name known to all plazma is a name known to all plazma is a name known to all plazma is a name known to all plazma is a name known to all plazma is a name known to all plazma is a name known to all plazma is a name known to all plazma's Avatar
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    Re: Let's Build a PO2 Monitor / Setpoint Controller For a Homebuild mCCR

    Hardware items first:

    I designed and made the new "cells in" pc board based on the TLC4502 self calibrating zero offset dual op amps: (parts from Digikey should be here Tuesday)

    http://focus.ti.com/lit/ds/symlink/tlc4502.pdf

    The board is layed out so that each cell feeds two of them. The first one has both halves set up in buffer mode to isolate the cell from anything additional you may want to drive off it. The second one has one half set up as a buffer and the other half as the 10X amp as shown in the diagram a few posts back.

    If you don't need to drive anything else off the cells, or it's already being done in another manner, then the board can be assembled with only 3 of the possible 6 op amps.

    I'm really pretty excited to see how this works out.
    So one cell feeds three buffers and one 10x amp. Why so many buffers? Only one is needed for extra computer like V£3. The primary and secondary needs one 10x amp each.
    The second hardware item is HUD related, more specifically, some changes in the voltage regulators board to allow the use of an adjustable regulator in place of the fixed 5V one.

    Depending on the conditions, the HUD brightness doesn't always match the need.

    Where I am, with bright sun all year long and clear water with nominally 100' plus visibility, I need really bright hud leds most of the time. Problem is that night dives and penetration dives, the buggers kill my night vision, even when I rotate the hud to to reduce the directness of the viewing angle. My friggin' hud is better than some led divelights (well almost). Well now it's adjustable from "retina frying" bright to "is it still on" dim. The HUD can now be adjusted to fit the need.
    Why not use pwm for dimming the led? With a regulator you waste power to heat. Pwm dimming is easy and you can control it with one value in the software. Just learn how to use timers.

  3. #43
    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 plazma  View Original Post
    So one cell feeds three buffers and one 10x amp. Why so many buffers? Only one is needed for extra computer like V£3. The primary and secondary needs one 10x amp each.

    Why not use pwm for dimming the led? With a regulator you waste power to heat. Pwm dimming is easy and you can control it with one value in the software. Just learn how to use timers.

    The primary and secondary can run off of 1 buffer, it's the mV readout that needs the X10 gain stage. One of these dual op amps for each cell is fine for this project as a stand-alone.

    It's only if you want to add actively isolated outputs for peripheral devices that you can take advantage of a second set of op amps, and being duals, you get 2 more buffers per cell.


    PWM works fine when the MCU has timers available to take advantage of, but that is Not the case here. With the limited resources available, using a digipot between 2 fixed resistors on an adjustable reg is as good as it gets. I think this one would be just right: http://datasheets.maxim-ic.com/en/ds/DS1804.pdf

    I'll work on a board that only uses 3 op amps (no extra buffers) and has the digipot for the hud dimmer on it jst to see how it works.

    Darlene
    Last edited by Scuba_Vixen; 5th July 2010 at 15:52.

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    Just add ice & water plazma is a name known to all plazma is a name known to all plazma is a name known to all plazma is a name known to all plazma is a name known to all plazma is a name known to all plazma is a name known to all plazma is a name known to all plazma is a name known to all plazma is a name known to all plazma is a name known to all plazma's Avatar
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    Re: Let's Build a PO2 Monitor / Setpoint Controller For a Homebuild mCCR

    Quote Originally Posted by Scuba_Vixen  View Original Post
    The primary and secondary can run off of 1 buffer, it's the mV readout that needs the X10 gain stage. One of these dual op amps for each cell is fine for this project.

    It's only if you want to add actively isolated outputs for peripheral devices that you can take advantage of a second set of op amps, and being duals, you get 2 more buffers per cell.


    PWM works fine when the MCU has timers available to take advantage of, but that is Not the case here. With the limited resources available, using a digipot between 2 fixed resistors on an adjustable reg is as good as it gets. I think this one would be just right: http://datasheets.maxim-ic.com/en/ds/DS1804.pdf

    Darlene
    To get it clear: do you use any buffer before the 10x amp?
    Both in buffer and 10x mode the op amp got a high impedance input. So there is no use for using a buffer before the 10x amp.

  5. #45
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    Re: Let's Build a PO2 Monitor / Setpoint Controller For a Homebuild mCCR

    Quote Originally Posted by plazma  View Original Post
    To get it clear: do you use any buffer before the 10x amp?
    Both in buffer and 10x mode the op amp got a high impedance input. So there is no use for using a buffer before the 10x amp.

    There is no buffer before the 10X. Each cell feeds a 10X and a buffer directly. The buffer output goes to the programmable gain stages on the analog processing board (which then go to the ADC) and the X10 output goes right to the ADC on that same board.

    Maybe the diagram was confusing, as to the "Cell In" label. To be more accurate, it should have been labelled "Buffered Cell In", as that's coming from the output of the "cells In" pcb.


    Sorry for the confusion.


    Darlene

  6. #46
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    Re: Let's Build a PO2 Monitor / Setpoint Controller For a Homebuild mCCR

    Week's Update,

    The new op amps are outstanding!

    Best results I've seen yet running a gain stage after a buffer with an input swing from low mV levels on up. These puppies rock.

    Almost makes me want to go redesign the Analog Processing board to use them in place of the OPA2340's, and go to surface mount digipots with them.

    I did redesign the cell input board to use just 3 of the new op amps, and added the single digipot I mentioned to work in conjuction with some slight redesign of the voltage regulators board to use an adjustable regulator for the HUD supply.

    I can now set the brightness of the HUD leds with the buttons. 13 steps from "effectively off " to "fry your eyeballs". I think I'm going to like that feature A LOT.

    This weekend, now that I have all the hardware mods I wanted, I'm going to see if I can get the depth to integrate with the solenoid ON time, and then I'll work on a block diagram and some schematics.


    Darlene

  7. #47
    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

    Great, moving along. I wondered why it got quiet here for a day or two

  8. #48
    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
    Great, moving along. I wondered why it got quiet here for a day or two

    Probably because there's only a handfull of people still following it


    I believe the RB community has, much like the amature radio community, become more appliance operators than hands-on nerds over the years.

    The flip side to that is that all the new appliances brought to market, have allowed the community to grow wayyy more than it otherwise would have.

    I'm having a great time with this project, learning yet new ways to leverage the rather dated Basic Stamp, creating a sharp looking display that belies the stamp's inability to do floating point math, and looking at more "outside the box" ideas. ... Like the user settable HUD brightness thing. ... Only problem with that; Is now I have to go back and add it to some other leccies packs I have.


    Darlene

  9. #49
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    Re: Let's Build a PO2 Monitor / Setpoint Controller For a Homebuild mCCR

    Quote Originally Posted by Scuba_Vixen  View Original Post
    Probably because there's only a handfull of people still following it


    I believe the RB community has, much like the amature radio community, become more appliance operators than hands-on nerds over the years.

    Darlene
    Well, I'm still following the project! It's good to see some original thinking and then someone who can put it together into a practical product

    Bob Sweeney

  10. #50
    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 bobmaggi  View Original Post
    Well, I'm still following the project! It's good to see some original thinking and then someone who can put it together into a practical product

    Bob Sweeney

    Thanks Bob,

    Maybe for my next trick, I'll replace the Stamp with a Propeller. That's the beauty of having the MCU on its own pcb. It could be a plug-it-up and go change over.



    Darlene

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