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Thread: DIY temp stick.

  1. #21
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    Re: DIY temp stick.

    couldn't you use bar drivers ( such as used in voltmeters),
    you woul dneed a calibration pod for each sensor so, and than just ahve a board with 10 tri-color leds.

    this would keep the whole thin analog and fairly failure proof

  2. #22
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    Re: DIY temp stick.

    Quote Originally Posted by Scuba_Vixen  View Original Post
    Interesting you should pop in on this at this time...


    Not that I need one of these, mind you, but it does seem to be an interesting challenge.

    I'm thinking more along the lines of an external unit with the sensors ( surface exposed) potted on a pcb that could then be thermally bonded to the outside of a scrubber housing. Using one more sensor than you need for scrubber measurements (on the opposite side of the pcb, & facing away from the scrubber housing) to monitor the ambient temp to use as a baseline.

    Darlene
    Hi,

    I was wondering, as I always do. Is what you are thinking too be used added to the side of a metalic axial scrubber? If so, what if the heat front were too be not so sraight (say the front was convex in nature and the middle drooped down alot futher than the temp stick would register) or a bleed of sorts were to occure at the opposing side of the can? Final question, thank you bearing with me so far, would a spiral wrap around the whole can possibly work or would 3 or 4 strips equally spaced around the can be necessary?

    Rambling,
    Hunter

  3. #23
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    Re: DIY temp stick.

    Sounds like that would be a fun winter project. All you need is some I2C thermal sensors to cut down the number of wires, a processor and display. I'll have to check out what type of sensors are out there. They don't even have to be terribly accurate since all you want is to detect the thermal 'wave' through the scrubber so I would think the sensors should be fairly inexpensive.

    Bob S

  4. #24
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    Re: DIY temp stick.

    Quote Originally Posted by 19Hunter68  View Original Post
    Hi,

    I was wondering, as I always do. Is what you are thinking too be used added to the side of a metalic axial scrubber? If so, what if the heat front were too be not so sraight (say the front was convex in nature and the middle drooped down alot futher than the temp stick would register) or a bleed of sorts were to occure at the opposing side of the can? Final question, thank you bearing with me so far, would a spiral wrap around the whole can possibly work or would 3 or 4 strips equally spaced around the can be necessary?

    Rambling,
    Hunter

    The number of ways you "could" do it are nearly endless.

    The number of "what ifs" are nearly equally as endless.

    The number of sensors you can employ in a practical manner is, on the other hand, definately limited.

    That's part of the reason why tempstiks are not the be-all / end-all of knowing what's going on in your scrubber.

    In truth, I question whether they have all that much real value overall.

    Which of course doesn't seem to keep me from wanting to have a go at making one.

    At best, they give you a reasonable guess at the general functioning of your scrubber. The more the scrubber is working like the "ideal theory", the more accurate the guess is. ..... But you'll never really know.

    The real gooal here is to use a reasonable number of sensors, with a minimal amount of additional hardware, and display it in a user friendly, intuitive manner with acceptable battery requirements, to afford you a reasonable guess at what's going on in the scrubber.

    Towards that end:

    I'm looking mostly at what would meet these criteria for now:

    1) Has to work on a Dolphin scrubber, as that's what I have to test on
    if it gets that far
    2) Has to be external, as I'm NOT putting holes in my scrubber housing
    3) Has to have a wire count of 5 or less to work with what I have trust in
    and have available
    4) Has to be able to be built on a pcb that I can make here
    5) Has to be small enough to house reasonably in a housing I can make
    6) Has to have reasonable battery life
    7) #6 rules out significant numbers of leds in a display
    8) Has to be "NO callibration required"
    9) #8 and #3 rule out analog design
    10) Has to be "stand-Alone" so I can put it on if I want, or go without it just
    as easily.

    I'm thinking of a design that would lay against the side of the scrubber held in place by a 1mm neoprene sleeve around the scrubber.

    If it all should end up working well, then other sensor mounting options could be worth exploring.



    Darlene

  5. #25
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    Re: DIY temp stick.

    Quote Originally Posted by bobmaggi  View Original Post
    Sounds like that would be a fun winter project. All you need is some I2C thermal sensors to cut down the number of wires, a processor and display. I'll have to check out what type of sensors are out there. They don't even have to be terribly accurate since all you want is to detect the thermal 'wave' through the scrubber so I would think the sensors should be fairly inexpensive.

    Bob S

    The Maxim DS18S20 or DS18B20 (or its economy twin the 1822) are Dallas OneWire protocol devices. You can put all you'd ever want on a 3 conductor line: +5, Gnd, & DQ.

    Each has a unique identifier hardcoded in ROM so the micro-controller can communicate to each sensor specifically.

    I don't think there's a simpler way to handle that part of the project.


    Darlene

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    Re: DIY temp stick.

    Do you need to know ambient temperature ? Could you not use the lowest reading as the baseline ? This would reduce the range that you need to display.

    Perhaps you could use the temp baseline from a few seconds ago so that it will show the entire scrubber warming during the pre-breathe and then settling to show the heat front. Any sudden changes in scrubber temp might be highlighted this way.

  7. #27
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    Re: DIY temp stick.

    Quote Originally Posted by Scubascooby  View Original Post
    Do you need to know ambient temperature ? Could you not use the lowest reading as the baseline ? This would reduce the range that you need to display.

    Perhaps you could use the temp baseline from a few seconds ago so that it will show the entire scrubber warming during the pre-breathe and then settling to show the heat front. Any sudden changes in scrubber temp might be highlighted this way.
    No you don't need to know the ambient temperature.

    The important thing is the temp profile through the scrubber.

    The way the temperatures are used you will find the front once the scrubber has settled down, this only takes a few mins.

    Don't forget this is a rough guide to the scrubbers health/use.

    The scrubber does not uniformly warm up, the active area is considerably hotter than the bit in front and the bit behind.

    You can only see this with quite a few sensors I used 10 over 8 inches, the stick was longer than the stack it went in diagonally (slightly) .

    You also don't need to display it as a graph, it could be a number 0-9 , 0 empty 9 full, or a character or two four I's " IIII " full - " " empty.

    As I said you don't need to know the exact temp its the difference between them that's the important thing.

    With the digital sensors I think you have to convert the data that the sensor gives to make sense of it, but if it just gives data, higher the number the hotter, then you could use that.

    The sensors could be got from Dallas Maxim, as samples....... Free!! You have to register.

    Sensors outside the scrubber?? might not work, you would may get a cold reading or garbage as the cold water would dramatically alter the temperature, ad the difference would be far smaller and harder to detect, bigger errors, minimum I would have thought would be to bond them onto the canister.
    Last edited by bubbleless2004; 22nd October 2009 at 17:37.

  8. #28
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    Re: DIY temp stick.

    With one sensor for ambient, (take ambient to mean a point of reference that isn't affected by the scrubber temp) you can use that for a baseline of the vertical graphs of each sensor. If the scrubber warmed up, say 20 degrees, you'd see the same height graph, regardless of whether the water was 80 or 40 degrees. By always looking at the temp delta, you maintain a common point of reference on every dive from start to finish. Additionally, the displayed range could be much less yielding better resolution.


    But as they say, YMMV


    Darlene

  9. #29
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    Re: DIY temp stick.

    If you measure the temperature in the scrubber, you can still make it go either way.
    1
    An accurate display of the real temperatures that are in the stack, with a complete graphics display to tell you the data, you could have all the separate temps displayed so you can judge whats going on right down to a tenth of a degree.
    2
    Graphical display similar to Steegles original, where each sensor is represented by a bar graph element.
    You still wouldn't need ambient as you could do temp difference lowist being at zero on the graph.
    3
    A representation, like the inspiration, 4 bars full no bars empty.

    I have done 1 and 3

    1 to get an idea whether it worked and to get an idea of ho to make 3 work as it was part of my RB controller display and didn't want all the display for the temp stick. I used a digit 9-0 to represent where the front was.

    I found the stick today , 10 18B20 TO92's mounted on pcb at about 1/2 inch appart, covered in epoxy putty and lacquer.

    I wrote the code in pic basic plus.(compiler)

    First I wrote the code to display the id numbers of the sensors, then the code for taking the temp.

    used 16x4 display and a 18f452 @4 mhz

  10. #30
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    Re: DIY temp stick.

    If the water is 5C and the hottest part of the scrubber is 30C and the coldest part is 25C then it will be hard to see the temp range of the scrubber on little bar graphs. I am just guesstimating some numbers.

    If you ignore ambient then you only have to handle the smaller temp range inside the canister.

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