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DIY Touch Screen Trimix Analyser

Discussion in 'Making your own Gear' started by stevetto, Feb 10, 2021.

  1. stevetto

    stevetto Registered


    I have used this analyser for a few times but I have never noticed this functionality. A friend of mine has it.
    But anyway, MOD display is only a confortable function (mine shows the calculated values for 1.2, 1.4 and 1.6 pO2 without pressing any button) and more usefule for novice divers.
    For tec and experienced divers it is not neccessary, especially if standard gases are used.
  2. Jarek Andrzejewski

    Jarek Andrzejewski Registered

    # of Dives: 100 - 199
    Location: Poland
    GOX-100T (T for "tauchen", which means "diving" in German) has only this option, AFAIK.
  3. stevetto

    stevetto Registered

  4. JahJahwarrior

    JahJahwarrior Solo Diver

    # of Dives: 500 - 999
    Location: West Palm Beach, Fl
    The CO sensor used by Cootwo is the S+4 2ECOH, available in UK.

    It's too bad you don't have 100% HE near you. I don't imagine you have a store like Grainger nearby, or how much it would cost for shipping, but they have calibration bottles of helium which could be used.
  5. stevetto

    stevetto Registered

    Thank you for the info. As I see it is only a sensor without temperature compensation. It would make the design more complicated. And it is non-linear.
    I might try this one later:

    I could buy 100% He from a local gas station but it would cost ~90 USD + tank + shipping.
    It is too much for less than 1 m3 He that I can not use later without having compressor or booster pump at home.
    That is why used balloon gas for the development (~ 30USD with tank).
    For the final calibration only a very small amount of gas would be necessary.
    I will solve it somehow.
  6. stepfen

    stepfen Contributor

    # of Dives: 200 - 499
    Location: Greece
    Getting nicer and nicer. Well done!!

    One question. How do you connect the He sensor to the PCB? I see the connector on the PCB but then how do you attach the wires to the sensor itself? Looking for neat ideas for my project. Cheers
  7. stevetto

    stevetto Registered

    The sensor has a separate pcb and it is soldered on it.
    The small and the main pcb then connected together with wires.
    You can see it above.
  8. Miyaru

    Miyaru Tec Instructor ScubaBoard Sponsor

    # of Dives: 2,500 - 4,999
    Location: below sea level
    That one has the same output and specs as the one that I used. Add another A/D converter to read the 0.4V - 2V output from pin 10 on the sensor. I also found that combining the CO sensor output with O2 or He output doesn't work reliably, so that's another reason for using a 2nd A/D converter.
    The rest is just software.
  9. stevetto

    stevetto Registered

    Have you ever tested how linear the output?
  10. Miyaru

    Miyaru Tec Instructor ScubaBoard Sponsor

    # of Dives: 2,500 - 4,999
    Location: below sea level
    For CO: no
    For He and O2: yes

    The moment I read more than 1 ppm, I won't dive that gas. However, for other applications, a proper calibration would be interesting and that would require a tank of CO.

    I have compared the MD62 sensor output with a DiveSoft analyser, same gas flowing through both analysers. Results were very consistent for the usual trimixes.
    To compare linearity, a setup would be required where one would start with 100% He and then constantly lowering the He content by replacing it with another gas (eg. N2 to eliminate the thermal conductivity of O2).

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