In part 1, I’ve explained that all the we really need is a millivoltmeter, but ideally, we’d like to see the oxygen percentage on some kind of display.
There are two way to achieve this. First is by using Ohm’s Law, amplify the voltage (so we have more resolution), add a voltage divider, with a potentiometer as one of the resistor, that’ll be the calibration tool. Expose the sensor to air, turn the knob until the number shows 20.9. This what the El Cheapo from OxyCheq really is.
The second way is by using a micro controller, Arduino if you will. Which is the approach I took, mostly because I have a lot of spare µC. And my main goal after learning that I can DIY the analyzer is to suppress as much cost as possible, just to see how cheap I can go. The comparison is this Analox O2EII Pro Nitrox Analyzer , sold by Master Selam for about US$400, while Leisure Pro has it for $266. The prices for scuba gears is so ridiculous here in Indonesia.
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DIY-ing O₂ analyzer is one of the simplest project you can do, for those of you who’s electronically literate will understand this after taking a look at a sensor’s data sheet. While when we mentioned this to other divers, they’ll say, “you’re making your own analyzer? You’ll die.”
So, I’ll split this into 2 parts. First is this post, I’ll basically just explaining data sheet and how the sensor operates. And I’ll go into the actual build, BOM, source code, etc. in part two. I’ll use my own sensor as an example, it is the cheapest one that checks all the boxes for it to be scuba oxygen analyzer. Let me know if you found anything cheaper 😜
Pictured above is the technical specs from the sensor data sheet. From the data sheet we know that if you expose the sensor to gas, it’ll spit out mV out of the other end. With the only caveat it being in the most ideal conditions, hence the calibration button. As mentioned in there, the numbers will drift over time, and humidity will affect the numbers too.
Let’s use the pic above as example, We know “air” is 20.9% oxygen, so 9mV = 20.9% we use this as the baseline, the calibration value if you will. From that, if we were to expose the sensor to EAN32, it’ll spit out 13.8 mV. 13.8 / 9 * 20.9 = 32.05
That’s it! All you really need is a millivoltmeter really, and you can math it out. But ideally, you’d want a screen that display the actual oxygen percentage to simplify a lot of things. As mentioned, I’ll get into the how to in part 2.