El cheapo analyzer build.

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The 390 ohm resistor seemed to bring the values within a workable range. I moved the potentiometer leads around but nothing changes the backwards nature of it. It seems more like I’m increasing attenuation as you turn to the right? Where these wires land on the R3 spot seems to make no difference. Goofy but I can live with it.

I calibrated in air reasonably and got reading on marked tanks that were close (within what I would say is normal variance). Next I calibrated to an air tank, after letting the sensor sit for a few minutes it certainly dropped a few 10ths of a percent (I’m in southern Louisiana so it’s like 70 and humid) again what I would expect and about what I would guess when looking at the temp/humidity chart analox puts out. So I’m happy with it. Here are some pictures. The box is bigger than needed but accessories can be stored in the lid and it should be splash proof or more when closed.
 

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https://www.shearwater.com/products/swift/

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