DIY Nitrox Analyzer (Arduino based)

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ScubaBunga

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Well ran last night and again today. It does adjust less than 2PPM over an hour but doesn’t change quickly. As to how fast it reacts on a tank, I don’t have one with CO to test, but running while I solder near it, it reacts pretty quick. The sensor is wired with a resistor as the spec calibration is in nanoamps. I started here. Then, like my O2 analyzer, I used an ads1115 and an arduino nano.
At this point even if it is not accurate, I know it reacts. A normal tank shouldn’t show much or nothing. If I get a reading of 5+ PPM, it will be worth questioning the tank. Hopefully, more testing and tweaking over the summer, if the virus lets me get out to dive this year.
 

Miyaru

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Making progress.....
analyzer0.jpg analyzer1.jpg analyzer2.jpg
Wheatstone bridge with the MD62 sensor is surprisingly fast when some helium flows over it.
Programming works fine, next job is a small tube with air in/out, sensors built into it.
 

Miyaru

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IMG-20200427-WA0019.jpeg

First version ready.

Several topics on SB helped me a lot with in-depth information about the theoretical versus real-life behavior of the O2 cells.
I added 100% O2 calibration and 100% He calibration.

In 100% He, after >1 minute the O2 cell still produces 0.25mV. I compared this with the cell from my analog nitrox analyzer - same behavior.

Since I don't have any old cells (I knew I should not have trashed them), could somebody do some measurements with old cells (2 years)? Voltage in air / 100% O2 / 0% O2.
 

James_SGP

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Guys, can someone help...

I`m trying to build this, i`m using an Arduino with an ADS1118 ADC (16bit ADC). I have the O2 cell connected to A0 and A1 and I`m measuring in differential mode, but I'm getting zero mV?
The cell is supposed to be functional....

James
 
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Pao

Pao

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Guys, can someone help...

I`m trying to build this, i`m using an Arduino with an ADS1118 ADC (16bit ADC). I have the O2 cell connected to A0 and A1 and I`m measuring in differential mode, but I'm getting zero mV?
The cell is supposed to be functional....

James

Do you have a multimeter? Can you check the cell? What library does the ADS1118 use? There are specific configurations peculiar to what you are trying to do. The ADC does not output a voltage but "talks" to the MCU via the I2C bus.

You can also feed the ADC a "dummy" voltage using a pot as a divider.
 
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Pao

Pao

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Guys, can someone help...

I`m trying to build this, i`m using an Arduino with an ADS1118 ADC (16bit ADC). I have the O2 cell connected to A0 and A1 and I`m measuring in differential mode, but I'm getting zero mV?
The cell is supposed to be functional....

James

I found a library on GitHub. It looks like the parameters are different and it uses the SPI instead of the I2C bus. Sampling is also different. You will have to re-write the code and change the wiring connections for that.
 

James_SGP

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Do you have a multimeter? Can you check the cell? What library does the ADS1118 use? There are specific configurations peculiar to what you are trying to do. The ADC does not output a voltage but "talks" to the MCU via the I2C bus.

You can also feed the ADC a "dummy" voltage using a pot as a divider.

Thanks, but chatting with Miyaru it would appear that me cell is dead (zero mV output). Interestingly, I just took it apart and there is about 200mV coming from the wires of the galvanic cell. So i`lll try n figure out if its an electronic component problem of the cell.
 
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James_SGP

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Yes, I`m using the ADS1118 library with my own code.
 
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Pao

Pao

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Thanks, but chatting with Miyaru it would appear that me cell is dead (zero mV output). Interestingly, I just took it apart and there is about 200mV coming from the wires of the galvanic cell. So i`lll try n figure out if its an electronic component problem of the cell.

200 mV is too high for an O2 cell.
 
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