Nitrox/Trimix & CO analyzer

[Miyaru]

You mean that I should calibrate on 2 mixes ( air and 100% o2 for example ), right?

Yes, and that's in the start of the thread and in the code.
A cell is not linear in real life and degrades over time. The software should be able to rectify that. Unless you consider a few percentages of miscalculation acceptable.
Linear drift is explained in the CCR topics.

 

[Sneruh]

Such a fantastic thread! I have a quick question: The ST7789 display shown looks great. My electronics parts supplier has one but i note that it says that their product has no chip select so cannot connect with other SPI devices. Can I still use it using Miyaru's build? Thank you.

 

[Miyaru]

Such a fantastic thread! I have a quick question: The ST7789 display shown looks great. My electronics parts supplier has one but i note that it says that their product has no chip select so cannot connect with other SPI devices. Can I still use it using Miyaru's build? Thank you.

As long as you don't use the SPI bus for anything else, it's no issue. The AD converters use the I2C bus, so no issue.

 

[Lidiano]

I am trying but in the various tests that I am trying I have seen that the cell that measures He, after a few minutes that is on becomes unstable, let me explain better there is no passage of helium but it begins to mark as there was helium (2 , 5%, 5% ec ..) with the potentiometer reset to 0% but it does not stand still, what can I do, you have some ideas, thank you very much

 

[lidas123]

Hi everyone, I am new to this forum, I have been drawn to this project, I am trying it but I am stuck on the CO sensor, I cannot see variations when I blow, do you know please help me, what can I do to understand if the sensor is working

 

[Wibble]

keeping in mind too that these galvanic oxygen sensors are typically spec'd accuracy at +/-1% of full scale or even +/-2%. In practice they seem better and more repeatable than that, but we perhaps put too much trust in them.

Thought: most rebreather divers have three or more of them on their units which get regularly switched out. Those sensors have plenty of life left in them at ambient pressure; just don't know how worn out they are. So why not have two or three on this unit?

 

[Miyaru]

Hi everyone, I am new to this forum, I have been drawn to this project, I am trying it but I am stuck on the CO sensor, I cannot see variations when I blow, do you know please help me, what can I do to understand if the sensor is working

Connect the sensor to a power supply (1st and 2nd pin) and use a voltmeter on the output (6th pin). It should show you a stable voltage of 0.4V. When you blow some smoke over the sensor, you should see the voltage rise to about 2V. That's how you check if the sensor works.

 

[Miyaru]

Thought: most rebreather divers have three or more of them on their units which get regularly switched out. Those sensors have plenty of life left in them at ambient pressure; just don't know how worn out they are. So why not have two or three on this unit?

If you already have a bunch of O2 sensors on the shelf, which are still good to go, adding 2 sensors can be done:

• add another ads1115 (on a different address)
• connect the 2 sensors to this new A/D converter
• modify the function that reads 3 sensors instead of one
• modify the calibration from one to three sensors.

On the other hand, is it worth it to use the CCR mechanism of cell elimination?

 

[lidas123]

Connect the sensor to a power supply (1st and 2nd pin) and use a voltmeter on the output (6th pin). It should show you a stable voltage of 0.4V. When you blow some smoke over the sensor, you should see the voltage rise to about 2V. That's how you check if the sensor works.

but if I just blow it should change or I absolutely have to put smoke, or I can try something else

 

[Miyaru]

but if I just blow it should change or I absolutely have to put smoke, or I can try something else

Well, it's a CO sensor. Your exhaled breath contains a tiny amount of CO, probably not enough to see a milivoltage difference on a multimeter. So testing with carbonmonoxide is easier.
CO is created with lots of burning reactions: wood, paper, coal, cigarettes, cigars, ....
Just burn something that creates a tiny bit of smoke.