Internal pH calibration

[jonri]

I've been happily using my robo-tank with reef-pi for a few months and decided it was time to add a pH probe.  Pulling bits of information from a few different threads, I've pieced together that it might be possible to calibrate a pH probe directly using a script rather than calibrating inside of reef-pi.

1. Is this actually possible to do?
2. Is there any documentation on how to do it?  I found the script that communicates with the pH board but didn't see a full command reference.

[Rob F]

Hi Jonri, unfortunately with what you have that can't be done. Originally I had that running on the attiny85 but I was having issues with the eeprom and sometimes program memory corrupting. With calibration running the program memory was 97% full so for a while I was thinking the problem was due to that so I removed it and brought it down to 32% but at the same time I also discovered this could happen from low voltage which the attiny85 has a fuse setting so processor shuts off if low voltage is detected. The problem is fixed and now I don't think it was due to full memory but I haven't added it back. So yeah you need to use reef-pi calibration.

[jonri]

Thanks for the detailed response! If you do bring it back someday and it's just a matter of reprogramming the attiny85, I'd be happy to test it out.

I've been thinking about additional ways to record historical data, but capturing calibrated data through reef-pi's mqtt integration will be just fine.

[Rob F]

Yeah it just needs repogramming, this is a tutorial on how to do it if it's your thing, I would be happy to send the program.

https://learn.sparkfun.com/tutorials/tin...1536322909

I like calibration on the circuit but now that a lot of controllers out don't have that feature I'm stuck to using the software approach which is nice if I discover something can be added or improved. For example the full program also calculates the scope of the probe which reflects it's overall condition but I'm not certain the math is correct and may need tweaking. I have been thinking about programming them with calibration but haven't yet, even though I won't be using it I think it's still nice to have especially for the standalone version.

[jonri]

Sure, I'll give it a shot. Just be sure to give me the original program as well in case i want to switch back ;-) I've actually used the attiny85 before, it's a handy little chip for simple things.

I have a Seneye I moved over to my QT, so it's easy for me to move it back and check things out if the numbers look suspect.

[Rob F]

Nice, yeah they are great, for larger things I go to the atmega32u4. I wish I was better at programming to get into the STM chips as they are low cost and powerful.

Let me know how close the numbers are. I'll send the files to your email.