Bad temperature reading between 0oC and -0.5oC

Question

Bad temperature reading between 0oC and -0.5oC

chris1howell opened this issue 5 years ago · comments

Hi, I have seen a problem with the OpenEVSE (firmware 5.0.1) with Wifi (firmware 2.8.1) when reporting temperature of -0.25oC. You can see from the attached picture of data logged to emoncms that there is systematically -256oC reading when the temperature crosses near 0oC. I see also the same from the OpenEVSE web page as you can see from two pictures taken a couple of seconds apart.

I've looked at the code here: https://github.com/OpenEVSE/open_evse/blob/stable/firmware/open_evse/open_evse.ino and it looks to me that the DS3231 detection mechanism at line 330 is the problem. The value of 0x3FF is a valid value of -0.25oC and does not indicates that the chip is not there. The I2C address ACK/NACK should be used for that purpose. Also, a valid check on the data would be a non-zero value in bits 0 to 5 of register 0x12, but that must be checked before shifting the byte and losing those bits of course.
Another remark also regarding this code section. From the DS3231 datasheet, it is recommended to check the BSY bit before starting a conversion with the CONV bit and waiting for both bits to be cleared before reading the temperature.

thanks a lot,
Jean-Pierre Lefebvre

lincomatic · Answer 1 · Mon Dec 16 2019 11:44:33 GMT+0800 (China Standard Time)

this sounds pretty serious.. does the guy who made the suggestions have some code i can merge? it would save me a lot of time not having to read the spec sheet and re-writing the code. i didn't write the original functions

Craig Kirkpatrick · Answer 2 · Tue Dec 17 2019 08:25:00 GMT+0800 (China Standard Time)

I’d like to fix this. The code change could take a few minutes. But I want to do it right by first re-creating the condition (freezing temperature) and then test the fix the same way. I also need to study if it potentially creates any unforeseen consequences. I have some time to work on this next week when I’m on vacation from work. I see that I really need to setup Arduino 1.6.15 instead of 1.8.1 to build OpenEVSE so I’ll take care to do that correctly. Best Wishes, Craig K.

On Dec 15, 2019, at 7:44 PM, lincomatic ***@***.***> wrote:

this sounds pretty serious.. does the guy who made the suggestions have some code i can merge? it would save me a lot of time not having to read the spec sheet and re-writing the code. i didn't write the original functions — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub, or unsubscribe.

lincomatic · Answer 3 · Wed Dec 18 2019 02:38:04 GMT+0800 (China Standard Time)

Wow, glad to see that you're alive & well, @craigk46 . I was worried, since I hadn't heard from you in so long. You don't have to change your Arduino UI.. just go into the Tools->Board Manager, and you can pick which version of the AVR toolchain you want to use.
Thanks for the help.

Craig Kirkpatrick · Answer 4 · Mon Dec 23 2019 08:05:23 GMT+0800 (China Standard Time)

I made the fix and handled it is as a commit to open_evse.ino. I'm a bit rusty with GitHub so let me know if I did things correctly vs doing a pull request.