SparkFun Forums

[joe5939]

New to coding and really new to Artemis.

Is it possible to get the Artemis Open Log to read loads in pos and neg directions?

I can't get negative values from my load cell (SEN-14727 100gm bar and Qwiic Scale SEN-15242 ) and my Artemis Open Log DEV-16832. I can cheat it by adding weight during the zeroing step of the calibration and removing it when prompted to add it. In my case, zero load had a 260 output. Less than 260 was a load in one direction and more than 260 was a load in the opposite. I'd rather just carry a sign.

Is the source of my problem from line 190 on this code and how do I change that if possible:
https://github.com/sparkfun/OpenLog_Art ... ensors.ino

As noob I can only understand the comment, not the code.

[TS-Russell]

Thanks for reaching out to us on this.

The hookup guide for the NAU7802 https://learn.sparkfun.com/tutorials/qw ... d-overview covers a few different scenarios you might want to set-up (it sounds like you want to adjust the zero offset and allow negative values, which requires using the functions covered in the guide)

Hope this helps, and happy sparking!

[joe5939]

Thank you. I ran across that page weeks ago and forgot about it. Though I am still a bit confused. I see a variable(?) listed on that page that I assume I need to change to "allowNegativeWeights = true". If that is the case where do I do that? Do I just type it into OLA setttings file? I don't see a prompt for it in the terminal window.

From tutorial:
float getWeight(bool allowNegativeWeights = false) - Once you've set zero offset and cal factor, you can ask the library to do the calculations for you. By default, negative weights will be returned as 0.

[PaulZC]

Hi Joe5939,
The OLA does not currently support negative weights with the NAU7802. We would need to add that as a new feature to the code. Please feel free to raise it as a [Feature Request] issue on the OLA GitHub repo and we will get to it if we can:
https://github.com/sparkfun/OpenLog_Artemis/issues
Best wishes,
Paul

[joe5939]

Thanks. Good not to be spinning my wheels.

[badepalle]

Hey,

Like Joe5939, I would like to be able to record negative values with a NAU7802.
Before I submit a request, did anything change since you had this discussion?

Thanks,

Baptiste

[TS-Russell]

I don't believe it has changed (I looked through the closed issues and didn't see one); feel free to open one regarding this

[PaulZC]

Hi,

getWeight has a parameter that enables / allows negative weights:

https://github.com/sparkfun/SparkFun_Qw ... ary.h#L183

getWeight(true); will get you going.

All the best,
Paul

[PaulZC]

Ah. Regarding negative weights on the OLA - those are (still) currently not supported. It looks like a Feature Request issue was never opened. If you’re wanting to measure negative weights on OLA, please go ahead and open a Feature Request.

Best wishes,
Paul

[badepalle]

Thanks TS-Russel and Paul for the responses.
I compiled the code with getWeight(true) in the Sensor.ino file and it seems to be working fine.

Best,

Baptiste

[gkadokura]

I created an issue here https://github.com/sparkfun/OpenLog_Artemis/issues/176