SparkFun Forums

[elliottaj]

Hi There,

I am building a 'rig' to log readings from 5x load cells as fast as possible. I went with I2C Qwiic Scale sensors to use with my OpenLog Artemis board but discovered the sensors all appear to have the same fixed I2C address, which is preventing me from properly reading them on I2C bus.

I've since purchased a Qwiic Mux board which I've gotten to work on my Arduino Uno, but I wanted to see if there is any way to use Qwiic Mux with OpenLog Artemis somehow? I've included materials, photo of current setup and example Arduino code below.

Thanks in advance for your help!
A.J.

Bill of Materials
- 5x Load Cell - 200kg, Disc (TAS606): https://www.sparkfun.com/products/13332
- 5x SparkFun Qwiic Scale (NAU7802) I2C Sensors: https://www.sparkfun.com/products/15242
- 1x SparkFun Qwiic Mux Breakout (TCA9548A): https://www.sparkfun.com/products/14685
- 1x OpenLog Artemis: https://www.sparkfun.com/products/15846

[YellowDog]

Hey A.J.

Artemis OpenLog isn't going to know what to do with the Qwiic Mux or what ports sensors are connected too.
I think you're stuck using the Uno to poll the sensors and then having the Uno send log data onto the Artemis OpenLog for logging.

[liquid.soulder]

You probably won't be able to use the Artemis OpenLog directly (that is without software changes) but I think it will be possible. You should, however, be able to make this work with a small amount of customization.

You can find the Artemis OpenLog firmware here: https://github.com/sparkfun/OpenLog_Art ... og_Artemis

You should be able to modify that a little, recompile, and upload it to the AOL. Since we do not have a variant for the Artemis OpenLog in Arduino I would assume that you should use the RedBoard Artemis ATP board definition when compiling. The engineer in charge, Nate, would know for sure - I'll check with him.

Once you have your firmware image you could (probably) either use the bootloader that is built into Arduino or you could use the Artemis Firmware Uploader GUI (https://github.com/sparkfun/Artemis-Firmware-Upload-GUI) on Windows.

The modifications to the code would probably be simple enough. I imagine you would just need to insert the proper instructions to use the mux in whatever code exists to poll sensors. You would also need to make sure that you repeat operations for each sensor that you have connected.

Hope this works well for you!

[sparky]

I was quietly hoping no one would want mux capabilities on the OLA, and then here you've given me a perfect good application: lots of scales. Ya, maybe it's time to figure it out.

Owen is correct, if you're savvy with Arduino, reprogramming OLA is pretty straight forward. There's a ton of example sketches (test sketches) within the OLA repo to get you started as well.

In the mean time, I'll open an issue on the OLA repo and see if I come up with an easy user experience for setting up and configuring multiple devices through a mux.

[joe5939]

I would find the MUX functionality useful if it came pre-loaded on the Artemis Open Log. In the meantime, if I don't need to be exact with my load could I connect two load cells in parallel (or series?) to get an average load?

[PaulZC]

Hi @joe5939,
This is quite an old thread. We added mux support on the OpenLog Artemis some time ago. Connecting multiple NAU7802's is one of our standard tests. The only thing you can not do is store the calibration values for each scale. You can calibrate each scale individually through the Qwiic Devices menu, but the calibration is lost each time the power is lost or if the Artemis resets.
Best wishes,
Paul

[brow]

In the meantime, if I don't need to be exact with my load could I connect two load cells in parallel (or series?) to get an average load?

As long as the load cells are ...
1. the same capacity and
2. close in output (a given load and excitation outputs the same millivolt signal) and
3. they're mounted in such a way that the load bears in the proper orientation
... you can put the cells in parallel.