SparkFun Forums

[santonio7]

Openlog artemis firmware 1.6 out of box works great (IMU and date-time stamps ) whether LiPo powered or direct USB connected and whether on SD card or on monitor.
When connected to Qwiic Scale (no other I2C devices and via Qwiic only) i get new column of data as expected but all values are "nan" as in "not a number" I presume
I used my Artemis Redboard with Qwiic and load the Arduino library for the Qwiic Scale and I first see negative numbers , so I switch green and white leads from load cell and now get positive numbers that vary appropriately with force applied to load cell. I figure maybe the OL Artemis doesn't know what to do with negative numbers from Qwiic Scale so with much hope, I reconnect to OLA and still see only "nan".
The OLA gathers data at 10 Hz so I do not think this is too fast to get data (?) from the Qwiic Scale - although ultimately I want to gather at 320Hz. I want the date-time stamp for logging (good old RTC on the OLA) and would rather not have to code the Artemis Redboard to print date-time with each force measurement, but if I have to ... well ?
I want to record times of load and no load events for students to observe distance and time in falling and bouncing in gravity (to start!)
thanks

[PaulZC]

Hi Santonio7,
Have you calibrated your NAU7802 sensor?
Please open the serial menu, select the "Configure Attached Devices" menu, select your NAU7802 from the list, select option 2 to calibrate.
Best wishes,
Paul

[santonio7]

Cannot calibrate via OLA - only see "inf" (no load) and "nan" (with load) reported .
Would a cailibration done with the Artemis Red Board Qwiic remain in effect when I hook up with the OLA? This sounds likely since the NAU should be holding the calibration information , right?
thanks

[PaulZC]

Hello Santonio7,
Are you sure you have your scale connected correctly?
The NAU7802 works OK for me. Here is what I see using a "kitchen scale" to weight a 100g weight. The first attachment shows the data in the serial monitor. The second shows the data in the serial plotter. The third shows the calibration process.
There is a hook-up guide here:
https://learn.sparkfun.com/tutorials/qw ... 1583443041
Best wishes,
Paul

[santonio7]

Paul - Thanks for your attention.

all connections from either the OLA or Artemis Redboard to the NAU are with qwiic

I was not able to use the NAU with the OLA (via qwiic) at the beginning , so I brought out my Artemis Redboard qwiic and as noted in my initial message , it was able to log raw values from my 5kg load cell but always negative and, with added weight, the values became more negative. When I switched the white and green wires from the load cell to the NAU , the raw values reported were now positive and increasingly positive with added weight.
No I did not calibrate the NAU while hooked to the Artemis Redboard qwiic, since I do not need calibrated weight. I just need to know if the load cell is at "rest" or "loaded" . Also since I do not get any numerical values when using the OLA with the NAU, I cannot calibrate it. Reviewing your attachments, it is clear that you must have
I can do a Artemis Redboard qwiic calibration once I get a mount for the reference weight .
thanks

[PaulZC]

Hello santonio7,
You can - and must - calibrate the NAU before the OLA will give you any sensible readings. It does not need to be an accurate, absolute calibration. Just a very simple approximate calibration to remove the sensor offset.
Please open the serial menu, select the "Configure Attached Devices" menu, select your NAU7802 from the list, select option 2 to calibrate.
With no load on the load cell, press enter.
Then put a small load on the load cell - it does not matter how much - and press enter.
Now enter a value. It does not matter what value you use. I suggest "100".
Exit the menu.
The NAU will now be 'calibrated' and you should now see values instead of "nan"?
Best wishes,
Paul