QWIIC NAU7802 Scale - Measurement changing when connected to computer vs adapter powered

Sensors Force & Weight
1

Hi, I am seeing a strange issue with the QWIIC NAU7802 scale. When my Arduino Nano is still connected to the computer after uploading the code, the Nextion display shows a scale reading of 15lbs correctly. As soon as I unplug the USB and let the Arduino be powered by a 12V adapter, the reading shows 13.2lbs instead of 15lbs, not sure why that value. I can’t imagine it being an issue with the Nextion display or the Arduino. The QWIIC NAU7802 is powered by the 3.3V pin of the Arduino Nano. Should I move it 5V?

Has anyone experienced an issue like this with their QWIIC NAU7802 scale?

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char buffer[10];

float wt = myScale.getWeight();

dtostrf(wt, 3, 1, buffer);

HMISerial.print(“txtWeight.txt=”);

HMISerial.print(“"”);

HMISerial.print(buffer);

HMISerial.print(“"”);

HMISerial.write(0xff);

HMISerial.write(0xff);

HMISerial.write(0xff);

Serial.print(“END”);

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2

Does the zero point shift down as well? In other words, if you remove the weight after switching to the adapter, does the scale read -1.8 lbs?

3

No, it simply goes back to zero. As you can see in the code snippet in my post above, all I am doing is taking the weight into a float variable, converting to a string, and sending it off to the Nextion display. The weight was showing correctly with an HX711 but due to soldering/loose connectivity issues, I switched to QWIIC. I am guessing this may have to do with voltage supply perhaps? With the Arduino wired to the USB, it gets 5V. Then I unplug the USB and power the Arduino with a 12V adapter and then the weight reading drops to the seemingly arbitrary value of ~13lbs from 15lbs. :frowning:

I do have a spare Arduino Nano. I’ll try it tonight and see if the issue was with a faulty Nano.

4

Is it a real Nano or a clone? Most of the regulators on the clones do not handle +12V or barely handles it. I could see an issue where the supply voltage to the HX711 is dropping (and maybe poorly regulated) if its input is been stressed because of the +12V input to an nano clone.

5

It’s a clone. I’ll try to get my hands on an original and see if that makes a difference. Thanks.

6

Unfortunately getting an authentic Arduino Nano made no difference. As soon as I remove the USB cord (that was connecting PC to Nano) while keeping the 12V adapter plugged into the Nano, my 15lb correct reading drops to an incorrect lower value ranging from 13.1lbs to 13.9lbs. Each time I turn off the adapter and turn on, I get a new value around ~13lbs.

I am suspecting I may have a faulty NAU7802. Can anyone please let me know if there are any other options to pursue before I buy another NAU7802? Alternatively, please let me know if there are any HX711 chips that are pre-soldered with headers/clips. Thanks.

7

I sort of missed the "Nextion display " mention the first time. Don’t those things draw like 200mA or more? Do you have a normal LCD you can use? Or what happens if you talk via RS232 to the PC instead of trying to use the display (i.e. so you are not hooking up the power-hungry display).

For HX711 there is the SFE offering: https://www.sparkfun.com/products/13879

I do like the following offering from Amazon, but that is because it comes with a platform that suits my needs to a tee.

https://www.amazon.com/MakerHawk-Conver … 782&sr=8-1

8

I finally gave up and used an old HX711 along with 4-pin terminal blocks and overcame my phobia of soldering, so now I have strong wire connections screwed in to the HX711/terminal blocks and also getting my correct weight reading of 15lbs test weight with and without the USB connection to the PC. The 12V power adapter is 10A so I can’t imagine any lack of juice flowing in.

Thank you nonetheless for your feedback.