Interfacing Loadcell and Sparkfun's Qwiic Scale NAU7802 with ESP32

Question

I am currently working on a IOT Project in which I am trying to interface Loadcell and Sparkfun's Qwiic Scale NAU7802 so that I can read Weight and Show it on Seven Segment Display.

For this I connected Following Pins :-

ESP32 Pin	Qwiic Scale Pin
36 (GPIO 22)	SCL
33 (GPIO 21)	SDA
2 (3V3)	3V3
38 (GND)	GND

First I Calibrated my Loadcell with 5 Kg Weight. After that I tried Fetching Weight From Qwiic Scale And Showing it on Seven Segment Display simultaneously using threading.
After Calibrating I placed same 5 kg weight on Loadcell to check readings, But I am getiing variable readings. I tried this loop of calibration and checking the output many many times but my output is still variable. Readings are very Fluctuating, around 50grams for 5kg.

Code I used >>

scale = QwiicScale() # Created Qwiic Scale Object
s = SevenSegment(scale) # Created Seven Segment Object

# Calibration code  
OF = scale.getZeroOffsetFromQwiic() # Get Offset From Loadcell without putting any weight
# Place Known Weight
KnownWeight = float(input('Enter Known Weight : ')) # Take input known Weight
cal = scale.getCalibrationFactorFromQwiic(KnownWeight) # Calculate Calibration Factor

#Created Thread for showing weight on Seven Segment Display
SevenSegmentThread = Thread(target=s.ShowOnSevenSegment)
SevenSegmentThread.start() #ran that thread here

# Loop continuously running to get weight and setting it to Seven Segment
while KeyboardInterrupt:
    Weight = float(scale.getWeightFromQwiicScale())
    print(Weight)
    Weight = str(int(Weight*1000))
    s.SetWeight(''.join(reversed(Weight)))

My Output without using threading >

Why does my output is variable, If I implement threading ?

Any Suggestion or help is much appreciated .....
Thanks in Advance...

Seems to match what's shown on [the official guide](https://learn.sparkfun.com/tutorials/qwiic-scale-hookup-guide#examples), where it varies from 4.23 to 4.28 — gre_gor, Jan 11 '22 at 14:31

score 0 · Answer 1 · answered Jan 11 '22 at 16:21

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That's quite normal. Load cells create tiny changes in voltage, which get amplified by the chip measuring the H-bridge output. The amplification creates noise which gives you a slightly different reading each time. A fluctuation of less than 0.5% is a rather clean result, by the way. Welcome to measuring things in the real world.

Anyway, round it to about 1% and you're done. The measurement accuracy of cheap bathroom scale load cells won't give you much more resolution anyway.

answered Jan 11 '22 at 16:21

Tarmo

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Firstly, Thanks for Reply. but I am not using any cheap Bathroom Scale , I bought it from Industrial Loadcell Reseller having a range of 200 Kg. And it does gives me accurate reading if I remove every thread in ESP32. What my question here is, after implementing threading why is it giving me Variable readings ? – BoGTx0705 Jan 17 '22 at 05:59
The operation of reading the result could be sensitive to timing. Which sounds like a bit of a bummer, because you'd probably need a much more complex solution than a synchronous Python driver to complete the operation in an uninterrupted manner. – Tarmo Jan 17 '22 at 14:32

score 0 · Answer 2 · answered Mar 19 '23 at 11:31

I came across this conversation while researching a different problem. I am going to suggest that the noise you see during multi-threading is due to small fluctuations in the supply voltage on the i2c bus to the QwiicScale board which, in turn, would cause a similar variation in V+ to the load cell. Thread switching on your ESP32 may cause a load condition that pushes the limits of the on-board voltage regulator. Digital circuits don't care about a 1% voltage swing but analog circuits would be quite sensitive to that! Try adding a capacitor to the load cell supply voltage line to see if that improves your results.

Interfacing Loadcell and Sparkfun's Qwiic Scale NAU7802 with ESP32

2 Answers2