Yorkshire Geek
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Joined: Tue Jan 21, 2020 8:01 pm

HX711 odd readings

Tue Jan 21, 2020 8:11 pm

Ok, this is puzzling me. I've been playing with load cells for the first time, I have 4 cells connected through an HX711 as is apparently the customary practice. If I apply a load the reading from the HX711 changes so all appears well but I have two oddities I don't quite understand.

1. The readings are negative rather than positive, Google didn't give me a clear answer on whether that's expected or not.

2. The output with just the load of the empty weighing platform is either around -130k or around twice that with a small number of random data points outside that range. I captured a reading every second for an hour or so and this is what the trace looks like. There's two clear lines, one at X and one at x*2. What could cause that? If it were random noise I'd blame my soldering but this is clearly not random.

Any assistance gratefully received.
82326664_2787277321355765_5083762285000785920_n.jpg
82326664_2787277321355765_5083762285000785920_n.jpg (29.65 KiB) Viewed 360 times

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joan
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Re: HX711 odd readings

Tue Jan 21, 2020 9:31 pm

It's negative because you have two wires swapped. I wouldn't worry about that, it's simplest to just account for that in the software you are using.

Yorkshire Geek
Posts: 3
Joined: Tue Jan 21, 2020 8:01 pm

Re: HX711 odd readings

Tue Jan 21, 2020 9:39 pm

Yeah, that one I can account for easily enough, ta for the explanation though. It's the second one I'm really mystified by. I can account for that in software too if I have to but would like to understand rather than just bodging it to discard the x*2 readings.

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joan
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Re: HX711 odd readings

Tue Jan 21, 2020 10:13 pm

What software are you using?

Yorkshire Geek
Posts: 3
Joined: Tue Jan 21, 2020 8:01 pm

Re: HX711 odd readings

Tue Jan 21, 2020 10:26 pm

This library and Python 3. Doing nothing fancy, literally taking the raw value and saving ir.

https://pypi.org/project/hx711/

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joan
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Joined: Thu Jul 05, 2012 5:09 pm
Location: UK

Re: HX711 odd readings

Tue Jan 21, 2020 10:39 pm


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