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Topic: HX711 drift porblem (Read 365 times) previous topic - next topic

EricEEEE

Hi,
I'm using an HX711 amplifier with  50Kg 4 load cells, like this:
https://learn.sparkfun.com/tutorials/load-cell-amplifier-hx711-breakout-hookup-guide

My problem is that the reads is drifting, even with no load on scale.

Board: ESP8266 e-12
Power source: MB102 Breadboard Power Supply Module 3.3V 5V For Arduino

I'm using Bogde's Hx711 library (https://github.com/bogde/HX711).
The code is very basic:

void loop() {
  if(scale.is_ready()){
   Serial.print(",");
  Serial.print(scale.read_average()); 
  }else{
     Serial.println("scale not ready"); 
  }

  delay(1000);
}

And the output is keep drifting up (see attachment).

Any ideas what cause the drift? and how do I fix it?

Thanks!

Eric

MarkT

Are all 4 loadcells at the same temperature?  This could be thermal drift.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

EricEEEE

Yes, all 4 are on the same surface (just a bathroom scale), with the same temperature.

MarkT

Battery voltage dropping?
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

EricEEEE

No. Power is fixed (using  MB102 Breadboard Power Supply Module 3.3).

This is the plot for about an hour read, with 20Kg on.
I'm a newbie with this kind of things, but why do the the raw reads has to drifts so much (even if it just 4% out of 200Kg)?

For my understanding , if all parameters are fixed - load, power source, temperature, code side - isn't the read suppose to be basically the same over time (lets say an hour)?


Wawa

The HX711 needs a 5volt supply for the 4.3volt excitation voltage regulator to work.
Excitation voltage (and load cell output) will be unstable on 3.3volt.

The ESP8266 might need 3.3volt logic. Not sure. Never used one.

If so, then you need level shifters between HX711 and ESP.
Leo..

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