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I am a software engineer and I don't have much experience with analog electronics.

I am doing a project of weight measurement using HX711 weighing sensor.

This is a rough schematic of my circuit:

enter image description here

I am trying to measure various weights. As I increase the load cell capacity the fluctuations seem to increase as well. For load cells of 1 ton and more the fluctions increase tremendously.

I have interfaced the HX711 with a Raspberry Pi using this library Tatobari-hx711.

I tried averaging that is given in this library. That doesn't seem to work.

I also read that the rxcitation voltage to the load cell through the HX711 is noisy so I am powering the load cell from the SMPS itself.

Questions

  1. Is there a simple way to reduce fluctions? What can I try?
  2. What can be done in software to reduce noise?
  3. If the output of load cells is same (0-20mv) why does this issue arise? Is it due to the multiplication factor? Lower range load cells work fine. Is it due to stable first bits of the ADC output?
  4. I read somewhere that the fluctuations can be reduced using some hardware peripherals like resistors. How does that work?
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  • \$\begingroup\$ Why don't you have the EXT+ and EXT- connected? Are you using a pcb that you made yourself, or something like the Sparkfun HX711 board? \$\endgroup\$
    – JRE
    Jan 22, 2017 at 18:20
  • \$\begingroup\$ @JRE if I connect Ext+ and Ext- i get more fluctuations , yes i am using a pcb that ive made .its simply HX711 and some connectors and i've also added a ground layer to PCB. \$\endgroup\$ Jan 22, 2017 at 18:36

2 Answers 2

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I experimented this fairly extensively as a mOhm meter set-up here: https://dannyelectronics.wordpress.com/2015/10/25/a-hx711-based-milliohm-meter/

1) Is there a simple way to reduce fluctions ? What can I try ?

you can try filtering, either in hardware or software. or using a different adc.

2)what can be done in software to reduce noise ?

filtering.

3)if the output of load cells is same (0-20mv) why does this issue arise ? is it due to multiplication factor ? lower range load cells work fine ..is it due to stable first bits of ADC output ?

not sure what you meant by "this issue". noise is inevitable, especially for high resolution adc. sometimes that noise can be a very useful feature in some applications.

4)I read somewhere that fluctions can be reduced using some hardware peripherals like resistors . how to do it ?

in some applications, yes. cannot see how resistors alone can help here.

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I had a similar issue.

I was reading the HX711 using an ESP32. Reducing its speed to match the HX711 solved the problem.

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