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Hello I am a software engineer and I dont have much experience of analog electronics.

I am doing a project of weight measurement using HX711 weighing sensor . below shown 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 fulctuations seems to increase as well . For load cells of 1 ton and more the fluctions increase tremendously . I have interfaced Hx711 with raspberry pi using this library Tatobari-hx711. i tried averaging that is given in this library ,that too doesnt seem to work. I also read that the Excitation vtg to load cell thru HX711 is noisy so i am powering the loadcell from 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 multiplication factor ? lower range load cells work fine ..is it due to stable first bits of ADC output ?

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

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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 '17 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\$ – Gaurang Deshpande Jan 22 '17 at 18:36
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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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