Help Needed: HX711 Raw Value Calculation Issues

Sensors Force & Weight
1

I’m trying to understand how the HX711 works and I’m facing some challenges. I recently conducted tests using a 5 kg load cell and applied standard weights while measuring the voltage across the strain gauge for each weight.

Here’s a summary of my procedure:

Connection of the Load Cell: I connected the wires of the load cell as follows:
Excitation terminals to E+ and E-
Output terminals to A+ and A- of the HX711.

Voltage Measurement: I measured the voltage across the gauge for each applied weight.

Retrieval of Raw Values: I then connected the load cell to the HX711 circuit and retrieved the raw values corresponding to the same weights used previously.

However, when I calculated the raw values using the following formulas, I found values that were very different from those measured:

Amplification Formula:
Vout=Gain×Vin (with Gain = 128)

Analog-to-Digital Conversion Formula:
Raw Value=(Vout/Vin)×(2n−1) (n=24)

Could anyone clarify this discrepancy in results? Does the HX711 use a different method for amplification or signal conversion?

Thank you for your help!

2

Can you please fill in the measured and calculated values that you’re asking about?

3

Connecing a multimeter to the load cell changes the resistance across the load cell and that will skew your readings.

There’s a calibration example sketch, have you run that?

4

Answered here: Help Needed: HX711 Raw Value Calculation Issues - Sensors - Arduino Forum