HX711 load cell signal and calibration calculator
Enter the load cell’s datasheet figures to see how much of the HX711’s input window the signal uses, how fine each step is, and how large the converter’s own noise is in grams. Then convert raw readings to grams with a two-point calibration.
1. Signal budget
2. Two-point calibration
Read the raw value with nothing on the scale, then with a known mass, then convert any later reading.
How the numbers are worked out
Full-scale signal (mV) is sensitivity (mV/V) multiplied by excitation (V), which is the arithmetic a load-cell vendor’s datasheet guide uses. The HX711 input windows are ±20 mV at gain 128, ±40 mV at gain 64 and ±80 mV on channel B at gain 32, and the datasheet gives input noise of 50 nV rms at 10 samples/s and 90 nV rms at 80 samples/s for gain 128. One step of the 24-bit converter is the full window (twice the plus-or-minus figure) divided by 224. Noise in grams is the rms noise divided by the signal per gram; real builds add wiring, supply and temperature effects on top, so treat it as a floor. Noise figures are shown only for gain 128, the case the datasheet values cover. Background and sources: HX711 load cell scale calibration, noise and temperature.