Comment by jmiskovic
8 days ago
Computing power is crazy cheap and does not help. The perceived slowness is because the taken measurements are averaged over second or so. When you step on the scale your weight shifts around and that affects the measurement by far more than half a kg. Averaging gives you better accuracy and more confidence in the result but it doesn't improve the measurement precision.
The scale precision comes from calibration of the measuring mechanism done on factory line at certain weights. If your specific body weight is far from the weights used in calibration, or too much time passed, then the calibration doesn't help much.
A better microcontroller doesn't help at all. Even a cheapest uC from decades ago is good enough. Better ADC and gauge sensor would help, but even more important is good analog engineering to produce self-correcting circuits with decent noise rejection.
In general this category of products is more for tracking changes in your body weight than getting the precise absolute value. And the body weight changes a lot just from hydration level, so the ±.5kg tolerance is considered good enough.
My fine spice recipe writing scale (20g max, 20k count) consistently over years of me having it keeps it's magnitude calibration of the 10g reference to a single digit count, i.e., comfortably within +-0.1%.
Ofc there's auto-zero on start involved, but translated to a people bathroom scale that'd be "comfortably better than +-100g".
A precise bathroom scale just would want a bit more effort on drift prevention as a sample mass at this scale is rather unwieldy, and critically it'd need a toe-operated button to select that you've finished climbing onto the scale, upon which it starts averaging the load to progressively improve the weight measurement accuracy. I'd expect using a bounce-height-freefall-duration based length of timing uncertainty at the start and end of the averaging period to allow proper Bayesian uncertainty quantification of the shown result, say by displaying both the 10th and the 90th percentile on the display which grow closer as you wait while standing on it.
With some cleverness a compact calibration mass might be usable to calibrate absolute scale, transferring up to the "people" range using just a random assortment of stuff that fits on the platform, totalling around 10kg.
Because building the scale to be linear in response good enough for 20k count of resolution is pretty straight-forward.