Sensor

When debugging ADC measurements, it is natural to focus on the input pin: sensor output, divider ratio, front-end filtering.

But the ADC result is not determined by input voltage alone. Reference voltage participates in every conversion.

A more accurate first model is:

ADC code ≈ Vin / Vref * full scale

The ADC reads the ratio between input voltage Vin and reference voltage Vref. If Vin changes, the result changes. If Vref changes, the result also changes.

Many sensor field problems look like unstable algorithms, ADC jitter, or poor modules. They often end up being ground and power problems.

The reading is stable when the device is idle, but jumps when a motor starts. Temperature moves during radio transmission. Pressure shifts after a relay turns on. USB power and battery power give different values. Short lab wiring works, while the field installation is noisy.

The physical quantity may not have changed. The measurement reference changed.