Analysis of Power Supply Interference Effects on Direct Sensor-to-Microcontroller Interfaces

Microcontrollers with embedded timers can directly measure resistive and capacitive sensors by determining the charging or discharging time of an RC circuit that includes the sensor. However, the same as classical signal conditioning circuits, these microcontroller-based interfaces are susceptible to power supply interference. This susceptibility is analyzed herein by using theoretical and experimental methods. The variability of the measurement depends on both the amplitude and frequency of the power supply interference, and also on the measurand. Experimental data obtained for a PIC microcontroller agree with the theoretical predictions. Adding a resistor to the circuit significantly improves interference rejection