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

This paper analyzes the effects of power-supply interference on direct sensor-to-microcontroller interfaces based on measuring the charging/discharging time of an RC circuit that includes the sensor. Power-supply interference becomes a source of trigger noise that affects the measurement of the charging/discharging time and, hence, the measurement of the sensor resistance or capacitance. The measurement uncertainty increases proportionally to the amplitude of the interference and depends on its frequency. Such interference effects are smaller when measuring the discharging time and can be further reduced by placing an additional resistor in the interface circuit. Experimental data obtained from a PIC microcontroller agree with the theoretical predictions