Time-domain measurement methods for R, L and C sensors based on a versatile direct sensor-to-microcontroller interface circuit

In the paper new time-domain measurement methods for determining values of resistive (R), inductive (L) and capacitive (C) sensors based on a versatile direct sensor-to-microcontroller interface for microcontrollers with internal analog-to-digital converters (ADCs) and analog comparators (ACs) are presented. The interface circuit consists of a reference resistor Rr working as a voltage divider, a given R, L or C sensor and a microcontroller (its peripherals: an ADC, an AC, a timer, I/O pins buffered by an inverter). A prototype of the proposed complete solution of a compact smart sensor based on an 8-bit microcontroller has been developed and tested. The maximum possible relative inaccuracy of an indirectly measurable resistance, inductance and capacitance were analysed. Also, experimental researches were made. The following relative errors of the sensor value determination were achieved: for the R sensor less than 3%, as well as very good results for the L sensor (less than 0.3%) and for the C sensor (less than 0.2%).