A Simple Direct Microcontroller Interface for Capacitively-Coupled Resistive Sensors

TL;DR: A novel approach to interface capacitively-coupled resistive sensors directly to a microcontroller, without using the synchronous demodulation technique adopted by conventional approaches, to realize a highly practical, low-power and low-cost measurement system.

Abstract: A novel approach to interface capacitively-coupled resistive sensors directly to a microcontroller is presented in this paper The existing schemes for the measurement of the resistance of a sensing element that is inaccessible, unless through capacitive coupling, are complex This paper presents a direct microcontroller interface solution for this category of sensors When a resistive sensor is coupled to the measurement system through capacitances, one of the main challenges is to make the resistance measurement insensitive to variations in the coupling capacitances This is achieved in the proposed direct microcontroller approach, without using the synchronous demodulation technique adopted by conventional approaches Additionally, the output is independent of the value of the charging capacitor, the supply voltage and the preset threshold voltage The feasibility study of the proposed scheme has been conducted in two steps by building suitable prototypes The test results from the initial study, in which the experimental setup was designed in such a way that its performance was not limited by the non-idealities of the microcontroller, showed a maximum error of 028% The subsequent study with the microcontroller interface exhibited a maximum error of 148% Thus, the accuracy of the proposed system is quite promising, with a measuring time of a few milliseconds Higher accuracy can be achieved by using a microcontroller with higher time resolution, and a comparator with lesser delay and noise This scheme does not use any expensive parts and can hence realize a highly practical, low-power and low-cost measurement system