Interfacing Differential Resistive Sensors to Microcontrollers: A Direct Approach

Abstract

This paper introduces and analyzes a novel circuit to directly connect differential resistive sensors to microcontrollers without using either a signal conditioner or an analog-to-digital converter (ADC) in the signal path. This new circuit relies on measuring the discharging time of several resistance-capacitance ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i> ) circuits that include the two sensor resistances. Such an operating principle makes the circuit simple, compact, low cost, low power, and accurate. The main uncertainty sources are the quantization of the discharging time measurement and the mismatch of internal resistances of the microcontroller. According to experimental results, the circuit shows errors in the range of 0.01% full-scale span (FSS), and the effective resolution can be up to 13 bits for a measuring time of 100 ms, which are very remarkable considering its simplicity.