Resistive Measurement Method for MQ Sensors Based on ADCs of Microcontrollers

Abstract

This paper proposes a system for measuring unknown resistances for metal oxide MQ gas sensors. The circuit configuration is based on the Anderson current loop interface, which connects directly to an Arduino Mega 2560. We analyze errors arising from variations in supply voltage of conventional divider circuits, including those introduced by the Analog-to-Digital Conversion (ADC) of microcontroller. To enhance the accuracy of resistance measurements, a voting technique for selecting the optimal unknown resistances is introduced. In this technique, the digital voltage at each node is analyzed to determine the frequency of occurrence of each level. If a particular voltage level has a frequency of occurrence greater than the reference threshold k, it is selected. If no voltage level meets this criterion, the average of the observed voltage levels is used. From the experimental results, unknown resistances were measured in the range of 362 – 15, $397~\Omega $ with a maximum approximated error of 0.55% with $k =90$ %, while the gas content was measured with a maximum error of approximately 0.24% under conditions of power supply voltage fluctuation from 4.9 to 5.1 V.