A microcontroller system for measurement of three independent components in impedance sensors using a single square pulse

A novel time domain method and its implementation in a simple smart impedance sensor controlled by an 8-bit microcontroller is presented in the paper. The method is based on stimulation of a voltage divider consisting of a resistor working as a current-to-voltage converter and the impedance sensor by a single square-voltage pulse with a duration time T directly generated by the output of the microcontroller and on sampling the resulting voltage on the sensor at three different selected moments T/8, T/2 and 7T/8 by the internal ADC of the microcontroller. The sensor is modeled by a three-components circuit. The duration time T is determined by the first timer and the ADC is triggered by the second timer of the microcontroller. The measurement procedure takes less than 1 ms and the determination of model component values is based on basic calculus. Thanks to this, smart sensors basing on this solution are energy-saving, they can work on the same batteries by a few years, and low cost on the level tens euros. Hence, they can be used in wireless sensor networks, especially basing on the ZigBee protocol. The results of the simulation investigation and the experimental verification of the method are included in this paper.