Development of differential sensor interface for GSM communication

Abstract

This research work focuses on the design, simulation and implementation of differential resistive sensor interface. The importance of the findings of this work lies in exploring problems such as non-linearity errors for better accuracy and reducing long interface-chain for ease and simplicity of the system. The interface is explored and used along with potentiometer and a thermistor, both connected in a differential manner. The potentiometer is ultimately representing displacement while thermistor represents environmental condition of temperature. The design involves using a 555- timer, external components of resistors, diodes and a capacitor. Identification of the non-linear regions of the thermistor curve is carried out and the circuit is configured to operate over a linear segment. The resulting circuit is interfaced to a microcontroller and a GSM/GPRS modem, both properly programmed in specified code instructions. The results obtained are benchmarked with other recently published work and a better linearized output of the thermistor response curve is obtained. The circuit is analyzed before it is simulated using ORCAD PSPICE and MATLAB code. A comparison between the simulation and experimental results show the circuit's preferential utility over the circuits currently in use for similar applications. A frequency and voltage output are obtained, showing how a small change in differential value of the resistor can bring galloping effect on the signal path at temperature of 600C and an error of 0.1% resolution is found and reported. Through experiments, frequency and duty cycle responses are obtained to show that the proposed system is reliable, more accurate as its preferential advantages.