Design of a Novel System to Automatically Sense Physical Quantities : Sensing Some Physical Quantities Using Nonlinear Resistor Devices

The goal of this project is to design a resistance to time converter capable of converting resistive change into pulse widths of proportional durations. This converter exhibits a compatibility of wider conversion range with a reasonable level of sensitivity required for industrial applications. The aim of the work is however aimed at to achieve a low-cost and compact transducer based on an inexpensive popular precision timing chip 555 timer for measurement of temperature of an ambience, force, light intensity and relative humidity using nonlinear sensitive resistors (Thermistors with negative temperature coefficient (NTC), Force Dependent Resistor, Light Dependent Resistor and Humidity Dependent Resistor) placed in a 555 timer circuit working in the astable mode. This forms the core of the measurement system which is without doubt cheap as well as compact. The circuit output, after further conditioning, is flow by frequency meter (convert change in frequency to current) which serves as the linearizer. Experimental results are shown to be compared with mathematical derivations, both reporting a good level of response matching very closely with the derived results.