Annual Research Proceedings, University of Colombo held on June 2011

Abstract

Abstract A novel, low cost and reliable method of using a microcontroller has been tested and evaluated for measuring temperature. Most of the microcontrollers come with a Watch Dog Timer (WDT) which is clocked by an internal Resistor Capacitor (RC) oscillator. The oscillating frequency of the RC oscillator depends on the temperature. The time-out periods (in counts) of WDT of Microchip PIC16F877A microcontroller were measured at different temperatures by means of a LM35 sensor from National Semiconductor Inc. It is found to give a good linear relationship (correlation coefficient R2 =0.997) between time- 302 out period and the temperature with a scale factor of 6 counts per 1 C and an accuracy of 0.8 C for the range ,5 C to 60 C when the microcontroller runs by a 4 MHz crystal oscillator. The response time is found to be 48 s with the water sealing material. There was no hysteresis effect found on these measurements and for the same series microcontroller the measurements lie within the given accuracy. The microcontroller is programmed to produce the reading in RS232 protocol and it can easily be software altered to any other standard protocol