We’ve already shown that the thermistors are similar to the changing resistances ,it changes with changing according the temperature .so as to measure the temperature in our project using Arduino we use the voltage divider theory first to get the value of the resistance . Since the arduino will easure the voltage between the thermistor and a known resistance ,so we can easily find the value of the resistance. At last , the Steinhart Hart equation is used to convert the resistance of the thermistor to a temperature reading.
The Steinhart Equation is an expression that has been determined to be the best mathematical expression for resistance temperature relationship of NTC thermistors.Before the connecting we measured the initial value of the te thermistor to the circuit we measure it ,so its temperature was 25oC and when we used the Resistance table the result was be 2.252 K ?,so we used it again attached in Appendix “A” we got the resistive value for the lowest temperature detected by the sensor which is -40oC and the highest temperature which is 100oC. then we enter these values into The Steinhart Equation calculator to find the values of the Steinhart model coefficients (c1, c2, c3) as shown in figure below. Finally we substituted the coefficients calculated in figure into the Steinhart and hart equation mentioned above and we got the value of the current temperature