LM35 Based Temperature Control System

Overview

This project illustrates the control of NPN power transistor using PIC16F876A to further drive DC brushless fans, LEDs, and buzzers when the specified temperature was detected.

Explanation

An LCD screen is used to always display the value of temperature as the analog voltage from temperature sensor LM35 is read by a PIC16F876A with an internal ADC. The DC brushless fan is driven by the power transistor with sufficient current. The CMOS Flash based 8-bit PIC16F876A microcontroller has 200 nanosecond instruction execution making it powerful but still easy to program.

To interface the PIC16F876A with temperature sensor LM35, the signal pin from LM35 can be connected to either one of analog input pin except AN3 while making sure a correct ADC configuration. Adding a  capacitor between the analog signal and GND for every analog input such as signal from LM35 and variable resistor is recommended for the user for more stability.

The voltage range of power source that could be provided for this project is between 7V and 15V. More heat will be produce at LM7805 voltage regulator with higher input voltage. The program is loaded in this project using In Circuit Serial programming (ICSP).