Temperature Controlled Fan

Here is another fan controller design based on PIC microcontroller, this time it’s temperature controlled and can be used to monitor Hard Drive temperature and adjust the fan speed accordingly or as a case fan controller. This post following recently published articles like 2 Channel PC Fan Controller and  PWM Fan Controller.Current Hardware/Software configuration supports 3 fan speed settings as a function of temperature. For T < 28C – Low Speed, Fan output voltage 7.5V, 38C > T >28C – Medium Speed, Fan output voltage 10.5V and for T > 38C – Hi Speed setting, Fan output voltage is 12V.The LM35 is a precision integrated circuit temperature sensor, whose output voltage is linearly proportional to the Celsius (Centigrade) temperature. LM35 in TO-220 package was used as it can be easily connected to various surfaces for better temperature readings.
Temperature Controlled Fan Schematic

Temperature sensor output is directly connected to AN1 input of PIC16F876A. Converted temperature is digitized by PIC analog to digital converter and its binary code is shown on LED bar graph connected to PORTC (only for prototyping – not present in schematic), also it’s used to determine the fan output voltage/speed settings. Additional 2 LED’s were used to indicate current voltage/speed range. Additional information can be found on the next page.


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