Description

Abstract :

In this project we will implement CPU Fan speed control technique when there is increase or decrease in IC temperature of FPGA kit and display temperature value in LCD display present in the Spartan6 FPGA Project kit.

Tool required :

Software:

• Xilinx ISE 14.7i

Language:

• VHDL

Hardware:

       1. Spartan6 FPGA Project kit

       2. 4 wire CPU Fan

Block Diagram of CPU Fan Speed Control Based on IC Temperature :

Driver Circuit to connect CPU Fan with FPGA :

4 Wire CPU Fan :

CPU fan work at 12v DC power supply. The motor works by inputting 25KHz PWM pulse at control pin ( Blue) of the CPU. The speed of the DC motor can be incremented or decremented by varying duty cycle of the 25KHz PWM pulse. The Speed at which motor rotate can be measured at sense pin of the CPU Fan. Sense pin outputs 2 pulse per rotation. 

Pin	Function	Wire Colour
1	GND	Black
2	12 V	Yellow
3	Sense	Green
4	Control	Blue

LM35 Temperature Sensor :

The LM35 series are precision integrated-circuit temperature sensors, whose output voltage is linearly proportional to the Celsius (Centigrade) temperature. The LM35 thus has an advantage over linear temperature sensors calibrated in ° Kelvin, as the user is not required to subtract a large constant voltage from its output to obtain convenient Centigrade scaling.

Working Principle :

CPU fan is connected with driver circuit. The driver circuit consist 12v AC power supply with bridge rectifier for DC conversion. NPN transistor to provide open collector PWM output and voltage divider at the sense pin with RPM output. Spartan6 FPGA kit generate 25Khz PWM output to the NPN transistor.

Spartan6 FPGA Project Kit consists of On board 2 channels ADC with channel2 connected with LM35 temperature sensor. VHDL code is developed to perform analog to digital conversion, read the LM35 data as digital output and display it to the 2×16 LCD.

Depending on the change in temperature value of LM35, the PWM duty cycle gets increased or decreased to maintain constant temperature at the FPGA board IC.

Sense output at the CPU Fan can be used to display RPM value in the on board LCD Display.

Conclusion :

The FPGA kit temperature is monitored using LM35 temperature sensor and fan speed has been incremented and decremented to maintain the constant temperature.