25-04-2012, 11:03 AM
Temperature Controlled DC Fan using PIC18F452 Microcontroller
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INTRODUCTION
In today’s hi-tech world computers have become part and partial of life. But temperature of the
processor inside the computing system needs to be controlled for proper functioning of the
semiconductor devices. Thus it is important to keep the temperature within the prescribed
limits.
Why use microcontroller?
To control the temperature it must be sensed and check in what range it lies according to which
the speed of the cooling fan is decided. These tasks can be performed very easily using a
microcontroller. It involves decision making steps, which can be easily achieved by using a
microcontroller instead of complex IC circuits.
Methodology
First of all the temperature will be sensed by a temperature sensor, which works as a
transducer and gives voltage equivalent of the sensed temperature. This analog signal will
be fed to the ADC of PIC microcontroller. Thereafter the adc will take the analog input and
convert it to digital domain. Now the digital data will be compared to the prespecified
conditions in the program. According to result of comparison, desired duty ratio will be
generated.
Project Objective
This project targets on designing, simulating, prototyping and testing of a temperature
controlled dc motor fan that is practically used for cooling the processor in computers.
The primary aim of our project is to control dc motor, fan in our project, using a pic micro
controller. The fan will be given an input duty ratio which increases in steps of 25% for
every 10 degree rise in temperature, starting from 25 degrees. The fan will be kept off for
temperature less than 25 degree and will run maximum speed for temperature above 55
degrees.
Hardware
PIC Microcontroller
For this project, we are using PIC18F452. PIC18 XXX is an 8 bit microcontroller. The other PIC
families are 10xxx ,12xxx ,14xxx & 17xxx. They all are 8 bit processors, meaning that the CPU
can work on only 8 bit data at a time. The data larger than 8 bit has to be broken into 8 bit
pieces to be processed by CPU. The PIC18f has an instruction size of 16 bit wide.
Control registers associated with ADC
i) ADCON0
The ADCONO register is used to set the conversion time and select the analog input channel
among other things. Figure 13-6 shows the ADCONO register. In order to reduce the power
consumption of the PIC 18, the ADC feature is turned
off when the microcontroller is powered up. We turn on the ADC with the ADON bit of the
ADCONO register, as shown in Figure 13-6. The other important bit is
the GO/DONE bit. We use this bit to start conversion and monitor it to see if conversion has
ended. Notice in ADCCONO that not all family members have all the 8 analog input channels.
Results and Conclusion
The prototype of the Temperature controlled DC fan using PIC18F452 microcontroller was simulated
and fabricated. The sensor was successfully interfaced with the microcontroller using ADC the
desired output pulses were observed in the simulation using PROTEUS software.