This document describes a temperature controlled fan speed controller circuit. The circuit uses an LM35 temperature sensor to monitor temperature. It sends the analog temperature reading to an ADC which converts it to a digital signal for a microcontroller. The microcontroller compares the temperature to set limits and controls the speed of a DC fan motor using PWM to vary the duty cycle and fan speed. It aims to efficiently cool components by increasing fan speed as temperature rises and decreasing it as temperature falls.

1. GUIDED BY :SUMAN SWAMI
PREPARED BY :SUCHITRA [10EEBEC081]
SUMAN SIDH [10EEBEC083]
SUSHMA TANWAR

2. Introduction
The circuit works on the feedback principle. The speed
of the fan varies with the variation in the temperature. The
speed of the fan increases if the temperature is increased and
the speed of the fan decreases with the decrease in the
temperature.
LM35 produces its output voltage corresponding to the
temperature. The temperature is given to ADC which converts
the analogue variation in the voltage into the digital form.
When the Vref is properly selected (1V in this case) then the
temperature value appears on the output pins of the ADC in
the binary form. This output is given as input to the 8051
microcontroller. The input is compared in the microcontroller
and the required output is produced.

3. List of components :-
• LM35
Temperature sensor
• Micro-controller unit
• Brushless variable speed DC Motor
• N mosfet
• Resistors
• Breadboard
• Red LED
• Voltage regulator IC
• Diodes
• Capacitors

4. Hardware
Micro controller unit is used as the controller to
maintain the DC motor speed at desired value,
based on the input from the temperature sensor, in
order to control the temperature. The duty cycle of
the PWM (pulse width modulation ) from
microcontroller will determine the speed of the DC
motor.

5. Circuit Diagram

6. ALGORITHM
1. Initialize Ports, LCD and Motor Driver IC Input.
2. Display project name on LCD.
3. Clear LCD.
4. Display set temperature range on LCD.
5. Read analog Voltage Value from Temperature Sensor on AN0 of PIC.
6. Temperature = Voltage / 10
7. If Temperature < Lower Temperature Range then
7.1. Switch ON Heater
7.2. Switch OFF FAN
8. If Temperature >= Lower Temperature Range & Temperature <= Upper
Temperature then
8.1. Switch OFF Heater
8.2. Switch OFF FAN
9. If Temperature > Upper Temperature Range then
9.1. Switch OFF Heater
9.2. Switch ON FAN and control its speed using PWM generation
10. Display Current Temperature range on LCD.
11. Repeat Steps 5 to 11 infinitely.

7. SPEED CONTROLLER:
To control the speed of the fan a PWM (pulse width modulation) is used.
.
PWM (PULSE WIDTH MODULATION):
In pulse width modulation the power delivered to the load is varied by changing the duty cycle of the output
voltage.
1.
2.
To deliver high power duty cycle is kept high
To deliver less power duty cycle is kept low
Normal case:
Pulse Width Modulation:

8. Construction
The construction started with mounting of the components on a
project-board(Breadboard). The project board circuit
arrangement is done stage by stage. The components for the
temperature measurement stage, ramp generator comparator
and ac power control components consisting of the optocoupler and power triac are connected together with jumper
wires. The temperature level control and power switch are put
in place and eventually the power supply is connected finally to
power the circuit. The analog to digital converter stage is also
set up including the LED seven segment display to display the
temperature value. The complete circuit is tested on project
board.

9. Testing :-
The power supply is connected first of all and
tested to ensure proper supply voltages. The
temperature sensor output is measured also
followed by the ramp generator, comparator, optocoupler, power triac and the ADC. The test carried
out is heating up the sensor and observing the
speed of the fan increasing with the increased
temperature picked up by the sensor and the test
is also carried to establish the relationship between
the temperature levels and the fan speed levels.

10. Applications :-
Temperature based fan speed controller is useful
for cooling the processor in the laptops and
personal computers “more efficiently”. Generally
fan in laptop comes with only two or three
possible speeds. So it results in more power
consumption. The fan designed in this project,
has different values of speed according to
temperature change. This can be also used in
small scale industries for cooling the
electrical/mechanical equipment. The whole
circuit except motor and fan can be
manufactured on a single PCB, and it can be
used for temperature based control operations.

11. THANK YOU