TEMPERATURE BASED AUTOMATIC FAN SPEED CONTROL USING MICROCONTROLLER AT89S52

AUTOMATIC FAN SPEED CONTROL

This project is a standalone automatic fan speed controller that controls the speed of an electric fan according to our requirements. Use of embedded technology makes this closed loop control system as efficient and reliable. Microcontroller AT89S52 allows dynamic and faster control .Liquid Crystal display makes the system user friendly. The sensed temperature and fan speed level values are simultaneously displayed on the LCD panel. It is very compact using few components and implemented for several applications including air-conditioners, water heaters, snow melters, heat-exchangers, ovens, mixers, incubators, furnaces, thermal baths and veterinary operating tables.

 AT89S52 Microcontroller is the heart of the circuit as it controls all the functions.

The temperature sensor LM35 senses the temperature and convert it into an electricl signal(analog),which is applied to the mocrocontroller through ADC. The analog signal is converted intodigital format by Analog to Digital converter (ADC).The sensed and set values of the temperature are displayed on the 16x2  LCD.The microcontroller drives control  relay by meens of ULN  driver circuit to control the fan speed with the help of high wattage tagged wire wound resistor.

Block diagram

Single Pole Douple Throw(SPDT) relays are connected to the microcontroller through a ULN driver circuit.The relays require 12 volts at a current of around  50mA,which can not provide by the microcontroller.So the ULN driver circuit is added.The relays are used to operate an electrical fan or any other electrical device.Normally the relays remains off.As soon as pin of the microcontroller goes high ,the relays operate.

This project uses 5V,500mA & 12V 500mA power supply.7805 and 7812  three terminal voltage regulators are used for voltage regulation .Bridge type full wave rectifiers are used to rectify the ac output of  230/12 V step down transmitter.This project is useful in process industries  for maintenance and controlling of boilers temperature.