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Embedded Temperature Based Fan Speed Controller using AT89S52
Microcontroller
This project is a standalone automatic fan speed controller that controls the speed of an electric fan according to our requirement. Use of embedded technology makes this closed loop feedback control system efficient and reliable. Micro controller (AT89S52) allows dynamic and faster control. Liquid crystal display (LCD) 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 can be implemented for several applications including air-conditioners, water-heaters, snow-melters, ovens, heat-exchangers, mixers, furnaces, incubators, thermal baths and veterinary operating tables. AT89S52 micro controller is the heart of the circuit as it controls all the functions.
The temperature sensor LM35 senses the temperature and converts it into an electrical (analog) signal, which is applied to the micro controller through ADC. The analog signal is converted into digital format by the analog-to-digital converter (ADC). The sensed and set values of the temperature are displayed on the 16x2-line LCD. The micro controller drives control relays by means of ULN driver circuit to control the fan speed with the help of high wattage tagged wire wound resistor.
Single pole dabble throw (SPDT) relays are connected to the micro controller through a ULN driver circuit. The relays require 12 volts at a current of around 50 mA, which can not provided by the micro controller. So the ULN driver circuit is added. The relays are used to operate the electrical fan or for operating any other electrical device. Normally the relays remain off. As soon as pin of the micro controller goes high, the relays operate.
This project uses regulated 5V, 500mA & 12V, 500mA power supply. 7805 and 7812 three terminal voltage regulators are used for voltage regulation. Bridge type full wave rectifier is used to rectify the ac out put of secondary of 230/12V step down transformer. This project is useful in process industries for maintenance and controlling of Boilers temperature..