Block Diagram

A temperature control system relies upon a controller, which is connected to a temperature sensor. It compares the actual temperature to the desired control temperature, or set point, and provides an output to a control element. Mostly the control element is a heater.

Our device consists of the following section

1.       Microcontroller.

2.       Keypad.

3.       ADC.

4.       Temperature Sensor.

5.       LCD.

6.       Relay.

7.       Power Supply

It is the heart of the unit. We have used ATMEL’s AT89S5I microcontroller. It performs all the functions like getting data from ADC, Comparing the current temperature to set temperature, Turning ON/OFF the relay & displaying the temperature & Set Point on the LCD.

The keypad consists of 2 keys i.e. Increment & Decrement. These TACTILE SWITCHES are used to Increase & Decrease the temperature set point correspondingly.

The ADC Converts the Analog voltage received from the Temperature Sensor into digital format & gives it to the microcontroller.

We will be using LM 35 as temperature sensor. The output voltage of LM 35 is directly proportional to the Celsius temperature. The output voltage changes 10mv per degree centigrade.

A two line, 16 characters LCD is used to display the status of the relay i.e. ON/OFF as well as to display the current temperature & the Set Point. Check this link for LCD interfacing Tutorial.

The controller cannot directly turn ON/OFF the Heater. So relay is used to ON/OFF the Heater.Tutorial for INTERFACING RELAY TO MICROCONTROLLER.

The complete circuit works on 5 volts. In this section this 5 volts is generated from 230v. Click here for Power Supply Details.

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