Written by Amol Shah, on May-2008

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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.The controller is connected to a Personal Computer using RS232 protocol. The Current Temperature can be seen on the PC. Whereas the Temperature Set Point can also be changed through the PC. The different sections of this project are:

1.       Microcontroller.

2.       Analog to Digital Converter (ADC).

3.       Temperature Sensor.

4.       Relay.

5.       MAX 232.

6.       Power Supply.

MICROCONTROLLER

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 & communicating with the PC.

Analog to Digital Converter

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

Temperature Sensor

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.

RELAY

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

MAX232

Communication with the PC is done through the SERIAL PORT. The protocol of serial port is RS-232, for interfacing the controller to the PC using RS 232 protocol we require MAX 232 IC.

POWER SUPPLY

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

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