Air Conditioner Controller

1. INTRODUCTION

Today, thanks to the advancement in the field of electronics, most of the manually controlled systems are getting replaced with sophisticated electronic circuits with intelligent controlls. These circuits are capable of monitoring, analyzing and controlling the systems. In earlier days these electronic circuits were fabricated around discrete hardware components such as transistors, logic ICs etc that made the system bulky and costly. Also since the component count was more the failure rate was also more. But now due to the introduction of single chip microcontrollers, the hardware part was drastically reduced; so also the cost and size of the hardware has come down to a large extent. As a result almost all of the control circuits are designed over single chip microcontrollers.

2. SCOPE OF THE PROJECT

The primary objective of this project is to make a simple circuitry for Air conditioner controller. This circuitry is based on the state of the art technology of Microcontrollers .The features of the project is has given below

1. Facility to set the temperature using a potentiometer.

2. A Display indicates the temperature - both the set value and the actual value.

3. An indication when the set range is beyond limits.

4. The system turns ON the Air conditioner when the set temperature.

5. A mode selector switch is provided to select between SET MODE and RUN MODE.

6. When the SET mode is selected the display indicates the set value. When RUN mode is selected the display indicates the actual room temperature.

The whole circuitry works on 230V AC. From this a series regulator is designed to derive +5V regulated supply for the microcontroller part. The circuitry is based on the popular microcontroller Atmel 89S8252 The project consists of necessary software and hardware for implementing the above function.

3. BLOCK SCHEMATIC OF THE PROJECT

The figure below shows the block schematic of the project. This consists of the following.

1. Power Supply Unit

2. Microcontroller Unit

3. A Potentiometer For Temperature Set.

4. A Temperature Sensor Circuit

5. A Display Circuit

6. A Relay Driver Circuit

It also consists of the following indications

1. Temperature Display on seven segment Display (2 digit)

2. A set range out indication.

The circuit turns on a relay when the set temperature is less than the room temperature. This relay turns ON the Air Conditioner.

4. STUDY OF MICROCONTROLLER

This project makes use of a microcontroller-based circuitry for decision making such as password checking and device control. The microcontroller used here is microchip make PIC series IC 16F870.

a. Microprocessors

A microprocessor, as the term has come to be known, is a general- purpose digital computer central processing unit (CPU). Although popularly known as a "computer on a chip," the microprocessor is in no sense a complete digital computer.

Figure 1.1 shows a block diagram of a microprocessor CPU, which contains an arithmetic and logic unit (ALU), a program counter (PC), a stack pointer (SP), some working registers, clock timing circuit and interrupt circuits.

To make a complete microcomputer, one must add memory, usually read only program memory (ROM) and random- access data memory (RAM), memory decoders, an oscillator, and a number of input/output (I/O) devices, such as parallel and serial data ports. In addition, special-purpose devices, such as interrupt Handlers and counters, may be added to relieve the CPU from time consuming counting or timing chores.

Equipping the microcomputer with mass storage devices, commonly a floppy and hard disc drives, and I /O peripherals, such as a keyboard and a CRT display, yields a small computer that can be applied to a range of general purpose software applications

The key term in describing the design of the microprocessor is general purpose. The hard ware design of a microprocessor CPU is arranged so that a small or very large system can be configured around the CPU as the application demands.

Fig 5.1 Contents of Microprocessor

The internal CPU architecture, as well as the resultant machine level code that operate that architecture, is comprehensive but as flexible as possible.

The prime use of a microprocessor is to read data, perform extensive calculations on that data, and store those calculations in a mass storage device or display the results for human use. The programs used by the microprocessor are stored in the mass storage device and loaded in to RAM as the user directs. A few microprocessor programs are stored in ROM.

The ROM-based programs are primarily small fixed programs that operate peripherals and other fixed devices that are connected to the system. The design of the microprocessor is driven by the desire to make it as expandable and flexible as possible, in the expectation of commercial success in the marketplace.

b. Microcontrollers

The Figure 5.2 below shows the block diagram of a typical microcontroller, which is a true computer on a chip. The design incorporates all of the features found in