Project Presentation on

DTMF Based Remote Controlling of Home Appliances Using Mobile Phone

ABSTRACT

Aim of the project is to use a mobile phone to control home appliances.

With this project a caller can remotely control home appliances by pressing different keypad buttons which generates identical DTMF signal.

To get desired controlling output using Microcontroller.

Control of home appliances involves 3 different phases

1. Perception2. Processing3. Action

INTRODUCTION

PERCEPTION

First part is the decoding of DTMF tone generated by pressing a key in calling phone.

Audio signal output from receiving phone is fed to DTMF decoder chip.

Decoder chip converts DTMF tone into binary codes to be fed to Microcontroller.

PROCESSING

After perception stage, microcontroller processes the binary codes it receives

Microcontroller is pre-programmed in ”C” to perform specific task according to input bits.

Program is written in AVR Studio and Simulated in Proteus7.7 software.

ACTION

Final stage is to switching ON/OFF the home appliances connected across the main power line of 220 V 50 Hz AC.

For switching purpose electromagnetic Relays were used.

BASIC BLOCK DIAGRAM OF THE PROJECT

Figure 1. Basic block diagram of the project (ref.p-4 )

DTMF- Dual Tone Multi Frequency.

• DTMF is the signal that generates upon pressing an ordinary telephone’s any keypad button.

• Signal generated by the superposition of two pure sinusoidal tones.

• One is high frequency & another is low frequency tone signal.

1 2 3 697

4 5 6 770

7 8 9 852

* 0 # 941

1209 1336 1477 Frequency(Hz)

Each button lies at the intersection of the two tonesTable 1- Row and column frequency correspondence

Structure of 8870 DTMF decoder

Figure 2- Structure of 8870 DTMF decoder (ref. p-6 )

DTMF Decoder 8870Decodes DTMF signals & converts into binary bits

Button Low Frequency(Hz) High Frequency(Hz) Q1 Q2 Q3 Q4

1 697 1209 0 0 0 1

2 697 1336 0 0 1 0

3 697 1477 0 0 1 1

4 770 1209 0 1 0 0

5 770 1336 0 1 0 1

6 770 1477 0 1 1 0

7 852 1209 0 1 1 1

8 852 1336 0 0 0 0

9 852 1477 1 0 0 1

0 941 1209 1 0 1 0

* 941 1336 1 0 1 1

# 941 1477 1 1 0 0

Table 2- Values of decoder output for various frequencies

ATmega 16 Microcontroller Features

High performance, Low power 8 bit Microcontroller.16 KB Flash Memory with read and write capabilities.512 Bytes EEPROM.1 KB Internal RAM.32*8 General purpose working Registers.Three timers.Internal/ External Interrupts.

Working ProcedureThe operation is initiated by calling the second mobile phone at

receiving end.Mobile at receiving end receives the DTMF signals, which is

generated by pressing the keypad of caller mobile phone.DTMF signal is passed to the DTMF decoder IC 8870 and

decodes binary outputs.Binary output is inverted using IC 7404. The inverted output is fed to the input PORT A of the

Microcontroller.The Microcontroller then gives desired output as it was

programmed.When any output pin of PORT D becomes high then connected

corresponding Relay become active and it makes the circuit close to switch ON any circuit or Device.

Number pressed by

user

Output of DTMF decoder

Input to microcontroller

Output from microcontroller

Action performed

2 0x020010

0x0D1101

0x0000000000

Both relays off

4 0x040100

0x0B1011

0x0100000001

One relay on

6 0x060110

0x091001

0x0200000010

Another relay on

8 0x081000

0x070111

0x0300000011

Both relays on

Table 3-Actions performed corresponding to the key pressed

• Microcontroller program was written in C language on AVR Studio.• Program was converted into desired Hex file using AVR Studio.• Circuit was simulated in Proteus 7.7 Software

Simulation circuit is given in Figure 3

Figure 3 – Simulation circuit using Proteus 7.7 (ref. p-13)

MAIN CIRCUIT DIAGRAM

Figure 4- Main circuit diagram (ref. p-15)

RELAY

Relay is an electromagnetic switch.It consists of a control coil and a load circuit. Control coil controls the operation and load circuit is a

switch.Current flowing through the control coil creates a small

magnetic field causes the load circuit switch to close and relay is then active.

Figure 5- Structural view of Relay.

Microcontroller output pin PD0 and PD1 are connected with relays through BC 547 transistor.

When transistor becomes ON then relay also be active.

A relay used as a switch of the home appliance which is connected across the main power supply 220 V- 50 Hz AC.

Here two 220V – 10 W bulbs are used as home appliances.

APPLICATION

The system can be used in controlling home appliances.Can be used in office, lab ,class and factory etc.

This setup with a little modification can be adapted to the following applications

1) Combination Lock2) Home Security System3) Mobile / Wireless Robot control4) Wireless Radio Control5) Continuous monitoring of system status