DTMF BASED HOME AUTOMATION (Project report for completion of B.Sc General Practical Exam)

Under gratitude guidance of

ARIJIT SARKAR

at

RAMAKRISHNA MISSION VIDYAMANDIRA

BELUR MATH , HOWRAH

SUBMITTED BY

AKASH PAREEK

BASUDEB ROY

SUBIR SARKAR

APRIL , 2016

ACKNOWLEDGEMENT

At this level of understanding it is often difficult to understand the wide spectrum of

knowledge without proper guidance and advice. Hence, we take this opportunity to

express our heartfelt gratitude to our project guide Arijit Sarkar who had faith in us

and allowed us to work on this project.

We would like to thanks Prof. Arnab kumar Ghoshal (H.O.D Computer Science

and Electronics) Prof. Goutam Bhattacharya for there immense interest, valuable

guidance, constant inspiration and kind co-operation throughout the period of work

undertaken, which has been instrumented in the success of our project.

We also acknowledge our profound sense of gratitude to all the teachers who have

been instrumental for providing us the technical knowledge and moral support to

complete the project with full understanding.

Equally we are thankful to our colleagues and students who compelled us to make

this project. Finally, we would like to thank all the people who directly or indirectly

have contributed to the completion of this project.

AKASH PAREEK

BASUDEB ROY

SUBIR SARKAR

Date:14/04/16

RAMAKRISHNA MISSION VIDYAMANDIRA

( A Residential Autonomous Degree College under Calcutta University)

Belur Math-711202, Howrah, West Bengal

CERTIFICATE

This is to cerify that Mr. Akash Pareek (170), Mr. Basudeb Roy (209) and

Mr. Subir Sarkar (111) has completed the project entitled “DTMF HOME

BASED AUTOMATION” for completion of B.Sc Electronics General

practical exam at Ramakrishna Mission Vidyamandira.

PROJECT GUIDE HOD BOARD OF EXAMINER

TABLE OF CONTENTS

TITLE

Abstract

Introduction

Block diagram

System Components

DTMFDTMF code

How to detect DTMF codeDTMF detection method

DTMF code to binary code

Binary to decimal decoder

Crystal Oscillator

Relay

Circuit

Working

Costing

Future scope

Bibliography

ABSTRACT

Traditionally electrical appliances in a home are controlled via switches that regulate

the electricity to these devices. As the world gets more and more technologically

advanced, we find new technology coming in deeper and deeper into our personal

lives even at home. Home automation is becoming more and more popular around the

world and is becoming a common practice. The process of home automation works

by making everything in the house automatically controlled using technology to

control and do the jobs that we would normally do manually. Home automation takes

care of a lot of different activities in the house.

This project uses the Dual-Tone Multi Frequency (DTMF) technique used in

telephones, to control multi electronic devices from long distances using the mobile

phone. A practical application case for this system was implemented to control three

electronic devices. A test to detect the DTMF signal received from different mobile

phones was also carried out. The automation features of this work makes it possible

for homeowners to remotely control a large number of appliances,such as TV

,AC,Fan ,light,bulb and many more using there mobile phone.

INTRODUCTION

The remote control used in home automation systems, is a wonderful feature that

everyone would like to enjoy, if they were not expensive to install, maintain, and able

to be use from long distance. With such automation one can switch ON and OFF

lights , Ac etc from a remote distance. In our project we have tried to implement this

home automation techinque using DTMF.

BLOCK DIAGRAM

SYSTEM COMPONENTS

DTMF

DTMF stands for dual tone multiple frequency. DTMF is a term which used in

telephone industry. When any key on telephone or mobile phone is pressed one tone

is generated and it is audible which is nothing but a DTMF tone.

DTMF CODE

When any of the key like “1”, “2”, “*”, “#” etc is pressed particular code is

transmitted. This code is consist of two frequency among which one is higher

frequency and second one is lower frequency. Following table shows the combination

of frequency for respected keys.

According to above table “8” is combination of lower frequency of 852 Hz and

higher frequency of 1336 Hz and “#” is of lower frequency of 941 Hz and higher

frequency of 1447 Hz.

HOW TO DETECT DTMF CODE

Today, most telephone equipment use a DTMF receiver IC. One common

DTMF receiver IC is the Motorola MT8870 that is widely used in electronic

communications circuits. The MT8870 is an 18-pin IC. It is used in telephones

and a variety of other applications. This IC can be used to encode the DTMF

code.

DTMF Detection Method

The scheme used to identify the two frequencies associated with the button that has

been pressed is shown in the figure below. Here, the two tones are first separated by a

low pass and a high pass filter. The passband cutoff frequency of the low pass filter is

slightly above 100 Hz, whereas that of the high pass filter is slightly below 1200 Hz.

The output of each filter is next converted into a square wave by a limiter and then

processed by a bank of bandpass filters with narrow passbands. The four bandpass

filters in the low-frequency channel have center frequencies at 697 Hz, 770 Hz, 852

Hz, and 941 Hz. The four band pass filters in the high-frequency channel have center

frequencies at 1209 Hz, 1336 Hz, 1477 Hz, and 1633 Hz. The detector following each

band pass filter develops the necessary dc switching signal if its input voltage is

above a certain threshold.

DTMF Code to Binary Code

The MT8870 IC produces a equivalent binary code whenever it receives a valid tone

pair .The binary code is the output of the button pressed from the mobile keypad.The

table below shows the DTMF data and the binary code associated with it.

BINARY TO DECIMAL DECODER

A decoder is a circuit that changes a code into some corresponding set of signals.A

binary to decimal decoder is a circuit which converts binary code to its equivalent

decimal form.In our circuit we have used a 4*16 binary to decimal decorder IC

whose input is the Binary code output obtained from converting the DTMF code . A

fairly popular 4*16 decoder IC with 24 pins is sn74154.IC sn74154 is given below

where the decimal outputs are 0,1,2,.....,15 and A,B,C,D are binary inputs. G1 and

G2 are always connected to high.IC 74154 gives low output.

The above figure is a typical relay device which have different parts.NC(normally

closed) and NO(normally open) are two modes by which the secondary circuit can be

operated.To trigger the secondary circuit the small current from the primary circuit is

feeded to one of the terminals A and B and the other terminal is connected to Vcc.

Pole is the input pin for bigger current circuit.

CRYSTAL OSCILLATORS

An electronic circuit that is used to generate an electrical signal of precise frequency

by utilizing the vibrating crystal’s mechanical resonance made of piezoelectric

material. There are different types of piezoelectric resonators, but typically, quartz

crystal is used in these types of oscillators. Hence, these oscillator electronic circuits

are named as crystal oscillators.

Crystal oscillator circuit works on the principle of the inverse piezoelectric effect, i.e.,

a mechanical deformation is produced by applying an electric field across certain

materials. Thus, it utilizes the vibrating crystal’s mechanical resonance which is made

of a piezoelectric material for generating an electric signal of a specific frequency.

RELAY

Many sensors are extremely sensitive type of electronic components and produce

only small output currents. But we need to drive bigger electrical machines using

these sensors. Relay makes it possible for small current to trigger bigger current

circuits. A relay is an electromagnetic switch , which is activated when a small

current is passed through it.

The above figure is a typical relay device which have different parts.NC(normally

closed) and NO(normally open) are two modes by which the secondary circuit can be

operated.To trigger the secondary circuit the small current from the primary circuit is

feeded to one of the terminals A and B and the other terminal is connected to Vcc.

Pole is the input pin for bigger current circuit.

CIRCUIT

The above circuit is configured to operate on three appliances which are connected to

the relay circuit. Suppose that the appliances are Fan , Tv and Bulb. Our circuit can

be operated by any mobile phone with same basic knowledge as how to ON and OFF

various appliances. We have used eight buttons in our circuit, namely

1,2,3,4,5,6,7and 8. What does this button does?

We have configured it in such a way that when a user presses 1 or 3 or 5 in the

trasmitter mobile Fan , Tv and Bulb are ON respectively. When 2 or 4 or 6 is pressed

Fan , Tv, Bulb are OFF respectively. The other two buttons 7 and 8 are used to ON all

the appliances when 7 is pressed and OFF all the appliances when 8 is pressed.

Now if someone has forget to off the Fan he just need to call the receiver mobile

which is always in automatic receive call mode and press 2, the fan will be off

nomatter from how far the person is calling. If we want to ON only Tv and bulb then

we can either press 3 and 5 or 7 and 2.When 3 is pressed Tv is ON and when 5 is

pressed Bulb is ON. But when 7 is pressed all Fan ,Tv ,Bulb is ON and by pressing 2

the Fan goes OFF making only Tv and Bulb in ON mode.

WORKING

There are two mobile phones used in the circuit one works as a receiver and other as

trasmitter. The receiver mobile in connected to the circuit via a headphone. One of the

two wires of the headphone is connected to pin2(IN-) and pin3(GS) of the DTMF

decoder IC MT8870 and the other is grounded. A 3.579545MHz crystal oscillator is

connected to pin7(OSC1) and pin8(OSC2) of MT8870.Pin16(ESt) and pin17(St) are

connected to Vcc via 0.1µF and 390kΩ resistance.

When the trasmitter sends a valid tone data.The receiver detects the frequency pair

and gives the appropriate binary code as the output of the DTMF decoder IC.The

binary output can be obtained by pin11 to pin14.

The data detected so far is a binary data and need to be converted to its proper

decimal form.This conversion from binary to decimal is done by a 4*16 decoder IC

sn74154.The input of the IC74154 is the binary code obtained from the DTMF

decoder.

Flip-flops are used to store the data given by the user from the trasmitter mobile.

Pin15(Std) of MT8870 works as clock for the flip-flops.

In the above circuit 1, 3, 5 of IC74154 are connected to J1 , J2 and J3 of flip-flops

by ORing with output 7 of IC74154 so that when any of 1,3,5 is pressed the flip-

flops have value 1 . 7 is ORed with 1 , 3 , 5 so that when 7 is pressed all the flip-flops

have output 1 simultaneously.

Output 2,4,6 of 74154 are connectecd to K1, K2, K3 of flip-flops by ORing with 8 so

that when any of these key 2, 4, 6 is pressed flip-flops have output 0. 8 is ORed

because when it is pressed all flip-flops have value 0 simultaneously.

The output of the flip-flops are fed to the relay circuits via trasistor to operate the

secondary circuit (appliances) such as Fan , Tv , Bulb.

COSTING

Name of Component Quantity Price

MT8870 1 30

sn74154 1 40

Relay (6v) 3 3*20=60

IC7476 3 3*5=15

IC7400 2 2*5=10

IC7432 2 2*5=10

BC574 3 3*4=12

CRYSTAL OSCILLATOR(3.579545 MHz)

1 15

CAPACITOR (0.1 µF) 1 6

HEADPHONE JACK(3.5mm) 1 10

100 Ω 3 3

100 kΩ 1 2

70 kΩ 1 2

330 Ω 1 2

WIRES,BREAD BOARD

5v DC POWER SUPPLY

TOTAL=217

FUTURE SCOPE

Our circuit is implemented on bread-broad and in future we want to make it on vero-

board so that it can be easily carried without any bad effect on the circuit. The circuit

also has some security flaws. Anyone can control the circuit by calling the receiver

mobile . So in future we would try to overcome this flaw by introducing a password

circuit which will activate the main circuit to control the appliances.

As the circuit is connected to the appliances via the realy circuit whose input are fed

from the flip-flops ,there can arise a situation if the power of the circuit is OFF ,then

the flip-flops may no longer carry the state before the power was OFF. To overcome

this situation we can use a ROM so that it can store the last state of the flip-flops even

when the power of circuit is OFF. But including a ROM can dramatically increase the

cost of the circuit.

BIBLIOGRAPHY

WEBSITES

1 Circuit Gallery

2.Google

3.Wikipedia