International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue4- April 2013
GSM BASED DEVICE SWITCHING
Parvathy.V. Menon*1, Anoop.T.K*2, Vijesh.E.P*3 and R.Satheesh#4
*123
`
U.G.Scholars
Department of EEE, SVS College of Engineering
Coimbatore, India
`#4
Assistant Professor,
Department of EEE, SVS College of Engineering
Coimbatore, India
Abstract - In this paper, we have developed a high security,
simple and reliable wireless communication system to monitor
and to control devices that are far away from the user by making
a call. The mobile which is connected to the system is kept in
‘auto answer’ mode. Using DTMF technology, any devices can be
switched and controlled by pressing the corresponding buttons
during the course of a call. These tones are then decoded by
using a DTMF decoder and the corresponding devices are
chosen.
Keywords— Dual tone multi-frequency (DTMF) technology,
DTMF decoder, controller, relay driver
I. INTRODUCTION
In this era where science and technology are extremely
dominant and more prominent, we experience changes in
every walk of life. People too respond to these changes very
quickly. In their busy schedule, they keep track of only what
appears important to them and consciously or willingly
forgetting what they think as least important ones. For
example, wastage of energy without switching off the devices
even after its usage, lack of proper security, etc., By keeping
this thought in mind that the ‘least becomes important’, we
have designed our project. The systems used so far involve
the remote control switches using infrareds, radio waves and
laser beams. Laser beams are really very harmful to mankind.
Remote control switches using infrared and radio waves can
be used only for short distances. There were also device
switching methods using SMS and Bluetooth technology. This
paper introduces a system which does not require any harmful
radiation and continuous control. Here the devices are
switched and controlled by the mobile possessed by the user
that makes a call to the mobile which is attached to the
system. During the course of a call, when a particular button
is pressed, a tone is heard at the other end of the call. This
tone is so called as ‘Dual tone multi-frequency’. The received
tone is decoded by using a DTMF decoder. This decided
signal is then send to a microcontroller for processing. Based
ISSN: 2231-5381
on the program loaded in the microcontroller,
corresponding relay is switched with the help of a relay
driver. Using this simple, reliable and flexible system, one
can monitor and control home appliances, industrial
automated machinery, irrigation purposes in the farm,
security systems employed in banks and other places where
high security is required. i.e., control of almost any devices
that are possible even from thousands to several thousand
kilometres.
II. DUAL TONE MULTI-FREQUENCY TECHNOLOGY
The technique used so far in this paper for the switching
and controlling of various devices that are far away from
the user is called DTMF (Dual Tone Multi-Frequency)
technique. It was named so because it uses a signal
comprising of two pure tones known as dual tone multifrequency signal. These DTMF tones are taken from a
matrix containing row (high) frequency and column (low)
frequency. The following table provides the DTMF keypad
frequencies.
TABLE.1 DTMF keypad frequencies
Hz
1209
1336
1477
1633
697
1
2
3
A
770
4
5
6
B
852
7
8
9
C
941
*
0
#
D
Thus the DTMF tone is an algebraic sum of the higher
and the lower frequencies. For example, if key 7 is
pressed, then a tone which is the summation of the two
frequencies 852Hz and 1209Hz is heard at the other end
of that call. These DTMF tones can be represented by
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International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue4- April 2013
using the following equation as,
F (t) = sin (2π t) + (2π t) + ….
(1)
Where sin (2π t) are two different Frequencies and F (t) as
the resultant DTMF signal, Also belongs to the low
frequency group and belongs to the high frequency group.
Each of these two frequencies represents the resultant
DTMF signal frequency. During the course of a call, if any
button is pressed, a tone corresponding to that particular
button is heard at the other end of that call. This tone is
called as dual tone multi-frequency tone. This received tone
is processed by ATMEGA168 microcontroller with the
help of the CM8870 DTMF decoder.
III. DUAL TONE MULTI-FREQUENCY DECODER
In this paper, the DTMF decoder used is CM8870. It
is used to decode the mobile’s audio signal, i.e., the keypad
tone. When the user presses a button in the keypad of the
mobile, it generates two tones at the same time. These tones
are taken from a table comprising of a row frequency and a
column frequency. Thus the resulting frequency signal is
known as “Dual Tone Multi-Frequency” signal. A DTMF
signal is an algebraic sum of two different frequencies, one
from the row frequency (higher frequency) group and another
from the low frequency (column frequency) group. The
CM8870 decodes the received DTMF tone and then sends its
equivalent binary code to the microcontroller. According to
the program loaded into the microcontroller, the
corresponding action starts. The DTMF controller used here is
ATMEGA168. It is ideal for control of almost any devices
even from remote places. This controller unit continuously
monitors the user’s phone line and identifies the proper user
touch tone sequences for the proper control of devices in and
around home, office, shop, barn or bank. It is comprised of
the features such as sensing of the tone, examining of the
incoming signals by using DTMF decoder and controls the
outputs by relay switching. At the time of calling, the mobile
attached to the system to be protected picks up the call
automatically. DTMF tone detection and decoding is done by
DTMF decoder. Based upon the program loaded into the
microcontroller, it senses which button is pressed and
corresponding actions takes place. It acts by utilizing the
DTMF signal. When the output of the relay driver is high,
then the corresponding relay can be switched and controlled,
thereby the control of devices that are connected to that
particular relay can be made possible. These devices can be
switched ON and OFF based on the program loaded into the
microcontroller by the user. Here, in this paper, the
microcontroller is programmed using arduino board.
ISSN: 2231-5381
IV.GSM BASED DEVICE SWITCHING MECHANISM
The relay driver used in this paper is ULN2004. When the
output pin of this relay driver is high, then the
corresponding relay can be switched and then controlled.
Ie., the devices connected to that relay can be switched ON
and OFF based on the command given by the user. In this
paper, it is possible to connect up to 8 devices using this
relay driver. The microcontroller can be pre-programmed
to output its decision to the relay driver ULN2004 in order
to drive the relay. In this paper, various devices are
switched and controlled by a mobile phone (sender) that
makes a call to the mobile phone (receiver) attached to the
system. This is clearly shown in the block diagram given
below. The first block is the sender mobile. The user makes
a call using this mobile to the second mobile, ie., the
receiver mobile which is connected to the system. This
receiver mobile is connected to the system via a
microphone. The incoming call is then picked up
automatically. When a particular key is pressed during the
course of a call, a corresponding tone is heard at the other
end of that call. This amplified DTMF tone is received and
decoded by using a DTMF decoder CM8870 and this
decoded signal is fed to the microcontroller ATMEGA168.
CM8870 will give the corresponding binary value of the
tone or key pressed.
DTMF Decoder
Microcontroller
(CM8870)
(ATMEGA168)
Channel
Audio Amplifier
Relay Driver
(ULN2004)
Mobile
(Receiver)
Microphone
Load
Mobile (Sender)
Fig.1 Block diagram of the GSM based device switching mechanism.
According to the program loaded in the microcontroller,
the relay performs the required action with the help of
the relay driver ULN2004. Once the connection
between these two mobile phones is established,
whatever the key is pressed at the sending end, the
corresponding DTMF tone is heard at the receiver side.
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International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue4- April 2013
V. CONCLUSION
The fields of GSM and DTMF technology are moving
towards an unimaginable path nowadays. This paper deals
with a simple and humble attempt to make people aware of
the new innovations in this field. Even though this project is
not an expensive one, its importance and future applications
make it very precious. This project has the capability that it
can be added with many additional features in the nearby
future. The GSM based device switching using DTMF
technology is thus really very efficient, simple and reliable
and also can be used for a variety of applications. Addition of
hardware and changes in programming would make the
project to have such an undertaking possible.
REFERENCES
[1]
[2]
[3]
[4]
[5]
[6]
Haddon.L (1995), “Home Automation: Research Issues”,
Second EMTEL Workshop, Amsterdam, Netherlands Electronics
for You.
Khiyal.M.S.,(2009), “SMS Based Wireless HACS for Automating
Appliances”, Issues in Informing Science and Information
Technology
Manju.A., (2010), “ZigBee for Multiple Device Control Using a
Single Remote”,
Ladwe.M.T., (2009), “Control of Home Appliances Using
DTMF Technology”
Pande.N., (2007), “DTMF Technology”, Electronics for
You
Shahriyar.R., (2008), “Remote Controlling of
Home
Automation
Using
Mobile Technology”, International
Journal of Smart Home.
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