08-02-2013, 10:11 AM
Control of Remote Domestic System Using DTMF
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Abstract
The human mind always needs information
of interest to control systems of his/her choice. In the
age of electronic systems it is important to be able to
control and acquire information from everywhere.
Although many methods to remotely control systems
have been devised, the methods have the problems
such as the need for special devices and software to
control the system. This paper suggests a method for
control using the DTMF tone generated when the user
pushes mobile phone keypad buttons or when
connected to a remote mobile system. The proposed
work has been done experimentally and has been
verified in real time.
INTRODUCTION
The remote control technologies have been used in the
fields like factory automation, space exploration, in places
where human access is difficult. As this has been achieved
in the domestic systems partially [1], many corporations
and laboratories are researching the methods which enable
human to control and monitor efficiently and easily in the
house or outdoor. Controlling the domestic system
regardless of time and space is an important challenge. As
the mobile phone enables us to connect with the outside
devices via mobile communication network regardless of
time and space, the mobile phone is a suitable device to
control domestic systems.
This paper proposes a method to control a domestic
system using a mobile phone, irrespective of the phone
model and mobile phone carrier. The system suggested
consists of the mobile phone normally registered in
communication service and a computer that can receive a
call from another phone. Existing methods for control and
monitoring, using mobile phones have usage problems
because the cost and need for continuous control. One of
the disadvantages, being the lack of feedback during the
process.
DTMF BASICS
DTMF is a generic communication term for touch tone
(a Registered Trademark of AT&T). The tones produced
when dialing on the keypad on the phone could be used to
represent the digits, and a separate tone is used for each
digit. However, there is always a chance that a random
sound will be on the same frequency which will trip up the
system. It was suggested that if two tones were used to
represent a digit, the likelihood of a false signal occurring
is ruled out. This is the basis of using dual tone in DTMF
communication.
DTMF dialing uses a keypad with 12/16 buttons. Each
key pressed on the phone generates two tones of specific
frequencies, so a voice or a random signal cannot imitate
the tones. One tone is generated from a high frequency
group of tones and the other from low frequency group.
The frequencies generated on pressing different phone
keys are shown in the Table 1.
SIGNAL CONDITIONING
Before a decoded tone pair is registered, the receiver
checks for valid signal duration (referred to as characterrecognition-
condition). This check is performed by an
external RC time constant driven by ESt. A logic high on
ESt causes VC (see block diagram Fig. 3) to rise as the
capacitor discharges. Provided that signal condition is
maintained (ESt remains high) for the validation period
(tGTF), VC reaches the threshold (VTSt) of the steering
logic to register the tone pair, thus latching its
corresponding 4-bit code (see DC Characteristics in Data
Sheet) into the output latch. At this point, the GT output is
activated and drives VC to VDD. GT continues to drive
high as long as ESt remains high. Finally, after a short
delay to allow the output latch to settle, the delayed
steering output flag (StD) goes high, signaling that a
received tone pair has been registered. The contents of the
output latch are made available on the 4-bit output bus by
raising the three-state control input (OE) to logic high.
The steering circuit works in reverse to validate the inter
digit pause between signals.
RESULTS AND DISCUSSION
The DTMF signal waveform is shown in Fig 4. The two
waves can have phase difference of an arbitrary value.
The system is immune to external noise and the ring tone
of the receiver mobile phone. There is a finite probability
that the system turns on or turns off due to ambient noises
like voice, sound arising from door latches etc.
The circuit was built and tested. Refer Fig.5 for the
picture of tested circuit. The device controlled was a
230V / 23W Power Saving Bulb. The mobile phone at the
receiver’s end is controlled by the computer using
hyperterminal and AT commands.
CONCLUSION
This paper presents a method to control a domestic
system using the DTMF tone generated by transmitting
telephone instrument when the user pushes the keypad
buttons of the mobile phone connected to the remote
domestic system. This control method uses commercial
mobile communication networks as the path of data
transmission. This enables the user to control the system
continuously by sending the mobile phone DTMF tone.
This system is implemented in the 2G mobile
communication network, so video data cannot be
obtained.