cell phone operated switch

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Mobil e DTMF Based Decode r Rela y Rela y Cell phone operated switch In Our project we have utilized the GSM for automating the lights on/off to facilitate the user a low cost home automation circuitary.Since it is operating on GSM networks a person is able to switch the load from any place in the world.

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Page 1: Cell Phone Operated Switch

MobileDTMFBasedDecoder

Relay

Relay

Cell phone operated switch

In Our project we have utilized the GSM for automating the lights

on/off to facilitate the user a low cost home automation

circuitary.Since it is operating on GSM networks a person is able

to switch the load from any place in the world.

Circuitry is based upon the DTMF (Dual Tone Multi Frequency)

tones which are received whenever the mobile call is

attended ,we noticed that when we press the keys on a standard

Page 2: Cell Phone Operated Switch

telephone keypad, an audible ‘beep’ is generated. These beeps

are actually the combination of two distinct frequencies. For

example, the tone you hear when you press the number ‘9’ on a

telephone, is actually a combination of a 1447 Hz and 852 Hz

signal. In a telephone exchange, these signals are decoded by a

computer which finally connects the dialer to the designated

phone line. For example, the tone of 1447 Hz and 852 Hz will be

decoded as binary ‘1001’. In this project, I have designed a simple

DTMF decoder circuit which allows me to control appliances in my

house from any place on Earth using a telephone.

I always wanted to be able to control things such as air-

conditioners, lights, etc, remotely…but I never thought about

Page 3: Cell Phone Operated Switch

putting the front door of my house under remote control. It’s a

door that will unlock when the correct knock pattern is

performed. After being inspired by the mechanical door opening

system in that site, We decided to do something similar to allow

us to switch on and off the load with a cell phone! Here we mean

c’mon, switches with keys are obsolete..everyone uses

them..they’re so old fashioned! They’ve been around for over

4,000 years. Yikes! It’s time for a little change.

The Main part of this project was to build a DTMF decoder circuit.

I used a CM8870PI tone decoder IC for doing this. The circuit I

have built is fairly simple, and can be used for controlling up to

four devices. If you want to control more than four devices, check

out this circuit. We had a Nokia 1100 cell phone lying around with

a hands-free accessory which was rarely used. So, I hacked its

hands-free accessory and connected it to the circuit (just cut the

wires which went into the earpiece). That’s about it! To control

Page 4: Cell Phone Operated Switch

things in the house, you just dial into the base station and the

Nokia 1100 auto-answers the phone call. Each function is just a

matter of pressing the appropriate number on the phone and the

DTMF chip decodes it and sends output to a transistor which

controls a relay. To turn on any load , we have to just dial the

phone, enter the code