cell phone operated switch
TRANSCRIPT
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
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
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
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