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You can call up on your colleague's mobile number and ask him/her to turn on or off the lights or other appliance of your office. You may be any where in the world at that time, as mobile network allows to to talk to anyone present anywhere in this world. But your colleague is too much for this simple job! Your may replace him/her with this smart gadget and let it operate the appliances. But how it will do that? well, it will listen to the audio output from a mobile phone and try to recognise the DTMF tones present in the output sound. DTMF is a way to encode numerical data into an audible sound which is then sent over an audio channel. Keypress on the other mobile will generate DTMF codes.

Keys like 1,2,3 and 4 are used to switch on/off up to four loads like light, fan, water pump in a building.

The user(who is away from home) using his/her mobile phone calls another mobile (which is present at the home and is attached to the this system) and then press keys on his/her mobile phone to controls the load in the home. The mobile attached to the system receives tones from the user's mobile and sends them to the DTMF decoder module over an audio cable. The DTMF decoder module converts this tone to a 4 bit binary number which is then sent to a ATmega8A AVR microcontroller which controls output relays using four of its port pins. These relays can be used to switch AC mains powered appliances like bulbs and fans.

home appliance control over mobile network

Things required

S. No Item Image Cost
1. 28 PIN AVR Development Board atmega8 development board
Rs. 286
2. DTMF Decoder Module with Audio Cable dtmf decoder
Rs. 130
3. Relay Board relay board
Rs. 100
4. Connecting wires wires
Rs. 50
5. 12V 1A Adapter adapter 12v
Rs. 134
6. Mobile phone with 3.5mm audio socket -
    Total Cost
Rs. 700

You can buy all of the required parts from eXtreme Electronics web store and get them delivered to your doorsteps!


Table: Connection between DTMF decoder and AVR development board

DTMF Decoder Board 28 PIN AVR Development Board
Std PC4
Q4 PC3
Q3 PC2
Q2 PC1
Q1 PC0

Table: Connection between Relay Module and AVR development board

DTMF Decoder Board 28 PIN AVR Development Board
V 12V

NOTE: You can connect up to four relay boards to the circuit. Connect the S pin of the relay boards to PB1, PB2 and PB3 pins.


Load your AVR development board with the HEX file of this project using eXtreme Burner AVR and also set high fuse = E1 and low fuse byte to D9


For best results

  1. Keep the volume level of the mobile phone (connected to the system) between 70-90%
  2. Mute your mobile, this will prevent it from picking up noise from the surrounding and sending them along with DTMF. When your mobile is muted, it will only send clean DTMF signals which will be easier to decode.

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Hanumant, Keivanjan, Alijraar, Ismail, Ragab Ali, DAWAR KATFUN PHILEMON, Florence, Shakir, Hanumant Dhande, Oleg, Jalil Ahmad, Girish Harmukh, Chockalingam, Adil, Thinleha6787, Rakesh, Aniket, Mahendra Pawase, Onome, Pushpa K, , Bibin Chacko, Davor, Abdulmajeed, Anurag,