Home Automation through Cellphone Keying (H.A.C.K)

I always wanted to control my lights and other appliances in my room remotely while I’m somewhere else. Many a times I forget to switch off the fan or AC in my room and then I have to go back and switch it off. I always wondered how cool it would be if I could control my appliances through something like my cellphone (which I never forget to take). Well now I can see that dream right in front of me. Yes, its yet another hobby project by Kaushani and me. Its the ‘Home Automation through Cellphone Keying(H.A.C.K)’ .

Fig.1 H.A.C.K’s Main Circuit

For those who are not aware of, for every key press on a standard telephone keypad an audible ‘beep’ is generated. It actually is a signal which is a combination of two distinct frequencies i.e. every key is uniquely defined by the combination of two distinct frequencies. Many (multiple) frequencies are used in which combination of any two defines a key on your keypad hence the name ‘Dual Tone Multiple Frequencies (DTMF)’‘

Fig.2  DTMF  Frequency Combinations

H.A.C.K uses a Full DTMF receiver CM8870 from CMD which gives the binary output of the key being pressed. For more details refer the datasheet.

Fig 3 DTMF Receiver Circuit

The DTMF receiver circuit is interfaced with an ATmega16 MCU which is used to drive the external appliances ON or  OFF. For demonstration purpose I’ve used 3 leds to be my external appliances. I’ve also used my old NOKIA 2300 in the automatic answer mode and the earphone is used to give input to the DTMF receiver circuit.

Working:

• Call the control phone from any other phone from anywhere in the world.
• The control phone being in the automatic answering mode picks up your call.
• Press the correct password to have access.
• If the password is correct a buzzer will ring which you can hear through your phone   otherwise you can’t control the appliances.
• Press Keys on your phone to control your appliances.
• I’ve used the keys 1 to 7 to control the LEDS  but the other keys 8,*,0,# can also be included.
• I’ve not used any password in the demonstration.

Feel free to post your queries and feedback in the comment section below.

GALLERY