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  Home automation BLOCK DIAGRAM:




                                         Figure 1 – Block diagram of the scheme (Proposed)


At first, user calls the cellphone connected to system. Cellphone connected to the controller is in auto-answering mode. User sends command by pushing the keys. Mobile at system receives the DTMF tone and passes it to the DTMF decoder, which decodes the keys and the code is send to the microcontroller (AT89c51). Based on the received code, microcontroller gives signal to the relay driver to operate on the devices.



                                   Figure 2 – Block diagram of the circuit performed


On performing the above circuit in fig.1, programming with microcontroller led to few irregularities in the output. So, we replaced the microcontroller with 4:16 Decoder to perform the same switching and selection action. The remaining circuitry is similar except that here the decoder provides the control signal to the relay driver to operate devices. Also we utilized J-K Flip Flop to latch or hold the output state and toggle it for the next control input to facilitate the switching action over devices.