26-11-2010, 12:29 PM
[attachment=7305]
HOME AUTOMATION USING MOBILE COMMUNICATION
INTRODUCTION:
Here is a circuit that lets you operate your home appliances like lights and water pump from your office or any other remote place. So if you forgot to switch off the lights or other appliances while going out, it helps you to turn off the appliance with your cell phone. Your cell phone works as remote control to your home appliances. You can control the desired appliance by presetting the corresponding key. The system also gives you voice acknowledgement of the appliance status.
The Project “Home Automation using mobile communication” has different sections such as:
1. Microcontroller
2. DTMF decoder
3. Voice recording and playback device
SPECIFICATION
1. Microcontroller
I/P Requirements
1. Operating Voltage -> 6-9Vdc ± 10%
2. Input current -> 100mA
3. Battery used -> 6V, 4.5A
O/P Requirements
1. O/P Voltage -> 6-9Vdc ± 10%
2. Ripple voltage -> 1-5%
3. Current -> 250mA
2. DTMF decoder
I/P Requirements
1. Operating Voltage -> 5-6Vdc ± 10%
2. Input supply -> 230Vac, 50Hz
3. Input current -> 250mA
4. Protection -> Medium blown Fuse
O/P Requirements
1. O/P Voltage -> 5v ± 10%
2. Ripple voltage -> 1-5%
3. Relay -> 6Vdc, 200Ω
4. RMS current -> 1A
3. Voice recording and playback device
I/P Requirements
1. Operating Voltage -> 12Vdc ± 10%
2. Input supply -> 230Vac, 50Hz
3. Input current -> 250mA
O/P Requirements
1. O/P Voltage -> 5v ± 10%
2. Ripple voltage -> 1-5%
3. Relay -> 12Vdc, 200Ω
4. RMS current -> 1A
APPLICATIONS
As name suggested, it is going to be used in home automation. It is used to control the home appliances by mobile phone from anywhere.
BLOCK DESCRIPTION
In the course of a call, if any button is pressed, a tone corresponding to the button pressed is heard at the other end of the call. This tone is called ‘dual-tone multiple-frequency’ (DTMF) tone. The received tone is processed by the AT89C51 microcontroller with the help of DTMF decoder MT8870. The decoder decodes the DTMF tone into its equivalent binary digit and this binary number is sent to the microcontroller.
DTMF signaling is used for telephone signaling over the line in the voice-frequency band to the call switching centre. The version of DTMF used for telephone tone dialing is known as ‘Touch-Tone.’ DTMF assigns a specific frequency (consisting of two separate tones) to each key so that it can easily be identified by the electronic circuit. The signal generated by the DTMF decoder is a direct algebraic summation, in real time, of the amplitudes of two sine (cosine) waves of different frequencies, i.e., pressing ‘5’ will send a tone made by adding 1336 Hz and 770 Hz to the other end of the line.
CIRCUIT DESCRIPTION
The circuit diagram shows the circuit diagram of home automation using mobile communication. It comprises microcontroller AT89C51, DTMF decoder MT8870, voice recorder and playback device APR9600 and a few discrete components.
Microcontroller AT89C51 is at heart of circuit. It is high performance, low power, 8 bit microcontroller with 4 KB of flash programmable and erasable read only memory used as on-chip program memory, 128 bytes of RAM used as internal data memory, 32 individually programmable input/output(I/O) lines divided into four 8bit ports. A 11.0592MHz crystal (XTAL1) is used to provide basic clock frequency for the microcontroller. Capacitor C3 and resistor R3 from power on reset circuit, while push to on switch S20 is used for manual reset.
Port pins P1.0 through P1.7 of the microcontroller are configured to get the input from push to on switches S1 through S8. Pins of port1 are pulled high via resistor network rnw1. Port pins p2.0 through p2.4 are configured to receive the decoded signal from DTMF receiver MT8870. The functions of corresponding switches (S1 through S8) and cell phone keys are shown in table I.
The DTMF decoder is used for decoding the mobile signal. It gets DTMF tone from the mobile headset’s speaker pins and decodes it into 4 bit digital signal. The DTMF decoder is operated with a 3.579 MHz crystal (XTAL2). In DTMF receiver MT8870 (IC3), capacitor C12 is used to filter the noise and resistors R6 and R7 help to amplify the input signal using the internal amplifier.
Pin 16 of IC3 connected to resistor R5 provides the early steering output. It goes high immediately when digital algorithm detects a valid tone pair (signal condition). Any momentary loss of signal condition causes ESt to return to low state. Pin 17 of IC3 connected to capacitor C11 is bidirectional, acting as steering input/guard time output (St/GT). A voltage greater than threshold of steering logic VTSt detected at St causes the device to register the detected tone pair. The guard time output resets the external steering time constant, and its state is a function of ESt and voltage.
The 230v AC main is stepped down by transformer X1 to deliver the secondary output of 9V, 500mA. The transformer output is rectified by a full wave bridge rectifier comprising diodes D1 through D4, filtered by capacitor C16 and then regulated by IC7806 (IC5). Capacitor C15 bypasses the ripples present in the regulated 6V power supply. LED3 acts as a power on indicator and resistor R16 limits the current through LED3.
Recording and Playback:
To record the voice in IC2, follow Table III. Close SPST switch S19 to make pin 27 of IC2 low. Thereafter, press and hold switches S9 through S16 to record corresponding voice message. LED2 flashes to indicate audio recording.
For playback of any device status, open SPST switch S19 and press the corresponding switch (S9 through S16). The recorded audio can be heard from the speaker connected to pins 14 and 15 of IC2.
