The mentioned project is based on the world,s most powerful intel controller 8051.You can open your door latch using your mobile phone or land line phone Not only it can operate the latch of your house it can also dial out a telephone number in case of security threat. The threat could be from fire or a inturder.
The device is password protected. User can change the password .and security telephone number ,the number on you will like to receive emergency call from your home /office in case of any security breach. After eight rings you will hear ‘please enter your password.’ When you enter the password. If your password is correct then device will open the latch only for ten seconds that is the enough time to enter the apartment or you keep the door open for the required period of time ,latch will shut automatically with its own spring tention when you shut the door.
The said project is designed on the dtmf decoding.our modern telephone and even our mobile phone uses dtmf coding for number dialing. These dtmf codes can be decoded and utilised for useful purposes. The circuit utilises ic8870 for dtmf decoding .
Microcontroller 89c51 reads these codes and takes the necessary action. Door latch can be opened by entering the correct password , you can also connect security sensors of your choice ,in case of any breach of security takes place , the device will dial out the prestored number and delivers an emergency message.
Circuit description: telephone line is connected at connector k1. Whenever someone calls this number, that time telephone line carries about 70v ringing signal signal is rectified by the bridge d5-d8 and filtered by c4, r20, and d9 and drives an opto coupler ic u8 mct2e .
Collector of the optocoupler will go low whenever bell rings. Since the collector is connected to p2.7 of microcontroller 89c51. Number of times it goes low is counted by microcontroller. After six to eight rings,p1.0 will go high and switch on transister t4 and energise the off hook relay rl1 . The contects of relay rl 1 will become closed and the telephone line will get connected to dtmf decoder ic 8870, through c7 and c8. Resistance r8 comes across the telephone line and that lowers the voltage,and this ultimately sends messages to exchange the user has lifted the hand set.
At the same time ,microcontroller pin p3.5 will trigger the voice ic api8208 where all the messages are stored. Caller will get the message”please inter the passward”the default password is 1-2-3-4-5-6. When caller enters this 6 digit password. Ic 8870 decodes these numbers and binary numebrs are available at q1 to q4 ,pin no 11-14 of dtmf decoder whenever new code comes pin no 15( stb) of dtmf decoder will pulse low, and is connected to p1.1 informing microcontroller that codes are available please take them.
Microcontroller will reads these codes one by one, through its line p1.2-p1.5. If the codes matches with the codes inside the microcontroller, microcontroller will switch on the electro magnetic operated latch for 10 seconds and user can enter the apartment . If the passward entered is not correct. Microcontroller will disconnect the telephone line without any reply, by making p1.0 low.
If the password entered is correct. You can also change the password stored. This password stored goes into serial eprom ic 9346 that is non volatile ram in case power fails the password is not lost
If you want to change the password follow these steps:-
Dial this number from other line after six to eight bells you will receive message ” please enter your password”. (1,2,3,4,5,6 and #)so you enter your password and wait for the message if you enter 2 then device will respond please enter new password when your password entry is over press # after passowrd entry indicate that your entry is over and microcontroller will respond “your password has been changed’’ keep the hendset back on the instrument from where you are calling.next time when you dial ,you will have to enter your new password.
Similarly you can also change the telephone number.
Ic u7 4047 acts like watchdog as long communication is going on it does nothing the movement communication is over its out put at pin no 10 connected to pin p3.2-int0 will interrupt the processor and processor will make the p1.0 low and disconnecting telephone line .the time to switch off the off- hook relay is decided by c6 and r19 connected to ic 4047.transister t1 and t2 drives the led d12 to give visual indication of communication. Transformer tr1 is 1:1 transformer (160 ohm) provides isolation between telephone line and speech circuit.
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