The project is proven to be opened by using Morse code to open doors operated by intercoms.
In order to apply Morse codes, electric strikes are entered for a few seconds just like dialing proper sequence of short and long signals. The microcontroller recognizes the pulses (tone melody) received by the system from CA line. The correctness and the type of entered symbol if a dot or dash are determined on the basis of counting their duration.
- For dot, it is represented by a pulse less than or equal to 0.3s
- For dash, it is represented by a pulse greater than 0.3s and less than or equal to 1s
- For checking the correct code, no pulse is received during 1.5s
Beeps are used to inform the caller of any errors since the system is connected to the microphone line. If the button is held down too long, 1 low beep is produced. For incorrect code, 2 low beeps and for too long code, 3 low beeps are produced. To avoid confusion for the unaware caller who usually calls once, errors are reported from the second entered symbol. The 4 high beeps will be heard and the electric strike will be released for 3 seconds when the code is entered properly.
An external power supply is needed because it is impossible to power it from microphone or electric strike since it consumes less more than 20mA during the operation of opening the lock.
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