High Level Design

E-Directory

The E-Directory has 5 basic modes whose functions and "responses" are described below:

Entry Mode:

  • Let user enter name (maximum 20 characters).

  • Press Enter.

  • Let user enter phone number (maximum 20 characters).

  • Display 'stored entry'.

Search Mode:

  • Let user enter name.

  • Press Enter.

  • Display name and phone number.  If not found, display the last entry in database.

 

Scroll Mode:

  • Display name and phone number of the current entry.

  • Let user scroll through database with button up and down.

 

Delete Mode:

 
  • Display name and phone number of the current entry obtained from scroll or search mode.

  • Ask if user wants to delete the current entry.  Display 'Delete?'

  • If user presses 'Enter', delete current entry and dispaly 'Deleted.'.

 

Dial:

 
  • Display name and phone number of the current entry obtained from scroll or search mode.

  • Ask if the user wants to dial the phone number of the current entry.  Display 'Dial?'.

  • If the user presses 'Enter', it dials the current phone number and display 'Dialing'.

 

 

Tone Generator

In a dual tone telephone system, the dial tone corresponding to each digit is in fact a superposition of two sine waves with different frequencies.  Once the user chooses a phone number from the e-directory to dial, the microcontroller will generate a "sequence" of DTMF pulses that correspond to the sequence of phone number digits.  Since the length of phone number varies according to the destination of the call, e.g. long distance call consists of 10 digits including the area code for the central office, our e-phone directory allows the user to dial up to 20 digits for the phone number.  The combination of frequencies corresponding to each digit is given below:

  Click on the numbers to see the waveform

 

 

 

 

DTMF Decoder

In order to check if the microcontroller has generated the correct dual tone signal, a DTMF decoder chip was used to decode the signal.  The decoder chip has 4 output pins that indicate the decoded digit.  To map these 4 output value to phone numbers, these 4 pins will be connected to another MCU which is interfaced with another LCD to displayed the decoded number.