Electronic Phone Directory with Built-In Automatic Dialer

Overview

The project was designed and implemented to allow user to dial, enter, search, and delete entries in an electronic phone directory.

Explanation

The Dual Tone Multi-Frequency (DTMF) signals is being generated by the Atmel 8515 microcontroller when dialing and corresponds to the phone number being dialed. A DTMF decoder was used to detect what number is dialed by the user in order to avoid building the phone circuit for the dialer. The 5 basic modes in the E-Directory include the entry, search, scroll, delete, and dial mode.

The dial tone corresponds to each digit in a dual tone telephone system which is a superposition of two sine waves with different frequencies. The microcontroller generates a sequence of DTMF pulses that correspond to the sequence of phone number digits when the user chooses a phone number.

A DTMF decoder decodes the signal in order to check if the microcontroller has generated the correct dual tone signal. The chip has 4 output pins that indicate the decoded digit, which will be connected to another MCU to map the 4 output value to phone numbers and interfaced with another LCD to display the decoded number.