Telephone Switching

INTRODUCTION

Telephone is the most useful and widely accepted innovations of this century. It is thru this medium that people come together even though residing at different parts of the globe. Due to the advancement in this technology not only voice but data as well as video information could be transferred.

With respect to dialing telephone instruments can be divided into two types, the rotary dialing type and the pushbutton type. The former type generates pulses mechanically and the latter electronically. Talking about pulses they are generated by the make/break of contacts, which actually connect/disconnect the line connected to the instrument, which travel across the line and the exchange recognizes them as numeric information. The advantage of the keypad type is that the keystrokes are recorded by an I.C, so that we dial at our will and still the pulses are sent in their normal and fixed duration and speed. The added advantage being that we also have redialing.

This form of dialing becomes tedious especially when dialing long numbers. So a new adaptation was invented known as tone dialing also known as fast dialing by many of then. The principle behind this technique is that every key is assigned a unique (or two!) tone or frequency. So 8 digits only generate 8 different tones instead of a multitude of pulses depending on the digits pressed. The technology is known as DTMF dialing (Dual Tone Multi-frequency). There is no make/break of the line so the person in conversation could even press the keys and the person on the other side can also here the tone. It is this concept that this project is banking on. The tones received are decoded into their relevant digital information, which becomes purposeful data to operate the unit.

Note: The telephone instrument could be switched into tone dialing mode by pressing the <*> button before dialing or some equipments have a permanent Tone / Pulse switch.

FEATURES

Ø 8051 compatible processor.

Ø Eight devices of 220v 5A rating can be directly connected.

Ø Relays used to switch applications ON or OFF for total isolation.

Ø Unit acknowledges with Different tones for different operations.

Ø Visual indication of channel & Lift status.

Ø Previous switch information retained even on power down.

Ø Data stored on EEprom.

Ø Auto cutoff after 10 Seconds if no response from the user.

Ø Isolated from telephone lines thru a Line Transformer for protection.

Ø Status of channels can be known.

Ø Only authorized users allowed to operate by entering an access code.

Ø Single supply operation.

Ø Fully embedded design.