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EE112 - Term paper

Land-line Cordless phone and Modem

By

Bhargava B (100070054)

Surya Kazipeta (100070055)

Savant Krishna (100070056)

I

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TABLE OF CONTENTS

1.Introduction 1

2.Receiver 2

3.Keypad 3

4. LCD Display 5

5.Main PCB of the phone 7

6.Dial-up Modem 8

7.Bibliography 9

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1 . Introduction :

This term paper focuses on the internal parts of a typical cordless landline phone and a

modem.

It will unveil the mechanism of working of the device and identify the role of each part of thedevice in the working. We attempted to learn the basic working of a cordless telephone and

also a modem.

The opening of the base :

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2.Parts of the device :

2.1 Receiver :The receiver is used for listening to the voice using the

speaker and talking to using the microphone.

The large metal piece is used to reduce attenuation

between the speaker and transmitter

(receiver/microphone).

Receiver

Microphone and earpiece of the receiver

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2.2 The keypad

The keypad uses a touch-

tone dialling and the Dual-

tone multi-frequency

signaling (DTMF), which is

used for telecommunication

signaling over analog

telephone lines in the voice-

frequency band between

telephone handsets and other

communications devices and

the switching center. The

version of DTMF that is used

in push-button telephones for

tone dialing is known asTouch-Tone. It was first used

by AT&T in commerce as a

registered trademark.

The Touch-Tone system,

using the telephone keypad,

gradually replaced the use of

rotary dial starting in 1963

and since then DTMF or

Touch-Tone became the

industry standard for bothcell phones and landline

service

The technology of touch-tone system :

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The technology uses the compression molding properties of silicone rubber to create angled

webbing around a switch center. On depression of the switch the webbing uniformly deforms

to produce a tactile response. When pressure is removed from the switch the webbing returns

to its neutral position with positive feedback. In order to make an electronic switch a carbon or

gold pill is placed on the base of the switch center which contacts onto a PCB when the web

has been deformed.

The silicone keypad looks like below.

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2.3 The Display :

The figure below shows the display chip. It is connected to the Main Board(Section 2.4) of the

telephone by a flex cable carrying about 26 lines. It also is connected to the keypad (Section2.2) byanother flex cable of 14 lines.

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The PCB is connected to the LCD

by a thin cable. LCDs with a small

number of segments such as here

in this case have individual

electrical contacts for each

segment. An external dedicated

circuit supplies an electric charge to

control each segment. This display

structure is unwieldy for more than

a few display elements. These are

known as Passive-matrix

addressed LCDs.

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2.4 The Main Board :

The block diagram of a complete solid-state telephone is as shown below

And the actual main chip photographed during the opening is shown below.

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Some ICs which have been identified are

UTC2410 - The UTC2410 is a bipolar integrated circuit designed for telephone bellreplacement.

LM7805 - The LM7805 is a 3-terminal positive voltage regulator.

Samsung S711 S1T8528X01 - It is a one-chip RF IC used in high performance CTO

CLP systems.

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2.5 The Modem :

Modemis an abbreviation for Modulator Demodulator. A modem converts data from digital

computer signals to analog signals that can be sent over a phone line (modulation). The

analog signals are then converted back into

digital data by the receiving modem

(demodulation). A modem is given digital

information in the form of ones and zeros by the

computer. The modem converts it to analog

signals and sends over the phone line. Another

modem then receives these signals, converts

them back into digital data and sends the data to

the receiving computer.

The important ICs in the modem are :

PCTEL PCT789T-C1 : It is a 56K micro-modem, the main chip of the board .

PCT303L & PCT303D : Modem components .

UTC LM386 :It is a low voltage audio power amplifier.

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Bibliography :

1. Data sheets for ICs

http://www.fairchildsemi.com/ds/LM%2FLM7805.pdf

http://samsung.icfull.com/datasheet/S1T8528X01-Q0R0-PDF.html

http://www.suncoming.com/pdf/UTC2410e.pdf

2. Wikipedia

http://en.wikipedia.org/wiki/Liquid_crystal_display

http://en.wikipedia.org/wiki/Telephone

http://en.wikipedia.org/wiki/Keyboard_technology

http://en.wikipedia.org/wiki/Silicone_rubber_keypad

http://en.wikipedia.org/wiki/Dual-tone_multi-frequency

3. Other Misc. webpages

http://www.madehow.com/Volume-5/Telephone.htmlhttp://antiquetelephonehistory.com/telworks.html

http://electronics.howstuffworks.com/lcd4.htm

http://www.nippyinternet.co.uk/

4. Understanding Telephone electronics byStephen J. Bigelow, Joseph J. Carr, Steve Winder

http://books.google.com/books?id=ITe2DyrbtdsC

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