How Telephone Works

Present by:Chongbo You

SeungJae Baek Qihui Yu

Description

Telephone

• It is one of the most important inventions 1800s and an useful tool of daily communication among people.

• Technology of telephone developed dramatically since the invention. Improvement of technology changed people’s life considerably.

• The functions of telephone became more and more various.

• In the 1870s, there were two

inventors for telephone, Elisha

Gray and Alexander Graham

Bell. They debated over the

invention of telephone and

Bell has won. Bell’s telephone

was based on telegraph

technology.

• The first telephone sent

signals to the air pressure of

the original sound and when

the voice passes the

transmitter, it changes into

variable electric current.

History and Development

Alexander Graham Bell's Telephone Patent Drawing, 03/07/1876.

• Soon Thomas Edison invented two

most important inventions. He

developed the first commercially

practical transmitter and receiver.

• Edison also invented carbon

microphone which produced louder,

cleaner signals travelling longer

distance.

History and Development

• In 1880s, there were no dial pads or the ring tone.

They had to contact the operators and the

operators were usually women who are pleasant.

• By 1900 the rotary dial was developed and slowly

placed into the phones. Slowly improvements

were made in quality of service and calling

capacity. Radio telephone links created the first

long distance service between England and the

U.S. in 1927.

History and Development

• The first computerized switchboard was put into

service in 1976. Furthermore, coaxial cables were

placed in 1940s that reduced interference and

increased calling capacity for the ever expanding

telephone system.

• Digital transmission was introduced in 1962. In

the old analog system, the electronic signal in the

wire looks like the sound waves in the air.

History and Development

• As technology continue to improve, telephone becomes smaller and smaller. Telephone develops into cellphones becoming portable.

• Cellphones are convenient and easy to operate. It becomes a trend to have cellphones.

• The functions of cellphones expand significantly. It not only can communicate by making calls and sending messages, but also can search on the Internet and use various applications.

History and Development

How Telephone Works

In order to understand how

telephone works, we will introduce

you the simplest phone structures,

and the functions and basic principle

of each part.

How Telephone Works

Basic Parts of a Telephone:• Speaker• Microphone• Hook Switch

From HowStuffWorks.com

How Speaker Works

How Telephone Works

Speaker: • Use a permanent magnet to transfer

electric signal to acoustic signal• Process:

Charge the voice coil inside speakerGenerate magnetic field around the coilChange directions of electrical current in the coilCoil’s polar orientation reversesMagnetic forces move coil and attached diaphragm back and forth

How Microphone Works

How Microphone Works

Microphone:• Use carbon granules compressed

between two thin metal plates and magnets to transfer acoustic signal to electric signal

• Process: Voice causes carbon granules to compress and decompress

Status of carbon granules changes resistance of the granules

Current flowing though microphone will modulate

How Telephone WorksHook Switch:• To connect and disconnect the phone

from the network• When one lifts handset, hook switch will

connect the network. When one puts the phone down, hook switch will disconnect the network.

How Telephone Connects Us

After introduced what’s inside the telephone, now it’s the

time to know the how the external parts work with it:

• The copper wire that is connected to the phone jack inside

our house is from the box down the road.

• Assume that we have two separate pairs of telephone lines,

then second pair is usually colored yellow and black inside

our house.

• Then what connect between the wire that comes from our

home and the local telephone company? It is a thick cable

packed with 100 or more copper pairs. We are going to

talk about it next.

• The picture shows a typical street box in

the southwestern, US.

• The green box is basically a place where

the 50-pair cable pops out and stretch out

through the underground so that a phone

company workers can splice into it.

Digitalizing and Delivering

• When we trace all the way to the phone company through the

wire, we met the concentrator which digitizes our voice at a

sample rate of 8,000 samples per second and 8-bit resolution.

• It then combines our voice with others and sends them all to a

single fiber-optic cable to the phone company office.

• Let’s say if we are calling someone who are connected by the

same office, then the switch simply creates a loop between your

phone and the phone of the person you called.

• Once the sound is digitized, the signal will be transferred to a

local exchange house, where the digital signal will delivered to

the other side of the recipients’ home.

Reference

• Brain, Marshall. “How Telephone Work”. HowStuffWorks.com 01 April 2000. Web. 02 December 2011.http://electronics.howstuffworks.com/telephone.htm

• Bruce, Robert V. Bell: Alexander Graham Bell and the Conquest of Solitude. Cornell University Press. 1990. Print.

• Coe, Lewis. The Telephone and Its Several Inventors: A History. McFarland, North Carolina. 1995. Print.

• Josephson, Mattew. Edison: A Biography. Whiley. 1992. Print.

Thank you!