How Telephone Works

1. How Telephone Works Present by: Chongbo You SeungJaeBaek Qihui Yu

2. 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.

3. History and Development • 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. Alexander Graham Bell's Telephone PatentDrawing, 03/07/1876.

4. History and Development • 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.

5. 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.

6. 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.

7. 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.

8. 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.

9. How Telephone Works • Basic Parts of a Telephone: • Speaker • Microphone • Hook Switch From HowStuffWorks.com

10. How Speaker Works

11. How Telephone Works • Speaker: • Use a permanent magnet to transfer electric signal to acoustic signal • Process: Charge the voice coil inside speaker Generate magnetic field around the coil Change directions of electrical current in the coil Coil’s polar orientation reverses Magnetic forces move coil and attached diaphragm back and forth

12. How Microphone Works

13. 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

14. How Telephone Works • Hook 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.

15. 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.

16. 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.

17. 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.

18. 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. CornellUniversity 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.

19. Thank you!