Although it may seem complicated, a telephone is actually one of the simplest devices you have in your house. It?s simple because the telephone connection to your house hasn?t changed in nearly a century. If you have a phone from the 1920s, you could connect it to the phone jack in your house and it would still work fine.
The simplest working telephone would look like this inside:
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It only contains 3 parts, which are all pretty simple:
A switch to connect and disconnect the phone from the network - This switch is generally called the hook switch. It connects when you lift the handset.
A speaker - This is generally a little 8-ohm speaker that emits sound.
A microphone - In the past, telephone microphones have been as simple as carbon granules compressed between two thin metal plates. Sound waves from your voice compress and decompress the granules, changing the resistance of the granules and modulating the current flowing through the microphone.
The problem with the phone shown above is that when you talk, you will also hear your own voice through the speaker. Many people find that annoying, so today's phones contain a device called a duplex coil or something used to block the sound of your own voice from reaching your ear. A modern telephone also has a bell so it can ring as well as a touch-tone keypad and frequency generator for dialing digits. Today's phone looks like this:
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Like the primitive phone, this is also a simple device. In a modern phone there is an electronic microphone, amplifier and circuit to replace the carbon granules and loading coil. The mechanical bell is usually replaced by a speaker and a circuit to generate a pleasant ringing tone.
