A Real Telephone

The only problem with the phone shown on the previous page (and directly below) is that when you talk, you will hear your voice through the speaker.

diagram of a simple telephone
A simple telephone

Most people find that annoying, so any "real" phone contains a device called a duplex coil or something functionally equivalent to block the sound of your own voice from reaching your ear. A modern telephone also includes a bell so it can ring and a touch-tone keypad and frequency generator. A "real" phone looks like this:

diagram of a real telephone
A "real" telephone

Still, it's pretty simple. In a modern phone there is an electronic microphone, amplifier and circuit to replace the carbon granules and loading coil. The mechanical bell is often replaced by a speaker and a circuit to generate a pleasant ringing tone. But a regular $6.95 telephone remains one of the simplest devices ever.

 

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