How telephones work

A telephone is a relatively simple device. It has five main components: a microphone, a speaker, a duplex block, a switch, a ringer, and a touch-tone keypad, which controls a frequency generator.

The small electronic microphone and the speaker, an amplifier used to increase the intensity of sound, are set in the hand piece to receive and send sounds.

The duplex coil blocks the speaker’s voice so it does not loop back to the earpiece while the speaker is talking. This helps prevent echoes on the line where you could hear yourself talking.

The switch turns the phone connection on and off. Usually operated by lifting or placing the handset into a phone cradle; you connect the phone by lifting the handset and disconnect by placing it back in the cradle.

The ringer consists of a electrical circuit that generates a ringing tone and an amplifier to make it loud enough to be heard.

The touch-tone number pad is on top of sensors, which convert the mechanical energy of pushing the buttons into electrical energy that can be transmitted to the telephone exchange. Each number is tuned to a slightly different electrical signal so that the exchange can tell them apart.