The improvements and inventions of telephone in history include: toner microphone, manual switchboard, dial, automatic telephone exchange, program-controlled telephone exchange, dual-tone multi-frequency dialing, voice digital sampling and so on. New technologies in recent years include ISDN, DSL, VoIP, analog mobile phone and digital mobile phone.

principle of operation

Telephone communication is a communication technology that uses electricity as the medium and transmits language through the mutual conversion of acoustic energy and electric energy. The easiest way for two users to communicate is to connect two phones with a pair of wires.

When the speaker picks up the phone and speaks into the microphone, the vibration of the vocal cords excites the air to vibrate, forming sound waves.

Sound waves act on the microphone to generate current, which is called speech current.

Voice current is transmitted along the line to the receiver of the other party's phone.

A receiver is just the opposite of a microphone-it converts current into sound waves, which are transmitted to people's ears through the air.

In this way, the simplest call process is completed.