The telephone was invented by American A.G. Bell in 1876. Two wires are used to connect two transmitters and receivers with the same structure, and a vibrating diaphragm is installed on the electromagnet, so that the two ends can talk at first. But the call distance is short and the efficiency is low. In 1878, the carbon microphone appeared, which greatly improved the efficiency of telephone microphone.
The earliest telephone was a magnet telephone, which was powered by its own battery and sent a call signal by a hand-cranked generator. In 188, the * * * electric telephone was changed to centralized power supply by the * * * electric exchange. In 1891, the rotary dial automatic telephone, which can send out DC dialing pulses, select the called party and automatically complete the switching function.
by the end of 196s, push-button all-electronic telephones appeared. In addition to the pulse signaling mode, there is a dual-tone multi-frequency signaling mode. With the development of program-controlled switches. Electronic telephone circuits are moving towards integration, and telephone application-specific integrated circuits have been widely used in various components of telephone circuits.
Extended information:
The telephone is set at the user side of the beginning and end of telephone communication, and is the user terminal equipment of the telephone network. Basic functions: 1. Acousto-electric interchange: Because of fast and long-distance communication, you can't directly transmit sound, but you must first turn the sound into an electrical signal, and then return the electrical signal to the other party.
2. Off-hook identification: When the calling party picks up the telephone, the switch should have the function of knowing that "someone wants to call" so that the switch can make preparations for connection. 3. The automatic telephone that sends signals directs the work of the telephone exchange by sending dialing signals, and then establishes the connection between the two telephones.
4. Ring the bell, that is, when the other party calls, the telephone can tell the host by ringing the bell: "Someone is calling." 5. In the electric connection telephone, the components that realize these five functions are: receiver, fork spring, dial (or press keyboard), telephone bell and telephone loop in turn.
Reference:
Baidu Encyclopedia-Telephone.