What is the working principle of a normal telephone?
The telephone is set at the user side of the start and end points of telephone communication, and is the user terminal equipment of the telephone network. Modern telephones can easily realize calls and conversations between end users, which have been formed through many people’s researches and countless improvements over a hundred years. Although their styles vary widely, they generally have the following basic functions;
1. Acoustic-electrical and electro-acoustic conversion functions. Because to carry out fast and long-distance communication, it is not possible to transmit sound directly, but must first convert the sound into an electrical signal (that is, use electricity as a carrier), and then restore the electrical signal to sound after reaching the other party.
2. When the calling party picks up the phone, the switch should have the function of knowing “someone wants to make a call”, so that the switch is ready for connection.
3. The function of sending dial signal. It is by sending dialing signals that automatic telephones direct the work of the telephone exchange, and then establish a connection between two telephones.
4. The function of ringing. That is, when the other party calls, the telephone can tell the host with a ringing tone: “Someone is calling.”
5. Electrical connection function with the switch.
In the telephone, the components that realize these five functions are: handset, hook switch, dial (or keypad), telephone ring and telephone loop.
The microphone is a small box containing carbon particles. The small box has a stationary electrode at the back and a vibrating membrane (called a vibrating electrode) at the front. When you speak into the microphone, the vibrating membrane vibrates in different amplitudes with the change of the sound, so that the carbon particles are sometimes compressed (resistance decreases), and then relaxed (resistance increases), so that the flow through the two The current between the electrodes also changes. In this way, the change in the size of the sound is transformed into a change in the strength of the electrical signal suitable for transmission on the circuit.
The body of the receiver is a permanent magnet with a coil wound around it. When the voice current from the other party passes through the coil, a magnetic field is generated, which attracts the thin iron sheet in front of the magnet to vibrate and emit sound. The magnitude of the vibration is determined by the magnitude of the current flowing through the coil. This is the simple reason why the receiver can restore the electrical signal to sound.
When we make a call, the first action is to “off-hook” (remove the handset from the phone). At this point, the part of the telephone that carries the handset (called the “hook”) bounces up, closing the circuit between the telephone and the switch. If the switch line is free at this time, it will send a continuous “dial tone” to the telephone, which tells you: “I am already on standby, please dial!”
The dial pad of the telephone There are rotary and push buttons. When dialing with them, a DC pulse or two-tone signal is sent. No matter what kind of signals, their function is to control the switch in the telephone office, so that it can complete the connection between the calling user and the called user.
If the called phone is idle, the switch sends a ringing current to it, causing the other party’s phone to ring. This is telling the other party: “Someone is calling!” At the same time, the calling party will hear a “ringback tone”. If the other party’s phone is not available, the switch will send a “busy tone” of “beep, beep, beep…” to the calling user.
