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5 Main Components of a Telephone

The telephone was originally patented by Scottish inventor Alexander Graham Bell in 1867. Although advances in electronics, such as the invention of the transistor in 1947, have allowed the telephone to become lighter, more compact and more sophisticated over the years, its fundamental design hasn̵7;t changed in more than 100 years.

Transmitter
- A telephone handset contains a transmitter and a receiver, with each connected to the base unit by separate pairs of wires. The transmitter is a microphone in the part of the handset into which a person speaks. The microphone converts the vibrations in the air, or sound waves, created by the speaker̵7;s voice into an electrical current, which becomes the audio signal. Inside the microphone, a diaphragm -- originally made from a thin layer of carbon, but more recently from a thin layer of plastic -- vibrates back and forth, causing small variations in voltage, which are amplified for transmission over the telephone line.
Receiver
- The receiver effectively works like the transmitter in reverse, converting fluctuating electric current into audible sound waves. The receiver consists of a permanent magnet, wound with coils of fine insulated wire, and a diaphragm. Variations in the electric current flowing through the coils vary the attraction of the permanent magnet for the diaphragm, causing it to vibrate back and forth and produce sound waves.
Dialer
- The dialer is the component of a telephone used to dial the number that the user wishes to call. Dialers can be rotary or, more commonly, push-button. The traditional rotary dialer uses the rotation of the dial against the tension in a spring to open and close a switch, which causes pulses in the flow of direct current to the switching office. Push-button dialing, on the other hand, produces a dual-tone signal -- with one high frequency and one low frequency -- specific to each button pushed.
Ringer
- The ringer is the component of a telephone that emits an audible ring, or tone, to alert the user to an incoming call. Ringers can be mechanical or electronic, but both types respond to incoming pulses of 20-hertz, 75-volt alternating current from the switching office. An electrical device known as a capacitor prevents direct current from passing through the ringer when the handset is lifted off the switch hook.
Anti-sidetone Circuit
- Sidetone is the term used for the sound of the speaker̵7;s own voice being reproduced by the receiver of a telephone. Telephones therefore employ a special circuit, known as an anti-sidetone circuit, which includes a transformer to divide the signal from the transmitter in two. The tranformer is an electric device consisting of two windings on the same core. The divided signals are out of phase, so they almost entirely cancel each other when they arrive at the receiver circuit.

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