You can carry the handset with you throughout the house or outside within the range of the base transmitter. The handset has all of the equipment of a standard telephone (speaker, microphone, dialing keypad), plus the equipment of an FM radio transmitter/receiver.
When you open up the handset, you see these components:
- speaker - converts electrical signals into the sound that you hear
- microphone - picks up your voice and changes it to electrical signals
- keypad - input for dialing
- buzzer or ringer - lets you know that you have an incoming call
- radio components - amplify electrical signals to and from microphone and speakers and send and receive FM radio frequencies
- LCD or LED displays - indicator lights
- re-chargeable battery - supplies electrical power to handset
The speaker receives the electrical signals from the audio amplifier in the radio components and converts them into sound. When you remove the cover from the speaker, you see a large round permanent magnet with a hole in the middle and a deep groove surrounding the hole. Within this deep groove is a coil of fine copper wire that is attached to a thin plastic membrane. The plastic membrane covers the magnet and coil.
To hear sounds, the following events happen:
- Electrical signals come from the radio components.
- The electrical signals travel in the coil of copper wire.
- The electrical signals induce magnetic currents in the coil of wire, thereby making it an electromagnet.
- The electromagnetic coil moves in and out of the groove within the permanent magnet.
- The coil moves the attached plastic membrane in and out at the same frequencies as the changes in electric currents.
- The movements of the membrane move air at the same frequencies, thereby creating sound waves that you can hear.
The microphone changes the sound waves from your voice into electrical signals that are sent to the audio amplifier of the radio components. A microphone is essentially a speaker that works in reverse. When sound waves from your voice move the membrane, they make tiny electric currents either by moving a coil of wire within a magnet or by compressing the membrane against carbon dust (see How do microphones work? for details).
The keypad allows you to dial a number. It transfers the pressure from your fingertip on the appropriate key into an electrical signal that it sends to the radio components. Below the rubber keypad is a circuit board with black conductive material under each button (shown above). The keypad works like a remote control. When you press a button, it makes a contact with the black material and changes its electrical conductance. The conductance sends an electrical signal to the radio components indicating that you have selected that number.
Buzzer or Ringer
When the radio components of the handset receive the ringer signal from the base, they send electrical signals to the buzzer. The buzzer changes those electrical signals into sound much like the speaker does. You hear the buzzer sound and know that someone is calling you. In some phones, the speaker is used to make the ringer sound and there is no need for a separate ringer.