Doorbell
Encyclopedia
A doorbell is a signaling device typically placed near a door
. Most doorbells emit a ringing sound to alert the occupant of the building to a visitor's presence, when the visitor presses a button
. Many modern doorbells are electric — they are actuated by an electric switch. The electric doorbell was invented by
Joseph Henry
in 1831.
Most people use their index finger
to push a door bell, but young people who have grown up with text messaging
are more likely to use their thumb
.
, bell
, or buzzer
) inside the building. This single-pole, single-throw (SPST) switch
momentarily closes the doorbell circuit. One terminal
of this button is wired to a terminal on a transformer
. A doorbell transformer steps down the 120–240-volt AC
electrical power to a lower voltage
, typically 10–20 volts. The transformer's other terminal connects to one of three terminals on the signaling device. Another terminal is connected to a wire that travels to the other terminal on the button. If there is another button (typically near a back door), it is connected between the transformer and the third terminal on the signaling device. The transformer, being energized constantly, does consume a small amount (about 1 to 2 W) of standby power
constantly,.
Most signaling devices consist of two solenoid
s and two flat bars. The flat bars are tuned to two pleasing notes. The flat bars are mounted loosely above and below the solenoids. When the doorbell button is pressed, the first solenoid's plunger strikes the bottom bar. When the button is released, a spring
on the plunger pushes the plunger up, causing it to strike the other bar. If the other bell is used, it will activate the other solenoid, which will strike only one bar — typically the bottom bar.
More elaborate signaling devices play a short musical tune, such as Westminster Quarters.
The deaf use visual signaling devices — typically light bulbs — rather than audible signaling devices.
. The transmitter sends a radio
signal to the doorbell radio receiver inside the building. When the radio signal is detected by the receiver
, it activates the doorbell. In larger metropolitan cities, a trend has developed over the past decade that uses telephone technology to wirelessly signal doorbells as well as to answer the doors. In many cities throughout the world, this is the predominant form of doorbell signalling.
Door
A door is a movable structure used to open and close off an entrance, typically consisting of a panel that swings on hinges or that slides or rotates inside of a space....
. Most doorbells emit a ringing sound to alert the occupant of the building to a visitor's presence, when the visitor presses a button
Button (control)
A push-button or simply button is a simple switch mechanism for controlling some aspect of a machine or a process. Buttons are typically made out of hard material, usually plastic or metal. The surface is usually flat or shaped to accommodate the human finger or hand, so as to be easily depressed...
. Many modern doorbells are electric — they are actuated by an electric switch. The electric doorbell was invented by
Joseph Henry
Joseph Henry
Joseph Henry was an American scientist who served as the first Secretary of the Smithsonian Institution, as well as a founding member of the National Institute for the Promotion of Science, a precursor of the Smithsonian Institution. During his lifetime, he was highly regarded...
in 1831.
Most people use their index finger
Index finger
The index finger, , is the first finger and the second digit of a human hand. It is located between the first and third digits, between the thumb and the middle finger...
to push a door bell, but young people who have grown up with text messaging
Text messaging
Text messaging, or texting, refers to the exchange of brief written text messages between fixed-line phone or mobile phone and fixed or portable devices over a network...
are more likely to use their thumb
Thumb
The thumb is the first digit of the hand. When a person is standing in the medical anatomical position , the thumb is the lateral-most digit...
.
Wired system
In most wired systems, a button, located around the height of the doorknob, activates a signaling device (usually a chimeTubular bell
Tubular bells are musical instruments in the percussion family. Each bell is a metal tube, 30–38 mm in diameter, tuned by altering its length. Its standard range is from C4-F5, though many professional instruments reach G5 . Tubular bells are often replaced by studio chimes, which are a smaller...
, bell
Electric bell
An electric bell is a mechanical bell that functions by means of an electromagnet. When an electric current is applied, it produces a repetitive buzzing or clanging sound...
, or buzzer
Buzzer
A buzzer or beeper is an audio signaling device, which may be mechanical, electromechanical, or piezoelectric. Typical uses of buzzers and beepers include alarm devices, timers and confirmation of user input such as a mouse click or keystroke....
) inside the building. This single-pole, single-throw (SPST) switch
Switch
In electronics, a switch is an electrical component that can break an electrical circuit, interrupting the current or diverting it from one conductor to another....
momentarily closes the doorbell circuit. One terminal
Terminal (electronics)
A terminal is the point at which a conductor from an electrical component, device or network comes to an end and provides a point of connection to external circuits. A terminal may simply be the end of a wire or it may be fitted with a connector or fastener...
of this button is wired to a terminal on a transformer
Transformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...
. A doorbell transformer steps down the 120–240-volt AC
Alternating current
In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....
electrical power to a lower voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
, typically 10–20 volts. The transformer's other terminal connects to one of three terminals on the signaling device. Another terminal is connected to a wire that travels to the other terminal on the button. If there is another button (typically near a back door), it is connected between the transformer and the third terminal on the signaling device. The transformer, being energized constantly, does consume a small amount (about 1 to 2 W) of standby power
Standby power
Standby power, also called vampire power, vampire draw, phantom load, or leaking electricity , refers to the electric power consumed by electronic and electrical appliances while they are switched off Standby power, also called vampire power, vampire draw, phantom load, or leaking electricity...
constantly,.
Most signaling devices consist of two solenoid
Solenoid
A solenoid is a coil wound into a tightly packed helix. In physics, the term solenoid refers to a long, thin loop of wire, often wrapped around a metallic core, which produces a magnetic field when an electric current is passed through it. Solenoids are important because they can create...
s and two flat bars. The flat bars are tuned to two pleasing notes. The flat bars are mounted loosely above and below the solenoids. When the doorbell button is pressed, the first solenoid's plunger strikes the bottom bar. When the button is released, a spring
Spring (device)
A spring is an elastic object used to store mechanical energy. Springs are usually made out of spring steel. Small springs can be wound from pre-hardened stock, while larger ones are made from annealed steel and hardened after fabrication...
on the plunger pushes the plunger up, causing it to strike the other bar. If the other bell is used, it will activate the other solenoid, which will strike only one bar — typically the bottom bar.
More elaborate signaling devices play a short musical tune, such as Westminster Quarters.
The deaf use visual signaling devices — typically light bulbs — rather than audible signaling devices.
Wireless system
A button near the door activates a built-in transmitterTransmitter
In electronics and telecommunications a transmitter or radio transmitter is an electronic device which, with the aid of an antenna, produces radio waves. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating...
. The transmitter sends a radio
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
signal to the doorbell radio receiver inside the building. When the radio signal is detected by the receiver
Receiver (radio)
A radio receiver converts signals from a radio antenna to a usable form. It uses electronic filters to separate a wanted radio frequency signal from all other signals, the electronic amplifier increases the level suitable for further processing, and finally recovers the desired information through...
, it activates the doorbell. In larger metropolitan cities, a trend has developed over the past decade that uses telephone technology to wirelessly signal doorbells as well as to answer the doors. In many cities throughout the world, this is the predominant form of doorbell signalling.
External links
- HowStuffWorks: How a Doorbell Works
- How to Repair a Doorbell
- Deaf doorbell circuit
- Comparison between wired and wireless doorbells