A doorbell is a signaling device typically placed near a door to a building's entrance. When a visitor presses a button the bell rings inside the building, alerting the occupant to the presence of the visitor. Although the first doorbells were mechanical, activated by pulling a cord, modern doorbells are electric, operated by a pushbutton switch. Modern doorbells often incorporate intercoms and miniature video cameras to increase security.
William Murdoch, a Scottish inventor, installed a number of his own innovations in his house, built in Birmingham in 1817; one of these was a loud doorbell, that worked using a piped system of compressed air. A precursor to the electric doorbell, specifically a bell that could be rung at a distance via an electric wire, was invented by Joseph Henry around 1831. By the early 1900s, electric doorbells had become commonplace.
In most wired systems, a button on the outside next to the door, located around the height of the doorknob, activates a signaling device (usually a chime, bell, or buzzer) inside the building. Pressing the doorbell button, a single-pole, single-throw (SPST) pushbutton 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 or 240-volt AC electrical power to a lower voltage, typically 10 to 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. Some signaling devices have a third terminal, which produces a different sound. If there is another doorbell button (typically near a back door), it is connected between the transformer and the third terminal. The transformer primary winding, being energized continuously, does consume a small amount (about 1 to 2 W) of standby power constantly; systems with lighted pushbutton switches may consume a similar amount of power per switch. The tradeoff is that the wiring to the button carries only safe, low voltage isolated from earth ground.
A common signaling device is a chime unit consisting of two flat metal bar resonators, which are struck by plungers operated by two solenoids. The flat bars are tuned to two pleasing notes. When the doorbell button is pressed, the first solenoid's plunger strikes one bar, and when the button is released, a spring on the plunger pushes the plunger up, causing it to strike the other bar, creating a two-tone sound ("ding-dong"). If a second doorbell button is used, it is wired to the other solenoid, which strikes only one of the bars, to create a single-tone ("ding") sound.
More elaborate doorbell chimes play a short musical tune, such as Westminster Quarters.
Fully battery-powered wired models are also common, either using a two-bar design or an electric bell. These do not consume standby power, but require the user to change the batteries, which are usually large primary cells located in the bell box.
A wireless doorbell is a modernized heir of the traditional doorbell, which is a basic method for announcing one’s arrival in a home. It particularly requires a radio signal that gets transmitted when the button is pushed.Wireless, by definition, is the transfer of information or power between two or more points that are not connected by an electrical conductor. Moreover, lesser visits to the electrician are guaranteed since the full operation of the system does not rely on any messy wires any longer.
During the Victorian Era, the earliest doorbells that were found came in two ways: twist doorbells and pull doorbells. A twist doorbell had the mechanism of a wind-up toy: a key-like structure is twisted outside the door that strikes the bell on the inside. Contrarily, a pull doorbell is identified to have a string that could be pulled from the outside to ring the bell on the inside.
Subsequently, the doorbell was redefined in the Industrial Revolution along with other technological advancements. The person behind the doorbell’s modernization is William Murdoch. His invention was a mechanized doorbell in which operated with compressed air and pipe. Soon, it was followed by the electric doorbell that was generated by Joseph Henry in 1831.
Presently, people continue to rely on doorbells to attend and see who comes for a visit. The innovation, creativity and technological advancements bore to companies that sell wireless doorbells like Ring, Skybell and SadoTech.Such wireless doorbell companies do not just limit their offerings to the use of a traditional doorbell but cater to specific needs such as assisted living for seniors and impaired individuals and a lot more application use cases.
Long Range Wireless Doorbells
Due to larger homes’ need, long-range wireless doorbells were made. Long-range wireless doorbells are meant to cater to larger homes with more than a range of 100ft of a standard wireless doorbell. They were designed to transmit information over a vast area even through thicker materials with its ability to transmit signals up to 1,000ft or more.
Wireless Doorbells for Persons With Disabilities
The wireless strobe light doorbell is particularly made to cater to the hearing impaired and the deaf. It is also recommended for office surrounded by loud noises as it is supported with a visual indicator. When it is pressed, the signaler effuses a bright light indicating the production of a loud chime. Recent innovations on this concept have been introduced with a vibrating receiver doorbell which allows the hearing impaired to wear a receiver on his or her hip belt and when the doorbell is triggered, the receiver will vibrate or “buzz” letting the carrier know someone is at the door
Wireless Video Doorbells with Motion Sensing
The wireless video doorbell with motion sensing is particularly useful for triggering an alert when motion is detected in a designated area. This gives an extra layer of security because of its ability to alert the homeowner when an unexpected person enters his or her yard or porch without ringing the doorbell. This motion sensor concept for the doorbell has been adopted for sensing when a car comes into a driveway. This driveway motion sensor doorbell alerts the homeowner of the car that has pulled into the driveway.
Wireless Video Intercom Doorbells
Generally, intercom systems have existed for decades. It was used to communicate from one room to the other. Usually in an office, to increase productivity by making communications systems easier and in hospitals, to make it easier for patients and healthcare providers to communicate especially in emergencies. Equipped with a handset, a monitor, a doorbell camera, the mechanism and system of the intercom doorbell serves allows the homeowner/s to speak, view and open the door wherever the homeowner is.
Wireless Video Doorbells
Wireless video doorbells1 have embedded video cameras, speakers and a microphone system that visually portrays the person outside the door in real time. Moreover, most video doorbells have internet-connected access that will alert the homeowner of a visitor arrival in his or her phone. The homeowner, despite being miles away, can attend to his or her visitor by speaking through the doorbell once the link is established through Wi-Fi. Jammie Siminoff, the CEO and founder of Ring Company, mentions, “The mission of our company is to reduce crime in communities.” Wireless video doorbells were particularly made to ensure security and longevity.
Musical and continuous power doorbellsEdit
As with wireless doorbells, musical doorbells have also become more common. Musical and continuous power doorbells serve as an attempt to bridge the gap between newer digital circuitry and older doorbell wiring schemes. A major difference between the standard setup of a wired doorbell and a musical doorbell is that the musical doorbell must maintain power after the doorbell button is released to continue playing the doorbell song. This can be achieved in one of two ways.
For simple single-pole, single-throw doorbell buttons, the chime device employs a rectifier diode and ballast capacitor at the voltage input stage of the circuit. Upon pressing the doorbell button, power is connected through the rectifier diode or series of rectifier diodes called a full wave rectifier, which allows the current to flow in only one direction, into the ballast capacitor. The ballast capacitor charges at a rate far greater than the rest of the circuit needs to complete a given song. Once the button is released, the capacitor retains the charge and maintains power for a short duration to the rest of the circuit.
For mixed wireless and wired input doorbells, a special doorbell button is needed to maintain power continuously to the doorbell chime. The circuit is similar to the one above, except that the rectifier diode is now moved into the doorbell button housing. Pressing the doorbell button allows both negative and positive sides of the AC power signal to flow into the circuit, while releasing the button only allows either the positive or negative side to flow into the circuit. By differentiating the full and half wave signals, the doorbell is able to function as it does in the previous wired case, while also providing continuous power to the doorbell for other purposes, such as receiving wireless doorbell button input.
Mechanical bell systemsEdit
With the adoption of the "Internet of Things" a number of internet connected bell systems, known as smart doorbells have appeared on the market.
Popular systems are the "Skybell", Ring doorbell, Nest Labs doorbell, the Google "Hello", and many others. These consist of a single unit which is located in place of the traditional push-button and in addition to the physical button, contain an HD camera, PIR sensor and WiFi electronics. The device is connected to the home wi-fi network, and notifications of a button-press or detected movement are pushed to a paired smartphone or other electronic device such as a tablet. When a notification is received, the user will typically see a live video stream from the device, clearly showing who is the door and they can enagage in a 2 way audio conversation.
The devices can be powered by an internal battery, or they may use the existing bell wiring for continuous power.
The video is typically recorded direct to a cloud internet service, meaning that if the unit is tempered with, damaged or stolen then this event will be captured and can be analysed to determine the identity of the responsible party.
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- Scientific writings of Joseph Henry, Volume 30, Issue 2. Smithsonian Institution. 1886. p. 434.
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