The door bell is a signal device placed near the door of the building entrance. If the person in the gap pushes the button of the doorbell, a bell or an electronic device sounds inside the building and warns the owner that there is a visitor in front of the door.

The first door knockers are mechanical. There was a bell on one side of the knee or a string on the other end. The mechanism that acted by pulling the rope down worked with the bell sound.

The Scottish inventor William Murdoch strong> built his first door ring system invented in Birmingham in 1817. But this bell system was using a piped compressed air system. The first of the electric door zillers was invented in 1831 by Joseph Henry strong>, which moved electric bells and a distant bell via a button.

How does the door handle work? H2>

In most wired systems, a button near the door handle’s height near the door, a signal inside the building (usually a ringing, bell, or ringing tones). When the door pushbutton is pressed, the single-pole, single-push (SPST) pushbutton instantly closes the door braking. One key of the button is connected to a transformer in the system. The door transducer reduces the 120 or 240 volt AC power to a lower voltage, typically 10 to 20 volts. The transformer is connected to one of the three ends of the signaling device. Another terminal connects to a telephone to the other terminal on the button. If there is another door bell (typically near a rear door), it is connected between the transformer and the third terminal. The primary winding of the transformer-energized transformer continuously consumes a small amount of standby power (approximately 1 to 2 W); In systems with illuminated push buttons, the same amount of power per key can be consumed.

A common signaling device is an acoustic unit containing two flat metal rod resonators, which are plunged by plungers driven by two solenoids. The flat bars are set to two nice notes. When the door ring button is pressed, the piston of the first solenoid hits a bar and when the button is released, a spring pushes a pump up the piston, and strikes the other bar to produce a two-tone sound (“ding-dong”). If a second door bell is used, the other solenoid that walks only one bar is cabled to create a single sound (“ding”).

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