Doorbell Chimes

Inside the doorbell signaling device is a circuit, the doorbell circuit. This is actually a model of a self-interrupting circuit. The 10-20 volt current from the transformer energizes and activates the electromagnet. This action attracts and pulls to it a movable contact arm. As this happens, the secondary circuit inside is opened, cuts off the current and thus, releases the arm. The contact arm falls back, closes the secondary circuit, and, until the visitor removes his finger from the button, the process is repeated. The buzzing sound is produced by the contact arm touching the magnet and falling back to a non-moving contact, of which the contact arm rests when inactive. Homes for the deaf use visual signaling devices, such as light bulbs.

The newer models come with chimes, called the chime doorbell. This unit makes the familiar ding-dong sound. A chime model utilizes a solenoid. A solenoid is another kind of an electromagnetic device. This device consists of a cylindrical coil of wire that surrounds a movable iron center. The iron core moves along the entire length of the coiled wire when it is energized by an electric current passing through it. It is akin to a metal piston.

The piston houses a metal that is magnetically-conductive. This makes it move along the coil back and forth. An electromagnetic field within the coil makes this possible. A regular chime model has two tone bars that are struck by the solenoid. In an inactive state, meaning the electromagnet is off, a spring holds the piston to one of the two tone bars that make the dong sound. When the button is pressed, the electrical circuit is closed, an electrical current flows, the solenoid electromagnet is switched on and an electromagnetic field is activated. This makes the iron core to slide through the coiled wire, striking the other tone bar and creates the ding sound.

As long the button is not released and the electromagnet is on, the iron core will remain at the ding position. When released, the current stops flowing, the electromagnet is turned off, and the piston returns to its original position striking the dong tone bar, creating the familiar ding-dong tune. This process is repeated for every short press of the button, repeating the ding-dong chime. Crafty and intricate sounds may be created with the addition of more solenoids and tone bars.