How Computer Keyboards Function

Keyboard Design

Most computer keyboards have a molded plastic exterior and a series of plastic keys that move independently. Small plastic brackets anchor these keys in place on top of a circuit board that is covered in a watertight rubber membrane. The vast majority of keyboard manufacturers use a design featuring small rubber domes underneath each key. The sides of these domes are flexible enough to allow easy key pressing but firm enough to force each key back to its original position after pressing. The centers of these domes are rigid and often made of carbon, which allows them to complete separated electrical circuits when they are pressed. A separate circuit is positioned under each key on the circuit board. Some of the pricier keyboards feature a more durable design with more precise keystroke abilities. Called capacitive keyboards, these designs do not feature electrical circuits that are ever actually completed. Instead, the keyboard matrix is fed a constant stream of electricity that is evenly distributed among the keys. When a key is pressed, an electrode on the underside of the key is moved closer to a larger circuit panel underneath, causing a surge in power in that one section of the keyboard matrix. Though the circuit never fully completes, the keyboard is capable of recognizing a power surge and pinpointing its location on the matrix.

Data Input

When a key is pressed, it sends an electrical signal to the processor built into the keyboard. This can happen when an electrical circuit is completed, such as in the case of rubber dome designs, or it can happen when an electrical surge occurs in a capacitive keyboard. But when this signal reaches the processor, the processor is not immediately aware of the actual letter, number of symbol that has been inputted. It is only aware of the pressed key's location on the keyboard grid. To determine the keyboard user's desired character, the location on the grid is compared to a character map stored in the keyboard's memory. A match between the location and a defined character is quickly established, at which point the keyboard transmits the data to the computer.

Data Processing

From the processor, the input data passes through an internal buffer in the keyboard's memory and then to the computer, either through internal wiring, USB cable, PS/2 cable or infrared signal. Once the data reaches the computer itself, an integrated circuit runs it past the computer's operating system. The operating system determines whether or not the input is a system-level command, which is a keystroke or combination of keystrokes designated to perform primary system functions rather than those specific to any applications that might be running. System level commands are executed immediately, and all other commands are passed along to the current running application. The software application then interprets whether the input is an application command or user content, and performs the user's desired function.