How Does a Computer Mouse Work?


Conversion of Movement Into Binary Data

  • While laser, optical and other cordless mice gain popularity, the optical mechanical computer mouse remains the most common and affordable mouse option for computer users. The conversion of mechanical energy into digital signals is done simply and elegantly with just a few moving parts and minimal circuitry.

External Parts of a Computer Mouse

  • The external moving parts of a computer mouse are the click buttons on the top of the mouse, a roller wheel located between the click buttons and the roller ball on the bottom of the mouse. An electronic cord is attached to the button end of the mouse

Roller Ball Controls the Screen Cursor

  • Inside the mouse, two rollers rest against the roller ball, perpendicular to one another. When the mouse is moved against a flat surface, the roller ball causes the two rollers to rotate. One roller is rotated by moving the mouse up and down (the screen cursor moves vertically). The other is rotated by side to side motion (the screen cursor moves horizontally).

Encoder Disks Convert the Motion of the Roller Ball Into Light Signals

  • Each roller is attached to a shaft with a flat wheel at the end. The wheel, called an encoder disk, has many small holes or notches on its circumference.The edge of each encoder disk is situated between an infrared light emitting diode (IR LED) and a light sensor. Whenever the mouse is plugged into the computer, a continuous beam of light is emitted from each IR LED. The sensor across from the IR LED detects the beam. The edge of the encoder disk between the IR LED and its sensor blocks the light beam; as the encoder disk rotates, the light beam intermittently shines through the holes. This causes the light sensor to detect a pulsing light beam. When the roller and disk turn faster, the light pulses faster. In this way, the sensor detects the speed and distance that the mouse moves.

Light Signals Are Converted to Binary Data and Sent to the Computer

  • The electronic signals from the light sensors pass to a processor chip. The chip converts the signals to binary data and sends the data to the computer through the mouse cord. The horizontal and the vertical signals are combined by the computer to precisely position the screen cursor according to the mouse movements.

Mouse Buttons Select Screen Items and Turn Menus On or Off

  • Two micro switches are located beneath the external click buttons. Each micro switch sends an on/off signal to the computer. Depending on the operating system, it tells the computer to display a menu or not display a menu. Or it tells the computer to select a screen item or unselect a screen item.

Rotation of the Roller Wheel Controls Screen Scrolling

  • To each side of the roller wheel are another light emitting diode and a sensor. In similar fashion to the encoder disks, the spokes of the roller wheel interrupt a light beam, and signals are sent to the processor chip. The processor chip coverts the signals to binary data that controls screen scrolling. Depressing the wheel activates a micro switch that sends an on/off signal to either allow or disallow roller ball control of screen scrolling.

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  • Photo Credit Ysabel Doran
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