Optical mouse

Inside an optical computer mouse

An optical mouse is much more hi-tech than a ball mouse. Where a ball mouse has quite a few moving parts, an optical mouse is almost entirely electronic (it has almost no moving parts).

Here's the inside of a typical optical mouse and a few of the main components. The most interesting bits are in the center (where the LEDlight shines down onto your desk) andat the front (where button presses are detected by switches):

1) An LED at the back generates red light and shines it horizontally, from the back of the mouse toward the front (from the left to the right of this photo).

2) A plastic prism bends (refracts) the light from the LED at an angle, down onto the desk.

3) A light-detector chip measures light reflected back up from the desk, converting the analog movements of your hand into digital signals that can be sent to your computer.

4) The scroll wheel at the front of the mouse is mounted on a switch mechanism that detects both how much it's rotated and whether you'vepressed it (it functions like the central button of a conventional mouse). Rotations of the scroll wheel can be detected in a variety of different ways. Some mice use potentiometers (broadly, variable resistors), similar to the volume control on a radio but able to turn around multiple times. Others use various kinds of rotary switches or optical (rotary) encoders to convert analog wheel movements to digital signals.

5) A microswitch detects when you press the right mouse button. There'san identical switch on the other side to detect the left mouse button.

6) The USB cable connection carries digital information from the mouse to your computer.