Bhavin H. Joshi

Mouse

A mouse is a pointing device about the size of palm. It rolls on a small ball and has one or more buttons on the top. When the user rolls the mouse across a flat surface, the screen cursor moves in the direction of the mouse movement.

For example, if the user rolls the mouse forward and left, the screen cursor also moves up left on the screen. Because the cursor follows the user's hand movement, the user has a better idea of pointing at something on the screen.

Positioning the cursor using a mouse is much more easier for the non-typists or the first time computer user, rather than pressing different combination of key for doing the same.

Mouse Type

Based on the technology used to detect the mouse movement and the method and the method used to transfer the mouse information to the computer, mouse can be divided into different categories.

There are three technologies to detect mouse movement

Mechanical
Opto-Mechanical
Optical

And there are five different interfaces to connect the mouse to the main computer system

Serial port mouse
A bus connection mouse
PS/2 port mouse
USB port mouse
Wireless mouse

Depending on the type of technology and interface, a mouse can have one, two or three buttons.

Mechanical Mouse

A mechanical mouse works by the mechanical action of its various parts. When mouse is rolled across a flat surface different rollers inside the mouse move and generate electrical signals.

These signals are given to the computer and computer converts them to proper action on the screen.

Let's see in detail.

As a mechanical mouse moves across a flat surface, a ball —made of rubber or rubber covering a steel ball, protruding from the underside of the mouse and touching the surface, starts to rotate in the direction of the movement.
Because of this movement of the ball, two rollers, touching the ball, start rotating. They are mounted at 90° to each other. One roller is for detecting the back and forth mouse movement and one for detecting the sideway movement of the mouse.
Both the rollers are attached with individual encoder. An encoder inside the mouse is a wheel like structure. The wheel is synchronized with the roller.
The direction in which the mouse is moving can be found out by finding the number of signals from these two vertical and horizontal rollers.
THe single generated by these rollers are sent serially to the pc over the connecting rod. The driver software for mouse converts these signals into the distance, direction, and speed necessary to move the screen cursor.
When we press the mouse button, a signal is generated and feed to the pc. Based on the button and the times it is pressed and the position of the cursor when the button is pressed, the mouse driver software performs a specific task.

Opto-Mechanical Mouse

The basic technique in Opto-Mechanical mouse is the same as of Mechanical mouse, the difference is that instead of the wheel, a combination of LED and photo detector is used to track the mouse position.

Optical Mouse

The optical track the mouse position using a light source and photo detector. You need not use a mouse pad. It can be used with virtually any flat surface.

The current technology in mouse has made it a palm held computer. It has a full pattern-recognition hardware/software in its digital processor IC.

The pattern-recognition capability allows the new optical mouse to be used on any surface without the need to use a special mouse pad.

As we move the mouse, the processor IC inside the mouse compares the current captured image with the previous stored image in memory. The outcome of this comparison is converted to screen co-ordinates.

The optical mouse has three basic parts

LED to illuminate the surface on which the mouse is used
A sensor made of photo-detector array, basically a small video camera to detect the pattern on the surface
Digital Signal Processor for pattern recognition purpose

Now let's have look how it works

The LED on the bottom part of the mouse shines the surface underneath it. The light is focused very close to the surface and directed at an angle to create pattern of dark and light areas even on a apparently smooth surface.
Sensor detects the pattern created by the LED on the work surface
This sensor contains a lens and photo-detector arrays. The lens is used to focus pattern on the photo-detector array. Photo-detector array is a matrix of light sensitive CMOS elements.
DSP samples the output of the sensor several thousand times per seconds. Each samples is compared with the previous sample to detect the direction and extend of change in the mouse position compared to the last position.
Based on the information from the DSP, mouse informs about the new position to the central unit and it converts this into screen co-ordinates.

An optical mouse can sample at a rate of 1500 to about 6000 images per second Because such mouse does not have movable parts, it lasts longer.

The only problem with this mouse is when we use it on a highly reflective surface or glass surface which does not have visible detail it may no work properly.

Mouse