Optical Mouse

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ABSTRACT

Topic OPTICAL MOUSE

Every day of our computing life, we reach out for our mouse whenever we want to move our cursor or

activate something. Our mouse senses our motion and our clicks and sends them to the computer so

that it can respond appropriately. It is amazing how simple and effective a mouse is, and it

is also amazing how long it took Mice to become a part of everyday life. Given that people

naturally point at things -- usually before they speak -- it is surprising that it took so long for a

good pointing device to develop. Although originally conceived in the 1960s, it took quite

some time for mice to become mainstream. In the beginning there was no need to point because

computers used crude interfaces like teletype machines or punch cards for data entry. The early text

terminals did nothing more than emulate a teletype (using the screen to replace paper), so it was many

years (well into the 1960s and early 1970s) before arrow keys were found on most terminals. Full

screen editors were the first things to take real advantage of the cursor keys, and they offered humans

the first crude way to point.

In this paper on WORKING OF OPTICAL MOUSE Ill take the cover off of

this important part of the human-machine interfaces and see exactly what makes it tick!


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INTRODUCTION

Optical Technology uses an optical sensor to track movement, rather than the standard ball and

moving parts. Optical Technology provides increased control and precision and works on most

surfaces. This superior technology translates into precise cursor movement and unmatched

responsiveness.

It is amazing how simple and effective a mouse is, and it is also amazing how long it took mice to

become a part of everyday life. Given that people naturally point at things -- usually before they

speak -- it is surprising that it took so long for a good pointing device to develop. Although

originally conceived in the 1960s, it took quite some time for mice to become mainstream.

In the beginning there was no need to point because computers used crude interfaces like

Teletype machines or punch cards for data entry before arrow keys were found on most terminals.

Full screen editors were the first things to take real advantage of the cursor keys, and they offered

humans the first crude way to point.

Light pens were used on a variety of machines, as a pointing device for many years, and graphics

tablets, joysticks and various other devices were also popular in the 1970s. None of these really

took off as the pointing device of choice, however, when the mouse hit the scene, it was an

immediate success. There is something about it that is completely natural. Compared to a

graphics tablet, mice are extremely inexpensive and they take up very little desk space. In the PC

world, mice took longer to gain ground, mainly because of a lack of support in the Operating

system. Once Windows 3.1 made Graphical User Interfaces (GUIs) a standard, the mouse became

the PC-human interface of choice very quickly.


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Mice first broke onto the public stage with the introduction of the Apple Macintosh in 1984, and

since then they have helped to completely redefine the way we use computers. Every day of our

computing life, we reach out for our mouse whenever we want to move our cursor or activate

something. Our mouse senses our motion and our clicks and sends them to the computer so it can

respond appropriately.

DATA INTERFACE

Most mice in use today use the standard PS/2 type connector, as shown here

These pins have the following functions (refer to the above photo for pin numbering):

1. Unused

2. +5 volts (to power the chip and LEDs)

3. Unused

4. Clock

5. Ground

A typical PS/2 connector: Assume that pin 1 is

located just to the left of the black alignment pin, and

the others are numbered clockwise from there.


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6. Data

Whenever the mouse moves or the user clicks a button, the mouse sends 3 bytes of data to the

computer. The first byte's 8 bits contain:

1. Left button state (0 = off, 1 = on)

2. Right button state (0 = off, 1 = on)

3. 0

4. 1

5. X direction (positive or negative)

6. Y direction

7. X overflow (the mouse moved more than 255 pulses in 1/40th of a second)

8. Y overflow

The next 2 bytes contain the X and Y movement values, respectively. These 2 bytes contain the

number of pulses that have been detected in the X and Y direction since the last packet was sent.

The data is sent from the mouse to the computer serially on the data line, with the clock line

pulsing to tell the computer where each bit starts and stops. Eleven bits are sent for each byte (1

start bit, 8 data bits, 1 parity bit and 1 stop bit). The PS/2 mouse sends on the order of 1,200 bits

per second. That allows it to report mouse position to the computer at a maximum rate of about

40 reports per second. If we are moving the mouse very rapidly, the mouse may travel an inch or

more in one-fortieth of a second. This is why there is a byte allocated for X and Y motion in the

data protocol.

Some mice use serial or USB type connectors.

MICE: HOW DO THEY WORK?


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Open up a mouse and inside it we will find two wheels, each one similar to the first drawing. The

wheel is usually made of black plastic with rectangular slots punched in it. I have shown only 6

slots at 60 spacing but they are a lot closer and many more. Shining through the slots are two

LEDs (light Emitting Diodes) shown by the black dots. Each LED shines on to a light sensitive

transistor. The two emitters are spaced so that, when one transistor can 'see' its LED through the

centre of its window, the other LED is looking at an edge and is therefore switching on or off. In

my illustration the LEDs are spaced at 105 (60 x 1.75). The output voltage from the transistor is

processed to switch rapidly from high to low as the LED's light is transmitted or occluded so that

the voltage is low when the transistor is lit and high when it is in darkness. In the diagram LED A

is fully illuminated and LED B is switching. Note that LED B may be switching from light to

dark or from dark to light - this depends on the rotation direction.

Now consider the second drawing. Here the wheel is shown in 4 different states, each 15 rotated

from the last. Diagram E is equivalent to diagram A, being 60 rotated. For clockwise rotation the

states follow each other in order A-B-C-D-E from left to right but if we read the states from right

to left, E-D-C-B-A, then these correspond to anticlockwise rotation.

Notice that LED 2 is changing state from light to dark in diagram A for clockwise rotation and in

diagram C for anticlockwise rotation. So if we measure LED1 every time LED 2 goes from light

LED A

LED B


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1) A ball inside the mouse touches the desktop and rolls when the mouse moves.

2) Two rollers inside the mouse touch the ball. One of the rollers is oriented so that it detects

motion in the X direction, and the other is oriented 90 degrees to the first roller so it

detects motion in the Y direction. When the ball rotates, one or both of these rollers rotate

as well.

3) The rollers each connect to a shaft, and the shaft spins a disk with holes in it. When a

roller rolls, its shaft and disk spin.


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4) On either side of the disk there is an infrared LED and an infrared sensor. The holes in

the disk break the beam of light coming from the LED so that the infrared sensor sees

pulses of light. The rate of the pulsing is directly related to the speed of the mouse and

the distance it travels.

5) An on-board processor chip reads the pulses from the infrared sensors and turns them

into binary data that the computer can understand. The chip sends the binary data to the

computer through the mouse's cord.

In this optomechanical arrangement, the disk moves mechanically, and an optical system counts

pulses of light. On this mouse, the ball is 21 mm in diameter. The roller is 7 mm in all is 21 mm

in diameter. The roller is 7 mm in diameter. The encoding disk has 36 holes. So if the mouse

moves 25.4 mm (1 inch), the encoder chip detects 41 pulses of light.

It is noticed that each encoder disk has two infrared LEDs and two infrared sensors, one on each

side of the disk (so there are four LED/sensor pairs inside a mouse). This arrangement allows the

processor to detect the disk's direction of rotation. There is a piece of plastic with a small,

precisely located hole that sits between the encoder disk and each infrared sensor.

This piece of plastic provides a window through which the infrared sensor can "see." The window

on one side of the disk is located slightly higher than it is on the other -- one-half the height of

one of the holes in the encoder disk, to be exact. That difference causes the two infrared sensors

to see pulses of light at slightly different times. There are times when one of the sensors will see a

pulse of light when the other does not, and vice versa.

THE OPTICAL MOUSE


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With advances in mouse technology, it appears that the venerable wheeled mouse is in danger of

extinction. The now-preferred device for pointing and clicking is the optical mouse.

Developed by Agilent Technologies and introduced to the world in late 1999, the optical mouse

actually uses a tiny camera to take 1,500 pictures every second.

Able to work on almost any surface, the mouse has a small, red light-emitting diode (LED) that

bounces light off that surface onto a complimentary metal-oxide semiconductor (CMOS)

sensor. The CMOS sensor sends each image to a digital signal processor (DSP) for analysis.

The DSP, operating at 18 MIPS (million instructions per second), is able to detect patterns in the

images and see how those patterns have moved since the previous image. Based on the change in

patterns over a sequence of images, the DSP determines how far the mouse has moved and sends

the corresponding coordinates to the computer. The computer moves the cursor on the screen

based on the coordinates received from the mouse. This happens hundreds of times each second,

making the cursor appear to move very smoothly.

In this photo, we can see the LED on the bottom of the mouse.

Optical mice have several benefits over wheeled mice:


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No moving parts mean less wear and a lower chance of failure.

There's no way for dirt to get inside the mouse and interfere with the tracking sensors.

Increased tracking resolution means smoother response.

They don't require a special surface, such as a mouse pad.

Although LED-based optical mice are fairly recent, another type of optical mouse has been

around for over a decade. The original optical-mouse technology bounced a focused beam of light

off a highly-reflective mouse pad onto a sensor. The mouse pad had a grid of dark lines. Each

time the mouse was moved, the beam of light was interrupted by the grid. Whenever the light was

interrupted, the sensor sent a signal to the computer and the cursor moved a corresponding

amount.

This kind of optical mouse was difficult to use, requiring that you hold it at precisely the

right angle to ensure that the light beam and sensor aligned. Also, damage to or loss of

the mouse pad rendered the mouse useless until a replacement pad was purchased.

Today's LED-based optical mice are far more user-friendly and reliable.

Inside An Optical Mouse

If we take apart an optical mouse and look inside, we will find a complete imaging system. The

mouse is essentially a tiny, high-speed video camera and image processor. As shown in figure

below, a light-emitting diode (LED) illuminates the surface underneath the mouse. The light from

the LED reflects off microscopic textural features in the area. A plastic lens collects the reflected

light and forms an image on a sensor. If we were to look at the image, it would be a black-and-

white picture of a tiny section of the surface. The sensor continuously takes pictures as the mouse

moves. The sensor takes pictures quickly-1500 pictures (frames) per second or more fast enough


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so that sequential pictures overlap. The images are then sent to the optical navigation engine for

processing.

:Optical mice illuminate an area of the work surface with an LED, to reveal

a microscopic pattern of highlights and shadows. These patterns are reflected

onto the navigation sensor, which takes pictures at a rate of 1500 images per

second or more.

The Basics of Optical Navigation

The optical navigation engine is the brain of the mouse. It identifies texture or other features in

the pictures and tracks their motion. Figure below illustrates how this is done. Two images were

captured sequentially as the mouse was panned to the right and upwards. Much of the same visual

material can be recognized in both frames. Through a patented image-processing algorithm, the

optical navigation engine identifies common features between these two frames and determines

ImageAcquisition

System

DigitalSignal

Processor

SerialParallel

Interface

Block diagram of optical sensing


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the distance between them. This information is then translated into X and Y coordinates to

indicate mouse movement.

The Navigation Engine identifies common features in sequential images to

determine the direction and amount of mouse movement. Image B was taken

while the mouse was moving, a short time after image A. It shows the same

features as image A, only shifted down and to the left.

BENEFITS OF OPTICAL TECHNOLOGY AND OPTICAL MOUSE

Improved tracking speed The most common complaint optical mouse users have is

that the cursor gets lost during periods of quick hand movement. The problem is, most

optical mouse products can only move up to 14 inches per second. But usability research

indicates that computer users can move the mouse up to 30 inches per second - far faster

than the tracking capability of todays mouse products. Microsoft Optical Technology is

remarkable. It enables the mouse to keep up with the hand, tracking up to 37 inches per

second.

Increased accuracy Due to the limits of existing optical mouse technology, the cursor

does not always land where you want it. This causes reduced accuracy and increased

frustration. Optical Technology provides superior accuracy and enables the cursor to

land where you want it.


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Consistent performance With no mouse ball or moving parts to keep clean or wear

out, the optical sensor stays precise over time.

Works on most surfaces The optical sensor works on most surfaces*, so you no longer

need a mouse pad. Use it on your desk, the kitchen counter, or even your pant leg.

Less frequent cleaning The recessed lens is enclosed and never touches your desk,

so less frequent cleaning is necessary.

The optical sensor performs best on surfaces with detail to track. It will not function

on surfaces without visible detail (such as glass) or surfaces on which it has a

reflection (such as mirrors or glossy surfaces). The optical sensor may also have

difficulty tracking on highly repetitive patterns (such as printed magazine or

newspaper photographs).

REFERENCES:

1) Internet sites

2) Electronics for you-02

3) Pc Quest-02

4) Digit-02

Date post:	07-Apr-2018
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Optical Mouse

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