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 “ I’ll take the cover off of this important part of the human-machine interfaces and see exactly what makes it tick!
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.
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.
Most mice in use today use the standard PS/2 type connector, as shown here
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.
These pins have the following functions (refer to the above photo for pin numbering):
2. +5 volts (to power the chip and LEDs)
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)
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?
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 to dark, if LED 1 is light then we are rotating clockwise but if LED 1 is dark, then we have anticlockwise rotation. The computer uses this fact to monitor direction: each time LED 2 goes from light to dark it samples LED 1 to determine the direction. It uses the number of transitions to measure the distance. In practice the system is a little bit more clever since there are problems if the wheel stops on an edge. Of course the two LEDs are interchangeable and it doesn't matter which one is used as the step and which as the direction. If, in re-wiring we get the two signals interchanged, the mouse will simply work upside down or left to right instead of right to left. The diagram below shows the corresponding electrical signals switching at 15° intervals.
There are two such wheels, one rotates for vertical movement and the other rotates for horizontal movement of the mouse ball. If we take our mouse to pieces we can easily see these two 'encoders'. The actual wheels have a lot more slots than we have shown.
INSIDE A MOUSE
The main goal of any mouse is to translate the motion of our hand into signals that the computer can use. Almost all mice today do the translation using five components.
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.
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.