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TANTA UNIVERSITY FACULTY OF SCIENCE. Fourth Year (First Semester). Advanced Computer Science (Computer Peripherals). Lecture Six. Dr. Hany Mahgoub. Input Devices. Outline. Keyboards Pointing Devices Mouse 6. Touch Screen Trackball 7. Light pen Touchpad 8. Electronic Pen

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Advanced Computer Science (Computer Peripherals)

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Advanced computer science computer peripherals



Fourth Year (First Semester)

Advanced Computer Science

(Computer Peripherals)

Lecture Six

Dr. Hany Mahgoub

Input devices

Input Devices



  • Keyboards

  • Pointing Devices

    • Mouse 6. Touch Screen

    • Trackball 7. Light pen

    • Touchpad 8. Electronic Pen

    • Pointing Stick 9. Graphics Tablet

    • Joystick

  • Scanners and Reading Devices

  • Digital Cameras

  • Audio Input

  • Video Input

  • Introduction


    An input device is any hardware component that allows the user to enter data, programs, commands, and user responses into the computer.

    Introduction cont

    Introduction (cont.)

    Two types of input are data and instruction. Instruction can be in the form of user responses, commands, and programs



    A typical desktop computer keyboard.

    Types of keyboards

    Types of Keyboards

    • In fact, the most common change has simply been the natural evolution of adding more keys that provide additional functionality. The most common keyboards are:

      • 101-key Enhanced keyboard

      • 104-key Windows keyboard

      • 82-key Apple standard keyboard

      • 108-key Apple Extended keyboard

    • Portable computers such as laptops quite often have custom keyboards that have slightly different key arrangements than a standard keyboard.

    How computer keyboards work

    How Computer Keyboards Work

    • A keyboard is a series of switches connected to a microprocessor that monitors the state of each switch and initiates a specific response to a change in that state.

    • In this section, you will learn more about this switching action, and about the different types of keyboards, how they connect and talk to your computer, and what the components of a keyboard are.

    Inside the keyboard

    Inside the Keyboard

    The processor in a keyboard has to understand several things that are important to the utility of the keyboard, such as:

    • Position of the key in the key matrix.

    • The amount of bounce and how to filter it.

    • The speed at which to transmit the typematics.

    The microprocessor and controller circuitry of a keyboard

    Advanced computer science computer peripherals

    A look at the key matrix

    • The processor monitors the key matrix for signs of continuity at any point on the grid.

    • When it finds a circuit that is closed, it compares the location of that circuit on the key matrix to the character map in its ROM.

    • The character map is basically a comparison chart for the processor that tells it what the key at x, y coordinates in the key matrix represents.

    Advanced computer science computer peripherals

    If more than one key is pressed at the same time, the processor checks to see if that combination of keys has a designation in the character map.

    • For example, pressing the key "a" by itself would result in a small letter "a" being sent to the computer. If you press and hold down the Shift key while pressing the key "a", the processor compares that combination with the character map and produces a capital letter "A."

    Advanced computer science computer peripherals

    • When the key presses the key switch against the circuit, there is usually a small amount of vibration between the surfaces, known as bounce.

      • The processor in a keyboard recognizes that this very rapid switching on and off is not caused by you pressing the key repeatedly. Therefore, it filters all of the tiny fluctuations out of the signal and treats it as a single key press.

    • If you continue to hold down a key, the processor determines that you wish to send that character repeatedly to the computer. This is known as typematics.

      • In this process, the delay between each instance of a character can normally be set in software, typically ranging from 30 characters per second (cps) to as few as two cps.

    Keyboard technologies

    Keyboard Technologies

    Keyboards use a variety of switch technologies.Let's take a look at these different technologies:

    • Rubber مطاطdome mechanical

    • Capacitive non-mechanical

    • Metal معدنcontact mechanical

    • Membrane غشاءmechanical

    • Foam رغوةelement mechanical

    Advanced computer science computer peripherals

    This keyboard uses rubber dome switches.



    • The most common keyboard connectors are:

      • 5-pin DIN (Deustche Industrie Norm) connector

      • 6-pin IBM PS/2 mini-DIN connector

      • 4-pin USB (Universal Serial Bus) connector

      • Internal connector (for laptops)

        An increasing number of new systems are dropping the PS/2 connectors in favor of USB.

      • Two principal elements are sent through the connecting cable:

        • The first is power for the keyboard. Keyboards require a small amount of power, typically about 5 volts, in order to function.

        • The cable also carries the data from the keyboard to the computer.

    Advanced computer science computer peripherals

    • The other end of the cable connects to a port that is monitored by the computer's keyboard controller.

    • This is an integrated circuit (IC) whose job is to process all of the data that comes from the keyboard and forward it to the operating system.

    USB Connector

    A PS/2 type keyboard connector

    Advanced computer science computer peripherals

    When the operating system is notified that there is data from the keyboard, a number of things can happen:

    • It checks to see if the keyboard data is a system level command. A good example of this is Ctrl-Alt-Delete on a Windows computer, which initiates a reboot.

    • The operating system then passes the keyboard data on to the current application.

    • The current application understands the keyboard data as an application-level command. An example of this would be Alt - f, which opens the File menu in a Windows application.

    • The current application is able to accept keyboard data as content for the application, or

    • The current application does not accept keyboard data and therefore ignores the information

    Pointing devices

    Pointing Devices

    A pointing device is an input device that allows you to control a pointer on the screen and interact with computer via a graphical user interface (GUI).

    • Common pointing devices include the mouse, trackball, touch pad, pointing stick, joystick, touch screen,light pen and graphics tablet.



    • A mouse is used to control the movement of a pointer on the screen and make selections from the screen.

    Advanced computer science computer peripherals

    The start menu displays the screen when you point to the Start button and then click the primary mouse button.

    Inside a mouse

    Inside a Mouse

    The main goal of any mouse is to translate the motion of your hand into signals that the computer can use. Almost all mice today do the translation using five components:

    Advanced computer science computer peripherals

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

    Advanced computer science computer peripherals

    2. Two rollers inside the mouse touch the ball and detect X and Y motion

    Advanced computer science computer peripherals

    3. The rollers each connect to a shaft, and the shaft spins a disk with holes in it. A typical optical encoding disk: This disk has 36 holes around its outer edge.

    Advanced computer science computer peripherals

    4. A close-up of one of the optical encoders that track mouse motion: There is an infrared LED (clear) on one side of the disk and an infrared sensor (red) on the other. 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.

    Advanced computer science computer peripherals

    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.

    Optical mouse

    Optical Mouse

    • The optical mouse actually uses a tiny camera to take 1,500 pictures every second.

    • 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.

    Advanced computer science computer peripherals

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

    Advanced computer science computer peripherals

    Optical mice have several benefits over wheeled mice:

    • No moving part means 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.



    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

    6. Data

    • 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.

    Advanced computer science computer peripherals

    Whenever the mouse moves or the user clicks a button, the mouse sends 3 bytes of data to the computer. The first byte's8 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

    Advanced computer science computer peripherals

    • 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).

    In the lab

    In the LAB

    DifferentKeyboard Technologies

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