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Peripherals

Peripherals. Looking at Keyboards Mouse Joystick. Keyboard. This is probably one of the most important peripheral (along with the monitor).

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Peripherals

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  1. Peripherals Looking at Keyboards Mouse Joystick

  2. Keyboard • This is probably one of the most important peripheral (along with the monitor). • The keyboard is organised in the same ways as a game of battleships, each key is a switch connecting a vertical and horizontal wire, giving a unique location for where the two lines crossed.

  3. When a key is pressed a signal is produced on two connections to a device called the keyboard encoder. • The encoder deals with key bouncing and produces a unique code (a scan code for that key) • The encoder sends the code to the computer. • A further device, the keyboard controller, receives code from the keyboard. • The controller performs all the necessary operations to translate the scan code into an ASCII code and then send it on to the Data Bus.

  4. Key press is converted to unique code in terms of the connections made, the code is sent to the computer decoded and a ASCII code for the key is put onto the data bus.

  5. Physical construction: • Mechanical keys - simplest switch. Pushing the switch makes contact between two plates, completing the circuit. Releasing the switch a spring pushes the switch back up and the circuit is broken. • Membrane keys - similar to the mechanical keys, but works by pushing a rod through a insulated sheet. • Capacitive keys - When a key is pressed two plates are brought closer together (but not touching), the capacitance changes and this is detected.

  6. Key Bounce • Digital logic works by being on or off. • When a key is pressed or released it can vibrate which can lead to the key appearing as if it had been pressed several times. • This is key bounce. • To overcome this the keyboard encoder contains de-bounce circuitry. One a voltage change is detected it prevents for a short period any further changes being detected.

  7. Mechanical mouse • A ball sits inside a case and can move any direction. • Inside the case there are two rollers at right angles to each other, these detect changes in that axis. • Each roller is connected to a rotating sensor. • The rotating sensor is done by a disc rotating around making and breaking contact. • It has a relatively short working lifetime because it is a mechanical device.

  8. Opto-mechanical mouse: • The same roller system as the mechanical device is used, but the rotating sensor in the mechanical mouse is replaced by an optical system. • The disc is opaque with transparent strips, one side of the disc there is a light source and the other side of the disc is a detector. As the disc rotates the light is detected through the strips producing electrical pulses. The more the mouse moves the more pulses produced.

  9. Optical Mouse • The early optical mice presented a practical problem, needing a special mat. When these mats go missing the mouse can not be used. Modern ones don’t need special mats. • A light source in the mouse shines on the surface and is reflected back to a sensor in the mouse. • As the mouse is moved the changes detected on the surface are detected and converted in electrical pulses.

  10. Advantages • Less wear and tear • Less open at the bottom so does not pick up as much dirt. • Modern version can be used on a variety of surfaces • Greater accuracy than a conventional mouse.

  11. Joystick • A conventional joystick usually connects through the sound-card or an add-on card. • Using a 15-pin sub D-socket, handling: • Four press switches • Four resistive inputs • Mechanically links two variable resistors that alter depending on the direction of motion, therefore altering voltages.

  12. Taken from http://inf33-www.informatik.unibw-muenchen.de/infothek/computer/tutorial/eprmhtml/eprm/253.htm

  13. Changes • USB connected joysticks • Force-feedback.

  14. Summary • When a key is pressed, it makes certain connection to a chip (keyboard encoder), which sends a code to the computer. • In the computer a further chip (keyboard controller) takes this code and converts it into something the computer can use. • Three keyboard types • Mechanical, • Capacitive, • Membrane.

  15. Three mouse types • mechanical • optical • optomechanical • A conventional joystick usually connects through the sound-card or an add-on card. Using a 15-pin sub D-socket, Mechanically links two variable resistors that alter depending on the direction of motion, therefore altering voltages.

  16. Sources for further reading • Chalk et al (2004) pages 142-148 • Dick (2002) PC support handbook pages 294-304. • Taken from http://inf33-www.informatik.unibw-muenchen.de/infothek/computer/tutorial/eprmhtml/eprm/253.htm

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