Visual display unit (VDU)

• A device usually used .for output to display the current status of programs and data files, but modified to accept light-pen input or touch
• Also referred to as the Screen

• To visually display information produced by the computer.
• This includes text, graphics, animation, video.

• The most common display type.
• Display is by a scanning electron gun over phosphor dots.
• Most Televisions use this method.
• Future: 8mm ThinCRT, dubbed field-emission displays, will offer brighter and wider viewing angles than LCD displays.
  (Santoni,A (Jul 1997)

Case study:

• Liquid Crystal Display
  • Liquid Crystals are charged to produce an image.
  • Common on digital watches
  • Very low power requirements, so popular on portable computers.
  • Difficult to read in some lighting settings.

• Thin Film transistor.
  • Common on many portabe and laptop PC's.
  • Either Passive Matrix, where light elements are kept in a grid pattern of wires. Pixels are lighted by charging the vertical and horizontal wires. Pixels may pass charges to other near ones, and cause a "bleeding" of colour.
    or Active Matrix, where each pixel has a dedicated circuit to tell the pixel to light up. More expensive than Passive Matrix to Manufacture but clearer picture.
• Note a 12.1 inch LCD monitor is equivalent in size to a 14inch CRT (15inch = 17 inch). Hospitals prefer LCD since they don't emit electromagnetic waves that could interfere with sensitive medical equipment, and graphics designers appreciate the fact that LCD screens are flat so provide straight lines on screen. Also low heat emissions, half the weight of a CRT, and have 40% power savings of the equivalent CRT monitor.

Case study:

• Gas plasma electrified to produce image.
• Used on early Portable PC's but tricky to manufacture.
• Clearer picture than LCD.

1. CPU sends instructions to video controller.
2. Video controller converts instructions into a video signal suitable for display on the monitor.
3. Electron gun fires streams of electrons towards the screen
4. Magnetic yoke guides streams from left to right, top to bottom of the screen..
5. Phosphor dots on back of screen glow when hit by electron beam.

1. CPU sends instructions to video controller.
2. Video controller converts instructions into a video signal suitable for display on the monitor.
3. Passive Matrix: Pixels are lighted by charging the transistors on the vertical and horizontal rows.
   Active Matrix: Transistors representing each pixel are lighted using their dedicated circuit.

Use

• Touch screen technology. Particularly useful for the "Multimedia" applications being developed for "public information systems" or "kiosks" sighted in airports and at information offices. Here the only way to access the data is via visual "Buttons" on the screen, that are touched.
• Pen based technology. Where the computer input consists of a entering data on an LCD type flat screen using "pen". Applications such "law enforcement", where a pen based computer is used instead of a manual form to enter offense notices.

Features

• "Visual buttons" are displayed on the screen and "touched" by the end user.
• Pen based input via an LCD (Liquid Crystal Display) type flat screen

Example

• DECface. Digital's smartface kiosk.Allow humans to interact with prople in a natural, human like way. Customers interact with a computer generated real-time customisable synthetic talking head, complete with six universally recognised human expressions; happinesss, sadness, surprise, anger, disgust and fear. It includes a prompter for action or help.
• Ref: Digital introduces Smark Kiosk (Dec/Jan 1998)