3.3.a Traditional Screens
Principle: Screen shows bit maps.
Every pixel consists of three sub-pixels: Red, Green and Blue. Controlling the amount of light from each pixel creates a full range of color.
|Cathode Ray Technology|
|Structure||For detail, see more in |
* A1 Physics Practical: Cathode Ray Oscilloscope.
* And A1 Physics Theory: Electric Field.
|For detail, see more in A2 Physics: Polarization of light.|
|How it works||There are no individual pixels. |
Pixels dots are created by controlling the direction of the electron beam fired.
When the beam is directed to a spot on the screen, the charge causes phosphor on screen to radiate. This emits light.
|The pixels do not emit light. Light comes from the backlight, from LED tubes.|
The alignment of liquid crystal is affected when a voltage is applied. This changes the polarization of light when it pass through.
This affects the final display.
Organic Light-emitting diode (OLED) screens is.a new technology. OLED can act as a light source, so there is no need for a back lighting.
3.3.b Touch Screens
Touch screens are both input and output device. There are two types of them: Capacitive and Resistive.
(The syllabus is much easier than the IGCSE!)
|Resistive Touch Screen||Capacitive Touch Screen|
|Structure||* Two layers, separated by thin space.|
* Screen is rigid.
|* Conductive layer beneath the screen.|
* Rigid surface.
|How it works||When the two layers meet, a voltage divider is produced, (Horizontally and vertically).||When touched, an electrical state (capacitance) change in circuit component happens beneath the surface.|
Next page: 3.4 Printers and Scanners