5.11 ELECTRONIC DISPLAYS

SYLLABUS

• 5.11 Electronic Displays - L2 • Principles of operation of common types of

displays used in modern aircraft, including – Cathode Ray Tubes– Light Emitting Diodes – Liquid Crystal Display.

CRT – CATHODE RAY TUBE

CONTROLLING THE DEFLECTION

• There are two separate ways to control the deflection:– Electromagnetic deflection- magnetic principle– Electrostatic deflection – depend on charges.

• Electromagnetic Deflection (Remember i=current)

ELECTROSTATIC DEFLECTION

Color TV Screen• A color TV screen differs

from a black-and-white screen in three ways: • Three electron beams (Red,

Green, Blue)that move simultaneously across the screen.

• The screen is coated with red, green and blue phosphors arranged in dots or stripes.

• On the inside of the tube, very close to the phosphor coating, there is a thin metal screen called a shadow mask. This mask is perforated with very small holes that are aligned with the phosphor dots (or stripes) on the screen.

• .

RASTER/STROKE SCANNING

• Raster Scanning for Attitude Sphere

• Stroke Scan for reminder

• Raster Scanning - weather return

• Stroke for texts, range,

Honeywell

ATT 2

AOA

CMDM .99200 DH DH 140 RA

I

G

GS

2020

10 10

20 20

10 10

F

S

STROKE SCANNING IS

USED FOR ALL OTHER DISPLAYED

DATA

RASTERSCANNING

10

20

30

40

WX

MODE(BLUE)

YELLOWGREEN

RED

RANGEDATA

(BLUE)

LED DISPLAY

• PN diode • Doping modify the color,

oxygen, nitrogen are used• 7 bar display for numbers.• Segment type display with

diffuser plate or plastic deflector to increase the size

P134

LED DISPLAY

Tapes and Pointers• LED's are also used to

replace the pointers or tapes on circular scale or vertical scale displays.

• individual diodes are arranged in groups to form the illuminated bars.

• example is the TCAS Electronic Vertical Speed Indicator ‘Fly-From’ and ‘Fly-To’ indications.

Dot Matrix Display• LED's are normally arranged

in a 9 X 5 matrix or a 4 X 7 matrix.

• requires special driver circuits.

• more common in fields outside aviation, with displays being produced using light bulbs, metal discs and electromagnetic devices.

LCD – LIQUID CRYSTAL DISPLAY

• Operating Principle– The liquid crystal is enclosed between two set of

polarizes glass (p137) .– In normal situation, the light can pass, but when

current is passed, the molecules of the crystal changes its alignment and control the light.

– Color is obtained by color filter on top of the LCD.

PASSIVE AND ACTIVE MATRIX

• Passive Matrix– Relies on grids of vertical / horizontal conductors– Scanning current through the horizontal

conductors.– pixel is off controlled by vertical conductors.

• Active matrix – TFT (Thin Film Transistors)– Pixels are controlled by individual transistors.– Expensive – 800x 600 resolution – 1.4 millions

transistors.