Electronic Displays Quiz

Electronic Displays (5.11)

• Learning Objectives:
  • 5.11.1.1: Describe the principles of operation of cathode ray tubes (CRTs) used in modern aircraft (Level 2).
  • 5.11.1.2: Describe the principles of operation of light-emitting diodes (LEDs) used in modern aircraft (Level 2).
  • 5.11.1.3: Describe the principles of operation of liquid crystal displays (LCDs) used in modern aircraft (Level 2).

LED Fundamentals

• LEDs: A type of optoelectronic device used to replace fragile incandescent light bulbs for indicators (on/off).
• Visible Light Emission: LEDs produce visible light when forward biased, with color determined by their material composition.
• Infrared LEDs: Also available, these are used for detection applications with infrared detectors.
• Diode Symbol: Designated by a standard diode symbol with two arrows pointing away from the cathode, indicating light emission.
• Operating Voltage: Low forward voltage (around 1.6 V).
• Operating Current: Typically around 10 mA.
• LED Life Expectancy: Very long, often exceeding 100,000 hours.
• Connection: The LED has a flat spot on its body, designating the cathode. Connect the cathode to the negative side and the anode to the positive side of the power supply.
• Current Limiting: Resistors are necessary to limit current for LEDs connected to power supplies above 2V.
• Safety: Refer to manufacturer's literature for proper power supply ratings and resistor values.

Peak Wavelength Single-Coloured (Monochromatic) LEDs

• Light Color: The color of light is determined by its wavelength. Wave lengths are measured in nanometers (nm).
• Peak Wavelength: Characterizes the color of the emitted light.
• Wavelength Range: Typical figures range from 450 nm (blue) to 950 nm (infrared).
• Emission Spectrum: The output of LEDs isn't focused to one specific wavelength.
• Intensity and Wavelength: Generally, a graph of intensity versus wavelength illustrates the peak at a specific wavelength.

Multi-Colored and Bi-Colored LEDs

• Multiple Chips: Multicolored LEDs incorporate separate semiconductor chips, each emitting a different single colour, within a single package.
• Sequential Emission: At a time, only one LED chip emits light from this setup.
• Current Control: Current flow direction governs which chip emits light.
• Resistors: One resistor is usually calculated the same way as for an individual LED..
• Colored Light Production: Bi-colored LED's can produce a third color by mixing two primary colors (e.g., a red and green led produces yellow when powered by AC).

Tri-Colored LEDs

• Multiple Chips: Tricolor LEDs have three separate semiconductor chips, each emitting a different colour.
• Common Terminals: Three-terminal components which use common cathode or anode configurations.
• Voltage Control: Switching the voltage between the chips allows selecting the color, by using one or more switches..

Seven-Segment LED Display

• Seven Segments: Display numbers 0 through 9 and other characters using arrangements of seven segments.
• Applications: Used in calculators, digital voltmeters, frequency counters.
• Common Cathode and Anode: Available in two configurations.

Alphanumeric LED Display

• Multiple Segments: Use 16 segments to display alphabets and numbers.
• Dot Matrix Displays: Displays are also available using a matrix of small LEDs.

Organic LEDs (OLEDs)

• Organic Material Components: Organic thin films are used between two conductive conductors.
• Light Emission: Electrical current causes light to be emitted from the organic molecules.
• Advantages over LCDs: Thinner, more efficient (no backlight required), faster refresh rate, better contrast.

Liquid Crystal Displays (LCDs)

• Liquid Crystal Characteristics: Liquid crystals possess a crystalline structure and exhibit refraction characteristics in certain temperature ranges.
• Polarization Technique: A polarized filter passes light waves in a single orientation, often micro-sized slits to filter light.
• Liquid Crystal Reorientation: When exposed to electric voltage, liquid crystal molecules will align in the direction of the field.
• Construction: Consists of two plates of glass with a liquid crystal layer between them, polarizers on the external surfaces and transparent conductive electrodes.
• Control: Voltage difference between electrodes controls the orientation of the liquid crystal molecules, thus regulating the passage of light.
• Operation (Voltage Based): LCDs are usually powered by alternating current (AC) to avoid power issues.

Color LCDS

• Subpixels: LCD color displays use three sub-pixels (red, green, and blue) with filters to create other colors.
• Voltage Control: Creating variations of voltage applied to each sub-pixel determines the intensity of each basic color.
• Color Combinations: Combining varying intensities of these three colors allows for millions of possible colors.

Additive Color Mixing

• Additive Primary Colors: Red, green, and blue are the foundation for forming other colors in LCDs and the human eye.
• Color Mixing: Combining different amounts of red, green, and blue light creates various hues/colors.

Cathode Ray Tube (CRT)

• Thermionic Emission: Electrons boil off from a heated filament due to heat.
• Edison Effect: Discovery that current flows between the filament and a plate within a vacuum.
• Electron Beam Focus & Acceleration: Controlling grids and anodes control the electron beam and redirect it to the screen, which is coated with a phosphor.
• Deflection: Electrostatic/magnetic methods manipulate the path of the electron beam and precisely move it on the display screen.

CRT Operation Review

• Electron Emission: Electrons are discharged from the cathode.
• Beam Control: The beam is concentrated into a precise area utilizing grids, focusing, and accelerating anodes.
• Deflection: Horizontal/vertical deflection plates direct the beam horizontally across and vertically down the screen.
• Screen Glows: The beam hitting the phosphor coating emits light/color at the impact point.

CRT Screen Shadow Mask

• Shadow Mask: A perforated metal mask that creates the specific pattern of colors on the CRT screen.

Simultaneous & Sequential Scanning

• Simultaneous Scanning: A method of displaying images on the CRT where all parts of the picture are generated/displayed at the same time.
• Sequential Scanning: A method of displaying images on the CRT one after the other to minimize flickering.

CRT Handling and Disposal

• Safety Precautions: Precautions to prevent implosion and damage for handling CRTs.
• Disposal Procedures: Method for removing CRTs, such as putting them into special containers before disposing them in order to prevent harm and damage.