Video Display and Audio Systems

1. Video Display and Audio Systems Basic PC Maintenance, Upgrade and Repair Mods 1 & 2

2. Display Concepts • There are a number of features common to all monitors. • These features such as dot pitch and size, greatly affect the quality of the picture, as well as the price the user pays for it. • Monitor Size – Standard sizes are 14”, 15”, 17”, 19”, and 21”. It is measured from one corner to the opposite corner of the monitor. • Dot Pitch – the distance measured in millimeters between two color dots on the screen. It directly affects the quality of the image displayed. • Generally, the smaller the dot pitch, the sharper the image displayed. • Common dot pitch is from 0.28 mm to 0.25 mm. It cannot be adjusted.

3. Display Concepts • Color Display Values – The color display quality is determined by the number of bits used to represent the individual colors of red, green, and blue. • This can also determine the possible number of color shades. • A byte contains 8 bits. • There are 256 combinations of 1’s and 0’s available with 8 bits. • This means that an 8 bit color pattern can reproduce 256 intensities of a specific color. • By mixing the intensities of red blue and green, other colors can be produced.

4. Display Concepts • Display Resolution – this term refers to the amount of detail a monitor is capable of displaying. • The term is also used by printers, digital cameras, etc. • The higher the value, the better the detail and quality of the picture. • Resolution is measured in pixels. A pixel is the smallest unit of color in a screen display.

5. Types of Displays • There are a number of different types of display systems for computers. • The two most common types are . . . . • CRT – Cathode Ray Tube • LCD – Liquid Crystal Display • Cathode Ray Tube – A picture tube in which a beam of electrons sweeps across a glass tube, exciting phosphorus dots in the screen. • Liquid Crystal Display – A type of monitor that uses polarized light passing through liquid crystal to create images on screen.

6. CRT’s • A CRT has two ends, Cathode and Anode

7. CRT’s • The Anode has a positive voltage potential between 16,000 to 25,000V.

8. CRT’s • A filament connected to the cathode is heated and it emits electrons. These electrons form a cloud.

9. CRT’s • The electrons are attracted to the positive Anode, are accelerated and focused into a pencil beam.

10. CRT’s • The accelerated electrons collide with the phosphor coating on the Anode and emit light.

11. CRT’s • Horizontal and vertical deflection coils position the pencil beam in the desired location on the phosphor screen

12. CRT’s • The pencil beam is moved across the screen and down in precise increments. • 525 horizontal lines are completed 60 times every second. The movement of the pencil beam uses the terms trace, retrace and blanking. • Trace is when the line of video is being produced. • Retrace is when the pencil beam is moved back to its horizontal starting position. • Blanking is the blocking of the pencil beam during retrace so it is not seen on the screen. • Color systems work similar, except there are three electron pencil beams being directed at pixels containing red, blue and green phosphors. • The intensity of each beam on the individual phosphors creates the specific color in that location

13. LCD’s • The LCD operates off of two principles: • Polarized light. • The effect of an electrical voltage applied to a crystal structure. • A typical light beam is composed of numerous waves of light. • They travel in parallel, but at different wave angles. • If a thin slot is cut in a material such as metal, only light waves with an angle matching the slot can pass through. This is polarized light. http://www.olympusmicro.com/primer/lightandcolor/polarization.html • When an electrical voltage is applied to a crystal, the crystal changes shape slightly or twists. • The amount of twist is directly related to the amount of voltage applied. • Light normally passes through the crystal in a straight line. • When a light is shined through a crystal and a voltage is applied to the crystal, the angle of the light wave changes as it passes through. http://electronics.howstuffworks.com/lcd3.htm

14. LCD Structure Sandwiched structure

15. Passive and Active Matrix Displays • The two types of LCD displays are Passive and Active Matrix. • Both use matrixes to determine how to select individual pixels • A passive matrix is a grid of semitransparent conductors that run to each crystal. It is divided into columns and rows. • Transistors running along the top and side of the display are activated in such a way as to activate a specific pixel (crystal) area. http://electronics.howstuffworks.com/lcd7.htm • An active matrix display uses a matrix that has a transistor that activates at each pixel (crystal) location. • The most common type is TFT (thin film transistor) LCD displays. It offers a brighter image that responds more quickly to changes. • There are over a million transistors spread across a display, three for each pixel (red, green, blue).

16. Other LCD Concepts • Contrast Ratio – a numeric expression in the form of a ratio that that describes the amount of contrast between the darkest and the lightest pixel in the image. • The higher the number the better. • Typical range is from 200:1 to 600:1 • A contrast ration of over 500:1 is considered a high quality display. • Brightness – in an LCD display, this is produced by the fluorescent backlight. • It determines the maximum amount of brightness produced in the display. • Levels typically range from 200 cd/m2 (candela per square meter) to 250 cd/m2.

17. Other LCD Concepts • Viewing Angle – a measurement of the angle at which a person can adequately see an image on a display without it looking excessively distorted. • Early LCD displays were quite limited in this area. • Today, most have a very acceptable viewing area. • Minimum around 150°, maximum around 170° (possibly even more). • Pixel Pitch – similar to CRT dot pitch, it is the distance between two same color pixels on the display area (i.e. two red pixels, two blue pixels, etc.) • Each color pixel is composed of three pels, one pel for each of the three colors that compose a pixel. • Pixel pitch is expressed in millimeters (mm) per inch.

18. Other LCD Concepts • Native Resolution – The resolution that matches the pixel design of the display • Although an LCD display is capable of showing a number of different resolutions, it will have the best images at its native resolution. • Response Time – the amount of time it takes a TFT pixel to display after a signal is sent to the transistor controlling that pixel. • Measured in milliseconds (ms). • A typical response is 15 to 40 ms. • The lower the response time, the better quality of the unit, especially with animation. • Aspect Ratio – A ratio of a display areas height and width. • Standard is 4:3 • New HD TV uses 16:10

19. Video Adapter Cards • Monitors can attach to computers in one of two ways: • It can plug into a video adapter card inserted into an AGP or PCI slot on the motherboard. • It can attach directly to the motherboard (that has integrated video components built in). • The heart of the video adapter card is the special IC chip known as a digital to analog converter (DAC). • It converts the computer’s digital video signal into an analog signal for the computer monitor. • The DAC can consist of one chip, or three, one for each color. • The video card also contains RAM, ROM, a video processor, and BIOS.

20. Pin Description • Red Video • Green Video • Blue Video • Monitor ID Bit 2 (Ground) • Ground • Red Return (Ground) • Green Return (Ground) • Blue Return (Ground) • Key (not used) • Sync Return (Ground) • Monitor ID Bit 0 (Ground) • Monitor ID Bit 1 (Not Used) • Horizontal Sync • Vertical Sync • Not Used Video Adapter Cards • A VGA monitor uses a 15-pin connector to connect to the video card.

21. Video Adapter Cards • Video cards are installed in PCI or AGP motherboard slots • AGP – Accelerated Graphics Port – is a slot used specifically for video cards and produces the highest quality result of the two technologies. • AGP is designed with graphics as a priority, using a computer’s memory to work more effectively with graphics. • AGP also has a faster bus speed.

22. Audio Systems • Audio is the second half of the multimedia experience. • All PC’s come with a small internal speaker, but that is not enough for most users. • Fancy sound cards, subwoofers, speakers and microphones have become standard equipment on many systems. • The human ear can detect sounds from approximately 20Hz to 20kHz. This is called the frequencyresponserange of the human ear. Sound waves (vibrations) above or below this range go undetected. • To convert analog sound to digital, a device called a Analog to Digital Converter (ADC) is needed. The method used with this ADC is called sampling.

23. Sampling • Sampling is the measurement of an analog signal at regular intervals. It is required to convert an analog signal into a digital signal. • The quality of the conversion is based on two main things: • Sampling rate • Number of bits used to represent the voltage level of the signal • A high sampling rate gives a better representation of an analog signal shape, but also requires more memory and hard disk space. • The number of bits available to represent analog voltage levels also can require more memory and hard disk space. • Older systems used 8 bits, while systems today use 16 bits. • 16 bits can much better represent the original sound.

24. 8-bit vs. 16-bit • Sounds recorded with 8 bit technology is limited to 256 different voltage levels, or binary codes, required to store a binary image of the sound wave sample. • 16 bit sound cards can use 65,536 binary codes to represent the analog voltage level during sampling. It is a more detailed representation of the sound wave pattern. • Another name given to the number of bits used is “resolution”.

25. Audio Devices • Microphone – a simple electronic device that converts sound waves in to electrical energy. • It converts air vibrations that strike it into voltage levels that are directly proportional to the strength and frequency of the vibrations • Speakers – a device that converts electrical energy to sound energy (waves) • The stored digital code representing the sound waves is converted by the sound card into an analog signal which is then sent to the speakers • The speaker cone vibrates at a rate proportional to the strength and frequency of the analog electrical signal • Sound Cards – Device that converts analog audio to digital audio and digital audio to analog audio. The output is a low level, so an amplified speaker system is required. • Most sound cards today are purchased as PCI adapter cards. This means they are usually PnP technology. • System resources (IRQ, DMA, I/O, Memory) are automatically detected and assigned.