PC video hardware page


    Typical PC graphics card consist of the following parts: bus interface, graphics controller, video memory and RAMDAC.RAMDAC (random access memory digital-to-analog converter) is a microchip thatconverts digital image data into the analog data needed by a computer display. A RAMDAC microchip is built into the video adapter in a computer. It combines a small static RAM (SRAM) containing a color table with three digital-to-analog converters (DACS) that change digital image data into analog signals that are sent to the display's color generators, one for each primary color - red, green, and blue. In acathode ray tube (CRT) display, an analog signal is sent to each of three electron guns. With displays using other technologies, the signals are sent to a corresponding mechanism.The SRAM part of the RAMDAC contains a color palette table. A logical color numberin the digital data input to SRAM is used to generate three separate values obtained fromthe table - one for each of red, green, and blue - that are output to one of three digital-to-analog converters. For displays with true color, the digital color data is fed directly to the DACs, bypassing the SRAM color lookup table. Typical modern PC graphics cards operate nowadays in true color mode (24 or 32 bits per pixel).The image in PC graphics card is stored to the video memory. The amount of video is a determining factor in the resolution and color depth of the display. Besides the storage of the displayed graphics, video card RAM is also often used to hold graphics-specific information such as 3-D geometry data and texture maps.

    Computer and TV

    Convergrence of computer and TV is a hot topic nowadays. PC is becoming a center of home multimedia system or the heart of modern home theater system. Modern technology allows you to use your PC (with right hardware + software) to ve used to view TV programs and edit video material. You can also view DVD movies on your PC and even connect your PC to a TV or video projector to get a larger picture than what your monitor gives. You can use a TV tuner to display television programs on your computer desktop.Scan converter is a general term basically used for products that convert the horizontal and vertical scan rate in order to make the Computer and Video devices compatible with each other. Manufacturers specifically describe a Scan Converter as a device that enables Computer (Workstations, PC, MAC) images to be displayed on a standard Video Monitor & TV set or for recording Computer images on videotape.Scan Conversion arose from the incompatibility between standards used in computer and video environments.Computers usually operate in a Non-lnterlaced mode, i.e. an image is made of one frame and the image is swept out line by line. The computer line frequency can be from 31 KHz to 130 KHz and the frame frequency is about 60 Hz to 100 Hz. Video (NTSC, PAL, SECAM) operates in an Interlaced mode, i.e. an image is made of 2 fields and the image is swept out in odd and even fields. In PAL/SECAM for example, the Video has a line frequency of 15.625 KHz and a field frequency of 50 Hz & a Frame Frequency of 25 Hz. In NTSC systems those values are 15.735 KHz / 60 Hz / 30 Hz.So, many Computer images can't directly be displayed or recorded on video mediums due to these differences. To display them, you first have to convert the computer signal into one compatible with your video device, using a suitable scan converter.

      TV picture to PC VGA monitor

      Adapting TV picture content to the PC monitor has gained the attention of home computer makers. Of particular interrest are PC graphics display technologies which allow the computer monitor to replace the family-room TV without any degration in TV picture. The nature of NTSC and PAL TV display format creates enormous challenges.TV signals and VGA monitors are incompatible with each other. The basic fundamentals are theoretically similar, but in application they are very different. There is a big difference in the scanning rates, CRT phosphor pitch, use of interlacing and overall design specs. Typical computer TV tuner card can do this complicated conversion without much for the user of the computer to worry about.

      • BTTV2 - A V4L2 driver for Bt8x8 based video capture cards. This is still a somewhat experimental v4l2 driver for the Bt8[47][89] based video capture cards.    Rate this link
      • Cards Tune In TV on Your PC - This article rounds up seven best-sellers and find that they work--within limits.    Rate this link
      • DScaler - DScaler is a piece of software that grabs analog, interlaced video, and deinterlaces it to make it a progressive scan feed then allows scaling to any resolution for use on your computer monitor or projector. This software is designed to work in Windows with a PCI TV card with a BT848 BT849 BT878 BT879 in it.    Rate this link
      • dTV - dTV is a piece of software that grabs analog, interlaced video, and deinterlace it to make it a progressive scan feed for use on your computer monitor or projector.    Rate this link
      • How to show video material in computer screen - Technical document on conversion of TV video signal to computer screen.    Rate this link
      • Is is possible to view VCR picture at SVGA monitor ? - short description about problems in this    Rate this link
      • Ruel's PC-TV Web Page - Watch TV On Your PC, lists of computer TV cards, video capturing cards and radio tuners, also PC to TV converters    Rate this link
      • Tuner Cards - Learning By Looking - Hopefully, this article will help people who'd like to consider writing device drivers for tuner cards, and others who're generally interested in how TV Tuner cards work.    Rate this link
      • - TV-card drivers, reviews and useful information.    Rate this link
      • TV Tuner Video Card Roundup - The concept of bringing TV to the desktop has gained quite a bit of momentum over the past few years. Initially flawed due to the small screen size of computer monitors, many current desktop monitors are larger than the televisions typically found in small apartments or dorm rooms. Add-in TV tuner cards that allow for cable input into a computer have been around for some time now, however these proprietary cards are quickly being replaced by video cards that combine computer display and TV input on one card.    Rate this link
      • TV Tuning Basic - A TV tuner for a computer does essentially the same thing that the tuner inside your television does: takes the signal sent to you via a RG59 cable or though the air and converts it into a image that can be displayed onto your computer display. Most TV tuner cards we have seen make use of a a Philips TV tuner module and TDA9800T video signal decoder.    Rate this link
      • Using Your Brooktree Chipset TV Card in Linux - The Brooktree chipsets TV cards (BT848 and BT787) are fully supported under Linux using the bttv drivers. Many popular TV cards are supported under bttv including: Lifeview Flyvideo cards, Hauppauge cards, Micro Cards and any other Brooktree based cards. In this article we'll take a look at what it takes to turn your Linux box into a fully functional television.    Rate this link
      • - TV card news, reviews, drivers, apps and message board    Rate this link
      • Vaihda viihteelle - Instructions how to build a PC which can acts as a set-top-box with the functionality of a multimedia center and digital video recorder. The text of this article is in Finnish.    Rate this link
      • Video overlays turn PCs into TVs - overlaying video and graphics on a VGA monitor requires abundant bandwidth and horsepower, forttunately there are number of video-connection schemes, high-bandwidth buses, and high-integration chips can transform postage-stamp-sized video overlays to full-screen, full-motion displays    Rate this link
      • What is a TV Tuner Card ? - A Tv card plugs into your PC and allows you to watch television on it. The PCI TV card hasn't really changed in design since they first became available around 5 years ago. Essentially there's not a lot to change or upgrade beyond adding NICAM Stereo sound and FM Radio tuners.    Rate this link

      PC digital TV

      • Linux TV - a platform for the development of open source software for digital television (DVB, DTV) receivers, Linux DVD players and tools to stream audio and video to the net    Rate this link
      • PC DTV - The PC DTV Promoters Group is an ad hoc assembly of companies interested in promoting the reception of rich DTV and/or data delivered by broadband broadcast signals from terrestrial broadcast, satellite or cable TV services. Each of these companies offers technology or services that enable PC users to receive digitally broadcast signals from terrestrial stations, cable services or satellite providers.    Rate this link

      Video from PC to TV or VCR

      Sometimes you might want to display your PC screen on a television. For example, you might want to make a videotape recording of a presentation, so you can display the presentation with a VCR. You can also use TV output to play games on your television, or record a tutorial for a friend.

      Using TC as computer display has it's limitation. Normal televisions are fairly primitive compared to computer monitors. Even high-quality televisions that advertise high vertical and horizontal resolutions may have problems displaying a computer image, due to limitations in the way video signals are encoded. Practically, that means that the maximum resolution that your television will display is probably less than 640x480 for NTSC video system (nearly 800x600 for PAL), a very low desktop resolution for a PC. VHS videotapes are even more limited. What I told above applies to normal TVs. The high definition televisions are another story.

      Besides different performance characteristics there are also other technical differences. Going from computer to TV is not technically trivial task. Naturally the computer graphics (VGA) and normal broadcast television (NTSC,PAL or SECAM standard) are very incomatible with each other. With suitable conversion it is possible to show VGA picture on TV screen with somewhat degraded quality. The picture resolutions vary from computer (typically from 640x480 well above 1024x768), where the broadcast TV uses a fixed resolution (nominally 525 or 625 lines in Y direction in signal, not all of them less visible; resolution in X direction not absolutely defined, usually effective X resolution beteen 300-600 pixels).

      When displaying computer graphics on TV screen you will very easily see the limitations of the TV itself and the TV broadcast standards. Anybody who has tried to display computer graphics on a television knows that they look bad. Colors wash out, detail is lost, and the whole thing flickers. And that's the best scenarios. Sometimes the graphics really get distorted. While everyone knows that televisions do bad things to computer graphics, few people are sure exactly what is happening. This confusion isn't surprising. NTSC and PAL encoding are quite complex, and the reasons that they distort graphics are not always obvious.

      Connecting the PC to the TV or VCR is an easy thing actually if you have a suitable graphics card with TV output and know how to use it. Nevertheless there are certain problems very often. One of these problems is that users get a b/w picture on TV only for example. The fact that more and more manufacturers spare certain connectors on their graphics boards can be very annoying also.

      Composite video is the most widespreaded standard. The main characteristic is that the video signal is transmitted on a single line only (plus ground). For the connection to the TV all you need is one line of a shielded cable. Composite video signal has disadvantages. There can be interferences between the chrominance (color) and the luminance (brightness) information. So you can see a pattern of colors in the checkered jacket of the news reader or some computer graphics for example. The best thing of composite video is that practically all TVs with some kind of AV-input can accept this video format, and so do the normal VCRs.

      There are also other common alternative for connection: S-video.Especially TVs of the higher price segment offer also a S-video input. The 'S' means super and shall clarify that this standard offers a better quality than normal composite video. S-video standard transmits video signals on two lines. On one line you find a b/w picture and on the other line there is the belonging color information. If your TV has S-video support then this is the preferred connection method.

      The third possibility to transmit a video signal is the RGB connection. Three images in the primary colors red, green and blue are sent over three single lines. The TV as well as the graphics card work with this technique internally, so this gives the best picture quality if it is available. Who wants to use RGB must usually select the graphics card to use very carefully and usually reach for a soldering iron to build the special cable which goes between the card and TV. The number of TVs whith RGB inputs is also limited, especially in USA. In Europe practically all TVs with SCART connector support RGB. RGB can only be used as PC to TV connection, because normal VCRs don't support RGB format. Which connection is recommended?

      In USA many modern TVs have interface called component video. This interface can tasport image quality comparable to RGB interface. There are several cards that can output component video format. Component vidoe connection is typically made with three RCA or BNC connectors.

      The recommendation is that use the best one you can make to work. Well, in most cases composite video is the solution which always works, but does not give the best picture quality. If you plan to record picture to VCR, them i recommend using composite video format. If your TV can handle S-video you should use this type of connection of course (many PC graphics card with TV output usually give this video format as the default format). If both your graphics card TV output and TV can handle RGB signals, then you should check if it possible to get or build a suitable cable for this connection (if this works this gives the best picture quality). Other notes on setup:

      • Select a suitable video format which is supported by both the signal source (PC graphics card) and your video signal receiving device (TV or VCR). Check the technical specifications of both of the devices you plan to connect carefully.
      • Get right kind of cables for the connection. Those might come with the card or you might need to buy some cables/adapters.
      • Connect the cables
      • Set your graphics card TV output settings right: TV output enabled, right signal format selected and right video standard selected (read your graphics card manual how to do this on your card)
      • Turn on the TV and select the sight video input source (and propably input signal format also on some TVs)
      • If you plan to record a presentation to videotape or play games in your living room, make sure to use a low desktop resolution and big fonts.
      • Where possible, always use S-Video connectors instead of standard RCA video plugs to get better picture quality.

      With those tips you should be able to get this connection to work immediatly or after some testing/tweaking. be prepared to spend some time on this project, because sometimes when thign do not work easily. In those cases you might need to go though few alternative settings or connection methods.

      Note for European users: SCART interface on typical TVs and VCRs supports typically composite video format in all cases. Practically all TVs support RGB in at least in one of their SCART interfaces. There is a way to carry S-video in SCART connector (there are connector adapters and cables for this connection), but not all TVs support this. To be able to use S-video on TV through SCART you need to make sure that your TV supports S-video, you use a SCART connector which supports S-video (on some TVs only one of SCARTS supports this) and you have S-video input mode enables in the TV. If you have any of those wrong, you easily end up getting no picture or get just black and white picture. When everything works and is supported, you get a nice S-video with all colors and full details through SCART connector. So the end result with SCART is that composite video connection works always with SCART. S-video gives better picture if supported but is not supported with all devices.

      Note on TV connection auto-detection: Some PC graphics cards try to auto-detect if the TV is connected to the TV output. Some cards go to TV out mode automatically when TV is connected. Some other cards do not allow you to go to TV mode unless you have TV connected. The PC graphics card with TV out looks for the 75 ohm termination as a way of detecting that the video out port is connected to a TV. It then switches from doing VGA out to TV video out mode. The TV connection auto detection is not completely foolproof and can fail on some TVs (this depends how video inputs on TV is implemented). Some TVs can have video inputs can be unterminated and the PC video adaptor won't switch over because it can't see that 75 ohm resistor it looks for. In some cases the video input can be AC terminated and the TV card can fail aso here, if it looks the termination with DC test voltage. Not all proper terminations (for video signal itsefl) can be measured with an ohmmeter! In those cases the auto-detection fails, adding an extra 75 ohm resistor between cable signal wire and ground on the TV end of the cable helps the card to detect that TV is connected. When resistor is on the cable, the PC grpahics card will detect that there is TV conneted always where there is this cable with resistor plugged in (no matter if there is a real TV on the other end of cable or not). The terminating 75 ohm resistor should be in the cable end that plugs to the TV, thus acting as terminator for those TVs that have unterminated input. You're supposed to solder the resistor across the plug, or make up a short plug/jack 'extender' with the resistor inside. This keeps youfrom fouling up the insides of the TV (which is not a good idea). In case the input was already terminated input, the the worst thing that could happen with this extra 75 ohm terminting resistor on the cable is that the video signal level will be a bit small (you can loose some picture quality).

      Flicker is a common problem in TV signal. The flicker is caused by the nature of the computer graphics and TV interlace interaction (normal TV programs do not flicker much becasue material is already compensated for this).When displaying PC grahics on TV, the data must be converted into interlaced format for display on a TV. If every second line is discarded of the noninterlaced data, flicker may occur if, forexample, video information is contained in just one noninterlaced line. Flicker will also be perceptibleat the top and bottom of multiline objects. A flicker filter overcomes these problems in computing a weighted average of two or three adjacent lines (noninterlaced) for each line of output (interlaced). Depending on the filter settings you can usually balance between picture resolution and amout of flicker (less flicker means more smoother out).

      There are differences how well the different TV outputs on different cards are implemented. The TV output quality (s-video output capabilities) seems to be a very overlooked feature present on a video card. Generally in your "average" video card review you see on magazine or web, at some point there will be a short mention that the card in question has s-video output functionality but it generally isn't tested or compared to anything. But the fact is that the quality of the signal you get from those output and now nice they are to use varies from card to card. Sometimes even the card drivers have effect on the quality you get (this depends how well those drivers utilize the that output, how well it configures it).

      Cables and pinouts for video card to TV connection

      The connection of a PC graphics card to your TV (or other suitable display device) can be sometimes a a quite of a saks of it's own. The cards do not necessarily come with the the right kind of cable which fits to the connector of your TV. The reason for this isthat the A/V connectors on the TVs vary somewhat. And also the connectors for TV signal on the graphics cards vary, and quite often the PC graphics cards use other connector types that used by other devices (this means that PC cards too oftenuse non-standard connectors for video signals). Here you can find information which can be useful when interfacing computervideo cards to TVs.

      • The SCART connector - Also known as Peritel, this standard provides a cheap multi-signal connector to domestic TVs and other video equipment. Arrangement 1 was the original and allows for composite video input/output, RGB inputs and stereo audio. Arrangement 2 was added to take S-video (S-VHS and Hi-8) inputs. This made pin 15 chrominance and pin 20 luminance.    Rate this link
      • Hollywood+ 7-pin S-video connector - This is one commonly used wiring for 7-pin non-standard S-video connector. This type of connector accepts slightly modified (one plastic pin removed) normal 4-pin S-video connector to get S-video signals. The additional pins carry other signals (here composite video signal).    Rate this link
      • S-video to composite video adapter - This simple adapter can be used to convert Y/C video (S-video) to a composite video. This adapter is useful in cases where your video output device has only S-video output but your signal source accepts only composite video input. This circuit works with both PAL and NTSC video standards.    Rate this link

    Monitor information

    PC monitor system is complicated system, but luckily for us it's one that's easy to understand. The following description is centered on traditional analogue CRT PC monitors.

    The video adapter in PC sends the signals from it's image memory at fixed rate (usually configurable) through the DAC (digital to analog converter) circuit to the monitor connector on the graphics card. The DAC converts numeric pixel color values to voltage levels for red, green, and blue which are sent to monitor through the monitor cable. Most monitors today use the traditional CRT, which works on the same scientific principle as a television set. This vacuum tube produces an image when an electron beam strikes the phosphorescent surface inside the monitor. Normal PC VGA monitors nowadays are so called "non-interlaced" monitors. The computer requires a "video Interface" sometimes referred to as a video card to communicate with your monitor. Your monitor is the single most important component of your computer system if you want to get good picture quality (also the graphics card can contribute to this).

    The visual quality, depends on the quality of your monitor. Consumers have now become more concerned about the visual quality. The flat screens, high resolution, high refresh rates, and recently the USB and solid state screens top the list of desirable features. The multimedia monitor includes oudspeakers of some sort, maybe a microphone and in some cases a camera for video conferencing all in the same box as the monitor.All analog monitors can produce thousands of colors, it is inherent in the design. The limitation on color registration is directly related to what is available in the interface card and the mode selected. There are practically infinite number of colors possible with the analog monitors (although they can not properly display all natural colors correctly).

    Resolution is the number of pixels the graphics card is describing the desktop with, expressed as a horizontal by vertical figure. Standard VGA resolution is 640 x 480 pixels. The commonest SVGA resolutions are 800 x 600 and 1024 x 768 pixels. A typical PC monitor is designed to accept signals at wide resolution and frequency range. When you change the seolution on refresh rate on monitos, just the scan frequencies that are changing to accomodate the new timing/pixel format. The focus (which is sort of the electron beam width, at least as it is seen at the screen) MAY be altered slightly as well, if the monitor has the capability of storing adjustments for that and other parameters (geometry, convergence, etc.) for specific timings, although it is VERY unusual for focus to be included in this. Please not that the monitor physical dot pitch can't change - that's a fixed physical parameter of the CRT itself - but the physical dots on the screen (or the holes in the shadow mask) really have nothing at all to do with the logical pixels of the image, other than being one of the things which ultimately limits the resolution. The scan frequencies do not necessarily change at all when you change the resolution. What happens is that the signal as seen on the VGA plug has (for example) 1024 discrete values between 2 consecutive line syncs as opposed to 800 discrete values and 768 line syncs between frame syncs as opposed to 600 (assuming non interlaced). Typical PC CRT monitor an display all resolutions from the lowest up to the highest supported resolution well. If you have a modern flat panel display, things can be different. On TFT monitors they specify a "recommended" resolution that the TFT works best at and when not run at this resolution they get seriously blocky and in some cases unreadable text.

    Refresh rate, or vertical frequency, is measured in Hertz (Hz) and represents the number of frames displayed on the screen per second. Too few, and the eye will notice the intervals in between and perceive a flickering display. The world-wide accepted refresh rate for a flicker-free display is 70Hz and above (preferably 75 Hz or more). The flicker is strongly dependent upon visual angle, because eye peripheral vision response is faster than the higher resolution centerof field vision. The bigger the monitor, or the closer you are to it, the worse the flicker will be, so you will need higher refresh rate to get "flicker free" picture. CFF (Critical Flicker Fusion) also depends on illumination levels. The CFF frequency is lower at lower illumination levels. As the height of the picture increases, it is necessary to increase the number of horizontal lines to create a smooth line-free display image. To do this, the monitor and the interface card increase the frequency of the repetitive horizontal scan rate.

    In order to consistently reproduce the video information at a high resolution, the monitor must have a wide video bandwidth. In order for the term to be meaningful for comparison purposes, the bandwidth expressed in mhz. must be within +- 3dB You might see a term "sync signal" sometimes.All computer monitors require a "sync" signal which determines the resolution of the display. Some monitors require the sync signal to be a separate electrical connection, some monitors require the sync signal to be mixed in with the green video signal (sync on green). Some monitors support both separate sync and sync on green. PC VGA card uses separate sync signals and PC monitors are designed to accept at least this sync format.

    The term "dot pitch" is the measurement in milimeters of the distance between two adjacent phosphor color elements. There are two color phosphor systems in use today in CRT monitors: triad dot shadow mask (most monitors) and aprature grille (used in the trinitron tube from SONY). NEC has developed a hybrid mask type, called slotted mask, which uses elliptically-shaped phosphors grouped vertically and separated by a slotted mask.

    Here are some guidelines for suitable resolutions for different monitors:

    • 14 inch monitor is adequate for 800 x 600 resolution.
    • 15 inch monitor is adequate for 1024 x 768 resolution.
    • 17 inch monitor is adequate for 1024 x 768 resolution.
    • 19 inch monitor is adequate for 1280 x 1024 resolution.
    • 21 inch monitor is adequate for 1600 x 1280 resolution.
    If you use a higher resolution exceeding these guidelines, a very good monitor may deliver adequate pictures but you can also run into a poor quality picture. Keep in mint aldo what frequencies and resolution your monitor can handle. Trying to use frequencies and resolutions that the monitor was NOT designed to support can severly damage your monitor. To make the monitor installation easy, VESA has produced several standards for plug-and-play monitors. Those standard features (like DDC) should in theory allow your system to figure out and select the ideal settings, but in practice this very much depends on the combination of hardware.

    Here is an overview of different video display resolution standards and de-facto standards in use:

    Computer Standard Resolution
    VGA 640 x 480 (4:3)
    SVGA 800 x 600 (4:3)
    XGA 1024 x 768 (4:3)
    WXGA 1280 x 768 (15:9)
    SXGA 1280 x 1024 (5:4)
    SXGA+ 1400 x 1050 (4:3)
    WSXGA 1680 x 1050 (16:10)
    UXGA 1600 x 1200 (4:3)
    UXGAW 1900 x 1200 (1.58:1)
    QXGA 2048 x 1536 (4:3)
    QVGA (quarter VGA) 320 x 240 (4:3)
    Analogue TV Standard Resolution
    PAL 720 x 576
    PAL VHS 320 x 576 (approx.)
    NTSC 640 x 482
    NTSC VHS 320 x 482 (approx.)
    Digital TV Standard Resolution
    NTSC (preferred format) 648 x 486
    D-1 NTSC 720 x 486
    D-1 NTSC (square pixels) 720 x 540
    PAL 720 x 486
    D-1 PAL 720 x 576
    D-1 PAL (square pixels) 768 x 576
    HDTV 1920 x 1080
    Digital Film Standard Resolution
    Academy standard 2048 x 1536

    In the late 1980s concern over possible health issues related to monitor use were raised. In Sweden this resulted a standard MPR1 to be developed. This was amended in 1990 to the internationally adopted MPR2 standard, which called for the reduction of electrostatic emissions with a conductive coating on the monitor screen. In 1992 a further stricter standard, entitled TCO (TCO92), was introduced by the Swedish Confederation of Professional Employees. Other relevant monitor safety standards include: ISO 9241 part 3 (the international standard for monitor ergonomics), EN60950 (the European standard for the electrical safety of IT equipment) and the German TUV/EG mark (monitor has been tested to ISO 9241 part 3, EN60950, MPR2 and German standard for basic ergonomics ZH/618). TCP99 is the latest iteration of the standard TCO99 give rgulations on screen refresh rates. To reduce eye fatigue caused by image flicker, the minimum required refresh rate is increased to 85Hz for displays of less than 20in, with 100MHz recommended, and to a minimum of 75Hz for 20in or greater.

    Power consumed by the monitor can also be a significant figure. In 1993, VESA initiated its DPMS standard, or Display Power Management Signalling, which allowed a DPMS compliant graphics card to turn the montor to standby more or suspend modes which consume considerably less power than normal operation. EPA Energy Star is a power saving standard, mandatory in the US and widely adopted in Europe, requiring a mains power saving mode drawing less than 30W. In 1995, TCO was expanded with a range of conditions to cover environmental issues. TCO95 became the first global environmental labelling scheme. Over and above TCO92, the product may not contain cadmium or lead, the plastic housing must be of biodegradable material and free of brominated flame retardants and the production process must avoid use of CFCs (freons) and chlorinated solvents.

    Monitor connections

      Analogue VGA interface

      Modern PC graphics cards even nowadays still use the old 15 pin VGA connector (known ad HD15 connector). The connector carries the video signal in RGB format. The sync information is carried through separate horizonal and verticna sync signal wires. This whole video signal format (video and sync) is generally referred as RGBHV signal format.The signal levels in RED, GREEN and BLUE signal are 0.7V peak to peak video signals terminated to 75 ohm load in video card and monitor ends. All other signals are TTL level signal (around 0..0.7V means logic 0 and 3..5V means logic 1). Analogue video signals are carried through 75 ohm coaxial conductors. The video signal carried vy VGA connector can also be carried with separate 5 coaxial cables with BNC connectors (some monitors and video projectors use this kind of interface and adapter cables for this are readily available). The pinout of video signals on VGA connector:

      • 1 Red Video
      • 2 Green Video
      • 3 Blue Video
      • 4
      • 5
      • 6 Red Return (ground)
      • 7 Green Return (ground)
      • 8 Blue Return (ground)
      • 9
      • 10 Sync Return (ground)
      • 11
      • 12
      • 13 Horizontal Sync
      • 14 Vertical Sync
      • 15
      In addition to video signal, the VGA connector has some monitor identification pins (pins 11, 12 and 15) that allow PC video cards to determine what type of monitor is connected to the graphics card. The originaal plan used to such that the monitors grounded some of those pins to tell that the monitor is there and what type of monitor is there. Modern plug&play monitor systems have changed their use in such way that pins 11 and 15 are used for DCC data communications between computer and monitor (pin 12 = DDC DATA, pin 15 = DCC Clock). The extra control signals are generally carried through separate wires (all inside one cable main shield). Pin 5 is sometimes referred as GND TEST and sometimes just ground.Pins 4 and 9 are not generally used. Not all connector pins are used in VGA cables. Generally pins 9 has been removed because is is used in many devices as key to stop plugging in full 15 pin connectors. In some cales also pin 15 have been removed for compatibility with all VGA computers (also older ones, because pins 9 and 12 pins were removed in early VGA cables and blocked in old VGA cards).Here is one common wiring used:
      Pin New VESA DDC     Old VGA
      1 Red Red
      2 Green Green
      3 Blue Blue
      4 No Connect Reserved
      5 Ground Ground
      6 Ground Red Ground
      7 Ground Green Ground
      8 Ground Blue Ground
      9 No Connect No connect
      10 Ground Ground for syncs
      11 No Connect Monitor ID 0 (ground)
      12 DDC DAT Monitor ID 1 (no connect)
      13 Horizonal Sync Horizonal Sync
      14 Vertical Sync Vertical Sync
      15 DDC Clock No Connet
      The video signals carried in VGA connector are designed to be matched to 75 ohm load and use coaxial cable. At least the RGB signals on the cable used to connect VGA signals must have 75 ohm coaxial construction to guarantee good quality high resolution image. A typical high quality VGA monitor cable or VGA extension cable has three three 75 ohm mini coax cables to carry RGB signals and 9 other wires (typically 24 AWG) to carry other signals like syncs and monitor identification. The whole cable has a good metallic shield around all of those wires. Some very high quality cables use five 75 ohm coaxial cables and for RGBHV signals and just few extra wires. In applications where monitor ID signals are not needed, just five 75 ohm coaxes are used to transfer VGA signals. Typical features of flexible mini coax cables (from for extra flexible miniature coax):
        1 MHz:   0.6 dB/100ft
      5 MHz: 1.3 dB/100ft
      10 MHz: 1.8 dB/100ft
      30 MHz: 10.2 dB/100ft
      100 MHz: 17.1 dB/100ft
      Some attenuation figures of high quality VGA extension cable (for reference of typical features):
       10 MHz:  1.6 dB/100ft
      50 MHz: 4.0 dB/100ft
      100 MHz: 6.1 dB/100ft
      200 MHz: 9.8 dB/100ft
      300 MHz: 13.0 dB/100ft
      400 MHz: 15.9 dB/100ft
      The connector uses in VGA connections is HD 15 connector. This ubiquitous connector is convenient, low cost, and most importantly, adopted by IBM, but technically not the best possible connector. The connector was originally selected to be good enough for the signals existing in the early days of VGA interface and was more than good enough for this use, but VGA connector has it's limitations at high resolutions. Does anyone know the impedance of a 15-pin VGA connector? Unfortuantely the HD15 connector used does not match to 75 ohm impedance (in reality the impedance of a typical VGA connection is about 100 ohms). Even though the connector impedance is not exactly right, the primary issue centers on the limited length of the connector interface, so it does not significantly hamper performance in systems we most often deal with.This HD15 connector is still used, because this ubiquitous connector is convenient, low cost, and most importantly, adopted by IBM. It is still with the limitations considered "good enough". And in practice one VGA connector on the route from the graphics card to the monitor does not cause too much problems for picture quality. The primary issue for this centers on the limited length of the connector interface. Because of the limited length, it does not significantly hamper performance in systems we most often deal with. Because there is no no significant effects, hence the popularity of the VGA connector as a low-cost, general interface for the PC even nowadays. The problems of connector impedance mismatch becomes visible if you happen to have more than one VGA connector on the route to monitor and you run high frequency video signal (high resolution at high refresh rate). Impedance mismatch degrades the picture quality. You can see the impedance matching problems usually when you use devices like VGA monitor switch boxes, VGA extension cables etc. A typical mechanical switch works around this way: Mechanical changeover switches/relays to select between two input signal sources. For VGA connection geneally pins 1,2,3,6,7,8,13,14, and 10 of the monitor connector are switched (usually also 12 and 15 so that DCC for plyg&play monitor connection works). There are some variations what pins are switched (some implementations do not switch the ground lines, they keep then always connected. some other switch also those lines). A mechanical switch will work for VGA signals quite acceptably when the internal wiring on the switch box is well made (preferably 75 ohm coax). Many modern VGA switching system use electronic switching of VGA signals.

      Digital Visual Interface (DVI)

      Digital Visual Interface (DVI) is the standard interface for high-performance connection between PCs and Flat Panel Displays, Digital CRT Displays, Projectors, and HDTV. DVI Cables deliver the high-performance, high-bandwidth interface needed for video displays of today, and leaving headroom for the products of tomorrow.

      DVI standard is defined by DDWG (Digital Display Working Group). DVI most commonly used digital video interface with PCs in DVI. It comes in theree version: DVI-A, DVI-D and DVI-I. The difference on those is that DVI-D support only digital signals, where DVI-I includes both digital and analogue video signals (analogue signals are same as used by VGA interface). DVI supports hot plugging of DVI display devices.

      DVI-A format is used to carry a DVI signal to an analogue display, such as a CRT monitor or an HDTV. Basically this interface has same signal as VGA connector has, but uses different shape connector. DVI-A can transmit a higher quality picture than standard VGA, because the connector user matches better to the needs of transported high frequency video signal than the old 15-pin VGA connector.

      DVI-D is a digital only connector version of DVI interface. DVI-D is the leading connector standard for digital only connection. It comes in two flavors: Single Link and Dual Link. The primary difference between Single Link and Dual link is that each supports varying resolution levels. DVI-D uses LVDS signaling for digital signal and supports cable length up to 5 meters (longer distances are possible with repeaters every 5 meters). In case of longer transmission distances are needed, you need to either have DVI repeater every 5 meters or use a special converter that converts DVI signals to fiber optics and back. Some manufacturers seem to make also 10 meters long DVI-D cables, but because those are longer than standard permits their operation is no guaranteed (causes unreliable operation and signal transmission errors on many equipment, but can work on some equipment). The DVI-D Single Link supports resolutions up to 1920x1080. For gher resolution there is a dual link version also available.

      Within the DVI system, parallel data from the computer graphic memory is serialized (similar to digital television) and transmitted differentially over a minimum of four twisted pair wires:a red channel, green channel, blue channel, and clock channel at about 165 mega-pixels/second per channel (1.65 Gbps on the basic system). The RGB data are not simply serialized and dumped onto the cables. Encoded sync information is carried along and the data is scrambled using a specific routine that minimizes errors during transmission from source to destination. The system operates on 3.3 volts and can operate at lower voltages. The twisted pair differential swing is about 1.0 volt peak-to-peak.

      The DVD-D dual link configuration provides enough bandwidth for resolutions up to 2048 x 1536, and is designed for digital use only. In dual link system the number of wires used to transport red, green and blue component data is doubled (giving total 7 pairs of wire used to transport data). The DVD-D dual link uses DVI-D 24-pin connectors and supports digital signal only. To support those high resolutions, very high data rates are needed in the cable. DVI achieves up to 9.9-Gbps dual-link or 4.95-Gbps single-link data speeds.

      DVI-I format is an integrated cable which is capable of transmitting either a digital-to-digital signal or an analog-to-analog signal.DVI-I can supports both digital DVI-D signals AND analog (RGB). The connector has a few more pins than digital only DVI-D. Many graphics cards manufacturers are offering this connector type on their products, so this can be connected to either digital or analogue display device. The signals from DVI-I connector can be adaped to analogue VGA signal by using a simple connector adapter (usually comes with graphics card, can be bought separately). DVI-I format is an integrated cable which is capable of transmitting either a digital-to-digital signal or an analog-to-analog signal. Make sure that you know what format each part of your equipment is before you purchase any DVI cables. Only equipment with a DVI port labeled 'DVI-I' will accept both a DVI-D and DVI-A source signal.

      Determining which type of cable to use for your DVI products is critical in getting the right product the first time. Check both of the female DVI plugs to determine what signals they are compatible with. There are two variables in every DVI connector cable, and each represents one characteristic. The flat pin on one side denotes whether the cable is digital or analog: a flat pin with four surrounding pins is either DVI-I or DVI-A, a flat pin alone denotes DVI-D. The pin sets vary depending on whether or not the cableis single- or dual-link: a solid 27-pin set (rows of 8) for a dual- link cable,two separated 9-pin sets (rows of 6) for a single-link cable. Note: To prevent pins being broken off of mistmatched cables, most manufacturers will make their female plugs with all available pins. This means that most every female DVI plug will look like a DVI-I, but this is not necessarily true. Be sure to look for a label, or check the product documentation to make sure you know what type it is.

      The physical cable used to do DVI connection has different conductor types depending on the signal they carry. The digital signals are carried through twisted pairs that have 100 ohm +/- 15% impedance (usually separately shielded twisted pairs). Analogue video signals are carried through 75 ohm coaxial conductors.

      Transmission of the TMDS (transition minimized differential signaling) format combines four differential, high-speed serial connections (in its base configuration) transmitted in a parallel bundle. When the DVI specification is extended to the dual mode operation, greater data rates for higher display resolutions are possible, but now there are seven parallel differential, high-speed pairs. Cabling and connection become extremely important. The DVI cable and its termination is very important. The physical parameters of the twisted pairs must be highly controlled. Specifications for the cable and the receiver are given in fractions of bit transmission time, so the requirements depend on the clock rate or signal resolution being used. Transferring the maximum rate (1600 x 1200 at 60 Hz) for a single link system means that one bit time (10 bits per pixel) is 0.1 (1/165 MHz), which is only 0.606 nanoseconds. Ten bit times describe one pixel in this system. The DVI receiver specification allows only 0.40 x bit time, or about 0.242 nanoseconds intra-pair skew (within the twisted pair). A cable for DVI-D should be evaluated on its insertion loss for a given length. The DVI transmitter output eye pattern is specified into a nominal cable impedance of 100 ohms. A normal signal swings +780 mV to -780 mV. The minimum positive signal swing is +200 mV and the minimum negative swing is -200 mV (total swing of 400 mV). When the signals are combined in the differential receiver, the resulting signal level is two times the swing value. But, for the cable situation, we must assume minimum performance on the transmitter side and best sensitivity on the receiver end. The receiver must operate on signals as low as +75 mV to -75 mV, or a total swing of 150 mV. This means that under worst-case conditions, the cable attenuation can be no more than 8.5dB at 1.65 GHz (10 bits/pixel times 165 MHz clock). As you can imagine, maintaining this type of performance on twisted pair wires is relatively difficult. The nominal DVI cable length limit is 4.6 meters (about 15 feet). Electrical performance requirements are similar to serial digital. Signal rise time (0.330 nanoseconds), cable impedance (100 ohms), far end crosstalk (FEXT) of no more than 5%, and signal rise time degradation (160 picoseconds maximum) are the key parameters highlighted in the DVI specification regarding the physical connection.

      Cable for DVI is application specific because maintaining these specifications is no easy feat since the actual bit rate per channel is 1.65 Gbps. And, we're talking twisted pair cable here. Upgrade your system's video performance by connecting VGA- or DFP-configured monitors to fast DVI cables.Use DVI to eliminate resolution or color changes and pixel-lock adjustments in laptop-to-projector connections, too.

      Cable building

      Sometimes you can see ferrites on ready made VGA monitor cables. The usual purpose of ferrites has nothing to do with performance, rather they are added so that the equipment does not radiate EMI (Electro-Magnetic Interference) in excess of FCC limits. The usual source of radiation is the outer shield of the cable.


    A simple Webcam consists of a digital camera attached to your computer. A piece of software connects to the camera and grabs a frame from it periodically. . The software then turns that image into a normal JPG file and uploads it to your Web server. The JPG image can be placed on any Web page (for information on creating Web pages and adding JPG images. Webcams are cheap camera products (cost less that 100 US dollars) that have also many other uses than just uploading images to web.

    Touch screen technology

    A touchscreen is any monitor, based either on LCD (Liquid Crystal Display) or CRT (Cathode Ray Tube) technology, that accepts direct onscreen input. The ability for direct onscreen input is facilitated by an external (light pen) or an internal device (touch overlay and controller) that relays the X,Y coordinates to the computer.

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