CRT question

This is a discussion on CRT question within the A Brief History of Cprogramming.com forums, part of the Community Boards category; I was wondering how a CRT screen works. After reading up I understand this much, that a 'gun' basically fires ...

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    CRT question

    I was wondering how a CRT screen works. After reading up I understand this much, that a 'gun' basically fires electrons towards a phosphor screen, the electrons release energy which emits light. What happens to the electrons after this? Are they 'recycled' and re-used by the gun, or are they made up in the incoming current powering the device?

    Yeah, I know, this question comes out of nowhere.
    I'm not immature, I'm refined in the opposite direction.

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    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by BobMcGee123 View Post
    I was wondering how a CRT screen works. After reading up I understand this much, that a 'gun' basically fires electrons towards a phosphor screen, the electrons release energy which emits light. What happens to the electrons after this? Are they 'recycled' and re-used by the gun, or are they made up in the incoming current powering the device?

    Yeah, I know, this question comes out of nowhere.
    The electrons return to ground through an incredibly fine wire mesh. If you look at your CRT through a high power magnifying glass, you may be able to see the grid.

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    Registered User Frobozz's Avatar
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    The superhaterodyne twomers's Avatar
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    The electrons aren't simply fired from the cathode through the grid either ... as far as I know there is a series of electromagnets which periodically set the 'x' and 'y' coordinates Z times a second in a loop. It does not fill the screen in one felled sweep - as far as I know the electromagnets set a place at which the electrons will be fired, controlled by the electromagnets. It does it pixel by pixel, row by row, screen by screen 30 (or more), times per second. The frequency 30 kHz seems to stick out in my mind for some reason. I believe that there are red, green and blue colours mixed together, their respective intensities set by the TV signals the antenna/dish receives, to fulfill the whole technicolour experience. The sound then (though not part of the actual CRT thing), is embedded within the signals.

    Now that's traditional TV (analogue), but with digital television I think it's only when a pixel changes that information is transmitted hence reducing the bandwidth greatly (especially for cartoons). So if a CRT is getting digital info through a box or whatever I can only assume that the box stores aforereceived pixels until they need updating.

    But then there's the whole question about whether or not electrons exist as we 'know' them ... way above my level of caring anyway.

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    Super Moderator VirtualAce's Avatar
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    The frequency 30 kHz ...
    TV's run at about 30 Hz or 30 FPS. There is also a huge cable/wire attached to the CRT just for the purpose of capturing excess electrons. This is the cable that must be discharged along with the analytic capacitors in the set before starting work on any of the components. Some recent sets have degauss circuits which drain excess magnetism from the CRT circuit. Most CRT monitors have a degauss feature as well.

    Just as you can control the rate of discharge from a capacitor using a resistor in series you can do the same with the cable attached to the CRT. Each description of how a CRT works is correct in that there is a beam of electrons emitted from the CRT. This beam is directed via electromagnets to the correct phosphors on the phosphor grid. The signal is what determines what magnets are used. Using these magnets it is possible to bend the beam to scan the entire screen.

    CRT monitors work the same way except they are receiving info from the video card and they also operate at much higher refresh rates, have more resolution, and have much better pitch.

    Even though the new craze is flat screen LCD I'm not a big fan of current LCD technology. The problem with LCD is that the transistors do not discharge fast enough which results in images 'ghosting'. Very early laptop LCDs really had major problems with this but newer models are much better. However my eye can still pick up the ghosting and as such I still use CRT monitors. LCD also has a tendency to lose brightness and contrast after years of use.

    The answer to LCD is the newer TI DLP technology and Sony's version of DLP. These work based on a 'light' CPU or a chip that has thousands of tiny mirrors that reflect light. A color wheel is then used to colorize the image. Since the technology is simply based on reflection of light there are no transistors in the screen to discharge and DLP does not ghost. DLP produces some of the crispest, brightest, and highest quality images I've ever seen.

    Many new theatres are using DLP technology and the end result is nothing short of amazing.
    I will probably end up buying a DLP TV very soon.
    Last edited by VirtualAce; 09-10-2007 at 02:09 AM.

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