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CRT circuitry

Discussion in 'Beginner Electronics' started by Bjarni Juliusson, Sep 14, 2005.

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  1. I bought a tiny little 5.5" B/W TV set, and I thought it would be an
    interesting thing to do to take the tube and try and build myself a
    little computer monitor - nothing fancy, just a device to take TTL
    horizontal and vertical sync signals and a video signal and give me a
    couple of hundreds of lines of picture at 50Hz.

    So I've been surfing around now for a while to find some information on
    the subject, and it's been very informative. But even though I have now
    got a general familiarity with the workings of a CRT, I have not been
    able to find anyone who has built any CRT control circuitry and written
    about it on the web. It doesn't seem at all impossible though.

    So does anyone have any suggestions? Any websites with detailed
    information that is not completely over the head of a beginner? I don't
    know much at all about analog electronics, being mostly a computer guy.
    Or does anyone have enough knowledge to offer an example layout of such
    a circuit for me to try?

    I'm grateful for any help at all!



    Quite an undertaking. My first thought is, "be careful" I am guessing the
    anode voltage on that tube is 3 to 5Kv and will be present even with no
    power is applied. Learn how to discharge the tube safely. If you are
    nervous at all doing it, then you shouldn't be doing it, especially alone.
    Use the, One hand in the pocket rule, Have a qualified tech demonstrate it
    for you.

    Learn and understand where the high voltage is located on the circuit board
    and be conscious of it when fiddling with the circuit when it is live.

    Secondly, the deflection circuits are not designed to run at typical
    computer monitor frequencies. This might prove to be difficult. If you are
    going to redesign the deflection circuits and have a limited knowledge of
    electronics then, well, you have a long road ahead of you.

    Not trying to be discouraging, whether you successful or not you will
    certainly learn something. But do be careful.
  3. Hi,
    Im doing a similar thing with a 1" Mullard Tube and found this website very
    It uses a LM1881 and two 555's and thats basically it for the basic version,
    he did a delux one for his oscilloscope which is a bit more complicated but
    Im giving this a try first.
    My LM1881's turned up today so as soon as I get some time I will be plugging
    it in and seing what it comes out with.

    Anyway good luck
    Oliver Hannaford-Day
  4. Check and double check. Don't worry about my safety.
    Which is why I decided to go with a resolution close to the original TV
    resolution, as I mentioned in the original post. If I can get 256 lines
    at 50Hz, I'll be very happy.
    It just so happens I found this:

    I found a small B/W junk TV/radio/cassette recorder, and when I looked
    inside it had a very conspicuous chip labeled AN5151, so I googled for
    datasheets. What I found was the site above. The guy (Hans) has done
    precisely what I want to do: he took a small B/W TV with an AN5151 chip
    in it and turned it into a computer monitor (he uses it for a spectrum
    analyser). The AN5151 takes care of generating the sweep signals from
    composite sync, and he built his circuit by simply drawing a diagram of
    the board in the TV and moving the relevant components to a new board. I
    think I'll do something similar. Hans' site has shown to me that this is
    not an unrealistic goal.
    I appreciate both your reply and your concern, but rest assured that I
    take the voltages seriously and have read up on the matter. I am also
    not completely unexperienced in electronics, just in this particular field.

  5. Jasen Betts

    Jasen Betts Guest

    So You've figured out how to get that sync rate out of your video card?
    (if not I have some suggestions)

    That's half the battle, then all you need to do is combine the sync signals
    and the video signal at the apropriate voltage levels and feed that to the
    composite in (or to a rf modulator and to the antenna connection)

    it may be possible to link directly into the sync circuits of the TV, but
    doing that could require detailed knowledge of those circuits (like having a
    service manual....)

  6. Yes, since I'll be designing the video card.
    I think you misunderstood my intentions. I'm not trying to hook my PC up
    to my TV, I'm trying to build my own CRT control circuits and video
    circuits. But see the website I linked to. I think I'll do it in a
    similar way.

    Thanks for your replies folks.

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