crt monitor into oscillograph

Discussion in 'General Electronics Chat' started by blackredrobin, Oct 13, 2011.

  1. blackredrobin

    Thread Starter New Member

    Sep 14, 2011
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  2. Adjuster

    Well-Known Member

    Dec 26, 2010
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    If you mean the kind of CRT monitor used for computer VDU or television use, these have magnetic (coil) deflection CRTs which are incapable of much deflection bandwidth. The article you linked to shows a CRT with internal electrostatic (plate) deflection, which is capable of responding to a broad frequency range.

    While perhaps not completely impossible, modifying a monitor in this way would involve working on circuits using quite high powers, and particularly high voltages: CRTs use tens of kilovolts. This is dodgy territory even for experts. Also, whilst operating a monitor in a single line / vector mode can produce very intense lines, it is also easy to get excessive intensity leading to screen burn or perhaps worse. I'm not sure if a stopped beam could actually cause an implosion, but surely we don't want to find out the hard way

    Rather than trying to modify a lot of difficult hardware with only limited possible performance, consider using some software to display the input to the sound card of a PC using that monitor. This will have limited performance, but probably better than what you could get by trying to modify the monitor. If you are willing / able to spend more money on it, there are more sophisticated adaptors which can be linked to a PC to give something a bit closer to a real scope, e.g. with a response extending down to DC, and perhaps to higher frequencies than the 20kHz or so limit of a sound card.
     
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  3. Georacer

    Moderator

    Nov 25, 2009
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    I have though alot about building a PC o'scope, but in the end I decided that 20KHz weren't enough for me.

    My alternative was this: http://www.jyetech.com/index_en.php
    The educational kit is at about $50 and so far I 'm happy with it. Look it up on Digikey or similar sites.
     
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  4. dataman19

    Member

    Dec 26, 2009
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    There are tons of software packages out there that will turn your computer into an O'Scope.
    ..
    All you need is a Small Form actor (SFF) Computer..
    Like a dell GX-270 SFF (a GX-280 SFF would actually be better. The GX-280 uses USB Mouse and Keyboard, the GX-270 uses PS2 Mouse and Keyboard Ports).
    ..
    Anyway, you can use a USB dongle to interface the Probes to the Computer..
    ..
    Or you can buy a Scope PCI card and put it in a Mid Tower case..
    ...
    Either way, the software or Plug-n-Plac PC cards are the best bet.
    ..
    I built an O'scope back in the 70's. Getting the video Instrumentation amps stable and calibrated is a pain. Possible, but a pain.
    ...
    Dave
    dataman19
     
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  5. Georacer

    Moderator

    Nov 25, 2009
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    Be careful! You can't just plug the probes to your sound card! Sound cards accept one or two volts maximum.

    You need to build a step down circuit using OpAmps to ensure that the input signal will be kept under a certain voltage threshold.
     
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  6. t06afre

    AAC Fanatic!

    May 11, 2009
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    A sound card is also a thumb rule(if not the rule) AC coupled. So DC to around 10 to 15 Hz. Will be blocked or attenuated. Due to the type AD converter used in most sound cards. Signals with step flanks may be some distorted. But some is much better than nothing. So if you are aware of the weakness inherent in a sound card. You may still have some fun with such a scope. And be careful not to zap it by using to high input voltage. As said by Georacer the input is max a few volt peak to peak
     
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  7. Georacer

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    Nov 25, 2009
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    What t06afre said about the DC voltage is also very important. I forgot to mention that.
     
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