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The Great CRT to Oscilloscope Project!

Discussion in 'General Electronics Discussion' started by Manticorp, Nov 4, 2012.

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  1. Manticorp

    Manticorp

    1
    0
    Nov 4, 2012
    Hello, and welcome to my latest project - turning a small CRT monitor into a fully functional oscilloscope.

    The monitor in question is a combined colour TV, radio and cassette player that I hope to rip the innards out of and turn into a nice oscilloscope.

    Here's a pic of the device in question:

    [​IMG]

    which I want to turn into something that more resembles this:

    [​IMG]

    The device has quite a few inputs/outputs/controls, to name a few:

    • For Power, it can accept:
      • AC in from 110V to 240V (it has a selector on the side for selecting which)
      • DC in 12V (a rather large barrel plug which I measured to be 6.67mm in diameter)
      • A Proprietary rechargeable battery
      • A gagillion (read: 10) D cell batteries
      • A switch for going from charging the battery to operation
      • A Power switch
    • The TV part has:
      • Aerial in, selectable from the built in aerial or external.
      • Degauss button
      • V-hold (adjusts vertical scan rate I think)
      • Picture brightness (there's a screw hole next to this knob that might also adjust brightness or maybe focus??)
      • Contrast Adjustment
      • Colour Adjustment
      • A little switch that says AFC off/on which I'm not really sure what it does. Wikipedia says this is "Automatic frequency control"
    • The radio part has the following
      • Remote in (3.5mm)
      • Mic in (3.5mm)
      • Earphone out (3.5mm)
      • An XLR port labelled 'Rec/PB'
      • A switch labelled 'Beat Cut' with 3 positions, used to declick AM recordings, from what I understand.
    • And on the front panel, there's:
      • A Volume knob
      • Tone knob
      • Mixer for mic/radio ratio
      • Switch between casette, radio and tv mode
      • TV tuning with switch between UHF, VHF L and VHF H
      • Radio tuning with switch between MW, LW and FM
    • There's also a small light switch and a counter for the tape player, which has it's own usual play/stop/record controls

    I've managed to get my arduino to output stuff to the little screen using the great TVTuner library and hooking the arduino up to the Aerial, so at least we know it works:

    [​IMG]

    Because all analogue TV has been switched off here, I wasn't able to test it otherwise (and I don't have an old VHS player or anything handy!)

    I'm going to try and follow this great instructables post where he transformed a regular television into something quite similar.

    Improvements I hope to make to this would be to calibrate it vertically to get accurate voltage readings and to be able to adjust the timebase accurately, so maybe instead of having the flyback transformer driving the horizontal frequency, using a different circuit.

    It would also be great to switch from magnetic deflection to electrostatic deflection to be able to measure higher frequencies, although this is a big ask.

    Any help and advice would be much appreciated, I don't have much experience working with these high voltage/frequency circuits!

    Stay tuned for updates though!

    Here's some more pics of the item:

    [​IMG][​IMG][​IMG]

    H
     
  2. Miguel Lopez

    Miguel Lopez

    252
    63
    Jan 25, 2012
    Has that CRT electrostatic deflection?

    I mean, most TV CRT had electromagnetic deflection, and that is not suitable for a high frequency operation, which would be required in an oscilloscope. If the CRT has no electrostatic deflection, I guess you won't be able to swith between both deflecting systems.
     
    Last edited: Nov 5, 2012
  3. Laplace

    Laplace

    1,252
    184
    Apr 4, 2010
    It's even worse than "not suitable" for high frequency operation. In a scope the vertical channel goes from DC to the highest frequency possible and the horizontal channel sweep rate varies over a wide range. In a TV the vertical channel operates at a very low fixed frequency (~60 Hz) and the horizontal channel operates at a somewhat higher fixed frequency (~15.8 KHz). Moreover, the horizontal oscillator operates the flyback transformer from which CRT beam current is derived. Vary the horizontal frequency and you may lose the CRT beam. As for using electrostatic deflection, does the CRT have any pins for electrostatic deflectors? I think not.

    A better alternative, since you can already drive the CRT with arduino, is to use the micro-controller to create a digital sampling oscilloscope using a TV display.
     
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