Oscilloscope Help

Discussion in 'The Projects Forum' started by Adamf001, May 12, 2012.

  1. Adamf001

    Thread Starter Member

    Sep 5, 2011
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    2
    After watching a few videos and reading some posts I decided to try and make my own Oscilloscope, I have a VERY old tv which I have converted, the tv it's self has 4 leads I presume two are for x axis and two are for the y axis,
    To make this easier I will name each wire according to the colour
    1 is blue
    2 is orange
    3 is black
    4 is yellow
    Now blue and orange are connected to the top deflection pad and black and yellow are connected to the bottom deflection pad,
    To generate a signal I have used my computer to play a song and attached a amp in between the computer and the tv to boost the signal.
    All I seem to get is a vibrating circle not a horizontal line with "bumps and peaks" on the axis
    In case somebody asks I have orange and yellow in the + terminal and blue and black in the - terminal of my amp... anyone have any ideas of how to get a proper oscilloscope wave on the screen?

    Pics attached Bellow
     
  2. #12

    Expert

    Nov 30, 2010
    16,262
    6,769
    You have missed the idea of a horizontal sweep generator. An oscilloscope makes a graph of amplitude across time, and time is very changable, depending on what you want to investigate. Better people than me have spent decades improving horizontal sweep generators. I can only hope you find one that suits your needs.
     
  3. MrChips

    Moderator

    Oct 2, 2009
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    It is amazing that you have gotten this far. Congratulations!

    Using a TV set for an oscilloscope has its limitations. Primarily, the deflection coils are not fast enough and you will be limited to examining low frequency signals.

    To display voltage vs time waveforms, you connect one channel from your audio source to the vertical deflection coils (y-axis) (after amplification).

    The horizontal deflection coil (x-axis, time scale) must be driven from a saw-tooth generator.
     
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  4. Adamf001

    Thread Starter Member

    Sep 5, 2011
    67
    2
    Since I have posted the initial thread I have determined the x axis coil leads (black and yellow)
    the x axis line that is produced does not expend to the whole screen unless I increase the signal, so if I have a non varying amplifier, I should be able to accomplish this right? by having a amplification that forces the x axis beam to cross the whole screen (as if having the amp at max volume), at the moment I have been using a amp with a volume control, makes the line smaller as the volume decreases.
    also if I add a saw tooth generator to the other wires I should start to see the initial wave form on the screen? and how do I go about this
    after I attach the saw-tooth generator,
    If i send a 5 v signal into the amp should I then see a sinusoidal wave, and if the 5 v signal is increased to 10 v will the sinusoidal wave double in size?
    Thanks
     
    Last edited: May 12, 2012
  5. MrChips

    Moderator

    Oct 2, 2009
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    I am not sure what you mean by a "non varying amplifier".

    If you apply a DC current to the deflection coil you should be able to position the dot to any position on the screen.

    Take your audio source, amplify and feed into the vertical deflection coil. You should see a vertical line.

    Apply a DC voltage to the horizontal deflection coil and you should be able to position the line to a different part on the screen.

    For waveform display, you need a signal that begins at a negative voltage and increases linearly (equally with time) to a positive voltage (a ramp) and then switches instantly back to the starting negative voltage.
     
    Last edited: May 12, 2012
  6. Adamf001

    Thread Starter Member

    Sep 5, 2011
    67
    2
    Ok I get it now thanks for the help,
    so to produce a wave form (how i understand it) i would need to convert the x dc voltage to a "saw-tooth" type of signal
    how would I produce a signal that starts negative, slowly increases to positive and drops back to negative? once I know that I'll try it out again and see what happens. Thanks
     
  7. MrChips

    Moderator

    Oct 2, 2009
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    Search for sawtooth generator. There are many circuits available.
    The voltage output is not important. It can be 0-1V or 0-5V.

    You will have to amplifier the signal with a high current amplifier.
    At this point you can shift the DC offset. An adjustable gain and offset will be required so that you can expand and position the trace on to the screen to your liking.
     
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  8. Adamf001

    Thread Starter Member

    Sep 5, 2011
    67
    2
    Ok cool, I'm going to a supply store tomorrow so I'll see if I can make it,
    Thanks for the help can't wait for it to work
     
  9. MrChips

    Moderator

    Oct 2, 2009
    12,431
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    Incidentally, while a TV oscilloscope has it limitations, there is nothing wrong with playing around with it. There is a lot to learn from doing so.

    If you wish, you can turn it into a audio-video show to impress your friends.

    Put one stereo channel into one axis and the second channel into the other axis.
    Take a combined mono signal into the Z-axis (spot brightness).
    If your audio source has good stereo separation you will be able to generate pulsating random spiral patterns on the screen in sync with the music. (I did the same project a number of years ago.)
     
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