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How does the TV know

  1. Feb 8, 2015 #1
    When I plug in a pair of headphones in the back of my tv, it cuts of the sound to the speakers. But If a I plug just an unsoldered 3.5mm jack, it still cuts of the sound to the speakers. How does it know there is a jack plugged in when, technically, the circuitry would detect that as the same as nothing in there. It's really just extending the leads by a little bit, with no connections being made.

    Is there an extra sensor in there the gets shorted when a jack goes in?
     
  2. jcsd
  3. Feb 8, 2015 #2

    DaveC426913

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    Don't overthink it. The insertion of the jack physically pushes open a contact to the speaker, cutting the circuit.

    See diagram
    jack-png.78784.png
     

    Attached Files:

    Last edited: Feb 8, 2015
  4. Feb 8, 2015 #3

    dlgoff

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    I wish my TV's designers hadn't over-thought it. These new-fangled digitals, as nice as they are, don't have audio channel BNCs and you can't use the these phone jacks to grab the signals and listen to the speakers at the same time. :oldgrumpy:
     
  5. Feb 9, 2015 #4

    jim hardy

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    It's everywhere.
    Tower of Babel myth is playing out.
     
  6. Feb 9, 2015 #5

    dlgoff

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    We can defeat them. If we live long enough. :oldwink:
     
  7. Feb 9, 2015 #6

    berkeman

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    Never anthropomorphize TV sets. They hate it when you do that. :-)
     
  8. Feb 9, 2015 #7

    NascentOxygen

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    Apparently, not all TVs cut audio to the speakers when the headphones are plugged in. Some require the speakers be silenced via the remote control. (This point arose in responses to someone asking for recommendations re a second TV for the bedroom.)
     
  9. Feb 9, 2015 #8

    dlgoff

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    Now that's over-thinking.
     
  10. Feb 9, 2015 #9

    NascentOxygen

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    There would be some situations where a hard-of-hearing viewer would like to have amplification via headphones, while the other partner wants to listen to the TV at normal volume.

    Then other situations where each wants a separate TV in the same room.
     
  11. Feb 10, 2015 #10

    jim hardy

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    Maybe the question should be

    "What does the TV know?"
    http://www.pcmag.com/article2/0,2817,2476476,00.asp

    Telemarketer's dream.
    I wonder if one could adapt an old analog tuner with the rotary channel switch to his digital TV.
     
  12. Feb 10, 2015 #11

    Averagesupernova

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    ^^^^^^^^^^^^^^^^^^^^^^^^^^
    This is the first thing I thought about when digital TV came into existence. The fact that it is no longer a one way path from the origination of programming to the TV set means that a lot of securities that we took for granted are out the window.
     
  13. Feb 10, 2015 #12

    jim hardy

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    If one reads the digital TV standards he finds there's amazing amount of control in the broadcast signal.
    The originating station can select your channel for you.

    If you have fifteen minutes to read a classic sci-fi short story about over-automation,

    http://www.gutenberg.org/files/29579/29579-h/29579-h.htm
     
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