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HDMI info needed

Discussion in 'General Electronics Discussion' started by Stuart Ian Naylor, Jan 6, 2015.

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  1. Stuart Ian Naylor

    Stuart Ian Naylor

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    Jan 6, 2015
    Hi,

    :)

    Is there anyway to check when a HDMI sink is connected?

    More specifically when you change the source on a monitor or device is there an easy signal to pick up?

    Pin 19 (or 18) is the hot plug but I presume this is a source signal and there all the time when a device is powered?

    I am trying to do things the other way round from the norm and just wondered is there a way to detect when a monitor or TV has the source set on a particular hdmi connection?

    Many Thanks

    Stuart
     
  2. Gryd3

    Gryd3

    4,098
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    Jun 25, 2014
    If I were you, this is where I would look :
    http://en.wikipedia.org/wiki/HDMI#DDC

    It's a bi-directional data line that you may be able to eves-drop on to determine when the sink is communicating to the device... the big questions would be:
    Does this data line remain active if the sink is powered on but not currently viewing this source?

    Do you have a logic probe, or oscilloscope?
     
    KrisBlueNZ likes this.
  3. Stuart Ian Naylor

    Stuart Ian Naylor

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    Jan 6, 2015
    Many thanks,

    I have done a bit of reading and its implementation varies apparently...
    No scope just an auto range multimeter and frequency up to 30Mhz is as good as its gets for me.
    So might have give a cheap PC scope a go.

    I was hoping one of you guys would know as to my surprise the HDMI standard doesn't seem to be that standard even on the same level 1.1, 1.3, 1.4...

    I was hoping the sink would just pull low on each initialization / connection.

    Stuart
     
  4. Gryd3

    Gryd3

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    Jun 25, 2014
    Nope. not quite that easy... there are even some HDMI specific ICs used for routing HDMI, and they aren't the easiest to read. There is a few different lanes of digital data in that cable.
    Considering the DDC wires carry I2C based communications, you may be able to eavesdrop using a microcontroller and a USB-Serial adaptor. Other than that, I think you will need to poke around yourself to start. Perhaps it's as easy as the source not sending any data on the channels 0 - 3 while the sink is not actually viewing the source.
     
  5. Stuart Ian Naylor

    Stuart Ian Naylor

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    Jan 6, 2015
    Cheers Gryd3, doh bad news though...

    Some poking needed I think.

    :)
     
  6. Gryd3

    Gryd3

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    Jun 25, 2014
    Best of luck Stuart. As well as poking around, try to find a pinout and ID each pin. Many of the pins dont appear to be bi-directional, so I'd ignore those first and see where it takes you. (If possible, while you experiment, set the source to 720p or reduce the frame-rate. Less data or a reduced clock may be easier to work with.)
     
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