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Detection of presence of video signal

 
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Haplo



Joined: 06 Sep 2003
Posts: 659
Location: Sydney, Australia

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Detection of presence of video signal
PostPosted: Mon Jan 05, 2004 9:24 pm     Reply with quote
Hi everybody,
In an application I need to detect the presence of a composite video signal (coming from Video-Out port of the TV). What is the best way of doing this?

Thanks in advance.
dyeatman



Joined: 06 Sep 2003
Posts: 1912
Location: Norman, OK

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Composite Video
PostPosted: Mon Jan 05, 2004 9:45 pm     Reply with quote
Do you need to sense purely the presence/absence or the actual level?

If simply presence the route I would take is to half wave rectify the video with a single signal diode/cap circuit and sense the resulting DC voltage present using PIC A/D.

If it is level you would have to be a little more careful as how you convert the signal to get a known level corresponding to the video output.

FWIW Smile
MarkD



Joined: 09 Sep 2003
Posts: 3
Location: Toronto, Canada

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Re: Detection of presence of video signal
PostPosted: Tue Jan 06, 2004 3:58 pm     Reply with quote
Haplo wrote:
Hi everybody,
In an application I need to detect the presence of a composite video signal (coming from Video-Out port of the TV). What is the best way of doing this?

Thanks in advance.


A reliable way to do this is to build a vertical sync detector (sync separator circuit feeding an external interrupt)

You then measure the frequency of the sync pulses, it should be 60 or 50 Hz (NTSC or PAL)

Here is a link to a sync detector circuit: http://www.qsl.net/kd2bd/vor.html
The circuit shown is stand-alone and does not need a micro. If you need to integrate this into a project that has a micro, feed the signal that goes into the PLL into an interrupt line of the micro instead.


Mark
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