View previous topic :: View next topic |
Author |
Message |
Haplo
Joined: 06 Sep 2003 Posts: 659 Location: Sydney, Australia
|
Detection of presence of video signal |
Posted: Mon Jan 05, 2004 9:24 pm |
|
|
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: 1934 Location: Norman, OK
|
Composite Video |
Posted: Mon Jan 05, 2004 9:45 pm |
|
|
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 |
|
|
MarkD
Joined: 09 Sep 2003 Posts: 3 Location: Toronto, Canada
|
Re: Detection of presence of video signal |
Posted: Tue Jan 06, 2004 3:58 pm |
|
|
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 |
|
|
|