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Thread: Video time base corrector to prevent blue screen / free when video signal is lost

  1. #1
    Pilot HeliShredder's Avatar
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    Video time base corrector to prevent blue screen / free when video signal is lost

    I have been thinking about how to capture video and display/record it on an android tabled. There are several UVC compliant frame grabbers out there that can be attached to android tablets using USB to capture video.

    Anyways, a common problem with FPV applications is that the video signal can be very poor or even drop out for a few seconds. The result is often that the capture adapter stops working due to missing video sync pulses and it is necessary to reset the adapter to get it working again. This is similar to the blue screen that shows up on some analog displays when the signal quality is poor.

    I found this thread and a possible solution could be to use a video time base corrector (see page 2 of the thread) to restore the video signal. Unfortunately, they are quite expensive.

    Does anyone have experience with using a time base corrector to improve the video quality to prevent blue screens / freezes?

  2. #2
    KC8UD GLEvideo's Avatar
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    It seems that blue screening is caused by a lack of video sync. When the video signal gets weak the sync tends to degrade more than any other part of the signal. The video signal is a one volt peak to peak signal with the sync only 40% of that entire signal. The other 60% is video picture information. When the signal becomes weak the sync degrades to a level that becomes unrecognizable by the monitor but there could still be a little signal left to recognize some video image. What a time base corrector does is restore sync, among other things such as adjust gain and black level and chroma level. A TBC is overkill for fixing our blue screen problem, although it would be a nice fix. So, a simple little circuit to restore or insert sync into the composite video signal from an FPV receiver should prevent any monitor from blue screening because a strong sync signal will always be present. This would be a very simple little circuit and I don't know why no one has jumped on this and started creating these little things. They'd be cheap and easy to make and almost every FPVer needs one, or two.

    http://www.intersil.com/content/dam/...n97/an9752.pdf

    http://books.google.com/books?id=sLv...serter&f=false

    http://cds.linear.com/docs/en/applic...ote/an57fa.pdf

    Even this circuit should work whether or not you want to use the text overlay function. It should keep the sync signal strong into the monitor and keep it from blue screening and allow the video to pass through no matter how degraded it may become.
    http://www.icircuits.com/prod_osdkb.html


    So now, maybe someone who has the means to tool up and start manufacturing will take on this project and start cranking them out.
    Airplanes LIKE to fly : Helicopters WANT to kill you.

  3. #3
    Engineer for Jesus Christ IBCrazy's Avatar
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    The reason nobody bothers is because FatShark has more or less cornered the market on FPV goggles... and they do not Blue Screen.

    There are many ways to prevent it including passing your video through an OSD. I used to pass mine through an AIPtek MPVR and it worked great. THE TBC works, but it isn't as good as manually passing a signal through a device that generates a hard pulse signal.

    -Alex
    If it is broken, fix it. if it isn't broken, I'll soon fix that.

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  4. #4
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    Quote Originally Posted by IBCrazy View Post
    The reason nobody bothers is because FatShark has more or less cornered the market on FPV goggles... and they do not Blue Screen.

    There are many ways to prevent it including passing your video through an OSD. I used to pass mine through an AIPtek MPVR and it worked great. THE TBC works, but it isn't as good as manually passing a signal through a device that generates a hard pulse signal.

    -Alex
    Hey that sounds nice. But would that be your still go to method? Does it give any kind of input lag? Iím a huge fan and sad that you want to quit

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