1410 with non standard signal

[Paul Q]

Hello

I posted a similair thread to a problem our group was having in configuring the 1410 to work with a certain video signal. It was never resolved. Attached is an image of our signal (purple) versus's a standard rs170 (blue). The signal has the same timing characteristics of a RS170 signal minus the blanking level. Our output to an analog monitor has no issues but when plugged into the 1410 we are viewing vertical lines throughout our image. Weve tried adjusting adjusting several settings in MAX to no avail. How could we go about getting a proper image from this signal? Thanks

-Paul

[J.Harv]

Paul--

      If you look at the signal for the RS 170 you can see that there is a frontporch, horizontal sync, and a backporch.  These qualities are required for any analog
signal.  The various types of analog signals vary by the level and timing. The signal that you provided is missing these components. More information about video signals can be found at the following link:

http://zone.ni.com/devzone/cda/tut/p/id/3020

 Is this a camera that you are building is it a camera that you purchased? if purchased, what is the name of the camera?

      A couple of things that you might want to look at is whether you are using the correct bit depth.  Is that signal for an 8 bit or a 16 bit signal? What is the bit depth of that signal?  Also, interlacing, the vertical lines could indicate an interlacing issue....although, I would bet the problem is that w/o the blanking signals (frontporch, etc)  IMAQ is going to have an issue locking onto the signal.  IMAQ is trying to locate a reference value with these signals and without them is using the wrong value, causing these lines.

    If you could provide more information, that would help.  If these suggestions didn't help, please, post back and let us know so that we can work through this.  Thanks.

Regards,

John H
Application Engineer
National Instruments
http://www.ni.com/support/

[Paul Q]

Hi John

    The camera is one we built using a sony ccd and timing chip. I know its missing the steps but is it still possible for IMAQ to lock onto this signal? We tried clamping onto the synch pulse but that saturates the screen white, if we clamp at 0 and continually increase the second clamp parameter it should average and set the blanking level somewhere in the middle of our signal shouldn't it? Those lines still appear however.
We have played around with the interlace settings however none affect the vertical lines, that is taking just the even or odd field shrinks the height of the image but leaves the width unaffected. When the 1410 says it deals with non standard signals does that refer to just the timing? does it still require a blanking level and steps as well? Thanks John

[J.Harv]

Paul--

     I do know that the 1410 is used for non-standard signals with respect to the timing; however, I'm still looking into whether IMAQ will be able to lock onto that singnal or not.  I will let you know as soon as I find out anything.  Should be within a day or two.

Regards,

John H.

[J.Harv]

Paul--

     Unfotunately, it is like I said, the 1410 will allow you to vary your signal quite a bit; however, without the "front porch" and "back porch" (clamping signals) everything I have found points to this signal not working.  I'm sorry.
    It does seem like you've tried quite a bit already, but if there is a chance, you could try to reduce the clamping location.  This is in the advanced tab. So basically make the clamp start and stop as low as possible, until it gives an error.  Usually they are supposed to be about 10 apart but without them actually being there we might be able to fool it by telling the driver they are just really close.  The stop will have to be higher than the start.  It is really a long shot, but shouldn't take too long to try.
    Best of luck. Let us know if you need anything else.

Regards,

John H.

[DrPhoton]

We are having a similar problem when using the External Lock mode. See http://forums.ni.com/ni/board/message?board.id=200&message.id=12711#M12711

[kellam]

Hi Paul,

As you noted, the signal you have lacks a porch.  That is the area that the 1410 uses to get a ground reference - the video signal is ac coupled, so the 1410 needs a reference to know where black is.  This is known as the clamping region. Because your signal isn't flat in the clamping region, the DC restore circuitry starts oscillating, and you get the line pattern that you see. 

In MAX, there are two parameters, called clamp start and clamp stop (I think - I don't have MAX in front of me).  If you decrease those (it may take some fiddling), you should be able to get the 1410 to clamp on the sync tip instead.  Those values are the number of pixel clocks to the start of the clamping area.  Since you have a scope, you should be able to calculate the clamp start and stop values to use.

Once you have the 1410 clamping on the blanking area, you will get an image without lines.  The contrast, however, will be way off.The black and white level settings are referenced to the clamping level (that was the whole point), but the clamping level was just dropped down about 300mV.  If you adjust your black and white levels to compensate, you should get a good image.

Good Luck!

Jeff