Newbie Needs Help with Video Inverter

[moonstruck]

Hello everyone,

I am brand new to electronic engineering. Other than building the simple LED/Capacitor flashing light type things.

I want to build a video inverter that will take a regular NTSC video signal and invert it so the blacks are white, the whites are black, etc. This way I can preview a film negative on the TV screen in the proper colors.

I found this schematic on the web but it looks like it was drawn by a 5th grader. I don't really know if it will work or exactly what it says.

Here is the link to the schematic: https://www.epanorama.net/pdf_redirect.php?url=http://oh3tr.ele.tut.fi/~ftp/video/videoinv.gif

Can anyone give me some direction with this? Will this schematic work? If so, can you re-write it so I can read it properly? Do you know of any better schematics for what I want to accomplish? Any help is appreciated.

Thanks,

Scott

 

[Nigel Goodwin]

No it won't do what you are wanting, you can't just invert the entire composite signal, you must invert just the video, leaving the sync pulses etc. as they were.

 

[moonstruck]

Thanks Nigel,

So essentially I have to seperate the Sync from the Video signal and then invert the Video signal before combining the two signals for output. Would that work?

-Scott

 

[audioguru]

Many years ago, pay-TV from analog cable-TV was scrambled by them reducing the amplitude of the sync. So the scrambled picture was out of sync.
Then they made the picture negative at times.
It wasn't difficult to unscramble.

 

[moonstruck]

Many years ago, pay-TV from analog cable-TV was scrambled by them reducing the amplitude of the sync. So the scrambled picture was out of sync.
Then they made the picture negative at times.
It wasn't difficult to unscramble.

That's funny. I remember those days. Every now and then you could barely make out a booby through the vertical smear of an adult channel.

 

[audioguru]

Electronics geeks didn't see a smear. Everything was as clear as can be.

 

[crutschow]

So essentially I have to seperate the Sync from the Video signal and then invert the Video signal before combining the two signals for output. Would that work?
-Scott

Yes, and it's not trivial. One conceptual approach is to extract the sync signal, block (blank) the video during the sync period, invert the video, and then re-insert the sync. Silicon Chip Online https://www.siliconchip.com.au/cms/A_30627/article.html discusses a fader circuit that uses a similar approach which they say could be adapted to doing the video inversion.

 

[Super_voip]

I built an earlier version and had the circuits to do wipes as well, try an LM1881 as a starting position. The output should also have the colour signal stipped off, use a colour killer circuit which is just a parallel inductor and cap. These do work well.

 

[Hero999]

That's funny. I remember those days. Every now and then you could barely make out a booby through the vertical smear of an adult channel.

Was that when you were a teenager?

I bet you used to watch the channel when your parents were out.

 

[Torben]

I found this schematic on the web but it looks like it was drawn by a 5th grader. I don't really know if it will work or exactly what it says.

Thanks,

Scott

Not that it helps 'cause you can't use it anyway, but it's in Finnish and says "Try electrolytics or tantalums".


Torben

 

[moonstruck]

Thanks Torben, that explains the language. Although I was more refering to the hand writing being so sloppy. And yes, I was a teenager during that time. Although we didn't have cable so I would see them when flipping through the channels at my friends house.

Thanks for the LM1881 suggestion. I was also looking at the LMH1981. I see it has VSout as well as VFout.

My next question, before I start writing my own schematic, is where do I buy these IC's?

-Scott

 

[mneary]

where do I buy these IC's?

Depends on where you are, and whether you use the net for purchases.

 

[moonstruck]

Depends on where you are, and whether you use the net for purchases.

I am in Cleveland, OH. Yes, I use the net all the time. Any suggestions?