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black 'n white into white 'n black

I am New in electronic and I would to design a circuit that will inevert a white paper with black letters into a black paper with white letters. With my little knowledge that I get from from electronic within my three years in the field of Electronic, I think if I use a Camera circuit and modify it with a Class A amplifier i can be able to get it, bt I am still struggling to get there. Can somebody help me or give me a better idea on how to go on with my project, because this project will help people with eyes promblems who cant see black in white. Pls Help me my colleagues in the field of electronic

Reply to
Cumin' Up
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first you need to seperate the video syncs from the video picture

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see figure 3 in the data sheet. The video is now referenced to ground. Then use an inverting amplifier, gain of -1, this will turn black to white .You need a bandwidth of at least 5MHz, Then you can resistively mix the syncs from the LM1881 with the inverted video to feed the TV

martin

Reply to
martin griffith

Hi

I Did this once, to make a simple reading system for someone who was visually impaired.

It consisted of a nice fast op-amp (Elantec?) wired as an inverter, with a

4066 analogue switch driven on a line by line basis by an LM1881 so that the active video period got inverted and the sync stayed the right way up. I think I had to do some messing to get the DC levels right and there was possibly an adjustable monostable in there somewhere to get the timing right.

Philip

Reply to
Electric dabbler

Some B/W TV circuits I've seen use a Schmitt trigger to detect whether a black/white components are present in a video signal. So I'd imagine reversing the polarities of the trigger would do the trick.

"Go easy with the whisky"

theJackal

Reply to
theJackal

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