V- and H-sync questions: Sony VPH 1042q - AVS Forum
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post #1 of 4 Old 06-22-2013, 07:35 PM - Thread Starter
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Hey A/V folks. I picked up an old second-hand CRT projector the other day for under fifty bucks for a little project I'm working on. It's a Sony VPH 1042q in good working condition other than a weird little yellow splotch in the picture. It has two input options: S-video; and 5 BNC connectors for RGBVH. I want to use the RGBVH because I'm using a circuit that I built specifically to generate the RGB signals and the separate connectors for each signals is just ideal for my use. However, after some research into sync signals, I'm afraid designing a circuit to generate high-precision H and V sync signals is a bit out of my depth. So, I bought a VGA signal generator on Ebay and just routed the Vsync and Hsync from that to the V and H on the projector. One issue that I'm running into though is that the resolution of the projector is definitely not one of the standard VGA, SVGA, etc. signals that the generator produces. So, while I'm getting images out of the projector, the sync stuff is definitely off.

Sorry for so much background, but I hope its all pertinent. This is pretty much just going to be used to project psychedelic visuals for a band I'm playing in, so at this point, I am considering building a circuit to provide the sync signals, even if they won't result in a perfect locked-in picture. My main issue is that I don't want to harm the CRT electron beam scanning mechanism or whatever by feeding it janky homebrew sync signals. Do you guys know if there would be any mechanical or electrical issues that could result from the H and V sync signals not having the proper blanking periods and pulse length? I don't mind if the image is all jittery and weird; in fact, it looks kinda cool. Feel free to tell me that this poor projector doesn't deserve this fate, cuz it does feels a little unceremonious using it in this manner. I really don't want to destroy an otherwise cool projector for my pet project.
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post #2 of 4 Old 06-23-2013, 07:25 AM
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THe RGB connections are pretty much useless, as the set scans 480i, composite video only. Unless you have an RGB source that puts out 320 X 240 resolution, all you can do is run a video input to it to use it. Building a box that converts composite video to RGBHV is pointless, as there's nothing to be gained by it. Sorry!

What you need is a data grade projector, which, if you look carefully, will be only a bit more expensive than what you paid for the 1042. No guarantees as to the tube condition, but even a worn tube data grade set willl most likely project a better image than the 1042.

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post #3 of 4 Old 06-23-2013, 09:45 AM - Thread Starter
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Thanks for the reply Curt. I'm still a little confused by some of what you're suggesting though. I read up on your site about the differences in video and data grade projectors, but I'm not sure if my application would require that kind of upgrade. My RGB inputs seem to be working in that I'm getting video output pretty similar to what I was hoping for. My main issue is that the VGA signal generator, which I'm only using for the H and v sync signals, has a couple different VGA resolutions, the lowest of which is 640 x 480 @ 60hz.

If I understand what you're saying, my projector wants to see 320 x 240 @ 60 Hz. Would the difference between a data grade set and video grade set be in both quality and functionality? If its only a difference in quality, I may consider just sticking with the 1042 to learn on. I can alter the RGB signals to fall within an appropriate range if I can fudge the V and H I think. The sync signals are still completely mystifying to me however, and I don't want to thrash this projector messing around with them. Is there a mathematical formula that will help me to find out exactly, or close to exactly what the H and V signals I need to synthesize might be?

What might be the consequences of just feeding the H and V square wave oscillations at different frequencies in order to achieve something closer to the range that the projector expects? Sorry if I completely missed the point of what you were trying to communicate. This video stuff is pretty foreign to me; I'm just testing the waters here and they're a bit confusing.
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post #4 of 4 Old 06-25-2013, 06:48 AM
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Maybe you understand baud rate and modems?

Assume that this projector is looking for a baud rate of 1200. Everything today is at a minimum of 56K. Your high resolution signal simply isn't going to communicate with a low resolution projector. Feed the set whatever you want, but unless you feed a signal, both sync and video, of 15Khz H scan rate and 760Hz V scan rate, you won't get a pix that's synced. I believe you can also nuke the projector if you feed it too high a resolution, but I'm not sure, I've never tried it.

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