Converting video bi-level to tri-level sync? - Page 1
Forum section: electronics / beginners

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: February 12, 2015, 09:50:28 am
content: As far as I can tell, I have a bi-level sync, that I'm feeding into a screen that needs tri-level.Its basically standard definition VS high definition.Is this an easy/simple task to perform? I'm not finding a lot of information online about it, but maybe I'm going about it the wrong way?Any suggestions would be great!Thanks!

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: February 14, 2015, 01:11:32 pm
content: I'm not actually sure if this is the issue.I have a Sega Megadrive, and Sega Master system, that I've added a 9 pin RGB socket to each.These connect to a scart (rgb) to ypbpr/yuv/component converter.This setup works fine on most of my TVs, but my newest tv's either say "not support" or do nothing at all?Now, the thing is, if I connect acompositesignal from either console to the "green"componentinput, once again, either "not support" or simply "no signal"However! I plugged in a handheld tetris console, component signal once again into the TVs "green" component input.... and it displays a black and white image as I'd expect?

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: February 17, 2015, 09:45:17 am
content: It seems that connecting the composite output from a nintendo gamecube to the "green" component input, will result in a synced black and white image.But connecting an Amiga or Sega Megadrive/Master System will result in a "not support" message...However, sticking a sync separator on the video signal (namely an LM1881) and then looking at the output with a scope, seems to suggest that both consoles are doing a 15.6Khz horizontal sync, and 50Hz vertical (although the segas are 49.7Hz, and the amiga was 49.9Hz from memory, while the gamecube was spot on 50Hz)Also, looking at the raw video signal, without the LM1881 in circuit, and they appear to have similar sync levels, and are the same polarity?So.... any ideas at all?

author: deephaven
author_rank: Frequent Contributor
timestamp: February 17, 2015, 11:58:44 am
content: Sounds like the TV doesn't like the slightly off vertical (and horizontal?) frequency of the devices. If it is a timing issue, I can't see a way round that short of putting the signal through an expensive synchroniser. What is the make and model of the TV that doesn't work?

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: February 17, 2015, 12:23:42 pm
content: Its a kogan tv, but other people have had the same issue with other, better brand tvs.

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: February 17, 2015, 08:43:26 pm
content: Is it likey to actually be that the timing is slightly off?This tv seems to suck at displaying anything connected to it anyway!Pick which horizontal sync you think would work?

author: deephaven
author_rank: Frequent Contributor
timestamp: February 17, 2015, 08:52:45 pm
content: I don't know what your timing reference is on those waveforms. From what you said before, it's more likely to be the frequency being slightly off that the TV is objecting to.

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: February 17, 2015, 09:07:32 pm
content: You mean the 50Hz being 49.7Hz? are tv's really that picky?

author: deephaven
author_rank: Frequent Contributor
timestamp: February 17, 2015, 09:17:42 pm
content: Well, that's the only thing you have said that is different between the working and non-working signals.

author: miguelvp
author_rank: Super Contributor
timestamp: February 18, 2015, 01:15:12 am
content: Here is how an NTSC signal looks like, you might have problems with the color burst amplitude or even the frequency:Some more info at:https://www.eevblog.com/forum/beginners/converting-15khz-analog-rgb-to-digital/msg478522/#msg478522Edit: VSynch (And a close up of the VSync itself, the bottom one is the composite VSync)Single redline (composite on top):Both images from page 3 on that thread linked above.More images of a full frame capture with some measurements:https://www.eevblog.com/forum/beginners/converting-15khz-analog-rgb-to-digital/msg459239/#msg459239Edit 2: Got too busy with other things so that project is on hold but I'm planning to get back to it in a couple of months from now.

author: deephaven
author_rank: Frequent Contributor
timestamp: February 18, 2015, 08:36:22 am
content: That doesn't look quite right. There are normally 6 broad pulses for NTSC vertical sync with 6 equalizing pulses either side.

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: February 18, 2015, 09:08:19 pm
content: My setups are all pal, and in both my readings, there is no video signal, just black (one was the mega drive with no cartridge, the other was the gamecube just before it booted/displayed anything)I have to assume that the vertical sync isn't the issue, or if it is, its nothing I can easily change anyway...

author: miguelvp
author_rank: Super Contributor
timestamp: February 19, 2015, 02:02:45 am
content: What I meant was that the color burst has to be between -20 to 20 percent of Vout peak to peak.At least on NTSC, the signal goes from 0V to 100 Percent of positive Vout, the HSync and VSync dips into -60 percent of Vout.from the scope readings you showed it seems one off the color burst peak-peak level is not quite the same as from the lower level of the color burst to the HSync. But then again PAL might be different.Also the frequency of the color burst dictates the pixel clock. I know PAL and NTSC are about the same other than the color encoding and timing parameters.But the only reason I was even looking at the composite output was to capture and synthesize the VSync and HSync so I could convert the signal to a non standard VGA output that I could deal with, so I didn't delve too much into the composite signal itself.

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: February 21, 2015, 02:49:55 am
content: Today I made a discovery...This time a Super Nintendo!The internet told me I needed to connect each of the R,G,B lines to ground, through 75 ohm resistors, but I decided to leave them out, and see what would happen...TV reports "Not Supported" and this was a TV that had worked with everything before... (Amiga, MegaDrive, Master System, N64, Gamecube)Stick the resistors in, works fine! SO I'm thinking the issue with the Kogan TV isn't a sync issue at all....