DIY S-Video to Component converter? - AVS Forum
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post #1 of 21 Old 01-24-2012, 10:09 AM - Thread Starter
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All,

I am looking for schematics for an S-Video (Y/C) to component (Y/Pb/Pr) converter. This would be used to connect a S-VHS tape recorder and some older game consoles to a new HDTV that lacks S-Video input. Many of the commercial converters on the market seem prohibitively expensive and I would like to try building one at home.

I do not need any sort of upscaling or deinterlacing as my television can handle 480i input and can upscale the content itself.

Most of the DIY projects I've seen seem to convert in the other direction. Can anyone help me?
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post #2 of 21 Old 01-24-2012, 11:04 AM
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Can anyone help me?

Do you need a schematic?

You need to decode the colour subcarrier...are you up for that?
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post #3 of 21 Old 01-24-2012, 11:38 AM
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Two approaches: Analog or Digital. The modern approach is to A/D the Y&C, digitally decode it and output RGB through DACs. You could then even output the digital RGB through DVI which is HDMI compatable (HDMI chip sets are licensed, even non HDCP, DVI is open). This is a bit much for a DIY project in your application.

For the analog approach, I would research 1980/90s color TV chip sets. Now of course these chips are out of production but there are the ECG/NTC service shop replacements you can cross reference to.

But why not look on EBAY for a used older model DVDO or Lumagen scaler? These are digital processing that will give you a DVI or HDMI output.

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post #4 of 21 Old 01-25-2012, 11:19 PM - Thread Starter
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You need to decode the colour subcarrier...are you up for that?

Yes. I was actually expecting that I'd need to convert the Y/C to RGBS before converting it to YPbPr, so I am preparing for a complex circuit.


But why not look on EBAY for a used older model DVDO or Lumagen scaler?

I dislike eBay. More than half of the products I've purchased turned out to be broken or fake. I closed my account with them years ago.
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post #5 of 21 Old 01-26-2012, 12:24 PM
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Originally Posted by Alyssa View Post

You need to decode the colour subcarrier...are you up for that?

Yes. I was actually expecting that I'd need to convert the Y/C to RGBS before converting it to YPbPr, so I am preparing for a complex circuit.

Actually it's the other way around. You demodulate the chroma carrier to I&Q or more likely R-Y & B-Y. The luminance would be filtered out prior to the chroma XY demodulator but in your case with Svideo, its already separated. If needed you would then convert the Y,R-Y,B-Y to RGB. You can use the classic MC1496 balanced demodulator chips or even built a discrete demodulator from transistors. After all that's what every consumer TV did in the 60 and early 70s. But honestly using a TV "jungle" chip is the bet bet in this day and age. Keep in mind, you also need to isolate the burst which requires making a flag pulse from extracted H sync and lock a local 3.58mhz oscillator to the burst. Most TV jungle chips have all these functions built in but there is still considerable interfacing circuitry to build out for this project.

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But why not look on EBAY for a used older model DVDO or Lumagen scaler?

I dislike eBay. More than half of the products I've purchased turned out to be broken or fake. I closed my account with them years ago.

I have been burned a couple of times as well but for the most part I find EBAY sellers honest and good citizens. And I have around 90 purchases over the past ten years.

Unless you are embarking on this project for the educational value, which is great, I would still suggest you look for a used older consumer scaler.

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post #6 of 21 Old 01-26-2012, 12:46 PM
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Entec had a great S-Video + Composite to Component + RGB box.
Contact me for information and/or the unit itself.
FWIW - as a big supporter of Lumagen, and one who has also used DVDO products, I will say that neither company's S-Video input and conversion processes are the best option.

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post #7 of 21 Old 01-26-2012, 09:30 PM
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How about a used DVD Recorder? I think many of the older ones were able to input a wide range of source types and output component or even HDMI.
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post #8 of 21 Old 01-26-2012, 10:17 PM - Thread Starter
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Actually it's the other way around. You demodulate the chroma carrier to I&Q or more likely R-Y & B-Y.

I looked around a bit and it appears that the NTE705a can decode the chroma signal and output R-Y and B-Y signals. And since the luma signal carried by an S-Video cable is compatible with the luma signal carried by a YPbPr component cable, I can just connect Y->Y.

There is also the NTE821, which differs from the NTE705a in that it has a chroma subcarrier frequency input. The datasheets don't mention what happens if you leave those inputs open, so I am hesitant to use it.
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post #9 of 21 Old 01-27-2012, 09:50 AM
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Originally Posted by Alyssa View Post

Actually it's the other way around. You demodulate the chroma carrier to I&Q or more likely R-Y & B-Y.

I looked around a bit and it appears that the NTE705a can decode the chroma signal and output R-Y and B-Y signals. And since the luma signal carried by an S-Video cable is compatible with the luma signal carried by a YPbPr component cable, I can just connect Y->Y.

There is also the NTE821, which differs from the NTE705a in that it has a chroma subcarrier frequency input. The datasheets don't mention what happens if you leave those inputs open, so I am hesitant to use it.

You need to run the Y through a delay line to match the processing delay of the chroma demodulator, typically a few hundred nanoseconds. I looked at the NTE821. You do need all the pins. The reference subcarrier inputs are what demodulates the chroma. They come form a 3.58 oscillator that is locked to the burst in the chroma signal. You need two subcarrier signals, one at 0 degrees and one phase shifted 90 degrees. The NTE705 has these inputs as well. They are just labeled as "Ref A" and "Ref B" There are plenty more devils lurking in the details here. There are also more complete chip solutions that have the 3.58 oscillator built in as well as the burst gate circuits.

I'll say it once more and drop it. It's going to be far less hassle to just buy a used scaler. Like I said above, there is some educational value here but just for the electronics knowledge. Remember that NTSC is an obsolete system. It's only around today for legacy support and that is quickly fading. Learning the low level engineering theory of NTSC is of no commercial use these days.

Also as you are starting with Svideo, a good comb filter decoder is not needed, useless in fact for your application. You are past the Y/C seperation stage.

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post #10 of 21 Old 01-27-2012, 03:43 PM
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There is I believe an Entech one on ebay right now in a sealed package for 50.00
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post #11 of 21 Old 01-27-2012, 07:27 PM
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Originally Posted by balboarules View Post

There is I believe an Entech one on ebay right now in a sealed package for 50.00

He should grab it. No way can this by done DIY at that price.

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post #12 of 21 Old 01-27-2012, 07:29 PM
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post #13 of 21 Old 01-27-2012, 07:43 PM
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post #14 of 21 Old 01-27-2012, 08:36 PM
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Is that comb filter any good in that unit?
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post #15 of 21 Old 01-28-2012, 02:28 PM
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Originally Posted by balboarules View Post

Is that comb filter any good in that unit?

If you are only using Svideo it doesn't matter. The comb filter is only used for composite. And not all decoders use a comb filter either. It could just have a cheap notch filter.

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post #16 of 21 Old 01-29-2012, 07:55 AM
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This - http://www.ebay.com/itm/Entech-Compo...item3f12fda6d5
is NOT the item discussed for years here. It is almost nothing more than a signal divider ...

The item you should look for is the CVSI-1. It looks similar to this one, with a black box and a different back panel -
http://www.ebay.com/itm/ENTECH-Direc...item3f0c17bc23

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post #17 of 21 Old 02-01-2012, 06:03 PM
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Interesting topic. I have a similar project in the works (currently on the back-burner). I'm going the digital route, because that way I could easily tag on an HDMI output as well. You never know when TVs will start dropping component inputs too... However, I was unaware that HDMI required licensing. Is there more information about this HDMI licensing? What are the consequences of not licensing? HDMI.org doesn't really go into much of the details for a newcomer like me. I feel that their documentation assumes you're a big company that already knows how to deal with technology licensing.

Those analog demodulator ICs are very interesting. I didn't know they still made stuff like that. Took a look at the NTE821 datasheet and am totally confused to why there are two chroma inputs and two subcarrier inputs. Glimmie, can you chime in on this?
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post #18 of 21 Old 02-02-2012, 12:50 PM
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Originally Posted by LordSte View Post

Interesting topic. I have a similar project in the works (currently on the back-burner). I'm going the digital route, because that way I could easily tag on an HDMI output as well. You never know when TVs will start dropping component inputs too... However, I was unaware that HDMI required licensing. Is there more information about this HDMI licensing? What are the consequences of not licensing? HDMI.org doesn't really go into much of the details for a newcomer like me. I feel that their documentation assumes you're a big company that already knows how to deal with technology licensing.

AFAIK, you can't buy HDMI chip sets on a "hobbiest" level. They are not distributed by the public parts vendors like Digikey, Mouser, etc. Even though you can legally build HDMI products that are not HDCP compatible and do not need licensing keys, I guess they feel the less HDCP capable chips floating around in garage labs, the better. And of course if you want to build a fully HDCP compliant product you must have a licensing agreement anyway to be granted key sets. OTOH, several manufactures now make their own DVI chip sets and since DVI is upward compatible with HDMI, you can just use DVI chips for an HDMI project, just not if HDCP is needed and DVI can also support HDCP.

Quote:


Those analog demodulator ICs are very interesting. I didn't know they still made stuff like that. Took a look at the NTE821 datasheet and am totally confused to why there are two chroma inputs and two subcarrier inputs. Glimmie, can you chime in on this?

NTSC chroma is encoded as a DSSC signal. Double Sideband Supressed Carrier. This is a radio technique where the carrier is surpressed and only the sidebands of the signal are transmitted. To reconstruct the full chroma signal prior to demodulation, you must generate an "in phase" and "quadrature phase" subcarrier signal from a local oscillator. That is zero and 90 degrees apart. And of course that oscillator must be locked to the oscillator that modulated the chroma on the transmission side. So to do that there is "burst". Burst is 8-10 cycles of the source subcarrier located on the trailing portion of the sync pulse. This burst is used to sync the oscillator in the receiver's chroma demodulator.

DSSC is still a valid radio transmission practice and can also be implemented digitally. However it's use in NTSC is now legacy and dying fast.

There are many references on line to the theory of NTSC television that dive into this in detail.

FWEIW, PAL, the British standard, is the the same as NTSC except they additionally invert the phase of the chroma sidebands ever other line. This improves stability in the decoding and is why PAL TV sets never had "tint" or hue controls. They didn't need them. Also the subcarrier frequency is different, 4.43mhz vs the 3.58mhz used in NTSC. This is due to the different line and frame rates in PAL. 625lines/50hz vs 525lines/60hz in NTSC.

SECAM, the French color system uses multiple FM carriers and is totally alien to NTSC and PAL. SECAM = Something Entirely Contrary to American Methods.

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post #19 of 21 Old 02-02-2012, 11:36 PM
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AFAIK, you can't buy HDMI chip sets on a "hobbiest" level. They are not distributed by the public parts vendors like Digikey, Mouser, etc.

I bought this from Mouser a while back. I noticed that NXP pulled the datasheet from their site sometime last year, but I still have the PDF saved on my desktop. So nobody will bust down my door if I use it???

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OTOH, several manufactures now make their own DVI chip sets and since DVI is upward compatible with HDMI, you can just use DVI chips for an HDMI project, just not if HDCP is needed and DVI can also support HDCP.

That's a good idea, but my interest in using HDMI is primarily for the built-in audio. As far as I know, if I used only a DVI transmitter I wouldn't be able to insert digital audio into the already encoded TMDS channels. It would have to go on a separate cable, which newer TVs are dropping support for.

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NTSC chroma is encoded as a DSSC signal. Double Sideband Supressed Carrier. This is a radio technique where the carrier is surpressed and only the sidebands of the signal are transmitted. To reconstruct the full chroma signal prior to demodulation, you must generate an "in phase" and "quadrature phase" subcarrier signal from a local oscillator.

Right. That explains two separate local subcarrier inputs. But what about the two "Chroma Inputs"? I'm assuming one is for signal ground in case it's different than the supply's ground. That datasheet is very vague throughout. It doesn't tell you which one's which so you could be hooking stuff backwards and completely out of phase.
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post #20 of 21 Old 02-03-2012, 10:28 AM
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Originally Posted by LordSte View Post

Right. That explains two separate local subcarrier inputs. But what about the two "Chroma Inputs"? I'm assuming one is for signal ground in case it's different than the supply's ground. That datasheet is very vague throughout. It doesn't tell you which one's which so you could be hooking stuff backwards and completely out of phase.

My guess is they brought out the inputs to both demodulators. In which case the two chroma inputs would be simply tied together. This would make the chip more versatile for other non NTSC applications. But without a block diagram we don't really know.

Note that NTC are really just service parts. They are not an IC manufacture and basically just relabel OEM chips. There should be an OEM part datasheet out there for that chip.

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post #21 of 21 Old 02-03-2012, 02:12 PM
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Originally Posted by Glimmie View Post

Note that NTC are really just service parts. They are not an IC manufacture and basically just relabel OEM chips. There should be an OEM part datasheet out there for that chip.

Good point. I guess that explains the rest. Thanks.

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SECAM, the French color system uses multiple FM carriers and is totally alien to NTSC and PAL. SECAM = Something Entirely Contrary to American Methods.

Missed this earlier. Nice.
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