Author Topic: RGB to Component Converter  (Read 1505 times)

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Online paul_g_787

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RGB to Component Converter
« on: October 17, 2021, 05:15:26 pm »
I have decided to re-visit this project now.

To summarise:
I have a new TV that has only one analogue input; component video input. (YPbPr / YCbCr).

I have all my old retro consoles hooked up via an Extron MVX84VGA-A video switcher. I have made custom Component cables for each console and one for connecting the output to the TV. This is working great! However some consoles only have SCART output (RGBS). I can no longer use these devices so I would like to build a passive converter. (see schematic I found online).

I attempted this before with minimal success. I got a picture in colour but it was very noisy, due to using the TL072 as an op-amp.

This is the old thread:
https://www.eevblog.com/forum/projects/rgb-to-component-(ypbpr-ycbcr)-video/


The two main issues I have encountered in this project are the cost of the LM6172 and also the power supply.

I would also like to, adapt the circuit so I can switch the converter on/off so that I can put it in-between my Extron input selector and TV. That way when I want to use a device that already has Component output I can bypass the converter in this unit.

The first think I want to tackle is the power supply.
Could anyone shed some light on the workings of power supply shown in the schematic?

I tried using a USB power supply feeding a LMC7660, however the 7660 could not handle the current used so the output voltage would just drop to around -2V.

So what would be a good alternate solution? Perhaps a linear AC supply with a 7805 and 7905?
 

Online Benta

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Re: RGB to Component Converter
« Reply #1 on: October 17, 2021, 07:23:48 pm »
1: what's your supply voltage (options)?
2: are you certain that your devices only output RGBS or could it be RGBY?

 

Online paul_g_787

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Re: RGB to Component Converter
« Reply #2 on: October 17, 2021, 07:27:20 pm »
I need +5v/-5V split rail for the supply voltage.

Yes they are RGBS:

The Extron only supports clean sync, so the cables for the RGB consoles have a LM1881N in the cable to strip the sync from the composite video.
 

Online Benta

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Re: RGB to Component Converter
« Reply #3 on: October 17, 2021, 07:33:23 pm »
I need +5v/-5V split rail for the supply voltage.

My question was: what's your supply (=INPUT) voltage? What's available to produce +/-5 V?

 

Online paul_g_787

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Re: RGB to Component Converter
« Reply #4 on: October 17, 2021, 07:37:12 pm »
Oh I see. Hehe :)

I have two options.

I could power the device from USB. So +5VDC.

Or I could power it from the 240V AC mains, which I would perhaps prefer.
 

Online Benta

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Re: RGB to Component Converter
« Reply #5 on: October 17, 2021, 08:10:02 pm »
I'm having problems with your problem description here.
SCART does not have a sync output anywhere. It's always embedded in the CVBS output. When you say "RGBS", do you mean that the CVBS output from your old consoles only contain sync information and no video?

Concerning the power supply: check out LM2663 from TI/National.

« Last Edit: October 17, 2021, 08:13:26 pm by Benta »
 

Online paul_g_787

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Re: RGB to Component Converter
« Reply #6 on: October 17, 2021, 08:33:26 pm »
I'm having problems with your problem description here.
SCART does not have a sync output anywhere. It's always embedded in the CVBS output. When you say "RGBS", do you mean that the CVBS output from your old consoles only contain sync information and no video?

Concerning the power supply: check out LM2663 from TI/National.

Some have RGBS e.g. the Sega Megadrive.
Some have RGB with Composite Video e.g. PlayStation.

This is an issue because the Extron requires a clean sync signal and won't work with composite video.

To rectify this, the consoles with composite video signal go via a LM1881N in the cable to remove the video signals, leaving just the sync signal.

So all my devices are therefore RGBS into the Extron.

The output of the Extron is also RGBS.
 
On my old TV I just had a VGA to SCART cable fron the Extron unit with the sync signal on pin 20 (composite video in).
 

Online Benta

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Re: RGB to Component Converter
« Reply #7 on: October 17, 2021, 09:05:57 pm »
OK, I have a clearer picture now. You have RGB.
Plus CVBS, which is sometimes only sync, and sometimes really CVBS. So only the sync part is generally useful.
Using the LM1881 to extract clean sync is probably the best solution; I like the part myself, and it's much better than the data sheet suggests.

Concerning power supply and consumption:
you have to think about three opamps having to drive 1.4 VPEAK into 150 ohms each.
This takes some current.

At "all-white" it's ~30 mA just for the outputs. Plus supply current for the parts etc. Reckon on 50...80 mA all in all. The LM2663 is not the worst choice here.

Cheers.
 

Online paul_g_787

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Re: RGB to Component Converter
« Reply #8 on: October 18, 2021, 03:33:54 pm »
Just had a look at the LM2663 and it looks like it will do the job.

The LMC7660 i tried did not work well but the lM2663 can supply 200mA! It should be more than enough. I have ordered a few to play with.

Now if I am using the LM2663, I would like to power this device from a USB socket.

Should I use some kind of regulator e.g. a 5V Zener diode on the USB input?

And what do i do with the data pins of the USB port? Do I just leave them floating?
« Last Edit: October 25, 2021, 05:07:30 pm by paul_g_787 »
 

Online Benta

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Re: RGB to Component Converter
« Reply #9 on: October 18, 2021, 03:55:21 pm »
You can place transient protection ot the input if you like, it depends on how harsh your environment is (probably not necessary for video).

Just leave the data lines open, or even better terminate them correctly.

 

Online paul_g_787

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Re: RGB to Component Converter
« Reply #10 on: October 18, 2021, 04:41:45 pm »
You can place transient protection ot the input if you like, it depends on how harsh your environment is (probably not necessary for video).

Just leave the data lines open, or even better terminate them correctly.

I think it would be wise to have some kind of protection. What is the standard practice?

What would be the correct way to terminate the unused USB data lines?

And would I need any kind of filtering between the USB connector shield and GND?
 

Online Benta

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Re: RGB to Component Converter
« Reply #11 on: October 18, 2021, 06:20:50 pm »
A Transzorb/TVS, I'd suggest 5.6 V. A simple Zener could also do it.
Here's a selection:
https://www.vishay.com/diodes/protection-tvs-esd/trans-zorb/

For USB termination: hey, you need to do a bit of research yourself.

« Last Edit: October 18, 2021, 06:23:40 pm by Benta »
 

Offline Terry Bites

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Re: RGB to Component Converter
« Reply #12 on: October 18, 2021, 10:25:05 pm »
A linear supply is a good idea in AV, not that switchers are no good, its just a potential problem you can eliminate off the bat.
TI's THS7315 is great vfm compared to the LM6172, about twice the price of a single genuine 072. Rohm used to make a dedicated IC  BA7230LS. Like so many analog video ICs its gone to meet its maker. I believe that there are still some MC1377s still in the aether. Comodore fan boys can help.

The TL072 would be problematic  The frequncy/ phase response of the opamp  is the obvious culprit. I'm not too sure its happy driving a low imopedance load. the video bandwith at SD it 12MHz. At unity gain this opamp is out of its depth.

I spent a small fortune on racks of analog matrix switches just before HDMI appeared. It made a grown man cry. Still, not my own cash!
 

Offline Terry Bites

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Re: RGB to Component Converter
« Reply #13 on: October 19, 2021, 01:43:40 pm »
Curiosity got the better of me see page 14 of https://www.analog.com/media/en/technical-documentation/data-sheets/65501fa.pdf
Life made easy and it runs happily on +-3V3. You can make it single supply but you'll be bogged down in coupling caps and the evils of sag.
The LM1981 is your dream sync detector, it works with all analog video formats including 1080p/s. A CD4541 timer can be contunually reset by H or V sync when sync lost, it starts counting down to turn-off.

« Last Edit: October 19, 2021, 04:22:25 pm by Terry Bites »
 

Online Benta

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Re: RGB to Component Converter
« Reply #14 on: October 19, 2021, 05:06:10 pm »
Curiosity got the better of me see page 14 of https://www.analog.com/media/en/technical-documentation/data-sheets/65501fa.pdf
Life made easy and it runs happily on +-3V3. You can make it single supply but you'll be bogged down in coupling caps and the evils of sag.
The LM1981 is your dream sync detector, it works with all analog video formats including 1080p/s. A CD4541 timer can be contunually reset by H or V sync when sync lost, it starts counting down to turn-off.

The pricing of LT6550 is not exactly a bargain compared to LM6172.
And the LMH1981 is not exactly cheap either ($6 at 1k units).
 

Offline Terry Bites

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Re: RGB to Component Converter
« Reply #15 on: October 20, 2021, 02:59:55 am »
Dont forget the LM6172 is just a single naked opamp. The LT6550 is three channel device with internal precsion gain set resistors. Its the same price or less than three LM6172s, but with handy features in a single package.

Yes the sync seperator costs about 5x the 1881, even if its not right for you purpose its worth knowing about your options. Also MAX have an SOT-5 Loss of sync device which may be of interest. The MAX7461 simply tells you your video link has been cut by a gaggle of ninjas.

 Many of us take inspration from devcies we havent come across before and sometimes dont use them as intended thereby broadening the art.
[attachimg=1]
« Last Edit: October 20, 2021, 07:20:57 am by Terry Bites »
 

Offline EPAIII

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Re: RGB to Component Converter
« Reply #16 on: October 20, 2021, 07:13:18 am »
Perhaps you just want to have fun building this, but it sounds like you are going to an awful lot of trouble for something that can be purchased for a few dollars (or whatever currency).

You are talking about an analog component converter: from one set of analog components to another set of analog components. These converters use simple, weighted summations of one set of components to arrive at the other. Active devices (op amps) are usually used to prevent cross talk between the input components and bring the output levels back up after passing through the summing resistors. Even if the one you buy does not do the exact conversion you want, that can be changed, probably with some simple resistor substitutions.

https://www.ebay.com/sch/i.html?_nkw=Rgb%20To%20Yuv%20Converter&norover=1&mkevt=1&mkrid=711-156598-679417-4&mkcid=2&keyword=rgb%20to%20yuv%20converter&crlp=435060840618_&MT_ID=585586&geo_id=10232&rlsatarget=kwd-298710865903&adpos=&device=c&mktype=&loc=9027887&poi=&abcId=1141816&cmpgn=6540152590&sitelnk=&adgroupid=80070761658&network=g&matchtype=b&gclid=CjwKCAjw2bmLBhBREiwAZ6ugo9vE1xUQ3QorWOg_uRefa2feYKdzKbwj2nADjCkVd3E0Ys9Va-QVvRoCA1MQAvD_BwE

https://www.amazon.com/s?k=rgb+converter&gclid=CjwKCAjw2bmLBhBREiwAZ6ugo-QPBrWd1IR4aFN5AV4zaNgNksKpJsNTEtay9PJYmXF9ooaw1ib0sBoCyQIQAvD_BwE&hvadid=409943030568&hvdev=c&hvlocphy=9027887&hvnetw=g&hvqmt=b&hvrand=2798272253927533571&hvtargid=kwd-29274101&hydadcr=24662_11410881&tag=googhydr-20&ref=pd_sl_747r4bo8j9_b

https://www.walmart.com/c/kp/rgb-converter

https://www.ebay.com/itm/273178172012

https://www.arcadexpress.com/en/video-converters/615-convertidor-de-video-rgbs-scart-a-ycbcr-ypbpr-.html

There are many, many more internet hits. Just search.
 

Online Benta

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Re: RGB to Component Converter
« Reply #17 on: October 20, 2021, 09:46:20 am »
The LM6172 is a dual.

 


Online paul_g_787

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Re: RGB to Component Converter
« Reply #19 on: October 25, 2021, 05:04:43 pm »
Perhaps you just want to have fun building this, but it sounds like you are going to an awful lot of trouble for something that can be purchased for a few dollars (or whatever currency).

You are talking about an analog component converter: from one set of analog components to another set of analog components. These converters use simple, weighted summations of one set of components to arrive at the other. Active devices (op amps) are usually used to prevent cross talk between the input components and bring the output levels back up after passing through the summing resistors. Even if the one you buy does not do the exact conversion you want, that can be changed, probably with some simple resistor substitutions.

https://www.ebay.com/sch/i.html?_nkw=Rgb%20To%20Yuv%20Converter&norover=1&mkevt=1&mkrid=711-156598-679417-4&mkcid=2&keyword=rgb%20to%20yuv%20converter&crlp=435060840618_&MT_ID=585586&geo_id=10232&rlsatarget=kwd-298710865903&adpos=&device=c&mktype=&loc=9027887&poi=&abcId=1141816&cmpgn=6540152590&sitelnk=&adgroupid=80070761658&network=g&matchtype=b&gclid=CjwKCAjw2bmLBhBREiwAZ6ugo9vE1xUQ3QorWOg_uRefa2feYKdzKbwj2nADjCkVd3E0Ys9Va-QVvRoCA1MQAvD_BwE

https://www.amazon.com/s?k=rgb+converter&gclid=CjwKCAjw2bmLBhBREiwAZ6ugo-QPBrWd1IR4aFN5AV4zaNgNksKpJsNTEtay9PJYmXF9ooaw1ib0sBoCyQIQAvD_BwE&hvadid=409943030568&hvdev=c&hvlocphy=9027887&hvnetw=g&hvqmt=b&hvrand=2798272253927533571&hvtargid=kwd-29274101&hydadcr=24662_11410881&tag=googhydr-20&ref=pd_sl_747r4bo8j9_b

https://www.walmart.com/c/kp/rgb-converter

https://www.ebay.com/itm/273178172012

https://www.arcadexpress.com/en/video-converters/615-convertidor-de-video-rgbs-scart-a-ycbcr-ypbpr-.html

There are many, many more internet hits. Just search.

I have tried a handful of these devices from Amazon/eBay. There are three problems I have faced.

1. The device says "SCART" to component. I have yet to find one that actually uses the RGB signals and not just the Composite video signal. They work, but with the worst picture possible! And are not compatible with all my devices.

2. The two that I found that do actually have true RGB input (which cost me £30 and £19 a piece!!) are marketed as an "active" converter. It processes the image digitally and causes a delay of between 50-100ms in my testing. This is OK for video e.g. a DVD player but not acceptable for gaming, especially fast-paced shooters etc...

3. None of them I purchased supported 240p which is common on games consoles such as the PS1 and others.

Now, my TV on the component (YCbCr) input only produces a delay of around 2-6ms which is perfectly acceptable and useable for gaming!
My TV also supports 240p, 240i, 480p, 480i, 576p, 576i, 720p, 720i and 1080i via the component input so therefore supports all the resolutions needed.

With this in mind the only difference between the RGB signals and the supported component signal of my TV is the colour mixing which is what this circuit is doing, but passively without the digital processing.
 

Online paul_g_787

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Re: RGB to Component Converter
« Reply #20 on: November 09, 2021, 11:46:54 am »
A linear supply is a good idea in AV, not that switchers are no good, its just a potential problem you can eliminate off the bat.
TI's THS7315 is great vfm compared to the LM6172, about twice the price of a single genuine 072. Rohm used to make a dedicated IC  BA7230LS. Like so many analog video ICs its gone to meet its maker. I believe that there are still some MC1377s still in the aether. Comodore fan boys can help.

The TL072 would be problematic  The frequncy/ phase response of the opamp  is the obvious culprit. I'm not too sure its happy driving a low imopedance load. the video bandwith at SD it 12MHz. At unity gain this opamp is out of its depth.

I spent a small fortune on racks of analog matrix switches just before HDMI appeared. It made a grown man cry. Still, not my own cash!

Interesting you say this as I actually have some 316 ICs left over from making my original gen XBOX component cable (look up xosvp for the schematic I used).

So here is my idea. I use regular transistors to buffer my R, G, B and Sync lines. Use my resistors to mix the signal to YCbCr, then output via a 7316. This could work but how would I combine the sync to the Y pin before the 7316?

I will draw a schematic later today of my idea.
 

Online NiHaoMike

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Re: RGB to Component Converter
« Reply #21 on: November 09, 2021, 01:36:57 pm »
2. The two that I found that do actually have true RGB input (which cost me £30 and £19 a piece!!) are marketed as an "active" converter. It processes the image digitally and causes a delay of between 50-100ms in my testing. This is OK for video e.g. a DVD player but not acceptable for gaming, especially fast-paced shooters etc...
Sounds like you'll be interested in the "OSSC", a low latency upscaler just for gaming. Main downside is that it's expensive, but since it's open source, it might be possible to DIY a cheaper version.
https://junkerhq.net/xrgb/index.php/OSSC
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