How to get Composite & S-Video from a GBC-Control (with help from Antonio Villena)

In today’s article I will show you how to piece together composite and s-video output from the GBS-Control. I’ll do this by using the “VGA->Composite/S-Video adapter” by Antonio Villena.

Lets start by looking at the adapter by Antonio. It is a small and relatively affordable device to allow s-video and composite from a MiSTer. You plug this into the IO board and you get a small switch for PAL or NTSC output.

The signal coming from the MiSTer is just RGBs, so 1 pin for red, 1 for green, 1 for blue and one for sync. The adapter has some components which do the work of converting RGBs into s-video and composite. To enable this, the adapter also needs 5v on VGA pin 9. This is part of the VGA spec but many devices don’t bother to output 5v on pin 9 if their use case doesn’t need it. The MiSTer IO board has an option to enable 5v on pin 9. When you set this jumper then the Antonio Villena adapter gets RGBs and 5v and this allows it do the job.

So in theory, all you need to do is provide the same input and you can use this adapter on other devices too.

Getting RGBs into the adapter

This is where the DIY RGBHV to RGBs dongle will help you. In my previous article I showed how I made one of these simple devices. It has a passive circuit which combined H & V sync together into C sync safely. If you plug this dongle into a GBS-Control and output 480i or 240p, then the output will be RGBs. This is good, this is what the Antonio Villena adapter wants. Step 1 or 2 complete.

Getting 5v into the adapter

If you are a hardware hacker or tinkerer, there are a few ways you can run 5v into this chain. I chose what I thought was the simplest for my setup: I ran a bodge wire on the GBS-Control from 5v directly to pin 9 of the output. This now sends 5v down the output of pin 9. When I made the dongle I then passed through pin 9 directly with a straight wire, so that means 5v reaches the Antonio Villena adapter.

So now we have

  • GBS-Control which outputs RGBHV and 5v on pin 9
  • A DIY dongle which converts RGBHV to RGBs and passes through pin 9
  • The Antonio Villena adapter, which accepts RGBs and 5v and produces composite and s-video

Set your GBS-Control to output 480i or 240p and you can now get this displayed on your regular consumer CRT.

Can this be used to get Composite or S-video from a Time Sleuth?

Sure but you need to do a little more work. The Time Sleuth outputs HDMI, which you then need to convert to VGA (RGBHV) using a standard, AliExpress level adapter. This adapter does have a micro USB input to provide 5v to the output, however my particular unit did not do this. I dont know what 5v is driving in this thing. You need to find a way to get 5v into pin 9, so you could open this HDMI to VGA adapter up and manually wire the USB 5v to pin 9 of the output.

Why does the Antonio Villena have a switch for PAL or NTSC output?

You know the backstory, PAL is EU/OZ, NTSC is the US/JP. PAL and NTSC (and SECAM) are color encodings for analog video. Back in the early days of TV there was only black and white (the brightness, known as luma). When color TV came around, they wanted to ensure backward compatibility with the old black and white sets. So the signal was separated into luma (black and white) and chroma (the color which goes on top). That is literally what S-video is: two pins, one for luma and one for chroma (sync is embedded in the luma wire). Composite video (yellow plug) is luma and chroma (and sync) combined into one cable.

So in RF, composite and S-Video, color is encoded separately from the brightness. That color can then be encoded using the PAL standard, the NTSC standard or the SECAM standard.

Note that this is separate from the refresh rate of the signal, you may be familiar with PAL being 50hz and NTSC being 60hz because that is the same frequency of the power networks in each region. Usually PAL is 50hz and NTSC is 60hz. However, there is nothing stopping you outputting a 50hz signal from your MiSTer and then encoding it as NTSC, essentially NTSC/50. Or you can output a 60hz signal and encode it as PAL, giving PAL/60 which was a legit thing in parts of the world (Southern America?).

RGB and Component video encode the video signal in a completely different way to composite or s-video and don’t use PAL or NTSC. So if your MiSTer, Time Sleuth or GBS-Control output is RGBs or RGBHV, when its converted to composite or s-video, you need to choose which color encoding it will use.

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