Scanline Generator for MD without upscaler

[samnunn92]

Hi all,

Firstly I'm new to this forum (hello!) but have referred to it a few times whilst modding etc so I'm really hoping I might be able to get a few more thoughts on an idea I've had. I saw the VGA scanline generator for Dreamcast that mmmonkey posted and have been trying to work out whether it would be possible to get that working for something with a 15Khz signal such as my beloved Mega Drive.

I thought that I could use a sync separator circuit to extract Hsync and Vsync from the Csync pin on the Mega Drive output, which could then drive the scanline generator circuit. The only problem I have is that I'm unsure whether it will work due to the Mega Drive outputting an interlaced signal and VGA obviously being progressive video. As far as my research has taken me, I believe that the SLG circuit grounds the RGB lines whenever it detects a Vsync pulse (indicating a new line of video). If the interlaced video draws all odd lines (1 field) then all even lines (the other field) but the circuit blanks alternate lines of each, will that not still give the scanline effect of the progressive video?

Apologies if this is a completely stupid question but I'm fairly new to creating/thinking about circuits (I am just starting an electronics course) but am really interested in whether this might work, or any advice/pointers anyone could give me would be really appreciated!

Thanks

[MaxWar]

This is not exactly my best area of expertise but I do not think that would work. The signal would need to be linedoubled before you use the scanline generator otherwise It would either not work at all or completely mess up the picture.

If you want glorious scanlines here are the two best options:
1.Use a good CRT
2.Get a Framemeister XRGB mini to use with HD panels.

[evildragon]

I recommend the CRT route.

[TwistedD85]

The SLG basically halves or dims half of the signal of a 480p picture to make the scan lines as far as I know. Even if you did manage to make it work on the Genesis' 240p signal you wouldn't get something nice like this.

480_Sonic.PNG

I'd imagine you'd probably get something more like this, super chunky.

240_Sonic.PNG

[SEGA.GENESIS1989]

I recommend the CRT route.

Hey! You didn't curse the poor build quality of (some of) Samsung's televisions. And yes I did catch your video regarding the subject matter. There is no question that Samsung's picture quality is fantastic but I've always had a concern regarding their quality of workmanship.

[samnunn92]

Thanks all for the replies, Twisted they are definitely a bit too chunky haha. I did have some doubts as to whether it would look how I wanted even if the circuit did function electronically. Never mind ta again!

[Ace]

I built a scanline generator for use on my GBS-8220 RGB/Component to VGA converter and the results were quite unimpressive. Not only does it darken the image quite considerably, it also dulls the colors down. I actually expected the scanlines generated to be like scanlines on an actual CRT display where the lines are pitch-black, but instead, they seem to just darken the area they're overlaid on. It looked quite crappy on an LCD display, it looked quite poor on a VGA CRT monitor and it especially looked bad on a CRT HDTV with the resulting VGA output with scanlines converted to HDMI at 720p. No amount of picture correction can compensate for this.

If you really want scanlines, I say you should just stick to a standard 4:3 CRT TV.