It's so nice that the site is back online. Hello all, I've been attempting for some months now to design and build a general purpose RGB to YPbPr encoder (S Video and Composite would also be nice). One of the main reasons I'm doing this is to get CRT Emudriver working on my CRT television, which doesn't accept RGB here in America. I also plan on using this circuit in a Dreamcast cable and perhaps inside of a PS1. I don't exactly have a degree in electrical engineering though and I've been running into a lot of problems. Here's a couple examples of the trouble I've run into. http://imgur.com/a/gaPuz The closest I ever got was using a transistor-only design that Helder posted on Sega-16. The image was still too dark though, and the capacitors were causing sync problems. Examining the waveforms on a cheap digital oscilloscope showed me that the DC offset of my signals was way too high, and I had just about no way to lower that. The avenues I'm looking at experimenting with next are 1) Use Helder's transistor-based model and amplify the outputs using a THS7316 (probably will cause capacitor problems because of high DC offset?) 2) Copy the NESRGB's encoder (which viletim has kindly supplied a schematic for but it requires an encoder that's difficult to get cheaply and a parallel resonance crystal; something I know nothing about) 3) Use the design by ACE from the Sega-16 forums (but he's working on a new revision of that and the current one is broke, so...) I guess I'm not sure what I'm asking for here other than any kind of knowledge about this. If anyone here has worked at all with analog video signals, pretty much anything they have to say to me will be useful info. I really don't know what I'm doing. (Oh, and I'm not interested in just buying a scart>YPbPr encoder. I didn't make an account on ASSEMBLERgames to BUY something...)
You could look into the rohm part used in the snes. You will find plenty of info on the snes component mod and that rohm part takes rgb as the input. So you could just copy that but used you own input
Now that is an interesting idea! I considered reverse engineering some old computer GPUs and the NESRGB but it didn't occur to me that I could just copy consoles! I had attempted a SNES YPbPr output mod a year ago or something but I didn't even know what I was doing well enough to check the datasheet on the thing before I started soldering. Oof. I just about forgot that SNES's could do that since I've got my HD Retrovision cable for that. Cursory google search found an archived thread on good ol /vr/. https://i.warosu.org/data/vr/img/0021/76/1421802092595.jpg I'll have to wait for these encoders to get to me from China now, but I'm feeling optimistic again.
I'd probably use a ths7413 rather than transistors though, as it's easier to put a voltage divider on the input of the ths7413 and then have proper 75 ohm on the output. Do you have a scope?
I do have a scope! I've got a cheap little digital scope from here: http://www.gabotronics.com/oscilloscopes/xprotolab-plain.htm I don't have any ths7413s handy but I've got a few ths7416 since they were what RetroRGB suggested for the N64 RGB mod. I figured it was better to have a low-pass filter than to not since I am pretty sure my sources don't have one maybe. As useful as it is to have a scope, I have more or less no idea what my YPbPr signals are SUPPOSED to look like. Thus far I've been just comparing the white/r/g/b screens of the 240p test suite from Wii to Dreamcast. I figure if it's the same image coming natively from the Wii, I should try and match it with my converter right?
