ramapcsx2
commented
2 years ago Hey, the 5V input capability is just assumed. It might be 5V tolerant. If you consider that the highest voltage on the ASIC is just 3.3V though, it becomes a bit questionable. I don't actually know whether a 3.3V IO bank can be made 5V tolerant or not.
I noticed the problems with the Gamecube sync as well. For some reason, it is more difficult to extract with an LM1881.
Using 3.3V on the LM1881 is clever, but sadly the device barely works at the lowered voltage. Maybe you can compromise, and give it more like 4V. Maybe there is a newer part that works on 3.3V.
An oscilloscope is required if you want to honestly get into the world of hobby electronics. It will be the best buy you make towards that. Make it at least a Rigol 1054Z ;)
tessc97
Hi there,
I'm trying to design an adapter board that one could use to get a cheaper way to connect retro consoles to the GBS than buying SCART cables. So far I've made a design (it's on my GitHub, but I realized I misunderstood a bunch of things so I'm gonna have to rework it) that takes the outputs of a Nintendo AV multiout connector and uses an LM1881 to get sync and outputs that to a VGA header. I've designed it in a way so that you could use the same PCB for lots of different consoles by including jumpers and spots for optional components such as resistors and capacitors. I've also included jumpers to select between Sync-on-Green, Sync-on-Composite or Sync-on-Luma (basically you can select which signal pin is on the input of the LM1881).
As I feel like I don't fully understand a few things, I wanted to ask a bunch of questions here.
So as I understand it, the GBS Sync/HSync (also VSync) take 5V TTL level signals, since those are the same as you get from VGA. Why do I need to put a 470R resistor in series on the output of the LM1881 then, instead of just terminating it? Wouldn't an unmodified GBS 8200 even expect that sort of signal, since the LM1881 outputs exactly that? I get that putting the 100R resistor between S and GND makes it work with lower amplitude signals, but is it required if I only ever put signals on there that I know are high enough power?
My goal with this whole thing is to design this board as a prototype, order a bunch of PCBs from JLCPCB or whatever and then build an adapter for every single console I have. I've also ordered multiout plugs from aliexpress for that to work but I'm not sure about some of the specifics and I don't want to unnecessarily spend money on something that might turn out not working.
Also I'm having a problem with my PAL Gamecube for which I've already made a prototype board with a DIP-8 LM1881N, as that constantly loses sync and has a noisy signal. I haven't increased the decoupling capacity on the GBS yet and I can still try other things, but I've also noticed that my Gamecube only outputs 4.7V on the 5V pin. I've also read that some people also use 3.3V on an LM1881 tho so I'm not sure. I don't have an oscilloscope sadly but I wanna try to find out what's the problem by using an Arduino to debug stuff. Any idea what it could be tho? If I don't plug in the CSync output of the LM1881N (with a 470R resistor and the 100R resistor between S and GND), I don't get any sync at all so the LM1881 has to ouput at least something.
Thanks in advance, kind regards! Tessa