Sync Separator make horizontal AND vertical sync?

[Talasonic]

I saw the sync separator page on the GameSX site.  

Does this output both horizontal sync and vertical sync, so you can use a 15khz computer monitor?  If not, what does?  

Thanks!

[benzaldehyde]

The LM1881 outputs composite and vertical syncs only. You can do some more manipulation of bith using some logic gates to get horizontal sync, but I'm still trying to get that to work myself.  <_<  Use on a monitor depends on what source the monitor will accept. 15kHz sounds like it would use composite, but some displays like separate. Check Monitor World to find yours and check the sync type. Some monitors will even accept composite sync on the honrizontal sync line with vertical sync properly wired. It may take some experimentation to get it to work well. To get real H sync right on an IC, the EL1883 is a solution, though as of yet it is hard to find and only available in surface mount size (i.e., very very small). Good luck.

[Talasonic]

Thanks for your quick response, benzaldehyde.  I am a little confused about the following two sentences, but in the end, it probably doesn't matter too much.  

15kHz sounds like it would use composite, but some displays like separate.

Most 15khz monitors will accept straight composite as the horizontal sync, if I get the LM1881 for vertical?  

Some monitors will even accept composite sync on the honrizontal sync line with vertical sync properly wired.

But now it sounds like that would be unusual.  

Anyway, my monitor is not listed in monitor world, it's the projector, NEC MT820 (as mentioned in the other post).  Since there doesn't seem to be any way to know for sure whether or not composite will work for horizontal, I think I should get something like the EL1883 that will be sure to work.  

I don't care about the surface mount issue on the EL1883, I am good enough at soldering to work around that.  The problem is that it doesn't seem to be available.  

I have had luck though.  Here is a site that talks all about this problem, has the circuit to make pure hsync.  They say that most monitors will accept the sync from LM1881, though.  

[benzaldehyde]

I'd bet your projector accepts composite video or composite sync at least. Such devices would normally have sync strippers and dividers in the system. Try wiring the C sync to the H sync input and see if it works. This may be all it needs.

Sorry for the confusion. Most 15kHz monitors are pretty old and primarily accept composite sync. There are a scant few that prefer to have H and V (i.e., separate) syncs. As for the other, some monitors don't mind using composite sync as an H sync signal. Amazing, but true! I tried the logic gate H sync isolator but I couldn't get it to work right. My monitor is a bit weird, though, so you might have better luck (it only needed the AND gate to get a good H sync going; but wouldn't that just give me another V sync?).

[Talasonic]

Thanks for all your help.  

I don't really know too much about logic circuits.  I know what a NAND and AND gate is, though.  You're right, it does seem strange that the NAND and AND circuit doesn't work for you.  It seems to me there are 3 possibilities:

1. The original circuit was wrong.

2. Your NAND and/or AND gate can't handle the frequency in use in the circuit.

3. You put the circuit together wrong.  

I'm leaning towards it being #2.  Have you checked that out?  

It might be something else, though.  Video signals can be weird.  A long time ago, I took a Genesis 1 and attempted to hook it to a Panasonic video data monitor from the trash.  When I hooked up all the connections with loose wires, I could get it working, but only when I connected the sync wire to the deck while it was running, and even then, not every time.  But I found that if I put a small resistor inline on the sync wire, then it worked reliably, on the first start.  I have no idea why this is the case.  

So maybe try fooling with it a little more.  

[matt]

Almost all monitors will work fine if you use the LM1881's Composite and vertical outputs for H and V sync respectively.  It's worth trying that out before bothering with more complicated options.

[Talasonic]

Well, I was mail-ordering the LM1881, and I found the 7400 chip was only 91 cents, so I got it, too.  The 7400 has 4 NAND gates, and 2 NAND gates can make an AND, so you only need that one chip in addition to the LM1881 (which was $6.57, btw, mcmelectronics.com).  I figure it will insure maximum compatibility if I convert to real horizontal sync.  I'll have a bypass, though, in case it somehow messes things up.  But I want maximum compatibility because I'd like to try a number of oddball monitors I have, and see if any of them handle 15khz.  I would hate to think that they don't work simply because they don't handle the composite sync.  

[Talasonic]

I just got the MT820 projector, and set up the sync separator circuit from gamesx.com.

It did not work.  So, I will assume that my projector cannot accept composite sync in lieu of horizontal sync, and build the additional circuit that uses the gates to make horizontal sync.

UPDATE:  Well, I built the gate circuit this morning.  It still didn't work.  That was annoying.  Then I read some more and found that composite sync on the HS input ALONE did the trick for most monitors.  So, I tried that, and it WORKED.  So, just like benzaldyhide, I was not able to get that stupid gate circuit working, but have the whole thing working anyway.  What's interesting and annoying is that the Genesis already outputs composite sync, so my whole LM1881 and 7400 circuit are completely unnecessary.  Just hook RGB up, and CS from the Gen to HS on the projector, and it all works great.  I'd still like to get HS generated properly, though, just like benzaldyhide.  Right now, I'm hard-wiring a DB-25 RGB, etc output onto my 32x, though, so I can get RGB out of my CDX for decent sound.

UPDATE #2: The projector, NEC MT820 does in fact work with RGB, just using the Genesis CSync as the HSync for the projector.  

However, the CSync from the Genesis is too strong!  I had to put a resistor on it to get it to stop shaking vertically every few seconds.  I used a 500 ohm pot, and I think it was set to about 325 when it worked right.  (It might have been 175, though, I don't remember which terminals I was using and don't want to turn the projector on again just for this.)  ALSO, the levels are too high.  Sonic's face is white when it should be tan.  So I'll need 3 more pots.  But that shouldn't be a problem.  

[matt]

LM1881 (which was $6.57, btw, mcmelectronics.com).

Next time, shop at jameco.com - LM1881s are only $3 or so

ALSO, the levels are too high. Sonic's face is white when it should be tan. So I'll need 3 more pots. But that shouldn't be a problem.

Yes, the Genesis is really overbright.  You can try turning down the contrast on your projector, or if that doesn't work, I've found that a 100ohm resistor on each line does a good job.

[Talasonic]

Yes, I noticed I got ripped off on the LM, but I was shopping there anyway.  As far as the overbright, I used 220's last night, and had to turn the contrast all the way up on the projector.  But, it was BEAUTIFUL!!!  Even better than I could have hoped.  It was so wonderful looking.  I have to use about 270 ohm resistor on the sync so it doesn't shake, and probably 100 ohm would be good for the R,G,B.

Another weird problem, when I first hooked it up, the Red didn't work.  It was just black.  I checked all the wiring, and it was all ok.  Finally, I tried bypassing the 220 resistor, and clearly the red signal was there.  But what was interesting was that when I removed the short across the resistor, the red started working normally!  But, when the game reset, the red was out again.  I found that if I touched some of the leads, I could get it working again that way, too.  So anyway, that was kind of funny.  Probably if the resistance is lower, I won't have this problem.  I don't have any 100's so I guess I'll use 2 220's for each.  Ahh well.