Splitting Video Output

rikitheshadow

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Heyas, still have this general question about making a video splitter for a set of arcade cabinets so that you can have the game played on the Cabinet Monitor as well as a TV at the same time. I've read a few topics about it, but they all talk about if that the wrong type of cables are used to split the outputs that it will cause ghosting on the cabinet monitor. Is this true? And can this be done easily?

I've sorta wanted to setup and arcade tournament with my Virtual On cabinets since I got them, but I want spectators to at least be able to watch without shoving and cramping all around the cockpits. Right now I have to rule out that the Virtual On boards don't have a live view monitor option, or relay mode....which is commonly used on some Model 2 Boards.

I don't know if an amp would be needed if lets say the cables to the TV were at least 8-10 feet long starting from the back of the cabinet? I already know I can buy some RGB/CGA converters that make it viewable on a typical computer monitor output VGA.
 
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If Sharp Dressed Man were hanging off the machine like that while I was playing, he might get an "accidental" "elbow smash" for his efforts.
 
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Everytime I see that flyer for the overhead monitors, I can't help but notice the face on the dude in the center. It looks like him and contestant #2 are double teaming the chick playing Satan's Hollow.
 
The only place I ever saw those extra monitors was at Disneyland in the arcade. They had a half dozen Tron machines, all with those hideous monitors.
 
Everytime I see that flyer for the overhead monitors, I can't help but notice the face on the dude in the center. It looks like him and contestant #2 are double teaming the chick playing Satan's Hollow.

I'm pretty sure that dude is in Crocodile Dundee. I'm gonna see if I can get a screen shot....
 


All i can say is that it makes those machines look like abominations. Otherwise they would be nicer looking if they set apart from the cabinets so people don't have to hurt their necks looking up even when it seems like in that picture they could just easily watch over their shoulder.

Anyways, question is still un-answered?? I couldn't find much about those Auxiliary Show Monitors really, no shopping results on google or ebay.

Just need a simple answer about the ghosting issue people talk about....really
 
I have just completed a commercial job where we had to design and build 200 video splitters to drive 2 monitors each from a source.

It is actually more complex than you might imagine. Each signal R,G,B,V sync & H sync need to be amplified and buffered if you want to avoid the issues you mention. It's all to do with the frequency response of the signals - if you just twist the two outputs together (much the same as they do with the cheap splitter cables) you will have all sorts of problems DEPENDING on the monitors and the input signal.

We used discreet transistors to do the job but the parts count was up around the 50pcs to do the job.
 
It is actually more complex than you might imagine. Each signal R,G,B,V sync & H sync need to be amplified and buffered if you want to avoid the issues you mention. It's all to do with the frequency response of the signals - if you just twist the two outputs together (much the same as they do with the cheap splitter cables) you will have all sorts of problems DEPENDING on the monitors and the input signal..

+1

Part of the problem is that monitors have 75ohm terminating resistors internally on the video signal lines. When you wire two monitors in parallel, you've screwed up the signal levels and everything looks dim. Some monitors/boards work better than others, but in general, it doesn't work - you need an amplifier. For arcade video signals, you should be able to do it with a simple two transistor amplifier circuit on the video lines. I have no idea what kind of circuit they used on the commercial external monitors, but it shouldn't be too hard to build something that does the job. Alternatively, a normal VGA amplified splitter should work. The signals are lower frequency for an arcade monitor, but as long as the splitter is a simple amplifier, and not trying to "detect" a signal, it should work. Only possible snag might come from the fact that VGA signal levels are 1v p-p, and arcade video is usually 5v p-p.

-Ian
 
+1

Part of the problem is that monitors have 75ohm terminating resistors internally on the video signal lines. When you wire two monitors in parallel, you've screwed up the signal levels and everything looks dim. Some monitors/boards work better than others, but in general, it doesn't work - you need an amplifier. For arcade video signals, you should be able to do it with a simple two transistor amplifier circuit on the video lines. I have no idea what kind of circuit they used on the commercial external monitors, but it shouldn't be too hard to build something that does the job. Alternatively, a normal VGA amplified splitter should work. The signals are lower frequency for an arcade monitor, but as long as the splitter is a simple amplifier, and not trying to "detect" a signal, it should work. Only possible snag might come from the fact that VGA signal levels are 1v p-p, and arcade video is usually 5v p-p.

-Ian

Actually... that's not quite true. Arcade monitors have much higher input impedance than TV and other video devices. The termination resistors of around 1k-10k (depending on the model) are common. The output impedance of the arcade boards doesn't match this... but instead is usually quite a bit lower, somewhere around 100 ohms... so the brightness is only a little bit dimmer. But yes, just twisting wires together will likely cause some artifacts.

The easy and ideal way would be to make an emitter follower circuit to buffer the signal to each monitor. If you're only splitting a couple ways, you probably don't even need to buffer the sync.

DogP
 
I'm going to do this with me afterburner cockpit with a glass 42" TV I have. The game already has the video outs for a TV built into the side of it already.
 
Actually... that's not quite true. Arcade monitors have much higher input impedance than TV and other video devices. The termination resistors of around 1k-10k (depending on the model) are common. The output impedance of the arcade boards doesn't match this... but instead is usually quite a bit lower, somewhere around 100 ohms... so the brightness is only a little bit dimmer. But yes, just twisting wires together will likely cause some artifacts.

The easy and ideal way would be to make an emitter follower circuit to buffer the signal to each monitor. If you're only splitting a couple ways, you probably don't even need to buffer the sync.

DogP

Man, woah....lets just say a lot of that flew by my head. I mean I have some principle of understanding electronics, but not that much...yet!

So basically If I really want to ensure there is no screen garbage I need to add an amplifier between the harness portion that would split off towards an exterior monitor (i just want one monitor for each). I can understand that, video signals are typically weak in that sense I understand because all the HDMI amplifiers we use to split all the signals to a multitude of televisions at work require a power source.

Now, I can understand some circuit diagrams and I have soldering experience. If there is anyone who would know a configuration or diagram of an amplifier that would work in this situation could ya'll please hook me up, I can work out the building and soldering parts easily. I really just want to add one exterior monitor to each one of my Virtual On cabinets that work on a RGB signal in Medium Resolution monitors. I'll work out converting the signal to the exterior monitors to something more manageble, but I would really need a basic diagram of a video amplifier circuit to help with these cabinets. PLEASE!
 
I am looking into these currently.
I didn't respond this post before becuase they haven't come in yet and I didn't want to raise your hope when i don't have a good answer to your question.


http://www.paradisearcadeshop.com/23-cga-vga-hd-video-converter.html

I know the chip can drive two monitors but I don't know if the software on the board will allow two of the same images to be driven at the same time.
 
Basically, I was just saying that while TVs and other video devices are typically 50 or 75 ohm impedance, an arcade monitor is somewhere around 1K to 10K ohm. An emitter follower is a transistor amplifier configuration (sometimes called common collector: http://en.wikipedia.org/wiki/Common_collector ), which has a high input impedance (so multiple inputs tied together won't load down the driving circuit) and low output impedance (so it can drive circuits of its own). It has good frequency response and near unity gain, so it's good for buffering video like this (output signal looks very close to input signal).

Having an amplifier for each monitor provides isolation, which should prevent degradation of the video signal from reflections and other problems you may encounter from simply tying the inputs together.

All that said, before making the circuit, I'd personally try just tying them together and see how it looks. You may get lucky and it may look just fine. There's very little risk of damaging anything, and with only two monitors connected, there's a reasonable chance of it looking fine.

If you do need to make a circuit, attached is a MS Paint schematic of how I'd build it (shown for n outputs). Build one of these circuits for each color, one for the sync if you'd like (though it's probably unnecessary for just two monitors, otherwise just tie them together), and of course tie all the video grounds together.

I feel like I've been talking about and using this circuit a lot... I never realized how much I like it. :p The output resistors are just a guess... that should be a good starting place, but you may need to tweak that value up or down a little bit.

Edit: Oops, I should have mentioned... the transistor is an NPN (which you can get from the schematic), and just about any will do, but I typically use a 2N3904, since it's VERY common, cheap, and performs well. Standard 1/4W resistors should be fine.

DogP
 

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I am looking into these currently.
I didn't respond this post before becuase they haven't come in yet and I didn't want to raise your hope when i don't have a good answer to your question.


http://www.paradisearcadeshop.com/23-cga-vga-hd-video-converter.html

I know the chip can drive two monitors but I don't know if the software on the board will allow two of the same images to be driven at the same time.

That should work for converting to VGA, (and output to two VGA monitors), but it sounds like he wants to keep the original Medium Resolution monitor in the cab, and hook up another Medium Resolution monitor on top. AFAIK, that won't convert from EGA to 2x EGA (just EGA to 2x VGA).

DogP
 
That should work for converting to VGA, (and output to two VGA monitors), but it sounds like he wants to keep the original Medium Resolution monitor in the cab, and hook up another Medium Resolution monitor on top. AFAIK, that won't convert from EGA to 2x EGA (just EGA to 2x VGA).

DogP

Yeah it won't but I'll be using something like that to connect it to a VGA monitor for viewing, I myself do not have any additional medium resolution monitors laying around to use.

So it would be something like this in the attached MS Paint pic
 

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The ONLY arcade game that I cam remember "back in the day" running an external monitor on top of it was Dragon's Lair. When it was relatively new, people really crowded around the screen to beta good look at it...
 
Raising this from the dead. Some good input on this thread. I actually been working on a JAMMA Dongle for this. The design is currently utilizing opamps but honestly reviewing this i may be able to get away with just a few transistors and greatly lower the cost.
 
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