Video splitter circuit- for testing/display 2 crts at once

[kayoteq]

I see a few setups here and there with folks having a second monitor external of the cabinet. Since I have more monitors than sense cabinets, I'd like to set up
something what would let me hook up a second monitor to a game for testing or fun.

It seems pretty simple, relatively, but I want to make sure both monitors have sufficient signal and won't damage each other in case of failure.
Ideas on how I can approach this with a reasonable budget?

[MonMotha]

For arcade monitors, which tend to be low (ish) speed signals with high impedance inputs, just split the wires.  Really.  For higher res and impedance matched signals, things get more complicated, but for arcade video, you can get by with just splitting the wires just fine.  At minimum, you should not damage anything, though the picture will appear a bit dimmer (turn up contrast slightly if necessary).

[kayoteq]

Cool, thanks. I generally do some crazy things with wires and splitters for other things, but wasn't sure how sensitive things were in regards to the signals.
All the research of varied hookups such as SCART splitters looked like it was just some wire in a case, But I might still consult with one friend to see if I can add some safety to it anyway, in case a monitor I'm testing has some unseen shorts, etc.  Basically examine what the maximum 'normal' signal is and make sure the wires don't
 transmit _more_ then they're supposed to (diode, fuse, some sort of amperage limiter.) Time to build a breakout box!  I think I'll model it on Doc Brown's flux capacitor.

[Ummon]

Well, that's what dual output video cards are good for - if they're true dual output. Meaning, it generally has to be at least a Geforce 4 or Radeon 7000 (or maybe 9000) to be.

[kayoteq]

Well, I'm currently planning this as a add-on to one of my standard arcade games. .
I currently don't have any PC MAME-Arcade setups if you don't count the x-box.


Based on some research into protection circuits, I'm thinking 5V max varistors tied to ground,
with a fuse to blow if that happens to protect each side.

For each color and the sync signal:

Signal--(fuse)---(VR)----Connector1(game monitor)
                                |--(VR)--(fuse)---Connector2(test/ second monitor)

But my theory may be completely flawed, but the idea is to take any rogue voltage that might get in the circuit
that's not 5V or less and ground it, popping the fuse, rather than going back into the game PCB or monitor.
Not likely to happen, but it's kind of a worst-case-scenario. rather change a fuse than rebuild a circuit.
Basically build a surge protector into a RGB cable, of sorts.

Or, I just make a splitting cable and check the voltages of the test monitor before hooking the signal cable up.
 I have a tendency to over-complicate things.

[MonMotha]

You are way overthinking this.  Just split the wires

[qrz]

You are way overthinking this.  Just split the wires

and make sure BOTH monitors are isolated from the AC mains.

should there be excessive signal loading, a simple "emitter follower " could be built as a buffer for the drive .

qrz

[MonMotha]

That is true, make sure both monitors are isolated.  This should be the normal case, anyway, but it is an important check to make.  Even in a single monitor configuration, isolation is more than a good idea: it is often necessary to make things work without smoke (and resulting non-workingness), but it's now two points to check in a dual monitor configuration.  Driving a non-isolated monitor from a PC will result in badness as PCs cannot be floated (power common *is* earth ground in a PC).

For most arcade monitors, input-Z is high enough that you shouldn't see excessive loading (may just need to tweak contrast up a bit).  If you do have major dimming issues, you can build various amps including the emitter follower that qrz mentioned.

[kayoteq]

Yep.. I'm going for the simple hookup. I went through my pile o' wires and have about 5 Jamma harnesses and plenty of sacrificial Merit industries inline molexes to make a safe set of divided connectors. A little keyed interconnect plug that I can hook up when I need it.. And my friend just brought home a set of pin pullers from work for
me to use- sweet!
 Shrink-tube and solder rather than twisted wires and electrical tape should keep me and my monitors safe.
Just wanted to see what the experts would opine on this, thanks.. I just never found the exact 'splitting the video signal' anecdote anywhere..
PC is another topic for later. I figure I'll go for some PC-based one if I ever do that..