One cpc and 2 monitors

[radu14m]

can i connect 2 monitors to one cpc ?
is something special needed ?

[ralferoo]

I don't think there are any special cables. You might be able to make one up with 33 ohm resistors before you split the signal to the 2 monitors, or 75 ohm resistors after the split, e.g.:

Code Select Expand


                     /----------o to monitor 1
from CPC o--| 33R |--+
                     \----------o to monitor 2

              /-----| 75R |-----o to monitor 1
from CPC o----+
              \-----| 75R |-----o to monitor 2


Whether this will actually work in practice is another matter, but it's worth a go.

Essentially, for each of the R, G, B and sync signals the monitor should have an impedance of 75R to ground. Connecting two monitors in parallel (assuming they are perfectly identical which might well not be the case), the impedance will effectively be 37.5R. The 33R solution is a bit easier and return the impedance to about 70R. The 75R solution involves more resistors (and ones that are a bit harder to find) but would make the impedance closer to ideal.

If you unplug either monitor, the impedance will go up to 108R for the first solution or 150R for the second, either way it won't look great. If you wanted something where the monitors could be unplugged individually, you could have a transistor per monitor and terminate the source with 75R and have a much higher resistance before the source going to the base of each transistor. This would be a more complicated circuit though, especially if you try to compensate for the voltage drop across the transistor...

[radu14m]

Oh i tought just to a simple wiring without resistors.
now i understand the risks.
i want to use my green cpc monitor and my cpc plus colour one 

nobody did this before ?

[ralferoo]

The green screen and colour monitor combo should actually be very easy and not need resistors...

The green screen only needs LUM and SYNC, the colour monitor only needs R,G,B and SYNC. IIRC, the SYNC signal on the CPC is actually TTL without a specified impedance so it probably doesn't actually need the resistor network required to match the impedances as would be required for 2 colour or 2 green screen monitors.

I just assumed you'd be trying to use two colour monitors!

[chinnyhill10]

Find a modern DVD recorder than has an RGB input. Then you can split the CPC out to as many devices as the recorder supports.


In theory with the kit I have here I could split a CPC out to 6 displays. Although 2 of them would have to be composite. Quite why I'd want to do that though is quite another matter.


Of course if you insist on using original monitors then the solution posted further up the thread is the one to go for.

[Bryce]

I used to have a GT65 and an MP1 in parallel without no extra resistors. Worked fine, but although they use separate signals both monitors are darker than they would be normally.

Bryce.

[TotO]

Why using 2 monitors to display the same picture?! 
Use the GT65 to display debug informations with an other CRTC. 

[Bryce]

The reason I did it: To play Tomahawk in colour. MP1 was in colour, but too blurred to decypher the Tomahawk lenslok. So the GT65 was connected to do that. I left the computer in that configuration permanently and used the GT65 for coding and the MP1 for gaming.

Bryce.

[Carnivius]

On my Amiga 1200 we used to have it plugged into a monitor and TV at same time for some multiplayer games such as Hired Guns so we could split into teams and put cardboard over the part of our screens that our opponents display area was.  It was just a simple way of turning games like that into a network-like deathmatch thing and adding in the tension of not knowing where the enemy was.   Worked well...until one of the opposing team turned into Mr Cheaty McCheat and took the cardboard off their screen to reveal my team's positions.   Tsk.

[TFM]

You should check out the VN96 from the WizCats. It provides couple multi player games for the CPC using a network (network card is only 2-3 Euros).


The VN96 would be also a great thing to put content on different monitors. 


Ok, since you all ask me so kindly for the link, here it comes....


VN96 Homepage

[Gryzor]

Why haven't we heard of that before?!

Pity this isn't a live page...

[Bryce]

The VN96 is well known. Not the fastest link in the world, but it works and it's simple to build.

Bryce.

[TFM]

Well, regarding 8 bit networks, it's not too slow ;-) But of course an RS485 network using some nice CPC Boosters is faster. 

[Token]

Oh i tought just to a simple wiring without resistors.
now i understand the risks.
i want to use my green cpc monitor and my cpc plus colour one 

nobody did this before ?

I did a quick test yesterday. A CPC 464 with GT64 & CTM644-2.
(no resistors)


On the GT64 the picture is a bit shifted on the left but brighness and contrast are normal.
The brightess is /2 on the CTM644-2, picture is well centered otherwise.

[radu14m]

Great !
did you just simple wire them directly ?


can you put a picture ?

[CraigsBar]

I did a quick test yesterday. A CPC 464 with GT64 & CTM644-2.
(no resistors)


On the GT64 the picture is a bit shifted on the left but brighness and contrast are normal.
The brightess is /2 on the CTM644-2, picture is well centered otherwise.

Any chance of a photo?

[Token]

Simple soldering, all 6 pins. So I could swap. I didn't tested LUM only & RGB.
It's hard to notice the shifted picture on the GT64, it's about 1cm.