Dual monitors on PC AND mirrored main input to LCD TV
February 17, 2010 7:25 AM   Subscribe

How do I connect my LCD TV (VGA input preferably but it also has an HDMI free) to my desktop computer, which has 2 monitors already hooked up to the 2 DVI-out ports on the graphics card?

I currently have a desktop computer I built with an ATI Radeon 4870 graphics card. The card has dual DVI out which both connect currently to 2 identical 24" Dell LCD monitors.

I also have a 46" LCD tv that has a VGA and HDMI in free. What I would like to do is either use the LCD TV as a third extended desktop to drag over movies, netflix, Hulu etc to that screen. Alternatively I wouldn't mind having my main 24" LCD be "mirrored" to the TV for the same purposes. Is there any way to do this?

I've looked up DVI to DVI/VGA splitters but I've seen that video cards will only output one signal at a time, either VGA or DVI...so is the mirroring not possible? Is there any way around this?
posted by PetiePal to Technology (7 answers total)
Response by poster: I feel like it might almost be easiest to use a laptop hooked up via VGA and just share my media with my Drobo instead...Then use maybe a wireless keyboard/mouse and be set.
posted by PetiePal at 7:30 AM on February 17, 2010

Response by poster: Technically yes, but I doubt I'd buy another ATI Radeon 4870. If anything I may upgrade my video card this spring to one of the 5000 series...if so I'd leave in the 4870 and that would make it easy although I've read a lot of issues with triple monitors in Windows 7.

Perhaps I can UltraVNC it or something with another laptop? Not sure how that would work with streaming
posted by PetiePal at 7:41 AM on February 17, 2010

Instead of a laptop, you could pick up a cheap desktop machine, then use VNC to connect and control it from your main machine - Streaming over VNC is possible, but it won't be as great as just letting a dedicated machine run as a media computer connected to the TV.
posted by pupdog at 7:46 AM on February 17, 2010

easiest way would be to buy another video card. hook the TV and the display you want to mirror to the same card and then mirror them. or, use the DVI splitter and get a DVI-to-HDMI cable - the video bits of HDMI are basically DVI, so it should work.
posted by mrg at 7:46 AM on February 17, 2010

There also apparently exist video cards with (at least) two DVI ports and one HDMI port:


Very pricey. For as much as you'd pay for one of those, you could just get another computer to connect to your TV...
posted by jrockway at 7:50 AM on February 17, 2010

Response by poster: That might be possible. My issue was that the DVI to VGA/DVI splitters only display one at a time. As the TV has only a VGA port I'd have to use a DVI to VGA adapter on that splitter then I might run into the only one signal working at a time issue.

Not sure if DVI to HDMI would work as it's all digital and should feasibly be able to be mirrored. I could hook up a laptop and just stream things via shared folders/WiFi....that might be the best option
posted by PetiePal at 7:54 AM on February 17, 2010

Be careful with getting a triple head single card; many of them only support two heads at once. The ati 5xxx series cards do support triple head on a single card, but one of them MUST be displayport; you can't use both hdmi and 2x dvi at once.

HDMI is DVI-D with audio in a different plug - it's not 'mostly' the same, it is the same digital video standard.

As you say though, you can't get one head on your 4870 to output both VGA and DVI simultaneously. That's fine though; VGA is analog, so you'll definitely get better quality from your pc using DVI or HDMI especially if it's a run of more than a couple of meters.

One solution would be a powered HDMI splitter (like one of these) to mirror your 24" and an HDMI lead to run to the TV - your pc will think it has two screens, but the TV will get the same signal the 24" gets; which also means you'd run the same resolution on both screens which may be an issue. The reason I recommend an HDMI splitter rather than DVI splitter is that they tend to be cheaper and better quality as there's more demand for them. Also, avoid non-powered DVI splitter cables - unless you have the setup juuuuust right, they're very prone to interference and sync problems.

You'll need a DVI-HDMI lead to go from your PC to the splitter, an HDMI-HDMI lead to go to your TV, and either DVI-HDMI or HDMI-HDMI to go to your 24" depending upon whether it has an HDMI input or not.

Option B is a cheap ATI card to run as a third head in your PC, and run the TV as a separate screen - either VGA or preferably HDMI-HDMI. The advantage here is you can run at a different resolution to your 24" dells. It doesn't have to be the same spec as your main card, as you're not going to use it for gaming or the like, and you don't want to crossfire it. Something like a radeon HD 3450 would be ample for video playback, assuming you have the spare pci-e slot.

Don't try it with nvidia though; ati/nvidia don't mix well for triple head.
posted by ArkhanJG at 11:16 AM on February 17, 2010

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