Thanks, but that's orders of magnitude fancier than I'm looking for.
I had a feeling that it would be, and that's fine. I just needed you to understand the level of knowledge and experience on tap here. After all, you're asking a bunch of strangers for advice, so it's useful to know whether they're just keyboard warriors or peope with real life practical experience in this area.
This is me, with laptop/ cameras, turning up at schools/societies and wanting to plug in, or visiting speakers doing likewise, to show Powerpoint stuff mostly.
Screens/projectors + laptops sometimes predate hdmi, cameras don't have VGA.
The visualiser I used last had XGA out. Also an HDMI connection but I'm not sure if it was for input for picture-in picture.
To use it I had to physically undo the (school) desktop connection and replace with the visualiser.
Would a very cheap 2-4 in, one out switches do that, or what sort of problems might I find?
Cables are usually short, but then snake god knows where to a ceiling projector or whatever.
Thanks for filling in a bit of the background.
The sort of mechanical switches you linked to will generally work just fine. The only things to watch are that they're metal cased (for shielding), and that you use decent shielded VGA cables, and that there's sufficient power in the VGA output of your source to drive the cable length.
That first two-way mechanical VGA switch, that looks like it might have a plastic case. Have a look at this one instead:
2 Port VGA SVGA Monitor Sharing 2 to 1 Selector Switch
Driving the cable properly is important. You're trying to get the image down all the bits of cable in the chain from source to display without too significant a loss. How much loss depends a lot on the cable quality, its length, and what other devices and joints the signal has to hurdle on the way. What you can never know as someone visiting 'after the fact' is how cheaply the install was done: Did someone who knows what they're doing install decent cable, or was it specified by a person with no real technical experience who just chose the lowest cost option without much understanding of the consequences?
The other immediate factor is how the cable is being driven from their gear compared to yours. The graphics card from a desktop PC will generally be able to throw a little more power in the signal down the cable so will cope better with longer lengths or poorer cable compared to a laptop. You can even up the playing field by using a powered VGA signal interface. This could be something as simple as a VGA distribution amp.
Why bandwidth is important?: When you have insufficient bandwidth and other problems such as impedance mismatches in the display chain then you'll start to see some obvious problems. You'll see ghosting (
see link), a softness in the image as resolution increases, and in really bad cases there'll be bending and image distortions.
In order to specify the distribution amp you need to know how much bandwidth your intended signal requires. This will be determined by the native display rate of the projector. Since you're dealing in the schools market, and that's a market driven by price, then in my experience you'll be dealing with two resolutions in general in the field - SVGA (800x600) and XGA (1024x768). Both of these are 4:3 picture ratios. Most of the price-fighter projectors fall in to one camp or the other, but XGA should be more prevalent now within classrooms as the older SVGA models have died and been replaced. XGA is very common in the ultra-short throw models. You may come across some some WXGA models too (1280x800). Once you know what you're dealing with, it is fairly easy to find the bandwidths required online, but here's a quick summary:
XGA.........4:3 format.....1024 x 768 @ 60Hz = 71MHz
WXGA....16:9 format.....1280 x 800 @ 60Hz = 92MHz
SXGA.......4:3 format.....1280 x 1024 @ 60Hz = 118MHz
As a general rule of thumb, any peripheral device in the chain such as an electronic switch or distribution amp should have a
minimum of double the bandwidth of your highest resolution signal. It's better though to spec at a x3 multiple if possible. As with all things, the higher bandwidth means better quality components and so that has an impact on price.
Now you know how to spec the peripherals, it's time to look at the claims of any manufacturer's gear to see if it matches up. Remember, if it's a mechanical switch (clunking buttons) then this doesn't apply as there's no electronics involved.
If you're looking at a device and the manufacturer can't give a bandwidth figure then move on to the next. It's not enough to claim "high resolution" or say it's compatible with some or other resolution. Just because a device passes a signal it doesn't automatically follow that it will do a good job.
If you're on a budget then go for used gear from reputable quality brands. Extron and Kramer are both very good. There's lots of their gear in the used market. It's well engineered, reliable, and cheap as used buys. My personal recommendation for you for a signal interface interface is an Extron RGB109. This is available as an 'RGB109plus' and an 'RGB109xi' but both do the same basic job. There's an RGB109plus on Ebay with a BuyItNow of £12. Absolute flipping bargain. This would have been over £200 new, but there's not much call for VGA gear now so used prices are rock bottom. [Type in:
Extron RGB 109 Plus Video Interface (E152) ] You'll need a 15pin D to 5 BNC breakout cable to go with it along with a 15pin D female back to back adapter. Remember to spec for decent shielded cable even on the small runs.
I like the Extron because it has adjustable output power (peaking) which means you can tailor the amount of drive it provides to meet the needs of your display.
As for the HDMI switches, that's much simpler. The gear will either work or it won't. There's a bit more to it than that, but with digital there's a very definite cut-off point where failure means no signal at all. We call it the Digital Cliff. If the gear is crap then you'll find this very quickly.
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