Wireless laptop to a projector in a hall. What bits?

[Justin Passing]

Hi
We (small society) use visitors' laptops and trailing wires, to connect to our old (VGA era) projector.
We'd like to do it without trailing wires.
I don't know what the £30 to £300 adapters I've seen, do exactly. Can we just plug a transmitter into the laptop and receiver in the projector (or lead to the projector)?
Do this century's laptops come with Wifi drivers built in?

Speakers (people) can bring anything from XP laptops to the latest anorexic Mac thing. Usually Powerpoint, sometimes peculiar(??) video from eg ultrasonic medical cameras. No idea what format they could be. (Does that matter as long as their laptop can handle it?)

The hall also does have a ceiling-installed Epson.
https://www.epson.co.uk/products/projectors/installation/epson-eb-1945w.
https://files.support.epson.com/pdf/pl1940/pl1940ug.pdf

We use a VGA adapter and a Mac adapter if necessary, which trail across the floor....

It looks like the ceiling Epson's HDMI is connected - sorry the pic is lousy:

as it seems the HDMI ole has a plug in it. I assume the lead comes out somewhere! Access to the hall is only when we have meetings so I can't looksee easily.

If we had to leave something dongling from the projector, I expect we could.
Lastly we want to replace our own laptop. Is there anything we would need it to have spec-wise to enable latest video playing?

Ta

 

[Lucid]

As you've already worked out, playing host to anything from an old steam driven laptop to the latest whizzy-bang super-thin Mac or PC-lookalike can be fraught with issues. The last thing you need is to complicate things further.

When it comes to laptops, wireless can mean all sorts of things. The small inexpensive wireless stubs are simply a way to make a non-Bluetooth laptop compatible with other Bluetooth enabled devices, or to upgrade the Wi-Fi capabilities to take advantage of the extra speed from a faster wireless router. Neither are the answer to your wireless video requirement.

In the middle-ground you have wireless adapters that enable a basic display to talk to tablets and smartphones that use a screen-sharing technologies such as Miracast or WiDi. The crucial bit of this is that the source devices already have the tech built-in. That's not going to help you with older laptops or devices that don't support the tech.

At the top of the tree you have what is in effect a wireless HDMI lead.

This sort of tech is ideal where you're dealing with a variety of sources because there's no reliance on a laptop to run any software or have any sort of advanced wireless feature built in. The laptop plugs in to a box that then sends the signal wirelessly to a receiver box with a HDMI output connected to the projector.

However, it's not all plain sailing. You still have to deal with the different types of video connector (VGA, HDMI, DisplayPort), as well as all the Apple Mac variants (USB-C, Lightning, mini-DisplayPort), not to mention setting the laptop resolution to match the either the 1024x768 or 1280x768 resolutions catered for by the WXGA display panel inside the Epson.

Your goal here is to end up with a HDMI output to connect to the transmitter box. Fortunately there are a wide variety of adapter cables that do the job of no only giving the right shape of connector, but more importantly, they electronically convert signals from one format to another. This translation part as really important; I can't stress that enough, particularly for analogue (VGA) to digital (HDMI) conversion . Simply connecting the pins of one socket type to the pins of another won't do the trick. That would be like you phoning someone in a country where you don't speak the language and they don't speak English. You're physically connected, but neither can understand each other because there's no one to translate.

Optoma is a well known and respected projector brand. Their WHD200 Wireless HDMI System is around £200 and would be a good starting point. Here's some info about Mac adapters. LINK

 

[Justin Passing]

We have adapters so it's just a Tx-Rx we'd need, then.
As the rx end needs separate power , a simple hdmi cable is looking attractive again.

The only unknown seems to be the aspect ratio that the video expects to be available, but since the projector does eveything up 1600 x 1200, that shouldn't be a problem?
Certainly not something we can do anything about.



One speaker has problems I don't understand :

"I'm not sure what the problem in running video clips is, but I do know that it is commonplace. The clips are ultrasound recordings made on commercially available clinical ultrasound machines but they frequently need reformatting. At the major international echocardiography conferences they have upwards of 30 technicians dedicated to this task."

EH?
Maybe they're trying to use multiple screens or something. Does anyone have other ideas on what might be his "commonplace" problem?

 

[Lucid]

We have adapters so it's just a Tx-Rx we'd need, then.
As the rx end needs separate power , a simple hdmi cable is looking attractive again.

The only unknown seems to be the aspect ratio that the video expects to be available, but since the projector does eveything up 1600 x 1200, that shouldn't be a problem?
Certainly not something we can do anything about.



One speaker has problems I don't understand :


EH?
Maybe they're trying to use multiple screens or something. Does anyone have other ideas on what might be his "commonplace" problem?

Aspect Ratios:

Your projector has two video/data connections wired up. One is HDMI, the other is a VGA socket. HDMI is digital and VGA is analogue.

In theory they should give identical results up to the native resolution of the projector which is 1280x800 pixels. In practice, as long as a digital signal makes it to the projector intact then it generally looks a bit more stable than analogue. With analogue, the quality of the cable and the distance the signal travels has an effect on how much amplitude is lost along the way. It's possible to use a Line Driver (a booster, if you will) to compensate for some of the loss. However, if the cable is not great quality then no matter how much boosting, it still won't overcome the bandwidth bottleneck in the cable which acts to soften and smudge fine detail.

There's another factor too. It's how much power the source device is able to push through the VGA socket. The graphics card in a desktop PC is normally faily potent. I've seen them drive 10m of middling quality VGA cable quite easily. Laptops tend not to be quite so highly spec'd in power though. They're happy driving 1.5-3.0m of VGA cable on a desktop, but the results might not be so good through the same 10m of cable that the desktop was happy to drive.

So, if VGA struggles with distance and power, the obvious question is why keep it?

The answer is partly in legacy compatibility, and partly in that it can handle a broader range of signal resolutions, aspect ratios and refresh rates.

HDMI uses a narrowly defined set of what we refer to as video timings. This is a combination of resolution (which includes aspect ratio) and refresh rates. Page 179 in your manual lists the HDMI display timings. Compare that to the timings listed on page 177 and 178 for VGA. You'll see a lot more listed, and specific listings for older Macs.

There are four optimum resolutions for your projector. 'Optimum' is defined as the signal resolution can be displayed without needing to be expanded or reduced or distorted in any way. We call this 1:1 Pixel Mapping. These four resolutions are:

XGA - 1024x768 - a 4:3 PC & TV format

HDTV - 1280X720 - a widescreen HDTV 720p format

WXGA - 1280x768 - a 16:9 widescreen PC format

WXGA - 1280x800 - a 16:10 widescreen PC format

If a laptop is set to output any of these resolutions, and the projector's Aspect setting is selected as Auto or as Native, then you will get the sharpest clearest image that the display panel is capable of producing.

The other aspect ratio choices from the projector menu will result in the image being expanded or shrunk, often with either a squashing or stretching effect that would turn a circle in to an oval, or it can show up as cropping so that some portion of the image is missing.


The thing that gets a bit messy is when the laptop is a different resolution to the projector.

Your speakers will generally want to use their laptop screen as the monitor during their presentation. Since most laptop and desktop VGA and HDMI outputs support only a single resolution at any one time, then if the laptop screen is say 1920 x 1080 resolution, the choice is either to feed the projector with a signal that it then has to compress, or run the laptop at 1280 x 768 which results in either a shrunken image or one that looks horribly distorted on the laptop screen.

There is a simple answer to this. Buy a desktop monitor that is also 1280x800 resolution, and then have the laptop set to 'external monitor only' mode and feed the one output signal in to a two-way distribution amplifier (an amplified splitter). Thus the presenter gets a good image and so does the audience.


The ultrasound clips; this isn't anything to do with resolutions or aspect ratios.... yet. It's the video format of the signal from the ultrasound equipment. My guess is that it is a custom format. In other words it's a PC or video platform compatibility issue. The fact that there is quite a large team of Tech's dedicated to the task would seem to confirm this.

Microsoft PowerPoint will support several different video formats as standard for embedded video clips. Here's a useful link. However, it's not exhaustive, so there's always a chance that some or other file will need to be converted.

Standalone playback is more flexible. Programs such as VLC media player will handle most of the commonly used video and audio file formats. LINK


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[Justin Passing]

Nub then seems to ask the guy if he can display the video on his own laptop. If so then showing it should work, give or take some squishing. Does that sound right? I've looked for Specifications on U?S imagers but not found anything.

I've never known VLC not play something.

So if we skip the wireless aspect for now, and assume laptops will all output HDMI, we'd either use VGA, short distance, to our old proj on a stand in the middle of the room using a "to VGA" adapter.
If we use the Epson then an HDMI cable would be 30ft or so total. OK?

VGA power doesn't sound onerous, at 0.7V into 75R. Is impedance or risetime the problem? I have a decent scope (Agi54616), I could have a look - but so far the image is ok. I have an Extron 109xi - never needed it.

 

[Lucid]

Yep, that's about it. So long as it plays on the laptop then that's fine. Also, as long as the laptop and projector are set up correctly then the aspect ratio of the source video file should be maintained.

I don't think it's safe to assume HDMI Out on all laptops. It is certainly becoming more common, but it's not yet unversal on new gear, and you can't guarantee what people might turn up with. Still, convert from VGA to HDMI if required, and that should take care of things.

30ft for HDMI @ 1280×800 60Hz is easy with any High Speed rated HDMI cable.

VGA voltage isn't a lot, you're correct; and virtually no current. That's why cable attenuation becomes important, and shielding to avoid crosstalk. Yes, the rise and the fall time is an indication of the cable's bandwidth capabilities. As frequency increases with resolution and refresh rate so the leading and trailing edges of a square wave will obecome more skewed due to the inductance and capacitance of the cable. There's not really a lot that can be done to overcome the inherent limits of the cable other than to drive it to compensate somewhat for the attenuation and to put some pre-emphasis in the signal to create the impression of retaining sharpness.

The 109xi gives you a nice way to do all that and get a local display for the presenter. In the end though a better VGA cable is ultimately the answer.

 

[foxhole]

Worth advising visitors to bring a copy of their presentation on a memory stick , then you have more chance of being able to run it from your laptop.

 

[Justin Passing]

Worth advising visitors to bring a copy of their presentation on a memory stick , then you have more chance of being able to run it from your laptop.

We do ask them for that.
But we usually recommend they try to bring whatever laptop they normally run it on, because many don't realize their xxx software is linking to yyy files which happen to be lurking on the same machine.
We have had, "Oh it must be your laptop that's NO GOOD, it runs the videos fine on my old thing...".
One guy turned up with a memory stick, and a CD to read files from, and I had to go through his file changing the links from E: to F: or whatever it was his software was linked to ...

Is there any particular presentation software anyone would advise to have on our laptop? We're just about to get ourselves a new one. Also renting Office 365 so committee can all have current s/w instead of various neanderthal versions.
If there's some software which claims to handle a wider than normal range, then we could buy it. Powerpoint seems to try to cover.

Some file formats I found stated as output options :
"H.264/AVC VISUAL STANDARD, THE VC-1 VIDEO STANDARD,THE MPEG-4 VISUAL STANDARD AND THE MPEG-2 VIDEO STANDARD"
which appear to be thought of as commonplace.

 

[SFK]

Justin
For Video files I would recommend "VLC media player" as it plays almost all Video standards.
SFK