How can I connect two external touchscreens on a Latitude E7240?

Question

Hi,we use a Dell Latitude E7240 for navigation on a sailboat. This Dell Latitude is located on the interior charttable.Now we would like to add two waterproof daylight visible touchscreens on the outside helmstations and connect them to the Dell Latitude.All three screens (1x internal and 2x external) should always show the same information.Any one of the screens should allow it to control the software of the Latitude. We will not manipulate the software from more than one screen at a time.But, we need to seamlessly switch between the input touchscreens and the interior screen with mouse.Say we sail from the portside exterior helmstation and control the navigation from there. Than we tack or jibe and continue by steering from the starboard exterior helmstation. We would than seamlessly like to use the touchscreen on that helmstation to control our navigation.Beeing able to switch a screen off when not using it would be beneficial but is not a necessity.How can we achieve this best? A hardwired solution is preferred.Thank you for your input.Fran

jphughan · Accepted Answer

@Lady Rover A touchscreen display setup involves a video output element and a touch input element. I'll address both here.

The best solution would be to get an E-Port Plus docking station and hardwire/fasten everything to that. You'd connect the video outputs to each display to either the DisplayPort or DVI outputs of the docking station, and then you'd have USB cables coming back from each display for touch input. Those could be connected to the dock's USB ports. You don't have to switch which display is used for touch input at any given time or even switch between touch and cursor input. All touchscreens and your mouse can all be active simultaneously, just as you can have multiple mice connected to the same PC and they'll all control the same cursor based on which is being used at any given time, with no need to switch which mouse is "active" and no separate cursors for each mouse within Windows. This dock-based solution is a bit more expensive than the alternative I'm about to describe (although E-Port Plus docks are inexpensive these days), but it means you'll be able to make this a fairly permanent installation while still retaining the option of removing the laptop from the docking station relatively easily whenever that might be necessary/convenient.

A less expensive but less convenient option would be to use the Mini-DisplayPort output to run both of your external displays. The way you would do this is by using a device called a DisplayPort MST hub. This is one example. The USB connector on that device is just for power, but Mini-DisplayPort allows a single output to run multiple displays independently, i.e. not mirrored, although you can certainly CHOOSE to mirror the displays if desired. (By comparison, other devices called "splitters" will split a single source video signal across multiple outputs and can therefore ONLY mirror, with no option to run displays independently at all). And then for the touch input from each display, you'll have separate USB cables plugged into the system, or if you don't have enough USB ports, you'd get a USB hub. But this means that you'll have a power adapter, an MST hub, and a USB hub or multiple USB cables all connected directly to the system, rather than having everything connected to a docking station and having the system just dropped into a dock.

Hopefully this helps!

jphughan · Answer

@Lady Rover  Two quick notes to add to my reply above.  First, regardless of whether you use the dock or the MST hub I suggested, the resolution of your two external displays would have to be no more than 2560x1600 60 Hz or 4K 30 Hz each.  And second, I just experimented with my setup involving a built-in laptop display and two external displays, and I wasn't able to get Windows to mirror the same signal across all three displays.  I could mirror one image between any two of those displays, but the third display was always run in Extend Mode, i.e. displaying separate content.  You might encounter the same issue.  But even if you don't, be aware that if you intend to mirror across 3 displays, ideally they would all have the same native resolution, because when mirroring, you can only choose resolutions that are common to all displays involved in the mirror.  So for example if your internal display is 1920x1080 and your external displays are 2560x1440, then the external displays would have to run at 1920x1080 to mirror the built-in display.  The issue is that displays don't look very good when run below their native resolution.  At a bare minimum, I would make sure that all displays have the same aspect ratio (proportions), i.e. 4:3 standard, or 16:9 widescreen, or 16:10 'tall widescreen'.  Running a lower resolution isn't great, but running a resolution that is lower and a different proportion from the physical display itself is worse.

Lady Rover · Answer

Great reply. So it is possible to do it.Thank you so much. I'll look into both solutions suggested.Fran

jphughan · Answer

@Lady Rover Sorry for the triple post here, but I've been mulling this over in my head. Based on my test above, this might be a situation where the limitation of a conventional video splitter actually becomes an advantage. The reason is that when you use a splitter, Windows doesn't realize that there are multiple external displays. It only sees a single external display, with no knowledge that it's being mirrored to multiple targets. And consequently, the limitation of not being able to mirror across 3 displays won't be an issue, because as far as Windows knows, there aren't 3 displays. You would instead be configuring Windows to mirror the built-in display to "the one external display that Windows sees, which just so happens to be multiple physical external displays". Of course this setup would mean that the external displays would ONLY ever be able to be mirrors of each other. You could technically run those two displays independently of the built-in display if that were ever desirable, but you would not be able to run the external displays independently of each other. Does that make sense?

If you want to go this route, the best way to do so would be with an HDMI splitter, like this one. (Note: This type of device is not to be confused with an HDMI switch, which allows you to connect multiple displays but only have one active at any given time, and sometimes allows you to connect multiple sources to choose which output shows which source at any given time. That is not what you need.) From that splitter, you'd run HDMI cables out to your displays.

If you do NOT want to use a docking station, you would just connect that splitter straight to the HDMI output built into the Latitude E7240 itself. If you DO want to use a docking station, then you'd want to rely on the dock's DVI output, since DVI and HDMI signals are electrically identical up to 1920x1200 resolution. In that case, you'd just need to add a female HDMI to male DVI adapter in order to plug that splitter into the DVI output of the dock. Here is an example. Note that since you'd be using a DVI source here, your displays would be limited to 1920x1200 resolution max. And since you now only need a single external video output, you technically could even get a regular E-Port docking station rather than an E-Port Plus; the latter allows two independent video outputs from the system, but you're not going to be using that.

Lady Rover · Answer

Thank you for the additional remarks.So, ideally I find touchscreens with the same dimensions as the built in Dell display 1366x768 pixels. 16:9Still that might be hard to find as waterproof touchscreen with 1000nits.So its the aspect ratio 16:9 I need to keep.The displays outside will most likely 7' or 10' so I guess their resolution might be smaller than the one of the Dells internal display.

Lady Rover · Answer

You truly deserve the Gold Star rating. Thank you!
If I have trouble actually putting this in reality, I'll get in touch, but right now it all makes sense.
Mind you I'll not be able to actually go for it before May 2021. But than!

jphughan · Answer

@Lady Rover  Happy to help!  One other item that occurred to me was a potential issue of having two separate touchscreen input source devices when there's only one display as far as Windows is concerned, but upon further research, it seems like that would be ok.  If you ever did want to show different content between those two external displays (using a solution other than the HDMI splitter), then Windows has a mechanism to allow you to tell it which touchscreen devices corresponds to which display, since it doesn't have a way to know that automatically.  Good luck whenever you get to it, and if I don't see this thread in May 2021 for a follow-up, feel free to send me a private message.