[HN Gopher] Using a laptop as an HDMI monitor for an SBC
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Using a laptop as an HDMI monitor for an SBC
Author : hasheddan
Score : 94 points
Date : 2025-10-09 13:36 UTC (9 hours ago)
(HTM) web link (danielmangum.com)
(TXT) w3m dump (danielmangum.com)
| kevmo314 wrote:
| Since there's monitors that work over USB-C, could one replace
| the capture card and somehow get the laptop to pull video like a
| USB-C monitor?
| detaro wrote:
| not really. The video stuff needs explicit hardware support, so
| the laptop would need to include what's essentially a capture
| card already. It'd be awesome if vendors did that, but to my
| knowledge nobody does.
| 05 wrote:
| I'm thinking a better solution for console would be an SSH to
| serial bridge using just a spare ESP32 and something like
| ESP32SerialSSHProxy[0]. Haven't tried myself yet, and there is
| suspiciously few stars on that repo, but that would be a nice
| lights out-ish management system for some hidden away home
| automation server.
|
| [0] https://github.com/programminghoch10/ESP32SerialSSHProxy
| jonathanberi wrote:
| That works _sometimes_. It can be flaky.
| hasheddan wrote:
| You can also throw together a cheap software KVM switch[0]
| using an ESP32 or similar.
|
| [0] https://euer.krebsco.de/a-software-kvm-switch.html
| thesandlord wrote:
| If you have an iPad with a USB-C port, you can use the free Orion
| app to do this too
|
| https://orion.tube/
| rahimnathwani wrote:
| My son uses the Genki Studio app on his iPad. It works well
| enough without payment.
|
| https://apps.apple.com/us/app/genki-studio/id6466343285
|
| I don't know how Orion compares.
|
| The home page says the one-time IAP unlocks 'AI-powered 4k
| upscaling', which sounds useful.
| dylan604 wrote:
| > The home page says the one-time IAP unlocks 'AI-powered 4k
| upscaling', which sounds useful.
|
| To what end? For displaying on a tablet only? Does it provide
| screen capture to save that 4k version?
| rahimnathwani wrote:
| iPads have high resolution screens.
|
| Cheap USB capture devices usually support a maximum of
| 1080p@60Hz output. If you buy a random '4k' USB capture
| device, it probably supports up to 4k _input_ but then
| scales it down to 1080p for output.
|
| So perhaps 4k upscaling on the ipad will make the image
| look better.
| morganw wrote:
| There's also the issue of chroma subsampling, giving you
| YUV 4:2:0 or 4:2:2 instead of YUV or RGB 4:4:4
|
| This page https://obsproject.com/forum/resources/capture-
| card-document... warned me about it, but I haven't seen
| any updated info on the newer AVermedia or Magewell
| interfaces, for instance
| https://www.magewell.com/products/usb-capture-hdmi-4k-pro
| This gives 4k60 4:4:4 only on the loop-thru output,
| higher resolutions require 20GBps USB 3.? but my Mac only
| goes to 10. I'd need Thunderbolt capture which start
| around $1000 https://www.bhphotovideo.com/c/product/15005
| 55-REG/blackmagi...
|
| I'm using an Elgato CamLink 4k at 1080p60 for now & I'm
| wondering if the awful mouse feel in Linux (with a Mac
| for display) is maybe due to delay. Going to get a cheap-
| ash monitor to simplify. I thought it would be nice to
| have my 6k Pro XDR display have windows from all
| computers, but it's just too messy.
| bombcar wrote:
| I presume this software has two users - those wanting to
| read text on a server, and those wanting to use their iPad
| as a screen to watch movies from a DVD or similar player.
|
| The second may like upscaling.
| MBCook wrote:
| I did that just last week to install Linux on a micro-PC I
| have. Its only display output is HDMI and I didn't want to
| unplug it and move it over to my TV just for the short time
| necessary to install a base system + SSH.
|
| Worked great!
|
| I've used the app for other things too. It's a great solution
| if you already have an iPad.
| hasperdi wrote:
| Does anyone know anything similar for Android?
| CYR1X wrote:
| Yes, $5 USB HDMI capture cards exist?
| actionfromafar wrote:
| Usually slow
| gsich wrote:
| In what regard? The common Macrosilicon chip MS2130 has
| <100ms.
| actionfromafar wrote:
| 10 fps isn't great, latency wise. Even typing or using a
| mouse is very clunky.
|
| I may have been unlucky, but I have seen even worse.
| detaro wrote:
| 100ms latency, they do at least 30fps.
| dlcarrier wrote:
| There's off-the-shelf semiconductors that perform the
| conversion in hardware, so all the dongles need is a simple
| breakout board for the component.
| RamRodification wrote:
| Crazy times
| frankus wrote:
| This would have been super helpful like 20 years ago when I was
| on the data center floor trying to debug rack-mount (headless)
| Linux servers. The center had like one KVM "crash cart" that
| needed to be plugged into a spare outlet in the rack that wasn't
| always easy to come by.
|
| I'm sure we could have improved on that setup but we were an
| inexperienced skeleton crew on a shoestring budget and not the
| best management.
|
| I always thought it would be great to have a "laptop without a
| motherboard" to manage these, and this is close enough given the
| price of the redundant hardware now.
| bombcar wrote:
| We actually HAD literally that - I don't recall which model it
| was, but someone found a laptop that internally had PS/2 and
| VGA I believe, and had rewired it to have cables hanging out of
| it.
|
| Advantage - battery still somewhat worked so you could get a
| few minutes (often all you needed) with just that.
| Havoc wrote:
| You can do similar with an Android tablet and a usb adapter
| hard_times wrote:
| is there no vendor offering HDMI-in or Display Port-in?
| EnigmaCurry wrote:
| GPD Pocket 4
| jollyllama wrote:
| It always used to baffle me that there wasn't support for this
| (or the historic equivalent) 20 years ago.
| dylan604 wrote:
| 20 years ago it would have been prohibitively expensive.
| theallan wrote:
| The Minisforum V3 does:
| https://store.minisforum.com/products/minisforum-v3 .
| rzzzt wrote:
| Some Alienware laptops had an HDMI input:
| https://youtu.be/Otln0Ao2z6M?t=36
| belthesar wrote:
| For use cases like attaching to an SBC or really any other
| computer, I'm sure this is great, but there are also USB crash
| cart consoles that can be gotten pretty cheaply like the NanoKVM-
| USB[0] or Cytrence's KIWI[1]. This gets you both video, keyboard
| and mouse.
|
| [0]
| https://wiki.sipeed.com/hardware/en/kvm/NanoKVM_USB/introduc...
|
| [1] https://www.cytrence.com/product-page/cytrence-kiwi
| rahimnathwani wrote:
| Is there anywhere I can buy a NanoKVM-USB? The page you linked
| has a 'preorder' page linked, but I'm not sure how long I'd
| have to wait and whether it's an actual product that people
| have successfully used.
| galaxy_gas wrote:
| GLI Comet is much better from my experience.
| rahimnathwani wrote:
| Can GLI Comet allow my laptop to control a device without
| needing a network connection?
|
| That seems to be what NanoKVM-USB does. But GLI Comet seems
| to be KVM-over-IP?
| all2 wrote:
| You might be able to use something like usbipd to forward
| the USB port from your target machine?
| galaxy_gas wrote:
| I use Comet in remote field by plug the ethernet it
| expects to the laptop. Both will set up the link local IP
| and accessible in browser without internet
| mwpmaybe wrote:
| Different use-cases. The Sipeed product comparable to the
| GL-RM1 is the NanoKVM Cube. Comparable to the GL-RM10 is
| the NanoKVM Pro (Desk).
|
| (Of course you could use the Cube on a crash cart, too.
| Just like you can use the butt of a screwdriver to hammer a
| nail.)
| chazeon wrote:
| Aliexpress has them
| mwpmaybe wrote:
| I see them on Amazon, sold by WayPonDEV. I've bought several
| NanoKVM brand devices from them and haven't had any problems
| (yet).
| craftkiller wrote:
| Those both look very nice, but I am disappointed that neither
| lists support for DP alt-mode as an input despite having a
| type-c port on the input side. If I were to buy such a device,
| I'd want it be future-proof while also supporting legacy video
| input like HDMI, but these are legacy-only. Good for my old
| raspberry pis and my ancient sandybridge NAS, but these days I
| only buy computers capable of single-cable operation (with
| exceptions for power cables for power-hungry devices like
| desktops).
| belthesar wrote:
| I feel like this is kind of looking a gift horse in the
| mouth, especially for the cost of these units. Certainly not
| impossible to add, but an increase in the BOM vs. the loads
| of off-the-shelf super cheap HDMI capture chips available,
| and questionable compatibility (DP Alt Mode is getting
| better, but plenty of devices still have interesting quirks
| with it depending on implementation). These devices aren't
| made with daily driving a system in mind so much as for
| installation and recovery of a system.
|
| Would it be handy to have this all in one cable on both ends?
| Sure, absolutely, that'd be killer. I personally don't think
| it's too big of an ask to use two cables in an installation
| or recovery case though, and if your devices only have USB-C
| ports for video out, an active USB-C to HDMI via DP-Alt cable
| can be had to meet that need.
| EvanAnderson wrote:
| Is there a VGA "story" for these devices? Most of the Dell and
| HP servers I'm physically proximate to don't have HDMI video.
| VGA connectors abound on the gear I work with.
| detaro wrote:
| worst case a VGA-to-HDMI adapter, they are less than 20 bucks
| but extra box/cables of course.
| EvanAnderson wrote:
| I've had poor luck with the couple of VGA-to-HDMI I've ever
| used over the years (latency, poor video quality) so I
| guess my question was more "Are there any known-working
| good adapters for VGA for these?"
| mwpmaybe wrote:
| > I've had poor luck with the couple of VGA-to-HDMI I've
| ever used over the years
|
| Yes, they're terrible, but...
|
| > latency, poor video quality
|
| For a crash cart? Who cares. For everything else...
|
| > Are there any known-working good adapters for VGA for
| these?
|
| No, you're AOL.
| yuvadam wrote:
| Openterface Mini-KVM also works great [1]
|
| [1] - https://openterface.com/
| mmetzger wrote:
| This is my current pick - simple, works exactly as expected,
| very small. Only thing I ever fight with is remembering to
| accept Mac OS's warning about connecting a USB device.
|
| For just video (or w/ separate keyboard/mouse), the Genki
| Shadowcast devices work really well.
| mwpmaybe wrote:
| Came here to endorse the NanoKVM USB. It's a great little
| device. Wendell made a video[0] on it. The web interface is
| super handy.
|
| I keep one in my tool bag and I've been meaning to buy a second
| one for a dedicated crash cart.
|
| I can't speak to the Kiwi or the Openterface as I haven't tried
| those.
|
| 0. https://www.youtube.com/watch?v=SAbyQcpR-yQ
| crimsontech wrote:
| I use a Cytrence Kiwi myself, really handy bit of kit, I just
| wish it could do higher resolution, even if it meant dropping
| the frame rate.
|
| I also have a PiKVM with the switch for network level access
| which works really well too.
| jmmv wrote:
| > digging up an HDMI monitor, finding somewhere to put it, and
| connecting it to the device is an annoying process. Furthermore,
| if I'm on the go I almost certainly don't have easy access to an
| external monitor.
|
| This has annoyed me many times as well with the headless
| computers I run... until recently, when I bought a USB-powered
| 7-inch HDMI monitor for an embedded project that didn't go
| anywhere. But now I have a spare little monitor that I can easily
| use in these situations and even carry it around if necessary.
| blensor wrote:
| You may be interested in this then
| https://github.com/mgschwan/viture_virtual_display
|
| Or now that I think of it, just use the glasses with a regular
| hdmi adapter ( but no 3dof tracking then )
| bombcar wrote:
| Those tiny HDMI monitors are soooooo useful in so many
| situations, especially if they do pass-through.
|
| I like https://feelworld.ltd/collections/5-6-inch-camera-
| monitor/pr... or similar, $100.
|
| I use it for projection - then I can run the projector as a
| second monitor through this thing (or similar) and not have to
| use binoculars to see what's on the screen from the back of the
| room.
|
| Larger ones can be used as portable second monitors, too.
| dgfitz wrote:
| I was stuck in a very remote location trying to update vehicle
| software. I needed both a monitor and keyboard (long story,
| serial wasn't outputting, no ssh, partition table was hosed)
| and I had neither a keyboard nor a monitor.
|
| I now carry a little HDMI screen and not one but two portable
| keyboards with me for all work travel. One of the keyboards is
| a larger but rolls up, the other is tiny but also has a mouse
| built into a touchpad.
|
| These devices have saved my bacon more than a few times. Highly
| recommend.
| asplake wrote:
| Anyone using a Intel iMac as a monitor for their much faster
| Apple CPU MacBook Pro? Wishing "target display mode" was still a
| thing...
| mwpmaybe wrote:
| You can modify the internal electronics to accomplish this.
| YouTuber Luke Miani did it a couple years ago. A quick google
| brings up a few guides including a couple user-contributed-but-
| ostensibly-QC'd guides on iFixit.
| crumpled wrote:
| I saw a video of this guy (the github project author) using the
| Lilygo T-deck as a VNC console. It's a fun looking solution, but
| it requires wifi.
|
| https://github.com/moononournation/T-Deck/blob/main/ArduinoV...
| jwr wrote:
| I use this approach with a long-throw HDMI microscope, cheap ones
| are available on Aliexpress. I put one over my desk, and I get
| the output with reasonably low latency through a HDMI capture
| adapter on my computer screen. Very useful for electronics work
| or taking a closer look at stuff.
| suddenlybananas wrote:
| Now is there a way to use a laptop's keyboard as input as well?
| chazeon wrote:
| you can just buy a nanokvm
| datadrivenangel wrote:
| You can also get an HDMI driver to turn the laptop screen into an
| HDMI monitor... Janky if you glue the board to the back of the
| screen.
| netsharc wrote:
| Matthias Wandel demoed a "brainless laptop": a screen and
| keyboard that can be "mated" with a Raspberry Pi:
| https://www.youtube.com/watch?v=CFA7iAnYZMs
| Lerc wrote:
| I have been looking at things like this and wondered if there is
| scope for an open source project to design boards that provide
| power and data access to a variety of common old laptop panels
| (and keyboard+touchpads) along with a holder for a compute
| module. Then let people lay out the location of their USB ports
| etc. in the shape of the motherboard of their old laptop and get
| one run off by JLCPCB or PCBWay
|
| I have several old laptops that still have good screens and
| keyboards, It would be nice to repurpose some of them. They are
| certainly large enough to house a compute module with plenty of
| extras.
| fmj wrote:
| I'd definitely be interested in a project like that, but I
| think customizing a PCB layout and sending it off for
| manufacturing would be too much for many people that would
| otherwise be interested in it. I think a project like that
| would gain more traction if it focused on designing high
| quality boards for a few popular laptop models (MacBooks or
| ThinkPads IMO) and making those available via on demand
| manufacturing and/or crowdsourcing a bulk run.
| PaulHoule wrote:
| Reminds me years ago of having a Nintendo Gamecube but no actual
| TV and just playing it on a computer with a TV capture card.
| thesandlord wrote:
| I played all of KOTOR2 on Xbox using a capture card without
| sound. Good times.
| ius wrote:
| Note most (all?) video players introduce quite some playback
| latency by default due to buffering - which is _really_ annoying
| using them as a 'monitor'.
|
| You'll want to look up the flags/settings for low latency
| playback to make it more usable, e.g. for mpv:
| https://mpv.io/manual/stable/#low-latency-playback
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