Using a laptop as an HDMI monitor for an SBC | Hacker News Reader

Using a laptop as an HDMI monitor for an SBC

danielmangum.com

168 pointshasheddan90 comments

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

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.

GLI Comet is much better from my experience.

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?

You might be able to use something like usbipd to forward the USB port from your target machine?

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

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.)

Aliexpress has them

I see them on Amazon, sold by WayPonDEV. I've bought several NanoKVM brand devices from them and haven't had any problems (yet).

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).

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.

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.

worst case a VGA-to-HDMI adapter, they are less than 20 bucks but extra box/cables of course.

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?"

> 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.

There shouldn't be more than few lines of delays in cheap VGA->HDMI adapters, they don't even come with one full frame worth of RAM.

Openterface Mini-KVM also works great [1]

[1] - https://openterface.com/

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.

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

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.

If you have an iPad with a USB-C port, you can use the free Orion app to do this too

https://orion.tube/

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.

> 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?

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.

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/1500555-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.

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.

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.

Does anyone know anything similar for Android?

> 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.

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 )

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.

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.

Exactly. I do quite a bit of dev on larger SBCs and it's much easier and more reliable to plug in a small HDMI monitor (powered through the USB) than it is to faff around with HDMI capture dongles, let alone networked KVM. The one I bought (on eBay, nothing special) has a wrap-around vinyl case which works rather like an iPad case in that it can function as a stand or as a screen cover, so you can just chuck it in a bag. Admittedly, it cost more than a capture card (I think it was around $70 USD in eBay), but that's still sufficiently cheap that if it and when it breaks I will not be devastated.

USB capture devices introduce latency, get surprisingly hot, can have frame rate issues, and streaming video from them seems much more CPU-intensive than, for example, playing an equivalent-sized h.264 video (I don't know why but presume it's because they encode using something basic like MJPEG). A portable display has none of these problems.

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.

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.

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.

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.

> I always thought it would be great to have a "laptop without a motherboard"

That's basically what a rack console is. At 1U it was skinnier than laptops from prior decades. They're not exactly a laptop form factor, but to get them smaller you would have had to accept a much lower screen resolution, which would risk some systems not being able to display (e.g. your server may have booted-up to 1280x1024 while your laptop could only do 800x600), or would have needed to be quite expensive to add an ultra-high DPI screen.

Still, at various times there were briefly devices like that available for purchase at closeout prices... like the failed "Motorola ATRIX lapdock":

https://www.cnet.com/reviews/motorola-laptop-dock-review/

https://www.amazon.com/AT-Laptop-Dock-Motorola-ATRIX/dp/B004...

I'd say the USB-HDMI capture card is a better solution all-around. I even prefer it to USB "crash carts" because you aren't dependent on the manufacturer keeping their proprietary software software updated for each subsequent Windows/Linux/Mac release.

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

I've used a few of these KVM products. Some quick thoughts:

ipkvm, I really like my 2 JetKVMs. It works very well, physically feels substantial, and the ATX power add-on makes remote management as good as any IPMI solution. I also have a sipeed NanoKVM and that works well, but I don't use it much at this point, just use the JetKVMs instead.

For usb KVM I'm trying to find something that works as a KVM so that I can use the nice display on my home computer but also control my work laptop. This is purely a convenience thing. I'm not trying to use the work laptop remotely or fool my employer. I just prefer my 4k oled display on my personal thinkpad over the crap 1080p dell display on the work laptop.

So I've tried two usb USB kvms.

Cytrence Kiwi - this is the one I settle on to use. The software works well and has had regular updates. It does keyboard capture which I never could get to work with the NanoKVM. The video quality is much better. Except for the inability to capture alt-tab is my only real complaint. :( However, they just (yesterday?) released a new software build that can map another set of keys to alt-tab. Maybe I can train my fingers to do windows-tab or something similar.

NanoKVM-USB - This one has some good ideas. I like the form factor. I like the USB port you can easily switch between host and target to copy images or whatever. As a crash cart type thingie, this is probably just fine. However, as stated above. Trying to use it full time with my work laptop was simply too frustrating. Video quality and lack of keyboard capture (maybe I just couldn't find it) just made it impossible.

So, in summary: JetKVM for ipkvm, cytrence kiwi for usbkvm.

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

That works sometimes. It can be flaky.

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

I used 1eur esp8266 with jee-link firmware:

http://www.zoobab.com/esp8266-serial2wifi-bridge

Yeah but do you really want to give everyone on your LAN unauthenticated access to the server console? :)

Does serial work for BIOS/UEFI access too?

I wonder why it hadn't been a built-in feature on some laptops.

No software, just a built-in hardware kvm exposing the screen, keyboard and pointing device to an external port.

A niche thing, but it shouldn't be expensive to implement, and the ports are already here (usb-c, hdmi).

> A niche thing, but it shouldn't be expensive to implement, and the ports are already here (usb-c, hdmi).

A Display Controller Board for driving a laptop screen from an external input is going to add at least $20 to the price of the laptop. Considerably more expensive than the $6 USB-HDMI capture devices which do the job (and have more utility).

The HDMI output port on your laptop (if you even have one, many only offer miniDP) can't just be run in reverse. The board would need to be updated to allow switching it between output and input, at considerable extra cost.

I owned an Alienware laptop (M17X R4) many years ago that had a dedicated HDMI input.

It was a strange laptop. MXM socketed GPU, 120Hz screen that came with Nvidia 3DVision shutter glasses, and the worst battery life I've ever experienced.

I saw a kind-of-laptop that did that.

I think this might be it?

https://gpdstore.net/blog/gpd-pocket-4-kvm-module-explained/

or there is a similar one. It was a tiny laptop, the kind that a devops/sysadmin would carry around in a server room.

I believe some alienware laptops used to do this https://youtu.be/Otln0Ao2z6M (Cathode Ray Dude video)

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.

I played all of KOTOR2 on Xbox using a capture card without sound. Good times.

I too own no external monitors and do my dev/CAD/photography stuff on one of three laptops (macOS, linux, windows 11) [0] depending on where I am, and as much of my writing/planning on my now quite old iPad Pro away from said devices as possible.

So I use one of those cheap HDMI capture devices that flooded eBay about three months into the pandemic to watch Raspberry Pi boot logs or function as ad-hoc console monitor, either with my MBP or with the iPad Pro. The iPad Pro functions usefully as an occasional second monitor for the MBP more directly with USB-C/wifi, of course, so it all works out rather well.

[0] mostly macOS, though I am finally building up a desktop linux escape strategy, 31 years after I first ran X on linux, which might get finally kicked up a notch depending on what happens with Affinity at the end of the month

> However, sometimes direct physical access to the SBC with a monitor and keyboard is useful for initial configuration, maintenance operations, or workloads that have a visual component

Shouldn't this be possible with a single direct ethernet link between laptop and device? I'm not actually sure on the specifics. Or would this require a router? I know you can forward graphical programs with X11 as well

This is one of those rough edges that I wish a Linux distro got right. It's rare, but once in a blue moon you do want to hook up two laptop (say one broken and one working one) and control one from the other (without the ability to configure stuff)

I mention https://www.aurga.com every time this comes up. Wireless HDMI, keyboard, and mouse to their app/desktop client for $95.

https://news.ycombinator.com/item?id=45317527#45318263

https://news.ycombinator.com/item?id=41138701#41140193

That says Linux is supported but apparently only on the input side, not on the viewer side.

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...

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.

I brought a portable screen, which is basically a laptop panel powered by usb, works well.

Yes, $5 USB HDMI capture cards exist?

Usually slow

In what regard? The common Macrosilicon chip MS2130 has <100ms.

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.

100ms latency, they do at least 30fps.

Latency, not FPS. Still suitable for using it as KVM.

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.

Crazy times

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

This is so close to perfect except that it doesn't charge over USB-C. I went down the rabbit hole a bit and found the UPerfect "Lapdock" which is just an incredible description of the concept.

So many times I want to dork with a raspberry pi or start mucking with an old computer... the rpi400 is nearly useless "as is" because you generally require a mouse and then everything goes to hell as far as "single device" goes.

The concept of a "mobile crash cart / workstation" in laptop form factor even makes this tempting as a "front end" for a Mac mini or something?!?

Sooo many times I want to bring the K/V/M to the computer instead of the computer to the K/V/M.

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?

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.

Those USB-C display outputs are real raw GPU output patched through electronically, not like image over USB protocol. They just use the connector, and they can't be captured as USB data.

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.

And you have to find a driver compatible with your laptops lcd panel. Not straightforward.

Nearly all LVDS ones are close enough that there's only a few common configurations. eDP is even simpler.

Anyone using a Intel iMac as a monitor for their much faster Apple CPU MacBook Pro? Wishing “target display mode” was still a thing…

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.

You can do similar with an Android tablet and a usb adapter

is there no vendor offering HDMI-in or Display Port-in?

GPD Pocket 4

It always used to baffle me that there wasn't support for this (or the historic equivalent) 20 years ago.

20 years ago it would have been prohibitively expensive.

20 years ago (well, 25) it was actually more common than it is now - many computers in the late 90's to early 2000's came with video capture cards built in. The Sony VIAO for example, or some "multimedia" machines. The Hauppage WinTV cards and similar knockoffs were popular as well. I remember working on the Linux kernel modules/drivers for these types of cards (I want to say that the project was called "Video4Linux" or similar).

Being able to "watch TV" on your computer used to be a somewhat popular request from well-to-do consumers, and as DVD's came out, people started wanting to digitize their VHS tapes, and video capture cards (the same concept as what the article is doing) allowed that.

I had one! Watching TV on my desktop was great in the pre-streaming era.

Most of them only supported the yellow RCA video in, not VGA or DVI. Just the VGA/DVI to RCA adapter costed some amounts too(not $49).

I think it was really right before COVID that HDMI capture devices finally dipped below $200. Then that Macro Silicon chip at $9 appeared out of the blue and solved PC video input problem. 20 years ago it indeed had been prohibitively expensive to capture desktop video outputs.

The challenge was high bandwidth nature of raw display outputs. Just 1024x768 @ 60Hz is over 1Gbps without overheads. A capture device for that is not something that can be "just" made.

The Minisforum V3 does: https://store.minisforum.com/products/minisforum-v3 .

Some Alienware laptops had an HDMI input: https://youtu.be/Otln0Ao2z6M?t=36

Now is there a way to use a laptop's keyboard as input as well?

you can just buy a nanokvm

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