Fixing other vendors' USB hub monitors with simple USB adapters

Okay, so I was just going to reply to the “Share your thoughts on Spectrum” thread but in the interest of keeping things tidy, I’m posting it here instead. The thing is that a whole bunch of monitors almost fit the bill of gaming-spec (4K+144Hz, QHD+240Hz) + USB hub + KVM, and then they get a tiny detail wrong that ruins the “single-cable solution”. And it seems the solution would be so simple, but somehow no one has fixed it yet. I’m also not aware of any plans or even basic recognition of the problem’s existence by accessory manufacturers.

My general use case is as follows:

  • One desktop PC with a GPU fast enough for hi-res gaming (and using VRR for overly demanding games). Connected via DisplayPort or HDMI.
  • One laptop with integrated graphics, fast enough to drive a high resolution and possibly high refresh rate for desktop use but definitely neither for gaming. Charges via USB-C and provides DP Alt Mode on the same USB-C, like any modern laptop should. Possibly a work laptop, or a personal laptop for extra portability. I want video, data and power in a single cable.
  • A single keyboard and mouse for both systems, connected to a single monitor.
  • The monitor, from a competing vendor, has a nice panel and USB hub functionality via USB-C DP Alt Mode but is flawed as described further below.

Should be a popular enough setup, especially now with WFH, no?

So given that this is a community hardware design forum, I thought I’d share my concepts to add the missing piece of functionality to those monitors. My two designs should be trivial for hardware manufacturers to implement, but still highly useful and somehow not available in the market. Perhaps because they’re too simple. Not sure.

Eve could be the ones fixing the competition. The downside, of course, is that it makes your own combo-functionality monitors less crucial to get so you’re handing your competitors a feature they don’t currently have. The upside, of course, is that many people are already stuck with inferior monitors and volumes might be higher. People might take a chance on your USB accessories, even if they pass on the monitors for one reason or another. Either way, here’s what’s broken and how it could be fixed.

The fix for this dilemma is a USB-C charge & data combination adapter, inserted between the monitor’s and the laptop’s respective USB-C port. (The desktop PC is already fine in this use case, connected to the monitor’s USB Type-B upstream and DisplayPort/HDMI. Monitor already provides KVM switch functionality.)

On the “upstream” end of your new adapter, connect your laptop’s single USB-C cable with video, data, and an expectation to be charged.

On the “downstream” end, you have two USB-C ports: one connecting to a USB-PD charger (probably your original laptop charger), and one connecting to your crappy Gigabyte/MSI monitor with video & USB hub data, which can’t power your laptop. Hook up the power pins to the charging port and the data pins to the monitor port.

Done! Now the “upstream” gets power and all of the monitor features in a single cable.

This is annoying because regular KVM switches fuck with the upstream’s display signal and degrade the video connection, often limiting refresh rates to 60Hz or disabling VRR. Not acceptable for hi-res/hi-refresh-rate monitors. Existing KVM switches also don’t generally allow for a combination of USB-C video and DP/HDMI video, and if they do they neuter the USB data and/or power delivery. Not to mention insane prices. So the challenge here is to get the desktop PC’s signal to the monitor unadulterated, while providing KVM switch functionality. The fix for this is slightly more difficult to implement than my first design, but still light years simpler than existing KVM switches and better quality.

On the “upstream” side, you have two USB-C ports connecting to laptop and desktop respectively. The desktop wants its USB data from your new adapter (via USB-A to USB-C cable, or native USB-C, doesn’t matter) but plugs its DP/HDMI cable directly into the monitor.

On the “downstream” side, you have a single USB-C port connecting to the aforementioned monitor. This will transport data when the desktop is active, or data+video+charge when the laptop is active. This port has its pins connected to both upstreams.

In addition, there’s a switch button. When you press it, the electronics disconnect all pins of the currently active upstream port from the monitor port, and then connect all the pins of the other upstream to the monitor port instead. The monitor already deals with USB data routing to its own downstream hub ports, there’s no need for that in this simplest possible KVM switch. USB-C lanes coming from the laptop don’t get divided and make it through to the monitor in one piece, no signal fuckery, no “handles data but not Alt Mode” bullshit. Turning all USB lanes on or off depending on the switch setting should be simple enough to implement, I hope. The equivalent of manually plugging and unplugging cables, but without reaching behind the monitor every time and wearing down the port.

If the monitor has a source preference setting or use-latest-connected-port functionality, the video will also switch because we’re connecting or disconnecting the laptop video, while the desktop PC always remains plugged into the monitor (directly) via DP or HDMI. If the monitor doesn’t auto-select the right input, the device is still useful because it allows all cables to remain connected with the best possible transmission quality & features, only one will have to switch in two places (adapter’s switch button + monitor OSD). Still a giant improvement.

[Edit: Maybe it would be possible to keep the power delivery pins connected to a single dedicated upstream (i.e. laptop) even if the other upstream is active. The desktop will never need the power, and the laptop might want it even when the desktop has KVM ownership. That said, I’m not a hardware person so I don’t know if USB power delivery requires negotiation on any of the non-power pins. But again, even if always-charging laptop isn’t a possibility, it’s still a giant improvement.]

I’d buy either of those adapters in a heartbeat, only one though, depending on monitor.

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^^^^^^ This. I’ll never need to power my desktop anything. But being able to power my VertexHUB and my laptop off the monitor hub would be a big bonus versus having both of those occupying more outlets on my UPS (or, as is the case currently, one of the 2 power strips I have plugged in to the UPS).

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