I am thinking about trying to build my own smart display for home assistant and other stuff. I was thinking about using one of those second screen monitor displays as they are touchscreens and pretty cheap on amazon (~50ドル). They are powered through usb-c. It would be great if there was a board that takes hdmi and power and combines them into a usb-c cable to connect to the monitor.

Does something like this exist? I looked around but couldn't find anything.

If you could post a link to the thing you have in mind it might help.

Oh no, not again.

Jason321 wrote: ↑

Fri Nov 14, 2025 9:21 pm

Does something like this exist? I looked around but couldn't find anything.

THhe problem is that Video over USB-C is always DisplayPort, not HDMI. HDMI as Alternate Mode is defined, but nobody uses it.

fchk wrote: ↑

Fri Nov 14, 2025 10:46 pm

Jason321 wrote: ↑

Fri Nov 14, 2025 9:21 pm

Does something like this exist? I looked around but couldn't find anything.

THhe problem is that Video over USB-C is always DisplayPort, not HDMI. HDMI as Alternate Mode is defined, but nobody uses it.

So you need something that takes HDMI, DSI (unless OP is using a zero series Pi), or DPI then converts it to Displayport and tunnels it over a USB C cable.

All while letting the Pi act as a USB host on the same cable so that the touchscreen works.

It'll also need to send any EDID (or equivalent) from monitor to Pi. I've no idea how that's done in displayport alt mode.

And handle any PD negotiation required for, power mode, host/device mode, USB C alt mode, etc.

Then again, as the OP hasn't provided any links to the monitors they're talking about, they could be using Displaylink (think VNC over USB though that's a simplification) and there's no support on Pi (or most Linux distros) for anything more recent than v1.X (IIRC there was a closed source binary driver for v2 displays on Ubuntu on x86 but I've never used it).

TBH, depending on the physical size of display required I'd be looking at the RPL 15", 7", or 5" displays. Or third party touchscreens interfacing over SPI, DPI, HDMI, DSI, etc.

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All advice given is based on my experience. it worked for me, it may not work for you.
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thagrol wrote: ↑

Sat Nov 15, 2025 12:06 am

It'll also need to send any EDID (or equivalent) from monitor to Pi. I've no idea how that's done in displayport alt mode.

at least for HDMI alt-mode, its tunneled over the PD protocol
and you also need to use the PD protocol to request DP or HDMI alt mode

so the adapter will need a MCU that can speak PD, which will emulate the EDID

fchk wrote: ↑

Fri Nov 14, 2025 10:46 pm

Jason321 wrote: ↑

Fri Nov 14, 2025 9:21 pm

Does something like this exist? I looked around but couldn't find anything.

THhe problem is that Video over USB-C is always DisplayPort, not HDMI. HDMI as Alternate Mode is defined, but nobody uses it.

+1

and I would be quite surprised If your monitor does.

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