4 ms·

I don't see that much of a reason you can't do a relay to "disconnect" one hdmi and plug in another. The computers would see the HDMI cable/USB cords unpluggin

I don't see that much of a reason you can't do a relay to "disconnect" one hdmi and plug in another. The computers would see the HDMI cable/USB cords unplugging and re-plugging. Obviously this can be problematic, but I can't see it being that expensive.

bartvk 5y ago
As soon as there's enough volume for someone to design a specialized IC (and reference PCB), and it gets produced by VIA or TI or whatever, sure, then it's neither a problem nor expensive.
Nextgrid 5y ago
Shielding might be a problem. You need your switching circuitry (which is most likely going to be solid state rather than individual relays for each line) to be equivalent to a good cable in terms of interference, crosstalk, etc.
wyager 5y ago
Because mechanical relays have high impedance at HDMI frequencies.
- TaylorAlexander 5y ago
  Yup. A quick search suggests HDMI runs at clock speeds of 25MHz to 340MHz. Not running that over a relay! Also HDMI is many pins, so you would need a low impedance high pole count relay even if it was possible, and such a relay plus the device wrapped around it plus some profit margin means you're not making it any cheaper.
mikepurvis 5y ago
Even outside of impedence issues, you can't just use relays because then every switch is basically an unplug/replug, meaning that: a) the display will flip out and spend multiple seconds re-syncing itself, and b) the sources may take actions such as resizing the desktop, switching to the internal display, pausing the game, whatever. Part of the point of a hardware KVM is that it negotiates its own connection to all of the devices involved, and only changes which signals are passed through at any given moment, resulting in instantaneous switchovers. Now, a multi-input monitor can also do this, but then you have to deal with whatever compat issues are involved in commanding it to switch over DDC (see for example https://github.com/haimgel/display-switch https://github.com/haimgel/display-switch), and it typically also won't be as fast as a hardware solution since input switching speed isn't a metric most people care about when monitor shopping.
loxias 5y ago
Spend just 5 minutes on the Wikipedia page for HDMI and you'll see how much of a folly this would be. :) It has like... 4? different physical layers running at different speeds and all sorts of other weirdness.

bartvk 5y ago

As soon as there's enough volume for someone to design a specialized IC (and reference PCB), and it gets produced by VIA or TI or whatever, sure, then it's neither a problem nor expensive.

Nextgrid 5y ago

Shielding might be a problem. You need your switching circuitry (which is most likely going to be solid state rather than individual relays for each line) to be equivalent to a good cable in terms of interference, crosstalk, etc.

wyager 5y ago

Because mechanical relays have high impedance at HDMI frequencies.

TaylorAlexander 5y ago
Yup. A quick search suggests HDMI runs at clock speeds of 25MHz to 340MHz. Not running that over a relay! Also HDMI is many pins, so you would need a low impedance high pole count relay even if it was possible, and such a relay plus the device wrapped around it plus some profit margin means you're not making it any cheaper.

mikepurvis 5y ago

Even outside of impedence issues, you can't just use relays because then every switch is basically an unplug/replug, meaning that: a) the display will flip out and spend multiple seconds re-syncing itself, and b) the sources may take actions such as resizing the desktop, switching to the internal display, pausing the game, whatever. Part of the point of a hardware KVM is that it negotiates its own connection to all of the devices involved, and only changes which signals are passed through at any given moment, resulting in instantaneous switchovers. Now, a multi-input monitor can also do this, but then you have to deal with whatever compat issues are involved in commanding it to switch over DDC (see for example https://github.com/haimgel/display-switch https://github.com/haimgel/display-switch), and it typically also won't be as fast as a hardware solution since input switching speed isn't a metric most people care about when monitor shopping.

loxias 5y ago

Spend just 5 minutes on the Wikipedia page for HDMI and you'll see how much of a folly this would be. :) It has like... 4? different physical layers running at different speeds and all sorts of other weirdness.