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I'd like to trigger the hot plug detection circuit for one of my graphics card's outputs so that Windows would "think" that it has secondary monitor attached.

I know that there is a pin in the HDMI socket that must be set to high to detect a connection but is it simply a matter of feeding 5V to that pin e.g. from the USB port? No ground connection is needed?

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    \$\begingroup\$ I don't know, but how isn't looking in the HDMI spec the obvious answer? \$\endgroup\$ Commented Sep 26, 2017 at 10:38
  • \$\begingroup\$ As I said I already have the general idea how to do this but I'd like a confirmation from someone more experienced before I mess up my HDMI port. \$\endgroup\$
    – mracer164
    Commented Sep 26, 2017 at 10:41
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    \$\begingroup\$ devel.milkymist.narkive.com/8Xt6fSAd/… discusses this; you need to (a) provide the 5V, which can probably be done from the 5V pin on the HDMI connector, and (b) provide an EDID readout. If you don't provide EDID, how is Windows going to know what size your invisible monitor is? \$\endgroup\$
    – pjc50
    Commented Sep 26, 2017 at 10:48
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    \$\begingroup\$ (the cheap solution to this may involve a HDMI-to-something converter, maybe one of those HDMI-to-LVDS boards) \$\endgroup\$
    – pjc50
    Commented Sep 26, 2017 at 10:50
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    \$\begingroup\$ This feels like an xy problem. Do you want this? \$\endgroup\$
    – Jeroen3
    Commented Sep 28, 2017 at 9:56

3 Answers 3

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HDMI has a 5V line that can just be connected to the HPD line (a resistor is never a bad idea, just for short protection, 1k or so should do), but you also need to provide EDID (Serial EEPROM with appropriate contents) powered from the 5V line and connected to the I2C lines (I cannot off the top of my head remember if you need to supply the I2C pullup or if this is done on the card).

Further some HDMI parts sense the termination of the clock pair, so you would want to terminate this pair in a manner appropriate to the CML drive).

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  • \$\begingroup\$ So if I write a sketch for Arduino feeding EDID data through I2C line I should be good to go? \$\endgroup\$
    – mracer164
    Commented Sep 26, 2017 at 11:05
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I've achieved the expected outcome of creating a "dummy" monitor simply by plugging another cable to my main screen so now I have DVI and HDMI plugged to my screen. I think it is the most elegant solution to my problem.

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These days, Amazon is full of cheap EDID emulators. You can buy one of those, plug it into the HDMI port, and you're done.

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  • \$\begingroup\$ This is a solution buy a ready made plug but it does not answer the question how to do it, if you for example want to make such a plug yourself. \$\endgroup\$
    – Justme
    Commented Jan 19 at 16:14

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