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Shortened version: I want to connect from an HDMI source (laptop) to an iMAC with a mini-displayport. Is it possible? If so how?

I spent many hours on this and my mind is about to explode.

Lengthy version:

I have an HP laptop with an HDMI port (source). I have a 2009 iMAC that has a mini-displayport. I would like to use the iMAC as my 2nd the monitor. I would like to connect from my HDMI source to mini-displayport on the iMAC. I don't have USB-C nor thunderbolt at all in any of my devices.

My question is: Is it possible, by using Cables and Adapters, to successfully connect my HP laptop to the iMAC to have it as a 2nd monitor? Regardless of with or without sound.

My research so far: I have searched up and see that HDMI and mini-displayports are different and it only works one way. mini-display -> HDMI and NOT the other way around.

I also found a mention online where a person, converted HDMI -> DVI -> mini-displayport. This solution doesn't transmit sound, but that is not a big deal to me. I then started to search up adapters to make this happen, but it doesn't seem possible to me because I only see mini-displayport -> DVI and not the other way around.

I have come to a conclusion that this is not possible with my current knowledge. But I don't like the word "IMPOSSIBLE" thus I thought I would post it on here to ask the community. I know there has to be a way. It may be more trouble than it is worth, but there has to be a way!

At this point, I'm extra curious and stubborn that I don't want to give up. :)

Someone please enlighten me!

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Natively, DisplayPort and HDMI use completely different signals. Both are digital, so passive converters do not work.

To solve this, DP (which is the newer of the two standards) has a compatibility mode where devices produce both, HDMI and DP signals - which is why it usually works to convert DP source to HDMI without active signal conversion. (This usually only works directly at the source, as HDMI uses 5V signals where DP only uses 3.3V, which means the converter has to amplify the signal. For that it needs power, which it draws from a dedicated pin on the display port output - but this pin is usually not connected in DP cables because connecting the pin source to sink would result in a short circuit. Specials cables that deliver the power exist, but may not ever be used to connect source to source without another cable in between).

HDMI however does not know anything about DisplayPort - so HDMI sources do not have any kind of dual mode where they also produce DP output. You need active signal converters, that decode the HDMI signal, and encode it into DP format. Those adapters do exist - since they need active components however they're pricey and also require external power supply (HDMI, unlike DisplayPort, does not have a pin to provide power to converters along the chain).

Also keep in mind that DRM protected video streams might refuse to play if there's an active signal converter on the chain.

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  • Thank you for your answer. So from your answer, I understand that I could get an active converter box, but even that might get blocked by DRM protected video streams. One converter box I looked at is priced at $80. Thus I should probably give up on this effort and just buy a new monitor?
    – Nhat Duong
    Commented Apr 8, 2020 at 21:26
  • You got that right. If you want to buy such adator or a different monitor however is something you have to decide for yourself.
    – Johannes H.
    Commented Apr 8, 2020 at 21:31
  • Thank you very much! Your answer was very helpful! :)
    – Nhat Duong
    Commented Apr 8, 2020 at 21:36

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