Power Signaling Over HDMI

Lots of people these days have home entertainment systems. These usually consist of a television, an audio system, and multiple source devices. The source devices typically include a DVD/Blu-Ray player, a Cable Box, one or more game consoles, maybe a computer, and maybe even something like the Roku. Despite these systems being incredibly common, almost nobody knows how to use them. I have an idea which can make things much much easier for everybody.

The fundamental problem is that people do not understand the concept of switching inputs. They simply do not get it that video and audio are separate. They don’t get that the audio and video come out of one box into another box. They do not comprehend that on the receiving box you must manually select which input you wish to currently be active. Now, people should learn this, but with a change to the HDMI spec, I think we can eliminate the problem in the long run.

Every cable box I have seen has a power outlet on it. Why is that? The reason is that you are supposed to plug your television into the cable box, and then plug the cable box into the wall. This will allow you to have the TV turn on and off when you turn the cable box on and off. Ideally this will eliminate the need for the TV remote control. Sadly, this only makes trouble in a more complicated system. For one thing, it means I have to turn the cable box on in order to play a video game. That’s just a waste of electricity.

The solution is to add one single additional wire to every HDMI cable. That wire will allow the devices to tell each other if and when they are on or off. The devices will also be able to command each other to turn on or off, or to switch inputs. It’s really so simple, I’m amazed it doesn’t already exist.

Here is an example scenario. You have a TV with an XBox and a DVD player. They are all off. You turn on the XBox. The XBox signals over the wire to the TV that it has turned on. The TV notices that it is off, so it turns on. Then it notices the XBox is the device which told it to turn on, and is the only device sending a signal. Therefore it automatically switches to that input.

Think about the difference that makes for the end user. They push the green button on the XBox controller, and they’re good to go. No fiddling with other remote controls. No juggling inputs. No nothing. Logitech probably wouldn’t like it, though, because it would ruin their Harmony product line.

I’m sure that you intelligent readers can figure out how the system will work in all sorts of other typical situations, but let me make a couple more examples. You turn off the TV, and it tells everything connected to it to turn off as well, saving lots of electricity. You turn off the XBox, and nothing else connected to the TV is still on, so the TV turns itself off. You have the XBox already on, but you turn on the Blu-Ray player. Well, it would be worse to switch away from a game in progress, so it should stay on the XBox. However, if the XBox turns off, it can switch to the Blu-Ray automatically.

Of course, the user will still need the ability to take manual control over which inputs are active, because the automatic setting will not be able to handle every single use case. Even so, such a system will drastically decrease the amount of times the user will have to manually switch inputs or turn devices on or off. It will also drastically reduce electricity usage because devices will almost never be on when they are in use.

Now, there are some extremely complicated situations that require figuring out. The best example I can think of is picture in picture. The TV and/or receiver has to be aware that picture in picture is a possibility. Maybe if you have picture in picture, and you turn on a second device, it opens in the small picture. Then if you turn off the second device, the small picture disappears. Even this complicated situation isn’t that difficult, you just have to spend some time figuring out the best possible default behavior for every possible scenario.

They’re adding all sorts of other great features to the HDMI specification like Ethernet, higher video resolution, audio return, etc. Those are far more complex than this simple one-wire feature. It will cost next to nothing to implement, and it will make a huge difference. There’s no rush, we can just do the usual thing we do with car safety equipment. All new products as of X date must support this feature. It will save a ton of electricity and reduce a ton of headaches. Too bad I’m just some guy and not an electronics manufacturer. I don’t even know the second step towards trying to make this a reality. The first step was this blog post.

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5 Responses to Power Signaling Over HDMI

  1. Christopher says:

    Actually, this exists. Its called Bravia Sync. The HDMI is what allows it to work. I have Sony and all Sony hardware. I turn on the TV, my Home Theater powers up. If I turn on the Home Theater, it powers up the TV. If I turn on my PS3, it turns on the TV and Home Theater. Same goes in reverse. So, is it standard across all brands, maybe not. But Sony has it.

  2. kernel says:


    Do you know about the SCART cables from the days of standard definition TV? Here in Europe, most VCRs, DVD players and whatever are connected with those (http://en.wikipedia.org/wiki/Scart). Wikipedia says they aren’t really used in America. The connectors are bulky and impractical, you can’t figure out which way to put them without looking, they keep falling out halfway and you end up with a yellow picture or no sound. But when they do work, they’re actually pretty nice. They have video and audio in and out and can carry composite video, RGB, S-Video and some other stuff.
    And they have a wire telling the TV when a device is powered on. So the TV can automatically switch to VCR, DVD or satellite box input when you turn the respective devices on. The wire should also tell the TV whether the image is 4:3 or widescreen, but I’ve never seen that feature used. And since most game consoles have special cables (many of them using RCA jacks and the RCA-to-SCART-adaptors you see in the wikipedia article), automatic switching doesn’t work with those.
    So the only thing SCART can do is switch from the built-in receiver of the TV (used mostly for cable TV over here) to a VCR or DVD player and back. No automatic power on and off or anything, but at least somehow like what you described in your article.

  3. James says:

    There is no need to add a wire to the HDMI cable, and in fact that would be a terrible idea as it would then break backwards compatibility. It is also entirely unnecessary. Remember, HDMI is a digital communications bus. If there needed to be an explicit signal then on vs off is just another piece of data. Even that new Ethernet feature of HDMI is implemented without changing the cables :)

    That said, you don’t even need an explicit signal because it is easily implied. There are HDMI switches that will detect activity and switch to that port. The better ones even have a priority setup based on input port, so you can handle the case of multiple devices on at the same time. I don’t know if any stereo receivers or TVs have the same feature, but it would not be a difficult one to implement. This is not even a new concept as many switches of older analog devices with component/composite connections will do this as well.

    In the end this type of feature is mainly just a function of software on the receiving device. Auto power off does exist on some TVs and most projectors when all input signals are inactive for a period of time. You are right that the complex remotes to automate your theater might not like it, but with the right consumer demand there is nothing preventing the makers of TVs and receivers from making things easier.

  4. Mike says:

    The assumptions made by the author are faulty to begin with. Let’s look at my system for example. I have a TiVo and a cablecard that tunes in my cable stations and cable music channels. The Tivo is connected to my receiver via HDMI and my receiver switches between TiVo, PS3, and various other components, all HDMI.

    I like to leave the receiver on all day, playing music from my TiVo box (since I work from home). According to the author, I would have to leave my TV on _all_day because after all, why on earth would I want to have my TiVo turned on if I didn’t have my television on at the same time?

    There are all kinds of scenarios that need to be supported. The author’s preconception that if you turn on your XBOX, that the TV must be turned on is only one of them.

  5. George says:

    This functionality has always existed in the HDMI spec. Pin 19 on the connector is ‘hot plug detect’. This enables devices to know when new devices have been plugged into them or switched on or off. They can then decide whether to turn themselves on of off. The problem is that very few manufacturers support this functionality.

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