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I was wondering if it was possible to power on/off a display using a computer connected via HDMI. Let me explain :

I want my computer to power off my monitors (not standby mode) when I don't use it (no keyboard/mouse input) for more than 15 minutes, and power them back when such input is received. My monitors are connected over HDMI, so I was wondering if it was possible to use the CEC functionality with a computer. If is it possible, then is there a hardware requirement ?

My point is that I often take a break from my computer, but forget to turn off the screens, and I would prefer to shut down the screens completely instead of putting them to standy mode

Thanks a lot

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What's wrong with leaving them in Standby mode? It's very low-power usage. If the display truly is off, then you won't be able to wake it remotely (as it will be off, and can't respond to anything). –  techie007 Sep 22 '13 at 17:42
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True -- and to get... well, technical... even when a device is fully "off" it's still "on" in that it's waiting for the power button to be pressed... –  Matt Sep 23 '13 at 4:20
    
@Matt That depends on how the power button is wired. If it's wired to actutate a contactor, relay or something else along those lines (electronic or electromechanical power switch; electronic power switches are commonly used for electronic equipment these days) then what you are saying is true: "off" is still a sort of "standby" mode. If it is electrical or mechanical (usually wired in-line with the mains power), like the power switch on old AT PSUs and the back of ATX PSUs as well as lots of home appliances, then turning off power with the power button actually turns power off. –  Michael Kjörling Sep 23 '13 at 7:16
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There are desktops which have a power outlet for monitors. I used to have one and the main advantage is that the screens are turned of when the desktop is. I'm not sure if the power outlet is reachable via some script. –  GroundZero Sep 23 '13 at 9:07
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I plug all my monitors into one power strip, with the power switch sticking out from under one of the monitors. This allows me to flip a single switch to turn them all off/on. –  Byte56 Sep 23 '13 at 13:24
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10 Answers

up vote 47 down vote accepted

I want my computer to power off my monitors (not standby mode) when I don't use it (no keyboard/mouse input) for more than 15 minutes, and power them back when such input is received.

What you want is exactly what you are trying to avoid.

If the monitor is actually, fully off, then it can’t turn back on from a signal on the video cable. To allow it to turn on like that, there needs to be some sort of circuit in the monitor that remains on and active to watch for the signal. Monitors already have such a circuit, but turning them off turns that circuit off as well.

To use that circuit, you need to leave some electricity in the monitor, and that is exactly what standby does: it turns the display (and speakers, and everything else) off while leaving that one small circuit active.

With most modern monitors, there is essentially no difference between standby mode and fully off other than a tiny low-voltage trickle in that circuit and the LED on the front.

I have to pay for electricity, so we always avoid using electricity as much as is humanly possible, yet, I leave it in standby when I am using the computer and need to step away for a while (I turn both off when I am done for the day).

Instead of letting the monitor remain on for 15 minutes for nothing, your best best is to do what I do and simply get into the habit of either turning the monitor off whenever you get up to step away, or to manually put it into standby mode. What I do is to use the AutoHotkey script below (can be compiled to an executble that runs in the background if desired) to let me press ⊞ Win+M to sleep the monitor whenever I get up. Other options include using a shortcut or program, using a script or program to do it with a mouse-cursor hot-corner, or even just reducing the timeout from 15 minutes to five or so.


;Monitor Standby Hotkey
;⊞ Win + M puts monitor in standby
#m::
  Sleep 1000 ; Pause for 1sec to prevent un-sleeping when key released

  SendMessage, 0x112, 0xF170, 2,, Program Manager
  ; 0x112 is WM_SYSCOMMAND, 0xF170 is SC_MONITORPOWER
  ; Use  1 in place of 2 to activate the monitor's low-power mode
  ; Use -1 in place of 2 to turn the monitor on
return
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+1 for the AHK script. I have been using essentially the same things for years. Works great on laptops too, where you can't actually turn off the screen manually without closing it. –  zeel Sep 22 '13 at 19:57
    
@zeel, you should at least be able to turn off the backlight, which saves a lot of battery. –  Synetech Sep 22 '13 at 19:59
    
well you can do that, but why do it when a hotkey to turn it off completely is so easy? Plus it kills all the lights, including key back-light - so I can sleep. –  zeel Sep 22 '13 at 20:06
    
True, infact one can even off the power while the monitor is in standby and it will continue being in standby for many seconds before dying. –  Ramchandra Apte Sep 23 '13 at 5:58
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"What you want is exactly what you are trying to avoid" - Gold. Pure gold. –  abstrask Sep 27 '13 at 14:35
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The HDMI-CEC specification, which allows HDMI-connected devices to act as a limited remote control any other connected CEC-enabled device, defines the command System Standby which would allow the "remote" to switch the target into standby mode.

This is the closest to what you have in mind that I know of. It requires that the target HDMI device (your monitor) be wired for CEC (which is mandatory under the spec, so it is) and that the device implement CEC in general and that command specifically (which is totally optional and not very common -- yet). It's pretty unlikely that your monitor implements CEC but may be possible to confirm from the manual or published spec, or perhaps easier to simply test by connecting a device via HDMI that sends CEC commands and seeing if your monitor responds.

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Yes, but you shouldn't. I think Synetech sums it up well, but if you must:

Exactly how depends on the screen, but if it has an IR receiver you can connect an IR blaster to your PC to signal shut off (though as Synetech pointed out, if the IR is working, power is still being drawn).

Alternatively you could use an Arduino or similar device to actually switch off the power to your monitor. This would take some work, and some DIY skills - but it is certainly a possibility.

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How would the Arduino not draw any power when the monitor is off? Seems to me like in that case you'd just be moving the power consumption elsewhere. I checked a very small sampling of TFTs in the 22-24 inch size range and the standby power consumption for those is specified as being between 0.2 W and 1.0 W, with an average somewhere around 0.5 W and a mean below 0.4 W. While I do believe in reducing power consumption: so what if the monitor draws 400 mW? How much power does the computer draw at the same time? –  Michael Kjörling Sep 23 '13 at 7:27
    
Arduino running off the USB port, connected to a mechanical arm or electrical relay. Computer goes off, arduino gets shutdown signal, disconnects power to monitor and does not consume power itself till PC is switched on again –  Akash Sep 23 '13 at 9:06
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@MichaelKjörling The Arduino Uno arduino.cc/en/Main/arduinoBoardUno can be powered by USB, thus its power would be directly tied to the computer. –  zeel Sep 23 '13 at 11:34
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In short, no, you can’t. Not on a desktop. The power of the monitor is independent of any kind of communication from the CPU.

It would be a nice feature, I’ll admit.

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My UPS does this for me. If the computer goes to sleep the monitor loses power. However it is not clear to me if you also want your computer to sleep.

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Actually this technically is possible, but I have not seen a practical implementation of it unfortunately. There used to be ( last I checked it had been unmaintained and was removed from Debian ) a Linux package I think it was called ddccontrol that let you manually make use of the ddc control signals, which are a standard set of messages over an i2c bus going to the monitor. One of the commands it has is to shut the monitor off. And yes, you can even command it to turn back on. When the monitor is off, the chip draws power from the PC so it can respond to the ddc commands, mostly so the PC can identify what kind of monitor is plugged in.

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Check out Steve Gibson's Wizmo utility, it has a "monoff" command that may work for you.

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While I agree with the previous answers regarding just using standby mode, I would add the following as a possible solution.

You could use an Arduino connected to a USB port and a Powerswitch Tail to switch the monitors off at the power source.

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Use the

LCD Off

small app for on/off the display manualy

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Here's my simple solution, which I've been using successfully for many years in my desktops:

Although it does use the sleep mode, sleep mode takes the computer's power consumption down to a (measured!) draw of under 4 watts. And one mouse or key touch rapidly returns it to full function, where you left off.

So my desktop computer is plugged into the sensing outlet of a SMART-STRIP, which kills power to all its remaining outlets when the computer goes to sleep mode. Now, when I leave the desk for a few minutes or over night, hitting sleep turns of my monitor, audio speaker amplifier, printer, scanner, a small lamp, and anything else I wish to completely power down upon entering sleep mode.

In my case, the monitor DOES NOT lose its settings, nor do the other devices when their power is removed in this fashion.

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